Effect of composition and thermo-mechanical processing on microstructure development in Ni-30Fe-Nb-C model alloys

The unavoidable phase transformation upon cooling makes a direct observation of austenite microstructure impossible. One of the methods to investigate the high temperature condition of austenite is to use a model alloy, which would not transform to martensite on quenching. In the present work the recrystallisation and grain growth of austenite during thermo-mechanical processing (TMP) were studied for three Ni-30Fe-Nb-C alloys containing 0.33, 0.85 and 1.42 wt% Nb. The austenite microstructures were characterised using optical and scanning electron microscopy, and energy dispersive X-ray spectroscopy. The austenite recrystallisation kinetics was investigated with respect to the precipitate distribution variations. A relative strength of the grain boundary pinning effect from solute Nb and precipitated particles is discussed.