M2 Steel Research Articles

Study of overloading retardation on fatigue crack propagation behavior in 300M steel

AbstractBased on the fatigue life change of 300M landing gear steel due to overload during service, this study innovatively designed four overload modes according to the actual load spectrum of the landing gear. In this study, the application of overload continued until the specimen failed, and the effects of overload ratio, overload type and specimen thickness on the crack propagation behavior of 300M steel were compared and analyzed. The fatigue crack growth rate and fracture morphology of the specimens were characterized and analyzed, and the influence mechanism of the crack growth rate at each stage under different types of overload conditions and the influence of the thickness of the specimen on the overload delay effect were discussed.

Tribological aspects of the Diamond-like carbon film applied to different surfaces of AISI M2 steel

This study investigated the influence of the roughness of AISI M2 steel substrate on the mechanical properties and performance of the DLC film exposed to a tribosystems with a hypoeutectic aluminum-silicon alloy, evaluating the adhesion properties, resistance to microabrasive wear and friction coefficient in sliding test. The film was deposited in samples with three distinct roughnesses, depending on the finishing condition: casted, grinded and polished. Results showed that the substrate roughness does not influence the structure of the DLC, but its morphology and tribological behavior. A better adhesion of the DLC was observed in the casted and polished substrates. In the microabrasive test, less wear resistance was found for rougher substrates, the polished substrate showed lower wear rate and specific wear coefficient. In the sliding test, different film behaviors were observed in the running-in and steady state regimes, with the casted substrate responsible for the lowest friction coefficient.

Progression of galling during punching of AA5754 Al sheets with DLC-coated and uncoated steel tools

Galling is a commonly observed type of sliding contact-induced damage that occurs as a result of material transfer from the aluminum alloys to the tool surfaces during forming and shaping of aluminum sheets. Progression of galling on uncoated AISI M2 steel tools and tools coated by non-hydrogenated diamond-like carbon (NH-DLC) with amorphous carbon (a-C) structure was investigated during the punching of AA5754-O sheets. Experiments were done either by lubricating aluminum sheets with mineral oil-based lubricant (LUB1), a method commonly used in industry, or by lubricating both the sheet and the punch prior to the initial punching stroke (LUB2). Galling rates were determined using the galling volume per punching stroke (between 20th and 125th strokes) measured using white light interferometry (WLI). Galling rates were lower for LUB2 punching compared to LUB1. In punching with NH-DLC-coated tools using LUB1, the coating was removed from the punch surface after 30 strokes, whereas for LUB2 punching, a negligible amount of aluminum transfer was detected by scanning electron microscopy (SEM) and WLI after 500 strokes, and the coating remained intact.

Microstructure and tribological performances of M50 bearing steel processed by ultrasonic surface rolling

To prolong service life of M50 steel for the main shaft bearing, ultrasonic surface rolling process (USRP) was utilized to improve surface performances. The effects of USRP on surface integrity and tribological behavior were investigated. The results show the effect of USRP parameters on surface performances follows the order: feed rate > load > rolling times. During the USRP treatment, plastic deformation layer with 24 µm thickness is formed, and fine grain strengthening increases the microhardness (15.56%) and residual stress (79.61%) and decreases the surface roughness (−68.09%), respectively. Friction coefficient and wear rate of USRP sample are lower than those of untreated sample, because USRP helps form a smooth tribolayer and changes the main wear mechanism to slight adhesive wear.

Microstructure and mechanical properties evolution of aviation M50 steel fabricated by the multiple electro-assisted rolling

The poor plastic forming ability of aviation M50 steel has seriously affected the high-performance manufacturing of aero-engine bearings. In this work, the multiple electro-assisted rolling (ESR) was applied by introducing the multiple electroshocking treatments into the rolling of M50 steel. The evolution of microstructure, mechanical properties, and damage of M50 steel fabricated by ESR has been investigated. The microstructure observation indicates that the dislocation density and residual stress of the ESR specimens decrease by 14.0% and 31.3%, respectively. Besides, fewer microcracks around the carbides are generated during the ESR. The mechanical property tests of ESR specimens show that the Vickers hardness is decreased by 8.7%, while the tensile elongation is increased by 33.4% without significant change in ultimate tensile strength as comparing with the CR specimens. Moreover, the TEM observation shows that subgrains are formed and higher lattice distortions are generated at grain boundaries after the ESR process. This could significantly promote the nucleation of recrystallization. After quenching and tempering, the prior austenite grain of ESR specimens is refined from 13.23 μm to 11.52 μm, while the ultimate tensile strength and Vickers hardness are increased by 12.1% and 6.1%, accompanied by an increase in elongation by 16.0%. This work develops a novel method to improve the forming limit and comprehensive properties of M50 steel by tailoring the microstructure and dislocation state, which is of great engineering significance for the manufacturing of aviation M50 bearing.

