• 专利附录
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    • 专利摘要:
    A method for the manufacture of a hot-rolled coated steel sheet having a thickness of between 1.8 mm and 5 mm, comprising providing a semi-product having a composition comprising: 0.04% = c = 0 , 38%, 0.40% = mn = 3%, 0.005% = si = 0.70%, 0.005% = al = 0.1%, 0.001% = cr = 2%, 0.001% = ni = 2%, 0.001% = ti = 0.2%, nb = 0.1%, b = 0.010%, 0.0005% = n = 0.010%, 0.0001% = s = 0.05%, 0.0001% = p = 0.1%, mo = 0.65%, w = 0.30%, ca = 0.006%, hot rolling with a frt final rolling temperature to obtain a hot rolled steel product having a thickness between 1,8 mm and 5 mm, cool to a take-up take-up temperature meeting: 450 ° c = take-up = take-upmax with, take-upmax being expressed in degrees celsius and f designating the austenite fraction immediately before rolling and take up to obtain a hot-rolled steel substrate, pickling and coating of the substance hot-rolled steel alloy rat or aluminum alloy by continuous hot-dip in a bath to obtain a hot-rolled coated steel plate comprising a hot-rolled steel plate and an aluminum or aluminum alloy coating, having a thickness of between 10 and 33 µm on each side of the hot-rolled steel sheet.
    公开号:BR112019009708A2
    申请号:R112019009708
    申请日:2017-11-23
    公开日:2019-08-13
    发明作者:Beauvais Martin；Jacolot Ronan；Henrion Thomas
    申请人:Arcelormittal；
    IPC主号:
    专利说明:

    “METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, HOT COATED AND LAMINATED STEEL SHEET, METHOD FOR MANUFACTURING A HOT STEEL COATED STEEL PIECE AND USE OF A HOT STEATED COATED STEEL PIECE HOT STAMPED COATED STEEL PIECE ”Field of the invention [001] The present invention relates to a hot-stamped coated and hot-rolled steel plate, having a thickness between 1.8 mm and 5 mm, with an excellent adhesion of the coating after hot stamping and to a hot-stamped coated steel part, at least a portion of which is between 1.8 mm and 5 mm thick, with excellent coating adherence. The present invention also relates to a method for the manufacture of a hot stamped coated and hot-rolled steel sheet having a thickness comprised between 1.8 mm and 5 mm, and a method for the manufacture of a coated steel part hot stamped.
    Background of the Invention [002] As the use of high strength steels in automotive applications increases, there is an increasing demand for steels with increased strength and good conformability. The growing demands for weight savings and safety requirements motivate the intensive elaboration of new automotive steel concepts that can achieve greater ductility and resistance.
    [003] Thus, several steel families that offer various levels of resistance have been proposed. In recent years, the use of coated steels in hot stamping processes for the modeling of parts has become important, especially in the automotive field.
    Petition 870190044879, of May 13, 2019, p. 78/220
    2/65 [004] The steel sheets from which these parts are produced by hot stamping, having a thickness generally between 0.7 and 2 mm, are obtained through hot rolling and later cold rolling .
    [005] In addition, there is an increasing need for steel sheets for hot stamping having a thickness greater than 1.8 mm, and even greater than 3 mm, up to 5 mm. Such steel sheets are, for example, desired to produce chassis parts or suspension arms, which have, until now, been produced by cold pressing, or to produce parts obtained by custom-rolled sheets (TRB).
    [006] However, coated steel sheets for hot stamping having a thickness greater than 3 mm cannot be produced by cold rolling. Indeed, the existing cold rolling lines are not adapted to produce cold rolled steel sheets. In addition, the production of cold-rolled coated steel sheets having a thickness between 1.8 mm and 5 mm involves the use of a low reduction rate by cold rolling, which is incompatible with the recrystallization required in the annealing step after cold rolling. Thus, cold-rolled coated steel sheets, having a thickness comprised between 1.8 mm and 5 mm, would have an insufficient flatness, resulting, for example, in misalignment defects during production in custom welded blank.
    [007] Therefore, it has been proposed to produce steel sheets having a high thickness by hot rolling. For example, JP 2010-43323 discloses a process for the manufacture of hot-rolled steel sheets for hot stamping, having a thickness greater than 1.6 mm.
    [008] However, the inventors found that by producing
    Petition 870190044879, of May 13, 2019, p. 79/220
    3/65 steel sheets coated by hot rolling, the adhesion of the coating to the surface of the steel part, more than the hot stamping, is unsatisfactory, which leads to a poor adhesion of the paint on the hot stamped part. Paint adherence is, for example, assessed using a wet paint adherence test.
    [009] Furthermore, in some particular cases, the thickness of the coating, before and after hot stamping, cannot be rigidly controlled, so that the thickness of the coating obtained is not within the desired thickness range. This specific thickness range is generally between 10 pm and 33 pm, for example, the range from 10 pm to 20 pm, the range from 15 pm to 33 pm or the range from 20 pm to 33 pm. This uncontrolled coating thickness leads to low weldability.
    [010] In addition, as explained in more detail below, the inventors have found that coating adhesion can be improved under certain circumstances by slowing the blasting process without, however, improving coating thickness control. Instead, in these circumstances, the control of the coating thickness and therefore weldability is even worse, and the productivity of the line is reduced.
    Brief Description of the Invention [011] Therefore, the invention aims to provide a coated and hot-rolled steel sheet having a thickness comprised between 1.8 mm and 5 mm and a method to manufacture it, allowing to obtain an improved coating adhesion after hot stamping, allowing the control of the coating thickness of the coated and hot-rolled steel plate for the target range, especially in the range between 10 and 33 pm.
    [012] The invention also aims to provide a piece of steel
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    4/65 hot-stamped coated, wherein at least a portion has a thickness comprised between 1.8 mm and 5 mm, having an improved coating adhesion and a method for making the same. Finally, the invention aims to provide a process that does not reduce productivity in the pickling line.
    [013] For this purpose, the invention relates to a method for the manufacture of a coated and hot-rolled steel sheet having a thickness comprised between 1.8 mm and 5 mm, wherein said method comprises:
    supply a steel semi-product having a composition comprising, in percentage by weight:
    0.04% <C <0.38%
    0.40% <Mn <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <2%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting,
    Petition 870190044879, of May 13, 2019, p. 81/220
    5/65 hot rolling the steel semi-product with a final FRT rolling temperature, in order to obtain a hot rolled steel product having a thickness between 1.8 mm and 5 mm, cool the rolled steel product hot to a tempering winding temperature and winding the hot rolled steel product at said tempering winding temperature to obtain a hot rolled steel substrate, the winding temperature T winding satisfying:
    450 ° C - Tenrolamentomax - Tenrolamentomax, where Tenrolamentomax is a maximum winding temperature expressed as:
    Tenrolamentomax - 650 - 140 X fy
    Max coiling being expressed in degrees Celsius and fy designating the fraction of austenite in the hot rolled steel product immediately before winding, stripping the hot rolled steel substrate, coating the hot rolled steel substrate with Al or Al alloy by immersion continuous hot bathing, to obtain a coated and hot-rolled steel plate comprising a hot-rolled steel plate and an Al or Al alloy coating, having a thickness between 10 and 33 pm on each side of the plate hot rolled steel.
    [014] According to one embodiment, the Ni content is at most 0.1%.
    [015] In this embodiment, the composition comprises, in percentage by weight:
    0.04% <C <0.38%
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    6/65
    0.40% <Μη <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <0.1%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [016] Preferably, the composition comprises, in percentage by weight:
    0.04% <C <0.38%
    0.5% <Mn <3%
    0.005% <Si <0.5%
    0.005% <Al <0.1%
    0.001% <Cr <1%
    0.001% <Ni <0.1%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    Petition 870190044879, of May 13, 2019, p. 83/220
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    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.10%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting, [017] Preferably, the final FRT lamination temperature is between 840 Q C and 1000 Q C.
    [018] According to one embodiment, the composition is such that 0.075% <C <0.38%.
    [019] According to a particular embodiment, steel has the following chemical composition, in percentage by weight:
    0.040% <C <0.100% 0.80% <Mn <2.0% 0.005% <Si <0.30% 0.010% <Al <0.070% 0.001% <Cr <0.10% 0.001% <Ni <0, 10% 0.03% <Ti <0.08% 0.015% <Nb <0.1% 0.0005% <N <0.009% 0.0001% <S <0.005% 0.0001% <P <0.030% Mo <0.10% Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [020] According to another particular embodiment, the
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    8/65 steel has the following chemical composition, in percentage by weight:
    0.062% <C <0.095%
    1.4% <Mn <1.9%
    0.2% <Si <0.5%
    0.020% <Al <0.070%
    0.02% <Cr <0.1% where 1.5% <(C + Mn + Si + Cr) <2.7%
    3.4 χ N <Ti <8 χ N
    0.04% <Nb <0.06% where 0.044% <(Nb + Ti) <0.09%
    0.0005% <B <0.004% 0.001% <N <0.009%
    0.0005% <S <0.003% 0.001% <P <0.020% and, optionally, 0.0001% <Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [021] According to another particular embodiment, steel has the following chemical composition, in percentage by weight:
    0.15% <C <0.38%
    0.5% <Mn <3%
    0.10% <Si <0.5%
    0.005% <Al <0.1%
    0.01% <Cr <1%
    0.001% <Ti <0.2%
    0.0005% <B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
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    0.0001% <P <0.1% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [022] According to another particular embodiment, steel has the following chemical composition, in percentage by weight:
    0.24% <C <0.38%
    0.40% <Mn <3%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%,
    Petition 870190044879, of May 13, 2019, p. 86/220
    10/65 the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [023] Preferably, after blasting and before coating, the surface voids percentage in the hot rolled steel substrate surface region is less than 30%, the surface region being defined as the region that extends from the upper point of the hot rolled steel substrate surface to a depth, from this upper point, of 15 pm.
    [024] Preferably, the hot rolled steel sheet has an intergranular oxidation depth of less than 4 pm.
    [025] According to one embodiment, the bath contains, by weight percentage, 8% to 11% silicon and 2% to 4% iron, the remainder being aluminum or aluminum alloy and impurities inherent in the processing.
    [026] According to another embodiment, the bath contains, in percentage by weight, from 0.1% to 10% of magnesium, from 0.1% to 20% of aluminum, the rest being Zn or Zn alloy , optional additional elements such as Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr and / or Bi, and impurities inherent in the processing.
    [027] According to another embodiment, the bath contains, by weight percentage, from 2.0% to 24.0% zinc, from 7.1% to 12.0% silicon, optionally, from 1.1% to 8.0% of magnesium and, optionally, additional elements selected from Pb, Ni, Zr or Hf, the content of each additional element being less than 0.3%, the rest being aluminum and unavoidable impurities and residual elements, the Al / Zn ratio being above
    2.9.
    [028] According to another embodiment, the bath contains, by weight percentage, from 4.0% to 20.0% zinc, from 1% to 3.5% silicon,
    Petition 870190044879, of May 13, 2019, p. 87/220
    11/65 optionally, from 1.0% to 4.0% magnesium and, optionally, additional elements selected from Pb, Ni, Zr or Hf, the content of each additional element being less than 0, 3%, the rest being aluminum and unavoidable impurities and residual elements, the Zn / Si ratio being between 3.2 and 8.0.
    [029] According to another embodiment, the bath contains, by weight percentage, from 2.0% to 24.0% zinc, from 1.1% to 7.0% silicon, optionally, from 1.1% to 8.0% of magnesium when the amount of silicon is between 1.1 and 4.0% and, optionally, additional elements selected from Pb, Ni, Zr or Hf, the content of each additional element being less than 0.3%, the rest being aluminum and unavoidable impurities and residual elements, the Al / Zn ratio being above 2.9.
