Effect of the melt superheating treatment on microstructures of alloy 690

Abstract

The optical, scanning and transmission electron microscopes have been used to investigate the effect of the melt superheating treatment (MST) on the microsturctures and Vickers hardness of of alloy 690. The results indicate that the volume fraction and average size of primary TiN decrease as the superheating temperature increases, and its morphology converts from regular blocky to granular. After homogenizing annealing, there is a slight increase in volume fraction of primary TiN, while a moderate decrease in the average size. Additionally, it is found that a great deal of sub-micron Ti(C, N) precipitates dispersedly during recrystallization annealing, and its amount increases with the superheating temperature. These sub-micron Ti(C, N) particles can improve the Vickers hardness of alloy 690 as the strengtheners. © Right.