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In this paper, the effects of different carburizing quenching processes and tempering processes on the depth of the hardened layer and microstructure of 20CrMoH were studied by means of hardness analysis and SEM microstructure analysis. The results show that: when the quenching temperatures in the range of 820-880 °C, it has little effect on the depth of the hardened layer. And the hardness value at the same depth is at a considerable level, which is not affected by the quenching temperature. When the tempering temperature range is 150-280 °C, the tempering temperature has a great influence on the depth of hardened layer. And with the gradual increase of tempering temperature, the depth of hardened layer decreases gradually. Also the hardness value at the same depth from the edge shows a monotonous decreasing trend with the gradual increase of tempering temperature.

This study presents research results concerning the vacuum carburizing of four steel grades, specifically conforming to European standards 1.7243, 1.6587, 1.5920, and 1.3532. The experimental specimens exhibited variations primarily in nickel content, ranging from 0 to approximately 3.8 wt. %. As a comparative reference, gas carburizing was also conducted on the 1.3532 grade, which had the highest nickel content. Comprehensive structural analysis was carried out on the resultant carburized layers using a variety of techniques, such as optical and electron scanning, transmission microscopy, and X-ray diffraction. Additionally, mechanical properties such as hardness and fatigue strength were assessed. Fatigue strength evaluation was performed on un-notched samples having a circular cross-section with a diameter of 12 mm. Testing was executed via a three-point bending setup subjected to sinusoidally varying stresses ranging from 0 to maximum stress levels. The carburized layers produced had effective thicknesses from approximately 0.8 to 1.4 mm, surface hardness levels in the range of 600 to 700 HV, and estimated retained austenite contents from 10 to 20 vol%. The observed fatigue strength values for the layers varied within the range from 1000 to 1350 MPa. It was found that changing the processing method from gas carburizing, which induced internal oxidation phenomena, to vacuum carburizing improved the fatigue properties to a greater extent than increasing the nickel content of the steel.

High-temperature low-pressure carburizing significantly reduces the time required to produce carburized layers. However, its application promotes austenite grain growth and, consequently, the formation of coarse acicular martensite. In this study, the possibility of limiting this phenomenon in AMS 6265 and 18CrNiMo7-6 steels using the PreNitLPC® technology was evaluated. The process was carried out at 1050 °C, with pre-nitriding applied during charge heating. In both steels, comparable carbon concentration profiles and carburized layers with an effective case depth of approximately 1.0 mm were obtained. The introduction of nitrogen into the surface layer resulted in a local reduction in austenite grain growth compared with the core. The average grain size in the surface layer was approximately 14.5 µm for AMS 6265 steel and 12.5 µm for 18CrNiMo7-6 steel, whereas in the core it increased to approximately 25.1 µm and 24.1 µm, respectively. At the same time, AMS 6265 steel exhibited a higher fraction of retained austenite, approximately 20%, compared with approximately 15% for 18CrNiMo7-6 steel. This resulted in a lower near-surface hardness of AMS 6265 steel, approximately 750 HV0.1, compared with approximately 800 HV0.1 for 18CrNiMo7-6 steel, corresponding to a hardness difference of about 50 HV0.1. TEM/NBD/EDS investigations showed that nanoscale AlN precipitates formed in both steels and acted as the main factor inhibiting austenite grain-boundary migration. The results confirm that the PreNitLPC® technology enables high-temperature low-pressure carburizing without detrimental grain growth in the surface layer.

