Search Results (155)

The surface topography of the rolls used in skin-pass cold rolling determines the surface finish of rolled sheets. In this sense, work rolls can be intentionally textured to produce certain topographical features on the final sheet surface. The maskless electrochemical texturing method (MECT) is a potential candidate for industrial-scale application due to its reduced texturing cost and time when compared to traditional texturing methods. However, there are few studies in the literature that address the MECT method applied to the topography control of cold rolling work rolls. The present work aims to analyze the viability of surface texturing via MECT of work rolls used in skin-pass cold rolling. In this study, we first investigated how texturing occurs for tool steel using flat textured samples to facilitate the understanding of the dissolution mechanisms involved. In this case, a specially designed texturing chamber was built to texture flat samples extracted from an actual work roll. The results indicated that the anodic dissolution involved in tool steel texturing occurs preferentially in the metallic matrix around the primary carbides. Then, we textured a work roll used in pilot-scale rolling tests, which required the development of a special prototype to texture cylindrical surfaces. After texturing, the texture transfer from the work roll to the sheets was investigated. Rolling tests showed that the work roll surface textured with a dimple pattern generated a pillar-shaped texture pattern on the sheet surface, possibly due to a reverse extrusion mechanism. Full article

During the service life of automotive panel stamping dies, the surface is often subjected to high loads and repeated friction, resulting in excessive wear. This leads to die failure, reduced machining accuracy, and decreased production efficiency. To enhance the anti-friction and wear-resistant performance of die steel surfaces, this study introduces the concept of biomimetic engineering in surface science. By mimicking microstructural configurations found in nature with outstanding wear resistance, biomimetic functional surfaces were designed and fabricated. Specifically, quadrilateral dimples inspired by the back of dung beetles, pentagonal scales from armadillo skin, and hexagonal scales from the belly of desert vipers were selected as biological prototypes. These surface textures were fabricated on Cr12MoV die steel using high-speed ball-end milling. Finite element simulations and dry sliding wear tests were conducted to systematically investigate the tribological behavior of surfaces with different dimple geometries. The results showed that the quadrilateral dimple surface derived from the dung beetle exhibited the best performance in reducing friction and wear. Furthermore, the milling parameters for this surface were optimized using response surface methodology. After optimization, the friction coefficient was reduced by 21.3%, and the wear volume decreased by 38.6% compared to a smooth surface. This study confirms the feasibility of fabricating biomimetic functional surfaces via high-speed ball-end milling and establishes an integrated surface engineering approach combining biomimetic design, efficient manufacturing, and parameter optimization. The results provide both theoretical and methodological support for improving the service life and surface performance of large automotive panel dies. Full article

This study aims to comprehensively assess the suitability of post-processing annealing (at 900–1200 °C) for enhancing the key properties of 316L steel fabricated via laser powder bed fusion (LPBF). It adopts a holistic approach to investigate the annealing-driven evolution of microstructure–property relationships, focusing on tensile properties, nanoindentation hardness and modulus, impact toughness at ambient and cryogenic temperatures (−196 °C), and the corrosion resistance of LPBF 316L. Annealing at 900–1050 °C reduced tensile strength and hardness, followed by a moderate increase at 1200 °C. Conversely, ductility and impact toughness peaked at 900 °C but declined with the increasing annealing temperature. Regardless of the annealing temperature and testing conditions, LPBF 316L steel fractured through a mixed transgranular/intergranular mechanism involving dimple formation. The corrosion resistance of annealed steel was significantly lower than that in the as-built state, with the least detrimental effect being observed at 1050 °C. These changes resulted from the complex interplay of annealing-induced structural transformations, including elimination of the cellular structure and Cr/Mo segregations, reduced dislocation density, the formation of recrystallized grains, and the precipitation of nano-sized (MnCrSiAl)O₃ inclusions. At 1200 °C, an abundant oxide formation strengthened the steel; however, particle coarsening, combined with the transition of (MnCrSiAl)O₃ into Mo-rich oxide, further degraded the passive film, leading to a sharp decrease in corrosion resistance. Overall, post-processing annealing at 900–1200 °C did not comprehensively improve the combination of LPBF 316L steel properties, suggesting that the as-built microstructure offers a favorable balance of properties. High-temperature annealing can enhance a particular property while potentially compromising other performance characteristics. Full article

