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    • 专利摘要:
    Abstract “Steel Sheets, Steel Sheet Fabrication Methods and Vehicle” The present invention relates to a hot dip coated, cold rolled steel sheet that has tensile strength of over 1000 - 50 x mpa, elongation uniform of more than 15% and low density. the steel comprises, in percentage by weight: 0.1 = c = 0.5%, 3.5 = mn = 10.0%, 0 = al = 9.0%, si = 5.0%, ti = 0 .2%, v = 0.2%, nb = 0.2%, s = 0.004%, p = 0.025%, 0.5 = si+al = 9.0%, b = 0.0035, cr = 1 %, where the equilibrium is fe and impurities and the microstructure which contains 25% to 90% ferrite, 10% to 50% austenite, cape precipitates below 5% and martensite below 25%. the steel according to the present invention has the ability to be coated using full oxidation.
    公开号:BR112015032233B1
    申请号:R112015032233-6
    申请日:2014-07-03
    公开日:2019-10-15
    发明作者:Franco Del Frate；Jean-Michel Mataigne；Jonas Staudte；Astrid Perlade；Ian Alberto Zuazo-Rodriguez
    申请人:ArcelorMittal Investigación y Desarrollo, S.L.；
    IPC主号:
    专利说明:

    Field of the Invention [001] The present invention relates to cold rolled steel sheets that have, at the same time, high mechanical properties, good forming capacity and good ability to receive coating.
    Background of the Invention [002] In particular, the aforementioned steel sheets require resistance to TS tension greater than or equal to 1000 - 50xAl MPa, uniform elongation UEI greater than or equal to 15%, expansion of HE orifice greater than or equal to 20% and a surface reactive that allows adhesion by moistening and coating.
    [003] In addition, some achievements of the aforementioned steel sheets that contain high amounts of silicon or aluminum may have low density and be more than 10% lighter compared to so-called Advanced High Strength Steels as Dual Phase, multiple phase concepts , bainitic or TRIP (Transformation Induced Plasticity).
    [004] In the automotive industry in particular, there is a continuing need to make vehicles lighter and increase safety. Thus, several steel families like the ones mentioned above have been proposed that offer various levels of strength and formability.
    [005] First, steels have been proposed that contain microalloy elements whose hardening is obtained simultaneously through precipitation and grain size refinement. The development of these steels was followed by the Advanced High Strength Steels mentioned above.
    [006] In order to obtain even higher levels of resistance to tension, steels have been developed that exhibit TRIP behavior with highly advantageous combinations of properties (tensile strength / formability). These properties are associated with the structure of these steels, which consists of
    Petition 870190089909, of 9/11/2019, p. 13/46
    2/28 a ferritic matrix containing bainite and residual austenite. Residual austenite is stabilized through the addition of silicon or aluminum, in which these elements delay the precipitation of carbides in austenite and bainite. The presence of residual austenite provides high ductility to an undeformed sheet.
    [007] To achieve even higher stress resistance, that is, a level of more than 800-1000 MPa, multiphase steels with a predominantly bainitic structure were developed. However, the properties of forming capacity and orifice expansion are insufficient for the next generation of automotive parts.
    [008] International Patent Application WO 2009/142362 describes a cold-rolled steel sheet and a hot-dip galvanized steel sheet, which shows improved fracture resistance delay, tensile strength of 980 MPa or more and an elongation of 28% or more by adding an appropriate amount of Al to increase the stability of retained austenite and resistance against delayed fracture in an ideal composition that can increase the amount of retained austenite. In one or more aspects of the present state of the art, a sheet of high-strength cold-rolled steel and a sheet of galvanized steel are provided, each consisting of 0.05 to 0.3% by weight of C, 0.3 to 1.6% by weight of Si, 4.0 to 7.0% by weight of Mn, 0.5 to 2.0% by weight of Al, 0.01 to 0.1% by weight of Cr, 0 , 02 to 0.1% by weight of Ni and 0.005 to 0.03% by weight of Ti, 5 to 30 ppm of B, 0.01 to 0.03% by weight of Sb, 0.008% by weight or less S, Fe balance and impurities. However, these steels are difficult to coat due to the high content of alloying elements.
    [009] International Patent Application WO 2012/147898 is intended to provide high strength steel with excellent orifice expansion as well as stability of material properties and method of manufacture, the high strength steel plate with a TS of at least 780 MPa and a TSxEL of at least 22,000 MPa% in a low C steel composition.
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    3/28
    High-strength steel has good forming capacity and stability of material properties and has a composition of ingredients that includes, in terms of percentage by weight, 0.03% -0.25% C, 0.4% -2.5 % Si, 3.5% -10.0% Mn, 0.1% or less P, 0.01% or less S, 0.01% -2.5% Al, 0.008% or less N and Si + Al at least 1.0%, where the rest is Fe and unavoidable impurities, the steel structure has, by area reason, 30% -80% ferrite, 0% -17% martensite and, by volume reason, 8% or more residual austenite and the average crystalline particle diameter of the residual austenite is 2 pm or less. However, these steels are difficult to coat due to the high content of alloying elements.
    [0010] Eventually, patent application EP 2383353 describes steel with an A80 break elongation of at least 4% and tensile strength of 900-1500 MPa. It comprises iron, unavoidable impurities and carbon (up to 0.5%), manganese (4-12%), silicon (up to 1%), aluminum (up to 3%), chromium (0.1-4%), copper ( up to 2%), nickel (up to 2%), nitrogen (up to 0.05%), phosphorus (up to 0.05%) and sulfur (up to 0.01%) and, optionally, up to 0.5% of one or more elements that comprise vanadium, niobium or titanium. The flat rolled steel product made of steel comprises 30-100% martensite, tempered martensite or bainite and residual amount of austenite. However, this steel will have low levels of ductility, generating low capacity for forming the obtained steel sheet.
    Description of the Invention [0011] The present invention is intended to provide a cold-rolled steel sheet that simultaneously features:
    - resistance to TS voltage greater than or equal to 1000 - 50xAl MPa;
    - uniform elongation of UEI greater than or equal to 15%;
    - HE orifice expansion greater than or equal to 20%; and
    - reactive surface that allows adhesion by moistening and
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    4/28 coating.
