A development program has been conducted on M-50 to determine the improvements possible in bearing steels by the incorporation of a hot-cold working (ausforming) treatment in their processing. Primary emphasis was on the improvements possible in rolling contact fatigue. In support of this, heat-treat, corrosion, hardness, and microstructural studies have been performed. It has been shown that a certain process for working steel in the metastable austenitic condition as applied to the rolling contact fatigue life of M-50 bearing steel will substantially improve life, thereby increasing bearing reliability. The remarkable improvements in life (exceeding 800 percent) will be a significant factor in meeting the long-life-bearing requirements for advanced air-breathing propulsion systems. A metallurgical analysis has been conducted and a mechanism is proposed which is thought to be the primary factor in providing the significant improvements in rolling contact fatigue life. It is shown that these improvements in life are possible without any significant increase in hardness of the subject materials. Evidence is presented which indicates that the life improvement is primarily due to more uniform carbide dispersion, reduction of massive carbide particles, and reduction in martensite platelet size. These microstructural changes are believed to be associated with strain-induced precipitation and its interplay with strain-hardening during the deformation cycle.
Discussion: “Effect of Hardness, Surface Finish, and Grain Size on Rolling-Contact Fatigue Life of M-50 Bearing Steel” (Baughman, R. A., 1960, ASME J. Basic Eng., 82, pp. 287–294)
