M2 Steel Research Articles

Rolling contact fatigue performance of M50 steel: A combined experimental and analytical approach to determine life

This article presents an experimental and analytical investigation into the rolling contact fatigue (RCF) performance of AISI M50 bearing steel across a range of Hertzian contact pressures (Ph=2.6GPa to 3.4GPa). RCF experiments were conducted using a ball-on-rod test rig at three contact pressures to experimentally establish the relationship between contact pressure (contact stress) and the RCF life of M50. Simultaneously, a previously developed continuum damage mechanics finite element (CDM-FE) model, employing the Fatemi-Socie critical plane approach as the failure criteria, was utilized to provide analytical predictions of RCF life. The CDM-FE model’s damage rate equation was calibrated using open literature AISI M50 bearing steel torsion stress life (SN) data. The CDM-FE model incorporated Voronoi tessellations to represent the material microstructure and capture the material topological effect on fatigue scatter. RCF simulations were conducted at seven contact pressures ranging from 1.0 GPa to 3.4 GPa in 0.4 GPa increments. Similar to the experimental results, the analytical RCF life data set yielded a relationship between contact pressure and simulation life for M50. Good corroboration is observed between the contact pressure – life relationships from the experimental and analytical RCF life data sets. This is significant as it supports the use of a hybrid approach combining experimental tools (e.g. torsion fatigue and ball-on-rod) and a CDM-FE computational model to efficiently assess the RCF performance of bearing materials.

Tribological Evaluation of Boride Layers Formed on an AISI M2 Steel Substrate by the Powder Packing Method.

Tribological Evaluation of Boride Layers Formed on an AISI M2 Steel Substrate by the Powder Packing Method.

Effect of the Surface Carbon Content on Microstructure and Deformation of M50 Steel

Effect of the Surface Carbon Content on Microstructure and Deformation of M50 Steel

Effects of surface defects on rolling contact fatigue of M50 steel with consideration to both the transgranular and intergranular damage

Surface-initiated pitting and subsurface-initiated spalling of M50 bearing steel were investigated, considering transgranular and intergranular damage. The damage initiation and propagation for contact surface with defects produced by different size particles were analyzed using integrated model combined continuum damage method (CDM) and cohesive zone method (CZM). Pitting and spalling mechanism, and defect size effect on damage evolution were discussed. The results indicated both pitting and spalling include intergranular and transgranular damage evolution. As the defect size increases, the RCF mode change from spalling to pitting. Damage evolution mode of spalling and pitting is the plastic deformation and damage accumulation mode, respectively. Moreover, the prediction accuracy for the damage evolution of the integrated model is higher than single-CDM and single-CZM models.

Microstructure Evolution and Wear Resistance Improvement of Ultrasonic Peened M50 Steel via Electromagnetic Shocking

Herein, the effect of electromagnetic shocking treatment (EST) on microstructure evolution and wear resistance of M50 steel treated by ultrasonic shot peening (USP) is investigated. The microstructure observation indicates that the EST promotes the precipitation of nanoscale carbides. The average grain size decreases slightly and the submicron grain layer increases after EST. The low‐angle grain boundaries generated by USP will transform into high‐angle grain boundaries, thereby refining the grains on the surface during EST. In addition, the surface hardness of USP‐M50 steel decreases slightly, accompanied by the reduction of surface residual stress after EST. The wear resistance results indicate that the wear loss of the EST specimens decreases by 15.7% comparedwith the specimens after USP. The improvement of wear resistance induced by EST is attributed to the increased fine precipitations. These precipitations hinder the grinding of abrasive particles into the matrix and connect with wear debris and oxide particles to form well consolidated self‐lubricating films to prevent wear losses. The refinement of surface structure is another important reason for the improvement of wear resistance.

