Gas Nitriding Research Articles

Optimization and control of gaseous nitriding of a 33CrMoV12-9 steel

Abstract This work propose a new experimental methodology to optimize the gaseous nitriding process of 33CrMoV12-9 steel grade, widely used in the mechanical industry for the fabrication of gears, pinions, and bearings. Several nitriding experiments were conducted at a temperature of 520 °C in the interval between 4 and 55 h using both constant and variable nitriding potential K N . The obtained results allowed us to determine the optimal conditions and to propose a sequenced cycle consisting of three steps. Multiple characterizations using X-ray diffraction (XRD), optical microscopy (OM), Vickers microhardness testing (HV), and electron probe microanalysis (EPMA) indicate a surface hardness of 810 HV0.5, nitrogen diffusion depth of approximately 0.7 mm. finally, a metallurgical structure devoid of complex networks of nitrides and carbonitrides. The validation results confirmed the effectiveness of the proposed methodology, thereby paving the way for improving the nitriding process in the mechanical industry. This work represents a significant contribution to the optimization of thermochemical treatments for materials used in demanding environments.

Titanium Nitriding: A Systematic Literature Review

In the last twenty years, the manufacturing of titanium and its alloys for commercial use continued to expand. As this material has several very advantageous properties, leading to increasing applications in various industries, it is seldom used in mechanical engineering applications due to its tribological properties, which are unfavourable. The nitriding process is one of the most frequently used thermochemical processes designed to enhance the surface characteristics of titanium alloys and improve tribological properties. Various types of nitriding for titanium are studied, such as ion nitriding, plasma nitriding, laser nitriding and gas nitriding. This article provides a comprehensive examination of research papers on different advancements through a systematic literature review conducted in the period 2017-2023 about titanium nitriding for its process parameters, characteristics and functionalities of the product, particularly emphasising their contributions in surface characteristics and mechanical properties. The review seeks to offer an understanding of how the predominant processing factors, specifically temperature and time, affect the microstructure and the creation of novel phases. This review suggests a challenge for future researchers to investigate mechanisms of microstructure evolution and its impact on mechanical properties in conditioned environments to microhardness and ability to withstand rusting of titanium and its alloys.

Production and Mechanical Characterization of Steel/Al-B4C Layered Circular Hybrid Composite Materials

This study aimed to develop a layered circular metal composite that would combine high strength, low density, and developable surface properties. The outer part of this composite material called the sheath was made of AISI 4140 steel, and the inner part, as the core, was composed of Al/B4C (boron carbide) mixed metal matrix composite. Al/B4C powder mixing ratios were determined by volume rate as 5, 15, and 25% B4C. Al2024 powder with an average particle size of 40 µm and B4C with particle sizes of 5, 17, and 58 µm were used. Composite materials were produced by forming the pre-products obtained by compressing Al/B4C powder mixtures into steel tubes using the drawing method. The drawing process was carried out at room temperature, 250 °C, and 400 °C, and with three different deformation extents (16, 30, and 37%). In the composite materials produced under all temperature conditions, increasing of the deformation extent increased the compression strength of the materials. Compression strength also increased with B4C reinforcement at all temperature conditions, but it decreased when the ratio of reinforcement passed over 15%. The gas nitriding process was applied to the produced composites to improve their surface properties. Strength values showed improvement after the nitriding process, and a thicker nitride layer was obtained on the steel sheath in highly deformed materials. As a result, the study presented the production of a composite with different sheath-core materials by rod drawing method and the effect of production variables on the material's mechanical properties. In addition, it was shown that the desired surface quality can be obtained by the gas nitriding process at low temperatures.

