WO2025070760A1 - 成形体 - Google Patents

成形体 Download PDF

Info

Publication number
WO2025070760A1
WO2025070760A1 PCT/JP2024/034743 JP2024034743W WO2025070760A1 WO 2025070760 A1 WO2025070760 A1 WO 2025070760A1 JP 2024034743 W JP2024034743 W JP 2024034743W WO 2025070760 A1 WO2025070760 A1 WO 2025070760A1
Authority
WO
WIPO (PCT)
Prior art keywords
less
bending
content
steel sheet
steel plate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2024/034743
Other languages
English (en)
French (fr)
Japanese (ja)
Inventor
匠 小山内
武 豊田
栄作 桜田
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Priority to CN202480050356.8A priority Critical patent/CN121646648A/zh
Priority to JP2025541835A priority patent/JPWO2025070760A1/ja
Publication of WO2025070760A1 publication Critical patent/WO2025070760A1/ja
Anticipated expiration legal-status Critical
Pending legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a molded body having a bent portion formed from a steel plate.
  • Patent Document 1 discloses a high-strength hot-rolled steel sheet with excellent bending workability, which is used in the manufacture of automobile suspension parts and the like. Specifically, Patent Document 1 discloses a hot-rolled steel sheet containing C, Si, Mn, and sol. Al as chemical components, in which the sum of the average pole density of the orientation group consisting of ⁇ 211 ⁇ 111> to ⁇ 111 ⁇ 112> and the pole density of the crystal orientation ⁇ 110 ⁇ 001> is 0.5 or more and 6.0 or less in the surface region, and which has a tensile strength of 780 MPa or more and 1370 MPa or less.
  • Patent Document 2 discloses a high-strength steel plate having excellent bending workability and fatigue properties as a steel plate used for manufacturing automobile suspension parts, etc.
  • Patent document 3 discloses a high-strength steel plate with excellent bending properties for punched members with large clearances, which is used in the manufacture of automobile suspension parts, etc. Specifically, Patent Document 3 discloses a high-strength steel sheet having a chemical composition containing C: 0.04-0.20%, Si: 0.6-1.5%, Mn: 1.0-3.0%, P: 0.10% or less, S: 0.030% or less, Al: 0.10% or less, N: 0.010% or less, one or more of Ti, Nb, and V at 0.01-1.0% each, with the balance being iron and unavoidable impurities, with a structure in which bainite accounts for more than 50% by area, the average grain size at a position 50 ⁇ m from the steel sheet surface in the sheet thickness depth direction is 2500 ⁇ [tensile strength TS (MPa)] - 0.85 ⁇ m or less, the amount of C in precipitates with a grain size of less than 20 nm precipitated in the steel is 0.005 mass
  • Patent Document 4 also discloses a high-strength structural steel material with excellent cold bending properties as a steel plate used in the manufacture of automobile suspension parts and the like. Specifically, Patent Document 4 discloses a high-strength structural steel material that is composed of, by weight, C: 0.02-0.1%, Si: 0.01-0.6%, Mn: 1.7-2.5%, Al: 0.005-0.5% or less, P: 0.02% or less, S: 0.01% or less, N: 0.0015-0.015%, with the remainder being Fe and other unavoidable impurities, and that is microstructurally divided along the thickness direction into an outer surface layer and an inner center portion, with the surface layer portion containing tempered bainite as the base structure and the center portion containing bainitic ferrite as the base structure.
  • automotive suspension parts have bent sections formed by press-molding materials such as steel plate into a prescribed shape for each purpose. If the material has insufficient formability, the inside of the bent section may be deformed as if it is woven during press molding, and fine cracks may occur on the inner surface of the bent section. Currently, even if such fine cracks occur, there is no particular effect on the impact resistance of the parts. However, in order to respond to future weight reductions and further complexity of automotive parts, it is desirable to have parts with fewer such fine cracks and even better impact resistance.
  • the present invention aims to provide a molded product with excellent impact resistance at the bent portion through a novel configuration.
  • the present invention includes the following aspects:
  • the chemical composition of the steel sheet is, in mass%, C: 0.02-0.30%, Si: 0.03-2.00%, Mn: 0.50-3.00%, Al: 0.01-1.00%, Ti: 0.06-0.20%, P: 0.100% or less, S: 0.010% or less, N: 0.0100% or less, Nb: 0 to 0.10%, Ca: 0-0.0060%, Mo: 0-1.00%, Cr: 0-1.00%, V: 0 to 0.40%, Ni: 0 to 0.40%, B: 0 to 0.0020%, Cu: 0 to 1.00%, W: 0-1.00%, Sn: 0 to 0.50%, Zr: 0 to 0.050%, and
  • the molded body according to the above aspect 1 or 2 characterized in that the balance is Fe and impurities.
  • FIG. 1 is an end view of a cross section parallel to a plate thickness direction TP including a bent portion 2 in a formed body 1 according to one embodiment of the present invention.
  • FIG. 2(a) is a cross-sectional SEM photograph of the inner surface layer at the bent portion of a molded body sample serving as a comparison standard
  • FIG. 2(b) is a cross-sectional SEM photograph of the inner surface layer at the bent portion of a molded body sample manufactured using the same steel plate as FIG. 2(a) but with the bending direction changed.
  • FIG. 3(a) is a cross-sectional SEM photograph of the inner surface layer at the bent portion of a molded body sample used as a comparison standard
  • (c) is a cross-sectional SEM photograph of the inner surface layer at the bent portion of a molded body sample manufactured in the same bending direction as (a) using a steel plate different from (a).
  • the molded body sample in (a) of FIG. 3 is the same as the molded body sample in (a) of FIG. 2.
  • FIG. 4 is a schematic diagram for explaining a method for measuring the average Taylor factor in the inner surface layer of a bent portion.
  • FIG. 5 is a schematic diagram for explaining the relationship between the bending axis AB and the rolling direction DR when a blank p is punched out from a hot-rolled steel sheet SP and is subjected to bending.
  • the inventors conducted detailed studies on the causes of cracks occurring on the inner surface layer of the bent part of the formed body and on the means of suppressing them.
