Search Results (1,231)

Wire arc additive manufacturing (WAAM) is increasingly being considered for large marine components because it offers design flexibility, reduced material waste, and potential benefits for manufacturing cost. However, the fatigue and fracture performance of WAAM materials in seawater remains insufficiently established for safety-critical applications such as marine propellers. This study evaluates the corrosion fatigue and fracture behavior of WAAM-manufactured 316L/316LSi austenitic stainless steel intended for propeller applications. A propeller-representative WAAM component was manufactured using gas metal arc welding, and fatigue specimens were extracted in both the weld and build directions. Axial fatigue testing was performed mainly in artificial seawater at stress ranges of 200, 250, 280, 300, and 330 MPa, with a test frequency of 5 Hz and a run-out criterion of 1 × 10⁶ cycles. Chemical composition, ferrite prediction, hardness, Charpy impact behavior, S–N response, and SEM/EDS fractography were assessed to evaluate the impact on structural integrity. The deposited material showed a chemical composition consistent with 316L/316LSi stainless steel and an estimated ferrite content of approximately 8%, indicating a generally sound austenitic weld–metal microstructure. Several specimens reached run-out at stress ranges up to 250–300 MPa, whereas valid gauge-section fatigue failures occurred in higher stress ranges. Premature failures outside the gauge section were attributed to fixture-related effects and were not considered representative of intrinsic material behavior. SEM/EDS examination of a valid fatigue fracture identified an aluminum- and oxygen-rich crack-initiation feature consistent with an aluminum oxide inclusion. This observation indicates that the fatigue response of WAAM 316L/316LSi should be interpreted not only based on stress-life data but also using principles of fracture mechanics and damage tolerance, where surface or near-surface discontinuities may act as initial flaws and promote ΔK-driven crack growth in seawater. The results demonstrate promising fatigue performance within the experimentally validated range, but they also show that bulk mechanical properties alone are insufficient for qualifying WAAM propeller components. For the investigated WAAM process route, specimen surface conditions, stress ratio (R = 0.053), artificial seawater environment, and experimentally validated cycle range of up to 1 × 10⁶ cycles, a preliminary engineering stress-range limit of Δσ = 200 MPa is recommended for pilot applications. This value should not be interpreted as a general design limit and should not be extrapolated to other WAAM processes, geometries, surface conditions, environments, stress ratios, or service-life regimes without additional qualification testing. Further high-cycle fatigue testing, mean-stress correction, fatigue crack-growth testing in seawater, fracture-toughness assessment, realistic defect-size characterization, non-destructive testing correlation, and component-scale validation are required before broader class acceptance of WAAM-manufactured propeller components. Full article

The service performance of austenitic stainless steel is substantially affected by the presence of residual ferrite. In this paper, as-cast 12.5% Ni 316L austenitic stainless steel billets are taken as the research object, and samples are selected from the edge, quarter-thickness, and center positions of the billet, as well as two directionally solidified specimens prepared at different withdrawal speeds. By means of metallographic analysis, Thermo-Calc thermodynamic calculations, and EBSD phase analysis, the characteristics of residual ferrite and precipitated phases in the two types of as-cast 12.5% Ni 316L stainless steel were systematically investigated. The results show that the ferrite morphologies at the edge, quarter-thickness, and center positions of the billet are granular and short-rod, skeletal, and clustered net-like and lath-like, respectively. The ferrite morphologies of the two directionally solidified specimens are similar, both being predominantly skeletal structures; the main difference is that in the high-withdrawal-speed directionally solidified specimen (No. 2), the ferrite is finer and more densely distributed. The residual ferrite contents measured at the edge, quarter-thickness, and center positions of the billet are 4.88%, 5.90%, and 8.99%, respectively; those of directionally solidified specimens No. 1 and No. 2 are 6.4% and 7.7%, respectively. For the billet, the ferrite content increases progressively from the edge to the center. Regarding precipitated phases, the edge of the billet exhibits a mixed microstructure of secondary precipitates, namely Sigma phase and Chi phase; at the quarter-thickness position, the coupled precipitation of these two phases is more pronounced; at the center, part of the ferrite has completely decomposed, with the Chi phase disappearing and only the Sigma phase remaining. In the two directionally solidified specimens, only a small amount of the Sigma phase is precipitated as secondary phases, and the ferrite remains relatively intact. Based on the morphology analysis of the ferrite structure, the solidification mode of the billet is determined to be the FA mode, which is consistent with both the Scheil calculation results and the chromium-nickel equivalent calculation results; however, it differs from the thermodynamic equilibrium solidification results obtained using Thermo-Calc. Full article

