Nitrided Steel Research Articles

Surface Structural–Phase Modification of Structural Steels during Gas Nitriding

The formation of a composite nitride layer in an ammonia atmosphere with the addition of carbon– and oxygen–containing gases during gas nitriding is considered. The conditions for the formation of cementite during nitriding of steel and the influence of carbon in the matrix on the release of cementite are given. After oxidation of the nitride layer, modified nitride compositions with stable gradient structural–phase states were obtained.

Tribocorrosive Aspects of Tungsten Carbide, Silicon Nitride, and Martensitic Steel under Fretting-like Conditions

Water-based lubrication faces the common challenge of component lifetime extension which is impaired by tribocorrosion due to material surface depassivation. However, such mechanisms in a pH-neutral and low-halide electrolyte require additional understanding. A ball-on-flat configuration study of hard-phase materials in a low amplitude–high frequency sliding contact against martensitic chromium steel with contact pressures around 200 MPa is presented. Under lubrication by purified water, tungsten carbide-based metal matrix composite (MMC) with NiCr binder and silicon nitride-based ceramic (SiAlON) against DIN/EN 1.4108 steel yielded coefficients of friction above unity. Wear scar enlargement led to fretting-like conditions with adhesion becoming the fundamental wear mechanism. A tribocorrosion-induced depletion of tungsten carbide and nickel was determined for MMC. SiAlON materials suffered extreme wear under the formation of abrasive SiO2, while heat-treated DIN/EN 1.4125 steel showed lower friction and wear, but also showed signs of hydrogen embrittlement. Results from accompanying single-material corrosion experiments could not satisfactorily explain the phenomena. Including galvanic interaction and the influence of contact geometry, a new tribocorrosion model for fretting conditions is proposed. It describes an expanding anodic belt located at the inner-most crevice position of an otherwise cathodically polarized material. Low conductivity of the electrolyte is seen as a key player in this process, while the galvanic situation between two materials in contact was shown to invert when water was substituted by a wet organic phase.

Wear performance under dry and lubricated conditions of duplex treatment TiN/TiCrN coatings deposited with different numbers of CrN interlayers on steel substrates

Cold work steels are used in harsh conditions including high load, wear, corrosion, and mechanical stresses that can easily lead to degradation and wear of the material. Generally, multilayer ceramics coatings are attractive candidates to develop engineering components by combining positive characteristics of different coatings. In this study, the TiN/TiCrN coatings with the different number of CrN interlayers were successfully deposited on nitrided and non-nitrided DIN 1.2379 steel, and their wear behavior was investigated at dry and lubrication conditions under different loads. The relationship between coating architectures and coating characteristics was explored. The microstructure and composition of the specimens were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) with Energy dispersive X-ray analysis (EDX) and Atomic force microscopy (AFM).The nano-hardness were measured by nanoindenter, respectively. The adhesion and tribological behavior were evaluated using the Rockwell-C indentation and reciprocating tribometer tests, respectively. The results reveal that the nitrided samples with the TiN/TiCrN coatings with the different number of CrN interlayer showed much better wear resistance than the non-nitrided coatings at dry conditions. On the other hand, nitrided and nitride + coated TiN/TiCrN with the different number of CrN interlayer specimen showed better wear resistance at lubricated conditions. In addition, the fact that uncoated and nitrided steels have higher wear resistance at lubricated conditions than coated samples shows that TiN/TiCrN coatings are not proper even with a lubricant additive over a certain load value.

