WO2021181866A1 - 局所的に軟化された部分を有する鋼部品の製造方法 - Google Patents
局所的に軟化された部分を有する鋼部品の製造方法 Download PDFInfo
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- WO2021181866A1 WO2021181866A1 PCT/JP2021/001266 JP2021001266W WO2021181866A1 WO 2021181866 A1 WO2021181866 A1 WO 2021181866A1 JP 2021001266 W JP2021001266 W JP 2021001266W WO 2021181866 A1 WO2021181866 A1 WO 2021181866A1
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 145
- 239000010959 steel Substances 0.000 title claims abstract description 145
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 77
- 238000000034 method Methods 0.000 title claims abstract description 26
- 238000001816 cooling Methods 0.000 claims abstract description 71
- 238000012545 processing Methods 0.000 claims abstract description 64
- 238000010438 heat treatment Methods 0.000 claims abstract description 52
- 239000000203 mixture Substances 0.000 claims abstract description 20
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 16
- 239000012535 impurity Substances 0.000 claims abstract description 13
- 239000000126 substance Substances 0.000 claims abstract description 13
- 229910052742 iron Inorganic materials 0.000 claims abstract description 8
- 238000000465 moulding Methods 0.000 claims description 38
- 238000003754 machining Methods 0.000 claims description 8
- 238000005452 bending Methods 0.000 claims description 4
- 238000005242 forging Methods 0.000 claims description 4
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- 101100268670 Caenorhabditis elegans acc-3 gene Proteins 0.000 claims description 2
- 238000010583 slow cooling Methods 0.000 abstract description 26
- 229910000859 α-Fe Inorganic materials 0.000 description 17
- 229910001566 austenite Inorganic materials 0.000 description 16
- 230000000694 effects Effects 0.000 description 13
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- 238000007542 hardness measurement Methods 0.000 description 11
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- 239000002436 steel type Substances 0.000 description 7
- AFCARXCZXQIEQB-UHFFFAOYSA-N N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CCNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 AFCARXCZXQIEQB-UHFFFAOYSA-N 0.000 description 6
- 230000001965 increasing effect Effects 0.000 description 6
- 229910000734 martensite Inorganic materials 0.000 description 6
- WZFUQSJFWNHZHM-UHFFFAOYSA-N 2-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperazin-1-yl]-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)N1CCN(CC1)CC(=O)N1CC2=C(CC1)NN=N2 WZFUQSJFWNHZHM-UHFFFAOYSA-N 0.000 description 5
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- 210000004872 soft tissue Anatomy 0.000 description 5
- HMUNWXXNJPVALC-UHFFFAOYSA-N 1-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperazin-1-yl]-2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)N1CCN(CC1)C(CN1CC2=C(CC1)NN=N2)=O HMUNWXXNJPVALC-UHFFFAOYSA-N 0.000 description 4
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- 238000007747 plating Methods 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
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- 230000001737 promoting effect Effects 0.000 description 3
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
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- 238000005260 corrosion Methods 0.000 description 2
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- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical class [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 235000010724 Wisteria floribunda Nutrition 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229940069428 antacid Drugs 0.000 description 1
- 239000003159 antacid agent Substances 0.000 description 1
- 230000001458 anti-acid effect Effects 0.000 description 1
- ZDVYABSQRRRIOJ-UHFFFAOYSA-N boron;iron Chemical compound [Fe]#B ZDVYABSQRRRIOJ-UHFFFAOYSA-N 0.000 description 1
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- 229910052757 nitrogen Inorganic materials 0.000 description 1
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- 229910052698 phosphorus Inorganic materials 0.000 description 1
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- 229910052717 sulfur Inorganic materials 0.000 description 1
- 229910006540 α-FeOOH Inorganic materials 0.000 description 1
Images
Classifications
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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
- C21D8/0252—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with application of tension
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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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
- B21D22/20—Deep-drawing
- B21D22/26—Deep-drawing for making peculiarly, e.g. irregularly, shaped articles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
- B21J1/02—Preliminary treatment of metal stock without particular shaping, e.g. salvaging segregated zones, forging or pressing in the rough
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
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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
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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
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
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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
- C21D1/84—Controlled slow cooling
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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
- C21D6/002—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
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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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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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
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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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C—ALLOYS
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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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
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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
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the present disclosure relates to a method for manufacturing a steel part having a locally softened portion.
- Patent Document 1 discloses a method of covering a portion to be softened when a steel sheet is heated to an austenite single-phase temperature range. As a result, the portion covered with the heat shield is less than the austenite single-phase temperature range even during heating, and the martensitic transformation of the portion after quenching is suppressed, and the portion is compared with the portion not covered with the heat shield. Softens.
- Patent Document 2 discloses a method of providing a portion where the contact between the steel sheet and the mold is poor when the steel plate is brought into contact with the mold from the austenite single-phase temperature range and rapidly cooled. As a result, a soft structure (ferrite and / or pearlite) is precipitated in the portion, and the portion is softened.
- Patent Documents 1 and 2 it is not possible to soften only the portion to be softened due to the influence of heat transfer or the like in the steel sheet.
- Patent Document 1 only the portion covered with the heat shield cover should be softened to be less than the austenite single-phase temperature range, but at the end of the portion covered with the heat shield cover, from the adjacent portion not covered with the heat shield cover. Since heat is transferred, as a result, it cannot be sufficiently softened at the end of the portion covered with the heat shield cover.
- Patent Document 2 only the portion having poor contact with the mold should be softened without quenching, but heat is transferred from the portion to the adjacent portion having good contact with the mold, resulting in the mold and the mold. A softening effect can also be exerted on the adjacent portion of the. Therefore, it is difficult to locally soften only the portion to be softened by the method of softening by local temperature control as in Patent Documents 1 and 2.
- the embodiment of the present invention has been made in view of such a situation, and one of the objects thereof is to produce a locally softened high-strength steel part without local temperature control. To provide a method.
- Aspect 1 of the present invention is C: 0.05 to 0.40% by mass, Si: 0 to 2.0% by mass, Mn: 1.0 to 3.0% by mass, Al: 0.010 to 1.0% by mass, P: More than 0% by mass and less than 0.100% by mass, S: More than 0% by mass and 0.010% by mass or less, N: More than 0% by mass and 0.010% by mass or less, B: 0.0005 to 0.010% by mass, and the balance: a step of preparing a steel sheet having a chemical composition consisting of iron and unavoidable impurities, and A step of heating the steel sheet to a temperature of 1 point (° C.) or more and 3 points (° C.) of Ac and less than 10 ° C.
- a machining step of adding 0.5% or more of strain at a machining temperature of 675 ° C. or higher and Ac 3 points (° C.) + 10 ° C. or lower After the processing step, a step of holding at the processing temperature for 1 second or more and 120 seconds or less, or a step of slowly cooling for 1 second or more and 120 seconds or less at an average cooling rate of more than 0 ° C./sec and 15 ° C./sec or less. After the step of holding or slowly cooling, the step of cooling to the Ms point (° C.) -50 ° C. is included. This is a method for manufacturing steel parts, in which the average cooling rate from the temperature of the heating step to the Ms point (° C.) -50 ° C. is controlled to 10 ° C./sec or more.
