Grain refinement and microstructural evolution of grain boundary allotriomorphic ferrite/granular bainite steel after prior austenite deformation

The prior compressive deformation of austenite followed by air cooling was simulated by Gleeble-1500 machine on the grain boundary allotriomorphic ferrite/granular bainite (FGBA/Bg) dual phase steel. FGBA grains of less than 5 μm and intragranular ferrite grains less than 3 μm were obtained in the specimen with 30% compressive deformation at 780 °C. The prior compressive deformation of austenite promotes the formation of granular structure instead of granular bainite, reduces the length of bainitic plates and results in a random distribution of ultrafine martensite–austenite (MA) islands. The results of Vickers hardness and Charpy V-notch (CVN) impact experiments show that the prior austenite deformation with air cooling is an effective way to improve both the strength and toughness of this dual phase steel.