CN117441033A - Method for producing a steel component and steel component - Google Patents

Method for producing a steel component and steel component Download PDF

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Publication number
CN117441033A
CN117441033A CN202180099057.XA CN202180099057A CN117441033A CN 117441033 A CN117441033 A CN 117441033A CN 202180099057 A CN202180099057 A CN 202180099057A CN 117441033 A CN117441033 A CN 117441033A
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China
Prior art keywords
steel
temperature
product
cold
steel component
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Pending
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CN202180099057.XA
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Chinese (zh)
Inventor
马里恩·弗罗泰
贝尔纳德·雷西亚克
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ArcelorMittal SA
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ArcelorMittal SA
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Publication of CN117441033A publication Critical patent/CN117441033A/en
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C—CHEMISTRY; METALLURGY
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
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    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
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    • C21D2211/00—Microstructure comprising significant phases
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    • C21D2211/00—Microstructure comprising significant phases
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0436—Cold rolling
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following hot rolling
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing

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  • Chemical Kinetics & Catalysis (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

A method for producing a steel component, comprising: 0.05% C0.15%, 0.01% Si 1%,1.2% Mn 2%,0.1% Cr 2%, 0.001% Al 0.1%,0.003% N0.01%, 0.015%, 0.P 0.015%,0% Ni 1%, 0.01% B0.01%, 0% Mo 1%,0% Ti 0.04%,0% Nb 0.1%, 0% V0.5% and the remainder of the alloy of iron and unavoidable impurities, annealing the semifinished product at an annealing temperature strictly lower than the Ac1 temperature of the steel; cooling the semi-finished product to room temperature; cold forming the semifinished product into a cold-formed product; subjecting the cold formed product to a heat treatment comprising: heating the cold formed product to a heat treatment temperature that is greater than or equal to the complete austenitizing temperature Ac3 of the steel; quenching to room temperature; the product is optionally heated at a holding temperature of 180 ℃ to 400 ℃ for a period of 15 minutes to 2 hours.

Description

Method for producing a steel component and steel component
Technical Field
The present invention relates to a method for manufacturing assembled parts such as screws, bolts, etc. of chassis or hub assemblies commonly used in the automotive industry for vehicles by cold forming, in particular via cold heading.
Background
As is known, the automotive industry is continually striving to reduce vehicle weight; this can be achieved by improving its security components. Weight savings require ever decreasing component sizes. However, these components are still subjected to the same mechanical stresses and must therefore have increasingly high mechanical properties, in particular tensile strength.
WO2016/158470 is an age-hardened steel excellent in workability before aging treatment and excellent in fatigue characteristics, toughness and low cycle fatigue characteristics after aging treatment, that is, an age-hardened steel containing predetermined amounts of C, si, mn, S, cr, al, V, nb, ca and REM, restricting the content of P, ti and N to a predetermined amount or less, the balance being Fe and impurities, and the area ratio of bainitic structure being 70% or more. However, the steel of WO2016/158470 lacks hydrogen embrittlement.
WO2011/124851 is a mechanical steel part with steel having high properties, characterized in that it has a composition (in weight%) of 0.05% C0.25%; mn is more than or equal to 1.2 percent and less than or equal to 2 percent; cr is more than or equal to 1 percent and less than or equal to 2.5 percent; wherein the content of C, mn and Cr is 830-270C-90 Mn-70 Cr% less than or equal to 560; si is more than 0 and less than or equal to 1.55; ni is more than 0 and less than or equal to 1 percent; mo is more than 0 and less than or equal to 0.5 percent; cu is more than 0 and less than or equal to 1 percent; 0<V is less than or equal to 0.3 percent; al is more than 0 and less than or equal to 0.1 percent; 0<B is less than or equal to 0.005 percent; ti is more than 0 and less than or equal to 0.03 percent; nb is more than 0 and less than or equal to 0.06 percent; 0<S is less than or equal to 0.1 percent; ca is more than 0 and less than or equal to 0.006 percent; te is more than 0 and less than or equal to 0.03 percent; se is more than 0 and less than or equal to 0.05 percent; bi is more than 0 and less than or equal to 0.05 percent; pb is more than 0 and less than or equal to 0.1 percent; the remainder of the steel component is iron and impurities resulting from the working, and wherein the structure of the steel is bainitic and comprises not more than 20% in total of martensite and/or proeutectoid ferrite and/or pearlite. But the steel of WO2011/124851 does not exhibit hydrogen embrittlement and a reduction of area of 58% or more.
