HIGH-STRENGTH HOT-DIP GALVANIZED STEEL PLATE HAVING EXCELLENT IMPACT RESISTANCE AND METHOD FOR PRODUCING SAME AND HIGH-STRENGTH ALLOYED HOT-DIP GALVANIZED STEEL SHEET AND METHOD FOR PRODUCING SAME

摘要

The base steel sheet has a hot-dip galvanized layer formed on its surface, and the retained austenite phase of the steel sheet structure in the range of 1/8 thickness to 3/8 thickness centered on the 1/4 thickness from the surface of the sheet thickness has a volume fraction And a bainitic ferrite phase, a fresh martensite phase and a tempering martensite phase in a volume fraction of not less than 40%, an average effective crystal grain diameter of not more than 5.0 mu m, a maximum effective crystal grain diameter of not more than 20 mu m The decarburized layer having a thickness of 0.01 to 10.0 탆 is formed on the surface layer portion, the density of the oxide dispersed in the decarburized layer is 1.0 × 10 ¹² to 1.0 × 10 ¹⁶ / m ² , the average particle diameter of the oxide is 500 nm or less.