M50NiL Steel Research Articles

Effect of carbonitride on the friction and wear properties of M50NiL steel after sequential carburizing and nitriding treatment

In this work, M50NiL steel was carburized at 950 ℃ for 1 h (C samples) and subsequently nitrided at 520 ℃ for 7 h (CN samples). The carbonitrides of the samples that underwent the sequential carburizing and nitriding treatment were observed before and after wear and analyzed via SEM, FIB, and TEM. The friction and wear properties of the CN samples were compared with those of the C samples. The results show that the surface hardness and surface residual stress of the CN samples were 1.6 and 4.2 times greater than those of the C samples, respectively, i.e., the CN samples were less likely to spall during wear. The carbonitride particle sizes of the CN samples were 100–500 nm before wear and less than 10 nm after wear, indicating that carbonitrides enhanced the wear resistance of the CN samples. The wear area of the CN samples decreased by 95.6 % at 20 N and 87.4 % at 40 N.

First-Principles Calculate the Stability, Mechanical Properties and Electronic Structure of Carbide MC, M2C and M6C in M50NiL Steel.

In this paper, the stability, mechanical properties and electronic structure of carbides in steel were calculated using the first-principles method based on the density functional theory (DFT). Firstly, the MC, M2C, M6C (M = Cr, Mo, V, Fe) carbides models were established. Then, different interphases' lattice constants, formation enthalpy, binding energy and elastic modulus were calculated. The stability, hardness, ductility and anisotropy of each phase were finally analyzed. The results show that these phases are stable, and the stability is closely related to the electron loss ability of its metal elements. The stronger the electron loss ability of its metal elements, the more stable the formed phase. As for MC carbides, MoC has the largest bulk modulus and hardness. As for M2C carbides, the Poisson's ratio of Cr2C is the smallest, and all phases except for Cr2C show toughness and ductility. The anisotropy of M6C carbides is relatively poor.

Ultrahigh surface hardness and excellent hardness gradient induced by ultrafine dual-carbides in a novel stainless bearing steel

A novel alloy composition design (Fe–14Cr–13Co–5Mo–2Ni–1W–1V-0.16C-0.12Nb-0.074Si-0.027Mn, wt. %) was proposed for modification on that of the conventional CSS-42L stainless steel. The present homogeneous structure without carburizing displays an excellent synergy of yield strength and fracture toughness, which should improve the performance of the corresponding case-carburized steels under the contact/bending fatigue conditions. An ultrahigh surface hardness (71 HRC) and an excellent hardness gradient along the depth are achieved in the present case-carburized gradient structure. Higher surface hardness at a temperature range of 200–400 °C is also observed in the present case-carburized gradient structure, as compared to the other case-carburized advanced bearing/gear steels, such as the M50 steel, the M50NiL steel and the conventional CSS-42L steel. Besides the previously reported M6C carbides in the case-carburized conventional CSS-42L steel, M7C3 carbides are newly discovered in the present case-carburized gradient structure due to the novel chemical design. The ultrahigh surface hardness at both room and high temperatures and the excellent hardness gradient distribution in the present case-carburized gradient structure should be attributed to the increased amount of dual-carbides, as well as the ultrafine dual-carbides embedded in the ultrafine martensite matrix. The superior mechanical properties of the present case-carburized gradient structure should be desirable for real bearing/gear applications.

Study on the Evolution of Inclusions in Ce-Modified M50NiL Steel Through the CALPHAD Approach and a Novel Inclusion Prediction Condition

Study on the Evolution of Inclusions in Ce-Modified M50NiL Steel Through the CALPHAD Approach and a Novel Inclusion Prediction Condition

Argon ion sputtering bridging plasma nitriding and GLC film deposition: Effects on the mechanical and tribological properties

A duplex coating consisting of a nitrided layer and a GLC (Graphite-like carbon) film was deposited on the surface of the M50NiL steel via a one-step process in a plasma nitriding system. The influence of argon ion sputtering, a critical process bridging plasma nitriding and GLC film deposition, was studied. Effects of argon ion sputtering on the growth of the GLC film were investigated by means of Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The mechanical and tribological properties of the duplex coating were evaluated by a Vickers hardness tester, a scratching tester and a rotating ball-on-disc tribometer. Results reveal that pre-treatment by ion sputtering improves the surface condition of the nitrided layers and increases its surface energy, thus facilitating nucleation growth and GLC film adhesion. The combined effect of better film-substrate adhesion, strong interfacial chemical interaction and the self-lubricating features of the GLC films are the main reasons for the excellent tribological properties of the coating. This study may provide a new idea for optimizing the duplex coating (nitrided layer + GLC film) with excellent tribological properties and high durability.

