High-strength plated steel sheet and method for producing same

Abstract

Provided are a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet having a tensile strength of at least 980 MPa, having excellent plating properties, and having excellent workability in terms of extensibility, bendability and hole expandability, and delayed fracture resistance. Disclosed is a high-strength plated steel sheet that is a plated steel sheet having a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on the surface of a base material steel sheet, and that comprises, in order from the interface between the base material steel sheet and the galvanized layer toward the base material steel sheet side: an inner oxide layer including at least one type of oxide selected from the group consisting of Si and Mn; a soft layer that is a layer including said inner oxide layer, and that has a Vickers hardness which is 90% or less of the Vickers hardness at a t / 4 position of the base material steel sheet, where t is the thickness of the base material steel sheet; and a hard layer constituted by a structure including, with respect to the entire metallographic structure, greater than or equal to 70% by area of a low-temperature transformation-forming phase, from 0% to 10% by area, inclusive, of polygonal ferrite, and greater than or equal to 5% by volume of retained austenite. The average depth D of the soft layer is 20 mum or greater, the average depth d of the inner oxide layer is 4 mum or greater and less than D, and the tensile strength is 980 MPa or greater.

Description

technical field [0001] The present invention relates to a high-strength plated steel sheet having a tensile strength of 980 MPa or higher, good platability, workability including elongation, bendability, and hole expandability, and delayed fracture resistance, and further relates to a method for producing the same. The coated steel sheet of the present invention includes both hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet. Background technique [0002] Hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets commonly used in the fields of automobiles and transport aircraft are not only required to have higher strength, but also require elongation, bendability, and hole expandability (same as stretch flangeability) It has excellent processability, and is further required to have excellent delayed fracture resistance. [0003] In order to ensure high strength and workability, it is effective to add a large amount of strengthening ...

AI Technical Summary

Problems solved by technology

However, Si and Mn are easily oxidizable elements, and the wettability of hot-dip galvanizing is significantly deteriorated due to Si oxide, Mn oxide, and composite oxide film having a composite oxide of Si and Mn formed on the surface. Problems such as non-plating occur

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