Patent ID: 7347902

Claim:
A high-strength hot rolled steel sheet having excellent shape fixability and fatigue durability after forming comprising: C: not less than 0.02 mass % but not more than 0.2 mass %, Si: not less than 0.5 mass % but not more than 2.0 mass %, Mn: not less than 1.0 mass % but not more than 3.0 mass %, Al: not less than 0.01 mass % but not more than 0.1 mass %, N: not less than 0.002 mass % but not more than 0.006 mass %, P: not more than 0.03 mass %, S: not more than 0.01 mass % and solid-soluted (C+N): not less than 0.0010 mass % and the remainder being Fe and inevitable impurities, and having a steel structure that a primary phase is ferrite and a secondary phase is martensite phase of 5-30% at a volume ratio and a total of both is not less than 95% as a volume ratio, and an average crystal grain size of ferrite of not more than 8 μm, and 0.001 to 0.005% of the solid-soluted C. N is present in grains of the ferrite.