    [0012] The present invention covers, as a first object, a cold rolled steel sheet comprising, in percentage by weight:
    0.1 <C <0.5%
    3.5 <Mn <10.0%
    Al <9.0%
    Si <5.0%
    0.5 <Si + Al <9.0%
    Ti <0.2%
    V <0.2%
    Nb <0.2%
    B <0.0035
    Cr <1%
    S <0.004%
    P <0.025% where the rest of the composition is iron and unavoidable impurities resulting from smelting and the microstructure contains 10% to 50% austenite, 25% to 90% ferrite, less than 5% of precipitates and less than 25% of martensite and the mentioned leaf presents, from the upper surface, the following successive layers:
    - an upper layer of pure metallic iron whose thickness varies from 50 to 300 nm; and
    - a first sublayer made of metallic iron that also contains one or more oxide precipitates selected from Mn, Si, Al, Cr and B, whose thickness varies from 1 to 8 pm.
    [0013] The present invention can also cover other additional characteristics, taken alone or in combination:
    - a cold rolled steel sheet in accordance with this
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    5/28 invention that further comprises a second sublayer, which rests under the first sublayer, made of ferrite, whose thickness varies from 10 to 50 pm.
    [0014] In a preferred embodiment, the present invention covers a cold rolled steel sheet whose composition includes:
    - a cold rolled steel sheet whose composition contains 5.0 to 9.0% manganese content;
    - a sheet of cold-rolled steel whose composition contains a carbon content of 0.1 to 0.3%, with a range of 0.15 to 0.25% being preferred;
    - a sheet of cold-rolled steel whose composition contains aluminum content of 1.5 to 9%, with a range of 5 to 8% being preferred; and
    - a sheet of cold-rolled steel whose composition contains a silicon content less than or equal to 1.5%, with additionally preferred silicon content less than or equal to 0.3%.
    [0015] In another preferred embodiment, the steel according to the present invention covers:
    - a sheet of cold-rolled steel whose microstructure contains 15 to 40% austenite, preferably a range of 20 to 40% austenite, more preferably a range of 25 to 40% austenite;
    - a sheet of cold-rolled steel whose microstructure contains 50 to 85% ferrite;
    - a sheet of cold-rolled steel whose microstructure contains less than 15% of martensite, in which this martensite is possibly tempered; and
    - a sheet of cold-rolled steel whose microstructure does not contain precipitated layers.
    [0016] Ideally, the cold-rolled steel sheet according to the present invention has resistance to TS tension greater than or equal to 1000 - 50
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    6/28 x% Al in MPa, uniform elongation UEI greater than or equal to 15% and expansion of HE orifice greater than or equal to 20%.
    [0017] Another object of the present invention is a sheet of metallic rolled steel obtained by coating a sheet of cold rolled steel according to the present invention, in which this coating is carried out by means of a process selected from hot dip coating, electrodeposition and vacuum coating, possibly followed by hot treatment. In a preferred embodiment, that metallic coated steel sheet is galvanized [0018] The cold-rolled and possibly coated steel sheet according to the present invention can be manufactured by any suitable method. It is preferred that this method is compatible with continuous annealing lines and has low sensitivity to variation in process parameters.
    [0019] Another object of the present invention is a process of producing a cold rolled steel sheet that comprises the following steps:
    - feeding and scaling a hot-rolled strip or thin sheet whose composition is in accordance with the present invention;
    - the hot-rolled strip or thin sheet is then cold-rolled with a cold-rolling ratio of 30% to 75% to obtain a cold-rolled steel sheet;
    - the steel sheet then undergoes heating at an Hrate heating rate of at least 1 ° C / s, until the Tanneal annealing temperature is between Tmin = 721-36 * C-20 * Mn + 37 * Al + 2 * Si (in ° C) and Tmax = 690 + 145 * C-6.7 * Mn + 46 * Al + 9 * Si (in ° C) for 30 to 700 seconds followed by immersion at the mentioned temperature, heating of 550 ° C to Tanneal and at least the first part of the immersion takes place in an oxidizing atmosphere for
    Petition 870190089909, of 9/11/2019, p. 18/46
    7/28 produce an upper layer of iron oxide with a thickness of 100 to 600 nm and the aforementioned layer of iron oxide is completely reduced thereafter.
    [0020] This reduction occurs during the second part of the immersion, in a reduction atmosphere that contains from 2% to 35% of H2 and has a dew point below -10 ° C to completely reduce the aforementioned iron oxide layer, in that the steel sheet is additionally cooled under a Vcooling2 refrigeration rate above 5 ° C / s and below 70 ° C / s to room temperature.
    [0021] Optionally, the second part of the immersion takes place in an atmosphere whose dew point is less than -30 ° C.
    [0022] In another embodiment, the steel sheet is cooled to Vcooling2 to Toa temperature from 350 ° C to 550 ° C, kept in Toa for a period of time from 10 to 300 seconds, and then the steel sheet is additionally cooled at Vcooling3 cooling rate from 5 ° C / s to 70 ° C / s to room temperature.
    [0023] In another embodiment, the reduction can also occur after the cooling of the aforementioned steel sheet under cooling rate Vcooling2 above 5 ° C / s and below 70 ° C / s to room temperature and is then carried out by means of chemical pickling.
    [0024] Ideally, the coating is carried out through a process selected from hot dip coating, electrodeposition and vacuum coating, possibly followed by hot treatment.
    [0025] Preferably, the metallic coating is carried out with hot treatment by means of galvanization.
    [0026] There are different ways of obtaining the hot-rolled strip, one of which is a process that comprises the following steps:
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    - molding of steel whose composition is in accordance with the present invention to obtain a plate;
    - reheating the plate to a Treheat temperature of 1100 ° C to 1300 ° C;
    - hot rolling of the plate reheated under a temperature of 800 ° C to 1250 ° C to obtain a strip of hot-rolled steel;
    - cooling of the hot rolled steel strip under Vcooling1 refrigeration speed of at least 10 ° C / s until the winding temperature Tcoiling less than or equal to 700 ° C; and
    - winding of the Tcooling-cooled hot-rolled strip.
    [0027] In another embodiment, the hot-rolled strip is obtained by means of a process called intrinsically known compact strip processing that leads to a thin sheet, in order to avoid the hot lamination step.
    [0028] In another embodiment, the hot rolled strip is additionally annealed using a process selected from annealing in batches from 400 ° C to 600 ° C for 1 to 24 hours and continuous annealing from 650 ° C to 750 ° C of 60 to 180 s.
    [0029] In a preferred embodiment, using a direct fire furnace for heating, the atmosphere for iron reduction contains 20 to 35% H2, in which the balance is nitrogen and unavoidable impurities.
    [0030] In a preferred embodiment, using a radiant tube furnace for heating, the atmosphere for iron reduction contains from 2 to 8% H2, in which the balance is nitrogen and unavoidable impurities.
    [0031] Optionally, the cold-rolled and annealed steel is tempered at a temperature of 200 to 400 ° C for a period of time of 200 to 800 s.
