Method for producing high-strength hot-dip galvannealed steel sheet

A method for producing a high-strength hot-dip galvannealed steel sheet, the method comprising:

• pickling a high-strength steel sheet;
• drying the high-strength steel sheet;
• further pickling the high-strength steel sheet;
• preplating the high-strength steel sheet with between about 0.2 g/m2 and about 2.0 g/m of Ni;
• heating the high-strength steel sheet in a nonoxidizing atmosphere to a temperature between about 430° C. and about 500° C.;
• plating the high-strength steel sheet in a hot-dip galvanizing bath containing between about 0.05% and about 0.2% of Al;
• and
• alloying the high-strength steel sheet using a heat treatment to produce the high-strength hot-dip galvannealed steel sheet.

A method for producing a high-strength hot-dip galvannealed steel sheet, the method comprising:

• pickling a steel sheet comprising at least one of (i) a pickled hot rolled steel sheet comprising between about 0.02% and about 0.2% of C, between about 0.15% and about 2.5% of Mn, and a balance of Fe and unavoidable impurities, or (ii) an annealed and pickled cold rolled steel sheet;
• rinsing the steel sheet;
• preplating the steel sheet with between about 0.2 g/m2 and about 2.0 g/m2 of Ni without drying the steel sheet after the steel sheet is rinsed;
• preparing the steel sheet by heating the steel sheet in at least one of a nonoxidizing atmosphere or a reducing atmosphere to a sheet temperature of about 430° C. to 500° C. at a rate of at least about 30° C./sec;
• hot-dip plating the steel sheet in a galvanizing bath comprising between about 0.05% and about 0.2% of Al;
• wiping the steel sheet;
• immediately heating the steel sheet to a temperature between about 470° C. and about 550° C. at a rate of at least about 30° C./sec;
• and
• cooling the steel sheet to form the high-strength hot-dip galvannealed steel sheet.

A method for producing a high-strength hot-dip galvannealed steel sheet, the method comprising:

• pickling a steel sheet comprising at least one of (i) a pickled hot rolled steel sheet comprising between about 0.02% and about 0.2% of C, between about 0.15% and about 2.5% of Mn, and a balance of Fe and unavoidable impurities, or (ii) an annealed and pickled cold rolled steel sheet;
• preplating the steel sheet with between about 0.2 g/m2 and about 2.0 g/m2 of Ni without rinsing or drying the steel sheet after the pickling;
• preparing the steel sheet by heating the steel sheet in at least one of a nonoxidizing atmosphere or a reducing atmosphere to a sheet temperature of 430° C. to 500° C. at a rate of at least about 30° C./sec;
• hot-dip plating the steel sheet in a galvanizing bath comprising between about 0.05% and about 0.2% of Al;
• wiping the steel sheet;
• immediately heating the steel sheet to a temperature between about 470° C. and about 550° C. at a rate of at least about 30° C./sec;
• and
• cooling the steel sheet to form the high-strength hot-dip galvannealed steel sheet.