WO2014046007A1 - 焼入れ鋼管部材、焼入れ鋼管部材を用いた自動車用アクスルビーム、及び、焼入れ鋼管部材の製造方法 - Google Patents
焼入れ鋼管部材、焼入れ鋼管部材を用いた自動車用アクスルビーム、及び、焼入れ鋼管部材の製造方法 Download PDFInfo
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- WO2014046007A1 WO2014046007A1 PCT/JP2013/074687 JP2013074687W WO2014046007A1 WO 2014046007 A1 WO2014046007 A1 WO 2014046007A1 JP 2013074687 W JP2013074687 W JP 2013074687W WO 2014046007 A1 WO2014046007 A1 WO 2014046007A1
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- steel pipe
- galvanized steel
- pipe member
- hardened steel
- galvanized
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- 229910000760 Hardened steel Inorganic materials 0.000 title claims abstract description 26
- 238000004519 manufacturing process Methods 0.000 title claims description 26
- 238000000034 method Methods 0.000 title claims description 25
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 41
- 239000010959 steel Substances 0.000 claims abstract description 41
- 239000002344 surface layer Substances 0.000 claims abstract description 37
- 229910001297 Zn alloy Inorganic materials 0.000 claims abstract description 16
- 229910001335 Galvanized steel Inorganic materials 0.000 claims description 59
- 239000008397 galvanized steel Substances 0.000 claims description 59
- 238000010438 heat treatment Methods 0.000 claims description 48
- 239000000463 material Substances 0.000 claims description 33
- 238000001816 cooling Methods 0.000 claims description 26
- 230000002093 peripheral effect Effects 0.000 claims description 12
- 238000000465 moulding Methods 0.000 claims description 9
- 238000005246 galvanizing Methods 0.000 claims description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 abstract description 10
- 239000011701 zinc Substances 0.000 abstract description 10
- 229910052725 zinc Inorganic materials 0.000 abstract description 10
- 239000010953 base metal Substances 0.000 abstract 2
- 230000000694 effects Effects 0.000 description 30
- 238000005261 decarburization Methods 0.000 description 13
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 13
- 238000001556 precipitation Methods 0.000 description 9
- 238000010791 quenching Methods 0.000 description 9
- 230000000171 quenching effect Effects 0.000 description 9
- 230000007423 decrease Effects 0.000 description 8
- 239000000126 substance Substances 0.000 description 7
- 229910052742 iron Inorganic materials 0.000 description 6
- 229910000734 martensite Inorganic materials 0.000 description 6
- 238000005275 alloying Methods 0.000 description 5
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 238000007747 plating Methods 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 229910052796 boron Inorganic materials 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000010410 layer Substances 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 229910052717 sulfur Inorganic materials 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- KFZAUHNPPZCSCR-UHFFFAOYSA-N iron zinc Chemical compound [Fe].[Zn] KFZAUHNPPZCSCR-UHFFFAOYSA-N 0.000 description 2
- 229910052748 manganese 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
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 230000002195 synergetic effect Effects 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- 238000003466 welding Methods 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
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000010363 phase shift Effects 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000006104 solid solution Substances 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
- B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60B—VEHICLE WHEELS; CASTORS; AXLES FOR WHEELS OR CASTORS; INCREASING WHEEL ADHESION
- B60B35/00—Axle units; Parts thereof ; Arrangements for lubrication of axles
- B60B35/02—Dead axles, i.e. not transmitting torque
-
- 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
- C21D1/34—Methods of heating
-
- 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
- C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
- C21D1/60—Aqueous agents
-
- 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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- 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
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
-
- 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
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
-
- 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
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
- C23C2/29—Cooling or quenching
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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
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- 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
- C23C2/36—Elongated material
- C23C2/38—Wires; Tubes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60B—VEHICLE WHEELS; CASTORS; AXLES FOR WHEELS OR CASTORS; INCREASING WHEEL ADHESION
- B60B2360/00—Materials; Physical forms thereof
- B60B2360/10—Metallic materials
- B60B2360/102—Steel
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
Definitions
- the present invention relates to a hardened steel pipe member, an automobile axle beam using the hardened steel pipe member, and a method of manufacturing a hardened steel pipe member.
- Axle beams for automobiles are members that connect the left and right axles, and are subjected to repeated loads during travel, so high fatigue characteristics are required.
- Patent Document 1 a method of manufacturing an automobile axle beam is proposed in which a steel pipe is hardened after press forming to increase the strength and ensure fatigue characteristics.
- this method has a problem that heating time is long because quenching is performed in a furnace, the outermost surface of the member is decarburized and softened, and sufficient fatigue characteristics cannot be obtained.
- Patent Document 2 in order to suppress this softening of the surface layer, as shown in Patent Document 2, by applying galvanization to the surface of the steel pipe and heating, a carbon concentrated layer is formed on the surface of the steel material, and the surface layer after quenching is hardened. Techniques to make it have been proposed. However, this method also requires heating for a long time in order to perform heating in a furnace, during which zinc volatilizes. Therefore, there has been a problem that it is necessary to apply extra weight of zinc including the amount of volatilization, which requires a great deal of cost.
- Patent Document 3 discloses an axle beam excellent in fatigue characteristics obtained by press-forming a steel pipe into a V-shaped cross section under predetermined pressing conditions. However, this Patent Document 3 aims to provide an axle beam that can exhibit excellent fatigue characteristics without performing a heat treatment such as quenching, and mentions nothing about the decarburization of the outermost surface by the heat treatment as described above. Not done.
