Enhanced Carburising Using a Novel Accelerant

It is well known that carbonitriding can bring benefits compared to standard carburising particularly for shallow case depths. The major benefits are an increased effective case depth in a given time and a higher case hardenability. The major drawback of the process is that it can only be carried out at relatively low temperatures. If ammonia is used as the source of nitrogen, the time required to achieve deeper cases can be significantly longer than for the equivalent higher temperature carburising process. For carbonitriding to be effective at higher temperatures, another source of nitrogen is required that so that it can produce the nascent nitrogen necessary for diffusion at higher processing temperatures.

Several sources of nitrogen were investigated. One was found that produced a significant carbonitriding effect at higher temperatures. Samples of SAE8720 and SAE9315 were carburised and carbonitrided under identical conditions and the case depths compared. Carbonitriding with the new nitrogen source was found to increase the effective carburising rate by about 20% at case depths of around 0.75mm, with higher values for shallower cases.