| 摘要 |
According to an exemplary embodiment of the present invention, a bake-hardening hot-rolled steel sheet with excellent workability can be provided. The exemplary steel sheet can contain, in terms of mass %, C of about 0.01 to 0.2%, Si of about 0.01 to 2%, Mn of about 0.1 to 2%, P of about 0.1% or less, S of about 0.03% or less, Al of about 0.001 to 0.1%, N of about 0.01% or less, Nb of about 0.005 to 0.05%, and as the remainder, Fe and unavoidable impurities. A microstructure of the steel sheet can be a polygonal ferrite and/or a continuous-cooled microstructure having an average particle diameter of about 2 mum to 8 mum, and the grain boundary abundance ratio of solute C and/or solute N may be about 0.28 or lower. An exemplary embodiment of the present invention can also be directed to a method for manufacturing a hot-rolled steel sheet. In this exemplary method, a slab containing aforementioned components can be heated to at least a temperature satisfying the equation of SRT (° C.)=6670/{2.26-log(% Nb)(% C)}-273. The heated slab can be subjected to a rough rolling, a finish rolling under a condition where the final temperature can be in a range of the Ar3 transformation point temperature or higher and (Ar3 transformation point temperature+100° C.) or lower to obtain a rolled steel. The rolled steel can be cooled at a cooling rate of about 80° C./sec or higher from cooling initiation down to a temperature range of about 500° C. or lower to obtain a hot rolled steel sheet; and such hot rolled steel sheet can be coiled. |