However, it is desirable to further improve the hydrogen embrittlement resistance of the component.
Disclosure of Invention
It is therefore an object of the present invention to provide such a steel component: it can be used as an assembly part for motor vehicles and it has improved resistance to hydrogen embrittlement, while having:
an ultimate tensile strength of greater than or equal to 1100MPa, and preferably greater than 1150MPa, or even greater than 1180MPa,
yield strength of greater than or greater than 880MPa, and preferably greater than 900MPa,
a total elongation of 12% or more, and preferably 13% or more,
a hydrogen embrittlement index of less than 0.09, and preferably less than or equal to 0.08,
-a reduction of area of greater than 58%, and preferably greater than 60% or greater, and more preferably 62% or greater.
In a preferred embodiment, the steel component exhibits a hardness of 360 to 405Hv.
The invention will be better understood from reading the following description, given by way of example only.
Throughout the patent application, the content is expressed in weight% (wt%).
The steel part according to the invention has a composition comprising by weight:
0.05％≤C≤0.15％
0.01％≤Si≤1％
1.2％≤Mn≤2％
0.1％≤Cr≤2％
0.001≤Al≤0.1％
0.003％≤N≤0.01％
0≤S≤0.015％
0≤P≤0.015％
optionally
0％≤Ni≤1％
0％≤Mo≤1.0％
0％≤Nb≤0.1％
0％≤Ti≤0.04％
0≤V≤0.5％
0％≤B≤0.01％
The remainder consisting of iron and unavoidable impurities.
Carbon is present in the steel of the invention at 0.05% to 0.15%. Carbon imparts strength to steel by solid solution strengthening, and carbon is a gamma phase generating element (gamma-phase), thus delaying ferrite formation. Carbon is an element that affects the formation of cementite-free lath-like bainite. A minimum of 0.05% carbon is required to achieve a tensile strength of 1100MPa, but if carbon is present at more than 0.15%, carbon deteriorates ductility and workability of the final product due to cementite formation. The carbon content is advantageously in the range of 0.08% to 0.14% to obtain both high strength and high ductility, and more preferably 0.09% to 0.14%.
Silicon is present in the steel of the invention at 0.01% to 1%. Silicon imparts strength to the steel of the present invention by solid solution strengthening. In particular, at the above content, silicon has an effect of hardening the bainitic microstructure by solid solution hardening. Silicon reduces cementite nucleation formation because silicon impedes carbide precipitation and diffusion-controlled growth by forming a Si-rich layer around the precipitate nuclei. Thus, lath-shaped bainite without cementite is produced. Silicon also acts as a deoxidizer. A minimum of 0.01% silicon is required to impart strength to the steel of the present invention. An amount of more than 1% increases the activity of carbon in austenite, promotes its transformation into proeutectoid ferrite, which may deteriorate strength, and also causes a delay in formation of lower bainite in continuous cooling, so that excessive austenite remains at the end of cooling. The preferable limit of silicon is 0.01% to 0.9%, and more preferably 0.01% to 0.5%.
Manganese is added in the steel of the present invention at 1.2% to 2%. Manganese provides hardenability to steel. It allows to reduce the critical cooling rate, for which purpose the bainite transformation can be obtained in continuous cooling without any prior transformation, and manganese reduces the bainite starting temperature of the steel and thus leads to refinement of the bainitic structure to form lath bainite and thus to increase the mechanical properties of the component. In order to obtain the desired bainitic microstructure, a minimum content of 1.2 wt% is necessary. Above 2%, however, manganese has a negative effect on the steel of the invention, since the retained austenite can transform into MA islands or fresh martensite, and these phases are detrimental to the properties. In addition, manganese forms sulfides such as MnS. These sulfides can increase processability if the shape and distribution are well controlled. Otherwise, they may have a very detrimental effect on the elongation. The preferable limit of manganese is 1.3% to 1.9%, and more preferably 1.4% to 1.9%.
Chromium is present in the steel of the invention at 0.1% to 2%. Chromium is an indispensable element for creating a bainitic structure, particularly lath bainite, and imparts elongation and ductility to the steel of the present invention. The addition of chromium promotes a uniform and finer bainitic microstructure over the temperature range of Bs to room temperature. To produce the target bainite microstructure, a minimum content of 0.1% chromium is required, and chromium also slows down softening during tempering treatment, allowing higher holding temperatures, which favors degassing, and also forms carbides that trap hydrogen. However, the presence of chromium content of 2% or more excessively increases the hardness of the steel, which makes it difficult to form the steel by cold forming, and particularly cold heading. It is advantageous to have 0.2% to 1.6% and more preferably 0.3% to 1.4% chromium.