Study on sliding friction and wear behavior of M50 bearing steel with rare earth addition

This study aims to investigate the influence of rare earth (RE) addition on the friction and wear behavior of M50 bearing steel. The results show that RE addition has little effect on friction coefficient, but can reduce wear volume especially under harsh wear conditions. This mainly results from modification of RE elements to primary carbides. M50 steel without RE addition has bigger proportion slenderer rod-like M2C carbides, which are more likely to cause carbides fracture broken or peeling off, forming bigger wear debris with irregular shape to aggravate the wear. However, M50 steel with RE addition has more spherical MC carbides, which are more easily worn into spherical crowns, forming smaller wear debris which could not increase the subsequent wear.

DESIGNED AND ANALYSIS OF AN SC-17M MAIN LANDING GEAR LOADING ACTION

The concept of SC-17M aircraft design was initiated to address the shortfalls on the DO-228 and Hawker Beechcraft King Air 350i aircraft. Until recently by using a standard specification, an SC-17M landing gear design has been carried out. Detailed study of sub-part C of the certification standard aided the application and determination of the necessary loads on the landing gear. The comprehensive design employed 300M steel as the best structural material to be used in the fabrication of the landing gear. The maximum bending moment in the shock absorber and wheel axle were calculated and validated with the use of Strand7 software in the model stress analysis. The reserve of strength calculated shows that the landing gear was able to withstand the applied loads without experiencing any failure.

Effect of phase and elemental composition, structure, and texture of multilayer coatings based on TiCN and TiNbCN on the electrochemical behavior of high-speed steel in 3% NaCl solution

Thin multilayer TiCN and TiNbCN coatings were obtained on a high-speed steel M2 by pulsed magnetron sputtering. The content of N2 and CH4 in the gas mixture was changed to obtain nanostructured layers with different phase and elemental compositions, structure, and texture. The microstructure, defects, and elemental composition of the coatings were investigated using an Ultra 55 field emission electron microscope with an EDX microanalysis system. The phase composition and texture of the coatings were determined using a Shimadzu XRD-6000 X-ray diffractometer with Cu-Kα radiation. Voltammetry and impedance spectroscopy on the coated samples were performed in a 3% NaCl solution. The corrosion behavior of the coatings was characterized by the corrosion current density and polarization resistance (at the corrosion potential). It is shown that the investigated coatings are electrochemically active, and corrosion processes occur not only on the substrate in the discontinuities of the coating but also on the surface of the coating. The TiN-TiCN-TiCN multilayer coating with a maximum content of the three-component phase TiC0.496N0.502, a minimum content of the carbide phase TiC, a maximum texture coefficient, a minimum crystallite size, lower internal stresses and deformations of the crystal lattice has the lowest corrosion current density 0.75 µA cm−2 among the investigated coatings. Niobium improves corrosion resistance, but the presence of a significant amount of the TiC carbide phase in the TiNbCN coating reduces this effect. The morphology of the coating surface after the electrochemical test was studied. The maximum damage of the surface layer is observed for the multilayer TiCN (1) coating.

Effect of Cold Treatment Temperature on Size Stability and Mechanical Properties of M50 Bearing Steel

By using field‐emission scanning electron microscope (SEM), transmission electron microscope (TEM), X‐Ray diffraction (XRD), and tensile‐property tests, the effect of cold treatment temperature on size stability and mechanical properties of M50 bearing steel is studied. Results show that when the thermal treatment temperature is fixed to be 440 °C, the number of precipitated secondary carbides (SC) in the steel increases first and then decreases with the decrease of cold treatment temperature in the range of −50 to −90 °C. The amount of the precipitated carbides and the transformed residual austenite (RA) reaches the maximum at −70 °C. Carbide precipitation during cold treatment reduces the size of M50 steel, while martensitic transformation leads to the size increase. The size change of M50 steel is the smallest at −80 °C, about 0.5 μm. The elongation of the steel is 3.16% before stabilization treatment, which is improved after stabilization treatment under different conditions. The tensile strength and yield strength decrease at −60 °C and increase at −80 °C, and the other cold treatment temperature has little effect on the tensile strength of the steel.

