Search Results (74)

This work systematically investigated the effect of Si content on the impact-abrasive wear mechanism of medium-carbon low-alloy steels processed through different heat treatment processes, quenching and tempering (QT), austempering, and quenching and partitioning (QP). Three experimental steels with different Si contents were subjected to optimized heat treatment parameters. Microstructural characterization revealed that Si addition significantly enhanced the volume fraction and mechanical stability of retained austenite (RA), refined bainitic and martensitic structures, and suppressed carbide precipitation. The results of mechanical properties demonstrated that austempering yielded the optimal balance of strength, hardness, ductility, and toughness. Impact-abrasive wear tests showed that the 2 B-300 steel exhibited the lowest wear mass loss due to its high work-hardening capacity, deep strain-hardened layer, and low residual tensile stress. In contrast, QT and QP processes resulted in higher wear losses, correlated with high residual tensile stress and reduced RA stability. The above results underscore that Si alloying, combined with appropriate heat treatment, effectively tailors microstructural evolution and residual stress distribution, thereby enhancing impact-abrasive wear resistance for applications in mining and mineral processing equipment. This study provides a comprehensive framework for optimizing Si content and heat treatment parameters to achieve superior wear performance in medium-carbon low-alloy steels. Full article

This research introduces a new model to predict the roll force during hot rolling of steel, based on a statistical analysis of approximately 38,980 sets of measurements in a commercial mill with five finishing stands. The study includes ten different steel grades and features models of both single grades and the entire dataset. Three models are developed and compared: a temperature-dependent strain rate model (M1), a strain rate model (M2), and a simplified strain rate model (M3). The decrease in temperature with roll stand has a strong cross-correlation with compensating decreases in strain and contact length by roll stand, such that both the temperature and strain terms are statistically insignificant. The final model (M3)—$F\left[\mathrm{N}\right]=113.1·\dot{ϵ}{\left[{\mathrm{s}}^{-1}\right]}^{0.3141}·w\left[\mathrm{mm}\right]·\ell \left[\mathrm{mm}\right]$—relates force (F) to strain rate ($\dot{ϵ}$), width (w), and contact length (ℓ) and achieves an $R^2$ fit of 0.946 over all 10 steel grades. Although the single-grade models show slightly higher accuracy, the final model retains robust predictive capability with only two fitting parameters. This model enables fast and easy estimation of roll force for commercial hot rolling of low-carbon, medium-carbon, and high-strength–low-alloy steels. Full article

As an essential highway safety facility, roadside W-beam guardrails effectively prevent errant vehicles from entering hazardous zones or causing secondary collisions by blocking and redirecting them, thereby reducing accident severity. With the rapid development of the automotive industry, the front bumper height of small passenger cars generally ranges between 405 mm and 485 mm. However, the lower edge height of the current Chinese Class A W-beam guardrail is 444 mm above the ground, which leads to a high risk of “underride” during collisions, resulting in elevated occupant injury risks. To address this issue, this paper proposes an optimized guardrail structure composed of a double W-beam and a C-type beam, aiming to reduce the underride risk for small passenger cars while accommodating multi-vehicle protection needs. In this design, the double W-beam is installed at a height of 560 mm and the C-type beam at 850 mm, connected to circular posts using a regular hexagonal anti-obstruction block. The beam thickness is uniformly 3 mm, while the thickness of other components is 4 mm. To systematically evaluate the impact of material strength on both safety performance and cost, two material configurations are proposed: Scheme 1 uses Q235 carbon steel for all components; Scheme 2 reduces the thickness of the C-type beam to 2.5 mm and employs Q355 high-strength low-alloy steel, with the thickness of the connected anti-obstruction block reduced to 3.5 mm, while the other components retain Q235 steel and unchanged structural dimensions. Using finite element simulation, collisions involving small passenger cars, medium trucks, and buses are simulated, and performance comparisons are conducted based on vehicle trajectory and guardrail deformation. For the small passenger car scenario, risk quantification indicators—Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV), and Post-impact Head Deceleration (PHD)—are introduced to assess occupant injury. The results demonstrate that Scheme 2 not only meets the required protection level but also significantly reduces occupant risk for small passenger cars, lowering the injury rating from Class C to Class B. Moreover, the overall structural mass is reduced by approximately 1407 kg per kilometer, with material costs decreased by about RMB 10,129, demonstrating favorable economic efficiency. The proposed structural optimization not only effectively mitigates small car underride and improves multi-vehicle protection performance but also provides the industry with a novel guardrail geometric design directly applicable to engineering practice. The technical approach of enhancing material strength and reducing component thickness also offers a feasible reference for lightweight design, material savings, and cost optimization of guardrail systems, contributing significantly to improving the safety and sustainability of road transportation infrastructure. Full article

