WO2018098485A1 - Method for production for press hardened steel with increased toughness - Google Patents
Method for production for press hardened steel with increased toughness Download PDFInfo
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- WO2018098485A1 WO2018098485A1 PCT/US2017/063490 US2017063490W WO2018098485A1 WO 2018098485 A1 WO2018098485 A1 WO 2018098485A1 US 2017063490 W US2017063490 W US 2017063490W WO 2018098485 A1 WO2018098485 A1 WO 2018098485A1
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- Prior art keywords
- temperature
- steel
- rolling
- coiling
- slab
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- 229910000760 Hardened steel Inorganic materials 0.000 title description 17
- 238000004519 manufacturing process Methods 0.000 title description 3
- 238000000034 method Methods 0.000 claims abstract description 100
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 99
- 239000010959 steel Substances 0.000 claims abstract description 99
- 238000005096 rolling process Methods 0.000 claims abstract description 57
- 238000010438 heat treatment Methods 0.000 claims abstract description 7
- 238000012545 processing Methods 0.000 claims abstract description 6
- 239000000203 mixture Substances 0.000 claims description 42
- 238000001816 cooling Methods 0.000 claims description 31
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 16
- 239000010955 niobium Substances 0.000 claims description 9
- 229910052758 niobium Inorganic materials 0.000 claims description 9
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 9
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 8
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 8
- 229910052782 aluminium Inorganic materials 0.000 claims description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims description 8
- 239000011733 molybdenum Substances 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 8
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 7
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 7
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 7
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 7
- 229910052796 boron Inorganic materials 0.000 claims description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 229910052804 chromium Inorganic materials 0.000 claims description 7
- 239000011651 chromium Substances 0.000 claims description 7
- 229910052748 manganese Inorganic materials 0.000 claims description 7
- 239000011572 manganese Substances 0.000 claims description 7
- 229910052710 silicon Inorganic materials 0.000 claims description 7
- 239000010703 silicon Substances 0.000 claims description 7
- 239000010936 titanium Substances 0.000 claims description 7
- 229910052719 titanium Inorganic materials 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 238000007781 pre-processing Methods 0.000 description 80
- 239000000463 material Substances 0.000 description 15
- 229910000734 martensite Inorganic materials 0.000 description 11
- 230000007423 decrease Effects 0.000 description 8
- 238000009864 tensile test Methods 0.000 description 8
- 229910045601 alloy Inorganic materials 0.000 description 7
- 239000000956 alloy Substances 0.000 description 7
- 239000006104 solid solution Substances 0.000 description 7
- 238000005728 strengthening Methods 0.000 description 7
- 239000003381 stabilizer Substances 0.000 description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 4
- 229910052802 copper Inorganic materials 0.000 description 4
- 239000010949 copper Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000003672 processing method Methods 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000012994 industrial processing Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
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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
- C21D8/0294—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a localised treatment
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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
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- 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
- C21D8/0226—Hot rolling
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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
- C21D8/04—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
- C21D8/0405—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 of ferrous alloys
-
- 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
-
- 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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- 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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- 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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- 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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- 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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- 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
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- 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
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- 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
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- 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
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- 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
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- 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
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- 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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
- B21B2001/028—Slabs
Definitions
- the present application relates to an improvement in press hardened steels, hot press forming steels, hot stamping steels, or any other steel that is heated to an austenitization temperature and formed and quenched in a stamping die to achieve desired mechanical properties in the final part.
- These types of steels are also sometimes referred to as “heat treatable boron-containing steels.” In this application, they will all be referred to as “press hardened steels.”
- a common structural member where press hardened steels are employed in the automobile structure is the B-pillar.
- Residual toughness refers to the toughness the material has in the press hardened condition.
- the strength-ductility property of embodiments of the present steel alloys include ultimate tensile strengths greater than or equal to 1100 MPa and elongations of approximately 8%.
- Fig. 1 shows a thermal profile and processing schematic for
- Fig. 2 shows another thermal profile and processing schematic for embodiments of the present alloys.
- Fig. 3 shows a plot of stress-strain curves for composition 4310, with results from a first pre-processing method shown in solid-line form and results from a second pre-processing method shown in dashed-line form.
- Fig. 4 shows a plot of stress-strain curves for composition 4311, with results from the first pre-processing method shown in solid-line form and results from the second pre-processing method shown in dashed- line form.
- Fig. 5 shows a plot of stress-strain curves for composition 4312, with results from the first pre-processing method shown in solid-line form and results from the second pre-processing method shown in dashed- line form.
- Fig. 6 shows a plot of stress-strain curves for composition 4313, with results from the first pre-processing method shown in solid-line form and results from the second pre-processing method shown in dashed- line form.
- Fig. 7 shows the results of a double edge-notch tensile test for
- Fig. 8 shows the results of a double edge-notch tensile test for
- Fig. 9 shows the results of strain energy computations for
- Fig. 10 shows a photomicrograph of composition 4310 after being subjected to the first pre-processing method.
- Fig. 11 shows a photomicrograph of composition 4310 after being subject to the second pre-processing method.
- Fig. 12 shows a photomicrograph of composition 4311 after being subjected to the first pre-processing method.
- Fig. 13 shows a photomicrograph of composition 4311 after being subjected to the second pre-processing method.
- Fig. 14 shows a photomicrograph of composition 4312 after being subjected to the first pre-processing method.
- FIG. 15 shows a photomicrograph of composition 4312 after being subjected to the second pre-processing method.
- Fig. 16 shows a photomicrograph of composition 4313 after being subjected to the first pre-processing method.
- FIG. 17 shows a photomicrograph of composition 4313 after being subjected to the second pre-processing method.
- Press hardened steels are generally desirable for their high strength characteristics. In practice, this permits manufacturers to produce components having greater strength and less weight relative to components produced of non-press hardened steels. These high strength characteristics are generally achieved through formation of a predominately martensitic microstructure.
- the blank is first subjected to an austenitization heat treatment. During this heat treatment, the temperature of the blank is raised to greater than the A3 temperature for the particular composition of the blank to thereby transform the microstructure of the blank into predominately austenite.
- the stamping process In addition to shaping the blank, the stamping process also has the effect of rapidly cooling the blank below the martensite start temperature (M s ). As a consequence, the predominately austenitic microstructure of the blank is transformed to a microstructure of predominantly martensite. Because martensite is generally characterized as a strong and hard microstructure, the stamping process generally results in a final part having high strength and high hardness.
- M s martensite start temperature
- FIG. 1 shows a conventional pre-processing method (10).
- Pre-processing method includes subjecting a steel sheet to a plurality of pre-processing steps (20, 30, 40, 50). These steps (20, 30, 40, 50) are generally performed prior to hot stamping and prior to formation of press hardened steel blanks for the final hot stamping process. Generally, these steps (20, 30, 40, 50) are performed on sheet material in a continuous rolling mill.
