Nitrided Steel Research Articles

Повышение качества диффузионного слоя ввысоколегированных сталях после газоциклических процессов азотирования

The study results of gas-cyclic nitriding of corrosion-resistant austenitic and martensitic steels with alternating atmospheres of ammonia and air in the mode of an isothermal process and a stepwise process with a final stage with reduced activity of the saturating atmosphere are discussed. The factors of improving the quality of the diffusion layer were determined, contributing to increased wear resistance and maximum preservation of steel resistance to shock loads due to reduced stresses at the boundary of the layer with the matrix.

Influence of Artificially Altered Engine Oil on Tribofilm Formation and Wear Behaviour of Grey Cast Cylinder Liners

This work investigates the influence of altered engine oil on the tribological performance, focusing in particular on wear and interconnected tribofilm formation. For this purpose, Zinc dialkyldithiophosphate (ZDDP) additivated engine oils of different degradation levels, produced in an artificial oil alteration process, were used in tribometer tests with a nitride steel piston ring against a grey cast iron cylinder liner model contact. Parameters were chosen to simulate the boundary and mixed lubrication regime typical for the top dead centre conditions of an internal combustion engine of a passenger car. Wear of the cylinder liner specimens was continuously monitored during the tribometer tests by the radio-isotope concentration (RIC) method, and tribofilms were posteriorly investigated by X-ray photoelectron spectroscopy (XPS). The results clearly show that the steady-state wear rates for experiments with altered lubricants were significantly lower than for the experiments with fresh lubricants. XPS analysis on the formed tribofilms revealed a decrease in sulphide and an increase in sulphate states for altered oils evaluated at 120 °C oil temperature, correlating with a decrease in steady-state wear rate. This finding emphasizes the role of sulphate species in the tribofilm formation process and its anti-wear capabilities, in contrast to the sulphide species and the (poly-)phosphate species, as outlined in most of the ZDDP literature. Moreover, the RIC signal that represents the amount of wear in the engine oil showed a decrease over time for specific altered lubricants and test conditions. These “negative” trends in the wear signal are remarkable and have been identified as an incorporation of wear particles from the lubricant into the tribofilm. This finding is supported by XPS results that detected an iron-oxide layer with a remarkably similar quantity within the tribofilm on the surface. Based on these findings, an assessment of the minimum film formation rate and particle incorporation rate was achieved, which is an important basis for adequate tribofilm formation and wear models.

Material Influence on the Micropitting and Wear Resistance of Nitrided External and Internal Gears

Abstract Due to increasing performance requirements and sometimes tribologically challenging operating conditions in gears (such as those found in wind turbines), alternative heat treatment processes to quenching and tempering or case hardening are becoming more and more important. Nitriding can significantly increase the load-carrying capacity of gears compared to the quenched and tempered initial state. The nitrided surface layer is characterized by a hard compound layer on the surface that is just a few micrometers thick and a diffusion zone that extends deeper into the material. The structure of the compound layer of iron and alloy element nitrides is primarily decisive for the wear behavior of nitrided components. Previous studies on nitrided gears with regard to micropitting and wear focus primarily on a systematic variation of the compound layer on gears made of nitriding steel 31CrMoV9. Results on the influence of the base material on the micropitting and wear resistance of nitrided gears are not yet available. In systematic load and speed stage tests, nitrided gears made from a quenched and tempered steel (42CrMo4) and a material with an alternative alloy composition (34CrNiMo6) were examined in addition to the reference (nitriding steel 31CrMoV9). Both external and internal gear pairings were tested, with the alternative materials showing more favorable tribological behavior in some cases. The results are presented and categorized according to the current state of the art. Finally, recommendations for the practical use of nitrided gears are derived.