Low temperature nitriding behavior in annealed 2205 duplex stainless steel

ABSTRACT Low-temperature gaseous nitriding response of annealed 2205 stainless steel was investigated through a series of nitriding treatments at different temperatures in the range 380–430°C for 25 h. Reflected light microscopy, X-ray diffraction and hardness indentation were utilized to investigate the dependence of the formation of nitrides and cracks on pre annealing temperatures and subsequent nitriding parameters. For most annealing and nitriding conditions applied, the surface adjacent region of the steels was transformed into expanded austenite, or a mixture of expanded austenite and expanded ferrite, supplemented by the presence of iron-based nitrides. Nitriding at a relatively low temperature at a gentle nitriding potential was found to be acceptable as it resulted in a sound nitrided case, where neither chromium nitrides nor cracks developed. Annealing at a relatively low temperature can improve the threshold of nitriding temperature up to 400°C without cracking, while annealing at a high temperature promotes the formation of nitrides.

Corrosion protection of highly porous titanium by surface engineering

The corrosion resistance of highly porous titanium in a 20 % HCl solution was investigated using various surface engineering methods, including ball burnishing (BB) and gaseous nitriding (GN) below the polymorphic transformation temperature (α + β) and their combination (DDT). SEM, EDS, XRD, as well as micro- and nano-hardness testing methods, were employed to assess the microstructure of the formed barrier layers and determine their depth. After treatments, the corrosion was significantly reduced, with the corrosion current density being 8.7 to 25 times lower compared to the initial state of highly porous titanium. The results suggest that a DDT yielded the most substantial enhancement in the corrosion resistance of highly porous titanium.

Preparation of Cr-N coatings on 316H stainless steel via pack chromizing and gas nitriding, and their resistance to liquid metal corrosion in early stages

Liquid metal corrosion has become a critical issue in lead-cooled fast reactor when the steel encounters lead–bismuth eutectic (LBE). Although various coatings applied in LBE have garnered interest from many researchers, there are few reports on the compatibility of chrome carbide or chromium nitride coatings in LBE. Thus, Cr carbide and Cr-nitride coatings with thicknesses of 80 μm were prepared on 316H stainless steel (SS) to investigate the corrosion behavior in contact with static liquid LBE at 550 °C for 25, 76, and 207 h. These coatings were synthesized via pack chromizing and subsequent gas nitriding. The results showed that a distinct LBE penetration layer appeared on the surface of the as-received 316H SS after exposure to LBE. Pack-chromized coating and pack-chromized + gas nitride coating did not undergo obvious consumption in LBE in the early stages. Cracks in the pack-chromized coating promoted the preferential diffusion of oxygen and PbBi. The Cr in the pack-chromized + gas nitride coating slightly diffused outward to combine with oxygen to form Cr-oxide scale on the coating surface. These coatings act as a barrier to LBE corrosion, making the surface of the coating impermeable to LBE.

Fatigue performance of hierarchically porous titanium scaffolds produced by additive manufacturing and its possible improvement by gas nitriding

This contribution focuses on the nitriding of hierarchically porous titanium scaffolds to enhance their fatigue behaviour. Firstly, recent experimental findings that demonstrate the benefits of intra-filament porosity in improving fatigue resistance are discussed, providing details on crack growth shielding micromechanisms. Subsequently, the study explores the application of titanium scaffolds nitriding as a promising technique to prolong fatigue crack initiation. The scaffolds, prepared using the direct ink writing method with intra-filament porosity of ~ 6% and inter-filament porosity of ~ 68%, underwent gas nitriding at 1100 °C for 2 h. This process resulted in the formation of a consistent 42 μm thick nitriding case across the entire structure. Preliminary experiments showed a minimal decrease in fatigue strength within the low cycle fatigue region, attributed to the fracturing of a thick brittle compound zone under high applied loading. These results suggest that nitriding has the potential to improve fatigue performance after process optimization.

