WO2015152263A1 - ホットスタンプ鋼材 - Google Patents
ホットスタンプ鋼材 Download PDFInfo
- Publication number
- WO2015152263A1 WO2015152263A1 PCT/JP2015/060185 JP2015060185W WO2015152263A1 WO 2015152263 A1 WO2015152263 A1 WO 2015152263A1 JP 2015060185 W JP2015060185 W JP 2015060185W WO 2015152263 A1 WO2015152263 A1 WO 2015152263A1
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- Prior art keywords
- layer
- hot
- solid solution
- steel
- steel material
- Prior art date
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 238
- 239000010959 steel Substances 0.000 title claims abstract description 238
- 239000000463 material Substances 0.000 title claims abstract description 148
- 239000010410 layer Substances 0.000 claims abstract description 239
- 239000006104 solid solution Substances 0.000 claims abstract description 86
- 238000010791 quenching Methods 0.000 claims abstract description 39
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 23
- 239000002344 surface layer Substances 0.000 claims abstract description 13
- 229910052742 iron Inorganic materials 0.000 claims abstract description 7
- 238000005496 tempering Methods 0.000 claims description 67
- 230000000171 quenching effect Effects 0.000 claims description 37
- 238000010438 heat treatment Methods 0.000 claims description 34
- 241000446313 Lamella Species 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 9
- 238000003825 pressing Methods 0.000 claims description 6
- 238000012545 processing Methods 0.000 claims description 4
- 239000011701 zinc Substances 0.000 abstract description 80
- 238000007747 plating Methods 0.000 abstract description 34
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 abstract description 17
- 239000012071 phase Substances 0.000 description 66
- 238000000034 method Methods 0.000 description 46
- 238000012360 testing method Methods 0.000 description 38
- 229910019142 PO4 Inorganic materials 0.000 description 32
- 239000010452 phosphate Substances 0.000 description 32
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 32
- 239000000126 substance Substances 0.000 description 24
- 239000000203 mixture Substances 0.000 description 21
- 230000000694 effects Effects 0.000 description 20
- 229910000734 martensite Inorganic materials 0.000 description 19
- 238000004519 manufacturing process Methods 0.000 description 17
- 238000005259 measurement Methods 0.000 description 12
- 238000005246 galvanizing Methods 0.000 description 11
- 238000001878 scanning electron micrograph Methods 0.000 description 11
- 238000002791 soaking Methods 0.000 description 10
- 238000010521 absorption reaction Methods 0.000 description 9
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 9
- 239000003921 oil Substances 0.000 description 9
- 230000035939 shock Effects 0.000 description 9
- 239000010936 titanium Substances 0.000 description 9
- 230000009466 transformation Effects 0.000 description 9
- 239000011651 chromium Substances 0.000 description 8
- 239000011572 manganese Substances 0.000 description 8
- 229910001566 austenite Inorganic materials 0.000 description 7
- 239000012535 impurity Substances 0.000 description 7
- 239000010955 niobium Substances 0.000 description 7
- 238000007545 Vickers hardness test Methods 0.000 description 6
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 6
- 238000005275 alloying Methods 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 6
- 238000001816 cooling Methods 0.000 description 6
- 238000009792 diffusion process Methods 0.000 description 6
- 238000005191 phase separation Methods 0.000 description 6
- 229920006395 saturated elastomer Polymers 0.000 description 6
- 239000010960 cold rolled steel Substances 0.000 description 5
- 239000013078 crystal Substances 0.000 description 5
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 4
- 238000005260 corrosion Methods 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 238000005554 pickling Methods 0.000 description 4
- 230000002265 prevention Effects 0.000 description 4
- 229910001335 Galvanized steel Inorganic materials 0.000 description 3
- 229910052796 boron Inorganic materials 0.000 description 3
- 238000004453 electron probe microanalysis Methods 0.000 description 3
- 239000008397 galvanized steel Substances 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 238000010008 shearing Methods 0.000 description 3
- 239000002436 steel type Substances 0.000 description 3
- 239000011787 zinc oxide Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000005097 cold rolling Methods 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000010894 electron beam technology Methods 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
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- 239000012847 fine chemical Substances 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 229910000765 intermetallic Inorganic materials 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 238000010587 phase diagram Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229910002056 binary alloy Inorganic materials 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000003750 conditioning effect Effects 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 238000005244 galvannealing Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
- 238000010422 painting Methods 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000003449 preventive effect Effects 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- LRXTYHSAJDENHV-UHFFFAOYSA-H zinc phosphate Chemical compound [Zn+2].[Zn+2].[Zn+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O LRXTYHSAJDENHV-UHFFFAOYSA-H 0.000 description 1
- 229910000165 zinc phosphate Inorganic materials 0.000 description 1
- NWONKYPBYAMBJT-UHFFFAOYSA-L zinc sulfate Chemical compound [Zn+2].[O-]S([O-])(=O)=O NWONKYPBYAMBJT-UHFFFAOYSA-L 0.000 description 1
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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
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
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- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
- C23C30/005—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process on hard metal substrates
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- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/22—Electroplating: Baths therefor from solutions of zinc
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D7/00—Electroplating characterised by the article coated
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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
- C21D2221/00—Treating localised areas of an article
- C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively
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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
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Definitions
- the present invention relates to a hot stamped steel material.
- Hot stamping is a method of rapidly cooling a steel sheet with a mold while pressing the steel sheet heated to AC3 or higher with a mold. That is, in hot stamping, pressing and quenching are performed simultaneously. According to the hot stamp, a structural member with high shape accuracy and high strength can be manufactured.
- Steel materials (hot stamp steel materials) manufactured by a manufacturing method including such a hot stamp are disclosed in Patent Document 1, Patent Document 2, and Patent Document 3, for example.
- the hot stamped steel materials disclosed in these patent documents are steel materials manufactured by performing hot stamping on a galvanized steel sheet in order to enhance corrosion resistance.
- hot stamping is performed at the same time as pressing.
- the hot stamp is suitable for manufacturing a structural member having high shape accuracy and high strength. Therefore, generally, the strength (tensile strength) of hot stamped steel is as high as about 1500 MPa or more.
- tensile strength tensile strength
- a material having a low strength is preferred in order to increase the shock absorption. It is known that the strength of a hot stamped steel material is changed to some extent by changing the alloy element amount of the steel plate and the hot stamping conditions.
- a hot stamping steel material having the same chemical composition as that of a hot stamping steel material that can obtain a strength of about 1500 MPa or more by quenching with a hot stamping has a corrosion resistance equivalent to or higher than that of a conventional steel, and has a strength of about 600 to 1450 MPa. Stamp steel is required.
- Patent Documents 1 to 3 described above do not disclose a method for reducing the strength of hot stamped steel without reducing corrosion resistance.
- the surface of hot stamped steel applied to automobile members is often painted.
- phosphatability is high.
- no technology has been reported so far for improving the phosphate treatment property of hot stamped steel having a galvanized layer.
- An object of the present invention is to provide a hot stamping steel material having a galvanized layer, which has higher shock absorption than conventional hot stamping steel materials having the same chemical composition and is excellent in phosphate treatment. .
- the gist of the present invention is as follows.
- a hot stamped steel material according to an aspect of the present invention is a position at a depth of 1 ⁇ 4 of the plate thickness from the surface layer when water quenching is performed after heating to a temperature of Ac3 point or higher and holding for 30 minutes.
- the Vickers hardness is defined as the maximum quenching hardness
- a base material that is a steel material including a tempered portion having a hardness of 85% or less of the maximum quenching hardness and the tempered portion of the base material is formed.
- a galvanized layer wherein the galvanized layer includes a solid solution layer composed of a solid solution phase containing Fe and Zn dissolved in the Fe, and a lamellar layer composed of the solid solution phase and a capital gamma phase,
- the area ratio of the lamella layer is 30% to 100%, and the area ratio of the solid solution layer is 0 to 70%.
- the area ratio of the lamellar layer in the galvanized layer may be 80% or more.
- the tempered portion may have a Vickers hardness of 180 to 450 Hv.
- the tempered portion may have a hardness of 65% or less of the maximum quenching hardness.
- the hot stamped steel material according to any one of the above (1) to (4) is subjected to simultaneous processing and quenching by press working using a mold after being heated to Ac 3 point or higher. And thereafter tempering at 500 ° C. to less than 700 ° C.
- a part of the base material may be the tempered portion.
