HIGH STRENGTH HOT DIP GALVANIZED STEEL PLATE HAVING EXCELLENT MOLDABILITY WEAK MATERIAL ANISOTROPY AND ULTIMATE TENSILE STRENGTH OF 980 MPA OR MORE HIGH STRENGTH ALLOYED HOT DIP GALVANIZED STEEL PLATE AND MANUFACTURING METHOD THEREFOR

摘要

Provided is a hot dip galvanized steel plate having a hot dip galvanized layer on the surface of a base material steel plate. The base material steel plate contains 0.1 to less than 0.40% C 0.5 to 3.0% Si 1.5 to 3.0% Mn by mass the quantity of O is limited to 0.006% or less quantity of P to 0.04% or less quantity of S to 0.01% or less quantity of Al to 2.0% or less and quantity of N to 0.01% or less by mass with the remainder consisting of iron and unavoidable impurities. The microstructure of the base material steel plate contains 40% or more ferrite 8 to less than 60% residual austenite in volume fraction with the remainder consisting of bainite or martensite. In a plate thickness range of 5/8 to 3/8 from the surface of the base material steel plate the polar density of specific crystal orientation is within a predetermined range. The hot dip galvanized layer contains less than 7% by mass Fe with the remainder consisting of Zn Al and unavoidable impurities. Thus the high strength hot dip galvanized steel plate of the invention has excellent moldability weak material anisotropy and an ultimate tensile strength of 980 MPa or more.