SUS304鋼の高温疲労特性に及ぼすふん囲気の影響

抄録

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 Δε_ij-N_ij were determined by the strain-range partitioning approach.
The main results obtained in this study are as follows:
(1) Δε_pp-N_pp and Δε_cc-N_cc properties are sensitive to environmental effects, while not Δε_pc-N_pc and Δε_cp-N_cp properties.
(2) Each of Δε_ij-N_ij properties in air and vacuum is insensitive to the test temperature.
(3) Δε_pp-N_pp and Δε_cc-N_cc properties in vacuum can be estimated by the Manson-Coffin equations as follows:
Δε_pp=D_p^0.6N_pp^-0.6(D_p=-ln(1-ψ_p)), Δε_cc=D_c^0.6N_cc^-0.6(D_c=-ln(1-ψ_c))
where ψ_p and ψ_c are the values of the reduction in area during tensile and creep rupture test, respectively.
(4) When Δε_pp-or Δε_cc-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 N_pp or N_cc.
(5) On the other hand, the reason of no environmental effects on Δε_pc-N_pc and Δε_cp-N_cp is probably due to the fact that the specimen failure is caused by the tensile failure mode when Δε_pc-type of strain is cycled and by the coalescence or connection of grain-boundary cracks inside the specimen when Δε_cp-type of strain is cycled.