- Aspect 2 of the present invention C: 0.05 to 0.40% by mass, Si: 0 to 2.0% by mass, Mn: 1.0 to 3.0% by mass, Al: 0.010 to 1.0% by mass, P: More than 0% by mass and less than 0.100% by mass, S: More than 0% by mass and 0.010% by mass or less, N: More than 0% by mass and 0.010% by mass or less, B: 0.0005 to 0.010% by mass, and the balance: a step of preparing a steel sheet having a chemical composition consisting of iron and unavoidable impurities, and A step of heating the steel sheet to a temperature of Acc 3 points (° C.) + 10 ° C. or higher and 1100 ° C.
- the step of cooling to the Ms point (° C.) -50 ° C. is included. This is a method for manufacturing steel parts, in which the average cooling rate from the temperature in the heating step to the Ms point (° C.) -50 ° C. is controlled to 10 ° C./sec or more.
- the steel plate is The production method according to Aspect 1 or 2, further comprising one or more selected from the group consisting of Cu: more than 0% by mass and 0.50% by mass or less, and Ni: more than 0% by mass and 0.50% by mass or less. ..
- the steel plate is Ti: More than 0% by mass and less than 0.10% by mass, Described in any one of aspects 1 to 3, further containing one or more selected from the group consisting of Cr: more than 0% by mass and 3.0% by mass or less, and Nb: more than 0% by mass and 0.10% by mass or less. It is a manufacturing method of.
- Aspect 5 of the present invention is the manufacturing method according to any one of aspects 1 to 4, which comprises applying the strain by overhang molding.
- Aspect 6 of the present invention is the manufacturing method according to any one of aspects 1 to 4, which comprises applying the strain by forging.
- Aspect 7 of the present invention is the manufacturing method according to any one of aspects 1 to 4, which comprises applying the strain by bending back at the time of draw molding.
- Aspect 8 of the present invention is the manufacturing method according to any one of aspects 1 to 4, which comprises applying the strain by shearing.
- Aspect 9 of the present invention is the manufacturing method according to any one of aspects 1 to 8, which comprises applying the strain by a plurality of times of processing.
- Aspect 10 of the present invention is the manufacturing method according to aspect 9, wherein the plurality of times of processing includes a process of adding a deformation and a process of performing the process so as to return the deformation.
- FIG. 1 is a graph showing the relationship between temperature and displacement when a steel sheet is heated from a low temperature in a four-master test.
- FIG. 2 is a graph showing the relationship between temperature and displacement when the steel sheet is cooled from a high temperature in the Formaster test in addition to the relationship shown in FIG.
- FIG. 3 is a schematic view showing a sampling position of an evaluation sample of an example.
- FIG. 4 is a schematic cross-sectional view taken along line XX shown in FIG.
- the inventors of the present application examined from various angles in order to realize a method for manufacturing locally softened high-strength steel parts without local temperature control.
- a steel plate having a predetermined chemical composition is heated to a state in which austenite is relatively unstable, such as a two-phase region of austenite and ferrite, and a slight strain is applied to the portion to be softened, thereby only the portion to be softened.
- austenite relatively unstable, such as a two-phase region of austenite and ferrite
- a slight strain is applied to the portion to be softened, thereby only the portion to be softened.
- Embodiment 2 of the present invention nucleation of soft tissue can be promoted only in the portion to be softened.
- the “steel part” refers to a steel plate processed into a predetermined shape by the processing steps of the first and second embodiments of the present invention.
- the production method according to the first embodiment of the present invention is (A) The process of preparing the steel plate and (B) After the step (a), the step of heating and (C) After the step (b), the step of processing and (D) After the step (c), the step of holding or slowly cooling, and (E) After the step (d), the step of cooling and including.
- the chemical composition of the steel plate according to the first embodiment of the present invention is C: 0.05 to 0.40% by mass, Si: 0 to 2.0% by mass, Mn: 1.0 to 3.0% by mass, Al: 0.010 to 1.0% by mass, P: more than 0% by mass and 0.100% by mass or less, S: more than 0% by mass and 0.010% by mass or less, N: more than 0% by mass It consists of 0.010% by mass or less, B: 0.0005 to 0.010% by mass, and the balance: iron and unavoidable impurities.
- each element will be described in detail.
- the C content determines the strength of the steel part.
- the C content is 0.05% by mass or more, preferably 0.10% by mass or more, and more preferably 0.20% by mass or more.
- the C content is 0.40% by mass or less, preferably 0.38% by mass or less, and more preferably 0.36% by mass or less.
- Si is an element optionally contained in the steel sheet. Si contributes to the hardness stability of the steel sheet by increasing the temper softening resistance. Therefore, it is preferable that Si is contained in the steel sheet in an amount of more than 0% by mass.
- Si facilitates the formation of retained austenite ( ⁇ ) and promotes a decrease in yield strength (YS) and segregation of Mn. Therefore, the Si content is 2.0% by mass or less, preferably 1.8% by mass or less.
- Mn 1.0 to 3.0% by mass
- Mn contributes to increasing the strength of steel parts by enhancing the hardenability of the steel sheet.
- the Mn content is 1.0% by mass or more, preferably 1.2% by mass or more, and more preferably 1.4% by mass or more.
- the Mn content is 3.0% by mass or less, preferably 2.8% by mass or less, and more preferably 2.6% by mass or less.
- Al 0.010 to 1.0% by mass
- Al is an element that acts as an antacid.
- the amount of Al is 0.010% by mass or more.
- the amount of Al is preferably 0.020% by mass or more, more preferably 0.025% by mass or more.
- the amount of Al is set to 1.0% by mass or less.
- the amount of Al is preferably 0.80% by mass or less, and more preferably 0.70% by mass or less.
- P More than 0% by mass and less than 0.100% by mass
- P is an element that is inevitably contained and deteriorates the weldability of the steel sheet, but is also an element that has an effect of contributing to the solid solution strengthening of the ferrite phase.
- the amount of P is set to 0.100% by mass or less.
- the amount of P is preferably 0.050% by mass or less, and more preferably 0.020% by mass or less.
- P is an impurity that is inevitably mixed in steel, and it is impossible for industrial production to reduce the amount to 0% by mass, and usually exceeds 0% by mass, and further 0.00050% by mass or more. Can be contained in.
- S is an element that is inevitably contained and deteriorates the weldability of the steel sheet. Therefore, the amount of S is set to 0.010% by mass or less.
- the amount of S is preferably 0.0080% by mass or less, and more preferably 0.0050% by mass or less. Since the amount of S should be as small as possible, the lower limit is not particularly limited, but it is impossible for industrial production to set the amount to 0% by mass, and usually exceeds 0% by mass, further 0.00010% by mass or more. Can be contained in.
- N More than 0% by mass and 0.010% by mass or less
- N is an element that is inevitably contained, and when it is contained in an excessive amount, AlN is generated and the deoxidizing effect of Al is reduced. Therefore, the amount of N is set to 0.010% by mass or less.
- the amount of N is preferably 0.0080% by mass or less, and more preferably 0.0050% by mass or less. Since the amount of N should be as small as possible, the lower limit is not particularly limited, but it is impossible for industrial production to set the amount to 0% by mass, and usually exceeds 0% by mass, further 0.00010% by mass or more. Can be contained in.
