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The most common materials used in rolling element bearings include 52100 chrome steel, 440C stainless steel and M50 tool steel. While these standard materials are suitable for most applications, extraordinary operating conditions often require the use of more advanced alloys such as BG42®, M50 NiL and Cobalt-based alloys, which offer superb performance at high speeds, extreme temperatures, heavy loads and in corrosive conditions. Although cost considerations occasionally override longevity, the expense involved in more frequent bearing replacement often justifies the higher initial costs of specifying longer-lasting specialty metals.

A detailed analysis of the factors involved in a specific application is required before selecting the correct material. The following table, while not a complete list of available alloys, is a helpful starting point to the selection process. Please contact NHBB’s Applications Engineering department for help with making a final determination.

Material Specification Melt Method Features And Advantages Hardness At Room Temp. (HRC) Operating Temp. Limit Heat Treatment Attributes
52100 AMS 6440 Vacuum degassed Available in tube form 60-64 310 °F Good wear and fatigue properties
AMS 6444 CEVM* Premium quality
Very low impurity level
58-62 400 °F Improved thermal stability
60-64 310 °F Good wear and fatigue properties
58-62 400 °F Improved thermal stability
440C AMS 5880 Air melt or vacuum degassed Corrosion resistance 58-62 325 °F Good wear properties
56-60 825 °F Thermal stability with corrosion resistance
AMS 5618 CEVM* Premium quality
Low impurity level
58-62 325 °F Good wear properties
56-60 825 °F Thermal stability with corrosion resistance
M50 AMS 6491 VIM/VAR** Premium quality
High temperature capabilities
60-64 975 °F Excellent fatigue properties
High thermal stability
BG42® AMS 5749 VIM/VAR** Premium quality
Corrosion resistance
High temperature capabilities
61-65 950 °F Excellent wear properties
High thermal stability
Nitrogen enriched steel AMS 5898 P-ESR‡ Extreme Corrosion resistance 60-64 850 °F Improved toughness
Improved compressive strength
Cobalt-based alloys AMS 5759 CEVM* Chemical resistance
High temperature capabilities
50 (min.) 1000 °F Good thermal stability
Low hardness reduction at elevated temperatures
M50 NiL AMS 6278 VIM/VAR*** Carburized
High temperature capabilities
Case: 60 (min.) 975 °F High fracture toughness of core
Accommodates high hoop stresses and cyclic loading

HiTech purchases all products per AMS industry standards and/or NHBB product engineering standards.

* Consumable Electrode Vacuum Melted.
** Vacuum Induction Melted/Vacuum Arc Remelted.
‡ Pressure Electroslag Remelting.

Fatigue Life

Bearing steels possess specific characteristics that play a critical role in bearing performance. Choosing a material with the correct values for hardness, corrosion resistance, strength, fracture toughness and fatigue life ensures that a bearing will function reliably within an application’s operational and environmental parameters. During the material selection process, these characteristics are weighed against an application’s specific conditions of temperature, load and corrosiveness.

The most important result of material selection is a bearing’s longevity. Since different materials possess varying amounts of fatigue life, each alloy is assigned a life adjustment factor which is determined through empirical testing. This value provides a basis for calculating a dependable bearing-life estimate. The life adjustment factors for various bearing steels are listed in the section titled Load Ratings and Bearing Life.

Materials Processing

NHBB maintains exacting metallurgical control of all materials from the originating mill through all manufacturing processes. Materials are heat-treated and tempered in-house under controlled atmospheres to bring about the uniform grain structure and specific hardness appropriate for the intended application.

Materials Laboratory

Our Materials Laboratory is specifically designed and equipped to perform complex chemical, metallurgical and visual analyses of the many component parts in ball and roller bearings. Alloy composition is determined with X-ray diffraction spectrography and nondestructive test methods. Metallurgical studies are conducted with a metallograph, which performs microstructure photography at magnifications from 25 to 2000 times, and microhardness testers, which investigate surface effects and alloy homogeneity. The lab also utilizes a scan electron microscope (SEM) to inspect topographies of materials. The SEM has a magnification range that encompasses that of optical microscopy and extends it to the nanoscale.