This paper describes bearing life under water-infiltrated lubrication, which is often much shorter than the calculated bearing life. Bearings that failed in the field under water-infiltrated lubrication were analyzed to identify the mechanism. However, this was difficult due to insufficient information of the failure process. New fatigue life test methods were then developed to reproduce short life under water-infiltrated lubrication, to precisely observe the flaking process, and to study what material parameters affect the bearing life. It was found that failure under water-infiltrated lubrication initiates from nonmetallic inclusions on the rolling contact surface and propagates initially following grain boundary and then cutting through the grain, which eventually results in flaking. Higher cleanliness, which means less failure initiations, and nickel (Ni), which strengthens grain boundaries, improves bearing life under water-infiltrated lubrication. Hydrogen-induced failure is also experimentally studied to further understand water-induced failure. Hydrogen-induced failure is different from water-induced failure in the mechanism.

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.

Apparatus of the type used in liquid crystal and semiconductor production facilities, medical inspection facilities, and linear motor cars utilize a magnetic field. When operated, either driven or rotated, they may experience a disturbance of the ambient magnetic field. This is more likely to occur if the driven or rotating portion of the apparatus is formed from a magnetic material. In recent years, bearings use in apparatus utilizing a magnetic field were made in precipitation hardening stainless steels such as Mn-Cr-V series or Mn-Cr-Ni-V series. Although these steels have excellent corrosion resistance, compared to martensitic stainless steels like AISI 440C, it is still not sufficient. In addition, the typical hardness of a precipitation hardening stainless steel used for bearings is about 446 HV. The low hardness of the steel means that the durability of the bearing is often unsatisfactory. Therefore, work was undertaken to develop a bearing steel with improved properties. In addition, to having improved corrosion resistance and durability, the steel must also have a very low magnetic permeability. This led to the development of a carburized AISI 316L austenitic stainless steel. The carburizing was carried out at 500°C to produce a surface layer with a hardness around 800∼1000 HV, while retaining the excellent corrosion resistance and low magnetic permeability associated with this type of steel. Tests carried out have shown that despite the thinness of the hardened layer and low core hardness, in certain applications bearings made in carburized AISI 316L exhibited excellent durability together with low friction characteristics.

Apparatus of the type used in liquid crystal and semiconductor production facilities, medical inspection facilities, and linear motor cars utilize a magnetic field. When operated, either driven or rotated, they may experience a disturbance of the ambient magnetic field. This is more likely to occur if the driven or rotating portion of the apparatus is formed from a magnetic material.In recent years, bearings use in apparatus utilizing a magnetic field were made in precipitation hardening stainless steels such as Mn-Cr-V series or Mn-Cr-Ni-V series. Although these steels have excellent corrosion resistance, compared to martensitic stainless steels like AISI 440C, it is still not sufficient. In addition, the typical hardness of a precipitation hardening stainless steel used for bearings is about 446 HV. The low hardness of the steel means that the durability of the bearing is often unsatisfactory.Therefore, work was undertaken to develop a bearing steel with improved properties. In addition, to having improved corrosion resistance and durability, the steel must also have a very low magnetic permeability. This led to the development of a carburized AISI 316L austenitic stainless steel. The carburizing was carried out at 500°C to produce a surface layer with a hardness around 800–1000 HV, while retaining the excellent corrosion resistance and low magnetic permeability associated with this type of steel.Tests carried out have shown that despite the thinness of the hardened layer and low core hardness, in certain applications bearings made in carburized AISI 316L exhibited excellent durability together with low friction characteristics.

The guide roll bearings for a continuous casting machine (CCM) are used under extremely low rotation speed, high load, and debris-contaminated and water-infiltrated lubrication. Therefore, raceway surfaces usually wear severely and outer rings are sometimes fractured. The purpose of this study is to prolong the CCM bearing life by material and heat-treatment technologies. We investigated the fracture process of CCM bearings and developed a new material, case hardened steel, that shows superior wear resistance to SAE 52100 steel. Optimum control of retained austenite and hardness extends rolling contact fatigue life under contaminated lubrication. In the simulation tests of a CCM guide roll, superior wear resistance was confirmed under water-infiltrated lubrication conditions.