Stainless Steel Structures Research Articles

The effect of boron on the properties and structure of austenitic stainless steels

The effect of boron on the properties and structure of austenitic stainless steels

Mechanical and Corrosion Behaviour in Simulated Body Fluid of As-Fabricated 3D Porous L-PBF 316L Stainless Steel Structures for Biomedical Implants.

Laser powder bed fusion (L-PBF) is one of the most promising additive manufacturing technologies for creating customised 316L Stainless Steel (SS) implants with biomimetic characteristics, controlled porosity, and optimal structural and functional properties. However, the behaviour of as-fabricated 3D 316L SS structures without any surface finishing in environments that simulate body fluids remains largely unknown. To address this knowledge gap, the present study investigates the surface characteristics, the internal porosity, the corrosion in simulated body fluid (SBF), and the mechanical properties of as-fabricated 316L SS structures manufactured by L-PBF with rhombitruncated cuboctahedron (RTCO) unit cells with two distinct relative densities (10 and 35%). The microstructural analysis confirmed that the RTCO structure has a pure austenitic phase with a roughness of ~20 µm and a fine cellular morphology. The micro-CT revealed the presence of keyholes and a lack of fusion pores in both RTCO structures. Despite the difference in the internal porosity, the mechanical properties of both structures remain within the range of bone tissue and in line with the Gibson and Ashby model. Additionally, the as-fabricated RTCO structures demonstrated passive corrosion behaviour in the SBF solution. Thus, as-fabricated porous structures are promising biomaterials for implants due to their suitable surface roughness, mechanical properties, and corrosion resistance, facilitating bone tissue growth.

A new plastic global analysis approach for the fire design of steel and stainless steel structures

The new generation of structural codes for stainless steel allow carrying out global plastic analyses on certain types of stainless steel structures with plastic cross-sections at room temperature if the joints conforming the structure are classified as full-strength joints, a capability that has been long recognised for carbon steel structures. However, the requirements for the fire design of carbon and stainless steel structures in current and upcoming European design standards are still primarily based on the resistance of individual members, disregarding the redistribution of internal forces and strain hardening effects. Recent studies have proven that carbon and stainless steel frames with plastic cross-sections and full-strength joints are capable of redistributing internal forces at elevated temperatures, and failed describing global plastic collapse mechanisms under fire situation, suggesting that system effects are also relevant at elevated temperatures and could be taken into account for more efficient designs. On this basis, this paper develops an extensive numerical study focused on carbon and stainless steel frames under fire situation, and proposes a new methodology based on plastic global analysis to estimate the resistance of such structures under fire situation accounting for their redistribution capacity, improving the accuracy of the predicted fire time resistances significantly for the two materials.

Investigation of pitting corrosion of 304L stainless steel in algerian manufacturing

Stainless steel structures are subjected to gradual deterioration of their fundamental qualities when subjected to both mechanical stress and harsh conditions. The objective of this work is to examine the influence of tension-induced cold deformation on the localized roughness corrosion of 304L steel in a 3% NaCl solution, which mimics the conditions of saltwater. The samples underwent corrosion testing using standardized and deformed tensile specimens of algerian industrial manufacturing at different deformation rates: 2.18%, 3.63%, 10.90%, and 16.36%. The results, which encompassed corrosion susceptibility, pitting tendencies, and repassivation potentials, were compared and examined in relation to the deformation rate. The findings suggest that when the deformation rates increase, all of these potentials decrease, except for the roughness potential, which shows a considerable decrease. This decline indicates a reduction in the material's ability to resist corrosion. The main reasons why stainless-steel samples exposed to the phenomenon of corroded pits fail in Algerian industrial manufacturing are directly related to their resistance and strength characteristics, which in turn affect the mechanical behavior of 304L steel and its electrochemical behavior in aggressive solutions.

