Comparison Between the Hydrogen Embrittlement Behavior of an Industrial and a Lightweight Bearing Steel

Hydrogen embrittlement (HE) is a widely occurring problem, also in the automotive industry. Therefore, this study compares the resistance to HE of two types of bearing steels: an industrial 100Cr6 steel and an innovative Fe-8Al-1.1C steel. The innovative character of the Fe-8Al-1.1C steel is found in the fact that a high weight fraction of Al is added to a simplified Fe-1.1C alloy which results in a low-cost martensitic steel with a similar hardness but a lower density, compared to the industrial 100Cr6 steel. The density reduction offers the opportunity to reduce the vehicle weight and as such to reduce the CO2 emission of fuel-based cars or extend the driving range of electrical vehicles. Both alloys are subjected to a similar heat treatment resulting in a martensitic matrix with specially induced carbides. (In-situ) H bending tests and subsequent post-mortem fracture surface analysis are performed to investigate the mechanical degradation of both steels in a H rich environment. For the industrial steel grade, the large Cr-based carbides act as fracture initiation sites for H-assisted cracks. In contrast, the fracture behavior of the Fe-8Al-1.1C material is similar in air and in an H containing environment, indicating that the Fe-8Al-1.1C steel has a better resistance to HE. Although these results are very promising, further optimization of the innovative alloy is needed to improve the mechanical behavior in the absence of H since the presence of microcracks cause premature failure when tested in air.