    [030] According to one embodiment, the method further comprises, after coating the hot rolled steel sheet with Al or Al alloy, a step of depositing a Zn coating on the Al or Al alloy coating through of cementation, through electrodeposition or through sonic vapor jet deposition, the Zn coating having a thickness less than or equal to 1.1 pm.
    [031] The pickling is preferably carried out in an HCI bath for a time between 15 and 65 s.
    [032] In one embodiment, the hot-rolled steel sheet has a structure composed of ferrite and perlite.
    [033] The invention also relates to a method for the manufacture of a coated and hot-rolled steel sheet having a thickness comprised between 1.8 mm and 5 mm, wherein said method comprises:
    supply a steel semi-product having a composition comprising, in percentage by weight:
    Petition 870190044879, of May 13, 2019, p. 88/220
    12/65
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting, hot rolling the steel semi-product with a final FRT rolling temperature between 840 Q C and 1000 Q C, in order to obtain a hot rolled steel product having a thickness
    Petition 870190044879, of May 13, 2019, p. 89/220
    13/65 between 1.8 mm and 5 mm;
    cooling the hot rolled steel product to a temperature coiling temperature and winding the hot rolled steel product to said temperature cooling temperature to obtain a hot rolled steel substrate, the temperature of the winding T satisfying:
    450 ° C - Coiling - 495 ° C, stripping the hot rolled steel substrate, coating the hot rolled steel substrate with Al or Al alloy by continuous hot dip bathing, to obtain a coated and rolled steel plate hot, comprising a hot-rolled steel sheet and a coating of Al or Al alloy, having a thickness between 10 and 33 pm on each side of the hot-rolled steel sheet.
    [034] Preferably, after blasting and before coating, the surface percentage of voids in the hot rolled steel substrate surface region is less than 30%, the surface region being defined as the region extending from the point surface of the hot rolled steel substrate to a depth, from this upper point, of 15 pm.
    [035] Preferably, the hot rolled steel sheet has an intergranular oxidation depth of less than 4 pm.
    [036] In one embodiment, the hot-rolled steel sheet has a structure composed of ferrite and perlite.
    [037] The invention also relates to a coated and hot-rolled steel plate, comprising:
    a hot-rolled steel sheet having a thickness between 1.8 mm and 5 mm, the composition of which comprises,
    Petition 870190044879, of May 13, 2019, p. 90/220
    14/65 by weight percentage:
    0.04% <C <0.38%
    0.40% <Mn <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <2%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from casting, said hot-rolled steel sheet having an intergranular oxidation depth of less than 4 pm, an Al or Al alloy coating, having a thickness between 10 and 33 pm, on each side of the hot-rolled steel sheet.
    [038] According to one embodiment, the composition is such that Ni <0.1%.
    [039] In this embodiment, the composition preferably comprises, in percentage by weight:
    0.040% <C <0.100%
    Petition 870190044879, of May 13, 2019, p. 91/220
    15/65
    0.80% <Μη <2.0%
    0.005% <Si <0.30%
    0.010% <Al <0.070%
    0.001% <Cr <0.10%
    0.001% <Ni <0.10%
    0.03% <Ti <0.08%
    0.015% <Nb <0.1%
    0.0005% <N <0.009%
    0.0001% <S <0.005%
    0.0001% <P <0.030%
    Mo <0.10%
    Ca <0.006% the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting, [040] According to one embodiment, the composition is such that 0.075% <C <0.38%.
    [041] According to a particular embodiment, steel has the following chemical composition, in percentage by weight:
    0.040% <C <0.100%
    0.80% <Mn <2.0% 0.005% <Si <0.30%
    0.010% <Al <0.070%
    0.001% <Cr <0.10%
    0.001% <Ni <0.10%
    0.03% <Ti <0.08%
    0.015% <Nb <0.1%
    0.0005% <N <0.009%
    0.0001% <S <0.005%
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    0.0001% <P <0.030%
    Mo <0.10%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [042] According to another particular embodiment, steel has the following chemical composition, in percentage by weight:
    0.062% <C <0.095%
    1.4% <Mn <1.9%
    0.2% <Si <0.5%
    0.020% <Al <0.070%
    0.02% <Cr <0.1% where 1.5% <(C + Mn + Si + Cr) <2.7%
    3.4 x N <Ti <8 x N
    0.04% <Nb <0.06% where 0.044% <(Nb + Ti) <0.09%
    0.0005% <B <0.004% 0.001% <N <0.009%
    0.0005% <S <0.003% 0.001% <P <0.020% and, optionally, 0.0001% <Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [043] According to another particular embodiment, steel has the following chemical composition, in percentage by weight:
    0.15% <C <0.38%
    0.5% <Mn <3%
    0.10% <Si <0.5%
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    0.005% <Al <0.1%
    0.01% <Cr <1%
    0.001% <Ti <0.2%
    0.0005% <B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [044] According to another particular embodiment, steel has the following chemical composition, in percentage by weight:
    0.24% <C <0.38%
    0.40% <Mn <3%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
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    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [045] Preferably, the coating comprises an intermetallic layer, having a thickness of at most 15 pm, that is less than or equal to 15 pm.
    [046] According to one embodiment, the coated and hot-rolled steel sheet further comprises, on each side, a Zn coating having a thickness less than or equal to 1.1 pm.
    [047] In one embodiment, the hot-rolled steel sheet has a ferrite-pearlitic structure, that is, a structure consisting of ferrite and perlite.
    [048] The invention also relates to a coated and hot-rolled steel sheet comprising:
    a hot-rolled steel sheet having a thickness between 1.8 mm and 5 mm, whose composition comprises, in percentage by weight:
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
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    0.25% <Ni <2%
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting, said hot-rolled steel sheet having an intergranular oxidation depth of less than 4 pm, an Al or alloy coating A1, having a thickness comprised between 10 and 33 pm, on each side of the hot-rolled steel sheet.
    [049] Preferably, the coating comprises an intermetallic layer having a thickness of at most 15 pm, that is less than or equal to 15 pm.
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    20/65 [050] According to one embodiment, the coated and hot-rolled steel sheet further comprises, on each side, a coating of Zn having a thickness less than or equal to 1.1 pm.
    [051] In one embodiment, hot-rolled steel has a ferrite-pearlitic structure, that is, a structure consisting of ferrite and perlite.
    [052] The invention also relates to a method for manufacturing a hot-stamped coated steel part, which comprises the steps of:
    supply a coated and hot rolled steel sheet according to the invention or execute the method according to the invention, cut the coated and hot rolled steel sheet to obtain a blank, heat the blank in an oven to a temperature Tc to obtain a heated blank, transfer the heated blank to a die and hot stamp the heated blank in the die, thus obtaining a hot stamped blank, cool the hot stamped blank to a temperature below 400 Q C for a hot-stamped coated steel part.
    [053] According to one embodiment, after cutting the coated and hot-rolled steel sheet to obtain the blank and before the blank is heated to temperature Tc, the blank is welded to another blank steel having a composition comprising, in percentage by weight:
    0.04% <C <0.38%
    0.40% <Mn <3%
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    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <2%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [054] Preferably, said other raw piece has a composition such that Ni <0.1%.
    [055] According to another embodiment, after cutting the coated and hot-rolled steel plate to obtain the blank and before the blank is heated to temperature Tc, the blank is welded to another blank steel having a composition comprising, in percentage by weight:
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
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    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [056] The invention also relates to a hot-stamped coated steel part, comprising at least a portion having a thickness comprised between 1.8 mm and 5 mm, said hot-stamped coated steel part comprising a coating of Al or Al alloy, the coating having a surface percentage of porosity less than or equal to 3%.
    [057] According to an embodiment, said portion is made of steel having a composition that comprises, in percentage by weight:
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    0.04% <C <0.38%
    0.40% <Μη <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <2%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [058] According to one embodiment, the composition of the steel in said portion is such that Ni <0.1%.
    [059] According to another embodiment, said portion is made of steel having a composition that comprises, in percentage by weight:
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
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    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [060] The invention also relates to the use of a hot-stamped coated steel part, according to the invention, or produced by a method, according to the invention, for the manufacture of chassis or body parts -in-white parts) or suspension arms for automotive vehicles.
    Brief Description of the Figures [061] The invention will now be described in detail and illustrated by examples without introducing limitations, with reference to the attached Figures, among which:
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    - Figure 1 is a cross section of a hot-rolled coated steel part, illustrating the evaluation of the coating's adhesion after hot stamping;
    - Figure 2 is a cross section of a hot rolled steel substrate, before coating and hot stamping, illustrating the determination of the surface percentage of voids on the hot rolled steel substrate surface.
    Detailed Description of the Invention [062] By hot-rolled steel product, substrate, sheet or part, it should be understood that the product, substrate, sheet or part is hot-rolled, but not cold-rolled.
    [063] The present invention relates to a hot rolled steel sheet that has not yet been cold rolled.
    [064] Hot rolled sheets or substrates differ from cold rolled sheets or substrates with respect to the following characteristics: in general, the hot and cold rolling steps create some damage around the second phase particles due to differences in behavior between the matrix and the particles of the second phase (oxides, sulfides, nitrides, carbides ...). In the case of cold rolling, voids can accumulate and grow around cementite, carbides or perlite. In addition, the particles can be fragmented. This damage can be seen in plates cut and prepared by ion beam polishing. This technique avoids artifacts due to the flow of metal in the mechanical polishing that can partially or completely fill any voids. An additional observation of the presence of occasional voids is carried out through Scanning Electron Microscopy. In comparison to a hot-rolled steel sheet wound in the austenitic strip, the local damage observed around or inside the cementite particles can be specifically attributed to the rolling
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    26/65 cold, since these particles are not present in the hot rolling stage. Thus, the damage observed in or around cementite, carbides or perlite in a rolled steel sheet is an indication that the steel sheet has been cold rolled.
    [065] In addition, in the following, a hot rolled steel substrate will designate the hot rolled steel product that is produced by executing the manufacturing method before any coating step, and a hot rolled and coated steel plate designate the product resulting from the manufacturing method, including the coating step. The hot-rolled and coated steel sheet, therefore, results from the coating of the hot-rolled steel substrate and comprises a steel product and a coating on each side of the steel product.
    [066] To distinguish the steel product from the hot-rolled and coated steel plate (ie excluding the coating) from the hot-rolled steel substrate before coating, the steel product from the hot-rolled and coated steel plate hereinafter referred to as “hot-rolled steel sheet”.
    [067] Hot-rolled steel substrates are generally produced from a semi-finished steel product which is heated, hot-rolled to the desired thickness, cooled to the winding temperature Tenroiring, rolled to the winding temperature and blasted to eliminate fouling.
    [068] Hot-rolled steel substrates can then be coated to create coated and hot-rolled steel sheets, which are intended to be cut, heated in an oven, hot stamped and cooled to room temperature to obtain the desired structure .
    [069] The inventors investigated the problem of the adhesion of the coating to the hot stamping, and found that this lack of
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    27/65 adhesion occurs mainly in parts of the plates that were located in the region of the core and longitudinal axis of winding during the winding.
    [070] The inventors further investigated this phenomenon and found that the lack of adhesion of the coating after hot stamping is caused by the intergranular oxidation that occurs during winding.
    [071] In particular, shortly before winding, steel comprises austenite. After winding, part of this austenite turns into ferrite and perlite, generating heat. The heat that is generated leads to an increase in temperature in the coiled steel substrate, especially in the core and in the coil shaft region.
    [072] The core of the coil is defined as the portion of the substrate (or plate) that extends, along the longitudinal direction of the substrate, from a first end located at 30% of the total length of the substrate, to a second end located at 70% of the total substrate length. In addition, the axis region is defined as the region centered on the medium longitudinal axis of the substrate, having a width equal to 60% of the total width of the substrate.
    [073] In the region of the core and axis, during the winding, the windings are contiguous, and the partial pressure in oxygen is such that only the elements more easily oxidizable than iron, especially silicon, manganese or chromium, are oxidized.
