Patent ID: 9150946
Filing Date: 2015-10-06
Classification: B32B,C21D,C22C,C23C

Abstract:
1. A production method of a hot dip galvanized high strength steel sheet from a slab consisting of, by mass %, C: 0.08 to 0.35%, Si: less than 0.2%, 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%, N: 0.010% or less, Ti: 0.0002% or less, optionally one or more of Nb: 0.01 to 0.3%, V: 0.01 to 0.3%, Cu: 1% or less, Ni: 1% or less, Cr: 1% or less, or B: 0.0001 to 0.0030%, and a balance of Fe and unavoidable impurities, the method comprising the steps of: hot rolling the slab to make a steel sheet, coiling the sheet at a temperature of 400 to 750° C., cold rolling the sheet, annealing the cold rolled sheet by a continuous annealing process at a temperature of 680 to 930° C., overaging the annealed sheet at a temperature of 300 to 500° C. for 60 seconds to 20 minutes, cooling the overaged sheet to the martensite transformation point or less, heating the cooled sheet to 250 to 600° C., then hot dip galvanizing the heated sheet, wherein the hot dip galvanized sheet has by area percent, 3.5% to 10% of tempered martensite, and by volume percent, 7% or more of residual austenite.