Nitrided Steel Research Articles

Adhesion-Related Phenomena of Stellite 6 HVOF Sprayed Coating Deposited on Laser-Textured Substrates.

The focus of this research is to examine the feasibility of using laser texturing as a method for surface preparation prior to thermal spraying. The experimental part includes the thermal spraying of a Stellite 6 coating by High Velocity Oxygen Fuel (HVOF) technology on laser-textured substrates. The thermal spraying of this coating was deposited both on conventional substrate material (low carbon steel) and on substrates that had been previously heat treated (nitrided steel). The properties of the coatings were analysed using scanning electron microscopy (SEM), optical microscopy (OM) and Raman spectroscopy. Adhesion was assessed through a tensile adhesion test. The results showed the usability of laser texturing in the case of carbon steel, which was comparable or even better than traditional grit blasting. For nitrided steel, the problem remains with the hardness and brittleness of the nitrided layer, which allows for the propagation of brittle cracks near the interface and thus reduces the adhesion strength.

Evaluation of wear and corrosion resistance in acidic and chloride solutions of Cathodic Arc PVD chromium nitride coatings on untreated and plasma nitrided AISI 4140 steel

Chromium nitride ceramic like coatings are well known for their hardness and wear resistance, especially under severe conditions. When deposited on mild steel, nitriding is required for such applications to create a gradient hardness profile and improve the coating adhesion and the system's mechanical properties. Corrosion resistance is also necessary since these chromium coatings are recommended for applications in the plastic mould and injection industry. Therefore, in this work, the combination of a nitriding without white layer pretreatment and CrN coating was studied in a chloride and an acidic electrolyte, to asses if the diffusion layer also plays an important role as a corrosion protection treatment. Coating microstructure, adhesion to both nitrided and non-nitrided steel, wear resistance, and corrosion resistance in chloride and acidic media were evaluated. For comparison, bare and nitrided steel were also examined. Results indicated an improvement in the adhesion for the duplex treatment (nitriding + CrN). The CrN coating demonstrated a considerably lower coefficient of friction and wear rate compared to both non-nitrided and nitrided steel. Regarding corrosion, the iron nitride layer provides some protection in chloride environments; however, in acidic media, only the CrN coating plays a protective role. In both media, localized attack occurred at sites where the coating had defects, such as pores or pinholes through which the electrolyte comes into contact with the substrate. The duplex treatment proved to be the most effective surface treatment for AISI 4140, achieving excellent tribological properties, good adhesion, and high corrosion resistance in both neutral chloride and acidic solutions.

Kinetics of Iron Nitride Layer Growth during the Nitriding of AISI 1085 Non-Alloy Steel and AISI 52100 Alloy Steel.

This paper presents a comparison of two-component ammonia-based inlet atmospheres diluted with either hydrogen (NH3/H2) or nitrogen (NH3/N2). Taking advantage of the features of inlet atmospheres diluted with nitrogen and hydrogen, four two-stage processes were designed and carried out, which were juxtaposed with two single-stage processes carried out only in an NH3 atmosphere. A common parameter of the processes carried out was the same value of nitrogen availability in each process stage. The gas nitriding process was carried out on ASIS 1085 non-alloy steel and ASIS 52100 alloy steel. It was found that the chemical composition of the steels studied, for the adopted nitriding process parameters, did not affect the kinetics of the growth in the mass of nitrided samples as a function of the nitriding time. However, the additions of alloying elements present in the steels studied significantly affected the nitrogen distribution between the resulting iron nitride layer and the diffusion zone in the nitrided substrate. Because of the presence of chromium in AISI 52100 steel, a larger mass of nitrogen accumulated in the nitriding zone in the solution compared with unalloyed AISI 1085 steel. As a result, with the same increase in the mass of nitrided steel, a thicker layer of iron nitrides formed on AISI 1085 steel than on AISI 52100 steel.

