High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having a tensile strength of 980 mpa or more, excellent coating adhesion, formability, and hole expandability, and manufacturing method thereof

Abstract

A high-strength hot-dip galvanized steel sheet having a tensile strength of 980 MPa or more and excellent coating adhesion, formability, and hole expandability, which is a hot-dip galvanized steel sheet having a hot-dip galvanized layer on the surface of a base steel sheet, The above-mentioned base material steel plate contains C: 0.05%-0.4%, Si: 0.01%-3.0%, Mn: 0.1%-3.0%, Al: 0.01%-2.0%, and Si+Al>0.5%, limited P: 0.04% or less, S: 0.05% or less, N: 0.01% or less, and the remainder is composed of iron and unavoidable impurities. The microstructure of the aforementioned base metal steel plate contains more than 40% of Martensite and bainite, containing more than 8% retained austenite by volume fraction, the rest of the microstructure is ferrite, or ferrite and pearlite less than 10% by volume fraction, The aforementioned martensite contains 10% or more of two or more of the three types of martensite (1), (2), and (3) in terms of total fraction, and the hot-dip galvanized 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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