- the present invention aims to solve the above-described conventional problems and provide a hardened steel pipe member having excellent fatigue characteristics and low cost, an axle beam for automobiles, and a method for manufacturing a hardened steel pipe member. .
- a first aspect of the present invention is formed from a GI galvanized steel pipe, and a cross section perpendicular to the longitudinal direction at the center in the longitudinal direction of the GI galvanized steel pipe has an inner circumference of the GI galvanized steel pipe.
- the surface has a substantially V-shape including a contact portion where the surfaces contact each other, the contact portion is integrated by an Fe—Zn alloy phase, and the micro Vickers hardness at a depth of 50 ⁇ m from the base material surface layer is the base material surface layer.
- a hardened steel pipe member having a micro Vickers hardness of 95% or more at a depth of 200 ⁇ m.
- the micro Vickers hardness at a position of 50 ⁇ m depth from the base material surface layer of the GI galvanized steel pipe may be 500 Hv or more.
- the contact portion may be formed over a length of 50% or more of the total length of the GI galvanized steel pipe.
- a second aspect of the present invention is an automobile axle beam using the quenched steel pipe member according to any one of (1) to (3) above.
- the GI galvanized steel pipe has a cross section perpendicular to the longitudinal direction at the center in the longitudinal direction of the GI galvanized steel pipe, and the inner peripheral surfaces of the GI galvanized steel pipe are Press forming process for press forming so as to have a substantially V-shape including a contact portion, a galvanizing amount A (g / m 2 ), a maximum heating temperature T (° C.) of 850 ° C.
- the heated and held GI zinc The plated steel pipe may be water cooled to 200 ° C. or lower at a cooling rate of 30 ° C./s or higher.
- the said zinc plating amount A may be 60 g / m ⁇ 2 > or more.
- the contact portion is 50% or more of the total length of the GI galvanized steel pipe.
- the GI galvanized steel pipe may be press-formed so as to be formed over the length.
- the GI galvanized steel pipe may be heated by current in the heating and holding step.
- the press-formed GI galvanized steel pipe in the heating and holding step, is at a temperature equal to or higher than the Ac3 point of the steel material. Heating may be performed so that the region is held for 3 seconds or more and 30 seconds or less.
- the GI galvanized steel pipe may have a component system with an Ac3 point of 850 ° C. or lower.
- hardened steel pipe member since it is formed of a GI galvanized steel pipe, high surface layer hardness can be ensured and fatigue characteristics can be improved by suppressing decarburization of the surface layer by galvanization.
- FIG. 2 is a phase diagram of an Fe—Zn alloy.
- an automotive axle beam (hereinafter referred to as an axle beam) according to an embodiment of the present invention will be described in detail.
- an axle beam is cited as a specific example of a hardened steel pipe member, but the hardened steel pipe member according to the present invention is not limited to this, and a structural member for industrial machinery, a structural member for construction, etc. Including various hardened steel pipe members that require high fatigue properties.
- FIGS. 1A and 1B are a plan view and a perspective view showing an axle beam 1 according to the present embodiment.
- 1C is an IC-IC cross-sectional view of FIG. 1A
- FIG. 1D is an ID-ID cross-sectional view of FIG. 1A.
- the axle beam 1 according to the present embodiment is configured so that the GI galvanized steel pipe 10 has a substantially V-shaped cross section (hereinafter referred to as a vertical cross section) perpendicular to the longitudinal direction thereof. It is formed by press molding.
- the axle beam 1 has a contact portion 11 in which inner peripheral surfaces come into contact with each other at the center in the longitudinal direction.
- the contact portion 11 is integrated with the Fe—Zn alloy phase by performing a quenching process in a state where the galvanized surfaces of the inner peripheral surfaces of the GI galvanized steel pipe 10 are in contact with each other.
- the contact part 11 in the site
- the contact portion 11 is preferably formed over a length of 50% or more of the total length of the GI galvanized steel pipe 10, and a length of 70% or more. More preferably, it is formed over the entire length.
- the axle beam 1 which concerns on this embodiment is obtained by performing the quenching process after press forming the GI galvanized steel pipe 10, it performs a quenching process, suppressing the decarburization from a surface layer by the effect of galvanization. As a result, the hardness of the entire axle beam 1 can be increased. That is, by suppressing decarburization at the surface layer portion of the axle beam 1, it is possible to ensure the same hardness as that of the central portion of the plate thickness (thickness), thereby improving the fatigue characteristics.
- the micro Vickers hardness at a position of 200 ⁇ m depth from the base material surface layer is X
- the micro Vickers hardness at a position of 50 ⁇ m depth from the base material surface layer is Y
- the value of (Y / X) ⁇ 100 is 95 or more.
- the micro Vickers hardness is measured with a load of 50 g. If the value of (Y / X) ⁇ 100 is less than 95, the fatigue life may be reduced due to fatigue cracks from the surface layer.
- the value of (Y / X) ⁇ 100 is preferably 96 or more, more preferably 97 or more.
- micro Vickers hardness Y at a position of 50 ⁇ m depth from the surface layer of the base material is preferably 500 Hv or more in terms of micro Vickers hardness, and more preferably 540 Hv or more in order to ensure high fatigue characteristics.
- the axle beam 1 which concerns on this embodiment, since it forms with the GI galvanized steel pipe 10, while decarburization of a surface layer is suppressed by the effect of galvanization, the hardness of a surface layer improves and it is fatigued.