One of the most critical aspects of turning, and machining in general, is the surface roughness of the finished product, which directly influences the performance, functionality, and longevity of machined components. The accurate prediction of surface roughness is vital for enhancing component quality and machining efficiency. This study presents a machine learning-driven framework for modeling mean roughness depth (Rz) during the dry machining of super duplex stainless steel (SDSS 2507). SDSS 2507 is known for its exceptional mechanical strength and corrosion resistance, but it poses significant challenges in machinability. To address this, this study employs flank-face textured cutting tools to enhance machining performance. Experiments were designed using the L₂₇ orthogonal array with three continuous factors, cutting speed, feed rate, and depth of cut, and one categorical factor, tool texture type (dimple, groove, and wave), along with surface roughness as an output parameter. Gaussian Data Augmentation (GDA) was employed to enrich data variability and strengthen model generalization, resulting in the improved predictive performance of the machine learning models. MATLAB R2021a was employed for preprocessing, the normalization of datasets, and model development. Two models, Least-Squares Support Vector Machine (LSSVM) and Multi-Gene Genetic Programming (MGGP), were trained and evaluated on various statistical metrics. The results showed that both LSSVM and MGGP models learned well from the training data and accurately predicted Rz on the testing data, demonstrating their reliability and strong performance. Of the two models, LSSVM demonstrated superior performance, achieving a training accuracy of 98.14%, a coefficient of determination (R²) of 0.9959, and a root mean squared error (RMSE) of 0.1528. It also maintained strong generalization on the testing data, with 94.36% accuracy and 0.9391 R² and 0.6730 RMSE values. The high predictive accuracy of the LSSVM model highlights its potential for identifying optimal machining parameters and integrating into intelligent process control systems to enhance surface quality and efficiency in the complex machining of materials like SDSS. Full article

Surface texturing is designed to improve the functional properties of machine elements by generating dimples on the surface contacted. Friction and wear resistance can also be improved by creating diamond-like carbon (DLC) coatings. These two techniques were combined to extend the lifetime of the elements and minimise friction in reciprocating conformal sliding contact. This work is functionally important for assemblies operating under high normal loads. Experiments were carried out in initially lubricated reciprocating sliding contact using an Optimol SRV 5 tribotester in the flat-on-flat configuration. The disc samples were untextured, laser textured, and DLC-coated untextured and textured. The combination of DLC coating and surface texturing caused an enhancement of the tribological performance of the sliding pair compared to that of untextured discs with and without DLC coating and textured discs without DLC coating. The DLC coating of the untextured disc caused a growth in the lifetime of a friction pair by a factor of 2.4. Seizure resistance also increased due to surface texturing of the steel disc for pit area ratios of 9 and 13%. Combining surface texturing with pit area ratios of 3 and 9% and DLC coating led to a decrease in the coefficients of friction of sliding pairs compared to only textured and coated discs. The DLC coating caused a decrease in the wear of the disc sample and reduction in wear levels of the counter samples in comparison to those of textured discs without DLC coatings. Full article

Annealing and rolling play critical roles in improving the mechanical properties of arc spraying coatings. In this work, we successfully fabricated copper–steel bimetallic sheets (CSBSs) using an arc spray-rolling short process and achieved excellent internal bonding of the copper coating and improved deep-drawing of the CSBSs via annealing and rolling synergistic treatment. The results indicate that the microstructure of the copper coating became dense, and the porosity effectively reduced after annealing–rolling–annealing (ARA) treatment. Tight bonding was also observed between the copper coating and steel substrate. The copper coating had a porosity of less than 0.2%, an average grain size of 3.8 μm, and a micro-hardness of 55 HV_0.05. After tensile testing, the As-sprayed coating generated brittle fractures and delamination. The A-R-A coating also displayed elongated dimples, with the majority oriented along the TD direction, and bonded well with the steel substrate. In addition, the As-sprayed coating fell off directly after deep drawing. In contrast, the A-R-A coating did not exhibit cracks and fall off. The fracture mechanism gradually changed from falling off and cracking, to toughness deformation due to the reduced porosity and tighter grain boundaries, and finally to cooperative deformation due to the metallurgical bonding of the sprayed particles and good interface bonding properties. These findings provide guidance and reference for the practical application of thermal spray additive manufacturing. Full article