    [074] The diagram of the iron-oxygen phase at 1 atmosphere shows that iron oxide formed at high temperatures, namely wustite (FeO), is not stable at temperatures below 570 Q C and is transformed, in thermodynamic equilibrium, into two other phases: hematite (Fe2O3) and magnetite (Fe3O4). Conversely, if the temperature rise in some parts of the coil during winding, especially in the core and in the
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    28/65 coil, if the temperature exceeds 570 Q C, the hematite and magnetite will turn into wustite, one of the products of this decomposition being oxygen.
    [075] The oxygen resulting from this reaction combines with elements more easily oxidizable than iron, especially silicon, manganese, chromium and aluminum, which are present on the surface of the steel substrate.
    [076] These oxides naturally form at the grain boundaries, rather than diffusing homogeneously in the matrix. As a result, oxidation is more pronounced at the grain boundaries. This oxidation will be said here afterwards as intergranular oxidation.
    [077] Thus, at the end of the coil, the winding comprises intergranular oxidation, on the surface and to a certain depth, which can reach 17 micrometres.
    [078] The inventors found that an important intergranular oxidation on the hot rolled steel substrate and, consequently, on the hot rolled steel sheet, results in poor coating adhesion after hot stamping. In fact, after coating, when the plate is heated to be hot stamped, carbon diffuses into the coating and encounters intergranular oxides, in particular manganese and silicon oxides. This carbon diffusion results in a reaction between SIO2 and C, between MnO and C, and between Mn2SIO4 and C, to form carbon oxides. These carbon oxides migrate and dissolve until the final coating solidifies, when they come together to form pockets, resulting in porosity in the coating and thus poor adhesion of the coating.
    [079] The impact of intergranular oxidation on coating adhesion is specific to hot-rolled steel sheets, which are not
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    29/65 subjected to cold rolling, in addition to winding, in contrast to cold rolled steel sheets. In fact, during the production of such cold-rolled sheets, the intergranular oxidation that may be present on the substrate surface, before cold rolling, is subjected during cold rolling, like the entire sheet, to a reduction in thickness. Consequently, the depth of intergranular oxidation of the cold-rolled sheet, prior to hot stamping, is greatly reduced compared to the depth of intergranular oxidation of a hot-rolled steel sheet.
    [080] Intergranular oxidation can be reduced or even removed, before coating, by intensive pickling of the steel substrate, for example in an HCI bath for a time of 375 s.
    [081] However, intensive pickling requires very low line speed, which is not compatible with industrial processing.
    [082] Furthermore, this intensive pickling results in a very important developed surface, on the surface of the steel substrate. The developed surface designates the total surface area of the steel substrate, which is in contact with the bath during coating.
    [083] This important developed surface results in a more intense dissolution of iron from the steel surface during hot dip coating in the bath, resulting in a growth of the intermetallic layer, which is not limited to a single limited region of the coating adjacent to the steel sheet, but reaches the surface of the coating. As a consequence, the thickness of the coating cannot be controlled in the desired thickness range. The intermetallic layer is made of a solid state compound composed of metal elements with a defined stoichiometry, having a crystalline structure in which the atoms occupy specific positions.
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    30/65 [084] The inventors have therefore discovered that the suppression or limitation of intergranular oxidation during winding allows the manufacture of a coated and hot-rolled steel sheet having a thickness between 1.8 mm and 5 mm having a thickness improved coating adhesion after stamping, while allowing coating thickness control for the target range, especially between 10 and 33 pm, and maintaining good productivity in the industrial pickling line.
    [085] The composition of the steel is such that the steel can be hot stamped to create a part with a tensile strength greater than or equal to 500 MPa, or greater than or equal to 1000 MPa, or greater than or equal to 1350 MPa, or greater than or equal to 1680 MPa.
    [086] A composition of steel according to a first aspect of the invention is disclosed below.
    [087] With regard to the chemical composition of steel, carbon plays an important role in the hardenability and tensile strength obtained after hot stamping, thanks to its effect on the hardness of martensite.
    [088] Below a content of 0.04%, it is not possible to obtain a tensile strength above 500 MPa after stamping under any cooling conditions. Above 0.38%, in combination with the other elements of the composition according to this first aspect, the adhesion of the coating after hot stamping is not satisfactory. Without being bound by theory, a C content greater than 0.38% can result in an important formation of carbon oxides during the heating of the plate before hot stamping, aggravating the negative impact of intergranular oxidation on the adhesion of the coating. In addition, above 0.38%, crack resistance and steel toughness decrease.
    [089] The C content depends on the desired tension force TS of the
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    31/65 hot stamped part, produced by hot stamping of the steel sheet. Especially, for carbon contents ranging from 0.06% to 0.38% by weight, the TS tensile strength of hot stamped parts produced through total austenitization and stamping, followed by a martensitic quench, depends practically only on the content of carbon and is linked to the carbon content by the expression:
    TS (MPa) = 3220 (C%) + 908, where C% designates the carbon content, in percentage by weight.
    [090] According to one embodiment, the C content is greater than or equal to 0.75%.
    [091] In addition to its role in deoxidation, manganese has an important effect on drying capacity, in particular when its content is at least 0.40%, with the C content being at most 0, 38%. Above 3%, the stabilization of austenite by Mn is very important, which leads to the formation of a structure with very pronounced bands. According to one embodiment, the Mn content is less than or equal to 2.0%.
    [092] Silicon is added in a content of at least 0.005% to help deoxidize liquid steel and contribute to steel hardening. Its content should, however, be limited in order to avoid excessive formation of silicon oxides. In addition, the silicon content must be limited to avoid a very important stabilization of austenite. The silicon content is therefore less than or equal to 0.70%, for example, less than or equal to 0.5%. Preferably, the Si content is at least 0.10%.
    [093] Aluminum can be added as a deoxidizer, with the Al content being less than or equal to 0.1% and greater than 0.005%, generally greater than or equal to 0.010%. Preferably, the Al content is less than or equal to 0.070%.
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    32/65 [094] Optionally, the steel composition comprises chromium, tungsten and / or boron, to increase the drying capacity of the steel.
    [095] Especially, Cr can be added to increase the curing capacity of steel and contributes to achieving the desired tensile strength after hot stamping. When Cr is added, its content is greater than or equal to 0.01%, up to 2%. If no voluntary addition of Cr is performed, the Cr content can be as low as 0.001%.
    [096] W can be added to increase the drying capacity and the hardenability of steel forming tungsten carbides. When W is added, its content is greater than or equal to 0.001% and less than or equal to 0.30%.
    [097] When B is added, its content is greater than 0.0002% and preferably greater than or equal to 0.0005%, up to 0.010%. The B content is preferably less than or equal to 0.005%.
    [098] Up to 0.1% niobium and / or up to 0.2% titanium are optionally added to provide precipitation hardening.
    [099] When Nb is added, its content is preferably at least 0.01%. In particular, when the Nb content is between 0.01% and 0.1%, the Nb precipitates of fine hardening carbides (CN) are formed in austenite or ferrite during hot rolling. The Nb content is preferably less than or equal to 0.06%. Even more preferably, the Nb content is between 0.03% and 0.05%.
    [0100] When Ti is added, its content is preferably at least 0.015%, up to 0.2%. When the Ti content is between 0.015% and 0.2%, precipitation at very high temperatures occurs in the form of TiN and then, at low temperature, in austenite in the form of fine TiC, resulting in hardening. In addition, when titanium is added in addition to boron, titanium prevents the combination of boron with nitrogen, combining the
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    33/65 nitrogen with titanium. Thus, the titanium content is preferably greater than 3.42 N. However, the Ti content must remain less than or equal to 0.2%, preferably less than or equal to 0.1% , to avoid the precipitation of coarse TiN precipitates. If no voluntary addition of Ti is performed, Ti is present as an impurity with a content of at least 0.001%.
    [0101] Molybdenum can be added in a maximum content of 0.65%. When Mo is added, its content is preferably at least 0.05%, for example, less than or equal to 0.10%. Mo is preferably added together with Nb and Ti, to form co-precipitates that are very stable at high temperatures and limit the growth of the austenitic grain by heating. An optimal effect is obtained when the Mo content is between 0.15% and 0.25%.
    [0102] Nickel is present as an impurity in a content that can be as low as 0.001% and less than or equal to 0.1%.
    [0103] Sulfur, phosphorus and nitrogen are generally present in the steel composition as impurities.
    [0104] The nitrogen content is at least 0.0005%. The nitrogen content must be at most 0.010%, in order to avoid the precipitation of coarse TiN precipitates.
    [0105] When in excessive amounts, sulfur and phosphorus reduce ductility. Therefore, its content is limited to 0.05% and 0.1%, respectively.
    [0106] Preferably, the S content is at most 0.03%. Achieving a very low S content, that is, less than 0.0001%, is very expensive and without any benefit. Therefore, the S content is generally greater than or equal to 0.0001%.
    [0107] Preferably, the phosphorus content is at most
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    0.05%, still preferably at most 0.025%. Achieving a very low P content, that is, less than 0.0001%, is very expensive. Therefore, the P content is generally greater than or equal to 0.0001%.
    [0108] Steel can be subjected to a treatment for globularization of sulfides made with calcium, which has the effect of improving the flexion angle, due to the globularization of MnS. Thus, the steel composition can comprise at least 0.0001% Ca, up to 0.006%.
    [0109] The remainder of the steel composition consists of iron and unavoidable impurities resulting from smelting.
    [0110] According to a first embodiment, steel has the following chemical composition, in percentage by weight:
    0.040% <C <0.100%
    0.80% <Mn <2.0%
    0.005% <Si <0.30%
    0.010% <Al <0.070%
    0.001% <Cr <0.10%
    0.001% <Ni <0.10%
    0.03% <Ti <0.08%
    0.015% <Nb <0.1%
    0.0005% <N <0.009%
    0.0001% <S <0.005%
    0.0001% <P <0.030%
    Mo <0.10%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [0111] With this composition, steel parts can be produced having, after hot stamping, a tensile strength of at least
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    500 MPa.
    [0112] According to a second embodiment, steel has the following chemical composition, in percentage by weight:
    0.062% <C <0.095%
    1.4% <Mn <1.9%
    0.2% <Si <0.5%
    0.020% <Al <0.070%
    0.02% <Cr <0.1% where 1.5% <(C + Mn + Si + Cr) <2.7%
    3.4 χ N <Ti <8 χ N
    0.04% <Nb <0.06% where 0.044% <(Nb + Ti) <0.09%
    0.0005% <B <0.004%
    0.001% <N <0.009%
    0.0001% <S <0.003%
    0.0001% <P <0.020% and, optionally, 0.0001% <Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [0113] With this composition, steel parts can be produced having, after hot stamping, a tensile strength of at least 1000 MPa.
    [0114] According to a third embodiment, steel has the following chemical composition, in percentage by weight:
    0.15% <C <0.38%
    0.5% <Mn <3%
    0.10% <Si <0.5%
    0.005% <Al <0.1%
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    0.01% <Cr <1%
    0.001% <Ti <0.2% 0.0005% <B <0.08% 0.0005% <N <0.010% 0.0001% <S <0.05% 0.0001% <P <0.1 % the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [0115] With this composition, steel parts can be produced having, after hot stamping, a tensile strength of at least 1350 MPa.
    [0116] A steel composition according to a second aspect of the invention is disclosed below.
    [0117] The C content is between 0.24% and 0.38% if the Mn content is between 0.40% and 3%. Carbon plays an important role in the hardenability and tensile strength obtained after hot stamping, thanks to its effect on martensite hardness. A content of at least 0.24% allows to achieve a tensile strength TS of at least 1800 MPa after hot stamping, without adding expensive elements. Above 0.38%, when the Mn content is between 0.40% and 3%, the resistance to cracking delay and the toughness of the steel decrease. The C content is preferably between 0.32% and 0.36% if the Mn content is between 0.40% and 3%.
