Precipitation-hardenable iron-nickel-based metastable austenitic steels

Age-hardenable austenitic steels, in which they phase undergoes a martensit ic transformation upon cooling to temperatures below M-s and a gamma --> al pha' martensitic transformation upon deformation at temperatures below M-d were studied. In this case, M-d is always above M-s, and M-s is below room temperature. Upon heating of a quenched austenitic steel, the supersaturate d solid solution decomposes with the precipitation of fine intermetallics o r carbides. Aging of the gamma phase changes the physicomechanical characte ristics such as the lattice parameter, resistivity, critical temperatures o f martensitic transformation, yield strength, ultimate tensile strength, re lative reduction in area, and relative elongation. It was established that some aging regimes provide an increase in the relative elongation due to an increase in the plasticity induced by the gamma --> alpha' transformation (TRIP effect) and a simultaneous increase in the yield strength. No such ef fect is observed in the austenitic age-hardenable steels in which the gamma phase is stable (no gamma --> alpha' transformation occurs). The effects o f various regimes of thermomechanical treatment including plastic deformati on in a wide temperature range and aging were studied with changing sequenc es of the aging and deformation processes. It was shown that plastic deform ation substantially affects the physicomechanical properties of the aged ga mma phase and, compared with pure aging, enhances the TRIP effect.