Experimental investigation of in-situ transformations of the M7C3 carbide in the cast Fe–Cr–Ni alloy

Abstract

The microstructure and the phase composition of a heat-resistant Fe–Cr–Ni alloy (0. 45C–25Cr–35Ni) has been investigated in the cast state and after annealing at 1150°C for 2–100 h. After a 2-h high-temperature annealing, the fragmentation of the crystal structure of the eutectic M₇C₃ carbides into domains of ~500 nm in size with a partial transition into M₂₃C₆ carbides is observed. After a 100-h holding, the complete transition of the hexagonal M₇C₃ carbides into M₂₃C₆ with a face-centered cubic structure occurs. The carbide transition M₇C₃ →M₂₃ can be considered to be an in situ transformation.