This work reports on a systematic investigation of the microstructure and comprehensive performance of Cu–Fe immiscible composite coatings prepared through the combination of mechanical alloying and laser cladding. The samples were characterized by scanning electron microscopy with an energy dispersive analysis, X-ray diffraction, a digital microhardness tester, a current tester, an electrochemical analyzer, and a magnetometer. The results show that the immiscible composite coatings are mainly composed of α-Fe particle dispersion in the ε-Cu matrix due to liquid phase separation, and this is exacerbated by the addition of more Fe content. Concentrated distribution of Fe-rich particles at either the top or bottom of the immiscible composite coatings is driven by the dominant mechanism of Marangoni and Stokes motion. With the increased fraction of Fe content, the microhardness and electrical resistivity increased, but with a degradation in corrosion resistance. With the increased ball milling time, the electrical resistivity increased, and the corrosion resistance improved. Compared to the medium-carbon steel substrate, the immiscible composite coatings can achieve an improved corrosion resistance, as well as a maximum saturated magnetization of 10.172 emu/g and the lowest coercivity at 17.249 Oe. Full article

Welding, as a critical process for achieving permanent material joining through localized heating or pressure, is extensively applied in mechanical manufacturing and transportation industries, significantly enhancing the assembly efficiency of complex structures. However, the associated localized high temperatures and rapid cooling often induce uneven thermal expansion and contraction, leading to complex stress evolution and residual stress distributions that compromise dimensional accuracy and structural integrity. In this study, we propose a combined heat source model based on the geometric characteristics of the weld pool to simulate the arc welding process of large flange shafts made of Fe-C-Mn-Cr low-alloy medium carbon steel. Simulations were performed under different welding durations and shaft diameters, and the model was validated through experimental welding tests. The results demonstrate that the proposed model accurately predicts weld pool geometry (depth error of only 2.2%) and temperature field evolution. Meanwhile, experimental and simulated deformations are presented with 95% confidence intervals (95% CI), showing good agreement. Residual stresses were primarily concentrated in the weld and heat-affected zones, exhibiting a typical “increase–steady peak–decrease” distribution along the welding direction. A welding duration of 90 s effectively reduced residual stress differentials perpendicular to the welding direction by 19%, making it more suitable for medium carbon steel components of this scale. The close agreement between simulation and experimental data verifies the model’s reliability and indicates its potential applicability to the welding simulation of other large-scale critical components, thereby providing theoretical support for process optimization. Full article

This study investigates the influence of key heat treatment parameters on the microstructure and mechanical properties of the powder metallurgy tool steel Vanadis 60. A fractional factorial design of experiments was applied to evaluate the effects of austenitising temperature, quenching medium, tempering temperature, and number of tempering cycles on hardness, flexural strength, and microstructure, using detailed phase characterisation by X-ray diffraction. The results reveal two distinct processing routes tailored to different performance objectives. Maximum hardness was achieved by combining austenitisation at 1180 °C, rapid oil quenching, and tempering at 560 °C. These conditions enhance the solubility of carbon and other alloying elements, promote secondary hardening, and reduce retained austenite. Conversely, higher toughness and ductility were obtained by austenitising at 1020 °C, air cooling, and tempering at 560 °C. These parameters favour the formation of a bainitic microstructure, together with lower martensite tetragonality and minimal retained austenite. A statistically significant interaction was identified between the austenitising temperature and the number of tempering cycles; three temperings were sufficient to compensate for the lower hardness associated with reduced austenitising temperatures. The results provide a robust guidance for optimising thermal processing in highly alloyed tool steels, enabling the precise tailoring of microstructure and properties in accordance with specific mechanical service requirements. Full article

