Practical nitriding and ferritic nitrocarburizing / David Pye p. cm. Includes bibliographical references and index. 1. Nitriding. 2. Case hardening. 3. Steel— Heat. FERRITIC NITROCARBURIZING is a diffusion process that is a modified form of nitriding, not a form of carburizing. In the process, nitrogen and carbon are. Practical NMR Spectroscopy pdf epub ebooks download free, download Practical Nitriding and Ferritic Nitrocarburizing by David Pye (
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Nitriding and ferritic nitrocarburizing offer unique advantages compared to other surface hardening heat treatments. This book provides a comprehensive guide. FURNACE ATMOSPHERES 3 Nitriding and Nitrocarburizing. 1. Furnace .. It has been the practice to maintain a constant gas composition and gas flow rate. In order to validate the nitriding model and FEM post-process technology, the .. 1 Pye D. Practical Nitriding and Ferritic Nitrocarburizing.
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The download practical nitriding and ferritic nitrocarburizing will find matched to your Kindle framework. A schematic of the specimen and a representative strip as well as the finite element mesh are shown in Figure 2.
Diffusion calculations Figure 3 depicts the evolution of the nitrogen concentration profile versus depth for gas nitriding for S30C steel. It is observed that the nitrogen concentration gradient is steep by magnification of one rectangular. The Figure 3 b shows the comparison between the simulated and experimental data.
Although there are detailed discrepancies, it can be seen that good agreement is achieved between the numerical results and EPMA measured results. The corresponding simulated results are shown in Figure 5. One possible explanation of inconsistent distributions is that a phenomenological equation equation 3 is employed in the present model.
In addition, it is neglected that the replacement of some nitrogen atoms in iron-nitrogen phase by larger carbon atoms. Hardness profiles after nitriding are calculated by an experimental regression equation 5 and are shown in Figure 7 for S30C steel.
The calculated hardness data result in good agreement with the measured ones in the compound layer and substrate. However, there are discrepancies between calculations and observations in critical diffusion layers.
The measured values are greater than the calculated ones. The problem probably lies in the precipitation of fined alloy nitride such as CrN in the diffusion zone, which can increase hardness in diffusion layers significantly. As shown in Figure 4 - 7 , it can be concluded that the FEM model can be employed to predict the nitrogen content and the nitride layer depth in the nitriding process.
Interpolation results To validate the interpolation program, the different FEM mesh size is employed to model the nitriding process of S30C steel. Processing temperature and time are the same as the previous calculations. The FEM model and mesh are shown in Figure 8.
Secondly, the critical value of nitrogen potential, which was directly obtained from the Lehrer diagram of pure iron, may not be accurate for grey cast iron. Furthermore, for the analyzed grey cast iron, the largely distributed graphite may also have some uncertain effects on the nitriding potential value. Nevertheless, the accuracy of the numerical simulations is considered to be acceptable, which is a guarantee of the following effect analysis of nitriding process parameters.
Effect of Nitriding Temperature on the Threshold Value of Nitriding Potential Nitriding temperature is a crucial process parameter which greatly affects the gas nitriding process.
In the study, a threshold value of nitrogen potential is adopted instead of the traditional critical value, which is a significant advantage of the present model in comparison with the existing ones [ 5 — 7 ].
The relationship between the threshold value and temperature is given in Figure 6. As temperature increases, the threshold value decreases significantly. Under the circumstances, the time needed to form the compound layer decreases at higher nitriding temperature. Figure 6: The threshold value of nitrogen potential at different temperatures. In order to investigate the influence of nitrogen potential, numerical simulations were conducted with respect to different nitriding potential values, that is, 0.
Figure 7 presents the calculated nitrogen concentration profile for different nitriding potentials. It can be observed that the nitrogen potential has no effect on the case depth. However, the nitrogen concentration on the workpiece surface is of great difference, which exhibits the highest value for nitriding potential of 3. The analysis results directly demonstrate that the nitriding potential has great effect on the phase composition of compound layer, since it strongly influences the nitrogen concentration on the surface.
Figure 7: The nitrogen concentration distributions with different nitriding potentials. Effect of Nitriding Time To investigate the influence of nitriding time on the case depth, numerical calculations were performed with different nitriding time of 7, 11, 24, and 40 hours.
Figure 8 shows the calculated nitrogen concentration profile for different nitriding time. Because the threshold values of nitriding potential at the nitriding time of 7 and 11 hours are higher than those of the present nitriding potential, no compound layer is formed on the surface.
When nitriding time is 24 and 40 hours, the compound layer is formed and the nitrogen concentration on the workpiece surface turned into the same value. At the same time, the case depth increases as nitriding time increases from 24 to 40 hours.
Figure 8: The nitrogen concentration distributions with different nitriding time. Conclusions Based on the gas nitriding experiments and numerical simulations, the following conclusions can be drawn. The proposed numerical simulations for nitriding layer prediction and analysis can be a reference for practical engineering applications.
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