The content of steel aluminium is 0.001 to 0.1 wt%. Aluminum is a deoxidizer for steel in liquid form. Which then in the form of nitrides helps to control austenite grain coarsening during hot rolling. On the other hand, too large an amount is present, which may lead to coarsening of aluminate-type inclusions in the steel, which may result in impairment of the properties of the steel, in particular its toughness. In particular, the aluminum content may be a content of 0.001 to 0.09 wt.%.
In the steel according to the invention, the nitrogen content is 0 to 0.01% by weight. Nitrogen traps boron by forming boron nitride, which negates the role of this element in the hardenability of the steel. Therefore, in the steel according to the present invention, the nitrogen content is limited to 0.01 wt%. However, with a small addition, it makes it possible to avoid excessive austenite grain coarsening during the heat treatment undergone by the steel by forming, in particular, titanium nitride (TiN) and aluminum nitride (AlN). Similarly, in this case, it also allows the formation of carbonitride precipitates that will contribute to the capture of hydrogen. Therefore, in the steel according to the invention, the nitrogen content is greater than or equal to 0.003 wt.%.
The steel according to the invention comprises up to 0.015% by weight of phosphorus and up to 0.015% by weight of sulfur. The effects of phosphorus and sulfur are particularly detrimental in the steel according to the invention for several reasons. In fact, since these elements are inhibitors of hydrogen recombination, they bring about a higher concentration of atomic hydrogen capable of penetrating into the material, thus increasing the risk of delayed fracture of the component in use. In addition, phosphorus and sulfur reduce their cohesion by segregating at grain boundaries. So their content must be kept very low. For this purpose, measures must be taken to ensure that the steel is dephosphorized and desulphurised during melting in the liquid state.
The steel may optionally comprise 0.01 to 1 wt% nickel. This element provides an increase in the strength of the steel and has a beneficial effect against brittle fracture. It also improves the corrosion resistance of the steel in a known manner.
Boron is an optional element and may be present in the alloy at a level of 0.0003 wt% to 0.01 wt%. By segregation at the prior austenite grain boundaries, boron strengthens the grain boundaries even at a very low content, and makes it possible to increase hydrogen-induced delayed fracture resistance. Boron increases the cohesion of these grain boundaries by its inherent effect but also by making segregation of phosphorus at the grain boundaries more difficult. Boron also greatly increases the hardenability of the steel and thus makes it possible to limit the carbon content required to obtain the desired bainitic microstructure. Finally, boron cooperates with molybdenum and niobium, thus increasing the effectiveness of these elements and their own effects allowed by their respective contents. However, excessive amounts of boron (greater than 0.01 wt.%) will result in the formation of brittle iron boron carbides.
Molybdenum is an optional element and is 0.003 wt% to 1 wt%. Molybdenum interacts strongly with phosphorus and limits the destructive effects of phosphorus by limiting the segregation of phosphorus at the prior austenite grain boundaries. Furthermore, it exhibits a pronounced carbide forming behaviour. For a given mechanical property, it allows a higher holding tempering temperature, which thus favors the development of carbides that will act as hydrogen traps. Therefore, it is an element that increases the delayed fracture resistance.
Titanium is an optional element and is present in the alloy in a content of 0.01 to 0.04 wt.%. Titanium is added to liquid steel to increase the hardness of the material. Here, it also increases the delayed fracture resistance in several ways within the demonstration. Which helps in austenite grain refinement and forms precipitates that trap hydrogen. Finally, the hardening effect of titanium allows tempering operations to be carried out at higher holding temperatures. The maximum titanium content is set here to avoid obtaining precipitates of too large a size (which would then reduce the resistance of the steel to delayed fracture).
