Gas carburizing with quenching is one of the most useful heat treatment processes for steel parts. However, after quenching distortion is still occurs. The nitriding and nitrocarburizing are the surface hardening heat treatment methods with low distortion, but these methods require the long treating time to obtain a thick hardened layer. Austenitic nitriding and quenching (ANQ) solves these problems. In ANQ process, nitrogen is infiltrated into the steel parts in austenite phase, and they are quenched to harden. The ANQ process can also be applied to cheap low carbon steel such as the Cold Rolled Carbon Steel Sheet. In this study, the effect of ANQ on mechanical properties was examined. For infiltrating the nitrogen into the steel parts, the steel parts were heating to 750°C or higher in an ammonia atmosphere and heating to 750°C or higher in a nitrogen glow discharge. After the ANQ process, hardness profiles, structure, nitrogen and carbon concentration profiles were observed. Also, distortion, tribological properties, impact value and fatigue strength were examined. The effective case depth, which is treated by ANQ, is larger than the effective case depth of gas nitrocarburizing for same period of time. Distortion of ANQ is much smaller than that of gas carbonitriding, and it is almost equal with that of gas nitrocarburizing. The seizure load is same as with other surface hardening heat treatment processes. The wear loss of ANQ is a lower, in the amount of about 1/2 that of the carbonitrided specimen and 1/3 that of the gas nitrocarburized specimen. The ANQ is an effective heat treatment process for parts which require wear resistance. The tempering softening resistance is improved by nitrogen infiltration. ANQ also improves the impact value and fatigue strength.

Surface modification involves the chemical or physical impartation of enhanced functionality to the surface of materials, and has become increasingly important in recent years. Nitriding is a surface modification method that hardens the surface of metallic materials by causing nitrogen to permeate and diffuse into the surface to form various nitrides or by supersaturating a solid solution of nitrogen in the metal. This is effective in improving the hardness, corrosion resistance, and wear resistance. Plasma nitriding, a type of nitriding process, has several advantages, such as low energy consumption, short processing time, and low environmental impact. In contrast, the conventional plasma nitriding method forms plasma on the surface of the treated material, which may cause phenomena that lead to defects in the treated material. Therefore, the directcurrent plasma nitriding with screen (S-DCPN) method reduces these problems because plasma is formed not only on the treated material but also on the surface of the screen. Stainless steel has excellent corrosion resistance; however, nitriding treatment above a certain temperature reduces the corrosion resistance owing to chromium nitride precipitation. In this study, the S-DCPN treatment, a type of plasma nitriding method, was applied to form a thick nitrided layer without reducing corrosion resistance. The S-DCPN treatment was performed using ferritic stainless steel SUS430 as the sample and austenitic stainless steel SUS304 as the screen material at treatment temperatures of 633 and 653 K, treatment times of 5 and 15 h, a gas pressure of 200 Pa, and a gas composition of 75% N 2 - 25% H 2 . Consequently, the α N phase with supersaturated nitrogen solid solution was identified under all conditions. Nitrogen diffusion and hardness increased with increasing treatment temperature and time. In the corrosion tests, corrosion resistance improved under all conditions.

The Lehrer diagram often serves as a guide for selecting gas mixtures for nitriding alloy steels, but it is only accurate for ammonia gas nitriding processes when hydrogen is used as the diluting gas. This paper presents the results of a study showing that the use of pure nitrogen as a diluent has a marked effect on the phase boundary lines of the standard Lehrer diagram, essentially shifting them to the left. The paper also includes examples showing where the use of nitrogen is advantageous and where it is not.

For decades, industrial gas providers have tried to develop a compelling reason for metal thermal processing shops to switch from the dominant dissociated ammonia atmosphere technology to hydrogen/nitrogen blended gas “synthetic” atmospheres. Two problems interfered with this business approach – ammonia for dissociation was generally very cheap, and the alternatives that the industrial gas companies proposed did not solve all of the issues faced by the thermal processors. The offerings of the industrial gas providers failed to displace dissociated ammonia in most installations because the cost of the atmosphere was high as compared with dissociated ammonia, and the solution proposed by the industrial gas providers simply replaced one highly hazardous gas delivery and storage problem – ammonia – with another – hydrogen. Users and their local Authorities Having Jurisdiction did not find the tradeoff attractive to swap ammonia storage for hydrogen storage. Onsite hydrogen generation technology makes it possible to replace delivered, stored hazardous ammonia with “zero-inventory” onsite generated hydrogen and stored or generated nitrogen. This approach eliminates the hazardous material objection to ammonia replacement for thermal processors and makes it much more interesting to consider replacement of dissociated ammonia with hydrogen/nitrogen. While economic issues remain, a look at total costs of operation makes hydrogen/nitrogen generation a viable and growing solution for thermal processors. This paper reviews results for several customers that transitioned successfully from dissociated ammonia to hydrogen/nitrogen. The discussion addresses costs, regulatory compliance, and process results.

