Fatigue and Structural Changes of High Interstitial Stainless Austenitic Steels

Steels with 18 to 19 mass% Cr and Mn each were studied in the as-cast condition containing 0.85 mass% C + N and in the elektro-slag-remelted and hot worked condition containing 0.96 mass% C + N after final solution annealing. The latter was also tested after 20% prestraining. The results of tensile tests were compared to those of rotating bending and push/pull loading. The higher C + N content raised the 0.2% proof strength to about 600 MPa of which 70% were retained as fatigue limit of rotating bending at 10(7) cycles and a failure probability of 50%. Prestraining further improved this limit but lowered it in relation to the proof strength. The structural components of cold work hardening under unidirectional loading and cyclic loading were similar (planar slip, dislocation, twins and epsilon-martensite) except for precipitates in the latter. Nitrides appeared in the austenite and carbides in the epsilon-plates.