Microstructural Effects in the Low-Cycle Fatigue of Fe-Ni-Cr Austenite

Abstract

A series of low-cycle fatigue tests was performed at 593 deg C on Fe-20 Cr-10 Ni and Fe-20 Cr-20 Ni (in weight percent) austenitic alloys in both the cast and wrought conditions. The as-cast alloys exhibited substantially longer cyclic lives than the wrought alloys or wrought Type 304 stainless steel. An effect of Ni content on fatigue life was noted for the cast alloys, but not for the wrought. Striation, measurements indicated that the majority of the cyclic life was spent in crack initiation and early growth in all cases, and the superiority of the cast alloys was almost entirely due to a greater resistance to crack initiation. Macroscopic crack-growth rates were found to be essentially independent of composition and microstructure. A 1-min tension hold time per cycle produced a significant reduction in cyclic life in all cases except for the as-cast high Ni alloy. The decrease in life appeared to be associated with the initiation of cracks from localized deformation at grain boundaries.