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High-strength cold rolled steel sheet having high yield ratio and method for producing said sheet

A cold-rolled steel sheet and a manufacturing method technology, applied in the field of high-strength cold-rolled steel sheet and its manufacturing, can solve the problems of cracks, hole expandability (deterioration of extension flangeability, etc., and achieve high yield ratio, elongation and elongation). Excellent flangeability

Active Publication Date: 2016-03-30
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, this TRIP steel sheet has a problem in that retained austenite transforms into martensite during punching, whereby cracks occur at the interface with ferrite and hole expandability (stretch flangeability) deteriorates.

Method used

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  • High-strength cold rolled steel sheet having high yield ratio and method for producing said sheet
  • High-strength cold rolled steel sheet having high yield ratio and method for producing said sheet
  • High-strength cold rolled steel sheet having high yield ratio and method for producing said sheet

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Embodiment 1

[0122] Hereinafter, examples of the present invention will be described. However, the present invention is of course not limited to the following examples, and can be appropriately modified and implemented within the range that can suit the gist of the present invention, and all of them are included in the technical scope of the present invention.

[0123] Steel with the chemical composition shown in Table 1 was melted and cast to produce a slab, and hot-rolled under the conditions that the slab heating temperature (hot rolling start temperature) was 1250°C and the finish rolling finish temperature (FDT) was set in Table 2. , to make a hot-rolled steel plate with a thickness of 3.2 mm. After finishing the hot rolling, start cooling within the time T (seconds) shown in Table 2, and cool with the first average cooling rate (cooling rate 1) shown in Table 2. to the first cooling temperature, and then cooled to the coiling temperature (CT) shown in Table 2 at the second average co...

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PUM

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Abstract

Provided is a high-strength cold rolled steel sheet exhibiting exceptional elongation and stretch-flangeability as well as a high yield ratio. A high-strength cold rolled steel sheet having a high yield ratio, which: contains 0.05-0.15% of C, 0.6-2.5% of Si, 2.2-3.5% of Mn, 0.08% or less of P, 0.010% or less of S, 0.01-0.08% of Al, 0.010% or less of N, 0.002-0.05% of Ti, and 0.0002-0.0050% of B, the remainder comprising Fe and unavoidable impurities (percentages given with respect to mass); includes 20-55% by volume of ferrite with an average crystal particle diameter of 7 [mu]m or less, 5-15% by volume of residual austenite, and 0.5-7% by volume of martensite with an average crystal particle diameter of 4 [mu]m or less; includes a structure of bainite and / or tempered martensite having an average crystal particle diameter of 6 [mu]m or less; and has a microstructure in which the difference in nanohardness between the ferrite and the bainite and / or tempered martensite structure is 3.5 GPa or less, and the difference in nanohardness between the bainite and / or tempered martensite structure and the martensite is 2.5 GPa 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 particularly relates to a high-strength cold-rolled steel sheet suitable as a structural member of automobiles and the like. Background technique [0002] In recent years, due to the upsurge of attention to environmental issues, CO 2 Emission regulations have become stricter, and in the automotive field, improvement of fuel efficiency by reducing the weight of the vehicle body has become a major issue. Therefore, thinning by applying high-strength steel sheets to automotive parts is being promoted. In particular, the application of high-strength steel sheets with a tensile strength (TS) of 980 MPa or more to automotive parts is being promoted. [0003] High-strength steel sheets used for automobile structural parts, reinforcement parts, and other automotive parts are required to have excellent formability. Espec...

Claims

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Application Information

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IPC IPC(8): C22C38/00C21D9/46C22C38/14C22C38/58
CPCC21D1/25C21D1/84C21D6/004C21D6/005C21D6/008C21D8/0205C21D8/0221C21D8/0226C21D8/0236C21D8/0263C21D8/0278C21D8/0463C21D8/0473C21D9/46C21D2211/001C21D2211/002C21D2211/008C22C38/00C22C38/001C22C38/002C22C38/005C22C38/02C22C38/04C22C38/06C22C38/08C22C38/12C22C38/14C22C38/16C22C38/28C22C38/32C22C38/38C22C38/18
Inventor 高岛克利小野义彦长谷川浩平
Owner JFE STEEL CORP
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