UDC 66.07 © Jerzy Michalski, Piotr Wach CONTROLLED GAS NITRIDING OF 40HM AND 38HMJ STEEL The article describes the results of investigations of controlled gas nitriding processes of alloyed structural steel grades 40HM and 38HMJ, used for machine components exposed to corrosion, wear and contact fatigue in service. <...> Examples are given of process design enabling the formation of nitrided cases on alloyed steels with an iron nitride compound layer at the surface, designated for fatigue applications and as substrate for duplex processes. <...> Keywords: controlled gas nitriding, nitriding potential, iron nitrides, nitriding atmosphere, diffusion layer INTRODUCTION The article is dedicated to problems connected with porous in its external zone, which facilitates its impregnation with a rust inhibitor; – with a compact layer of iron nitrides and with a and a microstructure composed of + ( + ’precip. lesser proportion of the phase and a composition of + ’precip. , with an external porous zone limited to a minimum ( 2.5 m); – without an iron nitride compound layer. <...> All nitrided cases, taking into account their expected exposure to corrosion, tribological or contact fatigue hazards, should be characterized by high hardness as well as appropriate thickness of the iron nitride layer and its particular zones for corrosion resistance (first two cases), or by an appropriately deep effective case depth, to counteract contact fatigue (third type of case). <...> Cases containing the compound nitride layer should also be characterized by a limited thickness of the latter, on account of the narrow dimensional tolerances of the components for which they are designated. <...> Similarly, the problem of formation of nitrided cases without compound layers on alloyed steels, despite a definite interest in them for fatigue applications, is limited to only very few mentions, these being mainly concentrated on Nitralloys [6-8]. <...> MATERIALS USED For the investigations, two alloyed steels were used, the 40HM and 38HMJ grades, widely used for nitriding. <...> The heat treatment parameters and hardnesses are given in Table. the formation of nitrided cases on structural alloyed steel grades 40HM (4140 per AISI) and 38HMJ (Nitralloy 135M) with the presence of a surface iron nitride layer of varying phase composition or without this layer, designated for application for precision components of machines, equipment and vehicles subjected to corrosion, wear and fatigue in service <...>