Ammonia (NH3) is injected into the furnace during heating and breaks apart upon contact with the workpiece. Processing temperature for nitriding will most often be between 975°F and 1050°F (524°C and 566°C), but it can be as low as 650°F (343°C) for certain applications. This can be accomplished due to the fact that the part’s dimensional integrity remains uncompromised from distortion through lower processing temperatures and lack of a quench. There are two general types of nitriding processes: 1. Gas Nitriding is a low temperature case hardening process that is ideal for producing hardened surfaces on pre-heat treated alloy steels such as 4140 and 4340, pre-heat treated tool steels such as H13, and specialty grades such as Nitralloy 135M. The process is also applicable to tool steels such as hot-work, cold-work and mould steels. For gas nitriding, process variables used in this thermochemical treatment are represented by nitrogen, dissociated ammonia (bottled or from a dissociated ammonia generator), and ammonia. In general, nitriding of parts involves a thermal process that provides a tough, corrosion-resistant, and wear-resistant surface with less distortion compared to other case hardening processes due to processing temperature and no need for quenching. Favoured for components that are subjected to heavy loading, nitriding imparts a high surface hardness which promotes high resistance to wear, scuffing, galling and seizure. The gas nitriding temperature is 520°C, lower than the 550°C to 570°C temperature required for the liquid nitriding process. In the process of gas nitriding, nitrogen is introduced into the surface of a solid ferrous alloy by maintaining the metal at a suitable temperature while in contact with a nitrogenous gas, usually ammonia. Case hardening with subsequent hardening operation, Case hardening without subsequent hardening operation, Fluidised bed/salt bath nitriding/nitrocarburising, Precipitation hardening: Stainless steels, Sub-critical annealing / intercritical annealing, Powdermet® Selective surface net shape (SSNS), Anti-Slavery and Human Trafficking Statement. 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 gas and plasma nitrocarburising process takes place best at a temperature of 550 to 580 °C in a nitrogen releasing gas mixture. the second stage). To investigate the time effect on the nitriding process, the kinetics during the gas nitriding process should be investigated. The atmosphere can be controlled to eliminate the white layer or at least reduce it to less than 0.007 mm (0.0003″) for minimal post-nitride machining/grinding. In order to meet specifications for nitriding, a common control variable used to measure the amount of nitriding is KN (nitriding potential). 2). Heat treatment of aluminum, quenching Part III, Get to know IHEA’s new member: DELTA H TECHNOLOGIES, AMS2750 pyrometry revisions tweak a crucial process, Low pressure carburization modeling with carbide formation and dissociation, The cutting edge of thermal processing in a forge environment, Increased Productivity Combining C/C Fixturing and LPC, Performance and Properties of a new Alternative Gear Steel. These process parameters for gas nitriding include (i) furnace temperature, (ii) process control, (iii) time, (iv) gas flow, (v) gas activity control, and (vi) process chamber maintenance etc. The higher the amount of ammonia is present, the lower the amount of dissociation (DA), and the greater the activity of nitrogen on the surface. Slow process taking up to 80 hours, which is more suited to low volumes. If a carbon spending gas is added, the process is called gas nitrocarburising. Although beneficial for some applications, the white layer may not be desired in the process based on manufacturing steps and performance requirements for the finished goods. Nitriding is a popular case hardening technique renowned for the qualities it delivers at relatively low process temperatures. Gas Nitriding. In this case Corr-I-Dur® might be considered as the preferred choice. The salts used also donate carbon to the workpiece surface making salt bath a nitrocarburizing process. Write CSS OR LESS and hit save. The Nitriding process is an established and successful means of … KN is mathematically defined in Equation 1: Many specifications require tight tolerances on the amount of white layer on the surface, which requires a control system to monitor the furnace atmosphere and control the potential of nitrogen that is available to react at the surface of the part. 