TÔLE D'ACIER LAMINÉE À FROID À HAUTE RÉSISTANCE MÉCANIQUE ET SON PROCÉDÉ DE PRODUCTION

摘要

A high-strength cold rolled steel sheet has both high strength, i.e. a tensile strength of 900 MPa or more, and high workability, i.e. a total elongation of 20 % or more, and also has a low yield ratio of less than 60 %. The high-strength cold rolled steel sheet comprises: a predetermined chemical composition; and a steel structure having, in area ratio, ferrite: 30 % to 75 %, martensite: 15 % to 40 %, and retained austenite: 10 % to 30 %. In the case where a distribution of crystal grain circularity of the retained austenite is represented by a histogram with a class range of more than 0.1 × (n - 1) and 0.1 × n or less and a class value of 0.1 × n (n is an integer from 1 to 10), a mode of the crystal grain circularity of the retained austenite is 0.7 or more.