Tailored carburization gradient microstructure and enhanced wear properties of M50NiL steel via introduced prior cold rolling

M50NiL (Chinese grade G13Cr4Mo4Ni4V) steel is widely used in aircraft bearing raceways that require excellent wear resistance under harsh service conditions. However, the impact of cold rolling, as an advanced forming process for bearings, on the carburization process and wear properties is still unknown. Therefore, the gradient microstructure and dry sliding wear performance of the cold-rolled M50NiL disc against Si3N4 ceramic ball have been investigated. The results show that with the increase of cold rolling reduction to 40 %, the carbon concentration of surface is increased by 17.1 % due to the growing percentage of grain boundaries (GB) and dislocation density. The carbide content is increased by 29 % with average size declined by 21.2 %, which contributes to a 7.4 % increase in the surface hardness. Additionally, the wear test indicates that the average friction coefficient and wear rate are respectively reduced by 17.3 % and 47.1 % when the rolling reduction increases to 40 %. After prior rolling, the wear mechanism changes from severe abrasion to adhesion and tribochemical reactions accompanied with the enhancement of wear properties, which is mainly attributed to the uniform distribution of finer carbides with higher fraction on the surface and subsurface.

Leveraging Deep Neural Networks for Estimating Vickers Hardness from Nanoindentation Hardness.

This research presents a comprehensive analysis of deep neural network models (DNNs) for the precise prediction of Vickers hardness (HV) in nitrided and carburized M50NiL steel samples, with hardness values spanning from 400 to 1000 HV. By conducting rigorous experimentation and obtaining corresponding nanoindentation data, we evaluated the performance of four distinct neural network architectures: Multilayer Perceptron (MLP), Convolutional Neural Network (CNN), Long Short-Term Memory network (LSTM), and Transformer. Our findings reveal that MLP and LSTM models excel in predictive accuracy and efficiency, with MLP showing exceptional iteration efficiency and predictive precision. The study validates models for broad application in various steel types and confirms nanoindentation as an effective direct measure for HV hardness in thin films and gradient-variable regions. This work contributes a validated and versatile approach to the hardness assessment of thin-film materials and those with intricate microstructures, enhancing material characterization and potential application in advanced material engineering.

Influence of δ ferrite on impact toughness of M50NiL bearing steel

M50NiL bearing steel is widely used in the aerospace field because of its excellent properties. δ ferrite would affect the impact toughness of steel, but there is little research on it in M50NiL bearing steel. In this study, the effect of the δ-ferrite content on the impact toughness of M50NiL bearing steel and the corresponding mechanism were investigated through microstructure characterization and mechanical property testing. The results indicated that the impact toughness of the steel at room temperature, as well as the energy needed for crack initiation and crack propagation, improved with δ-ferrite content reduction. This suggests that the presence of δ ferrite in M50NiL steel is detrimental to its impact toughness and that reducing the δ-ferrite content can suppress crack initiation and crack propagation, significantly improving the impact toughness. The adverse effect of δ ferrite on impact toughness is mainly attributed to the fact that δ ferrite is prone to crack initiation and cannot effectively prevent crack propagation due to its low strength and shear resistance. Additionally, the difference in microstructure and strength between the δ ferrite and martensite matrix may weaken the interface, which is conducive to crack initiation and rapid propagation.

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.