    [0032] In another embodiment, the cold rolled and annealed steel suffers
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    9/28 phosphate conversion treatment.
    [0033] In another embodiment, the steel that did not pass through the reducing atmosphere during annealing is then pickled at the exit of the continuous annealing line using typical pickling baths, such as formic acid, hydrochloric acid, sulfuric acid or others to extinguish the surface oxides present, which results in a mostly metallic surface.
    [0034] The present invention also covers a vehicle that comprises a structural part made of a sheet of steel according to the present invention.
    [0035] Other features and advantages of the present invention will emerge from the following paragraphs of the detailed specification.
    Brief Description of the Drawings [0036] The attached figures are provided as examples and should not be considered limitations of the scope of the present invention.
    [0037] The figures are:
    Figure 1 illustrates the microstructure of Example A2 after cold rolling and annealing; the dark phase is austenite, the white phase is ferrite;
    Figure 2 illustrates the stress curve of Example A2 after cold rolling and annealing;
    Figure 3 shows the GDOS profile of example A6 that was produced by means of the present invention;
    Figure 4 shows the GDOS profile of Example A3 that was produced according to the present invention;
    Figure shows the result of the stitch bending test on the
    Example A6;
    Figure shows the result of the point bending test in example A3;
    Figure shows the result of the stitch bending test on the
    Petition 870190089909, of 9/11/2019, p. 21/46
    10/28 example A4;
    Figure 8 shows the thermal path of the annealing cycle according to Example A2; and Figure 9 shows the impact of Al on the stability of the tensile strength for steel D (0.2 C 5 Mn).
    Description of Embodiments of the Invention [0038] According to the present invention, the chemical composition of steel is balanced to achieve property targets. The elements of the following chemical composition are provided in percentage by weight.
    [0039] The aluminum content must be less than 9.0%, as it must be kept strictly less than this value to avoid brittle intermetallic precipitation.
    [0040] Aluminum additions are interesting in many ways, such as to increase the stability of retained austenite by increasing carbon in the retained austenite. Furthermore, the present inventors have shown that, surprisingly, although Al is supposed to stabilize ferrite, in the present invention, the higher the Al content, the better the stability of the austenite formed during annealing.
    [0041] The improved robustness during the annealing addition of Al leads to the lower variation of austenite fraction as a function of temperature during annealing over several continuous annealing lines.
    [0042] Al is the most efficient element, capable of opening a large window of viability for continuous annealing, as it favors the annealing of complete recrystallization under Tanneal annealing temperatures above the non-recrystallization temperature, as well as austenite stabilization.
    [0043] Al also allows the reduction of steel density by up to 10%. In addition, this element reduces the damaging effects of high-strength steels, such as elastic oscillation, hydrogen embrittlement and loss of rigidity. According
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    11/28 shown in Figure 9, above 1.5% of Al, the strength of the steel is improved and the resistance to delta stress is less than or equal to 10 MPa / ° C of the annealing temperature. It does, however, have an impact on the tensile strength that can be achieved. It reduces the tensile strength by 50 MPa per percentage of added aluminum.
    [0044] Like aluminum, silicon is an element for reducing the density of steel. Silicon is also very efficient for increasing resistance through a solid solution. However, its content is limited to 5.0% because, in addition to this value, fragility problems are encountered during cold rolling.
    [0045] According to the present invention, the carbon content is from 0.10 to 0.50%. Carbon is a gamma-forming element. He promotes, with Mn, the beginning of austenite. Below 0.10%, it is difficult to achieve mechanical strength above 1000 - 50xAl in MPa. If the carbon content is more than 0.50%, cold rolling is reduced and the welding capacity is reduced.
    [0046] Manganese should be at 3.5% to 10.0%. This element, also austenite stabilizer, is used to stabilize sufficient austenite in the microstructure. It also has hardening of solid solution and refining effect on the microstructure. For Mn content of less than 3.5%, the stabilization of the austenite retained in the microstructure is not sufficient to allow the combination of uniform elongation above 15% and the tensile strength above 1000 - 50 x% Al in MPa. Above 10.0%, the welding capacity is reduced. Segregations and inclusions deteriorate the damage properties.
    [0047] Microalloy elements, such as titanium, vanadium and niobium, can be added in amounts less than 0.2%, respectively, to obtain additional precipitation hardening. In particular, titanium and niobium are used to control grain size during solidification. However, limitation is necessary because, in addition to this, a saturation effect is obtained.
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    12/28 [0048] Chromium is tolerated up to 1%. Above this limit, harmful surface oxides may appear.
    [0049] Above sulfur content of 0.004%, ductility is reduced due to the presence of excess sulfides, such as MnS, which reduce ductility, particularly during orifice expansion tests.
    [0050] Phosphorus is an element that hardens in solid solution, but reduces the local welding capacity and hot ductility, particularly due to its tendency to segregate at the grain boundaries or cosegregation with manganese. For these reasons, its content needs to be limited to 0.025% and preferably 0.015%, to obtain good local welding capacity.
    [0051] The maximum boron content allowed by the present invention is 0.0035%. Above this limit, a level of saturation with respect to grain refinement is expected.
    [0052] The balance is composed of iron and unavoidable impurities.
    [0053] To achieve the desired properties, the microstructure of the steel sheet according to the present invention must contain, as a surface fraction, 10% to 50% austenite, 25% to 90% ferrite, precipitated layer below 5 % and martensite below 25%.
    [0054] Austenite is a structure that brings ductility, its content needs to be more than 10% so that the steel according to the present invention is sufficiently ductile with uniform elongation above 15% and its content needs to be below 50% because above this value, the balance of mechanical properties deteriorates.
    [0055] Ferrite in the present invention is defined by a central cubic structure obtained by means of recovery and recrystallization by annealing the preceding ferrite formed during solidification or bainite or martensite of hot rolled steel. Its content needs to be 25 to 90% to have a minimum of (1000 - 50 x% Al) in MPa of tensile strength and at least
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    15% uniform elongation.
    [0056] Layer in the present invention is defined by precipitates whose stoichiometry is (Fe, Mn) 3AlCx, where x is strictly less than 1. The surface density of the layer precipitates can be up to 5%. Above 5%, ductility is reduced and uniform elongation above 15% is not achieved. In addition, uncontrolled layer precipitation around the limits of ferrite grain can occur, which consequently increases efforts during hot and / or cold rolling. Preferably, the surface density of layer precipitates should be less than 2%. As the microstructure is uniform, the surface fraction is equal to the volume fraction.
