A steel sheet having (a) a dual phase microstructure with a martensite phase and a ferrite phase and (b) a composition containing by percent weight: 0.01≦C≦0.2; 0.3≦Mn≦3; 0.05≦Si≦2; 0.2≦Cr+Ni≦2; 0.01≦Al≦0.10; 0.0005≦Ca≦0.01, with the balance of the composition being iron and incidental ingredients. Also, the steel sheet is made by a batch annealing method, and has a tensile strength of at least approximately 400 megapascals and an n-value of at least approximately 0.175.