| 摘要 |
The invention provides a high strength hot-rolled steel sheet with a tensile strength of not less than 590 MPa which exhibits excellent bake hardenability and stretch-flangeability, and a method for manufacturing the same. The chemical composition includes, in terms of mass%, C at 0.040 to 0.10%, Si at not more than 0.3%, Mn at 1.7 to 2.5%, P at not more than 0.030%, S at not more than 0.005%, Al at not more than 0.1% and N at 0.006 to 0.025%. The microstructure is such that a bainite phase represents not less than 60%, the total of a ferrite phase and a pearlite phase represents not more than 10%, and the bainite phase includes grains among which cementite grains have been precipitated at not less than 1.4 x 10 4 grains/mm 2 and the cementite grains have an average grain diameter of not more than 1.5 µm. |
