Hydrogen absorption and conservation of operational capabilities in remanufactured bearing steel exposed to corrosion

Abstract

The corrosion of bearing steel often leads to accelerated damage and loss of properties that condition their service life. This damage is further exacerbated with the absorption of hydrogen into the material, generated from corrosion reactions happening at the surface. A remanufacturing process is proposed to recover the operating capabilities of bearings after exposure to corrosive environments, during which the bearings are polished until the surface is visually clean, out of any corrosion product. The process offers the recoverability of the operating capabilities and turns the corroded bearings into a reconditioned useful part avoiding the operational effort, economic cost, and repair that the replacement of a bearing entails. However, atomic hydrogen in the bulk can be entrapped and might still condition bearings operation, often resulting in hydrogen enhanced damage in the steel.

The goal of the current research is to quantify the hydrogen uptake and critically evaluate the reapplication of such remanufactured bearings. The study analyses a bearing that experienced corrosion during its operation in the pulp and paper industry (P&P), primarily due to the cooling water used in the machines. For a better understanding of the effects of the operating environment on bearings, extreme corrosive environments were simulated in a climate corrosion chamber (CCC). The absorbed bulk hydrogen is quantified through the Melt Extraction Tester (MET), and the trapping behaviour analysed through Thermal Desorption Spectrometry (TDS). The effect of the environmental conditions is studied through a microscopical characterization of the formed corrosion product. Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS) are the laboratory equipment used for this purpose.

It was found that the remanufacturing did not ensure meeting the acceptable hydrogen content limit in extreme environments, suggesting that the polishing process is often not sufficient, and should be adapted to specific operating conditions. However, due to material inhomogeneities such as surface pits and plastic deformation-induced traps, no clear correlation could be established between polished material and bulk hydrogen. Nonetheless, a smooth polished surface was proven to minimize the presence of microreaction sites and subsurface defects, thus reducing the absorbed hydrogen. Additionally, corrosive media also affect hydrogen behaviour in the material. In the present work the trapped hydrogen concentration is seen to be dominant, reducing the risk of hydrogen damage. However, reversibly trapped, and diffusible hydrogen is also detected, and can be desorbed or redistributed into other trapping sites during the corrosion process.