Tribological behavior of a novel Si- and WC- co-reinforced a-C multilayer coating at 25– 500 °C

To improve the applicability of a-C coatings in a wide temperature range, a novel Si- and WC- co-reinforced amorphous carbon coating (SiC-nWCC), consisting of Si-doped a-C nanolayers and WC/a-C nano-multilayers, is proposed in this paper. A series of SiC-nWCC coatings with different modulation ratios (0.49–1.98) were fabricated by a closed field unbalanced magnetron sputtering system. The influences of modulation ratio on the microstructure, mechanical properties together with thermal stability of SiC-nWCC coatings were explored. The tribological behaviors of SiC-nWCC coatings against M50 steel balls were investigated at room temperature to 500 °C in ambient air. The results show that the SiC-nWCC coating with the modulation ratio of 1.98 achieved superior wide-temperature applicability, featuring the average friction coefficient lower than 0.17 and the wear rate less than 9.84 × 10−6 mm3/N·m in the whole temperature range of 25–500 °C. The excellent wide-temperature tribological performance of the SiC-nWCC coating are mainly attributed to the good thermal stability and the formation of temperature adaptive tribological layers. At 25 °C, sp2-rich carbon is the main lubrication phase of tribological layers, and at 200– 400 °C, the lubrication performance of coating relies on both sp2-rich carbon and Si-rich oxides, and at 500 °C, the self-lubrication phases of Si-rich oxides and WO3 are account for the outstanding lubricating performance of coating. This work provides a profound insight for developing the wide-temperature applicable a-C based coatings.

Understanding the recrystallization and phase transformation of gradient nanostructured M50 steel under the athermal effect of electrical pulses

M50 steel is a commonly used material for aeroengine main shaft bearings. In this study, a gradient nanostructured M50 steel was fabricated by an efficient surface nanocrystallization method, i.e., ultrasonic shot peening (USP) technology. The recrystallization behavior and phase transformation of gradient nanostructured M50 steel under the athermal effect of electrical pulses were investigated. Compared with the USPed sample, the ferrite structure size was 32.5% smaller, and the structure size uniformity was 51.5% greater in the 0–50 μm region after USP treatment and electrical pulsing treatment (EPT) with 38 A/mm2–1 s. Athermally induced ferrite recrystallization by EPT accompanied with obvious precipitation of VC and Mo2C carbides, and decomposition of austenite occurred during ferrite structure coarsening. EPT has different responses to different depths of gradient M50 steel, and there is an optimal current density to achieve structure refinement in different depths. However, the coarse-grain tempered M50 steel did not undergo obvious ferrite structure refinement under the same EPT parameters. The results revealed that the EPT promoted static recrystallization of incompletely recrystallized structures after USP processing by activating the release of stored deformation energy. Static recrystallization under the athermal effect of EPT was achieved by promoting the migration of the subgrain boundary to absorb the surrounding dislocations and increase the misorientation between itself and the surrounding ferrite structure. The mechanism of the athermal effect of EPT was based on electron-defect interactions, such as dislocations and lattice distortions. High-density nonequilibrium grain boundaries, acting as “active sites”, accelerating the process of recrystallization under the effect of electric pulses. This study proposed a method for optimizing EPT parameters through the change in instantaneous resistance to evaluate the degree of recrystallization of the gradient structure.

Alternative approach for the growth of a TiB2/TiC multilayer on M2 steel using the duplex method: Cathodic arc physical vapor deposition and cathodic reduction and thermal diffusion boriding