- the effect of improving the characteristics is obtained, and the contact portion 11 where the inner peripheral surfaces of the GI galvanized steel pipe 10 are in contact with each other is integrated by the Fe—Zn alloy phase, so that the fatigue life is reduced due to friction between the inner peripheral surfaces. It can suppress and can improve a fatigue characteristic synergistically. For this reason, it is possible to reduce the thickness and weight, and it is possible to significantly reduce the cost.
- the chemical component of the steel material of the GI galvanized steel pipe 10 is not particularly limited, but a preferable component composition will be described.
- % related to the content of the chemical component means mass%.
- the chemical component of the steel material of the GI galvanized steel pipe 10 may contain C, Si, Mn, Ti, and B in the following ranges. *
- C 0.15-0.30%
- C is an element that determines the intensity of the axle beam 1.
- the C content is preferably 0.15% or more, and more preferably 0.20% or more.
- the hardness Hv500 or more it is preferable to make it 0.24% or more.
- C content shall be 0.30% or less, and it is more preferable to set it as 0.25% or less.
- Si 0.05 to 0.35%
- Si is a deoxidizing element and contributes to solid solution strengthening. In order to acquire those effects, it is preferable to contain 0.05% or more. Moreover, toughness is securable by making Si 0.35% or less.
- the lower limit of the Si content is more preferably 0.20%, and the upper limit of the Si content is more preferably 0.30%.
- Mn 0.5 to 2.0% Mn is an element that improves hardenability, and is preferable because the effect of improving hardenability can be sufficiently secured by setting the Mn content to 0.5% or more. In addition, it is preferable that the Mn content is 2.0% or less because deterioration of delayed fracture characteristics can be suppressed, precipitation of MnS can be suppressed, and a decrease in fatigue strength in the vicinity of the ERW weld can be avoided. .
- the lower limit of the Mn content is more preferably 1.0%, and the upper limit of the Mn content is more preferably less than 1.7%.
- Ti acts to stably and effectively improve the hardenability by adding B by fixing N in steel as TiN and suppressing precipitation of BN. Therefore, it is preferable to add at a ratio of 3.42 times or more of the N content so as to meet the stoichiometry of TiN, and the preferable range of the Ti content is automatically determined from the range of the N content. However, since there is a portion that precipitates as a carbide, in order to ensure the fixation of N, it is preferable to set the content within a range of 0.005 to 0.05% higher than the theoretical value. More preferably, the content is 0.01 to 0.02%.
- B 0.0005 to 0.005%
- B is an element that greatly improves the hardenability of the steel material by adding a small amount. Since the effect which improves hardenability is suitably acquired by making B content 0.0005% or more, it is preferable and it is more preferable to set it as 0.001% or more. Further, if B is 0.005% or less, it is preferable because formation of coarse B-containing precipitates can be suppressed and embrittlement can be suppressed, and more preferably 0.002% or less.
- the chemical components of the steel material of the GI galvanized steel pipe 10 may be limited to the following ranges for Al, P, S, N, and O. *
- Al 0.08% or less
- Al is an element useful as a deoxidizer for molten steel, and it is preferable to add 0.01% or more.
- Al is an element that fixes N, the amount of Al greatly affects the crystal grain size and mechanical properties. It is preferable for the Al content to be 0.08% or less because generation of product surface defects due to non-metallic inclusions can be suppressed.
- the Al content is more preferably 0.05% or less.
- P 0.05% or less
- P is an element that adversely affects weld cracking resistance and toughness, so it is preferably 0.05% or less, and more preferably 0.03% or less.
- S Less than 0.0030% S degrades toughness and decreases the fatigue strength near the ERW weld due to MnS precipitation, so the S content is preferably less than 0.0030%. It is more preferable to set it to 0026% or less.
- the product value of the Mn content and the S content is set to 0. .0025 or less is preferable. By setting the product value of the Mn content and the S content to 0.0025 or less, the fatigue strength in the vicinity of the ERW weld can be sufficiently secured.
- N 0.006% or less
- N is an element having an effect of increasing the strength by precipitating nitride or carbonitride.
- the hardenability decreases due to the precipitation of BN, and as described above, the Ti added to prevent the precipitation of BN causes a decrease in hot workability and fatigue strength due to the precipitation of TiN.
- a decrease in toughness becomes a problem.
- TiN also has the effect of suppressing the coarsening of the ⁇ grain size at high temperatures and improving the toughness. Therefore, in order to optimize the balance of hot workability, fatigue strength, and toughness, the N content is preferably 0.006% or less.
- the N content is more preferably 0.001 to 0.005%, still more preferably 0.002 to 0.004%.
- O 0.004% or less
- O is an element that becomes CaO and impairs the effect of addition of Ca. Therefore, the O content is preferably limited to 0.004% or less.
- the chemical component of the steel material of the GI galvanized steel pipe 10 may contain one or more of Mo, Cr, Nb, V, and Ni as selective elements in the following ranges as necessary. *
- Mo 0.05 to 0.5% Mo is an element having an effect of improving hardenability. If the Mo content is less than 0.05%, these effects cannot be sufficiently expected. On the other hand, if the Mo content exceeds 0.5%, the alloy cost increases. A range of 0.5% is preferable.
- Cr 0.05 to 1.0% Cr is not an essential additive element, but is an element added for the purpose of improving hardenability.
- the Cr content is preferably 0.05% or more, and more preferably 0.10% or more.
