Search Results (1,205)

The Charpy impact resistance of monolithic high-strength and dissimilar structured steel was studied. A gas metal arc welding process was used to fabricate the structured steel by depositing a layer of austenitic stainless steel, followed by a layer of hardfacing material over the high-strength steel plate. ANSYS LS-DYNA^TM was used to simulate pendulum–striker impacts on steel Charpy samples. A Cowper–Symonds constitutive model was employed to capture the strain rate behavior. The corresponding material constitutive model parameters were obtained from the literature for the monolithic materials; an iterative numerical optimization method was used to couple the parameters of the structured steel simulation and experimental results. Numerical simulation results showed close agreement with experimental ones. Simulation is a valuable tool for explaining the fracture mechanism in the Charpy impact test and can be used to efficiently design parts made of structured steel that will be subjected to impacts or high-speed deformations. Full article

Marine transportation and storage of liquid hydrogen (LH2) has gained increasing interest, while potential LH2 membrane-type tanks could utilize 316L corrugated austenitic stainless-steel sheets. The corrugation process results in a strain-induced martensitic transformation in the material, introducing rapid diffusion pathways for hydrogen atoms and promoting the formation of hydrogen-trapping sites that alter hydrogen transport and reduce the material’s resistance to hydrogen embrittlement. In this study, 316L sheets were subjected to different levels of uniaxial pre-strain (10, 20, 30, and 40%) with two different strain-rates, to replicate the varying degrees of pre-deformation caused by the corrugation. Microstructural analysis using Electron Backscatter Diffraction (EBSD) (Thermo Fisher Scientific, Waltham, MA, USA) and X-Ray Diffraction (XRD) (Bruker, Billerica, MA, USA) combined with quantitative phase analysis using the Rietveld Method on XRD data, provided valuable insights into the induced phase transformations. Cathodic hydrogen charging method was implemented on as-received and pre-strained material, followed by slow strain rate tensile testing (SSRT) and thermal desorption spectroscopy (TDS) to examine the hydrogen effect on each condition. Experimental results indicated that although 316L exhibits considerable phase stability, it undergoes strain-induced phase transformation resulting in a significant amount of martensite, reaching 5% in the 40% pre-strained condition. Pre-deformation increased hydrogen embrittlement, as evidenced by fractographic analysis which indicated a Relative Reduction of Area (RRA) of 0.83, and by increased hydrogen uptake. These findings contribute to a better understanding of phase transformations and the role of hydrogen in austenitic stainless steels. Full article

This study systematically investigates the effect of solution treatment on the microstructure and corrosion resistance of duplex stainless steel SAF2507 fabricated by direct hot isostatic pressing (HIP). The HIP specimens were solution treated at 1080 °C for 1 h, followed by comprehensive characterization using SEM, EDS, EBSD, XRD, XPS, and electrochemical testing in 3.5 wt% NaCl solution. Results indicate that solution treatment effectively dissolved intermetallic precipitates, promoted a more uniform distribution of ferrite and austenite phases, and reduced microstructural heterogeneity. Electrochemical impedance spectroscopy and potentiodynamic polarization tests showed that the treated samples exhibited a wider passive region and higher charge transfer resistance, indicating enhanced passivation behavior. XPS analysis further revealed an increased proportion of Cr₂O₃ and O²⁻ and decreased ${\mathrm{Fe}}_{\mathrm{hy}}^{3+}$ and H₂O content in the passive film, suggesting improved compactness and chemical stability. Surface morphology analysis confirmed a significant reduction in pitting corrosion after treatment. These findings demonstrate that solution treatment is an effective post-processing method to enhance the corrosion resistance of HIP-fabricated SAF2507 duplex stainless steel. Full article

This study focuses on the low-cycle fatigue behavior and microstructural damage mechanisms of 316L austenitic stainless steel in cryogenic environments to enhance understanding of its fatigue performance and failure mechanisms over a wide temperature range. Uniaxial tensile and strain-controlled low-cycle fatigue tests were performed at 293 K, 173 K, and 77 K; microstructural evolution and damage mechanisms were explored via interrupted tests combined with multiple microscopic techniques and quantitative martensite analysis. The results show that the room temperature fatigue stress response has three stages, while low temperatures induce continuous cyclic hardening that stabilizes quickly; fatigue life increases with lower temperature and strain amplitude, more notably at high strains. Low temperatures enhance strength, increase hardness, slightly reduce plasticity, but maintain good toughness, suppressing crack initiation and propagation with ductile fracture. The findings clarify cryogenic fatigue damage mechanisms, providing experimental and theoretical support for cryogenic pressure-bearing component design and safety assessment. Full article

