Abstract
The effect of thermal aging on the elevated temperature low-cycle fatigue life of 304 and 321 stainless steels was studied using the creep-fatigue analysis by the strain-range partitioning approach. The Δ∈pp-Npp and Δ∈cp-Ncp properties were determined based on the results of strain-controlled lowcycle fatigue tests with a symmetrical and an asymmetrical triangular wave form. The test with a trapezoidal strain-wave form was also conducted and the effec to fhold time was examined. Aging temperatures of 650 and 700°C and aging times of 1000 and 3000 hours were employed for 321 steel, and for 304 steel only one condition of 650°C and 1000 hours was examined.
Thermal aging produced beneficial results relative to unaged material in the creep-fatigue properties Δ∈pp-Npp and Δ∈cp-Ncp of 321 steel and in the Δ∈pp-Npp of 304 steel, whereas the Δ∈cp-Ncp property of 304 steel was not influenced by thermal aging. It is suggested that the precipitation of the various carbides is responsible for the beneficial effect. On the other hand, the effect of hold time was more detrimental in aged material than in unaged one and the reduction in fatigue life was much greater than that predicted by creep effect.
