Nitrided Steel Research Articles

Tribological behaviour of a multilayer CrN/DLC coating obtained using PVD-MS

Diamond-like Carbon (DLC) coatings are used as protective layers for steel components due to their hardness, chemical inertia and interesting tribological properties. Reducing wear and friction coefficient is of great importance for industries today in order to increase energy efficiency and reduce harmful emissions to the environment. In this paper, a multilayer CrN/DLC coating is analysed. It was deposited using a commercial Plasma Enhanced Magnetron Sputtering over nitrided and not nitrided mild-alloy steel AISI 4140, produced for the first time in Argentina, at the firm Coating.Tech by Flubetech-Tantal. The base of the coating is an anchor layer made of CrN and the top layer is a chromium-dopped hydrogenated amorphous carbon (a-C:H:Cr), which provides excellent tribological properties. Wear tests were carried out in a Pin-on-Disk apparatus, using an Al2O3 ball as counterpart, with Hertzian contact stress from 1370 up to 1460 MPa. The friction coefficient was μ ∼ 0.1, which is 80% less than the untreated steel and the wear volume loss was reduced several times. The adhesion was evaluated by means of Scratch Test, where major improvement was noticed in the samples which were nitrided as pre-treatment, increasing critical load from 25 N up to 65 N.

Effect of trace water in ammonia on breaking passive film of stainless steel during gas nitriding

The dense passive film on the surface of austenitic stainless steel isolates the corrosion medium from the matrix, which makes it have excellent corrosion resistance. However, it also hinders the penetration and diffusion of nitrogen atoms in the process of gas nitriding. During gas nitriding of stainless steel, we found a very interesting phenomenon. When trace water in ammonia is at a certain threshold, ammonia, water, and chromium oxide passivation film will undergo gas-solid reaction to break the passivation film on the surface of stainless steel. The results show that the trace water content in ammonia during gas nitriding is very important for in-situ breaking of passive film. When the trace water content exceeds the upper threshold, oxidation will occur on the surface of stainless steel. On the other hand, when the trace water content is lower than the lower threshold, the passivation film hinders the diffusion of nitrogen atoms, and the nitride layer cannot be obtained. The mechanism of in-situ removal of passive film by trace water during gas nitriding of stainless steel is revealed for the first time, which provides a new idea and method for the study of surface modification of stainless steel by gas nitriding.

Investigation on the influence of structural rigidity on the stiffness of aerostatic guideway considering fluid-structure interaction

The static performances of the aerostatic guideway are significantly influenced by the fluid-structure interaction (FSI) effect. This paper investigates the FSI process between the air film and two-stage cantilever structure of the slider based on a two-way transient FSI model, in which the thickness and shape of actual air film can be acquired. Moreover, the stiffness of the aerostatic guideway system with two different materials 38CrMoAl nitriding steel and 7075 aluminum alloy, is investigated numerically and compared experimentally. It proves that the structural rigidity of the slider has a non-negligible impact on the stiffness of the aerostatic guideway system. The inner mechanism of this phenomenon is further discussed to provide meaningful guidance for the design of the aerostatic guideway system.

Evolution of Microstructure and Hardness of the Nitrided Zone during Plasma Nitriding of High-Alloy Tool Steel

Plasma nitriding is widely used in various industrial applications to improve surface hardness and wear properties. Especially for tool steels, it is also used to improve the support and adhesion of diamond-like carbon (DLC) coatings. The properties of the nitrided zone produced by plasma nitriding are influenced by the applied process parameter, in particular temperature and time. However, for high-alloy tool steels, a deeper understanding of the underlying diffusion processes of the nitrogen and the interaction with the existing microstructure, as well as the effects on the case depth is still lacking. Therefore, in this study, specimens of high-alloy tool steel X153CrMoV12 were plasma nitrided at varying temperatures (480 °C, 520 °C, 560 °C) and treatment times (2 h, 4 h, 16 h). The resulting nitrided zones were investigated by optical and scanning electron microscopy (OM and SEM), depth-dependent glow discharge optical emission spectroscopy (GDOES), X-ray diffraction (XRD), and hardness measurements to characterize their microstructure, chemical composition, and hardness depending on the process parameters. The distribution of carbides (M7C3), e.g., chromium carbides, affects the diffusion of the nitrogen and the layer growth. An increase of temperature and duration leads to an increased layer thickness. The composition of the compound layer is, e.g., influenced by the process parameters: ε nitrides (Fe2–3N) occurred preferentially at lower temperatures, while γ′ nitrides (Fe4N) appeared mostly at higher temperatures. In order to investigate the influence of the carbides of the high-alloy tool steel on the nitriding process, a new methodology was developed by means of finite element analysis (FE), which makes it possible to analyze this influence on the development of the nitrogen concentration profile. This methodology makes it possible for the first time to map the heterogeneous nitrogen evolution and distribution.