Constructing processing map of M50NiL steel by artificial neural network model

The processing map for M50NiL steel was established by hot compression tests at temperatures of 950–1150 °C and strain rates of 0.002–1.0 s−1. Based on the experimental results of hot compression tests, the predictability in both reproducing experimental flow stresses and predicting flow stresses using the Arrhenius, physical-based, and artificial neural network (ANN) models was compared. The results showed that the average absolute relative errors of Arrhenius, physical-based, and ANN models in both reproducing and predicting flow stresses were 6.04 % and 8.01 %, 6.61 % and 7.78 %, and 1.91 % and 4.74 %, respectively. The ANN model had a considerably higher accuracy in reproducing and predicting flow stresses than the other two models. In addition, a processing map of M50NiL steel was established using the predicted flow stresses by the ANN model. This processing map indicated that the optimized processing parameters were 975–1050 °C/0.01–0.002 s−1. Instability occurred during deformation at 950–975 °C at 1.0 s−1 and 1075–1150 °C at 0.01 s−1. The instability prediction was verified by the microstructure evolution.

Effect of Pre-Modification by Water Jet Blasting Prior to Nitriding Vein-Like Precipitates in the Composite Diffusion Layer of M50NiL Steel

In this study, M50NiL steel was carburized (C), nitrided (N), and compound-carburized then nitrided (C + N). Vein-like grain boundaries (VLGBs) were observed in the diffusion layers of both the N and C + N states due to the limited opportunity for diffusion. Transmission electron microscopy (TEM) observation revealed that the VLGB organization differed in the N and C + N states. The VLGB organization consisted mainly of Fe4N in the N state and Fe3C and Fe4N in the C + N state. When the C state was pre-modified by a 200 MPa water jet and then nitrided (C + 200P + N), the increase in dislocation density resulted in a dislocation entanglement phenomenon that split the grains to form subcrystals. The increases in grain boundaries and dislocation density promoted the diffusion of atoms, and thus the VLGB structure was not observed in the diffusion layer of the C + 200P + N state.

The high-cycle fatigue behavior of carburized M50NiL steel with high-energy modification and compound infiltration: A comparative study

In this study, ultrasonic rolling (C + USRP) and plasma nitriding (C + N) is performed on the surface of M50NiL steel after carburizing， the tension-compression fatigue test of R = −1 on different samples. The results show that the maximum fatigue limit of C + N, C + USRP, and single carburizing are 770 MPa, 676 MPa, and 412 MPa, respectively. The residual stress relaxation in the fatigue process of C + N and C + USRP is tested and found that the initial residual compressive stress of C + N is lower than that of C + USRP, but its attenuation value is considerably smaller. The microscopic characterization of samples is conducted after the fatigue tests. The nanometer nitrogen compounds in the composite permeability layer showed a strong pinning effect, however, microplastic deformation limits the fatigue process. The C + N demonstrates a much lower residual compressive stress relaxation, consequently, the C + N short crack propagation effective driving force ΔKeff value decreases. As a result, due to the higher crack closure effect, the C + N fatigue limit is observed higher than the C + USRP.

Evaluation of the impact of electron beam welding parameters on the mechanical properties and microstructure of the resulting joint for 39CrMoV13 and M50NiL steel grades

The paper covers a study consisting on the implementation of the electron beam welding process of two steel grades: 39CrMoV13 and M50NiL. The welding process was carried out for two values of electron beam debunching, obtaining a joint having different widths. Then, for the samples, after each welding variant, heat treatment was carried out consisting of double tempering at 520 °C for 3 h, and single freezing at − 84 °C for 3 h, combined with single tempering at 520 °C for 3 h. The impact of the parameters of the electron beam welding process and the subsequent heat treatment process on the mechanical properties and microstructure of the resulting joint was analysed. The conducted tests allowed to select the optimum welding technology combined with the heat treatment process for the tested steel grades ensuring that a weld is obtained in which the level of mechanical properties was close to the level of values obtained for the base material.

On the growth of functionally graded self-lubricating layer during a plasma-assisted thermochemical treatment of M50NiL steel

Diamond-like carbon (DLC) with excellent mechanical properties has aroused great interest. However, the weak adhesion between the DLC film and steel substrate restricts its application. Considering that the addition of interlayers needs cumbersome steps, fabricating a functionally graded self-lubricating layer through one-step remains a challenge. We reported a novel integrated self-lubricating layer, inspired by the gradient structure formed during the traditional thermochemical treatment. That integrated layer from DLC structure gradual transition to nitrided diffusion layer is in-situ fabricated on the M50NiL steel through a plasma-assisted thermochemical treatment. The gradient structure possesses excellent wear resistance due to the self-lubricating of the DLC structure and provides sufficient adhesion strength. A deep insight into the relation between Fe5C2 crystal facet and growth of DLC is conducted by first-principle calculation and find low Miller Index of Fe5C2 facets are favorable for the growth of DLC. The thermodynamic calculation reveals that gradient structure formation is the collaboration effect of non-equilibrium and equilibrium processes.