    [0118] An increased C content between 0.38% and 0.43% can be used when the Mn content is reduced to the range between 0.05% and 0.40%. The reduction in the Mn content is thus offset by the increase in the C content, while achieving improved corrosion resistance under stress.
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    37/65 [0119] In addition to its deoxidizing role, manganese has an important effect on the drying capacity.
    [0120] When the C content is between 0.24% and 0.38%, the Mn content must be at least 0.40% and less than or equal to 3%. A Mn content of at least 0.40% is necessary to reach a temperature Ms, with the temperature at which the transformation from austenite to martensite starts after cooling down low enough to achieve the desired strength level (TS tensile strength of at least 1800 Mpa in this embodiment).
    [0121] Above 3%, the stabilization of austenite by Mn is very important, which leads to the formation of a structure with very pronounced bands. The Mn content is preferably less than or equal to 2.0%.
    [0122] Alternatively, the Mn content can be reduced to the range between 0.05% and 0.40% if the C content is increased to the range between 0.38% and 0.43%. Decreasing the Mn content allows greater resistance to stress corrosion.
    [0123] The contents of Mn and C are preferably defined together with the content of Cr.
    [0124] When the C content is between 0.32% and 0.36%, an Mn content between 0.40% and 0.80% and a Cr content between 0.05% and 1.20 % allow achieving a high resistance to cracking delay.
    [0125] When the C content is between 0.24% and 0.38%, the Mn content being between 1.50% and 3%, spot weldability is particularly satisfactory.
    [0126] When the C content is between 0.38% and 0.43%, the Mn content being between 0.05% and 0.40%, and preferably between 0.09% and 0.11 %, resistance to corrosion under stress is
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    38/65 highly increased.
    [0127] These composition ratios make it possible to reach an Ms temperature between about 320 QC and 370 -C, which guarantees a very high resistance of the hot-stamped parts.
    [0128] Silicon is added in a content between 0.10% and 0.70% by weight. A content of at least 0.10% provides additional hardening and helps to deoxidize liquid steel. Its content should, however, be limited in order to avoid excessive formation of silicon oxides. In addition, the silicon content must be limited to avoid a very important stabilization of austenite. The silicon content is therefore less than or equal to 0.70%.
    [0129] When the C content is between 0.24% and 0.38%, the Si content is preferably at least 0.50% to avoid a quenching of the fresh martensite that can occur when the steel is kept inside the matrix after the martensitic transformation.
    [0130] Aluminum can be added as a deoxidizer, the Al content being less than or equal to 0.070% and greater than or equal to 0.015%. Above 0.070%, thick aluminates can be created during preparation, reducing duetility. Preferably, the Al content is between 0.020% and 0.060%.
    [0131] Optionally, the steel composition comprises chromium and / or tungsten to increase the drying capacity of the steel.
    [0132] Chromium increases the curing capacity of steel and contributes to obtaining the desired tensile strength TS after hot stamping. When Cr is added, its content is greater than or equal to 0.01%, up to 2%. If no voluntary addition of Cr is performed, the Cr content can be as low as 0.001%.
    [0133] When the C content is between 0.24% and
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    0.38%, the Cr content is preferably between 0.30% and 0.50%. When the Mn content is between 1.50% and 3%, the addition of Cr is optional, and the quench is achieved by adding sufficient Mn.
    [0134] When the C content is between 0.38% and 0.43%, a Cr content greater than 0.5% is preferred, and preferably between 0.950% and 1.050%, in order to increase the corrosion resistance under stress.
    [0135] In addition to the conditions defined above, the levels of C, Mn, Cr and Si must satisfy the following condition:
    2.6C + - + - + -> 1.1%
    5.3 13 15 [0136] Under this condition, the fraction of self-tempering martensite resulting from the tempering of the martensite that can occur while the piece is kept in the matrix is very limited, so that the fraction of very high fresh martensite allows to achieve a resistance to at least 1800 MPa.
    [0137] W can be added to increase the drying capacity and the hardenability of steel forming tungsten carbides. When W is added, its content is greater than or equal to 0.001% and less than or equal to 0.30%.
    [0138] B is added in a content greater than 0.0005%, up to 0.0040%. B increases the temper. By diffusing at the grain boundaries, B prevents the intergranular segregation of P.
    [0139] Up to 0.06% niobium and / or up to 0.1% titanium are optionally added to provide precipitation hardening.
    [0140] When Nb is added, its content is preferably at least 0.01%. In particular, when the Nb content is between 0.01% and 0.06%, the precipitated Nb carbides precipitate
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    40/65 (CN) are formed in austenite or ferrite during hot rolling. Nb thus limits the growth of austenitic grains during heating before stamping. The Nb content is, however, less than or equal to 0.06%. In fact, above 0.06%, the rolling load can become very high. Preferably, the Nb content is between 0.03% and 0.05%.
    [0141] Ti is added in a content of at least 0.015%, up to 0.1%. When the Ti content is between 0.015% and 0.1%, precipitation at very high temperatures occurs in the form of TiN and then, at low temperature, in austenite in the form of fine TiC, resulting in hardening. In addition, titanium prevents the combination of boron with nitrogen, combining nitrogen with titanium. Thus, the titanium content is greater than 3.42 N. However, the Ti content must remain less than or equal to 0.1%, to avoid precipitation of coarse TiN precipitates. Preferably, the Ti content is comprised between 0.020% and 0.040% to create fine nitrides that limit the growth of austenitic grains during heating before stamping.
    [0142] Molybdenum can be added in a maximum content of 0.65%. When Mo is added, its content is preferably at least 0.05%. Mo is preferably added together with Nb and Ti, to form co-precipitates that are very stable at high temperatures and limit the growth of the austenitic grain by heating. An optimal effect is obtained when the Mo content is between 0.15% and 0.25%.
    [0143] Nickel is added to increase the steel's delayed fracture resistance, in a content between 0.25% and 2%.
    [0144] The nitrogen content is at least 0.003% to achieve a precipitation of TiN, Nb (CN) and / or (Ti, Nb) (CN), limiting the growth of austenitic grains, as explained above. The nitrogen content must be a maximum of 0.010%, in order to avoid precipitation of TiN precipitates
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    41/65 gross.
    [0145] When in excessive amounts, sulfur and phosphorus reduce ductility. Therefore, its content is limited to 0.005% and 0.025%, respectively.
    [0146] The S content is a maximum of 0.005% to limit sulfide precipitation. Achieving a very low S content, that is, less than 0.0001%, is very expensive and without any benefit. Therefore, the S content is generally greater than or equal to 0.0001%.
    [0147] The phosphorus content is a maximum of 0.025%, thus limiting the segregation of P within the limits of austenitic grains. Achieving a very low P content, that is, less than 0.0001%, is very expensive. Therefore, the P content is generally greater than or equal to 0.0001%.
    [0148] Steel can be subjected to a treatment for globularization of sulfides made with calcium, which has the effect of improving the angle of flexion, due to the globularization of MnS. Thus, the steel composition can comprise at least 0.0005% Ca, up to 0.005%.
    [0149] The rest of the steel composition consists of iron and unavoidable impurities resulting from smelting.
    [0150] As explained above, the inventors found that the lack of adhesion of the coating on a steel part, produced by hot stamping of a coated and hot rolled steel sheet, results from the intergranular oxidation present on the surface of the steel sheet hot rolled and coated, before hot stamping, and through a certain thickness.
    [0151] First, the inventors sought a criterion that must be met by the hot-stamped coated steel part to ensure satisfactory adhesion of the coating.
    [0152] The inventors found that the quality of adhesion
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    42/65 of the coating can be evaluated by determining the surface percentage of porosity in the coating.
    [0153] The percentage of surface porosity in the coating is determined on the hot-stamped coated steel part, that is, after hot stamping and cooling to room temperature.
    [0154] The surface percentage of porosity in the coating is determined by looking at five different cross sections of a sample under an optical microscope, with a magnification of 1000 times. Each cross section has an Iref length, which is selected to characterize the coating in a representative way. The Iref length is selected as 150 pm.
    [0155] As illustrated in Figure 1, for each cross section, an image analysis is performed, through an image analysis, for example, Olympus Stream Essentials®, to determine the percentage of porosity surface in the coating in this cross section . For this purpose, the upper and lower limits B1 and B2 of the coating are identified. In particular, the upper limit follows the contour of the coating, at the interface with the surrounding environment, and the lower limit separates the steel material from the coating. Then, the total surface occupied by the coating, including the P porosities, between the lower and upper limits is determined, and the surface occupied by the porosities that are located between the lower and upper limits is evaluated (gray areas in Figure 1). The percentage of porosity surface in the coating of the cross section under consideration is then calculated as the ratio between the surface occupied by the porosities and the total surface occupied by the coating (multiplied by 100).
    [0156] Finally, the surface percentage of porosity in the coating is determined as the average of the five values thus obtained.
    Petition 870190044879, of May 13, 2019, p. 119/220
    43/65 [0157] The adhesion of the coating is considered satisfactory if the surface percentage of porosities in the coating is less than or equal to 3%. In contrast, if the surface percentage of porosity in the coating is greater than 3%, the adhesion of the coating is considered unsatisfactory.
    [0158] In addition, the inventors have identified two criteria that must be satisfied, by the hot-rolled steel substrate and the hot-rolled steel plate, respectively, to ensure that the coating thickness can be controlled to be within the target range , especially in the range 10 to 33 pm, for example between 20 and 33 pm or between 10 and 20 pm, and that, after stamping, the adhesion of the coating will be satisfactory.
    [0159] The first criterion is related to the surface condition of the hot rolled steel substrate, after pickling and before coating.
    [0160] Especially, as explained above, the developed surface of the hot-rolled steel substrate immediately before coating must be controlled to prevent the intense dissolution of iron from the steel surface and the uncontrolled growth of the intermetallic layer during hot immersion in the bath, which would result in the inability to control the thickness of the coating within the target range.
    [0161] In fact, the intergranular oxidation of the hot-rolled steel substrate can be reduced by intensive pickling, which in turn allows to reduce the intergranular oxidation of the hot-rolled steel sheet. However, due to this intensive pickling, the substrate would have a surface state (i.e., a developed surface) incompatible with controlling the thickness of the coating.
    [0162] The inventors found that in order to ensure that the
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    44/65 thickness of the coating will be comprised in the target range, ie between 10 and 33 pm, the thickness of the intermetallic layer formed during the coating must remain less than 15 pm, and that in order to obtain an intermetallic layer thickness less than 15 pm, the surface percentage of voids in the hot rolled steel substrate surface region, after any pickling and before coating, should be less than 30%. The thickness of the intermetallic layer here designates the thickness of the intermetallic layer of the coating of the hot-rolled and coated steel sheet.
    [0163] The criterion relating to the superficial percentage of voids must, in particular, be fulfilled in the region of the hot rolled steel substrate located in the core and in the region of the coil axis during winding.
    [0164] As illustrated in Figure 2, the surface region is defined as the region that extends from the upper point of the surface of the hot-rolled steel substrate to a depth, from this upper point, of 15 pm. The surface percentage of voids in the surface region is determined from five distinct cross sections representative of the hot rolled steel substrate, each cross section having an Iref length of 150 pm. The cross sections are preferably taken from a sample taken from the core and from the coil axis region. In each cross section, a sample surface region is determined by means of image analysis, for example, Olympus Stream Essentials®, as a rectangular region whose upper side joins the two highest points Pt1 and Pt2 of the surface profile of the cross section and whose bottom side is distant from the top side of 15 pm. Thus, each surface region of the sample has an Iref length of 150 pm and a depth of 15 pm.
    [0165] For each cross section, the regions of the region of
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    45/65 sample surfaces that are not steel are identified, and the total surface of these regions is determined. The surface percentage of voids in the sample surface region is then determined as the ratio between the total surface of the non-steel regions and the total surface area of the sample surface, multiplied by 100. Finally, the surface percentage of the voids of the hot-rolled and pickled steel substrate is determined as the average of the five values thus obtained.
