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    • 专利摘要:
    The present invention relates to a steel composition comprising, in percentages by weight of the total composition: Carbon: 0.01-0.20, preferably 0.02-0.18; Chromium: 2.5-5.0, preferably 3.0-4.5; Molybdenum: 4.0-6.0; Tungsten: 0.01 - 3.0; Vanadium: 1.0-3.0, preferably 1.5-2.5; Nickel: 2.0-4.0; Cobalt: 9.0-12.5, preferably 9.5-11.0; Iron: balance as well as unavoidable impurities, optionally further comprising one or more of the following: Niobium: ≤ 2.0; Nitrogen: ≤ 0.50, preferably ≤ 0.20; Silicon: ≤ 0.70, preferably 0.05-0.50; Manganese: ≤ 0.70, preferably 0.05-0.50; Aluminum: ≤0.15, preferably ≤ 0.10; the combined Niobium + Vanadium content being in the range 1.0-3.5; and the carbon + nitrogen content being in the range 0.05-0.50. It also relates to its manufacturing process, the steel blank obtained and a mechanical member or an injection system comprising it.
    公开号:FR3078978A1
    申请号:FR1852202
    申请日:2018-03-14
    公开日:2019-09-20
    发明作者:Jacques Bellus；Atman Benbahmed；Johanna Andre；Fredrik Sandberg
    申请人:ERASTEEL；Aubert and Duval SA；
    IPC主号:
    专利说明:

    The present invention relates to a new steel of lOCrMoNiVCo type with low carbon content and high cobalt content for thermochemical treatment, in particular intended for the field of transmissions such as bearings and gears. The alloy according to the invention can also be used for other applications requiring high surface hardness combined with good toughness at the core, for example in the case of injection systems.
    Rolling bearings are mechanical parts that allow relative and constrained movements in orientation and direction between two parts. The bearings include several components: internal ring, external ring as well as rolling bodies (ball or cylinder) arranged between these two rings. To ensure reliability and performance over time, it is important that these different elements have good properties in rolling fatigue, wear, etc., ...
    Gears are mechanical organs for power transmission. To ensure a favorable power density (power ratio transmitted by the size of the gears) and operating reliability, the gears must have good properties in structural fatigue (tooth base) and contact fatigue (tooth blanks).
    Conventional techniques for producing these metal components use methods for developing an electrical steelworks followed by possible reflow operations, or simple or multiple vacuum rejections. The ingots thus produced are then shaped by hot transformation processes such as rolling or forging in the form of bars, tubes or rings.
    There are two types of metallurgy to ensure the final mechanical properties.
    1st Type: the chemical composition of the component makes it possible to obtain the mechanical properties directly after suitable heat treatment.
    2nd Type: the component requires a thermochemical treatment to enrich the surface with interstitial chemical elements such as carbon and / or nitrogen. This generally superficial enrichment then makes it possible to obtain high mechanical properties after heat treatment over depths of a few millimeters maximum. These steels generally have better ductility properties than steels of the 1st Type.
    There are also thermochemical processes applied to steels of the 1st type aimed at enriching the surface with nitrogen to obtain very high mechanical properties.
    The first of the properties required in the field of rolling bearings or gears is the obtaining of a very high level of hardness. These type 1 and type 2 steels generally have surface hardness levels greater than 58 H RC. The most common shades known under the term M50 (0.8% C-4% Cr-4.2% Mo-1% V) or 50NÎL (0.12% C-4% Cr-4.2% Mo -3.4% Ni-1% V) do not exceed a surface hardness of 63 H RC after any thermochemical treatment and suitable heat treatment. Obtaining hardnesses greater than 64 H RC is now required to significantly improve the properties of the component.
    Application GB2370281 describes a steel for a valve seat by powder metallurgy technology compacted from mixtures of powder with an iron base and harder particles. The matrix, which constitutes only part of the steel, has the following composition, in percentages by weight of the total composition:
    Carbon: 0.2-2.0;
    Chrome: 1.0-9.0;
    Molybdenum: 1.0-9.0;
    Silicon: 0.1-1.0;
    Tungsten: 1.0-3.0; Vanadium: 0.1-1.0;
    Nickel + Cobalt + Copper: 3.0-15.0;
    Iron: balance
    However, this matrix comprises from 5 to 40% by volume of perlite, which results in a lack of ductility of this matrix and therefore embrittlement. In addition, the material also contains porosity (up to 10%) which does not allow good properties in mechanical strength and fatigue to be achieved. Finally, this document does not suggest using a low copper content and on the contrary indicates that its content can go up to 15% by weight. However, a high copper content is not sought for the applications of the present invention because copper is a known embrittler, the content of which should not exceed 0.5% by weight relative to the total weight of the composition of the steel. .
    Patent application WO2015 / 082342 describes a bearing steel having the following composition, in percentages by weight of the total composition:
    Carbon: 0.05-0.5;
    Chromium: 2.5-5.0;
    Molybdenum: 4-6;
    Tungsten: 2-4.5;
    Vanadium: 1-3;
    Nickel: 2-4;
    Cobalt: 2-8;
    Iron: balance as well as unavoidable impurities, optionally further comprising one or more of the following:
    Niobium: 0-2;
    Nitrogen: 0-0.5;
    Silicon: 0-0.7;
    Manganese: 0-0.7; Aluminum: 0-0.15;
    and in particular the composition MIX5 grade (0.18% C-3.45% Cr4.93% Mo-3.05% W-2.09% V-0.30% Si-2.89% Ni-5 , 14% Co-0.27% Mn) which is the most interesting since it has the greatest surface hardness. This shade achieves a surface hardness after solution treatment at 1150 ° C and returned to 560 ° C at a maximum hardness level of about 800 HV, equivalent to a maximum of 64 HRC. However, this request indicates that the Co content must be limited to at most 8% and even it is preferable for it to be at most 7% and even more preferably at most 6% because the Co increases the level of hardness. of the base material which causes a decrease in toughness. The preferred MIX5 grade thus has a Co content of 5.14%.