- the press hardened steel initially begins as an as-cast slab comprising a predetermined composition. The slab then enters a re-heat furnace (20) and is subj ected to a re-heat temperature of approximately 2300° F (1260° C).
- the slab is elevated to the re-heat temperature via the re-heat furnace (20), the slab is subjected to rough rolling (30) and then finishing rolling (40). These rolling steps progressively reduce the thickness of the slab to a final sheet thickness.
- the temperature of the slab continuously decreases from the initial 2300° F (1260° C) re-heat temperature to a roughing temperature associated with rough rolling (30). In some examples the roughing temperature is approximately 2000° F (1093° C).
- finishing rolling (40) the slab is subject to a finishing temperature of approximately 1600° F (871 ° C). As the temperature decreases, the slab is subjected to rolling operations that progressively reduce the thickness of the slab by relatively large amounts during rough rolling (30) to relatively small amounts during finishing rolling (40).
- the press hardened steel material is in a steel sheet form.
- the steel sheet is subj ect to coiling (50).
- Coiling (50) can be performed at a coiling temperature of approximately 1200° F (649° C).
- coiling (50) can begin immediately after finishing (40).
- coiling (50) may begin at temperatures above 1600° F (871 ° C) and decrease to the coiling temperature of approximately 1200° F (649° C).
- the steel sheet Prior to coiling (50), the steel sheet can be cooled to the coiling
- the steel sheet is cooled relatively slowly at between about 18° F/second and about 20° F/second.
- the coiled steel sheet is permitted to cool to ambient or room temperature.
- the coiled steel sheet is then subsequently formed into blanks of steel material for press hardening.
- the blanks can then be subjected to the hot stamping process described above.
- toughness can be improved by refining the grain size of the press hardened steel material by modifying certain parameters of the pre-processing steps described above.
- FIG. 2 shows modified pre-processing method (100).
- pre-processing method (100) of the present example includes a series of pre-processing steps (120, 130, 140, 150). As similarly described above, these steps (120, 130, 140, 150) are generally performed prior to hot stamping and prior to formation of press hardened steel blanks for the final hot stamping process. Generally, these steps (120, 130, 140, 150) are performed on sheet material in a continuous rolling mill.
- the press hardened steel initially begins as an as-cast slab comprising a predetermined composition. The slab then enters a re-heat furnace (120), where the slab is subjected to a re-heat temperature. Like with the reheat temperature described above with respect to re-heat furnace (20), the reheat temperature in the present example is approximately 2300° F (1260° C).
- finishing rolling (140) is performed at a relatively lower temperature.
- this relatively lower temperature can lead to increased grain refinement when performed in connection with a modified coiling temperature.
- the slab is subjected to rolling operations that reduce the thickness of the slab by relatively large amounts during rough rolling (130) to relatively small amounts during finishing rolling (140).
- the temperature of the slab decreases at a relatively constant rolling cooling rate (112). This cooling rate is similar to the rolling cooling rate (12) of the prior process.
- the press hardened steel material is in a steel sheet form.
- the steel sheet is subject to coiling (150).
- Coiling (150) can be performed at a coiling temperature of approximately 1050° F (566° C).
- coiling (150) can begin immediately after finishing (140).
- coiling (150) may begin at approximately 1600° F (871° C) and decrease to the coiling temperature of approximately 1050° F (566° C).
- coiling (150) can be delayed until the steel sheet reaches the coiling temperature of approximately 1050° F (566° C). Once the coiling temperature is reached (150), the steel sheet may be held isothermally for the entirety of coiling (150).
- the finishing (140) is performed at the finishing temperature of about 1600° F (871° C), the steel sheet is lowered to the coiling temperature of 1050° F (566° C), and coiling (150) is performed while the steel sheet is held at the coiling temperature.
- the coiling temperature of approximately 1050° F (566° C) is generally low relative to the coiling temperatures described above with respect to conventional pre-processing method (10). As will be understood, this reduced coiling temperature can generally result in improved grain refinement of the steel sheet that can lead to increased residual toughness in a final work product after hot stamping.
- the steel sheet Prior to coiling (150), the steel sheet can be cooled to the coiling
- the cooling rate (114) is between about 35 °F/second and about 50° F/second.
- cooling rate (114) in the present example is generally relatively fast. This relatively fast cooling rate can be achieved using a run-out-table accelerated cooling method. As will be understood, this relatively fast cooling rate (114) can generally lead to increased grain refinement and associated improved residual toughness in a final work product after hot stamping.
- the coiled steel sheet is permitted to cool to ambient or room temperature.
- the coiled steel sheet is then subsequently formed into blanks of steel material for press hardening.
- the blanks can then be subjected to the hot stamping process described above.
- the pre-processing methods (10, 100) can be performed using an as-cast slab comprising a predetermined composition. It should be understood that the particular composition of the slab can be varied such that a variety of compositions can be used with the methods (10, 100) described above. As will be described in greater detail below, various elements can be added to the slab to influence numerous metallurgical properties of the final work product.
- Carbon is added to reduce the martensite start temperature, provide solid solution strengthening, and to increase the hardenability of the steel. Carbon is an austenite stabilizer. In certain embodiments, carbon can be present in concentrations of 0.1 - 0.5 mass %; in other embodiments, carbon can be present in concentrations of 0.2 - 0.30 mass %.
- Manganese is added to reduce the martensite start temperature, provide solid solution strengthening, and to increase the hardenability of the steel.
- Manganese is an austenite stabilizer.
- manganese can be present in concentrations of 0.75 - 3.0 mass %; in other embodiments, manganese can be present in concentrations of 1.15 - 1.25 mass %.
- Silicon is added to provide solid solution strengthening.
- Silicon is a ferrite stabilizer.
- silicon can be present in concentrations of 0.02 - 1.5 mass %; in other embodiments, silicon can be present in concentrations of 0.15 - 0.30 mass %.
- Aluminum is added for deoxidation during steelmaking and to provide solid solution strengthening.
- Aluminum is a ferrite stabilizer.
- aluminum can be present in concentrations of 0.0 - 0.8 mass %; in other embodiments, aluminum can be present in concentrations of 0.02 - 0.15 mass %. In other embodiments, aluminum is entirely optional and can be therefore omitted or limited to an impurity element in some embodiments.
- Titanium is added to getter nitrogen.
- titanium can be present in concentrations of 0.0-0.060 mass %; in other embodiments, titanium can be present in concentrations of a maximum of 0.045 mass %. In other embodiments, titanium is entirely optional and can be therefore omitted or limited to an impurity element in some embodiments.
- Molybdenum is added to provide solid solution strengthening and to increase the hardenability of the steel. In certain embodiments, molybdenum can be present in concentrations of 0-0.5 mass %; in other embodiments, molybdenum can be present in concentrations of 0-0.3 mass %. In other embodiments, molybdenum is entirely optional and can be therefore omitted or limited to an impurity element in some embodiments.
