On the Microstructure and Properties of a High Al-Alloyed 100Cr6 Steel

Macroscopic failure of high-performance components such as the bearings in a gearbox of wind converters is usually caused by effects occurring on a microscopic scale, e.g., crack initiation at non-metallic inclusions. Failure of these components leads to high maintenance costs. This work focuses on modifying the chemical composition of the standard bearing steel 100Cr6 in order to increase its strain-hardening potential, and thus its damage tolerance while maintaining the degree of cleanliness. Al alloying is used to adjust a suitable combination of strengthening mechanisms. Dilatometric and metallographic analyses are performed to identify the phase transformation behavior and the microstructure constituents of the designed alloy. Special attention is paid to the formation and morphology of the kappa-phase, a Fe3AlC-phase which contributes to the strain-hardening potential of the material. The mechanical properties are determined at several heat-treatment states and compared to the ones of conventional 100Cr6 steel. It is shown that the k-phase may be used for tailoring the strain-hardening potential during local plastic deformation, and thus reduce stress concentrations at inclusions.