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High-yield ratio high-strength cold-rolled steel sheet and manufacturing method thereof

A technology of cold-rolled steel plate and high yield ratio, which is applied in the field of high-strength cold-rolled steel plate and its manufacturing, which can solve the problems of poor hole expandability and achieve high hole expandability, high elongation, and high tensile strength Effect

Active Publication Date: 2018-06-08
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in this TRIP steel sheet, the residual austenite transforms into martensite during punching, and therefore cracks occur at the interface with ferrite, resulting in poor hole expandability.

Method used

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  • High-yield ratio high-strength cold-rolled steel sheet and manufacturing method thereof
  • High-yield ratio high-strength cold-rolled steel sheet and manufacturing method thereof
  • High-yield ratio high-strength cold-rolled steel sheet and manufacturing method thereof

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Embodiment 1

[0114] Hereinafter, examples of the present invention will be described. However, the present invention is not limited by the following examples, and can be implemented by adding appropriate changes within the range consistent with the gist of the present invention, and these changes are also included in the technical scope of the present invention.

[0115] Steels having the chemical compositions shown in Table 1 were melted and cast (remainder components: Fe and unavoidable impurities), and slabs were produced. Next, the heating temperature of the hot rolling was set at 1250° C., and the finishing temperature (FDT) of the finish rolling was set at the conditions shown in Table 2, and hot rolling was carried out so that the plate thickness became 3.2 mm. 1 Average cooling rate (cooling rate 1) cooling to the first cooling temperature, then cooling at the second average cooling rate (cooling rate 2), and coiling at the coiling temperature (CT) to obtain a hot-rolled steel shee...

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PUM

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Abstract

Provided are a high-strength cold-rolled steel sheet having excellent elongation, hole expandability, and delayed fracture resistance and high yield ratio, and a method for producing the steel sheet. A high-yield-ratio, high-strength cold-rolled steel sheet has a composition containing, in terms of % by mass, C: 0.13% to 0.25%, Si: 1.2% to 2.2%, Mn: 2.0% to 3.2%, P: 0.08% or less, S: 0.005% or less, Al: 0.01% to 0.08%, N: 0.008% or less, Ti: 0.055% to 0.130%, and the balance being Fe and unavoidable impurities. The steel sheet has a microstructure that contains 2% to 15% of ferrite having an average crystal grain diameter of 2 µm or less in terms of volume fraction, 5 to 20% of retained austenite having an average crystal grain diameter of 0.3 to 2.0 µm in terms of volume fraction, 10% or less (including 0%) of martensite having an average grain diameter of 2 µm or less in terms of volume fraction, and the balance being bainite and tempered martensite, and the bainite and the tempered martensite having an average crystal grain diameter of 5 µm or less.

Description

technical field [0001] The present invention relates to a high-strength cold-rolled steel sheet having a high yield ratio and a method for producing the same, and more particularly to a high-strength cold-rolled steel sheet suitable as a member of structural parts such as automobiles. Background technique [0002] In recent years, due to the aggravation of environmental problems, CO 2 Emission regulations have become stricter, and vehicle body weight reduction for fuel efficiency improvement has become an issue in the automotive field. Therefore, thinning by application of high-strength steel sheets to automobile parts, especially application of high-strength cold-rolled steel sheets having a tensile strength (TS) of 1180 MPa or more, is being pursued. [0003] High-strength steel sheets used for structural and reinforcing members of automobiles are required to have excellent formability. In particular, high-strength steel sheets used for parts with complex shapes are requ...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22C38/00C21D9/46C22C38/14C22C38/58
CPCC21D9/46C21D1/25C21D8/0226C21D8/0236C21D8/0263C21D8/0273C21D8/0278C21D8/0473C21D2211/001C21D2211/002C21D2211/005C21D2211/008C22C38/001C22C38/002C22C38/005C22C38/02C22C38/04C22C38/06C22C38/08C22C38/12C22C38/14C22C38/16C22C38/28C22C38/38C22C38/58C23G1/00
Inventor 高岛克利长谷川浩平
Owner JFE STEEL CORP