High-throughput investigation of Cr-N cluster formation in Fe-35Ni-Cr system during low-temperature nitriding

The expanded austenite (γN) produced by low-temperature nitriding of austenitic stainless steels with a Cr content of 18–20 at% is conventionally regarded as a nitrogen-supersaturated fcc solid solution with Cr-N short-range ordering, while obvious clustering between Cr and N in γN was recently reported for a Fe-35Ni-10Cr (at%) alloy. To investigate the dependence of Cr-N cluster formation on Cr concentration in γN, a high-throughput approach is proposed in the present work where a diffusion couple of Fe-35Ni and Fe-35Ni-30Cr alloys was plasma-nitrided at 673 K for 30 h. Systematic nanostructure characterization of the γN conducted by transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP) revealed the variations in nanosized Cr-N clustering as modulated structures with different Cr content. Considering a simultaneous concentration fluctuation of Cr and N, computational thermodynamics of chemical driving force, strain energy, and modulation wavelength for coherent spinodal were performed, and the results were consistent with observed nanostructure evolution. The nanostructures of γN in austenitic stainless steels were also understood as further increments of Cr and N from a moderate composition lowered the driving force. The spinodal decomposition is also promoted by increasing Ni content in the alloys.

Effect of plasma nitriding substrate current density on the adhesion strength of in situ PVD TiN coatings

TiN coatings were in situ deposited on un-nitrided and nitrided M2 high speed steels by electrically enhanced cathodic arc evaporation technology. The morphology, microstructure, phase composition, as well as microhardness and nano-hardness of the samples were analyzed by scanning electron microscope, optical microscope, X-ray diffraction, Vickers hardness tester, and nano-indentation, respectively. In especially, the effect of nitriding substrate current density on the adhesion strength of in situ TiN coatings was investigated by Rockwell indentation and scratch tests. The results showed that the nitrided layer thickness increased with increasing substrate current density and “bright” nitrided layer was achieved. In the Rockwell indentation test, the radial cracks on the surface of the duplex-treated samples originated from the hard and brittle nitrided layer as compared to the nitrided substrate, which corresponded to the failure mechanism of brittle fracture. In the scratch test, the adhesion strength of coating to substrates was significantly improved by nitriding pretreatment. Furthermore, the critical load of the duplex-treated samples increased with the increase of nitriding substrate current density. In addition, tensile cracks only occurred in the case of the N120/TiN sample.

Sliding wear behaviour of salt bath nitrided 316LN austenitic stainless steel

The wear behaviour of AISI 316LN austenitic stainless steel has been studied by varying the duration of nitriding. AISI 316LN steel was nitrided using salt bath nitriding which consist of a mixture of 70:30 ratio of alkaline cynates and carbonates. Nitriding was carried out for two time durations namely 60 min and 100 min. Pin-on-Disc wear test were carried out for both the untreated and treated sample at room temperature. The wear parameters were changed to understand the wear mechanism of AISI 316LN steel along with the nitrided sample by varying the sliding distance for 250 m, 500 m and 1000 m. Due to the presence of different wear mechanism the rate of wear varies as a function of sliding distance. For untreated sample the wear mechanism was dominant with adhesion, abrasion and plastic deformation. An optical micrograph, X-ray diffraction analysis, wear morphology, hardness measurement and surface roughness were carried out. Due to the presence of compound layer as a result of nitriding AISI 316LN austenitic stainless steel, the mechanism of wear was restricted to abrasive wear. Untreated specimens have more significant wear loss when compared to treated specimen as work hardening and an increase in hardness of wear track resulted in material pull out. Stability of the compound layer is achieved as a result of longer duration of nitriding. Abrasive wear is resisted to a greater extend due the availability of compound layer. AISI 316LN steel which was nitrided for 100 min exhibited a more stable compound layer when compared to the same nitrided for 60 min.

Wear resistance of structural steels nitrided in a cyclically switched discharge with dry friction

