9Cr-1Mo Steel Research Articles

Rapid reversion of martensite in low-alloy steel under electropulsing treatment: Exploring feasibility of reversible transformation

Reversibility is an essential feature of martensitic transformation but is always believed impossible in FeC alloys since martensite (α') is unstable, which decomposes and forms cementite (θ) before reversion begins. Here we used electropulsing treatment (EPT) to inhibit θ precipitation and explored the feasibility of reversible transformation without α' decomposition in low-alloy steels (22MnB5 and 35CrMo steels). The reversion behaviors of the electropulsed specimens were analyzed by morphology, orientation, elemental distribution, and final microstructure. The result shows that in low carbon, low-alloy steel (22MnB5 steel), acicular γ abruptly grows through the whole pack without composition change. The prior γ grains are reproduced with the same grain size, shape, and orientation, indicating that inhibiting the θ precipitation does make steels with low carbon content achieve the reversibility of martensitic transformation. This phenomenon mainly results from reducing the effective driving force for θ precipitation by the current. However, in low-alloy steel with higher carbon content (35CrMo steel), 3D orientation distributions reveal that the prior γ grain is divided into equiaxed grains with various orientations and irregular grains with slightly changed orientations. This result suggests that when carbon content increases above a limit, high dislocation densities lead to recrystallization and destroy the original orientation relationship.

Simulation study of turning-ultrasonic rolling compound processing for 42CrMo steel

The ultrasonic rolling processing technology has been shown to significantly reduce surface roughness and enhance the residual stress of parts, thereby improving their surface properties and extending their service life. This technology is particularly effective for the precision machining and surface strengthening of ultra-high-strength steel 42CrMo. This study aims to investigate the impact of turning pre-processing on the distribution of residual stress during ultrasonic rolling, a simulation model incorporating turning pre-processing was developed and used to conduct ultrasonic rolling simulation experiments, enabling the analysis of residual stress distribution patterns. Concurrently, ultrasonic rolling strengthening experiments were performed to validate the accuracy of the simulation model. The results confirm that with increasing rotational speed and feed rate, residual stress decreases, whereas with increasing static pressure and amplitude, residual stress increases. The residual stress variation obtained from the simulation of combined turning and ultrasonic rolling closely matched the results of experimental ultrasonic rolling tests. This consistency validates the accuracy of the simulation model. This study offers a novel approach for simulating and experimentally validating ultrasonic rolling processes, particularly for shaft-like parts that undergo turning as a pre-processing step.

THE INFLUENCE OF THE CUTTING PARAMETERS ON THE SURFACE ROUGHNESS AND VIBRATION SIGNAL IN THE TURNING PROCESS

The performance of the final part of the turning process, a topic of practical importance, heavily depends on the cutting parameters. Surface quality, a crucial product attribute in manufacturing, often tops consumer demands during machining due to its significant influence on product functionality. This paper assesses the correlation between the detected vibration signal, statistical parameters (Crest, Kurtosis and I-kaz3D coefficient) and surface roughness and provides valuable insights for practical applications. When the tool experiences vibrations during material removal, these oscillations leave a ripple effect on the surface of the workpiece. We aim to determine the impact of cutting parameters on surface roughness while turning 42CrMo4 steel using a carbide tool insert. Cutting parameters, such as spindle speed, feed, and depth of cut, were used. Signal processing is carried out using different techniques to identify the effect of the cutting parameters on vibration signals. Finally, we delve into the interaction effects between the cutting parameters, vibration signals and surface roughness, offering a comprehensive understanding of real-world manufacturing scenarios. Higher I-kaz3D coefficients correspond to higher surface roughness values. The I-kaz3D coefficient decreases as the surface roughness measurements decrease, indicating that the I-kaz3D technique can accurately indicate an increase or decrease in surface roughness. On the other hand, the cutting force Fc was the component most strongly correlated with surface roughness (Ra), yielding the best results across all indices (adjusted R²adj = 95.1%, er=.8 ± 2.3%).

