Kinetic parameters-analysis and prognosis items of the nitriding process (original) (raw)
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Modeling the Nitriding Process of Steels
2012
Nitriding is a thermochemical surface treatment in which nitrogen is transferred from an ammonia atmosphere into steel below the eutectoid temperature[1, 2]. Due to the low solubility of nitrogen in ferrite[3], ε and/or g’ nitrides (Fe2-3(C, N) and Fe4N, respectively) precipitate during the nitriding process. A compound layer and underlying diffusion zone (case) are formed near the steel surface after nitriding. The compound layer (also known as white layer) consists of nitrides, and can greatly improve wear and corrosion resistance[4]. The hardened diffusion zone significantly enhances fatigue endurance. Because nitriding is a low temperature process, it minimizes distortion and deformation of the heat treated parts[2]. The properties of nitrided steels depend on nitriding process parameters. Conventionally, trial and error methods were used to define parameters to meet specifications; an expensive, time consuming, and hard to control method. Therefore, an effective simulation tool...
Parameter Optimization of Nitriding Process Using Chemical Kinetics
Metallurgical and Materials Transactions A, 2016
Using the dynamics of chemical kinetics, an investigation to search for an optimum condition for a gas nitriding process is performed over the solution space spanned by the initial temperature and gas composition of the furnace. For a two-component furnace atmosphere, the results are presented in temporal variations of gas concentrations and the nitrogen coverage on the surface. It seems that the exploitation of the nitriding kinetics can provide important feedback for setting the model-based control algorithms. The present work shows that when the nitrogen gas concentration is not allowed to exceed 6 pct, the N ad coverage can attain maximum values as high as 0.97. The time evolution of the N ad coverage also reveals that, as long as the temperature is above the value where nitrogen poisoning of the surface due to the low-temperature adsorption of excess nitrogen occurs, the initial ammonia content in the furnace atmosphere is much more important in the nitriding process than is the initial temperature.
Designing nitriding processes using simulator of the kinetics of nitrided layer growth
Journal of KONES, 2016
This article presents simulator of the kinetics of nitrided layer growth. Simulator of the kinetics of nitrided layer growth is an application, which supports new method of controlled gas nitriding called ZeroFlow. ZeroFlow method is used for nitriding selected car engine parts, such as crankshafts, camshafts, piston rings, poppet valve springs and discs, piston pins or nozzles for unit injectors. Through the use of simulation models, it is possible to develop the especially dedicated processes with specific parameters for each of this parts, which means that simulator of the kinetics of nitrided layer growth enables forming of nitrided layer with strictly defined properties: required phase structure with thicknesses of particular zones that occurs in it and required hardness distribution. Moreover, using simulation models this layers are obtained in the shortest possible time, which is connected with the lowest energy and gases consumption; therefore, nitriding process using ZeroFl...
The Effects of Modifying the Activity of Nitriding Media by Diluting Ammonia with Nitrogen
Materials, 2021
This paper discusses the issue of the effects of modifying the activity of nitriding media by diluting ammonia with nitrogen and the concomitant variation in the degree of ammonia dissociation on the layer’s growth kinetics and their phase composition. To understand and quantify the effects of the variation in the main parameters that influence the layer growth kinetics, the experimental programming method was used and mathematical models of interactions between influence and kinetics parameters were obtained for two metallic materials: Fe-ARMCO and 34CrAlMo5 nitralloy steel. It was concluded that the nitriding operating temperature and the degree of nitrogen dilution of the ammonia have statistically significant influences on the kinetics of the nitrided layer. In the same context, it was analytically proved and experimentally confirmed that the ammonia degree dissociation from the gaseous ammonia-nitrogen mixture, along with the dilution degree of the medium with nitrogen, signifi...
The Law of Growth of Nitrided Layer in 31CrMoV9 Steel
Acta Physica Polonica A, 2016
The law of growth of nitrided layers produced by gaseous nitriding of 31CrMoV9 alloy steel at different process parameters is described. 31CrMoV9 steel specimens were subjected to nitriding process in ammonia gas at three different temperatures: 510, 550 and 590 • C, and for each temperature four different nitriding times were used. This way twelve specimens were produced. Nitrided specimens were investigated with optical microscopy, electron probe micro-analysis and x-ray diffraction. The nitrogen depth concentration profiles, deduced from electron probe micro-analysis, in conjunction with results of optical microscopy, were used to determine the thickness of the nitrided layers, i.e. the diffusion depth of nitrogen. From the dependence of the nitrided layer thickness on process parameters (temperature and time) it was possible to deduce the law that governs the growth of the nitrided layer for 31CrMoV9 alloy steel. Through this law, then, it is possible to predetermine the layer thickness for every real process parameter in nitriding of 31CrMoV9 steel, which is very important for technological applications.