- thermoforming steel material having a galvanized layer that has lower strength than conventional hot stamping steel materials having the same chemical composition and is excellent in phosphate treatment. it can.
- the present inventors examined a method for improving the impact absorbability and phosphate processability of a hot stamped steel material having a galvanized layer. As a result, the present inventors obtained the following knowledge.
- the present inventors examined the influence of the tempering temperature on the galvanized layer and the influence of the configuration of the galvanized layer on the phosphatability in the following manner.
- a plurality of steel plates having a thickness of 1.6 mm satisfying a preferable chemical composition described later were prepared.
- a galvanized layer was formed on these steel plates by a hot dip galvanizing method with an adhesion amount of 60 g / mm 2 .
- hot stamping was performed on the steel sheet on which the galvanized layer was formed. Specifically, the steel sheet was charged into a heating furnace whose furnace temperature was set to 900 ° C., which is a temperature equal to or higher than the AC3 point of the steel sheet, and heated for 4 minutes. At this time, the steel plate temperature reached 900 ° C. in about 2 minutes after charging into the furnace.
- hot stamping processing and quenching
- the cooling rate during hot stamping was 50 ° C./second or more up to the martensitic transformation start point even at a slow part.
- the martensitic transformation start (Ms) point can be determined by measuring the thermal expansion when the material heated to the austenitizing temperature is rapidly cooled and measuring the volume expansion from austenite to martensite.
- Tempering was performed on each manufactured hot stamping steel.
- the tempering temperature was different from each hot stamping steel material within the range of 150 ° C. to the Ac 1 point of the base material.
- the heating time for each hot stamped steel in tempering was 5 minutes.
- the A c1 point and the A c3 point indicate the austenite transformation start temperature and the austenite transformation end temperature when the steel material is heated, respectively.
- the A c1 point and the A c3 point can be determined by measuring the thermal expansion when the steel material is heated by a four master test or the like. Specifically, it can be determined by observing volumetric shrinkage upon transformation from ferrite to austenite.
- the martensitic transformation start point can be determined by measuring the thermal expansion when the steel material heated to the austenitizing temperature is rapidly cooled. Specifically, it can be determined by measuring the volume expansion from austenite to martensite.
- FIG. 1 is a photographic image of a galvanized layer of hot stamped steel and its surrounding cross-section when the tempering temperature is 400 ° C.
- FIG. 4 is an XRD measurement result from the surface of the cross section.
- FIG. 2 is a photographic image of a galvanized layer of hot stamped steel and its surrounding cross-section when the tempering temperature is 500 ° C.
- FIG. 5 shows XRD measurement results from the surface of the cross section.
- FIG. 3 is a photographic image of the galvanized layer of the hot stamped steel material and its surrounding cross-section when the tempering temperature is 700 ° C.
- FIG. 6 is an XRD measurement result from the surface of the cross section.
- the microstructure of the cross section was observed as follows. That is, the cross-sectional portion was etched with 5% night for 20 to 40 seconds, and after the etching, the microstructure was observed with a 2000 times SEM.
- the broken line L4 in FIGS. 4 to 6 indicates the intensity peak position of the ⁇ -Fe phase.
- a broken line L3 indicates an intensity peak position of a solid solution phase having a small solid solution Zn content (Zn content is 5 to 25% by mass, hereinafter may be referred to as a low Zn solid solution phase).
- a broken line L2 indicates an intensity peak position of a solid solution phase having a large amount of solid solution Zn (Zn content is 25 to 40% by mass, hereinafter may be referred to as a high Zn solid solution phase).
- a broken line L1 indicates the intensity peak position of the ⁇ phase. As the intensity peak position shifts from the broken line L4 to L2, the amount of Zn solid solution in the solid solution phase increases.
- the galvanized layer forms a solid solution layer 10, and this solid solution layer 10 has a high Zn solid solution phase whose intensity peak position is L 2.
- Reference numeral 20 in FIG. 1 is a tempered portion of the base material, and reference numeral 30 is a zinc oxide layer formed on the galvanized layer. Since zinc oxide is not in a metal state, it is not included in a part of the plating layer.
- this lamellar structure layer was a lamellar structure layer (hereinafter referred to as a lamellar layer) mainly composed of a ⁇ phase and a low Zn solid solution phase.
- the tempering temperature is 500 ° C.
- the galvanized layer is composed of a lamellar layer 40 having an area ratio of 30% or more and a solid solution layer having an area ratio of 0 to 70% (consisting of a high Zn solid solution phase). 10 and contained.
- the lamellar layer 40 was formed on the solid solution layer 10. That is, the lamellar layer was formed on the surface layer side of the galvanized layer rather than the solid solution layer.
- the tempering temperature was 600 ° C.
- the entire galvanized layer was substantially a lamellar layer.
- the galvanized layer was provided with a slight lamella layer 40 on the surface layer and the solid solution layer 10 under the lamella layer 40 (steel material side).
- the area ratio of the lamellar layer 40 in the galvanized layer was 20% or less.
- an intensity peak of the solid solution phase that was not detected when the tempering temperature was 500 ° C. to less than 700 ° C. position of the broken line L2 appeared.
- the intensity peak of the ⁇ phase (position of the broken line L1) was smaller than when the tempering temperature was 500 ° C. to less than 700 ° C.
- the structure of the galvanized layer changed based on the tempering conditions. Therefore, the phosphate treatment ability of hot stamped steel materials tempered at each tempering temperature was investigated. As a result, the present inventors have found that when the galvanized layer includes a lamellar layer having an area ratio of 30% or more, an excellent phosphate processability can be obtained.
- hot stamping steel according to an embodiment of the present invention (hereinafter, sometimes referred to as hot stamping steel according to the present embodiment) is heated to a temperature of Ac 3 point or higher and held for 30 minutes, followed by water quenching
- the base material is a steel material including a tempered portion having a hardness of 85% or less of the maximum quenching hardness And a galvanized layer formed on the tempered portion of the steel sheet.
- the galvanized layer includes a solid solution layer composed of a solid solution phase containing Fe and Zn dissolved in Fe, and a lamellar layer composed of the solid solution phase and a capital gamma phase.
- the area ratio of the lamellar layer is 30% to 100%, and the area ratio of the solid solution layer is 0 to 70%.
- the base material is a steel material, and is formed, for example, by hot stamping a steel plate.
- the base material includes a tempering portion.
- the tempered portion refers to a portion whose hardness (Vickers hardness) is 85% or less of the maximum quenching hardness of the steel material.
- the maximum quenching hardness means the Vickers hardness at a position of a depth of 1/4 of the plate thickness from the surface layer of the steel material when the steel material is heated to Ac 3 point or higher, held for 30 minutes, and then subjected to water quenching. To do.
- This maximum quenching hardness can be measured using another steel material having the same chemical composition (a steel material different from a hot stamped steel material having a tempered portion).
- the hot stamped steel material according to the present embodiment includes a tempered portion in which the base material has a hardness of 85% or less of the maximum quenching hardness, so that the hot stamped steel material has the same chemical composition and is not tempered. In comparison, the strength is low and the shock absorption is excellent.
- the hardness of the tempered portion is 65% or less of the maximum quenching hardness. In this case, the shock absorption is further excellent.
- Martensite has a high hardness and decreases in hardness when tempered. Therefore, it has a chemical composition that undergoes martensitic transformation when the base material is water-quenched, resulting in a hardness of 85% or less of the maximum quenching hardness.
- the tempering part which has can be easily provided. Therefore, the base material preferably has a chemical composition that undergoes martensitic transformation when water-quenched from a temperature of the Ac 3 point or higher.
- a tempering part contains 95% or more of tempered martensite by volume%, and less than 5 volume% retained austenite.
- the chemical composition of the base material need not be limited, but preferably has the following chemical composition, for example.
- the base material has such a chemical composition, it is advantageous to obtain mechanical properties suitable for use in automobile parts.
- “%” related to elements means mass%.
- Carbon (C) is an element that increases the strength of the steel material (hot stamp steel material) after hot stamping. If the C content is too low, the above effect cannot be obtained. Therefore, when obtaining this effect, the lower limit of the C content is preferably 0.05%. A more preferable lower limit of the C content is 0.10%. On the other hand, when C content is too high, the toughness of a steel plate will fall. Therefore, it is preferable that the upper limit of the C content is 0.4%. The upper limit with more preferable C content is 0.35%.