  • the susceptibility of cracks occurring on the inner surface layer of the bent part is affected by the orientation of the crystals that develop on the surface layer of the steel plate in the bent part.
  • M value the average Taylor Factor
  • the formed body 1 is formed by forming a steel plate into a predetermined shape, and has a predetermined bent portion 2 as shown in FIG. 1 and a plate-shaped portion 3 connected to the bent portion 2 and not bent.
  • the bent portion 2 has an inner surface layer 21 and an outer surface layer 22 that face each other in the plate thickness direction TP.
  • the bent portion 2 functions as a rib for ensuring the strength of the formed body 1, and is formed in a stress generating portion such as an edge portion where stress transmitted from the outside is likely to concentrate.
  • the bent portion 2 may be formed not only in such a stress generating portion but also in other portions. For example, the bent portion 2 may be formed over substantially the entire outer peripheral edge portion of the formed body 1.
  • the position where such a bent portion 2 is formed can be determined depending on the part structure, shape, application, etc. to which the molded body 1 is applied.
  • the maximum stress generation part in the lower arm where stress is most likely to concentrate is the edge part located on the tire side in the longitudinal direction of the lower arm, and it is preferable that the bent portion 2 is formed in a position that includes at least this maximum stress generation part.
  • a maximum stress generation part is also determined depending on the overall structure, shape, application, etc. of the molded body such as an automobile suspension part.
  • the means for forming the bent portion 2 is not particularly limited, and the bent portion 2 can be formed using general processing means and processing conditions such as press forming (particularly cold press forming).
  • the formed body 1 of this embodiment has a characteristic configuration in which the average Taylor factor (M value) of the inner surface layer 21 of the bent portion 2 is 3.300 or less. As a result, in the formed body 1, cracks are less likely to occur in the inner surface layer 21 of the bent portion 2 when the steel plate is press-formed, and as a result, the formed body has fewer cracks in the inner surface layer 21 of the bent portion 2.
  • the inner surface of the bent part refers to the area within the range from the surface of the steel plate inside the bent part to a depth position of 1/8 of the plate thickness in the plate thickness direction. The same applies to the outer surface of the bent part. Note that if the steel plate surface is painted or plated, the thickness of these coatings or plating is excluded.
  • a means for controlling the average Taylor factor M value of the inner surface layer 21 of the bent portion 2 within a range of 3.300 or less will be described.
  • the inventors have studied a means for controlling the average Taylor factor M value, and have found the following. That is, the inventors have found that when a material with a high M value before bending and a material with a low M value before bending are deformed by the same bending process, the M value of each material decreases from the value before bending, but the relationship between the M values of each material before bending is maintained.
  • the inventors have found that when the relationship between the rolling direction of the steel plate, which is the constituent material of the formed body, and the position where bending is scheduled to be performed changes, the M value before bending also changes, and as a result, the bending workability and the M value after bending also change. Based on these findings, the inventors have found that the M value after bending can be controlled within a predetermined range by adjusting the punching direction of the blank material from the steel plate (i.e., the plate cutting direction) so that the bent portion has a low M value below a certain level.
  • FIG. 2 is a cross-sectional SEM photograph of the inner surface layer at the bent portion of a molded body sample that serves as a comparison standard
  • (b) is a cross-sectional SEM photograph of the inner surface layer at the bent portion of a molded body sample manufactured using the same steel plate as (a) but with a different bending direction. Note that in Figure 2, the multiple arrows each point to a multiple crack that has occurred.
  • the formed body sample shown in FIG. 2(a) and the formed body sample shown in FIG. 2(b) use the same steel plate as the material, but the sheet cutting direction of the steel plate, i.e., the punching direction of the blank from the steel plate, is different, and as a result, the M value before bending is different.
  • the formed body sample shown in FIG. 2(a) is a formed body sample formed by punching a blank from a steel plate so that the bending axis A B when bending the blank intersects with the rolling direction of the steel plate when punching the blank from the steel plate, and using the blank.
  • 2(b) is a formed body sample formed by punching a blank from a steel plate so that the bending axis A B when bending the blank does not intersect with the rolling direction of the steel plate when punching the blank from the steel plate, and using the blank.
  • the relationship between the bending axis A B and the rolling direction when punching the blank from the steel plate and bending will be described in detail in the description of the manufacturing method of the formed body described later.
  • the molded body sample shown in Figure 2(a) has an M value of 3.285 before bending and an M value of 3.268 after bending.
  • the molded body sample shown in Figure 2(b) has an M value of 3.337 before bending and an M value of 3.312 after bending.
  • the M value after bending decreases from the value before bending, but the relationship between the values before bending is maintained.
  • FIG. 3 is a cross-sectional SEM photograph of the inner surface layer at the bent portion of a molded body sample used as a comparison standard
