Search Results (304)

8Cr4Mo4V bearing steel is a critical material for main shaft bearings in aero-engine applications. However, the current understanding of the micro-mechanical properties of its matrix and primary carbide phases (vanadium-rich and molybdenum-rich carbides) remains insufficient. This knowledge gap readily induces various forms of deformation damage during grinding, severely compromising the surface integrity of the workpiece. To address this, nanoindentation and nano-scratch techniques were employed to systematically quantify the micro-mechanical properties of each phase and investigate the deformation damage behavior of the steel under load. Results showed that MC carbides exhibited the highest elastic modulus and microhardness, which made them more susceptible to becoming crack initiation sites during grinding. Nano-scratch testing further revealed that crack initiation at carbide edges and localized spalling were the primary damage mechanisms. This study provides a micro-mechanical foundation for controlling the grinding surface quality of 8Cr4Mo4V bearing steel, holding significant implications for optimizing grinding processes, suppressing crack initiation, and elucidating the grinding damage mechanism. Full article

Tool steels are critical for high-load applications, e.g., forging and metal-forming, where they face thermal cracking, fatigue, erosion, and wear. This study evaluates the impact of gas nitriding and S-phase PVD coatings on the mechanical and tribological properties of four tool steels: 40CrMnNiMo8-6-4, 60CrMoV18-5, X50CrMoV5-2, and X38CrMoV5-3. Samples were heat-treated (quenched and tempered at 600 °C), then gas-nitrided at 575 °C for 6 h with nitriding potentials (Kn) of 0.18, 0.79, or 2.18, or coated via reactive magnetron sputtering in Ar/N₂ or Ar/N₂/CH₄ atmospheres at 200 °C or 400 °C. Characterization involved XRD, LOM, FE-SEM, GDOES, Vickers hardness (HV0.1), and ball-on-disk wear testing with Al₂O₃_ counter-samples. Gas nitriding produced nitrogen diffusion layers (80–200 μm thick) and compound layers (ε-Fe_(2-3)N, γ’-Fe₄N) at higher Kn, increasing hardness by 80–100% (up to 1100 HV0.1 for steel X38CrMoV5-3). S-phase coatings (1.6–3.6 μm thick) formed expanded austenite with varying N content, achieving comparable hardness (up to 1100 HV0.1) in high-N₂ atmospheres, alongside substrate diffusion layers. Both types of treatment enhance load-bearing capacity, adhesion, and durability, offering superior wear resistance compared to conventional PVD coatings and addressing demands for extended tool life in industrial applications. Full article

The effects of multiple austenitizing and quenching (AQ) thermal cycles on the microstructure and hardness of AISI O2 (90MnCrV8), D2 (X153CrMoV12), and D3 (X210Cr13) tool steels were systematically investigated. Up to four consecutive AQ treatments were applied to assess the influence of repeated austenitization on grain refinement, carbide dissolution, martensitic transformation, and retained austenite. The microstructure was investigated by optical and SEM observations, supported with XRD analyses. The results were correlated with Rockwell and Vickers hardness measurements. In AISI O2, the mean austenitic grain size decreased from (6.5 ± 0.8) μm to (4.3 ± 0.4) μm, accompanied by an increase in hardness from ~800 HV1 to ~950 HV1 (63 HRC), mainly due to the progressive carbide dissolution and a reduction in retained austenite. In AISI D2 and D3, repeated AQ cycles led to a marked reduction in carbide size and volume fraction (up to 25%), with D2 showing partial coarsening beyond the third cycle and D3 exhibiting continuous dissolution owing to higher carbide stability. A linear correlation between the carbide volume fraction and Rockwell hardness was established. Compared with conventional single-step treatments, the multi-cycle AQ approach also promote spheroidization of small carbides. Full article

Enhancing the surface mechanical properties and extending the service life of 45CrNiMoV mold steel are critical goals in mold development. To achieve these objectives, electron beam (EB) irradiation was employed to treat the 45CrNiMoV mold steel. This high-energy physical process enables precise modification of the surface microstructure. By meticulously controlling EB parameters, including energy, dose, and scanning mode, significant structural alterations occur in the surface layer. Consequently, the surface microhardness more than doubles, reaching 812.7 HV. This enhancement is attributed to grain refinement, increased dislocation density, and potential formation of new phases induced by EB irradiation. Beyond hardness improvement, the wear resistance of the treated specimen increases by 2.5-fold. Under standardized testing conditions, wear loss decreases markedly from 0.28 mg to 0.11 mg. This reduction in wear loss not only extends the mold’s operational lifespan but also minimizes maintenance and replacement requirements, thereby reducing production downtime and associated costs. This study transcends mere presentation of experimental data by comprehensively elucidating the intricate relationship between surface microstructure and the overall mechanical properties of 45CrNiMoV mold steel. Advanced characterization techniques, including scanning electron microscopy (SEM) and X-ray diffraction (XRD), were utilized to uncover the underlying mechanisms. The refined microstructure, characterized by fine grains and elevated dislocation density, impedes dislocation movement and crack propagation, thereby enhancing both hardness and wear resistance. Full article