- Si 0.5% or less Silicon (Si) is an element inevitably contained in steel. Si also has the effect of deoxidizing steel. Therefore, the Si content may be 0.05% or more for the purpose of deoxidation. However, when the Si content is high, it has a function of increasing the AC3 point of the steel sheet. When the AC3 point of the steel plate rises, there is a concern that the heating temperature at the time of hot stamping exceeds the evaporation temperature of Zn plating. Further, Si in the steel diffuses during heating in the hot stamp, and an oxide is formed on the steel plate surface. This oxide may reduce the phosphate processability. When the Si content is more than 0.5%, the above problem becomes remarkable. Therefore, the upper limit of the Si content is preferably set to 0.5%. A more preferable upper limit of the Si content is 0.3%.
- Mn 0.5 to 2.5%
- Manganese (Mn) is an element that increases hardenability and increases the strength of hot stamped steel.
- the lower limit of the Mn content is preferably 0.5%.
- the minimum with preferable Mn content is 0.6%.
- the upper limit of the Mn content is preferably 2.5%.
- the upper limit with more preferable Mn content is 2.4%.
- Phosphorus (P) is an impurity contained in steel. P segregates at the grain boundaries and lowers the toughness and delayed fracture resistance of the steel. For this reason, the P content is preferably as low as possible. However, when the P content exceeds 0.03%, the influence becomes significant, so the P content may be 0.03% or less.
- S 0.010% or less Sulfur (S) is an impurity contained in steel. S forms sulfides and reduces the toughness and delayed fracture resistance of steel. For this reason, the S content is preferably as low as possible. However, when the S content exceeds 0.010%, the influence becomes significant, so the S content may be 0.010% or less.
- Al 0.10% or less
- Aluminum (Al) is an element effective for deoxidation of steel.
- the lower limit of the Al content may be 0.01%.
- the upper limit of the Al content is preferably 0.10%.
- a more preferable upper limit of the Al content is 0.05%.
- the Al content in this embodiment is sol.
- N 0.010% or less Nitrogen (N) is an impurity inevitably contained in steel. N is an element that forms nitrides and lowers the toughness of steel. Moreover, N combines with B and reduces the amount of solid solution B, when B contains. When the amount of solute B decreases, the hardenability decreases. For the above reasons, the N content is preferably as low as possible. However, when the N content exceeds 0.010%, the effect becomes significant, so the N content may be 0.010% or less. .
- the base material part of the hot stamped steel material according to the present embodiment may have a chemical composition including, for example, the above-described elements and the balance of Fe and impurities.
- the base material part of the hot stamped steel material according to the present embodiment is optionally replaced with a part of Fe having the above chemical composition for the purpose of improving the strength or toughness, B, Ti, Cr, Mo, One or more elements selected from Nb and Ni may be further contained within a range described later.
- an impurity means what mixes from the ore as a raw material, a scrap, or a manufacturing environment, when manufacturing steel materials industrially.
- B 0.0001 to 0.0050% Boron (B) increases the hardenability of steel and increases the strength of hot stamped steel.
- the preferable lower limit of the B content is 0.0001%.
- the upper limit of the B content is preferably 0.0050%.
- Ti 0.01 to 0.10% Titanium (Ti) combines with N to form nitride (TiN). As a result, the bond between B and N is suppressed, and a decrease in hardenability associated with BN formation can be suppressed. Moreover, Ti refines the austenite grain size at the time of hot stamping heating by the pinning effect, and improves the toughness of the steel material. When obtaining these effects, the preferable lower limit of the Ti content is 0.01%. However, if the Ti content is too high, the above effects are saturated, and Ti nitride is excessively precipitated to lower the toughness of the steel. Therefore, even when contained, the upper limit of the Ti content is preferably 0.10%.
- Chromium (Cr) increases the hardenability of the steel.
- the preferable lower limit of the Cr content is 0.1%.
- the upper limit of the Cr content is preferably 0.5%.
- Mo 0.05 to 0.50% Molybdenum (Mo) increases the hardenability of the steel.
- the preferable lower limit of the Mo content is 0.05%.
- the upper limit of the Mo content is preferably 0.50%.
- Niobium (Nb) forms carbides and refines crystal grains during hot stamping. As crystal grains become finer, the toughness of steel increases. When obtaining this effect, the preferable lower limit of the Nb content is 0.02%. However, if the Nb content is too high, the above effects are saturated and the hardenability is lowered. Therefore, even when contained, the upper limit of the Nb content is preferably 0.10%.
- Ni 0.1 to 1.0%
- Nickel (Ni) increases the toughness of the steel. Further, Ni suppresses embrittlement due to molten Zn during heating by hot stamping of a galvanized steel material.
- the preferred lower limit of the Ni content is 0.1%. However, if the Ni content is too high, the above effects are saturated and the cost is increased. Therefore, even when contained, the upper limit of the Ni content is preferably 1.0%.
- a part of the base material may be a tempering part, or the whole base material may be a tempering part.
- members called tailored properties that have different requirements for performance such as strength and ductility depending on the position.
- a skeleton member called a B pillar (center pillar) is required to have high strength in the upper part constituting the riding area and to have high shock absorption in the lower part.
- a member having both the high strength portion and the shock absorbing property as described above can be obtained.
- the hot stamped steel material has a galvanized layer, it is excellent in corrosion resistance.
- the tensile strength of the tempered portion of the base material is 600 to 1450 MPa, and the Vickers hardness is 180 to 450 Hv.
- the strength of the tempered portion of the hot stamped steel is lower than that of a conventional hot stamped steel that does not perform tempering. Therefore, it is excellent in shock absorption compared with the conventional hot stamping steel material.
- the Vickers hardness of tempered martensite is lower than the Vickers hardness of martensite. Therefore, it can be determined from the Vickers hardness whether or not the structure of the tempered portion is tempered martensite.
- the Vickers hardness can be determined by a Vickers hardness test based on JIS Z2244 (2009).
- the hot stamped steel material according to the present embodiment has a galvanized layer at least on the tempered portion of the base material.
- the galvanized layer includes a lamellar layer of 30% or more and a solid solution layer of 0 to 70% in terms of area ratio in the galvanized layer.
- the solid solution layer consists of a solid solution phase.
- the solid solution phase contains Fe and Zn dissolved in Fe.
- the Zn content in the solid solution layer is 25 to 40% by mass. More preferably, the Zn content in the solid solution layer is 30 to 40% by mass.
- the galvanized layer may not have a solid solution layer. That is, the galvanized layer may be composed only of a lamellar layer, and the area ratio of the solid solution layer may be 0%.
- the lamellar layer has a lamellar structure of a solid solution phase and a capital gamma ( ⁇ ) phase.
- the lamella structure is a structure in which different phases (in this embodiment, a solid solution phase and a ⁇ phase) are alternately repeated.
- the ⁇ phase is an intermetallic compound (Fe 3 Zn 10 ).
- the Zn content in the solid solution phase of the lamella layer is 5 to 25% by mass, which is lower than the Zn content in the solid solution layer.
- the lamellar layer is formed on the surface layer of the galvanized layer. That is, when a solid solution layer is present, the lamellar layer is formed on the solid solution layer.
- the lamellar layer is superior in phosphate treatment than the solid solution layer.
- the following can be considered as the reason.
- the lamellar layer has a lamellar structure of a solid solution phase (low Zn solid solution phase) and a ⁇ phase.
- the solid solution phase and the ⁇ phase extend in a direction substantially perpendicular to the surface of the base material.
- the lamellar layer is formed on the surface layer of the galvanized layer. Therefore, when the galvanized layer is observed from the cross section, both the solid solution phase and the ⁇ phase are observed on the surface layer.
- the surface of the galvanized layer that is, the lamella layer is etched by phosphoric acid.
- a portion having a high zinc concentration is preferentially etched.
- the Zn concentration in the ⁇ phase in the lamellar layer is higher than the Zn concentration in the solid solution phase, the ⁇ phase is preferentially etched over the solid solution phase by phosphoric acid. As a result, fine irregularities are formed on the surface of the galvanized layer, and phosphate easily adheres.
- the phosphatability of a galvanized layer having a lamellar layer as a surface layer is higher than that of a galvanized layer having only a solid solution layer as a surface layer. If the area ratio of the lamella layer in a galvanization layer is 30% or more, the phosphate processability of a galvanization layer will become high. Therefore, in the hot stamped steel material according to the present embodiment, the area ratio of the lamella layer in the galvanized layer needs to be 30% or more. Preferably, the area ratio of the lamellar layer is 80% or more. When the area ratio of the lamella layer is 80% or more, the phosphate treatment property is further improved. In addition, it is expected that the chemical conversion crystals become finer and the paint adhesion and the like are improved.
