Rolling-element bearings, whether ball bearings or roller bearings with spherical, straight, or tapered rollers, are fabricated from a wide variety of steels. This article discusses the production process, characteristics, nominal compositions, and types of bearing steels. These include standard bearing steels, such as high-carbon bearing steels and carburizing bearing steels; and special-purpose bearing steels, such as high-temperature service bearing steels and corrosion-resistant bearing steels.

This article provides information on the nominal compositions of high-carbon bearing steels and carburizing bearing steels. It discusses the bearing fundamentals with emphasis on surface contact, stresses, and fatigue life of bearings. The article describes bearing life prediction using three factors, namely, reliability, material, and application. It analyzes the bearing damage modes and concludes with information on fatigue failure considerations.

Bearing steels, which include high-carbon and low-carbon types, can be divided into service-based classes, such as normal service, high-temperature service, and service under corrosive conditions. This article discusses the importance of matching the hardenability and quenching of a bearing steel. It also discusses the typical microstructure of a high-carbon through-hardened bearing, and shows typical case and core microstructures in carburized bearing materials. Apart from a satisfactory microstructure, which is obtained through the proper combination of steel grade and heat treatment, the single most important factor in achieving high levels of rolling-contact fatigue life in bearings is the cleanliness, or freedom from harmful nonmetallic inclusions, of the steel. Alloy conservation and a more consistent heat-treating response are benefits of using specially designed bearing steels. The selection of a carburizing steel for a specific bearing section is based on the heat-treating practice of the producer, either direct quenching from carburizing or reheating for quenching, and on the characteristics of the quenching equipment.

Case hardening involves various methods and each method has unique characteristics and different considerations in the selection of steels This article reviews the various grades of carburizing steels, carbonitriding steels, nitriding steels, and steels for induction, or flame hardening. This review is based on their process characteristics, compositions, applications, and mechanical properties, which help in selecting steels for case hardening.

This article discusses the composition, properties and applications of bearing steels. It focuses on the typical wear modes that rolling-element bearings experience: contact fatigue wear, abrasive wear, adhesive wear, and corrosive wear. The article provides information on reliability factor and ABMA and ISO environmental factors.

The choice of heat treatment depends on the service requirements of a given bearing and how the bearing will be made. This article describes the design parameters, material characteristics required to sustain performance characteristics, metallurgical properties, and dimensional stability. It also provides a description of various extensively-used heat treatment processes, namely, carburizing, carbonitriding, induction surface hardening, and nitriding associated with various bearings. In addition, the article explores the factors to be considered in selecting a process and explains why it is optimum for a specific application.

The mechanism of contact fatigue can be understood in terms of several sources of stress concentration, or stress raisers, within the macroscopic Hertzian stress field. This article focuses primarily on rolling contact fatigue of hardened bearing steels. It discusses Hertzian shear stresses at and below the contact surfaces and briefly summarizes bearings and gear characteristics. The article provides an overview of the key types of gear and bearing steels. It analyzes two types of macropitting that result from the subsurface growth of fatigue cracks, namely, subsurface-origin macropitting and surface-origin macropitting. The article describes the factors influencing contact fatigue life of hardened steel bearings and gears, including hardness, inclusions, carbides, and residual stresses.

Contact fatigue is a surface-pitting-type failure commonly found in ball or roller bearings. This article discusses the mechanisms of contact fatigue found in gears, cams, valves, rails, and gear couplings. It discusses the statistical analysis of rolling contact bearing-life tests. The article concludes with information on various approaches that improve the contact fatigue resistance of rolling contact systems.

The surface of irons and steels can be hardened by introducing nitrogen (nitriding), nitrogen and carbon (nitrocarburizing), or nitrogen and sulfur (sulfonitriding) into the surface. This article lists the principal reasons for nitriding and nitrocarburizing, and summarizes the typical characteristics of nitriding processes along with a general comparison of carburizing processes in a table. It describes the two most common nitriding methods: gas nitriding and ion (plasma) nitriding. The article discusses the wear behavior of nitrided layers and the wear resistance of selected steels. Rolling-contact fatigue (RCF) occurs in rolling contacts such as bearings, rolls, and gears. The article provides a discussion on rolling-contact fatigue of nitrided steels for aerospace bearing components.

This article describes the microstructure, properties, and performance of carburized steels, and elucidates the microstructural gradients associated with carbon and hardness gradients. It provides information on case depth measurement, the factors affecting case depth, and the formation and causes of microcracks. The article discusses the effects of alloying elements on hardenability, the effects of excessive retained austenite and massive carbides on fatigue resistance, the effects of residual stresses and internal oxidation on fatigue performance of carburized steels. In addition, the causes of intergranular fracture at austenite grain boundaries and their prevention methods are explored. The article also describes the major mechanisms of bending fatigue crack initiation in carburized steels.