    [0057] Martensite is a structure formed during refrigeration after immersion of unstable austenite. Its content needs to be limited to 25% for the orifice expansion to remain above 20%. In a preferred embodiment, this martensite is tempered before or after the coating step, depending on the type of coating.
    [0058] Another main characteristic of the steel sheet according to the present invention is its reactive surface, which can be described as it comprises the following successive layers:
    - top layer of pure metallic iron whose thickness varies from 50 to 300 nm; and
    - first sublayer made of metallic iron that also contains one or more oxide precipitates selected from Mn, Si, Al, Cr and B, whose thickness varies from 1 to 8 pm.
    [0059] This structure guarantees reactivity during the treatment by conversion of phosphate from bare steel, good wetting and adhesion of metallic coatings such as zinc or aluminum coatings. This increases the electrodeposition ability of the ink.
    [0060] As long as that surface is obtained, any method of
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    14/28 Proper fabrication can be employed.
    [0061] For example, a method of producing steel according to the present invention involves molding steel with the chemical composition according to the present invention.
    [0062] Molded steel is reheated from 1100 ° C to 1300 ° C. When the strip reheat temperature is less than 1100 ° C, for Al <4% by weight, the rolling loads increase too much and the hot rolling process becomes difficult; for Al> 4% by weight, the last hot rolling passage is hardly maintained above 800 ° C due to thermal losses during the rolling process. Above 1300 ° C, oxidation is very intense, which leads to scale loss and surface degradation.
    [0063] The reheated strip can then be hot rolled at a temperature of 1250 ° C to 800 ° C, where the last hot rolling step occurs at a temperature Tlp greater than or equal to 800 ° C. If Tlp is below 800 ° C, hot applicability is reduced.
    [0064] The steel is cooled at a Vcooling1 refrigeration speed of at least 10 ° C / s until the winding temperature Tcoiling less than or equal to 700 ° C. If the cooling speed Vcooling1 is below 10 ° C / s, in the case where> 4% by weight and Mn> 4% by weight, harmful precipitates precipitate at the interfaces between ferrite and austenite.
    [0065] Tcoiling must be less than or equal to 700 ° C. If the winding temperature is above 700 ° C, there is a risk of the formation of a hardened microstructure consisting of:
    - hardened ferrite and bainite structure when the Al content is less than 4% by weight; and
    - cap carbides at the interfaces between ferrite and austenite when the Al content is greater than or equal to 4% by weight of Al and Mn above 4% Mn.
    [0066] Steel is then cold rolled with cold rolling ratio
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    15/28 from 30% to 75% to obtain cold rolled steel. Below 30%, recrystallization during subsequent annealing is not favored enough and uniform elongation above 15% is not achieved due to the lack of recrystallization. Above 75%, there is a risk of edge cracking during cold rolling.
    [0067] Then, the steel is heated under an Hrate heating rate of at least 1 ° C / s to the Tanneal annealing temperature. If the heating rate is below 1 ° C / s, the recrystallization force is too low, which prevents the achievement of the target microstructure.
    [0068] During heating, from 550 ° C until the end of the immersion in Tanneal, the steel goes through an oxidation atmosphere to produce predominantly an iron oxide with a thickness of 100 to 600 nm.
    [0069] If the iron oxide is thinner than 100 nm, the iron oxide will disappear too soon, which again allows the selective external oxidation of the alloying elements during the subsequent reductive annealing, which prevents the surface reactivity during the coating process.
    [0070] If the iron oxide is above 600 nm, the risk of non-adherent iron oxides is provided by pollution in the furnace furnace lamination due to collection problems and causes defects in the surface by notching. A thickness of more than 600 nm can also lead to only partial reduction of iron oxide during the immersion or refrigeration step, or immersion and refrigeration when applying a reductive atmosphere.
    [0071] If radiant tubes are used in the furnace for heating, the atmosphere for iron reduction will contain 2 to 8% H2, in which the balance is nitrogen and unavoidable impurities.
    [0072] If the H2 content is less than 2%, the reducing capacity of the atmosphere is too low to completely reduce iron oxide.
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    16/28 [0073] If the H2 content is more than 8%, the reduction process will be completed, but it will no longer be economically viable.
    [0074] The steel is then annealed at a Tanneal temperature of Tmin ° C to Tmax ° C for 30 and 700 seconds. The control of the annealing temperature is an important feature of the process, as it allows controlling the fraction of austenite and its chemical composition. The annealing temperature should be high enough to form more than the 10% of retained austenite required in the final microstructure and to avoid precipitation of more than 5% of cap carbides. The annealing temperature should not be too high to avoid the formation of more than 50% of austenite and to avoid the hardening of the grain, which generates tensile strength below 1000-50xAl (%) when Al> 4% by weight. The annealing temperature must also be high enough to allow sufficient recrystallization of the cold rolled structure. As the phase transformations depend on the chemical composition, the preferred Tanneal is preferably defined as follows:
    [0075] The annealing temperature Tmin is defined as: Tmin = 721-36 * C-20 * Mn + 37 * Al + 2 * Si (in ° C). Below this temperature, the minimum fraction of austenite is not formed, or its stability is too high, which generates limited stress resistance.
    [0076] The annealing temperature Tmax is defined as: Tmax = 690 + 145 * C-6.7 * Mn + 46 * Al + 9 * Si (in ° C). Above Tmax, there is also a risk of forming too many martensites, which generates limited uniform stretching and orifice stretching capacity.
    [0077] During immersion in Tanneal to 600 ° C, the steel passes through an atmosphere containing 2% to 35% H2, in which the balance is nitrogen and unavoidable impurities to reduce the iron oxide formed by heating, applying dew point below the critical dew point for iron oxidation normally below -10 ° C.
    Petition 870190089909, of 9/11/2019, p. 28/46
    17/28 [0078] If the H2 content is less than 2%, the reducing capacity of the atmosphere is too low to completely reduce iron oxide.
    [0079] If the H2 content is more than 35%, the reduction process is completed, but it is no longer economically viable.
    [0080] Preferably, the dew point during iron reduction is less than -30 ° C to allow rapid reduction kinetics.
    [0081] In a preferred embodiment, the H2 content is more than 20%, but less than 35%.
    [0082] In another embodiment, the reduction step is bypassed and the iron oxide is removed by pickling (formic acid, hydrochloric acid, sulfuric acid) after the completion of the entire annealing treatment. This is because, if the steel does not go through a reductive atmosphere, slight reoxidation may occur and this layer must be removed. In the present invention:
    - the first part of the immersion medium means heating and up to 90% of the immersion time;
    - at the same time, the second part of the immersion means the remaining immersion time and the cooling of the annealing temperature to 600 ° C.