The Effect of Heat Treatment on the Plasma Nitriding of Hot-rolled 17–7 PH Stainless Steel

17–7 PH stainless steel is a highly versatile material with a multitude of applications in a diverse range of fields, including aerospace, chemistry and petrochemistry, and medicine. The material’s exceptional mechanical properties and corrosion resistance render it the optimal selection for numerous components and instruments. Nevertheless, the surface properties of 17–7 PH stainless steel are inadequate for applications requiring high hardness and wear resistance in certain extreme environments. Due to its excellent mechanical properties and corrosion resistance, it can be utilized in the manufacturing of pharmaceutical equipment components. However, certain specialized environments still require surface nitriding treatment. Considering the complex heat treatment process required for this material, this paper reports a detailed study of the surface performance changes of 17–7 PH steel before and after ion nitriding following aging heat treatment. The study employs rolled 17–7 PH stainless steel as the subject material. The impact of heat treatment on plasma nitriding of stainless steel is investigated by comparing and analyzing the influence of martensite content and dislocation density within the martensite of the material prior to and following heat treatment on the hardness, thickness, and corrosion resistance of the nitrided layer on the surface of the steel after nitriding. The results demonstrate that 17–7 PH stainless steel, which does not undergo heat treatment, exhibits a high internal dislocation density, a high nitriding efficiency, and consequently, a high surface hardness. Following the application of a heat treatment, there is an increase in the martensite content of 17–7 PH stainless steel, a decrease in the dislocation content, and an increase in the matrix hardness.

Complex electron-ion-plasma surface modification of high-alloy stainless steel

The work is devoted to identification and analysis of patterns of change in the elemental and phase composition, defective substructure, mecha­nical (microhardness) and tribological (wear resistance and friction coefficient) properties of stainless high-chromium steel subjected to complex processing, combining vacuum irradiation of the samples surface layer with an intense pulsed electron beam of submillisecond exposure duration and subsequent nitriding under electron-ionic heating conditions. High-chromium steel AISI 310S, which in the initial state is a polycrystalline aggregate based on γ-iron, was used as the research material. Pulsed electron beam treatment of steel was carried out on a “SOLO” installation equipped with an electron source with a plasma cathode based on a low-pressure pulsed arc discharge with grid stabilization of the cathode plasma boundary and an open anode plasma boundary. Steel nitriding was carried out on a “TRIO” installation with a chamber size of 600×600×600 mm, equipped with a switching unit to implement the electron-ionic processing mode. Nitriding was carried out at 723, 793, and 873 K temperatures for 1, 3 and 5 h. It was found that electron-ionic nitriding of the samples pre-irradiated with an electron beam (10 J/cm2, 200 μs, 3 pulses at 723 and 793 K for 3 h) is accompanied by the formation of a ceramic layer containing only iron and chromium nitrides. The highest values of steel wear resistance after electron-ionic nitriding, exceeding the wear resistance of the initial steel by more than 700 times, are observed at nitriding parameters of 793 K, 3 h.

Surface Modification of Chromium–Nickel Steel by Electrolytic Plasma Nitriding Method

Electrolytic plasma nitriding is an attractive chemical heat treatment used to improve the surface properties of steel by implementing nitrogen saturation. This method is widely applied to steel and iron-based alloys operating under various operating conditions. In this work, using liquid-phase plasma nitriding technology, a nitrided layer was obtained on the surface of 40CrNi steel in electrolytes of different concentrations. The microstructure and phase composition of the nitrided layer were investigated and analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and we performed Vickers hardness and wear resistance tests using the ball-on-disc method. The microhardness and wear resistance of nitrided 40CrNi steel were significantly improved due to the lubricating properties of the ε-Fe2N phase formed on its surface.