Understanding Stacking Fault Tetrahedron Formation in FCC Stainless Steel: A Fusion of Transmission Electron Microscopy, Molecular Dynamics, and Machine Learning

The stacking fault tetrahedron (SFT) formation displays a pronounced size effect, progressing from vacancy equilateral triangular plate to perfect SFT, and eventually to truncated SFT, as demonstrated in numerous irradiated face-centered cubic metals. However, the presence of distinct SFT structures in F321 stainless steel has not been reported. This study explored the SFT formation mechanism in irradiated F321 stainless steel using transmission electron microscopy (TEM), molecular dynamics (MD) simulations, and machine learning. SFTs, Frank loops, and Lomer-Cottrell locks were found to be widely generated in the irradiated F321 steel. The critical size for truncated and perfect SFTs was determined using MD simulations; the results were consistent with the theoretical predictions. Additionally, the twin boundaries observed through TEM, which were attributed to the elevated tensile stress near the boundaries, facilitated the formation of perfect SFTs. Moreover, interstitial Frank loops also facilitated the formation of perfect SFTs. This study also explored the influence of variations in Ni and Cr concentrations on the critical size n1 for the transition from vacancy plates to perfect SFTs and n2 for the transition from perfect SFTs to truncated SFTs, using a combination of MD and machine learning methods. As the Ni concentration increased and the Cr concentration decreased, n1 and n2 increased; conversely, the critical sizes decreased when the Ni concentration decreased and the Cr concentration increased. These insights reveal the systematic mechanism of SFT formation under varied conditions, offering new perspectives for understanding the nano-defects in F321 stainless steel.

Evaluation of the Mechanical Properties of Structural Stainless Steel Additive Manufactured by Powder Bed Fusion

Evaluation of the Mechanical Properties of Structural Stainless Steel Additive Manufactured by Powder Bed Fusion

Short Immobilization in a Sling Does Not Lead to Increased Salivary Cortisol Levels in Pigs

The goal of the present study was to evaluate the potential stress developed in farm hybrid pigs and miniature laboratory pigs briefly restrained in a sling, by measuring salivary cortisol levels. The study was performed in 20 healthy pigs grouped into three groups: group HYB-F: hybrid female pigs (n = 12), housed at the CREBA facility (Lleida, Spain); group MIN-F: Specipig® miniature female pigs (n = 4), housed at the CREBA facility; group MIN-M: Specipig® miniature male pigs (n = 4), housed at the Almirall facility (Barcelona, Spain). Upon arrival, the animals were enrolled in a social habituation and training program, which included habituation to a restraint sling. The sling was a stainless steel structure with a canvas hammock which had four openings for placing the animal’s feet. The assessment of stress levels in the sling was carried out by measuring cortisol levels in saliva samples. Five saliva samples were collected from each animal over 4 days: Sample 1 (basal sample): taken after animals perceived the presence of the technicians in the pen; Sample 2: taken after animals saw the sling in the pen; Sample 3: taken when animals were in the sling; Sample 4: taken 1 min after the previous one; Sample 5: taken after animals were released back on the floor. In group HYB-F, five animals (5/12) showed strong resistance and could not be restrained in the sling on at least one day. All animals in the groups of miniature pigs could be restrained on all the days. Within each group, the manipulation phase did not affect salivary cortisol levels. Likewise, salivary cortisol levels did not change significantly across days in either group. In conclusion, salivary cortisol levels did not increase when pigs were lifted and briefly restrained in the sling, even though some of them (in particular, the hybrid pigs) showed apparent signs of stress. The lack of correlation between such apparent stress and salivary cortisol levels might be because the vocalizations and movements were not really signs of stress, but simply a way of releasing discomfort, learned in the process of socialization and habituation. In light of this unexpected conclusion, further studies are needed to collect other physiological and behavioral data to clarify what actually happens when pigs are restrained in a sling.

Non-invasive ultrasonic sensing of internal conditions on a partial full-scale spent nuclear fuel canister mock-up

The safe storage of spent nuclear fuel (SNF) in dry cask storage systems (DCSSs) is critical to the nuclear fuel cycle and the future of nuclear energy. A critical component of DCSSs is the SNF canister. The canister is a sealed stainless-steel structure, which is first vacuum dried and then backfilled with helium. The structural deterioration within a canister can be monitored through its internal gas properties. This monitoring serves as the driving force behind the non-invasive ultrasonic sensing approach in this paper. A major challenge in collecting gas-borne signals using ultrasonic sensing is the impedance mismatch between the stainless-steel canister and the helium gas inside. Only a small fraction of the ultrasonic signal makes its way from the transmitter to the receiver through the gas medium. In this paper, experimental studies on a partial full-scale canister mock-up were carried out to capture the gas-borne signals. Damping materials were applied on the outside, and blocking and unblocking tests were conducted to identify the gas-borne signal. The research results showed that the excitation frequency played an important role in maximizing the gas-borne signals. The gas-borne signal was successfully detected at around the theoretical time-of-flight (TOF) at 225 kHz. A high signal-to-noise ratio (SNR) was achieved in the measurements. Next, acoustic impedance matching (AIM) layers were added, and it was found that the gas signal energy was improved by 160.4% compared with that of no AIM layers. Subsequently, the relative humidity (RH) level and temperature of the gas were varied to simulate abnormal internal conditions of the canister. The non-invasive testing system demonstrated reliability and sensitivity in detecting gas temperature and RH variations. Theoretical calculations demonstrated the potential for detecting low-level xenon and air within an actual SNF canister filled with helium. Last, an active noise cancellation (ANC) method, previously developed by the authors, was verified on the canister mock-up for the first time. The results showed that the SNR of the gas signal was improved by 213.6% compared with that of no ANC.

