Chapter 12 | Wear and Debris Contaminant Testing, Lubricant Additive Effects—Tribo-Metallurgy

Abstract

Rolling bearing steel wear testing and properties are multifaceted. A combination of tribology and related physical metallurgy is summarized in this chapter. ISO 15243-2017 describes rolling bearing damage terms, characteristics and failure origins. Wear failure modes exist in rolling bearings and ASTM G40-21a, Standard Terminology Relating to Wear and Erosion, defines abrasive and adhesive wear. A form of abrasive wear can be observed in rolling bearings operating with contaminated lubricants. The nature of the contaminant is important in steel technology related mitigation measures. For example, metallic contaminants result in different raceway tribology characteristics as compared to abrasive contaminants. Three-body abrasive wear properties can be critical in aviation rolling bearing steels and for this reason appropriate bearing steel, cage steel, and alumina abrasive tests have been developed. Adhesive wear can occur if the lubricant film thickness is insufficient. The factors influencing the occurrence of adhesive wear are defined and microstructure and the steel heat treated hardness are key parameters. Traction coefficient measures are used particularly for assessment of the steel technology combinations such as rolling element materials and stainless carburized steel rolling contacts. Sliding wear, micropitting, and macropitting properties may be assessed using standard tests, and such tests are of importance in integrated rolling bearing and gear products. Applications involving slip in the contacts requires specific tribology testing and as such near surface hardness is important. Raceway surface solid contaminant effects are studied using indent tests. Raceway artificial dents are often used and predented contaminate tests can be applied to test rolling contact fatigue strength in the presence of raceway indentation. Such raceway surface damage may be classified as surface distress, the most common failure mode in modern rolling bearings. The use of extreme pressure (EP) additives can have a profound effect on the rolling bearing steel tribo-system.