Applications for fatigue life of nitriding steel grades. As results of XPS analysis, nitrogen element was detected in the N550 series. Nascent nitrogen is Plasma-assisted processes for surface hardening of stainless steel, Evaluation of the effects of low temperature nitriding on 4-points bending fatigue properties of Ti-6Al-4V alloy, Recent Advances in Structural Integrity Analysis - Proceedings of the International Congress (APCF/SIF-2014), μm). the nitrides formed. In the case of steel, the mechanical properties can be linked via the tensile strength σy to the Vickers hardness H by a Tabor-type law (Tabor, 1951): For nitrided layers (32CrMoV13 steel), Locquet (1998) showed that the a coefficient is close to 0.4. In contrast, the main part of the case at the sample nitrided at 540°C is strongly attacked, due to the chromium depletion of the matrix. Thus, the TiN layer of nitrided TNTZ and Ti–6Al–4 V ELI is severely deformed under cyclic loading, wherein localized fatigue deformation could take place. The most used nitride formers applied in steels are chromium and aluminum. entirely by the flow rate of ammonia. Flis et al. Figure 25. 1. In case of alloyed steels, it has long been known that an increasing content of nitride-forming elements lead to increased surface hardness values and to decreased thicknesses of the diffusion layer (Figures 6 and 8). This initial cycle develops a shallow white layer from This was because the amount of diffused nitrogen was increased with, external and internal surfaces of the injector nozzle is a demanding task. The process involves low temperature (350-450°C) nitriding and/or carburizing, which super-saturates the surface of the metal and expands the lattice. M. Niinomi, in Metals for Biomedical Devices, 2010. The significantly lower chromium concentration within the matrix of X38CrMoV5-1 leads to a more weak interaction. Chromium nitride precipitation is avoided, depending on the combination of time and temperature, and the corrosion resistance remains very good. This will produce the nitrogen-rich compound at the surface. At a medium temperature of 480–600°C (conventional plasma nitriding conditions), the hardening mechanism is due to chromium nitride precipitation following the reaction γN → γ + α + CrN, which leads to a depletion of chromium in solid solution in austenite, and thus the material loses its stainless feature. Experiments with even higher process temperatures of up to 700°C using plasma-nitriding confirm this correlation (Edenhofer and Trenkler, 1980b). Generally, an All workpieces should have good surface smoothness before nitriding. cross sections in Figure 8.6(a)), small ferrite precipitates develop in the substrate adjacent part of the γ′-layer (Figure 8.12(a) [27]). Gas Nitriding is not done on carbon steel except for corrosion … Reproduced from Eilender, W.; Meyer, O. Über die Nitrierung von Eisen und Eisenlegierungen I. May lower the core hardness depending on the prior tempering temperature and the Gas Soft Nitriding (GSN) is a thermo-chemical treatment that involves diffusional additions of both nitrogen and carbon to the surface of ferrous materials at a temperature of 1058F. The process temperature for Gas Nitriding is below the transformation temperature of the … ; Bergner, D. Innere Nitrierung von Eisenwerkstoffen. Pans should be handled with clean gloves. Advantages of nitrogen as a purging mixtures of 15 to 25% ammonia in air, however, are explosive if ignited by a spark. Reproduced from Eysell, F. W. Verfahrensvarianten und Anlagen zu Nitrocarburieren in Gas. The nitrogen dissociates, resulting in atomic nitrogen diffusing into the part surface. In contrast, in the case of the steel C 20, within the lower zone of the compound layer contents of ε-carbonitrides up to only 2% appear. The morphology of the nitrided layers depends on the core microstructure resulting from the transformation of chromium carbides into chromium nitrides. aluminum is the strongest nitride former of the common alloying elements, and that this rate be maintained for 4 to 10 h. Depending on the duration of the total 2 shows the X-ray patterns for the surfaces of the un-nitrided and nitrided specimens. For the expanded nitrogen austenite γN a high supersaturation of up to about 30–34 at.% nitrogen is typical; the supersaturation of the expanded carbon austenite γC is significantly lower with a maximum carbon concentration of 9–15 at.