Gas Nitriding and Gas Nitrocarburizing of Steels

Abstract

This article summarizes the terminology for gas reactions, and discusses low-temperature nitriding and nitrocarburizing of stainless steels. It describes the various nitriding processes, namely, high- and low-pressure nitriding, oxynitriding, sulfonitriding, oxysulfonitriding, ferritic nitrocarburizing and austenitic nitrocarburizing. The article includes a discussion on the difficulties in specimen cleaning, importance of furnace purge, uses of pre and post oxidation, depassivation, or activation, and requirements for perfect nucleation in nitriding process. In nitriding, the successful atmosphere control depends on various potentials. The article summarizes the methods of measuring potentials in nitriding and nitrocarburizing, provides useful information on the furnaces used, and the safety precautions to be followed in the nitriding process. It also describes the sample preparation procedures and testing methods to ensure the quality of the sample.

Improvement of mechanical properties of bevel gears by nitrocarburizing

“…This difference in properties, between the surface and the core of the parts, can be accentuated, for most thermochemical treatments, by the subsequent application of thermal treatments, from which the two areas behave differently [8]. Nitrocarburized layers are obtained by the thermochemical treatment of nitrocarburizing, also known as low-temperature carbonitriding [7][8][9][10].…”

“…The purpose of the application of nitrocarburizing is to increase surface hardness, wear resistance, corrosion resistance, hot resistance and binding resistance properties [8], [9].…”

“…After nitrocarburation, mechanical processing is not recommended in order not to destroy the white layer (of combinations). Only a smooth finish or neat polishing can be applied [9].…”

The Effects of Secondary Phases on the Characteristics of Diffusion-Induced Functional Surface Treatments

“…FNC is a thermochemical surface treatment in which nitrogen (and carbon to a lesser extent) is transferred from an ammonia atmosphere into the surface of a workpiece and forms a nitride film (also called compound or white layer) at temperatures within the ferrite and carbide phase region, which is typically between 550 and 580ºC (or 1020 and 1075ºF). One of the notable advantages of the FNC process is that the dissociation of the nitrides in the compound layer is low thus a high nitrogen potential can be established to achieve fast growth of a film thickness for improved productivity and reduced production cost [2]. Figure 2 shows the FNC compound layer of low alloy steel that is mostly uniform in thickness versus an uneven one of a gray iron (brake rotor).…”