- the Zn content in the solid solution phase can be measured by the following method. That is, in the case of the Zn content in the high Zn solid solution phase, the Zn content (mass%) is measured by EPMA (electron beam microanalyzer) at any five locations in the high Zn solid solution phase, and the five Zn locations are measured. What is necessary is just to define the average of content as Zn content in a high Zn solid solution phase. Even in the low Zn solid solution phase, the Zn content can be determined by the same method as in the high Zn solid solution phase.
- EPMA electron beam microanalyzer
- the hot stamped steel material according to the present embodiment is not limited to the manufacturing method as long as it has the base material and the galvanized layer described above, and can exert its effects.
- the following steps for preparing a steel material as a base material base material preparation step
- a step for forming a galvanized layer on the base material zinc plating process step
- a base material provided with a galvanized layer base material provided with a galvanized layer
- it can manufacture by a manufacturing method provided with the process (hot stamp process) which implements a hot stamp, and the process (tempering process) which performs tempering with respect to hot stamped steel materials.
- hot stamp process which implements a hot stamp
- tempering process which performs tempering with respect to hot stamped steel materials.
- a steel plate used as a base material is prepared.
- molten steel having the above-described preferred range of chemical composition is produced.
- a slab is manufactured by a casting method such as continuous casting using the manufactured molten steel.
- an ingot may be manufactured by an ingot-making method using the manufactured molten steel.
- the manufactured slab or ingot is hot-rolled to manufacture a steel plate (hot rolled steel plate). If necessary, the hot-rolled steel sheet may be pickled, and the hot-rolled steel sheet after the pickling may be cold-rolled to obtain a steel sheet (cold-rolled steel sheet).
- hot rolling, pickling, and cold rolling what is necessary is just to perform by a well-known method according to the characteristic requested
- the above steel plate (hot rolled steel plate or cold rolled steel plate) is subjected to galvanizing treatment to form a galvanized layer on the surface of the steel plate.
- the method for forming the galvanized layer is not particularly limited, and may be a hot dip galvanizing process, an alloyed hot dip galvanizing process, or an electrogalvanizing process.
- the formation of the galvanized layer by the hot dip galvanizing process is performed, for example, in the following manner. That is, the steel sheet is immersed in a plating bath (hot dip galvanizing bath) to deposit the plating on the surface of the steel sheet.
- the steel plate with the plating attached is pulled up from the plating bath.
- the plating adhesion amount on the steel sheet surface is adjusted to 20 to 100 g / m 2 .
- the amount of plating can be adjusted by adjusting the pulling speed of the steel sheet and the flow rate of the wiping gas.
- the Al concentration in the hot dip galvanizing bath is not particularly limited.
- Formation of the galvanized layer by alloying hot dip galvanizing treatment (hereinafter also referred to as alloying treatment) is performed, for example, in the following manner. That is, the steel sheet on which the hot dip galvanized layer is formed is heated to 470 to 600 ° C. After heating, soaking is performed as necessary, and then cooled. The soaking time is preferably within 30 seconds, but is not limited. Moreover, it may cool, without performing soaking immediately after heating to the said heating temperature. The heating temperature and the soaking time are appropriately set according to the desired Fe concentration in the plating layer. A preferred lower limit of the heating temperature in the alloying treatment is 540 ° C.
- a hot stamping steel plate (GA) including a galvanized layer (alloyed galvanized layer) is manufactured.
- the formation of the galvanized layer by the electrogalvanizing process is performed, for example, in the following manner. That is, any of a well-known sulfuric acid bath, hydrochloric acid bath, zincate bath, cyan bath, etc. is prepared as an electrogalvanizing bath. The above steel plate is pickled and the steel plate after pickling is immersed in an electrogalvanizing bath. A current is passed through the electrogalvanizing bath with the steel plate as the cathode. Thereby, zinc precipitates on the steel sheet surface, and a galvanized layer (electrogalvanized layer) is formed. Through the above steps, a hot stamping steel plate (EG) including a galvanized layer (electrogalvanized layer) is produced.
- EG hot stamping steel plate
- the preferred amount of the galvanized layer is the same as that of the hot dip galvanized layer. That is, the preferable adhesion amount of these galvanized layers is 20 to 100 g / m 2 .
- These galvanized layers contain Zn.
- the chemical composition of the hot dip galvanized layer and the electrogalvanized layer is composed of Zn and impurities.
- the chemical composition of the alloyed hot-dip galvanized layer contains 5 to 20% Fe, and the balance consists of Zn and impurities.
- Hot stamping is performed on the steel sheet for hot stamping provided with the above-described galvanized layer.
- the heating before quenching in the hot stamping process it is preferable to perform heating mainly using radiant heat for heating.
- the hot stamping steel plate is charged into a heating furnace (a gas furnace, an electric furnace, an infrared furnace, or the like).
- the steel sheet for hot stamping is heated to AC 3 point to 950 ° C. and held at this temperature (soaking).
- Zn in the plating layer is liquefied, and by soaking, molten Zn and Fe in the plating layer are mutually diffused to form a solid solution phase (Fe—Zn solid solution phase).
- Hot stamping pressing and quenching
- a preferred soaking time is 0 to 10 minutes, a more preferred soaking time is 0 to 6 minutes, and a more preferred soaking time is 0 to 4 minutes.
- a steel plate is pressed using a mold in which a cooling medium (for example, water) is circulated.
- a cooling medium for example, water
- the steel plate is quenched by heat removal from the mold.
- the hot stamping steel material is manufactured by the above process.
- the steel material for hot stamping was heated using a heating furnace.
- the steel material for hot stamping may be heated by energization heating.
- the steel plate is soaked for a predetermined time by energization heating, and the molten Zn in the galvanized layer is turned into a solid solution phase. After the molten Zn in the galvanized layer becomes a solid solution phase, the steel sheet is pressed using a mold.
- Tempering is performed on hot stamped steel (steel after hot stamping).
- the tempering temperature is 500 ° C. to less than 700 ° C.
- the galvanized layer after tempering includes a lamellar layer having an area ratio of 30% or more. Further, when the microstructure of the base material after quenching is martensite, the microstructure of the base material after tempering becomes tempered martensite, and a tempered portion having a hardness of 85% or less of the maximum quenching hardness is obtained. .
- FIG. 7 is a binary phase diagram of Fe—Zn.
- the galvanized layer of hot stamped steel manufactured by hot stamping is composed of a solid solution phase in which about 25 to 40% by mass of Zn is dissolved in ⁇ -Fe.
- a structure that is, a lamellar layer
- the solid solution phase of the galvanized layer after hot stamping is a solid solution in which Zn is supersaturated.
- the Zn concentration in the galvanized layer is 35% by mass in FIG. 7 (corresponding to point A1 in the figure).
- the driving force for two-phase separation from the solid solution phase to the low Zn solid solution phase and the ⁇ phase is generated on the low temperature side from the point B on the boundary line Ax, and becomes stronger as the distance from the point B to the low temperature side increases.
- the diffusion rate in the galvanized layer increases as the temperature increases. Therefore, whether or not a lamellar layer is formed after tempering is determined by the relationship between the driving force for two-phase separation and the diffusion rate. Specifically, the lamellar layer is more easily formed as the driving force for two-phase separation is higher and the diffusion rate is higher.
- tempering temperature When the temperature in the galvanized layer during tempering (tempering temperature) is in a low temperature range (150 ° C. to less than 500 ° C.) (for example, point A1 at 300 ° C.), it is sufficiently far from the boundary line Ax (point B). In this case, the driving force for two-phase separation is high. However, because of the low temperature, the diffusion rate of Zn is too low. Therefore, even if tempering is performed, the galvanized layer is not separated into two phases, and a lamellar layer is not formed.
- the temperature range approaches the boundary line Ax (point B), but has a certain distance (for example, point A2 in the figure). In this case, a driving force for two-phase separation is generated to some extent. Furthermore, since the temperature range is higher than the low temperature range, the diffusion rate is high. As a result, the galvanized layer is separated into two phases to form a lamellar layer.
- a lamellar layer is formed by separating into a ⁇ phase (C2 in the figure) having a Zn content of about 70% by mass and a solid solution phase (C1 in the figure) having a Zn content of about 10% by mass. Is done.