Predicting creep life of CrMo pressure vessel steel using machine learning models with optimal feature subset selection

The data-driven approach for creep life prediction typically integrates numerous characteristics, including material compositions, manufacturing details, and service conditions, into machine learning models. In this study, a machine learning-based creep life prediction approach with optimal feature subset selection is established for 2.25Cr1Mo pressure vessel steel. Before model training and testing, six critical features that significantly impact the creep life of 2.25Cr1Mo steel are selected, specifically the applied stress, temperature, and chemical compositions consisting of Cr, Ni, Mn, and Mo. Various machine learning algorithms, along with the traditional L–M method, are utilized for model training and performance evaluation. Additionally, the developed models undergo validation using experimental data independent of the training and testing datasets to assess their generalization abilities. The results reveal that, among all tested models, the support vector regression (SVR) model, coupled with the optimal feature subset, demonstrates superior prediction accuracy and generalization capability. Finally, the creep life prediction model exhibiting optimal performance is deployed into a software application, leveraging the Python programming language. This predictor tool facilitates rapid and precise creep life predictions for 2.25Cr1Mo pressure vessel steel, relying solely on a limited amount of input information, and provides a clear and visual presentation of the prediction results.

Study of the Martensitic Transformation of Steel During the Induction Hardening Process by means of Acoustic Emissions

Non-Destructive Testing (NDT) technology known as Acoustic Emission (AE) has been used to investigate the phase transformation of 42CrMo4 steel in a cylinder during an induction hardening process. The objective of this study is to characterize the martensitic transformation of the material using the data obtained by the AE sensor during the process. The heating process of the cylinder is carried out statically, focusing the heat on the area to be treated and then analyzing it. After quenching, destructive tests are carried out to determine the hardness and three-dimensional geometry of the steel microstructure after the process (hardness and X-ray diffraction tests). Once the microstructure of the material is known, it is possible to relate the results with the signals obtained by AE, making possible in future induction hardening processes the estimation of martensite by non-destructive techniques.

Miniaturized-specimen creep testing: an alternative method for evaluating the remaining service life of CrMo steel components

Miniaturized-specimen creep testing: an alternative method for evaluating the remaining service life of CrMo steel components

A comparative study on corrosion and mechanical properties of laser-cladded X2CrNiMoN22-5-3 duplex stainless steel on 42CrMo4 steel substrate

Duplex stainless steel is an alloy that combines the advantages of austenitic stainless steel and ferritic stainless steel. It has excellent corrosion resistance, high strength, and good weldability. One of the main problems in marine shafts using X2CrNiMoN22-5-3 Duplex Stainless Steel (2205) is bending and warping over time. In this study, 42CrMO4 (MO40) steel was clad with 2205 dual-phase steel using direct metal deposition with wire to simultaneously utilize the mechanical properties, and corrosion resistance. Perform metallographic imaging, corrosion test, and tensile test, to maintain the quality of the cladding. The results show that the corrosion potential of 2205 cladding layer is −0.65 (including semi-passive zone), while the control sample of 2205 had a corrosion potential of −0.26, and the MO40 substrate had a corrosion potential of −0.1 (highlighting the advantage of the cladding in thermodynamics term). EIS results showed that the REISMO40=2325Ω, REIS2205=24315Ω, and REIS2205cladded=216133Ω. The corrosion rate for the substrate, control sample, and laser-clad sample were 0.33, 0.15, and 0.00095 mm/year, respectively, without significant loss in tensile properties. The final strength for MO40(with 2205 clad) reaches 672 MPa with a 14 % decrease from 788 for MO40. In this case, we still have a 36 % increase in strength compared to the 2205 sample. It seems that the bent problem of the pure 2205 marine shaft can be solved completely in this case and continues to be solved in our ongoing work.

The effect of aluminum addition on plasma nitriding for 42CrMo steel

In order to enhance the efficiency and performances of nitriding layer, aluminum was primarily introduced in the furnace during plasma nitriding by adding some FeAl around the samples. The results show that the process efficiency is dramatically enhanced more than 5 times comparing with traditional plasma nitriding (PN), with the effective hardening layer increasing from 224 μm to 1246 μm at 520 ℃/4h. Meanwhile, ultra-high surface hardness and excellent wear behaviors are obtained by Al-PN due to the formation of dispersed strengthening phases of AlN and FexAl in the nitriding layer, with the surface hardness increasing from 755 HV0.025 to 1251 HV0.025, and the wear rate decreased by a factor of approximately 2.