Modeling of the carburizing and nitriding processes
Computational Materials Science, 2009
The thermo-chemical diffusional process of carburizing and nitriding was modeled in this study. The analysis led to the prediction of surface hardened layers dimensions and hardness in commercial steels. Diffusion model based on Fick's laws was applied to such steels in order to describe the growth kinetics of layers, then the analytical model was employed to perform finite element calculations. In such way it was possible to calculate the carbon and nitrogen concentration in the cross sections of cylindrical samples and the consequent hardness profiles coupled with the residual stresses ones. The results from analytical model and FE calculations were compared with experimental data.
Comparison of experimental curves of alloy steels after gas nitriding
International Journal of Computational and Experimental Science and Engineering, 2021
This study is concerned with experimental curves of: hardness, residual stress and concentration of nitrogen at the precipitation layer at alloy steels after gas nitriding. The purpose of this treatment is that through experimental curves to identify the relationship and causality between hardness, on one side, and on the other, residual stress respectively concentration of nitrogen. Comparing the shape and slope of these curves we can conclude that, concentration of diffused nitrogen on the steel lattice, respectively ferrite, is a cause of increased hardness at the precipitation layer. More to the point, as a result of nitrogen diffusion, residual stress emerge which cause increase of hardness. The intensity and slope of the curves of hardness depends on the intensity and slope of the nitrogen concentration respectively residual stress.
International Journal of Microstructure and Materials Properties, 2007
In the paper is presented results of nitriding of alloy steel without white layer and are described mathematical relationship for continuously change the nitriding potential during process. It is advisable to reduce the value of the nitriding potential as time of process proceeds, in order not to exceed the border concentration of nitrogen in the diffusion zone, which would cause the formation of the ε (Fe 2-3 N) or γ'(Fe 4 N) phases on the steel surface. The highest rise of the diffusion zone occurs when the nitriding potential K N of the atmosphere corresponds to the upper limit of nitrogen concentration in the α zone (diffusion nitrided layer). Further increase of the nitriding potential causes the formation on the steel surface of the ε phase and with the rise in the thickness of the ε zone, there comes about a reduction in the rate of growth of the zone with the α phase. approximately 200 publications and over 15 patents on various aspects of heat treatment, strength properties, tribology and mechanical properties of materials. Currently, he is the Director of Institute of Precision Mechanics in Warsaw, Poland.
Computer simulation of nitrided layers growth for pure iron
Computational Materials Science, 2004
This paper presents results of simulations of diffusional process of nitrogen on pure iron, it makes emphasis on choice of the nitriding potential of NH 3 -H 2 atmosphere on microstructural constitution and growth kinetics of nitrided layers. On the basis of latest investigations about experimental results from nitrogen absorption-isotherms theory, we have showed that is possible to predict both microstructural nature and thicknesses of nitrided layers as well as the nitrogen profile within the formed phases during gas nitriding. Diffusion model based on FickÕs laws was applied to pure iron in order to study the growth kinetics of layers, and we have compared the results from analytical model and the results from nitrogen absorption-isotherms data with the experimental ones.
Application of computational modeling to the kinetics of precipitation of aluminum nitride in steels
2012
In previous works the possibilities and limitations of the application of calculations in the Al-Fe-N system to describe the precipitation of AlN in steel, both in the solid state and during the solidification were discussed and some difficulties related to the extension of these calculations to more complex steel systems, due to limitations in the thermodynamic data were also presented. Presently, the precipitation kinetics of AlN in ferrite (BCC) and austenite (FCC) is discussed. The correct description of the precipitation of AlN in both phases is relevant to: (a) the precipitation at higher temperatures, in the austenite field, that occurs in some steels, (b) the concurrent precipitation of this nitride with the annealing treatment, when the steel is mostly ferritic, used in the processing of some types of deep drawing steels (c) the precipitation of this nitride in some silicon alloyed electric steels at relatively high temperatures, when these steels can have significant fractions of BCC and FCC in their microstructure. The precise knowledge of the precipitation-dissolution behavior of AlN in special in these two latter classes of steels is of great importance to their correct processing. In this work, a computational tool for simulating multiparticle precipitation kinetics of diffusion-controlled processes in multi-component and multi-phase alloy systems is employed in an attempt to describe these precipitation processes. The results are compared with experimental data on precipitation. The assumptions necessary for the application of the multi-particle modeling tool are discussed, agreements and discrepancies are identified and some possible reasons for these are indicated. Furthermore, the impact of the use of different sources of data on steel processing development is discussed and the need for further studies highlighted.