The present study evaluates three static recovery term (SRT) formulations incorporated into the Ahmadzadeh–Varvani (A-V) kinematic hardening framework for predicting ratcheting under tensile peak hold loading at room temperature. Linear, power-law, and nonlinear SRTs were assessed using experimental data for austenitic stainless steels SUS304 and SS304. The constitutive parameters were first calibrated using monotonic, strain-controlled, hysteresis loop, and no-hold ratcheting data. The SRT coefficients were then calibrated using peak hold experiments involving hold durations of 60 s for SUS304 and 10 s for SS304. All three formulations reproduced the increased hysteresis loop translation and ratcheting strain caused by the tensile holds more accurately than the baseline model without static recovery, which underpredicted ratcheting strain by an absolute strain difference up to 1.5%. The three SRTs produced comparable overall ratcheting predictions after calibration; however, they generated different coefficient evolutions, recovery histories, and intermediate cycle responses. The nonlinear formulation provided improved agreement for portions of the SUS304 loop evolution, while the linear model offered the simplest implementation. The results demonstrate that static recovery is essential for modelling dwell-assisted ratcheting and that model selection should consider internal variable evolution in addition to final accumulated strain. Full article

Laser beam welding (LBW) offers low thermal distortion for thin austenitic stainless steel sheets but is sensitive to butt-joint fit-up and edge quality. This study compared machined and sheared joint edges under selected autogenous and ER308L filler-wire LBW conditions. Bead geometry, defects, microstructure, microhardness, tensile properties, and fracture behavior were characterized using conventional microscopy, EBSD-KAM, and three-dimensional digital image correlation (3D-DIC). The machined-edge autogenous condition (LBW-A-M) produced a stable bead with 0.04 mm top underfill and only a small number of internal discontinuities, while its tensile properties remained close to those of the base metal and fracture occurred in the base metal. In contrast, the sheared-edge autogenous condition (LBW-A-S) exhibited 0.24 mm top underfill, 0.18 mm misalignment, multiple pores, and localized strain near the weld, with tensile strength and elongation of 682.31 MPa and 44.04%, respectively. Under the selected filler-wire conditions, no measurable top underfill was observed, although pores remained. Because the autogenous and filler-wire modes used different process parameters and heat inputs, cross-mode differences are condition-specific rather than isolated filler-wire effects. Overall, joint-edge preparation and fit-up control remained important for thin-sheet LBW. Full article

Abrasive Water Jet Machining (AWJM) is increasingly used for post-weld surface modification of dissimilar metallic joints; however, the depth-dependent surface response of welded stainless–carbon steel joints remains insufficiently quantified. In this study, four dissimilar welded systems, TIG 316, TIG 309, ARC 316, and ARC 309, were systematically investigated to elucidate the combined influence of welding technology, filler composition, and jet parameters on surface integrity. Surface roughness was evaluated at multiple jet-penetration depths using amplitude (R_a, R_q, R_t, R_z) and statistical (R_sk, R_ku) descriptors. The results reveal three distinct hydrodynamic erosion regimes governing texture evolution. Duplex welds (TIG 309 and ARC 309) exhibited highly stable erosion behavior, with R_a confined to 1.91–2.99 µm, low roughness gradients (ΔR_a/Δdepth = 0.012–0.015 µm·mm⁻¹), and near-Gaussian surface statistics (R_sk ≈ 0, R_ku ≈ 3–4). In contrast, austenitic welds (TIG 316 and ARC 316) showed pronounced depth-dependent instability, with R_a increasing up to 4.54 µm and the normalized roughness ratio R_z/R_a reaching 5.69 in TIG 316 near the jet exit. Strong inter-parameter correlations in duplex welds (r ≥ 0.94) confirm uniform erosion kinetics, whereas weakened correlations in austenitic systems (r ≈ 0.70–0.83) reflect jet-energy dissipation. These findings establish a mechanistically grounded AWJM performance window for achieving R_a ≤ 3 µm in dissimilar welded steels. Full article