Evaluation of adhesive damage in a nitrided stainless steel under cyclic contact loading

In this study, adhesive damage in a nitrided AISI 316L stainless steel is evaluated by cyclic contact loading. The AISI 316L steel was hardened by the salt bath nitriding process at a constant temperature (580 °C) and three different exposure times (1 h, 3 h and 5 h). Mechanical properties such as Young's modulus (E) and hardness (H) were obtained by nanoindentation testing, where the H3/E2 ratio was used as an indicator of the fracture resistance of the nitride layers. Cyclic contact loads were applied to the nitrided steels using a spherical indenter of 3 mm in diameter. The layer/substrate systems were evaluated under 50,000 load cycles and a constant frequency of 5 Hz. Adhesive damage was observed at the interface between the compound-layer and the diffusion zone, where the samples with a thicker nitride layer showed more severe damage. In addition, the finite element method was used to obtain the stress field in the nitrided AISI 316L steel caused by cyclic contact loading, where both the maximum principal stress and the maximum shear stress were related to the adhesive damage observed in the experimental test.

Catalytic Growth of High-Performance Graphite-like Carbon Films on a Nitrided Substrate: Experimental Study and First-Principles Calculations.

This study reports a novel process for the fabrication of high-performance graphite-like carbon (GLC) films on nitrided substrates through successive steps in a plasma nitriding system. Unlike films fabricated via conventional dual treatments (nitriding + film deposition), here-fabricated GLC films were grown on the surface of nitrided steel via a catalytic reaction. A transition zone having a nanocrystalline and amorphous structure was observed at the interface between the nitrided substrate and GLC films, which increased the durability of GLC films because this structure enhanced the adhesion of GLC films on the nitrided substrate, improving resistance to spallation and wear. Experimental study and first-principles calculations showed that the Fe3N phase had a stronger catalytic effect on GLC films than the Fe4N phase, and GLC films grown on the nitrided layer dominated by Fe3N were thicker with stronger adhesion and excellent frictional and wear properties compared with GLC films grown on the nitrided layer dominated by Fe4N because of the beneficial structure formed at the interface. This study reports a simple and inexpensive method to fabricate a dual layer containing high-performance GLC films via a catalytic growth and interface matching mechanism.

Influence of increased voltage on the nitriding zone during plasma nitriding

AbstractPlasma nitriding is an established process for increasing the corrosion and wear resistance of steel. However, the possibilities of modern developments in the field of high‐voltage plasma power supplies have been hardly investigated. For example, modern plasma generators allow improved arc management, which enable plasma nitriding at higher voltages.In the present work, the influence of increased voltage (up to 800 V) on the nitriding of a ferritic steel X38CrMoV5‐1 was investigated. It was found that the thickness of the compound layer increases with increasing voltage. Especially at short process times the increased voltage leads to increased growth. An increase in the nitriding depth was also observed.Furthermore, the increased voltage has an effect on the composition of the compound layer too. A moderate increase in ϵ‐nitride in the compound layer was observed.One explanation for the observed behavior is the over proportional increase in power with increasing voltage, indicating an increased ionization rate of the plasma. Due to this, more diffusible species would be available for nitriding.The presented results could be used to reduce process times, particularly where the formation of a compound layer is the aim of the process. An example of such a process is oxy‐nitriding.

Electrolyte-Plasma Nitriding of Austenitic Stainless Steel under Cathodic and Anodic Polarity

Electrolyte-Plasma Nitriding of Austenitic Stainless Steel under Cathodic and Anodic Polarity

Наукоёмкие технологии в материаловедении: высокотемпературное сквозное азотирование жаростойкой стали

