Effect of Cold Treatment Temperature on Size Stability and Mechanical Properties of M50 Bearing Steel

By using field‐emission scanning electron microscope (SEM), transmission electron microscope (TEM), X‐Ray diffraction (XRD), and tensile‐property tests, the effect of cold treatment temperature on size stability and mechanical properties of M50 bearing steel is studied. Results show that when the thermal treatment temperature is fixed to be 440 °C, the number of precipitated secondary carbides (SC) in the steel increases first and then decreases with the decrease of cold treatment temperature in the range of −50 to −90 °C. The amount of the precipitated carbides and the transformed residual austenite (RA) reaches the maximum at −70 °C. Carbide precipitation during cold treatment reduces the size of M50 steel, while martensitic transformation leads to the size increase. The size change of M50 steel is the smallest at −80 °C, about 0.5 μm. The elongation of the steel is 3.16% before stabilization treatment, which is improved after stabilization treatment under different conditions. The tensile strength and yield strength decrease at −60 °C and increase at −80 °C, and the other cold treatment temperature has little effect on the tensile strength of the steel.