Method for manufacturing high strength steel strips with superior formability and excellent coatability
A method for manufacturing a steel sheet used for structural members, elements, etc. of automobiles including a front side member, pillar, and the like, and more particularly, a method for manufacturing a steel sheet having a high strength and formability as well as hot-dip galvanizing properties is disclosed. In the method, after an aluminum killed steel slab, which comprises, by weight %: C: 0.05% to 0.25%; Si: 0.1% to 1.5%; S: 0.02% or less; N: 0.01% or less; Al: 0.02% to 2.0%; Mn: 1.0% to 2.5%; P: 0.001% to 0.1%; Sb: 0.005% to 0.10%; the balance of Fe and other unavoidable impurities, is subjected to a homogenization treatment at a temperature range of 1050° C. to 1300° C., the aluminum killed steel slab is subjected to a hot rolling under a finishing hot rolling temperature of 850° C. to 950° C. and a coiling temperature of 400° C. to 700° C., followed by a cold rolling under a cold rolling reduction ration of 30% to 80%, and annealing the cold rolled steel sheet.
1. A method for manufacturing a steel sheet having high strength and formability and being suitable for hot dip galvanizing, comprising:
performing a homogenization treatment on an aluminum killed steel slab at a temperature of 1050° C. to 1300° C., the aluminum killed steel slab comprising, by weight %: C: 0.05% to 0.25%; Si: 0.1% to 1.5%; S: 0.02% or less; N: 0.01% or less; Al: 0.455% to 2.0%; Mn: 1.0% to 2.5%; P: 0.001% to 0.1%; Sb: 0.005% to 0.10%; the balance of Fe and other unavoidable impurities;
hot rolling the aluminum killed steel slab under a finishing hot rolling temperature of 850° C. to 950° C. and a coiling temperature of 400° C. to 700° C., to form a hot rolled steel sheet;
cold rolling the hot rolled steel sheet under a cold rolling reduction ratio of 30% to 80% and annealing the cold rolled steel sheet at a temperature of 700° C. to 870° C., and then cooling the annealed steel sheet to a temperature range of 620° C. to 700° C. at a cooling rate of 1 to 7° C./sec, the steel sheet having a microstructure consisting of ferrite and austenite.
2. The method according to claim 1 , wherein one or more elements selected from the group consisting of Nb: 0.001% to 0.10%, Mo: 0.05% to 0.5%, and Co: 0.01% to 1.0% are added into the aluminum killed steel slab.