Enhancing the hardness and damage-tolerance of CoCrNiAlTi coatings through dual-phase and nanotwinned structures

A series of CoCrNiAlTi coatings were deposited, via direct current (DC) magnetron sputtering, onto M2 steel substrates employing a range of substrate bias voltages (−20 V ~ -120 V). Dual phase (fcc and hcp) microstructures, with high compositional homogeneity, were observed for all as-deposited coatings. Highly refined columnar grains, with a high density of twin boundaries that were oriented perpendicular to the coating growth direction, were identified. As the bias voltage increased, elements in the high entropy alloy exhibited different sputtering yields that led to different degrees of re-sputtering in the deposited films. This, in turn, played a critical role in determining the coating composition and hence stacking fault energy. Accordingly, the ratio between the hcp and fcc phases varied, with a maximum fraction of the hcp phase observed at a bias voltage of −80 V. The fraction of the hcp phase then decreased as the voltage increased to −120 V. An exceptional hardness of value of ~9.5 GPa, along with appreciable damage-tolerance, was exhibited in the coating deposited at −80 V. It is suggested that the presence of nanotwins, as well as the dual-phase microstructure, contributed to this excellent strength-ductility unity.

Thermal shock of subsurface material with plastic flow during scuffing

The thermal shock of subsurface material with shear instability and severe plastic flow during scuffing was investigated. The scuffing damage of M50 steel was tested using a high-speed rolling—sliding contact test rig, and the transient temperature during scuffing was calculated using the Fourier transform method considering the effects of both frictional heat and plastic work. The results show that a thermal shock with a rapid rise and subsequent rapid decrease in the contact temperature is generated in the subsurface layers. The frictional power intensity generates a high temperature rise, leading to the austenitization of the subsurface material. Consequently, the plastic flow is generated in the subsurface layer under the high shear stress, and the resulting plastic strain energy generates a further temperature increase. Subsequently, a rapid decrease in the contact temperature quenches the material, resulting in clear shear slip bands and retained austenite in the subsurface layers of the M50 steel.

A novel route to improve the fatigue properties of aviation M50 steel via tailoring the bainite content and cold deformation

The microstructure, mechanical and fatigue properties of M50 steel by combining austempering processing with cold deformation have been investigated. The results show that the introduction of bainite can effectively refine the multiphase microstructure. When the bainite content is 10.5%, the finest microstructure and the best combination between strength and toughness can be obtained. It is also found that 20% cold deformation leads to a slight improvement of tensile strength and impact toughness, while the mechanical properties deteriorates significantly under larger cold deformation. It is concluded that the mechanical properties can be improved by tailoring the bainite content at about 10% and cold deformation degree at 20%. For the tailored specimen, the specific life of rolling contact fatigue is 114.1% longer than that of traditional martensitic quenched specimen. The slope parameter of Weibull distribution function also shows an increase from 1.8267 to 2.2992, reflecting the more stable of RCF life. There are fewer microcracks in the subsurface of peeling pits, which should be attributed to the higher toughness and finer carbides. Additionally, owing to the higher density of grain/phase boundaries, the tailored specimen with a lower hardness shows better resistance to plastic deformation under the wear trace. This finding provides a novel route to improve the RCF properties of M50 steel via strictly tailoring the bainite content and cold deformation degree.

Formation mechanism and influence of white etching area on contact fatigue spalling of M50 bearing steel

Contact fatigue spalling failure ocurred in the M50 steel bearings during test due to the formation of white etching area (WEA). In this paper, characteristics, formation mechanism, influence on contact fatigue spalling failure and control methods of the WEA were obtained by examining loctaions and morphological characteristics, composition analysis, hardness test and microstructure analysis of the WEA in the two failure bearing and the other three bearing which are not failure. The results show that the WEAs origin from the boundary between matrix and primary carbides or inclusions which located in the subsurface of raceway, show irregular block shape morphologies, have length direction of about 30°-50° degrees to the rolling direction and microstructure of body centered cubic ferrite nanocrystalline. There is no obvious difference between the WEA and matrix in chemical compositions, while hardness of the WEA is higher than that of the matrix. Formation mechanism of WEA is phase transformation driven by accumulation of plastic deformation induced by high stress in micro region. The smaller the distance between WEA and the raceway surface, the faster of WEA growth rate are reached. And WEA is more likely to cause contact fatigue spalling of the bearing as the deformation coordination between WEA and matrix is poor. The initiation and propagation of WEA can be controlled by reducing the material defects and avoiding the bearing from high working stress.

