High-strength steel sheet and method for producing same

Abstract

Through the disclosed method, it is possible to obtain a highly ductile and high tensile strength high-strength steel sheet having a tensile strength of at least 1470 MPa and a tensile strength total elongation of at least 29000 MPa.% by means of: a steel composition containing at least 0.30% and no more than 0.73% C, no more than 3.0% Si, no more than 3.0% Al, at least 0.7% Si+Al, at least 0.2% and no more than 8.0% Cr, no more than 10.0% Mn, at least 1.0% Cr+Mn, no more than 0.1% P, no more than 0.07% S, and no more than 0.010% N, the remainder being Fe and unavoidable impurities; and a steel structure of which the area ratio of martensite to the total steel sheet structure is 15-90% inclusive, the amount of residual austenite is 10-50% inclusive, at least 50% of said martensite is tempered martensite, the area ratio of said tempered martensite to the total steel sheet structure is at least 10%, and the area ratio of polygonal ferrite to the total steel sheet structure is 10% or less (including 0%).

Description

technical field [0001] The present invention relates to a high-strength steel sheet having a tensile strength (TS) of 1,470 MPa or higher, which is used in industrial fields such as automobiles and electrical equipment, and has excellent workability, especially ductility, and a method for producing the same. Background technique [0002] In recent years, improving the fuel efficiency of automobiles has become an important issue from the viewpoint of protecting the global environment. Therefore, studies are being actively conducted to reduce the weight of the vehicle body itself by reducing the thickness of vehicle body parts by increasing the strength of vehicle body materials. [0003] Generally, in order to increase the strength of a steel sheet, it is necessary to increase the ratio of hard phases such as martensite and bainite to the entire structure of the steel sheet. However, increasing the strength of the steel sheet by increasing the ratio of the hard phase leads t...

AI Technical Summary

Problems solved by technology

However, since the main phase is polygonal ferrite, it is difficult to achieve both high strength and workability with a tensile strength (TS) exceeding 1180MPa.

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