The paper examines the method of conducting tribological studies in the dry mode of friction of nitrided and unhardened structural steels 20 and 45 in order to achieve comparable results of laboratory tests with operational characteristics. Preliminary studies of anodized steels of the same steels indicate that under conditions of extreme friction it is extremely difficult, and in some cases impossible, to use such values of specific pressure on the friction surface, at which it would be realistic to compare the results obtained for different samples made of different brands materials and processed using various technological processes. Since during the tests, constant lubrication of the friction zone was ensured, a layer of lubricant was present on the friction surface up to a certain pressure value, which led to extremely small indicators of linear wear. However, depending on the characteristics of the modified surface, there was a critical value of pressure at which the layer of lubricant was squeezed out of the friction zone, which led to instant adhesion of the surfaces. Thus, the study of wear resistance in the dry mode of friction ensures a significantly higher productivity of experiments.
 Unlike experiments with limit friction, dry friction can be used for different steels at the same pressure value, which eliminates the problem of comparability of results and contributes to the objectivity of conclusions regarding the effectiveness of various modification processes.
 According to the results of previous experiments, such a compromise pressure value can be 16 MPa.
 Another important phenomenon for the analysis of the influence of the modification results on the wear resistance characteristics of the surface is established - the effect of relaxation processes in the near-surface layers, which have already acquired structural transformations under the influence of pressure in the friction zone.
 For all steels, there is some slowing down of the intensity of wear after a break with a gradual return to the intensity characteristic of a certain brand of steel. The reason for such a phenomenon can only be the relaxation of stresses and the equalization of the characteristics of the structure in the near-surface layers. At the same time, the result is the strengthening of the surface, which explains the decrease in the intensity of the wear process. over time, as the strengthened layer breaks down, the indicators of the surface condition become equal to those before the break and the intensity of wear is restored.

Influence of High-Temperature Annealing on the Structure and Microhardness of a Multilayer Composite Based on Nitrided Steel and Fe–Cr–V Alloy

Influence of High-Temperature Annealing on the Structure and Microhardness of a Multilayer Composite Based on Nitrided Steel and Fe–Cr–V Alloy

Low-Temperature Plasma Nitriding of Martensitic and Austenitic Steels to Increase Tribocorrosion Resistance*

Abstract Tribocorrosion is the simultaneous occurrence of wear and corrosion in a tribosystem and their interaction. In many applications, such as media-lubricated rolling bearings and (cutting-)tools in the food industry or medicine, tribocorrosion occurs and leads to a high material loss and damage to materials. The tribocorrosion resistance of mechanically and chemically stressed steel surfaces can be significantly increased by low-temperature plasma nitriding at T < 400 °C. In this process, nitrogen is forcibly dissolved in the surface area (up to approx. 20 μm) in high contents of 15 wt.-% without precipitation. This results in an extreme expansion and distortion of the metal lattice (“expanded martensite”, “expanded austenite”), which leads to an increase in hardness of up to 1000 HV with the same or even increased pitting corrosion resistance. Due to the formation of expanded martensite/austenite, the tribocorrosion resistance of the martensitic steels X40Cr14 and X54CrMnN13-2 and that of an austenitic CrMn steel can be significantly improved compared to the initial state, which is expressed in a 40–70 % lower material loss under tribocorrosive attack. It was found that the tribocorrosion resistance depends on the process parameters of the surface treatment and on the chemical composition of the steels and their crystal lattice.

Effect of AISI H13 Steel Substrate Nitriding on AlCrN, ZrN, TiSiN, and TiCrN Multilayer PVD Coatings Wear and Friction Behaviors at a Different Temperature Level

Moving components of industrial machines and tools are subjected to wear and friction. This reduces their useful life and efficiency in running conditions, particularly at high temperatures. One of the most popular solutions is to apply an appropriate surface coating to the tribocouple's base materials. In this study, tribometer experiments were used to evaluate the tribological performance of cathodic arc physical vapor deposited (CAPVD) AlCrN, TiSiN, CrTiN, and ZrN coatings on the gas nitrided AISI H13 tool steel to explore the effects of nitriding the steel on wear and friction behavior of these coatings at ambient and elevated temperatures. The coatings characterization is split into three main parts: mechanical, morphological, and chemical characterization. Nanoindentation has been used for mechanical characterization, thin film X-ray diffraction (XRD), and an energy-dispersive X-ray spectrometer mounted on a scanning electron microscope for chemical characterization, optical profilometer, and atomic force microscopy (AFM) for morphological characterization. Significant improvements in the adhesion qualities of the coatings to the substrate were achieved as a result of nitration. Due to this circumstance, the coatings' load-bearing capacity and high-temperature wear resistance ratings were enhanced. The wear results showed that the AISI H13 tool steel nitriding with AlCrN and ZrN layers decreased wear rates by two to three times at 700 °C.

