The excess nitrides diffuse into the gear material during the heat-treating cycle, leaving a white layer on the top surface. However, this is at the expanse of increasing its ECD. 0.002-0.010. A typical Carbonitriding process cycle using the FC35 25. Also laboratory tests have been carried out to investigate the conduct of the material under adhesive wear as well as under corrosive attacks. There are fundamental differences between the two processes. Nitriding. The nitrided part can be renitrided to meet the case depth requirement. Total Case Depth (inches) 1020, 1045, Cast Iron. NCT recommends products to be stress relieved at 1050 Fahrenheit. Fig. All Rights Reserved. Space out the parts to be treated to enable the passage of the plasma. Total Case Depth (inches) 1020, 1045, Cast Iron. Using simulated gear samples in the form of V‐notch bars, the nitrided case depth was determined to be quite uniform around the entirety of the notch geometry. 2 shows a 400 series stainless steel alloy that has been nitrided to improve its wear and fatigue properties. Plasma nitriding is a smart choice whenever parts are required to have both nitrided and soft areas. Unlike other hardening methods, plasma nitriding can deliver precisely repeatable cycles providing uniform case depths. Their ECD is notably higher then the samples that have prior been treated with high nitrogen. Under certain conditions a nitriding depth of up to 65 µm and a microhardness of up to 1210 HV0,1 was achieved. Measurement of the nitrogen depth profile in the plasma nitriding process is a key factor in the evaluation of this, the thermochemical process and the performance of nitrided components [1]. This layer is also a good choice when a plating or surface coating will be applied to the product after processing. Plasma nitriding can also clean the surface by sputtering. Considerations when choosing your case depth. It is important to stress relieve your product prior to plasma nitride processing. The conclusions drawn from the above experiment are as follow: Understand the parts to be treated and define the place not to be nitrided. Plasma Nitrided Surface Hardness. Large gear for an industrial application nitrided to a 0.040" case depth. This is especially noticeable on complex ge- ometries where gas nitriding case depths can be non-uniform. Copyright © 2006 TPP Information Centre. Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. Gear hub, bore and web faces have been masked to prevent nitriding to allow for post heat treatment machining. In order for a subsequent plating or coating to adhere to the substrate the white layer must be removed. 1 shows the expected hardness for the various alloys at different case depths. However, times for gas nitriding can be quire long, that is, from 10 to 130 h depending on the application, and the case depths are relatively shallow, usually less than 0.5 mm. A single cycle nitriding heat treat run is generally 48hours at temperature and results in a case depth of 0.015 – 0.020″. With a wide range of process control and optimization possibilities, plasma nitriding makes it possible to achieve stringent requirements not capable by gas or salt bath nitriding. It is evident that the effective case depth is increased by increasing the treatment temperature and time. Nitriding Effect - Properties of Nitrided Layers A surface exposed to a nitriding medium will generally form two distinct layers. If the glow is not uniform, pressure should be increase. If the process produces a hard case depth, the plasma process can compete with it. The plasma process competes well with gas nitriding, carburizing and salt bath processes. Plasma nitriding allows faster nitriding times, and the quickly attained surface saturation of the plasma process results in faster diffusion. The surface should Reworking improves the hardness profile and increases the ECD. Particularly when applied to higher alloyed steels, plasma nitriding imparts a high surface hardness which promotes high resistance to wear, scuffing, galling and seizure. Plasma nitriding is a smart choice whenever parts are required to have both nitrided and soft areas. A deep nitride layer on a thin walled section will cause the job part to become brittle and fracture in service. 550 – 850. 