    Patent application WO2017216500 describes a bearing steel having the following composition, in percentages by weight of the total composition:
    Carbon: 0.05-0.40, preferably 0.10-0.30;
    Chromium: 2.50-5.00, preferably 3.0-4.5;
    Molybdenum: 4.0-6.0;
    Tungsten: 0.01-1.8, preferably 0.02-1.5;
    Vanadium: 1.0-3.0, preferably 1.5-2.5;
    Nickel: 2.0-4.0;
    Cobalt: 2.0-8.0, preferably 3.0-7.0;
    Iron: balance as well as unavoidable impurities, optionally further comprising one or more of the following:
    Niobium: <2.0;
    Nitrogen: <0.50, preferably <0.20;
    Silicon: <0.70, preferably 0.05-0.50;
    Manganese: <0.70, preferably 0.05-0.50; Aluminum: <0.15, preferably <0.10;
    the combined Niobium + Vanadium content being in the range 1.00-3.50;
    and the content of Carbon + Nitrogen being in the range 0.050.50. and
    In particular in the examples, the shade C of composition (0.180.20% C-3.90-4.00% Cr-5.00-5.20% Mo-0.10-0.20% W-2, 10 to 2.30% V-0,140,16% Si-3.05 to 3.09% Ni-5.00 to 5.40% Co-0.18-0.22% Mn-0.03 to 0, 05% AI) is preferred since it has the greatest surface hardness. This nuance makes it possible to achieve a surface hardness after solution treatment at 1100 ° C-1150 ° C and returned to 500 ° C at a maximum hardness level of approximately 66-67 H RC which is much higher than the hardness. surface obtained with a shade according to application WO2015 / 082342 (shade A: Figure 1). However, this request also indicates that the Co content must be limited to at most 8% and even it is preferable that it be at most 7% and even more preferred by at most 6% because it increases the level of hardness. of the base material which causes a decrease in toughness. The preferred grade C thus has a Co content of 5.00-5.40%.
    Obtaining surface hardnesses greater than 67 HRC, in particular using a heat treatment for dissolving at a temperature less than or equal to 1160 ° C., is therefore difficult to obtain while they would make it possible to improve significantly the properties of the component.
    The inventors have surprisingly found that by increasing the cobalt content of the steel described in applications WO2015 / 082342 and W02017216500 to a content between 9 and 12.5%, while maintaining the carbon content at a level less than or equal to 0.2% (new carbon / cobalt balancing), the steel obtained exhibited, after thermochemical treatment, in particular case hardening and / or nitriding, a very high surface hardness and even greater than 67 HRC, in particular greater than or equal to 68 HRC and a hardness at 1mm greater than 860 HV (which corresponds to approximately 66HRC according to standard ASTME140-12b published in May 2013) after a heat treatment for dissolution at a temperature in the range 1100 ° C 1160 ° C and returned to a temperature greater than or equal to 475 ° C, while having a hardness level of the base material between 400 and 650 HV.
    This was not at all obvious in the light of these documents which encouraged the use of a low content of cobalt such as in the grade MIX5 (5.14% of cobalt) and in the grade C (5.00-5.40 % cobalt) which are considered to be the compositions having the best hardness.
    The patent US8157931 describes a Ni-Co type steel having a cobalt content of between 9.9 and 10% and a carbon content of between 0.1 and 0.12% and having a high surface hardness of the order of 68-69 HRC. However, such a steel has a high chromium content (5.35.4%), a low vanadium content (0.20-0.21%) and Molybdenum (2.5-2.52%) and does not contain no tungsten. This balancing of nuances leads after thermochemical treatment and associated quality treatment (comprising quenching at 1110 ° C and tempering at 482 ° C) to an interesting surface hardness but which decreases very quickly with depth, it is thus from 600 µm in depth already identical to that of the base metal (Figure 1). This is probably due to the lower carbon content in the cemented layer that the shade can support in order to avoid any risk of formation of weakening graphite phase. Claim 1 of this patent thus stipulates a carbon content in the cemented layer limited to about 0.8%. Indeed graphite could appear from 1% by weight of C in the cemented layer (surface layer obtained after cementation).
    It is therefore not easy to find the right balance of the grade (including Cr, Mo, V, W, C) in view of this document to arrive at an optimization of both the surface hardness and the hardness profile ( depth) and tenacity (of which one has an idea by the hardness at heart). In addition it was not obvious from this document to achieve a deep carburizing layer which allows to introduce much more carbon than the nuances of the state of the art (up to 1.5 % by weight of C) while limiting the risk of appearance of graphite.