This study investigates the thermal response and surface modification of low-carbon manganese-alloyed 20GL steel during electrolytic plasma hardening. The objective was to evaluate the feasibility of surface hardening 20GL steel—traditionally considered difficult to quench—by combining high-rate surface heating with rapid cooling in an electrolyte medium. To achieve this, a transient two-dimensional heat conduction model was developed to simulate temperature evolution in the steel sample under three voltage regimes. The model accounted for dynamic thermal properties and non-linear boundary conditions, focusing on temperature gradients across the thickness. Experimental temperature measurements were obtained using a K-type thermocouple embedded at a depth of 2 mm, with corrections for sensor inertia based on exponential response behavior. A comparison between simulation and experiment was conducted, focusing on peak temperatures, heating and cooling rates, and the effective thermal penetration depth. Microhardness profiling and metallographic examination confirmed surface strengthening and structural refinement, which intensified with increasing voltage. Importantly, the study identified a critical cooling rate threshold of approximately 50 °C/s required to initiate martensitic transformation in 20GL steel. These findings provide a foundation for future optimization of quenching strategies for low-carbon steels by offering insight into the interplay between thermal fluxes, surface kinetics, and process parameters. Full article

To address the issue of cracking in cold-rolled medium manganese steel caused by the formation of a large amount of martensite after hot rolling, intermediate annealing was conducted prior to cold rolling. The research results indicate that after 1 h of intermediate annealing at a temperature of 700 °C, some martensite is replaced by ferrite and residual austenite, leading to a reduction in rolling stress. The dissolution of cementite leads to an increase in the solubility of the alloying elements in austenite. This increases the volume fraction and carbon content of austenite. Following cold rolling and final heat treatment, the Mn content is higher in both martensite and residual austenite, while it is relatively lower in ferrite. Elevated C and Mn content enhances the stability of the austenite. The elongation of the sample with intermediate annealing increased from 17% to 27%, and the yield strength slightly decreased. During the tensile process, ferrite provides plasticity during the early stage of deformation. As strain increases, martensite begins to deform, making a significant contribution to the material’s strength. The TRIP effect of austenite contributes most of the plasticity, especially the stable thin-film residual austenite. When the residual austenite is exhausted, the incompatibility between ferrite and martensite leads to crack propagation and eventual fracture. Full article

A total of 0.3%C-Cr-Mo-V steel, a high-strength alloy steel widely used in rocket motor housings, suspension systems in high-performance vehicles, etc., is noted due to its high strength-to-weight ratio. However, its high carbon equivalent (CE > 1%) makes it challenging to weld, as it is prone to brittle martensitic formation, which increases the risk of cracking and embrittlement. The present paper focuses on enhancing the microstructure and mechanical properties of 0.3% C-Cr-Mo-V steel by gas tungsten arc welded (GTAW) joints, utilizing post-weld heat treatment and cooling strategies (PWHTCS). A systematic experimental approach was employed to ensure a defect-free weld through dye penetrant testing (DPT) and X-ray radiography techniques. Subsequently, test specimens were extracted from the welded sections and subjected to PWHT protocols, including hardening, tempering, and rapid quenching using air and oil cooling (AC and OC, respectively) mediums. Results show that OC has enhanced tensile strength and hardness while simultaneously maintaining and improving ductility, ensuring a well-balanced combination of strength and toughness. Fractography analysis revealed ductile fracture in AC samples, whereas OC weldments exhibited a mixed ductile–brittle fracture mode. Thus, the findings demonstrate the critical role of PWHTCS, with OC, as an effective method for achieving enhanced mechanical performance and microstructural stability in high-integrity applications. Full article