The steel of the present invention may optionally contain niobium in a content of 0.01 to 0.1 wt.%. Niobium improves the hydrogen resistance, since it on the one hand limits the formation of boron carbide Fe 3 (C,B)、Fe 23 (C,B) 26 It consumes and therefore reduces the "free" boron content available for segregation at the grain boundaries and on the other hand limits austenitic grain growth by forming carbonitrides. Refinement of the grains gives a larger overall length of grain boundaries and thus better distribution of harmful elements such as phosphorus and sulfur in lower concentrations. In addition, the reduction of the austenite grain size causes an acceleration of the kinetics of the bainite transformation. The maximum niobium content is set to avoid obtaining precipitates of too large a size (which would then reduce the resistance of the steel to delayed fracture). Furthermore, when added in too large an amount, niobium causes an increased risk of "crack" defects at the surface of billets (billets) and blooms (bloom) at the time of continuous casting. If these defects cannot be completely eliminated, they can be very detrimental in terms of the integrity of the characteristics of the final part, in particular with respect to fatigue strength and hydrogen resistance, as a result. This is why the niobium content remains less than 0.1% by weight.
Further optionally, the steel may include vanadium in a content of less than or equal to 0.5 wt%. When present, vanadium allows tempering operations to be carried out at higher temperatures, due to its hardening effect. The maximum vanadium content is set to avoid obtaining precipitates of too large a size (which may reduce the resistance of the steel to delayed hydrogen fracture). In particular, the vanadium content may be a content of 0.05 to 0.5 wt%.
The remainder of the composition is iron and unavoidable impurities, in particular those resulting from the processing.
More particularly, the composition of the steel component consists of the elements described above.
The steel part according to the invention is more particularly a cold formed steel part and more particularly a cold headed steel part.
The steel component has a microstructure comprising, in surface fraction or area%, at least 80% bainite and 1% to 25% of retained austenite and martensite which are cumulatively present.
Bainite is present as a matrix phase in the steel according to the invention and imparts strength to such steel. Bainite is present in the steel in an area fraction of at least 80%, and preferably in an area fraction of 80% to 95%, and more preferably in an area fraction of 85% to 95%. Bainite is formed during quenching. Such bainite may include lath-like bainite and lower bainite without cementite. The cementite-free lath-like bainite consists of bainite in the form of laths and contains carbides between the laths such that the number of lath-to-lath carbides N per unit surface area greater than 0.1 micrometers is less than or equal to 50000/mm 2 . The cementite-free lath-like bainitic structure imparts good hydrogen resistance to the steel of the present invention. The lower bainite consists of bainite in the form of laths and includes fine iron carbide rods precipitated inside the laths. The lower bainite structure provides elongation and tensile strength to the steel of the present invention. The lath structure of both lower bainite and cementless lath bainite allows better distribution of hydrogen that tends to segregate, so such improved hydrogen distribution that may be present in the bainitic region of the microstructure increases hydrogen resistance.
The retained austenite and martensite are cumulatively present in the steel according to the invention in an area fraction of 1% to 25%. Martensite is formed during cooling after soaking from unstable austenite formed during annealing. Martensite is composed of thin laths elongated in one direction from the inside of each grain produced from the main austenite grains, with thin iron carbide rods 50nm to 200nm long precipitated between the laths along the <111> direction. Martensite imparts ductility and strength to the steel of the present invention. However, when the accumulation of martensite and retained austenite is present above 25%, it imparts excessive strength, but reduces the elongation beyond the acceptable limits of the steel of the present invention, because martensite has the same amount of carbon content as retained austenite, and thus fresh martensite is brittle and hard. For the steel of the present invention, the retained austenite and martensite that are cumulatively present are preferably limited to 4% to 22%, and more preferably 4% to 20%.
The steel component according to the invention can be advantageously used as a component for chassis, hub applications. In particular, these steel components may be used as bolts and screws for such applications, and for example chassis bolts, hub-to-bearing bolts, rim-to-hub bolts.
The diameter of the steel component is for example less than or equal to 22mm, and more particularly less than or equal to 20mm, and even more particularly less than or equal to 16mm. More particularly, the diameter of the steel component is for example greater than or equal to 5.5mm.
The above steel part may be obtained, for example, using a method comprising:
-providing a semifinished product made of steel;
-annealing the semifinished product at an annealing temperature strictly lower than the Ac1 temperature of the steel;
-cold forming the semifinished product into a cold-formed product;
-subjecting the cold-formed product to a heat treatment to obtain a cold-formed steel part, the heat treatment comprising:
heating the cold formed product to a heat treatment temperature higher than or equal to the complete austenitization temperature (Ac 3) of the steel,
quenching to room temperature and then cooling to room temperature,
-then optionally, after which,
-maintaining the product at a holding temperature of 100 ℃ to 400 ℃ for a period of 15 minutes to 2 hours.
