P. L. J. Olund, G. Wicks, C. Fallqvist, Ovako Hofors AB, Hofors, Sweden
By utilizing a novel approach in the selection of the alloying elements, gear steels can be produced which exhibit a dramatically reduced tendency for the formation of internal oxidation during conventional gas carburizing.
In the work presented here, the reduction in the amount of internal oxidation and non-martensitic microstructure at the near surface was to such an extent that it resulted in a marked increase in the materials fatigue strength, thereby allowing for a significant increase in the power density of the transmission.
The challenge with this work was not only to produce a steel grade that exhibited a dramatic reduction in internal oxidation. But, it was to match the heat treatment response, as close as possible to the existing carburizing steel grade in use, such that the new gear steel grade could be seamlessly introduced into the existing production process.
The development of a special gear steel for carburized drive train components was in response to a customer demand for gears with an increased surface fatigue strength.
The approach taken was to use a novel alloying strategy in the steel manufacture so as to achieve a dramatic reduction of the near surface internal oxidization that occurs during the atmosphere carburizing process.
Test data showed that we did indeed achieve a marked increase in the materials fatigue strength, thereby allowing for a significant increase in the power density of the transmission.
