M2 Steel Research Articles

Effect of alternative magnetic fields with different intensities on microstructure and mechanical properties of M50 steel during vacuum arc remelting

Effect of alternative magnetic fields with different intensities on microstructure and mechanical properties of M50 steel during vacuum arc remelting

Microstructure and properties of TiC ceramic powder on a cobalt-based alloy obtained via electromagnetic-assisted laser metal deposition

The crack sensitivity of laser metal ceramic deposition is an important factor restricting its development. In this paper, a TiC-reinforced cobalt-based alloy was deposited on 300M steel using electromagnetic-assisted laser metal deposition technology. The electromagnetic composite effect on the microstructure, mechanical properties, magnetic properties, wear resistance and crack sensitivity of the laser metal deposition layer was discussed. Under the action of an electromagnetic field, the size of the TiC decreased by 54.6% compared with that of the deposited layer without an electromagnetic field. The effect of the electromagnetic composite field can reach the bottom of the molten pool, thus refining the grain size at the bottom of the coating. This resulted in a 22% increase in the hardness of the deposition layer. The electromagnetic field effect reduces the elastic modulus of the deposition layer, thus improving the mechanical properties of the coatings. In addition, compared with that of the deposition layer without an external field, the wear of the deposition layer with an electromagnetic force is obviously reduced. With increasing electromagnetic parameters, the wear resistance of the deposit increased gradually, and the thermal expansion coefficient decreased significantly, which played an important role in improving the crack resistance and comprehensive properties of the deposition layer under extreme working conditions.

Effect of electrical current on sliding friction and wear mechanisms in a-C and ta-C amorphous Carbon coatings

This study investigated the sliding wear behaviour of amorphous carbon (a-C) and tetrahedral amorphous carbon (ta-C) coatings, two forms of diamond-like carbon (DLC) coatings, against SAE 52100 steel using a modified ball-on-disk tribometer with applied electrical currents ranging from 100 mA to 1800 mA. It focused on the variations in sliding friction and wear characteristics of these coatings as electrical currents increased under constant load and speed conditions. The a-C coatings exhibited lower coefficient of friction (COF) values and reduced volumetric wear losses up to 1500 mA, while ta-C coatings studied displayed higher wear, similar to uncoated M2 steel, at 300 mA with degradation occurring at low currents, resulting in failure due to severe oxidational wear. The a-C coatings showed no significant electrical damage at these currents. Raman spectroscopy revealed structural changes on the wear tracks of sp2-rich a-C coatings, specifically the formation of graphene layers. In comparison, the wear tracks of sp3-rich ta-C coatings did not display such transformation under the conditions studied. The graphene coverage on the surfaces of the a-C coatings increased with the increase in the current as revealed by the Raman intensity maps of 2D peaks and this increase was accompanied by a higher defect density in the graphene. The low COF of graphene-covered a-C surfaces was consistent with the proposed mechanisms of moisture adsorption. However, at currents exceeding 900 mA, surface temperatures of a-C coatings exceeded 100 °C, impairing graphene's ability to maintain low friction, resulting in an increased COF.

Effect of the Absorption Layer on the Microstructure and Mechanical Properties of M50 Steel by Laser Shock Peening

Effect of the Absorption Layer on the Microstructure and Mechanical Properties of M50 Steel by Laser Shock Peening

Study on corrosion behavior and first-principle analysis of M50 steel in lubricating oil contaminated by salt water

The corrosive wear of M50 steel in lubricating oil contaminated with saline is a form of wear that often occurs within the main shaft bearings of aviation engines carried by aircraft working at sea. In the present paper, the corrosion behavior of M50 steel in lubricating oil contaminated with saline was studied. The open-circuit potential, polarization curve and impedance spectrum were analyzed by rotating electrochemical corrosion wear test. A three-layer interface microscopic molecular model was established with Materials Studio to simulate the dynamic corrosion evolution process of M50 steel self-matching pairs and the adsorption energy was calculated. The results show that the corrosion type is pitting corrosion. With the increase of saline concentration, the corrosion area becomes wider and shallower, and the size of the pitting core gradually decreases. The weight loss of M50 steel increases over time, but the trend slows down, which is also shown in the MS simulation results. Electrochemical tests show that the tribocorrosion of M50 steel is related to load, speed. As the load increases, the corrosion rate decreases. And, as the speed increases, the corrosion rate increases. This has practical significance for extending the understanding of tribocorrosion of M50 steel in marine atmospheric environments.

