Effects of phosphorus and sulfur on the thermoplasticity of high manganese austenitic steel

The thermoplastic characteristics of high manganese austenitic steels were investigated using a Gleeble-3500 type thermal simulation testing machine. The results indicate that the zero-ductility temperature of the steels was low and the temperature range for plasticity was small. Through comparing the high-temperature thermoplasticity of several high manganese austenitic steels with different phosphorus and sulfur contents, the nature of thermoplasticity of the steels was explored. The results showed that phosphorus was concentrated at the boundaries of austenite grains and formed (FeMn)3P, a low-melting-point eutectic, which tended to melt the boundaries of the austenite grains. Furthermore, sulfur and manganese tended to form MnS inclusions, which were incompatible with the plastic deformation of the austenite matrix when deformed at high temperatures. Hence, the zero-ductility temperature and the plasticity temperature range of the high manganese austenitic steels were reduced significantly with an increase in the content of phosphorus or sulfur. It is thus believed that the large amount of low-melting-point eutectic of phosphorus in the grain boundaries of the austenite and the MnS inclusions were responsible for the poor thermoplastic performances of the high manganese austenitic steels. The relationship between the zero-ductility temperature of the high manganese austenitic steel and the content of phosphorus and sulfur can be expressed by T=1248−1530ws−1651wpT=1248−1530ws−1651wp. Consequently, a process for forged high manganese austenitic steel crossing was proposed based on which the mechanical properties of the forged steel was almost doubled when compared with the conventional cast high manganese austenitic steel crossing.