The effects of sigma (σ) phase morphology and distribution on the corrosion behavior of superduplex stainless steel (SDSS) were investigated. The aim of this study was to establish the relationship among distinct σ-phase morphologies, chromium redistribution, and the resulting corrosion mechanisms using electrochemical and microstructural characterization techniques. Heat treatments at 700 °C and 800 °C produced distinct σ-phase morphologies and volume fractions. Microstructural characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM), and corrosion behavior was evaluated using open-circuit potential (OCP), cyclic polarization, and double-loop electrochemical potentiodynamic reactivation (DL-EPR). Statistical analysis of chromium (Cr) distribution was used to link microstructural evolution to corrosion susceptibility. Lamellar σ promotes selective attack between lamellae of σ and secondary austenite due to localized Cr depletion, whereas σ at grain boundaries causes sensitization and intergranular corrosion. Notably, the sample aged at 800 °C for 30 h did not exhibit pitting during cyclic polarization. However, it showed clear signs of sensitization and selective attack in the DL-EPR test, indicating that temperature-driven Cr partitioning increases Cr gradients around σ. These gradients, together with the morphology and fraction of σ, ultimately govern the transition between lamellar-selective corrosion and grain-boundary sensitization. Overall, the findings underscore the importance of combining microstructural and electrochemical assessments to accurately predict localized corrosion and sensitization in SDSS. Full article

Super duplex stainless steels are widely used in seawater desalination plants due to their high mechanical strength and excellent corrosion resistance in chloride-rich environments. However, during reverse osmosis processes, the salinity of the reject stream increases progressively, generating concentrated brines with concentrations close to 7 wt.% NaCl, which represent a chloride-rich service environment that may affect passive film stability and promote localized corrosion. This study investigates the effect of novel La Geria-inspired microstructures (LGMs) generated by laser surface texturing on the microstructure, microhardness, and electrochemical behavior of UNS S32750 super duplex stainless steel in 3.5 wt.% and 7.0 wt.% NaCl solutions, simulating seawater and concentrated desalination brine. Electrochemical results show that textured surfaces exhibit improved corrosion resistance, with more stable corrosion potentials, lower corrosion current densities, and higher impedance values. Microhardness measurements revealed a homogeneous mechanical response, confirming that laser texturing does not alter the mechanical integrity of the material. Microstructural observations showed reduced surface degradation and improved preservation of the duplex ferrite–austenite structure in textured samples after exposure to chloride solutions. These findings demonstrate that biomimetic laser surface texturing enhances corrosion resistance by modifying interfacial conditions and stabilizing the passive film, providing experimental evidence of the beneficial effect of LGMs in aggressive desalination environments. Full article

AISI 316L austenitic stainless steel is extensively used in petrochemical storage and processing equipment because of its excellent corrosion resistance. However, exposure to concentrated hydrochloric acid severely destabilizes its passive film, promoting active dissolution and localized corrosion. This work investigates the corrosion behavior of AISI 316L stainless steel in hydrochloric acid solutions of 7.2, 9.6, and 12 M at room temperature. Cyclic potentiodynamic polarization (CPP) tests were performed according to ASTM G61, and the corrosion morphology was characterized using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and metallographic cross-sections. The electrochemical results revealed an active dissolution regime characterized by the absence of a stable passive region and positive hysteresis loops in all HCl solutions, indicating irreversible surface damage and poor repassivation. The corrosion current density increased from the order of 10⁻¹ mA cm⁻² in 7.2 and 9.6 M HCl to the order of 10¹ mA cm⁻² in 12 M HCl, demonstrating a significant acceleration of the corrosion kinetics. SEM and cross-sectional analyses confirmed the development of localized pitting corrosion, with pit depths reaching approximately 0.87 mm. The results demonstrate that concentrated hydrochloric acid promotes the coexistence of generalized active dissolution and localized pitting corrosion, while increasing HCl concentration modifies the morphology and propagation mode of the pits. Full article