Laser processing is an effective and precise micro-structure fabrication technique. At present, micro-structure processing is primarily applied to planar surfaces. However, for curved surfaces, variations in the incident angle of the laser beam lead to distortions in micro-structural morphology. In this study, an experimental investigation was conducted to characterize micro-structural ablation under oblique laser incidence. Initially, a single-factor parametric study was performed on the surface of stainless steel. The results indicate that grooves measuring 45 μm in width and 43 μm in depth were achieved under the conditions of a single-pulse energy of 10 μJ, a laser frequency of 70 kHz, a scanning speed of 10 mm/s, and 20 processing cycles. Subsequently, the influence of the laser incidence angle on groove morphology was further examined. The results demonstrate that for incidence angles below 11°, the groove removal rate approaches 1, and the root mean square of shape error (RMS) remains below 1.5 μm. To reduce the deformation of the micro-structure at oblique incidence, a curve-guided surface projection (CGSP) method was developed, and the micro-dimples were fabricated at laser incidence angles of 10° and 14°. Compared with the conventional direct projection (DP) method, the CGSP approach significantly mitigates structural distortion resulting from oblique incidence. Finally, the CGSP method was applied to fabricate the micro-dimples at various locations on a spherical surface. The removal rates of 0.988 and 0.936 were closer to unity than those achieved via direct projection, while the RMS values were reduced by 56.4% and 76.2%, respectively. These findings offer a promising solution to the challenge of oblique laser incidence in curved micro-structuring and further broaden the application scope of laser processing technology. Full article

Additive manufacturing is increasingly used to produce metallic biomaterials, and post-processing is gaining increasing attention for improving the properties of as-built components. This study investigates the effect of work hardening followed by recrystallisation annealing on the tensile and nanoindentation behaviour of laser powder bed-fused (LPBF) 316L stainless steel, with the aim of optimising its mechanical properties. As-built and thermally stabilised (at 900 °C) specimens were prestrained in a uniaxially tensile manner at room temperature (0.12 plastic strain, ~75% of maximum work hardening) and subsequently annealed (at 900 °C or 1050 °C for 1 h). The microstructure and mechanical properties were then characterised by optical microscopy, SEM, EBSD, XRD, nanoindentation, and tensile testing. It was found that prestraining increased yield tensile strength (YTS) 1.2–1.7 times (to 690–699 MPa) and ultimate tensile strength (UTS) ~1.2 times (to 762–770 MPa), but decreased ductility 1.5 times. Annealing led to recovery and partial static recrystallisation, decreasing YTS (to 403–427 MPa), restoring ductility, and increasing the strain hardening rate; UTS and indentation hardness were less affected. Notably, the post-LPBF thermal stabilisation hindered recrystallisation and increased its onset temperature. Mechanical property changes under prestraining and annealing are discussed with respect to microstructure and crystalline features (microstrain, crystal size, dislocation density). All specimens exhibited ductile fractures with fine/ultra-fine dimples consistent with the as-built cellular structure. The combined treatment enhanced tensile strength whilst preserving sufficient ductility, achieving a strength–ductility product of 40.3 GPa·%. This offers a promising approach for tailoring LPBF 316L for engineering applications. Full article

To compare them with PTFE-40# steel tribo-pairs, the tribological properties of textured PEEK-40# (AISI 1040) steel friction pairs were researched under full-film lubrication conditions by manufacturing micro-dimples with different dimensions on the contact surfaces of 1040 steel discs using laser surface texturing (LST). After repeated tribological tests, the coefficients of friction (COFs), wear losses, and wear morphologies of the PEEK-1040 steel friction pairs were measured and analyzed. The results show that micro-dimples do not significantly reduce the average COFs of PEEK-1040 steel friction pairs when lubricated with a sufficient amount of hydraulic oil, but they do reduce the wear losses of most groups. When the dimple diameter was 250 μm, the dimple depth was 5 μm, the area ratio was 6.6%, and the mass loss of the 1040 steel disc was reduced by 90% compared to the smooth reference. In comparison to the behavior of the PTFE-1040 steel tribo-pairs, PEEK-1040 steel friction pairs can provide better tribological performance, whether smooth or dimple-textured. This study offers important insights for the design of seals in machinery. Full article