The topicality of the research is occasioned by exaggeration of working conditions of products used at high temperatures and made of heat-resistant sheet alloys, including in particular austenitic chromium-nickel steels. When steel parts under load are operated in an oxidizing atmosphere and aggressive environments, besides resistance to electrochemical and gas corrosion, they require increased strength, hardness, and heat resistance. The increase in the characteristics of these proper-ties is achieved by three-dimensional and surface hardening techniques, which include the nitration process. The applica-tion of traditional technologies of furnace gas nitriding for chromium-nickel steels is complicated due to the problems of the low rate of the nitrogen saturation, which significantly increases the process time, and the formation of chromium nitrides, which negatively affects corrosion and heat resistance. The development of new technologies for nitrogen hardening of high-alloyed chromium-containing steels is carried out in the direction of saturation process intensification and regulation of the phase composition of the nitrided layer to minimize the formation of chromium nitrides. The article is aimed at defin-ing rational technological options and modes of gas austenitic nitriding of austenic steel, making it possible to increase strength characteristics at RT and higher temperatures without sacrificing its heat resistance. Thermodynamic modeling of the phase composition based on the CALPHAD technique shows that primary ways for minimizing the release of chromium nitrides on the nitrided surface are to increase the concentration of titanium in steel and to reduce the activity of the saturat-ing gas atmosphere, which is achieved by inert gas dilution of nitrogen. Experimental studies were carried out on sheet samples of 1.5 mm thick austenic steel of the type X18N10T with a standard (0.5%Ti) and increased (1%Ti) titane content. The experiments were carried out on a laboratory installation for high-temperature nitriding (900.1200 °); pure nitrogen and mixtures of nitrogen with argon were used as saturating media. Two-stage processes consisting of nitrogen hardening in nitrogen followed by argon afterburning were also investigated. Metallographic analysis showed that at the same nitrid-ing temperature, the amount of chromium nitrides decreases in experimental steel with an increased titanium content, and dilution of nitrogen with argon reduces the temperature of chromium nitride release. According to the study of saturation process kinetic, the time of through-the-thickness nitriding of a sheet sample under different saturation modes was deter-mined, as well as the duration of de-nitriding annealing, calculated on the basis of the known thickness of the chromium nitride zone. It was found that the dispersion hardening of the zones of internal nitriding with titanium nitrides leads to an increase in the strength characteristics of steels both at RT and higher temperatures compared to the characteristics of base steel 08X18N10T after typical heat treatment, while the greatest hardening effect is achieved due to through-the-thickness nitriding of steel with 1%Ti. Recommended options for the processes of through-the-thickness nitriding of 1.5 mm sheet of experimental steel: tn=1050 ℃, N2, 16 h; tn= 1100 ℃, 50%N2 + 50%Ar, 22 h; tn=1100 ℃, N2, 5 h + tann=1200 ℃, Ar, 9 h. The temporary passive hardness of nitrided steel at RT increases by 45...50%, and when tested at 800 ℃ - by 40... 65%, de-pending on the process mode. Through-the-thickness nitriding makes it possible to raise the working temperature of steels by 100.150 ° with the same long-term strength. The heat resistance at 900 ℃ remains at the level of non-carbonated steel after two-stage processes that ensure maximum chromium nitrides removal from the surface at the annealing stage.

Effect of laser shock peening on plasma nitriding microstructure and properties of H13 steel

Laser shock peening (LSP) was conducted on H13 steel prior to plasma nitriding (PN). The optical microscopy (OP), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microhardness tester and ball-on-disk wear tester were employed to investigate the microstructure and properties of plasma nitrided H13 steel coupled with LSP processing. The results show that a large number of dislocations, as well as dislocation cells and nanocrystals composed of high-density dislocations, are observed in H13 steel after LSP treatment. Compared with the PN sample, the diffraction peak intensities of the Fe3N phase in the LSP + PN sample are slightly enhanced and the diffraction peaks shift to the right as a whole. Compared to the PN sample, the LSP + PN sample exhibits significant improvements in various aspects. Specifically, the white bright layer and diffusion layer of the LSP + PN sample increased by approximately 25 % and 119.4 %, respectively. Additionally, the thickness of the effective hardened layer increased by around 50 %, and the microhardness increased by approximately 31.3 %. The LSP + PN sample has the better wear resistance than that of the PN sample, with the friction coefficient, wear scar width, wear volume, and wear rate reduced by 11.1 %, 8.4 %, 7.9 %, and 7.3 %, respectively. Through parallel experiments, the experimental error is controlled within 2 %.

