9Cr-1Mo Steel Research Articles

(Ti, Nb)(C, B)/IN625 In-Situ Reactive Coating Prepared by Ultra-High-Speed Laser Cladding: Interfacial Characterization, Residual Stress and Surface Wear Mechanisms

In this study, homogeneous (Ti, Nb)(C, B)/IN625 composite coatings with almost defect-free microstructures were successfully prepared on a 42CrMo steel substrate by coupling ultra-high-speed laser cladding (USLC) with the direct reaction synthesis (DRS) technique to introduce the in-situ exothermic reaction into the cladding materials; these were comparatively analyzed with the pure IN625 coating prepared only by USLC. Our results showed that the interface of the composite coating/substrate was greatly affected by about 670 kJ Joule heat released from the in-situ reaction happening during the cladding process, which was sufficient to remelt the as-deposited materials and significantly increased the coating/substrate interface width to around 24 μm, six times the interface width of pure IN625 coating. Furthermore, the residual stress inside the coating and across the interfacial region was also reduced, alleviating the interface stress mismatch. However, the surface hardness of (Ti, Nb)(C, B)/IN625 composite coating was found to be lower than that of the IN625 coating, and the average wear weight loss was only 10% of that of the IN625 coating, attributable to the in-situ authigenic TiCB, TiC, NbMo3B4 and NbMo2B2 phases providing load transfer from the hard phases to the IN625 composite matrix to achieve abrasion reduction and wear resistance. It was also found that the formation of nano-equiaxial ultrafine grains in the depth range of 250 nm below the wear surface was facilitated by the coupling of the three fields of plastic rheology-heat-force, which dynamically strengthened the wear surface. Based on these findings, it is suggested to promote the strategy of combing USLC and DRS techniques to achieve an additional ability to enhance the coating microstructure and reduce residual stress, to achieve better tribological performance.

Prediction of Impact Strength of TIG Welded Cr-Mo Steel Using Artificial Neural Networks

Welding is a critical and energy-intensive process with significant importance in the manufacturing industry, enabling the creation of joints capable of withstanding diverse loads without failure. Accurate prediction of welding parameters' effects on the thermal cycle and strength of metals during and after welding is essential to ensure the reliability of welds. This study investigates the influence of welding parameters such as welding current, material thickness, number of weld passes, and electrode diameter on the impact strength of Cr-Mo steel bars. Pure tungsten with 2% thoriated Tungsten Inert Gas (TIG) electrodes was used to join the metal sheets autogenously. Artificial neural network (ANN) was used in creating the model that predicts the impact strength of the steel. Sample with welding parameters of 15 mm thickness, 90 A current, 3 weld passes, and Ø2.4 mm electrode size exhibited the highest impact strength. Furthermore, the analysis of variance (ANOVA) results show that the material thickness and number of weld passes contribute significantly to the impact strength of the steel. The ANN model trained by the Levenberg-Marquardt algorithm had an average training dataset root mean square error (RSME) of 4.12%. This study contributes to the reliability and performance of welded joints in various applications.

Aspects Regarding the Influence of Hot Deformation on the Mechanical and Structural Properties of 42CrMo4 steel

The aim of the paper is to analyze the experimental results of the influence of elevated temperatures and strain rate on the mechanical and structural properties of steel 42CrMo4. The experiments were based on uniaxial tension and compression tests at high temperatures between 700 °C and 1000 °C and strain rates range 0.0018 - 0.1 s-1. The influence of temperature and strain rate on yield stress, strain to fracture, hardness, structural changes, and fracture characteristics were analyzed. Due to the dynamic recrystallization phenomenon present during the hot tensile tests, an increase in the flow stress is observed at the beginning of the deformation, after which it decreases until the fracture. By increasing the deformation temperature from 700 °C to 1000 °C, the tensile stress decreases significantly for all strain rates. The increase in the strain rate leads to the increase in the tensile stress. In compression tests by increasing the strain rate, the true strain is slightly increasing, but this depends on the temperature. The non-uniformity of deformations obtained at different values of the strain rate and temperature were also analyzed. Analysis by scanning electron microscopy showed the ductile behavior of the material. The degree of damage of the material caused by the presence of cavities increases by increasing the deformation temperature. For all the presented deformation conditions, the presence of the fracture through the ductile fracture mechanism was produced by the localized of necking and the coalescence of microvoids. By increasing the deformation temperature and reducing the strain rate, the fracture behavior of 42CrMo4 steel can be improved.