An alternative approach for producing a hard TiB2/TiC multilayer on M2 high-speed steel was introduced by combining cathodic arc physical vapor deposition (CA-PVD) and cathodic reduction and thermal diffusion-based boriding (CRTD-Bor). In this regard, the CRTD-Bor process was applied on CA-PVD Ti-deposited M2 steel and the effects of boriding parameters (i.e., temperatures and durations) on multilayer growth were examined. During boriding, Ti coating on the substrate was converted into Ti-borides on the top surface and a TiC layer was simultaneously formed at the interface of the Ti deposit and the steel matrix. The growth of boride and carbide phases was found to obey the parabolic law. The pre-exponential factors (K0) and the activation energy (Q) values were calculated as 7.50 × 10−9 m2/s and 146.10 kJ/mol for TiB2 growth and 1.81 × 10−7 m2/s and 187.31 kJ/mol for TiC formations, respectively. Additionally, empirical equations for estimating the thicknesses of TiB2 and TiC layers were derived. The penetration depth-dependent hardness measurements revealed the TiB2 layer hardness as 41 ± 5 Gpa, which decreased gradually toward the TiB region (24 ± 2 GPa) and fell to 13 ± 1 GPa in the Ti-rich area. The hardness then increased to 20 ± 1 GPa with the contribution of the TiC layer adjacent to the substrate. This multilayer coating exhibited −5.5 to −4.5 GPa compressive stress and good adhesions (HF1) to the substrates. Also, the results of tribological tests indicated a sevenfold increase in wear resistance under dry sliding conditions.

Deformation behavior and microstructure evolution of 300M ultrahigh strength steel subjected to high strain rate: an analytical approach

In this paper, the deformation behavior and microstructure evolution of 300M steel are comprehensively studied by using the split-Hopkinson pressure bar technology, with an emphasis on the analytical estimate of material flow and microstructure distribution subjected to high strain rate. It is found that the grains have been significantly refined due to dynamic recrystallization (DRX) and major continuous DRX supplemented by few discontinuous ones governs the microstructure evolution. The dislocation activities associated with the angle change of grain boundaries and mechanical twinning dominate the deformation mechanism of 300M steel under high strain rate. Besides, nanoparticles in the form of carbide precipitation are uniformly distributed in the deformed zone, which strengthens the material by pinning the dislocations. A thermo-mechanical coupled analytical model considering dynamic recovery and dynamic recrystallization was innovatively developed, based on which the distribution of grain size and microhardness was predicted. The results indicated that the flow behavior described by the models and the calculated grain size as well as microhardness are proven to agree well with the results of experimental analysis.

Numerical Simulation of Crack Condition in Forging Products of M50 Bearing Steel Based on Processing Map Theory

The microstructure of forged products significantly impacts their properties, and defects or carbide distribution are not visible to the naked eye. Isothermal compression tests on M50 steel with a Gleeble 3500 tester were conducted to study microstructure behavior during forging. Tests examined the hot deformation behavior within a temperature range of 900–1200 °C and a strain rate range of 0.01–10 s−1. Power dissipation efficiency (η) and flow instability (ξ), which are crucial processing map parameters, were employed to analyze the high-temperature deformation behavior of M50 steel. The 3D processing map determined the optimum forging conditions, indicating that hot working should start at an initial temperature of 1050 °C or higher and a strain rate of 1 s−1, decreasing the strain rate and temperature as the strain increases. The 3D power dissipation efficiency map displayed an average value of 0.43 or higher at a strain rate of 0.1 s−1 and a temperature of 1150 °C before reaching a strain rate of 0.8. The Finite Element Method (FEM) simulated results, revealing ξ and η distributions, and confirmed that microstructure observation during deformation matched the hot forging parameters. This approach can effectively predict microstructure changes during hot forging.

Formation mechanism and microstructure evolution of light etched region during rolling contact fatigue in M50 steel

The microstructure evolution and formation mechanism of lighting etched region (LER) during rolling contact fatigue (RCF) in M50 steel are systematically investigated. The results indicates that LER is a kind of microstructure degeneration due to the accumulation of plastic strain. Finite element simulation indicates that, under 5 GPa contact pressure, the equivalent stress at the subsurface exceeds the yield strength of M50 steel and, thus, induces plastic deformation. The dislocation density and fraction of grain boundaries increase in LER and thus the grain size is refined and the micro-hardness increases. The microstructure evolution in LER during RCF is divided into four stages. Stage 1: dislocations and GBs increase significantly, while the micro-hardness remains almost unchanged with the increase of RCF cycles; Stage 2: GBs and micro-hardness increase gradually with the increase of RCF cycles; Stage 3: LAGBs evolve to HAGBs and thus the total length of LAGBs decreases and the total length of HAGBs increases. Dislocation density and micro-hardness both increase with the increase of RCF cycles; Stage 4: dislocations and GBs continue to increase with the increase of RCF cycles due to accumulation of plastic deformation, and the micro-hardness also increases.