2 shows a 400 series stainless steel alloy that has been plasma nitrided. After rework using plasma nitrocarburisation, the surface was noted to have became harder. The compound layer generally ranges from 0.0002" to 0.0012". Fretting wear is a good example of a wear mode which would require a lubricant to be held at the interface. The Plasma nitriding process produces a hard outer skin on the material being nitrided. Fatigue strength is increased mainly by the development of surface compressive stresses. Even higher surface hardness can be developed than by carburising, although the case depths obtainable are less. In another words, a specific surface hardness would be achieved for each set of parameters no regardless of its previous treatment. However, times for gas nitriding can be quire long, that is, from 10 to 130 h depending on the application, and the case depths are relatively shallow, usually less than 0.5 mm. Doing so will deprive the top surface of a nitriding layer. However, if the top surface was to be nitrided, the ‘Sandwich’ effect is not recommended. This is particularly useful when the product is subjected to impact or severe loading. The outside layer is called a compound layer (or white layer) and its thickness generally falls between zero and 0.001″ (25 µm). Apply a metallic masking or a protective coating of paint, With low pressure, the thickness of the glow is high, so that the plasma cannot penetrate in deep holes, With high pressure, the effect is a small glow, that follows the contour, Job should always be kept under watch through the potholes, and pressure should be adjusted accordingly. The "white layer" or compound layer is thicker than the gamma prime and will increase in thickness as the process time is increased. How It Works The possibility of generating a compound layer free diffusion layer is often used in plasma nitriding prior to DLC coating. The epsilon plasma nitride layer is not as ductile as the gamma prime but provides a higher degree of wear and a lower friction coefficient. 14-8. Reworking has the capability to bring the surface hardness down if it was too high. A finish between 15 and 30 RMS is recommend for plasma nitrided products. 3 shows how the metallurgical properties of the nitride layer and the white layer can be controlled in the plasma nitriding process by adjusting the process gas composition. The slope is more gradual for low alloy steels and very sharp for highly alloyed steels. 0.025 – 0.70. The passive layer of the stainless steel is removed through sputtering. 105 York Street This process is done in a vacuum vessel at low temperatures (750°-1040°F or 400°-560°C) and can be applied to any ferrous metal. Considerations when choosing your case depth. Plasma nitriding (H2+N2) least affects the surface finish of the product. Plasma nitriding allows faster nitriding times, and the quickly attained surface saturation of the plasma process results in faster diffusion. Plasma nitriding can also clean the surface by sputtering. EN40, 722M24, 31CrMoV9. +0.4 -0.5 effective case depth Pulse plasma nitriding systems deliver more uniform case-hardening and increased speed of processing when treating high wear industrial components. The gamma prime is more ductile than the epsilon layer. Recommended Core Hardness. Ionitriding® (Ion Nitriding or Plasma Nitriding) Is a method of surface hardening producing nitrided cases, using the glow discharge technology to generate nitrogen ions to the surface of a metallic part for diffusion. Gear measures 12' in diameter by 12' tall and weighs approximately 24,000 pounds. 12/11/20, 12:21 PM | Processing & Handling, Design & Development | Power PR. EN41, 905M39, Nitralloy. The graph in Fig. Fig. A low alloy steel such as 4140 would have a lower overall surface hardness and a gradual transition zone between the nitrided layer and the core material; however, the overall penetration of the nitride layer would be deeper. Workpieces made of ferrous materials exhibit better wear, strength and corrosion properties after nitriding. Plasma Nitrided Surface Hardness. Plasma nitriding, on the other hand, offers a greater control on the thickness of the compound layer, which means greater control on growth. The low alloy steel will provide a deeper case depth but a lower overall hardness. Due to the difficulties in obtaining optimized process parameters in industry [2], great attention is paid to develop appropriate analytical models. Carburizing times for the same case depth are shorter. Job parts with thin walled section are not recommended for nitriding treatment, unless a shallow case depth is specified. EN3A, 070M20, 080M40, Mild Steels. In contrast to case hardening, nitriding involves the surface layer being enriched with nitrogen rather than carbon. 0.025 – 0.50 750 – 1000. The hardness achieved on the surface decreases with depth until the core hardness is reached. This process is sometimes referred to as ion nitrocarburizing or plasma ferritic nitrocarburizing (FNC). Underneath the … 750 – 1100. Samples that have previously under gone low nitrogen plasma nitrocarburising treatment are more susceptible to reworking using low nitrogen plasma nitrocarburising. The most common applications are … 1 shows the expected hardness for the various alloys at different case depths. An experiment on renitridng CA6N was carried out and the results are given in Tables 1-3 and Figs.1-5. The thicker compound layer also provides a higher degree of corrosion resistance. Gas nitriding is normally used for parts that require a case-depth between 0.2 and 0.7 mm. 52-58. Nitriding may be done in electric-heating furnaces. The depth of nitriding hardness may reach 500 μm with maximum hardness levels of > 1000 HV. Since warming up and cooling down occurs slowly and the basic structure does not undergo any transfor- mation or change in volume, there is only a low risk of deformation. A uniform glow discharge that envelops the entire surface achieves a consis- tent hardness and case depth. The "white layer" or compound layer will only build to between 0.0001 and 0.0004". A deep nitride layer can cause a thin walled section to become brittle and fracture in service.  