- B (B: 0.0005 to 0.010% by mass) B contributes to increasing the strength of steel parts by enhancing the hardenability of the steel sheet.
- the B content is 0.0005% by mass or more, preferably 0.0010% by mass or more, and more preferably 0.0015% by mass or more.
- the B content is 0.010% by mass or less, preferably 0.0080% by mass or less, and more preferably 0.0060% by mass or less.
- the balance is iron and unavoidable impurities.
- Inevitable impurities are elements that are brought in depending on the conditions of raw materials, materials, manufacturing equipment, and the like. It should be noted that, for example, there are elements such as P, S and N, which are usually preferable as the content is smaller, and therefore are unavoidable impurities, but the composition range thereof is separately specified as described above. Therefore, in the present specification, the term "unavoidable impurities" constituting the balance is a concept excluding elements whose composition range is separately defined.
- the steel sheet according to the first embodiment of the present invention may selectively contain the following optional elements as necessary, and the characteristics of the steel parts are further improved according to the contained components.
- Cu 1 or more selected from the group consisting of more than 0% by mass and 0.50% by mass or less, and Ni: more than 0% by mass and 0.50% by mass or less
- Cu also has the effect of promoting the formation of iron oxide: ⁇ -FeOOH, which is said to be thermodynamically stable and protective even in the rust generated in the atmosphere.
- the Cu content is preferably more than 0% by mass, more preferably 0.05% by mass or more, and further preferably 0.10% by mass or more.
- the Cu content is preferably 0.50% by mass or less.
- Ni has the same effect as Cu. Therefore, the Ni content is preferably more than 0% by mass, more preferably 0.05% by mass or more, and further preferably 0.10% by mass or more. On the other hand, the Ni content is preferably 0.50% by mass or less.
- Ti 1 or more selected from the group consisting of more than 0% by mass and 0.10% by mass or less, Cr: more than 0% by mass and 3.0% by mass or less, and Nb: more than 0% by mass and 0.10% by mass or less
- Ti reduces the amount of BN produced in the steel sheet by producing TiN.
- the Ti content is preferably more than 0% by mass, more preferably 0.0050% by mass or more, still more preferably 0.0250% by mass or more and 0.050% by mass. That is all.
- the Ti content is preferably 0.10% by mass or less, more preferably 0.080% by mass or less, and further preferably 0.070% by mass or less.
- the Cr content is preferably more than 0% by mass.
- the Cr content is preferably 3.0% by mass or less, more preferably 2.5% by mass or less. Yes, more preferably 2.0% by mass or less.
- the Nb content is preferably more than 0% by mass, more preferably 0.0050% by mass or more.
- Nb is contained in an amount of 0.10% by mass or less. It is preferably 0.070% by mass or less, and more preferably 0.050% by mass or less.
- the steel sheet is heated to Ac 1 point (° C.) or more and Ac 3 points (° C.) + 10 ° C. If it is less than one point of Ac, austenite transformation does not occur, and it becomes difficult to obtain a high-strength steel part after the step (e) cooling described later. On the other hand, when the temperature is set to less than 3 points of Ac + 10 ° C., nucleation of ferrite and / or pearlite, which are soft structures, can be easily promoted in the step (c) processing described later.
- FIG. 1 is a graph showing the relationship between temperature and displacement when a steel sheet is heated from a low temperature in a four-master test.
- the steel In the low temperature region, the steel can expand linearly with an increase in temperature at an expansion coefficient corresponding to the crystal structure (bcc) of ferrite. Further increases in temperature may produce austenite with a denser crystal structure (fcc) and begin to shrink.
- the temperature at which the temperature begins to deviate from the straight line can be set as the Ac1 point.
- the temperature at which the temperature begins to deviate from the straight line can be set to the Ac3 point.
- (C) Processing step After the above-mentioned (b) heating step, processing is performed in which a strain of 0.5% or more is applied at a temperature of 675 ° C. or higher and Ac 3 points + 10 ° C. or lower. At the above temperatures, a large number of grain boundaries, which are nucleation sites of ferrite and / or pearlite, which are soft structures, may be present in the steel sheet. By applying a slight strain (that is, 0.5% or more) in such an unstable state, nucleation of ferrite and / or pearlite, which is a soft structure, is remarkably promoted in the strained portion. can do. More preferably, a strain of 5.0% or more is applied, and even more preferably, a strain of 9.0% or more is applied.
- ... (1) d 0 is the plate thickness of the steel plate before processing or the plate thickness of the unprocessed portion of the steel plate after processing, and d 1 is the plate thickness of the processed portion of the steel plate after processing. In each case, the unit is mm.
- the strain may be, for example, the equivalent plastic strain obtained by FEM analysis. That is, if the equivalent plastic strain obtained by FEM analysis is 0.5% or more, it can be softened in the same manner.
- FIG. 2 is a graph showing the relationship between temperature and displacement when the steel sheet is cooled at a relatively high cooling rate after the heating, in addition to the temperature-displacement relationship during heating described in FIG.
- steel can shrink linearly with a temperature drop at a shrinkage rate according to the crystal structure of austenite. When the temperature is further lowered, it can transform into martensite and begin to expand. The temperature at which the temperature begins to deviate from the straight line can be set as the Ms point.
- the heating temperature in the step (b) heating is set to Ac 1 point (° C.) or more and Ac 3 points (° C.) + 10 ° C., and the processing temperature is set to less than 675 ° C., the transformation into a soft structure becomes active. The softening of the non-processed portion is also remarkable, and it becomes difficult to manufacture the locally softened steel part only in the processed portion.
- the heating temperature of the above (b) heating step is set to Ac 1 point (° C.) or higher and Ac 3 points (° C.) + 10 ° C.
- the processing temperature is set to Ac 3 points + 10 ° C. or higher, crystals that are nucleation sites of soft tissue. Grain boundaries are reduced, and even a slight strain cannot promote nucleation of soft tissue.
- the processing temperature may be the same as or different from the heating temperature of the step (b) heating. If different, an additional heating and / or cooling step may be included between the steps (b) and (c) above. Further, a step of holding the temperature at a constant temperature may be included after the step (b) and before the step (c).
- the above processing may be any processing, but for example, press processing, overhang forming, forging, bending back at the time of draw forming, shearing, etc. are preferably used.
- step (D) Step of holding or slowly cooling After the step of (c) processing described above, holding or slowly cooling is performed at an average cooling rate of 0 to 15 ° C./sec for 1 second or more and 120 seconds or less. That is, it is held at the above processing temperature for 1 second or more and 120 seconds or less, or slowly cooled for 1 second or more and 120 seconds or less at an average cooling rate of more than 0 ° C./sec and 15 ° C./sec or less.
- ferrite and / or pearlite which are soft structures nucleated in the step (c) of the above, can be grown.
- the holding time or slow cooling time is preferably more than 1 second, more preferably 3 seconds or more, and further preferably 6 seconds or more.
- the holding or slow cooling time exceeds 120 seconds, ferrite and / or pearlite, which are soft structures, precipitate and grow even in the unprocessed portion, and high-strength steel parts cannot be obtained. It is preferably 12 seconds or less.
