| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolling steel sheet having high strength with tensile strength of 780 MPa or more and excellent in processability and punchability.SOLUTION: There is provided a high strength hot rolling steel sheet having a composition containing, by mass%, C:0.030 to 0.090%, Si:0.3% or less, Mn:0.2 to 2.0%, P:0.03% or less, S:0.005% or less, N:0.006% or less, Al:0.1% or less, Ti:0.070 to 0.220% and satisfying C*≥0.010, where C*=C-(12/48)×Ti+(12/14)×N+(12/32)×S-(12/51)×V-(12/93)×Nb-(12/96)×Mo is defined, a ferrite phase having an area ratio of 95% or more and a structure in which 1.0×10/mor more of carbide having an average particle diameter of 10 nm or less and 10/10000 μmor more of cementite particle are deposited with difference between hardness of a sheet thickness middle position and hardness of a sheet thickness 1/4 position, &Dgr;HVof 20 HV or less. |
