Pulsed-plasma nitriding of a niobium–alloyed PM tool steel

The aim of this work is to describe the processes during plasma nitriding of Nb-containing, powder metallurgy prepared (PM) tool steel. PM steel was studied containing 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb and 1.0% W, produced by melt atomization and hot isostatic pressing. The hardened and tempered steel was plasma nitrided at temperatures ranging from 470 to 530 °C. The nitriding time was 30–180 min. Optical microscopy, electron microscopy, XRD, EDS, WDS and hardness measurements were used to study the steelʹs properties, microstructure, phases and chemical composition. The nitriding temperature of 470 °C was found to be unsuitable for practical use because the layers prepared at this temperature were non-uniform. The compound layer formed by M2,3(C,N) and M4N was found after nitriding at temperatures of 500 and 530 °C for at least 60 min. The effect of niobium on the formation of this layer was studied.