Two stainless steel parts used in automotive engines are carburized in the course of their production to achieve desired properties. To reduce costs and improve product quality, the gas carburizing process that had been used was replaced by low-pressure vacuum carburizing. The two parts are similar in composition except that one contains 0.25 wt% Mo and the other 0.4 wt% Mo. Both also contain around 17 wt% Cr and thus naturally form a Cr 2 O 3 passivation layer that provides corrosion resistance but also acts as a barrier to carbon. As a result, the parts are etched in a pickling solution prior to carburizing. In the initial assessment of the new carburizing and pretreatment process, engineers observed differences in the pitting and oxide regeneration behaviors of the two stainless steels. The paper describes how the engineers determined the cause of the pitting and the extent to which it could be controlled. Because of the tradeoffs involved, the engineers decided to make both parts from the same material and optimize process parameters accordingly.

Case carburizing grade steel forgings are often normalized or iso-annealed to improve machinability. The aim here is to get a uniform ferrite-pearlite microstructure and controlled, uniform hardness. Since during forging material is above austenitizing temperature, controlled slow cooling after trimming can give similar results. In this work, the effect of forging temperature and cooling rate at different stages on microstructure is studied. Further the effect of this process on machinability and distortion behavior of gears during case carburizing is studied. It was observed that the controlled cooled gear blanks had coarse grain size resulting in superior machinability, and no change was observed in the distortion behavior of the gears during case carburizing.