  • (c) is a cross-sectional SEM photograph of the inner surface layer at the bent portion of a molded body sample manufactured using a blank material punched in the same cutting direction as (a) from a different steel plate than (a). Note that in Figure 3 as well, multiple arrows point to multiple cracks that have occurred.
  • both the formed body samples shown in Fig. 3(a) and (c) are formed body samples formed by punching out a blank from a steel sheet so that the bending axis A- B when bending the blank intersects with the rolling direction of the steel sheet, and then forming the blank.
  • the molded body sample shown in Figure 3(a) has an M value of 3.285 before bending and an M value of 3.268 after bending.
  • the molded body sample shown in Figure 3(c) has an M value of 3.311 before bending and an M value of 3.309 after bending.
  • the M value after bending decreases from the value before bending, but the relationship between the values before bending is maintained.
  • the molded body sample (c) has more cracks on the inner surface layer of the bent part than the molded body sample (a), which has a smaller M value after bending than the molded body sample (c).
  • the molded body sample shown in Figure 3(c) has a smaller M value after bending than the molded body sample shown in Figure 2(b), and as a result, it can be seen that there are fewer cracks on the inner surface layer of the bent part than in the molded body sample shown in Figure 2(b).
  • the M value of the average Taylor factor of the inner surface layer of the bent part is most influenced by the sheet cutting direction of the steel sheet, i.e., the relationship between the bending axis A B and the rolling direction of the steel sheet when the blank material is punched out from the steel sheet and bending is performed, and then by the type of steel sheet, i.e., the chemical composition of the steel sheet.
  • the M value of the average Taylor factor of the inner surface layer of the bent part can be controlled within the above-mentioned predetermined range, and cracks in the inner surface layer of the bent part can be reduced. Furthermore, by adjusting the texture of the steel sheet, i.e., by adjusting the chemical composition of the steel sheet, the M value of the steel sheet before bending can be more reliably lowered to a certain level or less, so that the M value of the average Taylor factor of the inner surface layer of the bent part after bending can be more easily controlled within the above-mentioned predetermined range. As a result, cracks in the inner surface layer of the bent part can be further reduced.
  • examples of means for making it easier to control the M value of the average Taylor factor of the inner surface layer of the bent portion within the above-mentioned specified range include means for softening at least the surface layer of the steel plate or other material in the portion corresponding to the bent portion, thereby concentrating strain on the surface layer and lowering the M value after bending, and means for ensuring high formability of the steel plate or other material, thereby applying large strain during bending and lowering the M value after bending.
  • the M value of the average Taylor factor of the inner surface layer of the bent portion is greater than 3.300, numerous cracks are likely to occur in the bent portion. Therefore, in order to obtain the effects of the present invention, it is necessary to control the M value to 3.300 or less.
  • the M value may be 3.200 or less, 3.100 or less, or 3.000 or less. There is no particular limit to the lower limit of the M value, but the effects of the present invention can be obtained better as the M value is lower. However, by definition, the M value cannot be less than 2.000.
  • the M value may be 2.100 or more, 2.400 or more, or 2.700 or more.
  • the average Taylor factor M value of the inner surface layer of the bent portion can be calculated by measuring a cross section perpendicular to the bending axis, which includes the entire thickness of the sample, by EBSD.
  • Fig. 4 is a schematic diagram for explaining a method for measuring the average Taylor factor of the inner surface layer of the bent portion 2.
  • the crystal orientation is measured from a rectangular measurement region MR centered on the apex of the inner surface of the bent portion 2.
  • the surface of the sample including the measurement region MR is finished by mirror polishing and then electrolytic polishing.
  • an EBSD analysis device consisting of a thermal field emission scanning electron microscope (e.g., JSM-7200F manufactured by JEOL) and an EBSD detector (e.g., EDAX Velocity (registered trademark) ultra-high speed EBSD detector) is used.
  • the degree of vacuum in the device is 9.6 ⁇ 10 ⁇ 5 Pa or less
  • the acceleration voltage is 25 kV
  • the irradiation current level is 15 to 18, and the WD (Working Distance) is 15 mm.
  • the measurement region MR is set as a rectangular region having a thickness direction length that fits in the surface layer region, i.e., a thickness direction length smaller than 1/8 of the thickness, as a short side, and a length of 750 ⁇ m perpendicular to the thickness direction length.
  • the measurement region MR may be a rectangular region having a short side in the thickness direction of 300 ⁇ m and a long side perpendicular to the thickness direction of 750 ⁇ m.
  • the measurement step is 2 ⁇ m. From the thus obtained information on the multiple crystal orientations, the average Taylor factor is calculated using EBSD analysis software, such as Ver.
  • the slip system is assumed to be 12 types of ⁇ 110 ⁇ 111> system, which is the main slip system of BCC, and the calculation is performed.
  • the deformation of the inner surface layer of the bent part is calculated using a tensor assuming compressive deformation under plane strain conditions. In other words, it is assumed that the expansion to keep the volume constant occurs only in the plate thickness direction against the compression caused by the bending deformation.
  • the diagonal components of x, y, and z of the given tensor are 0, -1, and 1, respectively, and all off-diagonal components are 0.
  • the minimum radius of curvature r on the inside of the bent portion 2 is not particularly limited.
  • the minimum radius of curvature r may be 8.0 mm or less, 5.0 mm or less, or 3.0 mm or less.
