STEEL SHEET HOT-DIP-COATED WITH ZN-AL-MG-BASED SYSTEM HAVING EXCELLENT WORKABILITY AND METHOD FOR MANUFACTURING SAME

摘要

The purpose of the present invention is to provide a steel sheet hot-dip coated with a Zn-Al-Mg-based system, which has such strength, ductility and hole-expandability as being suitable for working processes, for example, press working and stretch flanging, and high corrosion resistance. A high-strength steel sheet hot-dip coated with a Zn-Al-Mg-based system, which has excellent workability with a tensile strength of 400 MPa or greater, wherein: a steel sheet material thereof has a definite chemical composition; the Ti/C equivalence ratio represented by formula (1) is 0.4-1.5; a bainitic ferrite single phase or a phase comprising a bainitic ferrite phase and a ferrite phase exists as a main phase; the area ratio of a hard second phase and cementite is 3% or less; the ratio of a small angle boundary with a difference in crystal orientation of 2-15° is 30-75%; and a Ti-containing carbide having an average grain size of 20 nm or less is dispersed and deposited. Ti/C equivalence ratio = (Ti/48)/(C/12) (1)