Solar-light-driven photocatalytic conversion of monosaccharide by oxygen-doped graphitic carbon nitride/artificial steel converter slag composite

The development of high performance, low-cost and resource-efficient photocatalysts with improved solar light harvesting capabilities can significantly enhance the practicability and viability of photocatalytic conversion of biomass-based substances to value-added chemicals. This work reports the construction of heterojunction between oxygen-doped graphitic carbon nitride and artificial steel converter slag (OCN/artCS) as efficient photocatalysts for conversion of biomass-derived monosaccharide to lactic acid under the simulated solar light. The OCN/artCS composites were facilely fabricated by the thermal polymerization of the mixtures of dicyanamide (DA) and oxalic acid (OA), which are precursors of OCN. The artCS acts as photocatalyst support for OCN to grow on its surface and can provide Ca2Fe2O5 semiconductor to possibly form the OCN/Ca2Fe2O5-containing artCS heterojunction. Compared with pristine OCN, the OCN/artCS composites exhibited higher photocatalytic performance for selective production of lactic acid, possibly due to the effective separation of photogenerated charge carriers after creation of OCN/artCS heterojunction. At the optimal content of artCS in the composites, the OCN/5%artCS delivered 99% glucose conversion and 90% lactic acid yield within 60 min at 50 °C under the simulated sunlight irradiation. This work can be a platform for the efficient utilization of industrial solid wastes for production of high-performance photocatalysts, enabling their promising applications in photobiorefinery and other photocatalytic processes.

Comparison of physical, mechanical and chemical properties of barrel steel 32CrMoV12-10 and nitriding steel 31CrMoV9 after nitriding in gas

32CrMoV12-10 and 31CrMoV9 steels are used not only for components in the automotive industry, but also for firearms parts in the weapons industry. In these applications, high strength and surface layer hardness is required while maintaining the toughness of the core, which is achieved by nitriding. The aim of the work was to determine which of the steels exhibits better physical, mechanical and chemical properties after nitriding in a gaseous atmosphere. Metallographic samples were made to compare the structure of the nitride layer after nitriding. Hardness and fracture toughness were measured and Charpy impact testing and corrosion resistance evaluation were also carried out. The test results revealed that 31CrMoV9 steel shows better physical and chemical properties than 32CrMoV12-10 steel.

A strain rate-dependent analytical approach for low-velocity impact on the beam composed of silicon-nitride and stainless-steel

Purpose The purpose of this study is to investigate the strain rate effect on the problem of low-velocity impact (LVI) on a beam, including silicon nitride and stainless steel materials. Design/methodology/approach Based on the nonlinear Hertz impact mechanism, the energies related to the impactor and the beam are written, and motion equations are derived using the Lagrangian mechanics and Ritz method. The strain rate term is represented as a damping matrix in the equations of motion. In the issue of LVI on the silicon nitride and stainless steel beam, the effect of internal viscous damping coefficient in simply–simply and clamped–free boundary conditions are studied. Also, the influence of the volume fraction index in the range between zero and one and greater than one on the impact response is investigated. Findings The results make it clear that the strain rate parameter had little effect on the response in LVI. Also, an increase in the volume fraction index has led to a decrease in the contact force and an increase in the rebound velocity of the impactor. Originality/value The effect of strain rate on LVI is theoretically studied in this paper, while in most of the papers, this effect is investigated experimentally and numerically.

Effect of Machine Pin-Manufacturing Process Parameters by Plasma Nitriding on Microstructure and Hardness of Working Surfaces

This work concerns two stages of research into plasma nitriding (change of nitriding steel and modification of nitriding parameters). In the first stage, pins obtained from currently used steel were compared with pins made of an alternative material available on the market, using the same nitriding process parameters. As a result of the metallographic tests carried out, in the first case, the presence of a thin, porous, and heterogeneous nitrided layer or its absence was found, with the core in its raw state and not thermally improved. In the second case, the presence of a nitrided layer of small thickness with noticeable porosity on the surface of the sample was found, but with a core after heat treatment (incorrect process parameters). Therefore, modification of the parameters of the nitriding process was proposed, in terms of a mixture of gases, currents, time, and temperature of the nitriding process. As a result, a satisfactory effective thickness of the nitrided layer was obtained, consisting of a white near-surface zone with ε and ε + γ′-type nitrides with a thickness of 8.7 to 10.2 µm, and a dark zone of internal nitriding with γ′ nitrides. The nitrides layer was continuous, compact, and well adhered to the steel surface. In the core of the samples, the presence of a fine-needle tempering sorbite structure with a small amount of fine bainite, which is correct for the steel after heat treatment and nitriding, was found. The most favorable parameters of the ion nitriding process were gas flow rate (1.5 L/min N; 0.4 L/min H; 0.3 L/min Ar); currents (BIAS—410 V 4.0 A, SCREEN—320 V 4.0 A); time (26 h and 35 min); and temperature (550 °C).