Modeling Microstructure Development upon Continuous Cooling of 42CrMo4 Steel Grade for Large-Size Components

42CrMo4-type steel grades are widely used in a great variety of components that require ad hoc mechanical properties. However, due to the dimensions of large components and the previous thermomechanical treatments, the presence of heterogeneities in the chemical compositions are expected to impact those mechanical properties. In the present work, a detailed analysis of phase transformation behavior upon cooling was carried out through a dilatometry test on samples of 42CrMo4 belonging to a component that has a non-homogeneous chemical distribution. The analysis of the dilatation signals and the quantitative metallography shows a rather complex behavior depending on the cooling rate as well as on the region of observation. Two different phase transformation models based on Li’s approach were applied to the present composition to determine the CCT curve as well as the fraction of the microconstituents. An extensive discussion was carried out on some aspects about Kirkaldy-based approaches that need to be improved so as to attain more reliable quantitative results when modeling phase transformations in heterogenous systems.

Effect of heat input on the microstructure and hydrogen embrittlement susceptibility of the coarse-grain heat-affected zone of CrMo steels generated using a Gleeble 3500 welding simulator

The changes in microstructure and hydrogen embrittlement (HE) susceptibility of the simulated coarse-grain heat-affected zone (CGHAZ) of CrMo steels under three distinct heat input conditions were investigated. The cooling time from 800 °C to 500 °C, represented by t8/5, increased from 100 s to 200 and 400 s.. The sample with t8/5 = 100 s has a microstructure consisting of martensite and a small amount of lower bainite. When the t8/5 was increased to 200 s and 400 s, the HAZ consisted of 65.43 % martensite and 34.57 % lower bainite and 4.53 % martensite with 95.47 % bainite, respectively. The HE susceptibility was assessed by slow strain rate tensile (SSRT) testing of hydrogen-charged samples, and the HE susceptibility index (IHE) declined from 87.89 % to 61.37 % when t8/5 increased from 100 to 400 s. The high dislocation density and hydrogen concentration in the sample with t8/5 = 100 s led to intergranular fracture and incresaed HE susceptibility. The martensite lath and cementite/ferrite interface are the sites of crack initiation in the sample with t8/5 = 200 s. In the sample with a cooling time of 400 s, the martensite/ferrite interfaces are the main crack initiation sites under hydrogen charging.

Development of a novel approach to correlate small punch fatigue with uniaxial ratcheting fatigue

The miniaturization of fatigue specimens has seen significant advancements, realized either by scaling down conventional specimens while preserving their geometry or by experimenting with novel specimen shapes and loading configurations. In this study, the small punch test (SPT) technique, which is well-established for estimating tensile, creep, and ductile-to-brittle transition temperature (DBTT), is employed to predict the cyclic deformation behaviour of SS 316LN and modified 9Cr-1Mo (P91) steels. The small punch fatigue (SPF) experiments demonstrated continuous displacement accumulation, similar to strain accumulation in ratcheting. The study evaluates the influence of various load parameters, such as amplitude and mean load, on SPF outcomes and compares these to the effects of stress amplitude and mean stress on ratcheting results. The differences in deformation behaviour between ratcheting and small punch fatigue and the effect of biaxiality in SP configuration life is analysed. Finally, to establish a correlation between SPF and ratcheting results, the three life prediction models (Gerber, Goodman, and Smith-Watson-Topper) are examined and a new correlation is proposed by introducing a novel damage parameter.

Effect of Welding Process on Microstructure and Mechanical Properties of Boron Containing Modified 9Cr-1Mo Steel

The influence of Shielded Metal Arc (SMA) welding and Activated Tungsten Inert Gas (A-TIG) welding on the microstructure and mechanical properties of boron containing Modified 9Cr-1Mo steel has been investigated. The tensile strengths of SMA weld joints at room temperature and 550℃ (730, 710 MPa) are higher than those of A-TIG weld joints (520, 465 MPa); whereas A-TIG welds (66, 18J) show better impact energies at room temperature and 0℃ than SMA welds (53, 12J). Creep resistances of both the weld metals, as estimated by impression creep technique are comparable; while, the A-TIG heat affected zone (HAZ) possesses higher creep resistance than the SMA HAZ. The fracture toughness of the A-TIG weld metal is inferior (64 kJ.m-2) to that of SMA weld metal (181 kJ.m-2) and brittle fracture is seen. It has been observed that the multiple passes of SMA process are advantageous in modifying the delta ferrite present in the weld metal although they cause severe damage to the HAZ microstructure.