The directional transformation of carbon dioxide (CO 2 ) with renewable hydrogen into specific carbon-heavy products (C 6+ ) of high value presents a sustainable route for net-zero chemical manufacture. However, it is still challenging to simultaneously achieve high activity and selectivity due to the unbalanced CO 2 hydrogenation and C–C coupling rates on complementary active sites in a bifunctional catalyst, thus causing unexpected secondary reaction. Here we report LaFeO 3 perovskite-mediated directional tandem conversion of CO 2 towards heavy aromatics with high CO 2 conversion (> 60%), exceptional aromatics selectivity among hydrocarbons (> 85%), and no obvious deactivation for 1000 hours. This is enabled by disentangling the CO 2 hydrogenation domain from the C-C coupling domain in the tandem system for Iron-based catalyst. Unlike other active Fe oxides showing wide hydrocarbon product distribution due to carbide formation, LaFeO 3 by design is endowed with superior resistance to carburization, therefore inhibiting uncontrolled C–C coupling on oxide and isolating aromatics formation in the zeolite. In-situ spectroscopic evidence and theoretical calculations reveal an oxygenate-rich surface chemistry of LaFeO 3 , that easily escape from the oxide surface for further precise C–C coupling inside zeolites, thus steering CO 2 -HCOOH/H 2 CO-Aromatics reaction pathway to enable a high yield of aromatics. The transformation of CO2 with renewable hydrogen into high-value products presents a sustainable route for net-zero chemical manufacture. Here the authors introduce a LaFeO3 perovskite-mediated tandem conversion of CO2, achieving remarkable performance by separating the CO2 hydrogenation and C-C coupling domains in the catalyst system.

Purpose Today, wear and tear is a metaphor whose cost cannot be ignored by real sector. For this reason, many sectoral and academic studies are carried out to minimize the wear effect. This study aims to create a perspective against wear problems for the automotive industry as well. Design/methodology/approach The 16MnC5 material, which is used as the U-joint material in the powertrain of the automotive industry, was subjected to heat treatment such as normalization and carburization at certain temperatures and duration. By subjecting the resulting carbide thickness to the abrasion process, the maximum effective heat treatment parameters against wear were determined. Findings It has been determined that the ideal cementation condition for 16MnCr5 steel to be used in the wear system is carburized samples at 900 °C for 3.5 h with a hardness depth of 1.04 mm. Originality/value The variation in which the surface hardness thickness and surface roughness obtained by different heat treatment variations of the U-joint part, which is one of the cardan shaft components that provide power transmission of heavy commercial vehicles, show the best wear resistance, were investigated. As a result of this study, the study is to prevent the waste of limited materials in the world and to reduce the repair and maintenance costs of commercial vehicles. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0152/

Carburizing process optimization requires accurate prediction of multiple interrelated outcomes, yet existing models either oversimplify the physics or require prohibitively large datasets. Here, we present a physics-informed machine learning (PIML) cascade model for vacuum carburizing of 20Cr2Ni4 gear steel that predicts surface carbon content, maximum hardness, and effective case depth through a three-stage sequential architecture. The model integrates Fick’s diffusion law and empirical carbon–hardness relationships with ensemble learning using physics-derived features to reduce data requirements while maintaining interpretability. Validation against experimental data yields coefficient of determination values of 0.968 (surface carbon, RMSE = 0.0023 wt%), 0.963 (maximum hardness, RMSE = 1.27 HV), and 0.999 (case depth, RMSE = 0.0053 mm) on physics-augmented test data; leave-one-out cross-validation (LOOCV) on original experimental data yields R2 = 0.87–0.95, representing true generalization capability. Feature importance analysis reveals that physics-derived features collectively account for over 70% of the prediction power, with the characteristic diffusion length (Dt) contributing 42.2%, followed by temperature-related features (22.4%) and time-related features (14.8%). Compared to pure physics-based and data-driven approaches, the proposed framework achieves superior accuracy for case depth prediction while preserving physical consistency. The methodology demonstrates potential for adaptation to other vacuum-carburizing applications with similar Cr-Ni steel compositions, although extension to fundamentally different processes (e.g., gas carburizing and nitriding) would require process-specific recalibration.

The vacuum low pressure carburizing and high pressure gas quenching processes of 20CrMo, 20CrMnTi and 20Cr2Ni4 with acetylene as carburizing medium were investigated. The results show that the carburizing and diffusion time significantly affected the carburizing performance. Carburized with the process of C2H2 flow rate 10L/min, N2 flow rate 10L/min, carburizing pressure 3kPa, carburizing time 42min, diffusion time 140min and gas quenching pressure 1.5MPa, 20CrMo, 20CrMnTi and 20Cr2Ni4 can obtain the surface carbon content of 0.74%-0.78% and carburizing depth of 0.81mm-0.83mm. Meanwhile, the microstructure showed first grade carbide, and there was no internal oxidation laye on the surface. The carburizing constant and the diffusion time to carburizing time ratio were modified to be more suitable for the carburizing process.

