Search Results (491)

This study investigates the impact of arc-hardening parameters on a groove-shaped S45C steel tube, with a focus on surface hardness and microstructure. According to the findings, when arc quenching occurs, the tube’s surface hardness increases significantly compared to its original hardness. The surface layer hardness can increase to 50.3 HRC, which is 3.4 times greater than the untreated surface. Changing arc quenching parameters such as current intensity, gas flow rate, arc length, scan speed, heating angle, and cooling angle causes a variation in surface hardness due to the balance of heat input and cooling value. Moreover, the microhardness distribution is divided into three zones: the hardened zone (with a high hardness value), the heat-affected zone (HAZ), which has rapidly declining hardness, and the base metal (with a low hardness value). The hardened zone could have a hardness with a load of 0.3 N of 440 HV and a case depth of about 900 μm. The next zone is the HAZ, where the hardness with a load of 0.3 N drops significantly. The hardness in the base metal zone recovers to its original value of 152 HV. Interestingly, the microstructure, under the hardness distribution, illustrates the relationship between the hardness value and its phases. The hardened zone consists of martensite and residual austenite phases, resulting in a high hardness value. The bainite phase constitutes the HAZ, which correlates to the zone of rapid hardness reduction. Finally, the base metal zone has ferrite and pearlite microstructures, indicating the softest zone. The investigation’s findings may increase our understanding of the arc-hardening process and widen its industrial applications. Full article

Welded structures, such as offshore platforms, require robust toughness in their heat-affected zones (HAZ) to withstand low-temperature environments. The coarse-grained HAZ (CGHAZ) adjacent to the fusion boundary often exhibits reduced toughness due to grain coarsening, particularly under high heat input welding conditions aimed at enhancing productivity. To address this, high-nitrogen steels containing TiN particles were developed to suppress austenite grain growth by leveraging the thermal stability of TiN precipitates. Three high-nitrogen steels with varying carbon contents (0.09%, 0.11%, and 0.15%) were fabricated and subjected to crack tip opening displacement (CTOD) testing at −20 °C and −40 °C to evaluate low-temperature HAZ toughness. Results indicate that high-nitrogen TiN steels exhibit superior CTOD values (1.38–2.73 mm) compared to conventional 490-MPa class steels, with no significant reduction in toughness despite increased carbon content. This is attributed to the presence of stable TiN particles, which restrict austenite grain growth during welding thermal cycles, and the formation of fine ferrite–pearlite microstructures in the HAZ. These findings highlight the efficacy of high-nitrogen TiN steels in enhancing low-temperature fracture resistance for welded structures. Full article

The occurrence of the welding heat-affected zone in Q420C steel may lead to a reduction in the toughness of the welded joint and disruption of high strength-toughness combination of Q420C. This study investigates the microstructure and mechanical properties of Q420C steel welded joints under three heat in-puts of 25 kJ/cm, 100 kJ/cm, 200 kJ/cm, and 300 kJ/cm, with high-strength matching adopted for the welded joints, Charpy impact tests at 0 °C, −20 °C, and −40 °C were conducted on the weld metal, fusion line(FL), and heat-affected zone (HAZ). The weld metal maintains high impact toughness across all tested temperatures. However, increasing the heat input leads to coarsening of the microstructure in the overheated zone of the HAZ, accompanied by the formation of ferrite. At a heat input of 300 kJ/cm, significant amounts of coarse intergranular ferrite and intragranular blocky ferrite develop in the overheated zone. These microstructural changes result in a marked reduction in the impact toughness of both the fusion zone and HAZ, and the fracture mode shifts from ductile to cleavage fracture. To ensure adequate impact toughness of Q420C welded joints, the welding heat input should be kept below 200 kJ/cm. Full article

Wood–plastic composites (WPCs) offer a sustainable alternative to solid wood, yet their heterogeneous structure presents challenges in laser machining due to thermal sensitivity and inconsistent material behaviour. This study investigates the optimization of CO₂ laser-cutting parameters for WPCs, focusing on feed rate and assist-gas pressure. Using a 1500 W CO₂ laser, a full factorial experimental design was employed to cut 18 mm thick WPC panels at varying feed rates (1000–3000 mm/min) and gas pressures (1–3 bar). Statistical analyses including MANOVA and linear regression were conducted to evaluate their effects on key machining responses: cutting depth, heat-affected zone (HAZ) width, cut-edge quality, and surface finish. Results indicated that feed rate significantly influences both cutting depth and thermal damage, while gas pressure plays a major role in improving surface quality and reducing HAZ. Optimal combinations were identified for various performance goals, and validation trials at the selected parameters confirmed alignment with predicted outcomes. The optimized settings yielded high-quality cuts with reduced HAZ and enhanced surface characteristics. This study demonstrates the effectiveness of a statistical optimization approach in refining CO₂ laser-cutting conditions for WPCs, offering insights for improved process control and sustainable manufacturing applications. This study also introduces a multi-objective optimization approach that verifies the interaction effects of feed rate and assist-gas pressure, enabling precise and efficient CO₂ laser cutting of 18 mm thick WPCs. Full article