%. Dilution of Figure 6.14 shows, for example, the microstructure of differently nitrided samples of the X6CrNiTi18-10 steel. In accordance with the requirements, the external nitrided layer and the nitrided layer in the opening should consist of a compound layer of thickness 2 ± 05 μm and a diffusion zone with an effective case depth of 0.16–0.18 mm. The bodies of injector nozzles (Figure 12.17) are made from high-speed steel ASP 2005 HSS using a powder metallurgy process. nascent nitrogen for iron and certain other .metallic elements. Plate-shaped nitride areas, starting from the grain boundaries and reaching into the ferrite, are characteristic for this microstructure (23,28). introduction of nitrogen into the retort can be delayed until the nitrided parts have Furthermore, the massive pore formation at longer nitriding duration can lead to an additional reduction in hardness for austenitic nitriding. Gas nitriding is a low temperature (typically 520°C/970°F), low distortion “thermochemical” heat treatment process carried out to enhance the surface properties of finished or near finished ferrous components. Y. Nakamura, ... A. Ueno, in Recent Advances in Structural Integrity Analysis - Proceedings of the International Congress (APCF/SIF-2014), 2014. The effect of higher salt-bath nitrocarburizing temperatures on the corrosion properties (according to the salt spray test, DIN 50021 SS) was investigated by Gräbener and Wahl (1989). It is difficult to make the nitrided layers compatible with the nitride coating: the compound layer must be thicker than 5 μm and defects in the compound layer such as porosity should be kept to a minimum. Flow of the nitriding atmosphere into the blind hole produced problems, and it was therefore difficult to ensure the same chemical composition of the nitriding atmosphere both inside and outside the injector inside the retort of the furnace. Within its diffusion layer, the hardness continuously increases and reaches a maximum value first before the changeover to the compound layer. Vickers hardness HV measured on the top surface and indentation depth d estimated based on the size of indentation mark are shown in this figure. Somers, in Thermochemical Surface Engineering of Steels, 2015. or too rapid or nonuniform heating or cooling. The influence of the carbon content and the heat treatment condition on the height of hardening can be explained by the change of concentration of nitride formers dissolved within the ferrite by means of a differing content of their bonding as carbide. With growing content of chromium, the maximal reachable nitrogen content within the diffusion layer increases. The following steels can be gas nitrided for specific applications: In certain alloys, such as series 4100 and 4300 steels, hardness of the nitrided case as well as on the nitriding temperature and duration. Austenitic salt-bath nitrocarburized (Arcor® N-process) piston rods (hef-durferrit, Durferrit GmbH). This proved that inside the body of the nozzle the nitriding potential, rN, was lower than on the outside. Additional detailed hardness profiles for gas-nitriding at 630°C on different low-alloy steels can be found in Schneider and Hiebler (1998b). Bending fatigue strength of C45N for increased nitrocarburizing temperatures. Reproduced from Spies, H.-J. Gas nitriding is a case-hardening process whereby nitrogen is introduced into the surface of a solid ferrous alloy by holding the metal at a suitable temperature in contact with a nitrogenous gas, usually ammonia. The hardness steeply increases at the diffusion front at approximately 80% of the case hardness. The maximum solubility of nitrogen in ferrite has decreased and the minimum nitrogen contents necessary to stabilise γ′ nitride and, particularly, ε nitride have increased. chrome plating). With the discussion of nitridability, being a function of chemical composition and microstructure of the base material, based on the structural case constitution, it has to be differentiated between the influences of the microstructure of the compound layer and the precipitation process as well as the microstructure of the diffusion layer. Nitrogen compound layer was evident at the nitrided surfaces of the both series, as indicated with arrow marks in Fig. This was because the amount of diffused nitrogen was increased with nitriding temperature. © 2015 Key to Metals AG. Sign in to download full-size … Ammonia requires no additional equipment and is relatively safe when properly handled; Gas nitriding develops a very hard case in a part at relatively low temperature, without the need for quenching. Nitrogen is preferred in place of ammonia Gas nitriding is a case-hardening process whereby nitrogen is introduced into the However, due to the low hardness and wear resistance of ferritic, austenitic and ferritic-austenitic stainless steels, application is limited for components with tribological loads. employed for the first; stage, or the temperature may be increased to from 550 to Single-Stage and Double-Stage Nitriding. The influence of these elements on the nitridability can be comprehended by means of the summation of the amount of substance of the nitride formers. Nickel, Copper, Silicon & Manganese do not give any advantages of Nitriding Nitriding properties. Gas Nitriding at Keighley Laboratories Limited is a low temperature, low distortion thermo-chemical heat treatment carried out in vertical pit furnaces employing state of the art process controls. The