5th International High Manganese Steel Conference - HMNS 2022

The effect of QP heat treatment on the phase transformation of Fe-8Mn-2.5Al-0.5Si-0.2C-1.6Cu (in wt.%) medium manganese steel was studied by thermal dilatometer and EBSD characterization. It was found that the key factor determining the microstructure (phase content) of QP heat treatment of medium manganese steel is quenching temperature. When the quenching temperature is low, a small amount of austenite after quenching can be stabilized in the partition process, and martensite transformation is not easy to occur during the second cooling after partition. However, this method of stabilizing austenite is limited because the upper limit of the final austenite content is the austenite content obtained at the first cooling. When the quenching temperature is high, although there is more austenite after quenching, the partition process has little effect on its stability due to the limited element diffusion, and a sharp transformation will occur during the second cooling. Therefore, moderate quenching temperature combined with the blending process is the key to obtain sufficient austenite. In addition, the morphology and size of martensite are determined by the first cooling stage when the quenching temperature is low, showing a large lath morphology. While, the small and needle-like martensite is mainly determined by the second cooling stage when the quenching temperature is high.