Patent ID: 9290835
Filing Date: 2016-03-22
CPC Classification: B21B,C21D,C22C,C23C

Claim Text:
1. A method of producing a cold-rolled steel sheet excellent in paint bake hardenability and ordinary-temperature non-aging property comprising: a slab consisting of in mass %, a balance of Fe and unavoidable impurities; hot rolling the slab at a temperature of (Ar cold rolling the hot-rolled slab at a reduction ratio of 90% or less; annealing the cold-rolled product to reach a maximum temperature of 750-920° C.; and during a post-annealing cooling process, holding the annealed product for 20 to 50 seconds at a temperature range of 550-750° C., wherein the steel satisfies the relationship N−0.52 Al>0%, 50% or more of solute N form pairs with Cr or segregate around oxides or precipitates, and the steel sheet has a yield point elongation equal to or less than 0.08% and a bake hardenability of at least 82 MPa, wherein the cold-rolled steel sheet comprises a structure that consists of ferrite and/or bainite as the main phase, and optionally contains martensite.