The presence of ferrite in 316 austenitic stainless steel affects its magnetic permeability, and the secondary precipitates formed by ferrite decomposition can further degrade the corrosion resistance, limiting its application in industries such as nuclear power and medical devices. In previous studies, the characteristics of ferrite and precipitates in several 316 stainless steel continuous-casting billet samples with different Ni contents were analyzed. In this work, remelting experiments were further conducted on several 316L stainless steels with different Ni contents using a tube furnace; according to the Ni content, they are designated as L-316, M-316, and H-316 stainless steels. Metallographic analysis and electron back-scattered diffraction (EBSD) characterization were employed. The effects of Ni content and cooling rate on the microstructure of 316 stainless steel were systematically investigated. The results show that for the L-316 stainless steel, the ferrite morphologies in water-cooled, oil-cooled, air-cooled, and furnace-cooled samples change successively as follows: skeletal and lath-like, clustered network, lath-like and clustered network, and short rod-like. For the M-316 stainless steel remelted samples, the ferrite morphologies are network and skeletal, network and short rod-like, semi-network and short rod-like, and semi-network, respectively. The solidification modes of the L-316, M-316, and H-316 stainless steel remelted samples are FA, FA, and AF modes, respectively. Increasing Ni content reduces the ferrite content under all cooling conditions. When the Ni content increases from 10% to 12.17%, the ferrite content decreases significantly, with a greater reduction at higher cooling rates; when the Ni content further increases to 14.25%, the decrease in ferrite content slows down, indicating that after Ni content reaches a certain level, its inhibiting effect on ferrite formation weakens. The effect of cooling rate on ferrite content depends on the solidification mode: in the FA mode, slow cooling promotes diffusional transformation of ferrite to austenite, so the ferrite content decreases with decreasing cooling rate—for L-316 stainless steel, the ferrite content drops from 22.44% in the water-cooled sample to 2.71% in the furnace-cooled sample. In the AF mode, slow cooling favors the enrichment of elements at grain boundaries and promotes ferrite nucleation and growth; the overall trend of ferrite content increases as the cooling rate decreases. For the H-316 stainless steel specimens, the ferrite content is similar between water-cooled specimens (0.36%) and oil-cooled specimens (0.26%); for air-cooled specimens, the ferrite content increases significantly to 1.49%; and finally, it reaches 1.94% for the furnace-cooled specimen. Regarding secondary precipitates, the phase constituents of the L-316 stainless steel specimens after water cooling, oil cooling, and air cooling consist of an austenite matrix and ferrite, with a secondary precipitated Chi phase forming only under furnace cooling conditions. For the M-316 stainless steel, the Sigma phase and Chi phase begin to form under oil cooling conditions, and the Sigma phase also precipitates in the oil-cooled specimens of the H-316 stainless steel. In the air-cooled and furnace-cooled specimens of both M-316 and H-316 stainless steels, the secondary precipitated phase is the Sigma phase. All three types of water-cooled stainless steel specimens exhibited no secondary precipitate phase; increasing the cooling rate suppresses atomic diffusion, thereby reducing the precipitation of Chi phase and Sigma phase; however, a higher Ni content shifts the solidification mode toward the AF mode, making secondary precipitates more prone to form. Full article

Additive manufacturing (AM) of stainless steel has been gaining industry attention in recent years due to the need to manufacture complex steel components. Many sectors stand to benefit from the design flexibility, customization, and rapid production capabilities of AM. However, the industry’s adoption of this technology remains limited due to concerns about the mechanical integrity and reliability of AM products. This experimental study examines the wear and tribological behavior of Wire Arc Additive Manufactured (WAAM) austenitic stainless steel 316L. Pin-on-disk tests were conducted using a 5 mm tungsten carbide ball under dry sliding conditions at normal loads of 1.5 and 2.5 N and sliding speeds between 0.03 and 0.229 m/s. The results showed that the coefficient of friction remained relatively stable at approximately 0.6, while wear volume generally decreased with increasing sliding speed. Lower normal loads resulted in lower wear volume, whereas the wear factor showed only limited sensitivity to the applied load. Optical microscopy revealed a ferrite–austenite microstructure with residual δ-ferrite that contributes to the observed wear behavior. These findings demonstrate the suitability of WAAM-produced 316L stainless steel for tribological applications requiring stable frictional performance. Full article