- Cooling step After the above-mentioned (d) holding or slow cooling step, cooling is performed to the Ms point (° C.) -50 ° C. At this time, the average cooling rate from the heating temperature of the step (b) heating (that is, Ac1 point (° C.) or more and Ac3 point (° C.) + 10 ° C. or less) to Ms point (° C.) -50 ° C. is 10 ° C./. Control over seconds. As a result, martensitic transformation can occur at least in the unprocessed portion, and the strength of the unprocessed portion can be sufficiently ensured.
- the cooling rate from the Ms point (° C.) -50 ° C. to room temperature is not particularly limited.
- the production method according to the second embodiment of the present invention is different from the production method according to the first embodiment of the present invention in terms of (b) heating step and (c) processing step.
- steps different from the first embodiment of the present invention will be described below as (b') heating steps and (c') processing steps.
- the steel sheet is heated to Ac 3 points (° C.) + 10 ° C. or higher and 1100 ° C. or lower.
- the heating is performed at Ac 3 points + 10 ° C. or higher in the heating step, if a relatively large strain is applied in the step of processing (c') described later, the same as the first embodiment of the present invention.
- nucleation of the soft structures ferrite and / or pearlite can be significantly promoted.
- the temperature exceeds 1100 ° C., decarburization of the steel surface becomes remarkable and the target strength cannot be secured.
- (C') Processing step After the above (b') heating step, processing is performed in which strain is applied by 10% or more at a temperature of Ms point (° C.) + 50 ° C. or higher and Ac 3 point (° C.) + 10 ° C. or lower.
- Ms point (° C.) + 50 ° C. or higher and Ac 3 point (° C.) + 10 ° C. austenite becomes relatively unstable. Therefore, the strain was applied by applying a relatively large strain (10% or more). Nucleation of the soft structures ferrite and / or pearlite can be significantly promoted in the portions. More preferably, a strain of 15% or more is applied, and even more preferably, a strain of 40% or more is applied.
- the strain can be calculated by the above equation (1). Further, the strain may be, for example, an equivalent plastic strain obtained by FEM analysis. That is, if the equivalent plastic strain obtained by FEM analysis is 10% or more, it can be softened in the same manner.
- austenite becomes a relatively stable state, and even if a relatively large strain is applied, it becomes difficult to promote nucleation of ferrite and / or pearlite, which are soft tissues.
- Ms point (° C.) + 50 ° C. martensitic transformation may occur, and it becomes difficult to promote nucleation of ferrite and / or pearlite, which are soft tissues.
- the processing of the above (c') processing step may be any processing, but for example, press processing, overhang forming, forging, bending back at the time of draw forming, shearing, etc. are preferably used.
- the strains in the processing steps (c) and (c') described above may be applied by a plurality of processings.
- the strain due to the multiple times of processing can be calculated by the following formula (2).
- d n is the thickness of the processed portion of the steel sheet after the nth processing, and the unit is mm.
- the strain of the above formula (2) may be, for example, the sum of the equivalent plastic strains obtained by FEM analysis after each processing.
- processing steps (c) and (c') are single steps, it is difficult to apply a predetermined strain (0.5% or more in the first embodiment and 10% or more in the second embodiment). In some cases. In such a case, it is advantageous to carry out the steps (c) and (c') above by a plurality of times to accumulate the strain, so that the strain can be easily increased to a predetermined value or more.
- the transport time from the steps (c) and (c') to the cooling step (e) is less than 1 second.
- D It may be difficult to secure the time (1 second or more) for the step of holding or slowly cooling.
- the transfer time between the plurality of processing steps is allocated to the time for holding or slowly cooling the above steps (d). It is advantageous because it can be done.
- the above-mentioned multiple times of processing may include a processing of adding deformation and a processing of returning the deformation. This makes it possible to apply the above strain to the initial steel plate shape without changing the final steel part shape.
- the above-mentioned (d) holding or slow cooling step may be performed after each process.
- a step of performing the first process, then performing the first holding or slow cooling step, and then performing the second process, and then performing the second holding or slow cooling step. May be done.
- the total of the time of the first holding or slow cooling step and the time of the second holding or slow cooling step is the time specified in step (d) of Embodiments 1 and 2 of the present invention, that is, It may be 1 second or more and 120 seconds or less.
- the temperatures of the steps (a) to (e), (b') and (c') above are the surface temperatures of the steel plate (or steel parts), and may be measured using a thermocouple or a radiation thermometer.
- the correspondence between the ambient temperature of the heating line, etc. and the surface temperature of the steel sheet (or steel part) measured by thermoelectric pair, etc. is investigated in advance, and the ambient temperature of the heating line, etc. is used to determine the correspondence between the steel sheet (or steel part).
- the surface temperature may be read.
- a method for producing a high-strength steel part in which only a portion to which a predetermined strain or more is strained by processing is locally softened without local temperature control. It is possible to do.
- the mixture was slowly cooled for 6 seconds at an average cooling rate of 10.8 ° C./sec. Then, it was water-cooled to the Ms point (° C.) -50 ° C. (that is, 335 ° C.) so that the average cooling rate from 880 ° C. to 335 ° C. was 39.5 ° C./sec. Then it was allowed to cool to room temperature.
- the above is referred to as Production Example 1-2.
- the Ac1 point, Ac3 point, and Ms point were obtained by the Formaster test. The four master test was conducted under the following conditions.
- Formaster testing machine FTM-10 manufactured by Fuji Denpa Koki Specimen size: Plate thickness 2.0 mm x width 3.0 mm x length 10 mm (However, there are two holes of ⁇ 0.7 mm x depth 2.0 mm for inserting a thermocouple) Number of tests: 7 times (only the cooling rate is changed, the others are under certain conditions) Heating rate: 10 ° C / s (room temperature to heating temperature) Heating temperature: 950 ° C Holding time at heating temperature: 180 seconds Cooling rate: 2, 5, 10, 15, 20, 30, and 40 ° C./s (heating temperature to room temperature) Further, in Table 1, the steel type No. Since the Cu content of A was at the level of unavoidable impurities (less than 0.01% by mass), it was described as "-".
- the plate thickness of the overhanging molded portion A is the central portion of the steel part, a position 3.75 mm vertically away from the central portion (referred to as an intermediate portion), and a position 7.5 mm vertically away from the central portion (hem portion). ), Each of which was obtained. Then, using the above equation (1), the central portion of the steel part, the intermediate part and the thickness of the skirt portion and the plate thickness d 1 of the working portion, the thickness of the steel sheet before working the thickness of the non-working part B As d 0 , the strains at the center, middle and hem of the steel part were determined.
- the Vickers hardness was measured at three points (center part, middle part and hem part) of the overhanging molded part A and at the unprocessed part B.
- the measurement was carried out using a Vickers hardness tester under the conditions of a load of 1 kg and a holding time of 10 seconds.
- As for the measurement position when the plate thickness was d, three points of d / 4 from the surface of the steel part were measured in the plate thickness direction.
- FIG. 4 is a schematic cross-sectional view taken along line XX shown in FIG. 3, showing the hardness measurement position of the overhang molding portion A.
- the hardness measurement position of the non-processed portion B is not shown, three points of d / 4 from the surface of the steel part in the vertical and horizontal directions and the plate thickness direction of the non-processed portion B were measured.
