Evaluation of rolling contact fatigue behaviour of nitrided SCM435 in a contaminated lubrication

• Published in: Kikai Gakkai ronbunshū = Transactions of the Japan Society of Mechanical Engineers Vol. 87; no. 893; p. 20-00093
• Main Authors: SADAMORI, Tomoya, KOIKE, Hitonobu, TAKAHASHI, Koji, KUBOTA, Tsuyoshi
• Format: Journal Article
• Language: Japanese
• Published: The Japan Society of Mechanical Engineers 2021
• Subjects: Contaminated lubrication; Nitrided SCM435; Rolling contact fatigue
• ISSN: 2187-9761
• DOI: 10.1299/transjsme.20-00093

In this study, the rolling contact fatigue (RCF) life of nitrided Cr-Mo steel, which has three types of different nitride compound layers, was investigated under contaminated lubrication. Specimen-γ’ has nitride compound layer which crystal structure is adjusted to γ’-Fe4N. Specimen-ε and specimen-εpor have the ε-Fe2-3N type nitride compound layer, however specimen-εpor has a porous layer on its outermost surface. To investigate the crucial factors on RCF life, material characteristics of the surface such as Vickers hardness, residual stress, resistance to indentations were evaluated. Changes of surface topography around Vickers indentation were measured through the RCF test under clean lubrication. As a result, the specimens with ε-Fe2-3N type nitride compound layer showed higher RCF fatigue life than that of specimen with γ’-Fe4N. The RCF life of specimen-εpor was the longest among the specimens, which was about 3-5 times longer than the RCF life of specimen-γ’. The rate of reduction in unevenness around the indentations was dramatically improved by the wear of the friable porous layer on the surface of specimen-εpor. Thus, the specimen-εpor with the hard ε-Fe2-3N type nitride compound layer and the friable porous layer kept the RCF life long under contaminated lubrication, because the stress concentration around the indentations decreased due to smooth indentation edge on the εpor surface.