The increasing demand for enhanced wear resistance and mechanical integrity in tooling applications has driven the development of advanced surface engineering strategies for high-alloy steels. Böhler K390 MICROCLEAN, a powder-metallurgical V–Cr–Mo–W cold work tool steel with high vanadium content, features a composite metal matrix–carbide microstructure, consisting of uniformly distributed coarse vanadium carbides and finer carbides (M₇C₃, M₆C/MC) embedded in a ferritic matrix. This study investigated the effects of non-melting laser surface treatment (LST) applied to both as-received and bulk heat-treated K390 specimens. Microstructural characterization using SEM, EBSD, XRD, and EDX revealed the formation of a hardened surface layer comprising a structureless mixture of ultrafine-grained martensite and retained austenite, localized around vanadium carbides. Lattice parameter analysis and Williamson–Hall evaluation demonstrated increased carbon content, lattice distortion, and crystallite size reduction, contributing to high dislocation density (6.4 × 10¹⁴ to 2.6 × 10¹⁵ m⁻²) and enhanced hardness. Microhardness was increased by up to 160% compared to the initial state (reaching 835–887 HV₂₀), and dry-sliding testing showed up to 3.94 times reduced volume loss and decreased friction coefficients. Wear occurred via the formation and delamination of thin oxide tribo-layers, which enhanced the wear behavior. The combined approach of bulk heat treatment followed by LST produced a graded microstructure with superior mechanical stability, offering clear advantages for extending tool life under severe contact loads in stamping and forming operations. Full article

Nickel–tungsten carbide (Ni/WC) multi-pass fused cladding layers with different cerium (IV) oxide (CeO₂) contents were applied to Cr12MoV cold work tool steel surfaces using the coaxial powder feeding method for laser cladding. Scanning electron microscopy, energy spectrum analysis, X-ray diffraction, and wear experiments were conducted to study how adding CeO₂ to change the properties of WC-reinforced Ni-base composite coatings in turn alters the microstructure and properties of Cr12MoV cold work tool steel. The results show that laser cladding is effective when the process parameters are as follows: a power of 1500 W, a 24 mm defocusing distance, a 6 mm/s scanning speed, a 5 mm spot diameter, and a powder delivery of 0.1 g/s. Laser-fused cladding coatings are mainly composed of dendrites, crystalline cells, strips, and bulk microstructures. The addition of CeO₂ is effective at improving the microstructure and morphology of the coating—the size and distribution of the reinforcing phase change very significantly, and the shape changes from irregular and lumpy to spherical. With a 2% CeO₂ content, the enhanced phase, now spherical and white, is more diffusely distributed in the tissue. The maximum microhardness of the composite-coated specimen after the addition of CeO₂ is about 986 HV, which is approximately 20% higher than the hardness of the composite coating with no CeO₂ added. Full article

In addition to the minerals naturally present in grapes, wine can acquire additional minerals during its production and storage from materials that come into contact with it, including bottling materials. This study aimed to evaluate the concentration of a wide range of elements in white wine samples packaged in 0.75 L green glass bottles sealed with two different closure systems: natural cork stoppers and metal screw caps with a plastic liner. No statistically significant differences were observed between the two closure types for most elements (Li, Be, Fe, Co, Ni, Zn, Se, Rb, Sr, Mo, Sb, Cs, Ba, and Tl). For V, Cr, Mn, Cu, As, Cd, and Pb, some differences were observed, but without a clear pattern. However, the concentration of Sn was significantly higher in wines packaged in bottles sealed with metal screw caps plus plastic liner. Elemental analysis of the original, unused liners showed negligible content of Sn and other studied elements, suggesting that the Sn in the wine comes from the Sn-plated steel screw cap, despite the presence of the plastic liner. Although the changes in the natural elemental composition under these bottling conditions are not very high and unlikely to pose a health risk to consumers, they may still influence wine stability and sensory attributes. Understanding these effects is important for both wine producers and consumers to ensure optimal wine quality and preservation. Full article