  • the minimum radius of curvature r may be 0.8 mm or more, 1.2 mm or more, 1.6 mm or more, or 2.0 mm or more.
  • the steel plate used in the formed body of this embodiment is not particularly limited in terms of requirements other than that, so long as the average Taylor factor M value of the inner surface layer of the bent portion of the formed body can be adjusted to fall within the above-mentioned specified range.
  • the strength, thickness, etc. of the steel plate can be the specified strength, thickness, etc. required for the part to which the formed body is applied.
  • the strength of the steel plate suitable for application of the present invention is, for example, tensile strength of 780 MPa or more.
  • the Vickers hardness at 1/4 of the plate thickness of the steel plate having such high strength is greater than 250 HV. Normally, such steel plate is more likely to develop cracks on the inner surface layer of the bent portion after bending as the strength is increased.
  • the formed body 1 of the present embodiment can reduce cracks on the inner surface layer of the bent portion even if a steel plate having a Vickers hardness of 250 HV or more at 1/4 of the plate thickness is used, because the average Taylor factor M value of the inner surface layer of the bent portion is 3.300 or less.
  • the 1/4 position of the plate thickness refers to a position in the plate thickness direction starting from the surface of the steel plate, which is a distance that is 1/4 of the total plate thickness from the surface of the steel plate.
  • the Vickers hardness of the steel plate at the 1/4 position of the plate thickness may be 252HV or more, 255HV or more, 258HV or more, or 260HV or more, from the viewpoint of the impact resistance of the formed body. There is no particular upper limit to the Vickers hardness of the steel plate at the 1/4 position of the plate thickness.
  • the Vickers hardness of the steel plate at the 1/4 position of the plate thickness may be 450HV or less, 400HV or less, 350HV or less, or 300HV or less.
  • the present invention can also be applied to steel plates with a Vickers hardness of less than 250 HV.
  • Such steel plates have low tensile strength and therefore excellent bending workability, so by applying the present invention, it is possible to more reliably suppress the occurrence of cracks.
  • the Vickers hardness at 1/4 of the plate thickness of the steel plate can be measured according to JIS Z 2244:2009.
  • the Vickers hardness at 1/4 of the plate thickness of the steel plate can be obtained by measuring 10 times at 1/4 of the plate thickness of the steel plate at a location other than the bent portion with a load of 1 kgf (approximately 9.80 N) and taking the average value of the 10 measured values. At this time, the distance between the measurement positions is ensured to be at least three times the distance of the indentation.
  • the thickness of the steel plate is measured with a micrometer from a relatively smooth position on the part (formed body). Note that areas where the plate thickness has been locally reduced due to thinning caused by press working, etc., are not included in the measurement.
  • the steel plate used for the formed body 1 is C: 0.03 to 0.30%, Si: 0.03-2.00%, Mn: 0.50-3.00%, Al: 0.01-1.00%, Ti: 0.06-0.20%, P: 0.100% or less, S: 0.010% or less, N: 0.0100% or less, Nb: 0 to 0.10%, Ca: 0-0.0060%, Mo: 0-1.00%, Cr: 0-1.00%, V: 0 to 0.40%, Ni: 0 to 0.40%, B: 0 to 0.0020%, Cu: 0 to 1.00%, W: 0-1.00%, Sn: 0 to 0.50%, Zr: 0 to 0.050%, and It is preferable that the alloy has a specific chemical composition of which the balance is Fe and impurities.
  • C is an element that increases the strength of the steel sheet.
  • the C content is preferably 0.02% or more.
  • the C content may be 0.03% or more, 0.04% or more, or 0.05% or more.
  • the C content is preferably 0.30% or less.
  • the C content may be 0.25% or less, 0.20% or less, or 0.15% or less.
  • Si is a deoxidizing element for steel and is a solid solution strengthening element effective for increasing the strength of the steel sheet without impairing the ductility.
  • the Si content is preferably 0.03% or more.
  • the Si content may be 0.05% or more, 0.08% or more, or 0.10% or more.
  • the Si content is preferably 2.00% or less.
  • the Si content may be 1.80% or less, 1.60% or less, or 1.40% or less.
  • Mn is an element that improves the hardenability of steel and contributes to improving strength.
  • the Mn content is preferably 0.50% or more.
  • the Mn content may be 0.60% or more, 0.80% or more, or 1.00% or more.
  • the Mn content is preferably 3.00% or less.
  • the Mn content may be 2.80% or less, 2.60% or less, or 2.40% or less.
  • Al 0.01-1.00%
  • Al is an element that functions as a deoxidizer and is a solid solution strengthening element that is effective in increasing the strength of steel. Moreover, Al is also an element that suppresses the generation of carbides and makes it easier to form retained austenite.
  • the Al content is preferably 0.01% or more.
  • the Al content may be 0.05% or more, 0.10% or more, or 0.15% or more.
  • the Al content is preferably 1.00% or less.
  • the Al content may be 0.80% or less, 0.60% or less, or 0.40% or less.
  • Ti is an element that controls the morphology of carbides and increases the strength of ferrite.
  • the Ti content is preferably 0.06% or more.
  • the Ti content may be 0.08% or more or 0.10% or more.
  • the Ti content is preferably 0.20% or less.
  • the Ti content may be 0.18% or less, 0.16% or less, or 0.14% or less.
  • P is an element that is mixed in during the manufacturing process and is an impurity.
  • P may segregate at prior austenite grain boundaries and reduce the formability of the steel sheet due to grain boundary embrittlement. For this reason, the lower the P content, the better.
  • the P content may be 0%.
  • the P content may be 0.0001% or more, 0.0005% or more, or 0.001% or more.
  • the P content may be 0.100% or less.
  • the P content may be 0.080% or less, 0.060% or less, or 0.040% or less.
  • S is an element that is mixed in during the manufacturing process and is an impurity.
  • S may generate nonmetallic inclusions such as MnS in the steel, which may lead to an increase in hardness and a decrease in ductility of the steel sheet. Therefore, the lower the S content, the better.