The Diagnostics of Power Boilers in Terms of Their Sustainability

Diagnosing steam pipelines is crucial because they are subjected to a water vapor environment and exhaust gases. Layers of oxides/deposits formed on steel utilized at elevated temperatures for long time periods have a significant impact on elements operating in power plants as well as in combined heat and power plants. Currently, these devices are an important topic of sustainable energy development. The aim of this work was to characterize the structure of the steel and of the oxides/deposit layer formed on the steam superheaters of power boilers and its impact on the durability of power equipment. The tests were carried out on 13CrMo4-5 steel utilized at various temperature and time parameters. In order to assess the degradation of the material, the following research methods were used: light microscopy, X-ray structural analysis, and infrared spectroscopy with Fourier transform. The use of the FTIR method in this type of diagnostics has deepened the existing analysis of oxide/sediment layers. The obtained test results showed that the kinetics of the corrosion process on steel being used for long periods at elevated temperatures is complex and depends, among others, on the element’s operating temperature, the operating time, and the flow medium.

Early corrosion behavior of 35CrMo steel for high-strength bolt in simulated shallow and deep sea environments

Early corrosion behavior of 35CrMo low-alloy steel for high-strength bolt in the simulated shallow seawater and deep-sea environment was studied using mass loss measurement, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Raman spectrometer, X-ray photoelectron spectrometer (XPS) and 3D microscope. The results show that the corrosion of 35CrMo steel initiates mainly at the steel matrix around the inclusions of CaO–MgO–Al2O3, (Ca, Mn)S and their mixed composite. The corrosion rate in the simulated deep-sea environment is lower than that in the shallow seawater, which is declined with immersion time. The corrosion products formed in the two environments are composed of γ-FeOOH, α-FeOOH, Fe3O4 and little Cr(III) oxide or/and hydroxide, but the rust layer produced in the deep-sea environment is thin and uniform. The steel has pits in a shallow dish shape and tends to develop uniform corrosion in the deep-sea environment.

Experimental Investigation of Creep Behaviour of 35CrMo Steel at High-temperature

The creep behaviour of 35CrMo steel have been investigated by high temperature creep experiments. It shows that the steady-state creep rate of 35CrMo steel under 450℃ (400 MPa, 450 MPa, 500 MPa), 500℃ (400 MPa, 450 MPa, 500 MPa) are 8.3980×10-5 h-1, 1.2223×10-4 h-1, 1.5749×10-4 h-1, 6.2995×10-4 h-1, 9.7457×10-4 h-1, 1.1975×10-3 h-1, respectively. The stress index of 35CrMo steel during creep is 2.8599. And the apparent activation energy of 35CrMo steel is 189.57 kJ/mol. The results of this study can provide some technical references for the safety management of 35CrMo steel at high-temperature.

In-Situ Hydrogen Charging Effect on the Fracture Behaviour of 42CrMo4 Steel Submitted to Various Quenched and Tempering Heat Treatments

In-Situ Hydrogen Charging Effect on the Fracture Behaviour of 42CrMo4 Steel Submitted to Various Quenched and Tempering Heat Treatments

Hydrogen-related degradation of fracture properties and altered fracture behavior of Cr–Mo steel used in hydrogen stationary vessels

This study comprehensively analyzes the effect of high-pressure hydrogen gas on the elastic-plastic fracture toughness, fatigue crack growth rate (FCGR) properties, and the corresponding fracture behavior of Cr–Mo steel in hydrogen stationary vessels. The fracture toughness value under 99 MPa hydrogen pressure significantly reduced by approximately one-third of the value tested in ambient air while FCGRs tested under hydrogen environments at a specified ΔK exhibited an approximate two-order magnitude increase compared to those observed in ambient air. The hydrogen-assisted fracture mechanism, encompassing crack initiation, propagation, and crack arrested, was meticulously examined. The distinct variations in fracture modes with changes in the ΔK range can be attributed to the synergistic interaction of HELP and HEDE mechanisms. Leak before break (LBB) behavior was not satisfied for the hydrogen vessel due to a significant reduction in the fracture toughness of materials when exposed to 99 MPa H2.

