| Two types of austenitic alloy, precipitation hardening austenitic Fe-Ni-Ti alloy and unprecipitation hardening austenitic Fe-Ni alloy, were prepared by high frequency induction melting, and then the effects of cyclic heat treatment and deformation degree on hardness of these reverted austenites have been investigated. (1) The hardness of reverted austenitic Fe-Ni-Ti alloy shows a maximum value at about 700℃ when ausaged for 1 hour at various temperatures, and then decreases as the temperature further increases above 700℃. (2) The Ms temperature of austenitic Fe-Ni-Ti alloy is raised with ausaging treatment. (3) The hardness of reverted austenitic Fe-Ni alloy increases rapidly at 1 cyclic heat treatment, and gradually increases up to 4 cyclic heat treatment. However, at all cycles above 4 cycles the hardness of the reverted austenitic Fe-Ni alloy shows a nearly constant value, independent of cyclic heat treatment number. (4) The hardness of reverted austenitic Fe-Ni-Ti alloy increases rapidly at 1 cyclic heat treatment, and maintains a nearly constant value at all cycles above 1 cycle. (5) When both Fe-Ni and Fe-Ni-Ti alloy subjected to prior deformation are transformed to reverted austenite, the increase in hardness due to reverse transformation is greater in the former alloy than in the latter alloy. At the same deformation degree, the hardness of reverted austenite is slightly higher in case of deformed martensite than deformed austenite. (6) The reverted austenitic Fe-Ni-Ti alloy is mare stable at elevated temperature than the reverted austenitic Fe-Ni alloy. |
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