- the average Vickers hardness values of the three points (center part, middle part and hem part) of the overhanging molded part A and the three points of the non-processed part B were adopted as the respective Vickers hardness.
- the temperature (° C.) (referred to as molding temperature), the overhang height (mm), the cooling rate during slow cooling (° C / sec), the slow cooling time (seconds), and the slow cooling time (seconds) from Production Example 1-2.
- Steel parts were manufactured by changing the average cooling rate (° C./sec) from the heating temperature to the Ms point ⁇ 50 ° C. (referred to as Production Examples 1-1 and 1-3 to 1-8). Then, the strain and Vickers hardness of each steel part were evaluated in the same manner as in the steel parts obtained in Production Example 1-2. The results are shown in Table 2. In Table 2, the underlined values indicate that the values are outside the scope of the first embodiment of the present invention.
- At least one of the central portion, the middle portion and the hem portion has a Vickers hardness of 20 HV or more lower than that of the non-processed portion, and the hardness of the non-processed portion is reduced. It was judged that the product having a value of 310 HV or more was a production example satisfying the standard as "locally softened high-strength steel parts". In a more preferable production example of the "locally softened" steel part, at least one of the central portion, the intermediate portion and the hem portion has a Vickers hardness of 40 HV or more lower than that of the unprocessed portion. A more preferable production example is one in which the Vickers hardness is reduced by 100 HV or more.
- a more preferable production example has a Vickers hardness of a non-processed portion of 400 HV or more, and a more preferable production example has a Vickers hardness of 500 HV or more. The same judgment is made in Examples 2 and 3 described later.
- Production Examples 1-1 to 1-4 in Table 2 are examples that satisfy all the requirements specified in the first embodiment of the present invention, and are more than a predetermined value by processing without local temperature control. It was possible to produce a high-strength steel part in which only the portion to which strain (0.5% or more in the first embodiment of the present invention) was applied was locally softened.
- Production Examples 1-5 to 1-8 in Table 2 are examples in which the requirements specified in the first embodiment of the present invention are not satisfied, and strains equal to or more than a predetermined value due to processing (in the first embodiment of the present invention, 0. It was not possible to produce locally softened high-strength steel parts in the portion to which 5% or more) was added.
- the forming temperature was 650 ° C. or 550 ° C., which was less than 675 ° C., so that the entire steel part including the non-processed portion was softened, and the locally softened high strength.
- the steel parts could not be manufactured.
- a second overhang molding was performed.
- the second overhang molding was performed by pressing a ⁇ 10 mm hemispherical punch from the direction opposite to the first overhang molding (that is, from the surface) against the portion where the first overhang molding was performed. ..
- the mixture was slowly cooled for 6 seconds at an average cooling rate of 6.7 ° C./sec.
- water cooling was performed to the Ms point (° C.) -50 ° C. (that is, 335 ° C.) so that the average cooling rate from 880 ° C. to 335 ° C. was 26.2 ° C./sec. Then it was allowed to cool to room temperature.
- the above is referred to as Production Example 2-1.
- the strain and Vickers hardness of the steel parts obtained in Production Example 2-1 were evaluated in the same manner as in Example 1.
- the strain was calculated using the above equation (2). Since the first overhang molding is performed in the same manner as in Production Example 1-2, it is assumed that the plate thickness after the first overhang molding is the same as that in Production Example 1-2, and the strain is strained. Is being calculated. The results are shown in Table 3. Since the second overhang molding was performed in the opposite direction to the first overhang molding, the second overhang height was set to a negative value.
- Production Example 2-1 in Table 3 is an example that satisfies all of the requirements specified in the first embodiment of the present invention, and is a strain of a predetermined value or more due to processing without local temperature control (implementation of the present invention).
- Reference numeral 3-33 is an example in which the requirements specified in the second embodiment of the present invention are not satisfied, and locally in a portion where a strain of a predetermined value or more (10% or more in the second embodiment of the present invention) is applied by processing. It was not possible to produce softened high-strength steel parts.
- Production Examples 3-1 to 3-3, 3-8, 3-10, 3-13 and 3-19 in Table 4 and Production Examples 3-33 in Table 5 are all in the central portion, the middle portion and the hem portion. Since the strain was less than 10%, it was not possible to produce locally softened high-strength steel parts.
- Production Examples 3-12 and 3-17 in Table 4 and Production Examples 3-28 and 3-29 in Table 5 have a slow cooling rate of more than 15 ° C./sec (that is, slow cooling) in the step of (d) holding or slow cooling. Since the time was less than 1 second), it was not possible to produce locally softened high-strength steel parts.
- the strain applied by processing is 8% in the central portion, which does not satisfy the strain of 10% or more specified in the second embodiment of the present invention, but is referred to as the non-processed portion.
- the difference in hardness was 20 HV or more. This is the part No. It is possible that manufacturing conditions other than strain (heating temperature, cooling rate, slow cooling time, etc.) were preferable conditions in the central portion of 3-18, but the details are unknown.
- a second overhang molding was performed.
- the second overhang molding was performed by pressing a ⁇ 10 mm hemispherical punch from the direction opposite to the first overhang molding (that is, from the surface) against the portion where the first overhang molding was performed. ..
- the mixture was slowly cooled for 6 seconds at an average cooling rate of 5.3 ° C./sec.
- water cooling was performed to the Ms point (° C.) -50 ° C. (that is, 335 ° C.) so that the average cooling rate from 950 ° C. to 335 ° C. was 16.6 ° C./sec. Then it was allowed to cool to room temperature.
- the above is referred to as Production Example 4-1.
- the strain and Vickers hardness of the steel parts obtained in Production Example 4-1 were evaluated in the same manner as in Example 1.
- the strain was calculated using the above equation (2).
- the plate thickness of the central portion was 1.39 mm
- the plate thickness of the intermediate portion was 1.22 mm
- the plate thickness of the hem portion was 1.58 mm. Since it was confirmed separately, the strain is calculated by using these plate thicknesses as the plate thickness after the first overhang molding in Production Example 4-1.
- the results are shown in Table 6. Since the second overhang molding was performed in the opposite direction to the first overhang molding, the second overhang height was set to a negative value.
- Production Example 4-1 in Table 6 is an example that satisfies all of the requirements specified in the second embodiment of the present invention, and is a strain equal to or more than a predetermined value due to processing without local temperature control (implementation of the present invention).
