Patent ID: 8343288

Claim:
A cold rolled steel sheet having a composition comprising, by mass %: 0. 03 to 0.30% of C; 0. 1 to 5.0% of Mn; not more than 0.1% of P; less than 0.01% of S; not more than 0.01% of N; 0. 01 to 1.00% of Al; and 0.5 to 3.0% of Si, wherein the cold rolled steel sheet further has a structure comprising tempered martensite with an area ratio of not less than 50%, including 100%, and ferrite comprised in the balance of the structure, wherein at least one structure factor selected from the group consisting of cementite particles in the tempered martensite, ferrite grains, and dislocation density of the whole structure, is controlled, wherein; the tempered martensite has a hardness of not more than 380 Hv; the number of cementite particles having a diameter of an equivalent circle of 0.1 μm or more, present in the tempered martensite, is not more than 2.3 pieces per 1 μm 2 of the tempered martensite; and the number of inclusions having an aspect ratio of not less than 2.0, present in the whole structure, is not more than 200 pieces per 1 mm 2 .