Optimization of the ion-plasma nitriding of structural steel

V R Baraz,E A Ishina,E A Yurchenkov

doi:10.1088/1757-899x/966/1/012057

Abstract

Mathematical planning was used in order to determine the optimal mode for ion nitriding the structural steel 0.38C–2Cr–2Ni–Mo. This was justified by the requirement to preserve strictly limited functional parameters obtained as a result of diffusion saturation: hardness in the range of 450–650 HV in a layer 0.15–0.40 mm deep. According to of X-ray diffraction analysis in addition to reflections from the matrix phase (alloyed ferrite α-Fe), the reflexes of nitride compounds are recorded, namely, the γ′-phase with a FCC lattice (Fe4N) and the ε-phase with a HCP lattice (Fe3N) with a high nitrogen content. An analytical expression in the form of a linear function for the studied optimization parameters (microhardness and depth of nitration) was obtained by implementing factor planning and regression processing of the obtained data. This made it possible to assess the degree and direction of influence of the investigated factors on the optimization parameters under study.

Highlights

As is well known, ion-plasma nitriding is an effective form of diffusive nitrogen saturation for the surface layers of processed products [1,2,3]
The purpose of this work was to study changes in the hardness and depth of the nitration during nitrogen saturation of 0.38С–2Cr–2Ni–Mo steel in an ion-plasma nitriding unit, as well as the selection of optimal nitriding parameters according to specified criteria, namely certain ranges of the diffusion layer’s hardness and depth
To find the optimal regime for nitriding this steel in a glow discharge, experimental research based on mathematical planning was carried out

Summary

Introduction

Ion-plasma nitriding is an effective form of diffusive nitrogen saturation for the surface layers of processed products [1,2,3]. It is carried out in a glow discharge excited on a cathode’s surface in a nitrogen-containing gaseous medium (ammonia, nitrogen, etc.) under conditions of deep rarefaction. Nitrogen ions enter the high-tension zone, accelerate to high speeds, and, colliding with the cathode, are embedded in its surface. The high kinetic energy possessed by the nitrogen ions is converted into thermal energy. The cathode is heated to a temperature of 450–600 °C in a short period of time (approximately 15–30 minutes), at which point diffusion occurs

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