High-strength hot-dipped galvanized steel sheet and high-strength alloyed hot-dipped galvanized steel sheet, each having tensile strength of 980 mpa or more, excellent plating adhesion, excellent formability and excellent bore expanding properties, and method for producing same

Abstract

A high-strength hot-dipped galvanized steel sheet which has a tensile strength of 980 MPa or more, while having excellent plating adhesion, formability and bore expanding properties. This high-strength hot-dipped galvanized steel sheet has a hot-dipped zinc plating layer on the surface of a matrix steel sheet, and the matrix steel sheet contains, in mass%, 0.05-0.4% of C, 0.01-3.0% of Si, 0.1-3.0% of Mn and 0.01-2.0% of Al, while satisfying Si+Al>0.5% and suppressing P to 0.04% or less, S to 0.05% or less and N to 0.01% or less, with the balance made up of iron and unavoidable impurities. The microstructure of the matrix steel sheet contains 40% by volume or more of martensite and bainite in total, 8% by volume or more of residual austenite, with the balance made up of ferrite or ferrite and 10% by volume or less of pearlite. The martensite contains two or more of the three kinds of martensite (1), (2) and (3) in an amount of 10% by volume or more in total, and the hot-dipped zinc plating layer contains less than 7% by mass of Fe.

Description

technical field [0001] The present invention relates to a high-strength steel sheet excellent in formability (ductility and hole expandability), an alloyed hot-dip galvanized steel sheet utilizing the TRIP (Transformation Induced Plasticity) phenomenon, and a method for producing the same. [0002] This application claims priority based on Japanese Patent Application No. 2011-216967 for which it applied in Japan on September 30, 2011, and takes in the content here. Background technique [0003] In order to achieve both weight reduction and safety of automobile bodies and parts, the strengthening of steel sheets, which are raw materials, is progressing. Generally, when the strength of a steel sheet is increased, the formability (ductility and hole expandability) is impaired. In order to use high-strength steel sheets as automotive components, a balance between strength and formability is required. To meet such demands, so-called TRIP steel sheets utilizing the transformatio...

AI Technical Summary

Problems solved by technology

[0006] However, for hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets, the temporarily formed martensite softens when reheated in the galvanizing process, and the desired strength may not be obtained.

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