Abstract
In order to improve the high-temperature strength of the heat-resistant alloy A286, it was suggested from the previous work (Zairyo Shiken, 10 (1961) No. 90, p. 70; Tetsu-to-Hagané, not yet published) that grain boundary precipitates such as G phase (Ni13Si6Ti8) and η phase (Ni3Ti) had to be eliminated by proper selections of heat treatment and/or chemical composition. From a point of view as abovementioned, the effect of heat treatment on the high-temperature strength was investigated in the present work. Solution temperatures were varied from 900°C to 1100°C and aging temperatures were selected at 650°C and 718°C. Creep rupture tests and short-time tensile tests at 650°C were carried out. X-ray diffraction was tested and an electron-microscope was used for the study of microstructures.
The results obtained showed that the grain boundary precipitates diminished with increasing solution temperature and decreasing aging temperature, and the high-temperature strength was increased with disappearance of grain boundary precipitates. In the microstructures as heat-treated with using a solution-temperature higher than 1040°C and an aging temperature of 718°C, precipitations of TiC with various flake-type morphology were observed at grain boundaries. These precipitates, however, seemed to have little effect on the high temperature strength.
