Abstract
The effects of cooling rate and reheating conditions after solid solution treatment on mechanical properties, especially low temperature embrittlement, have been investigated by using Fe-32Mn-7Cr-(0.3-0.4)N, Fe-33Mn, Fe-33Mn-0.3C, Fe-44Mn, Fe-44Mn-0.3C, Fe-58Mn, and Fe-32Mn-7Cr-0.3N-(0.002-0.02)P-(0.0002-0.001)B steels melted in vacuum furnaces. It was found that intergranular fracture was suppressed and toughness increased in all these steels through cooling at an intermediate rate from solid solution treatment temperature or through reheating at around 723-773 K. After such toughening heat treatments no change in microstructures was revealed under an electron microscope and the decrease in tensile strength was very small if any. Autoradiography using α particle fission tracks showed that the grain boundary segregation of boron corresponded to the toughening. The reason for the high susceptibility to low temperature intergranular embrittlement of high Mn non-magnetic steels was also discussed together with the mechanism for the toughening resulting from the heat treatments.
