Abstract
The effects of thermomechanical treatments on the reverse transformation behaviour from twinned plate martensite to austenite in Fe–31·1%Ni have been studied. The variation of both diffusion controlled and diffusionless reverse transformation with temperature and time was examined. Diffusional reversion was dominant at lower reheating temperatures and led to a fine martensite–austenite duplex microstructure with a grain size of 0·01–0·1 μm, which caused a remarkable hardening ∆Hv of 170–230 HV during aging. Cold working of the martensite promoted diffusional reversion and enhanced age hardening. X-ray analysis indicates that the age hardening is caused mainly by elastic strain resulting from coherent precipitation of austenite in martensite.
MST/1414
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