    [0166] The second criterion is a maximum depth of intergranular oxidation of the hot-rolled steel sheet, that is, of the steel product after coating. In fact, the inventors found that, in order to obtain satisfactory adhesion of the coating after hot stamping, the depth of intergranular oxidation of the hot rolled steel sheet must be less than 4 pm.
    [0167] This criterion must, in particular, be fulfilled in the region of the coated and hot-rolled steel plate that was located in the core and in the region of the coil axis during winding.
    [0168] The depth of intergranular oxidation is determined on the coated and hot-rolled steel plate, that is, after coating.
    [0169] The depth of intergranular oxidation is defined as the thickness of the region of the hot-rolled steel sheet, the surface of the hot-rolled steel sheet (ie, the interface between the coating and the hot-rolled steel sheet) into the hot-rolled steel sheet, in a direction orthogonal to this surface, on which intergranular oxidation is observed.
    [0170] Especially, intergranular oxidation is observed with an optical microscope with a magnification of 1000 times, in five different cross sections, each with a length of 150 pm, from a sample taken from the nucleus and from the axis region of the coil. In each
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    46/65 cross section, the maximum depth of intergranular oxidation is measured. Finally, the depth of intergranular oxidation is determined as the average of the five values thus obtained.
    [0171] Thus, in order to ensure that, after coating, the coating thickness can be controlled to be within the target range and that, after hot stamping, the coating adhesion will be satisfactory, that is, the surface percentage of porosity in the coating will be less than or equal to 3%, the following two conditions must be met:
    - the superficial percentage of voids in the hot rolled steel substrate surface area, after stripping and before coating, should be less than 30%, and
    - the depth of intergranular oxidation of the hot-rolled steel sheet, after stripping and coating, must be less than 4 pm.
    [0172] Hot rolled steel products can be produced by casting a steel having a composition as mentioned above, in order to obtain a steel semi-product, reheating the steel semi-product to a temperature of Reheating between 1150 Q C and 1300 -C, and hot rolling of the reheated steel semi-product, with a final FRT rolling temperature, in order to obtain a hot rolled steel product. The reheat temperature is, for example, between 1150 Q C and 1240 Q C [0173] The final FRT rolling temperature is generally between 840 Q C and 1000 Q C.
    [0174] The reduction of hot rolling is adapted so that the product of hot rolled steel has a thickness between 1.8 mm and 5 mm, for example, between 3 mm and 5 mm.
    [0175] The hot rolled steel product is then cooled in
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    47/65 flow table to reach the winding temperature Tearing and rolled to obtain a hot rolled steel substrate.
    [0176] The Tearing winding temperature is selected in order to avoid or at least limit intergranular oxidation.
    [0177] In particular, the coiling winding temperature is selected so that the depth of intergranular oxidation of the hot rolled steel substrate is less than 5 pm. Indeed, if the depth of intergranular oxidation of the hot-rolled steel substrate is less than 5 pm, the depth of intergranular oxidation of the hot-rolled steel sheet, after coating, will remain below 4 pm. Even more preferably, the Tenroiamento winding temperature is selected in such a way that intergranular oxidation does not occur.
    [0178] With a steel composition according to the first aspect, the inventors found that in order to obtain a depth of intergranular oxidation of the hot-rolled steel sheet of less than 4 pm, the winding temperature must be less than a maximum temperature winding Tenroiamentomax, which depends on the fraction of austenite just before the winding, denoted fy.
    [0179] In fact, a high fraction of austenite before winding will result in a substantial transformation of austenite during winding, hence an important increase in temperature, especially in the region of the coil and the plate axis during winding. On the other hand, if the fraction of austenite fy before the winding is low, no or little transformation of the austenite will occur during the winding, so that the increase in the plate temperature will be reduced.
    [0180] As a consequence, the maximum winding temperature Tenroiamentomax is a decreasing function of the austenite fraction fy just before the winding.
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    48/65 [0181] The inventors found that, in order to obtain a depth of intergranular oxidation in the hot-rolled steel sheet of less than 4 qm, the maximum winding temperature Tenroiamentomax is expressed as:
    Tenrolamentomax = 650 - 140 X fy where Tenrolamentomax is expressed in degrees Celsius, and fy designates the fraction of austenite in the steel immediately before winding, comprised between 0 (corresponding to 0% austenite) and 1 (corresponding to 100% austenite ). The maximum winding temperature Tenrolamentomax is therefore between 510 Q C and 650 Q C.
    [0182] Thus, the Tearing winding temperature must satisfy:
    Tensing - 650 - 140 X fy [0183] The fraction of austenite ίγ in steel immediately before winding can be determined using a non-destructive non-destructive electromagnetic (EM) technique using a device for detecting the magnetic properties of the plate steel.
    [0184] The principle of this technique, which is described, for example, in the document “Online electromagnetic monitoring of austenite transformation in hot strip lamination and its application for process optimization - Online electromagnetic monitoring of austenite transformation in hot strip rolling and its application to process optimization ”, AV Marmulev et Al., Revue de Métallurgie 110, pp. 205-213 (2013), is based on the difference between the magnetic properties of austenite, which is paramagnetic, and the magnetic properties of ferrite, perlite, bainite and martensite, which are ferromagnetic phases.
    [0185] A device for determining the fraction of austenite fy is, for example, disclosed in US 2003/0038630 A1.
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    49/65 [0186] The fraction of austenite ίγ immediately before winding depends on the composition of the steel, especially the C content, the final FRT rolling temperature and the cooling process between the final FRT rolling temperature and the winding temperature Tendering.
    [0187] In particular, the higher the C content of the steel, the greater the fraction of austenite fy in the plate before winding. Thus, with all other parameters being equal, the higher the C content, the lower the maximum winding temperature Tenroiamentomax. Especially, if the C content of steel is greater than or equal to 0.075%, the fraction of austenite in the substrate remains greater than 0.5, so that the winding temperature Tenrolamentomax is less than 580 Q C.
    [0188] The maximum winding temperature Tenrolamentomax can be determined, for a steel having given composition and thickness, in a given line, fixing the final rolling temperature, determining the fraction of austenite in the steel product during the cooling of the temperature of final FRT lamination, and comparing, during cooling, the temperature T of the substrate to the value 650 - 140 ίγ '(Τ), ίγ' (Τ) being the austenite fraction of the substrate at temperature T during cooling.
    [0189] The maximum winding temperature Tenrolamentomax is the temperature at which T = 650-140 ίγ ’(Τ).
    [0190] In general, the coiling temperature is preferably less than 580 -C, again less preferred embodiment Q 570 C.
    [0191] However, the winding temperature must remain above 450 -C in order to avoid an unwanted increase in the mechanical properties of the steel that would result from a low winding temperature.
    [0192] Under these conditions, intergranular oxidation in the substrate
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    50/65 hot rolled steel is limited, so that the depth of intergranular oxidation of the hot rolled steel sheet after coating will be less than 4 pm.
    [0193] With a steel composition according to the second aspect, the inventors found that in order to obtain a depth of intergranular oxidation of the hot-rolled steel sheet of less than 4 pm, the winding temperature Tenroiamento must still be restricted compared to compositions according to the first aspect, and set to values less than or equal to 495 Q C.
    [0194] The rules given above to guarantee the adhesion of the parallel coating and the thickness of the coating in the target range are still valid. However, due to the presence of Ni greater than or equal to 0.25%, they are not sufficient to induce good productivity at the pickling line at the same time. In fact, the inventors found that the presence of Ni above 0.25% induces a greater fouling adherence in the hot strip mill. The presence of such encrustation, highly adherent to the surface, impairs the ability of the plate to coat. This scale can be removed by intense pickling, which, however, would greatly reduce productivity in the pickling line. The inventors found that reducing the winding temperature less than or equal to T windingmax = 495 Q C could help reduce the amount of scale formed on the flow table in the hot strip mill. Therefore, the metal nickel formed at the interface between the scale and the steel is reduced, which finally facilitates the breaking of scale and stripping in the stripping line and, consequently, provides a process with greater productivity in this last line.
    [0195] After winding, the hot rolled steel substrate is stripped. Since the depth of intergranular oxidation is limited,
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    51/65 pickling conditions do not influence the adhesion of the coating after hot stamping or the thickness of the coating.
    [0196] Especially, even if a light pickling is carried out, due to the low depth of intergranular oxidation before pickling, the depth of intergranular oxidation in the hot rolled steel sheet after pickling and coating will in any case be less than 4 pm, from so that or not carbon oxides will be formed during heating prior to hot forming, and that the adhesion of the coating after hot stamping will not be impaired.
    [0197] Furthermore, even if intensive pickling is carried out, due to the low depth of intergranular oxidation before pickling, the surface percentage of voids in the hot rolled steel substrate surface region after pickling will remain below 30%. Thus, there is no intense dissolution of iron from the steel surface and there will be no uncontrolled growth of the intermetallic layer during the hot dip coating of the steel sheet in the bath, and the thickness of the coating can be controlled to the desired thickness.
    [0198] The pickling is carried out, for example, in an HCI bath, for a time between 15 and 65 s.
    [0199] The hot-rolled steel substrate, which is stripped, thus obtained thus satisfies the first criterion defined above, that is, it has a void surface percentage in the surface region of less than 30%. In addition, the hot-rolled and pickled steel plate has little or no intergranular oxidation, which makes it possible to satisfy the second criterion defined above, that is, to obtain an intergranular oxidation depth of less than 4 pm in the hot-rolled steel plate after the coating.
    [0200] After pickling, the hot rolled and pickled steel substrate can be oiled or an organic film can be applied, for example
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    52/65 example Easyfilm® ΗΡΕ, to temporarily protect the plate surface.
    [0201] The hot-rolled and pickled steel substrate is then continuously coated by hot dipping in a bath, with Al or an Al alloy, in order to obtain a coated and hot-rolled steel plate.
    [0202] For example, the coating can be an Al-Si coating. A typical bath for an Al-Si coating in general contains in its basic composition, weight percent, from 8% to 11% of silicon, from 2% to 4% of iron, the rest being aluminum or aluminum alloy and impurities inherent in processing. The alloying elements present in aluminum include strontium and / or calcium, between 15 and 30 ppm each.
    [0203] As another example, the coating can be a Zn-AI-Mg coating. A typical bath for a Zn-AI-Mg coating contains, in weight percent, between 0.1% and 10% magnesium, between 0.1% and 20% aluminum, the rest being Zn or Zn alloy, optional additional elements such as Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr and / or Bi, and impurities inherent in the processing.
    [0204] For example, the bath contains between 0.5% to 8% aluminum, between 0.3% and 3.3% magnesium, the rest being Zn or Zn alloy, optional additional elements like Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr and / or Bi and impurities inherent in the processing.
    [0205] As another example, the coating is an Al-Zn-Si-Mg coating.
    [0206] A first bath example for an Al-Zn-Si-Mg coating contains, by weight, 2.0% to 24.0% zinc, 7.1% to 12.0% silicon, optionally from 1.1% to 8.0% magnesium and, optionally, additional elements selected from Pb, Ni, Zr or Hf, the content of each additional element being less than 0.3%, the remainder being aluminum and unavoidable impurities and residual elements, with the Al / Zn ratio above
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    53/65
    2.9.
    [0207] A second bath example for an Al-Zn-Si-Mg coating contains, by weight percentage, from 4.0% to 20.0% zinc, from 1% to 3.5% silicon, optionally from 1.0% to 4.0% of magnesium and, optionally, additional elements selected from Pb, Ni, Zr or Hf, the content of each additional element being less than 0.3%, the rest being aluminum and unavoidable impurities and residual elements, with the Zn / Si ratio between 3.2 and 8.0.