- Cr content shall be 1.0% or less at the point which suppresses the defect generation
- Nb 0.01 to 0.1%
- Nb has the effect of reducing the crystal grain size of the steel material and improving toughness. If the Nb content is 0.01% or more, the effect of improving strength and toughness can be sufficiently obtained. On the other hand, even if the Nb content exceeds 0.1%, no further improvement effect can be expected, and only an increase in cost is caused, so the Nb content is 0.01 to 0.1%. It is preferable to set it as the range.
- V 0.01 to 0.1%
- V is an element having an effect of precipitation strengthening by V carbonitride. By setting the V content to 0.01% or more, these effects can be suitably exhibited, which is preferable. On the other hand, even if the V content exceeds 0.1%, no further improvement effect can be expected, and only an increase in the alloy cost is brought about. Therefore, the V content is set to 0.1% or less. It is preferable.
- Ni 0.1 to 1.0%
- Ni is an element having an effect of improving hardenability and toughness. By setting the Ni content to 0.1% or more, the effect can be suitably exhibited, which is preferable. On the other hand, if the Ni content exceeds 1.0%, the alloy cost increases, so the Ni content is preferably 1.0% or less.
- the chemical components of the steel material of the GI galvanized steel pipe 10 include C, Si, Mn, Ti, and B in the above range, Al, P, S, N, and O are limited to the above range, and Mo is selected as a selective element.
- One or more of Cr, Nb, V, and Ni are contained in the above range as necessary, and the remainder may be a chemical component composed of Fe and inevitable impurities.
- a critical cooling rate Vc90 (° C./s) known conventionally from “Iron and Steel, 74 (1988) P. 1073” may be used.
- This is an index represented by the following (formula A) and means a cooling rate at which the volume ratio of martensite is 90% or more. Therefore, the lower the Vc90, the higher the hardenability and the martensitic structure can be obtained even when the cooling rate is slow.
- B boron
- (Formula A) changes to (Formula A ').
- logVc90 2.94 ⁇ 0.75 ( ⁇ ′ ⁇ 1)
- (Formula A ′) 2.7C + 0.4Si + Mn + 0.8Cr + Mo + 0.45Ni.
- the method for manufacturing the axle beam 1 according to the present embodiment includes at least a press molding process, a heating and holding process, and a cooling process.
- a press molding process As shown in the flowchart of FIG. 2, the method for manufacturing the axle beam 1 according to the present embodiment includes at least a press molding process, a heating and holding process, and a cooling process.
- a heating and holding process As shown in the flowchart of FIG. 2, the method for manufacturing the axle beam 1 according to the present embodiment includes at least a press molding process, a heating and holding process, and a cooling process.
- the GI galvanized steel pipe 10 is press-molded into a substantially V shape by giving a displacement from the outside to the inside along the longitudinal direction thereof, so that the shape of the axle beam 1 is obtained. That is, with respect to the GI galvanized steel pipe 10, the cross section perpendicular to the longitudinal direction at the center in the longitudinal direction has a substantially V shape including the contact portion 11 where the inner peripheral surfaces of the GI galvanized steel pipe 10 are in contact with each other. Press molding.
- the specific shape is as shown in FIGS. 1A to 1D.
- a contact portion 11 where the inner surfaces of the steel pipes are in contact with each other is formed at the center in the longitudinal direction.
- the both ends are made into the shape where the steel pipe was crushed flat.
- A is the galvanized amount (g / m 2 ) of the GI galvanized steel pipe 10
- T is the maximum heating temperature (° C.) of 850 ° C. or more
- t is the maximum heating temperature holding time (hr ).
- (T + 273.15) ⁇ (logt + 20) related to the heating condition is referred to as a heat treatment parameter B.
- the value of (Y / X) ⁇ 100 can be 95 or more.
- the maximum heating temperature is set to 850 ° C. or higher, the quenched structure can be made martensite.
- the maximum heating temperature is lower than 850 ° C., it becomes a two-phase region, and a portion where no quenching occurs occurs, and the fatigue characteristics are drastically lowered. That is, by heating and holding the GI galvanized steel pipe 10 under the condition satisfying the above-described formula (1), the fatigue effect is improved by suppressing surface decarburization and the fatigue property is improved by alloying the contact portion 11. It is possible to synergistically improve the fatigue characteristics.
- the galvanizing amount A of the GI galvanized steel pipe 10 is 60 g / m 2 or more in terms of more reliably suppressing surface layer decarburization in the heating and holding step.
- the heating method in the heating and holding step may be, for example, energization heating, induction heating, or furnace heating. However, in consideration of productivity, energization heating is more preferable.
- the upper limit of the maximum heating temperature is not particularly specified, but if the temperature is excessively high, zinc may volatilize from the surface of the steel pipe. Therefore, in order to suppress surface decarburization more reliably, 1100 ° C. may be set as the upper limit.
- the holding time is preferably 3 seconds or more in the temperature range of Ac3 point or higher.
- the holding time is 3 seconds or more, the temperature variation can be more reliably suppressed, and thus the hardness variation after quenching can be reduced.
- the contact portion 11 can be integrated stably by the Fe—Zn alloy phase.
- the holding time is preferably 30 seconds or less. It is because it can suppress that iron diffuses excessively in a zinc plating layer by making holding time into 30 seconds or less.
- the temperature range that can be maintained is widened by reducing the Ac3 point of the steel material as much as possible in order to heat and hold at the maximum heating temperature of 850 ° C. or more. Since production becomes easy, it is preferable to use a component steel pipe having an Ac3 point of 850 ° C. or lower.