Grain refinement of Fe4N compound layer in nitrided steel

This study elucidated the microstructure of the Fe4N (γ’) compound layer in specimens subjected to the nitriding to the specimens with various finished surfaces. Gyrofinishing produces a specimen surface with an ultra-fine-grained (UFGed) structure and a rough surface, whereas the buff-finished specimen exhibited a coarse grain but smooth surface. The γ’ grains formed on the gyrofinished specimens after nitriding were considerably finer and more equiaxial compared with those on the buff-finished specimen. The γ’ nucleated from the grain boundary in the matrix, indicating that the grain boundaries act as a nucleation site. Therefore, the UFGed structure promotes the nucleation of γ’ during the nitriding, resulting in fine grains. Numerous pores were formed in the γ’ layer of the gyrofinished specimen owing to the rough surface. The UFGed structure and surface roughness before nitriding are key factors for controlling the microstructure in the γ’ compound layer.

Microstructure characterization and high-temperature wear behavior of plasma nitriding mold steel

Considering the cyclic variation of temperature and load in the glass molding, the mechanical properties and wear behavior of the nitriding mold steel at high temperatures are necessary to investigate. In this research, the microhardness variation of mold steel after plasma nitriding is elucidated and associated with the microstructure. The high-temperature nanoindentation experiments are conducted to clarify the impact of temperature on mechanical behavior of the nitriding steel. The hardness and elastic modulus of the nitriding steel are decreased by 40.9 % and 19.5 % when the temperature increased from room temperature to 400 °C. Correspondingly, due to the hardness dropping, the wear resistance of the nitriding mold steel decreases gradually with the temperature. However, the wear resistance of the nitriding mold steel under high temperatures is still superior to that of conventional mold steel. A wear schematic model is developed to elucidate the wear behavior evolution mechanism of the nitriding steel with temperatures. This work provides a comprehensive investigation of the mechanical and wear behavior of the nitriding mold steel under high temperatures which avoids mold wear failure in glass compressing molding.

Modeling of Plasma Nitriding of Austenitic Stainless Steel through a Mask

In this work, 2D simulations of stainless steel nitriding through a mask were performed with two configurations: with and without lateral adsorption under the mask, depending on the strength of the mask adhesion. The stress-induced diffusion and trapping–detrapping process are included as the main mechanisms of nitrogen mass transport. The main focus is on the analysis of the swelling process, which affects the expansion of the material. The surface concentration profiles and topographical profiles along the surface are calculated and compared with experimentally registered ones taken from the literature, and they show a good agreement. This allows for estimation of the values of model parameters. Because nitriding processes takes place in vertical and horizontal directions, the anisotropic aspect of nitriding are analyzed. It is shown that the adherence of the mask significantly influences the topographical profile and the anisotropy of nitriding, because in the case of a weakly adhered mask, a lateral adsorption process takes place under the mask. The influence of swelling and anisotropy in the case of pattern nitriding in small dimensions is discussed.

Measuring depth-dependent residual stresses in gaseous nitrided steels using indentation method

Measuring depth-dependent residual stresses in gaseous nitrided steels using indentation method

Understanding crack growth within the γ′ Fe4N layer in a nitrided low carbon steel during monotonic and cyclic tensile testing

Nitriding is a cost-effective method to realize simultaneous improvements in tensile and fatigue properties and resistance to abrasion and corrosion. Previous studies reported that nitriding pure Fe enhances tensile strength by ~ 70% and fatigue limit by ~ 200%. It is due to the increase in surface hardness caused by the formation of γ′(Fe4N) and ε(Fe2-3N) nitrogen-containing intermetallic compound phases. However, the intermetallic compound layer is prone to brittle-like cracking. To better design nitrided steels, it is crucial to identify the crack growth mechanisms via analysis of the microstructural crack growth paths within the ~ 4–6 µm thick nitride layer. In the current work, we statistically evaluate the crack propagation behavior in the γ′ Fe4N layer during monotonic and cyclic tensile deformation in nitrided low-carbon steel (0.1 wt% C). Since nitriding typically results in the formation of columnar grains, the effect of morphology needs to be clarified. To this end, the steel was shot-peened and subsequently nitrided to promote equiaxed nitride grains morphology (~ 16% increase). Crack growth paths were comparatively evaluated for multiple cracks, and no significant effect of nitride morphology was observed. {100}γ′ is the predominant transgranular crack path in the monotonic tensile tested specimen, followed by {111}γ′. It is despite the elastic modulus of {111}γ′ < {100}γ′. This contrary behavior is explained by {100}γ′ plane having the lowest surface energy (density functional theory calculations). In the cyclic tensile loaded specimen, experiments revealed that transgranular cracking along {100}γ′ (cracking via symmetric dislocation emission) or {111}γ′ (slip plane cracking) is equally likely.Graphical abstract