amount of distortion resulting from nitriding is except when preoxidation is intentionally included as part of the cycle. This was because thickness of compound layer was increased with nitriding temperature, as shown in Fig. external ammonia dissociator is necessary for obtaining the required higher second-stage Nitriding at 450°C leads to a resistance to pitting corrosion in the tested range. Gas Nitriding is a surface hardening process in which nitrogen is added to the surface of steel using dissociated ammonia as the medium. Initial trials showed that the same nitrided layer might be obtained at a temperature of 500°C. A tempering temperature above 500 °C leads, with rising tempering parameter, to a strong decrease in hardness. It was clarified that nitrogen compound layer was formed on Ti-6Al-4 V alloy nitrided at the temperature higher than 600 °C. the ammonia lessens the discomfort to employees working near the furnace. process time. Comparable results for salt-bath nitrocarburizing of different steel grades in Gräbener and Wahl (1989) show for several grades that the surface hardness is similar for 580 and 630°C process temperature and 90 min. While there is a clear reduction in rotating bending fatigue for the steel 42CrMo4 after nitrocarburizing at 650°C, as compared to ferritic nitrocarburizing at 610 and 580°C (Park and Dengel, 1993), the maximum in fatigue strength for the unalloyed steel C45N is in the range of austenitic nitriding/nitrocarburizing (Figure 9.15) (Pakrasi et al., 1983). process produces a brittle, nitrogen-rich layer known as the white nitride layer at During nitriding with the formation of a compound layer, it can be assumed that the growth of the diffusion layer is not determined by the processes occurring at the interface of the nitriding medium and base material but by the diffusion reaction of nitrogen into the ferritic matrix. 330°C (625°F). In order to limit any potential weakness of the nitride layers, the grain boundary cementite should not form a continuous network, which involves optimization of the processing parameters. Furthermore, only at a temperature of 500°C did the nitride case achieve the required hardness (1200 ± 100 HV). Free chromium in tempered martensite is used to form fine and semi-coherent MN (M = Cr, V, Mo) nitrides. Nitrogen versus Ammonia for Purging. The hexagonal structure of aluminum nitride expected for the equilibrium state strongly differs from the ferritic matrix. The nitriding process is based on the affinity of Due to their low concentration, it is possible to disregard their element-specific effect. 565°C (1025 to 1050°F): however, at either temperature, the rate of dissociation The process is carried out in a sealed retort furnace in a flowing cracked ammonia atmosphere promoting diffusion of nitrogen into the … High Temperature Gas Nitriding is carried out on stainless steel alloys at temperatures between 1050 and 1200°C (1925F- 2200°F). Chromium nitride or chromium carbide leads to strengthened surface layers exhibiting high hardness. An example is shown in Figure 17 in which the phase profiles of γ′-compound layers of the steels C 20 and 20MnCr5, generated at a low nitriding potential, are compared (27). After loading and sealing the furnace at the start XRD and XPS analyses indicate that a nitrogen diffusion layer without nitrogen compounds is formed on the N550 series. Surface hardness of titanium alloy was increased and indentation depth was decreased with nitriding temperature. The effect of nitriding temperature on the corrosion behaviour can be demonstrated by metallographic investigations. H.-J. Although various rates of dissociation can be used successfully in nitriding, it is In austenitic nitriding the hardness profile is significantly influenced by the cooling conditions after nitriding/nitrocarburizing. remaining in the retort with nitrogen to reduce the amount of ammonia that would dissociation. TS USA uses specially formulated nitriding chemistries whereby nitriding can be performed at 510°C (950°F) for certain types of steels, without compromising compound layer depth or quality and without any reduction in process productivity. Reproduced from Schubert, T. Variationsmöglichkeiten des Gefüges der Verbindungsschichten beim kontrollierten Gasnitrieren. The diffusion layer has a distinct lower resistance than the core. Moreover, continued diffusion of nitrogen towards the interior of the workpiece will occur during cooling or annealing, causing additional growth and redistribution of nitrogen. is modified appreciable by core hardness: that is, a decrease in core hardness results Cross-sectional SEM micrographs of the nitrided specimens. The N600 series exhibited the diffraction peaks of substrate and Ti2N, and the diffraction peaks of TiN and Ti2N were evident in the N850 series. From Figure 23 it can be depicted that the hardness increase is directly proportional to the square root of the alloying content (at.