A software simulation tool, CarbonitrideTool, has been developed by Center for Heat Treatment Excellence (CHTE) to predict the Nitrogen and Carbon concentration profiles in selected steels. In this paper, the introduction of the software will be presented. In addition, enhancements have been made to improve the CarbonitrideTool. The diffusion of nitrogen increases the amount of retained Austenite (RA) by changing the Ms temperature. In this paper, the modification has been made to calculate the RA fraction. The empirical prediction of microhardness profile will also be presented. The results of verification experiments will be presented and discussed.

Nitrogen (N 2 ) atmospheres with different, not always optimized levels of reducing and carburizing gases are often used to prevent decarburizing and oxidation of steel parts during annealing in continuous furnaces. The type and concentration of these additives in N 2 should correlate to the extent of air leakage into furnace, entrainment of air with loaded parts, steel composition, and complex reaction kinetics in the gradients of oxygen (O 2 ) and temperature existing between the entrance and hot zones of the furnace. This study explores the effect of small, 0.1 vol.% - 0.4 vol.% propane (C 3 H 8 ) additions on composition of air-contaminated N 2 atmosphere in the temperature range of 500°C - 860°C. Microstructures are presented for AISI 1045 steel exposed to the atmospheres produced. Atmosphere compositions compared include those produced by a new type of plasma activated, in-situ reformer for N 2 -diluted C 3 H 8 . The latter method extends the atmosphere protection to the lower range of annealing temperatures. Present results may assist heat treaters in optimizing their neutral hardening operations.

Plasma nitriding is a thermochemical surface heat treatment of steel components to produce nitride layers which increase wear-, corrosion- and fatigue resistance. Research into plasma nitriding lately showed that there is a significant and characteristic amount of ammonia formed off the process gases nitrogen and hydrogen. This research paper is aimed to analyze the influence of plasma treatment parameters, such as pressure, voltage, temperature and nitrogen to hydrogen ratio on the atmosphere and the formation of ammonia during plasma nitriding. The ammonia content is measured in the exhaust gas. By correlating the measured ammonia with the treatment parameters and modeling the nitriding process, the ammonia content can then be predicted. Further a plasma nitriding potential, comparable to the gas nitriding potential, based on ammonia content is calculated and its practicability as process control parameter is shown by correlating the potential with the nitriding results, e.g. the formation of ε and γ’ nitride phases.

Thermochemical surface engineering by nitriding/carburizing of stainless steel causes a surface zone of expanded austenite, which improves the wear resistance of the stainless steel while preserving the stainless behavior. As a consequence of the thermochemical surface engineering, huge residual stresses are introduced in the developing case, arising from the volume expansion that accompanies the dissolution of high interstitial contents in expanded austenite. Modelling of the composition and stress profiles developing during low temperature surface engineering from the processing parameters temperature, time and gas composition is a prerequisite for targeted process optimization. A realistic model to simulate the developing case has to take the following influences on composition and stress into account: - a concentration dependent diffusion coefficient - trapping of nitrogen by chromium atoms - the effect of residual stress on diffusive flux - the effect of residual stress on solubility of interstitials - plastic accommodation of residual stress. The effect of all these contributions on composition and stress profiles will be addressed.

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.

Titanium use in aerospace and medical applications continues to grow. Alpha case formation is a diffusion reaction that occurs at the surface of titanium when processing at elevated temperature in atmospheres containing oxygen, nitrogen, and/or carbon, with oxygen being the prominent element associated with alpha case. Oxygen is solution strengthening at low concentrations, but greatly decreases ductility and forms alpha case at higher concentrations. Thus, alpha case is brittle and has a detrimental effect on part performance and longevity. Higher temperatures increase alpha case depth. Temperatures less than 550°C (1022°F) limit oxygen mobility and keep case depth from increasing. Above 480°C (896°F), air or water vapor will start to produce alpha case.