- the tempering temperature further rises to 700 ° C. or higher, the temperature range exceeds the boundary line Ax or exceeds the boundary line Ax.
- the diffusion rate increases due to the temperature rise, the driving force for the two-phase separation is extremely small or no driving force is generated. As a result, separation into two phases hardly occurs, and the area ratio of the lamellar layer in the galvanized layer is less than 30%.
- the structure of the galvanized layer changes according to the tempering temperature.
- the tempering temperature 500 ° C. to less than 700 ° C.
- a lamellar layer having an area ratio of 30% or more can be formed in the galvanized layer. In this case, a high phosphate processability is obtained.
- Tempering can also be performed on only a portion of the hot stamped steel.
- tempering can be performed on a part of the hot stamped steel by induction heating using high frequency or energization heating.
- the strength of the same member can be changed between the part that has been tempered and the part that has not been tempered.
- Such a member can be applied to a member that is required to have high strength in the upper portion and high impact absorbability in the lower portion, such as a B pillar of an automobile. Even in the case of partial tempering, the tempering part is equivalent to the tempering part when the whole is tempered.
- a base material including a tempered portion having a hardness of 85% or less of the maximum quenching hardness and a galvanized layer is provided, and in the galvanized layer, the area of the lamella layer Hot stamped steel with a rate of 30% or more can be manufactured.
- the manufacturing method of the hot stamped steel material according to the present embodiment may further include the following steps.
- a rust-preventing oil film forming step may be further included between the galvanizing treatment step and the hot stamping step.
- a rust prevention oil film is formed by applying rust prevention oil to the surface of the steel material for hot stamping.
- the steel material for hot stamping may have a long period from when it is rolled to when the hot stamping process is performed. In that case, the surface of the steel material for hot stamping may be oxidized. According to this process, since the rust preventive oil film is formed on the surface of the steel material for hot stamping, the surface of the steel plate is hardly oxidized, and the generation of scale is suppressed.
- the above-described manufacturing method may further include a blanking process between the rust-preventing oil film forming process and the hot stamping process.
- the steel material for hot stamping is subjected to shearing and / or punching, etc., and formed into a specific shape (blanking).
- bladenking the shearing surface of the steel plate after blanking is easily oxidized, if a rust-preventing oil film is formed on the steel plate surface, the rust-preventing oil spreads to the shearing surface to some extent. Therefore, the oxidation of the steel plate after blanking is suppressed.
- a slab was manufactured by a continuous casting method using molten steel having chemical compositions A to G shown in Table 1, and the slab was hot-rolled to manufacture a hot-rolled steel sheet. After pickling the hot-rolled steel sheet, cold rolling was performed to produce a cold-rolled steel sheet having a thickness of 1.6 mm. The obtained cold-rolled steel sheet was used as a steel sheet used for manufacturing hot stamped steel.
- test number 6 a hot dip galvanized layer (GI) was formed on the steel sheet by hot dip galvanizing.
- the alloying process was further implemented with respect to the steel plate which has a hot dip galvanization layer, and the galvannealing layer (GA) was formed.
- the maximum temperatures were all about 530 ° C., heated for about 30 seconds, and then cooled to room temperature.
- the Fe content in the alloyed hot-dip galvanized layer was 12% by mass.
- the Fe content was obtained by the following measuring method. First, a steel plate sample including an alloyed hot dip galvanized layer was collected. The Fe content (% by mass) was measured with EPMA (electron beam microanalyzer) at any five locations in the alloyed hot-dip galvanized layer in the sample. The average value of the measured values was defined as the Fe content (% by mass) of the alloyed hot-dip galvanized layer with the test number.
- EPMA electron beam microanalyzer
- the adhesion amount of these plated layers was measured by the following method. First, a sample including a plating layer was collected from each steel plate, and the sample plating layer was dissolved with hydrochloric acid in accordance with JIS H0401. The plating adhesion amount (g / m 2 ) was determined based on the sample weight before dissolution, the sample weight after dissolution, and the area where the plating layer was formed. The measurement results are shown in the column “Adhesion amount” in Table 2.
- each steel plate was charged into a heating furnace whose furnace temperature was set to 900 ° C., which is a temperature equal to or higher than the AC 3 point of the steel plate, and radiant heat caused each of the AC 3 points or higher for each of the steels A to G.
- the mixture was heated at 900 ° C. for 4 minutes.
- the steel plate temperature reached 900 ° C. in about 2 to 2.5 minutes after charging in the furnace, and each steel plate was soaked at 900 ° C. for 1.5 to 2 minutes.
- hot stamped steel steel plate
- steel plate steel plate
- quenching was performed so that the cooling rate to the martensite transformation start point was 50 ° C./second or more even in the portion where the cooling rate during hot stamping was slow.
- tempering was performed on the steel materials of test numbers 1 to 13, 15 and 16 after hot stamping.
- each steel material was charged into a heat treatment furnace. That is, the whole steel material was tempered.
- Test No. 16 a current was partially passed by direct current heating and partially tempered.
- the tempering temperature for each test number was as shown in Table 2, and the heating time was 5 minutes when charged in the furnace, and 20 seconds for current heating. Tempering was not performed on the steel material of test number 14.
- hot stamped steel materials having test numbers 1 to 16 were produced. These test numbers 1 to 16 were subjected to a Vickers hardness test, observation of the microstructure of the galvanized layer, and a phosphate treatment evaluation test. About the hot stamped steel material of the test number which partially tempered, the tempered part was evaluated.
- the area ratio of the lamellar layer was further determined by the following method.
- the area ratio (%) of the solid solution layer and the area ratio (%) of the lamellar layer with respect to the entire area of the galvanized layer were obtained in any five visual fields (50 ⁇ m ⁇ 50 ⁇ m) in the cross section.
- the Zn oxide layer (reference numeral 30 in FIG. 1) that floats on the surface is not in a metal state and is not a plating layer, and thus was not included in the area of the galvanization layer.
- Table 2 shows the area ratio (%) of the obtained solid solution layer and lamella layer.
- the measurement by EPMA was performed by the above-mentioned method with respect to the solid solution layer observed by micro structure observation.
- the Zn content in the observed solid solution layer was 25 to 40% by mass.
- FIG. 8 is an SEM image (1000 times) of the surface of the hot stamped steel after the above-described phosphate treatment is performed on the hot stamped steel (test number 6) having a tempering temperature of 500 ° C.
- a binarization process was performed on the SEM image.
- FIG. 9 is an image obtained by binarizing the SEM image of FIG. In the binarized image, fine chemical crystals are formed in the white portion. The more fine chemical crystals, the higher the phosphate treatment ability. Therefore, the area ratio TR of the white portion was obtained using the binarized image. If the area ratio TR was 30% or more, it was judged that the phosphate treatment was excellent.
- Table 2 shows the area ratio TR obtained for each test number. “G” in the table is GOOD, and “NG” is NO GOOD.
- FIG. 10 is an SEM image (1000 times) of the surface of the hot stamped steel after the above-mentioned phosphate treatment is performed on the hot stamped steel having a tempering temperature of 400 ° C. (test number 10). It is the image which binarized FIG. FIG. 12 is an SEM image (1000 times) of the surface of the hot stamped steel after the above-mentioned phosphate treatment is performed on the hot stamped steel having a tempering temperature of 700 ° C. (test number 10). It is the image which binarized FIG.
- the microstructure of the hot stamped steels of test numbers 1 to 8 tempered at 500 to 650 ° C. is composed of tempered martensite, and the Vickers hardness is 180 to 450 HV. It was 85% or less of the hardness. That is, the hardness of the hot stamped steel materials of these test numbers was a hardness corresponding to a strength of 1450 MPa or less. Moreover, the hot stamped steel materials of these test numbers have an area ratio of the lamellar layer in the galvanized layer of 30% or more, and as a result, the area ratio TR in the phosphate treatment evaluation test is 30% or more. It was. That is, the hot stamped steel materials having test numbers 1 to 8 showed excellent impact absorbability and phosphatability.
- test numbers 9 to 13 the tempering temperature was less than 500 ° C. or 700 ° C. or more.
- the area ratio of the lamellar layer in the galvanized layer was less than 30%. Therefore, the area ratio TR in the phosphate treatability evaluation test was less than 30%, and the phosphate treatability was poor.