- Chromium is added to reduce the martensite start temperature, provide solid solution strengthening, and increase the hardenability of the steel.
- Chromium is a ferrite stabilizer.
- chromium can be present in concentrations of 0-0.5 mass %; in other embodiments, chromium can be present in concentrations of 0.15-0.25 mass %.
- Boron is added to increase the hardenability of the steel.
- boron can be present in concentrations of 0-0.005 mass%; in other embodiments, boron can be present in concentrations of 0.003-0.005 mass %.
- Nickel is added to provide solid solution strengthening and reduce the martensite start temperature.
- Nickel is an austenite stabilizer.
- nickel can be present in concentrations of 0.0-0.6 mass %; in other embodiments, nickel can be present in concentrations of 0.02-0.3 mass %. In still other embodiments, nickel is entirely optional and can be therefore omitted or limited to an impurity element in some embodiments.
- Niobium is added to provide improved grain refinement. Niobium can also increase hardness and strength. In certain embodiments, niobium can be present in concentrations of 0-0.090 mass%.
- Example 1 A plurality of alloy compositions shown in Table 1 were prepared using standard steel making processes, except as noted below.
- Table 1 Composition range. Compositions are in mass pet.
- Composition 4310 of Table 1 in Example 1 was subjected to both preprocessing methods (10, 100) described above.
- the steel underwent simulated hot stamping. The steel was heated to approximately 930 °C for 5 min and then quenched in water-cooled copper dies. Samples subjected to each pre-processing method (10, 100) plus simulated hot stamping were then subjected to tensile testing to generate stress-strain curves. The resulting stress-strain curves are shown in FIG. 3 with preprocessing method (10) shown in solid-line form and pre-processing method (100) shown in dashed-line form.
- the samples subjected to pre-processing method (100) generally resulted in improved residual toughness relative to samples subjected to pre-processing method (10).
- FIGS. 10 and 11 Photomicrographs were prepared for each sample in the hot-rolled condition prior to the simulated hot stamping and are shown in FIGS. 10 and 11, with FIG. 10 corresponding to pre-processing method (10) and FIG. 11 corresponding to pre-processing method (100).
- pre-processing method (100) generally resulted in a more refined grain structure relative to the grain structure produced from preprocessing method (10).
- improved residual toughness was observed in FIG. 3.
- Composition 4311 of Table 1 in Example 1 was subjected to both preprocessing methods (10, 100) described above.
- the steel underwent simulated hot stamping. The steel was heated to approximately 930 °C for 5 min and then quenched in water-cooled copper dies. Samples subjected to each pre-processing method (10, 100) plus simulated hot stamping were then subjected to tensile testing to generate stress-strain curves. The resulting stress-strain curves are shown in FIG. 4 with preprocessing method (10) shown in solid-line form and pre-processing method (100) shown in dashed-line form.
- the samples subjected to pre-processing method (100) generally resulted in improved residual toughness relative to samples subjected to pre-processing method (10).
- FIGS. 12 and 13 Photomicrographs were prepared for each sample in the hot-rolled condition prior to the simulated hot stamping and are shown in FIGS. 12 and 13, with FIG. 12 corresponding to pre-processing method (10) and FIG. 13 corresponding to pre-processing method (100).
- pre-processing method (100) generally resulted in a more refined grain structure relative to the grain structure produced from preprocessing method (10).
- improved residual toughness was observed in FIG. 4.
- Composition 4312 of Table 1 in Example 1 was subjected to both preprocessing methods (10, 100) described above.
- the steel underwent simulated hot stamping. The steel was heated to approximately 930 °C for 5 min and then quenched in water-cooled copper dies. Samples subjected to each pre-processing method (10, 100) plus simulated hot stamping were then subjected to tensile testing to generate stress-strain curves. The resulting stress-strain curves are shown in FIG. 5 with pre- processing method (10) shown in solid-line form and pre-processing method (100) shown in dashed-line form.
- the samples subjected to pre-processing method (100) generally resulted in improved residual toughness relative to samples subjected to pre-processing method (10).
- FIGS. 14 and 15 Photomicrographs were prepared for each sample in the hot-rolled condition prior to the simulated hot stamping and are shown in FIGS. 14 and 15, with FIG. 14 corresponding to pre-processing method (10) and FIG. 15 corresponding to pre-processing method (100).
- pre-processing method (100) generally resulted in a more refined grain structure relative to the grain structure produced from preprocessing method (10).
- improved residual toughness was observed in FIG. 5.
- Composition 4313 of Table 1 in Example 1 was subjected to both preprocessing methods (10, 100) described above.
- the steel underwent simulated hot stamping. The steel was heated to approximately 930 °C for 5 min and then quenched in water-cooled copper dies. Samples subjected to each pre-processing method (10, 100) plus simulated hot stamping were then subjected to tensile testing to generate stress-strain curves. The resulting stress-strain curves are shown in FIG. 6 with preprocessing method (10) shown in solid-line form and pre-processing method (100) shown in dashed-line form.
- the samples subjected to pre-processing method (100) generally resulted in improved residual toughness relative to samples subjected to pre-processing method (10).
- FIGS. 16 and 17 Photomicrographs were prepared for each sample in the hot-rolled condition prior to the simulated hot stamping and are shown in FIGS. 16 and 17, with FIG. 16 corresponding to pre-processing method (10) and FIG. 17 corresponding to pre-processing method (100).
- pre-processing method (100) generally resulted in a more refined grain structure relative to the grain structure produced from preprocessing method (10).
- improved residual toughness or retained ductility was observed in FIG. 6.
- a sample for each composition (e.g., 4310, 4311, 4312, 4313) was subject to each pre-processing method (10, 100) described above. Steels then underwent a simulated press hardening procedure in which they were austenitized at approximately 930 °C for 300 s and then quenched in flat, water-cooled dies. Double-edge notched tensile tests were then performed. Plots were then prepared of the resulting data for each composition as shown in FIGS. 7 and 8. For instance, FIG. 7 shows the results for each sample subjected to pre-processing method (100).
- FIG. 7 shows the results for each sample subjected to pre-processing method (100).
- FIG 8 shows the results for each sample subjected to pre-processing method (10).
- the data for each composition is identifiable by symbols. For instance, circles correspond to composition 4310, triangles correspond to composition 4311, stars correspond to composition 4312, and crosses correspond to composition 4313.
- FIGS. 7 and 8 are indicative of pre-processing method (100) resulting in increased toughness or retained ductility.
- Example 7 The data discussed above with respect to Example 6 was analyzed further. In particular, integration of the area under the force- displacement curves shown in FIGS. 7 and 8 can be used to obtain a value of strain energy. Strain energy is considered a measure of material toughness. Accordingly, a measure of material toughness for each sample discussed above with respect to Example 6 was generated.