Influence of shot-peening on the self-heating behavior and fatigue properties of 300M steel

Shot peening is an established cold working process used to introduce residual compressive stresses on a surface and is extensively studied using conventional fatigue tests. However, it has not been widely studied using the self-heating method. Specifically, the heterogeneity of the dissipation field has not been estimated, with only an average approach being used. Previous investigations in the case of 300M steel demonstrated that the effect of shot peening on the high cycle fatigue properties can be either beneficial or detrimental. This study proposes to apply the self-heating method on polished 300M and to investigate the effect of mean stress and shot peening on the dissipation behavior. A modified self-heating model is proposed and calibrated for 300M steel. Combined with residual stress profiles, a method to compute and determine the shot peening effect on self-heating behavior through single point surface measurements is proposed. Application on 300M steel shows excellent results, the over-dissipation being mainly due to the sub-surface compressive residual stresses. The self-heating method has proven useful to quickly estimate fatigue properties of polished 300M steel. Based on the understanding of the self-heating curve of shot peened 300M steel, a quantification of shot-peening effect on fatigue limit is discussed.

Rolling contact fatigue property of gradient rare earth addition M50 bearing steel with surface nano-grains and its inhibited martensite decay

A gradient nanostructured surface layer of ∼600 μm in thickness was prepared on M50 steel with rare earth additions by a surface mechanical rolling treatment. The initial microstructure was refined into nanosized grains (∼29 nm in diameter) in the top surface layer, causing a significant increase of surface hardness. Meanwhile, the grain size increases, and the microhardness decreases gradually to the matrix values with increasing depth. Rolling contact fatigue tests showed that the fatigue lives are significantly increased by the gradient nanostructured surface layer. Analysis of failure mechanism revealed that both softening in the near surface layer and hardening in the subsurface occur under rolling contact testing. And surface spalling is the predominant failure mode, of which the cracks initiate from primary carbides in the top surface layer owing to surface softening. In gradient nanostructured samples, the nano-grains inhibit carbon migration by impeding dislocation movement in the near surface layer, so that martensite decay is suppressed. Consequently, the crack initiation is inhibited, and the fatigue property is enhanced.

Electric current-induced directional slip of dislocation and grain boundary ordering

The evolution of lattice dislocations in metals can be induced by electric current. However, the effect of electric current on the interaction between lattice dislocations and grain boundaries (GBs) remains unclear. Herein, we investigate the evolution of lattice dislocations and grain boundary dislocations (GBDs) induced by electric current in M50 steel via in-situ TEM characterization, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations. Our findings reveal that electric current induces the directional slip of lattice dislocations towards GBs, while the reduction of GB contrast is attributed to the decomposition and reorganization of GBDs. DFT calculations demonstrate that electric current enhances the force on atoms in defect regions. These in-situ TEM observations are well reproduced by MD simulations incorporating electric current, which include a virtual temperature rise at defect regions to reflect the electric current force on defect atoms. Based on these observations, we propose a novel GB accommodation model under electric current. These results provide valuable insights into the mechanisms by which electric current tailors lattice dislocation behavior and enhances GBDs ordering in metallic materials.