Improvement in Fatigue Strength of Chromium–Nickel Austenitic Stainless Steels via Diamond Burnishing and Subsequent Low-Temperature Gas Nitriding

Chromium–nickel austenitic stainless steels are widely used due to their high corrosion resistance, good weldability and deformability. To some extent, their application is limited by their mechanical characteristics. As a result of their austenitic structure, increasing the static and dynamic strength of the components can be achieved by surface cold work. Due to the tendency of these steels to undergo intercrystalline corrosion, another approach to improving their mechanical characteristics is the use of low-temperature thermo-chemical diffusion processes. This article proposes a new combined process based on sequentially applied diamond burnishing (DB) and low-temperature gas nitriding (LTGN) to optimally improve the fatigue strength of 304 steel. The essence of the proposed approach is to combine the advantages of the two processes (DB and LTGN) to create a zone of residual compressive stresses in the surface and subsurface layers—the enormous surface residual stresses (axial and hoop) introduced by LTGN, with the significant depth of the compressive zone characteristic of static surface cold working processes. DB (both smoothing and single-pass hardening), in combination with LTGN, achieves a fatigue limit of 600 MPa, an improvement of 36.4% compared to untreated specimens. Individually, smoothing DB, single-pass DB and LTGN achieve 540 MPa, 580 MPa and 580 MPa, respectively. It was found that as the degree of plastic deformation of the surface layer introduced by DB increases, the content of the S-phase in the nitrogen-rich layer formed by LTGN decreases, with a resultant increased content of the ε-phase and a new (also hard) phase: stabilized nitrogen-bearing martensite.

Influence of aisi 304 austenitic stainless steel by aqueous soluted nitriding and gas nitriding

AISI 304 austenitic stainless steel has great corrosion resistance,but it lacks in hardness,strength and wear resistance.So in order to improve these various hardening techniques are followed.In the present research salt bath nitriding and gas nitriding were carried out to improve hardness and wear resistance.Three samples are treated with salt bath nitriding and the other three samples are treated by gas nitriding and the one sample is kept aside to compare the results.The samples were wear tested on pin on disc apparatus after the heat treatment.Then the samples are subjected to Scanning electron microscope test and then the results were compared

Investigation on AISI 253 Stainless Steel by Gas Nitriding Process for Sustainable Applications

Austenitic stainless steel is highly valued in many industries due to its unique properties, which make it appropriate for various sustainable applications like wind turbine blades, solar panel components, biomass converter equipments. AISI 253 stainless steel were chosen for this research and gas nitrided were underwent at a low temperature of about 550°C. The samples were nitride for 8 hours of nitriding, the sample was found to move from austenitic to expanded austenite phase. Extending the nitriding time to 16 hours resulted in the formation of ferrites and an increasing concentration of nitrogen in succeeding layers. The specimens were carried out with nitriding for 24 hours. Cr-N phase were formed was This new phase contributes to increase in surface hardness. Wear loss and volume loss were analyzed from the wear test. In this work , there was considerable improvement in the wear resistance after 24hours of nitriding. The samples nitrides for 24 hrs also had high hardness of 1080Hv and had negligible wear, volumetric wear loss of the specimens. The microstructure and surface morphology analysis of the nitrided samples was carried out using scanning electron microscopy which helped in establishing the microstructural behaviour of the AISI 253 stainless steel.

Boron-doped graphene topological defects: unveiling high sensitivity to NO molecule for gas sensing applications.

Global air quality has deteriorated significantly in recent years due to large emissions from the transformation industry and combustion vehicles. This issue requires the development of portable, highly sensitive, and selective gas sensors. Nanostructured materials, including defective graphene, have emerged as promising candidates for such applications. In this work, we investigated the B-doped topological line defect in graphene as a sensing material for various gas molecules (CO, CO2, NO, and NH3) based on a combination of density functional theory and the non-equilibrium Green's function method. The electronic transport calculations reveal that the electric current can be confined to the line defect region by gate voltage control, revealing highly reactive sites. The B-doped topological line defect is metallic, favoring the adsorption of NO and NH3 over CO and CO2 molecules. We notice changes in the conductance after gas molecule adsorption, producing a sensitivity of 50% (16%) for NO (NH3). In addition, the recovery time for nitride gases was calculated for different temperatures and radiation frequencies. At 300 K the ultraviolet (UV) has a fast recovery time compared to the visible (VIS) one by about two orders of magnitude. This study gives an understanding of how engineering transport properties at the microscopic level (by topological line defect and chemical B-doping) leads to promising nanosensors for detecting nitride gas.

