The steel cleanliness of railway wheels has been one of the main improvement concerns of wheel suppliers especially with increased train speeds in Europe. Microcleanliness measurements and NDT testing have been combined to avoid shatter rims in service. As the fracture of just one wheel can have disastrous consequences, it is the purpose of this paper to define the state of the art in the different ways of controlling the steel micro-cleanliness of railway wheels. Valdunes has begun a research program with the company Ascometal in order to qualify the heats in the steel mill at the beginning of the process. This approach is similar to those developed for bearing steel. The aim is to determine a criterion by which it can be decided, right from the steel mill to assign a heat to a high speed or heavy goods application without having to wait for micrographic characterization. Therefore, the steel manufacturing process rating has to be combined with the micro and macrographic inclusionary cleanliness measures, with a fatigue test to estimate in-service behaviour. It is in fact necessary to validate the criteria to be used for steel manufacture. A gigacyclic fatigue approach has been used. Experience has shown that failures can occur beyond 10 -7 cycles and that the fatigue resistance continues to decrease as the number of cycles increases. In terms of damage mechanisms, most of the fracture examinations reveal that the crack initiation takes place at an internal defect, such as inclusion, in gigacyclic fatigue. This method has been used to link the process and the steel application in order to define new steel mill criteria and the results will be presented during the session. These new methods have been associated with new NDT criteria developed for the EN standards (equivalent flat hole of 1mm).
Steel cleanliness and railway wheels: Control of cleanliness, impact on shatter rims, main improvements and developments
2003
5 Seiten, 6 Bilder, 3 Tabellen, 7 Quellen
Aufsatz (Konferenz)
Englisch
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