Abstract
The creep fracture mode for SUS 316 stainless steel under constant creep loading was examined. The intergranular fracture due to the growth of wedge-type intergranular cracks was observed in the case of high stress at temperature below 550°C. The intergranular fracture due to the growth of cavity-type intergranular cracks which were associated with intergranular carbide and σ phase precipitation was observed in the case of low stress at temperatures above 650°C. Between these two conditions, the transgranular fracture was observed.
The combined creep-fatigue loading tests were carried out under three loading conditions at 550°C, 650°C and 750°C, which gave the intergranular fracture caused by wedge-type intergranular cracks, the transgranular fracture and the intergranular fracture caused by cavity-type intergranular cracks under constant creep loading, respectively. Under these conditions the fatigue specimens were fractured by the transgranular growth of surface cracks.
The data obtained from the combined creep-fatigue loading tests were evaluated using the linear life fraction damage rule. The rupture life under combined creep-fatigue loading at 550°C was affected strongly by creep damage, φc, and fatigue damage, φf, and the relation of φc and φf was φc+φf<<1. The specimens at 650°C were ruptured by an accumulation of either φc or φf. The rupture life at 750°C was affected by φc and φf, and the relation of φc and φf was φc+φf≈1.
