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Low-yield-ratio high-strength cold-rolled steel sheet and method for manufacturing same

A low-yield ratio, cold-rolled steel plate technology, used in manufacturing tools, metal rolling, furnaces, etc., can solve the problems of interface cracks and poor stretch-flange properties of TRIP steel plates, and achieve excellent stretch-flange properties and elongation. excellent rate

Active Publication Date: 2015-08-26
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, since retained austenite transforms into martensite during punching, cracks occur at the interface with ferrite.
Therefore, the TRIP steel plate has the disadvantage of poor stretch flangeability

Method used

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  • Low-yield-ratio high-strength cold-rolled steel sheet and method for manufacturing same
  • Low-yield-ratio high-strength cold-rolled steel sheet and method for manufacturing same
  • Low-yield-ratio high-strength cold-rolled steel sheet and method for manufacturing same

Examples

Experimental program
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Effect test

Embodiment 1

[0143] Steels having the chemical compositions shown in Table 1 were melted and cast to produce billets with a thickness of 230 mm. Next, the steel slab was heated, and the steel slab temperature was set to 1200° C., and the finish rolling temperature (FDT) was set to the temperature shown in Table 2 for hot rolling. Time and the average cooling rate (cooling rate) were used for cooling, and after the plate thickness was adjusted to 3.2 mm, coiling was performed at the coiling temperature (CT) shown in Table 2 to obtain a hot-rolled steel sheet. Next, the obtained hot-rolled steel sheet was pickled, and then cold-rolled to manufacture a cold-rolled sheet (sheet thickness: 1.4 mm). Then, heat at the average heating rate shown in Table 2, anneal with the soaking temperature and soaking time shown in Table 2, and cool to the first average cooling rate (cooling rate 1) shown in Table 2 after annealing. 1 cooling temperature, cooled to the second cooling temperature shown in Table...

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PUM

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Abstract

Provided are: a high-strength steel sheet having excellent stretchability and stretch flangeability, and a low yield ratio; and a method for manufacturing the high-strength steel sheet. A low-yield-ratio high-strength cold-rolled steel sheet having a chemical composition containing, by mass, 0.05 to 0.10% of C, 0.6 to 1.3% of Si, 1.4 to 2.2% of Mn, 0.08% or less of P, 0.010% or less of S, 0.01 to 0.08% of Al, and 0.010% or less of N, with the remainder made up by Fe and unavoidable impurities. The low-yield-ratio high-strength cold-rolled steel sheet has a microstructure in which the average crystal grain size of ferrite is equal to or smaller than 15 μm, the volume fraction of ferrite is equal to or greater than 70%, the volume fraction of bainite is equal to or greater than 3%, the volume fraction of residual austenite is 4 to 7%, the average crystal grain size of martensite is equal to or smaller than 5 μm, and the volume fraction of martensite is 1 to 6%. The average C concentration (mass%) in the residual austenite is 0.30 to 0.70%. The steel sheet characteristics are such that the yield ratio is equal to or less than 64% and the tensile strength is equal to or greater than 590 MPa.

Description

technical field [0001] The present invention relates to a high-strength cold-rolled steel sheet having a low yield ratio and a method for producing the same, and particularly relates to a high-strength cold-rolled steel sheet suitable for use as members of structural parts such as automobiles. Background technique [0002] In recent years, due to the intensification of environmental problems, CO 2 Emission regulations have become stricter, and in the automotive field, increased fuel consumption due to weight reduction of car bodies has become a major issue. As a result, thinning by application of high-strength steel sheets to automobile parts has progressed, and application of steel sheets with a tensile strength TS of 590 MPa or more is progressing. [0003] High-strength steel sheets used in structural members and reinforcing members of automobiles are required to be excellent in elongation and stretch-flange-formability. In particular, high-strength steel sheets used fo...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00B21B3/00C21D9/46C22C38/06C22C38/58
CPCC22C38/02C21D2211/001C22C38/58C22C38/04C21D8/0247C22C38/14C22C38/005C22C38/08C22C38/16C22C38/06C21D2211/008C21D9/46C22C38/12B21B3/00C22C38/001C22C38/00C22C38/002C22C38/18C21D2211/005C21D2211/002C22C38/38C21D6/001C21D6/002C21D6/005C21D6/008C21D8/0205C21D8/0226C21D8/0236C21D8/0263
Inventor 高岛克利田路勇树木村英之长谷川浩平
Owner JFE STEEL CORP
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