Thermomechanical Modeling and Numerical Simulation of Orthogonal Turning of 42CrMo4 Steel: Case of Workpiece/Tool Studies

Thermomechanical Modeling and Numerical Simulation of Orthogonal Turning of 42CrMo4 Steel: Case of Workpiece/Tool Studies

Preparation of bainite phase microstructure by laser-electromagnetic induction hybrid solid-state phase transformation

Increasing the proportion of bainite and martensite phases is one of the effective ways to enhance the toughness of medium-carbon low-alloy steel(42CrMo). In this paper, the surface heat treatment of 42CrMo steel is carried out by using a laser heat source to achieve complete austenitization, then with electromagnetic induction heating for several times to implement insulation, and eventually to promote bainite phase transformation. In conjunction with the temperature history curves, OM, SEM, and EBSD are used to characterize the bainite morphology and percentage of bainite via different parameters of the hybrid process. The results demonstrate that the hybrid process combined with twice electromagnetic induction heating can yield a considerable proportion of bainite phase in 42CrMo steel. The resulting duplex structure, consisting of bainite and a minor fraction of martensite, exhibits a significant increase (81.1%) in tensile strength, while maintaining similar impact toughness. The elongation after fracture only has a slight reduction of 5.5% compared to that of the substrate. This innovative process provides a practical alternative to traditional bainite isothermal treatment method which must perform in a heat treatment furnace. Therefore, it is presented as a promising solution for enhancing the mechanical properties of medium-carbon low-alloy high strength steels.

Influence of turning parameters on residual stresses and roughness of 42CrMo4 + QT

Residual stresses and surface roughness have been recognized to play a critical role in the fatigue strength of metal components. Machining processes can induce different roughness and residual stress conditions depending on the parameters used in the process. Therefore, it is essential to develop knowledge that helps to predict the residual stresses and roughness that would be obtained from different machining conditions. Due to the growing interest from the industry in the use of 42CrMo4 steel because of its excellent mechanical properties, the main objective of this work is to establish two phenomenological models to accurately predict the residual stress and roughness values in turned specimens of this material. The models are derived from data of four process variables: (a) insert tip radius; (b) feed rate; (c) cutting speed; and (d) depth of cut. For this purpose, a wide experimental campaign has been developed, which includes the machining of 68 specimens under various cutting scenarios, and their subsequent measurement of residual stresses and roughness. Once the experimental data were obtained, the response surface method based on the central composite design was used to fit the models, obtaining a correlation index R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}^{2}$$\\end{document} higher than 0.9 in both cases. In this article, it is concluded that feed rate and insert radius have a greater effect on the residual stress and roughness obtained, while cutting speed and depth of cut have a lesser impact on the results. It is hoped that the findings will establish a groundwork for the machining of this material type, ensuring controlled conditions of residual stress and roughness.

Study on low cycle fatigue properties of Cr-Mo steel in 50 MPa gaseous hydrogen

At present, a lack of fatigue design curves for Cr-Mo steel in high-pressure gaseous hydrogen worldwide impedes the use of the design fatigue curve (S-N curve) evaluation for vessel fatigue design, necessitating reliance on fracture mechanics methods related to the initial crack size. In this study, strain-controlled fatigue tests with a strain ratio of −1 were carried out in 50 MPa gaseous hydrogen to study the low cycle fatigue properties of Cr-Mo steel. Results indicate that hydrogen reduces the fatigue life of 4130X under high strain amplitudes. Under 0.5 % strain amplitude, different from characteristics of ductile fracture in air, the fracture in 50 MPa gaseous hydrogen showed quasi-cleavage and intergranular fracture characteristics. Based on the test results, the S-N curve in 50 MPa gaseous hydrogen was obtained with fatigue life safety factor 20 and stress amplitude safety factor 2. The S-N curve in 50 MPa gaseous hydrogen is under the curve in KD-320.2 M of the 2023 ASME Boiler & Pressure Vessel Code VIII-3, which does not consider the effect of hydrogen, when the number of cycles to failure is less than 1×106. This indicates that the fatigue life calculated by the S-N curve in KD-320.2 M cannot ensure that 50 MPa high-pressure hydrogen storage vessels avoid fatigue failure under high stress amplitudes.