Effect of surface nanocrystallization produced by laser shock processing on the corrosion fatigue behavior of 300M steel

The effect of surface nanocrystallization produced by laser shock processing (LSP) on the corrosion fatigue behavior of 300M steel was systematically investigated. The surface integrity, microstructure evolution and residual stresses before and after corrosion fatigue were characterized. The results showed that afte LSP the surface grain size of 300M steel was sufficiently refined down to nanoscale after LSP, and a large residual compressive stress formed. Under the same loading stress level, the corrosion fatigue life of LSP-treated 300M steel was improved significantly. This improvement increased with increase of LSP pulse energy. After corrosion fatigue, the surface grain of LSP-treated 300M steel remained at the nanoscale, showing a good stability. The dislocation density and the number of deformation twins in the subsurface layer became higher with increase of LSP pulse energy to accommodate deformation. Surface residual compressive stress induced by LSP has a relaxation during corrosion fatigue, depending on the laser pulse energy and fatigue loading force.

Bilayer growth kinetics and tribological characterization of boronized AISI M2 steel

Abstract The AISI M2 steel has been treated by solid boriding between 1123 and 1273 K for an exposure time of 2–8 h. In these circumstances, a bilayer constituted by FeB and Fe2B has been formed with interfaces nearly flat. The tribological behavior and decohesion resistance of boride coatings were studied by using the following characterizations: (Rockwell-C cohesion, pin-on-disc and wear scratch tests). The modeling of process kinetics was undertaken based on two different approaches (the mass balance equations and the integral method). The assessed values of boron activation energies in FeB and Fe2B arising from the two models were nearly similar. In addition, the predicted layers’ thicknesses at 1243 and 1273 K during 10 h were concordant with the experimental values.

Effect of Minor Carburizing on Microstructure and Mechanical Properties of M50 Bearing Steel

Herein, by using scanning electron microscopy, transmission electron microscope, X‐ray diffraction, residual stress analyzer, and mechanical‐property tests, the effect of minor carburizing on the microstructure and mechanical properties of M50 steel is studied. It is shown in the results that after minor carburizing, the austenite content in the surface layer of the quenched M50 steel increases, while the martensite content and the hardness decrease. After tempering, the retained austenite in the surface layer is transformed into martensite, and a large amount of uniformly distributed carbides are precipitated. The hardness of the surface layer increases to exceed that of the core region in the steel. After the minor carburizing, there is a carbon concentration gradient between the surface layer and the core region of the M50 steel, which influences the phase transformation behavior and the residual stress state in the surface layer during the tempering process. Minor carburizing increases the rotational bending fatigue limit of the steel by 16.7% and improves the tensile strength, yield strength, and impact absorption energy of the steel.

In situ investigation of the fracture of primary carbides and its mechanism in M50 steel

The tensile crack initiation and propagation of M50 bearing steel were investigated. It is found that the primary carbides were fractured during the tensile test by in situ SEM, while decohesion of the carbide/matrix interface was hardly observed. In order to capture the initial tensile crack, quasi-in situ X-ray microtomography was performed, indicating that the earliest crack was formed from the broken interior carbides. This indicates that multiple cracks already existed in the matrix when they were observed on the sample surface. Electron backscattered diffraction (EBSD) and the finite element method (FEM) were applied to analyze the fracture behavior of carbide particles. The fracture of carbide particle is produced by the incompatible deformation between the matrix and carbides. The frequency of carbide fracture was found to be related with its fracture strength, size and shape. M 2 C carbide fracture was more easily broken than the MC carbide during tensile test. In addition, the long axis of most M 2 C carbides is approximately parallel to its (0001) plane and normal to tensile stress, leading to cracking more easily. Finally, a suggestion of adding pre-deformation is proposed to make M 2 C carbides broken sufficiently and further refine the primary carbides. • X-ray microtomography is applied to analyze the evolution of primary carbides. • Incompatible deformation between the matrix and particles leads to carbide fracture. • M 2 C carbide is more easily broken than MC carbide. • Pre-deformation before diffusion annealing should be applied to refine carbides.