- the Ac3 point can be calculated by the following equation (2).
- Vc90 means a cooling rate at which 90% or more becomes martensite.
- the galvanized phase on the surface of the steel pipe enters the hatched region in the phase diagram of FIG. 3, and when cooled rapidly from here, becomes a Fe—Zn alloy phase.
- part is integrated.
- a decrease in fatigue life due to rubbing between the inner peripheral surfaces of the GI galvanized steel pipe 10 can be suppressed, and the fatigue strength is improved.
- inadequate diffusion of iron into the plating phase shifts to the left side of the hatched region, and even if quenched, a mixed phase of iron-zinc alloy phase and iron is not preferable.
- the heated GI galvanized steel pipe 10 is water-cooled to integrate the contact portion 11 with the Fe—Zn alloy phase.
- it is preferable to cool to 200 ° C. or lower at a cooling rate of 30 ° C./s or higher because fatigue characteristics can be further improved by martensite formation. More preferably, the cooling rate is 50 ° C./s or more.
- the cooling method may be spray cooling, submerged cooling, air-water cooling, or the like, but spray cooling is preferable in consideration of productivity.
- the axle beam 1 according to the present embodiment thus obtained has the contact portion 11 integrated by the Fe—Zn alloy phase, and the micro Vickers hardness at a depth of 50 ⁇ m from the base material surface layer is the base material. Since it is 95% or more of the micro Vickers hardness at a depth of 200 ⁇ m from the surface layer, the fatigue property is synergistically improved by the effect of improving the fatigue property by suppressing the surface decarburization and the effect of improving the fatigue property by alloying the contact portion 11 It becomes possible to improve.
- Examples are shown below.
- Inventive Examples 1 to 6 and Comparative Examples 1 to 3 a GI steel sheet having a component of 0.24% C-0.2% Si-1.2% Mn-0.02% Ti-10 ppmB was subjected to ERW welding.
- Axle beams are manufactured by performing press working, energization heating, and spray cooling, micro Vickers hardness at a position of 50 ⁇ m depth from the base material surface layer, micro Vickers hardness at a position of 200 ⁇ m depth from the base material surface layer, and Fatigue properties were measured.
- the contact portions were integrated by alloying. Table 1 shows various setting conditions and measurement results.
- A is weight per unit area (g / m 2 ), T is maximum heating temperature (° C.), t is holding time (hr), B is heat treatment parameter, X is micro Vickers hardness at 200 ⁇ m depth from the base material surface layer, Y Means micro Vickers hardness at a depth of 50 ⁇ m from the surface layer of the base material.
- High fatigue characteristics can be obtained by synergistic effect with the improvement of fatigue characteristics by crystallization.
