WIND turbines play a crucial role in the global transition towards a sustainable energy future. Maximizing energy production and ensuring a reliable operation is essential to harnessing the full potential of wind energy. Among the critical components, the main shaft bearings have for several years been a focal point due to their significant downtime. In this context, a tribochemical treatment called case-carburization has gained notable attention for enhancing the microstructure of these bearings, to improve their reliability. Case-carburization is a surface treatment technique capable of modifying steel to exhibit a combination of properties such as high fatigue strength, toughness, and wear resistance, that are essential for these bearings as they operate in high-load-bearing environments. In a multi-stage heat treatment process involving case-carburization as the initial stage, the microstructure development at each stage is affected by the final microstructure of the preceding stage. Therefore, a comprehensive understanding of the microstructure at every stage is crucial for assessing its impact on the final microstructure and its properties. This Ph.D. research investigates the microstructure evolution throughout a four-stage heat treatment: carburization, sub-critical isothermal treatment, hardening, and tempering. The second stage is where the sole difference lies with regard to the heat treatment parameters, and is performed along two different routes, also in industrial practise, called the "bainitic route" and "pearlitic route". One of the primary goals of this research is to understand the microstructure development during the different stages of the two heat treatment routes and to provide an understanding of the microstructural features that can potentially affect the properties/performance of bearings. Additionally, this research also aims to identify the specific stage at which these features form and to provide insight into their formation mechanisms to explore strategies to rectify or mitigate the formation of detrimental features in the microstructure....@en

Wind turbine (WT) gear boxes are prone to failure well below the expected 20 years’ lifetime of a WT. It has been identified that most of the failures observed are due to white etch crack flaking. Although this type of failure has been intensely studied, the underlying mechanisms have not been identified; however, recent advances have shown that non-metallic inclusions might act as crack initiators. In this work, different bearings presenting this type of damage will be examined via microtomography scans and high precision serial sectioning to reveal surfaces displaying crack-inclusion interactions. Furthermore, by means of energy dispersive X-ray spectrometry it will be possible to investigate the chemical composition of the non-metallic inclusions. The findings will be compared to current initiation and propagation theories proposed in literature; Thus, this study will add experimental observations to current investigations using a novel technique.