Effect of Martensite–Bainite Duplex Microstructure on Carbide Precipitation and Mechanical Properties of M50 Steel

By means of microstructure observation, phase analysis, and mechanical‐property tests, the effect of martensite–bainite (M–B) duplex microstructure on carbide precipitation and mechanical properties of M50 steel is studied. In that results, it is shown that the distribution of secondary carbides in specimens with M–B duplex microstructure is more uniform and finer, and the stability of retained austenite (RA) in the steel is also improved, so that the content of RA in specimens with M–B duplex microstructure is 2.34%, which is higher than the 0.94% of the specimens with full martensite microstructure. The M–B duplex microstructure leads to the reduction of tempering hardness of M50 steel to 60.9 unit of Rockwell hardness (HRC), compared to the 61.6 HRC of the specimens with full martensite microstructure, but the wear resistance is slightly enhanced. Moreover, the M–B duplex microstructure effectively improves the impact toughness and fatigue properties by refining the microstructure and carbides in the steel, and the increase amplitude is 47.4% and 41.0%, respectively.

Residual fatigue life prediction based on a novel improved Manson-Halford model considering loading interaction effect

The classical nonlinear fatigue cumulative damage model Manson-Halford is widely used in fatigue life analysis and prediction, but this model lacks consideration for the effects of load interaction. At present, some studies have proposed new correction models to overcome the shortcomings of classical models. However, the problem with these models is that the parameters are difficult to determine, resulting in a cumbersome application process or the correction process is based only on a single parameter. Insufficient correction leads to large fluctuations in life prediction errors. To overcome the above problems, this article proposes a new correction method and establishes a new improved model. Unlike existing models, the newly improved model is based solely on S-N curve parameters and does not require additional material parameters. It fully considers the relationship between adjacent loads and the difference in fatigue life under different stress states, and dynamically modifies the classical model based on larger influence weights. By conducting multi-level fatigue tests on 300M steel, a new improved model was used to accurately predict its remaining fatigue life. Compared with the classical model, the prediction error was reduced by 11.75 %. Utilized fatigue test data from various other materials to predict the fatigue life of the improved model under different levels of stress loading. The results indicate that in the vast majority of cases, the improved model has the highest prediction accuracy among all compared models, with a minimum relative prediction error of only 3.79 % and small fluctuations in prediction error. Compared with the classical model, the maximum reduction in relative prediction error after model improvement reached 28.73 %, indicating the effectiveness and accuracy of the new improved model.

Effect of Compound Treatment of Laser Shock Peening and Nitriding on Wear Resistance of M50 Steel

Effect of Compound Treatment of Laser Shock Peening and Nitriding on Wear Resistance of M50 Steel

Contact fatigue of thin hard diamond-like carbon films on M50 steels under cyclic spherical micro-indentation

Contact fatigue behaviors of thin hard diamond-like carbon (DLC) films on M50 steels during cyclic spherical micro-indentations were investigated. The stress-strain evolution of the entire system was analyzed by finite element methods. The film fracture mechanisms and interfacial bearing responses under monotonic and repeated contacts were comprehensively explored. Concentrated tensile and shear stresses were found to, respectively, govern the initiation and propagation of the surface ring cracks. Elevated tensile stresses at the initiation and epilogue of each indentation cycle enhanced bottom radial cracking. At the interfaces, the maximum tensile (σnmax) and shear (σtmax) stresses occurred at the end of unloading and loading processes, respectively. With increasing maximum indentation forces, σnmax initially increased and then gradually decreased, while σtmax increased monotonically.

Surface melt nitriding and strengthening mechanism of plasma torched M50 bearing steel