Elevated Temperature Plasma Nitriding of CrMoV Tool Steel for the Enhancement of Hardness and Wear Resistance

Elevated Temperature Plasma Nitriding of CrMoV Tool Steel for the Enhancement of Hardness and Wear Resistance

Initial phase formation during nitriding of austenitic stainless steel

Expanded austenite formed by inserting nitrogen into austenitic stainless steel is a puzzling phase since its discovery about 30 years ago: variable nitrogen concentration correlated with a variable lattice constant together with an unusual depth profile normally indicating a compound layer instead of a diffusion layer. While expanded austenite has been described for nitriding experiment durations as low as 5 min and >48 h, the initial phase transition has not been investigated in detail. Here, very low ion current density experiments prolonging the initial phase together with in-situ X-ray diffraction (XRD) experiments during nitriding are presented. Additionally, the formed layers are investigated by depth-resolved in-situ XRD measurements during successive removal of the surface layer. It is shown that two phases, a low expansion phase and a high expansion phase, are formed sequentially over time with the growth rate of the latter phase being much higher, thus obliterating any trace of the initial phase. It is surmised that the driving force is a threshold in the nitrogen concentration.

Investigation of the Structural, Tribological, and Electrochemical Properties of Nitrided and Boronized AISI 316L Stainless Steel

Investigation of the Structural, Tribological, and Electrochemical Properties of Nitrided and Boronized AISI 316L Stainless Steel

Structure of the surface layer of high-chrome steel nitridated in the elion regime in the plasma of a suspended arc discharge with a heated cathode

The purpose of this work is to reveal the patterns of formation of the structure of the surface layer of high-chromium steel subjected to nitriding in a low-pressure gas discharge plasma using a plasma generator with a hot cathode "PINK". Heating of the samples to the nitriding temperature was carried out by the ionic component of the plasma, as well as by the electron and ionic components of the plasma (elion mode). The object of the study was heat-resistant corrosion-resistant steel of the austenitic class grade 20X23H18 (foreign analogue of AISI310S). The relevance of research is due to the relatively low level of hardness and wear resistance of steels of this class. Nitriding of steel was carried out on the TRIO installation, retrofitted with a switching unit for implementing the aelion (electronic and ionic) processing mode. It has been established that the thickness of the hardened layer is (55-60) pm and weakly depends on the method of nitriding, temperature (in the range of 793-873 K), and duration (3-5 hours) of the process. A nitriding regime has been revealed that makes it possible to form a surface layer with a microhardness of 13.7 GPa (ionic heating mode) and 10.8 GPa (elion heating mode). It has been established that the high strength and tribological properties of nitrided steel are due to the formation of a nanocrystalline structure in the surface layer, the main phases of which are iron nitrides Fe4N and chromium nitrides CrN. It is shown that heating the samples to the nitriding temperature in the aelion mode, which uses the electron and ion components of the plasma, leads to a significantly lower level of material roughness compared to the samples heated during nitriding by the ion component of the plasma.

Evaluation of hybrid spindle bearings with nitriding raceway steels under high rotational speeds

The further development of high-precision bearings regarding higher speeds and load-carrying capacity is becoming increasingly challenging. One approach to meet the increased requirements is to use new high-performance raceway steels. Particularly for a highly stressed lubricant film, where seizure may occur, the bearing material properties can make a key contribution in increasing the lifetime. In the following, the test results of hybrid spindle bearings of type 7008 made of nitriding steel are analysed. The bearings were tested in an endurance run for a constant speed parameter of 2.5 million ndm and a maximum contact stress of 2,900 MPa at the inner ring contact. The operational behaviour was validated based on the bearing outer ring temperature and the acceleration level in the test rig. A further sample test in endurance runs with an increased speed parameter of 2.8 million ndm and a maximum contact stress of 3,200 MPa at the inner ring shows that the performance limit of the bearing is even higher than initially assumed. The microscope analyses of the bearing steels after the test show low wear. An analysis of the test conditions in terms of contact stresses, lifetime and the pv value illustrates that the bearings can run far above standard conditions. The experimental results show that the operational limits of hybrid spindle bearings with a raceway made of nitriding steels are significantly higher than expected.