  • the S content may be 0%.
  • the S content may be 0.0001% or more, 0.0005% or more, or 0.0010% or more.
  • the S content may be 0.010% or less.
  • the S content may be 0.008% or less, 0.006% or less, or 0.004% or less.
  • N is an element that is mixed in during the manufacturing process. Like C, N is an element that is effective in increasing the strength of steel, but it is also an element that affects the occurrence of cross slip of dislocations during forming, especially during cold press forming. If the N content is high, the concentration of strain cannot be suppressed during forming of the steel sheet, causing the occurrence of voids, and thus the formability is reduced. From the viewpoint of ensuring good formability, the lower the N content, the better.
  • the N content may be 0%. However, from the viewpoint of shortening the refining time and ensuring good productivity, the N content may be 0.0001% or more, 0.0005% or more, or 0.0010% or more. On the other hand, from the viewpoint of ensuring good bending workability, the N content may be 0.0100% or less. The N content may be 0.0080% or less, 0.0060% or less, or 0.0050% or less.
  • the preferred basic chemical composition of the steel plate used in the formed body 1 is as described above.
  • the steel plate may contain one or more of the following optional elements in place of a portion of the remaining Fe, as necessary. These optional elements are described in detail below.
  • Nb is an element effective for controlling the morphology of carbides, and is also effective for refining crystal grains and improving the toughness and bending workability of steel sheets.
  • the Nb content may be 0%, but in order to fully obtain these effects, the Nb content may be 0.001% or more.
  • the Nb content may be 0.005% or more, 0.007% or more, or 0.010% or more.
  • the Nb content may be 0.10% or less. From the viewpoint of economy, the Nb content may be 0.08% or less, 0.06% or less, or 0.04% or less.
  • Ca is an element that contributes to finely dispersing inclusions and enhances toughness. That is, Ca is an element that contributes to improving the formability of the steel sheet.
  • the Ca content may be 0%, but in order to fully obtain such effects, the Ca content may be 0.0001% or more.
  • the Ca content may be 0.0005% or more, 0.0010% or more, or 0.0015% or more.
  • the Ca content is preferably 0.0060% or less.
  • the Ca content may be 0.0050% or less, 0.0040% or less, or 0.0030% or less.
  • Mo is an element that suppresses phase transformation at high temperatures and contributes to improving the strength of the steel sheet.
  • the Mo content may be 0%, but in order to fully obtain such effects, the Mo content may be 0.001% or more.
  • the Mo content may be 0.01% or more, 0.05% or more, or 0.10% or more.
  • the Mo content may be 1.00% or less.
  • the Mo content may be 0.80% or less, 0.60% or less, or 0.40% or less.
  • Cr is an element that improves the hardenability of steel and contributes to improving the strength of steel plate.
  • the Cr content may be 0%, but in order to fully obtain such effects, the Cr content may be 0.001% or more.
  • the Cr content may be 0.01% or more, 0.10% or more, 0.20% or more, or 0.30% or more.
  • the Cr content may be 1.00% or less.
  • the Cr content may be 0.80% or less, 0.60% or less, or 0.50% or less.
  • V is an element effective for controlling the morphology of carbides, and is also effective for refining crystal grains and improving the toughness and bending workability of steel sheets.
  • the V content may be 0%, but in order to fully obtain such effects, the V content may be 0.001% or more.
  • the V content may be 0.005% or more, 0.01% or more, or 0.02% or more.
  • the V content may be 0.40% or less.
  • the V content may be 0.30% or less, 0.20% or less, or 0.10% or less.
  • Ni is an element that suppresses phase transformation at high temperatures and contributes to improving the strength of the steel sheet.
  • the Ni content may be 0%, but in order to fully obtain such effects, the Ni content may be 0.001% or more.
  • the Ni content may be 0.01% or more, 0.03% or more, or 0.05% or more.
  • the Ni content may be 0.40% or less.
  • the Ni content may be 0.30% or less, 0.25% or less, or 0.20% or less.
  • B is an element that suppresses phase transformation at high temperatures and contributes to improving the strength of the steel sheet.
  • the B content may be 0%, but in order to fully obtain such an effect, the B content may be 0.0001% or more.
  • the B content may be 0.0005% or more, 0.0010% or more, or 0.0015% or more.
  • the B content may be 0.0020% or less.
  • the B content may be 0.0018% or less, 0.0016% or less, or 0.0015% or less.
  • Cu is an element that exists in the steel in the form of fine particles and contributes to improving the strength of the steel sheet.
  • the Cu content may be 0%, but in order to fully obtain such an effect, the Cu content may be 0.001% or more.
  • the Cu content may be 0.01% or more, 0.03% or more, or 0.05% or more.
  • the Cu content may be 1.00% or less.
  • the Cu content may be 0.80% or less, 0.60% or less, or 0.40% or less.
  • W is an element that suppresses phase transformation at high temperatures and contributes to improving the strength of the steel sheet.
  • the W content may be 0%, but in order to fully obtain such effects, the W content may be 0.001% or more or 0.005% or more.
  • the W content is set to 1.00% or less.
  • the W content may be 0.08% or less.
  • Sn is an element that suppresses the coarsening of crystal grains and contributes to improving the strength of the steel sheet.
  • the Sn content may be 0%, but in order to fully obtain such effects, the Sn content may be 0.001% or more.
  • the Sn content may be 0.01% or more, 0.05% or more, or 0.08% or more.
  • the Sn content may be 0.50% or less.
  • the Sn content may be 0.40% or less, 0.30% or less, or 0.20% or less.
  • Zr is an element that contributes to improving the formability of the steel sheet.
  • the Zr content may be 0%, but in order to fully obtain such an effect, the Zr content may be 0.0001% or more.
  • the Zr content may be 0.0005% or more, 0.0010% or more, or 0.0015% or more.
  • the Zr content may be 0.050% or less.
