In high humidity, chemical and sanitary environments, bearings are easily damaged due to the presence of a large amount of corrosive media. In view of this, NSK developed ES1 (premium stainless steel) material. Compared with traditional AISI 440C steel, ES1 has excellent corrosion resistance in humid and aggressive environments, so it can greatly extend the service life of bearings. Using this material helps reduce machinery maintenance, downtime and replacement bearing costs.
Before ES1 material, AISI 440C has been the general choice for bearing applications, where corrosion resistance is the main issue. The performance of AISI 440C is always unsatisfactory due to the presence of coarse eutectic carbides in the steel, which can become crack initiators under rolling contact stress.
ES1 steel does not contain eutectic carbides. This material consists of fine carbides, nitrides and strong martensite, which improves corrosion resistance and fatigue. ES1 also has an optimized nitrogen content and a lower carbon content, which inhibits the generation of eutectic carbides in traditional steelmaking processes. The new material's performance has been proven through extensive testing by NSK, including 5% sodium chloride aqueous solution immersion tests, salt spray tests, 5-N sulfuric acid and 5-N hydrochloric acid solution immersion tests, and water life tests, with ES1 performing significantly better than other stainless steels.
In the sodium chloride aqueous solution immersion test, specimens of ES1, 13Cr stainless steel, and AISI 440C were immersed in a 5% sodium chloride aqueous solvent at room temperature for 8 hours. Prior to immersion in the solution, all surfaces of the specimens were polished and then passivated. The test showed that conventional AISI 440C and 13Cr stainless steels rusted, while ES1 did not. Similar results were recorded in the salt spray test, with both AISI 440C and 13Cr showing considerable rust, while ES1 did not.
Additional performance advantages of ES1 were recorded in water immersion tests, where a 51305 thrust ball bearing with a fluororesin cage and silicon nitride balls was subjected to a load of 980N (maximum contact pressure 1470MPa) and a rotation speed of 1000rpm until the bearing vibration level reached approximately five times its initial value. The test results showed that ES1 lasted approximately five times longer than AISI 440C.
Because bearings made of stainless steel are often exposed to cleaning solutions of sulfuric acid and hydrochloric acid, NSK conducted further corrosion tests to evaluate the corrosion resistance of ES1, 13Cr stainless steel and AISI 440C in 5-N aqueous sulfuric acid and 5-N hydrochloric acid solutions. In the tests, samples of each type of steel were immersed in the solution at room temperature for 20 hours, and the amount of corrosion was then measured. The results showed that ES1 outperformed both conventional stainless steels in resistance to these acids.
