Chapter 3 | Guide to Steel and Heat Treatment Selection—Rolling Bearing Material Design Relationships

Abstract

The steel technology parameters included in the rolling bearing steel metallurgical design are described. Steelmaking process costs related to metallurgical quality is explained. Air-melt steel is applied in less demanding applications and costly remelt high alloy and heat treatment formulations are used in high demanding bearings such as aerospace. Ball contact rolling bearings require somewhat different steel technologies as compared to line contact rolling bearings. Examples of metallurgical design relationships are explained with examples for ball and hub bearing units. The steel technology design correlations with dimensional stability, rolling contact fatigue, structural strength and tolerance to contamination, hydrogen and high temperature are explained. Steelmaking bloom, billet and bar reduction ratio, raceway forming flow conformance and large size ring hot forming dendritic breakdown requirements and relationships are clarified. The metallurgical parameters associated with through, case carburizing, and surface induction hardening are given for clean and contaminated rolling bearing operating environments. The use of secondary hardening steels for elevated temperature applications is introduced. The need for high metallurgical cleanliness is presented and its relationship with steelmaking processes. The three parameter cost—quality—manufacturing volume relationship is given. Metallurgical cleanliness measures such as oxygen content, micro, macro inclusion and titanium carbo-nitrides related to rolling contact fatigue strength are summarized. The factors to be considered in selection of appropriate heat treatments are described and in particular for elevated temperature rolling bearing used in aerospace applications. The importance of forming flow conformance in high alloy secondary hardening steels and the advantage of powder metallurgy processing of such steel technologies is introduced. High-temperature aircraft turbine engine bearing steel design parameters are given and in summary the key to cost-effective rolling bearing design is to know the requirements precisely and to apply the appropriate steel technologies.