Change in Physical Properties during Tempering of Gamma Type Fe-Co-Cr-Ni Base Heat-Resisting Alloy, LCN-155

Studies on tempering process of γ-type heat-resisting alloys-I

Abstract

The tempering process of the solution-treated γ type heat-resisting alloy consisting mainly of Fe, Co, Cr and Ni, and the effects of solution-treating temperatures and the additional elements (C, N, Mo, W and Cb) on its process were investigated by measurements of dilatation, specific heat, electrical resistance, and hardness.
These results were summarized as follows:
1. The tempering process of this alloy quenched in water from an elevated temperature was divided into two distinct stages about at 500°C and 750°C.
2. At the first stage, an increase of electrical resistance, an evolution of heat, a contraction of the length, and no marked change of hardness were observed. It was considered that the change in properties during the first stage of tempering was not due to a precipitation of carbide or nitride but due to an unknown change in the Fe-Co-Cr-Ni quaternary alloy containing of no additional elements.
3. At the second stage, a decrease of electrical resistance, an evolution of heat, a contraction of the length, and remarkable change of hardness were observed. The change in properties during this second stage of tempering was obviously due to the precipitation of carbides, nitrides, and intermetallic compounds. The amount of these precipitates and the velocity of precipitation were remarkably affected with the additional elements and the solutiontreating temperatures.
4. It was considered that the change of the first stage advanced in processes as follows:
Room temp.500°C 650°C °
In quenching states ……A→A→A→A→A650 A: A stable state at high temp.
In quenching states …_??_A': A stable state at low temp.