The development of efficient catalysts for Fischer–Tropsch (FT) synthesis, a core reaction in the utilization of non-petroleum carbon resources to supply energy and chemicals, has attracted much recent attention. ε-Iron carbide (ε-Fe 2 C) was proposed as the most active iron phase for FT synthesis, but this phase is generally unstable under realistic FT reaction conditions (> 523 K). Here, we succeed in stabilizing pure-phase ε-Fe 2 C nanocrystals by confining them into graphene layers and obtain an iron-time yield of 1258 μmol CO g Fe −1 s −1 under realistic FT synthesis conditions, one order of magnitude higher than that of the conventional carbon-supported Fe catalyst. The ε-Fe 2 C@graphene catalyst is stable at least for 400 h under high-temperature conditions. Density functional theory (DFT) calculations reveal the feasible formation of ε-Fe 2 C by carburization of α-Fe precursor through interfacial interactions of ε-Fe 2 C@graphene. This work provides a promising strategy to design highly active and stable Fe-based FT catalysts. ε-Fe 2 C has been identified as the highly active phase for Fischer-Tropsch synthesis (FTS), but is stable only at low-temperature. Here, the authors show that ε-Fe 2 C phase can be stabilized even at ~ 573 K by being encapsulated inside graphene layers, and retains high activity in FTS.

The tooth width and length of face gear limit control the strength of face gear, and heat treatments are often used to improve the hardness and strength of face gear. However, heat treatments will often cause additional deformations, which will affect the dimensional accuracy of the face gear. In this paper, to effectively control the deformation and ensure the accuracy of the face gear, the finite element method was used to establish the calculation model of the face gear die quenching method, and thus, the influence of die on the gear quenching deformation was analyzed. Next, the accuracy of the calculation model was verified by the pressure quenching experiment. The results demonstrated that the inconsistent phase transformation between the surface and the center of the face gear was the key factor affecting the deformation due to the influence of the carbon content. Compared with die-less quenching, the inner hole-die can effectively limit the radial shrinkage deformation of the face gear. With the increase of the upper-die pressure, the axial and radial deformations of the face gear gradually became stable. In the actual production, the load of dies should be reasonably selected based on the gear accuracy requirements.

Sustainable CO 2 conversion is crucial in curbing excess emissions. Molybdenum carbide catalysts have demonstrated excellent performances for catalytic CO 2 conversion, but harsh carburization syntheses and poor stabilities make studies challenging. Here an unsaturated Mo oxide (Mo 17 O 47 ) shows a high activity for the reverse water–gas shift reaction, without carburization pretreatments, and remains stable for 2,000 h at 600 °C. Flame spray pyrolysis synthesis and Ir promoter facilitate the formation of Mo 17 O 47 and its in situ carburization during reaction. The reaction-induced cubic α-MoC with unsaturated Mo oxycarbide (MoO x C y ) on the surface serves as the active sites that are crucial for catalysis. Mechanistic studies indicate that the C atom in CO 2 inserts itself in the vacancy between two Mo atoms, and releases CO by taking another C atom from the oxycarbide to regenerate the vacancy, following a carbon cycle pathway. The design of Mo catalysts with unsaturated oxycarbide active sites affords new territory for high-temperature applications and provides alternative pathways for CO 2 conversion. While Mo carbide catalysts have demonstrated excellent performance for CO 2 conversion chemistry, these catalysts require harsh synthetic conditions and have poor reaction stabilities. Here flame-synthesized unsaturated Mo oxides are shown to undergo carburization during the reverse water–gas shift reaction, and reaction-induced Mo oxycarbide active sites provide excellent catalytic performance.