M2 Steel Research Articles

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.

Plating Al coating on high-strength steel in chloroaluminate ionic liquid under pulse current modes

Aluminum coating is a potential candidate for cadmium coating replacement due to its excellent corrosion resistance and nontoxicity. Among the fabrication methods of Al coating, plating Al via ionic liquids has drawn major attention of researchers because of the superiority of controllability, stability and low energy consumption. However, the evolution rules of plating aluminum on high-strength steel via pulse current modes at room temperature requires deeper investigation. In this work, pulse current density and pulse duty factor are regulated to reveal the plating patterns of Al on 300M high-strength steel in AlCl3-EMIC (2:1 in mole) ionic liquid. It is found that higher current density can significantly facilitate the nucleation of Al grains and the compactness of morphology, while an enlarged pulse duty factor tends to result in more regular Al crystals. When the current density and the pulse duty factor are fixed at 20 mA cm−2 and 80 %, the densest and most uniform aluminum coating is obtained. The component of Al coating is verified to be pure Al crystals with good adhesion and the plating process achieves a high current efficiency of 97.27 %. Under the protection of Al coating, the impedance and galvanic corrosion current density of 300M steel substrate are optimized by two orders of magnitude, and the corrosion current density is markedly decreased from 5.58 μA cm−2 to 0.77 μA cm−2.

Application of honeycomb pattern to Ti2AlN MAX phase films by plasma etching

The honeycomb pattern possesses a distinctive hexagonal structure capable of seamless repetition on a flat surface, leaving no gaps. Moreover, all arm thicknesses and angles are equal to one another. This remarkable configuration is deemed biomimetic, with numerous examples found in nature. Notably, it exhibits remarkably low density and exceptional mechanical strength. MAX phase films have gathered significant attention due to their exceptional capacity to amalgamate the essential properties of both metals and ceramics. Additionally, they possess the unique ability to effectively mend surface cracks that may arise as a result of friction-wear, restoring the material to a certain degree of integrity. In this study, Ti2AlN MAX phase thin films were deposited on M2 steel substrates by a closed field unbalanced magnetron sputtering system (CFUBMS). 750 °C heat treatment was applied to obtain the produced films in crystalline form. In addition, plasma etching parameters suitable for the phase structure of the deposited film were determined. With the inductive coupling plasma etching (ICP) process, the honeycomb pattern was given to the Ti2AlN MAX phase films with a continuous and smooth geometry at a depth of 2 μm. This study gives ideas for the development of multi-coating systems in which patterns of different geometries are included in a single layer.

Study of the corrosion behaviors of M50 steel in brine-contaminated lubricating oil

In the present paper, the wasted oil with the saltwater droplet was prepared to simulate the corrosion behaviors of M50 steel in the salt fog condition. The comprehensive characterization of the local corrosion area on the surface of M50 displays the corrosion behaviors of M50 steel in saltwater-contaminated lubricating oil. The experimental results show that the surface of M50 steel has two types of local corrosion area morphology: pit-like corrosion spots and isolated outer regions, which are found after immersion in saltwater-contaminated lubricating oil. The larger the outer area, the larger the inner area and the probability of occurrence becomes high. The local corrosion areas have an inward depression and an outward protrusion, and the formation mechanisms are galvanic corrosion and uniform corrosion. These finding are helpful to understand the corrosion problems and mechanisms of roller bearings exposed in salt fog contaminated lubricating oil.

Understanding the thermal stability and friction behavior of ultrasonic shot peening-introduced gradient nanostructured M50 bearing steel

The M50 steel is a common material for main shaft bearings in aerospace applications. The thermal stability of gradient ultrafine grains/nanograins steels is of critical importance for engineering applications. Here, we fabricated gradient nanostructured M50 steel using ultrasonic shot peening and subsequent annealing. This study investigated the effect of annealing treatment on the microstructure evolution of gradient nanostructured M50 steel and the thermal stability of the USPed sample post-annealing. Furthermore, the friction behavior of gradient nanostructured M50 steel was also examined. After annealing at 350 °C for 30 min, ferrite phase at the depth span of 0–100 μm has better thermal stability, and formed a high-density dislocation network and cells at the top surface of the gradient layer. When annealed samples were continued annealed at 350 °C for 100 h, the average ferrite phase size at the depth span of 0–100 μm reduced to a fixed value (∼434 nm). High-density dislocation cells with smaller and more dispersed ordered B2 phases have a stronger pinning effect of dislocation. Hetero-deformation induced hardening by a dislocation network of grain interior and dislocation wall (∼200 nm thick) and precipitation hardening of dislocation cells with more dispersed ordered B2 phase is the main reason for the high microhardness of the samples annealing at 350 and 450 °C for 30 min. The USPed sample within the 100–200 μm depth span exhibits better friction properties attributed to the strengthened martensitic matrix, partial decomposition of spherical carbides, and the presence of high-density dislocations, which reduce the cracking of carbides and matrix, and carbide spalling. Although heat treatment results in a slight decrease in the friction properties of the USPed sample, they still surpass those of the tempered sample. This reduction in friction properties post-annealing primarily arises from the annihilation of high-density dislocations.