The influence of tempering temperature within the range of 520 °C to 640 °C on the microstructure and mechanical properties of 04Cr13Ni5Mo maraging stainless steel was systematically studied. The evolution of crystallographic orientation information, such as phase ratio and grain boundary ratio of the studied steel at different tempering temperatures, was studied by utilizing the electron backscatter diffraction (EBSD) technique. Furthermore, the element distribution at typical tempering temperatures was quantitatively analyzed by utilizing the electron probe microanalysis (EPMA) technique. Results indicated that the microstructure of the studied steel at different tempering temperatures is mainly composed of tempered sorbite. As the tempering temperature increased from 520 °C to 640 °C, the proportion of low-angle grain boundaries gradually increased while the proportion of large-angle grain boundaries decreased. The content of reversed austenite showed a sharp increase with the elevation of tempering temperature and peaked at approximately 9.0% at a tempering temperature of 640 °C. With the tempering temperature increasing from 520 °C to 640 °C, the strength of the studied steel showed a trend of first decreasing, then stabilizing, and then decreasing again, while the plasticity showed a stable upward trend. When the tempering temperature was 610 °C, the strength, plasticity, and toughness of the studied steel achieved the optimal match. The enrichment of the Ni element during the austenite reverse phase transformation process was confirmed as the predominant factor ensuring the stability of the reverse austenite to room temperature. Full article

Wire drawing is a key processing method for producing ultrahigh-strength stainless steel wires. In metastable austenitic steels, the strain-induced martensitic transformation is known to govern strain hardening. However, the transformation mechanism and kinetics behavior under wire drawing remain unclear due to the distinct deformation conditions compared to those of conventional loading modes. In this work, the microstructural evolution, transformation kinetics and strengthening behavior of the 304 stainless steel during cold wire drawing are systematically analyzed. The results show that the transformation is dominated by the austenite → twin→ α′-martensite pathway, with the ε-martensite effectively suppressed. The martensite fraction follows a sigmoidal evolution with the equivalent drawing strain and could be well described by the Olson–Cohen model. The yield strength is increased from 320 MPa to 2 GPa and exhibits a linear relationship with the martensite fraction, indicating a dominant composite strengthening mechanism. These findings clarify the deformation-mode-dependent transformation mechanism and its role in governing mechanical properties during wire drawing. Full article

This study investigates in situ methodologies for enhancing austenite formation in Laser Powder Bed Fusion (LPBF)-processed Super Duplex Stainless Steel (SDSS), aiming to eliminate the requirement for post-process heat treatments. The evaluated approaches included layer remelting, increased layer thickness (from 40 μm to 80 μm), and chemical modification by blending SDSS with Stainless Steel SS316L at a 50/50 weight ratio. Microstructural characterization and macro-hardness testing were conducted, complemented by nanoindentation analyses to assess the local mechanical response of the austenite and ferrite phases in samples exhibiting the highest austenite content. The findings indicate that neither layer remelting nor increased layer thickness alone substantially elevated austenite content; the as-built microstructure remained predominantly ferritic under these conditions. In contrast, compositional adjustment through SS316L powder blending yielded a significant increase in austenite, resulting in a duplex microstructure. These compositional changes and the resulting phase balance were associated with a reduction in macro-hardness relative to the ferritic microstructures. Nanoindentation results showed comparable nanomechanical properties in both phases, suggesting that the decreased macro-hardness in the duplex microstructure is primarily attributable to changes in chemical composition and diminished solid-solution strengthening, rather than the increased austenite fraction itself. These results highlight the limitations of thermal strategies alone in achieving phase balance in LPBF-processed SDSS and demonstrate the effectiveness of compositional tuning in promoting favorable duplex microstructures. Full article

