Volume 3, Issue 9 (October 2006)
The Development of an Austenitic Stainless Steel Bearing with High Corrosion Resistance and High Nonmagnetic Property
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.