The evolution of hardness and tribofilm growth during running-in of case carburized steel under boundary lubrication

Abstract

Many engineering tests start with a run-in procedure, as it is commonly accepted that running-in at some fraction of the target load is beneficial due to a reduction in surface roughness. However, the choice of load and duration is often based on historical context or the experience and philosophies of the testing personnel. The objectives of this study were to (1) evaluate the effects of contact pressure and initial composite roughness on the surface evolution during the initial stage of testing, and (2) use this information to determine if there is an optimal load and time for the run-in portion of a test. These tests were conducted with a disc-type machine using carburized steel specimens with a circumferential lay direction and oil with anti-wear additives under specific conditions of slide-to-roll ratio, entraining velocity, oil spin-off temperature, and oil/additive package. The specimen surface was inspected using non-contact profilometery every minute for the first 10 minutes of testing, with a subsequently increasing inspection interval for a total of 150 minutes. The data demonstrate that the surface roughness reduces within the first few minutes of testing and remains stable for a period, which is dependent on the pressure and initial composite roughness. Additionally, hardness measurements indicate that hardness gains are occurring during the test, but over a longer timeframe.

Investigating the effect of retained austenite and residual stress on rolling contact fatigue of carburized steel with XFEM and experimental approaches

“…The finite element model was setup as shown in Figure 1. The FE model was based on the 'roller to ring contact' in the experimental Micro Pitting Rig (MPR) setup by PCS instrument (London, UK) [25], as shown in Figure 1a. The setup of a two-dimensional (2D) plane strain RCF model was created in commercial FE software, ABAQUS 6.14 as shown in Figure 1b.…”

“…Rolling contact fatigue tests were performed using a Micro Pitting Rig (MPR) by PCS instruments (London, UK) [25]. A schematic representation of the experimental setup is shown in Figure 14.…”