| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high-strength hot-dip galvanized steel sheet which has a TS of 780 MPa or higher and is superior in hole-expandability and bendability, and to provide a method of manufacturing the same. <P>SOLUTION: This galvanized steel sheet has a component composition comprising, by mass%, 0.05 to 0.15% C, 0.8 to 2.5% Si, 1.5 to 3.0% Mn, 0.001 to 0.05% P, 0.0001 to 0.01% S, 0.001 to 0.1% Al, 0.0005 to 0.01% N, 0.1 to 1.0% Cr, 0.0005 to 0.1% Ti, 0.0003 to 0.003% B and the balance iron with unavoidable impurities. The steel sheet has a structure in which a ferrite phase occupies 30% or more and a martensite phase occupies 30 to 70% by an area rate. In the martensite phase, a tempered martensite phase occupies 20% or more by a ratio with respect to the total martensite phase, and furthermore, martensite phases with particle diameters of 1 micron or smaller occupy 10% or less by a ratio with respect to the total martensite phase. <P>COPYRIGHT: (C)2009,JPO&INPIT |