Research on Deep Hole Machining Based on Aircraft Landing Gear

A landing gear is the main large bearing structural part of an aircraft. The change of material and structure makes the processing of the aircraft landing gear more difficult. Aiming at the structural characteristics of the aircraft landing gear deep cavity, the deep hole processing technique of a 300M steel workpiece was studied. A separated NC deep hole drilling and boring machine was adopted to process the workpiece. Cavity hole special cutting tools were introduced. Fixture and sealing mode were improved. NC programs were optimized. Thus, the processing problems of deflection, vibration, chip breaking and chip removal were solved. The workpiece with width to diameter ratio greater than 10 and surface roughness of hole is 3.2 μm was successfully machined by machining experiment, and the high efficiency machining of deep hole of ultra-high strength steel was realized. Thus the theoretical foundation is laid for the machining of complex cavity deep holes for cutting high-strength alloy materials.

Quenching induced residue stress in M50 steel ring: a FEM simulation

A finite element method (FEM) combined with subroutines was established and used for tracing the evolution of stresses in M50 steel in quenching. The constitutive relation and thermal physical properties of M50 steel were tested and integrated into the modeling. The finite element analysis, taking into account of thermal stresses and martensitic phase transformation, predicts accurately the high-velocity nitrogen (HNQ) induced residual stresses in the M50 steel bulk. The simulation results suggested that the residual stresses in M50 steel is compressive at the surface while tensive at the center, along with very strong residual stresses at edges. The residual stress reaches to the high level of −810.3 MPa and −1436 MPa in the case of HNQ and water quenching, respectively. The evolution of stress is found to be jointly driven by the thermal stress and phase transformation stress. The thermal stress dominates the evolution at the initial stage while the phase transformation stress becomes dominating once the martensite transformation begins.

Laser shock peening rounds influencing microstructural and mechanical properties of 300M steel

Laser shock peeing (LSP) was introduced to produce surface gradient structures on 300M steel to improve its performance, service life and related workpiece safety. The influences of LSP rounds on microstructural and mechanical properties were investigated to optimise the LSP processing. Smoother surface, surface nanocystallization, and gradient structure, hardness, compressive residue stress was observed LSP. Strength and plasticity of 300M steel improved significantly due to the surface changes induced by one round of LSP. However, excessive LSP rounds tend to deteriorate the surface roughness and mechanical properties despite increased surface nanocrystallization, hardening zone depth and compressive residual stress.

Artificial intelligence modeling of induction contour hardening of 300M steel bar and C45 steel spur-gear

Artificial intelligence modeling of induction contour hardening of 300M steel bar and C45 steel spur-gear

Effect of heat treatment on microstructure and mechanical properties of directed energy deposition-Arc 300M steel

Effect of heat treatment on microstructure and mechanical properties of directed energy deposition-Arc 300M steel

Sliding wear and rolling contact fatigue behavior of M50 steel coated with atomic layer deposited lubricious oxide nanolaminates