Study on microstructure of 42CrMo steel by ultrasonic surface rolling process

To explore the microstructure formation mechanism of 42CrMo steel under the strengthening of ultrasonic surface rolling process (USRP), the combination of theoretical analysis and experiment was used to conduct in-depth research on USRP. Firstly, according to contact mechanics and Hertz contact theory, the calculation model of contact stress distribution and elastoplastic strain between the rolling ball and the part during USRP is obtained. Secondly, the USRP processing test was carried out by single-factor experimental design method, and the microstructure of 42CrMo steel after USRP was analyzed by LEXT OLS5100 3D laser surface topography instrument and VEGA3 tungsten filament scanning electron microscopy, which found that with an increase in static pressure, residual stress and plastic strain gradually increase, the hardness firstly increases and then decreases, while surface roughness exhibits an initial decrease followed by an increase. The results show that USRP produces violent plastic deformation inside the material under the superposition of high-frequency impact and static pressure, at the same time, it refines the grains, so as to improve the surface performance of the part and improve its fatigue resistance.

Effects of Loading Frequency, Mean Stress and Stress Amplitude on Ratchetting-Fatigue Behavior in 42CrMo Steel Under Near-Yield Stress-Controlled Condition

Effects of Loading Frequency, Mean Stress and Stress Amplitude on Ratchetting-Fatigue Behavior in 42CrMo Steel Under Near-Yield Stress-Controlled Condition

Development of slurry erosion prediction model and studying the effect of slurry erosion parameters on erosion of WC10Ni5Cr coated 35CrMo steel

Development of slurry erosion prediction model and studying the effect of slurry erosion parameters on erosion of WC10Ni5Cr coated 35CrMo steel

Effects of hydrogen pressure on hydrogen-assisted fatigue crack growth of Cr-Mo steel

The fatigue crack growth rates (FCGRs) of 4130X steel in 45, 70, 87.5 and 100 MPa hydrogen were measured, and the hydrogen concentrations at the crack tip of test specimens were analyzed by establishing a hydrogen transport model. This model can describe the hydrogen behaviors in the process of environmental embrittlement. Results show that the FCGR increases with the increase in hydrogen pressure. However, the acceleration reaches the threshold under 87.5 MPa. Hydrogen pressure has the same influence on hydrogen concentration, and the threshold of the effect is probably related to the fact that the hydrogen absorption on the material surface reaches the limit.

Impact of Alloy Elements on the Adsorption and Dissociation of Gaseous Hydrogen on Surfaces of Ni–Cr–Mo Steel

In this study, the effect of alloying elements on the adsorption and dissociation behaviors of hydrogen molecules on the bcc-Fe (001) surface has been investigated using first-principles calculations. H2 molecules can easily dissociate on the hollow site, and the dissociated hydrogen atoms bond with the surrounding metal atoms. Doping Cr and Mo atoms on the surface would reduce the H2 molecule adsorption energy, which promotes the H2 molecule adsorption and dissociation. When only one or two Ni atoms doping on the surface, it improves the adsorption energies, which in turn can hinder the H2 molecule adsorption and dissociation. However, three or four Ni atoms doping on the surface is beneficial to the H2 molecule adsorption and dissociation. Thus, the nickel content in Ni–Cr–Mo steel should be reasonably controlled to improve the hydrogen embrittlement resistance of the steel.