Historically, this carburizing has been performed in an endothermic gas consisting of CO 2 , CH 4 , CO, etc, but carburizing in low pressure with the proper gas mixture changes the landscape. Using C 2 H 2 , the process is no longer endothermic as C 2 H 2 is a catalytically decomposable hydrocarbon and dissociates in the presence of an iron catalyst. LPC is a recipe driven in contrast to the constant monitoring of the carbon potential in atmospheric gas carburizing, and with the wide acceptance of simulation programs, recipes are no longer created by trial and error. Introduction of nitrogen to the steel, followed by carbon with higher temperatures, can dramatically reduce cycle times and still control grain growth.

Due to the absence of oxygen-containing gas components, nitrogen-based atmospheres offer a low-cost alternative to the case hardening treatments typically carried out using vacuum furnaces and, in several local economies, may cost less than the traditional atmospheres. When activated at the furnace inlet with electric plasma, nitrogen mixed with just a few percent of hydrocarbon, e.g. methane or propane, is effectively carburizing, and nitrogen mixed with ammonia and some hydrocarbon can be used to carbonitride lean steels within the high, austenitic temperature range, as well as nitride stainless steels in the low-temperature ranges. While offering quality advantages such as intergranular oxide-free cases, critical for non-machined surfaces or diverse near net shape products, the nitrogen atmospheres are non-equilibrium, i.e. require different sensing and process control techniques than the endothermic or methanol atmospheres. This paper provides an update on recent developments concerning process control of nitrogen-based carburizing atmospheres.

This paper investigates the effects of process time and temperature during plasma nitriding on the wear and fatigue properties of AISI 4330 steels. Nitriding, a thermochemical treatment involving nitrogen deposition and diffusion into metallic materials, has been widely used to enhance surface properties, wear resistance, fatigue strength, corrosion resistance, and friction characteristics of dynamically loaded components. The plasma nitriding process is conducted in a vacuum chamber where the specimen acts as a cathode, with high voltage (300-1000 V) applied between the cathode and the vessel (anode) at gas pressures of 1-13 mbar, creating an abnormal glow discharge that envelops the specimen. The process typically begins with hydrogen-atmosphere cleaning and pre-heating, followed by nitrogen introduction to initiate and maintain the nitriding action. Performance improvements were evaluated using pin-on-disk wear testing and rotating and bending fatigue testing methodologies.

This study examines the critical but often overlooked role of surface roughness in gaseous nitriding processes. While nitriding technology fundamentally relies on gas-solid interactions through multiple stages—including ammonia diffusion to the metal surface, dissociation reactions, nitrogen transfer, and bulk diffusion—the authors highlight how surface conditions significantly impact treatment outcomes, particularly at the relatively low processing temperatures (380-590°C) where surface reactions become rate-limiting. The research investigates how surface roughness affects the gas-metal contact area and consequently influences nitrogen uptake kinetics, challenging the traditional assumption that nitriding produces negligible changes in surface morphology. Working with commercial furnaces that use nitriding potential as the primary process control parameter, the researchers correlate various surface finishes with nitrogen absorption rates, ammonia dissociation, and atmosphere activity. The ultimate goal is to incorporate surface roughness—a specification widely used in metalworking industries—as a formal parameter in control systems, thereby enhancing process predictability and meeting increasingly stringent industrial standards for surface quality in nitrided components.

Atmospheric pressure carburizing and neutral carbon potential annealing in nitrogen containing small additions of hydrocarbon gases can offer cost and steel surface quality alternatives to the comparable, endothermic atmosphere or vacuum operations. An experimental program was conducted for refining real-time process control methods in carburizing of AISI 8620 steel under N 2 -C 3 H 8 blends containing from 1 to 4 vol% of propane at 900°C and 930°C. Multiple types of gas analyzers were used to monitor residual concentrations of H 2 , CO, CO 2 , H 2 O, O 2 , CH 4 , C 3 H 8 , and other hydrocarbons inside furnace. A modified shim stock technique and the conventional oxygen probe (mV) were additionally evaluated for correlation with gas analysis and diffusional modeling using measured carbon mass flux values (g/cm 2 /s). Results of this evaluation work are presented.