Gradient self-organized dislocation in expanded austenite layer during low temperature nitriding

Abstract A typical nitrogen expanded austenite layer is formed by plasma-based low-energy nitrogen ion implantation (PBLEII) on AISI 304L austenitic stainless steel at a moderate temperature of 380° C. The dislocation self-organization structure in the nitrogen expanded austenite layer is characterized as an evolution from partial and Lomer-Cottrell dislocations in the inner layer near the interface to multilayer stacking faults in the outer nitrided layer. The self-organized dislocation density and forms are essentially dependent on the plastic deformation, strain-gradient, and nitrogen-related stacking fault energies, respectively, due to the constrained expansion in the nitrided layer. As the nitrogen concentration in the austenitic matrix increases, the stacking fault energy gradually decreases, resulting in the transformation of the defect from Lamer-Cottrell dislocations to a multilayer stacking faults. The appropriate stress, which is associated with orderly stress relief during dislocation self-organization, preserves the integrity of the nitrided layer with a combinedly improved in wear and corrosion resistance. Nitriding-induced dislocation self-organization is basically explored as the formation mechanism of the nitrogen expanded austenite layer, contributing to development of the specific low-temperature nitriding austenitic steel.

Tribocorrosion Behavior of γ′-Fe4N Nitride Layer Formed on Mild Steel by Plasma Nitriding in Chloride-Containing Solution

Nitriding has long been used to engineer the surfaces of engineering steels to improve their surface and subsurface properties. The role of the surface compound layer (γ′-Fe4N and/or ε-Fe2-3N) in improving the tribological and corrosion-resistant properties of nitrided steels has been established. However, there have been very few studies on the response of the compound layer to tribocorrosion in corrosive environments. In this work, the tribocorrosion behavior of a 5 μm thick γ′-Fe4N nitride layer produced on mild steel (MS) by plasma nitriding has been studied in a NaCl-containing solution under various electrochemical conditions. The results show that at a cathodic potential of −700 mV (saturated calomel electrode, SCE), where mechanical wear is predominant, the total material removal (TMR) from the γ′-Fe4N layer is 37% smaller than that from the untreated MS, and at open circuit potential, TMR from the layer is 34% smaller than that from the untreated MS, while at an anodic potential of −200 (SCE), the γ′-Fe4N layer can reduce TMR from mild steel by 87%. The beneficial effect of the γ′-Fe4N nitride layer in improving the tribocorrosion behavior of mild steel is derived from its high hardness and good corrosion resistance in the test solution and its ability to resist both mechanical wear and corrosion and to reduce wear–corrosion synergism.

Improved mechanical and wear properties of H13 tool steel by nitrogen-expanded martensite using current-controlled plasma nitriding

Nitrogen-expanded martensite is a crystalline structure formed by incorporating nitrogen atoms into the interstitial sites of martensitic steels. It has recently gained significant industrial attention due to its excellent mechanical and wear-resistance properties. However, the major challenge in synthesizing nitrogen-expanded martensite is obtaining a phase free of iron or chromium nitrides precipitates. In this study, the effects of varying temperature (460, 480, and 500 °C) and plasma current density (0.5, 1.0, and 1.5 mA/cm2) during plasma nitriding of H13 tool steel were investigated to evaluate their influence on crystalline phases. The results of X-ray diffraction analysis indicate that expanded martensite free of nitride precipitates can be obtained at a temperature of 480 °C and low current density. Moreover, wear analysis using a ball-on-disk wear tester showed that the lowest wear rates were achieved under similar conditions. Grazing incidence X-ray diffraction analysis revealed that the outer region of the nitrided zone had a disordered structure, which could be attributed to a nano crystallization process. The nanoindentation analysis demonstrated that the expanded martensite phase has rigid-elastic properties characterized by high elastic energy (144.5 nJ) and high resistance to plastic deformation.

