Phase transformations in reduced-activation duplex alloy Fe52Mn30Cr18 under isothermal heat treatment

Reduced-activation Fe-Mn-Cr alloys have been regarded as the candidate structural materials for advanced nuclear systems. The phase stability of one alloy at high temperature is critically required for its application. In this work, a series of phase transformations in a new type reduced-activation duplex alloy Fe52Mn30Cr18 under isothermal heat treatment were investigated. The ferrite phase in the alloy converted to χ phase after the alloy treated at 550°C for 3 h. The cube-on-cube orientation relationship was found between χ phase and the original ferrite phase with the lattice constant ratio of 3:1. The χ phase was eutectoid decomposed into austenite and σ phases with lamellar structures due to the diffusion of Cr atoms at temperatures above 800 °C. According to the evolution of the crystal structure and magnetic properties, the transformation from ferrite to χ phase was considered as atomic rearrangement in the adjacent unit cells, accompanied by the disappearance of ferromagnetism in the alloy. The microhardness results indicated that the χ phase formation could be one of the potential reasons for the intermediate temperature embrittlement in the high Cr Fe-based alloys.