A review on heat treated bearing steels for aerospace applications

Aerospace Bearings are specially designed for aircraft systems where these bearings has to operate at high speeds like 0 Rpm to 60,000Rpm and high temperature ranges from −54 °C to 150 °C so bearing should posses good reliability, In order to ensure optimal performance level of bearing,material selection, structural design and manufacturing methods plays key role where bearings have to work at high speed and high temperature conditions and for this generally steels like AMS6491(M50) steel, AMS6444 (carbon chrome steel),AMS5930,SS,titanium carbide coated steels are used. and the key considerations for bearing reliability are material selection, structural design, and manufacturing methods where Performance evaluation and surface treatments shows effective results.in this paper it is reviewed that bearing material selection and how the operating conditions shows effect on performance characteristics are studied by introducing new materials and reliability of shaft bearing systems is also studied and later impact of conventional heat treatment methods like liquid and gas nitriding process on bearing steels like M50 Nil Steel which increases mechanical properties like rolling fatigue, wear resistance and tribological properties.

Effect of plasma nitriding on M50 NiL steel – A review

Chemical Diffusion Process like Nitriding has important role in modern surface hardening. Plasma nitriding is one of the best method to improve surface hardness, wear and corrosion resistance of material, and also plasma nitriding improves surface properties. M50 NiL Steel is a low carbon high alloy steel with good strength, hardness, and wear and corrosion resistance at elevated temperatures. It is frequently utilised in the aerospace sector due to its unique features. To determine the corrosion and wear resistance of double element alternate implanted M50 NiL steel, detection methods such as scanning electron microscopy (SEM), X-Ray diffraction method (XRD), transmission electron microscopy (TEM), and potentio dynamic polarisation were utilised. The purpose of this paper is to identify the effects of plasma nitriding on M50 NiL Steel and to know the progress of surface hardening properties like micro hardness and wear for M50 NiL steel after plasma nitriding. The bearing made out of this steel is operated under heavy loads and high speeds in air craft engine. Effects of nitriding temperature on microstructure, micro hardness, and wear resistance of nitride layers with only a diffusion layer and no standard compound layer. and surface hardness is improved at low nitriding temperatures, When the nitriding temperature exceeds 575 °C, the nitride layer thickness increases, while the core and surface micro hardness drops. Mechanical Properties of nitride surfaces are studied by using Vickers hardness test and polarization tests. M50 NiL Steel was Plasma nitro carburized at low temperature and rare earth (RE) atoms are diffused into the specimen surface for better surface hardness and increased corrosion resistance. Some times to achieve exceptional properties duplex hardening is preferred and this process can be useful to obtain good hardness and same can be done for both hardened and case hardened bearing steels, with relative increase in rolling contact fatigue resistant and better tribological properties.

Effect of deep tempering on microstructure and hardness of carburized M50NiL steel

Through the deep medium-temperature tempering treatment, microstructure observation and hardness test of the carburized M50NiL bearing steel, the influence of the temperature and times of deep tempering on the microstructure and hardness of the steel were studied. The results show that the deep medium-temperature tempering is beneficial to the dissolution of large-size carbides in the carburized layer of the steel at the initial state, uniform distribution of carbides, and the precipitation of granular carbides from lath martensite. During deep tempering treatment, some granular carbides are connected to form rod-like carbides. With the increase of the number of deep tempering, the lath martensite in the steel is decomposed and the size is obviously refined, and more carbides in the core area are precipitated, whose distribution is more dispersed uniform. The deep tempering at 460 °C and 480 °C can slightly increase the surface hardness of bearing steel, but five times of medium temperature tempering at 500 °C makes the hardness of the steel slightly decreased. There exists the lowest point of hardness in the subsurface layer of the initial-stated M50NiL steel, which is however eliminated after 5-time deep tempering at 460 °C and 500 °C, and this is related to the elimination of stripe-like carbides after the two deep tempering processes.

