Abstract
The effect of environment on high temperature fatigue properties of 304 stainless steel was studied. Strain-controlled low-cycle fatigue tests were conducted with a symmetrical and an asymmetrical strain-wave forms at 700° and 800°C in air and vacuum. The results were analyzed and the partitioned strain-life relations Δεij-Nij were determined by the strain-range partitioning approach.
The main results obtained in this study are as follows:
(1) Δεpp-Npp and Δεcc-Ncc properties are sensitive to environmental effects, while not Δεpc-Npc and Δεcp-Ncp properties.
(2) Each of Δεij-Nij properties in air and vacuum is insensitive to the test temperature.
(3) Δεpp-Npp and Δεcc-Ncc properties in vacuum can be estimated by the Manson-Coffin equations as follows:
Δεpp=Dp0.6Npp-0.6(Dp=-ln(1-ψp)), Δεcc=Dc0.6Ncc-0.6(Dc=-ln(1-ψc))
where ψp and ψc are the values of the reduction in area during tensile and creep rupture test, respectively.
(4) When Δεpp-or Δεcc-type of strain is cycled, a crack tends to initiate at the specimen surface and grow to the final failure. This fact is probably the main reason of the remarkable effect of environment on partitioned fatigue life Npp or Ncc.
(5) On the other hand, the reason of no environmental effects on Δεpc-Npc and Δεcp-Ncp is probably due to the fact that the specimen failure is caused by the tensile failure mode when Δεpc-type of strain is cycled and by the coalescence or connection of grain-boundary cracks inside the specimen when Δεcp-type of strain is cycled.