Exploring the sensing potential of Fe-decorated h-BN toward harmful gases: a DFT study.

Gas sensing technology has a broad impact on society, ranging from environmental and industrial safety to healthcare and everyday applications, contributing to a safer, healthier, and more sustainable world. We studied pure and Fe-decorated hexagonal boron nitride (h-BN) gas sensor for monitoring of carbon-based gases using density functional theory (DFT). The calculations utilized the Generalized Gradient Approximation with the Perdew-Burke-Ernzerhof (GGA-PBE) exchange-correlation functional. The novelty of our study lies in the investigation of the adsorption of harmful gases such as carbonyl sulfide, carbinol, carbimide, and carbonyl fluoride on both pure and Fe-decorated h-BN. The deviation in structural, electronic, and adsorption properties of h-BN due to Fe decoration has been studied along with the sensing ability to design said material towards carbon monoxide (CO), carbon dioxide (CO2), carbonyl sulfide (COS), carbinol, (CH4O), carbimide (CH2N2), and carbonyl fluoride (CF2O) gases. Gases such as CO, COS, CH2N2, and CF2O exhibited chemisorption, while CO2, and CH4O exhibited physisorption behavior. The introduction of Fe altered the semiconductor properties of h-BN and rendered it metallic. Enhanced electronic properties were observed due to a robust hybridization occurring between the d-orbitals of Fe-decorated BN and the gas molecules. The extended recovery periods observed for gases, aside from CO2, indicate their adhesive interactions with Fe-decorated h-BN. The reduction in desorption duration as temperature rises allows Fe-decorated h-BN to function as a reversible gas sensor. This research opens up a novel pathway for the synthesis and advancement of cost-effective, environmentally friendly double-atom catalysts with high sensitivity for capturing and detecting molecules such as CO, COS, CH2N2, CO2, CH4O, and CF2O.

Study on Fatigue Performance of Pulsed Tungsten Inert Gas Welding Joint of Duplex Stainless Steel Thin Tube.

To solve the shortage of austenite phase precipitation caused by nitrogen loss in the welding process of UNS S2205 duplex stainless steel (DSS), shielding gas nitriding was investigated by adding different N2 contents in Ar shielding gas during the welding process. A good thin-walled pipe butt joint was formed using the pulsed tungsten inert gas (P-TIG) welding method with Ar-N2 shielding gas. High cycle fatigue tests of the weld joints were conducted to study the effect of shielding gas nitriding on the fatigue properties. Fatigue tests at three stress levels of 225 MPa, 270 MPa, and 360 MPa were carried out on the weld joints with different N2 contents, and the fatigue samples were all fractured in the high temperature heat-affected zone (H-HAZ). Within the current process parameters, the fatigue life of the 4 vol.% N2 welded joints was optimal. Fatigue striations appeared in the fatigue crack propagation zone, and the transient fracture zone was similar to the tensile fracture. Under the low-stress level, the area of the crack propagation zone under 4 vol.% N2 was the highest, the tear ridges all expanded around the crack source area, and the fatigue crack propagation zone presented a radial distribution. The proliferation and expansion of dislocations were mainly carried out in the austenite grains, and the dislocation density of the fatigue specimens under 4 vol.% N2 was smaller than that of the Ar specimens. Shielding gas nitriding effectively improved the balance of the two-phase ratio and the hardness of austenite phase, optimized the internal slip system, inhibited the proliferation of dislocations in the austenite phase, and improved the fatigue life of weld joints.

ANALISIS SURFACE HARDNESS ALUMINUM 6061 HASIL GAS NITRIDING DENGAN VARIASI HOLDING TIME

The nitriding coating process is widely applied in the industry. Gas nitriding is a technique used to improve the mechanical properties of a metal. This study aims to determine the influence of holding time variations on surface hardness and diffusion depth in aluminum alloy 6061 (Al-Mg-Si) that undergoes gas nitriding. The independent variable used in this study was holding time, namely, initial specimen (without holding time treatment), and specimens that experienced holding ranging from 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours. The cooling medium used after gas nitriding was air. The highest surface hardness value was obtained in aluminum alloy 6061 specimens without holding time treatment, namely with a hardness value of 141 VHN while the lowest surface hardness value was produced by the specimen with a holding time of 5 hours. The lowest surface hardness value was 55.4 VHN. Based on the results of the EDAX composition test known that the specimen of aluminum alloy 6061 with a holding time of 5 hours diffused nitrogen element of 1.57% and oxygen element of 5.27%.