- FIG. 9 utilizes a different symbolic scheme to identify the correspondence between specific data points and composition. For instance, in FIG. 9, circles correspond to composition 4310, crosses correspond to composition 4311, triangles correspond to composition 4312, and squares correspond to composition 4313.
- FIG. 9 depicts a comparison of samples subjected to pre-processing method (10) and samples subjected to pre-processing method (100). In each case, the steels underwent simulated hot stamping prior to testing.
- solid symbols represent processing method (10) and open symbols represent processing method (100).
- composition 4313 included the highest niobium concentrations and also included the highest strain energy or toughness measurements.
- Example 8 A press hardenable steel comprising by total mass percentage of the steel : wherein said steel is subject to the following processing: heating a slab of the press hardenable steel to a re-heat furnace temperature of approximately 2300 °F;
- Examples comprising 0.2 - 0.3 mass % carbon.
- Example 16 A press hardenable steel of any one of Examples 8 through 15 or any one of the following Examples, comprising 0.15-0.25 mass% chromium.
- a press hardenable steel of any one of Examples 8 through 23 or any one of the following Examples further comprising the step of cooling the press hardenable steel from the re-heat furnace temperature to the rolling temperature at a first cooling rate, and cooling the press hardenable steel from the rolling temperature to the coiling temperature at a second cooling rate, wherein the second cooling rate is greater than the first cooling rate.
- Example 27 A press hardenable steel of any one of Examples 8 through 26, wherein the temperature of the slab during the finish rolling operation is approximately 1600° F to 1700°F.
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Abstract
A method for processing a press hardenable steel includes first heating a slab of the press hardenable steel. The slab is heated to a re-heat furnace temperature of approximately 2300 °F. The slab is subjected to rolling into a steel sheet having a predetermined thickness. The temperature of the slab during rolling corresponds to a rolling temperature that is greater than or equal to 1600 °F.The steel sheet is coiled. The temperature of the steel sheet during coiling corresponds to a coiling temperature of approximately 1050 °F.
Description
METHOD FOR PRODUCTION FOR PRESS HARDENED STEEL WITH INCREASED TOUGHNESS
John Andrew Roubidoux
Erasmus Amoateng
PRIORITY
[0001] This application claims priority to U. S. Provisional Application Serial
Nos. 62/426,788 filed November 28, 2016, entitled "Press Hardened Steel with Increased Toughness and Method for Production;" the disclosure of which is incorporated by reference herein.
BACKGROUND
[0002] The present application relates to an improvement in press hardened steels, hot press forming steels, hot stamping steels, or any other steel that is heated to an austenitization temperature and formed and quenched in a stamping die to achieve desired mechanical properties in the final part. These types of steels are also sometimes referred to as "heat treatable boron-containing steels." In this application, they will all be referred to as "press hardened steels."
[0003] Press hardened steels are primarily used as structural members in
automobiles where high strength, low weight, and improved intrusion resistance are desired by automobile manufacturers. A common structural member where press hardened steels are employed in the automobile structure is the B-pillar.
[0004] Current industrial processing of press hardened steel involves heating a blank (piece of steel sheet) to a temperature greater than the A3 temperature (the austenitization temperature), typically in the range 900-950°C, holding the material at that temperature for a certain duration, placing the austenitized blank into a hot stamping die, forming the blank to the desired shape, and quenching the material in
the die to a low temperature such that martensite is formed. The end result is a material with a high ultimate tensile strength and a fully martensitic microstructure.
[0005] The as-quenched microstructure of prior art press hardened steel is fully martensitic. Conventional press hardened steels have ultimate tensile strengths of approximately 1500 MPa and total elongations on the order of 6%.
SUMMARY
[0006] The steels and methods of the present application improve upon
currently available press hardened steel alloys by using chemistry and processing to achieve higher residual toughness in the press hardened condition. Residual toughness refers to the toughness the material has in the press hardened condition.
[0007] The strength-ductility property of embodiments of the present steel alloys include ultimate tensile strengths greater than or equal to 1100 MPa and elongations of approximately 8%.
DESCRIPTION OF DRAWINGS
[0008] Fig. 1 shows a thermal profile and processing schematic for
embodiments of the present alloys.
[0009] Fig. 2 shows another thermal profile and processing schematic for embodiments of the present alloys.
[0010] Fig. 3 shows a plot of stress-strain curves for composition 4310, with results from a first pre-processing method shown in solid-line form and results from a second pre-processing method shown in dashed-line form.
[0011] Fig. 4 shows a plot of stress-strain curves for composition 4311, with results from the first pre-processing method shown in solid-line form
and results from the second pre-processing method shown in dashed- line form.
[0012] Fig. 5 shows a plot of stress-strain curves for composition 4312, with results from the first pre-processing method shown in solid-line form and results from the second pre-processing method shown in dashed- line form.
[0013] Fig. 6 shows a plot of stress-strain curves for composition 4313, with results from the first pre-processing method shown in solid-line form and results from the second pre-processing method shown in dashed- line form.
[0014] Fig. 7 shows the results of a double edge-notch tensile test for
embodiments of the present alloys after being subjected to the second pre-processing method.
[0015] Fig. 8 shows the results of a double edge-notch tensile test for
embodiments of the present alloys after being subjected to the first preprocessing method.
[0016] Fig. 9 shows the results of strain energy computations for
embodiments of the present alloys plotted as a function of niobium concentration.
[0017] Fig. 10 shows a photomicrograph of composition 4310 after being subjected to the first pre-processing method.
[0018] Fig. 11 shows a photomicrograph of composition 4310 after being subject to the second pre-processing method.
[0019] Fig. 12 shows a photomicrograph of composition 4311 after being subjected to the first pre-processing method.
[0020] Fig. 13 shows a photomicrograph of composition 4311 after being subjected to the second pre-processing method.
[0021] Fig. 14 shows a photomicrograph of composition 4312 after being subjected to the first pre-processing method.
[0022] FIG. 15 shows a photomicrograph of composition 4312 after being subjected to the second pre-processing method.
[0023] Fig. 16 shows a photomicrograph of composition 4313 after being subjected to the first pre-processing method.
[0024] FIG. 17 shows a photomicrograph of composition 4313 after being subjected to the second pre-processing method.
DETAILED DESCRIPTION
[0025] Press hardened steels are generally desirable for their high strength characteristics. In practice, this permits manufacturers to produce components having greater strength and less weight relative to components produced of non-press hardened steels. These high strength characteristics are generally achieved through formation of a predominately martensitic microstructure. In particular, during a hot stamping process associated with a press hardened steel blank, the blank is first subjected to an austenitization heat treatment. During this heat treatment, the temperature of the blank is raised to greater than the A3 temperature for the particular composition of the blank to thereby transform the microstructure of the blank into predominately austenite.
