Hot dip galvanized composite high strength steel sheet excellent in shapeability and hole enlargement ability and method of production of same

Abstract

The present invention provides a hot dip galvanized composite high strength steel sheet excellent in shapeability and hole enlargement ability and a method of production of the same, that is, a hot dip galvanized composite high strength steel sheet excellent in shapeability and hole enlargement ability containing C: 0.01 to 0.3%, Si: 0.005 to 0.6%, Mn: 0.1 to 3.3%, P: 0.001 to 0.06%, S: 0.001 to 0.01%, Al: 0.01 to 1.8%, and N: 0.0005 to 0.01% and having a metal structure of ferrite and, by area rate, 5% to 60% of tempered martensite and a method of production of the same comprising hot rolling, then cold rolling a slab including the above ingredients, heating the sheet in the hot dip galvanization heating process to Ac1 l to Ac3+100° C., holding it there for 30 seconds to 30 minutes, then cooling it by a 1° C./s or higher cooling rate to 450 to 600° C., hot dip galvanizing it at that temperature, then cooling it at a 1° C./s or higher cooling rate to the martensite transformation point or lower in temperature, holding it there at 200° C. to 500° C. for 1 second to 5 minutes, then cooling it at a 5° C./s or higher cooling rate to 100° C. or less.

Dependencies are inferred from the claim text.