- High fatigue characteristics can be obtained by synergistic effect with the improvement of fatigue characteristics by crystallization.
- Invention Examples 1 to 6 Invention Examples 1 to 5 having a micro Vickers hardness of 500 Hv or more at a depth of 50 ⁇ m from the surface layer of the base material showed better fatigue characteristics than those of Invention Example 6.
- Comparative Examples 1 and 2 in which the value of B / A does not satisfy the range of the present invention the hardness of the surface layer portion is reduced by decarburization from the surface layer, and the fatigue characteristics are improved by alloying of the contact portion. A synergistic effect with the effect could not be obtained, and high fatigue characteristics could not be obtained.
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Abstract
Description
しかし、この方法では炉で焼入れを行うために加熱時間が長く、部材の最表層面が脱炭して軟化してしまい、十分な疲労特性を得ることができないという問題があった。
しかし、この方法も炉で加熱を行うために長時間加熱をしなければならず、その間に亜鉛が揮発する。従って、揮発してしまう分も含めて亜鉛を余分に目付けしなければならず、多大なコストがかかるという問題があった。
しかし、この特許文献3では、焼入れ等の熱処理を行わなくても優れた疲労特性を発揮出来るアクスルビームを提供することを目的としており、上述のような熱処理による最表面の脱炭に関しては何ら言及していない。
(1)本発明の第一の態様は、GI亜鉛めっき鋼管から形成され、前記GI亜鉛めっき鋼管の長手方向の中央部における、前記長手方向に垂直な断面が、前記GI亜鉛めっき鋼管の内周面同士が接触する接触部を含む略V字形状を有し、前記接触部が、Fe-Zn合金相により一体化し、母材表層から50μm深さ位置のマイクロビッカース硬さが、前記母材表層から200μm深さ位置のマイクロビッカース硬さの95%以上である焼入れ鋼管部材である。
(2)上記(1)に記載の焼入れ鋼管部材では、前記GI亜鉛めっき鋼管の前記母材表層から50μm深さ位置のマイクロビッカース硬さが、500Hv以上であってもよい。
(3)上記(1)又は(2)に記載の焼入れ鋼管部材では、前記接触部が、前記GI亜鉛めっき鋼管の全長の50%以上の長さにわたり形成されていてもよい。
(4)本発明の第二の態様は、上記(1)から(3)のいずれか一項に記載の焼入れ鋼管部材を用いた自動車用アクスルビームである。
(5)本発明の第三の態様は、GI亜鉛めっき鋼管に対し、前記GI亜鉛めっき鋼管の長手方向の中央部における前記長手方向に垂直な断面が前記GI亜鉛めっき鋼管の内周面同士が接触する接触部を含む略V字形状を有するようにプレス成形するプレス成形工程と、亜鉛めっき量A(g/m2)と、850℃以上の最高加熱温度T(℃)と、最高加熱温度保持時間t(hr)とが下記(I)式を満たす条件で、プレス成形された前記GI亜鉛めっき鋼管を加熱保持する加熱保持工程と、加熱保持されたGI亜鉛めっき鋼管を水冷により冷却することにより、前記接触部をFe-Zn合金相により一体化させる冷却工程と、を備える焼入れ鋼管部材の製造方法である。
(T+273.15)×(logt+20)/A≦340 ・・・(I)式
(6)上記(5)に記載の焼入れ鋼管部材の製造方法では、前記冷却工程では、加熱保持された前記GI亜鉛めっき鋼管を30℃/s以上の冷却速度で200℃以下まで水冷してもよい。
(7)上記(5)又は(6)に記載の焼入れ鋼管部材の製造方法では、前記亜鉛めっき量Aが60g/m2以上であってもよい。
(8)上記(5)から(7)のいずれか一項に記載の焼入れ鋼管部材の製造方法では、前記プレス成形工程において、前記接触部が、前記GI亜鉛めっき鋼管の全長の50%以上の長さにわたり形成されるように前記GI亜鉛めっき鋼管をプレス成形してもよい。
(9)上記(5)から(8)のいずれか一項に記載の焼入れ鋼管部材の製造方法では、前記加熱保持工程において、前記GI亜鉛めっき鋼管を通電加熱してもよい。
(10)上記(5)から(9)のいずれか一項に記載の焼入れ鋼管部材の製造方法では、前記加熱保持工程において、プレス成形された前記GI亜鉛めっき鋼管を鋼材のAc3点以上の温度域に3秒以上、30秒以下保持するように通電加熱してもよい。
(11)上記(5)から(10)のいずれか一項に記載の焼入れ鋼管部材の製造方法では、前記GI亜鉛めっき鋼管が、Ac3点が850℃以下の成分系を有してもよい。
図1A、図1Bに示すように、本実施形態に係るアクスルビーム1はGI亜鉛めっき鋼管10を、その長手方向に垂直な断面(以下、垂直断面と呼ぶ)が略V字状となるようにプレス成形することにより形成される。
この接触部11は、GI亜鉛めっき鋼管10の内周面の亜鉛めっき同士が接触した状態で焼入れ処理が行われることにより、Fe-Zn合金相により一体化している。
このような構成によれば、アクスルビーム1の剛性を高める効果に加え、GI亜鉛めっき鋼管10の内周面同士の擦れによる疲労寿命の低下を抑制することができ、疲労特性を向上させることができる。
ただし、疲労特性を向上させる効果をより好適に発揮させるためには、接触部11がGI亜鉛めっき鋼管10の全長の50%以上の長さにわたり形成されていることが好ましく、70%以上の長さにわたり形成されていることがより好ましい。