Supportless lattice structure of 316L stainless steel fabricated by material extrusion additive manufacturing: Effect of relative density on physical, microstructural and mechanical behaviour

Studies on lattice structures fabricated by material extrusion additive manufacturing for metal, leveraging the advantages of additive manufacturing, are limited. In this work, by varying the number of unit cells, the effects of density on the macro- and microstructure, and on the physical and mechanical properties of 316L stainless steel fabricated by our in-house developed 316L metal-filled filament were investigated. Utilising our in-house developed 316L metal-filled filament, supportless octet-truss lattice specimens with relative density ranging from 16 % to 55 % were successfully fabricated. The relative density increased with the number of unit cells, compressive strength, Young's modulus, and energy absorption, consistent with the Gibson-Ashby's porous material model. Stretch-dominated behaviour was observed in the 2 × 2 × 2 and 3 × 3 × 3 unit cells, while the 4 × 4 × 4 and 5 × 5 × 5 units exhibited bending-dominated behaviour. The deformation behaviour was well simulated by finite element analysis with the core-shell structure. The successful fabrication of supportless lattice structures highlights their potential for manufacturing lightweight materials and their future application.

Superior thermal response of additive manufactured porous stainless steel with carbon nanotubes

The temperature rise in the battery cells during continuous operation leads to a thermal runaway that affects the life and performance of electric vehicles. For such reasons, heat sinks with high thermal conductivity will be of utmost importance in maintaining optimal operating temperatures. This paper presents the development of a 3D-printed SS 316L porous structure with carbon nanotubes coated on it through a chemical vapour deposition method to enhance thermal management. The carbon nanotubes (CNTs)-coated porous Stainless Steel (SS) structure showed enhanced thermal performance. It absorbed heat 7 % faster than the non-coated and dissipated heat 138 % more at a heat input of 36.5 W. For the fixed 120-second time, a temperature difference existed of 3.9 °C during heating and up to 4.4 °C during cooling. These results demonstrate that the CNT coating dramatically improves the thermal response of the porous SS structure. This original approach for integrating CNT coatings with 3D-printed porous SS structures opens up a potential avenue for the efficient design and manufacturing of a heat sink, thus increasing the reliability and durability of the battery systems in electric vehicles.

Multiscale characterization of the additive-manufacturing-induced cell structure in 316L stainless steel: A comparative study

Multiscale characterization of the additive-manufacturing-induced cell structure in 316L stainless steel: A comparative study

Investigating the influence of post-deposition heat treatment (PDHT) on the characteristic changes in wire arc additively manufactured 410 martensitic stainless steel thin-wall structure

Obtaining the desired material characteristics of an as-deposited martensitic stainless steel (MSS) structure fabricated by wire arc additive manufacturing (WAAM) is challenging due to several factors like inhomogeneity, precipitation, phase transition, etc. This investigation elucidates the impact of post-deposition heat treatment (PDHT) on the microstructural and mechanical properties of the WAAM-processed 410 MSS thin-wall structure and compares it with the as-deposited 410 thin-wall structure. The MSS thin-wall structure consists of retained austenite (γ), delta (δ) ferrite, martensite laths and Cr-rich M23C6 type carbide. The M23C6 volume fraction increases by up to 18 %, and the γ-phase fraction reduces by up to 40 % by applying PDHT. The PDHT process significantly changed the texture from {110}<011> to {001}<110>. The PDHT process increases the dislocation density (1.974 × 10−15 m−2) than the as-deposited condition (0.924 × 10−15 m−2). The total low energy boundary (LAGB+CSL) contribution of the as-deposited sample is 19.5 %, whereas the PDHT sample demonstrated a higher fraction of low energy boundaries of 32.4 %. The PDHT sample showed a much smaller distribution of grains with an average grain size of 11 μm compared to the as-deposited condition. The overall hardness increases from 468 HV to 487 HV after PDHT compared to the as-deposited condition with lower inhomogeneity across the build direction. The mean 0.2 % proof stress, ultimate tensile stress, and elongation of the PDHT sample increased by 17 %, 5 %, and 60 %, respectively, compared to the as-deposited sample.