  • the Zr content may be 0.040% or less, 0.030% or less, or 0.020% or less.
  • the remainder of the steel sheet other than the above elements is composed of Fe and impurities.
  • the impurities are components that are mixed in due to various factors in the manufacturing process, including raw materials such as ores and scraps, when industrially manufacturing the steel sheet.
  • impurities include H, O, Na, Cl, Co, Zn, Ga, Ge, As, Se, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Te, Cs, Ta, Re, Os, Ir, Pt, Au, Pb, Bi, Sb, and Po.
  • the impurities may be contained in an amount of 0.100% or less in total.
  • the chemical composition of the steel plate can be measured by a general analytical method.
  • the chemical composition of the steel plate can be measured using inductively coupled plasma atomic emission spectrometry (ICP-AES).
  • ICP-AES inductively coupled plasma atomic emission spectrometry
  • C and S can be measured using the combustion-infrared absorption method, N using the inert gas fusion-thermal conductivity method, and O using the inert gas fusion-non-dispersive infrared absorption method.
  • the molded body 1 of this embodiment has few cracks on the inner surface of the bent portion. For this reason, the molded body of this embodiment can be applied to various automobile suspension parts that require high impact resistance, such as upper arms, lower arms, torsion beams, and stabilizers.
  • a steel plate is first manufactured.
  • the method for producing the steel sheet is not particularly limited, but it is preferable to obtain a steel sheet having the above-mentioned specific chemical composition.
  • An example of the method for producing such a steel sheet includes a casting step of casting a slab having the above-mentioned specific chemical composition, and a hot rolling step of hot rolling the cast slab. Preferred conditions for these steps will now be described.
  • the casting step is a step of casting a slab having the specific chemical composition described above.
  • the casting step uses a continuous casting machine having a plurality of reduction rolls adjacent to each other in the conveying direction of the slab, the roll pitch of the adjacent reduction rolls being 290 mm or less.
  • the hot rolling process is a process of hot rolling the cast slab.
  • the heating temperature is 1300°C or less.
  • the heated slab is subjected to rough rolling and finish rolling.
  • the steel plate can have the above-mentioned preferred specific Vickers hardness, and the M value of the average Taylor factor of the inner surface layer of the bent part 2 formed after bending can be easily controlled within the above-mentioned specific range.
  • the starting temperature for rough rolling is, for example, 1150°C or lower. If the starting temperature for rough rolling is 1150°C or lower, the effect of heat removal by the rolling rolls is reduced, and the steel plate can be rolled evenly on both sides. On the other hand, the starting temperature for rough rolling is, for example, 1050°C or higher. If the starting temperature for rough rolling is 1050°C or higher, the rolling reaction force can be controlled so that it does not become excessively large.
  • the end temperature of the finish rolling is, for example, 800°C or higher. If the end temperature of the finish rolling is 800°C or higher, the average crystal grain size of the hot rolled steel sheet and the final product can be reduced, and sufficient yield strength can be ensured. On the other hand, although there is no particular upper limit to the end temperature of the finish rolling, from an economical point of view, the end temperature of the finish rolling is, for example, 980°C or lower.
  • the diameter of the rolling rolls used in the hot rolling process is, for example, 100 mm or more. If the diameter of the rolling rolls is 100 mm or more, strain is less likely to concentrate on the surface in contact with the rolling rolls, and the steel sheet can be rolled evenly on both sides. On the other hand, the upper limit of the diameter of the rolling rolls is not particularly limited, but from an economical point of view, it is, for example, 700 mm or less.
  • the rolling rolls used in the hot rolling process may be heated in advance. If the rolling rolls are heated in advance, the removal of heat from the steel sheet by the rolling rolls is suppressed, and unevenness in the removal of heat from the steel sheet by the rolling rolls can be reduced.
  • the hot-rolled steel sheet obtained in the hot rolling process is wound at a winding temperature of, for example, 450 to 600°C.
  • a winding temperature of, for example, 450 to 600°C.
  • the strength of the hot-rolled steel sheet does not become excessively high, and deterioration of bending workability can be suppressed.
  • the winding temperature at 600°C or lower, coarse ferrite and pearlite are less likely to form in the structure of the hot-rolled steel sheet, and bainite is more likely to be obtained in the structure of the hot-rolled steel sheet, improving the strength of the steel sheet.
  • the coiling temperature of the hot-rolled steel sheet may be, for example, 450°C or lower. By setting the coiling temperature to 450°C or lower, a large amount of structures such as bainite and martensite are formed, making it easier to ensure the desired strength even with the addition of a small amount of alloying elements.
  • the coiling temperature may be, for example, 200°C or lower. By setting the coiling temperature to 200°C or lower, a large amount of martensite is formed, making it possible to improve the strength of the steel sheet even with a small amount of alloying added.
  • the hot-rolled steel sheet obtained by the hot rolling process may be subjected to skin pass rolling for the purpose of correcting the shape. Note that since skin pass rolling is not included in cold rolling, the steel sheet after skin pass rolling is also a hot-rolled steel sheet.
  • Hot rolled steel sheets Steel sheets obtained by hot rolling or steel sheets obtained by skin pass rolling (hereinafter collectively referred to as "hot rolled steel sheets”) may be subjected to any processing step such as plating, if necessary.
  • the hot-rolled steel sheet obtained by the above manufacturing method is then subjected to the next forming step.
