A novel route to improve the fatigue properties of aviation M50 steel via tailoring the bainite content and cold deformation

Abstract

The microstructure, mechanical and fatigue properties of M50 steel by combining austempering processing with cold deformation have been investigated. The results show that the introduction of bainite can effectively refine the multiphase microstructure. When the bainite content is 10.5%, the finest microstructure and the best combination between strength and toughness can be obtained. It is also found that 20% cold deformation leads to a slight improvement of tensile strength and impact toughness, while the mechanical properties deteriorates significantly under larger cold deformation. It is concluded that the mechanical properties can be improved by tailoring the bainite content at about 10% and cold deformation degree at 20%. For the tailored specimen, the specific life of rolling contact fatigue is 114.1% longer than that of traditional martensitic quenched specimen. The slope parameter of Weibull distribution function also shows an increase from 1.8267 to 2.2992, reflecting the more stable of RCF life. There are fewer microcracks in the subsurface of peeling pits, which should be attributed to the higher toughness and finer carbides. Additionally, owing to the higher density of grain/phase boundaries, the tailored specimen with a lower hardness shows better resistance to plastic deformation under the wear trace. This finding provides a novel route to improve the RCF properties of M50 steel via strictly tailoring the bainite content and cold deformation degree.