Surface hardening improves the wear resistance of steel parts. This article focuses exclusively on the methods that involve surface and subsurface modification without any intentional buildup or increase in part dimensions. These include diffusion methods, such as carburizing, nitriding, carbonitriding, and austenitic and ferritic nitrocarburizing, as well as selective-hardening methods, such as laser transformation hardening, electron beam hardening, ion implantation, selective carburizing, and surface hardening with arc lamps. The article also discusses the factors affecting the choice of these surface-hardening methods.

This article is concerned with gear tooth failures influenced by friction, lubrication, and wear, and especially those failure modes that occur in wind-turbine components. It provides a detailed discussion on wear (including adhesion, abrasion, polishing, fretting, and electrical discharge), scuffing, and Hertzian fatigue (including macropitting and micropitting). Details for obtaining high lubricant specific film thickness are presented. The article describes the selection criteria for lubricants, such as oil, grease, adhesive open gear lubricant, and solid lubricants. It discusses the applications of oil and gear lubricants and the types of standardized gear tests. The article presents some recommendations for selecting lubricants and lubricant viscosity for enclosed gear. It provides some examples of failure modes that commonly occur on gears and bearings in wind turbine gearboxes.

This article discusses the classification of wear based on the presence or absence of effective lubricants, namely, lubricated and nonlubricated wear. Variations in ambient temperature, atmosphere, load, and sliding speed, as well as variations in material bulk composition, microstructure, surface treatment, and surface finish of steel are also considered. The article discusses the types, wear testing, wear evaluation, and hardness evaluation of abrasive wear. It describes the selection criteria of steels for wear resistance. The article also describes the importance of hardness and microstructure as factors in resistance to wear. It provides a discussion on the resistance of various materials to wear in specific applications. The wear resistance of austenitic manganese steels is also discussed. The article discusses the applications of phosphate coatings, wear-resistant coatings, and ion implantation. It concludes with information on interaction of wear and corrosion.

This article focuses on various heat treatment practices recommended for different types of high-speed tool steels. Commonly used methods include annealing, stress relieving, preheating, austenitizing, quenching, tempering, carburizing, and nitriding. The article describes hardening for various types of cutting tools, namely, broaches, chasers, milling cutters, drills, taps, reamers, form tools, and hobs, and for thread rolling dies, threading dies, and bearings.

This article presents the different hardness test methods used to measure the effectiveness of surface carbon control in carburized parts of steel. Common test methods include Rockwell hardness measurements, superficial Rockwell 15N testing, and microhardness testing. The article provides information on the microscopic method used to detect smaller variations in carbon content, and reviews consecutive cuts analysis and spectrographic analysis that are used to accurately evaluate the carbon concentration profile of carburized parts. It describes procedures of and precautions to be undertaken during shim stock analysis, which is used to measure the atmosphere carbon potential. The article includes a discussion on the electromagnetic nondestructive tests that are used to evaluate the case depth of case-hardened parts.

Rolling-element bearings, also called rolling bearings and antifriction bearings, tend to have very low friction characteristics compared to plain bearings or simple sliding bearings. This article discusses the types of rolling-element bearings, namely, ball bearings and roller bearings. It provides information on the bearing component materials. The article describes the lubrication requirements and lubrication methods, namely, elastohydrodynamic lubrication and grease lubrication. It reviews the adjustment factors influencing fatigue life of the bearing. The article also provides information on bearing load ratings, standard bearing geometries, rolling bearing friction factors, and wear and its control methods. It concludes with a discussion on damage modes of bearings.

This article describes the uses of the liquid carburizing process carried out in low and high temperature cyanide-containing baths, and details the noncyanide liquid carburizing process which can be accomplished in a bath containing a special grade of carbon. It presents a simple formula for estimating total case depth, and illustrates the influence of carburizing temperature, duration of carburizing, quenching temperature, and quenching medium with the aid of typical hardness gradients. The article provides information on controlling of cyaniding time and temperature, bath composition, and case depth, and presents examples that relate dimensional change to several shapes that vary in complexity. It also provides information on the quenchant removal and salt removal processes, lists the applications of liquid carburizing in cyanide baths, and discusses the process and importance of cyanide waste disposal in detail.

This article commences with a brief introduction on the hardenability of carburized steels, and then reviews the factors used in the selection of carburizing steels and heat treatment methods. The factors include quench medium, stress considerations, case depth, and type of case. The article provides information on steels for carburized gears with emphasis on gear design requirements, selection process, selection of carbon content, case and core hardness, microstructure, and toughness and short-cycle fatigue.

Case hardening is defined as a process by which a ferrous material is hardened in such a manner that the surface layer, known as the case, becomes substantially harder than the remaining material, known as the core. This article discusses the equipment required, process variables, carbon and hardness gradients, and process procedures of different types of case hardening methods: carburizing (gas, pack, liquid, vacuum, and plasma), nitriding (gas, liquid, plasma), carbonitriding, cyaniding and ferritic nitrocarburizing. An accurate and repeatable method of measuring case depth is essential for quality control of the case hardening process and for evaluation of workpieces for conformance with specifications. The article also discusses various case depth measurement methods, including chemical, mechanical, visual, and nondestructive methods.