HIGH STRENGTH STEEL SHEET HAVING EXCELLENT FORMABILITY AND METHOD FOR MANUFACTURING THE SAME

摘要

A method for manufacturing the high strength steel sheet having excellent formability includes hot-rolling a steel slab having a chemical composition containing, by mass %, C: 0.03% or more and 0.35% or less, Si: 0.5% or more and 3.0% or less, Mn: 3.5% or more and 10.0% or less, P: 0.1% or less, S: 0.01% or less, N: 0.008% or less and the balance comprising Fe and inevitable impurities, coiling the hot-rolled steel sheet at a temperature range of the Ar1 transformation point to the Ar1 transformation point+(the Ar3 transformation point−the Ar1 transformation point)/2, cooling the coiled steel sheet down to 200° C. or lower, heating and holding the cooled steel sheet at a temperature range of the Ac1 transformation point−200° C. to the Ac1 transformation point for 30 minutes or more, pickling the heated steel sheet, cold-rolling the pickled steel sheet under the condition that the rolling reduction is 20% or more, and heating and holding the cold-rolled steel sheet at a temperature range of the Ac1 transformation point to the Ac1 transformation point+(the Ac3 transformation point−the Ac1 transformation point)/2 for 30 seconds or more.

主权项

1. A method for manufacturing a high strength steel sheet having excellent formability, the method comprising:
hot-rolling a steel slab having a chemical composition containing, by mass %, C: 0.03% or more and 0.35% or less, Si: 0.5% or more and 3.0% or less, Mn: 3.5% or more and 10.0% or less, P: 0.1% or less, S: 0.01% or less, N: 0.008% or less and the balance comprising Fe and inevitable impurities; coiling the hot-rolled steel sheet at a temperature range of the Ar1 transformation point to the Ar1 transformation point+(the Ar3 transformation point−the Ar1 transformation point)/2; cooling the coiled steel sheet down to 200° C. or lower; heating and holding the cooled steel sheet at a temperature range of the Ac1 transformation point−200° C. to the Ac1 transformation point for 30 minutes or more; pickling the heated steel sheet; cold-rolling the pickled steel sheet under the condition that the rolling reduction is 20% or more; and heating and holding the cold-rolled steel sheet at a temperature range of the Ac1 transformation point to the Ac1 transformation point+(the Ac3 transformation point−the Ac1 transformation point)/2 for 30 seconds or more.