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. Typical applications include gears, crankshafts, camshafts, cam followers, valve parts, springs, extrusion screws, die-cast tooling, forging dies, aluminium-extrusion dies, injectors and plastic-moulds. ZeroFlow® is a modern, energy-saving and ecological gas nitriding technology used in HRN/VRN type furnaces, allowing for the precise development of the preset composition of the nitrided layer, composed only of alpha, alpha+gamma’ or alpha+gamma’+epsilon … The temperature is held for a length of time proportionate to the case depth requirement. Gas nitriding. Gas nitriding of sintered steels with low density is not recommended. If a carbon spending gas is added, the process is called gas nitrocarburising. Very precise temperature control – this leads to consistent and predictable case depth / hardness / dimensional stability; Full coverage of nitriding - even inside holes and bores; Great for large quantities of small parts (batch style product) Great for alloy steels and low carbon steels; Gas Nitriding Cons For more information, email joakes@supersystems.com or go to www.supersystems.com. All these factors help to reduce distortion during the process… If the atmosphere is using N2 for blending, the volume of gas flowing into the retort of the furnace will be used in our calculation. For alloy steels containing strong nitride-forming elements. Through the addition of carbon, the normal treatment times are shortened in relation to the pure nitriding process. Enhanced Properties of 17-7 PH Stainless Steel, Recent progress in three areas of induction-heating technology. During gas nitriding, steel is heated to a temperature between 500°C and 580°C in the ammonia atmosphere. He has extensive experience working in the heat treating and software/IT industries. For optimum results, the material should be in a hardened and tempered condition prior to gas nitriding. Generally, parts are heat treated to the required mechanical properties, then … Salt bath nitriding —also known as ferritic nitrocarburizing (FNC)— is one of the most popular ways to achieve these results, but it isn’t the only way. Dimensional distortion is minimal in the process and there is a predictable dimensional growth due to the diffused layer. KN is a derived measurement of an atmosphere’s potential to allow for the diffusion of nitrogen into a material — specifically, iron, in this case. When nitriding gears, it is common to see requirements that specify no white layer for the finished part. The original Gas Nitride treatment is a “low temperature” furnace treatment with an atmosphere of Ammonia. Two processes have here procedurally established themselves, namely gas nitriding and plasma nitriding. It is important to note that, unlike in carburizing, the gases used in gas nitriding are extremely pure, and accordingly the calculations used in nitriding process control are stable, and reproducible. In salt bath nitriding the nitrogen donating medium is a nitrogen-containing salt such as cyanide salt. For gas nitriding, the process variables are time, temperature, and atmosphere. Since nitriding changes the chemical composition of the surface of the substrate and the process is carried out at medium temperature, it is classified as a thermo chemical process. The measurement of hydrogen in the exhaust provides enough data to calculate DA or KN. The compound layer on the surface … In general, the investigatory work focused on process temperature. The white layer, also known as the compound layer, is a hard, brittle layer that is formed during nitriding but can be reduced or virtually removed through process control. Final machining is normally not performed post nitriding. Gas Nitriding Pros. Besides temperature and nitriding potential, time is another important process control parameter. Processing temperature for nitriding will most often be between 975°F and 1050°F (524°C and 566°C), but it can be as low as 650°F (343°C) for certain applications. the first stage) and a reduced nitrogen atmosphere to allow for diffusion of the nitrogen into the steel (a.k.a. Gas nitriding is a case hardening process where nitrogen is imparted to workpieces heated in furnaces at around 1,000 degrees Fahrenheit. The Nitriding process is an established and successful means of generating a hard case on a component. The nitriding temperature for all steels is between 923 and 1050°F (495 and 565°C). To control the gases introduced to the furnace, today’s automated controls use feedback from the atmosphere being measured. Gas nitriding is a thermo-chemical process of steel surface hardening. Fatigue strength is increased mainly by the development of surface compressive stresses. Too much ammonia could lead to a significant compound layer, nitride networking, and a brittle surface. A low temperature application is nitriding of spring steels to prolong the fatigue life of springs for automotive use. The furnace atmosphere will be continuously