We evaluated friction fatigue-induced changes in the microstructure and residual stress of carburized steel. By eddy current testing (ET) and x-ray diffractometry (XRD), the voltage rate (after/before fatigue testing) obtained by ET had a strong correlation with the retained austenite phase and the full width at half maximum of XRD. The results are useful for the analysis of fatigue damage in the microstructure of carburized steel.
To investigate the microstructure and damage of friction-fatigued carburized martensitic steels for the reliability of remanufacturing parts, the retained austenite (£) phase and residual stress were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). We evaluated their changes before and after roller pitching tests, and before and after the operation of the gear parts.In the roller pitching tests, the retained £ phase decreased with increasing load and number of cycles, presumably due to martensitic transformation caused by the cyclic load. The residual stress ratio (after/before the test) was significantly lower at high loads than that before testing, which was ascribed to the appearance of surface microcracks and the resultant release of internal stress. From SEM observations of the cross-section of the friction surface, we confirmed that the changes in the retained £ phase and residual stress ratio reflect the process of formation of multiple microcracks in the 10 µm surface layer. The decreases in both the retained £ phase ratio and the residual stress ratio would therefore appear to rule out reuse. A decision on the potential for gear reuse can be made by means of non-destructive testing, i.e., investigating the relationship between the retained £ phase ratio and the residual stress ratio.
In this study, we assessed the environmental impact of the remanufacturing of mining machinery components, by analyzing commonly used parts in a machine setup. No previous studies have conducted a detailed environmental impact assessment of any manufacturing processes for new or remanufactured components used in mining machinery. We analyzed the system boundaries and conducted inventory analysis to understand their function and determine their unit role in the machine. Then, we evaluated the environmental impacts of the manufacturing processes for the subparts and assy parts, along with the impact of logistic and remanufacturing processes. In particular, we assessed hydraulic equipment, which is a common component of mining machinery, and conducted a comparative assessment of the environmental impacts of new and remanufactured components. Our results indicated that the global warming potential (GWP) per mining machine throughout its lifecycle (LC) could be reduced by ~194 ton-CO₂eq./LC. Assuming that the number of mining machinery in operation at a global scale is 571 machines (or units) per year, the GWP would be reduced by ~110,000 ton-CO2eq./year.
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