Laser-arc hybrid welding was applied to Q355 medium-thick steel plates to improve weld tensile properties, with experimental verification comparing welds to the base material. Numerical simulations identified optimal process parameters, analyzing the effects of heat source distance, welding speed, laser power, and arc power on temperature field distribution and molten pool morphology. Heat source distance had the greatest influence, followed by welding speed, laser power, and arc power. Maintaining a peak welding temperature of 900–1000 K refined the weld grain structure, enhancing the tensile performance. Under optimal parameters (laser power: 800 W, arc power: 1200 W, wire distance: 5 mm, welding speed: 15 mm/s), the weld achieved a 77% elongation rate compared to the base material’s 73% at a loading rate of 0.5 mm/min, demonstrating superior tensile properties. These results comply with the Code for Welding of Steel Structures. SEM analysis showed uniform, deep dimples in both the weld and base material, indicating a dense structure, excellent plasticity, and strong fracture resistance. This study offers theoretical and experimental insights for optimizing laser-arc hybrid welding processes. Full article

Resistance spot welding (RSW) is now the primary joining process used in the automobile and aerospace sectors. Mechanical parts, when put into service, often undergo cyclic stress. As a result, avoiding fatigue failure should be the top priority when designing these parts. Given that spot welds are a type of localised joining that results in intrinsic circumferential notches, they increase the likelihood of stress concentrations and subsequent fatigue failures of the structure. Most of the fatigue failures in automotive parts originate around a spot weld. To that end, this study seeks to examine the mechanical properties and fatigue behaviour RSW joints made of titanium (Ti) grade 2 alloy and AISI 304 austenitic stainless steel (ASS) with equal and unequal thicknesses of 0.5 and 1 mm. Based on the mechanical properties and fatigue life results, the maximum tensile shear strength and fatigue life for the RSW titanium joint were 613 MPa and 7.37 × 10⁵ cycles for the 0.5–0.5 mm case, 374.7 MPa and 1.39 × 10⁶ cycles for the 1–1 mm case, and 333.5 MPa and 7.69 × 10⁵ cycles for the 1–0.5 mm case, respectively. The maximum shear strength and fatigue life of ASS welded joints were 526.8 MPa and 4.56 × 10⁶ cycles for the 1–1 mm case, 515.2 MPa and 3.35 × 10⁶ cycles for the 0.5–0.5 mm case, and 369.5 MPa and 7.39 × 10⁵ cycles for the 1–0.5 mm case, respectively. The assessment of the shear strength and fatigue life of the dissimilar joints revealed that the maximum shear strength and fatigue life recorded were 183.9 MPa and 6.47 × 10⁵ cycles for the 1 mm Ti–0.5 mm ASS case, 115 MPa and 3.7 × 10⁵ cycles for the 1 mm Ti–1 mm ASS case, 156 MPa and 4.11 × 10⁵ cycles for the 0.5 mm Ti–0.5 mm ASS case, and 129 MPa and 4.11 × 10⁵ cycles for the 0.5 mm Ti–1 mm ASS case. The fatigue life of titanium and stainless steel welded joints is significantly affected by the thickness, particularly at maximum applied stress (0.9% UTS), meaning that similar thicknesses achieve a greater fatigue life than unequal thicknesses. Conversely, the fatigue life of the dissimilar joint reached the greatest extent when an unequal thickness combination was used. The ductile failure of similar Ti and ASS welded joints was demonstrated by the scanning electron microscopy (SEM) examination of fatigue-fractured surfaces under the high-cycle fatigue (HCF) regime, in contrast to the brittle failure noticed in the low-cycle fatigue (LCF) regime. Brittle failure was confirmed by the SEM fatigue of dissimilar joint fractured surfaces due to interfacial failure. The Ti and ASS fractured surfaces presented river-like cleavage facets. On the Ti side, tiny elongated dimples suggest ductile failure before fracture. The topography results showed that the roughness topography parameters of similar and dissimilar fractured specimens made from Ti grade 2 and AISI 304 for the HCF regime were lower than those of the fractured specimens with LCF. The current study is expected to have practical benefits for the aerospace and automotive industries, particularly the manufacturing of body components with an improved strength-to-weight ratio. Full article

