COLD-ROLLED STEEL SHEET, PLATED STEEL SHEET, METHOD FOR PRODUCING COLD-ROLLED STEEL SHEET, AND METHOD FOR PRODUCING PLATED STEEL SHEET.

摘要

This cold-rolled steel sheet contains, in mass%, from 0.020% to 0.080% (inclusive) of C, from 0.20% to 1.00% (inclusive) of Si, from 0.80% to 2.30% (inclusive) of Mn and from 0.010% to 0.100% (inclusive) of Al, while containing Nb and/or Ti so that the condition 0.005% ≤ Nb + Ti < 0.030% is satisfied. The metal structure of this cold-rolled steel sheet is composed of ferrite, bainite and other phases; and the area ratio of the ferrite is 80% or more but less than 95%, the area ratio of non-recrystallized ferrite in the ferrite is 1% or more but less than 10%, and the area ratio of the bainite is from 5% to 20%. The total of the fractions of the other phases is less than 8%. A carbonitride containing one or both of Nb and Ti has a circle-equivalent diameter of from 1 nm to 10 nm (inclusive). This cold-rolled steel sheet has a tensile strength of 590 MPa or more.