Coating is one of the most widespread post-production processes for steel parts. For bearings, coatings are often used to increase hardness and/or corrosion resistance, both of which are needed for high performance.
In this post, we’ll look at common coatings used for bearing applications as well as the potential drawbacks of coatings. Then we’ll present some steel coating alternatives, including specialty corrosion resistant nitrogen (CREN) grades.
The ideal bearing meets performance requirements and lasts as long as possible. The problem bearing manufacturers face is that corrosion-resistant stainless grades may not be hard enough to resist wear, yet high-hardness steels tend to be susceptible to corrosion.
A coating can solve this by improving surface hardness and/or corrosion resistance, and it can be targeted to certain areas of a part (ie, the bearing race) through masking or by machining the coating off where it’s not needed.
Coating also:
Extends part life
Reduces maintenance
Prevents failures
Coatings are a traditional and relatively inexpensive way to enhance the performance of a less expensive grade of steel such as 52100, 8620, or 9310.
Steel coating is a well-established technology that’s been in place for years (recent environmental regulations are driving change, however).
Some common coatings used in the bearing industry include:
“Coatings sound simple and attractive, but there are always challenges.”
– John Normandin, Owner of Bearing Consultants
Like any solution, coating a bearing to enhance performance has its downsides.
Luckily, coating isn’t the only way for a bearing steel to achieve superior hardness and corrosion resistance.
"One option is to avoid coating in the first place, by using a high nitrogen steel, such as a CREN."
- Todd Chavanne, Technical Product Manager at Sullivan Steel
Corrosion resistant nitrogen steels (CRENs) have inherently high hardness and corrosion resistance—a rare combination. These specialty steels require a higher upfront cost but provide superior performance with minimal post-processing, no risk of varying surface quality, and no need for vetting or managing coating suppliers.
Sullivan stocks the following CREN bearing grades:
Depending on the application, it may be possible to upgrade a steel and polish it instead of applying a coating, particularly for situations where coating is used to improve lubricity or smoothness of a surface.
Polishing a high-cleanliness grade is simple and cost-effective when compared to the cost and complications associated with applying a coating.
Case hardening methods, such as nitriding, carburizing, or induction hardening, improve hardness with no or minimal dimensional changes. Just like coating, it’s possible to target only certain areas of a component.
Sullivan’s experts are highly knowledgeable in case hardening and are available to help guide the process.
If you’re having challenges related to coating quality or if coating is no longer an option, Sullivan Steel can help.
We begin with understanding the purpose and objectives for your part and coating. Then, we work with you on application-specific solutions, possibly consulting with mill metallurgists or even vetting your heat treatment process.
Of course, the surest solution is to use a material that doesn’t require coating. As suppliers of specialty steel, Sullivan offers high hardness, corrosion resistant steel grades that inherently give your bearing the properties it needs.
Start a live chat or contact Sullivan Steel today.