Low-cost and low-alloy dual-phase (DP) steel with a tensile strength (TS) above 1000 MPa and high ductility is in great demand in the automobile industry. An approach to using a medium-carbon and fibrous DP structure for developing such new DP steel has been proposed. The microstructure and mechanical performance of fibrous DP steel obtained via partial reversion from martensite in Fe-C-Mn-Si low-alloy steel have been investigated. The TS of the as-quenched DP steel is above 1300 MPa, while the total elongation is less than 6%. The total elongation was increased to above 13%, with an acceptable loss in TS by performing additional tempering. The fibrous tempered-martensite/ferrite DP steel exhibits an excellent balance of strength and ductility, surpassing the current low-alloy DP steels with the same strength grade. Plate-like or quasi-spherical fine carbides were precipitated, and the relatively high-density dislocations were maintained due to the delay of lath recovery by the enrichment of Mn and C in martensite (austenite before quenching), contributing to the tempering softening resistance. In addition, nanotwins and a very small amount of retained austenite were present due to the martensite chemistry. High-density dislocations, fine carbide precipitation, and partially twinned structures strengthened the tempered martensite while maintaining relatively high ductility. Quantitative strengthening models and calculations were not included in the present work, which is an interesting topic and will be studied in the future. Full article

In the context of the global energy structure transformation, concentrated solar power (CSP) technology has gained significant attention. Its future trajectory is oriented towards the construction of ultra-high temperature (700–1000 °C) power plants, aiming to enhance thermoelectric conversion efficiency and economic competitiveness. Chloride molten salts, serving as a crucial heat transfer and storage medium in the third-generation CSP system, offer numerous advantages. However, they are highly corrosive to metal materials. This paper provides a comprehensive review of the corrosion behaviors of stainless steels and high-temperature alloys in molten salts. It analyzes the impacts of factors such as temperature and oxygen, and it summarizes various corrosion types, including intergranular corrosion and hot corrosion, along with their underlying mechanisms. Simultaneously, it presents an overview of the types, characteristics, impurity effects, and purification methods of molten salts used for high-temperature heat storage and heat transfer. Moreover, it explores novel technologies such as alternative molten salts, solid particles, gases, liquid metals, and the carbon dioxide Brayton cycle, as well as research directions for improving material performance, like the application of nanoparticles and surface coatings. At present, the corrosion of metal materials in high-temperature molten salts poses a significant bottleneck in the development of CSP. Future research should prioritize the development of commercial alloy materials resistant to chloride molten salt corrosion and conduct in-depth investigations into related influencing factors. This will provide essential support for the advancement of CSP technology. Full article

Friction surfacing (FS) is increasingly recognized as an advanced technique for coating similar and dissimilar materials, enabling superior joint quality through plastic deformation and grain refinement. This study investigates the deposition of AA6082-T651 alloy on a medium-carbon steel EN14B substrate using FS, with process parameters optimized, and the effect of axial load, rotational speed, and traverse speed on coating integrity. The optimal sample was subjected to heat treatment (HT) at 550 °C for 24, 36, and 48 h to further enhance mechanical properties. Comprehensive microstructural and mechanical analyses were performed on both heat-treated and non-heat-treated samples using optical microscopy (OM), field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness testing, and micro-tensile techniques. The optimized sample was processed with a 6 kN axial load, a rotational speed of 2700 rpm, and a traverse speed of 400 mm/min, and demonstrated superior bond quality and enhanced mechanical properties. The highest interfacial hardness values, 138 HV0.1 were achieved for the sample annealed for 48 h, under an axial load of 6 kN. Annealing for 48 h significantly improved atomic bonding at the aluminum–steel interface, confirmed by the formation of Fe₃Al intermetallic compounds detected via FESEM-EDS and XRD. These compounds were the primary reason for the enhancement in the mechanical properties of the FS deposit. Furthermore, the interrelationship between process and thermal parameters revealed that a peak temperature of 422 °C, heat input of 1.1 kJ/mm, and an axial load of 6 kN are critical for achieving optimal mechanical interlocking and superior coating quality. The findings highlight that optimized FS parameters and post-heat treatment are critical in achieving high-quality, durable coatings, with improved interfacial bonding and hardness, making the process suitable for structural applications. Full article