Contribution of thermal dissociation during steel nitriding in electron beam plasma

We report the results of measurements of mass-to-charge ion composition of the beam plasma generated by a forevacuum plasma-cathode electron source in a nitrogen atmosphere during electron beam interaction with the surface of a steel sample. It has been found that as the sample surface temperature increases from 540 ℃ to 930 ℃, the fraction of atomic nitrogen ions in the spectrum increases by 4-10%. This increase in atomic nitrogen occurs at the backdrop of decreasing number of molecular nitrogen monoxide ions and is associated with thermal dissociation of its molecules.

Formation of diffusion nitride-oxide coatings

It is known that nitro-oxide coatings were developed based on nitriding, which are obtained using a two-stage technology consisting of nitriding at the first stage of the process and vaporization at the second stage. Such processing provides high physical and mathematical characteristics of hardened parts. This technological process was improved by us due to preliminary oxidation, which made it possible to accelerate the production of nitride-oxide with the necessary physical and mechanical properties. This work makes a theoretical calculation of the oxidation processes and subsequent nitriding of steels and a comparison with experimental data on the example of 38X2MYA. The article presents an analysis of the formation of oxynitride diffusion protective layers obtained by a three-stage nitriding method at a temperature of 580° C, which consists of preliminary oxidation, nitriding, and subsequent steam oxidation. The article also describes the effect of the oxide film on the nitriding process during preliminary oxidation and nitriding under short-term conditions at a temperature of 580 S.

Structural-phase transformations during nitro oxidation of steels and surface properties

Structural and phase changes in the surface diffusion layer during gas nitriding of steel were studied, with the formation of a crystallographic structure of the nitride layer for subsequent oxidation in water vapor. The conditions for forming carbides and nitrocarbides with simultaneous diffusion of nitrogen and decarburization of the steel matrix are determined depending on the nitrogen potential of the saturating medium. The structural-phase states of the surface diffusion layer with a stepwise change in the nitrogen potential during nitriding at the first stage and followed by oxidation at the second stage, the formation of a surface oxide layer, as well as the conditions for participation in mutual diffusion processes of carbon in the nitride layer, decarburized from the steel matrix with the formation compositions of modified nitride phases. The nitride-oxide layer’s corrosion properties and gradient properties in various structural-phase states of nitride phase compositions have been studied.

Physical and Technological Parameters of Cr28 Steel Nitriding in an Ammonia Environment

Physical and Technological Parameters of Cr28 Steel Nitriding in an Ammonia Environment

Wear Behavior of Roller‐Burnished High Interstitial Austenitic Stainless Steel Parts in Glass‐Reinforced Plastic Melt

Herein this investigation, profiled high interstitial austenitic stainless steel parts are burnished on a profile‐rolling machine, and afterward, the wear behavior is analyzed in a melt of glass‐reinforced polypropylene. Wear and corrosion resistance are significant properties of steel parts in the plastics and food industries. The high work‐hardening ability of high interstitial austenitic stainless steel enables burnishing parts with a significant local hardness to increase up to maximum values of ≈600 HV 1. Wear tests on a recently developed test stand reveal that the burnished austenitic stainless steel surface performs similarly to a nitrided surface of the standard nitriding steel 31CrMoV9 + QT with a hardness of ≈830 HV 0.5. Regarding the given advantage of corrosion resistance, it is concluded that roller burnishing supports the applicability of high interstitial austenitic stainless steel in plastics and food industries.