Previous investigations focused on the microstructural decay resulting from RCF with the most common bearing steel, grade 52100. The microstructure of 52100 steel comprises tempered carbides, residual cementite (RC), and a martensitic matrix. Types of microstructural decay identified during RCF include the formation of dark etching regions, white etching bands, and carbide dissolution (RC and tempered carbides). This decay becomes apparent after a high number of stress cycles, leading to a decrease in hardness and subsequent degradation of the bearing.

The ability of a material to withstand RCF depends on its composition and heat treatment. Using materials that resist softening can extend the lifespan of bearings. The Promise of Hybrid Steel In recent years, Ovako has introduced Hybrid Steel 60. This is a novel grade combining secondary hardening and intermetallic precipitates. It was developed to overcome the limitations of existing materials, particularly for bearings subject to challenging operational conditions such as in corrosion and hydrogen environments. However, a more comprehensive understanding of how it behaves under RCF is crucial to predict its response to cyclic loading. This was the basis for this PhD project which comprised extensive laboratory testing and analysis to identify how Hybrid Steel 60 decays under RCF.