The corrosion behaviour of AISI 420 martensitic stainless steel, frequently employed in dental prosthetics due to its mechanical strength and cost-effectiveness, necessitates a thorough and multidimensional investigation. While this steel offers advantageous machinability, its lower corrosion resistance compared to that of austenitic steels raises concerns, particularly when influenced by factors such as inclusions, residual stresses, and contamination from machining processes. This study aims to elucidate the causes of pitting corrosion on prosthetic keys fabricated from AISI 420. It highlights critical manufacturing stages, particularly washing and passivation processes, which are vital for mitigating corrosion risks. Experimental analyses revealed that corrosion initiation can be attributed to metal residues, inadequate passivation, and contaminated washing water. Furthermore, it was determined that the presence of rust is more closely associated with improper storage and drying practices than with inherent material defects. These findings underscore the importance of meticulous handling and verification of prosthetic components prior to packaging and highlight the need for standardised procedures during sterilisation in clinical settings. The outcomes of this research contribute significantly to enhancing the longevity and reliability of dental prosthetic applications, emphasising the necessity for technological interventions to prevent corrosion in clinical environments. Full article

The perforated backup plate of KARL KROYER MP 2C120 diaphragm pumps, used in the starch processing food industry, exhibits recurrent in-service fractures whose quantitative explanation and redesign solution have not been previously addressed in the literature. To solve this problem, an integrated analytical model is developed that combines, in a calibrable expression, small-magnitude spherical curvature, regular square-pattern perforation, and stepped peripheral clamping, calibrated against finite element numerical simulation and applied to the screening of eighteen geometrically feasible configurations. The chemical composition of the installed material was verified by portable optical emission spectrometry (PMI), identifying it as austenitic stainless steel AISI 301/1.4310 X10CrNi18-8, with nominal annealed yield strength ${\sigma }_y=195$ MPa according to EN 10088-2. The calibration quantifies an overestimation of $22.6\%$ for the simply supported edge model and an underestimation of $51.7\%$ for the clamped edge model; the dimensionless parameter ${\eta }_{\mathrm{BC}}=0.695$ describes the effective degradation of clamping due to the reduced stiffness of the perforated belt adjacent to the edge and supports the use of the simply supported model as a conservative screening bound. The currently installed configuration operates with a safety factor $F{S}_{\mathrm{op}}=0.89$ with respect to yield strength, quantitatively explaining the observed fractures. Within the standard manufacturable space, the configuration $d=5$ mm, $p=7.5$ mm ($\eta =0.333$) minimizes the maximum equivalent stress predicted by the conservative screening model; this selection corresponds to the configuration with the maximal ligament efficiency and is preserved under the single-point calibration, which acts as a single global positive scale factor. The screening is verified by a direct finite element campaign performed on the complete $d=5$ mm family (configurations 1, 2 and 3) with the experimentally verified material properties. The verification confirms the predicted ranking and the peripheral location of the critical region, but shows that the smooth cross-center field is essentially invariant across configurations ($187.3$, $195.0$ and $186.0$ MPa), so the linear-scaling estimate previously used to anchor absolute margins is not supported; the benefit of the redesign accrues at the governing hole-edge concentration, which decreases from $338.2$ to $261.5$ MPa ($22.7\%$ reduction) yet remains above the yield strength of the annealed material. Geometric modification alone is therefore insufficient, and industrial adoption requires combining configuration 3 with material substitution to a cold-worked hardened state (C700: $FS=1.91$ on the governing peak) or a duplex alloy ($FS=1.76$), together with periodic non-destructive inspection. The central contribution of this work is the parameter ${\eta }_{\mathrm{BC}}$ as a quantitative descriptor of effective clamping degradation and the proposal of an industrially feasible redesign, integrated with complementary mitigation strategies, for KARL KROYER MP 2C120 pumps and geometrically equivalent equipment. Full article