This paper employs in situ Electron Backscatter Diffraction (EBSD) tensile technology to thoroughly consider the evolution of microstructure, grain size, grain boundary characteristics, orientation differences, and dislocation density of H13 steel during the elastic and plastic stages of room temperature tensile testing. The study unveils the deformation mechanisms of inclusions, carbides, and the matrix in H13 steel during the various stages, providing a comprehensive explanation for the slightly superior tensile properties of H13 steel when refined by Vacuum Induction Melting combined with Vacuum Arc Remelting (VIM + VAR) over those when refined by Electroslag Remelting (ESR). This discrepancy is primarily attributed to the differences in inclusions and carbides present in the two refining processes. The quantity and size of inclusions and carbides are closely related to material fracture. Large-sized carbides and inclusions were shown to be more likely to cause dislocation pile-ups and stress concentration. This, in turn, leads to faster crack initiation and propagation during plastic deformation. Conversely, the formation of micro-pores within these fine inclusions and the matrix is contingent on greater plastic deformation, resulting in a gradual and incremental linkage of these micro-pores to form dimples beneath the influence of slip. Full article

This paper presents a numerical analysis of dimple spot welding (DSW) as an innovative joining technique for dissimilar materials, namely steel and aluminium alloys. Employing a finite element (FE) model, the study simulates the fatigue performance of DSW joints, considering crucial factors such as contact friction and cyclic loading conditions. While various numerical models are proposed, the simulation incorporating friction and fatigue loading appears to offer the highest accuracy. The research highlights that the fatigue behaviour of DSW joints can be effectively investigated through the non-local theory of the implicit gradient approach by utilising the fatigue curve of arc-welded structures composed of steel or aluminium alloys. Specifically, simulations incorporating friction and fatigue loading demonstrate that the steel spot weld does not represent the weakest point within the joints. Full article

In this paper, we investigated the effects of the matrix and precipitates in Cr-Ni-Mo-V rotor steel on its mechanical properties after water quenching and tempering (450–700 °C). The results indicate that the microstructure and mechanical properties of the steel can be significantly adjusted by changing the tempering temperature. An excellent combination of tensile strength (1028.608 MPa) and elongation (19%) was obtained upon tempering at 650 °C. This is attributed to the martensite lath with a high dislocation density, solid solution strengthening and the strengthening effect of spherical Mo₂C and VC particles. At a tempering temperature of 550 °C, the precipitation and development of rod-shaped Fe₃Mo₃C resulted in a considerable drop in strength. At 650 °C, the dissolution of Fe₃Mo₃C and dispersion precipitation of Mo₂C and VC led to a large rise in strength. At 700 °C, the coarsening of Mo₂C and VC, together with the recrystallization of the martensite lath, resulted in a loss in strength. Meanwhile, as the tempering temperature was increased from 450 °C to 700 °C, the tensile fracture characteristics of Cr-Ni-Mo-V rotor steel gradually changed from cleavage fractures to dimple fractures. Full article

To improve the microstructure and mechanical properties of heat-resistant 12Kh1MF steel after long-term operation in the stretched bend zone of the main steam pipeline of a thermal power plant, restorative heat treatment (RHT) was proposed. The RHT mode consisted of two normalization stages (from temperatures of 1100 and 960 °C, respectively) followed by tempering at a temperature of 740 °C. The RHT mode, regulated for steel in the initial state, was applied only after its normalization from a significantly higher temperature (1100 °C). It was shown that the proportion of fine grains in the steel structure increased to 55% over the entire pipe wall thickness after using RHT. At the same time, the proportion of large grains in the restored steel decreased significantly (to 10%), while in exploited steel, their proportion reached almost 50%. The proposed RHT mode increased the hardness, strength, plasticity, and resistance to brittle fracture of the restored steel relative to the corresponding characteristics of the operated steel. The maximum positive effect of the RHT was obtained during impact testing. The fractographic features of the exploited and restored steel were studied on fractures of samples tested by tension. The main fractographic feature of the operated steel was nanosized particles at the bottom of large dimples. These tiny particles were considered to be fragments of large carbides formed due to their final decohesion from the matrix during tensile testing. However, such nanosized particles were not found on the samples’ fracture surfaces in the steel after restorative heat treatment. In addition, the ductile dimples on the fractures of the restored steel were more prominent, which indicated high energy costs for their formation. Thus, all the obtained research results suggest the possibility of using the proposed RHT mode to extend the service life of long-operated critical elements of a thermal power plant’s steam pipelines. Full article