HIGH-STRENGTH HOT-DIP-GALVANIZED STEEL SHEET HAVING EXCELLENT MOLDABILITY, AND METHOD FOR PRODUCTION THEREOF

摘要

Disclosed is a high-strength hot-dip-galvanized steel sheet having a TS value of 780 MPa or more and having excellent hole-expanding properties and excellent bendability. Also disclosed is a method for producing the steel sheet. The steel sheet has the following chemical composition (% by mass): C: 0.05-0.15%, Si: 0.8-2.5%, Mn: 1.5-3.0%, P: 0.001-0.05%, S: 0.0001-0.01%, Al: 0.001-0.1%, N: 0.0005-0.01%, Cr: 0.1-1.0%, Ti: 0.0005-0.1% and B: 0.0003-0.003%, with the remainder being iron and unavoidable impurities. The steel sheet has a structure composed of a ferrite phase at an area ratio of 30% or more and a martensite phase at an area ratio of 30 to 70% (inclusive), wherein a tempered martensite phase makes up 20% or more of the total area of the martensite phase and a martensite phase having a particle diameter of 1 µm or less makes up 10% or less of the total area of the martensite phase.