Ionic nitriding in cathodic cage of AISI 420 martensitic stainless steel

Cylindrical shape samples of AISI 420 martensitic stainless steel were nitrided by cathodic cage plasma nitriding technique at temperatures of 623, 673 and 773 K for 5 h. In this technique the samples are placed on an insulating plate inside a cage that shields the cathodic potential. A systematic study was made to test the efficiency of this technique, when compared with conventional ionic nitriding, related to the elimination of defects such as edge effect. The process present a bigger nitriding rate and the samples nitrided using this new technique displayed crystalline phases and hardness comparable with those obtained using conventional ionic nitriding. Moreover, it was possible to eliminate completely the erosion rings often present in conventionally ionic nitrided samples due to edger effects.