Effects of surface topography at different scales on the dispersion of the wetting data for sessile water droplets on nitrided austenitic stainless steels

Plasma nitriding is used to increase the durability of steels. The wettability of nitrided surfaces is poorly studied. The ability of nitriding in modifying the wetting and evaporation of sessile droplets on austenitic stainless steel is studied. Transferred plasma for nitriding provides independent substrate biasing giving the opportunity to tailor the surface before and during the nitriding treatments. It was shown that a cleaning treatment (ArH2 plasma) produces topographical modifications of the surface by selective sputtering of the grains giving contact angles between 80 and 90°. Similar results are obtained when the nitriding treatments are carried out with a rather high bias voltage. It is explained using the skewness (Ssk) topographical roughness parameter which reveals the asymmetry of the profile. The more the Ssk is, the higher the contact angle is. During nitriding treatments, the very high internal stresses leads to the formation of spikes at the grain boundaries. Pinning of the three-phase contact line on peaks localized at grain boundaries are responsible for high contact angles. For nitriding treatments carried out with lower bias, surface contamination occurs and a discontinuous oxynitride layer is formed. The nanostructure formed by these oxides gives contact angles up to 120°.

Switching Optimally Balanced Fe–N Interaction Enables Extremely Stable Energy Storage

The interaction between electrode materials and charge carriers is one of the central issues dominating underlying energy storage mechanisms. To address the notoriously significant volume changes accompanying intercalation or formation of alloy/compounds, we aim to introduce and utilize a weak, reversible Fe–N interaction during the (de)intercalation of ammonium ions (NH4+) within iron(III) hexacyanoferrate (FeHCF), inspired by manipulating the electrostatic adsorption between N and Fe in the early stages of ammonia synthesis (Bosch‐Harber Process, Chemical Engineering) and steel nitriding processes (Metal Industry). Such strategy of switching well‐balanced Fe–N interaction is confirmed in between the nitrogen of ammonium ions and high‐spin Fe in FeHCF, as observed by using X‐ray absorption spectroscopy. The resulting material provided an extremely stable energy storage (58 mAh g−1 after 10 000 cycles at current density of 1 A g−1) as well as high‐rate performance (23.6 mAh g−1 at current density of 10 A g−1).

Evaluation of inkjet-printed spinel coatings on standard and surface nitrided ferritic stainless steels for interconnect application in solid oxide fuel cell devices

Inkjet printing technology was employed for the application of protective layer coatings in SOFC metallic interconnects. Aqueous-based spinel coatings were inkjet-printed on standard and surface nitrided K41 ferritic stainless-steel substrates. Inkjet-printed substrates were exposed to high-temperature oxidation and Area Specific Resistance (ASR) tests for 1000 h at 700 °C in air with 3% volume humidity, simulating SOFC cathode environment. Performance of inkjet printed coatings and effect of nitriding stainless-steel substrates were evaluated based on chromium migration/retention and Area Specific Resistance. Sol-gel infiltration was introduced to develop a scaffold layer over the porous microstructure. With the ASR reduced to a level ∼60 mΩ cm2 and chromium concentration in the getter (cathode) material below 1 atomic%, close to the detection threshold, the protective layers produced via inkjet printing present a promising solution for SOFC interconnector applications.