The semifinished product provided during the providing step has the following composition by weight:
0.05％≤C≤0.15％
0.01％≤Si≤1％
1.2％≤Mn≤2％
0.1％≤Cr≤2％
0.001≤Al≤0.1％
0.003％≤N≤0.01％
0≤S≤0.015％
0≤P≤0.015％
optionally
0％≤Cu≤1％
0％≤Ni≤1％
0％≤Mo≤1.0％
0％≤Nb≤0.1％
0％≤Ti≤0.04％
0≤V≤0.5％
0％≤B≤0.01％
The remainder consisting of iron and unavoidable impurities.
The composition corresponds to the composition described previously for the steel part.
The semifinished product is in particular a wire, for example, having a diameter of 5mm to 25 mm.
As mentioned above, the annealing step is performed at an annealing temperature strictly lower than the Ac1 temperature of the steel. As is conventional, the Ac1 temperature is the temperature at which austenite begins to form during heating.
The annealing step aims to temporarily reduce the tensile strength of the steel in preparation for cold forming. For example, at the end of the annealing step, the tensile strength of the steel is less than or equal to 600MPa. Such annealing is called spheroidization (spheroidization) annealing or spheroidization (spheroodization) annealing.
More particularly, during the annealing step, the semifinished product is heated to an annealing temperature higher than or equal to Ac1-20 ℃.
During the annealing step, the semifinished product is preferably kept at the annealing temperature for such a time: the time is selected according to the annealing temperature such that the tensile strength of the steel after annealing is less than or equal to 600MPa. For example, the holding time at the annealing temperature is 5 hours to 9 hours.
According to a specific example, the annealing step is carried out at an annealing temperature equal to 720 ℃ and the retention time at the annealing temperature is equal to 5 hours.
The annealing step is preferably carried out in a neutral atmosphere, for example in an atmosphere consisting of nitrogen.
After holding at the annealing temperature, the semifinished product is cooled to room temperature.
The cooling is preferably carried out at a rate selected to avoid precipitation of pearlite and formation of bainite and thus to maintain a tensile strength of less than or equal to 600MPa after cooling. The cooling rate can be determined without difficulty using CCT maps of steel.
According to a specific example, the cooling from the annealing temperature is performed in three stages: a first cooling stage from the annealing temperature to about 670 ℃ in which the steel is cooled at a cooling rate of less than or equal to 25 ℃/hour, a second cooling stage from about 670 ℃ to about 150 ℃ at a cooling rate of less than or equal to 250 ℃/sec, and a third cooling stage from about 150 ℃ down to ambient temperature at a cooling rate corresponding to cooling in ambient or natural air. This three-step cooling and the corresponding temperatures and speeds are given by way of example only, and different temperatures and speeds may be used, in particular, depending on the composition of the steel and the desired final tensile strength.
The cold forming step is, for example, a cold heading step such that a cold-headed product is obtained at the end of the cold forming step and a cold-headed steel part is obtained at the end of the heat treatment.
The method optionally includes the step of cold drawing the annealed semifinished product to reduce its diameter between the annealing step and the cold heading step. The cold drawing step is in particular a wire drawing step.
Preferably, the cold drawing step is preceded by a surface pretreatment comprising a step of cleaning the surface of the semi-finished component, followed by a step of forming a lubricating coating on the surface of the semi-finished component.
The cleaning step comprises, for example, degreasing and/or mechanical or chemical descaling or pickling, optionally followed by neutralization. In this context, neutralization is a cleaning process for cleaning all foreign particles or substances from the surface of the steel to reduce the risk of corrosion.
The step of forming the lubricating coating includes, for example, phosphate treatment and soaping.
After cold forming, subjecting the cold formed steel part to a heat treatment comprising:
-heating the cold-formed product to a heat treatment temperature higher than or equal to the complete austenitization temperature Ac3 of the steel;
-quenching to room temperature;
then, optionally, the product is held at a holding temperature of 100 ℃ to 400 ℃ for a period of 15 minutes to 2 hours.
The optional heat treatment is a tempering heat treatment.
According to one example, during the holding step, the product is held in the oven at a holding temperature. According to another example, the product may be maintained at a holding temperature by immersion in a molten salt bath.
After the holding step is completed, the product is allowed to cool to ambient temperature in ambient or natural air.
The heating step is performed in such a way that the steel component has a fully austenitic microstructure at the end of the heating step.
The austenite grains formed during this heating step have an average size of less than or equal to 20 μm, and in particular from 8 μm to 15 μm. This dimension is measured, for example, with a 500:1 magnification.