    The present invention therefore relates to a steel composition, advantageously cementable and / or nitriding, more advantageously cementable, comprising, advantageously consisting essentially of, in particular consisting of, in percentages by weight of the total composition:
    Carbon: 0.01-0.20 preferably 0.02-0.18;
    Chromium: 2.5-5.0, preferably 3.0-4.5;
    Molybdenum: 4.0-6.0;
    Tungsten: 0.01-3.0;
    Vanadium: 1.0-3.0, preferably 1.50-2.50;
    Nickel: 2.0-4.0;
    Cobalt: 9.0-12.5, preferably 9.5-11.0;
    Iron: balance as well as unavoidable impurities, optionally further comprising one or more of the following:
    Niobium: <2.0;
    Nitrogen: <0.50, preferably <0.20;
    Silicon: <0.70, preferably 0.05-0.50;
    Manganese: <0.70, preferably 0.05-0.50; Aluminum: <0.15, preferably <0.10;
    the combined Niobium + Vanadium content being in the range 1.0-3.5;
    and the content of Carbon + Nitrogen being in the range 0.05-0.50.
    A particularly advantageous composition advantageously comprises essentially of, in particular consists of, in percentages by weight of the total composition:
    Carbon: 0.02-0.20, preferably 0.08-0.18;
    Chromium: 3.0-4.5, preferably 3.5-4.5;
    Molybdenum: 4.0-6.0, preferably 4.5-5.5;
    Tungsten 0.01 - 3.0;
    Vanadium: 1.5-2.5, preferably 2.0-2.3;
    Nickel: 2.0-4.0, preferably 2.5-3.5; Cobalt: 9.5-12.5, preferably 9.5-10.5; Iron: balance as well as unavoidable impurities, optionally further comprising one or more of the following:
    Niobium: <2.0;
    Nitrogen: <0.20;
    Silicon: <0.70, preferably 0.05-0.50; Manganese: <0.70, preferably 0.05-0.50; Aluminum: <0.10;
    the combined Niobium + Vanadium content being in the range 1.00-3.50;
    and the content of Carbon + Nitrogen being in the range 0.05-0.50.
    In particular the inevitable impurities, in particular chosen from Titanium (Ti), Sulfur (S), Phosphorus (P), Copper (Cu), Tin (Sn), Lead (Pb), Oxygen ( O) and their mixtures, are kept at the lowest level. These impurities are generally due mainly to the manufacturing process and the quality of the oven. Advantageously, the composition according to the invention comprises at most 1% by weight of unavoidable impurities, advantageously at most 0.75% by weight, even more advantageously at most 0.50% by weight, relative to the total weight of the composition.
    The carbide-forming elements, which also have a stabilizing effect on ferrite, so-called alphagenic elements, are essential to the steel composition according to the invention so as to provide sufficient hardness, resistance to heat and to wear. . In order to obtain a microstructure free of ferrite which would weaken the component, it is necessary to add stabilizing elements for austenite, so-called gamma elements.
    A correct combination of austenite stabilizing elements (Carbon, Nickel, Cobalt and Manganese) and ferrite stabilizing elements (Molybdenum, Tungsten, Chromium, Vanadium and Silicon) makes it possible to obtain a steel composition according to the invention having superior properties, in particular after thermochemical treatment such as case hardening.
    The steel composition according to the invention therefore comprises carbon (C) in a content comprised in the range 0.01-0.20%, preferably 0, ΟΣΟ, 20%, more preferred 0.02-0.18 %, even more preferred 0.08-0.18%, by weight relative to the total weight of the composition. Indeed, Carbon (C) stabilizes the austenitic phase of steel at heat treatment temperatures and is essential for the formation of carbides which provide mechanical properties in general, in particular mechanical resistance, high hardness, heat resistance and to wear. The presence of a small amount of carbon in a steel is beneficial to avoid the formation of undesirable and fragile intermetallic particles and to form small amounts of carbides to avoid the excessive growth of the grain size during the dissolution before quenching operation. The initial carbon content should not however be too high since it is possible to increase the surface hardness of the components formed from the steel composition by case hardening. It is also known that, generally speaking, increasing the carbon content makes it possible to significantly increase the level of hardness, which is generally detrimental with regard to the ductility properties. It is for this reason that the carbon content is limited to 0.20% maximum to obtain a hardness level at the heart of the material of maximum 650 HV. During carburizing, carbon is implanted in the surface layers of the component, so as to obtain a hardness gradient. Carbon is the main element for controlling the hardness of the martensitic phase formed after carburizing and heat treatment. In case-hardened steel, it is essential to have a core part of the material with a low carbon content while having a hard surface with a high carbon content after thermochemical carburizing treatment.
    The steel composition according to the invention also comprises chromium (Cr) in a content in the range 2.5-5.0%, preferably 3.04.5%, even more preferred 3.5-4 , 5%, even more advantageously 3.84.0% by weight relative to the total weight of the composition.
    Chromium contributes to the formation of carbides in steel and is one of the main elements which controls the hardenability of steels.
    However, chromium can also favor the appearance of ferrite and residual austenite. The chromium content of the steel composition according to the invention must therefore not be too high.
    The steel composition according to the invention also comprises Molybdenum (Mo) in a content in the range 4.0-6.0%, preferably 4.5-5.5%, even more preferred 4.8- 5.2%, by weight relative to the total weight of the composition.
    Molybdenum improves the resistance to tempering, the wear resistance and the hardness of steel. However, the Molybdenum has a strong stabilizing effect on the ferrite phase and must therefore not be present in too large a quantity in the steel composition according to the invention.
