NSK has developed ES1 (excellent stainless steel) for use in bearings operating in high-humidity, chemical and hygienic environments, where corrosion might otherwise impair the reliable long-term operating life of rolling bearings. ES1 is claimed to provide superior corrosion resistance and rolling contact fatigue life compared with conventional AISI 440C steel in wet and aggressive environments; this improvement helps to reduce maintenance, downtime and replacement bearing costs.
Until the development of ES1, AISI 440C had been the general choice for use in bearing applications where corrosion resistance was a primary concern. Because the steel contains coarse eutectic carbides that can act as crack initiators under rolling contact stress, the performance of AISI 440C had not always proven satisfactory.
ES1 steel, however, has no eutectic carbides but consists of fine carbides, nitrides and strong martensite, resulting in improved resistance to corrosion and fatigue. ES1 also has an optimised nitrogen content and lower carbon content to suppress the eutectic carbides generated in conventional steelmaking processes. The operating benefits of this new material specification have been proven following extensive testing by NSK: ES1 outperformed other stainless steels in a 5 per cent aqueous sodium chloride immersion test, a salt-water spray test, 5-N sulphuric acid and 5-N hydrochloride solution immersion tests, and during life tests in water.
Additional performance advantages were recorded for ES1 in the water immersion test. The test bearings were 51305 thrust ball bearings with fluororesin cages and silicon nitride balls. They were subjected to a load of 980N (maximum contact pressure 1470MPa) and rotating speed of 1000rpm until the bearing vibration level reached about five times its initial value Under these conditions the test results revealed that ES1 provided approximately five times longer life than AISI 440C.
Because bearings manufactured from stainless steel are routinely exposed to cleaning solutions of sulphuric acid and hydrochloric acid, a further corrosion test was undertaken. This evaluated the corrosion resistance of ES1, 13Cr stainless steel and AISI 440C in a 5-N aqueous sulphuric acid solution and 5-N hydrochloric acid solution. In the test, samples of each type of steel were immersed in the solutions at room temperature for 20 hours, after which the amount of corrosion was measured. This revealed that ES1 performed better than both conventional stainless steels in terms of resistance to sulphuric and hydrochloric acids.
For more information, visit www.nsk.com
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