This study investigates the performance of tangential turning in machining two industrially relevant materials, 42CrMo4 low-alloy steel and X5CrNi18-10 austenitic stainless steel. A full factorial experimental design was employed to evaluate the effects of cutting speed, feed, and depth of cut on cutting force components, areal surface roughness parameters, and derived performance indicators. Regression models were developed to describe the relationships between process parameters and machining responses, resulting high coefficients of determination (0.935–0.996 for force components and 0.869–0.961 for surface parameters). Response surface analysis revealed that feed and depth of cut dominate cutting force behavior, while feed and cutting speed primarily influence surface roughness. Material-dependent differences were clearly observed. 42CrMo4 exhibited 10–30% higher cutting forces and higher roughness values, while X5CrNi18-10 showed lower forces but more variable surface characteristics due to strain hardening effects. Pareto front analysis demonstrated that 42CrMo4 enables simultaneous improvement of productivity and surface quality, whereas X5CrNi18-10 shows weaker coupling between these objectives. A composite sustainability index was introduced to integrate mechanical load, productivity, efficiency, and surface integrity. The results indicate that optimal conditions for 42CrMo4 reduce the sustainability index by up to 65%, while X5CrNi18-10 exhibits 20–40% higher index values under comparable conditions. The study highlights the importance of material-dependent analysis and multi-objective optimization for sustainable machining of advanced materials. Full article

Hot-rolled A283 Gr C carbon steel/A240 TP 316L stainless steel-clad plates are widely used in structural applications. However, the hot-rolling process introduces residual stresses and microstructural heterogeneities near the interface, which can adversely affect mechanical performance. This study aims to optimize stress-relief annealing parameters for hot-rolled A283 Gr C/A240 TP 316L-clad steel in order to enhance toughness while preserving microstructural integrity. A Taguchi experimental design based on an L9 orthogonal array was employed to evaluate the effects of holding temperature, holding time, and heating/cooling velocity on Charpy impact toughness. Signal-to-noise (S/N) ratio analysis and ANOVA were used to identify the most influential parameters. Microstructural observations, microhardness profiling, and Charpy impact testing were conducted before and after heat treatment. The results indicate that stress-relief annealing does not alter the base microstructures of either the carbon steel substrate or the austenitic stainless steel-clad layer, nor does it induce carbide precipitation or secondary phase formation in the A240 TP 316L stainless steel. A noticeable reduction in the thickness of the decarburized ferrite zone near the interface was observed, suggesting improved interfacial stability. Microhardness measurements revealed a moderate decrease in hardness near the interface, accompanied by a significant increase in Charpy impact toughness under optimized conditions. ANOVA results show that holding temperature is the dominant factor influencing toughness, followed by heating/cooling velocity, while holding time has a minor effect. The optimal stress-relief annealing conditions were identified as 550 °C for 45 min, with a heating/cooling velocity of 100 °C/h. These findings demonstrate that the Taguchi method is an effective approach for optimizing heat treatment parameters and improving the mechanical integrity of hot-rolled stainless steel-clad plates. Full article

Wire Arc Additive Manufacturing (WAAM) has emerged as a cost-effective and high-deposition-rate technique for fabricating large-scale metallic components; however, the complex thermal history inherent to the process leads to heterogeneous microstructures that can significantly influence tribological performance. In this study, the dry sliding wear behavior of WAAM-fabricated austenitic stainless steel 308L (SS308L) was systematically investigated using a pin-on-disk configuration. The influence of applied normal load (1.5–15 N) and sliding speed (0.03–0.229 m/s) on wear volume, specific wear rate, coefficient of friction (COF), and tangential force was evaluated. Optical microstructural observations indicated features consistent with a ferritic–austenitic solidification structure, including regions resembling polygonal ferrite, Widmanstätten ferrite, and austenitic dendritic morphologies. Wear results showed that wear volume and cross-sectional area increased monotonically with increasing load, while the effect of sliding speed was comparatively less significant. The specific wear rate remained on the order of 10⁻⁴ mm³/N·m with minor variations across test conditions. The COF decreased with increasing load up to 10 N, followed by a speed-dependent response at higher loads. The findings demonstrate that load is the dominant factor governing wear behavior in WAAM SS308L, while microstructural heterogeneity may contribute to frictional stability and wear resistance. This study provides valuable insight into the structure–tribology relationship of WAAM stainless steels and supports the optimization of process parameters for wear-critical applications. Full article