PREDICTION OF DEPTH OF NITRIDE LAYER IN IRON DURING GAS NITRIDING USING NEURAL NETWORK

Surface engineering of materials can add economic value to the material. Gas nitriding in iron is a typical thermochemical surface engineering process at eutectoid temperatures, where nitrogen diffuses to the surface to form nitride layers in the form of gamma phase and epsilon phase. In this study, a computational approach will be taken to predict the formation of the nitriding layer. In the prediction, a backpropagation neural network is used with input parameters of temperature, nitriding potential and time with an output of nitriding layer depth. This prediction does not distinguish the phase formed in the nitriding layer. The best results were obtained in the model of single hidden layer with 5 neurons and two hidden layers with the formation starting with 6 neurons followed by 5 neurons. The mean square error of the training data for the single hidden layer is 0.0027. While for two hidden layers the value is higher at 0.0032. The results obtained for the absolute mean error and root mean square values for the single hidden layer model are 0.6117 and 0.9670. For the two hidden layers model, the absolute error and root mean square values are 0.5894 and 1.0472. It can be seen from the correlation coefficient that both models can only predict well at depths of more than 10 μm.

To elucidate the effect of alloying elements for enhanced nitriding of aluminum: A multiscale computational study

The limitations of aluminum (Al) are discussed in certain industrial applications, owing to its low hardness and wear resistance. To overcome these limitations, surface modification techniques, such as the formation of aluminum nitride (AlN) layers on the Al surface, have been explored. However, conventional surface-nitriding processes have low productivity, and it is essential to develop a cost-effective method to ensure higher nitriding rates. This paper presents the results of a multiscale computational study on the atomic-scale mechanisms involved in gas nitriding processes and the effects of alloying elements on reaction kinetics using density functional theory calculations. This study also provides insights into the thermodynamic stability and kinetics of the process, contributing to the design and optimization of the nitriding process for the formation of AlN on Al surfaces using Thermo-Calc. and microkinetic analyses. This study demonstrates the potential of multiscale computational methods for advancing the understanding of surface modification techniques and their applications for nitriding on the surface of Al and suggests the best alloying element to enhance the nitriding rate.

Depth profiling analysis of the nitriding layer formed by gas nitriding of Ti13Nb13Zr alloy

The gas nitriding of Ti13Nb13Zr alloy was performed in a pure nitrogen atmosphere at 1200 °C with different holding times. The variations in the phase constituents, microstructure, and mechanical properties of the nitriding layer with depth were characterized by SEM, XRD, and nanoindentation. Depending on the phase distributions in depth, the nitriding layer could be sequentially divided into an external nitride layer mainly consisting of TiN, an internal nitride layer consisting of TiN, Ti2N and TiN0.3, and an N diffusion region consisting of TiN0.3. The mechanical properties were closely associated with the phase constituents, where the nanohardness of the internal nitride layer, internal nitride layer N diffusion region and substrate were about 17.126±0.399, 12.120±0.386, 5.627±1.080, and 3.632±0.116 GPa, respectively. In the nitriding process, the N diffusion region containing needle-like TiN0.3 precipitates formed in the initial nitriding stage, and then the precipitates were gradually converted to the external and internal nitride layers, whose thickness increased with the nitriding time. Furthermore, the influence of the alloying element redistribution on the N diffusion mechanism was discussed.

