Patent ID: 7294412
Filing Date: 2007-11-13
Classification: C21D,C22C,C23C,Y10T

Abstract:
1. A high-strength hot-dip galvanized steel sheet characterized by: containing, in weight, C: 0.03 to 0.25%, Si: 0.05 to 2.0%, Mn: 0.5 to 2.5% P: 0.03% or less, S: 0.02% or less, Al: 0.01 to 2.0%, Ni: 0.01 to 2.0% and Mo: 0.01 to 0.5%, balance Fe and unavoidable impurities; with the relationship among Si, Mn and Al and the relationship among Si, Al and Ni satisfying the following expressions: with the relationship between Ni and Mo satisfying the expression: 1/20×Ni(%)≦Mo(%)≦10×Ni(%); and said steel sheet contains retained austenite in the range from 2 to 20% by volume; a hot-dip plating layer being formed on each of the surfaces of said steel sheet; and 5 to 80% of the surface area of said steel sheet being occupied by Si, Mn and Al oxides when said steel sheet surface is observed with a scanning electron microscope after a hot-dip plating layer is dissolved by fuming nitric acid; where said surface area of said steel sheet occupied by said Si, Mn and Al oxides is on the surfaces of said steel sheet interfacing with said hot-dip plating layer prior to said hot-dip plating layer being dissolved by said fuming nitric acid; and wherein said Si, Mn and Al oxides have a maximum length of 3 μm and said Si, Mn and Al oxides have gaps between them.