Liquid nitrocarburizing is a well-known surface treatment when it comes to tribological parts and systems. The surface layers formed through liquid nitrocarburizing processing (compound layer and diffusion zone) make it possible to combine the corrosion, wear, and fatigue resistance properties of the treated materials (mainly ferrous alloys, from low-carbon to high-alloy steels and even cast iron) while enhancing their tribological behavior. Based on its worldwide presence, its continuous improvement and high industrial maturity, HEF Groupe’s Liquid Nitrocarburizing is the technology ready for future with its CLIN 4.0 program and it ambitious ECOCLIN program which allow the recycling of wastes from nitriding installations and their transformation into directly reusable consumables. That is why HEF’s liquid nitrocarburizing is proven to be not only an alternative to other surface treatments (such as Chromium plating) on both technical aspects and price competitiveness but also a real solution answering the current environmental challenges. Thanks to the implementation of Life cycle Assessment methods, HEF’s liquid nitrocarburizing continuously improve its sustainability and continuously lower its impacts on global resources, making it an iterative routine to decrease environmental impact on all resources (Energy, water, raw materials,…)

Anti-wear, anti-galling and scratch resistance are well-known properties associated with FNC processes. The marked demand for expansion of the scope of processes in equipment available, has led to the development of tailored FNC process for application to low alloyed steel, and alloyed steel. The process had to be oxygen free, as the equipment is also applied in expanded austenite processes for corrosion resistant alloys. Utilizing our mass flow controller equipped furnaces the tight control of the parameters is possible resulting in high repeatability and a consistent compound layer formation. The process has been applied to a number of different alloys, showing good results for unalloyed steels and steels in quenched and tempered condition.

Gas nitriding and ferritic nitrocarburizing have seen tremendous growth. Today, it continues to accelerate as more uses are being found, especially in the growing electric vehicles (EV) sector. This success is due to the ability to control protective white layers consistent with the needs of an automotive engineer. Steels and cast irons are still the materials of choice for many applications and the nitrided layer is wellknown for its tribological features (some would say even more than three) which include wear resistance, lubricity, and a low coefficient of friction. Corrosion resistance in particular has become an important advantage and depends on white layer formation and quality. The white layer (known as the compound zone) consists of two iron nitrides, epsilon (Fe 2-3 [N]) and gamma prime (Fe 4 N). In addition, the epsilon layer can contain varying amounts of iron carbides and/or iron carbonitrides, Fe 2-3 [C]. This paper will focus mainly on the how’s and why’s of white layer: how to control its composition and properties; and how to minimize it, if required. Just as importantly, some applications of how the EV component engineers have found uses for this important steel treatment are discussed, including brake rotors.

A physics-based software model is being developed to predict the nitriding and ferritic nitrocarburizing (FNC) performance of quenched and tempered steels with tempered martensitic microstructure. The microstructure of the nitrided and FNC steels is comprised of a white compound layer of nitrides (ε and γ’) and carbides below the surface with a hardened diffusion zone (i.e., case) that is rich in nitrogen and carbon. The composition of the compound layer is predicted using computational thermodynamics to develop alloy specific nitriding potential KN and carburizing potential KC phase diagrams. The thickness of the compound layer is predicted using parabolic kinetics. The diffusion in the tempered martensite case is modeled using diffusion with a reaction. Diffusion paths are also developed on these potential diagrams. These model predictions are compared with experimental results.

Secondary phases in the microstructure of cast alloys can greatly increase the complexity of functional film development, particularly when film growth is induced by diffusion. This paper examines the effect of secondary phases on the diffusion behaviors of aluminum, oxygen, and nitrogen, each of which plays an important role in the formation of functional films on cast aluminum and gray cast iron alloys. In general, a fine and evenly distributed phase morphology improves the uniformity of functional films regardless of whether the secondary phase accelerates or delays mass transfer during diffusion.

Controlled nitriding and ferritic nitrocarburizing can significantly improve the corrosion and wear resistance of carbon and low-alloy steels. The framework for maintaining these processes is based on standards, such as AMS 2759/10 and 2759/12A, that specify tolerances for control parameters. This work investigates the impact of admissible deviations in control parameters on the performance of treated alloy samples. The findings of the study demonstrate that although tolerances are allowed, precise control in specific furnace classes is necessary to consistently obtain superior results.

Ferritic-nitrocaburizing is becoming a more popular process to improve a part’s mechanical properties and corrosion resistance on plain carbon and low alloy constructional steels. Advertised as a major contribution to enhanced corrosion resistance, post-oxidation of ferritic-nitrocarburized steel is used to prevent/delay corrosion in service. There are different methods of oxidizing the steel after this heat treatment process. Different trademarked processes claim to provide more corrosion resistance than other similar processes. This paper focuses on the post-oxidation process specifically and compares several of the most common oxygen-containing media used for post-oxidation to determine if corrosion resistance is a function of the oxygen-bearing media or a function of the oxygen percentage during the process. In addition to comparing oxidized samples, rust preventative oil (RPO) is compared as most commercial Ferritic-nitrocarburizing with Post-Oxidation processes involve the application of an RPO after the process as well. Salt-spray testing determined that none of the oxygen-bearing media are significantly better than another when all other variables are held relatively constant. It also shows that parts coated with RPO perform significantly better in salt-spray testing than the same “dry” parts without any additional protective coatings. The salt-spray results also indicated that there is no significant difference in corrosion resistance between parts with and without the post-oxidation process.