Atomic layer deposition (ALD) was employed to deposit highly conformal and uniform nanolaminate coatings of ZnO/Al2O3/ZrO2/Al2O3 on M50 bearing steel substrates for sliding wear testing, as well as on CrN coated M50 bearing steel cylindrical rods and cups for three-ball on rod rolling contact fatigue (RCF) testing. The nanocrystalline ZnO top layer was structurally-engineered to achieve low surface energy, textured (0002)-oriented grains. To achieve this preferred orientation, amorphous Al2O3 was deposited as a seed layer, while crystalline ZrO2 acted as a high toughness/load bearing layer. The ALD nanolaminates reduced both the sliding wear rate (2 × 10-7 mm3/N·m) and enhanced the RCF resistance of M50 steel out to 6 million rolling contact fatigue cycles with no signs of spall. Based on cross-sectional transmission electron microscopy studies inside the wear surfaces, it was determined that sliding and rolling-induced plastic deformation was observed in ZnO layer where basal plane stacking faults were sheared parallel to the sliding and rolling directions. This intrafilm shear velocity accommodation mode mitigates the friction, reduces wear, and inhibits brittle fracture. Therefore, ALD ZnO/Al2O3/ZrO2/Al2O3 nanolaminates are candidate coatings that provide both sliding and RCF resistance in moving mechanical assemblies that require thin (∼10-300 nm), uniform and conformal solid lubricants.

Tribological Performance of a Composite Cold Spray for Coated Bores

The tribological performance of a thermal sprayed, mirror-like surface with localized protuberances was investigated through tribotests and computational simulation. A composite coating with a 410L steel matrix and M2 tool steel hard particles was applied by the cold spray process as a bore coating for combustion engines. The presence of protuberances promoted the quick formation of an antifriction tribofilm when tested with an SAE 0W-16 containing ZDDP and MoDTC, which significantly reduced the asperity friction in comparison to the conventional engine coated bores in reciprocating tribological tests. An in-house computational model using deterministic numerical methods was used for the mixed and hydrodynamic lubrication regime. Lubricant film thickness and friction were simulated for a piston ring versus the proposed coating. The computer simulations showed that the protuberances reduced the hydrodynamic friction by increasing the otherwise very thin oil film thickness of mirror-like surfaces. Although not intuitive, this result was caused by the reducing of the oil film shear rate.

Influence of multiple quenching treatment on microstructure and tensile property of AISI M50 steel

Microstructure and tensile property of AISI M50 under a series of multiple quenching treatments is studied in this paper. With quenching number increasing from 1 to 3, the grain size increases from 15.06 μm to 60.16 μm and the morphology of martensite transforms from cryptocrystalline type into plate type. The volume fraction of retained austenite decreases quickly from 21 % to 8 % when quenching number increases from 1 to 2, and keeps at a stable level of 4 % under triple quenching. The ultimate tensile strength peaks at 2834 MPa under double quenching, and lowers down to 2715–2730 MPa with quenching time increasing from 2 to 4. A 2.8GPa AISI M50 steel with elongation rate of 2.4 % is obtained under double quenching, which indicates that multiple quenching is promising in the strengthening of high carbon steels.

Crack initiation mechanism of M50 bearing steel under high cycle fatigue

The fatigue properties of M50 bearing steel under high cycle fatigue were studied by rotating bending fatigue test at room temperature. The fatigue cracks of M50 bearing steel were primarily nucleated at MgO-Al2O3 inclusions and MC/M2C primary carbides. The voids were initiated through inclusion debonding from the matrix and primary carbide cracking under cyclic loading. Small cracks were initiated on the void along the direction perpendicular to the tensile stress. Small cracks propagated at a speed of 8.81 × 10-10 m/cycle with hysteresis in the fine granular area (FGA). When the stress intensity factor range for the subsurface defect was lower than the stress intensity factor range threshold for M50 steel, the initiation stage of fatigue crack was composed of crack nucleation caused by defects and fatigue process in FGA. The fatigue cracks propagated at the fish-eye area (FiE) when the stress intensity factor range at the FGA front exceeded ΔKth. There was a stress concentration at the inclusion-matrix interface or the primary carbide-matrix interface during a long-term cyclic loading which resulted in the nucleation of fatigue cracks. A fatigue crack nucleation model was established based on the true stress at the defect, size of the defect, and number of cycles. A fatigue life model was constructed based on fatigue crack nucleation and fatigue crack propagation processes.