  • the steel sheet used for the formed body of this embodiment is preferably a hot-rolled steel sheet, since this makes it easier to obtain the effects of the present invention with greater certainty.
  • the forming process includes a punching process in which a steel plate is punched into a predetermined shape, and a bending process in which a blank material punched into the predetermined shape is bent.
  • the punching process is a process in which a blank material having a planar shape corresponding to the shape of the formed body 1 before bending is punched out of the rolled steel sheet, i.e., the hot-rolled steel sheet.
  • FIG. 5 is a schematic diagram for explaining the relationship between the bending axis A B and the rolling direction DR when the blank p is punched out from the hot-rolled steel sheet SP and bent.
  • the punching direction of the blank p i.e., the sheet cutting direction
  • the sheet cutting direction is adjusted so that the angle ⁇ between the bending axis A B and the rolling direction DR intersects at an angle of 45 degrees to 135 degrees.
  • the punching process and the bending process of the hot-rolled steel sheet SP are performed so that the bending axis A B of the part to be the bending part 2 in the hot-rolled steel sheet SP intersects with the rolling direction DR of the hot-rolled steel sheet SP at an angle of 45 degrees to 135 degrees.
  • the blank p is shown with a rectangular planar shape for convenience, but in reality it has a planar shape that corresponds to the formed body 1 before bending.
  • the average Taylor factor M value of the inner surface layer of the bent portion can be controlled within the above-mentioned specified range.
  • the cutting direction of the blank p is not particularly limited as long as it is an angle between 45 degrees and 135 degrees. However, from the viewpoint of impact resistance, it may be within a range of 60 degrees or more and 120 degrees or less, within a range of 85 degrees or more and 95 degrees or less, or may be 90 degrees.
  • the direction in which the bending axis of the molded body extends may not be constant.
  • the bending axis may be curved, or there may be multiple bending axes.
  • the punching direction of the blank material i.e., the sheet cutting direction
  • the punching direction of the blank material can be set to match the part where cracks need to be reduced the most, taking into account the direction of stress expected in the usage environment of the part to which the molded body is applied and the dimensions of the bent part.
  • the bending axes may be parallel to each other or may intersect at an angle other than perpendicular.
  • the bending process is a process in which a blank material that has been punched into a predetermined shape is bent.
  • the means for bending the blank material is not particularly limited, and examples include press forming.
  • such bending means as press forming may be performed only once, or may be performed in stages multiple times.
  • the bending process is performed on the blank material after it has been punched into a predetermined shape in the punching process, but the present invention is not limited to this embodiment.
  • the bending process may be performed by bending a predetermined location of the blank material while punching the blank material in the punching process.
  • the punching process and the bending process may be performed in parallel, or the bending process may be performed after the punching process as described above.
  • the molded body obtained by the above molding process may be subjected to painting or other surface treatment processes for the purpose of improving the appearance and design.
  • a molded body according to one embodiment of the present invention was produced under various conditions, and the impact resistance properties of the bent parts of the resulting molded body were investigated.
  • Step plate manufacturing A slab having the chemical composition shown in Table 1 below was cast by a continuous casting method using a continuous casting machine equipped with a plurality of reduction rolls arranged with a roll pitch of 290 mm or less.
  • the hot rolling process was carried out on the obtained slab. Specifically, the slab was heated to a temperature of 1250°C, and rough rolling and finish rolling were carried out. The starting temperature of rough rolling was 1050°C, and the ending temperature of finish rolling was 940°C to 980°C. The coiling temperature of the obtained hot-rolled steel sheet was 450°C to 480°C. In this way, a hot-rolled steel sheet with a thickness of 3 mm was obtained.
  • the obtained rectangular blank material was press molded according to JIS Z2248:2006 "6.3 V-block method” to produce a molded body.
  • the bending angle of the punch used in this press molding was 90 degrees. In this way, molded bodies No. 1 to 8 shown in Table 2 were obtained.
  • the average Taylor factor M value of the inner surface layer of the bent part was measured according to the above-mentioned "Method for measuring the average Taylor factor M value of the inner surface layer of the bent part", and further, the Vickers hardness was measured according to the above-mentioned “Method for measuring Vickers hardness at the 1/4 position of the plate thickness of the steel plate”. Then, the following impact resistance test was carried out on the formed bodies No. 1 to 8, and the impact resistance of the bent parts of these formed bodies was evaluated. The measurement and evaluation results are shown in Table 2 below.
  • the molded body to be tested is cooled to -40°C.
  • the cooled molded body is placed on a horizontal test stand with the outer surface of the bent part facing up.
  • a cone weighing approximately 120 kg is placed at a height of 0.18 m from the surface of the test stand and allowed to freely fall to collide with the outer surface of the bent part of the molded body. Note that the cone is placed with its bottom surface facing downward before being allowed to freely fall.
  • a cone with a bottom surface area large enough to cover the entire bent part of the part is used.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
PCT/JP2024/034743 2023-09-28 2024-09-27 成形体 Pending WO2025070760A1 (ja)

