The Character of Observed Porosity and Its Possible Effects on Rolling Contact Fatigue Life of M-50 Steel.
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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This thesis studied a warm-rolling of AISI M-50 steel at 750 C 1382 F. Samples of both warm-rolled and as-received spheroidized annealed M-50 were austenitized at 1036 C 1897 F for various times and subsequently tempered. The heat treated samples were subjected to rolling contact fatigue RCF testing. In all cases prior warm-rolling degraded the RCF life at both the L10 and L50 levels. Scanning electron microscopy was used to examine the microstructure of the as-received and warm-rolled material between 4000X and 10,000X magnification. It is thought that the increase in the void diameters accounts for the decrease in RCF performance of warm-rolled M-50. The degraded RCF performance is due to both the increase in mean void diameter and the increase in larger sized voids that accompany warm rolling. A qualitative model was developed to account for the origin of voids in as-received material and for the increase in void diameter in warm-rolled material. Keywords Thermomechanical processing, Residual carbides, Porosity, Void Size Distribution, Bearings, Void Origin Model.
- Metallurgy and Metallography