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High-strength hot-rolled steel sheet

A hot-rolled steel plate, high-strength technology, applied in the field of hot-rolled steel plate, can solve the problems of increased alloy cost, etc., and achieve the effect of ensuring light weight and excellent hole expandability

Inactive Publication Date: 2018-03-27
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in the technique of Patent Document 5, in order to obtain a granular bainitic ferrite structure, it is necessary to contain a large amount of Si and Mn, so there is a problem that the cost of the alloy is increased.

Method used

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  • High-strength hot-rolled steel sheet
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  • High-strength hot-rolled steel sheet

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0136] Smelt steel with the chemical composition shown in Table 1 in the laboratory, and cast a slab to figure 1 The patterns shown are heating, hot rolling, cooling, and coiling. At this time, the conditions of each step are as shown in Table 2. In Table 2, SRT, R1, R2, R3, FT, MT, t, and CT represent the following items, respectively.

[0137] SRT: Slab Heating Temperature

[0138] R1: Cumulative reduction rate above 1050°C and below 1150°C

[0139] R2: Cumulative reduction rate below 1050°C

[0140] R3: reduction ratio in the final processing pass

[0141] FT: Finishing temperature

[0142] MT: primary cooling stop temperature

[0143] t: secondary cooling time

[0144] CT: coiling temperature

[0145] The hot-rolled steel sheet thus obtained was pickled, and hot-dip galvanized for the conditions shown as "plating" in the column of "Treatment" in Table 3, and then, from a direction perpendicular to the rolling direction of the hot-rolled steel sheet, Direction to p...

Embodiment 2

[0164] Next, among the steels having the chemical compositions shown in Table 1, five steel grades A to C and G and H were tested. figure 1 Hot rolled and cooled as shown. Thereafter, descaling treatment was carried out, and cold rolling was not carried out, and a continuous heat treatment simulator was used to carry out figure 2 The shown model simulates the heat treatment of alloying hot-dip galvanizing production line. At this time, the conditions of each step are as shown in Table 5. In Table 5, RA, LTH, DIP, and GA represent the following items.

[0165] RA: maximum heating temperature

[0166] LTH: Low temperature hold temperature

[0167] DIP: Zn bath temperature

[0168] GA: alloying temperature

[0169] From the hot-rolled steel sheets thus obtained, JIS No. 5 tensile test pieces were prepared from a direction perpendicular to the rolling direction. Using this sample, a tensile test was performed to measure yield strength (YS), tensile strength (TS), yield rat...

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Abstract

This high-strength hot-rolled steel sheet has a prescribed chemical composition, said composition containing 80% or more of polygonal ferrite, no more than 5% of martensite and austenite in total, andno more than 5% of pearlite and cementite in total (percentages being expressed in terms of area), the remainder being one or more selected from bainitic ferrite and bainite. sigmaHV, which is the standard deviation in microhardness of 50 arbitrary polygonal ferrite grains present in a range of + / -100 [mu]m from the center plane in the direction of sheet thickness, is no greater than 30. At least5x107 Ti-containing carbides / mm2 are present in the polygonal ferrite grains. At least 50% of the Ti-containing carbides have an aspect ratio of less than 3, the aspect ratio being the ratio of the long-side length to the short-side length. The tensile strength is at least 540 MPa.

Description

technical field [0001] The present invention relates to a hot-rolled steel sheet, and in particular, to a high-strength hot-rolled steel sheet excellent in hole expandability, which is suitable for running parts of automobiles and the like formed into various shapes by press working or the like. Background technique [0002] Hot-rolled steel sheets produced relatively cheaply are widely used in various industrial equipment including automobiles. In recent years, from the viewpoint of carbon dioxide emission restrictions accompanying global warming measures, it is required to improve the fuel economy of automobiles, and for the purpose of reducing the weight of the vehicle body and ensuring collision safety, high-strength automotive parts are expanding. Application of hot rolled steel plate. [0003] It goes without saying that steel sheets used for automotive parts must satisfy not only strength requirements but also various workability requirements for parts forming such a...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C21D9/46C22C38/54
CPCC22C38/00C22C38/54C21D9/46C21D8/0226C21D2211/005C22C38/04C22C38/06C22C38/34C22C38/42C22C38/44C22C38/46C22C38/48C22C38/50C22C38/002C22C38/02C22C38/12C22C38/14C23C2/06C23C2/40
Inventor 杉浦夏子田中泰明横山卓史
Owner NIPPON STEEL CORP
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