replenished with an atmosphere that provides a potential of nitrogen to diffuse into the steel and form nitrides. Nitriding and Metallurgical Behavior. By controlling and adjusting the process atmosphere, the constitution of the layer can be influenced from thin compound layers for fatigue strength improvement to thick nitrogen and carbon rich compound layers in case of gaseous nitrocarburising and post oxidation if good wear and corrosion resistance is desired. The process temperature range is 500˚C – 530˚C (930˚F – 975˚F). For example, if we measure 30-percent hydrogen in the exhausted atmosphere, that would leave us with 10-percent nitrogen, meaning that 40-percent of the atmosphere is dissociated ammonia. Nitriding is carried out at temperatures below the transformation temperature of alloy steels, so that with proper manufacturing techniques, there is little or no distortion as a result of the process. Process Selection and Quality Control. Several unique features of nitriding are: Nitriding is a (relatively) low-temperature process compared to other case-hardening processes (Fig. Gas nitriding develops a very hard case in a component at relatively low temperature, without the need for quenching. If the residual ammonia is available, the percentage of dissociated ammonia (% DA) can be determined and then analyzed to adjust the flow rates of the process gas. Continuous measurement of the exhaust gas using a hydrogen analyzer provides a method of closed-loop control by varying the process gases to meet a desired control variable setpoint. One of the major problems with gas nitriding is the understanding of surface preparation in terms of surface cleaning. For the process chemically active, hence atomic, nitrogen is needed. Gas Nitriding requires precise control of the treatment process. This article focuses on gas nitriding. At temperatures lower than the nitriding temperature, the homogeneity ranges of the phases in the Fe-N phase diagram (Figure 1.10(a) in Chapter 1, Section 1.6) differ from those at the nitriding temperature.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. This article was co-authored by Matt Specter, also with Super Systems. By adding carbon to the workpiece surface, the process of nitrocarburizing is performed. CTRL + SPACE for auto-complete. Two-stage nitriding processes are used to create proper surface and case conditions. It cannot be over emphasized, how important the … In this case, atmosphere control variables are KN/DA and gas flows, which will facilitate delivery of nitrogen to the processed part. Other special nitriding processes are also used for certain types of stainless steels involving the decomposition of nitrogen gas at high temperatures, but these will not be the focus of this discussion. Referring back to Fig 1, we will deal with the problems usually associated with process problems. Nitriding is a case-hardening process of enriching the solid steel surface with nitrogen at a low temperature, normally in the range of 500-575°C (i.e., below A 1), when the steel is ferritic. Principal reasons for nitriding are: The layer usually consists of two zones – the compound layer (white layer) which can be a cubic or hexagonal nitride and the diffusion layer below with dissolved nitrogen and hard nitride precipitations. The wide range of possible temperatures and case depths, which allow adjustment of different properties of the treated parts, give gas nitriding a broad field of applications. High Temperature Gas Nitriding of stainless steels is a unique case hardening process for cavitation, wear, and pitting resistance. If the process gas decomposition is not monitored, there is a serious risk of nitride networks forming. The diffusion layer contributes improved fatigue strength and works as a support for the hard compound layer. The process temperature for Gas Nitriding is below the transformation temperature of the material. Although the white layer can be machined off, the typical goal would be to reduce or even eliminate the post-nitride machining. The upper temperature was significantly lower than the temperatures employed by Machlet, which ranged from 480 to 980 °C (900 to 1800 °F). The nitriding temperature for all steels is between 495 and 565°C (925 and 1050°F). Gas Nitriding: the part is heated in dry ammonia gas (NH3) at temperatures up to 530°C. 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. Troubleshooting and Prevention of Cracking in Induction Hardening of Steels: Lessons Learned –... Troubleshooting and Prevention of Cracking in Induction Hardening of Steels:... Heat treatment of PM parts by hot isostatic pressing. The compound layer on the surface of the parts is responsible for the major benefit of high resistance to wear, scuffing, galling and seizure. The Gas Nitriding Process. For higher contents of alloying elements and for gas nitriding of stainless steel, plasma nitriding might be considered. Our residual 60-percent would be represented by ammonia. 