This article presents a new combined post-processing concept to improve the quality of laser powder bed fusion (LPBF) of 17-4PH stainless steel (SS) cylindrical parts fabricated from N₂-atomised LaserForm 17-4PH (B) powder. The concept is based on consecutive heat treatment procedures and diamond burnishing (DB) processes. A two-stage study was conducted. The first stage was an LPBF process experiment. The following combination of LPBF parameter values was selected after optimisation: a laser power of $\mathrm{P}=150 \mathrm{W}$, laser scanning speed of v = 1200 mm/s, and layer thickness of $\mathrm{t}=40 \mathsf{\mu }\mathrm{m}$. In the second stage, this combination was used to evaluate the effects of two heat treatment procedures (HT1 and HT2) and two DB processes (using burnishing forces of 100 N and 300 N) on the tensile properties and surface integrity of LPBF 17-4PH SS cylindrical samples. The HT2 procedure, including annealing $({1200}^{\circ }$, $4 \mathrm{h})$, solution treatment (${1060}^{\circ }$, $1 \mathrm{h})$, cooling (${-70 }^{\circ }\mathrm{C},2 \mathrm{h}$), and ageing (${482}^{\circ }$, $4 \mathrm{h}$) led to yield limit, tensile strength, and Vickers hardness values of $\mathrm{Y}\mathrm{L}=1071 \mathrm{M}\mathrm{P}\mathrm{a}$, $\mathrm{T}\mathrm{S}=1410 \mathrm{M}\mathrm{P}\mathrm{a}$, and $523 \mathrm{H}\mathrm{V},$ respectively. The concept presented takes advantage of the combination of the transformation, precipitation and strain-hardening effects. The combined effect was most pronounced in the samples subjected to the HT2 procedure and subsequent DB (300 N), for which a retained austenite fraction of 6.93%, surface microhardness of ${563 \mathrm{H}\mathrm{V}}_{0.05}$ and the maximum values of the compressive axial and hoop RSs of $-1426.3 \mathrm{M}\mathrm{P}\mathrm{a}$ and $-1095.9 \mathrm{M}\mathrm{P}\mathrm{a}$, respectively, were measured. Full article

This study examines the microstructural characteristics and tensile properties of autogenous orbital gas tungsten arc (GTA) circumferential butt welds produced on commercially rolled 304 stainless steel seam pipes (outer diameter 38.1 mm, wall thickness 2.0 mm) for high-purity fluid distribution systems. A three-segment current profile was employed using an AMI 8-4000 orbital system, with peak currents of 70, 67, and 65 A for the penetration, remelting, and downslope (crater-fill) segments, respectively, under high-purity Ar (99.999%) shielding with back purging. Electron backscatter diffraction (EBSD) analysis, including image quality (IQ), inverse pole figure (IPF), and kernel average misorientation (KAM) mapping, showed that the weld metal consists of epitaxially grown columnar austenite grains strongly oriented along the solidification direction, whereas the heat-affected zone (HAZ) exhibits finer equiaxed grains with an increased Σ3 twin boundary fraction and elevated low-angle boundary fraction, indicative of partial recrystallization. Only sparse, discontinuous δ-ferrite stringers were detected in the fusion zone, and no non-metallic inclusions were observed on fracture surfaces, supporting the weld metal’s suitability for semiconductor-grade cleanliness. Vickers microhardness profiles revealed modest hardness differences (typically within 10–20 HV) between the weld metal, HAZ, and base metal, with no pronounced HAZ softening. Cross-weld tensile tests conducted in accordance with ASTM E8/E8M-22 yielded yield strengths above 200 MPa, ultimate tensile strengths of 650–680 MPa, and total elongations approaching 40%, comparable to the as-received pipe. Scanning electron fractography confirmed fully ductile failure via microvoid coalescence without evidence of cleavage, intergranular decohesion, or weld-defect-induced embrittlement. Collectively, these results demonstrate that the three-segment autogenous orbital GTAW procedure produces structurally sound, particle-clean joints suitable for 304 stainless steel seam pipes used in high-purity industrial piping. Full article

