High-strength composite organization cold-rolled steel sheet and manufacturing method thereof having a uniform and high n value in a wide strain range

摘要

PURPOSE: To provide a steel sheet having high and uniform n-value in a wide strain range and also having high strength and high ductility, to obtain a steel sheet free from defects and excellent in press formability by enabling the desirable production of the steel sheet, and to reduce the weight of a steel sheet for automotive body in particular. ;CONSTITUTION: This steel sheet is a high strength cold rolled dual-phase steel sheet satisfying TS×El≥2500, having high and uniform n-value satisfying an operation expression f(n)=1/(n₅+n₂₀)²+25%||n₅-n₂₀)||≤4.5 in a strain range of 5-20%, and excellent in press formability (where n is an n-value at 5% strain n₂₀ is an n-value at 20% strain and ||n₅-n₂₀|| is the absolute value of a difference between n₅ and n₂₀). By combinedly adding at least one element among Ti, Nb, V, Zr, and Mo and B and also optimizing continuous annealing conditions, the cold rolled sheet of high strength dual-phase steel having high and uniform n-value and excellent in press formability can be produced.;COPYRIGHT: (C)1994,JPO&Japio