Patent ID: 7662243

Claim:
A hot-rolled steel sheet having a superior press moldability, a superior bake hardenability, and a superior stretch flangability, the hot-rolled steel sheet comprising: at least one portion which comprises, in terms of percent by mass, C of approximately 0.01% to less than 0.1%, Si of approximately 0.01% to 2%, Mn of approximately 0.1%to2%, P of at most approximately 0.1%, S of at most approximately 0.03%, Al of approximately 0.001% to 0.1%, N of at most approximately 0.01%, and Fe and unavoidable impurities as a remainder, wherein a microstructure of the hot-rolled steel sheet substantially comprises a homogeneous continuous-cooled microstructure in the amount of more than 80% and polygonal ferrite (PF) in the amount of 20% or less, wherein the continuous-cooled microstructure consists of bainitic ferrite (α o B ), granular bainitic ferrite (α B ), quasi-polygonal ferrite (α q ), residual austenite (γ r ), and martensite-austenite (MA), and the total amount of residual austenite (γ r ) and martensite-austenite (MA) is 3% or less, wherein interfaces between hard phases and soft phases do not exist, wherein the difference in average Vickers hardness (ΔHv) at ¼t and ½t of the sheet thickness (t) and at a depth of 0.2 mm below the surface layer is 15 Hv or less, wherein an average crystal grain size of the microstructure is greater than approximately 8 μm and at most approximately 30 μm; wherein the bake hardenability of the hot-rolled steel sheet facilitates the hot-rolled steel sheet to obtain a BH amount of about 50 MPa or more, and wherein the hot-rolled steel sheet has a strength of 370 to 490 MPa.