Impacts of Internal Oxidation and Quenching Path on Fatigue of Powertrain Components

Atmospheric case hardening of powertrain components may cause internal oxidation and thus reduce hardenability at the surface zone. This may affect the fatigue strength, which restricts the maximum cyclic load on steel components and hence is a major impediment for powertrain development and design.  Here we have investigated the effects of furnace gas atmosphere and quenching path on fatigue of powertrain components. The results show that the detrimental effect of internal oxidation on fatigue may be compensated for by altering of the furnace atmosphere. Moreover, it is shown that the quenching path below the martensite start temperature also has an impact on the fatigue properties. These experiments were done in a full-scale industrial furnace on gearwheels and bars in steel grades 16MnCr5 and 20NiMo9-7F.