Vacuum Nitriding of Heat-Resistant Steel After Laser Processing

Vacuum Nitriding of Heat-Resistant Steel After Laser Processing

Degradation Processes of Two Compound Layers on Nitrided Surfaces During the Wear Test by “Block on Hot Al Cylinder”

The results obtained in the study help to explain the degradation process of the nitrided steel compound layer. Compound layers with different properties on gas-nitrided H10 tool steel blocks were tested for wear with “block on hot Al cylinder”. Degradation processes were observed on both compound layers with different properties and at three contact pressures. In order to observe the degradation processes in the compound layers, the wear tests were interrupted at various fixed time intervals and the resulting changes were closely monitored. The comprehensive analysis highlighted the complexity of the degradation process in the compound layers and emphasized the existence of complex relationships between the above-mentioned parameters. The reaction of the nitrided steel surface with hot Al is more pronounced in areas with lower contact pressure, while adhesive removal and furrow formation are pronounced in areas with low and medium contact pressure. This process begins with a sufficient density of the areas where islands of adhesive removal are located, their enlargement during the test, the breaking up of the walls between them, and finally the removal of the compound layer in the sliding direction, which appears as furrowing in the final phase of wear.

Insight into the corrosion behaviors and mechanism of arc discharge plasma nitrided H13 steel in molten Al-Si

AISI H13 steels were nitrided via arc discharge plasma nitriding (ADPN) with various arc currents (55, 70, 85, and 100 A) at 400 °C. The surface microhardness, wear resistance, and molten Al-Si corrosion resistance of nitrided H13 steel exhibited significant enhancements. The surface microhardness and wear resistance of nitrided H13 steel were significantly improved due to the lubricity property of the ɛ-Fe3N phase formed on the surface and the solid solution strengthening of the αN. Meanwhile, the nitrided layer led to a change in the corrosion mechanism from dissolution to pitting. Compressive internal stresses in the nitrided layer inhibited crack formation and promoted passivation layer formation. The high-efficiency ADPN process not only yields a wear-resistant surface but also provides a potential solution for improving the corrosion resistance against molten alloys.

Optimized Compound Layer Design for Highly Loaded Nitrided Gears

AbstractNitriding is a thermochemical surface hardening process, which can be used to improve the performance properties of gears. In particular, the tooth flank and tooth root load-carrying capacity can be significantly increased by nitriding. Previous work has shown that tribological dominated failure modes and limits, such as the micro-pitting and wear load-carrying capacity of gears, can be significantly increased by a suitable compound layer structure. In this work, the relationship between compound layer design and macro-pitting load-carrying capacity of nitrided gears is explored based on experimental investigations. For this purpose, the materials EN31CrMoV9 and EN42CrMo4 were nitrided under varying nitriding conditions to produce compound layers with different structures and properties. The characteristics of the compound layer such as phase composition, compound layer thickness and pore seam were extensively characterized by means of metallographic techniques, XRD, GDOES, and EBSD. Experimental investigations of the macro-pitting load-carrying capacity were carried out on an FZG back-to-back gear test rig with center distance a = 52 mm. It was shown that the pitting load-carrying capacity depends to a large extent on the characteristics of the compound layer, in particular on the formation of the pore seam. A minimum pore seam thickness of CLTP ≥ 1.8 µm has a positive effect on the pitting load-carrying capacity. The test results for the pitting load-carrying capacity are above (σH lim ≥ 1690 N/mm2) or, in some cases, significantly above (σH lim = 1979 N/mm2) the strength values specified in ISO 6336-5:2016 for nitrided nitriding steels (σH lim = 1450 N/mm2; material quality ME) and case-hardened alloy steels (σH lim = 1650 N/mm2; material quality ME).

