Current investigations concentrate on the relation between microstructural gradients in the wheel rim and the resulting fatigue behaviour of high-speed passenger-traffic and commercial-freight transportation railway wheel and tyre steels at different service-relevant temperatures. Microstructural gradients are a consequence of the industrial heat treatment and the component size. Total-strain-controlled experiments were carried out with servohydraulic testing systems at ambient temperature and temperatures between 200°C ≤ T ≤ 550°C. Plastic strain amplitude, change in temperature and change in electrical resistance measurement techniques were used to characterise the fatigue behaviour under special consideration of the local wheel microstructure. The measured values depend on deformation-induced changes of the microstructure in the bulk material and represent the actual fatigue state on the basis of physical variables like the defect density of the material. It is shown, that test temperatures strongly influence the fatigue life of railway wheel steels, e. g. pronounced dynamic strain ageing effects are observed at about T = 350°C. In this investigation the microstructural characterisation was done by optical and scanning electron microscopy, together with digital image processing.
展开▼
