Acceleration of Bainite Transformation at Low Temperature by Warm Rolling Process

In this paper, the acceleration effect of warm rolling process on bainite transformation at 230oC for a high-carbon, silicon-rich steel with nanostructured bainite was studied. The warm rolling temperature was determined by simulation experiments using a Gleeble 3500 thermal and mechanical testing system. It is found that the bainite transformation will take more than 50 hours to complete at the same isothermal temperature without warm rolling, while the incubation time can be shortened from 6 hours to 0.5 hours when warm rolling was conducted within a temperature range 300-600oC. In addition, the quantitative X-ray analysis indicated that the volume fraction of retained austenite after warm rolling (total strain 0.20) and isothermal transformation for 20 hours was about 33.8%, keeping a same level compared with the austempering bainite transformation process (no strain) which austenite volume fraction was about 32%. Low temperature bainite transformation can be accelerated by warm rolling effectively without compromising strength. And the ultimate tensile strength of warm rolling nanostructured bainite steel is 2127 MPa.