Patent ID: 8465600

Claim:
A high strength steel sheet comprising C: 0.03 to 0.20% (% by mass in chemical compositions; hereafter, the same holds true), Si: 0.50 to 2.5%, and Mn: 0.50 to 2.5%, wherein a metal structure includes ferrite and low temperature transformation phase, a mean grain size of the low temperature transformation phase is 3.0 μm or less, grains having a grain size of 3.0 μm or less occupy 50% or more by area ratio of the low temperature transformation phase, and an average aspect ratio of the low temperature transformation phase is 0.35 or more, wherein the steel sheet has a tensile strength of 780 MPa or more, wherein the steel sheet is a cold rolled steel sheet, and wherein the low temperature transformation phase contains martensite, bainite and pseudo pearlite.