    [0208] A third bath example for an AlZn-Si-Mg coating contains, by weight percentage, from 2.0% to 24.0% zinc, from 1.1% to 7.0% silicon, optionally, from 1.1% to 8.0% of magnesium when the amount of silicon is between 1.1 and 4.0% and, optionally, additional elements selected from Pb, Ni, Zr or Hf , the content of each additional element being less than 0.3%, the remainder being aluminum and unavoidable impurities and residual elements, with the Al / Zn ratio above
    2.9.
    [0209] After deposition of the coating by hot dip, the coated steel sheet is generally cleaned with gas ejection nozzles on both sides of the coated steel sheet, and the coated steel sheet is then cooled.
    [0210] The coated and hot-rolled steel plate thus obtained comprises a hot-rolled steel plate and, on each side of the hot-rolled steel plate, a coating of Al or Al alloy.
    [0211] The hot-rolled steel sheet generally has a ferrite-pearlite structure, that is, a structure consisting of ferrite and perlite.
    [0212] The thickness of the Al or Al alloy coating on each side of the hot-rolled steel sheet is between 10 pm and 33 pm.
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    54/65 [0213] According to a first embodiment, the thickness of the coating is controlled to be comprised between 20 pm and 33 pm.
    [0214] According to a second embodiment, the thickness of the coating is controlled to be comprised between 10 pm and 20 pm.
    [0215] According to a third embodiment, the thickness of the coating is controlled to be comprised between 15 pm and 25 pm.
    [0216] After coating, the depth of intergranular oxidation in the hot rolled steel sheet remains less than 4 pm, generally less than 3 pm due to pickling. This depth extends from the surface of the hot-rolled steel sheet (i.e., the surface that separates the hot-rolled steel sheet from the cladding) into the interior of the steel sheet.
    [0217] In addition, due to the low surface percentage of voids in the hot rolled steel substrate surface region before coating, even after stripping, the coating thickness is within the desired thickness range, especially between 10 pm and 33 pm, on each side of the hot-rolled and coated steel sheet, and at each location on each side of the hot-rolled and coated steel sheet.
    [0218] The hot-rolled and coated steel sheet is intended to be hot stamped.
    [0219] For this purpose, the coated and hot-rolled steel sheet is cut to obtain a blank. Optionally, this part can be welded to a second blank, in order to obtain a custom welded blank (TWB) which comprises a first blank cut of a coated and hot rolled steel sheet according to the invention.
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    55/65 and a second blank. The second blank can also be obtained from a coated and hot-rolled steel sheet according to the invention, or it can be a cut in a blank from a cold-rolled and coated steel sheet. In particular, the first blank, having a thickness comprised between 1.8 mm and 5 mm, can be welded to a second blank, having a different thickness and / or made of steel having a different composition. The second blank is preferably made of steel having a composition that comprises, in percentage by weight:
    0.04% <C <0.38%
    0.40% <Mn <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <2%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65% W <0.30% Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [0220] The second blank can also be made of steel having a composition that comprises, in percentage by weight:
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    56/65
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [0221] For the sake of simplicity, the term "blank" will be used below to designate a piece obtained from a hot-rolled and coated steel plate according to the invention, or a piece
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    57/65 gross welded to measure including this blank.
    [0222] The blank is then heat treated in an oven before hot stamping and hot stamping to obtain a hot stamped coated steel part.
    [0223] In particular, the blank is heated in an oven to a temperature Tc which makes it possible to obtain at least partial transformation into austenite on the steel substrate. This temperature is, for example, between 860 QC and 950 -C, and in general between 880 QC and 950 -C, thus obtaining a heated blank.
    [0224] The heated blank is then removed from the oven and transferred from the oven to a die, where it is subjected to a hot deformation (hot stamping), in order to obtain the desired geometry of the part to obtain a stamped blank the hot. The crude stamped piece is heat Q cooled to 400 C at a cooling rate Vr is greater than the preferred form -Cl 10 are also preferably higher than 30 s -Cl, thereby obtaining a coated steel piece stamped with hot.
    [0225] The hot-stamped coated steel part that is obtained in this way has a very satisfactory coating adhesion.
    [0226] In particular, the surface porosity percentage in the coating of the hot-stamped coated steel part is less than or equal to 3%.
    [0227] In addition, after painting, for example, by spraying, the paint's adhesion is very satisfactory. The adhesion of the paint can, in particular, be assessed by carrying out a wet paint adhesion test in accordance with ISO 2409: 2007. The adhesion of the paint is considered good if the result of the wet paint adhesion test is less than or equal to 2, and bad if the result of the
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    58/65 wet paint adherence is greater than 2.
    Examples [0228] Hot-rolled and coated steel sheets were produced by casting semi-products having the compositions disclosed in Table 1, in percentage by weight:
    Table
    Steel Ç(%) Mn(%) Si(%) Al(%) Cr(%) Ni(%) You(%) Nb(%) B(%) N(%) s(%) P(%) Mo(%) w(%) Here(%) THE 0.23 1.13 0.24 0.037 0.159 0.013 0.036 0.001 0.0016 0.005 0.0017 0.015 0.003 0.003 0.0016 B 0.06 1.64 0.022 0.024 0.027 0.016 0.067 0.048 - 0.005 0.004 0.016 0.003 0.002 0.0015 Ç 0.36 1.24 0.226 0.032 0.111 0.105 0.034 0.001 0.0032 0.006 0.0014 0.015 0.021 0.004 0.0021 D 0.344 0.61 0.541 0.030 0.354 0.417 0.034 0.038 0.0039 0.005 0.0004 0.008 0.205 0.003 0.0006 AND 0.07 1.62 0.36 0.040 0.09 0.012 0.021 0.051 0.0030 0.006 0.0010 0.012 - 0.003 0.0004
    [0229] The Ni content reported in Table 1 for steels A, B and E corresponds to the presence of Ni as residual (or impurity).
    [0230] The semi-products were hot rolled to thickness, with a final FRT lamination temperature.
    [0231] The hot rolled steel products were cooled to the Tenroiamento winding temperature and rolled to the Tenroiamento winding temperature to obtain hot rolled steel substrates.
    [0232] The hot-rolled steel substrates were then stripped in an HCI bath for a period of time. After pickling, the samples were taken from the core and from the axis region of the hot-rolled steel substrates, and for each sample, the percentage of voids in the surface region was determined according to the procedure described above.
    [0233] The hot-rolled steel substrates were then coated by hot dipping. Table 2 shows the bath compositions used for hot immersing the samples. A coating thickness
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    59/65 between 20 and 33 pm on each side of the plate was targeted.
    Table 2
    Coating Si (%) Fe (%) Zn (%) Mg (%) Al (%) + impurities α 9 3 <0.1 <0.1 88 β 3.4 1.4 15.6 1.8 77.8
    [0234] After the hot dip coating, some of the hot rolled and coated sheets were subjected to a 0.7 pm Zn deposition on the Al alloy coating via electrodeposition.
    [0235] After coating, the samples were taken from the core and from the region of the plate axis, and for each sample, the depth of intergranular oxidation was determined according to the procedure described above. In addition, the thickness of the coating and the thickness of the intermetallic layer were determined.
    [0236] The hot rolled and coated steel sheets thus obtained were cut to obtain raw parts. The cut parts of the core and the region of the axis of the hot-rolled and coated steel sheets were heated in an oven to a temperature of 920 Q C for a time tc. This time tc includes the heating phase to the desired temperature and the waiting phase at this temperature. The heated blanks were then transferred to a die, hot stamped and cooled to room temperature.
    [0237] From each part coated with hot stamping, a sample was taken and the adhesion of the coating was evaluated by determining the percentage of porosity in the coating according to the procedure described above. In addition, the coating thickness was measured.
    [0238] Finally, a 20 pm electrodeposited paint was applied to one side of each piece, and the paint adhesion on the pieces was
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    60/65 assessed by a wet paint adhesion test, according to ISO 2409: 2007. The paint adhesion was considered good if the result of this test was less than or equal to 2, or bad if the result of this test test was greater than 2.
    [0239] In all these examples, the width of the plates was equal to 1 m.
    [0240] The manufacturing conditions (steel composition, thickness after hot rolling, final FRT rolling temperature, austenite fraction just before the fy winding and maximum winding temperature Tenroiamentomax, winding temperature Tenroiamento, pickling time and setting time heating tC) for each part are shown in Table 3.
    Table 3
    Sample Steel Coating Electroplatingcoatingfrom Zn th(mm) FRT(= C) ÍY Tensingmax ( Q C) Finishing ( Q C) stripping(S) tc(s) 1 THE α NO 3.3 875 0.65 559 585 25 600 2 THE α NO 3.3 875 0.65 559 655 45 600 3 THE α NO 3.3 875 0.65 559 585 45 600 4 THE α NO 3.3 875 0.65 559 585 375 600 5 THE α NO 3.3 850 0.61 565 540 375 600 6 THE α NO 3.3 850 0.59 567 515 16 600 7 THE α NO 3.3 850 0.59 567 515 21 600 8 THE α NO 3.3 885 0.87 528 520 28 600 9 THE α NO 3.3 885 0.87 528 520 35 600 10 THE α NO 3.3 905 0.88 527 510 26 600 11 THE α NO 3.3 905 0.88 527 510 23 600 12 THE α NO 3.3 865 0.61 565 533 63 600 13 THE α NO 3.3 905 0.87 528 519 22 600 14 THE α NO 3.3 904 0.87 528 515 15 600 15 THE α NO 3.3 867 0.64 560 554 52 600 16 THE α NO 3.3 861 0.64 560 548 24 600
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    61/65
    17 THE α NO 3.3 851 0.85 531 476 45 600 18 THE α NO 3.3 857 0.83 534 504 60 600 19 B α NO 2.6 845 0.1 636 655 41 520 20 B α NO 2.6 905 0.1 636 555 25 520 21 B α NO 2.6 845 0.1 636 555 60 520 22 Ç α NO 3.2 905 0.8 538 655 21 600 23 D α NO 3.2 875 0.9 495 531 28 600 24 D α NO 3.2 872 0.9 495 495 38 600 25 D α NO 3.2 874 0.9 495 581 20 600 26 AND α NO 3.3 880 0.5 580 545 24 600 27 THE β NO 3.1 885 0.65 559 655 25 600 28 THE β NO 3.1 885 0.84 532 515 21 600 29 THE α YES 3.3 862 0.62 563 515 22 600
    [0241] In this table, the underlined values are not in accordance with the invention.
    [0242] The properties measured on each hot rolled steel substrate, plate or piece (percentage of SVSS voids in the surface region of the hot rolled steel substrate, depth of intergranular oxidation DIO of the hot rolled steel sheet, Coating thickness Ct, IMt thickness of the intermetallic layer and the percentage of porosity surface in the coating of the hot stamped part (Coating and the quality of the paint adhesion - good or low) are shown in Table 4.
    Table 4
    Sample SVSS(%) DIO(μη) Ct (μη) IMt (μη) SPrevest.<3% Paint adhesion 1 18.1 5 27.5 11.4 NO Weak 2 17.1 ίο 30.52 8.6 NO Weak 3 17.5 4 27.9 11.2 NO Weak 4 37.1 ΝΑ 37.6 37.6 YES Good 5 5.7 0 31.8 10.9 YES Good 6 18.2 0 31.2 12.8 YES Good 7 11 0 29 11 YES Good
    Petition 870190044879, of May 13, 2019, p. 138/220
    62/65
    8 15.3 0 29.6 12 YES Good 9 19.9 0 24.3 10.4 YES Good 10 na 2 23 10.4 YES Good 11 11.5 2 21.3 11.7 YES Good 12 10.8 0 21.9 10.3 YES Good 13 14.2 2 26.9 12.6 YES Good 14 14.4 0 28.4 10.5 YES Good 15 20.2 0 23.5 10.2 YES Good 16 13.9 0 22.7 10.9 YES Good 17 13 0 26.5 9.9 YES Good 18 16 0 27.2 11.1 YES Good 19 na 9 28.2 8.7 NO Weak 20 na 0 22.6 11.8 YES Good 21 na 0 26.8 10.3 YES Good 22 na 12 30 10 NO Weak 23 na 8 27.6 10.1 NO Weak 24 na 0 24.9 9.9 YES Good 25 na 9 28.4 11.5 NO Weak 26 7.0 0 27.1 11 YES Good 27 na 13 23 7 NO Weak 28 na 2 28.1 10.7 YES Good 29 na 0 26.2 11.1 YES Good
    [0243] In Table 4, nd means “not determined”, and NA means “not applicable”.