A Review—Effect of Accelerating Methods on Gas Nitriding: Accelerating Mechanism, Nitriding Behavior, and Techno-Economic Analysis

Gas nitriding, as a surface modification technology to improve the wear resistance of workpiece surfaces, is widely used in wind turbine gears, pressure vessel gears, high-precision die casting abrasives, and other areas. However, the gas nitriding time is too long, reaching 40–60 h, which reduces the efficiency of nitriding and hinders the development of gas nitriding. Therefore, various accelerating methods are born accordingly. This review first introduces the basic principle, microstructure, and process parameters of conventional gas nitriding. Then, five common accelerating methods are summarized: process parameter optimization, surface mechanical nano-crystallization, surface-active catalysis, surface pre-oxidation, and surface laser treatment. Then, the effect of acceleration methods on gas nitriding is analyzed for the acceleration mechanism, nitriding behavior, and nitriding efficiency. Finally, the technical economy of the acceleration methods is compared for three aspects: energy consumption, carbon dioxide emission, and cost. And, the technical maturity of the acceleration methods is compared according to technology readiness level (TRL) technology. Based on the above content, the advantages and disadvantages of the five accelerating methods are reviewed, and the concept of a multi-technology collaborative processing acceleration method is proposed.

Diffusion Nitride Coatings for Heat-Resistant Steels.

The effect of ion nitriding and nitriding in a melamine-based powder mixture on the structure and properties of AISI A290C1M steel was studied in the paper. Using ion nitriding made it possible to shorten the technological cycle's duration by 5-6 times compared to two-stage nitriding, optimize the diffusion layer's composition, provide a technologically simple process automation scheme, and improve the quality of nitride coatings. After the proposed mode of ion nitriding, a saturated layer depth of 0.25-0.32 mm, hardness up to 1000 HV, and an increase in wear resistance by 2.17 times were obtained. Using 95% melamine + 5% sodium fluoride during nitriding in a powder mixture significantly simplified the technological process. It did not require additional expensive equipment, which in turn significantly simplified the nitriding process with energy savings. The proposed technology and the composition of the mixture contributed to a significant acceleration of the nitriding process of AISI A290C1M steel, compared to traditional gas nitriding, and to obtain a hardness of the nitride layer of 970 HV and an increase in wear resistance by 2.6 times. A nitriding speed is explained by a significantly higher amount of atomic nitrogen when using melamine instead of ammonia and by the almost simultaneous disintegration of nanodispersed particles when the nitriding temperature was reached. After nitriding in a powder mixture, steel was subject to the slightest wear.

The Impact of Heating Rate on the Kinetics of the Nitriding Process for 52100 Steel.

The aim of this study was to determine the impact of the heating rate of steel balls made of AISI 52100 alloy steel on the kinetics and efficiency of the gas nitriding process when carried out using a chemical reactor with precise thermo-gravimetric measurements, which allowed for changes in sample mass during heating and nitriding to be monitored with an accuracy of 50 µg. In the chemical reactor, the examined alloy steel was subjected to a heating process at the selected nitriding temperature of 590 °C. Two heating variants were used: the first variant relied on heating to the nitriding temperature with different rates-1 °C per minute, 2 °C per minute, 5 °C per minute and 10 °C per minute, respectively-whereas the second variant relied on the fast-25 °C per minute-heating of treated specimens to a temperature of 475 °C, at which, the nitrogenous potential of the atmosphere promotes faster nitrogen diffusion deep into the nitrided substrate, followed by reheating up to the nitriding temperature at different rates: 1 °C per minute, 2 °C per minute, 5 °C per minute, and 10 °C per minute, respectively. To evaluate the impact of heating rate kinetics and effectiveness during nitriding on the obtained surface layer quality, we investigated the phase composition, microhardness distribution, and thickness of the obtained diffusion layers. It was found that heating to a temperature of 475 °C in the nitriding process does not significantly affect the average mass gain of a sample. Above this temperature, within the range of nitriding temperatures, the extension of time increases the sample's mass gain. Simultaneously, it was found that the use of a constant heating rate allows for thicker nitrided layers and a greater sample hardness to be obtained. Dual-stage heating, in turn, is more effective in the context of sample mass gain per time unit.