    [0083] The steel is then cooled at a cooling rate Vcooling2 of common annealing lines; preferably, this cooling rate is more than 5 ° C / s and below 70 ° C / s. If the refrigeration rate is less than 5 ° C / s, there is a risk of forming more than 5% cover carbide when the Al content is more than 4% by weight. The cooling atmosphere contains 2% to 35% H2 to prevent reoxidation of the reduced iron oxide formed by applying dew point below the dew point critical for iron oxidation normally below -10 ° C.
    [0084] Optionally, the steel is cooled to Vcooling2 until
    Petition 870190089909, of 9/11/2019, p. 29/46
    18/28 Toa temperature from 350 ° C to 550 ° C and kept at Toa for a period of time from 10 to 300 seconds. It has been shown that this heat treatment to facilitate the Zn coating by means of a hot dip process, for example, does not affect the final mechanical properties.
    [0085] The steel is additionally cooled at a Vcooling3 cooling rate from common annealing lines to room temperature; preferably, this cooling rate is more than 5 ° C / s and less than 70 ° C / s to obtain cold rolled and annealed steel.
    [0086] In another realization, after maintaining the Toa steel, the steel is coated by hot immersion with Zn or Zn alloys, which means that the Zn content is the highest in the alloy in percentage.
    [0087] In another realization, after the maintenance of the Toa steel, the steel is coated by hot immersion with Al or Al alloys, which means that the Al content is the highest in the alloy in percentage.
    [0088] Optionally, the cold rolled and annealed steel is tempered at room temperature from 200 to 400 ° C for a period of time from 200 to 800 seconds. This treatment allows martensite seasoning, which may be formed during refrigeration after immersion of unstable austenite. The martensite stiffness is then reduced and the orifice expansion capacity is improved. Below 200 ° C, the seasoning treatment is not efficient enough. Above 400 ° C, the loss of resistance becomes high and the balance between resistance and orifice expansion is no longer improved.
    [0089] In another embodiment, the annealed and cold-rolled steel undergoes phosphate conversion treatment.
    [0090] In another embodiment, the annealed and cold rolled steel is coated with Zn, Zn, Al alloys or Al alloys applied by means of electrodeposition or vacuum technologies. Zn and Al alloys mean that, respectively, Zn and Al are the main components of the coating.
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    19/28 [0091] Semi-finished products were developed from a steel mold. The chemical compositions of semi-finished products, expressed as a percentage by weight, are shown in Table 1 below. The rest of the steel composition in Table 1 consists of iron and unavoidable impurities resulting from smelting.
    Table 1
    Chemical composition (% by weight):
    Steel ç Mn Al Si Cr Si + Al Comment THE 0.21 8.2 7.4 0.26 0.02 7.66 Invention B 0.2 3.8 0 1.5 0.3 1.5 Invention Ç 0.15 19 0.05 0.2 0.2 0.25 Comparative example D 0.196 5.01 1.03 0.012 <0.010 1,042 Invention AND 0.189 5.01 2.85 0.02 <0.010 2.87 Invention F 0.2 4 6.2 <0.050 <0.010 6.2 Invention G 0.19 6.2 6 <0.050 <0.010 6 Invention H 0.12 5.15 2.31 0.509 <0.010 2,819 Invention
    Steel s P You V Nb Comment THE <0.005 <0.025 <0.010 <0.010 <0.010 Invention B <0.005 <0.025 <0.010 <0.010 <0.010 Invention Ç <0.005 <0.025 <0.01 <0.01 <0.01 Comparative example D 0.002 0.022 <0.010 <0.010 <0.010 Invention AND 0.0021 0.02 <0.010 <0.010 <0.010 Invention F 0.0031 0.02 <0.010 <0.010 <0.010 Invention G 0.004 0.017 <0.010 <0.010 <0.010 Invention H <0.005 0.017 <0.010 <0.010 <0.010 Invention
    [0092] These steels do not contain boron.
    [0093] The products were first hot rolled. The hot-rolled plates were then cold-rolled and annealed. The production conditions are shown in Table 2 with the following abbreviations:
    - Treheat: is the reheat temperature;
    - Tlp: is the final annealing temperature;
    - Vcooling1: is the cooling rate after the last lamination step;
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    20/28
    - Tcoiling: is the winding temperature;
    - Rate: is the rate of reduction of cold rolling;
    - Hrate: is the heating rate;
    - Tanneal: is the immersion temperature during annealing;
    - tanneal: is the duration of immersion during annealing;
    - Vcooling2: is the refrigeration rate after immersion;
    - tOA: is the period of time during which the plate is kept at a Toa temperature; and
    - Vcooling3: is the cooling rate below Toa.
    Table 2
    Hot rolling and cold rolling and annealing conditions:
    T reheat(° C) Tlp(° C) Vcooling1(° C / s) Tcoiling(° C) Rate(%) Hrate(° C / s) Tanneal(° C) tanneal(s) Vcooling2(° C / s 'S -1 O o TOO(s) Vcooling3(° C / s) TO 1 1180 905 50 500 74 15 830 136 50 50 A2 1180 964 50 500 74 15 850 136 50 50 A3 1180 964 50 500 74 15 790 136 50 50 A4 1180 964 50 500 74 15 900 136 50 50 A5 1180 964 50 500 74 15 850 136 50 50 A6 1180 964 50 500 74 15 900 136 50 50 A7 1180 964 50 500 74 15 900 136 50 50 A8 1180 964 50 500 74 15 830 136 50 50 B1 1250 900 30 550 50 5 790 130 20 470 38 20 B2 1250 900 30 550 50 5 790 130 20 470 38 20 B3 1250 900 30 550 50 5 675 130 20 470 38 20 C1 1250 900 30 550 60 10 800 60 20 460 10 20 D1 1250 930 15 600 50 16 710 120 20 400 300 5 E1 1250 930 15 600 50 16 770 120 20 400 300 5 F1 1200 950 60 450 75 15 900 136 50 410 500 20 F2 1200 950 60 450 75 15 900 136 50 410 500 20 F3 1200 950 60 450 75 15 900 136 50 410 500 20 F4 1200 950 60 450 75 15 900 136 50 410 500 20 G1 1200 950 60 450 75 15 850 136 50 410 500 20 G2 1200 950 60 450 75 15 850 136 50 410 500 20 H1 1250 900 10 600 50 10 770 120 20 410 500 5
    [0094] The products were annealed under different annealing atmospheres. Table 3 shows the atmospheres of
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    21/28 annealing and stripping in formic acid after the continuous annealing cycle is completed. “Yes” if a pickling treatment was applied, “No” if no pickling treatment was applied.