[0026] Once the austenitization heat treatment is complete, the blank is
stamped into a predetermined shape using an internally cooled die set. In addition to shaping the blank, the stamping process also has the effect of rapidly cooling the blank below the martensite start temperature (Ms). As a consequence, the predominately austenitic microstructure of the blank is transformed to a microstructure of predominantly martensite. Because martensite is generally
characterized as a strong and hard microstructure, the stamping process generally results in a final part having high strength and high hardness.
[0027] Although a high strength of the final hot stamped part is generally desirable for a wide variety of applications, in some circumstances additional toughness may be desirable. For instance, as described above, hot stamping generally results in a final part with high strength and high hardness. With high levels of hardness, the final part generally has relatively low ductility and thus relatively low toughness. Thus, in some circumstances it may be desirable to have a press hardened steel having the high strength characteristics of a conventional press hardened steel, but with improved residual toughness characteristics.
[0028] Prior to the hot stamping process described above, press hardened steels are subj ected to a variety of pre-processing steps. FIG. 1 shows a conventional pre-processing method (10). Pre-processing method includes subjecting a steel sheet to a plurality of pre-processing steps (20, 30, 40, 50). These steps (20, 30, 40, 50) are generally performed prior to hot stamping and prior to formation of press hardened steel blanks for the final hot stamping process. Generally, these steps (20, 30, 40, 50) are performed on sheet material in a continuous rolling mill. For instance, the press hardened steel initially begins as an as-cast slab comprising a predetermined composition. The slab then enters a re-heat furnace (20) and is subj ected to a re-heat temperature of approximately 2300° F (1260° C).
[0029] Once the slab is elevated to the re-heat temperature via the re-heat furnace (20), the slab is subjected to rough rolling (30) and then finishing rolling (40). These rolling steps progressively reduce the thickness of the slab to a final sheet thickness. During the rolling process, the temperature of the slab continuously decreases from the initial 2300° F (1260° C) re-heat temperature to a roughing
temperature associated with rough rolling (30). In some examples the roughing temperature is approximately 2000° F (1093° C). During finishing rolling (40), the slab is subject to a finishing temperature of approximately 1600° F (871 ° C). As the temperature decreases, the slab is subjected to rolling operations that progressively reduce the thickness of the slab by relatively large amounts during rough rolling (30) to relatively small amounts during finishing rolling (40).
[0030] From the initial re-heat temperature associated with the re-heat furnace
(20) to the temperature associated with finishing rolling (40), the temperature of the slab decreases at a relatively constant rolling cooling rate (12).
[0031] After completion of rolling, the press hardened steel material is in a steel sheet form. In the steel sheet form, the steel sheet is subj ect to coiling (50). Coiling (50) can be performed at a coiling temperature of approximately 1200° F (649° C). In some examples, coiling (50) can begin immediately after finishing (40). Thus, in some examples coiling (50) may begin at temperatures above 1600° F (871 ° C) and decrease to the coiling temperature of approximately 1200° F (649° C).
[0032] Prior to coiling (50), the steel sheet can be cooled to the coiling
temperature at one or more different cooling rates (14, 16) as shown in FIG. 1. For instance, at a first cooling rate (14) or second cooling rates (16), the steel sheet is cooled relatively slowly at between about 18° F/second and about 20° F/second.
[0033] At the conclusion of coiling (50), the coiled steel sheet is permitted to cool to ambient or room temperature. The coiled steel sheet is then subsequently formed into blanks of steel material for press hardening. The blanks can then be subjected to the hot stamping process described above.
[0034] As described above, in some circumstances it may be desirable to increase the toughness of press hardened steel parts. In some circumstances, toughness can be improved by refining the grain size of the press hardened steel material by modifying certain parameters of the pre-processing steps described above.
[0035] FIG. 2 shows modified pre-processing method (100). As with preprocessing method (10) described above, pre-processing method (100) of the present example includes a series of pre-processing steps (120, 130, 140, 150). As similarly described above, these steps (120, 130, 140, 150) are generally performed prior to hot stamping and prior to formation of press hardened steel blanks for the final hot stamping process. Generally, these steps (120, 130, 140, 150) are performed on sheet material in a continuous rolling mill. For instance, the press hardened steel initially begins as an as-cast slab comprising a predetermined composition. The slab then enters a re-heat furnace (120), where the slab is subjected to a re-heat temperature. Like with the reheat temperature described above with respect to re-heat furnace (20), the reheat temperature in the present example is approximately 2300° F (1260° C).
[0036] Once the slab is elevated to the re-heat temperature of re-heat furnace
(120), the slab is subjected to rough rolling (130) and then finishing rolling (140). This progressively reduces the thickness of the slab to a final sheet thickness. As an example, during the rolling process, the temperature of the slab continuously decreases from the initial 2300° F (1260° C) re-heat temperature of the re-heat furnace (120) to a roughing temperature of approximately 2000° F (1093° C) associated with rough rolling (130). Next, the slab is further reduced to a finishing temperature of approximately 1600° F (871 ° C) associated with finishing rolling (140). Unlike finishing rolling (40) in the conventional pre-processing method (10) described above, finishing
rolling (140) in the present example is performed at a relatively lower temperature. As will be described in greater detail below, this relatively lower temperature can lead to increased grain refinement when performed in connection with a modified coiling temperature. As the temperature decreases, the slab is subjected to rolling operations that reduce the thickness of the slab by relatively large amounts during rough rolling (130) to relatively small amounts during finishing rolling (140).
[0037] From the initial re-heat temperature associated with the re-heat furnace
(120) to the temperature associated with finishing rolling (140), the temperature of the slab decreases at a relatively constant rolling cooling rate (112). This cooling rate is similar to the rolling cooling rate (12) of the prior process.
[0038] After completion of rolling, the press hardened steel material is in a steel sheet form. In the steel sheet form, the steel sheet is subject to coiling (150). Coiling (150) can be performed at a coiling temperature of approximately 1050° F (566° C). In some examples, coiling (150) can begin immediately after finishing (140). Thus, in some examples coiling (150) may begin at approximately 1600° F (871° C) and decrease to the coiling temperature of approximately 1050° F (566° C). Alternatively, in some examples coiling (150) can be delayed until the steel sheet reaches the coiling temperature of approximately 1050° F (566° C). Once the coiling temperature is reached (150), the steel sheet may be held isothermally for the entirety of coiling (150). Preferably, the finishing (140) is performed at the finishing temperature of about 1600° F (871° C), the steel sheet is lowered to the coiling temperature of 1050° F (566° C), and coiling (150) is performed while the steel sheet is held at the coiling temperature.
[0039] Regardless of how the coiling temperature is reached, it should be understood that the coiling temperature of approximately 1050° F
(566° C) is generally low relative to the coiling temperatures described above with respect to conventional pre-processing method (10). As will be understood, this reduced coiling temperature can generally result in improved grain refinement of the steel sheet that can lead to increased residual toughness in a final work product after hot stamping.