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Abstract
Description
C :0.05~0.40質量%、
Si:0~2.0質量%、
Mn:1.0~3.0質量%、
Al:0.010~1.0質量%、
P:0質量%超0.100質量%以下、
S:0質量%超0.010質量%以下、
N:0質量%超0.010質量%以下、
B :0.0005~0.010質量%、および
残部:鉄および不可避不純物
からなる化学組成の鋼板を用意する工程と、
前記鋼板をAc1点(℃)以上Ac3点(℃)+10℃未満の温度に加熱する工程と、
前記加熱する工程後、675℃以上Ac3点(℃)+10℃未満の加工温度で、ひずみを0.5%以上加える加工工程と、
前記加工工程後、前記加工温度で1秒以上120秒以下保持するか、または0℃/秒超15℃/秒以下の平均冷却速度で1秒以上120秒以下徐冷する工程と、
前記保持または徐冷する工程後、Ms点(℃)-50℃まで冷却する工程と、を含み、
前記加熱する工程の前記温度から、Ms点(℃)-50℃までの平均冷却速度を10℃/秒以上に制御する、鋼部品の製造方法である。
C :0.05~0.40質量%、
Si:0~2.0質量%、
Mn:1.0~3.0質量%、
Al:0.010~1.0質量%、
P:0質量%超0.100質量%以下、
S:0質量%超0.010質量%以下、
N:0質量%超0.010質量%以下、
B :0.0005~0.010質量%、および
残部:鉄および不可避不純物
からなる化学組成の鋼板を用意する工程と、
前記鋼板をAc3点(℃)+10℃以上1100℃以下の温度に加熱する工程と、
前記加熱する工程後、Ms点(℃)+50℃以上Ac3点(℃)+10℃未満の加工温度でひずみを10%以上加える加工工程と、
前記加工工程後、前記加工温度で1秒以上120秒以下保持するか、または0℃/秒超15℃/秒以下の平均冷却速度で1秒以上120秒以下徐冷する工程と、
前記保持または徐冷する工程後、Ms点(℃)-50℃まで冷却する工程と、を含み、
前記加熱する工程における前記温度から、Ms点(℃)-50℃までの平均冷却速度を10℃/秒以上に制御する、鋼部品の製造方法である。
Cu:0質量%超0.50質量%以下、および
Ni:0質量%超0.50質量%以下
よりなる群から選択される一種以上を更に含有する態様1または2に記載の製造方法である。
Ti:0質量%超0.10質量%以下、
Cr:0質量%超3.0質量%以下、および
Nb:0質量%超0.10質量%以下
よりなる群から選択される一種以上を更に含有する態様1~3のいずれか1つに記載の製造方法である。
なお、本明細書において、「鋼部品」とは、本発明の実施形態1および2の加工する工程により所定形状に加工された鋼板のことをいう。
本発明の実施形態1に係る製造方法は、
(a)鋼板を用意する工程と、
(b)工程(a)の後、加熱する工程と、
(c)工程(b)の後、加工する工程と、
(d)工程(c)の後、保持または徐冷する工程と、
(e)工程(d)の後、冷却する工程と、
を含む。
以下、各工程について説明する。
本発明の実施形態1に係る鋼板の化学組成は、C:0.05~0.40質量%、Si:0~2.0質量%、Mn:1.0~3.0質量%、Al:0.010~1.0質量%、P:0質量%超0.100質量%以下、S:0質量%超0.010質量%以下、N:0質量%超0.010質量%以下、B:0.0005~0.010質量%、および残部:鉄および不可避不純物からなる。
以下、各元素について詳述する。
C含有量は、鋼部品の強度を決定する。鋼部品の十分な強度を得るために、C含有量は0.05質量%以上であり、好ましくは0.10質量%以上であり、より好ましくは、0.20質量%以上である。
Siは任意で鋼板に含まれる元素である。Siは焼戻し軟化抵抗を高めることにより、鋼板の硬度安定性に寄与する。そのため、Siは鋼板に0質量%超で含まれていることが好ましい。
Mnは、鋼板の焼入れ性を高めることにより鋼部品の高強度化に寄与する。この効果を発揮させるために、Mn含有量は、1.0質量%以上とし、好ましくは1.2質量%以上であり、より好ましくは1.4質量%以上である。
Alは、脱酸剤として作用する元素である。こうした効果を発揮させるために、Al量は、0.010質量%以上とする。Al量は、好ましくは0.020質量%以上、より好ましくは0.025質量%以上である。しかしながら、Alを過剰に含有させることは、製造上のコストアップに繋がると共に、Ac3点を著しく高め、素材加熱温度の高温化による表面品質の悪化(脱炭や減肉)を引き起こす。そのため、Al量は1.0質量%以下とする。Al量は、好ましくは0.80質量%以下であり、より好ましくは0.70質量%以下である。
Pは、不可避的に含有する元素であり、鋼板の溶接性を劣化させる元素であるが、フェライト相の固溶強化に寄与する効果を有する元素でもある。このような効果を発揮させつつ鋼板の溶接性を劣化させないためには、P量は0.100質量%以下とする。P量は、好ましくは0.050質量%以下であり、より好ましくは0.020質量%以下である。なお、Pは鋼中に不可避的に混入してくる不純物であり、その量を0質量%にすることは工業生産上不可能であり、通常0質量%超、さらには0.00050質量%以上で含有し得る。
Sは、不可避的に含有する元素であり、鋼板の溶接性を劣化させる。したがって、S量は0.010質量%以下とする。S量は、好ましくは0.0080質量%以下であり、より好ましくは0.0050質量%以下である。S量は、できるだけ少ない方が良いため、下限は特に限定されないが、その量を0質量%にすることは工業生産上不可能であり、通常0質量%超、さらには0.00010質量%以上で含有し得る。
Nは、不可避的に含有する元素であり、過剰に含まれるとAlNを生成させ、Alによる脱酸効果を低減させる。したがって、N量は0.010質量%以下とする。N量は、好ましくは0.0080質量%以下であり、より好ましくは0.0050質量%以下である。N量は、できるだけ少ない方が良いため、下限は特に限定されないが、その量を0質量%にすることは工業生産上不可能であり、通常0質量%超、さらには0.00010質量%以上で含有し得る。
Bは、鋼板の焼入れ性を高めることにより鋼部品の高強度化に寄与する。この効果を発揮させるために、B含有量は、0.0005質量%以上とし、好ましくは0.0010質量%以上であり、より好ましくは0.0015質量%以上である。
好ましい1つの実施形態では、残部は鉄および不可避不純物である。不可避不純物は、原料、資材、製造設備等の状況によって持ち込まれる元素である。
なお、例えば、P、SおよびNのように、通常、含有量が少ないほど好ましく、従って不可避不純物であるが、その組成範囲について上記のように別途規定している元素がある。このため、本明細書において、残部を構成する「不可避不純物」という場合は、別途その組成範囲が規定されている元素を除いた概念である。
Cuを含むことにより、鋼板自体の耐食性が向上するため、鋼板の腐食による水素発生を抑制し、耐遅れ破壊性を改善することができる。またCuは、大気中で生成する錆の中でも熱力学的に安定で保護性があるといわれている酸化鉄:α-FeOOHの生成を促進する効果も有している。当該錆の生成促進を図ることで、発生した水素の鋼板への侵入を抑制でき、過酷な腐食環境下において水素による助長割れを抑制することができる。そのため、Cu含有量は0質量%超とすることが好ましく、より好ましくは0.05質量%以上であり、さらに好ましくは0.10質量%以上である。一方、Cu含有量が過剰になると、鋼板製造時のめっき工程でのめっき性およびホットスタンプ後の化成処理性が劣化する。そのため、Cu含有量は0.50質量%以下とすることが好ましい。
