HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET, HIGH-STRENGTH ALLOYED HOT-DIP GALVANIZED STEEL SHEET EXCELLENT IN BAKE HARDENABILITY, AND MANUFACTURING METHOD THEREOF

摘要

The present invention relates to a steel which contains C, Si, Mn, P, S, Al, N, and O each, a remainder of which is formed of Fe and inevitable impurities. In a range between a 1/8 thickness around a 1/4 plate thickness from a surface of a base material steel sheet to a 3/8 thickness around the 1/4 plate thickness from the surface, a formation of the base material contains a residual austenite aspect with a volume fraction of 3% or higher, a ferrite phase of 50% or lower, and a hard aspect of 40% or higher. An average dislocation density is 5×1013/m2 or higher, and the solution C amount contained in the residual austenite aspect is from 0.70 wt% to 1.00 wt%. A random strength ratio of an X ray of an FCC iron of an aggregate structure of the residual austenite aspect is 3.0 or below. A ratio of a particle diameter with respect to a rolling direction of the residual austenite aspect to a particle diameter with respect to a plate width direction is from 0.75 to 1.33. A galvannealed layer is formed at a surface of the base material. The plate thickness is from 0.6 mm to 5.0 mm.