| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel plate excellent in low temperature toughness and mainly used for an automobile undercarriage member or the like.SOLUTION: Provided is a high strength hot rolled steel sheet having a composition comprising, by mass, 0.030 to 0.100% C, 0.001 to 1.5% Si, 0.5 to 3.0% Mn and 0.03 to 0.20% Ti, in which P is limited to 0.1% or lower, S is limited to 0.005% or lower, Al is limited to 1% or lower and N is limited to 0.010%, and the balance Fe with inevitable impurities, in which the average crystal grain size thereof is 8 μm or lower, the segregation amount of C to large angle crystal boundaries with an orientation angle of 15° or higher is 4 to 15 atoms/mm, the number of TiC precipitates with a sphere equivalent diameter of 3 nm or higher on the large angle crystal boundaries is below 0.01 piece/nm, and the ratio of the crystal grains in which the piece density of TiC precipitates with a sphere equivalent diameter in the crystal grains of 0.8 to 2 nm is 8×10pieces/cmis 10 to 70%. |
