Bearing Materials

The most common bearing material is 52100 Chrome Steel. This material makes up the vast majority of standard bearings as it has excellent mechanical properties and are suited for basic machine applications. It is especially resistant to corrosion due to it having low chromium properties as well as being readily available and cost-effective.

51200 Chrome Steel can withstand high temperatures up to 120°C depending on the cage material. If desired, it can run up to 150°C, however, hardness values deteriorate at this temperature which significantly reduces the bearing lifespan.

One of the most common and reputable bearing grades is stainless steel 440C. This is a martensitic stainless steel with a very high carbon content. The has additional chromium content as well as additional nickel. These properties make it far more resistant to corrosion in comparison to 52100 but remains weak to many chemicals is exposed to moisture. 440C is magnetic as opposed to the 300 series stainless steels.

This material can operate in temperatures up to 250°C and can be pushed to 300°C, but only intermittently. If the bearing needs to operate consistently at increased temperatures, heightened bearing internal clearance is required.

This bearing material is best used when minor corrosion-resistance is required, and a project requires a readily available bearing.

One of the most common and widely used austenitic stainless steels is 316. Although this material is comparatively soft for a bearing, its corrosion-resistant properties are excessive. This material is often used in offshore applications due to its impressive performances in salt spray tests. Similar corrosion resistance can be found in Cronidur30, without a loss in hardness and fatigue life. 316 is also known to be one of the mostly non-magnetic which can also be advantageous.

316 bearings can run up to 500°C if there is no cage. This material is non-hardenable so it can only allow for semi-precision applications with low loads on low speeds.

Silicon nitride has stronger high-temperature capabilities than the majority of metals that combine retention of high-strength and creep-resistance with oxidation resistance. As well as this, its low thermal expansion coefficient gives strong thermal shock resistance compared with most ceramic materials.

Silicon nitride is the ideal choice for many specialist applications, including medical devices, ultra-high vacuum, semiconductors, and many others. Silicon Nitride is 85% lighter than traditional steel, providing a weight-saving benefit. This weight reductions means that there is a reduction in centripetal force generated by the rolling elements, offering a significantly increased fatigue life time. Unlike other ceramic materials, silicon nitride has the capability to carry similar loads to that of bearing steel. However, the hardness of the material application with shock loading is unsuitable for use of silicon nitride or any other ceramic materials for races.

The lower density of this material provide both weight savings and an increased life as the centripetal forces act upon the bearing is less, which reduces the wear on the rolling elements. Due to the surface finish limitations and hardness, a full silicon nitride bearing is not suitable for low-noise applications and hybrid version would be better suited.

Speed ratings are reduced when a fully silicon nitride bearing is used. Hybrid arrangements significantly increase speed capabilities to traditional steel bearings. There are also lower load ratings to a traditional steel bearing.

These bearings also have strong corrosion resistance and a large temperature range from -210°C to 800°C without a cage. They are also electrically insulating and non-magnetic.

Zirconia (ZrO2) was initially used and developed in the 1960s and ‘70s, where it was used to make external to create a thermal barrier to allow space shuttles to re-enter the earth’s atmosphere. The properties that Zirconia possess allow it to be the ideal material for use in high-temperature applications. The density and thermal expansion of Zirconia is similar to steel, which means that it does not have the same weight saving and thermal-shock-resistant properties as other ceramic materials.

This material is best used under low loads, the bearing is commonly used in temperatures between -190°C and 850°C without a cage and in highly-corrosive applications. Similar to other ceramic materials, this material is non-magnetic and electrically insulating.

Zirconia has a similar Thermal Expansion Coefficient to 52100 Chrome Steel and the same as 440C Stainless Steel. This allows for mechanical systems to expand and contract in sync throughout temperature gradients.

Although this material is highly corrosion resistant, it may show signs of degradation following consistent exposure to steam or hot water. If you are interested in this bearing material then please contact our bearing experts to discuss the degradation at low temperatures to determine if this bearing is the right option for your application.  

This bearing is less frequently used than other ceramic bearings due to the cost of its raw materials and difficulty to machine. However, silicon carbide provides the best heat and corrosion resistance of all ceramic bearings.