Dual beam laser welding of UNS S32750 superduplex stainless steel was performed to investigate the effect of beam-power distribution on microstructure and mechanical properties. Plates with a thickness of 3 mm were welded at a constant total power and travel speed using leading and lagging power splits of 50:50, 80:20, and 65:35. The heat affected zone width was metallographically estimated at approximately 100 µm for all conditions, consistent with comparable gross thermal exposure under constant nominal linear energy input (P_total/v). A slight modification to the power distribution altered the solidification texture and austenite morphology. The 50:50 configuration produced a refined ferritic matrix with a continuous network of grain boundaries, Widmanstätten, and intragranular acicular austenite. The 80:20 condition increased ferrite path continuity, while the 65:35 split produced an intermediate morphology. Vickers hardness reached a maximum for the 80:20 split (HAZ: 345 HV; weld metal: 349 HV). Ultimate tensile strength remained statistically constant between 908 MPa and 914 MPa, whereas elongation decreased from 28% at 50:50 to 24% at 80:20 and 23% at 65:35. All welds exhibited ductile fracture with microvoid coalescence, and electrochemical performance was comparable, with critical pitting temperature values between 78 °C and 91 °C. Beam power distribution primarily affects solidification morphology and enables control of the hardness-to-ductility balance, with a 50:50 split providing the most favorable combination of properties. Full article

In this study, 310S austenitic stainless-steel was welded using a laser with varying amounts of Nb to systematically investigate the effect of Nb on solidification cracking susceptibility, mechanical properties, and corrosion resistance of the weld. Under the present experimental conditions, the critical restraint width was higher for the 0.58 wt.% Nb and 1.45 wt.% Nb welds than for the Nb-free and 2.3 wt.% Nb welds, indicating that Nb addition affected the solidification cracking response of the weld. At low-to-moderate Nb contents, Nb can aggravate compositional segregation and increase the presence of low-melting-point liquid films, thereby increasing cracking susceptibility. At higher Nb contents, the reduced cracking susceptibility was accompanied by microstructural refinement and changes in the distribution of Nb-rich constituents during solidification. With increasing Nb content, the number of precipitated phases in the weld increases, mainly distributed at the austenite grain boundaries in granular, elongated, and chain-like forms. The introduction of Nb generally increases the microhardness and tensile strength of the welded joint, attributed to grain refinement strengthening and solid-solution strengthening. The reduction in area first increased and then decreased, suggesting that excessive Nb addition may reduce ductility because of the increased amount of grain-boundary precipitates and local strengthening heterogeneity. With increasing Nb content, the Ir/Ia ratio decreased from 67.6% to 52.2%, suggesting improved intergranular corrosion resistance. This improvement is likely related to the preferential reaction of Nb with carbon, which may suppress the formation of Cr-depleted zones at grain boundaries. Overall, Nb addition improved the corrosion resistance and increased the hardness and tensile strength of the weld; however, its effect on solidification cracking susceptibility was non-monotonic, indicating that careful control of Nb content is required to balance cracking susceptibility, mechanical properties, and corrosion resistance. Full article

This study establishes an integrated qualification workflow combining mechanical testing, microstructural characterization, and statistically defined eddy current testing (ECT) on the same material heats to provide a coherent and traceable material qualification methodology. Forged 316 and rolled 304L were fully annealed and subsequently subjected to a 700 °C/1 h low-temperature stress-relief (recovery) treatment. Room-temperature tensile testing and Charpy impact testing at room and cryogenic temperatures were performed alongside optical and electron microscopy to quantify grain size, δ-ferrite content, and representative fracture morphology under the investigated conditions. ECT responses were evaluated using a statistically defined threshold (T = μ + 3σ) as a decision criterion for indication screening under assumed noise conditions and calibrated near-surface inspection sensitivity. The tested specimens showed stable measured mechanical responses, the examined fracture surfaces were consistent with predominantly ductile fracture behavior, and no reportable ECT indications were observed above the adopted threshold. The proposed framework provides a reproducible and scalable strategy for reducing uncertainty in material qualification and strengthening integration between destructive and non-destructive evaluation in stainless steel applications. Full article