    The steel composition according to the invention also comprises Tungsten (W) in a content in the range 0.01-3.0%, preferably 0.01-1.5%, even more preferably 0.01 -1.4%, advantageously 0.01-1.3%, by weight relative to the total weight of the composition.
    Tungsten is a stabilizer of ferrite and a highly carbide-forming element. It improves resistance to heat treatment and wear and hardness by the formation of carbides. However, it can also lower the surface hardness of the steel and especially the ductility and toughness properties. In order for this element to fully play its role, it is necessary to carry out solutions at high temperature.
    The steel composition according to the invention also comprises Vanadium (V) in a content in the range 1.0-3.0%, preferably 1.52.5%, even more preferred 1.7-2 , 3%, advantageously 2.00-2.3%, in particular 2.0-2.2%, by weight relative to the total weight of the composition.
    Vanadium stabilizes the ferrite phase and has a strong affinity for carbon and nitrogen. Vanadium provides resistance to wear and income by the formation of hard vanadium carbides. Vanadium can be partially substituted by niobium (Nb), which has similar properties.
    The combined Niobium + Vanadium content must therefore be in the range 1.0-3.5% by weight relative to the total weight of the composition.
    If Niobium is present, its content must be <2.0% by weight relative to the total weight of the composition. Advantageously, the steel composition according to the invention does not comprise Niobium.
    The steel composition according to the invention also comprises Nickel (Ni) in a content included in the range 2.0-4.0%, preferably 2.5-3.5%, even more preferred 2.7- 3.3%, advantageously 3.0-3.2%, by weight relative to the total weight of the composition.
    Nickel promotes the formation of austenite and therefore inhibits the formation of ferrite. Another effect of Nickel is to decrease the temperature Ms, that is to say the temperature at which the transformation of austenite into martensite begins upon cooling. This can prevent the formation of martensite. The amount of Nickel must therefore be controlled so as to avoid the formation of residual austenite in the cemented components.
    The steel composition according to the invention also comprises Cobalt (Co) in a content included in the range 9.0 -12.5%, preferably 9.512.5%, advantageously 9.5-11.0%, more advantageously 9.5-10.5%, by weight relative to the total weight of the composition. The Cobalt content is measured according to the standards ASTM-E1097-12 published in June 2017 and ASTM E1479_16 published in December 2016. The measurement error of the Cobalt content of the steel according to the invention is thus ± 2, About 5% relative and evaluated according to ISO5724-1 (December 1994), ISO5725-2 (December 1994), ISO5725-3 (December 1994), ISO5725-4 (December 1994), ISO5725-5 (December 1994), ISO5725 standards -6 (December 1994) and the NF ISO / CEI Guide 98-3 standard of July 11, 2014.
    Cobalt is a strongly stabilizing element of austenite which prevents the formation of unwanted ferrite. Unlike Nickel, Cobalt increases the Ms temperature, which in turn decreases the amount of residual austenite. Cobalt, in combination with Nickel, allows the presence of ferrite stabilizers such as the carbide-forming elements Mo, W, Cr and V. The carbide-forming elements are essential for the steel according to the invention because of their effect on hardness, resistance to heat and wear. Cobalt has a small effect of increasing hardness on steel. However, this increase in hardness is correlated with the decrease in toughness. The steel composition according to the invention must therefore not contain too large a quantity of Cobalt. The addition of Co makes it possible to limit the content of C by avoiding the promotion of ferrite for a composition according to the invention (containing the contents of Cr, Mo, V, Ni and W as described above). This carbon limitation makes it possible to compensate for the increase in hardness linked to the addition of Co.
    The steel composition according to the invention can also comprise silicon (Si) in a content <0.70%, by weight relative to the total weight of the composition. Advantageously, it comprises silicon, in particular in a content included in the range 0.05-0.50%, preferably 0.05-0.30%, advantageously 0.07-0.25%, even more advantageously 0 , 10-0.20%, by weight relative to the total weight of the composition.
    Silicon strongly stabilizes ferrite, but is often present during the steel manufacturing process during the deoxidation of liquid steel.
    Low oxygen contents are in fact also important for obtaining low levels of non-metallic inclusions and good mechanical properties such as resistance to fatigue and mechanical resistance.
    The steel composition according to the invention may also comprise Manganese (Mn) in a content <0.70%, by weight relative to the total weight of the composition. Advantageously, it comprises manganese, in particular in a content included in the range 0.05-0.50%, preferably 0.05-0.30%, advantageously 0.07-0.25%, even more advantageously 0 , 10-0.22%, even more particularly 0.10-0.20% by weight relative to the total weight of the composition.
    Manganese stabilizes the austenite phase and decreases the Ms temperature in the steel composition. Manganese is generally added to steels during their manufacture due to its affinity for Sulfur, thus Manganese sulfide is formed during solidification. This eliminates the risk of the formation of iron sulphides which have an unfavorable effect on the hot machining of steels. Manganese is also part of the deoxidation stage like Silicon. The combination of Manganese with Silicon gives a more effective deoxidation than each of these elements alone.
    Optionally, the steel composition according to the invention can comprise nitrogen (N), in a content <0.50%, preferably <0.20%, by weight relative to the total weight of the composition.
    Nitrogen promotes the formation of austenite and lowers the transformation of austenite into martensite. Nitrogen can to some extent replace the Carbon in the steel according to the invention to form nitrides. However, the carbon + nitrogen content must be within the range 0.05-0.50% by weight relative to the total weight of the composition.