Silicon Carbide is ideal for low loads in highly corrosive environments. It exhibits the strongest corrosion resistance out of the popularly utilised bearing ceramics. Silicon Carbide also allows for one of the highest temperature ratings, at up to 1600°C without a cage. This bearing material is non-magnetic and electrically conductive.

Alumina is a popular technical ceramic but is less commonly used for bearings. Similar to other bearings, it is an excellent electrical insulator and exhibits high mechanical strength. The material is corrosion resistant, unless it is in contact with hydrochloric acids, hydrofluoric acids, or strong alkaline solutions. It can be provided between 96%-99.8%, all of which impact mechanical performance.

Our technical bearing experts have the expertise to guide you through the process of choosing the most suitable ceramic bearings for your applications. Alumina may be the right one for you.

M50 steel is also known as ‘Tool Steel’ and has high hardness and corrosive strength at both standard and elevated temperatures with strong hot harness and excellent rolling fatigue characteristics. This material has been the natural choice for critical aircraft engine breaking that are being used up to temperature of 500°C, due to its hardness remaining at approximately 55 HRC at this temperature.

These properties, in conjunction with its superior fatigue resistance mean that it is the suitable material for high-temperature and load-bearing applications where stability and precision are paramount. Typically, suitable applications include gas turbines and semiconductor assemblies.

CRONIDUR® 30 is a martensitic through-hardened steel with similar corrosion resistance to 316L stainless steel, and offers a noticeable improvement over 440C stainless steel. This material is enriched with nitrogen with supreme corrosion resistance and exceptional wear resistance.

Other powerful properties of this bearing include high compressive strength, extreme durability and both high and low temperature stability.

CRONIDUR® 30 bearings are proven to be suited to applications such as oil exploration down-hole equipment, cryogenic pumps and precise optical equipment. Bearing life can be increased significantly by adding ceramic balls to form a hybrid bearing.

Provided as AMS 5898, these bearings have a long history of working on the most challenging aerospace and space applications. This material is a trusted performer when coupled with support from UNASIS bearing experts.

BG42 is a martensitic high-temperature steel that excels at high speeds. It is known to combine the corrosion resistance of 440C stainless steel with the high temperature hardness of M50 Tool Steel.

These powerful properties make BG42 common in high-pressure turbine sections within gas turbines or other flight-critical locations. The added molybdenum enhances its resistance to corrosion, complemented by the high chromium content and also provides some self-lubrication characteristics.

It is supplied as AMS 5749 and has a long lineage in both aerospace and space heritage so it can be trusted for the most challenging bearing environments.

Stellite is a material that consists of complex carbides in an alloy matrix. This material provides a combination of superbly resistant properties that can be used for the components of a rolling element bearing. Some of the core benefits include resistance to wear, galling, and corrosion even when operating at extremely high temperatures of 500°C, retaining it hardness of 45HRC, and non-magnetic properties at this temperature.

Stellite has be used extensively in aerospace applications, including inline jet engine valves, landing gear, and actuation equipment. This has driven the popularity of the material amongst engineers to turn to this material when other alloys and ceramics have not been ideal or suited in bearing applications such as high temperature valves, equipment operating within a range of Tesla magnets, semiconductor applications, and cryogenic pumps.

Beryllium copper is a high-strength alloy that is similar to steel with non-magnetic properties which can be heat treated for use in bearings.

This material offers many benefits in extreme environments, including strong heat dissipation with a thermal conductivity, a powerful structure that allows it to be suited for applications of occasional overload, impact, high and low temperatures, and marginal lubrication.

The properties of this material make it suitable for cryogenic, ultra-high vacuum, and magnetically sensitive environments, as well as some corrosive applications.

Due to the diversity of environments where engineers and designers are now expecting bearings to operate bearings can be produced in many speciality materials and metal and alloy combinations to produce specific solutions.

Bearings can be produced from the following materials: Inconel, Titanium, Monel, XD15NW, BG42 VIM-VAR, M48 Powder Metal High Speed Steel.

Additional speciality ball options include: Ruby, glass, PEEK, NYLON, Toloron, titanium, the above list is not exhaustive as new materials are constantly becoming available.