    [0095] If the annealing atmosphere of 550 ° C until the end of the immersion in Tanneai oxidized iron when adjusting the dew point and the hydrogen content, the indication “Oxidation” was included in the column “Atmosphere of 550 ° C until the end of immersion in Tanneai ”; if the atmosphere was reduced to iron, indicate “Reduction”. In addition, the H2 content and the dew point of the annealing atmosphere are provided.
    [0096] If the annealing atmosphere during immersion in Tanneal up to 600 ° C was reducing for iron oxide, the indication "Reduction" was included in the column "Atmosphere during immersion in Tanneal up to 600 ° C". If the annealing atmosphere was oxidizing to iron, "oxidation" is indicated. In addition, the H2 content and the immersion point of the annealing atmosphere are provided.
    [0097] In Table 3 below, EG means electrogalvanized, while Gl means galvanized.
    Table 3
    Annealing conditions to create the appropriate reactive surface after annealing, balance N2:
    Steel 550 ° C atmosphere until the end of the first part of the immersion Atmosphere during the second part of immersion in Tanneal up to 600 ° C Pickling in formic acid after continuous annealing Type of coating TO 1 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG A2 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG A3 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG A4 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG
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    Steel 550 ° C atmosphere until the end of the first part of the immersion Atmosphere during the second part of immersion in Tanneai up to 600 ° C Pickling in formic acid after continuous annealing Type of coating A5 Oxidation - Dew Point + 30 ° C, 5% H2 Oxidation - Dew Point + 30 ° C, 5% H2 No EG A6 Reduction - Dew point - 40 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG A7 Oxidation - Dew Point + 30 ° C, 5% H2 Oxidation - Dew Point + 30 ° C, 5% H2 No EG A8 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 Yes Gl B1 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No Gl B2 Reduction - Dew point - 40 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No Gl B3 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No Gl C1 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No Gl D1 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG E1 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG F1 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG F2 Reduction - Dew point - 40 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG F3 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No Gl F4 Reduction - Dew point - 40 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No Gl G1 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG G2 Reduction - Dew point - 40 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG
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    Steel 550 ° C atmosphere until the end of the first part of the immersion Atmosphere during the second part of immersion in Tanneal up to 600 ° C Pickling in formic acid after continuous annealing Type of coating H1 Oxidation - Dew Point + 30 ° C, 5% H2 Reduction - Dew point - 40 ° C, 5% H2 No EG
    [0098] Samples A6, B2, F2, F4 and G2 were annealed under a regular reduction atmosphere (dew point = -40 ° C, 5% H2), which created poor surface reactivity. The GDOS profile of these surfaces is characterized by a first zone in which the Fe signal is very low, while the O signal is high and reaches more than 50% on the free surface. In this zone, Mn enrichment is also detected. Below that layer, the Fe signal increases and the O signal falls at a rate of about 1% per nanometer. This trace of oxygen signal is typical of the presence of an external selective oxide layer, whose oxygen atoms are partially captured and partially implanted in the substrate during the measurement. A little surface pollution is visible due to the transfer of samples from the annealing simulator to the GDOS analysis. In Figure 3, In (A) a little surface pollution is visible due to the transfer of samples from the annealing simulator to the GDOS analysis.
    [0099] Table 4 presents the following characteristics:
    - Ferrite: "OK" refers to the presence of ferrite with a volume fraction of 25 to 90% in the microstructure of the annealed sheet. “KO” refers to comparative examples where the ferrite fraction is outside this range.
    - Austenite: “OK” refers to the presence of austenite with a volume fraction of 10 to 50% in the microstructure of the annealed sheet. “KO” designates comparative examples where the austenite fraction is outside this range.
    - Martensite: “OK” means the presence or absence of martensite with a volume fraction of less than 25% in the microstructure of the annealed sheet. “KO” designates comparative examples in which the martensite fraction is more
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    24/28 of 25%.
    K: “OK” means the presence or absence of precipitates in the cover microstructure with a volume fraction of less than 5%. This measurement is performed with a scanning electron microscope. When it says “KO”, the fraction of precipitated cape is more than 5%.
    UTS (MPa) designates the stress resistance measured by means of a stress test in the longitudinal direction relative to the rolling direction.
    UEI (%) designates the uniform elongation measured by means of a stress test in the longitudinal direction relative to the rolling direction.
    HE (%) designates the orifice expansion ratio according to ISO 16630 2009. The HE% orifice expansion ratio method is used to assess the ability of a metal to resist the formation of a cutting edge . It consists of measuring the initial diameter D1 of the orifice before forming, so that the final diameter of the orifice Df after formation, determined when observing deep cracks on the edges of the orifice. It then determines the HE% orifice expansion capacity using the following formula:
    HE% = 100 x tPf ~ Di)
    Di [00100] In this method, the initial orifice diameter is 10 millimeters.
    Table 4
    Properties of annealed and cold-rolled sheets:
    Steel Ferrite Austenite Martensita K TS (MPa) UEI (%) He (%) TO 1 OK (81%) OK (17%) OK (0%) OK (2%) 831 15 30% A2 OK (80%) OK (20%) OK OK (0%) 800 15 42 A3 OK OK (15%) OK (0%) KO (> 5%) Not measured Not measured Not measured A4 OK OK (25%) OK OK (0%) 730 20 Not measured A5 OK (80%) OK (20%) OK OK (0%) 800 15 42 A6 OK OK (25%) OK OK (0%) 730 20 Not measured A7 OK OK (25%) OK OK (0%) 730 20 Not measured
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    Steel Ferrite Austenite Martensita K TS (MPa) UEI (%) He (%) A8 OK (81%) OK (17%) OK (0%) OK (2%) 831 15 30% B1 KO KO (8%) KO (92%) OK (0%) Not measured Not measured Not measured B2 KO KO (8%) KO (92%) OK (0%) Not measured Not measured Not measured B3 OK (60%) OK (30%) OK (10%) OK (0%) 1092 17 30 C1 OK (40%) KO (0%) OK (10%) OK (0%) 820 14 23 D1 OK (50%) OK (28%) OK (22%) OK (0%) 1075 22.8 Not measured E1 OK (66%) OK (32%) OK (2%) OK (0%) 1023 24.4 Not measured F1 OK (79%) OK (21%) OK (0%) OK (0%) 723 25 Not measured G1 OK (74%) OK (26%) OK (0%) OK (0%) 702 20 Not measured H1 OK (69%) OK (23%) OK (8%) OK (0%) 965 16 Not measured
    [00101] B1 was not measured due to brittle behavior.
    For C1, the rest of the microstructure (50%) is made of bainite. C1 has a tensile strength of 820 MPa, which is too low for the present invention.
