Abstract
High-temperature fatigue properties for austenitic heat-resisting materials A286, Alloy718 and 304L were investigated in region between 103 and 107 cycles. A286 and Alloy718 are precipitation hardening type-austenitic alloys, and 304L is a solid-solution hardening type-austenitic steel.
The fatigue strengths for A286 and Alloy718 in high-cycle region over 104 cycles showed a grain size effect. The fatigue strengths for the coarse-grain alloys are lower than those for the fine-grain alloys. Initiation sites of the fracture were the facets corresponding to the austenitic grain size. On the other hand, the fatigue strengths under104 cycles showed no the grain size effect. Initiation sites of the fracture were the surface of the specimens.
Therefore, the high-cycle fatigue strengths for the precipitation hardening type-austenitic alloys depend on their austenitic grain size. The ratio (σW⁄σB) of the fatigue limit (σW) normalized by the tensile strength (σB) decrease to below 0.5 for the alloys with coarse grain.