Study the variation of current density & corrosion behavior of modified M2 tool steel: Simulation & experimental

In this study, the simulation of the current density was carried out through COMSOL Multiphysics on surface-modified M2 high-speed tool steel. The results demonstrated that in the presence of the nitride layer on the surface of M2, the current density was increased remarkably in the nitride layer and M2 was immune, and consequently, it can be predicted that the corrosion resistance was increased. For verification, the surface modification through plasma nitriding was applied on the M2 steel corrosion resistance and was evaluated through polarization and electrochemical impedance spectroscopy (EIS) in the 3.5 wt% of NaCl solution. The results confirmed the simulation outcomes; therefore, optimization of the parameters was performed. The impression of the variation of the process parameter of plasma nitriding such as temperature (500, 550, and 600 °C), time (4, 6, and 8 h), and ratio of inserted gases (N2/H2: 1:3, 1:1, 3:1) on the growth of the diffusive layer was assessed by X-Ray Diffractometry (XRD). Outcomes illustrated that applying plasma nitriding causes the formation of the different nitride phases on the top surfaces of the M2 substrate and Fe3N is the dominant phase. The diffusive nitride layer has a higher current density based on simulation results. The microhardness of the surface increased remarkably and 2414 HV was reached as a maximum surface hardness. By considering the obtained results, 500 °C, 6 h, and a ratio of 1:1 of N2/H2 were chosen as optimum conditions of the plasma nitriding of M2 high-speed tool steel, and a corrosion rate of 1.62 mpy was calculated.

Short time nitriding and nitrocarburizing of martensitic stainless steel

Plasma assisted thermochemical diffusion treatments have been extended to stainless steel and the usual process parameters are still in discussion regarding wear and corrosion performance as well as energy efficiency. In this work, a short time route for the thermochemical treatment for AISI 420 martensitic stainless was chosen, setting the duration to 2 h, changing other parameters such as temperature and N2 partial pressure. Temperatures of 420 and 440 °C were used, and two different atmospheres were applied, N2-H2 for nitriding, and N2-H2-CH4 for nitrocarburizing. The microhardness was measured, and microstructure was analyzed by XRD. Pin on disk tests were carried out according to G99 standard using alumina as counterpart, and abrasion wear tests were done following ASTM G65 standard. Corrosion behavior was evaluated using the salt spray fog test and electrochemical tests in NaCl solution. Modified layers between 5 and 15 μm thickness were obtained and surface hardness was always above 1000 HV. In XRD measurements martensite expanded by nitrogen/carbon and iron nitrides or carbonitrides were detected. The sample nitrocarburized at 440 °C showed better wear resistance under sliding conditions, however, the samples nitrided at 440 °C had the lowest mass loss in abrasive wear tests. Regarding the corrosion resistance, the sample nitrocarburized at 440 °C exhibited the best results in the salt spray fog test and in electrochemical tests. This behavior was related to the presence of the carbonitrides and the layer thickness.