Ferritic/martensitic (F/M) steel is a candidate material for key structures in fourth-generation nuclear energy systems (such as fusion reactors and fast reactors). Irradiation hardening behavior is a core index to evaluate the material’s stable performance in a high-neutron-irradiation environment. In this study, based on 2048 composition and property data, a correlation model between key elements and their interactions and irradiation hardening in F/M steel was constructed using a Bayesian optimization neural network, which realized quantitative prediction of the effect of composition on hardening behavior. Studies have shown that the addition of about 9.0% Cr, about 0.8% Si, Mo content higher than about 0.25%, and the addition of Ti, Mn can effectively suppress the irradiation hardening of F/M steel, while the addition of N, Ta, and C will aggravate its irradiation hardening, and the addition of W and V has little effect on the irradiation hardening of F/M steel. There is an interaction between the two elements. C-Cr has a strong synergistic mechanism, which will cause serious hardening when the content is higher than 0.05% and the Cr content is higher than 10%. Cr-Si has a strong antagonistic mechanism, which can achieve the comprehensive irradiation hardening effect in the 9Cr-0.8Si combination. N-Mn needs N controlled lower than 0.01%. Mo-W needs to control Mo content higher than 0.5% to alleviate irradiation hardening. There is a weak synergistic effect in Si-V; when the content is between 0.3% and 0.8% and the V content is between 0.2% and 0.3%, it can assist in optimizing the composition of F/M steel. Through the optimization of multi-element combination, the composition of F/M steel with lower irradiation hardening can be designed. Full article

Stable service performance of spring steel under complex working conditions is essential, and under the synergistic effect of corrosive environment and stress, stress corrosion cracking is very likely to occur. Austempering can change the microstructure of spring steel and thereby improve its stress corrosion sensitivity. In this study, methods such as scanning electron microscopy and slow strain tensile tests were adopted to investigate the effects of different austempering temperatures on the microstructure and stress corrosion resistance of 52CrMoV4 spring steel. The results show that crack initiation during stress corrosion cracking in the test steel is mainly related to anodic dissolution. The coarsening of bainite laths and the increase in the area of martensite–austenite islands accelerate stress corrosion cracking once stress concentration occurs. The steel austempered at 310 °C has the best resistance to stress corrosion, with a stress corrosion sensitivity value of only 2.4%, which is much lower than those of specimens under traditional processes (15.5–23.7%). Full article

In the field of energy production, creep–fatigue interaction is a typical failure mode that might compromise the structural integrity of both rotating equipment and pressure vessels. Common design practices approach the problem in a conservative way by using high safety factors, which typically results in additional costs for manufacturing companies. The aim of this article, in the framework of continuum damage mechanics approaches, is to present a novel fatigue damage-based constitutive law. The presented law is directly inspired by well-assessed creep-based rules, suggesting a similarity in the behavior. On the other hand, creep deformation and damage are calculated with a more recent approach. The identification of the model parameters was carried out by interpreting experimental results obtained from low-cycle fatigue and creep relaxation tests performed on a commonly used ferritic–martensitic steel for power generation rotor forgings. To validate the proposed models, they were used to estimate material life consumption when the material was subjected to fully reversed axial loading conditions with hold time under tensile load. Different loading conditions at different total strain ranges and hold times were simulated, and good agreement was found between the predicted and experimental life, thus confirming the validity of the proposed models. Full article

In this study, we utilized Thermo-Calc software (2023a) to optimize the heat treatment process of martensitic stainless steel 90Cr18MoV through phase diagram calculations. The microhardness of 90Cr18MoV was characterized using a nanoindentation instrument. The microstructural morphology of the samples was analyzed using scanning electron microscopy (SEM). The composition of the samples was characterized through scanning electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Additionally, laser confocal microscopy (FIB) and transmission electron microscopy (TEM) were employed to characterize the precipitate phase composition and size before and after heat treatment, while also observing the dislocation structure within the samples. The relationship between the quenching temperature and the percentage of residual austenite content in the material was established. The influence of the dislocation structure and precipitate size on the hardness of the samples was investigated. The research findings confirm that the observed secondary hardening phenomenon in tempered samples is attributed to the co-precipitation of two types of carbides, M₂₃C₆ and MC, within the matrix. The study investigated the effects of the tempering temperature and duration on the size of secondary precipitates, indicating that M₂₃C₆ and MC particles with sizes less than or equal to 20 nm contribute to enhancing the matrix, while particles larger than 30 nm lead to a reduction in hardness after tempering. Notably, during the tempering process, M₂₃C₆ precipitated from the matrix nucleates on MC. Full article