The transition to high-energy-density lithium metal batteries (LMBs) is essential for advancing electric vehicle (EV) technologies beyond the limitations of conventional lithium-ion batteries. A key challenge in scaling LMB production is the precise, contamination-free separation of lithium metal (LiM) anodes, hindered by lithium’s strong adhesion to mechanical cutting tools. This study investigates high-speed, contactless laser cutting as a scalable alternative for shaping double-coated LiM anodes. The effects of pulse duration, pulse energy, repetition frequency, and scanning speed were systematically evaluated using a nanosecond pulsed laser system on 30 µm LiM foils laminated on both sides of an 8 µm copper current collector. A maximum single-pass cutting speed of 3.0 m/s was achieved at a line energy of 0.06667 J/mm, with successful kerf formation requiring both a minimum pulse energy (>0.4 mJ) and peak power (>2.4 kW). Cut edge analysis showed that shorter pulse durations (72 ns) significantly reduced kerf width, the heat-affected zone (HAZ), and bulge height, indicating a shift to vapor-dominated ablation, though with increased spatter due to recoil pressure. Optimal edge quality was achieved with moderate pulse durations (261–508 ns), balancing energy delivery and thermal control. These findings define critical laser parameter thresholds and process windows for the high-speed, high-fidelity cutting of double-coated LiM battery anodes, supporting the industrial adoption of nanosecond laser systems in scalable LMB electrode manufacturing. Full article

Lithium metal is a promising anode material for next-generation batteries due to its high specific capacity and low density. However, conventional mechanical processing methods are unsuitable due to lithium’s high reactivity and adhesion. Laser cutting offers a non-contact alternative, but photothermal effects can negatively impact the cutting quality and electrochemical performance. This study investigates the influence of pulse duration on the cutting-edge characteristics and electrochemical behavior of laser-cut 20 µm lithium metal on 10 µm copper foils using nanosecond and picosecond laser systems. It was demonstrated that shorter pulse durations significantly reduce the heat-affected zone (HAZ), resulting in improved cutting quality. Electrochemical tests in symmetric Li|Li cells revealed that laser-cut electrodes exhibit enhanced cycling stability compared with mechanically separated anodes, despite the presence of localized dead lithium “reservoirs”. While the overall pulse duration did not show a direct impact on ionic resistance, the characteristics of the cutting edge, particularly the extent of the HAZ, were found to influence the electrochemical performance. Full article

E36 steel, widely used in shipbuilding and offshore structures, offers moderate strength and excellent low-temperature toughness. However, its welded joints are highly susceptible to fatigue failure. Cracks typically initiate at weld toes or within the heat-affected zone (HAZ), severely limiting the fatigue life of fabricated components. Traditional life prediction methods are complex, inefficient, and lack accuracy. This study proposes a machine learning (ML) framework for efficient fatigue life prediction of E36 welded joints. Welded specimens using SQJ501 filler wire on prepared E36 steel established a dataset from 23 original fatigue test data points. The dataset was expanded via Z-parameter model fitting, with data scarcity addressed using SMOTE. Pearson correlation analysis validated data relationships. After grid-optimized training on the augmented data, models were evaluated on the original dataset. Results demonstrate that the machine learning models significantly outperformed the Z-parameter formula (R² = 0.643, MAPE = 16.15%). The artificial neural network (R² = 0.972, MAPE = 4.45%) delivered the best overall performance, while the random forest model exhibited high consistency between validation (R² = 0.888, MAPE = 6.34%) and testing sets (R² = 0.897), with its error being significantly lower than that of support vector regression. Full article