    [00102] Table 5 presents the results of electroplating coating of a zinc coating.
    [00103] The target surface and the microstructure of the subsurface are indicated as “OK” if the surface is made of an outer layer of metallic iron, with thickness ranging from 50 to 300 nm, which covers an inner layer made of metallic iron and contains precipitates of internal oxides of Mn, Al, Si, Cr and B and other elements more oxidizable than iron, whose thickness varies from 1 to 8 pm, superimposed on a decarbonized layer, mainly made of ferrite, whose thickness varies from 10 to 50 pm. If the surface and subsurface differ from the target surface, the microstructure is considered to be insufficient, “KO”.
    [00104] The quality of the coating is characterized by the coverage ratio and coating adhesion.
    [00105] The coverage ratio is indicated as “OK” when complete coverage is observed with the naked eye and “KO” if coating defects are observed, such as uncoated areas or exposed locations.
    [00106] The adhesion of the coating was tested in a test of
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    26/28 3-point fold (180 °) on 1 mm sheets using a 3 mm punch with a 1.5 mm radius tip. Adhesion is considered excellent “OK” if no zinc coating peeling is observed after application and removal of adhesive tape. If peeling or peeling is observed, adherence is considered to be insufficient “KO”.
    Table 5
    Surface properties of coated, annealed and cold-rolled sheets:
    Target surface and subsurface microstructure Coverage ratio Coating adhesion Type of coatingTO 1 OK OK OK EG Invention A2 OK OK OK EG Invention A3 OK OK OK EG Invention A4 OK OK OK EG Invention A5 KO KO KO EG Reference A6 KO KO KO EG Reference A7 OK OK OK EG Invention A8 OK OK OK Gl Invention B1 OK OK OK Gl Invention B2 KO KO KO Gl Reference B3 OK OK OK Gl Invention C1 OK OK OK Gl Invention D1 OK OK OK EG Invention E1 OK OK OK EG Invention F1 OK OK OK EG Invention F2 KO KO KO EG Reference F3 OK OK OK Gl Invention F4 KO KO KO Gl Reference G1 OK OK OK EG Invention G2 KO KO KO EG Reference H1 OK OK OK EG Invention
    [00107] In Figure 5, the coating adhesion was tested in a 3-point (180 °) fold test on 1 mm sheets using a 3 mm punch with a 1.5 mm radius tip. The non-adherence of the zinc coating is observed in the example of A6 steel (according to the present invention). In (a), a coated part is visible, which was under low request
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    27/28 during the bend test. In (b), the steel substrate is visible after peeling the coating; this part was under high demand in the bending test.
    [00108] A1, A2, A3, A4, A7, A8, B1, B3, C1, D1, E1, F1, F3, G1 and H1 sheets are sheets whose chemical composition and processing method are in accordance with the present invention .
    [00109] For sample A3, production was carried out under an oxidizing atmosphere (dew point = +30 ° C) followed by a reducing atmosphere. The surface is composed of a first layer in which the Fe GDOS signal reaches a maximum and oxygen, a minimum, as shown in Figure 4. This layer (B) is made of metallic iron. The second layer (C) is characterized by a continuous reduction of the oxygen signal at low speed, about 1% per 100 nm, and corresponds to a zone in which internal selective oxides of Mn and Al have precipitated. It extends to an oxygen level of 5% which corresponds to a thickness of 4 pm at this point. In (A), a little surface pollution is visible due to the transfer of samples from the annealing simulator to the GDOS analysis.
    [00110] For sample A3, the coating adhesion was tested in a 3-point bend test (180 °) on 1 mm sheets using a 3 mm punch with a 1.5 mm radius tip. Very good adherence of the zinc coating was observed for the A3 steel example (according to the present invention), as shown in Figure 6. In (c), a coated part is visible, which was under low stress during the bending test. In (d), the coating exhibits excellent adhesion and this part was under high demand in the bend test.
    [00111] The coating adhesion was also tested in a 3-point (180 °) fold test on 1 mm sheets using a 3 mm punch with a 1.5 mm radius tip for A4, as shown in Figure
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    28/28
    7. Very good adherence of the zinc coating was observed for the example of steel A4 (according to the present invention). In (e), a coated part is visible, which was under low stress during the bending test. In (f), the coating shows excellent adhesion, this part was under high demand in the bend test.
    [00112] The microstructure of sheet A1 is illustrated in Figure 1. Its stress curve is shown in Figure 2.
    [00113] B2 is not in accordance with the present invention due to the undirected microstructure and coating method. Its annealing temperature is off target.
    [00114] A5 did not undergo a pickling step although it only suffered oxidation during annealing; consequently, the coating adhesion and coverage ratio are poor.
    [00115] A6, B2, F2, F4 and G2 suffered only a reduction during annealing; consequently, the results of coating adhesion and coverage ratio are poor.
    [00116] For the steels according to the present invention, in addition to good coating capacity by means of electroplating (EG) or galvanizing, the tensile strengths are over 1000 - 50xAl MPa and their uniform elongation is over 15 %. In addition, the orifice expansion is also above 20%.
    [00117] The steel sheets according to the present invention will be used beneficially for the manufacture of structural or safety parts in the automotive industry.
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    权利要求:
    Claims (25)
    [1]
    1. Cold-rolled STEEL SHEET, characterized by consisting of, in percentage by weight:
    0.1 <C <0.5%
    3.5 <Mn <10.0%
    Al <9.0%
    Si <5.0%
    0.5 <Si + Al <9.0%
    Ti <0.2%
    V <0.2%
    Nb <0.2%
    B <0.0035
    Cr <1%
    S <0.004%
    P <0.025% where the rest of the composition is iron and unavoidable impurities resulting from smelting and the microstructure contains 10% to 50% austenite, 25% to 90% ferrite, less than 5% of precipitates and less than 25% of martensite and the leaf presents, from the upper surface, the following successive layers:
    an upper layer of pure metallic iron whose thickness varies from 50 to 300 nm; and a first sublayer made of metallic iron that also contains one or more oxide precipitates selected from Mn, Si, Al, Cr and B, whose thickness varies from 1 to 8 pm.
    [2]
    2. Cold-rolled STEEL SHEET, according to claim 1, characterized in that it additionally consists of a second sublayer underlying the first sublayer, made of pure ferrite, whose
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    2/5 thickness ranges from 10 to 50 pm.
    [3]
    Cold rolled steel sheet according to any one of claims 1 to 2, characterized in that the steel composition contains a 5.0 to 9.0% manganese content.
    [4]
    Cold rolled steel sheet according to any one of claims 1 to 3, characterized in that the steel composition contains a carbon content of 0.1 to 0.3%.
