Excellent fatigue characteristics and ductility, and small in-plane anisotropy of ductility high-strength hot-dip galvanized steel sheet and a method of manufacturing the same

摘要

PROBLEM TO BE SOLVED: To provide a high-strength hot-dip galvanized steel sheet having a TS of 780 MPa or more, excellent fatigue characteristic and ductility as well as a small in-plane anisotropy of ductility, and to provide a manufacturing method of the same.;SOLUTION: In the high-strength hot-dip galvanized steel sheet containing a hot-dip galvanized layer on the surface of the steel sheet, the steel sheet comprises a composition consisting a specified quantity of C, Si, Mn, P, S, Al, N, Ti, B and the balance Fe with inevitable impurities and a structure containing ferrite having an area ratio of 30% or more and martensite having an area ratio of 20% or more, wherein the ferrite satisfies |(AR_L+AR_C-2×AR_D)/2|0.2 with an average crystal grain size of 10 μm or less. Accordingly, the high-strength hot-dip galvanized steel sheet satisfies |(EL_L+EL_C-2×EL_D)/2|1.0 and|( U.EL_L+U.EL_C-2×U.EL_D)/2|0.6, where AR_L is an aspect ratio of ferrite crystal grain in L cross section, AR_C is an aspect ratio of ferrite crystal grain in C cross section, AR_D is an aspect ratio of ferrite crystal grain in D cross section, EL_L is a total elongation in L direction, EL_C is a total elongation in C direction, EL_D is a total elongation in D direction, U.EL_L is a uniform elongation in L direction, U.EL_C is a uniform elongation in C direction, U.EL_D is a uniform elongation in D direction.;COPYRIGHT: (C)2014,JPO&INPIT