Abstract
The effect of sintering treatment on the creep rupture life of a 316 stainless steel has been investigated. Creep rupture tests were carried out at 750°C and 37MPa, and three kinds of sintering treatments were used: (a) stress-free annealing at 750°C; (b) hot isostatic pressing at 750°C and 37MPa; and (c) compressive creep at 750°C and 37MPa. These sintering treatments were conducted in order to remove creep-induced grain boundary cavities by interrupting the creep, and the treated specimens were then retested at the original temperature and stress. The repetitive creep/sintering cycles were continued to the rupture of the specimens.
The results obtained were as follows;
(1) The stress-free annealing had no significant effect the rupture properties. Considerable amounts of grain boundary cavities and cracks were observed in the specimens given the repetitive creep/annealing cycles. It is thought that the limited rupture life extension is attributable to this insufficient sintering of cavities as well as overaged microstructure due to annealing.
(2) The hot isostatic pressing and the compressive creep could remove the grain boundary cavities almost completely, and no developed cavity was observed in the ruptured specimens. The rupture was caused not by linkage of grain boundary cavities but by growth of oxidized surface nucleated cracks which could not be healed by the sintering treatments. It is suggested that the growth of surface cracks is the reason why the rupture life extension was not significant.