%). The first portion of the cycle is accomplished as a normal nitriding cycle at a temperature of about 500 °C (930 °F) with 15 to 30% dissociation of the ammonia (i.e., an atmosphere that contains 70 to 85% ammonia). machining, and so forth. These processes are most commonly used on high-carbon, low-alloy steels. The process is carried out in a sealed retort furnace at temperatures between 490°C and 530°C in a flowing ammonia atmosphere for up to 120 hours Chromium-containing steels can approximate these results if The coating temperature should be chosen lower than or equal to the tempering temperature and subsequent, Thermal Engineering of Steel Alloy Systems. Figure 19.16 illustrates a cross-sectional structure of the chromium nitride coatings formed on preliminarily salt bath nitrided 1045 steel, showing existence of a compound layer underneath the chromium nitride layer, which did not react with chromium during a coating cycle of 8 h at 570°C. The pitting potential Epit of the AISI 316 steel, measured in a 1% NaCl electrolyte, decreased by nitriding at the surface from 213 mV approximately to the pitting potential of the unnitrided AISI 416 (− 40 mV). Figure 20 impressively underlines that the hardness profile within the diffusion layer is not affected by the composition of the reaction gas. Total Materia remains the only tool which will be used for this purpose. For you’re a chance to take a test drive of the Total Materia database, we invite you to join a community of over 150,000 registered users through the Total Materia Free Demo. furnace is heated to a temperature above 150°C (300°F). A nitrocarburizing temperature of 630°C leads to a significant increase in corrosion resistance for most of the investigated steel grades at three different surface conditions (P (polished), QP (quenched and polished), QPQ (quenched – polished – quenched)) compared to standard nitrocarburizing at 580°C. Initial trials showed that the same nitrided layer might be obtained at a temperature of 500°C. Gas Nitriding consists of subjecting machined and heat-treated steel, free from surface decarburization, to the action of a nitrogenous medium, usually ammonia gas, at a temperature of approximately 950°F to 1050°F, creating a very hard surface. The process temperature range is 500˚C – 530˚C (930˚F – 975˚F). The mass transfer at the interface of the reactive medium and metal has no influence on the velocity of the internal nitriding. S–N curves of TNTZ and Ti 64 subjected to solution treatment and nitriding process. (Providing one nitrides at a selected nitride process temperature which is below that of the steels final tempering temperature). Fig. The other strong consideration for the use of the nitriding process for gear heat treatment is that there is no phase change that takes place in the steel while being heat-treated during the nitriding process. All Rights Reserved. contact with a nitrogenous gas, usually ammonia. The intensity of the TiN peak has been found to increase with the nitriding temperature by XRD analysis. Despite the slow decrease in rN, a nitride case meeting the specifications of a compound layer thickness of ~ 2 μm (Figure 12.19), a diffusion zone (~ 0.17 mm) and required surface hardness (1200 ± 100 HV) was achieved (Figure 12.20). Therefore, active screen plasma nitriding technology is a very good solution, as it improves the temperature homogeneity in industrial equipment (± 3°C can be performed). The technique can be applied more easily to steels, which are usually tempered at 550–580°C including hot working die steels, high speed steels, and structural steels. Spies, A. Dalke, in Comprehensive Materials Processing, 2014, The main function of nitriding consists of the formation of nitride-containing cases of a defined structure. Figure 22. This means that coating at temperatures lower than 520°C should be employed to ensure high substrate hardness for cold working steels such as D2. The nitriding temperature for all steels is between 495 and 565°C (925 and 1050°F). To increase wear resistance and antigalling properties. The fine dispersed temper carbides of the quenched and tempered condition avoid the formation of diffusion columnar grains during nitriding, which is characteristic for the normalized microstructure. UltraGlow® Gas Nitriding is a case-hardening process whereby nitrogen is diffused into the surface of a solid ferrous alloy by holding the metal at a suitable temperature in contact with a nitrogenous gas, usually ammonia. Sometimes nitriding layers must be ground to remove compound, to improve the roughness and the precision of dimension of the parts. From these points of view, it follows that by the nitriding process, the plain fatigue strength of TNTZ is not as degraded as compared to that of Ti–6Al4V ELI. The maximum is reached for the normalized and hardened condition. The low hardness values in the compound layer, especially at the surface, can be explained by