- Test No. 9 since the tempering temperature was low, the hardness of the base material did not fall below 85% of the maximum quenching hardness even after tempering.
- Test number 14 is an example in which tempering was not performed. Therefore, the microstructure of the base material was martensite (fresh martensite). Therefore, the Vickers hardness exceeded 450 HV and exceeded 85% of the maximum quenching hardness. Furthermore, the area ratio of the lamella layer in the galvanized layer was less than 30%, and the phosphate treatment ability was low.
- thermoforming a hot stamped steel material having a galvanized layer that has lower strength than conventional hot stamped steel materials having the same chemical composition and is excellent in phosphate treatment.
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Abstract
Description
本願は、2014年03月31日に、日本に出願された特願2014-073811号に基づき優先権を主張し、その内容をここに援用する。
このようなホットスタンプを含む製造方法で製造された鋼材(ホットスタンプ鋼材)は、たとえば、特許文献1、特許文献2及び特許文献3に開示されている。これらの特許文献に開示されるホットスタンプ鋼材は、耐食性を高めるために亜鉛めっきが施された鋼板に対してホットスタンプを実施して製造された鋼材である。
一般に、亜鉛めっき層を有する鋼材(亜鉛めっき鋼材)にホットスタンプを行うと、りん酸塩処理性が低下することが知られている。しかしながら、亜鉛めっき層を有するホットスタンプ鋼材のりん酸塩処理性を高める技術についてはこれまで報告されていない。
(1)本発明の一態様に係るホットスタンプ鋼材は、Ac3点以上の温度に加熱して30分間保持した後に水焼入れを実施した場合の表層から板厚の1/4の深さの位置におけるビッカース硬さを最高焼入れ硬さと定義した場合、前記最高焼入れ硬さの85%以下の硬さを有する焼戻し部を含む鋼材である母材と、前記母材の前記焼戻し部上に形成される亜鉛めっき層とを備え、前記亜鉛めっき層は、Fe及び前記Feに固溶したZnを含有する固溶体相からなる固溶体層と、前記固溶体相とキャピタルガンマ相とからなるラメラ層と、を含み、前記亜鉛めっき層において、前記ラメラ層の面積率が30%~100%であり、前記固溶体層の面積率が0~70%である。
(2)上記(1)に記載のホットスタンプ鋼材は、前記亜鉛めっき層中の、前記ラメラ層の面積率が80%以上であってもよい。
(3)上記(1)または(2)に記載のホットスタンプ鋼材は、前記焼戻し部のビッカース硬さが180~450Hvであってもよい。
(4)上記(1)~(3)のいずれか一項に記載のホットスタンプ鋼材は前記焼戻し部の硬さが、前記最高焼入れ硬さの65%以下であってもよい。
(5)上記(1)~(4)のいずれか一項に記載のホットスタンプ鋼材は、Ac3点以上に加熱された後、金型を用いたプレス加工によって加工と焼入れとが同時に施され、その後、500℃~700℃未満で焼き戻しされることによって製造される。
(6)上記(1)~(4)のいずれか一項に記載のホットスタンプ鋼材は前記母材のうちの一部が前記焼戻し部であってもよい。
マルテンサイト変態開始(Ms)点はオーステナイト化温度まで加熱した材料を急冷した際の熱膨張を測定し、オーステナイトからマルテンサイトへの体積膨張を測定することにより決定することが可能である。
図1は、焼戻し温度が400℃の場合のホットスタンプ鋼材の亜鉛めっき層及びその周辺の断面部の写真画像である。図4は、その断面部の表面からのXRD測定結果である。
図2は、焼戻し温度が500℃の場合のホットスタンプ鋼材の亜鉛めっき層及びその周辺の断面部の写真画像である。図5は、その断面部の表面からのXRD測定結果である。
図3は、焼戻し温度が700℃の場合のホットスタンプ鋼材の亜鉛めっき層及びその周辺の断面部の写真画像である。図6は、その断面部の表面からのXRD測定結果である。
また、XRD測定は、Co管球を用いて行った。XRDにおいて、α-Feの強度ピークは、回折角2θ=99.7°に現れ、Zn固溶量が多くなるほど、低角度側にシフトする。Fe3Zn10の金属間化合物であるキャピタルガンマ(Γ)の強度ピークは、回折角2θ=94.0°に現れる。図4~図6中の破線L4はα-Fe相の強度ピーク位置を示す。破線L3は固溶Zn量が少ない固溶体相(Zn含有量が5~25質量%、以下、低Zn固溶体相と言う場合がある)の強度ピーク位置を示す。破線L2は固溶Zn量が多い固溶体相(Zn含有量が25~40質量%、以下、高Zn固溶体相と言う場合がある)の強度ピーク位置を示す。破線L1はΓ相の強度ピーク位置を示す。強度ピーク位置が破線L4からL2にシフトするにしたがって、固溶体相中のZn固溶量が多くなる。
焼戻し温度が500℃~700℃未満の場合、いずれも、亜鉛めっき層は、面積率で30%以上のラメラ層40と、面積率で0~70%の固溶体層(高Zn固溶体相からなる)10とを含有していた。また、ラメラ層40は、固溶体層10上に形成されていた。つまり、ラメラ層は固溶体層よりも亜鉛めっき層の表層側に形成されていた。また、焼戻し温度が600℃の場合には、亜鉛めっき層全体が実質的にラメラ層であった。
以下、本実施形態に係るホットスタンプ鋼材について詳細に説明する。
母材は鋼材であり、たとえば鋼板をホットスタンプすることにより形成される。また、母材は焼戻し部を含む。焼戻し部とは、その硬さ(ビッカース硬さ)が、鋼材の最高焼入れ硬さの85%以下である部分を指す。最高焼入れ硬さとは、鋼材をAc3点以上に加熱し、30分間保持した後、水焼入れを実施した場合の鋼材の表層から板厚の1/4の深さの位置におけるビッカース硬さを意味する。この最高焼入れ硬さは同じ化学成分を有する他の鋼材(焼戻し部を有するホットスタンプ鋼材とは別の鋼材)を用いて測定することができる。
本実施形態に係るホットスタンプ鋼材は、母材が最高焼入れ硬さの85%以下の硬さを有する焼戻し部を含むことにより、同じ化学組成を有し、かつ、焼戻しを実施しないホットスタンプ鋼材と比較して、強度が低く、衝撃吸収性に優れる。好ましくは、焼戻し部の硬さは、最高焼入れ硬さの65%以下である。この場合、さらに衝撃吸収性に優れる。
炭素(C)は、ホットスタンプ後の鋼材(ホットスタンプ鋼材)の強度を高める元素である。C含有量が低すぎれば、上記効果が得られない。そのため、この効果を得る場合、C含有量の下限を0.05%とすることが好ましい。C含有量のより好ましい下限は0.10%である。一方、C含有量が高すぎると、鋼板の靭性が低下する。したがって、C含有量の上限を0.4%とすることが好ましい。C含有量のより好ましい上限は0.35%である。
シリコン(Si)は鋼中に不可避的に含有される元素である。また、Siは鋼を脱酸する効果を有する。そのため、脱酸を目的として、Si含有量を0.05%以上としてもよい。しかしながら、Si含有量が高いと、鋼板のAC3点を上昇させる働きを有する。鋼板のAC3点が上昇するとホットスタンプ時の加熱温度が、Znめっきの蒸発温度を超えてしまうことが懸念される。また、ホットスタンプにおける加熱中に鋼中のSiが拡散し、鋼板表面に酸化物が形成される。この酸化物はりん酸塩処理性を低下させる場合がある。Si含有量が0.5%超の場合に、上記の問題が顕著となるので、Si含有量の上限を0.5%とすることが好ましい。より好ましいSi含有量の上限は0.3%である。