NiもCuと同様の効果があることが知られている。そのため、Ni含有量も0質量%超とすることが好ましく、より好ましくは0.05質量%以上であり、さらに好ましくは0.10質量%以上である。一方、Ni含有量は0.50質量%以下とすることが好ましい。
Tiは、TiNを生成することにより鋼板中におけるBNの生成量を少なくする。これにより、鋼板中における固溶Bの量が増加し、Bによる焼入れ性向上の効果を高めることができる。この効果を発揮させるために、Ti含有量は、0質量%超とすることが好ましく、より好ましくは0.0050質量%以上であり、さらに好ましくは0.0250質量%以上、0.050質量%以上である。
一方、鋼板中にTiが過剰に含まれると、結晶粒界に炭化物が析出し、鋼板の焼入れ性が劣化する。このため、Ti含有量は、0.10質量%以下とすることが好ましく、より好ましくは0.080質量%以下であり、さらに好ましくは0.070質量%以下である。
一方、鋼板中にCrが過剰に含まれると、鋼板の割れ等を引き起こすおそれがあり、Cr含有量は、3.0質量%以下とすることが好ましく、より好ましくは2.5質量%以下であり、さらに好ましくは2.0質量%以下である。
一方、鋼板の組織が微細化することで、熱処理時の逆変態は促進されるものの、冷却中にフェライト生成を促進し、鋼部品の強度低下を招き得る。このような効果は、その含有量が増加するにつれて大きくなる。また、冷間圧延性が悪化するという不都合も生じる。こうした観点から、Nbは0.10質量%以下で含有させることが好ましい。好ましくは、0.070質量%以下であり、より好ましくは0.050質量%以下である。
本発明の実施形態1では、上記鋼板をAc1点(℃)以上Ac3点(℃)+10℃未満に加熱する。
Ac1点未満では、オーステナイト変態が起きず、後述する(e)冷却する工程後に高強度鋼部品とすることが困難となる。一方、Ac3点+10℃未満にしておくことで、後述する(c)加工する工程において、軟質組織であるフェライトおよび/またはパーライトの核生成を促進しやすくなる。
上記の(b)加熱する工程後、675℃以上Ac3点+10℃未満の温度でひずみを0.5%以上加える加工を行う。
上記のような温度では、鋼板中に、軟質組織であるフェライトおよび/またはパーライトの核生成サイトである結晶粒界が多く存在し得る。このような不安定な状態で、若干の(すなわち0.5%以上の)ひずみを加えることで、当該ひずみを加えた部分に、軟質組織であるフェライトおよび/またはパーライトの核生成を顕著に促進することができる。より好ましくは、5.0%以上のひずみを加えることであり、さらに好ましくは9.0%以上のひずみを加えることである。
なお、ひずみは下記式(1)により計算され得る。
ひずみ(%)=|(d0-d1)/d0×100| ・・・(1)
d0は加工前の鋼板の板厚または加工後の鋼板における非加工部分の板厚であり、d1は加工後の鋼板のうち加工部分の板厚である。いずれも単位はmmである。
なお、ひずみは、例えばFEM解析により求めた相当塑性ひずみとしてもよい。すなわち、FEM解析で求めた相当塑性ひずみが0.5%以上であれば、同様に軟化させることができる。
上記(b)加熱する工程の加熱温度をAc1点(℃)以上Ac3点(℃)+10℃未満とした上で、加工温度をAc3点+10℃以上とすると、軟質組織の核生成サイトである結晶粒界が少なくなり、若干のひずみを加えるだけでは、軟質組織の核生成を促進することができなくなる。
上記の(c)加工する工程後、0~15℃/秒の平均冷却速度で1秒以上120秒以下保持または徐冷する。すなわち、上記加工温度で1秒以上120秒以下保持するか、0℃/秒超15℃/秒以下の平均冷却速度で1秒以上120秒以下徐冷する。これにより、上記の(c)加工する工程で核生成された、軟質組織であるフェライトおよび/またはパーライトを成長させることができる。
一方、保持または徐冷する時間が120秒超だと、非加工部分においても軟質組織であるフェライトおよび/またはパーライトが析出および成長してしまい、高強度鋼部品を得ることができない。好ましくは12秒以下である。
上記の(d)保持または徐冷する工程後、Ms点(℃)-50℃まで冷却する。この際、上記(b)加熱する工程の加熱温度(すなわち、Ac1点(℃)以上Ac3点(℃)+10℃以下)から、Ms点(℃)-50℃までの平均冷却速度を10℃/秒以上に制御する。これにより、少なくとも非加工部分において、マルテンサイト変態を起こすことができ、非加工部分の強度を十分に確保できる。平均冷却速度10℃/秒以上の冷却をMs点(℃)-50℃超で終了させてしまうと、非加工部分において十分にマルテンサイト変態を起こすことができない。また、平均冷却速度が10℃/秒未満であっても、非加工部分において十分にマルテンサイト変態を起こすことができない。
本発明の実施形態2に係る製造方法は、本発明の実施形態1に係る製造方法と比較して、(b)加熱する工程および(c)加工する工程の条件が異なる。以下、本発明の実施形態1とは異なるそれらの工程を、(b’)加熱する工程および(c’)加工する工程として以下に説明する。
本発明の実施形態2では、前記鋼板をAc3点(℃)+10℃以上1100℃以下に加熱する。本発明の実施形態1とは異なり、加熱する工程においてAc3点+10℃以上に加熱しても、後述する(c’)加工する工程で比較的大きなひずみを加えれば、本発明の実施形態1と同様に、軟質組織であるフェライトおよび/またはパーライトの核生成を顕著に促進できる。一方、1100℃超だと鋼表面の脱炭が顕著になり狙いの強度が確保できなくなる。また、酸化が進み減肉する可能性もある。めっき材であれば、酸化や合金化が進み、めっきの硬度が高くなりすぎて後の加工工程で剥離してしまう(鋼板の酸化、押しキズ)などの問題が生じる。
上記の(b’)加熱する工程後、Ms点(℃)+50℃以上Ac3点(℃)+10℃未満の温度でひずみを10%以上加える加工を行う。Ms点(℃)+50℃以上Ac3点(℃)+10℃未満では、オーステナイトが比較的不安定な状態となるため、比較的大きな(10%以上の)ひずみを加えることで、当該ひずみを加えた部分に、軟質組織であるフェライトおよび/またはパーライトの核生成を顕著に促進することができる。より好ましくは、15%以上のひずみを加えることであり、さらに好ましくは40%以上のひずみを加えることである。なお、ひずみは上記式(1)により計算され得る。また、ひずみは、例えばFEM解析により求めた相当塑性ひずみとしてもよい。すなわち、FEM解析で求めた相当塑性ひずみが10%以上であれば、同様に軟化させることができる。
上記(c)および(c’)の加工する工程におけるひずみを、複数回の加工により加える場合、複数回の加工によるひずみは、下記式(2)のように計算され得る。
なお、上記Ac1点、Ac3点およびMs点は、フォーマスタ試験により求めた。フォーマスタ試験は、以下の条件で行った。
フォーマスタ試験機:富士電波工機製FTM-10
試験片サイズ:板厚2.0mm×幅3.0mm×長さ10mm(ただし、熱電対を挿入するため、Φ0.7mm×深さ2.0mmの穴2箇所あり)
試験回数:7回(冷却速度のみ変更し、他は一定条件)
加熱速度:10℃/s(室温~加熱温度)
加熱温度:950℃
加熱温度での保持時間:180秒
冷却速度:2、5、10、15、20、30、および40℃/s(加熱温度~室温)
また、表1において、鋼種No.AのCu含有量は、不可避不純物レベル(0.01質量%未満)であったため、「-」と記載した。
張出成形部Aの板厚は、鋼部品の中央部、中央部から縦方向に3.75mm離れた位置(中間部と称する)、中央部から縦方向に7.5mm離れた位置(裾部と称する)においてそれぞれ求めた。そして、上記式(1)を用いて、鋼部品の中央部、中間部および裾部の板厚を加工部分の板厚d1とし、非加工部Bの板厚を加工前の鋼板の板厚d0として、鋼部品の中央部、中間部および裾部のひずみを求めた。
