A study of retained austenite in a fine-grained Fe-12Ni-0.25Ti alloy

The behavior of retained austenite in a fine-grained Fe-12Ni-0.25Ti cryogenic alloy system was investigated. When the alloy was held at a temperature within the two phase (α + γ) field austenite reversion occurred by a diffusion-controlled process. The redistribution of solute elements appeared to control the stability of the reverted austenite. The microstructural appearance of the retained austenite was examined using transmission electron microscopy. A preferential distribution of the austenite phase along martensite lath boundaries was observed. A precipitate-correlated austenite was also found to occur. The beneficial effect of introducing retained austenite appeared in the improvement in the tensile elongation as well as in the Charpy impact toughness at low temperatures. The retained austenite in this system did not improveK _IC at ?196°C. On the contrary, samples containing retained austenite showed increased susceptibility to unstable crack propagation in low temperature fracture toughness tests.