This paper presents a new plasma torch nitriding technology for the first time to realize the surface nitriding of bearing steel for strengthening. By adjusting the plasma torch current parameters in the range of 120–160 A, M50 bearing steel was carried out at a nitriding speed of 2 s/cm2. After nitriding, the nitrogen content was increased from 0.00732 wt% in the original M50 steel up to 0.416 wt%, and the thickness of the nitrided layer was up to 2.51 mm. FeN0.076, Fe2N and Fe3N phases were formed in the steel, which was beneficial to increase the hardness and strength of bearing steel. The Vickers hardness of the original M50 bearing steel was 241 HV0.2. However, the highest surface hardness of specimen after nitriding was increased up to 778 HV0.2, which was attributed to the effect of sub-surface hardness strengthening within 2 mm from the depth of nitride surface. The average wear coefficient and the volumetric wear rate of the specimen after nitriding were decreased by about 32 % and 70 %, respectively. TEM observation showed that after nitriding, the structure of nitrided layer was martensite. The precipitates in the steel changed from large-sized, irregular and aggregated carbides (M23C6, M4C3 and M2C) to small-sized, spherical and uniformly distributed carbon‑nitrogen composite precipitates (M23(C, N)6, M7(C, N)3) in the steel sub-surface, but no obvious precipitates were formed on the surface of nitrided specimens. At depths of 1 mm and 2 mm, the size of the precipitates was reduced by about 68 % and 41 %, respectively, and the area of the precipitates was reduced from 18.4 % to 2.3 % and 3.7 %, respectively, compared to the original M50 bearing steel. It was concluded that the nitrided layer were strengthened synergistically with nitrogen solid solution, nitrogen-containing precipitates and martensite.

Effect of Temperature on the Structure and Tribological Properties of Ti, TiN and Ti/TiN Coatings Deposited by Cathodic Arc PVD

Monolayers of Ti and TiN coatings, as well as a Ti/TiN bilayer coating, were deposited on AISI M2 steel substrates using the PVD cathodic arc technique. The coatings had a thickness close to 5 μm and an average roughness between 98.6 and 110.1 μm due to the presence of microdroplets on the surface. The crystalline structure of the materials was analyzed using Grazing Incidence X-ray Diffraction (GIXRD) with an increase in temperature to study the dynamics of oxide formation. A phase composition study was conducted using the Rietveld refinement method. At the temperatures where critical growth of titanium oxides, both anatase and rutile, was observed, pin-on-disk tests were performed to study the tribological properties of the materials at high temperatures. It was determined that the oxidation temperature of Ti is around 450 °C, promoting the formation of a combination of anatase and rutile. However, the formation of rutile inhibits the formation of anatase, which is stable above 600 °C. In contrast, TiN showed an oxidation temperature of 550 °C, with an exclusive growth of the rutile phase. The Ti/TiN bilayer exhibited mixed behavior, with the initial growth of anatase promoted by Ti, followed by the formation of rutile. Oxidation and tribo-oxidation dominated the wear behavior of the surfaces, showing a transition from mechanisms related to abrasion at low and medium temperatures to a combination of abrasion and adhesion mechanisms at high temperatures (800 °C).

Effect of corrosion on the fatigue damage behavior of M50 steel treated by ultrasonic surface rolling process

Ultrasonic surface rolling process (USRP) can improve the fatigue performance of M50 steel, but corrosion during service may affect the anti-fatigue performance. Microstructure and corrosion resistance of M50 steel treated by USRP is analyzed by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS). Besides, the fatigue behavior of USRP sample under corrosion is analyzed by conducting fatigue tests after immersion corrosion tests. Results show that USRP treatment refines the surface grains to nanoscale (29.8 nm), introduces a certain residual compressive stress and decrease the precipitations of M50 steel, which improve the density of passive film and the resistance to local corrosion for M50 steel. Compared to M50 steel matrix, USRP sample has fewer and smaller corrosion pits at the same corrosion time, thereby reducing the risk of crack initiation. Meanwhile, the residual compressive stress value of USRP sample remains at a higher level. So the fatigue life of USRP sample is always higher than that of untreated sample under the same corrosion time. However, the corrosion process still leads to the destruction of surface integrity and the release of residual compressive stress, and the fatigue performance of USRP sample will gradually decrease with increasing the corrosion time.

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.

