Contact Yield Initiation in Case Hardened Steel

Donglong Li ^1,2, Mengqi Zhang³, Q. Jane Wang ^2*, Zhanjiang Wang ⁴, Ning Zhao³ and Zhongrong Zhou⁴

¹State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing, 400030, China

²Center for Surface Engineering and Tribology, Northwestern University, Evanston, Illinois, USA

³School of Mechanical Engineering, Northwestern Polytechnical University, Xian, China

⁴Department of Mechanical Engineering, Southwest Jiaotong University, Sichuan 610031, China

*Corresponding author: Q. Jane Wang

E-mail address: qwang@northwestern.edu

Abstract

Stress distributions and plastic deformation zones are factors directly influencing the contact fatigue life of components. Surface hardening has been an effective approach to improve the surface resistance to fatigue failure, which builds a yield strength gradient to steel from the surface to the core. For case hardened steels, the contact yield initiates in the subsurface but not necessarily at the location of the maximum von Mises stress; rather, it is at the point where the depth curve of the von Mises stress intersects the line representing the yield strength reduction from the surface. Further, the maximum contact load for a case-hardened steel without subsurface yield could be determined by the point of tangent of the two. A group of formulas are derived to relate the load and location of contact yield initiation to the material hardening profile. The results are applied to examine the rolling contact fatigue behaviors of case hardened steels.