[0040] Prior to coiling (150), the steel sheet can be cooled to the coiling
temperature at a cooling rate (114) as shown in FIG. 2. In the present example, the cooling rate (114) is between about 35 °F/second and about 50° F/second.
[0041] Unlike cooling rates (14, 16) described above, cooling rate (114) in the present example is generally relatively fast. This relatively fast cooling rate can be achieved using a run-out-table accelerated cooling method. As will be understood, this relatively fast cooling rate (114) can generally lead to increased grain refinement and associated improved residual toughness in a final work product after hot stamping.
[0042] At the conclusion of coiling (150), the coiled steel sheet is permitted to cool to ambient or room temperature. The coiled steel sheet is then subsequently formed into blanks of steel material for press hardening. The blanks can then be subjected to the hot stamping process described above.
[0043] As described above, the pre-processing methods (10, 100) can be performed using an as-cast slab comprising a predetermined composition. It should be understood that the particular composition of the slab can be varied such that a variety of compositions can be used with the methods (10, 100) described above. As will be described in greater detail below, various elements can be added to the slab to influence numerous metallurgical properties of the final work product.
[0044] Carbon is added to reduce the martensite start temperature, provide solid solution strengthening, and to increase the hardenability of the steel. Carbon is an austenite stabilizer. In certain embodiments, carbon can be present in concentrations of 0.1 - 0.5 mass %; in other embodiments, carbon can be present in concentrations of 0.2 - 0.30 mass %.
[0045] Manganese is added to reduce the martensite start temperature, provide solid solution strengthening, and to increase the hardenability of the steel. Manganese is an austenite stabilizer. In certain embodiments, manganese can be present in concentrations of 0.75 - 3.0 mass %; in other embodiments, manganese can be present in concentrations of 1.15 - 1.25 mass %.
[0046] Silicon is added to provide solid solution strengthening. Silicon is a ferrite stabilizer. In certain embodiments, silicon can be present in concentrations of 0.02 - 1.5 mass %; in other embodiments, silicon can be present in concentrations of 0.15 - 0.30 mass %.
[0047] Aluminum is added for deoxidation during steelmaking and to provide solid solution strengthening. Aluminum is a ferrite stabilizer. In certain embodiments, aluminum can be present in concentrations of 0.0 - 0.8 mass %; in other embodiments, aluminum can be present in concentrations of 0.02 - 0.15 mass %. In other embodiments, aluminum is entirely optional and can be therefore omitted or limited to an impurity element in some embodiments.
[0048] Titanium is added to getter nitrogen. In certain embodiments, titanium can be present in concentrations of 0.0-0.060 mass %; in other embodiments, titanium can be present in concentrations of a maximum of 0.045 mass %. In other embodiments, titanium is entirely optional and can be therefore omitted or limited to an impurity element in some embodiments.
[0049] Molybdenum is added to provide solid solution strengthening and to increase the hardenability of the steel. In certain embodiments, molybdenum can be present in concentrations of 0-0.5 mass %; in other embodiments, molybdenum can be present in concentrations of 0-0.3 mass %. In other embodiments, molybdenum is entirely optional and can be therefore omitted or limited to an impurity element in some embodiments.
[0050] Chromium is added to reduce the martensite start temperature, provide solid solution strengthening, and increase the hardenability of the steel. Chromium is a ferrite stabilizer. In certain embodiments, chromium can be present in concentrations of 0-0.5 mass %; in other embodiments, chromium can be present in concentrations of 0.15-0.25 mass %.
[0051] Boron is added to increase the hardenability of the steel. In certain embodiments, boron can be present in concentrations of 0-0.005 mass%; in other embodiments, boron can be present in concentrations of 0.003-0.005 mass %.
[0052] Nickel is added to provide solid solution strengthening and reduce the martensite start temperature. Nickel is an austenite stabilizer. In certain embodiments, nickel can be present in concentrations of 0.0-0.6 mass %; in other embodiments, nickel can be present in concentrations of 0.02-0.3 mass %. In still other embodiments, nickel is entirely optional and can be therefore omitted or limited to an impurity element in some embodiments.
[0053] Niobium is added to provide improved grain refinement. Niobium can also increase hardness and strength. In certain embodiments, niobium can be present in concentrations of 0-0.090 mass%.
[0054] Example 1
[0055] A plurality of alloy compositions shown in Table 1 were prepared using standard steel making processes, except as noted below.
[0056] Table 1: Composition range. Compositions are in mass pet.
C B Cr Mn Nb Si
4310 0.21 0.003 0.21 1.18 0.000 0.24
4311 0.21 0.0029 0.19 1.19 0.029 0.24
4312 0.21 0.0029 0.20 1.20 0.043 0.24
4313 0.22 0.003 0.19 1.20 0.052 0.25
[0057] Example 2
[0058] Composition 4310 of Table 1 in Example 1 was subjected to both preprocessing methods (10, 100) described above. The steel underwent simulated hot stamping. The steel was heated to approximately 930 °C for 5 min and then quenched in water-cooled copper dies. Samples subjected to each pre-processing method (10, 100) plus simulated hot stamping were then subjected to tensile testing to generate stress-strain curves. The resulting stress-strain curves are shown in FIG. 3 with preprocessing method (10) shown in solid-line form and pre-processing method (100) shown in dashed-line form.
[0059] As can be seen in FIG. 3, the samples subjected to pre-processing method (100) generally resulted in improved residual toughness relative to samples subjected to pre-processing method (10).
Photomicrographs were prepared for each sample in the hot-rolled condition prior to the simulated hot stamping and are shown in FIGS. 10 and 11, with FIG. 10 corresponding to pre-processing method (10) and FIG. 11 corresponding to pre-processing method (100). As can be seen, pre-processing method (100) generally resulted in a more refined grain structure relative to the grain structure produced from preprocessing method (10). As a consequence of this, improved residual toughness was observed in FIG. 3.
[0060] Example 3
[0061] Composition 4311 of Table 1 in Example 1 was subjected to both preprocessing methods (10, 100) described above. The steel underwent simulated hot stamping. The steel was heated to approximately 930 °C for 5 min and then quenched in water-cooled copper dies. Samples subjected to each pre-processing method (10, 100) plus simulated hot stamping were then subjected to tensile testing to generate stress-strain curves. The resulting stress-strain curves are shown in FIG. 4 with preprocessing method (10) shown in solid-line form and pre-processing method (100) shown in dashed-line form.
[0062] As can be seen in FIG. 4, the samples subjected to pre-processing method (100) generally resulted in improved residual toughness relative to samples subjected to pre-processing method (10).
Photomicrographs were prepared for each sample in the hot-rolled condition prior to the simulated hot stamping and are shown in FIGS. 12 and 13, with FIG. 12 corresponding to pre-processing method (10) and FIG. 13 corresponding to pre-processing method (100). As can be seen, pre-processing method (100) generally resulted in a more refined grain structure relative to the grain structure produced from preprocessing method (10). As a consequence of this, improved residual toughness was observed in FIG. 4.