Full-field measurements of the microstructure’s effect on the mechanical behaviour of a wire and arc additively manufactured duplex stainless steel

Wire and Arc Additive Manufacturing (WAAM) is particularly well suited to the fabrication of large-scale structural components. Its use for the deposition of Duplex Stainless Steel (DSS) structures is especially sought upon by the naval industry. Although additively manufactured materials usually come with heterogeneous microstructure, residual stresses, internal and surface defects that must not jeopardize the structural integrity of components. In this context, the present study aims to analyse the as-deposited microstructure of a WAAM DSS and its influence on the mechanical behaviour via mechanical field measurement using both Digital Image Correlation (DIC) and Thermoelastic Stress Analysis (TSA).

Chemical and UV Durability of Hydrophobic and Icephobic Surface Layers on Femtosecond Laser Structured Stainless Steel

Femtosecond laser processing significantly alters the surface structure and chemical composition, impacting its wetting properties. Post-treatments such as immersion in a hydrocarbon liquid (petrol) or storage in a vacuum can significantly reduce ice adhesion, making the surfaces interesting for anti-ice applications. This study investigates their durability against acetone, ethylene glycol, and UV radiation. The laser-structured surfaces were immersed in the respective liquids for up to 48 h. The results indicate limited durability of the superhydrophobic and icephobic layers when submerged in acetone and ethylene glycol, with more favorable results for petrol treatment than vacuum treatment. Similar results were obtained after 100 h of UV exposure, showing a decrease in superhydrophobic properties and an increase in ice adhesion. However, repeated vacuum treatments conducted after the chemical durability tests revealed the potential for partial recovery of the hydrophobic and icephobic properties. XPS analysis was performed throughout the experiments to evaluate changes in surface chemistry resulting from the post-laser treatments and the durability tests.

The Role of Dislocation Type in the Thermal Stability of Cellular Structures in Additively Manufactured Austenitic Stainless Steel.

The ultrafine cellular structure promotes the extraordinary mechanical performance of metals manufactured by laser powder-bed-fusion (L-PBF). An in-depth understanding of the mechanisms governing the thermal stability of such structures is crucial for designing reliable L-PBF components for high-temperature applications. Here, characterizations and 3D discrete dislocation dynamics simulations are performed to comprehensively understand the evolution of cellular structures in 316L stainless steel during annealing. The dominance of screw-type dislocation dipoles in the dislocation cells is reported. However, the majority of dislocations in sub-grain boundaries (SGBs) are geometrically necessary dislocations (GNDs) with varying types. The disparity in dislocation types can be attributed to the variation in local stacking fault energy (SFE) arising from chemical heterogeneity. The presence of screw-type dislocations facilitates the unpinning of dislocations from dislocation cells/SGBs, resulting in a high dislocation mobility. In contrast, the migration of SGBs with dominating edge-type GNDs requires collaborative motion of dislocations, leading to a sluggish migration rate and an enhanced thermal stability. This work emphasizes the significant role of dislocation type in the thermal stability of cellular structures. Furthermore, it sheds light on how to locally tune dislocation structures with desired dislocation types by adjusting local chemistry-dependent SFE and heat treatment.

Numerical Analysis of Stainless Steel of Crevice Corrosion Initiation Behavior with Varying External Potentials and Initial Crevice Gaps

The potential, current density, pH, and crevice profile distribution within the crevice structure of stainless steel in seawater were numerically analyzed. The crevice corrosion phenomena were mathematically modeled with the initial boundary value problem of diffusion and static electrical field, respectively. This initial boundary value problem was discretized using a finite difference method. The predicts of the crevice corrosion behaviors, set for various external potentials and initial crevice gaps, were classified into three categories: the pitting type, the active type, and no corrosion. The pitting type crevice corrosion was predicted to occur in conditions where the external potentials were noble and the initial crevice gaps were narrow. The active type crevice corrosion was predicted to occur in conditions where the external potentials were less noble and the initial crevice gaps were narrow. The range of external potential conditions where crevice corrosion was predicted not to occur increased in conditions with wide initial crevice gaps. Crevice corrosion was predicted to occur at all external potentials in conditions where the initial crevice gaps were 2 μm or less.