Design characteristics of the strength of VKS-9M and 300M steels

The mechanical properties of square section (up to 350 mm) forgings made of domestic steel VKS-9M (obtained by the duplex process of vacuum induction melting plus vacuum arc remelting) are studied. The mechanical properties of steel VKS-9M and American high-strength structural steel 300M are compared in terms of the calculated characteristics of materials. We extend the concept of «design characteristics of materials» to all the mechanical properties of materials used in determination of the strength and durability of structures. The design characteristics of materials include the strength characteristics under quasi-static tension, compression, crushing and shearing, as well as the strength under variable loads and the crack resistance of the material. The correctness of comparing the calculated values of the static strength of steels VKS-9M and 300M is based on the identity of test methods and the equivalence of processing and presentation of test results. The determination of the strength characteristics was carried out according to domestic standards, which are basically harmonized with the American standards. A difficult situation arises when determining the strength indicators of a newly developed material. Nowel material, as a rule, is developed in laboratory conditions, produced on experimental equipment in small volumes, and, therefore, the statistical assessment of the general population at the development stage is unreliable. In conditions of the full-scale manufacture of industrial semi-finished products, a statistical assessment of their strength characteristics becomes necessary. In the aviation industry, a statistical assessment of the calculated values of the strength characteristics of the material is prescribed by the law. The airworthiness standards set the levels of the calculated values of strength characteristics with a certain probability of non-destruction. For parts, the destruction of which can lead to an accident, the calculated values of the strength characteristics of materials should be selected in such a way that the strength of the material is to be ensured with a probability of 99% — with a 95% confidence interval (basis «A»). Statistical evaluation of the static strength characteristics of two heats of VKS-9M steel on the basis of «A» revealed their insignificant excess in comparison with steel 300M. The data obtained allow us to believe that the calculated values of the static strength characteristics of VKS-9M steel will not be lower than the calculated values for 300M steel. Large-scale fatigue tests of VKS-9M steel were carried out, which proved that the fatigue characteristics of VKS-9M and 300M steels practically coincide, as well as the arrays of their determinations. The equivalence of the strength characteristics of the VKS-9M and 300M steels allows replacement of the American 300M steel by the domestic VKS-9M steel.

High-Temperature Deformation Behavior of M50 Steel

The hot deformation characteristics of M50 steel in the temperature range of 900–1150 °C and strain-rate range of 0.01–10 s−1 was investigated in this study using a Gleeble-3800 thermal simulation testing machine. The true stress–strain curves showed that the deformation resistance increased with decreasing deformation temperature, and increasing strain rate before the peak stress was reached. After the peak stress, dynamic reversion occurred, and consequently, the deformation stress decreased. The softening phenomenon was more obvious when the strain rate was low. The calculated values of the thermal deformation-activation energy Q and stress index n were 233,684.2 J/mol and 5.025568, respectively. On this basis, the Arrhenius-type constitutive equation was established, and in addition, a polynomial fit based on strain was performed to obtain the 9th-order strain-compensated constitutive equation with high fitting accuracy. By processing the flow stress curves, the processing maps of M50 steel were constructed, and the optimal processing range was predicted to be in the range of 1070–1150 °C and 0.01–1 s−1. The recrystallization behavior of M50 steel was also studied by constructing a dynamic recrystallization kinetic model and combining optical microscope (OM) and electron backscatter diffraction (EBSD) observation. The results show that with the increase of deformation temperature, the degree of recrystallization transformation increased accordingly, and the original grains were gradually replaced by recrystallized grains. Besides, in the optimal process zone for thermal processing, the recrystallized grains grew with decreasing strain rate and increasing temperature.

Optimization of wear and cracks in roller contact under different coating and a range of loads and temperature with fixed speed using design expert (DOE) and finite element model

Superior coating technology and roller materials such as M50 steels (0.8C–4.2Cr–4.3Mo–1V wt. %) and (1.0C–2.0Cr–0.5Mo–1.0Mn– 0.5Si wt. %) are well recognized in modern technology. The aim is to present all the external and internal parameters that affect the rolling system by taking into consideration the microstructure importance in identifying the service life of such rolling technique. The most dangerous defects are the cracks and wear under high loading contact and temperature formed during the rolling process.Finite elements method was used to simulate rolling and to calculate the extensive wear in order to use DOE to optimize several conditions from coating to load and temperature. The analysis involved here used the steel rollers with and without coatings, which include titanium nitride (TiN), zirconium nitride (ZrN), and tungsten carbide (WC) under different temperature and loading conditions. Results showed that cracks propagation were limited to extreme load when using coating technology. Design Expert optimization confirmed that TiN and WC coatings would enhance the lifetime of rollers and inhibit cracks initiations and extensive wear that could results in severe plastic deformation.