(Y/X)×100の値が95未満であると、表層からの疲労き裂により疲労寿命を低下させる虞がある。(Y/X)×100の値は、好ましくは96以上であり、より好ましくは97以上である。
Cは、アクスルビーム1の強度を決定する元素である。十分な疲労特性を有するための強度を確保するためには、C含有量を0.15%以上にすることが好ましく、0.20%以上にすることがより好ましい。硬さをHv500以上にするためには、0.24%以上にすることが好ましい。また、焼割れの発生を抑制するためには、C含有量を0.30%以下とすることが好ましく、0.25%以下とすることがより好ましい。
Siは、脱酸元素であり、また固溶強化に寄与する。それらの効果を得るためには0.05%以上含有することが好ましい。また、Siを0.35%以下とすることで靱性を確保することができる。Si含有量の下限は、より好ましくは0.20%であり、Si含有量の上限は、より好ましくは0.30%である。
Mnは、焼入れ性を向上させる元素であり、Mn含有量を0.5%以上とすることで焼入れ性の向上効果を十分に確保することができるため好ましい。また、Mn含有量を2.0%以下とすることで遅れ破壊特性の劣化を抑制でき、MnSの析出を抑制でき、電縫溶接部近傍の疲労強度の低下を回避することができるため、好ましい。
Mn含有量の下限はより好ましくは1.0%であり、Mn含有量の上限はより好ましくは1.7%未満である。
Tiは、鋼中NをTiNとして固定してBNの析出を抑制することにより、B添加による焼入れ性を安定的かつ効果的に向上させるために作用する。従って、TiNの化学量論に見合うように、N含有量の3.42倍以上で添加することが好ましく、N含有量の範囲からTi含有量の好ましい範囲も自動的に決定される。
しかし、炭化物として析出する分もあるので、Nの固定をより確実にするために、理論値よりも高めの0.005~0.05%の範囲とすることが好ましい。なお、より好ましくは、0.01~0.02%である。
Bは、微量の添加で鋼材の焼入れ性を大幅に向上させる元素である。B含有量を0.0005%以上とすることで焼入れ性を向上させる効果が好適に得られるため好ましく、0.001%以上とすることがより好ましい。
また、Bを0.005%以下とすると、粗大なB含有析出物の生成を抑制でき、また、脆化を抑制できるため好ましく、0.002%以下とするとより好ましい。
Alは、溶鋼の脱酸材として有用な元素であり、0.01%以上を添加することが好ましい。また、AlはNを固定する元素でもあるため、Al量は結晶粒径や機械的性質に大きな影響を及ぼす。Al含有量を0.08%以下とすることで、非金属介在物による製品表面疵の発生を抑制することができるため、好ましい。Al含有量は、より好ましくは、0.05%以下である。
Pは、耐溶接割れ性および靱性に悪影響を及ぼす元素であるため、0.05%以下とすることが好ましく、0.03%以下とすることがより好ましい。
Sは、靱性を劣化させるとともに、MnSの析出により電縫溶接部近傍の疲労強度を低下させるため、S含有量は0.0030%未満とすることが好ましく、0.0026%以下とすることがより好ましい。
Nは、窒化物または炭窒化物を析出させ、強度を高める効果を有する元素である。しかし、B添加鋼においてはBNの析出による焼入れ性の低下や、前述のように、BNの析出を防止させるために添加されるTiによって、TiNの析出による熱間加工性や疲労強度の低下、さらには靱性の低下が問題となる。一方で、TiNは高温時でのγ粒径の粗大化を抑制し靱性を向上させる効果も有する。そのため、熱間加工性、疲労強度および靱性のバランスを最適なものとするために、N含有量は0.006%以下とすることが好ましい。なお、N含有量は、より好ましくは、0.001~0.005%、更に好ましくは0.002~0.004%である。
Oは、CaOとなってCaの添加効果を損なわせる元素であるため、O含有量は0.004%以下に制限することが好ましい。
Moは、焼入れ性を向上させる効果を有する元素である。Mo含有量が0.05%未満ではこれらの効果を十分期待することができず、一方、Mo含有量が0.5%を超えると合金コストが上昇するため、Mo含有量は0.05~0.5%の範囲とすることが好ましい。
Crは、必須の添加元素ではないが、焼入れ性を向上させる目的で添加される元素である。焼入れ性の向上効果を十分に得るためには、Cr含有量を0.05%以上とすることが好ましく、0.10%以上とすることがより好ましい。また、Cr含有量を1.0%以下とすることが、電縫溶接時の欠陥発生を抑制する点で好ましく、0.8%以下とすることがより好ましい。
Nbは、Nb炭窒化物による析出強化の効果を有するのに加えて、鋼材の結晶粒径を微細化し、靱性を向上させる効果を有している。Nb含有量が0.01%以上であれば、強度・靱性の向上効果を十分に得られる。一方、Nb含有量が0.1%を超えて含有しても、それ以上の向上効果は期待できず、コストの上昇をもたらすにすぎないため、Nb含有量は0.01~0.1%の範囲とすることが好ましい。
Vは、V炭窒化物による析出強化の効果を有する元素である。V含有量を0.01%以上とすることで、これらの効果を好適に発揮することができ、好ましい。一方、V含有量を0.1%を超えて含有させても、それ以上の向上効果は期待できず、合金コストの上昇をもたらすにすぎないため、V含有量は0.1%以下とすることが好ましい。
Niは、焼入れ性及び靱性を向上させる効果を有する元素である。Ni含有量を0.1%以上とすることで、その効果を好適に発揮することができ、好ましい。一方、Ni含有量が1.0%を超えると合金コストが上昇するため、Ni含有量は、1.0%以下とすることが好ましい。
ただし、β=2.7C+0.4Si+Mn+0.8Cr+2.0Mo+0.45Niである。
また、B(ボロン)が含まれない場合、(式A)は(式A′)に変わる。
logVc90=2.94-0.75(β′-1) ・・・(式A′)
ただし、β′=2.7C+0.4Si+Mn+0.8Cr+Mo+0.45Niである。
まず、プレス成形工程では、GI亜鉛めっき鋼管10を、その長手方向に沿って外方から内方に向かう変位を与えることにより略V字形状にプレス成形し、アクスルビーム1の形状とする。すなわち、GI亜鉛めっき鋼管10に対し、その長手方向の中央部における長手方向に垂直な断面がGI亜鉛めっき鋼管10の内周面同士が接触する接触部11を含む略V字形状を有するようにプレス成形する。