Effect of laser shock peening on wear resistance of M50 steel

The effects of laser shock peening (LSP) on the surface state and wear resistance of M50 steel are studied by microstructure observation, hardness, and residual stress detection. Results show that after LSP, the carbides on the surface of steel are broken and micro-pits appear. After removing the surface carbide damage by electrolytic polishing, the number of sub-surface carbides increases, and the maximum content is 26.1%. After LSP, the wear resistance of the steel is improved because LSP causes a large residual compressive stress on the surface. The wear performance of the sample after removing the surface damage becomes better, which is related to the elimination of many crack sources and the larger residual compressive stress.

High temperature lubrication performance of chlorophenyl silicone oil

Most studies of liquid lubricants were carried out at temperatures below 200 °C. However, the service temperature of lubricants for aerospace and aeroengine has reached above 300 °C. In order to investigate the friction mechanism and provide data for high temperature lubrication, the friction and wear properties of chlorophenyl silicone oil (CPSO)-lubricated M50 steel and Si3N4 friction pairs were investigated herein. Ball-on-disk experimental results show that the lubrication performance of CPSO varies significantly with temperature. Below 150 °C, coefficient of friction (COF) remains at 0.13–0.15 after the short running-in stage (600 s), while the COF in the running-in stage is 0.2–0.3. At 200 °C and above, the running-in time is much longer (1,200 s), and the initial instantaneous maximum COF can reach 0.5. Under this condition, the COF gradually decreases and finally stabilizes at around 0.16–0.17 afterwards. This phenomenon is mainly due to the different thickness of boundary adsorption film. More importantly, the wear rate of M50 steel increases significantly with the temperature, while the wear rate barely changes at temperatures above 200 °C. The anti-wear mechanism is explained as tribochemical reactions are more likely to occur between CPSO and steel surface with the increased temperature, generating the FeCl2 protective film on the metal surface. Accordingly, FeCl2 tribochemical film improves the lubrication and anti-wear capacity of the system. At high temperatures (200–350 °C), FeCl2 film becomes thicker, and the contact region pressure becomes lower due to the larger wear scar size, so the wear rate growth of M50 steel is much smaller compared with that of low temperatures (22–150 °C). The main findings in this study demonstrate that CPSO lubricant has good anti-wear and lubrication capacity, which is capable of working under temperatures up to 350 °C.

Effect of Cryogenic Time on Wear Resistance of M2 High Speed Steel

The wear resistance, residual austenite volume and carbon content in martensite of M2 steel were studied by means of universal vertical friction and wear testing machine, X-ray diffractometer (XRD), scanning electron microscope (SEM) and digital Rockwell hardness tester. The results show that a large number of fine carbide particles in M2 steel martensite are precipitated by cryogenic treatment and distributed uniformly and diffusely in the structure. With the increase of cryogenic time, the residual Austenite volume of M2 steel gradually decreases, while the Martensite volume increases, resulting in the wear resistance and Rockwell hardness increasing first and then decreasing. After 24 hours of cryogenic treatment of M2 steel, its wear resistance increased by 310%, hardness increased by 3.6%. Therefore, 24 hours is confirmed as the best cryogenic treatment time for the wear resistance and hardness of M2 steel.

Pulsed-dc bias magnetron sputtered TiB2 ceramic coating

Titanium diboride, TiB2, is well known as a ceramic material with a hexagonal structure which presents various attractive properties, such as high hardness and excellent corrosion, thermal oxidation, and wear resistance. However, one drawback of TiB2 coatings is their poor adhesion to substrate materials due to high compressive residual stress after deposition. The present study aimed to assess whether a PVD-TiB2 coating with both high hardness and sufficiently good adhesion to the substrate and good wear properties can be developed by a closed-field unbalanced magnetron sputtering system using pulsed-dc biasing. The TiB2 coating deposited on AISI M2 steel substrates was characterized in terms of the structural, mechanical and tribological property. From the experimental results, it can be concluded that a closed-field unbalanced magnetron sputtering system using pulsed-dc biasing can be used to produce a TiB2 coating with sufficiently good adhesion (82 N), and high hardness (2300 HK0.01), and low friction (0.34) under given deposition conditions. The deposition conditions, particularly substrate biasing and rotation, which inhibited the formation of (001) orientation, played a role in the coating's lack of superhardness.

