Fatigue Strength of 18Mn-5Cr Non-Magnetic Steel

Abstract

High-Mn non-magnetic steel is anticipated as a new structural material which sustains the development of future industry, e.g., an atomic power generator, linear motor car, et al., but the fatigue strength characteristics of this sort of the material has not been clarified yet sufficiently.
So, the fatigue strength of a newly developed 18Mn-5Cr non-magnetic steel, one of the high Mn non-magnetic steel, was investigated under the push-pull full reversed fatigue load condition. The material used in this experiment was especially developed as the material for the nonmagnetic retaining ring of a power generator, and was machine-finished to the ring-like shape after the cold working-stress relief annealing treatment done to obtain the high static strength. Therefore, to clarify the whole fatigue strength feature, a series of the experiments were conducted by using the material before and after the cold working.
At first, the fatigue strength of the material before cold working was studied by using the two sorts of the plain specimens: one was the specimen of 4mm in diameter and another was of 5mm. Here, it was observed that the S-N relation of this material well resembled to that of Ni-Cr austenitic steel and that the size effect on the fatigue strength appeared despite that there existed only a slight difference in diameter of 1mm.
Secondly, from the comparison of the fatigue strength between the materials before and after the cold working, it was clarified that the fatigue strength of thus treated material was much higher than that of the material before cold working, but that the fatigue limit of the cold worked material disappeared in the range of the experimental number of stress cycles in this study. Additionally, the impact fatigue strength of the cold worked material was also researched.
It seems to be possible to give a reasonable explanation for the fatigue strength behavior of 18 Mn-5Cr non-magnetic steel revealed in this study, when the knowledge on the fatigue behavior of ordinary Ni-Cr austenitic steel and that of the prestrained steel are refered to.