    Optionally, the steel composition according to the invention may comprise Aluminum (Al), in a content <0.15%, preferably <0.10%, by weight relative to the total weight of the composition .
    Aluminum (Al) can indeed be present during the steel manufacturing process according to the invention and contributes very effectively to the deoxidation of liquid steel. This is particularly the case during reflow processes such as the VIM-VAR process. The aluminum content is generally higher in steels produced using the VIMVAR process than in steels obtained by powder technology. Aluminum generates difficulties during atomization by obstruction of the casting nozzle by oxides.
    A low oxygen content is important to obtain good micro-cleanliness as well as good mechanical properties such as resistance to fatigue and mechanical resistance. The oxygen content obtained by ingot is typically less than 15 ppm.
    Advantageously, the composition according to the present invention is cementable, that is to say that it can undergo a cementation treatment, and / or nitriding, that is to say that it can undergo a nitriding treatment and even advantageously it can undergo a thermochemical treatment, in particular chosen from case hardening, nitriding, carbonitriding and case hardening followed by nitriding.
    These treatments make it possible to improve the surface hardness of the steel, by adding carbon and / or nitrogen elements. Thus, if case hardening is used, the Carbon content of the steel surface increases and therefore leads to an increase in surface hardness. The surface (surface layer advantageously having a thickness of 100 microns) is thus advantageously enriched in Carbon to obtain a final carbon content (final surface carbon content) of 0.5% - 1.7% by weight, more particularly of 0 , 8% - 1.5% by weight, more advantageously at least 1% by weight, in particular from 1-1.3% by weight, even more advantageously> 1.1% by weight, even more particularly between 1 , 2 and 1.5% by weight. In the remainder of this document, the surface carbon content will be understood to have been determined using a sampling of a surface layer to a depth of 100 microns.
    If nitriding is used, it is the nitrogen content which increases on the surface of the steel, and therefore also the surface hardness.
    If carbonitriding or carburizing followed by nitriding are used, it is the carbon and nitrogen contents on the surface of the steel which are increased and therefore also the surface hardness.
    These methods are well known to those skilled in the art.
    In an advantageous embodiment, the steel composition according to the invention has, after a thermochemical treatment, advantageously carburizing or nitriding or carbonitriding or carburizing then nitriding, followed by heat treatment, a higher surface hardness at 67HRC, in particular greater than or equal to 68 HRC, measured according to ASTM E18 standard published in July 2017 or equivalent standard. It also advantageously has a surface hardness greater than or equal to 910HV (approximately 67.25 HRC according to standard ASTM E140-12b published in May 2013), advantageously, greater than or equal to 920 HV, in particular greater than or equal to 940HV, measured according to standard ASTM E384 published in August 2017 or equivalent standard, in particular after being dissolved at a temperature of 1100 ° C. It also advantageously has a surface hardness greater than or equal to 930 HV (corresponding to approximately 67.75 H RC according to standard ASTM E140-12b published in May 2013), advantageously, greater than or equal to 940 HV (corresponding to 68 HRC according to standard ASTM E140-12b published in May 2013), in particular greater than or equal to 950 HV, measured according to standard ASTM E384 published in August 2017 or equivalent standard after being dissolved at a temperature of 1150 ° C.
    It more advantageously has a hardness at 1 mm in depth greater than or equal to 860 HV (which corresponds to approximately 66 HRC according to standard ASTM E140-12b published in May 2013), advantageously, greater than or equal to 870 HV, in particular greater than or equal to 880 HV, measured according to standard ASTM E384 published in August 2017 or equivalent standard, in particular after dissolving at a temperature of 1100 ° C. It also advantageously has a hardness at 1 mm in depth greater than or equal to 880 HV, advantageously greater than or equal to 890 HV, in particular greater than or equal to 900 HV, measured according to standard ASTM E384 published in August 2017 or equivalent standard.
    It also advantageously has a level of hardness of the base material (core material hardness) of between 440 and 650 HV, advantageously between 440 and 630 HV, measured according to standard ASTM E384 published in August 2017 or equivalent standard.
    The steel composition obtained thanks to these treatments advantageously has a carbon concentration on the surface (final surface content) of 1-1.3% by weight.
    Said heat treatment can include:
    - (1) dissolving the steel at a temperature between 1090 ° C-1160 ° C, advantageously between 1100 ° C-1160 ° C, more advantageously between 1100 and 1155 ° C, in particular between 1100 and 1150 ° C, more particularly 1150 ° C,
    - (2) advantageously followed by maintaining at this temperature until complete austenitization, in particular for a period of 15 minutes (quenching), (these 2 phases (1) and (2) allow the total or partial dissolution carbides initially present),
    - (3) then optionally a first cooling (quenching), in particular under neutral gas at, for example, a pressure of 2 bars (2 × 10 5 Pa), advantageously up to ambient temperature, (this phase makes it possible to obtain a microstructure mainly martensitic with residual austenite. This residual austenite is a function of the cooling temperature: the content decreases with the cooling temperature),
    - (4) possibly followed by maintaining at room temperature,
    - (5) then advantageously a second cooling to a temperature below -40 ° C, more advantageously less than -60 ° C, even more advantageously of approximately -70 ° C, in particular for 2 hours (this phase allows reduce the residual austenite content),
    - (6) and advantageously one or more incomes, more advantageously at least three incomes, advantageously at a temperature greater than or equal to 475 ° C, more advantageously between 475 ° C and 530 ° C, in particular 500 ° C, again more particularly for 1 hour each (this or these incomes allow the precipitation of carbides and the partial or total decomposition of the residual austenite. This makes it possible to obtain ductility properties).
