In-Depth Comparison of Powder and Ingot Metallurgical M50 Bearing Steels

Abstract

Powder metallurgy (PM) for bearing steel manufacturing was introduced several decades ago and mainly aimed at limiting segregation effects in high-alloy grades. Despite the significant potential of this relatively new process for producing high-performance bearing steels, its use in commercial applications is still very limited today. It is thought that the slow acceptance of this promising technology is partially due to a lack of understanding of how modern PM steels compare to conventional ingot metallurgical steels. Most of the comparative studies published on this topic have only focused on a few key mechanical properties, which are rarely related to the microstructure. For this study, several variants of M50 were produced using ingot metallurgical and PM processes. This grade was chosen as its performance is well known to be limited by segregation, and it could therefore benefit from a PM process route. The evolution of the microstructure during manufacturing, from solidification to tempering, was carefully investigated. After heat treatment, toughness, hardness, and rolling contact fatigue (RCF) life were measured. RCF tests were performed using a ball-on-rod configuration to compare the performance of the alloys as well as to evaluate the microstructural changes during testing. Differences in the populations of stress raisers (primary carbides and nonmetallic inclusions) were also assessed and used to explain the variations in RCF fatigue lives.

The influence of steel microstructure in high-speed high-load bearing applications

“…This finding was somewhat unusual since the steels in question were all alloyed with elements, such as chromium, at levels considered sufficiently high to destabilise the cementite phase. However, the presence of cementite in quenched and tempered tool steels was reported earlier in the literature, for example, in the M50 alloy microstructure, as confirmed by TEM [24]. This finding can be ascribed to the presence of segregation in the steel's microstructure.…”

Dry tribological properties of M50 bearing steel under different temperatures

“…However, the instantaneous slip of rolling contact fatigue bearings is similar to the sliding speed of 40 m s −1 , and there are often tens of seconds of oil-free period during the lift-off process of aero engines [17][18][19][20]. There is a micro-slip and rolling-slip mixing under the oil-free friction condition, and the sliding wear is the main wear mode for the bearing material, making the service conditions of engine bearings very harsh [21,22].…”

Relevance of Fracture Mechanics in Rolling Bearing: Functional Property Determination and Steel Quality Assurance

“…In some impact toughness tests on surface hardened variants, unnotched specimens were also used. 8]. In this project, M50 steel produced by the standard VIM-VAR steelmaking was compared with similar steel produced by high quality PM-HIP process and both fracture mechanics K IC and impact toughness testing were applied.…”