| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet having improved fatigue strength without bringing about its cost increase and deterioration in total elongation, and a production method thereof.SOLUTION: There is provided the high strength hot rolled steel sheet excellent in fatigue characteristics having composition containing, by mass%, C:0.10 to 0.20%, Si:0.01 to 2.00%, Mn:0.10 to 2.00%, P≤0.100%, S≤0.0100%, Al:0.005 to 0.050%, N≤0.0100% and the balance Fe with inevitable impurities. In the high strength hot rolled steel sheet excellent in fatigue characteristics, a micro structure in an area of thickness corresponding to at least 10% of sheet thickness from a surface and a rear face of the steel sheet is a bainite single phase, micro structure in the area of thickness corresponding to at least 50% of sheet thickness of a center part has a ferritic area fraction of 50% or more and the hardness of the area of thickness corresponding to at least 10% of sheet thickness from the surface and rear face is 1.15 times or more as an average hardness of the area of thickness corresponding to at least 50% of the sheet thickness of the center part. |
