High-strength steel sheet

a steel sheet, high-strength technology, applied in the direction of heat treatment apparatus, manufacturing tools, furnaces, etc., can solve the problem of degrading formability, and achieve the effect of high local elongation and high uniform elongation

Inactive Publication Date: 2020-03-19
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0070]According to the present invention, it is possible to obtain a high-strength steel sheet having a high uniform elongation and a high local elongation.

Problems solved by technology

In general, as a steel sheet is strengthened, its uniform elongation, local elongation, and hole-expansion properties deteriorate, which degrades its formability.

Method used

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  • High-strength steel sheet
  • High-strength steel sheet
  • High-strength steel sheet

Examples

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example

[0204]Slabs that were 240 mm thick and had chemical compositions shown in Table 1 were produced. The slabs were subjected to hot rolling under conditions shown in Tables 2 and 3 to be formed into hot-rolled steel sheets. At that point, a path of rolling with a large rolling reduction of 10% or more was performed at least three times. The hot-rolled steel sheets were coiled after cooled to the coiling temperature by water spray. The produced hot-rolled steel sheets were subjected to pickling to remove scales and subjected to cold rolling under conditions shown in Tables 2 and 3, to be manufactured into cold-rolled steel sheets having a thickness of 1.2 mm.

TABLE 1Chemical composition (in mass %, balance: Fe and impurities)Ac1SteelCSiMnPSAlNOothers(° C.)A0.201.405.890.0080.00070.0320.0030—701B0.131.268.670.0070.00090.0270.0034—667C0.551.124.990.0010.00100.0340.0029—702D0.201.293.940.0080.00070.0300.0030—718E0.200.0311.220.0080.00071.8100.0030—604F0.200.055.890.0080.00070.0320.0030—661G...

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Abstract

A high-strength steel sheet has a chemical composition consisting of, in mass percent, C: 0.10 to 0.24%, Mn: 3.50 to 12.00%, Si: 0.005 to 5.00%, Al: 0.005 to 5.00%, P: 0.15% or less, S: 0.030% or less, N: 0.020% or less, O: 0.010% or less, Cr: 0 to 5.00%, Mo: 0 to 5.00%, Ni: 0 to 5.00%, Cu: 0 to 5.00%, Nb: 0 to 0.50%, Ti: 0 to 0.50%, W: 0 to 0.50%, B: 0 to 0.010%, Ca: 0 to 0.05%, Mg: 0 to 0.05%, Zr: 0 to 0.05%, REM: 0 to 0.05%, Sb: 0 to 0.50%, Sn: 0 to 0.50%, As: 0 to 0.05%, and V: 0 to 2.0%, with the balance: Fe and impurities, and a steel micro-structure at a ¼ sheet-thickness position includes, in area percent, retained austenite: 10.0 to 55.0%, high temperature tempered martensite: 30.0 to 75.0%, and low temperature tempered martensite: 15.0 to 60.0%, with the balance including fresh martensite: 0 to 10.0%, pearlite: 0 to 5.0%, and bainite: 0 to 5.0%.

Description

TECHNICAL FIELD[0001]The present invention relates to a high-strength steel sheet, particularly to a high-strength steel sheet excellent in formability.BACKGROUND ART[0002]To ensure both safety and weight reduction of a body, components, and the like of an automobile, attempts have been made to improve strength of steel sheets. In general, as a steel sheet is strengthened, its uniform elongation, local elongation, and hole-expansion properties deteriorate, which degrades its formability. Accordingly, when high-strength steel sheets are to be used as members for an automobile, a proper balance between strengths (tensile strength, yield stress) and formability is needed.[0003]In regard to a demand for the uniform elongation, what is called a TRIP steel sheet, for which transformation induced plasticity of retained austenite is utilized has been proposed (e.g., see Patent Documents 1 and 2). In addition, Patent Documents 3 and 4 propose that steel micro-structure is made to mainly incl...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C22C38/42C22C38/00C22C38/02C22C38/06C22C38/60C21D9/46C22C38/44C22C38/50C22C38/58
CPCC21D2211/002C22C38/02C22C38/008C22C38/50C22C38/001C21D9/46C22C38/58C22C38/42C21D2211/008C22C38/002C22C38/06C21D2211/009C22C38/60C22C38/44C21D6/005C21D8/02C21D8/0205C21D8/0226C21D8/0236C22C38/00C22C38/005C22C38/04C22C38/08C22C38/12C22C38/14C22C38/16C22C38/38C23C2/06
Inventor SANO, KOHICHIOKAMOTO, RIKI
Owner NIPPON STEEL CORP
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