HIGH STRENGTH HOT-DIP GALVANIZED OR GALVANNEALED STEEL SHEET HAVING IMPROVED PLATING ADHESION AND PRESS FORMABILITY AND PROCESS FOR PRODUCING THE SAME

摘要

Disclosed are a high strength hot-dip galvanized orgalvannealedsteel sheet, which has improvedpressformabilityand plating adhesion and is useful as a member for automobile,building, electric or other members, and a process forproducing the same.This high strength hot-dip galvanized or galvannealedsteel sheet comprises: (a) a steel sheet substrate comprising,by weight, carbon (C): 0.05 to 0.2%, silicon (Si) : 0.2to 2.0%, manganese (Mn) : 0.2 to 2.5%, and aluminum (Al) : 0.01to 1.5%, the silicon and the aluminum having a mutualrelationship represented by formula 0.4 (%) =Si + 0.8A1 (%)= 2.0 (%), the steel sheet substrate further comprising atleast one member selected from the group consisting of (i)0.003 to 1.0% of tin (Sn), (ii) 0.005 to 1.0% in total ofat least one member selected from antimony (Sb) , bismuth (Bi ),and selenium (Se), (iii) 0.005 to 1.0% in total of at leastone member selected from beryllium (Be), magnesium (Mg),calcium (Ca) , and zirconium (Zr) , and (iv) 0.005 to 1.0% intotal of at least one member selected from scandium (Sc),yttrium (Y) , lanthanum (La) , and cerium (Ce) , with the balanceconsisting of iron (Fe) and unavoidable impurities, the volumefraction of retained austenite in the steel structure being2 to 20%; and (b) a zinc (Zn) coating layer provided on saidsteel sheet substrate.