    The advantage of the steel according to the invention is therefore to obtain high levels of hardness with a limited heat treatment (temperature between 1090 ° C-1160 ° C, advantageously between 1100 ° C-1160 ° C, more advantageously between 1100 ° C-1155 ° C, in particular between 1100 ° C1150 ° C, more particularly 1150 ° C).
    In a particularly advantageous embodiment, the steel composition according to the invention has, after a thermochemical treatment, advantageously carburizing or nitriding or carbonitriding or carburizing then nitriding, followed by heat treatment, a martensitic structure having a residual austenite content of less than 10% by weight, more advantageously less than 0.5% by weight, and free of ferrite and perlite, phases known to reduce the surface hardness of the steel.
    Said heat treatment can be as described above.
    The present invention further relates to a process for manufacturing a steel blank having the composition according to the invention, characterized in that it comprises:
    a) a stage of steel making;
    b) a steel transformation step;
    c) thermochemical treatment;
    d) and a heat treatment.
    Advantageously, the heat treatment of step d) of the method according to the present invention is as described above.
    Advantageously, the thermochemical treatment of step c) of the process according to the present invention consists of a cementation or nitriding or carbonitriding or cementation treatment then nitriding, advantageously it is a cementation treatment, more particularly allowing carbon enrichment at the surface resulting in a final surface carbon content of at least 1% by weight, even more advantageously> 1.1% by weight.
    In particular, step b) of the method according to the present invention consists of a rolling, forging and / or spinning step, advantageously forging. These methods are well known to those skilled in the art.
    In an advantageous embodiment, step a) of developing the process according to the present invention is implemented by a conventional production process in an arc furnace with refining and remelting under conductive slag (ESR), or by a VIM or VIM-VAR process, possibly with a reflow stage under conductive slag (ESR) and / or under vacuum (VAR), or by powder metallurgy such as gas atomization and compression by hot isostatic compaction (HIP) ).
    Thus, the steel according to the present invention can be produced by a VIM-VAR process. This process makes it possible to obtain very good inclusional cleanliness and improves the chemical homogeneity of the ingot. It is also possible to carry out a reflow path under conductive slag (ESR: Electro Slag Remelting) or to combine ESR and VAR operations (vacuum reflow).
    This steel can also be obtained by powder metallurgy. This process makes it possible to produce metallic powder of high purity by atomization, preferably atomization by gas, making it possible to obtain low oxygen contents. The powder is then compressed using, for example, a hot isostatic compaction (HIP).
    These methods are well known to those skilled in the art.
    The present invention also relates to a steel blank capable of being obtained by the method according to the invention. This blank is made from steel having the composition according to the present invention and as described above.
    It further relates to the use of a blank according to the invention or of a steel composition according to the invention for the manufacture of a mechanical member or of an injection system, advantageously of an element of transmission such as a gear, a transmission shaft and / or a bearing and therefore in particular a bearing.
    It thus relates to a mechanical member, advantageously a transmission element, in particular a gear, a transmission shaft or a bearing, more particularly a bearing or a gear, even more particularly a bearing, of steel having the composition according to the invention or obtained from a steel blank according to the invention. Finally, it relates to a steel injection system having the composition according to the invention or obtained from a steel blank according to the invention. Indeed, with the steel composition according to the invention, it is possible to combine the high surface hardness and the resistance to surface wear after thermochemical treatment with a core part of the material having a high resistance to fatigue and a high mechanical resistance.
    These steels can therefore be used in demanding fields such as bearings for the aerospace industry or injection systems.
    The invention will be better understood on reading the examples which follow which are given as a non-limiting indication.
    In the examples, unless otherwise indicated, all the percentages are expressed by weight, the temperature is expressed in degrees Celsius and the pressure is atmospheric pressure.
    Examples: Seven laboratory flows weighing approximately 9 kg each (6 examples according to the invention and a comparative example of composition 10 close to that of patent US 8157931: comparative example 1) were prepared by the VIM process according to the composition appearing in Table 1 below. below (in% by weight relative to the total weight of the composition), the balance being Fe:
    Table 1
    Element VS Or Cr MB V W Co Yes mn al NOT Example 1:GRADE A 0.18 3.1 3.9 5.1 2.1 1.18 10.0 0.2 0.18 0,023 0.005 Example 2:GRADE B 0.20 3.1 3.9 5.1 2.2 2.96 10.1 0.18 0.21 0.02 0,009 Example 3:GRADEC 0.16 3.1 3.9 5.1 2.1 1.19 10.0 0.21 0.18 0.02 0,009 Example 4:GRADE D 0.16 3.0 4.0 5.1 2.1 2.92 10.1 0.22 0.25 0.016 0.005 Example 5:GRADE E 0.16 3.1 3.9 5.0 2.1 0.01 10.0 0.123 0.2 0,042 0.005 Example 6:GRADE F 0.17 3.1 4.0 5.2 2.2 0.01 12.4 0.17 0.2 0,038 0.006 Comparative example 1: GRADE G 0.14 3.1 2.1 2.7 1.2 1.32 10.0 0.222 0.16 0,022 0,004
    The Nb content is below the detection limit. Nb <0.005% for all examples.
