HIGH-STRENGTH GALVANIZED STEEL SHEET EXCELLENT IN STRETCH-FLANGE FORMABILITY, IN-PLANE STABILITY OF STRETCH-FLANGE FORMABILITY, AND BENDABILITY, AND METHOD FOR PRODUCING SAME

摘要

Provided are a high-strength galvanized steel sheet which is excellent in stretch-flange formability, in-plane stability of stretch-flange formability, and bendability and a method for manufacturing the same. The high-strength galvanized steel sheet contains 0.12% to 0.25% C, 0.01% to 1.00% Si, 1.5% to 4.0% Mn, 0.100% or less P, 0.02% or less S, 0.01% to 0.10% Al, 0.001% to 0.010% N, 0.005% to 0.100% Ti, and 0.0005% to 0.0050% B, the remainder being Fe and inevitable impurities, Ti 4N being satisfied. The high-strength galvanized steel sheet contains 80% to 100% martensite in terms of area fraction, 5% or less (including 0%) polygonal ferrite in terms of area fraction, and less than 3% (including 0%) retained austenite in terms of area fraction. The average hardness of martensite is 400 to 500 in terms of Vickers hardness (Hv). The average grain size of martensite is 20 µm or less. The standard deviation of the grain size of martensite is 7.0 µm or less.