Abstract
The transformation mechanism from the Mo rich zone to the high temperature precipitate and the reversion behavior of zones in Fe-18%Ni-10%Co-5%Mo alloy were investigated by means of calorimetric analysis, hardness testing and electrical resistivity measurement. Hardness changes during reheating over the temperature range 500∼575°C after preaging at 400°C for 200 h show that the amount of the maximum reversion increases with temperature differance between preaging and reheating, but that tends to be saturated. And also, the results of calorimetric analysis show that the high temperature precipitate is not formed even in the maximum reverted state. Thus, it is suggested that some of the Mo rich zones formed in preaging at low temperature stably remain during reheating at high temperature, and that these stable zones are transformed into the high temperature precipitates in that situation. In isothermal aging, the Mo rich zones formed in the early stage are considered to be stabilized in the later stage, and then transformed into the high temperature precipitates in the same way. Upon isothermal aging under 450°C, however, this transformation does not proceed at the hardening stage but occurs at the overaging stage.