Macro and Micro Segregations and Prediction of Carbide Equivalent Size in Vacuum Arc Remelting of M50 Steel via Simulations and Experiments

Macro and Micro Segregations and Prediction of Carbide Equivalent Size in Vacuum Arc Remelting of M50 Steel via Simulations and Experiments

Hardening of Selective Laser Melted M2 Steel

Hardening of Selective Laser Melted M2 Steel

Multi-response optimization of M2 steel coatings deposited by co-axial laser cladding on A2 steel tool surfaces

Laser cladding is a highly effective technique used in additive manufacturing to enhance the surface properties of workpieces. It is employed to improve wear resistance, corrosion resistance, and high-temperature resilience of materials. This study explores the utilization of laser cladding technology to repair the surface of AISI A2 tool steel by applying a coating of M2 steel. Sixteen experiments were designed using an orthogonal methodology to investigate the intricate relationship between various processing parameters, including laser power, scan speed, powder feed rate, and overlapping ratio. These parameters were examined in conjunction with key mechanical properties of the coating, such as micro-hardness, friction-wear characteristics, and shear bond strength.Additionally, analytical techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) were employed to gain insights into the microstructure of the coatings and elucidate the underlying failure modes. Shear testing of the coatings indicated a tendency towards a brittle fracture mode within the coating, with the dominant wear mechanism involving a combination of abrasive and oxidative wear.Finally, a TOPSIS-Grey Relational Analysis (GRA) method was utilized to identify the optimal process parameters. These optimal parameters were determined to be a laser power of 1200 W, a scan speed of 5 mm/s, a powder feed rate of 14 g/min, and an overlapping ratio of 30 %. Subsequent validation experiments carried out with these parameters demonstrated superior performance compared to the optimal group identified in the orthogonal experiment.

Multi-objective optimisation of process parameters for laser-based directed energy deposition of a mixture of H13 and M2 steel powders on 4Cr5Mo2SiV1 steel

ABSTRACT In present paper, a universal method for multi-objective parameter optimisation of additive manufacturing processes was proposed and successfully applied to laser-based directed energy deposition (DED) experiments with mixtures of H13 and M2 steel powders that were deposited on 4Cr5Mo2SiV1 hot work die steel. The DED experiments were designed and completed based on the response surface method with 13 groups of laser parameters. The microstructure of the deposited alloy steel was observed and its mechanical properties were tested. The deposited steel alloy achieved an ultimate tensile strength (UTS) of 1821 ± 30 MPa with a reasonable elongation of approximately 4.5%, and the bond strength specimens achieved a bond toughness of ∼10.66% with a moderate UTS (1329 ± 28 MPa). A multi-objective optimisation method was proposed based on response surfaces which were established according to microstructural characteristics and mechanical properties data. It provided a basis for achieving high strength or high toughness DED-fabricated steel alloys.

High Cycle Fatigue Performance of Bare 300M Steel by Self-Heating Tests Under Cyclic Loadings

300M, an ultra-high strength steel used in aeronautics for landing gears, is generally shot-peened and coated with High Velocity Oxygen Fuel sprayed WC-10Co-4Cr to improve corrosion resistance and tribological behavior. In the literature, few process parameters have been tested to characterize the effect of surface integrity on fatigue properties. The self-heating method under cyclic loadings is used to quickly determine fatigue properties by coupling the fatigue mechanisms with dissipation mechanisms. This paper focusses on the methodology and results obtained on bare 300M.After implanting and validating a test and post-processing protocol, a self-heating model has been applied. The model shows a good description of the self-heating curve and a great correlation with conventional fatigue data. Mean properties as its scattering have been determined by self-heating tests. Then, geometric and loading parameters have been tested, such as the loading ratio and the coupon volume, showing various influence on self-heating curves.

Wear and corrosion behavior of TiC and WC coatings deposited on high-speed steels by electro-spark deposition

Abstract Electro-spark deposition (ESD) is one of the most effective methods for improving the surfaces of metallic materials by applying ceramic-based cermet coatings. In this study, TiC and WC coatings were deposited on the surface of AISI M2 high-speed steel using the ESD method. Subsequently, the coated surfaces were examined through microstructure, phase structure, microhardness, friction, wear, and electrochemical corrosion tests, and compared with untreated AISI M2 steel. The TiC and WC phase coatings obtained with ESD resulted in a significant improvement, with hardness levels exceeding four times that of AISI M2 steel, leading to reduced wear volume losses and friction coefficients. Furthermore, the cermet coatings formed on the surface exhibited 2–3 times improvement in corrosion resistance due to their lower conductivity. This study demonstrates that WC coatings may offer a more effective solution for enhancing the wear resistance of AISI M2 steel, while TiC coatings could be more effective in improving corrosion resistance.