The study investigates the influence of post-weld heat treatment (PWHT) on the microstructure and hardness of hardfacing layers applied to hot forging tools. The research focuses on three tool steels (55NiCrMoV7, X37CrMoV5-1, and a modified X38CrMoV5-3) and uses robotized gas metal arc welding (GMAW) with DO015 filler material. It examines the structural and mechanical differences in the hardfaced layers before and after heat treatment involving quenching and tempering. The findings reveal that PWHT significantly improves microstructural homogeneity and hardness distribution, especially in the heat-affected zone (HAZ), mitigating the risk of crack initiation and tool failure. The study shows that untempered as-welded layers exhibit microstructural inhomogeneity and extreme hardness gradients, which negatively impact tool durability. PWHT leads to tempered martensite formation, grain refinement, and a more stable hardness profile across the joint. These improvements are critical for extending the service life of forging tools. The results underscore the importance of customizing PWHT parameters according to the specific material and application to optimize tool performance. Full article

In order to obtain a gradient coating with excellent performance, novel titanium-modified plasma nitriding was primarily used as a support layer for the PVD coating of 38CrMoAl steel. The samples were subjected to titanium-modified plasma nitriding by placing sponge titanium around the samples, resulting in a thicker ductile diffusion layer and a thinner and denser compound layer. The research results showed that this thinner, denser compound layer formed by titanium-modified plasma nitriding provides stronger support for the AlCrN coating and thus bring about better performance compared to a conventional plasma nitrided layer, with the adhesion strength increasing from 16.8 N to 29.4 N, which is 42.8% higher than the conventional PN compound layer; the surface hardness increasing from 3650 HV_0.05 to 3780 HV_0.05; the friction coefficient and wear rate reducing from 0.64 and 5.4849 × 10⁻⁶ mm³/(N·m) to 0.61 and 2.3060 × 10⁻⁶ mm³/(N·m), respectively; and the wear performance improving by 137.85%. Additionally, the corrosion potential increased from −979.2 mV to −711.51 mV, and the value of impedance increased from 1.5515 × 10⁴ Ω·cm² to 9.4518 × 10⁴ Ω·cm², resulting in a significant improvement in corrosion resistance. In all, the novel support layer by titanium-modified plasma nitriding can provide much better support for AlCrN coating and thus bring about excellent enhanced performances, including adhesion strength and wear and corrosion resistance. Therefore, it is of great value in the PVD coating field, and it can provide valuable insights into gradient coating technology. Full article

The effects of intercritical quenching on the microstructure evolution and mechanical performance of Cr–Ni–Mo–V steel with a banded structure are studied. It is found that the intercritical quenching temperature has a significant effect on the morphology, distribution, and relative amount of ferrite/martensite, as well as the carbide precipitates upon tempering treatment. It is indicated that owing to the initial banded structure of Cr-Ni-Mo-V steel, the ferrite formation in intercritical heat treatment also exhibits a banded distribution. With the increase in quenching temperature, the proportion of ferrite in the Cr-Ni-Mo-V steel decreases from 30 ± 3.2 vol.% to 18 ± 2.8 vol.%. Tempering treatment has no significant effect on the distribution characteristics of ferrite, but it promotes the recovery of martensite laths and the precipitation of carbides. The mechanical properties of Cr-Ni-Mo-V steel are determined by both the changes in ferrite content induced by intercritical quenching and the evolution of carbide types during tempering. Delamination cracks are observed on the fracture surface, which is attributed to the lamellar microstructure, improving the plasticity of Cr-Ni-Mo-V steel through stress dispersion and a multi-stage energy absorption mechanism. Full article

Ship repair is hazardous, often presenting unsuitable working areas and risks due to the ship’s configuration. Welding tasks are particularly dangerous due to the high temperatures generated, high enough to melt the metal in structural elements, bulkheads, linings, and tanks. This study investigates the consequences of temperature distribution during the welding of naval plates and proposes some accident prevention measures. Industry working conditions were reproduced, including the materials, procedures, and tools used, as well as the certified personnel employed. DH 36-grade naval steel, with a composition of C max. 0.18%, Mn 0.90–1.60%, P 0.035%, S 0.04%, Si 0.10–0.50%, Ni max 0.4%, Cr max 0.25%, Mo 0.08%, Cu max 0.35%, Cb (Nb) 0.05%, and V 0.1%, was welded via FCAW-G (Gas-Shielded Flux-Cored Arc Welding), selected for this study because it is one of the most widely practiced in the naval industry. The main sensor used in the experiments was an FLIR model E50 thermographic camera, and thermal waxes were employed. The results for each thickness case are presented in both graphical and tabular form to provide accurate and actionable guidelines, prioritizing safety. After studying the butt jointing of naval plates of various thicknesses (8, 10, and 15 mm), safe distances to maintain were proposed to avoid risks in the most unfavorable cases: 350 mm from the welding seam to avoid burn injuries to unprotected areas of the body and 250 mm from the welding seam to avoid producing flammable gases. These numbers are less accurate but easier to remember, which prevents errors in the face of hazards throughout a long working day. Full article