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CN-117545867-B - Hot dip galvanized steel sheet, method for manufacturing same, and component

CN117545867BCN 117545867 BCN117545867 BCN 117545867BCN-117545867-B

Abstract

The invention provides a hot dip galvanized steel sheet, which has high YR and high ductility, stretch flangeability and bendability, and improves shearing workability, and TS is 1180MPa or more. The base steel sheet has a predetermined composition and a steel structure, and particularly has a ratio of the number of residual gamma particles of 2.0 or less to more than 50%, a hardness frequency of 0.25 or more to 1 group spacing, an area ratio of quenched martensite in the surface layer portion of 80% or less, a surface layer softening thickness of 10 [ mu ] m to 100 [ mu ] m, and a low-temperature region diffusible hydrogen content of 0.015 mass ppm or less.

Inventors

  • Nan Xiuhe
  • YUSUKE WADA
  • TOJI YUKI
  • Mu Shuiyangyi

Assignees

  • 杰富意钢铁株式会社

Dates

Publication Date
20260505
Application Date
20220316
Priority Date
20210624

Claims (7)

  1. 1. A hot dip galvanized steel sheet comprising a base steel sheet and a hot dip galvanized layer on the surface of the base steel sheet, the hot dip galvanized steel sheet having a tensile strength of 1180MPa or more, The base steel sheet has the following composition and steel structure, The composition of the components is 0.090% -0.390% by mass, 0.01% -2.50% by mass of Si, 2.00% -4.00% by mass of Mn, less than 0.100% by mass of P, less than 0.0200% by mass of S, less than 0.100% by mass of Al and less than 0.0100% by mass of N, the balance being Fe and unavoidable impurities, In the steel structure, at the position of 1/4 of the plate thickness of the base steel plate, the area ratio of martensite is 70% or more, the area ratio of ferrite is 10% or less, the area ratio of retained austenite is 0.5% or more and less than 10.0%, the number ratio of grains with an aspect ratio of 2.0 or less among the grains constituting the retained austenite exceeds 50%, In a histogram of hardness distribution at a position 1/4 of the plate thickness of the base steel plate, the number of group pitches having a frequency of 0.25 or more is 1, the rank range of the group pitches of the histogram exceeds (n-1) ×20+450 and is n×20+450 or less with a Vickers hardness HV meter, n is an integer of 1 to 10, In addition, the area ratio of the quenched martensite is 80% or less in the surface layer portion of the base steel sheet, which is a region ranging from the surface of the base steel sheet to a depth of 10 μm, The surface layer softening thickness of the base steel plate is 10-100 mu m, The surface layer softening thickness of the base steel sheet is a distance from the surface of the base steel sheet to a depth position of the deepest portion where the hardness is 0.85 or less of the standard hardness, using the hardness obtained at the 1/4 position of the plate thickness of the base steel sheet as the standard hardness, The amount of diffusible hydrogen in the low-temperature region of the base steel sheet is 0.015 mass ppm or less, Here, the low-temperature region diffusible hydrogen amount of the base steel sheet is an amount of hydrogen released from the base steel sheet when the base steel sheet is heated to 50 ℃.
  2. 2. The hot-dip galvanized steel sheet according to claim 1, wherein the composition of the base steel sheet further contains at least 1 selected from the group consisting of 0.0100% or less, 0.200% or less of Ti, 0.200% or less of Nb, 0.200% or less of V, 0.10% or less of Ta, 0.10% or less of W, 0.0100% or less of B, 1.00% or less of Cr, 1.00% or less of Mo, 1.00% or less of Ni, 0.010% or less of Co, 1.00% or less of Cu, 0.200% or less of Sn, 0.200% or less of Sb, 0.0100% or less of Ca, 0.0100% or less of Mg, 0.0100% or less of REM, 0.100% or less of Zr, 0.100% or less of Te, 0.10% or less of Hf, and 0.200% or less of Bi in mass%.
  3. 3. The hot-dip galvanized steel sheet according to claim 1 or 2, wherein the hot-dip galvanized layer is an alloyed hot-dip galvanized layer.
  4. 4. A method for producing a hot-dip galvanized steel sheet, comprising hot-rolling a steel sheet having the composition of claim 1 or 2 at a coiling temperature of 350 ℃ to 600 ℃ and a residence time of at least 5000s in a temperature range of 300 ℃ during cooling after coiling to obtain a hot-rolled steel sheet, Then, the hot-rolled steel sheet is subjected to acid washing, Then, the hot rolled steel sheet is subjected to a first heat treatment under the conditions that the heat treatment temperature is 450 ℃ to 650 ℃ and the retention time in the temperature range of 400 ℃ to 400 ℃ inclusive is 10 minutes or more, Subsequently, the hot-rolled steel sheet is subjected to cold rolling to obtain a cold-rolled steel sheet, Then annealing the cold-rolled steel sheet under the conditions that the average heating speed of the temperature region of 250-700 ℃ is more than 10 ℃ per second, the oxygen concentration of the temperature region of 250-700 ℃ is 0.5-5.0 volume percent, the annealing temperature is 820-950 ℃ and the dew point of the annealing temperature region is more than-35 ℃, Next, the cold-rolled steel sheet is subjected to a hot dip galvanization treatment to produce a plated steel sheet, Then, the plated steel sheet is cooled under the condition that the cooling stop temperature is 150 ℃ or less, Then, the plated steel sheet is subjected to a second heat treatment under the condition satisfying the following formula (1), 6.5≤(T+273)×{log(t×3600)+20}/1000≤13.0......(1), Here, T is the heat treatment temperature in the second heat treatment in the unit of °c, and T is the holding time in the second heat treatment in the unit of hours.
  5. 5. The method of manufacturing a hot-dip galvanized steel sheet as set forth in claim 4, wherein an alloying treatment is applied to the galvanized steel sheet after the hot-dip galvanization treatment.
  6. 6. A component comprising the hot-dip galvanized steel sheet as set forth in any one of claims 1 to 3.
  7. 7. The component of claim 6 for use in a skeletal structural member of an automobile.