Catalytic gas nitriding of M50NiL steel by LaFeO3 pervoskite oxide under low-pressure conditions

To generalize the application of the LaFeO3 oxide in catalytic nitriding of steels, the M50NiL steel, a typical high-alloy bearing steel, was nitrided under low-pressure conditions. The catalytic effect of the LaFeO3 oxide on nitriding kinetics of M50NiL steel was evaluated and a new understanding of the catalytic mechanism was proposed. The microstructure, phase composition, surface morphologies and depth of nitrided layers were characterized by optical microscope, X-ray diffraction, scanning electron microscope and microhardness tester, respectively. The wear resistance of nitrided layers was evaluated by a pin-on-disk wear tester and the chemical bonds on nitrided surfaces were identified by X-ray photoelectron spectroscopy to analyze the process of nitriding reactions. The results show that the LaFeO3 catalytic nitriding was suitable for M50NiL steel. The LaFeO3 catalytic nitriding could dramatically improve the toughness of nitrided layer via the suppression of nitrides formation. The adsorption and decomposition of NHx species on the LaFeO3 oxide were alternatively occurred on La-O terminated surfaces and Fe-O terminated surfaces, resulting in the fluctuate nitrogen concentration and rapid diffusion of active nitrogen atoms. The nitriding kinetics greatly depended on the oxidation state of nitrided surfaces. Namely higher oxidation capacity corresponded to higher nitriding efficiency.

Electrolyte-Plasma Nitriding of Austenitic Stainless Steel with Cathodic and Anodic Polarity

The results of modifying the surface of austenitic stainless steel by plasma electrolytic nitriding at the anode and cathode polarities of the processed product in an electrolyte based on ammonia (5%) and ammonium chloride (5%) are presented. The morphology and surface roughness, phase composition, and microhardness of diffusion layers, tribological and corrosion properties were studied. The influence of physico-chemical processes during anodic and cathodic treatments on the features of the formation of the modified surface and its operational properties is shown. Smoothing of micro-roughness and reduction of surface roughness during anodic nitriding due to electrochemical dissolution, and the course of surface erosion with increased roughness during cathodic nitriding due to electrical discharges were revealed. An increase in the hardness of the nitrided layers to 1150 HV was found with a twice decrease in roughness after anodic treatment, accompanied by an increase in the wear resistance by 166 times, with a decrease in the friction coefficient by 1.6 times. After cathodic treatment, it is possible to increase the hardness only to 580 HV and the wear resistance by 13.6 times. An increase in surface roughness after the cathodic treat-ment always leads to an increase in the friction coeffi-cient. In both cases, a decrease in the pitting formation in the medium of sodium chloride is shown.

Investigation of mechanical, tribological and magnetic properties after plasma nitriding of AISI 316L stainless steel produced with different orientations angles by selective laser melting

In this study, AISI 316L stainless steel samples were produced with different orientations (0°, 45°, and 90°) using selective laser melting (SLM). In addition, plasma nitriding of the samples produced with SLM was performed at 400 °C for 4 h. The effect of different orientation on the structural, mechanical, tribological, and magnetic properties of 316L stainless steel was investigated. The same measurements also were made after the plasma nitriding process. The results showed that the phase composition and microstructure of the non-nitriding and nitridied samples were affected from the built orientation. Especially the XRD peaks shifted to the left with a decrease in the orientation angle. It was obtained that the highest modified layer thickness was measured from the samples produced with an angle of 0°. It was observed that the surface hardness, residual stress, wear resistance and antimagnetization tendency values of nitridied samples were higher than the non-nitriding samples. Furthermore, these values tended to increase with the decrease in build orientation angles.

Effect of N2/Ar Ratio on Microstructure and Tribological Property of Arc Plasma-Assisted Nitrided 40CrNiMoA Steel

Effect of N2/Ar Ratio on Microstructure and Tribological Property of Arc Plasma-Assisted Nitrided 40CrNiMoA Steel