[0063] Example 4
[0064] Composition 4312 of Table 1 in Example 1 was subjected to both preprocessing methods (10, 100) described above. The steel underwent simulated hot stamping. The steel was heated to approximately 930 °C for 5 min and then quenched in water-cooled copper dies. Samples subjected to each pre-processing method (10, 100) plus simulated hot stamping were then subjected to tensile testing to generate stress-strain curves. The resulting stress-strain curves are shown in FIG. 5 with pre-
processing method (10) shown in solid-line form and pre-processing method (100) shown in dashed-line form.
[0065] As can be seen in FIG. 5, the samples subjected to pre-processing method (100) generally resulted in improved residual toughness relative to samples subjected to pre-processing method (10).
Photomicrographs were prepared for each sample in the hot-rolled condition prior to the simulated hot stamping and are shown in FIGS. 14 and 15, with FIG. 14 corresponding to pre-processing method (10) and FIG. 15 corresponding to pre-processing method (100). As can be seen, pre-processing method (100) generally resulted in a more refined grain structure relative to the grain structure produced from preprocessing method (10). As a consequence of this, improved residual toughness was observed in FIG. 5.
[0066] Example 5
[0067] Composition 4313 of Table 1 in Example 1 was subjected to both preprocessing methods (10, 100) described above. The steel underwent simulated hot stamping. The steel was heated to approximately 930 °C for 5 min and then quenched in water-cooled copper dies. Samples subjected to each pre-processing method (10, 100) plus simulated hot stamping were then subjected to tensile testing to generate stress-strain curves. The resulting stress-strain curves are shown in FIG. 6 with preprocessing method (10) shown in solid-line form and pre-processing method (100) shown in dashed-line form.
[0068] As can be seen in FIG. 6, the samples subjected to pre-processing method (100) generally resulted in improved residual toughness relative to samples subjected to pre-processing method (10).
Photomicrographs were prepared for each sample in the hot-rolled condition prior to the simulated hot stamping and are shown in FIGS. 16 and 17, with FIG. 16 corresponding to pre-processing method (10)
and FIG. 17 corresponding to pre-processing method (100). As can be seen, pre-processing method (100) generally resulted in a more refined grain structure relative to the grain structure produced from preprocessing method (10). As a consequence of this, improved residual toughness or retained ductility was observed in FIG. 6.
[0069] Example 6:
[0070] Toughness for samples having each composition identified in Table 1 of Example 1, above, was evaluated further using double-edge-notch tensile tests. A sample for each composition (e.g., 4310, 4311, 4312, 4313) was subject to each pre-processing method (10, 100) described above. Steels then underwent a simulated press hardening procedure in which they were austenitized at approximately 930 °C for 300 s and then quenched in flat, water-cooled dies. Double-edge notched tensile tests were then performed. Plots were then prepared of the resulting data for each composition as shown in FIGS. 7 and 8. For instance, FIG. 7 shows the results for each sample subjected to pre-processing method (100). FIG. 8 shows the results for each sample subjected to pre-processing method (10). For both FIGS. 7 and 8, the data for each composition is identifiable by symbols. For instance, circles correspond to composition 4310, triangles correspond to composition 4311, stars correspond to composition 4312, and crosses correspond to composition 4313.
[0071] As can be seen in FIGS. 7 and 8, materials subjected to pre-processing method (100) exhibited a higher peak load/force prior to fracture in compassion to the materials subject to pre-processing method (10). Thus, FIGS. 7 and 8 are indicative of pre-processing method (100) resulting in increased toughness or retained ductility.
[0072] Example 7
[0073] The data discussed above with respect to Example 6 was analyzed further. In particular, integration of the area under the force- displacement curves shown in FIGS. 7 and 8 can be used to obtain a value of strain energy. Strain energy is considered a measure of material toughness. Accordingly, a measure of material toughness for each sample discussed above with respect to Example 6 was generated.
[0074] The resulting strain energy for each sample was then plotted as a
function of niobium concentration in the corresponding composition for each sample. The resulting plot is shown in FIG. 9. Unlike FIGS. 7 and 8 discussed above, FIG. 9 utilizes a different symbolic scheme to identify the correspondence between specific data points and composition. For instance, in FIG. 9, circles correspond to composition 4310, crosses correspond to composition 4311, triangles correspond to composition 4312, and squares correspond to composition 4313. In addition, because the results for samples subjected to each preprocessing method (10, 100) are included in a single plot, FIG. 9 depicts a comparison of samples subjected to pre-processing method (10) and samples subjected to pre-processing method (100). In each case, the steels underwent simulated hot stamping prior to testing. In FIG. 9, solid symbols represent processing method (10) and open symbols represent processing method (100).
[0075] As can be seen in FIG. 9, samples subjected to pre-processing method
(100) generally resulted in increased strain energy and therefore increased toughness. In addition, some increase in toughness was observed in response to a composition with increased niobium. For instance, composition 4313 included the highest niobium concentrations and also included the highest strain energy or toughness measurements.
[0076] Example 8
A press hardenable steel comprising by total mass percentage of the steel : wherein said steel is subject to the following processing: heating a slab of the press hardenable steel to a re-heat furnace temperature of approximately 2300 °F;
rolling the slab into a steel sheet having a predetermined thickness, wherein the temperature of the slab during rolling corresponds to a rolling temperature that is greater than or equal to about 1600° F (871° C); and
coiling the steel sheet, wherein the temperature of the steel sheet during coiling corresponds to a coiling temperature of approximately 1050 °F.
Example 9
A press hardenable steel of Example 8 or any one of the following Examples, comprising by total mass percentage of the steel:
0.10 to 0.50% Carbon;
0.00 to 0.005% Boron;
0.0 to 0.50% Chromium;
0.75 to 3.0% Manganese;
0.090% or less Niobium;
0.02 to 1.50% Silicon;
0.0 to 0.8% Aluminum;
0.0 to 0.060% Titanium;
0.0 to 0.50% Molybdenum;
0.0 to 0.6% Nickel; and
[0091] the balance including iron and impurities,
[0092] Example 10
[0093] A press hardenable steel of Example 8 or 9 or any one of the following
Examples, comprising 0.2 - 0.3 mass % carbon.
[0094] Example 11
[0095] A press hardenable steel of any one of Examples 8 through 10 or any one of the following Examples, comprising 1.15-1.25 mass % manganese.
[0096] Example 12
[0097] A press hardenable steel of any one of Examples 8 through 11 or any one of the following Examples, comprising 0.15-0.30 mass% silicon.
[0098] Example 13
[0099] A press hardenable steel of any one of Examples 8 through 12 or any one of the following Examples, comprising 0.02 - 0.15 mass% aluminum.