The small grain size is due to the presence of microalloying elements in the steel that form precipitates capable of pinning grain boundaries to avoid grain growth during the austenitizing step. The austenite grain size is the prior austenite grain size of the cold formed and quenched and tempered steel component according to the present invention.
The heat treatment temperature is for example at least 50 ℃ higher than the complete austenitizing temperature Ac3 of the steel.
More particularly, during the heating step, the steel component is maintained at the heat treatment temperature for a time ranging from 5 minutes to 120 minutes.
Preferably, the holding temperature during the holding step is 200 ℃ to 380 ℃.
At the end of the holding step, a cold formed (and more particularly cold headed) and quenched steel part is obtained.
The steel part thus obtained has the microstructure described above for the steel part.
Experiment
Laboratory tests were carried out on castings having the chemical compositions I1 to I6 according to the invention. R1 to R4 are reference steel compositions not according to the invention.
Table 1: chemical composition of castings
Steel and method for producing same C Mn Si Cr Al P S N Ni Cu Mo Nb Ti B
I1 0.107 1.750 0.344 1.020 0.016 0.005 0.008 0.0038 0.016 0.010 0.047 0.047 0.021 0.0021
I2 0.124 1.760 0.093 0.789 0.019 0.003 0.003 0.0031 0.010 0.009 0.065 0.048 0.028 0.0013
I3 0.121 1.750 0.334 1.010 0.026 0.008 0.007 0.0050 0.103 0.011 0.198 0.034 0.025 0.0034
I4 0.130 1.800 0.370 1.250 0.026 0.009 0.008 0.0080 0.107 0.012 0.107 0.036 0.028 0.0035
I5 0.127 1.800 0.348 1.250 0.022 0.007 0.006 0.0050 0.109 0.011 0.105 0.022 0.026 0.0037
I6 0.118 1.590 0.350 1.380 0.016 0.007 0.007 0.0100 0.106 0.011 0.101 0.036 0.029 0.0034
R1 0.299 0.898 0.072 0.270 0.031 0.005 0.003 0.0073 0.034 0.047 0.096 0.001 0.037 0.0020
R2 0.443 0.940 0.169 1.480 0.025 0.005 0.005 0.0047 0.159 0.040 0.192 0.049 0.014 0.0008
R3 0.364 0.875 0.035 1.040 0.030 0.010 0.005 0.0049 0.018 0.007 0.002 0.002 ＜0,002 ＜0,0003
In table 1 above, the composition is expressed in weight percent and the underlined values are not in accordance with the invention.
In all the above compositions, the remainder of the composition consists of iron and unavoidable impurities.
TABLE 2 Process parameters
The inventive and reference steels were reheated at 1150 ℃ and then hot rolled in the form of 16mm diameter wire rods at a finishing temperature above 800 ℃. Thereafter, all wires (semi-finished products) of both the inventive and reference steels are subjected to an annealing comprising: the wire was held at a temperature of 720 ℃ for a holding time of 5 hours and then cooled. Cooling is performed in three stages, including: cooling to 670 ℃ at a cooling rate of 25 ℃/hour, then cooling to 150 ℃ at 250 ℃/hour, and finally natural or ambient air cooling to room temperature. These cooling rates are obtained by adjusting the heating conditions in the lehr accordingly, the heating being reduced or turned off as required in a manner known to the skilled person. Ac1 and Ac3 of both the inventive steels (I1 to I6) and the reference steels (R1 to R3) were calculated by dilatometry studies.
Thereafter, the cold formed steel part was subjected to heating and quenching heat treatments according to table 2.
TABLE 2 Process parameters
The underlined values in table 2 are not according to the invention.
Table 3: mechanical properties
The wires were directly subjected to tensile testing. The tensile test was performed according to standard NF EN ISO 6892-1, i.e. at a cross head speed of 8 mm/min. Each value is the average of three measurements.
Hardness spectra along sections of the samples were performed. The vickers hardness test was performed under a load of 30kg for a duration of 15 seconds. Hardness was measured according to standard NF EN ISO 6507-1. Each value is the average of three measurements.
The results of these tests are summarized in table 3 below.
Furthermore, the microstructure of the obtained products was analyzed based on the cross sections of these products. More particularly, the tissue present in the section is characterized by optical microscopy (light optical microscopy, LOM) and by scanning electron microscopy (scanning electron microscopy, SEM). LOM and SEM observations were performed after etching using a solution containing a nitric acid-ethanol etchant (Nital).