Experimental study on heat treatment and mechanical behaviour of M50 NiL steel – A review

M50 NiL Steel is low carbon high alloy steel with good strength, toughness, better wear and corrosion resistance at elevated temperature, because of this properties it is widely used in aerospace industry. Detection methods such as SEM, XPS, AES and TEM, and potentio dynamic polarization are used to find out corrosion resistance of double element alternate implanted M50 NiL steel. Hot Compression tests are used to study the behaviour of M50 NiL Steel during deformation. Potentio dynamic curves and electrochemical impedance spectroscopy are used to evaluate the corrosion properties for untreated and carbon ion implanted steels. Development of latest method like LPC Technology to meet the client requirements in industry, where the furnace design and operation has very crucial importance because of its flexibility to perform standard vacuum heat treatment and carburizing cycles. Different treatments like solution and tempering, gives precipitation behaviours of carbides [(V, Cr)-rich MC, (Mo, Fe)-rich M2C, Fe-rich M3C and (Fe, Cr)-rich M7C3] in M50 NiL Carburized Steel after heat treatment. The wear resistance behaviour of nitrided steel pieces will be enhanced by plasma nitriding process, where ultra fine grains and smooth surface of nitrided layer, posses high wear resistance. The mechanical behaviour of M50 Nil steel under carburizing and nitriding (dual) treatments, at the temperatures from 890 °C to 900 °C is helpful and Microstructure analysis can be characterized by XRD and SEM, TEM Methods. The objective of the paper is to review the mechanical behaviour and heat treatment process for better performance of M50 NiL Steel under various heat treatments and ion implementation methods.

Effect of Initial State and Deformation Conditions on the Hot Deformation Behavior of M50NiL Steel.

M50NiL steel, which belongs to a new generation of case-hardening steels used in aerospace bearing applications, is used mainly for the manufacturing of aerospace transmission components that operate under high temperatures. In this study, the effects of the hot deformation parameters and the initial microstructure on the hot deformation behavior of M50NiL steel were investigated through Gleeble-3500 isothermal hot compression tests. The experimental results demonstrated that the critical stain of dynamic recrystallization and the deformation activation energy of the coarse-grained samples were higher than those of the fine-grained samples. This is attributed to the difficulty of deformation and the dynamic recrystallization behavior of coarse-grained samples. Moreover, fine-grained samples contain a large number of dispersed phases, which can pin the grain boundaries and inhibit the growth of recrystallized grains. Such phenomena are beneficial for obtaining finer and more uniform microstructures in M50NiL steel. The experimental results can provide a useful reference for preparing M50NiL steel with excellent mechanical properties.

Effect of pre-existing carbides prepared by different heat treatments on the nitriding behaviour during a carburizing and nitriding duplex treatment of an M50NiL steel

This article reports the effect of pre-existing carbides prepared by different heat treatments on the nitriding behaviour during a carburizing and nitriding duplex treatment of an M50NiL steel. The goal was to achieve an improved understanding of the relationship between the pre-existing carbides and nitriding behaviour. The M50NiL steel was carburized at 950 °C, heat treated at different quenching temperatures (ranging from 1000 to 1150 °C) and tempering temperatures (ranging from 500 to 580 °C), and finally nitrided at 500 °C. The surface layers were characterized by means of X-ray diffraction (XRD), laser scanning confocal microscopy (LSCM), scanning electron microscopy (SEM), Vickers microhardness measurement and transmission electron microscopy (TEM). The results show that the formation of intergranular precipitates was greatly related to the presence of pre-existing carbides, which led to a change in the carbon content in the matrix and showed different dissolving capacities. The compound layers consisted of γ′ (Fe4N) and ε (Fe2-3N) phases as well as a minor amount of Fe3O4. The pre-existing carbides had no effect on the composition of the compound layer. For the diffusion of nitrogen, a density of pre-existing carbides that was too high or too low was unfavorable, as it greatly decreased the thickness of the nitrided layer. At the quenching temperature of 1100 °C and the tempering temperature of 540 °C, the thickest nitrided layer herein and a good hardness distribution were obtained, which was attributed to the optimum density of pre-existing carbides. This study provides information regarding how to obtain a thick nitrided layer by controlling pre-existing carbides during the duplex treatment of M50NiL steels.