Effect of Cr–Mo Addition on the Microstructure and Mechanical Properties of Medium‐Carbon Steel

Herein, the effects of Chromium–Molybdenum (Cr–Mo) addition on the microstructural evolution and mechanical properties of medium‐carbon steel after spheroidization annealing are systematically studied through scanning electron microscopy, electron backscatter diffraction, and tensile testing. Cr–Mo addition hinders the proeutectoid ferrite + pearlite transformation, thereby promoting the bainite transformation. Moreover, it refines the pearlite lamellar spacing as well as decreases the average carbide diameter, increases the number of carbides per unit area, and hinders ferrite recrystallization. Compared with those in the B1 steel annealed for 8 h, the size of carbides and their number per unit area in the CM1 steel are 30% lower and 2.2‐fold higher, respectively. Due to finer ferrite grains, smaller carbides, and a higher amount of carbides, the strength of steel improves, and the plasticity slightly reduces after Cr–Mo addition. After 2 h of annealing, the yield strengths of Cr–Mo steels are 77.5–109.5 MPa higher than those of base steels; the elongations are above 20%. The contributions of the strengthening mechanism of steel to the yield strength are as follows (from high to low): grain boundary, precipitation, solid solution, and dislocation strengthening.

Cavitation erosion resistance and tribological performance of PAI/PI/EP soft coating on 20CrMo

A polyamide-imine/polyimide/epoxy resin polymer coating is prepared on the surface of 20CrMo steel by liquid spraying technology which is used to replace the CuPb24Sn copper alloy in valve plates for pumps. Tribological and anti-cavitation erosive experiments of the polymer coating, 20CrMo steel and CuPb24Sn copper alloy are carried out under oil, oil + seawater + silt mixed environment and seawater + silt environment. The results demonstrate that the deposition coating on 20CrMo steel can effectively replace copper alloy for the valve plate of the pump under oil lubrication, oil + seawater + silt environment. Under oil lubrication, the coating exhibits adhesive wear and its average frictional coefficient is 36.63 % and 8.57 % lower than that of the steel and copper alloy, respectively. Likewise, the coating mainly exhibits abrasive wear under the complex working conditions of seawater + silt + oil and seawater + silt. The soft coating reduces the three-body wear and the three-body frictional loss due to the embeddability. Under the complex conditions of seawater + silt + oil, the cavitation mass loss of the coating is 20 % and 35.48 % lower than that of the steel substrate and copper alloy, respectively. In addition, the cavitation mass loss of the coating is 53.6 % and 62.09 % lower than that of the steel and copper alloy under the condition of seawater + silt, respectively. The main influencing factors of the aforementioned results are the lipophilicity of the coating, the large ratio of hardness to elastic modulus (H/E) and the good corrosion resistance.

Study on the Physical Characteristics of Plasma and Its Relationship with Pore Formation during Laser-Metal Active Gas Arc Hybrid Welding of 42CrMo Steel

The automobile industry puts forward higher requirements for the design and manufacture of steel pistons. However, the welding of 42CrMo steel pistons still has unsolved technical problems, especially welding defects that cannot be directly detected, such as pores, which are easily generated inside the weld. A plasma experiment of laser-metal active gas arc (MAG) hybrid welding 42CrMo steel was conducted in this paper, and plasma signals inside and outside the keyhole were detected during the laser welding, leading laser laser-MAG hybrid welding, and leading arc laser-MAG hybrid welding of 42CrMo steel. The characteristic parameters such as electron temperature and electron density were calculated and analyzed to investigate the relationship between plasma behavior and the formation of weld porosity in the welding process of 42CrMo steel. Based on the fluctuations in plasma electron temperature and electron density, the prediction of pore formation in the weld of 42CrMo steel was made, aiming to provide guidance for achieving a stable and reliable laser-MAG hybrid welding process for 42CrMo steel.

Microstructure and Wear Resistance of Fe3Al Coating on Grey Cast Iron Prepared via Direct Energy Deposition

In this study, the potential of Fe3Al coating material as an environmentally friendly alternative to coatings containing critical elements for brake discs was investigated. A buffer layer of Cr–Mo steel (Ferro 55) that was about 500 µm thick was applied on a gray cast iron disc to enhance the coating quality and prevent the formation of hot cracks during solidification. The microstructural analysis of the cross-section of the coating showed that the buffer layer diffused into the Fe3Al coating, forming a combination of Fe3Al, Fe, and Fe3AlC0.5 phases. The tribological properties of the Fe3Al-coated disc were evaluated using pin-on-disc tests against two different copper-free friction materials extracted from commercial brake pads. The wear results show a coefficient of friction comparable to that of an uncoated disc (≈0.55), but with a reduction in particulate matter (PM) emissions, which decreased from 600 to 476 #/cm3. The last issue is an interesting aspect that is gaining increasing importance in view of the upcoming international standards.