具体的な形状は図1A~図1Dに示す通りであり、図1Cに示すように長手方向の中央部では鋼管内面同士が接触する接触部11が形成されている。尚、両端部は鋼管が扁平に潰された形状とされている。
加熱保持工程では、このようにプレス成形されたGI亜鉛めっき鋼管10を、下記(1)式を満たす条件で加熱保持する。
(T+273.15)×(logt+20)/A≦340 ・・・(1)式
この(1)式を満たすように亜鉛めっき量Aと熱処理パラメータBとを設計することにより、母材表層から200μm深さ位置のマイクロビッカース硬さをX、母材表層から50μm深さ位置のマイクロビッカース硬さをYとして、(Y/X)×100の値を95以上とすることが出来る。
また、最高加熱温度を850℃以上としているため、焼入れ組織をマルテンサイトにすることが可能となる。一方、最高加熱温度が850℃よりも低温であると、2相域になってしまい、焼きが入らない部分が生じて疲労特性が急激に低下する。
すなわち、上述の(1)式を満たす条件でGI亜鉛めっき鋼管10を加熱保持することにより、表層脱炭の抑制による疲労特性の向上効果と接触部11の合金化による疲労特性の向上効果とにより疲労特性を相乗的に向上させることが可能となる。
また、保持時間は30秒以下とすることが好ましい。保持時間を30秒以下とすることにより鉄が亜鉛めっき層に過剰に拡散することを抑制できるためである。
なお、GI亜鉛めっき鋼管10を通電加熱により加熱すると電流が偏流して温度バラツキが生じることが懸念されるが、保持時間を3~30秒とすれば均一に焼きが入る温度範囲内に加熱できることが確認できた。
ここでAc3点は下記(2)式により算出することができる。
104×V+31.5×Mo+13.1×W ・・・(2)式
α=2.94-0.75×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr+2×Mo)
・・・(4)式
冷却工程では、加熱保持されたGI亜鉛めっき鋼管10を水冷することにより、接触部11をFe-Zn合金相により一体化させる。
冷却工程においては、30℃/s以上の冷却速度で200℃以下になるまで冷却すると、マルテンサイト化により疲労特性を更に向上させることできるため、好ましい。冷却速度を50℃/s以上とするとより好ましい。
冷却方法としては、スプレー冷却、浸水冷却、気水冷却などであればよいが、生産性を考慮するとスプレー冷却が好ましい。
発明例1~6、及び、比較例1~3として、0.24%C-0.2%Si-1.2%Mn-0.02%Ti-10ppmBの成分のGI鋼板を電縫溶接後、プレス加工、通電加熱、及びスプレー冷却を行うことでアクスルビームを製造し、母材表層から50μm深さ位置のマイクロビッカース硬さ、母材表層から200μm深さ位置のマイクロビッカース硬さ、及び、疲労特性を測定した。尚、発明例1~6及び比較例1、2に関しては、接触部を合金化により一体化させた。
表1に各種設定条件と測定結果を示す。Aは目付量(g/m2)、Tは最高加熱温度(℃)、tは保持時間(hr)、Bは熱処理パラメータ、Xは母材表層から200μm深さ位置のマイクロビッカース硬さ、Yは母材表層から50μm深さ位置のマイクロビッカース硬さを意味する。
10 GI亜鉛めっき鋼管
11 接触部
A 亜鉛目付量
B 熱処理パラメータ
t 保持時間
T 最高加熱温度
X 母材表層から200μm深さ位置のマイクロビッカース硬さ
Y 母材表層から50μm深さ位置のマイクロビッカース硬さ
Claims (11)
- GI亜鉛めっき鋼管から形成され、
前記GI亜鉛めっき鋼管の長手方向の中央部における、前記長手方向に垂直な断面が、前記GI亜鉛めっき鋼管の内周面同士が接触する接触部を含む略V字形状を有し、
前記接触部が、Fe-Zn合金相により一体化し、
母材表層から50μm深さ位置のマイクロビッカース硬さが、前記母材表層から200μm深さ位置のマイクロビッカース硬さの95%以上である
ことを特徴とする焼入れ鋼管部材。 - 前記GI亜鉛めっき鋼管の前記母材表層から50μm深さ位置のマイクロビッカース硬さが、500Hv以上である
ことを特徴とする請求項1に記載の焼入れ鋼管部材。 - 前記接触部が、前記GI亜鉛めっき鋼管の全長の50%以上の長さにわたり形成されている
ことを特徴とする請求項1又は2に記載の焼入れ鋼管部材。 - 請求項1から3のいずれか一項に記載の焼入れ鋼管部材を用いたことを特徴とする自動車用アクスルビーム。
- GI亜鉛めっき鋼管に対し、前記GI亜鉛めっき鋼管の長手方向の中央部における前記長手方向に垂直な断面が前記GI亜鉛めっき鋼管の内周面同士が接触する接触部を含む略V字形状を有するようにプレス成形するプレス成形工程と、
亜鉛めっき量A(g/m2)と、850℃以上の最高加熱温度T(℃)と、最高加熱温度保持時間t(hr)とが下記(1)式を満たす条件で、プレス成形された前記GI亜鉛めっき鋼管を加熱保持する加熱保持工程と、
加熱保持されたGI亜鉛めっき鋼管を水冷により冷却することにより、前記接触部をFe-Zn合金相により一体化させる冷却工程と、
を備えることを特徴とする焼入れ鋼管部材の製造方法。
(T+273.15)×(logt+20)/A≦340 ・・・(1)式 - 前記冷却工程では、加熱保持された前記GI亜鉛めっき鋼管を30℃/s以上の冷却速度で200℃以下まで水冷する
ことを特徴とする請求項5に記載の焼入れ鋼管部材の製造方法。 - 前記亜鉛めっき量Aが60g/m2以上である
ことを特徴とする請求項5又は6に記載の焼入れ鋼管部材の製造方法。 - 前記プレス成形工程では、前記接触部が、前記GI亜鉛めっき鋼管の全長の50%以上の長さにわたり形成されるように前記GI亜鉛めっき鋼管をプレス成形する
ことを特徴とする請求項5から7のいずれか一項に記載の焼入れ鋼管部材の製造方法。 - 前記加熱保持工程では、前記GI亜鉛めっき鋼管を通電加熱する
ことを特徴とする請求項5から8のいずれか一項に記載の焼入れ鋼管部材の製造方法。 - 前記加熱保持工程では、プレス成形された前記GI亜鉛めっき鋼管を鋼材のAc3点以上の温度域に3秒以上、30秒以下保持するように通電加熱する
ことを特徴とする請求項5から9のいずれか一項に記載の焼入れ鋼管部材の製造方法。 - 前記GI亜鉛めっき鋼管が、Ac3点が850℃以下の成分系を有する
ことを特徴とする請求項5から10のいずれか一項に記載の焼入れ鋼管部材の製造方法。
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