Mechanical and Tribological Behavior of Nitrided AISI/SAE 4340 Steel Coated with NiP and AlCrN

In this study, novel surface engineering strategies to improve the wear performance of AISI 4340 were investigated. The strategies were as follows: (i) NiP deposition on a previously nitrided steel substrate, followed by NiP interdiffusion heat treatment at either 400 °C or 610 °C (referred to as duplex treatment); (ii) the deposition of AlCrN PVD coating on NiP layers on a previously nitrided steel substrate (referred to as triplex treatment). Prior to the deposition of AlCrN, the NiP was subjected to the interdiffusion heat treatment at either 400 °C or 610 °C. These strategies were compared with the performance of the AlCrN coating directly applied on nitrided steel. To characterize the microstructural features of each layer, X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) analysis were conducted. We also carried out mechanical and tribological behavior assessments. The tribological tests were carried out using a ball-on-disc tribometer under a constant load of 20 N and a tangential speed of 25 cm/s; cemented carbide spheres with a diameter of 6 mm were the counterpart body. The friction coefficient was continuously monitored throughout the tests. The results reveal that the wear mechanism for the AlCrN coating is predominantly oxidative. The most wear-resistant surface architecture was the one comprising AlCrN over the NiP layer subjected to interdiffusion heat treatment at either 400 °C or 610 °C.

Diffusion Nitride Surface Layers on Aluminum Substrates Produced by Hybrid Method Using Gas Nitriding

While gas nitriding of steel is currently used in industry, nitriding of aluminum alloys remains an open challenge. The main obstacle is aluminum’s high susceptibility to passivation. The oxide film provides an effective barrier to nitrogen diffusion. Attempts to overcome this problem have mainly focused on glow discharge nitriding using cathode sputtering of an oxide layer. The produced AlN layers exhibit no diffusion zone and show limited performance properties. In this work, the effect of hybrid treatment aimed at producing diffusion layers of nitrides other than AlN on aluminum alloys was investigated on the model system of iron nitride–aluminum substrate. Hybrid treatment combines an electrochemical process involving the removal of the aluminum oxide layer from the substrate, its subsequent iron plating, and a further gas nitriding in high-purity ammonia. The obtained results prove that the hybrid treatment allows the production, at 530 °C/10 h, of diffusion layers of Fe3N iron nitrides on aluminum substrates with a nitrogen diffusion zone range in aluminum of ca. 12 µm. In alloys containing magnesium, its unfavorable effect on the nitrogen diffusion and the functional properties of the layers was observed. An interesting direction for further research is hybrid treatment of precipitation-hardened alloys without magnesium.

Износостойкость теплостойких сталей ВКС-7 и ВКС-10 после ионно-плазменного азотирования, вакуумной цементации и вакуумной нитроцементации

Tribotechnical characteristics of martensitic grade steels HSM-7 (16Cr2Ni3MoVNbNAl) and HSM-10 (13Cr3Ni3Mo2VNbNAl) were analyzed. Steels underwent ion plasma nitriding, low-pressure carburizing and low-pressure carbonitriding. The concept of a two-stage hardening technology has been implemented: the creation of a thermally stable finely dispersed state of steel at the first stage and the use of such a state for accelerated and qualitative saturation of the surface layer with nitrogen or carbon at the second stage. To create an ultra-finely divided state in the samples of steels under investigation, the method of intensive plastic deformation (IPD) was used. The method is based on the grinding of the microstructure due to large shear deformations. IPD was performed by the method of warm precipitation in a die with a degree of deformation of 80 % at a temperature of 700 ℃. The wear resistance tests of the samples were carried out on a special stand with reciprocating motion in the medium of a plastic lubricant material of mating samples having flat friction surfaces at a pressure of 10 MPa and an average velocity of 0,19 m/s. It is shown that HSM-7 and HSM-10 steels after ion-plasma nitriding and vacuum cementation have high wear resistance (wear intensity I  10-10). After low-pressure carbonitriding, the values of the wear intensity of the friction pair samples are almost the same and amount to 0,3·10-10, which is ~3,0 times less than after low-pressure carburizing. As a result of ion-plasma nitriding and low-pressure carbonitriding, a nanostructured surface layer is formed on steel surfaces contributing to wear resistance increase. The ideas concerning nitrided steel score resistance increase are given.