The microstructural evolution and strain-hardening mechanisms of a serviced 304 stainless steel during tensile deformation are investigated using quasi in situ EBSD measurements. This steel exhibits a high ultimate tensile strength of about 652 MPa alongside an exceptional fracture elongation of 83.4%. Its strain hardening behavior can be divided into three distinct stages. Deformation induces heterogeneous lattice rotation, which is dominated by the preferential activation of slip systems with the top two Schmid factors. With increasing strain, the deformation mechanism evolves sequentially from dislocation slip to mechanical twinning and then strain-induced martensite transformation. Mechanical twins act as the preferential nucleation sites for strain-induced martensite. In the latter two deformation stages, mechanical twinning serves as the primary driver of strain hardening, while strain-induced martensite merely contributes auxiliary hardening due to its limited volume fraction. This work elucidates the full-chain deformation mechanism of serviced 304 stainless steel. It provides experimental fundamentals for evaluating the residual ductility and failure risk of serviced austenitic stainless steel components. Full article

With contemporary advancements in additive manufacturing (AM), it has become possible to obtain hull structures for spacecraft made of relatively cheap materials. The possibility of substituting super-austenitic stainless steel Avesta SMO 254 X1NiCrMoCuN20-18-7 (EN 10088) for that already used in the Starship SpaceX 304 L-Modified is focused on achieving better thermal stability and durability in extreme conditions. The Directed Energy Deposition Arc (DED-Arc) method for AM has enabled the production of high-strength-to-weight ratios. The aim is to engage low-cost material with treatment optimization to provide greater corrosion resistance and high yield and tensile strength. For the DED-Arc, a filler wire was selected for the welding source, Fronius TPS 400i. A simulation via the RoboDK Robot Development Kit for the FANUC ARC Mate 100ID10L is provided. Additional shot pining/vibration treatment is proposed for the finished structure, which can be a substitute for the cold-worked initial metal. A comparison is made for stainless steel that has already been tested for space travel. Regimes for the manufacturing process are proposed, with representative samples of Avesta SMO 254 obtained and tested using microhardness measurements, microcracking detection, porosity measurements, interface zone assessment, and microstructural analysis. The DED-Arc process can be applied to large-space shell manufacturing. A comparison is made with a focus on the mechanical and corrosion advantages. For Avesta SMO 254, microhardness measurements ranged from 235 to 246 HV1 and increased after treatment. The controlled parameters provided a maximum heat input of 0.7 KJ/mm, no defects, and a fine microstructure. The successful use of stainless steel with AM increases the potential for multiple space missions. The advanced method shows high quality, allows cost savings and provides extended service life. Full article

Laser-welded stainless steel joints usually suffer from strain localization and premature failure in the weld metal (WM) due to microstructural heterogeneity introduced during welding. In this work, surface mechanical rolling treatment (SMRT) was applied to laser-welded 304 stainless steel plates to enhance the mechanical performance of the welded joints. Laser welding introduced multiple heterogeneous features in the WM, including local Ni compositional fluctuations, nanoscale oxide particles and heterogeneous grain structures. Among them, the local fluctuation of Ni concentration is considered to play a dominant role by locally modifying the stability of γ-austenite and promoting strain-induced martensitic transformation during SMRT. As a result, the WM exhibited more severe grain refinement and a stronger gradient nanostructure than base metal (BM) under identical processing conditions. The near-surface hardness of the WM reached ~500 Hv, which was noticeably higher than that of the BM. Uniaxial tensile tests revealed that the yield strength increased from ~350 MPa to ~700 MPa, while the ultimate tensile strength reached ~1000 MPa with ~40% elongation. More importantly, the fracture location shifted from the WM to the BM after SMRT. The enhanced martensitic transformation and gradient nanostructure effectively suppressed strain localization and improved the mechanical reliability of the welded joint. Full article