Abstract: In this study, a method was proposed to evaluate the shape, the size and the chemical compositions of oxide inclusions in railway wheel steel. The evaluation method which consists the surface strengthening process and the fatigue test was carefully designed. The ultrasonic inspection was first conducted to CL60 wheel to identity the regions which contains densely-distributed defects and single defect, respectively. The samples were taken from both of the identified regions, and then the shape, the size and the chemical compositions of the defect within the wheel steel were evaluated using the proposed method. The evaluation results show that the single defect is the macro-inclusion with millimeter scale, while the densely-distributed defect is the micro-inclusion with micrometer scale. The macro-inclusion mainly contains Ca, Si and Mg, while the micro-inclusion mainly contains of Al and Ca. Both of the inclusions are in a shape of slender ellipse. According to extreme values method, the largest micro-inclusion which can induces subsurface-initiated fatigue was predicted to be [752 μm，1 168 μm] within 95 % confidence intervals in a wheel.

Key words: railway wheel, fatigue test method, surface strengthening process, inclusion