    [0244] Samples 1-4, 19, 22, 23, 25 and 27 were produced at winding temperatures not in accordance with the invention. In particular, samples 1-4, 19, 22, 23, 25 and 27 were wound at a temperature higher than the maximum winding temperature Tenrolamentomax, leading to a high depth of intergranular oxidation before blasting.
    [0245] Samples 1-3, 19, 22, 23, 25 and 27 were pickled under normal conditions, that is, for a time between 15 and 65 s. As a consequence of the winding temperature and pickling conditions, the intergranular oxidation depth of the steel sheet
    Petition 870190044879, of May 13, 2019, p. 139/220
    63/65 (measured after coating) for samples 1-3 19, 22, 23, 25 and 27 is greater than or equal to 4 pm, ie greater than the maximum permissible oxidation depth.
    [0246] Thus, after hot stamping, the surface percentage of porosity in the coating is greater than 3% and the adhesion of the paint is weak.
    [0247] In addition, example 23, made of E steel that comprises 0.417% Ni, was rolled at a temperature of 531 Q C. As a consequence, a large amount of encrustation, adhering to the surface, was present on the plate before the pickling and after pickling. Removing this scale would require intensive pickling, which, however, would have greatly reduced the productivity of the pickling line.
    [0248] Similar results could have been obtained using a coiling temperature below 531 -C, but greater than Q 495 C. The sample 4 was extensively stripped for a time of 375 s. As a consequence of the winding temperature and pickling conditions, even if the hot-rolled steel sheet does not include intergranular oxidation after coating, the percentage of surface voids in the region of the steel substrate surface before coating was very high ( 37.1%). As a result, there was an uncontrolled growth of the intermetallic layer during the hot dip coating, so that the coating thickness could not be controlled in the range of 20-33 pm, with the coating thickness of sample 4 being 37.6 pm .
    [0249] In contrast, Sample 5 was intensively blasted for the same time as Sample 4, but, unlike Sample 4, it was produced at a winding temperature according to the invention. Thus, before blasting, the hot-rolled steel substrate contained little or no intergranular oxidation, so that after blasting, the
    Petition 870190044879, of May 13, 2019, p. 140/220
    64/65 percentage of voids on the steel substrate surface was low (5%), unlike Sample 4. As a result, the coating thickness can be controlled in the range of 20-33 pm. The comparison of samples 4 and 5 thus illustrates that the manufacturing conditions according to the invention allow an improved coating adhesion after hot stamping and an excellent paint adhesion, while allowing the coating thickness control.
    [0250] Furthermore, the comparison of Samples 5 and 6, which are pickled intensely (Sample 5) or slightly (Sample 6) shows that, under the condition that the winding temperature is selected according to the invention, the intensity of the Stripping has no influence on coating adhesion and does not affect the control of coating thickness.
    [0251] These results show that, in the process of the invention, the stripping intensity can be reduced without impairing the adhesion of the coating after hot stamping. The process of the invention therefore does not require intensive pickling. Therefore, the process of the invention makes it possible to produce a coated and hot-rolled steel sheet having a thickness between 1.8 mm and 5 mm with an improved coating adhesion after hot stamping, allowing the control of the thickness of the plate coating hot-rolled and coated steel for the target range, especially in the range between 10 and 33 pm, and without reducing productivity in the pickling line.
    [0252] Samples 5 to 18, 20, 21, 24, 26, 28 and 29 show that when the coated and hot rolled steel sheet is produced by a method according to the invention, the hot rolled steel sheet it comprises little or no intergranular oxidation, so that the percentage of porosity surface in the coating of the hot-stamped part is low, and the adhesion of the paint is good.
    Petition 870190044879, of May 13, 2019, p. 141/220
    65/65
    In addition, the depth of intergranular oxidation before blasting is low, so that the percentage of surface voids in the region of the steel substrate surface before coating is low. As a consequence, the thickness of the coating can be controlled in the range of 20-33 pm.
    [0253] In particular, sample 24 is made of D steel, having a composition according to the second aspect of the invention. The coiling temperature was less than or equal to Q 495 C. As a result of the coiling temperature, the hot rolled steel sheet comprises little or no intergranular oxidation, the percentage of surface porosity in the coating of the hot stamped part SPrevestimento is low, and the adhesion of the paint is good. In addition, the depth of intergranular oxidation before blasting is low, so that the surface percentage of voids in the surface region of the steel substrate before coating is low. As a consequence, the thickness of the coating can be controlled in the range of 20-33 pm. In addition, stripping time can be reduced to achieve high productivity in the stripping line.
    权利要求:
    Claims (31)
    [1]
    Claims
    1. METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, having a thickness between 1.8 mm and 5 mm, characterized by the fact that the method comprises:
    supply a steel semi-product having a composition comprising, in percentage by weight:
    0.04% <C <0.38%
    0.40% <Mn <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <0.1%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting, hot rolling the steel semi-product with a final FRT rolling temperature between 840 Q C and 1000 Q C, in order to obtain a product hot-rolled steel having a thickness between 1.8 mm and 5 mm;
    Petition 870190044879, of May 13, 2019, p. 202/220
    [2]
    2/19 cool the hot-rolled steel product to a temperature range, and wind the hot-rolled steel product to temperature, temperature to obtain a hot-rolled steel substrate, the temperature temperature:
    450 ° C - Tenrolamentomax - Tenrolamentomax, where Tenrolamentomax is a maximum winding temperature expressed as:
    Max. Rolling = 650 - 140 X fy,
    Max coiling being expressed in degrees Celsius and fy designating the fraction of austenite in the hot rolled steel product immediately before winding, stripping the hot rolled steel substrate, coating the hot rolled steel substrate with Al or Al alloy by immersion continuous hot bathing, to obtain a coated and hot-rolled steel plate comprising a hot-rolled steel plate, having a structure consisting of ferrite and perlite, and a coating of Al or Al alloy, having a thickness between 10 and 33 pm on each side of the hot-rolled steel sheet.
    2. METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, according to claim 1, characterized by the fact that the composition comprises, in percentage by weight:
    0.04% <C <0.38%
    0.5% <Mn <3%
    0.005% <Si <0.5%
    0.005% <Al <0.1%
    0.001% <Cr <1%
    0.001% <Ni <0.1%
    Petition 870190044879, of May 13, 2019, p. 203/220
    [3]
    3/19
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.10%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    3. METHOD FOR MANUFACTURING A COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 1 to 2, characterized by the fact that 0.075% <C <0.38%.
    [4]
    4. METHOD FOR MANUFACTURING A COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 1 to 2, characterized by the fact that steel has the following chemical composition, in percentage by weight:
    0.040% <C <0.100%
    0.80% <Mn <2.0%
    0.005% <Si <0.30%
    0.010% <Al <0.070%
    0.001% <Cr <0.10%
    0.001% <Ni <0.10%
    0.03% <Ti <0.08%
    0.015% <Nb <0.1%
    0.0005% <N <0.009%
    0.0001% <S <0.005%
    0.0001% <P <0.030%
    Petition 870190044879, of May 13, 2019, p. 204/220
    4/19
    Mo <0.10%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [5]
    5. METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, according to any one of claims 1 to 2, characterized by the fact that steel has the following chemical composition, in percentage by weight:
    0.062% <C <0.095%
    1.4% <Mn <1.9%
    0.2% <Si <0.5%
    0.020% <Al <0.070%
    0.02% <Cr <0.1% where 1.5% <(C + Mn + Si + Cr) <2.7%
    3.4 x N <Ti <8 x N
    0.04% <Nb <0.06% where 0.044% <(Nb + Ti) <0.09%
    0.0005% <B <0.004%
    0.001% <N <0.009%
    0.0005% <S <0.003%
    0.001% <P <0.020% and, optionally, 0.0001% <Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [6]
    6. METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, according to any one of claims 1 to 2, characterized by the fact that steel has the following chemical composition, in percentage by weight:
    Petition 870190044879, of May 13, 2019, p. 205/220
    5/19
    0.15% <C <0.38%
    0.5% <Μη <3%
    0.10% <Si <0.5%
    0.005% <Al <0.1%
    0.01% <Cr <1%
    0.001% <Ti <0.2%
    0.0005% <B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [7]
    7. METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, having a thickness between 1.8 mm and 5 mm, characterized by the fact that the method comprises:
    supply a steel semi-product having a composition comprising, in percentage by weight:
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    Petition 870190044879, of May 13, 2019, p. 206/220
    6/19
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting, hot rolling the steel semi-product with a final FRT rolling temperature between 840 Q C and 1000 -C, in order to obtain a hot rolled steel product having a thickness between 1.8 mm and 5 mm;
    cool the hot rolled steel product to a Tendering winding temperature and wind the hot rolled steel product to the Tendering winding temperature to obtain a hot rolled steel substrate, the Tendering winding temperature satisfying:
    450 ° C - Coiling <495 ° C stripping the hot rolled steel substrate, coating the hot rolled steel substrate with Al or Al alloy by continuous hot dip bathing, to obtain a coated and hot rolled steel plate hot plate comprising a steel plate
    Petition 870190044879, of May 13, 2019, p. 207/220
    7/19 hot rolled and a coating of Al or Al alloy, having a thickness between 10 and 33 pm on each side of the hot-rolled steel sheet.
    [8]
    8. METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, according to any one of claims 1 to 7, characterized by the fact that after stripping and before coating, the surface voids percentage in the surface region of the hot rolled steel substrate is less than 30%, the surface region being defined as the region extending from the upper point (Pt1, Pt2) of the surface of the hot rolled steel substrate to a depth, at from this upper point (Pt1, Pt2), from 15 pm.
    [9]
    9. METHOD FOR MANUFACTURING A COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 1 to 8, characterized by the fact that the hot-rolled steel sheet has an intergranular oxidation depth of less than 4 pm .
    [10]
    10. METHOD FOR MANUFACTURING A COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 1 to 9, characterized by the fact that the bath contains, in percentage by weight, from 8% to 11% of silicon and 2% to 4% iron, the remainder being aluminum or aluminum alloy and impurities inherent in processing.
    [11]
    11. METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, according to any one of claims 1 to 9, characterized by the fact that the bath contains, by weight percentage, from 2.0% to 24, 0% zinc, from 7.1% to 12.0% silicon, optionally, from 1.1% to 8.0% magnesium and, optionally, additional elements selected from Pb, Ni, Zr or Hf, the content of each additional element being less than 0.3%, the rest being aluminum and
    Petition 870190044879, of May 13, 2019, p. 208/220
    8/19 unavoidable impurities and residual elements, the Al / Zn ratio being above
    2.9.
    [12]
    12. METHOD FOR MANUFACTURING A COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 1 to 9, characterized by the fact that the bath contains, by weight percentage, from 4.0% to 20, 0% zinc, 1% to 3.5% silicon, optionally, 1.0% to 4.0% magnesium and, optionally, additional elements selected from Pb, Ni, Zr or Hf, the content of each additional element being less than 0.3%, the rest being aluminum and unavoidable impurities and residual elements, the Zn / Si ratio being between 3.2 and 8.0.
