Machining results are extremely influenced by the steel hardness. In rough machining, the best performance corresponds to the steel grade 20NiCrMo2 and the worst to the 40CrMoBi4 steel, being the machinability inversely proportional to the steel hardness in supply condition.

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On the other hand, in the finishing machining operations the result is the opposite, the steel grade 40CrMoBi4 showing the lowest tool wear and the 20NiCrMo2 the highest one.

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Annealed steel grades show lower machinability cost in rough machining operations and higher cost in hard machining compared to the steel grades used for nitriding and nitrocarburizing processes.