Understanding the wear behavior and mechanism of gradient nanostructured M50 bearing steel through nanoscratching tests

A gradient nanostructured M50 bearing steel with gradient structural size, carbides, and dislocation density was successfully fabricated by ultrasonic shot peening (USP) technology at room temperature. The friction behaviour and mechanism of gradient nanostructure M50 steel were investigated by using nanoscratch technology under various normal applied loads and depths. Under low normal applied load, gradient samples at ∼5 μm depth exhibited a 26.5 % maximum reduction in wear rate compared to the tempered sample; under high normal applied load, wear rates for samples at ∼100 μm depth exhibited a maximum reduction of 44.6 %. At low normal applied load, the wear mechanism involves plowing; while at high normal applied load, the wear mechanism shifts to cutting. Under low normal applied load, wear resistance correlates positively with hardness and negatively with structural size. Under high normal applied load, the increase in hardness of the martensite matrix and the partial decomposition of coarse spherical carbides enable the carbides on the surface of the USPed sample to withstand higher shear stress and stronger stress concentration, preventing cracking of the matrix and carbide edges, and spalling of carbides. High dislocation density (resulting in residual compressive stress) will slow down or inhibit the generation and expansion of cracks during the scratching process, potentially explaining why samples at ∼100 μm depths exhibit superior wear resistance.

Tribological Behavior of Polydiethylsiloxane (PDES) in a Si3N4 and M50 System under Low Temperatures from −80 to 25 °C

Lubricants must exhibit good tribological behavior at low temperatures to ensure reliable startups in very cold regions. This study investigates the performance of lubricants, with a specific focus on their capacity for high-temperature lubrication and ensuring reliable low-temperature startup in engines. Experiments were conducted to assess the friction and wear characteristics of polydiethylsiloxane in conjunction with a Si3N4 ball and M50 (8Cr4Mo4V) steel across a temperature range of −80 °C to 25 °C. The results indicate that the coefficient of friction, as determined through friction and wear tests at various temperatures, remained below 0.1. As temperatures progressively decreased, the system’s friction coefficient increased, and wear volumes recorded at 25 °C and −60 °C were 9749.513 µm³ and 105.006 µm³, respectively, culminating in lubrication failure at −100 °C. This failure is primarily attributed to the increased viscosity and decreased mobility of polydiethylsiloxane at extremely low temperatures. Additionally, the reduced temperature increases the strength of the quenched steel, leading to hard particles or protrusions on the material’s surface, which collide with the Si3N4 ball during friction, causing adhesion and spalling. Despite this, polydiethylsiloxane forms a stable protective oil film on the surface, enhancing the system’s lubrication performance. However, below −80 °C, this oil film begins to tear, leading to diminished lubrication efficacy. This study provides valuable data supporting the field of cryogenic lubrication.

Insights into room- and elevated-temperature micro-mechanisms of laser shock peened M50 steel with superior tribological performance

M50 steel, commonly utilized in aircraft engine bearings, is susceptible to friction-induced failures, particularly in high-temperature service conditions. To address this issue, various strategies have been proposed, with laser shock peening (LSP) garnering significant attention due to its deeper residual stress penetration and excellent surface integrity, whereas the underlying strengthening mechanisms have not yet been fully elucidated. In this study, we systematically investigate the impact of LSP treatment on the tribological properties of M50 steel at temperatures of 25 and 300 °C, alongside elucidating the relevant micro-mechanisms. Microstructural analysis reveals that laser impact strengthening primarily arises from dislocation proliferation, resulting in a surface hardness increase of approximately 14 % and the formation of a substantial compressive stress layer reaching a maximum value of about 1200 MPa, with a depth of around 2 mm. Friction test results demonstrate reduced coefficients of friction and wear rates following LSP treatment at both temperatures. Notably, a more pronounced reduction is observed at 300 °C, with values decreasing by 41.4 % and 55.8 %, respectively. The enhanced performance is attributed to the synergistic interplay of compressive residual stresses, work-hardening layers, increased density of dislocations, and substantial microstructure refinement.

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.