Bake-hardening hot-rolled steel sheet with excellent workability and method for manufacturing the same

摘要: This bake-hardening hot-rolled steel sheet with excellent workability, contains, in terms of mass %, C 0.01 to 0.2%, Si 2%, Mn 0.1 P 0.1% or less, S 0.03% Al 0.001 0.1%, N 0.01% Nb 0.005 0.05%, and as the remainder, Fe unavoidable impurities, wherein microstructure is a continuous-cooled having an average particle diameter 2 µm 8 µm, consisting polygonal ferrite which have grain boundary abundance ratio solute and/or 0.28 lower. method for manufacturing includes: heating slab containing aforementioned components at least temperature satisfying equation SRT (°C) = 6670/{2.26 - log(%Nb)(%C)} 273 (A); subjecting heated rough rolling, finish rolling under condition where final range Ar3 transformation point higher (Ar3 + 100°C) lower; cooling it rate 80°C/sec from initiation down 500°C coiling it.