[00100] Example 14
[00101] A press hardenable steel of any one of Examples 8 through 13 or any one of the following Examples, comprising a maximum of 0.045 mass% titanium.
[00102] Example 15
[00103] A press hardenable steel of any one of Examples 8 through 14 or any one of the following Examples, comprising 0 - 0.30 mass% molybdenum.
[00104] Example 16
[00105] A press hardenable steel of any one of Examples 8 through 15 or any one of the following Examples, comprising 0.15-0.25 mass% chromium.
[00106] Example 17
[00107] A press hardenable steel of any one of Examples 8 through 16 or any one of the following Examples, comprising 0.003 - 0.005 mass% boron.
[00108] Example 18
[00109] A press hardenable steel of any one of Examples 8 through 17 or any one of the following Examples, comprising 0.02 - 0.3 mass% nickel.
[00110] Example 19
[00111] A press hardenable steel of any one of Examples 8 through 18 or any one of the following Examples, comprising 0 - 1.0 mass% molybdenum.
[00112] Example 20
[00113] A press hardenable steel of any one of Examples 8 through 19 or any one of the following Examples, wherein the rolling step includes a rough rolling operation and a finish rolling operation.
[00114] Example 21
[00115] A press hardenable steel of any one of Examples 8 through 20 or any one of the following Examples, wherein the temperature of the slab during the rough rolling operation is greater than or equal to 2000 °F.
[00116] Example 22
[00117] A press hardenable steel of any one of Examples 8 through 21 or any one of the following Examples, wherein the temperature of the slab
during the finish rolling operation is greater than or equal to about 1600° F (871° C).
[00118] Example 23
[00119] A press hardenable steel of any one of Examples 8 through 22 or any one of the following Examples, further comprising the step of hot stamping at least a portion of the steel sheet after coiling the steel sheet.
[00120] Example 24
[00121] A press hardenable steel of any one of Examples 8 through 23 or any one of the following Examples, further comprising the step of cooling the press hardenable steel from the re-heat furnace temperature to the rolling temperature at a first cooling rate, and cooling the press hardenable steel from the rolling temperature to the coiling temperature at a second cooling rate, wherein the second cooling rate is greater than the first cooling rate.
[00122] Example 25
[00123] A press hardenable steel of any one of Examples 8 through 24 or any of the following Examples, wherein the step of cooling the press hardenable steel from the rolling temperature to the coiling temperature is performed using a run-out table accelerated cooling method.
[00124] Example 26
[00125] A press hardenable steel of any one of Examples 8 through 25 or the following Example, wherein the temperature of the slab during the rough rolling operation is approximately 2000 °F.
[00126] Example 27
A press hardenable steel of any one of Examples 8 through 26, wherein the temperature of the slab during the finish rolling operation is approximately 1600° F to 1700°F.
Claims
1. A method for processing a press hardenable steel, the method comprising:
(a) heating a slab of the press hardenable steel to a re-heat furnace
temperature of approximately 2300 °F;
(b) rolling the slab into a steel sheet having a predetermined thickness, wherein the temperature of the slab during rolling corresponds to a rolling temperature that is greater than or equal to about 1600° F (871° C); and
(c) coiling the steel sheet, wherein the temperature of the steel sheet during coiling corresponds to a coiling temperature of approximately 1050 °F.
2. The method of claim 1, wherein the rolling step includes a rough rolling operation and a finish rolling operation.
3. The method of claim 2, wherein the temperature of the slab during the rough rolling operation is greater than or equal to 2000 °F.
4. The method of claim 2, wherein the temperature of the slab during the finish rolling operation is greater than or equal to about 1600° F (871° C) .
5. The method of claim 2, wherein the temperature of the slab during the rough rolling operation is approximately 2000 °F.
6. The method of claim 2, wherein the temperature of the slab during the finish rolling operation is approximately 1600°F to 1700 °F.
7. The method of claim 1, further comprising hot stamping at least a portion of the steel sheet after coiling the steel sheet.
8. The method of claim 1, further comprising cooling the press hardenable steel from the re-heat furnace temperature to the rolling temperature at a first cooling rate, and cooling the press hardenable steel from the rolling temperature to the coiling temperature at a second cooling rate, wherein the second cooling rate is greater than the first cooling rate.
9. The method of claim 1, wherein the step of cooling the press hardenable steel from the rolling temperature to the coiling temperature is performed using a run-out table accelerated cooling method.
10. The method of claim 1 , wherein the press hardenable steel has a composition comprising:
0.10 to 0.50% Carbon;
0.00 to 0.005% Boron;
0.0 to 0.50% Chromium;
0.75 to 3.0%) Manganese;
0.090% or less Niobium;
0.02 to 1.50% Silicon;
0.0 to 0.80% Aluminum;
0.0 to 0.060%) Titanium;
0.0 to 0.50% Molybdenum;
0.0 to 0.60% Nickel; and
the balance including iron and impurities.
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CN111519103A (en) * | 2020-06-05 | 2020-08-11 | 东风商用车有限公司 | Preparation method of high-strength saddle shell |
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CN112011716A (en) * | 2020-08-06 | 2020-12-01 | 包头钢铁(集团)有限责任公司 | Preparation method for producing H40 steel by rare earth cerium micro-alloying |
MX2023002518A (en) * | 2020-09-01 | 2023-03-13 | Hyundai Steel Co | Hot stamping material and production method therefor. |
WO2022050500A1 (en) | 2020-09-01 | 2022-03-10 | 현대제철 주식회사 | Material for hot stamping, and method for manufacturing same |
WO2022050501A1 (en) * | 2020-09-01 | 2022-03-10 | 현대제철 주식회사 | Material for hot stamping and method for manufacturing same |
CN117568569A (en) * | 2022-08-08 | 2024-02-20 | 通用汽车环球科技运作有限责任公司 | Method for producing high-performance press-hardened steel component |
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JP6143355B2 (en) * | 2013-10-22 | 2017-06-07 | 株式会社神戸製鋼所 | Hot-rolled steel sheet with excellent drawability and surface hardness after carburizing heat treatment |
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2017
- 2017-11-28 TW TW106141452A patent/TW201829806A/en unknown
- 2017-11-28 US US15/824,533 patent/US20180147614A1/en not_active Abandoned
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US20110017360A1 (en) * | 2008-03-26 | 2011-01-27 | Naoki Yoshinaga | Hot-rolled steel sheet excellent in fatigue properties and stretch-flange formability and method for manufacturing the same |
US20130292009A1 (en) * | 2010-10-22 | 2013-11-07 | Kunio Hayashi | Method for manufacturing hot stamped body and hot stamped body |
US20160024610A1 (en) * | 2013-03-14 | 2016-01-28 | Nippon Steel & Sumitomo Metal Corporation | High strength steel sheet excellent in delayed fracture resistance and low temperature toughness, and high strength member manufactured using the same |
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