Ball bearings made of type 440C stainless steel hardened to 60 HRC and suspected as the source of intermittent noise in an office machine were examined. A number of spots on the inner-ring raceway were revealed by scanning electron microscopy. The metal in the area around the spot was evidenced to have been melted and welded to the inner-ring raceway. It was revealed by randomly spaced welded areas on the raceways that the welding was the result of short electrical discharges between the bearing raceways and the balls. The use of an electrically nonconductive lubricant in the bearings was...