Cooling Performance of Turning M2 steel by using copper nanofluids

Cooling Performance of Turning M2 steel by using copper nanofluids

Understanding the microstructural evolution and fretting wear behaviors of M50 bearing steel heat treated at different temperatures

For M50 bearing steel, which is widely used in aerospace engine main bearings, fretting wear is an important but neglected category of wear failure during engine cold startup. High temperature tempering is crucial in heat treatment to enhance its microstructure and wear resistance. In order to investigate the influence of different tempering conditions on fretting wear performance of M50 steel, it is essential to conduct a comprehensive study. This research explores how heat treatment processes affect the fretting wear properties of M50 steel by varying the tempering temperature (450 °C, 500 °C, 550 °C, 600 °C, and 650 °C). We analyzed the microstructure evolution and fretting wear behavior under different conditions using SEM, EDS, XRD and other characterization methods. The results show that the tempering temperature influences fretting wear through martensite, retained austenite, and carbide transformations. In the 450 °C–600 °C range, wear volume and wear rate decrease with hardness. At 550 °C tempering, M50 achieves the highest hardness (59.71 HRC) and a lower wear rate (9.661 × 10−8 mm3/(N·mm)). M50 steel exhibits optimal fretting wear performance at 550 °C tempering. Overall, wear behavior occurs in the mixed slip regime, shifting towards partial slip with higher tempering temperatures. When the tempering temperature is low, the fretting wear mechanism is predominantly dominated by fatigue wear and abrasive wear, while at higher tempering temperatures, the fretting wear mechanism is primarily governed by oxidative wear and adhesive wear.

The Effect of Bias Voltage and Acetylene Gas Flow Rate on the Wear Behavior of Diamond-like Carbon Coatings on M2 High-Speed Steel

This paper investigates the impact of bias voltage and acetylene flow rate on the mechanical, structural, and scratch performance of diamond-like carbon (DLC) coated high-speed steel (HSS) M2 commonly used in hydraulic vane pumps. The DLC coatings were produced through plasma-enhanced chemical vapour deposition, with micro-Raman spectroscopy used to analyze their structure via G-peak and D-peak measurements. Results showed that DLC deposited at 350 V and 100 sccm demonstrated high hardness (28.99 GPa) and modulus of elasticity (308.1 GPa), with the highest critical load of 167.246 mN indicating superior adhesion to the HSS M2 substrate at a higher bias voltage and lower flow rate. The minimum wear rate of 3.02 × 10−3 mm3/Nm was achieved with a thinner DLC coating deposited at 350V bias voltage and 100 sccm acetylene flow rate.

Rolling contact fatigue behaviour of M50 bearing steel with rare earth addition

The study aims to investigate the influence of rare earth (RE) addition on the rolling contact fatigue (RCF) behaviour of M50 bearing steel. Ball-on-rod RCF experiments were conducted on specimens extracted from M50 bearing steels with and without RE addition. Results indicate that RE addition remarkably improves the RCF life, and the L10, L50 and LVS fatigue life is increased by 96.2%, 61.7% and 55.0%, respectively. For M50 bearing steel, a criterion on RCF failure types is given for the first time. According to the criterion, the failure is mainly surface-initiated for the M50 steel with RE addition, whereas the failure is mixed and subsurface initiated for the M50 steel without RE addition. As a corroboration, compared with steel with RE addition, steel without RE addition exhibits higher density butterflies and longer accompanied cracks in the subsurface. This result shows that the ability of M50 bearing steel to resist subsurface damage from RCF can be greatly improved by the refined primary carbides resulting from RE addition. The RCF life of bearing steel with RE addition can be much higher than that of bearing steel without RE addition if the RCF failure is mainly subsurface initiated.

Influence of the heat treatment on the mechanical and tribological properties of cryogenically treated AISI M2 steel

Cryogenic treatments are known to increase the wear resistance and toughness of steel. However, the literature reports some contradictory results. This work aims to investigate and determine the optimum cryogenic parameters combined with cycles of quenching and tempering of AISI M2 tool steel to increase wear resistance and toughness. Charpy specimens were austenitized (1185 °C, 1200 °C or 1215 °C), quenched to room temperature, cryogenically treated to −196 °C (20 h or 28 h), and subjected to double tempering (520 °C, 535 °C or 550 °C). A Taguchi L9 DoE approach was used to determine the optimum set of heat treatment cycles. Mechanical and tribological properties were investigated in terms of wear, impact, hardness, and microhardness tests. The results show that austenitization temperature (AT), tempering temperature (TT), and cryogenic treatment (CT) time are interdependent. Depending on the AT and TT parameters used, CT can improve, have little influence, or even deteriorate the mechanical and tribological properties of AISI M2 steel. The amount of retained austenite after CT ranged from 4.3 to 7.6%. Cryogenic treatment improves wear resistance and impact toughness simultaneously.