42CrMo4 steel flow behavior characterization for high temperature closed dies hot forging in automotive components applications

The application of new forming processes as the high temperature hot forging in closed dies in an industrial environment still requires further investigation due to the lack of flow stress data at these temperatures. To determine the flow behavior of the 42CrMo4 steel at high temperatures hot compression tests have been carried out in a Gleeble® 3800 thermomechanical tester for a temperature range that covers the material behavior from the hot forging until the Nil Ductility Temperature (1250 °C-1375 °C) and for three different orders of magnitudes for the strain rates (0.1 s−1, 1 s−1 and 10 s−1). Then, the Hansel-Spittel model, widely used in automotive commercial software as FORGE®, has been employed to obtain the adequate constants of the constitutive equation for high temperatures.Finally, the newly obtained flow behavior model has been validated by comparison between experimental and simulated compression tests and by the process simulation of a commercial automotive component comparing the results of the simulation with the already made experimental tests in a laboratory cellule of the new technology.Hence, this paper shows the procedure for the determination and the obtention of a new constitutive model for the 42CrMo4 steel flow stress characterization at a temperature range between 1250 °C–1375 °C. This will contribute in the knowledge of material flow stress behavior models at high temperatures and will allow the prediction or simulation of high temperature hot forging in closed dies processes, enhancing the possibility of the application of these technologies from an industrial point of view.

Material Influence on the Micropitting and Wear Resistance of Nitrided External and Internal Gears

Abstract Due to increasing performance requirements and sometimes tribologically challenging operating conditions in gears (such as those found in wind turbines), alternative heat treatment processes to quenching and tempering or case hardening are becoming more and more important. Nitriding can significantly increase the load-carrying capacity of gears compared to the quenched and tempered initial state. The nitrided surface layer is characterized by a hard compound layer on the surface that is just a few micrometers thick and a diffusion zone that extends deeper into the material. The structure of the compound layer of iron and alloy element nitrides is primarily decisive for the wear behavior of nitrided components. Previous studies on nitrided gears with regard to micropitting and wear focus primarily on a systematic variation of the compound layer on gears made of nitriding steel 31CrMoV9. Results on the influence of the base material on the micropitting and wear resistance of nitrided gears are not yet available. In systematic load and speed stage tests, nitrided gears made from a quenched and tempered steel (42CrMo4) and a material with an alternative alloy composition (34CrNiMo6) were examined in addition to the reference (nitriding steel 31CrMoV9). Both external and internal gear pairings were tested, with the alternative materials showing more favorable tribological behavior in some cases. The results are presented and categorized according to the current state of the art. Finally, recommendations for the practical use of nitrided gears are derived.

How to replace the original material for the welded structure manufacturing

Abstract Due to difficult pandemic situation with COVID-19 decease, as well as due to current geopolitical circumstances in the world, we are facing the shortage of steel and therefore the impossibility of delivering the contracted products within the agreed deadlines. It is thus necessary to find suitable steel for replacement. The procedure for selecting one such steel for substituting the deficit steel 25CrMo4, for the purposes of producing a responsible welded assembly, is described in this paper. After the careful analysis, the steel 42CrMo4 was taken into consideration as a possible substitute material. Prior to applying the new selected steel, it was necessary to perform the following tests: analyze its chemical composition, determine its most important mechanical properties and evaluate its weldability. Then, the optimal welding and heat treatment technologies were determined, so that the quality of the responsible welded structure would meet all the requirements, as the structure made of originally used steel. For the new steel, all the mentioned and some additional tests were conducted and the appropriate welding technology was prescribed. To verify the selected technology, appropriate tests were conducted on the model welded samples, the results of which are presented in this paper. Based on the analysis of the obtained results, it was concluded that the 25CrMo4 steel can be replaced by the 42CrMo4 steel, however, with the mandatory application of appropriate supplementary measures.