非加工部Bの硬度測定位置については図示していないが、非加工部Bの縦および横方向における略中央、且つ板厚方向における鋼部品表面からd/4の位置を3点測定した。
なお、表2において、下線を付した数値は本発明の実施形態1の範囲から外れていることを示す。
なお、「局所的に軟化された」鋼部品として、より好ましい製造例は、中央部、中間部および裾部の少なくとも1つが、非加工部のビッカース硬度と比較して、40HV以上ビッカース硬度が低下したものであり、さらに好ましい製造例は、100HV以上ビッカース硬度が低下したものである。
また、「高強度鋼部品」として、より好ましい製造例は、非加工部のビッカース硬度が、400HV以上であり、さらに好ましい製造例は、500HV以上である。
後述する実施例2および3においても同様に判断している。
一方、表2の製造例1-5~1-8は、本発明の実施形態1で規定する要件を満たしていない例であり、加工により所定以上のひずみ(本発明の実施形態1では0.5%以上)を加えた部分において、局所的に軟化された高強度鋼部品を製造することができなかった。
なお、表4および表5において、下線を付した数値は本発明の実施形態2の範囲から外れていることを示す。
2 中央部における硬度測定1箇所目
3 中央部における硬度測定2箇所目
4 中央部における硬度測定3箇所目
5 中間部における硬度測定1箇所目
6 中間部における硬度測定2箇所目
7 中間部における硬度測定3箇所目
8 裾部における硬度測定1箇所目
9 裾部における硬度測定2箇所目
10 裾部における硬度測定3箇所目
A 張出成形部
B 非加工部
Claims (10)
- C :0.05~0.40質量%、
Si:0~2.0質量%、
Mn:1.0~3.0質量%、
Al:0.010~1.0質量%、
P:0質量%超0.100質量%以下、
S:0質量%超0.010質量%以下、
N:0質量%超0.010質量%以下、
B :0.0005~0.010質量%、および
残部:鉄および不可避不純物
からなる化学組成の鋼板を用意する工程と、
前記鋼板をAc1点(℃)以上Ac3点(℃)+10℃未満の温度に加熱する工程と、
前記加熱する工程後、675℃以上Ac3点(℃)+10℃未満の加工温度でひずみを0.5%以上加える加工工程と、
前記加工工程後、前記加工温度で1秒以上120秒以下保持するか、または0℃/秒超15℃/秒以下の平均冷却速度で1秒以上120秒以下徐冷する工程と、
前記保持または徐冷する工程後、Ms点(℃)-50℃まで冷却する工程とを含み、
前記加熱する工程の前記温度から、Ms点(℃)-50℃までの平均冷却速度を10℃/秒以上に制御する、鋼部品の製造方法。 - C :0.05~0.40質量%、
Si:0~2.0質量%、
Mn:1.0~3.0質量%、
Al:0.010~1.0質量%、
P :0質量%超0.100質量%以下、
S :0質量%超0.010質量%以下、
N :0質量%超0.010質量%以下、
B :0.0005~0.010質量%、および
残部:鉄および不可避不純物
からなる化学組成の鋼板を用意する工程と、
前記鋼板をAc3点(℃)+10℃以上1100℃以下の温度に加熱する工程と、
前記加熱する工程後、Ms点(℃)+50℃以上Ac3点(℃)+10℃未満の加工温度でひずみを10%以上加える加工工程と、
前記加工工程後、前記加工温度で1秒以上120秒以下保持するか、または0℃/秒超15℃/秒以下の平均冷却速度で1秒以上120秒以下徐冷する工程と、
前記保持または徐冷する工程後、Ms点(℃)-50℃まで冷却する工程とを含み、
前記加熱する工程の前記温度から、Ms点(℃)-50℃までの平均冷却速度を10℃/秒以上に制御する、鋼部品の製造方法。 - 以下の(a)および(b)のうち少なくとも1つをさらに含有する請求項1に記載の製造方法。
(a)Cu:0質量%超0.50質量%以下、およびNi:0質量%超0.50質量%以下よりなる群から選択される一種以上
(b)Ti:0質量%超0.10質量%以下、Cr:0質量%超3.0質量%以下、およびNb:0質量%超0.10質量%以下よりなる群から選択される一種以上 - 以下の(a)および(b)のうち少なくとも1つをさらに含有する請求項2に記載の製造方法。
(a)Cu:0質量%超0.50質量%以下、およびNi:0質量%超0.50質量%以下よりなる群から選択される一種以上
(b)Ti:0質量%超0.10質量%以下、Cr:0質量%超3.0質量%以下、およびNb:0質量%超0.10質量%以下よりなる群から選択される一種以上 - 張り出し成形により前記ひずみを加えることを含む、請求項1~4のいずれか一項に記載の製造方法。
- 鍛造により前記ひずみを加えることを含む、請求項1~4のいずれか一項に記載の製造方法。
- ドロー成形時の曲げ戻しにより前記ひずみを加えることを含む、請求項1~4のいずれか一項に記載の製造方法。
- せん断加工により前記ひずみを加えることを含む、請求項1~4のいずれか一項に記載の製造方法。
- 複数回の加工により前記ひずみを加えることを含む、請求項1~4のいずれか一項に記載の製造方法。
- 前記複数回の加工は、変形を加える加工と、前記変形を戻すように行う加工とを含む請求項9に記載の製造方法。
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EP21768018.0A EP4116003A4 (en) | 2020-03-11 | 2021-01-15 | PROCESS FOR MANUFACTURING A STEEL COMPONENT WITH LOCALLY SOFTENED SECTION |
CA3169085A CA3169085C (en) | 2020-03-11 | 2021-01-15 | Method for producing steel component having locally softened part |
MX2022011132A MX2022011132A (es) | 2020-03-11 | 2021-01-15 | Metodo para producir componente de acero con pieza ablandada localmente. |
KR1020227033512A KR20220145896A (ko) | 2020-03-11 | 2021-01-15 | 국소적으로 연화된 부분을 갖는 강 부품의 제조 방법 |
US17/905,221 US20230138493A1 (en) | 2020-03-11 | 2021-01-15 | Method for producing steel component having locally softened part |
CN202180019095.XA CN115279927A (zh) | 2020-03-11 | 2021-01-15 | 具有局部软化部分的钢零件的制造方法 |
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CA3169085C (en) | 2024-04-16 |
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CA3169085A1 (en) | 2021-09-16 |
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US20230138493A1 (en) | 2023-05-04 |
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