POST ANNEALED HIGH TENSILE STRENGTH COATED STEEL SHEET HAVING IMPROVED YIELD STRENGTH AND HOLE EXPANSION

摘要

A cold rolled, coated and post annealed steel sheet. The cold rolled steel sheet may comprise (in wt. %): C - 0.1 - 0.3 %; Mn - 1 - 3%; Si - 0.5 - 3.5%; Al - 0.05 - 1.5%; Mo + Cr is between 0 - 1.0%; and Mo + Cr is between 0.2 - 0.5%. The steel sheet may be coated with a zinc or zinc alloy coating. The coated steel sheet may be formed by cold rolling, zinc coating the cold rolled sheet and annealing said steel sheet after application of said zinc coating. The annealing is performed at a temperature and for a time sufficient to significantly increase the yield strength and hole expansion of the annealed coated cold rolled steel sheet as compared with the as coated sheet.