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High-strength cold-rolled steel sheet and method for producing same

A technology of cold-rolled steel sheet and manufacturing method, applied in the field of high-strength cold-rolled steel sheet and its manufacture, can solve problems such as poor hole expandability, and achieve the effects of high tensile strength, excellent delayed fracture resistance, and difficulty in delayed fracture

Active Publication Date: 2017-08-01
JFE STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0008] However, in this TRIP steel sheet, since retained austenite transforms into martensite during punching, cracks occur at the interface with ferrite, and the hole expandability is poor.

Method used

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  • High-strength cold-rolled steel sheet and method for producing same
  • High-strength cold-rolled steel sheet and method for producing same
  • High-strength cold-rolled steel sheet and method for producing same

Examples

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Embodiment

[0126] Hereinafter, examples of the present invention will be described.

[0127] Steel with the composition shown in Table 1 was smelted and cast to produce a slab, and hot rolled at a hot rolling start temperature of 1250° C. and a finish rolling finish temperature (FDT in Table 2) to produce a hot-rolled sheet thickness: 3.2 mm. Rolled steel. Within 1 second after the end of this rolling, after cooling to the first cooling stop temperature (cold stop temperature 1 in Table 2) at the first average cooling rate (cooling rate 1 in Table 2) shown in Table 2, 2 The average cooling rate (cooling rate 2 in Table 2) is cooled to the coiling temperature (CT in Table 2) (this coiling temperature corresponds to the second cooling stop temperature), and coiling is performed at this coiling temperature. Next, the obtained hot-rolled steel sheet was pickled, and then cold-rolled to manufacture a cold-rolled steel sheet (thickness: 1.4 mm). Thereafter, the first heating was performed un...

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Abstract

Provided are: a high-strength cold-rolled steel sheet which solves problems of prior art and has a good balance among a plurality of characteristics (yield ratio, strength, elongation, bore expanding properties and delayed fracture resistance); and a method for producing this high-strength cold-rolled steel sheet. A high-strength cold-rolled steel sheet which is characterized by having a specific component composition and by having a microstructure that is a composite structure which contains 10-25% by volume of ferrite having an average crystal grain size of 2 [mu]m or less, 5-20% by volume of residual austenite, and 5-15% by volume of martensite having an average crystal grain size of 2 [mu]m or less, with the balance made up of tempered martensite and bainite having an average crystal grain size of 5 [mu]m or less, in said microstructure the volume fraction (V1) of hard phases other than ferrite and the volume fraction (V2) of the tempered martensite satisfying the condition of formula (1) which is 0.35<=V2 / V1<=0.75 Formula (1).

Description

technical field [0001] The invention relates to a high-strength cold-rolled steel plate and a manufacturing method thereof. The high-strength cold-rolled steel sheet of the present invention having a tensile strength (TS) of 1180 MPa or more is particularly suitable as a material for structural components such as automobiles. [0002] In addition, in this specification, yield ratio (YR) means the value which shows the ratio of yield stress (YS) and tensile strength (TS), and expresses by YR=YS / TS. Background technique [0003] In recent years, due to serious environmental problems, CO 2 In order to reduce CO2 in the automotive field, stricter emission regulations 2 Emissions, weight reduction of the vehicle body to improve fuel efficiency has become a problem. In order to solve this problem, thinning of high-strength steel sheets suitable for automobile parts is being carried out. For example, thinned steel sheets with a TS of 1180 MPa or more are being used. [0004] H...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C21D9/46C22C38/14C22C38/58
CPCC21D1/28C21D6/001C21D6/002C21D6/005C21D6/008C21D8/0205C21D8/0226C21D8/0236C21D8/0247C21D8/0263C21D8/0273C21D8/0278C21D8/0405C21D8/0426C21D8/0436C21D8/0447C21D8/0463C21D8/0473C21D8/0478C21D9/46C21D9/48C21D2211/002C21D2211/008C22C38/001C22C38/002C22C38/005C22C38/02C22C38/04C22C38/06C22C38/08C22C38/12C22C38/14C22C38/16C22C38/18C22C38/00C22C38/58C21D2211/001C21D2211/005C22C38/28C22C38/32C22C38/38
Inventor 高岛克利长谷川浩平船川义正
Owner JFE STEEL CORP
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