An ultra-high-strength press-hardening steel (PHS) and a high-strength dual-phase steel (DP) were butt-joined by the gas metal arc welding (GMAW) process, aiming to assess the effects of a high heat input welding process on the structure-property relationship and residual stress. The post-weld microstructure, the microhardness profile, the tensile behavior, and the experimentally obtained residual stresses (by x-ray diffraction) of the steels in dissimilar (PHS-DP) and similar (PHS-PHS, DP-DP) pair combinations have been analyzed. Results indicated that the ultimate tensile strength (UTS) of the dissimilar pair PHS-DP achieves a similar strength to the DP-DP joint, whereas the elongation was similar to that of the PHS-PHS weldment. The failure location of the tensile specimens was expected and systematically observed at the tempered and softer sub-critical heat-affected zone (SC-HAZ) in all welded conditions. Compressive residual stresses were consistently observed along the weldments in all specimens; the more accentuated negative RS were measured in the PHS joint attributed to the higher volume fraction of martensite; furthermore, the negative RS measured in the fusion zone (FZ) could be well correlated to weld restraint due to the sheet anchoring during the welding procedure, despite the presence of predominant ferrite and pearlite microstructures. Full article

In this study, the effects of post-weld heat treatment (PWHT) on residual stress distribution and fatigue crack propagation (FCP) behavior in linear friction welded (LFW) Ti-6Al-4V joints were investigated. Microstructural evolution in the weld center zone (WCZ), thermomechanically affected zone (TMAZ), heat-affected zone (HAZ), and base metal (BM) was characterized using scanning electron microscropy (SEM) and electron backscatter diffraction (EBSD). Mechanical properties were evaluated via Vickers hardness testing and digital image correlation (DIC)-based tensile testing. Residual stresses before and after PWHT were measured using the contour method. The LFW process introduced significant residual stresses, with tensile stresses up to 709.2 MPa in the WCZ, resulting in non-uniform fatigue crack growth behavior. PWHT at 650 °C and 750 °C effectively reduced these stresses. After PWHT, fatigue cracks propagated uniformly across the weld region, enabling reliable determination of crack growth rates. The average crack growth rates of the heat-treated specimens were comparable to those of the base metal, confirming that PWHT, particularly at 750 °C, stabilizes the fatigue crack path and relieves internal stress. Full article

This research article examines the CO₂ laser cutting performance of Fused Filament Fabricated Acrylonitrile Styrene Acrylate (ASA) thermoplastics by analyzing the influence of plate thickness, laser power, and cutting speed on four quality characteristics: surface roughness (Ra), top kerf width (Top KW), bottom kerf width (Bottom KW), and bottom heat-affected zone (Bottom HAZ). Forty-five experiments were conducted using five thickness levels, three power levels, and three cutting speeds. To model and predict these outputs, seven machine learning approaches were employed: Autoencoder, Autoencoder–Gated Recurrent Unit, Autoencoder–Long Short-Term Memory, Random Forest, Extreme Gradient Boosting (XGBoost), Support Vector Regression, and Linear Regression. Among them, XGBoost yielded the highest accuracy across all performance metrics. Analysis of Variance results revealed that Ra is mainly affected by plate thickness, Bottom KW by cutting speed, and Bottom HAZ by power, while Top KW is influenced by all three parameters. The study proposes an effective prediction framework using multi-output modeling and hybrid deep learning, offering a data-driven foundation for process optimization. The findings are expected to support intelligent manufacturing systems for real-time quality prediction and adaptive laser post-processing of engineering-grade thermoplastics such as ASA. This integrative approach also enables a deeper understanding of nonlinear dependencies in laser–material interactions. Full article

Temperature and Cr content on the tensile and fracture mechanics properties of welded joints made of two Cr-Mo steels (A387 Gr. B and SA387 Gr. 91) are presented and analyzed. Tensile strength, yield stress and elongation, as well as the stress–strain curves are obtained by standard tensile tests using specimens extracted from welded joints. Fracture toughness testing was carried out to determine the critical stress intensity factor, K_Ic, and the critical crack length, a_c, for all three zones of the welded joint, parent metal (PM), heat-affected zone (HAZ) and weld metal (WM). Based on these results, the tensile and fracture mechanics properties of welded joints made of A387 Gr. B and SA387 Gr. 91 steels are compared and analyzed. Full article

