Author(s)

K. Morino, N. Kawagoishi, Q. Chen, K. Fukada & E. Kondo

Abstract

Internal fracture process in fatigue of radical nitrided bearing steel K. ~orino', N. ~ a w a ~ o i s h i ~ , Q. chen2, K. ~ukada~ & E. ond do^ * Tokuyama College of Technology, Tokuyama, Japan 2 Faculty of Engineering, Kagoshima University, Kagoshima, Japan 3 Kohan Kogyo Co. Ltd., Kudamatsu, Japan Abstract Rotating bending fatigue tests were carried out for a radical nitrided bearing steel in order to investigate the initiation and propagation behavior of an internal crack. Surface fracture occurred under high stress levels and fish-eye fracture happened under low stress levels so that the S-N curve appeared in the shape of two-step lines. The depth of the origin of internal fracture was confined in a relatively narrow region near the boundary between the hardened and nonhardened matrix. By two-step loading fatigue tests in the internal fracture region, a circular trace corresponding to the stress change was observed w i t h the fisheye. In the internal fracture region, a crack was initiated a

Keywords