Martensite start (Ms) temperature is a critical parameter in the production of parts and structural steels and plays a vital role in heat treatment processes to achieve desired properties. However, it is often challenging to estimate accurately through experience alone. This study introduces a model that predicts the Ms temperature of medium-carbon steels based on their chemical compositions using the artificial neural network (ANN) method and compares the results with those from previous empirical formulae. The results indicate that the ANN model surpasses conventional methods in predicting the Ms temperature of medium-carbon steel, achieving an average absolute error of −0.93 degrees and −0.097% in mean percentage error. Furthermore, this research provides an accurate method or tool with which to present the quantitative effect of alloying elements on the Ms temperature of medium-carbon steels. This approach is straightforward, visually interpretable, and highly accurate, making it valuable for materials design and prediction of material properties. Full article

Precipitation strengthening is one of the fundamental factors occurring at high temperatures in medium-alloy structural steels, which offer greater durability under service conditions. This research employed transmission electron microscopy (TEM) via carbon replicas combined with scanning electron microscopy (SEM) to analyze carbide evolution and its influence on both mechanical properties and high-temperature strength. During the tempering process, ε-carbides precipitate at 200 °C and subsequently transform into M₃C at 400 °C and coarser M₇C₃ at 600 °C. Coarser carbides (M₇C₃ and M₃C) and metastable carbides (ε-carbides) are not sufficient to make steel strong at high temperatures. Moreover, nucleating and growing at interfaces, rod-shaped M₃C diminishes the toughness of the steel. Under tempering at 600 °C, a substantial amount of nanoscale M₂C carbides precipitate. This improvement not only elevate the material’s toughness but also leads to an enhancement of yield strength (from 1237 ± 12 MPa to 1340 ± 8 MPa) along with a rise in high-temperature strength (from 388 ± 8 MPa to 421 ± 4 MPa). Combined with high toughness, nanoscale M₂C with high thermal stability promoted both yield strength at room temperature and high-temperature strength. The type and size of carbides serve as key determinants for yield strength while being decisive parameters for high-temperature strength. Full article

In this study, pre-treated low-carbon steel substrates were electroplated with Zinc–Nickel (ZN) alloy composite coatings enhanced by the incorporation of nano-silicon dioxide (SiO₂) particles in an alkaline solution. ZN deposits with varying concentrations of nano-SiO₂—specifically, 1, 2, 3, 5, and 10 wt%—were achieved by adjusting the ratio between the nano-SiO₂ and ZN alloy electroplating solutions. The influence of the nano-SiO₂ content on both the quality of the coating and its corrosion behavior was investigated in detail. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and an atomic force microscope (AFM) were utilized to assess the surface, cross-section structure, elemental composition, and thickness of the coatings. Notably, the addition of nano-SiO₂ improved the microstructure of the coating, leading to a reduction in grain size as well as enhancements in uniformity and density while revealing that co-deposition reached an optimal concentration at 3 wt% nano-SiO₂. The corrosion behavior of coated specimens was evaluated through electrochemical impedance spectroscopy (EIS) and polarization techniques within a 3.5 wt% NaCl solution serving as a corrosive medium. Specifically, for typical prepared coatings, the corrosion current density decreased from 1.410 × 10⁻⁴ A·cm⁻² to 5.762 × 10⁻⁶ A·cm⁻², which is a remarkable reduction by one to two orders of magnitude relative to the SiO₂-free coatings mentioned previously. These findings provide a straightforward approach for selecting 3 wt% nano-SiO₂ as an effective additive in ZN composite coatings. Full article