Study of the kinetics of wear of steels from the point of view of the provisions of the adhesive-hydrodynamic theory of wear

The article is devoted to the study of wear resistance of the surface layer of steels 40X and ШX15, when rubbed in oil I-20. A comparison of the surface layer of samples of raw and nitrided steels, before and after the tests. The study of the fine microstructure of the samples with the help of the LDFP microscope, allowed us to conclude that the samples that were subjected to ionic nitriding, improved roughness. In turn, increased the area of linear contact, reduced contact load. The graphic dependence of roughness indicators is constructed. After testing, we can conclude that nitrided steel has a long service life, namely high hardness, resistance to abrasion, durability and corrosion resistance. The mechanism for obtaining increased resources needs further study

A new experimental methodology to assess gear scuffing initiation

ABSTRACT This paper investigates the strong coupling between friction power losses and film thickness that prevent from clearly identifying the mechanism of scuffing through classical test procedures. As the film thickness appears of great influence on the phenomena, a new test method is presented, allowing scuffing initiation study with the film thickness as a key parameter. This new test method allows film thickness variation with minimal friction losses and bulk temperature variations. This procedure has been developed with nitrided steels and a synthetic base oil on a twin disks test rig. Even though asperity contact is considered necessary in literature for scuffing, the test result shows that it can be reached in full film lubrication, potentially through the collapse of the oil film. Different test methods allowing triggering scuffing through different parameters are identified, which shows that a variety of parameters is able to influence scuffing.

Temperature dependent erosion and Raman analyses of arc-deposited H free thick DLC coating on Cr/CrN coated plasma nitrided steel

Development of H and metal dopant-free single phase thick diamond like carbon (DLC) coating on metal nitride layer for automobile applications is still a challenging task due to internal stress developed during deposition of DLC films. A simple process was followed to deposit thick Cr/CrN/DLC (0.25/0.75/6 μm) coating on plasma nitrided steel using an un-filtered cathodic vacuum arc system without applying any high pulse bias voltage. In addition, the coating was deposited at room temperature and it showed very good adhesion on plasma nitrided steel surface and exhibited a very low coefficient of friction ~0.06 ± 0.005. Temperature dependent solid particle erosion tests were conducted according to ASTM-G-76-18 standards at an impinging angle of 45°. Erosion resistance of the coating is 33, 11, 7 and 6 times better than nitrided steel substrate at test temperatures of 25, 200, 300 and 400 °C, respectively. Better erosion resistance performance of a coating infers the long life of the coating on automobile components. A multi-wavelength Raman study gives a better understanding of the structural properties of DLC. So, the Raman spectra of the coating were recorded using three different laser wavelengths: 405 nm, 532 nm and 633 nm. The thermal stability of the coating was studied using temperature dependent Raman spectroscopy. The coating showed good thermal stability until a temperature of 425 °C.

Nanosized Cr-N clustering in expanded austenite layer of low temperature plasma-nitrided Fe-35Ni-10Cr alloy

Expanded austenite (γN) formed by low temperature nitriding of austenitic stainless steel is a N-enriched fcc containing Cr-N short range ordering, but no direct observation of Cr-N clustering has been reported. In the present study, the nanostructure of an Fe-35Ni-10Cr (at%) alloy plasma-nitrided at 673 K was investigated using transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP) technique in this study. Nanosized Cr-N clusters were directly observed in the γN accompanied with strong streaks in selected area diffraction, obvious modulated structure in TEM and Cr-N rich regions observed by 3DAP. Thermodynamic calculations suggested that Cr-N clusters were formed by spinodal decomposition due to a strong Cr-N attractive interaction. The hardness of the γN layer was much higher than that of Fe-N austenite steel, which indicates that the hardness is not only due to nitrogen solid-solution hardening but also to a synergetic effect of the coexistence of Cr and N.

Surface degradation of nitrided hot work tool steels under repeated impact-sliding contacts: Effect of compound layer

Wear behaviour of quenched and tempered (QT) hot work tool steels (Uddeholm QRO90) was investigated against SAE 52100 grade bearing steel balls after gas nitriding using a dedicated laboratory scale impact-sliding wear test rig. Gas nitriding was employed in a fluidised bed reactor under two alternative regimes: i. “High Temperature Nitriding (HTN)” carried out at 510 °C and ii. “Low Temperature Nitriding (LTN)” carried out at ≤ 400 °C. The HTN process resulted in the formation of ∼2 μm thick external compound layer, whereas the LTN processed steels were free of any surface compound layer formation. After the impact-sliding wear tests employed at room temperature (RT), the prevailing wear mechanisms of the examined steels were assessed as tribo-oxidation and fatigue wear. The testing at 600 °C induced different wear mechanisms for the HTN and the LTN steels. While tribo-oxidation and fatigue wear were preserved for the HTN steel, plastic deformation dominated the wear that progressed on the compound layer free surface of the LTN steel. Impact-sliding wear testing at 600 °C showed that the wear rate of LTN > HTN steels, as opposed to the wear rate at RT where wear rate of HTN > LTN.

