Influence of the pack thickness of the boronizing mixture on the boriding of steel

Boronizing, which involves diffusion of boron atoms into steel substrate to form iron borides, is a well-known diffusion coating process and numerous studies have demonstrated the outstanding tribological properties of boronized steel vis-à-vis carburized or nitrided steels. However, the high cost of the boronizing process has severely limited its applications. One way to bring down the cost of the boronizing process is to reduce the thickness of the boronizing mixture to be packed around the component (called pack thickness) to the minimum required level without compromising on the properties of the boride coating. The present study attempts to estimate the optimum pack thickness required to form boride coating of adequate thickness and property in the case of a low carbon steel boronized at 940°C for 2 h. Low carbon steel samples have been boronized with varying pack thickness in the range 2–25 mm and the resulting boride coatings have been examined for thickness, microstructure, microhardness profile and abrasion resistance. An analysis of the results obtained indicated that a pack thickness of 10 mm is sufficient to obtain boride coatings of adequate thickness and optimum properties.