| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-tension hot rolled steel sheet with tensile strength of 590 MPa or higher, which has a superior shape freezability in as-hot-rolled state, durable fatigue characteristics after forming, and further superior weldability and a chemical conversion coating property. SOLUTION: This high-tension hot rolled steel sheet has a composition containing 0.02-0.2 mass% C, 0.5-2.0 mass% Si, 1.0-3.0 mass% Mn, 0.1-0.6 mass% Mo, 0.01-0.1 mass% Al, 0.002-0.006 mass% N, 0.03 mass% or less P, 0.01 mass% or less S, 0.0010 mass% solution (C+N), and the balance Fe with unavoidable impurities, has a structure which consists of ferrite as a main phase and a martensitic phase of 5-30% by volume ratio as the second phase, while the total of the both phases is 95% or more by volume ratio, and further has an average crystal particle diameter of ferrite of 8μm or less.
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