Some Observations on Cavitation Damage under Creep and Creep-Fatigue Loading in Type 304 Stainless Steel.

摘要

Quantitative data are presented on cavitation damage in type 304 stainless steel caused by creep and creep-fatigue loading. Specimens from tests interrupted at various fractions of their nominal life were fractured intergranularly at cryogenic temperature to reveal cavities on grain boundaries. The results show that creep damage in this material is distributed bimodally. It consists of boundaries that are ''cracked,'' i.e., with area fraction of cavities greater than 20%, and boundaries that are ''cavitated,'' i.e., area fraction of cavities less than 10%. Cracked boundaries appear very early in life (10-20%) and constitute that dominant factor of damage by about 50% of life. Although initially the cavity number density increases with time, the cavity diameter at the peak of the distribution remains relatively constant. The distributions of densely cavitated boundaries with respect to their true and apparent angles with the stress direction were measured in a creep specimen. The results indicate that both normal and shear stresses on the boundary may be important in cavitation.