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. The temperatures selected ranged from 540 to 650 °C (1000 to 1200 °F). For gas nitriding, the process variables are time, temperature, and atmosphere. A normal nitriding depth goes from 0,01 mm up to 0,7mm for which the nitriding time can be up to 100 hours, and can rise the hardness of the steel up to 1200 HV . The assumption would be that only DA gas and ammonia were used as supply gases. Principal reasons for nitriding are: The nitride hardening process integrates into the bulk material, allowing the … In the past, the measurement was discontinuous using a water burette that would provide furnace operators with a method of measuring the percentage of residual ammonia in the atmosphere. High Temperature Gas Nitriding is carried out on stainless steel alloys at temperatures between 1050 and 1200°C (1925F- 2200°F). Similar to a carburizing boost and diffuse method, two-stage nitriding utilizes a nitrogen-rich atmosphere for the buildup of nitrogen concentration in the steel (a.k.a. Gas nitriding is a thermochemical case hardening process used to increase wear resistance, surface hardness and fatigue life by dissolution of nitrogen and hard nitride precipitations. Gas nitriding is a form of steel heat treatment in which one uses heat to diffuse nitrogen-rich gas onto the surface of the metal with the intention of hardening it. In general, all ferrous materials can be gas nitrided up to 5% chromium. Gas Nitriding Process. The importance of superior temperature control has been demonstrated, and is related to the To perform continuous closed-loop control, there must be a method of measurement for the atmosphere. The greater the flow of ammonia, the greater the amount of ammonia measured in the exhaust and the more ammonia to which the parts are exposed. The original Gas Nitride process is a “low temperature” furnace treatment with an atmosphere of Ammonia. The formation of nitrides This method is most commonly used with controlling the white layer thickness. Nitriding is most effective when applied to the range of steels containing nitride-forming elements such as chromium, molybdenum, vanadium and aluminium. The temperature used is typical of all nitrocarburizing processes: 550 to 570 °C. THE PROCESS Nitriding is a surface-hardening heat treatment that introduces nitrogen into the surface of steel while in contact with a nitrogenous gas, usually ammonia. Typical gas nitriding depths are.010”-.020”. The parts will be exposed to a non-oxygen-bearing, nitrogen-rich atmosphere typically produced by a mixture of nitrogen, ammonia, and dissociated ammonia. The success of a nitriding process depends on the ability to meet metallurgical requirements involving microstructures, surface hardness, case hardness, and, in some cases, the part’s appearance. There are different methods of nitriding, including gas nitriding, plasma/ion nitriding, and salt-bath nitriding. is vice president of business development for Super Systems Inc., where he oversees marketing and growth in multiple business channels and helps develop product innovation strategies in conjunction with customer feedback. The process of case hardening via gas nitriding is performed by heating previously hardened parts in a controlled atmosphere to a temperature below the previous tempering temperature. © 2018 Media Solutions inc. All rights reserved. ZeroFlow® – gas nitriding process Modern, energy-saving and ecological gas nitriding process used in HRN/VRN type furnaces. Nitriding is typically carried out in the temperature range of 495° to 565°C, while the steel is in the ferritic condition. The NV process allows the combination of temperature, time and gas composition to be freely controlled.-The lower the nitriding temperature, the smaller the strain and the smoother the surface.-Possible to set a wide range of nitriding temperatures from 400 to 600 degrees C. There is a layer of nitrides formed on the surface. The layer usually consists of two zones – the compound layer (white layer) which can be a cubic or hexagonal nitride and the diffusion layer below with dissolved nitrogen and hard nitride precipitations. The nitrogen dissociates, resulting in atomic nitrogen diffusing into the part surface. By understanding the amount of ammonia dissociated in the exhaust gas, the nitrogen activity on the surface can be deduced. Nitriding is typically carried out at 450 to 520°C and nitrocarburizing at 540 to 580°C. 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