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

Abstract

Provided is a high-strength cold-rolled steel sheet having excellent elongation and stretch flangeability, and a high yield ratio, as well as a method for manufacturing same. A high-strength cold-rolled steel plate comprising 0.10-0.27% of C, 0.8-2.4% of Si, 2.3-3.5% of Mn, 0.08% or less of P, 0.005% or less of S, 0.01-0.08% of Al, and 0.010% or less of N (percentages given with respect to mass), the balance comprising Fe and inevitable impurities. The average ferrite crystal grain size is 5 [mu]m or less. Ferrite is present in a volumetric ratio of 3-20%, residual austenite is present in a volumetric ratio of 5-20%, and martensite is present in a volumetric ratio of 5-20%. Bainite and / or annealed martensite are included in the remainder. Said steel plate has a microstructure in which the total quantity of residual austenite, martensite, or a phase combined therefrom, in which the crystal grain size is 2 [mu]m or less, is 150 or more per 2000 [mu]m2 within a plate-thickness cross section parallel to the rolling direction of the steel plate.

Description

technical field [0001] The present invention relates to a high-strength cold-rolled steel sheet and a method for producing the same, and more particularly to a high-strength cold-rolled steel sheet suitable for use as a member of structural parts such as automobiles and a method for manufacturing the same. 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 1180 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 excellen...

AI Technical Summary

Problems solved by technology

However, it has disadvantages in that stress concentrates on the interface between ferrite and martensite during deformation, and thus cracks are easily generated, and stretch flangeability is poor.

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.

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