Patent ID: 9200344
Filing Date: 2015-12-01
Classification: B32B,C21D,C22C

Abstract:
1. A high strength hot rolled steel sheet with excellent bendability, which has a composition comprising, in terms of mass %, C at 0.05 to 0.15%, Si at 0.2 to 1.2%, Mn at 1.0 to 2.0%, P at not more than 0.04%, S at not more than 0.0030%, Al at 0.005 to 0.10%, N at not more than 0.005% and Ti at 0.03 to 0.13%, the balance being represented by Fe and inevitable impurities, includes surface regions having an area fraction of bainite of less than 80% and an area fraction of a ferrite phase with a grain diameter of 2 to 15 μm of not less than 10%, the surface regions extending from front and back surfaces of the steel sheet each to a depth of 1.5 to 3.0% relative to a total sheet thickness, as well as an inner region other than the surface regions having an area fraction of a bainite phase of more than 95%, and has a tensile strength of not less than 780 MPa, wherein the total sheet thickness is from 8.0 mm or less to 1.8 mm or more, and a minimum bending radius without occurrence of a crack defined as a critical bending radius R in mm, divided by the total sheet thickness t in mm given as an R/t value, is from 0.5 or less to 0.17 or more.