While you are correct for nitriding of cranks via gas methods, one is to look at plasma nitrding of cranks which succumb very effectively to nitriding. Processing times are shorter, temperatures are lower, and no distortion of the crank is obtained via plasma nitrding - (hot-walled). With plasma one can process a crank with no compound (white) layer eliminating the tendency for this layer to release or spall with locallized impact and dynamic loads. If compound layer is chosen for the application, the plasma formed compound layer is more compact with no porosity as seen with gas methods - (amonia dissocation). Plasma can also differentiate the amount and type of compound layer formed at surfaces if required. Diffusion of nitride percipitates into the material forming a case of up to 0.60 mm pending on alloy and prior processing are obtained with no compound layer and low nitrogen potential programmed settings for a plasma treatment. One should reconsider when assessing nitridng as plasma is the best method for the time, price, cpabilities, technology and applications for crankshafts.