High strength steel sheet excellent in formability

A high strength steel sheet excellent in formability, resistant to delayed fracture and compatible with chemical conversion coating treatment and hot-dip galvanizing, said steel sheet consisting of, in mass,

• 0.03 to 0.20% C,
• 0.107 to 0.3% Si,
• 1.0 to 3.1% Mn,
• 0.001 to 0.06% P,
• 0.001 to 0.01% S,
• 0.0005 to 0.01% N,
• 0.2 to 1.2% Al,
• and not more than 0.5% Mo,
• at least one of 0.01 to 0.1% Ti, 0.005 to 0.05 Nb, and 0.01 to 0.1% V;
• with the balance consisting of Fe and unavoidable impurities;
• the amounts of Si and Al in mass % and the target strength (TS) of said steel sheet satisfy the following expression (1);
• and the metallographic structure of said steel sheet contains ferrite and martensite without containing retained austenite and has a tensile strength of 980 MPa or more and a value of TS×E1 of 16,000 or more;
• (0.0012×[target strength TS]−0.29-[Si])/2.45<Al<1.5−3×[Si] (1)
• where, [target strength TS] is the designed strength of said steel sheet in terms of MPa and [Si] is the amount of Si in terms of mass %.