| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet having excellent fatigue resistance, as well as superior shape freezing properties after slit processing, and a manufacturing method thereof.SOLUTION: A composition includes: by mass%, 0.06-0.13% C, over 0.5% to 1.5% or less Si, 1.0-1.8% Mn, 0.03% or less P, 0.006% or less S, 0.08% or less Al, 0.0080% or less N, and 0.09-0.16% Ti, and the balance Fe and inevitable impurities. A structure includes: ferrite phase and granular cementite, or perlite, additionally. In the structure, the area ratio of the ferrite phase is 85-97%, the average particle diameter of the granular cementite precipitated on a grain boundary of the ferrite phase in the granular cementite is 0.5 μm or less, the average particle diameter of carbide including Ti precipitated in the ferrite phase crystal grain is 10 nm, and an amount of solid solution Ti is 0.03% or less, by mass%. |
