HOT-ROLLED STEEL SHEET FOR HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET OR HIGH-STRENGTH ALLOYED HOT-DIP GALVANIZED STEEL SHEET, AND PROCESS FOR PRODUCING SAME

摘要

Provided is a hot-rolled steel sheet capable of obtaining a galvanized steel sheet or galvannealed steel sheet which have high strength (a tensile strength TS of 540 MPa or more) and which is excellent in surface appearance. The hot-rolled steel sheet has a composition containing 0.04 mass percent to 0.20 mass percent C, 0.7 mass percent to 2.3 mass percent Si, 0.8 mass percent to 2.8 mass percent Mn, 0.1 mass percent or less P, 0.01 mass percent or less S, 0.1 mass percent or less Al, and 0.008 mass percent or less N, the remainder being Fe and inevitable impurities. Internal oxides containing one or more selected from the group consisting of Si, Mn, and Fe are present at grain boundaries and in grains in a base metal. The internal oxides present at the grain boundaries in the base metal are located within 5 µm from the surface of the base metal. The difference between the depths at which the internal oxides are formed in the cross direction of the steel sheet is 2 µm or less.