Nippon Steel Sumitomo Metal Corporation

Toshiki Hattori

Hirokazu Taniguchi

Satoshi Kato

Kenichiro Matsumura

Satoshi Nippon Steel Corporation Kato

The present invention provides hot dip galvanized high strength steel sheet excellent in plating adhesion and hole expandability and a method of production of the same, that is, hot dip galvanization steel sheet excellent in plating adhesion and hole expandability containing, by mass %, C: 0.08 to 0.35%, Si: 1.0% or less, Mn: 0.8 to 3.5%, P: 0.03% or less, S: 0.03% or less, Al: 0.25 to 1.8%, Mo: 0.05 to 0.35%, and N: 0.010% or less and having a balance of Fe and unavoidable impurities, said hot dip galvanized high strength steel characterized in that the steel sheet has a metal structure having ferrite, bainite, by area percent, 0.5% to 10% of tempered martensite, and, by volume percent, 5% or more of residual austenite, and a method of production comprising annealing by a continuous annealing process at 680 to 930&#xb0; C. in temperature, then cooling to the martensite transformation point or less, then hot dip galvanizing the steel during which heating the steel to 250 to 600&#xb0; C., then hot dip galvanizing it.

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Tokai, Japan

Toshiki Hattori