    [13]
    13. METHOD FOR MANUFACTURING A HOT COATED AND LAMINATED STEEL SHEET, according to any one of claims 1 to 9, characterized by the fact that the bath contains, by weight percentage, from 2.0% to 24, 0% zinc, 1.1% to 7.0% silicon, optionally, 1.1% to 8.0% magnesium when the amount of silicon is between 1.1 and 4.0% and , optionally, additional elements selected from Pb, Ni, Zr or Hf, the content of each additional element being less than 0.3%, the rest being aluminum and unavoidable impurities and residual elements, the Al / Zn ratio being above 2.9.
    [14]
    14. METHOD FOR MANUFACTURING A COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 1 to 13, characterized by the fact that it also comprises, after coating the hot-rolled steel sheet with Al or aluminum alloy. Al, a step of depositing a Zn coating on the Al coating or Al alloy through cementation, electrodeposition or sonic jet vapor deposition, the Zn coating having a thickness less than or equal to 1 , 1 pm.
    Petition 870190044879, of May 13, 2019, p. 209/220
    9/19
    [15]
    15. COATED AND HOT-LAMINATED STEEL SHEET, characterized by the fact that it comprises:
    a hot-rolled steel sheet having a thickness between 1.8 mm and 5 mm, whose composition comprises, in percentage by weight:
    0.04% <C <0.38%
    0.40% <Mn <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <2%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from casting, the hot rolled steel sheet having an intergranular oxidation depth of less than 4 pm, the hot rolled steel sheet having a structure consisting of ferrite and perlite, a coating of Al or Al alloy, having a thickness between 10 and 33 pm, on each side of the hot-rolled steel sheet.
    Petition 870190044879, of May 13, 2019, p. 210/220
    10/19
    [16]
    16. STEEL SHEET COATED AND HOT-LAMINATED, according to claim 15, characterized by the fact that steel has the following chemical composition, in percentage by weight:
    0.04% <C <0.38%
    0.40% <Mn <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    0.001% <Ni <0.1%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [17]
    17. COATED AND HOT-LAMINATED STEEL SHEET, according to claim 16, characterized by the fact that the steel of the composition comprises, in percentage by weight:
    0.04% <C <0.38%
    0.5% <Mn <3%
    0.005% <Si <0.5%
    0.005% <Al <0.1%
    0.001% <Cr <1%
    Petition 870190044879, of May 13, 2019, p. 211/220
    11/19
    0.001% <Ni <0.1%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.10%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [18]
    18. COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 15 to 17, characterized by the fact that 0.075% <C <0.38%.
    [19]
    19. COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 15 to 17, characterized by the fact that steel has the following chemical composition, in percentage by weight:
    0.040% <C <0.100%
    0.80% <Mn <2.0%
    0.005% <Si <0.30%
    0.010% <Al <0.070%
    0.001% <Cr <0.10%
    0.001% <Ni <0.10%
    0.03% <Ti <0.08%
    0.015% <Nb <0.1%
    0.0005% <N <0.009%
    0.0001% <S <0.005%
    Petition 870190044879, of May 13, 2019, p. 212/220
    12/19
    0.0001% <P <0.030%
    Mo <0.10%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [20]
    20. COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 15 to 17, characterized by the fact that steel has the following chemical composition, in percentage by weight:
    0.062% <C <0.095%
    1.4% <Mn <1.9%
    0.2% <Si <0.5%
    0.020% <Al <0.070%
    0.02% <Cr <0.1% where 1.5% <(C + Mn + Si + Cr) <2.7%
    3.4 x N <Ti <8 x N
    0.04% <Nb <0.06% where 0.044% <(Nb + Ti) <0.09%
    0.0005% <B <0.004%
    0.001% <N <0.009%
    0.0005% <S <0.003%
    0.001% <P <0.020% and, optionally, 0.0001% <Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [21]
    21. STEEL SHEET COATED AND HOT-LAMINATED, according to any one of claims 15 to 17, characterized by the fact that steel has the following chemical composition, in percentage in
    Petition 870190044879, of May 13, 2019, p. 213/220
    13/19 weight:
    0.15% <C <0.38%
    0.5% <Mn <3%
    0.10% <Si <0.5%
    0.005% <Al <0.1%
    0.01% <Cr <1%
    0.001% <Ti <0.2%
    0.0005% <B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [22]
    22. COATED AND HOT-LAMINATED STEEL SHEET, characterized by the fact that it comprises:
    a hot-rolled steel sheet having a thickness between 1.8 mm and 5 mm, whose composition comprises, in percentage by weight:
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    Petition 870190044879, of May 13, 2019, p. 214/220
    14/19
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from casting, the hot-rolled steel sheet having an intergranular oxidation depth of less than 4 pm, an Al or Al alloy coating , having a thickness between 10 and 33 pm, on each side of the hot rolled steel sheet.
    [23]
    23. COATED AND HOT-LAMINATED STEEL SHEET, according to any one of claims 15 to 22, characterized in that the coating comprises an intermetallic layer having a thickness less than or equal to 15 pm.
    [24]
    24. COATED AND HOT-LAMINATED STEEL SHEET according to any one of claims 15 to 23, characterized in that the coated and hot-rolled steel sheet further comprises, on each side, a Zn coating having a thickness smaller than
    Petition 870190044879, of May 13, 2019, p. 215/220
    15/19 or equal to 1.1 pm.
    [25]
    25. METHOD FOR MANUFACTURING A HOT PRINTED COATED STEEL PIECE, characterized by the fact that it comprises the steps of:
    supplying a hot-rolled and coated steel sheet as defined in any of claims 15 to 24, or carrying out the method as defined in any of claims 1 to 14, thereby obtaining a hot-coated and coated steel sheet, cut the coated and hot-rolled steel plate to obtain a blank, heat the blank in an oven to a temperature Tc to obtain a heated blank, transfer the heated blank to a die and hot stamp the heated blank in the matrix, thereby obtaining a crude piece stamped hot, cooling the embossed hot raw part to a temperature below 400 Q C to obtain a coated piece of steel hot stamped.
    [26]
    26. METHOD FOR MANUFACTURING A HOT PRINTED COATED STEEL PIECE, according to claim 25, characterized by the fact that, after cutting the coated and hot-rolled steel plate to obtain the blank and before the blank raw material to be heated to temperature Tc, the raw material is welded to another raw material made of steel having a composition that comprises, in percentage by weight:
    0.04% <C <0.38%
    0.40% <Mn <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    Petition 870190044879, of May 13, 2019, p. 216/220
    16/19
    0.001% <Cr <2%
    0.001% <Ni <2%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65%
    W <0.30%
    Ca <0.006% the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [27]
    27. METHOD FOR MANUFACTURING A HOT PRINTED COATED STEEL PIECE, according to claim 25, characterized by the fact that, after cutting the coated and hot-rolled steel sheet to obtain the blank and before the blank raw material to be heated to temperature Tc, the raw material is welded to another raw material made of steel having a composition that comprises, in percentage by weight:
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    Petition 870190044879, of May 13, 2019, p. 217/220
    17/19
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [28]
    28. HOT PRINTED COATED STEEL PIECE, characterized by the fact that it comprises at least a portion having a thickness between 1.8 mm and 5 mm, the hot-stamped coated steel part comprising an Al or Al alloy coating , the coating having a surface porosity percentage (P) less than or equal to 3%, the portion being made of steel having a composition that comprises, in percentage by weight:
    0.04% <C <0.38%
    0.40% <Mn <3%
    0.005% <Si <0.70%
    0.005% <Al <0.1%
    0.001% <Cr <2%
    Petition 870190044879, of May 13, 2019, p. 218/220
    18/19
    0.001% <Ni <2%
    0.001% <Ti <0.2%
    Nb <0.1%
    B <0.010%
    0.0005% <N <0.010%
    0.0001% <S <0.05%
    0.0001% <P <0.1%
    Mo <0.65% W <0.30% Ca <0.006%, the remainder of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [29]
    29. HOT PRINTED COATED STEEL PIECE, according to claim 28, characterized by the fact that the steel composition in the portion is such that Ni <0.1%.
    [30]
    30. HOT PRINTED COATED STEEL PIECE, characterized by the fact that it comprises at least a portion having a thickness between 1.8 mm and 5 mm, the hot-stamped coated steel part comprising an Al or Al alloy coating , the coating having a surface porosity percentage (P) less than or equal to 3%, the portion being made of steel having a composition that comprises, in percentage by weight:
    0.24% <C <0.38% and 0.40% <Mn <3% or 0.38% <C <0.43% and 0.05% <Mn <0.40%
    0.10% <Si <0.70%
    0.015% <Al <0.070%
    0.001% <Cr <2%
    0.25% <Ni <2%
    Petition 870190044879, of May 13, 2019, p. 219/220
    19/19
    0.015% <Ti <0.1%
    0% <Nb <0.06%
    0.0005% <B <0.0040%
    0.003% <N <0.010%
    0.0001% <S <0.005%
    0.0001% <P <0.025%, titanium and nitrogen content satisfying the following relationship:
    Ti / N> 3.42, the levels of carbon, manganese, chromium and silicon satisfying the following relationship:
    2.6C + - + - + -> 1.1%,
    5.3 13 15 the chemical composition optionally comprising one of several of the following elements:
    0.05% <Mo <0.65%
    0.001% <W <0.30%
    0.0005% <Ca <0.005%, the rest of the composition consisting of iron and unavoidable impurities resulting from smelting.
    [31]
    31. USE OF A HOT PRINTED COATED STEEL PIECE, as defined in any of claims 28 to 30, or produced by a method, as defined in any of claims 25 to 27, characterized by the fact that it is for manufacturing chassis or body-in-white parts or suspension arms for automotive vehicles.
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    同族专利:
    公开号 | 公开日
    JP2020509160A|2020-03-26|
    EP3544808A1|2019-10-02|
    EP3656888B1|2021-07-21|
    MA46875B1|2021-04-30|
    CA3044772A1|2018-05-31|
    CN109982839A|2019-07-05|
    MA49659B1|2021-09-30|
    US20200224297A1|2020-07-16|
    CN113046633A|2021-06-29|
    PL3656552T3|2021-12-20|
    EP3544808B1|2021-04-14|
    EP3901321A1|2021-10-27|
    WO2018096387A1|2018-05-31|
    JP6998955B2|2022-01-18|
    MA49658B1|2021-08-31|
    RU2726165C1|2020-07-09|
    MX2019006106A|2019-08-21|
    PL3656888T3|2021-12-13|
    KR102308581B1|2021-10-05|
    EP3656552B1|2021-07-21|
    KR20190073462A|2019-06-26|
    KR20210074405A|2021-06-21|
    ES2868828T3|2021-10-22|
    MA49659A|2021-03-31|
    CN113046645A|2021-06-29|
    MA46875A|2019-10-02|
    PL3544808T3|2021-10-04|
    HUE055027T2|2021-10-28|
    EP3901321A4|2021-10-27|
    KR102272870B1|2021-07-06|
    ZA201903061B|2020-01-29|
    WO2018096487A1|2018-05-31|
    ES2886340T3|2021-12-17|
    EP3656552A1|2020-05-27|
    JP2021152217A|2021-09-30|
    CN109982839B|2021-03-19|
    MA49658A|2021-03-24|
    EP3656888A1|2020-05-27|
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    法律状态:
    2021-08-24| B06W| Patent application suspended after preliminary examination (for patents with searches from other patent authorities) chapter 6.23 patent gazette]|
    2021-10-05| B350| Update of information on the portal [chapter 15.35 patent gazette]|
    优先权:
    申请号 | 申请日 | 专利标题
    PCT/IB2016/057100|WO2018096387A1|2016-11-24|2016-11-24|Hot-rolled and coated steel sheet for hot-stamping, hot-stamped coated steel part and methods for manufacturing the same|
    PCT/IB2017/057370|WO2018096487A1|2016-11-24|2017-11-23|Hot-rolled and coated steel sheet for hot-stamping, hot-stamped coated steel part and methods for manufacturing the same|
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