Patent ID: 7553380

Claim:
A dual-phase steel sheet of excellent bake hardening property and stretch flange formability containing C: 0.01-0.20 mass %, Si: 0.5 mass % or less, Mn: 0.5-3 mass %, N: 0.0060 mass % or more, sol.Al: 0.025 mass % or less (inclusive 0 mass %), P: 0.15 mass % or less (exclusive 0 mass %), and S: 0.02 mass % or less (inclusive 0 mass %), wherein the steel sheet comprises as a matrix phase a member selected from the group consisting of tempered bainite; and tempered bainite and ferrite, the steel sheet comprises as a second phase from 1 to 30 area % of martensite, and the steel sheet satisfies the following relation (1): 0.0001%≦[N]−(14/27)×[sol.Al]≦0.001% (1) where [N] represents the content of N, and [sol.Al] represents the content of sol.Al.