Evaluation of the creep-fatigue damage mechanism of Type 316L and Type 316LN stainless steel

摘要

Low-cycle fatigue tests with continuous cycling and creep-fatigue tests with 10 min hold times at tensile maximum strain were conducted at 600 ℃ in air for Type 316L and Type 316LN stainless steels containing nitrogen contents of 0.04% and 0.10%. The creep-fatigue life was less than the fatigue life for both alloys. The fatigue and creep-fatigue life and saturation stress were increased with the addition of nitrogen. The fracture mode was transgranular for fatigue and intergranular for creep-fatigue regardless of the nitrogen content. The dislocation structure was cellular for Type 316L and planar for Type 316LN after fatigue and creep-fatigue tests. Carbides were precipitated at grain boundaries after creep-fatigue tests and nitrogen decreased the precipitation. Creep-fatigue life was well predicted by a model based on cavity nucleation and growth at grain boundaries. The increase of creep-fatigue life with the addition of nitrogen was due to the decrease of precipitation and stress relaxation by the change in dislocation structure.