Patent ID: 8691396
Filing Date: 2014-04-08
Classification: C21D,C22C,C23C,Y10T

Abstract:
1. A galvannealed steel sheet, obtained by subjecting a base steel sheet to hot-dip galvanization and then alloying the galvanization layer, wherein a base steel sheet of the galvannealed steel sheet is obtained by hot rolling a steel, the steel comprising: Fe; carbon (C) in a content of 0.02 to 0.25 percent by mass; silicon (Si) in a content of 1 to 3 percent by mass; manganese (Mn) in a content of 1 to 4 percent by mass; chromium (Cr) in a content of 0.03 to 1 percent by mass; aluminum (Al) in a content of 1.5 percent by mass or less, exclusive of 0 percent by mass; phosphorus (P) in a content of 0.03 percent by mass or less, exclusive of 0 percent by mass; sulfur (S) in a content of 0.03 percent by mass or less, exclusive of 0 percent by mass; titanium (Ti) in a content of 0.003 to 1 percent by mass; copper (Cu) in a content of 0.25 to 5.0 percent by mass; and nickel (Ni) in a content of 0.05 to 1.0 percent by mass, wherein: where [Cu] and [Ni] represent the contents, as a percent by mass, of Cu and Ni, respectively; the base steel sheet has a metal structure comprising retained austenite in a content of 3 percent by area or more; and the retained austenite has an average axial ratio, (major axis)/(minor axis), of grains of 5 or more.