Its carried out in a salt bath or in a furnace gas atmosphere. The nitride case provides a hard, wear resistant surface without spalling, galling or brittleness seen in conventional nitriding. This low temperature, low distortion process is used widely throughout the automotive, aerospace and general engineering sectors. Typical Plasma Nitriding Results. The case depth may be as high as 900 µm. With both layers an increase in process temperature will increase the thickness of the compound zone. The hardness achieved on the surface decreases with depth until the core hardness is reached. The overall appearance of a nitrided product is a chalky gray color. The hardness of this zone varies from the surface to the core and its case depth depends largely on the type of gear steel, the cycle time of nitriding, and the temperature. Its thickness is usually below 13 µm Thin walled sections should be avoided or a shallow case depth specified. These can be increased considerably through plasma nitriding. In some cases, parts may be produced with a black surface. The high alloy content of the stainless steel creates a high surface hardness and a sharp transition zone between the nitrided surface and the core material. The plasma can be used to treat all high-chrome-content, ferritic, austenitic and duplex steels. Like case hardening, nitriding is one of the thermochemical diffusion treatment processes. In harsh, corrosive, and abrasive environments common to oilfield drilling and exploration, More Headlines. 0.025 – 0.70. Nitriding is most commonly carried out on prehardened alloy steels like 4140, 4340 or Nitralloy 135M. Plasma-Nitriding Nitriding with compound layer (DIN 1.7131) (diffusion zone / compound layer) Nitriding without compound layer (DIN 1.4122) (diffusion zone) 100 μm 50 μm 100 μm Representation of the nitride case depth Further advantages of plasma-nitriding technique are: • Increase of resistance against abrasive wear • Decrease of adhesion Wind River and Curtiss-Wright Collaborate on … Products with a surface finish higher than 30 RMS may exhibit premature wear due to the surface roughness and parts under 15 RMS will need to polished after processing. The advantages of gaseous nitriding processes can be surpassed by plasma nitriding. This process is an excellent choice when the brittle white layer may crack and spall from impact or heavy loading. The surface should be cleaned by sand blasting prior to renitriding. 350 - 500. The thicker compound layer is also more porous than the zone produced during the gamma prime cycle and is an excellent choice you desire to hold a lubricant at the wear interface. Case Depth mm. In addition to this there is an infinite control on the process gas ratios and is not reliant on the decomposition of ammonia to a fixed decomposition. Pit furnaces are commonly used for large scale nitriding, whereas muffle furnaces are used for small scale nitriding. The gap must be at least 15mm, depending on different furnace. A finish between 15 and 30 RMS is recommended for plasma nitriding products. Case hardened surfaces are measured from the surface down to a hardness of (regularly) 50 HRc, so far correct (for Case hardening CDH) Nitriding depth is calculated from the opposite side. Product with a surface finish higher than 30 RMS may exhibit premature wear due to the surface roughness and parts under 15 RMS will need to be polish after … Sample that has previously under gone plasma nitriding is not very susceptible to reworking using plasma nitrocarburising. Along with the derivative nitrocarburizing process, nitriding often is used in the manufacture of aircraft, bearings, automotive components, textile machin-ery, and turbine generation systems. Plasma nitriding normally occurs at temperatures of 450 to 600 °C in a vacuum with the aid of plasma generated by a glow discharge on the workpiece surface. Parts can be surpassed by plasma nitriding is a lower-temperature heat treatment machining degree of corrosion resistance this process sometimes. Depths obtainable are less reworking has the capability to bring the surface was to be held the... Table 2 based on 400 HV steel effecting an increase in process temperature will increase the thickness of stainless! 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