Characterization of vein-like structures formed in nitrided layers during plasma nitriding of 8Cr4Mo4V steel

In this study, nitrided 8Cr4Mo4V was characterized, using optical microscopy, scanning electron microscopy, transmission electron microscopy (TEM), atom probe tomography (APT), electron probe microanalysis, and Thermo-Calc software, to study the vein-like structures formed during plasma nitriding. The structures existed in a certain zone in the nitrided layers, namely the posterior end of the N-content plateau and the anterior end of the N-content rapid-decline zones. The structures disappeared in the topmost surface layer with increasing nitriding time. For the first time, APT was used to observe these structures. Together, the APT and TEM images revealed that the main components of the structures were Fe3C and alloy nitrides. The structures and matrix were related through the (220) Fe3C//(110)α-Fe, [110] Fe3C//[001]α-Fe orientations. The appearance and disappearance of the structures were closely related to the C and N contents. In the alloy carbides, N replaced C to form alloy carbonitrides and released C and Fe to form Fe3C which appeared as the vein-like structures. In the topmost surface of the nitrided layers, the C content decreased because of decarburization. The Fe3C and alloy carbides were transformed into ferrite and alloy nitrides, and the structures disappeared.

Physical and Mechanical Characterization Study of Thin Nitriding Layers Produced by Plasma on Low Alloy Steel

The present study has been conducted in order to obtain iron nitrides layer on AISI4140 steel by using plasma nitriding treatment. As one of several parameters of this process, the nitrogen rate ranging from 10 to 70% with a step of 20% was chosen. The structure, the morphology, the thickness and the hardness of iron nitrides layer were investigated. As a result, the improvement of surface hardness of nitrided steel was identified related with the increase of compound layer thickness due to the increase of activation rate. The steel substrate treated at high activation rate presents hardness 3 times higher than that of untreated steel.

The “Expanded” Phases in the Low-Temperature Treated Stainless Steels: A Review

Low-temperature treatments have become a valuable method for improving the surface hardness of stainless steels, and thus their tribological properties, without impairing their corrosion resistance. By using treatment temperatures lower than those usually employed for nitriding or carburizing of low alloy steels or tool steels, it is possible to obtain a fairly fast (interstitial) diffusion of nitrogen and/or carbon atoms; on the contrary, the diffusion of substitutional atoms, as chromium atoms, has significantly slowed down, therefore the formation of chromium compounds is hindered, and corrosion resistance can be maintained. As a consequence, nitrogen and carbon atoms can be retained in solid solutions in an iron lattice well beyond their maximum solubility, and supersaturated solid solutions are produced. Depending on the iron lattice structure present in the stainless steel, the so-called “expanded austenite” or “S-phase”, “expanded ferrite”, and “expanded martensite” have been reported to be formed. This review summarizes the main studies on the characteristics and properties of these “expanded” phases and of the modified surface layers in which these phases form by using low-temperature treatments. A particular focus is on expanded martensite and expanded ferrite. Expanded austenite–S-phase is also discussed, with particular reference to the most recent studies.

Carbide formation accompanying internal nitridation of austenitic stainless steel

Internal oxidation, carburization, and nitridation are three forms of internal corrosion commonly experienced by high-temperature alloy components in industrial plants. They are characterized by ingress of an oxidizing species (oxygen, carbon or nitrogen) into the sub-surface region of the affected material, often accompanied by formation of precipitate phases. These microstructural changes can have a significant impact on mechanical performance. Management of such threats to equipment integrity therefore requires a comprehensive understanding of microstructural evolution, including rate information. In this work, we use optical, scanning electron, transmission electron, and atomic force microscopy to study precipitate phases and quantify internal corrosion rates in the austenitic stainless steel Alloy 800H subjected to nitriding in a 95% N 2 + 5% H 2 atmosphere at service-relevant temperatures (800–1000 °C). We identify and characterize carbide and carbonitride precipitates formed alongside the expected nitrides, and use the thermodynamic software Thermo-Calc to show that formation of carbides during nitridation is thermodynamically possible in this alloy. This work ultimately demonstrates that a wide-ranging analytical approach may be crucial to gaining a full picture of the effects of internal corrosion in complex industrial alloys. • M 23 C 6 carbides form during nitridation of Alloy 800H stainless steel at 800–1000 °C. • Both experiment and thermodynamic calculations needed to characterize phenomenon. • Carbide penetration kinetics during nitridation at 800–1000 °C have been quantified. • Classical oxidation theory can predict penetration in lieu of experimental data.