    These compositions are very similar except for the comparative example
    1. The main notable differences between Comparative Example 1 and Example 1 relate to the content of V, Mo and Cr.
    These laboratory castings were transformed into bars with a diameter of 40 mm by a hot forging process in a 2000 T press. Bars with a diameter of 20 mm were machined in the bar and case-hardened.
    The cemented bars were treated with (1) a solution solution
    1100 ° C or 1150 ° C, (2) holding for 15 min at this temperature for austenitization, (3) cooling under neutral gas at a pressure between 2 and 6 bars (2xl0 5 and 6X10 5 Pa), (4 ) a period at room temperature, (5) cooling to -70 ° C for 2 hours, and (6) 3 returning to a temperature of 500 ° C for 1 hour each.
    The surface hardness profiles in HV measured according to standard ASTM E384 published in August 2017 of Examples 1 to 6 and of Comparative Example 1 are indicated in Tables 2 and 3.
    Table 2 (solution at 1100 0 0
    Example Material core hardness Hardness at 1 mm depth Surface hardness Example 1: GRADE A 522 888 936 Example 2: GRADE B 485 863 927 Example 3: GRADE C 542 890 938 Example 4: GRADE D 495 878 934 Example 5: GRADE E 554 880 942 Example 6: GRADE F 567 927 976 Comparative example 1: GRADE G 576 835 847
    Table 3 (solution at 1150 ° W
    Example Material core hardness Hardness at 1 mm depth Surface hardness Example 1: GRADE A 550 888 949 Example 2: GRADE B 543 888 943 Example 3: GRADE C 603 933 957 Example 4: GRADE D 552 904 957 Example 5: GRADE E 612 934 940 Example 6: GRADE F 627 936 988 Comparative example 1: GRADE G 585 868 878
    For all chemical compositions except for Comparative Example 1, the surface hardness after cementation exceeds 920 HV for a solution temperature of 1100 ° C and exceeds 930 HV for a solution temperature of 1150 ° C. The hardness at 1 mm depth is always greater than 860 HV for a dissolution temperature of 1100 ° C and is always greater than 880 HV for a dissolution temperature of 1150 ° C for all examples except 10 l ' comparative example 1 (effect of the lack of alloying elements).
    The hardnesses on base materials are all less than 650 HV.
    权利要求:
    Claims (18)
    [1" id="c-fr-0001]
    1. A steel composition comprising, advantageously essentially consisting of, in percentages by weight of the total composition:
    Carbon: 0.01-0.20 preferably 0.02-0.18;
    Chromium: 2.5-5.0, preferably 3.0-4.5;
    Molybdenum: 4.0-6.0;
    Tungsten: 0.01-3.0;
    Vanadium: 1.0-3.0, preferably 1.5-2.5;
    Nickel: 2.0-4.0;
    Cobalt: 9.0-12.5, preferably 9.5-11.0;
    Iron: balance as well as unavoidable impurities, optionally further comprising one or more of the following:
    Niobium: <2.0;
    Nitrogen: <0.50, preferably <0.20;
    Silicon: <0.70, preferably 0.05-0.50;
    Manganese: <0.70, preferably 0.05-0.50;
    Aluminum: <0.15, preferably <0.10;
    the combined Niobium + Vanadium content being in the range 1.0-3.5;
    and the content of Carbon + Nitrogen being in the range 0.05-0.50.
    [2" id="c-fr-0002]
    2. Steel composition according to claim 1, characterized in that it advantageously comprises in that it consists essentially of, in percentages by weight of the total composition:
    Carbon: 0.02-0.20, preferably 0.08-0.18;
    Chromium: 3.0-4.5, preferably 3.5-4.5;
    Molybdenum: 4.0-6.0, preferably 4.5-5.5;
    Tungsten 0.01 - 3.0;
    Vanadium: 1.5-2.5, preferably 2.0-2.3;
    Nickel: 2.0-4.0, preferably 2.5-3.5;
    Cobalt: 9.5-12.5, preferably 9.5-10.5;
    Iron: balance as well as unavoidable impurities, optionally further comprising one or more of the following:
    Niobium: <2.0;
    Nitrogen: <0.20;
    Silicon: <0.70, preferably 0.05-0.50;
    Manganese: <0.70, preferably 0.05-0.50;
    Aluminum: <0.10;
    the combined Niobium + Vanadium content being in the range 1.0-3.5;
    and the content of Carbon + Nitrogen being in the range 0.05-0.50.
    [3" id="c-fr-0003]
    3. Steel composition according to any one of claims 1 or 2, characterized in that it comprises at most 1% by weight of unavoidable impurities, advantageously at most 0.5% by weight.
    [4" id="c-fr-0004]
    4. Steel composition according to any one of claims 1 to 3, characterized in that the inevitable impurities are chosen from Titanium, Sulfur, Phosphorus, Copper, Tin, Lead, Oxygen and their mixtures.
    [5" id="c-fr-0005]
    5. Steel composition according to any one of claims 1 to 4, characterized in that it is cementable and / or nitriding.
    [6" id="c-fr-0006]
    6. Steel composition according to any one of claims 1 to 5, characterized in that it exhibits, after a thermochemical treatment, advantageously of carburizing or nitriding or carbonitriding or carburizing then nitriding, followed by a heat treatment, a surface hardness greater than 67 HRC, in particular greater than or equal to 68 HRC and advantageously a hardness at 1 mm in depth greater than or equal to 66 HRC.