Priority Applications (2)

Application Number Priority Date Filing Date Title
CN202480050356.8A CN121646648A (zh) 2023-09-28 2024-09-27 成形体
JP2025541835A JPWO2025070760A1 (https=) 2023-09-28 2024-09-27

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2023168448 2023-09-28
JP2023-168448 2023-09-28

Publications (1)

Publication Number Publication Date
WO2025070760A1 true WO2025070760A1 (ja) 2025-04-03

Family

ID=95203251

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2024/034743 Pending WO2025070760A1 (ja) 2023-09-28 2024-09-27 成形体

Country Status (3)

Country Link
JP (1) JPWO2025070760A1 (https=)
CN (1) CN121646648A (https=)
WO (1) WO2025070760A1 (https=)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2020111231A (ja) * 2019-01-15 2020-07-27 日本製鉄株式会社 鋼板部材重ね合わせ構造、車体構造
WO2020230796A1 (ja) * 2019-05-16 2020-11-19 Ｊｆｅスチール株式会社 高強度部材、高強度部材の製造方法及び高強度部材用鋼板の製造方法
CN113322365A (zh) * 2021-05-19 2021-08-31 北京理工大学 一种同时提高低碳低合金钢强度和塑性的方法
JP2022132267A (ja) * 2021-02-28 2022-09-08 しのはらプレスサービス株式会社 ポンチストローク制御による金属材料の微振動プレス加工方法

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2020111231A (ja) * 2019-01-15 2020-07-27 日本製鉄株式会社 鋼板部材重ね合わせ構造、車体構造
WO2020230796A1 (ja) * 2019-05-16 2020-11-19 Ｊｆｅスチール株式会社 高強度部材、高強度部材の製造方法及び高強度部材用鋼板の製造方法
JP2022132267A (ja) * 2021-02-28 2022-09-08 しのはらプレスサービス株式会社 ポンチストローク制御による金属材料の微振動プレス加工方法
CN113322365A (zh) * 2021-05-19 2021-08-31 北京理工大学 一种同时提高低碳低合金钢强度和塑性的方法

Also Published As

Publication number Publication date
JPWO2025070760A1 (https=) 2025-04-03
CN121646648A (zh) 2026-03-10

Similar Documents

Publication Publication Date Title
CN105793455B (zh) 热成形钢板构件及其制造方法以及热成形用钢板
EP2823904B1 (en) Warm press forming method for a steel
EP3971308B1 (en) High strength member, method for manufacturing high strength member, and method for manufacturing steel sheet for high strength member
JP6485549B2 (ja) 高強度熱延鋼板
JP6958752B2 (ja) 鋼板、部材及びそれらの製造方法
TWI666331B (zh) Hot stamping
JP6947329B2 (ja) 鋼板、部材及びそれらの製造方法
CN102712982B (zh) 成形性和形状冻结性优良的冷轧钢板及其制造方法
CN111051554B (zh) 高强度钢板及其制造方法
KR20110018457A (ko) 냉연 강판 및 그 제조 방법 그리고 백라이트 섀시
WO2023181641A1 (ja) 高強度鋼板およびその製造方法
EP2803745B1 (en) Hot-rolled steel sheet and manufacturing method for same
WO2025070760A1 (ja) 成形体
JP7705065B2 (ja) 熱延鋼板
JP7817661B2 (ja) 自動車用足回り部品
EP4339307A1 (en) Steel sheet for hot stamping and hot-stamped molded item
WO2023189175A1 (ja) ホットスタンプ用鋼板及びホットスタンプ成形体
CN117178070A (zh) 热轧钢板
KR20260052166A (ko) 성형체
CN117062930B (zh) 高强度热轧钢板及其制造方法
KR102812229B1 (ko) 강판 및 그 제조 방법
JP7787482B2 (ja) 鋼板及び外板部材
TW201943868A (zh) 熱軋鋼板
JP7355994B2 (ja) 高炭素鋼板およびその製造方法
WO2026088565A1 (ja) 成形体

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 24872541

Country of ref document: EP

Kind code of ref document: A1

ENP Entry into the national phase

Ref document number: 2025541835

Country of ref document: JP

Kind code of ref document: A

WWE Wipo information: entry into national phase

Ref document number: 2025541835

Country of ref document: JP

REG Reference to national code

Ref country code: BR

Ref legal event code: B01A

Ref document number: 112025028041

Country of ref document: BR

WWE Wipo information: entry into national phase

Ref document number: 2601001544

Country of ref document: TH

WWE Wipo information: entry into national phase

Ref document number: 1020267008696

Country of ref document: KR