High-strength steel plate

Abstract

Provided is a high-strength steel plate which exhibits a large amount of bake-hardening and highly uniform bake-hardening properties, and contains, in mass%, C in the amount of 0.13-0.40%, Si in the amount of 0.500-3.000%, Mn in the amount of 2.50-5.00%, P in the amount of 0.100% or less, S in the amount of 0.010% or less, Al in the amount of 0.001-2.000%, and N in the amount of 0.010% or less, with the remainder constituting Fe and impurities, wherein: the martensite content by area ratio is at least 95%, and remaining structures occupy an area ratio of 5% or less; the ratio C1 / C2 of the upper-limit value C1 (mass%) of the Si concentration in a thickness direction cross-section to the lower-limit value C2 (mass%) thereof is 1.25 or less; the number density of precipitates exhibiting a major axis dimension of 0.05-1.00[mu]m, inclusive, and an aspect ratio of at least 1:3 is 30 per um2 or higher; and the tensile strength of the plate is 1,300 MPa or higher.

Description

Technical field[0001]The present invention relates to a high-strength steel sheet. Specifically, it relates to a high-strength steel sheet having a tensile strength of 1300 MPa or more and excellent bake hardenability suitable for structural members such as automobiles used mainly by press working.[0002]This application claims priority based on Japanese Patent Application No. 2018-141244 for which it applied to Japan on July 27, 2018, and uses the content here.Background technique[0003]In recent years, in order to protect the global environment, the fuel efficiency of automobiles is required to be improved. In automobile steel sheets, further increase in strength is required to reduce the weight of the car body and ensure safety. If the strength of the steel sheet is increased, the ductility generally decreases, so cold forming becomes difficult. Therefore, a material that is relatively soft and easy to form during forming processing, and has a high strength after forming, that is, ...

AI Technical Summary

Problems solved by technology

[0008] Thus, in a steel sheet with excellent bake hardenability, it is difficult to achieve both (1) a large amount of bake hardenability and (2) a small pre-strain dependence of the amount of bake hardenability (hereinafter referred to as "high uniform bake hardenability")

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