マンガン(Mn)は、焼入れ性を高め、ホットスタンプ鋼材の強度を高める元素である。この効果を得る場合、Mn含有量の下限を0.5%とすることが好ましい。Mn含有量の好ましい下限は0.6%である。一方、Mn含有量が2.5%を超えても、その効果が飽和する。したがって、Mn含有量の上限は2.5%とすることが好ましい。Mn含有量のより好ましい上限は2.4%である。
りん(P)は鋼中に含まれる不純物である。Pは粒界に偏析して鋼の靭性及び耐遅れ破壊性を低下させる。そのため、P含有量はなるべく低い方が好ましいが、P含有量が0.03%超となった場合にその影響が顕著となるので、P含有量を0.03%以下としてもよい。
硫黄(S)は鋼中に含まれる不純物である。Sは硫化物を形成して鋼の靭性及び耐遅れ破壊性を低下させる。そのため、S含有量はなるべく低い方が好ましいが、S含有量が0.010%超となった場合にその影響が顕著となるので、S含有量を0.010%以下としてもよい。
アルミニウム(Al)は鋼の脱酸に有効な元素である。この効果を得るため、Al含有量の下限を0.01%としてもよい。しかしながら、Al含有量が高すぎると、鋼板のAC3点が上昇して、ホットスタンプ時の必要な加熱温度がZnめっきの蒸発温度を超える場合がある。したがって、Al含有量の上限を0.10%とすることが好ましい。Al含有量のより好ましい上限は0.05%である。本実施形態におけるAl含有量は、sol.Al(酸可溶Al)の含有量である。
窒素(N)は鋼中に不可避的に含まれる不純物である。Nは窒化物を形成して鋼の靭性を低下させる元素である。また、Nは、Bが含有される場合、Bと結合して固溶B量を減らす。固溶B量が減ると、焼入れ性が低下する。上記の理由から、N含有量はなるべく低い方が好ましいが、N含有量が0.010%超となった場合にその影響が顕著となるので、N含有量を0.010%以下としてもよい。
本実施形態において、不純物とは、鉄鋼材料を工業的に製造する際に、原料としての鉱石、スクラップ、又は、製造環境などから混入するものを意味する。
ボロン(B)は、Bは鋼の焼入れ性を高め、ホットスタンプ鋼材の強度を高める。この効果を得る場合、B含有量の好ましい下限は0.0001%である。しかしながら、B含有量が高すぎれば、その効果が飽和する。したがって、含有させる場合でも、B含有量の上限を0.0050%とすることが好ましい。
チタン(Ti)は、Nと結合して窒化物(TiN)を形成する。その結果、BとNとの結合が抑制され、BN形成に伴う焼入れ性の低下を抑制できる。また、Tiはそのピン止め効果により、ホットスタンプ加熱時のオーステナイト粒径を微細化し、鋼材の靱性等を高める。これらの効果を得る場合、Ti含有量の好ましい下限は0.01%である。しかしながら、Ti含有量が高すぎると、上記効果が飽和するとともに、Ti窒化物が過剰に析出して鋼の靭性が低下する。したがって、含有させる場合でも、Ti含有量の上限を0.10%とすることが好ましい。
クロム(Cr)は鋼の焼入れ性を高める。この効果を得る場合、Cr含有量の好ましい下限は0.1%である。しかしながら、Cr含有量が高すぎると、Cr炭化物が形成され、ホットスタンプの加熱時に炭化物が溶解しにくくなる。その結果、鋼のオーステナイト化が進行しにくくなり、焼入れ性が低下する。したがって、含有させる場合でも、Cr含有量の上限を0.5%とすることが好ましい。
モリブデン(Mo)は、鋼の焼入れ性を高める。この効果を得る場合、Mo含有量の好ましい下限は0.05%である。しかしながら、Mo含有量が高すぎると、上記効果が飽和する。したがって、含有させる場合でも、Mo含有量の上限は0.50%とすることが好ましい。
ニオブ(Nb)は、炭化物を形成して、ホットスタンプ時に結晶粒を微細化する。結晶粒が微細化すると、鋼の靭性が高まる。この効果を得る場合、Nb含有量の好ましい下限は0.02%である。しかしながら、Nb含有量が高すぎると、上記効果が飽和するとともに、焼入れ性が低下する。したがって、含有させる場合でも、Nb含有量の上限は0.10%とすることが好ましい。
ニッケル(Ni)は、鋼の靭性を高める。また、Niは、亜鉛めっき鋼材のホットスタンプでの加熱時に、溶融Znに起因した脆化を抑制する。これらの効果を得る場合、Ni含有量の好ましい下限は0.1%である。しかしながら、Ni含有量が高すぎると、上記効果が飽和するとともに、コストの上昇を招く。したがって、含有させる場合でも、Ni含有量の上限は1.0%とすることが好ましい。
近年、テーラードプロパティと呼ばれる、位置によって強度や延性等の性能に対する要求が異なる部材が求められている。例えば自動車部材では、Bピラー(センターピラー)と呼ばれる骨格部材において、乗車エリアを構成する上部では高強度であることが求められ、下部では衝撃吸収性が高いことが求められている。
亜鉛めっき層を有するホットスタンプ鋼材の母材の一部のみを焼戻し部にすれば、上述のような強度が高い部分と、衝撃吸収性を併せ持った部材を得ることができる。また、ホットスタンプ鋼材が亜鉛めっき層を有するので、耐食性にも優れる。
焼戻しマルテンサイトのビッカース硬さは、マルテンサイトのビッカース硬さよりも低い。したがって、ビッカース硬さにより、焼戻し部の組織が焼戻しマルテンサイトか否かを判別できる。
ビッカース硬さは、JIS Z2244(2009)に準拠したビッカース硬さ試験により求めることができる。ビッカース硬さ試験の試験力は10kgf=98.07Nとする。
本実施形態に係るホットスタンプ鋼材は、少なくとも母材の焼戻し部上に亜鉛めっき層を有する。亜鉛めっき層は、亜鉛めっき層中の面積率で、30%以上のラメラ層と、0~70%の固溶体層とを含む。
亜鉛めっき層は固溶体層を有さなくてもよい。つまり、亜鉛めっき層がラメラ層のみからなり、固溶体層の面積率は0%であってもよい。
したがって、ラメラ層を表層に有する亜鉛めっき層のリン酸塩処理性は、表層に固溶体層のみを有する亜鉛めっき層よりも高くなると考えられる。
亜鉛めっき層中のラメラ層の面積率が30%以上であれば、亜鉛めっき層のりん酸塩処理性が高くなる。そのため、本実施形態に係るホットスタンプ鋼材において、亜鉛めっき層中のラメラ層の面積率を30%以上とする必要がある。好ましくは、ラメラ層の面積率は、80%以上である。ラメラ層の面積率が80%以上であれば、りん酸塩処理性がより向上する。また、化成結晶が細かくなり、塗装密着性等が向上することも期待される。
本実施形態に係るホットスタンプ鋼材は、上述した母材及び亜鉛めっき層を有していれば、その製造方法には限定されず、その効果を奏することができる。しかしながら、例えば以下に示す、母材である鋼材を準備する工程(母材準備工程)と、母材に亜鉛めっき層を形成する工程(亜鉛めっき処理工程)と、亜鉛めっき層を備える母材に対してホットスタンプを実施する工程(ホットスタンプ工程)と、ホットスタンプ鋼材に対して焼戻しを実施する工程(焼戻し工程)とを備える製造方法によって製造することができる。以下、各工程における好ましい例について説明する。
初めに、母材として用いる鋼板を準備する。たとえば、上述した好ましい範囲の化学組成を有する溶鋼を製造する。製造された溶鋼を用いて、連続鋳造などの鋳造法によりスラブを製造する。スラブの代わりに、製造された溶鋼を用いて、造塊法によりインゴットを製造してもよい。製造されたスラブ又はインゴットを熱間圧延して鋼板(熱延鋼板)を製造する。必要に応じて、さらに、熱延鋼板に対して酸洗処理を実施し、酸洗処理後の熱延鋼板に対して冷間圧延を実施して鋼板(冷延鋼板)としてもよい。熱間圧延、酸洗、冷間圧延については、適用する部材に要求される特性に合わせて、公知の方法で行えばよい。
上述の鋼板(熱延鋼板または冷延鋼板)に対して、亜鉛めっき処理を行い、鋼板の表面に亜鉛めっき層を形成する。亜鉛めっき層の形成方法は、特に限定されず、溶融亜鉛めっき処理であってもよいし、合金化溶融亜鉛めっき処理であってもよいし、電気亜鉛めっき処理であってもよい。
以上の工程により、亜鉛めっき層(溶融亜鉛めっき層)を備えるホットスタンプ用鋼板(GI)が製造される。
以上の合金化処理により、亜鉛めっき層(合金化溶融亜鉛めっき層)を備えるホットスタンプ用鋼板(GA)が製造される。
以上の工程により、亜鉛めっき層(電気亜鉛めっき層)を備えるホットスタンプ用鋼板(EG)が製造される。
上述の亜鉛めっき層を備えるホットスタンプ用鋼板に対して、ホットスタンプを実施する。ホットスタンプ工程における焼入れ前の加熱では、主に輻射熱を加熱に利用する加熱を行うことが好ましい。