Numerous trademarked, standardized or proprietary nitriding and ferritic nitrocarburizing recipes and control methods are used in industrial furnaces. Surface Combustion has developed a new tool to predict the in-process composition of nitriding and ferritic nitrocarburizing atmospheres from these different processes. In addition, the activities and potentials of carbon, nitrogen and oxygen can be found, leading to prediction of the associated equilibrium phase on the part surface. The theory behind the tool and the application of the tool to control nitriding and ferritic nitrocarburizing atmospheres will be discussed. An overview of different equipment designs that can use the tool will also be presented.

To achieve optimal component properties through controlled gas nitriding, a precise approach is required. This method utilizes nitride layers with a defined structure, tailored to the specific stresses each component will encounter. Success relies on three key factors: firstly, understanding the ideal layer structure for a given stress profile, which informs the desired properties of the surface layer. Secondly, in-depth knowledge of material behavior during nitriding, considering both the material itself and the nitriding conditions, is crucial for material selection and parameter optimization. Finally, achieving consistent and predictable results hinges on the precise measurement and control of nitriding conditions, particularly the nitriding potential.

This paper presents a new approach for predicting nitriding and nitrocarburizing results. The model calculates thermodynamic and kinetic effects based on material composition and pre-nitrided conditions. It can simulate up to three-stage recipes with varying temperatures, nitriding potentials, and carburizing potentials while also taking nucleation time into account. The simulation result gives compound layer thickness, precipitation layer, and total diffusion depth and calculates surface hardness, core hardness, and effective case depth.

A study was conducted on a set of H13 steels to enhance their performance as matrices and pins. The steels were austenitized in a high-pressure vacuum furnace at 1015 °C for 180 minutes, followed by nitrogen quenching in a high vacuum (2 bar). Two tempering treatments were applied: one at 540 °C and another at 580 °C, each for 180 minutes, with subsequent nitrogen cooling to room temperature. The nitrocarburizing process was carried out in a liquid bath salt furnace at 580 °C for varying durations of 45, 60, 90, 120, 150, and 180 minutes to assess the impact of treatment time on the quality of the nitrocarburizing layer. Post quenching and tempering, the steels exhibited hardness values ranging from 550 to 570 HV. After nitrocarburizing, the surface hardness increased to between 740 and 810 HV, with a nitrocarburizing layer thickness of less than 14 μm. The microstructural evolution of the compound layer was analyzed using scanning electron microscopy and X-ray diffraction. The characterization revealed a continuous nitrocarburizing ε-Fe 2–3 (C,N) layer. Specimens treated for 45 to 60 minutes demonstrated superior wear performance compared to those treated for 90 to 180 minutes.

This article examines the critical role of process control in nitriding and ferritic nitrocarburizing (FNC) treatments, focusing on the measurement and regulation of nitriding potential (K N ) and carbon activity (K C ). The author demonstrates how modern sensor technology combined with automated programmable control systems can effectively eliminate process variability and ensure consistent, high-quality outcomes. The discussion covers fundamental principles of K N and K C control through proper utilization of sensors, analysis of key input variables, and the relationship between gas ratios, temperature, and time on treatment results. Various monitoring technologies are reviewed, including hydrogen sensors, CO/CO 2 analyzers, oxygen probes, associated technical challenges, and maintenance requirements. By highlighting the importance of precise process parameter control, the article provides practical insights for achieving repeatable, high-quality surface treatments in industrial applications.

Ferritic Nitrocarburizing and nitriding processes are available in various atmosphere blends and a myriad of equipment designs. Atmosphere choices can dictate process capabilities. Equipment design should be reviewed to select the proper choice for the part application. Atmosphere control, nitriding potential calculations, as well as selecting atmospheres and proper heat treat equipment are included.

Die life is an important ingredient in cost of forgings, particularly in hot forgings. A number of surface hardening techniques are used to improve the die wear life. Surface hardening mainly constitutes surface preparation and its treatment to obtain desired properties. In this investigation gaseous ferritic nitrocarburizing was carried out on the DIN 1.2714(55NiCrMov7) steel that is used to manufacture dies for crankshafts and axle beams. The compound layer (White layer), diffuse layer, and core structure were identified using optical microscope. The effect of surface treatment (sand blasting) and process parameters like nitrogen and carbon activities on the formation of different layers during nitrocarburizing are reported and discussed in the paper. The wear rate with respect to sliding distance, sliding velocity and normal load are reported along with the analysis of wear mechanisms.