Effect of electric potentials on high‐temperature plasma nitriding of 2Cr13 stainless steel with active screen assisted

AbstractThe influence of electric potentials on the characteristics of modified layers with plasma nitriding of 2Cr13 stainless steel at a high temperature was investigated. Three active screens were placed on the cathodic plate. Three groups of 2Cr13 stainless steel samples were set with cathodic, anodic, and floating potentials. Samples were nitrided at 500 °C for 5 h in an ammonia atmosphere. The treated samples were analyzed using x‐ray diffraction, scanning electron microscopy with energy dispersive x‐ray spectroscopy, surface roughness tester, and atomic force microscopy. It is proved that nitriding treatments can be suitably carried out at three electric potentials, but the corresponding modified layers take on different microstructure, morphology, and hardness behaviors. It found that the three nitrided samples are mainly composed of the ϵ−Fe2‐3N and γ’−Fe4N phases. The order of thicknesses of the nitrided layers is: floating < anodic < cathodic potential. The results also demonstrated that electric potentials play essential roles in the corrosion resistance and tribological properties in plasma nitriding treatment. Because there is no visible precipitation of chromium nitride in the modified layer, the corrosion resistance of the floating nitrided sample is better than that of the other two samples.

Gaseous nitriding of additively manufactured maraging steel; nitriding kinetics and microstructure evolution

The nitriding response of additively manufactured M300 maraging tool steel was investigated through a series of nitriding treatments at different temperatures in the range 360–480 °C for a duration of 40 h. The interaction between nitrogen and alloying element nitrides (Ti and Mo) and intermetallics (Ni 3 Ti and Ni 3 Mo) was studied by comparing nitriding responses of as-solution treated and subsequently aged specimens. The nitriding behavior was found to depend strongly on the initial condition of the material and the nitriding temperature applied. Ultra-low temperature nitriding at 360 °C was found to be feasible as it resulted in a nitrided case, albeit with incomplete precipitation hardening of the bulk structure, thus resulting in a softer core. The application of a post-ageing treatment resulted in full bulk hardening and distinctly changed the appearance of the hardness profile. • Nitriding of solution treated and not aged maraging steel creates deeper case. • Nitride and intermetallic formation competes at increased nitriding temperatures. • Ultra-low temperature nitriding of maraging steel is feasible. • Post-ageing of ultra-low temperature nitriding creates promising hardness profile.

Effect of plasma nitriding ion current density on tribological properties of composite CrAlN coatings

CrAlN coatings were synthesized on pre-plasma nitrided M2 high speed steels using different ion current densities. The effect of plasma nitriding pretreatment on the microstructures and tribological properties of composite CrAlN coatings had been studied. The results showed that the nitriding efficiency could be significantly enhanced by higher ion current density. The thickness of nitrided layer increased from 43 μm to 63 μm with the increase of ion current density. The nitrided layers without either compound layer or grain boundary precipitation were produced with all experimental ion current densities. Radial cracks also appeared at the Rockwell-C indentation edge of the composite CrAlN coating due to the conformal effect. Moreover, radial cracks of the composite coatings originated from the hard and brittle nitrided layer. The highest interfacial adhesion of the composite CrAlN coating reached 105 N. Furthermore, the wear resistance of CrAlN coating was improved by combining nitriding pretreatment with coating deposition, and the composite coating (PN4/CrAlN) possessed the superior wear resistant.

Повышение стойкости инструмента из быстрорежущей стали при азотировании с регулируемым азотным потенциалом

The study of the gas nitriding method, which allows obtaining high-quality diffuse layers in high-speed steel P6M5 on the basis of an internal nitrogen hardening zone with no brittle nitride zone, has been viewed. Research results of phase composition of nitrided steel with a change in the nitrogen potential of the atmosphere during dilution of ammonia are presented. Nitrided tool increased resistance during drilling constructional steel and titanium alloy, which is due to precipitation hardening treatment of the internal nitrogenization zone using tungsten nitrides, is given.