Taguchi and post-heat treatment methods have been used in this study to optimize the metal inert gas (MIG) welding joints between SUS304 austenite stainless steel and plain carbon SS400 steel using AWS ER 308L filler wire. The dissimilar welding joints’ microstructure and tensile strength have been examined. The findings show that the fast cooling of the weld joint and the ferrite-forming element of the filler wire cause the dendrites’ δ-ferrite phase to emerge on both the weld bead and the heat-affected zone (HAZ) of the SUS304 side. The stickout parameter has the largest impact on the ultimate tensile strength (UTS), next to the welding speed, welding voltage, and welding current, due to the strong impact of the heat distribution. The optimal welding parameters are a welding current of 105 A, a welding voltage of 14.5 V, a stickout of 12 mm, and a welding speed of 420 mm/min, producing the UTS value of 445.3 MPa, which is close to the predicted value of 469.2 ± 53.6 MPa. Post-heat treatment with an annealing temperature that is lower than 700 °C could improve the optimized weld joints’ strength by up to 5%. The findings may provide a more realistic understanding of the dissimilar welding technology. Full article

This research provides a detailed investigation into the mechanical properties and microstructural evolution of heat-resistant steel P92 subjected to both initial (i) welding procedures and simulated (ii) repair welding. The study addresses the influence of critical welding parameters, including preheating temperature, heat input, and post-weld heat treatment (PWHT), with a particular emphasis on the metallurgical consequences arising from the application of repair welding thermal cycles. Through the analysis of three welding probes—initially welded pipes using the PF (vertical upwards) and PC (horizontal–vertical) welding positions, and a PF-welded pipe undergoing a simulated repair welding (also in the PF position)—the research compares microstructure in the parent material (PM), weld metal (WM), and heat-affected zone (HAZ). Recognizing the practical limitations and challenges associated with achieving complete removal of the original WM under the limited (in-field) repair welding, this study provides a comprehensive comparative analysis of uniaxial tensile properties, impact toughness evaluated via Charpy V-notch testing, and microhardness measurements conducted at room temperature. Furthermore, the research critically analyzes the influence of the complex thermal cycles experienced during both the initial welding and repair welding procedures to elucidate the practical application limits of this high-alloyed, heat-resistant P92 steel in demanding service conditions. Full article

This study presents numerical analyses of the thermal, metallurgical, and mechanical processes involved in welding. The temperature fields were computed by solving the transient heat transfer equation using the ABAQUS/Standard 2024 finite element solver. Two types of moving heat sources were applied: a surface Gaussian distribution and a volumetric model, both implemented via DFLUX subroutines to simulate welding on butt-jointed plates. The simulation accounted for key welding parameters, including current, voltage, welding speed, and plate dimensions. The thermophysical properties of the INC 738 LC nickel superalloy were used in the model. Solidification characteristics, such as dendritic arm spacing, were estimated based on cooling rates around the weld pool. The model also calculated transverse residual stresses and applied a hot cracking criterion to identify regions vulnerable to cracking. The peak transverse stress, recorded in the heat-affected zone (HAZ), reached 1.1 GPa under Goldak’s heat input model. Additionally, distortions in the welded plates were evaluated for both heat source configurations. Full article

Welding of maraging steels leads to a microstructural gradient from base material (BM) to weld metal (WM). During post-weld heat treatment (PWHT) the precipitation and reverted austenite (γ_r) reactions will occur defining the mechanical properties. These reactions are affected by the microstructure and local chemical composition of each zone in the “as welded” (AW) condition. This effect has not been clearly described yet nor the evolution of the microstructure. The objective of this work was to analyse the phase transformations at the different zones of the welded joint during the PWHT to explain the microstructure obtained at each zone. Samples of C250 maraging steel were butt-welded by GTAW-P (Gas Tungsten Arc Welding—Pulsed) process without filler material. The AW condition showed an inhomogeneous microhardness profile, associated with a partial precipitation hardening in the subcritical heat affected zone (SC-HAZ) followed by a softening in the intercritical (IC-HAZ) and recrystallized heat affected zone (R-HAZ). A loop-shaped phase was observed between low temperature IC-HAZ and SC-HAZ, associated with γ_r, as well as microsegregation at the weld metal (WM). The microstructural evolution during PWHT (480 °C) was evaluated on samples treated to different times (1–360 min). Microhardness profile along the welded joint was mostly homogeneous after 5 min of PWHT due to precipitation reaction. The microhardness in the WM was lower than in the rest of the joint due to the depletion of Ni, Ti and Mo in the martensite matrix related with the γ_r formation. The isothermal kinetics of precipitation reaction at 480 °C was studied using Differential Scanning Calorimetry (DSC), obtaining a JMAK expression. The average microhardness for each weld zone was proposed for monitoring the precipitation during PWHT, showing a different behaviour for the WM. γ_r in the WM was also quantified and modelled, while in the IC-HAZ tends to increase with PWHT time, affecting the microhardness. Full article