Fractal Characterization of the Fracture Surface of Untempered and Tempered Bainitic Modified 9Cr-1Mo Steel

Fractal Characterization of the Fracture Surface of Untempered and Tempered Bainitic Modified 9Cr-1Mo Steel

Fatigue life improvement by shot peening for pre‐fatigue tested carburized steel

AbstractThe effect of shot peening (SP) on pre‐fatigue tested carburized steel was investigated. Plane‐bending fatigue tests were conducted on carburized CrMo steel that was pre‐fatigue tested and treated with SP. Fatigue cracks were induced by pre‐fatigue tests with a stress amplitude of σa = 1000 MPa, and the number of the pre‐fatigue test cycles was 2.0 × 104 (L5 test) and 4.0 × 104 (L15 test). We compared the fatigue lives of the fatigue‐damaged and smooth specimens without fatigue damage treated with the same SP. The fatigue life of the L5 tested specimens with SP was longer than that of the non‐fatigue damaged smooth specimens after SP. Therefore, the fatigue cracks introduced by the L5 test can be rendered harmless by SP. Furthermore, near‐surface material properties were evaluated and the mechanisms of rendering surface cracks harmless were investigated.

Comprehensive analysis of the effect of structural parameters on erosion wear, structural stress, and deformation of high-pressure double-elbow in shale-gas fracturing

In field hydraulic fracturing operation of shale gas development, the high pressure and large displacement liquid-particle two-phase fracturing fluid can be forced to change direction many times through high-pressure double-elbow, and be transported from the outlet pipeline of the fracturing pump to the main pipeline. The high-pressure double-elbow is prone to be affected by erosion wear and Fluid-Structure Interaction (FSI), resulting in perforation and fracture, posing a potential safety threat to field operation. In this study, we conducted the erosion wear experiments on 35CrMo steel used for high-pressure double-elbow in shale-gas fracturing. The erosion rates under different impact angles and flow velocities were obtained, and proposed a novel model of erosion prediction for high-pressure double-elbow. Then the numerical investigation was employed to conduct a comprehensive analysis of erosion wear, structural stress and deformation by the coupling of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA). The effects of structural parameters such as connection straight pipe length, pipe inner diameter and fluid turning direction were discussed. The results indicate that with the increase of connection straight pipe length, the flow erosion decreases first then varies little, and the deformation gradually increases. Slight erosion wear but large structural stress and deformation in major inner diameter pipe. And the minimum degree of erosion and flow-induced deformation present with the fluid turning direction of double-elbow as 0°. The study can provide references for the design, installation and detection of high-pressure double-elbow and ensure safety in the process of shale gas fracturing.

Significant creep-strength improvement in modified 9Cr-1Mo steel via microstructural control through laser powder bed fusion

Modified 9Cr-1Mo steel was manufactured using laser powder bed fusion (LPBF). The as-built LPBF-sample microstructure comprised columnar δ-ferrite grains and fine martensite grains. The δ-ferrite was a unique phase that formed under the significantly rapid LPBF-induced solidification. Creep testing was performed for the LPBF sample at 923 K for up to 10,000 h. The LPBF-sample time-to-rupture and minimum creep rate were at least 10 times longer and 100 times smaller, respectively, than those of conventional modified 9Cr-1Mo steels at 923 K under 100 MPa. Microstructural characterization of the creep-ruptured samples revealed that creep deformation preferentially occurred in the martensite. Thus, the δ-ferrite contributed significantly to the enhanced creep strength. The intrinsic creep resistance of the δ-ferrite phase exceeded that of the martensite. The microstructural stability of the δ-ferrite grains (attributed to dense MX-phase precipitation at the grain boundary) was a likely strengthening factor. Overall, the modified 9Cr-1Mo steel creep strength was successfully improved via unique microstructural control through LPBF. This achievement is expected to extend LPBF application as a novel microstructural control process for steels and alloys, avoiding the diffusional transformation kinetics that occur in conventional heat-treatment processes.