The results of these analyses are summarized in table 4 below.
In table 3, the following abbreviations are used:
TS (MPa) refers to the tensile strength measured by a tensile test in the longitudinal direction with respect to the rolling direction,
YS (MPa) refers to the yield strength measured by the tensile test in the longitudinal direction with respect to the rolling direction,
RA (%) refers to the percentage of reduction of area measured by the tensile test in the longitudinal direction with respect to the rolling direction,
el (%) refers to the total elongation measured by the tensile test in the longitudinal direction with respect to the rolling direction,
HV30 refers to the result of the hardness measurement,
table 3: mechanical properties of the sample after quenching
The underlined values are not according to the invention.
Table 4: hydrogen embrittlementResults
For each of experiments I1 through I6 and R1 through R3, the sample was subjected to 10 by comparing the sample with the unfilled sample and then with the hydrogen filled sample according to the NF A-05-304 standard -5 Second of -1 The results of a slow strain rate tensile test performed on a smooth test sample of strain rate of (c) to determine the hydrogen resistance of the corresponding sample.
More specifically, the inventors determined the ductility (by percent reduction of area Ra) of filled and unfilled samples and compared the results by brittleness index.
The total H2 content in the sample before filling was equal to about 0.3ppm.
Using 2.5mg/L of thiourea added with hydrogen accelerator 2 SO 4 1N electrolytic solution was prepared by passing the solution at a current density I=0.8 mA/cm 2 The cathode was filled for 5 hours to perform hydrogen filling.
For each pair of samples (filled and unfilled), the brittleness index, I, was calculated as a function of percent reduction of area using the following formula Ra ：
I Ra ＝1-[RA(H2)/RA(H2＝0)]Where RA (H2) corresponds to the value of the percentage reduction of area measured for the sample filled with hydrogen and RA (h2=0) corresponds to the value of the percentage reduction of area measured for the unfilled sample.
Brittleness index I near 1 Ra Meaning that the grade is very sensitive to hydrogen embrittlement. In view of the desired application, a brittleness index I of less than 0.09 Ra Is considered satisfactory, and a brittleness index I of less than or equal to 0.08 Ra Is advantageous for the desired application.
The inventors further observed the fracture surface pattern in each case.
The results of these tests are summarized in table 4.
As can be seen from table 4 above, the ductility of the inventive steel is not significantly affected by hydrogen.
Steels having compositions I1 to I6 after quenching exhibited higher hydrogen resistance than reference grades R1 to R4.
Comparison of samples I1 to I6 having a bainite content of greater than or equal to 80% as shown in table 5 with samples having a martensitic microstructure of R1 to R4 as shown in table 5 shows that the bainitic structure is less susceptible to hydrogen embrittlement than the martensitic structure.
It can finally be observed that the samples according to the invention (I1 to I6) absorb less hydrogen than the comparative samples (R1 to R4) under the same filling conditions.
These experiments therefore show that the steel parts according to the invention are particularly well suited for applications as described above, that they have very good mechanical properties compared to prior art steel parts, and that in particular good tensile strength is associated with improved resistance to hydrogen embrittlement.
The method according to the invention also has the advantage of allowing to obtain a sufficiently low tensile strength after annealing, so as to be able to use conventional cold forming tools and reduce their wear, while at the same time resulting in a final part with a high tensile strength (greater than or equal to 1100 MPa).
Table 5: microstructure of microstructure
After 2% Nital etching, the microstructure of the steel was characterized using optical microscopy (LOM) Scanning Electron Microscopy (SEM). Quantitative X-ray analysis has been performed to determine the fraction of retained austenite.
The underlined values are not according to the invention.

Claims (16)

1. A method for producing a steel component, comprising:
-providing a semi-finished product made of steel comprising by weight:
0.05％≤C≤0.15％
0.01％≤Si≤1％
1.2％≤Mn≤2％
0.1％≤Cr≤2％
0.001≤Al≤0.1％
0.003％≤N≤0.01％
0≤S≤0.015％
0≤P≤0.015％
optionally
0％≤Ni≤1％
0％≤B≤0.01％
0％≤Mo≤1％
0％≤Ti≤0.04％
0％≤Nb≤0.1％
0≤V≤0.5％
The remainder consisting of iron and unavoidable impurities,
-annealing the semifinished product at an annealing temperature strictly lower than the Ac1 temperature of the steel;
-cooling the semifinished product to room temperature;
-cold forming said semifinished product into a cold formed product;
-subjecting the cold formed product to a heat treatment comprising:
-heating the cold formed product to a heat treatment temperature higher than or equal to the complete austenitization temperature Ac3 of the steel; and
-quenching to room temperature;
-optionally reheating the product at a holding temperature of 180 ℃ to 400 ℃ for a period of 15 minutes to 2 hours.