    [7" id="c-fr-0007]
    7. Steel composition according to any one of claims 1 to 6, characterized in that it exhibits, after a thermochemical treatment, advantageously cementation or nitriding or carbonitriding or cementation then nitriding, followed by a heat treatment, a martensitic structure having a residual austenite content of less than 0.5% by weight and free of ferrite and perlite.
    [8" id="c-fr-0008]
    8. Steel composition according to any one of claims 6 or 7, characterized in that the heat treatment comprises dissolving at a temperature between 1090 ° C-1160 ° C followed by quenching with optionally cooling , advantageously at a temperature below -40 ° C, and several tempers, advantageously at least three tempers, at a temperature between 475 ° C and 530 ° C, in particular 500 ° C.
    [9" id="c-fr-0009]
    9. A method of manufacturing a steel blank having the composition according to any one of claims 1 to 8, characterized in that it comprises:
    a) a stage of steel making;
    b) a steel transformation step;
    c) thermochemical treatment;
    d) and a heat treatment.
    [10" id="c-fr-0010]
    10. The manufacturing method according to claim 9, characterized in that step c) consists of a carburizing or nitriding or carbonitriding or carburizing treatment then nitriding, advantageously it is a carburizing treatment.
    [11" id="c-fr-0011]
    11. Manufacturing process according to any one of claims 9 or 10, characterized in that step c) consists of a carburizing treatment allowing a carbon enrichment at the surface resulting in a final surface carbon content of at least 1 % by weight, even more advantageously> 1.1% by weight.
    [12" id="c-fr-0012]
    12. The manufacturing method according to any one of claims 9 to 11, characterized in that step d) comprises dissolving at a temperature between 1090 ° C-1160 ° C, advantageously between 1100 ° C- 1150 ° C, followed by maintaining at this temperature until complete austenitization with possibly cooling to a temperature below -40 ° C, advantageously from -70 ° C, and several incomes, advantageously at least three incomes, at a temperature between 475 ° C and 530 ° C, in particular 500 ° C.
    [13" id="c-fr-0013]
    13. The manufacturing method according to any one of claims 9 to 12, characterized in that step b) consists of a rolling, forging and / or spinning step.
    [14" id="c-fr-0014]
    14. Manufacturing process according to any one of claims 9 to 13, characterized in that step a) of preparation is carried out by a conventional preparation process in an arc furnace and with refining and remelting under slag conductor (ESR), or by a VIM or VIMVAR process, possibly with a reflow stage under conductive slag (ESR) and / or under vacuum (VAR), or by powder metallurgy such as gas atomization and compression by hot isostatic compaction (HIP).
    [15" id="c-fr-0015]
    15. Steel blank capable of being obtained by a process according to any one of claims 9 to 14.
    [16" id="c-fr-0016]
    16. Use of a blank according to claim 15 or a steel composition according to any one of claims 1 to 8 for the manufacture of a mechanical member or an injection system, advantageously a rolling.
    [17" id="c-fr-0017]
    17. A mechanical member, advantageously a transmission element, in particular a bearing or a gear, made of steel having the composition according to any one of claims 1 to 8 or obtained from a steel blank according to claim 15.
    [18" id="c-fr-0018]
    18. A steel injection system having the composition according to any one of claims 1 to 8 or obtained from a steel blank according to claim 15.
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    同族专利:
    公开号 | 公开日
    US20210010116A1|2021-01-14|
    WO2019186016A1|2019-10-03|
    EP3765646A1|2021-01-20|
    FR3078978B1|2020-03-13|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US5424028A|1993-12-23|1995-06-13|Latrobe Steel Company|Case carburized stainless steel alloy for high temperature applications|
    JPH11210767A|1998-01-27|1999-08-03|Senshin Zairyo Riyo Gas Generator Kenkyusho:Kk|Rolling bearing|
    WO2015082342A1|2013-12-02|2015-06-11|Erasteel|A steel alloy and a component comprising such a steel alloy|
    WO2017216500A1|2016-06-17|2017-12-21|Aubert & Duval|Steel composition|CN110273103A|2019-07-15|2019-09-24|南京钢铁股份有限公司|A kind of non-hardened and tempered steel wire rod intensity homogeneity control method|
    CN110527911A|2019-09-16|2019-12-03|北京航空航天大学|Anti-corrosion gear-bearing steel of a kind of low-density high-strength height and preparation method thereof|JP2002129296A|2000-10-27|2002-05-09|Nippon Piston Ring Co Ltd|Iron-base sintered alloy material for valve seat, and valve seat made of iron-base sintered alloy|
    US8157931B2|2008-07-01|2012-04-17|Northwestern University|Case hardenable nickel-cobalt steel|RU2748448C1|2020-06-03|2021-05-25|Акционерное общество "Объединенная двигателестроительная корпорация" |Case-harden heat-resistant steel|
    法律状态:
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    优先权:
    申请号 | 申请日 | 专利标题
    FR1852202A|FR3078978B1|2018-03-14|2018-03-14|STEEL COMPOSITION|
    FR1852202|2018-03-14|FR1852202A| FR3078978B1|2018-03-14|2018-03-14|STEEL COMPOSITION|
    PCT/FR2019/050573| WO2019186016A1|2018-03-14|2019-03-14|Steel composition|
    US16/980,168| US20210010116A1|2018-03-14|2019-03-14|Steel composition|
    EP19742812.1A| EP3765646A1|2018-03-14|2019-03-14|Steel composition|
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