Method for manufacturing high strength steel sheet having excellent formability

摘要

A method of manufacturing a high strength steel sheet having excellent formability suitable for the material of an automotive part has a tensile strength (TS) of 980 MPa or more and total elongation (EL) is 25% or more. A steel slab has a chemical composition containing C: 0.03% to 0.35%, Si: 0.5% to 3.0%, Mn: 3.5% to 10.0%, P: 0.100% or less, S: 0.02% or less, and the remainder includes Fe and incidental impurities on a percent by mass basis is hot-rolled, a heat treatment is performed, in which an achieved temperature of Ac1 to Ac1+100° C. is held for 3 minutes or more, subsequently, cold rolling is performed at a rolling reduction of 20% or more and, annealing is performed, in which an achieved temperature of Ac1−30° C. to Ac1+100° C. is held for 1 minute or more.

主权项

1. A method of manufacturing a high strength steel sheet having excellent formability comprising:
preparing a steel slab having a chemical composition containing C: 0.03% to 0.35%, Si: 0.5% to 3.0%, Mn: 3.5% to 10.0%, P: 0.100% or less, S: 0.02% or less, and the remainder comprising Fe and incidental impurities on a percent by mass basis; hot-rolling the steel slab; subjecting the hot rolled steel sheet to a heat treatment in which an achieved temperature of Ac1 to Ac1+100° C. is held for 3 minutes or more; cold-rolling the steel sheet subjected to the heat treatment at a rolling reduction of 20% or more; and subjecting the cold rolled steel sheet to annealing in which an achieved temperature of Ac1−30° C. to Ac1+100° C. is held for 1 minute or more.