Effect of Ti, Al, C and Mo on Mechanical Properties of M252

Studies on nickel-base heat-resisting alloys-VII

Abstract

Effects of Ti, Al, C and Mo contents on stress-rupture properties of alloy M252 were investigated.
There seemed to be a peak stress-rupture life at 1.2% Al when Ti was 3.1%, and stress-rupture life was decreased in the case of specimens containing over 1.2% Al. Ti+Al atm. %=6.5 gave the peak of stress-rupture and creep ductility.
Effect of Ti and Al on stress-rupture characteristics was clear in the case of heat treatment B (1065°C×8h W.Q., 800°C×2.5h A.C. and 700°C×18h A.C.) but it was not clear in the case of heat treatment G (1065°C×8h. A.C., 760°C×15h. A.C.).
Carbon did not affect the short-time stress-rupture test, but it did so in the long time stress rupture test, and stress rupture life was decreased by the increase of carbon. Hardness after heat treatment was increased by carbon and nitrogen, but it seemed that overaging at high temperature was promoted by them and the decrease of long time stress rupture life was affected by overaging.
Ultimate strength of short-time tensile test between room temperature and 750°C, and stress-rupture strength less than 500 hours of the alloy containing 11% Mo was higher than those of the alloy containing 10% Mo. But strength was not increased by increasing Mo content up to 15%, although these values were higher than the alloy containing 10% Mo. The effect of Mo on increasing strength of alloy was not clear in the case of testing temperature of 816 and 850°C.
There was no embrittling effect by increasing Mo content in these test. But the net work which precipitates at grain boundaries was increased by heating 11% Mo alloy for 1000 hours at 850°C, and it lowered Charpy's impact value.
The resistance to oxidation in the air below 900°C was good enough, and it was not affected by increasing the Mo content.