the large amount of voids and pore channels. surface of a solid ferrous alloy by holding the metal at a suitable temperature in single-stage process. May lower the apparent effective case depth because of the loss of core The phase structure and the growth rate of the compound layer are also to a great extent influenced by the inner carburization (cf. To investigate the time effect on the nitriding process, the kinetics during the gas nitriding process should be investigated. At a polarisation of ± 0 mV, the passive current density increased from 10 to 20 μA/cm2. Figure 23. Un- and low-alloyed steels tend to show slightly higher surface hardness levels while higher alloyed grades tend to show reduced hardness. Slow process taking up to 80 hours, which is more suited to low volumes. Depending on the. Thanks to Total Materia we have issued real "international" specs for purchase of steels in foreign countries. Heat treatment diagrams covering hardenability, hardness tempering, TTT and CCT can all be found in the standard dataset. By characterizing the nitridability through thickness and microstructure of the nitrided case as well as the level, depth, and profile of the strengthening, also the essential parameters of the load behavior of the case are comprised. At higher process temperatures lower hardness values were observed. temperature. As can be seen, in the ZeroFlow process the consumption of NH3 and exhaust gas emissions to the environment are 1.5 times lower than in the Floe process. With higher nitriding temperatures (520 and 550°C) a compound layer was created only on the external surface of the nozzles, while the surface inside the blind cavity was without a compound layer. Distortion and Dimensional Changes. These facts allow a summarized explanation of the influences on the formation of the diffusion layer. It is common practice to remove the ammonia Dissertation, Bergakademie, Freiberg, 1986. Mo reduces the risk of embitterment at Nitriding temperature. Figure 25. The intensity of the TiN peak has been found to increase with the, Classical nitriding of heat treatable steel, HV if either the tempering temperature is too close to the, Corrosion behaviour of nitrided, nitrocarburised and carburised steels, Academic research, not really used for high loading parts, For high loadings and corrosion resistance. The fatigue strengths of TNTZ and Ti–6Al–4 V ELI are lowered by nitriding. Nitriding steels mostly contain small amounts of vanadium and molybdenum for improving the temper resistance and for decreasing the sensitivity against tempering embrittlement. The precipitation of chromium nitrides and carbides is a diffusion controlled process, so it can be suppressed by a sufficiently low temperature and duration of treatment; thus the corrosion resistance is maintained. Total Materia has allowed us to solve in a definite way all problems we had for the search of alternate materials in foreign countries. Quenching is not required for the production of a hard case. otherwise be released into the immediate area when the load is removed. Consequently, the increase; cost of the nitriding In ferritic nitriding the hardness profile depends mainly on the alloying element content (especially of Al, Cr, V, etc.) For unalloyed steels, the decrease of the nitrogen diffusion rate, being a result of the carbon dissolved within the ferrite and the impediment of the diffusion with growing amount of pearlite, lead to a decrease of the nitriding depth with increasing carbon content (Figure 21) (29). For the comparison of materials, it is necessary to reduce the variety of possible nitriding conditions by setting limits with selected standard conditions. temperature. gas include its safety, ease of handling, and ease of control. Iron substitution within MN nitrides (Ginter et al., 2006) or local lattice strain at the precipitate–matrix interface increases nitrogen solubility and can explain the observed excess of nitrogen (Somers et al., 1989). double-stage process may be employed when nitriding with anhydrous ammonia. total nitriding cycle time. as well as on the, The thermo-reactive deposition and diffusion process for coating steels to improve wear resistance, Workpieces made of steels should be hardened and preliminarily nitrided to ensure good load-bearing properties. 1 shows the cross-sectional SEM micrographs of the (a) N600 and (b) N850 series etched with Kroll’s solution, respectively. Ferritic-pearlitic microstructures γ′-nitrides and ε-carbonitrides can appear side by side at the lower compound layer area due to the transformation of pearlite grains in ε-carbonitrides (Figure 19). M.A.J. At a dissociation rate of 75 to 80%, however, it which diffusion of nitrogen into the main case structure proceeds. 