2. The method of claim 1, wherein during the heating step of the heat treatment, the cold formed product is heated to a heat treatment temperature at least 50 ℃ above the complete austenitizing temperature Ac3 of the steel.
3. The method of claim 1 or 2, wherein the annealing temperature is greater than or equal to Ac1 minus 20 ℃.
4. A method according to any one of claims 1 to 3, wherein the semifinished product is a wire having a diameter of 5mm to 25 mm.
5. The method of any one of claims 1 to 4, further comprising pre-treating a surface of the semi-finished product prior to the cold forming step, the pre-treating comprising cleaning the surface of the semi-finished product and forming a lubricating coating on the surface of the semi-finished product.
6. The method of claim 5, wherein the step of forming a lubricious coating on the surface of the semi-finished product comprises phosphating and soaping.
7. The method of any one of the preceding claims, wherein the steel has a carbon content of 0.08 to 0.14 wt%.
8. The method of any one of the preceding claims, wherein the manganese content of the steel is 1.3 to 1.9 wt%.
9. A method according to any one of the preceding claims, wherein the steel has a chromium content of 0.2 to 1.6 wt%.
10. The method of any one of the preceding claims, wherein the cold forming step is a cold heading step.
11. A method according to any one of the preceding claims, wherein during the maintaining step the product is maintained at the maintaining temperature by immersion in a molten salt bath.
12. A steel component made of an alloy comprising by weight:
0.05％≤C≤0.15％
0.01％≤Si≤1％
1.2％≤Mn≤2％
0.1％≤Cr≤2％
0.001≤Al≤0.1％
0.003％≤N≤0.01％
0≤S≤0.015％
0≤P≤0.015％
optionally
0％≤Ni≤1％
0％≤B≤0.01％
0％≤Mo≤1％
0％≤Ti≤0.04％
0％≤Nb≤0.1％
0≤V≤0.5％
The remainder consisting of iron and unavoidable impurities,
wherein the steel component has a microstructure comprising at least 80 area% bainite and 1 to 25 area% martensite and retained austenite that are cumulatively present, wherein the steel component has a tensile strength of 1100MPa or more.
13. The steel component of claim 12, wherein the martensite of the steel has iron carbide in the form of rods, wherein the rods are 50nm to 200nm long.
14. The steel component according to any one of claims 12 or 13, wherein the hardness of the steel component is 360HV to 405HV.
15. The steel part according to any one of claims 12 to 14, wherein the steel part has a hydrogen embrittlement index of less than 0.09.
16. The steel component of any one of claims 12 to 15, wherein the steel component has a reduction of area of greater than 58%.
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FR2958660B1 (en) 2010-04-07 2013-07-19 Ascometal Sa STEEL FOR MECHANICAL PIECES WITH HIGH CHARACTERISTICS AND METHOD FOR MANUFACTURING THE SAME.
JP6246621B2 (en) * 2013-05-08 2017-12-13 株式会社神戸製鋼所 Hot-dip galvanized steel sheet or alloyed hot-dip galvanized steel sheet with a tensile strength of 1180 MPa or more and an excellent balance between strength and bendability
KR101918432B1 (en) 2015-03-31 2018-11-13 신닛테츠스미킨 카부시키카이샤 Method for manufacturing parts using age hardening steel and age hardening steel
WO2018215813A1 (en) * 2017-05-22 2018-11-29 Arcelormittal Method for producing a steel part and corresponding steel part
KR20200004407A (en) * 2017-06-15 2020-01-13 닛폰세이테츠 가부시키가이샤 Rolled Wire for Spring Steel
WO2020058748A1 (en) * 2018-09-20 2020-03-26 Arcelormittal Cold rolled and coated steel sheet and a method of manufacturing thereof
WO2020229877A1 (en) * 2019-05-15 2020-11-19 Arcelormittal A cold rolled martensitic steel and a method for it's manufacture
WO2021009543A1 (en) * 2019-07-16 2021-01-21 Arcelormittal Method for producing a steel part and steel part
WO2021089851A1 (en) * 2019-11-08 2021-05-14 Ssab Technology Ab Medium manganese steel product and method of manufacturing the same

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