The corrosion rate and changes in the microstructure and fracture strength of alumina ceramics (93.0% A1203 and 99.5% A I 2 0 , j were studied in O.lm to 25m NaOH solutions at 150°C to 200"C, where m = mol/(kg of H20j. The attack of the caustic alkaline solution started at the grain boundaries. Consequently, the corrosion resistance increased with decreasing SiO, content in Al2O3 ceramics, and the corrosion resistance of 99.5% pure A1203 was similar to that of Si3N4 ceramics. Since large pits are formed by corrosion, the surface area increased first and the apparent corrosion rate increased with time in the initial stage of the corrosion. The corrosion rate of A1203 increased linearly with increasing NaOH concentration, and the activation energy was 102 kJ/mol. The fracture strength of corroded AIZO3 decreased monotonically as the degree of dissolution of alumina increased. [

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The operating environments of rolling bearings are remarkably varied. With the use of bearings in various corrosive environments increasing, interest in stainless steel is growing. AISI 440C has been widely used in applications where corrosion resistance is of primary concern. However, its performance has not always been satisfactory because it contains coarse eutectic carbides that act as crack initiators under rolling contact stress and reduce Cr content in the martensitic matrix to the carbides. In response, we performed research to determine the most suitable bearing steel composition for both long fatigue life and noise performance and high corrosion resistance. Carbide size and hardness comparable to AISI 52100 steel were essential for the new stainless bearing steel(ES1), so we lowered the carbon and chromium contents and increased the nitrogen content of AISI440C. To control production costs, we applied conventional steelmaking processes for the nitrogen alloying. We evaluated the fatigue life and corrosion resistance of the new bearing steel(ES1). The new steel(ES1) outperformed conventional martensitic stainless steels in a tap water immersion test, a 5% aqueous sodium chloride immersion test, a saltwater spray test, noise level measuring test, water submerge life test, and oil lubrication life test.