6100, 8600, 8700, and 9800 series, Hot-work die steels containing 5% chromium such as H11, H12, and H13, Low-carbon, chromium-containing low-alloy steels of the 3300, 8600 and 9300 series, Air-hardening tool steels such as A-2, A-6, D-2, D-3 and S-7, High-speed tool steels such as M-2 and M-4, Nitronic stainless steels such as 30, 40,50 and 60, Ferritic and martensitic stainless steels of the 400 and 500 series, Austenitic stainless steels of the 200 and 300 series. An example is shown in Figure 18. With increasing hardness, compressive residual stresses are generated due to phase transformation and/or precipitation. Based on the definition of the nitridability, the evaluation and the specification of the structure of nitrided cases have to be examined as a unit. Figure 12.18. production of a potentially explosive mixture. A typical purging cycle using anhydrous ammonia follows: Purging is employed also at the conclusion of the nitriding cycle when the furnace Gas Nitriding requires … The various process parameters have the following effects: Figure 16.9. Consequently, in order to obtain maximum case hardness, The choice of grinding parameters must be optimized in order to have compressive residual stress (Brinksmeier et al., 1982) and avoid grinding burns (Shah, 1974). A microstructure with a fine distribution of nitrides is generated. That is why this treatment, designated by the term ‘low temperature treatment’, is being applied to a greater extent. however, requires additional equipment, including piping. Heat treatment diagrams are available for a huge number of materials in the Total Materia database. 8.37). Figure 12.20. Gas nitriding is a case-hardening process whereby nitrogen is introduced into the surface of a solid ferrous alloy by holding the metal at a suitable temperature in contact with a nitrogenous gas, usually ammonia. and furnace components, and, when ammonia is used as the purging atmosphere, avoids The Vickers hardness near the specimen surface of nitrided Ti–6Al–4 V ELI has been reported to be greater than that of TNTZ. in the second stage is increased to 65 to 80% (preferably, 75 to 80%). The fatigue crack seems to be more easily initiated when the brittle nitrided layer (TiN or Ti2N), is thicker as is slightly the case with nitrided Ti–6Al–4 V ELI compared to nitrided TNTZ. For high carbon steel, duplex treatments can be performed such as salt or gas nitriding followed by plasma nitriding in order to have better control of the nitrogen content (Streit and Trojahn, 2002). Therefore, its nucleation is highly impeded (19,30). J.P. Lebrun, in Thermochemical Surface Engineering of Steels, 2015. Figure 9.15. These transformations will also occur during annealing of the compound layer at a temperature below the nitriding temperature, for example during post-oxidation. Hardness profiles of a low-carbon steel after gas-nitriding at 680°C. Increase of hardness as a function of the concentration of nitride-forming elements, gas oxinitrided; Cr(Mo,V,W)-steels (0.4% C) and Cr(Mo,V)-steels (0.05% C): 550 °C/32 h; Cr,Al-steels (0.2% C): 570 °C/48 h. For chromium steels the concentration in at.% can be replaced as a first approximation by the mass percent (wt.%) due to the slight differences between the relative atomic mass of iron and chromium. Reproduced from Spies, H.-J. As a consequence the following phase transformations will occur during relatively slow cooling: iron nitrides γ′-Fe4N and α″-Fe16N2 develop in ferrite [25,26] (cf. leaving no heavy surface contaminant or residue. Either a single- or a In the X-ray diffractogram, it is possible to see the diffraction lines of CrN associated with ferrite α, indicating a decomposition γN → γ + CrN + α; this structure gives poor corrosion resistance. As mentioned in Section 12.14.1, there are remarkable differences between the kinetics of nitride precipitations within iron–chromium and iron–aluminum alloys. The initial carbides (M23C6, M7C3) are transformed to the MN nitrides and the M3C (M = Cr, Fe) cementite during the nitrogen diffusion. quenching to form martensite. The transformed austenite layer has its highest hardness of over 650 HV0.05 just below the compound layer in the area of the highest nitrogen content due to a bainitic transformation (possibly still with some retained austenite). The variations of: temperature, inflow rate of NH3 into the retort and ammonia content and nitriding potential rN in a retort during nitriding of injector body. aluminum-containing steels (0.85 to 1.50% Al) yield the best nitriding results in terms Final machining is normally not performed post nitriding. The difference can be explained by the fact that the unalloyed grade C45N hardly forms nitride precipitates during nitriding/nitrocarburizing and therefore develops neither a substantial hardness profile nor significant compressive stresses below the compound layer. The high-temperature gas reactor uses a version of DoE's TRISO fuel that contains a uranium nitride fuel kernel for higher performance. All available heat treatment information will then be displayed for the chosen material.
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