HIGH-STRENGTH HOT-DIP ZINCED STEEL SHEET EXCELLENT IN MOLDABILITY AND SUITABILITY FOR PLATING, HIGH-STRENGTH ALLOYED HOT-DIP ZINCED STEEL SHEET, AND PROCESSES AND APPARATUS FOR PRODUCING THESE

摘要

Hot dip galvanized steel sheet excellent in shapeability and plateability comprised of high strength steel sheet containing, by mass%,
C: 0.05 to 0.25%,
Si: 0.3 to 2.5%,
Mn: 1.5 to 2.8%,
P: 0.03% or less,
S: 0.02% or less,
Al: 0.005 to 0.5%,
N: 0.0060% or less and
the balance of Fe and unavoidable impurities, on which having a galvanized layer containing Al: 0.05 to 10 mass% and Fe: 0.05 to 3 mass% and the balance of Zn and unavoidable impurities, said hot dip galvanized steel sheet characterized by the presence of oxides containing Si in an average content of 0.6 to 10 mass% at the crystal grain boundaries and in the crystal grains at the sheet steel side 5 µm or less from the interface between the high strength steel sheet and the plating layer and by the presence of Fe-Zn alloy with an average grain size of 0.5 to 3 µm at the plating side.