HIGH-RIGIDITY HIGH-STRENGTH THIN STEEL SHEET AND METHOD FOR PRODUCING SAME

摘要

Disclosed is a high-rigidity high-strength thin steel sheet having a tensile strength of not less than 590 MPa and a Young's modulus of not less than 225 GPa at the same time. The high-rigidity high-strength thin steel sheet has a composition consisting of, in mass%, C:0.02-0.15%, Si: 1.5% or less, Mn: 1.5-4.0%, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, N: 0.01% or less, Nb: 0.02-0.40%, and the balance of iron and unavoidable impurities, wherein the C, N and Nb contents satisfy the following relations: 0.01 <= C + (12/14) x N - (12/92.9) x Nb <= 0.06 and N <= (14/92.9) x (Nb - 0.01). The structure of such a steel sheet has a main phase composed of a ferrite phase, and contains not less than 1% of a martensite phase in the area ratio as a second phase.