Description

Hot dip galvanized steel sheet, method for manufacturing same, and component Technical Field The present invention relates to a hot dip galvanized steel sheet, a method of manufacturing the same, and a component. Background In order to reduce CO 2 emissions and improve collision resistance by reducing the weight of vehicles, steel sheets for automobiles are being advanced to have higher strength. In addition, new legal regulations are continually being put out. Therefore, in order to improve the strength of the vehicle body, the use of high-strength steel sheets, particularly those having tensile strength (hereinafter also simply referred to as TS) of 1180MPa or more, has been increasing with respect to main structural members and reinforcing members (hereinafter also referred to as framework structural members of automobiles, etc.) forming the framework of the automobile cab. In addition, a high-strength steel sheet used for a structural member of an automobile or the like is required to have high member strength when molded into a structural member of an automobile or the like. For improving the strength of the member, for example, it is effective to improve the yield strength in the longitudinal direction of the member (hereinafter also simply referred to as YS) and to improve the yield ratio (=ys/ts×100 hereinafter also simply referred to as YR) of the steel sheet. Thereby, the impact absorption energy (hereinafter also simply referred to as impact absorption energy) at the time of the collision of the automobile rises. Further, for example, a crash box or the like in a skeleton structural member of an automobile has a punched end surface and a bent portion. Therefore, from the viewpoint of formability, it is preferable to apply a steel sheet having high stretch flangeability and bendability in addition to high ductility to such a member. Further, from the viewpoint of rust inhibitive performance of a vehicle body, a hot-dip galvanized steel sheet obtained by hot-dip galvanizing may be used as a steel sheet for a material such as a skeletal structural member of an automobile. As a technique related to such a hot dip galvanized steel sheet, for example, patent document 1 discloses: A high-strength hot-dip galvanized steel sheet comprising a base steel sheet and a hot-dip galvanized layer formed on the surface of the base steel sheet, wherein the base steel sheet has a tensile strength of 780MPa or more, and comprises, in mass%, 0.050% -0.200% of C, 0.10% -0.90% of Si, 2.00% -3.50% of Mn, 0.001% -0.100% of P, 0.0200% or less of S, 1.000% or less of Al, 0.0100% or less of N, 0.0200% or less of Ca, and 0.300% or less of Cr, and [%Mn ]/[%Si ] satisfies a relationship of 2.9-11.7, and the balance is composed of Fe and unavoidable impurities, The base steel plate has the following steel structure: The total area ratio of 1 or 2 selected from bainitic and ferrite is 5-85%, The area ratio of tempered martensite is 65% or less, The area ratio of the quenched martensite is 5% -40% and the area ratio of the retained austenite is below 5.0%, The ratio of Si enrichment to Mn enrichment in the surface layer of the base steel sheet is 0.7-1.3, and the diffusible hydrogen content in the base steel sheet is 0.80 mass ppm or less. Wherein [%Mn ] and [%Si ] represent the contents (% by mass) of Mn and Si, respectively, in the steel. Prior art literature Patent literature Patent document 1 Japanese patent No. 6777267 Disclosure of Invention However, there is a concern that the high-strength steel sheet having a TS of 1180MPa or more, particularly the hot dip galvanized steel sheet, may be brittle cracked during the shearing process. Therefore, good shearing workability is also required. However, in the hot-dip galvanized steel sheet described in patent document 1, the shear workability is not considered. Therefore, from the viewpoint of increasing the application ratio of a high-strength steel sheet having a TS of 1180MPa or more, particularly a hot-dip galvanized steel sheet, to a skeleton structural member of an automobile or the like, there is a demand for development of a hot-dip galvanized steel sheet having a TS of 1180MPa or more, which has high YR and high ductility, stretch flangeability and bendability, and also has improved shear workability. The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a hot dip galvanized steel sheet having high YR (thereby obtaining high member strength when applied to a member), high ductility, stretch flangeability and bendability, and improved shear workability, and having a TS of 1180MPa or more. Another object of the present invention is to provide a method for producing the above-mentioned hot dip galvanized steel sheet. The present invention also provides a member using the hot dip galvanized steel sheet. Here, "high YR (high member strength)" means that YR is 65% or more. The YR is obtained by the following formul