HOT DIP ZINC PLATED HIGH STRENGTH STEEL SHEET EXCELLENT IN PLATING ADHESIVENESS AND HOLE EXPANDING CHARACTERISTICS

摘要

A hot dip zinc plated high strength steel sheet being excellent in the adhesiveness of the plating and in hole expanding characteristics, which has a chemical composition, in mass %, that C: 0.08 to 0.35 %, Si: 1.0 % or less, Mn: 0.8 to 3.5 %, P: 0.03 or less, S: 0.03 or less, Al: 0.25 to 1.8 %, Mo: 0.05 to 0.35 %, N: 0.010 % or less and the balance: Fe and inevitable impurities, and has a metal structure containing ferrite and bainite, and 0.5 to 10 area % of tempered martensite and 5 or more vol % of retained austenite; and a method for producing the above hot dip zinc plated high strength steel sheet, wherein a hot-rolled steel sheet is annealed in a continuous annealing process at a temperature of 680 to 930°C, the resultant sheet is cooled to a martensite transformation temperature or lower, and then the sheet is subjected to a hot dip zinc plating, which comprises subjecting it to the hot dip zinc plating after heating it to 250 to 600°C.