    [5]
    Cold rolled steel sheet according to any one of claims 1 to 4, characterized in that the steel composition contains a carbon content of 0.15 to 0.25%.
    [6]
    6. Cold-rolled STEEL SHEET according to any one of claims 1 to 5, characterized in that the steel composition contains aluminum content of 1.5 to 9%.
    [7]
    7. Cold rolled steel sheet according to any one of claims 1 to 6, characterized in that the steel composition contains an aluminum content of 5 to 8%.
    [8]
    8. Cold rolled steel sheet according to any one of claims 1 to 7, characterized in that the steel composition contains a silicon content less than or equal to 1.5%.
    [9]
    9. Cold rolled steel sheet according to any one of claims 1 to 8, characterized in that the steel composition contains a silicon content less than or equal to 0.3%.
    [10]
    10. Cold rolled steel sheet according to any one of claims 1 to 9, characterized in that the steel microstructure contains 25 to 40% austenite.
    [11]
    11. Cold-rolled STEEL SHEET according to any one of claims 1 to 10, characterized in that the steel microstructure contains 50 to 85% ferrite.
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    3/5
    [12]
    12. Cold rolled steel sheet according to any one of claims 1 to 11, characterized in that the steel microstructure contains less than 15% of martensite.
    [13]
    13. Cold-rolled STEEL SHEET according to any one of claims 1 to 12, characterized in that the steel microstructure does not contain precipitated layers.
    [14]
    14. Cold-rolled STEEL SHEET according to any one of claims 1 to 13, characterized by having a tensile strength TS greater than or equal to 1000 - 50 x% Al in MPa, uniform elongation UEI greater than or equal to 15% and HE orifice expansion greater than or equal to 20%.
    [15]
    15. STEEL SHEET with metallic coating obtained by coating a cold rolled steel sheet as defined in any one of claims 1 to 14, characterized in that the coating is carried out by means of a process selected from immersion coating hot, electrodeposition and vacuum coating.
    [16]
    16. Metallic coated STEEL SHEET according to claim 15, characterized in that the sheet is galvanized and annealed.
    [17]
    17. METHOD OF MANUFACTURING cold rolled steel sheet as defined in any one of claims 1 to 14, characterized by comprising the following steps:
    - feeding and scaling a hot-rolled strip or thin sheet whose composition is the same as that of a steel sheet as defined in any one of claims 1 to 9;
    - cold lamination of the hot-rolled strip or thin sheet with a cold-rolling ratio of 30% to 75% to obtain a cold-rolled steel sheet;
    - heat treatment of the steel sheet that undergoes heating at an Hrate heating rate of at least 1 ° C / s, up to the temperature
    Petition 870190089909, of 9/11/2019, p. 43/46
    4/5 annealing Tanneal is between Tmin = 721-36 * C-20 * Mn + 37 * Al + 2 * Si (in ° C) and Tmax = 690 + 145 * C-6.7 * Mn + 46 * Al + 9 * Si (in ° C) for 30 to 700 seconds, followed by immersion at temperature, heating from 550 ° C to Tannei and at least the first part of the immersion takes place in an oxidizing atmosphere to produce an upper layer of oxide of iron with a thickness of 100 to 600 nm, in which the iron oxide layer is then completely reduced.
    [18]
    18. METHOD, according to claim 17, characterized in that this reduction occurs during the second part of the immersion, in a reduction atmosphere that contains from 2% to 35% of H2 and with a dew point below -10 ° C to reduce completely the iron oxide layer, in which the steel sheet is additionally cooled at a Vcooling2 cooling rate above 5 ° C / s and below 70 ° C / s to room temperature.
    [19]
    19. METHOD according to claim 18, characterized in that the second part of the immersion takes place in an atmosphere whose dew point is below -30 ° C.
    [20]
    20. METHOD according to any one of claims 17 to 19, characterized by:
    - the steel sheet is refrigerated at Vcooling2 to a temperature of 350 ° C to 550 ° C and kept in Toa for a period of 10 to 300 seconds; and after that,
    - the steel sheet is additionally cooled at a Vcooling3 cooling rate of 5 ° C / s to 70 ° C / s to room temperature.
    [21]
    21. METHOD according to any of claims 17 and 20, characterized by the fact that this reduction occurs after cooling the steel sheet at a cooling rate Vcooling2 above 5 ° C / s and below 70 ° C / s to room temperature and is carried out by chemical pickling.
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    5/5
    [22]
    22. METHOD OF MANUFACTURING STEEL SHEET with metallic coating as defined in any one of claims 17 to 21, characterized by comprising the stages of coating carried out by means of a process selected from hot dip coating, electrodeposition and a coating vacuum.
    [23]
    23. METHOD, according to claim 22, characterized in that the metallic coated steel sheet undergoes galvanizing and annealing heat treatment.
    [24]
    24. METHOD, according to any of the claims
    17 to 23, characterized by the hot rolled strip being obtained by means of a process that comprises the following steps:
    - steel shaping whose composition is equal to that of a steel sheet as defined in any one of claims 1 to 9 to obtain a sheet;
    - reheating the plate to a Treheat temperature of 1100 ° C to 1300 ° C;
    - hot rolling of the plate reheated to a temperature of 800 ° C to 1250 ° C to obtain a strip of hot-rolled steel;
    - cooling of the hot-rolled steel strip at a Vcooling1 cooling speed of at least 10 ° C / s until Tcoiling winding temperature less than or equal to 700 ° C; and
    - winding of the Tcooling-cooled hot-rolled strip.
    [25]
    25. METHOD according to claim 24, characterized in that the hot-rolled steel strip is additionally annealed using a process selected from batch annealing from 400 ° C to 600 ° C for 1 to 24 hours and continuous annealing of 650 ° C to 750 ° C from 60 to 180 s.
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    KR20160027105A|2016-03-09|
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    法律状态:
    2018-11-06| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2019-06-25| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2019-10-15| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 03/07/2014, OBSERVADAS AS CONDICOES LEGAIS. (CO) 20 (VINTE) ANOS CONTADOS A PARTIR DE 03/07/2014, OBSERVADAS AS CONDICOES LEGAIS |
    优先权:
    申请号 | 申请日 | 专利标题
    IBPCT/IB13/001436|2013-07-04|
    PCT/IB2013/001436|WO2015001367A1|2013-07-04|2013-07-04|Cold rolled steel sheet, method of manufacturing and vehicle|
    PCT/IB2014/001258|WO2015001414A1|2013-07-04|2014-07-03|Cold rolled steel sheet, method of manufacturing and vehicle|
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