具体的には、初めに、ホットスタンプ用鋼板を加熱炉(ガス炉、電気炉、赤外線炉等)に装入する。加熱炉内で、ホットスタンプ用鋼板をAC3点~950℃に加熱し、この温度で保持(均熱)する。加熱によりめっき層中のZnが液化し、均熱によって、めっき層中の溶融ZnとFeとが相互拡散して固溶体相(Fe-Zn固溶体相)となる。めっき層中の溶融ZnがFe中に固溶化して固相となった後、加熱炉から鋼板を取り出す。加熱炉から取り出された鋼板に対してホットスタンプ(プレス加工および焼入れ)を実施してホットスタンプ鋼材とする。好ましい均熱時間は0~10分、より好ましい均熱時間は、0~6分、さらに好ましい均熱時間は、0~4分である。
ホットスタンプ鋼材(ホットスタンプ後の鋼材)に対して、焼戻しを実施する。焼戻し温度は500℃~700℃未満である。
図7は、Fe-Znの二元系状態図である。ホットスタンプにより製造されたホットスタンプ鋼材の亜鉛めっき層は、α-FeにZnが25~40質量%程度固溶した固溶体相からなる。しかしながら、自由エネルギー的には、室温では、α-Feに5~25質量%のZnが固溶した低Zn固溶体相と、Γ相との二相からなる組織(つまり、ラメラ層)が安定である。つまり、ホットスタンプ後の亜鉛めっき層の固溶体相は、Znが過飽和された固溶体である。
ホットスタンプ鋼材の一部に対してのみ焼戻しを行うことで、同一部材において、焼戻しを行った部分と焼戻しを行わなかった部分とで、強度を変化させることができる。このような部材は、例えば自動車のBピラーのように、上部では高強度であることが求められ下部では衝撃吸収性が高いことが求められる部材に適用することができる。なお、部分焼戻しの場合でも、焼戻し部については、全体を焼戻した場合の焼戻し部と同等である。
上述の製造方法では、さらに、亜鉛めっき処理工程とホットスタンプ工程との間に、防錆油膜形成工程を含んでもよい。
また、上述の製造方法はさらに、防錆油膜形成工程と、ホットスタンプ工程と間に、ブランキング加工工程を含んでもよい。
水焼入れ後の鋼板に対し、表層から板厚の1/4の深さの位置でビッカース硬さを測定し、得られたビッカース硬さを最高焼入れ硬さB0(HV)と定義した。ビッカース硬さ試験は、JIS Z2244(2009)に準拠し、試験力は10kgf=98.07Nとした。
これらの試験番号1~16のホットスタンプ鋼材に対し、ビッカース硬さ試験、亜鉛めっき層のミクロ組織観察、りん酸塩処理性評価試験を行った。部分的に焼戻しを行った試験番号のホットスタンプ鋼材については、焼戻し部について評価を行った。
各試験番号の鋼材(鋼板)の母材の板厚中央部からサンプルを採取した。サンプルの表面(鋼板の圧延方向に垂直な面(L断面)に相当)に対して、JIS Z2244(2009)に準拠したビッカース硬さ試験を実施した。試験力は10kgf=98.07Nとした。得られたビッカース硬さB1(HV10)、および、最高焼入れ硬さB0との比である、B1/B0×100(%)を表2に示す。
各試験番号の鋼材から、亜鉛めっき層を含むサンプルを採取した。サンプルの表面のうち、圧延方向に垂直な断面を5質量%のナイタールでエッチングした。2000倍のSEMにより、エッチングされた亜鉛めっき層の断面を観察し、固溶体層及びラメラ層の有無を判断した。
各試験番号のホットスタンプ鋼材に対して、日本パーカライジング株式会社製の表面調整処理剤プレパレンX(商品名)を用いて表面調整を室温で20秒実施した。さらに、日本パーカライジング株式会社製のりん酸亜鉛処理液パルボンド3020(商品名)を用いてりん酸塩処理を実施した。処理液の温度は43℃とし、ホットスタンプ鋼材を処理液に120秒間浸漬した。
SEM画像に対して、2値化処理を実施した。図9は、図8のSEM画像を2値化して得られた画像である。2値化された画像において、白色部分には微細な化成結晶が形成されている。微細な化成結晶が多いほど、りん酸塩処理性が高い。そのため、2値化された画像を用いて、白色部分の面積率TRを求めた。面積率TRが30%以上であれば、りん酸塩処理性に優れると判断した。各試験番号で得られた面積率TRを表2に示す。表中の「G」はGOODであり、「NG」はNO GOODである。
図10は、焼戻し温度が400℃のホットスタンプ鋼材(試験番号10)に対して上述のりん酸塩処理を実施した後の、ホットスタンプ鋼材表面のSEM画像(1000倍)であり、図11は図10を2値化した画像である。図12は、焼戻し温度が700℃のホットスタンプ鋼材(試験番号10)に対して上述のりん酸塩処理を実施した後の、ホットスタンプ鋼材表面のSEM画像(1000倍)であり、図13は図12を2値化した画像である。
20 焼戻し部
30 亜鉛酸化物層
40 ラメラ層
Claims (6)
- Ac3点以上の温度に加熱して30分間保持した後に水焼入れを実施した場合の表層から板厚の1/4の深さの位置におけるビッカース硬さを最高焼入れ硬さと定義した場合、前記最高焼入れ硬さの85%以下の硬さを有する焼戻し部を含む鋼材である母材と、
前記母材の前記焼戻し部上に形成される亜鉛めっき層とを備え、
前記亜鉛めっき層は、Fe及び前記Feに固溶したZnを含有する固溶体相からなる固溶体層と、前記固溶体相とキャピタルガンマ相とからなるラメラ層と、を含み、
前記亜鉛めっき層において、前記ラメラ層の面積率が30%~100%であり、前記固溶体層の面積率が0~70%である
ことを特徴とするホットスタンプ鋼材。 - 前記亜鉛めっき層中の、前記ラメラ層の面積率が80%以上である
ことを特徴とする請求項1に記載のホットスタンプ鋼材。 - 前記焼戻し部のビッカース硬さが180~450Hvである
ことを特徴とする請求項1または2に記載のホットスタンプ鋼材。 - 前記焼戻し部の硬さが、前記最高焼入れ硬さの65%以下である
ことを特徴とする請求項1~3のいずれか一項に記載にホットスタンプ鋼材。 - Ac3点以上に加熱された後、金型を用いたプレス加工によって加工と焼入れとが同時に施され、その後、500℃~700℃未満で焼き戻しされることによって製造される
ことを特徴とする請求項1~4のいずれか一項に記載のホットスタンプ鋼材。 - 前記母材のうちの一部が前記焼戻し部であることを特徴とする請求項1~5のいずれか一項に記載のホットスタンプ鋼材。
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JP2016511945A JP6288248B2 (ja) | 2014-03-31 | 2015-03-31 | ホットスタンプ鋼材 |
US15/129,775 US9976196B2 (en) | 2014-03-31 | 2015-03-31 | Hot-stamped steel |
CN201580017228.4A CN106133180B (zh) | 2014-03-31 | 2015-03-31 | 热冲压钢材 |
CA2943650A CA2943650C (en) | 2014-03-31 | 2015-03-31 | Hot-stamped steel |
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JP6288248B2 (ja) | 2018-03-07 |
EP3128038A4 (en) | 2017-10-04 |
TW201542828A (zh) | 2015-11-16 |
RU2016140280A (ru) | 2018-05-07 |
CA2943650A1 (en) | 2015-10-08 |
KR20160132928A (ko) | 2016-11-21 |
TWI609087B (zh) | 2017-12-21 |
CA2943650C (en) | 2018-05-22 |
US9976196B2 (en) | 2018-05-22 |
CN106133180B (zh) | 2019-08-30 |
EP3128038A1 (en) | 2017-02-08 |
MX2016012677A (es) | 2016-12-14 |
RU2016140280A3 (ja) | 2018-05-07 |
US20170145533A1 (en) | 2017-05-25 |
KR101846112B1 (ko) | 2018-04-05 |
CN106133180A (zh) | 2016-11-16 |
JPWO2015152263A1 (ja) | 2017-04-13 |
RU2659526C2 (ru) | 2018-07-02 |
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