Constructing surface protective film of V-Se-O to promote zinc ion storage by surface oxygen implantation strategy

Interfacial chemical modification is an effective strategy to adjust the strong Coulombic ion-lattice interactions with high valence cations experienced by electrode materials, facilitating the reaction kinetic. In this paper, a simple and fast surface oxygen implantation strategy was designed to adjust the electronic structure of stainless steel (SS) supported vanadium diselenide (VSe2) nanosheets and form a surface protective film, which effectively accelerates the reaction kinetics of Zn2+ and extends the cycle life of the battery. It is demonstrated that the conductivity, pseudocapacitance and specific capacity can be tuned by selectively introducing oxygen species to the surface, which provides an important reference for the design of electrodes with controlled surface chemistry. Density functional theory (DFT) calculations also confirm that the electronic structure can be adjusted by surface oxygen injection strategy, which not only improves the conductivity, but also adjusts the adsorption energy, thus providing favorable conditions for zinc ion storage. Benefiting from the selenium vacancies and pores generated by the removal of part of selenium, and the oxide film formed on the surfaces, the VSe2-xOx-SS-30 electrode showed higher specific capacity (188.4 mAh/g at 0.5 A g−1 after 50 cycles), better rate performance (107.1 mAh/g at 4 A g−1) and more satisfactory cycling stability (83.1 mAh/g at 5 A g−1 after 1800 cycles) than VSe2-SS electrode. Importantly, the flexible quasi-solid-state VSe2-xOx-SS-30//Zn battery also exhibits high specific capacity and excellent environmental adaptability. Furthermore, the zinc (de)intercalation and transformation reactions mechanism was revealed by some ex-situ/in-situ techniques.

Impact of nuclear heating distribution on the structural behavior of ITER first wall panel 11

The ITER blanket system safeguards the Tokamak's Vacuum Vessel and ex-vessel components from thermal and nuclear loads induced by the plasma. It comprises two parts: the First Wall panel facing the plasma and the Shield Block that provides the bulk of the shielding. The First Wall panels consist of Beryllium tiles on a CuCrZr layer, supported by stainless-steel structures which are cooled using a pressurized water circuit at 40 bar with an inlet temperature of 70 °C.Fusion for Energy has updated the thermal and mechanical analyses of ITER First Wall Panel 11 in preparation for the serial manufacturing. The panel will face heat flux up to 2 MW/m2 from plasma radiation, in addition to the volumetric nuclear heating, and the electromagnetic loads. A model with an enhanced detailed 3D geometry and heterogeneous materials indicates a 25% reduction of the deposited heating compared to the previous 2D model, from 625.4 kW (2D) to 455.4 kW (3D).The study embraces numerous thermal and mechanical analyses using Ansys software v19.2, incorporating 2D and 3D nuclear heating data. Responses are then compared and thus the possible impact of the two distributions on the thermal and mechanical behavior of the Fist Wall Panel 11 is assessed.

Effect of interlayer thickness and gap distance on vaporizing foil actuator welding of 5A06 aluminium alloy and 321 stainless steel

The composite structure of aluminium alloy and stainless steel provides a wide range of comprehensive advantages, encompassing properties such as lightweight, high strength, and corrosion resistance. These advantages make composite structure particularly suitable for various applications in industries such as transportation and chemicals. One innovative solid-phase welding technology that is well suited for joining dissimilar materials is vaporizing foil actuator welding. This technology allows for the welding of composite structures made of aluminium and stainless steel, despite the significant differences in physical and chemical properties. To enhance the vaporizing welding process, this paper proposes the introduction of an interlayer between the dissimilar materials. The interlayer consists of a third material that is added to bridge the gap between materials with differing hardness and plasticity. The main objective of introducing the interlayer is to minimise performance disparities and reduce the formation of intermetallic compounds at the interface. By examining the vaporizing foil actuator welding process of aluminium alloy and stainless steel with the interlayer, it aims to analyse the characteristics of the interface morphology. Additionally, this study investigates the energy conversion mechanism of the aluminium foil gasification process and explore the influence of the interlayer on the microstructure and mechanical properties of the interface between aluminium alloy and stainless-steel joints.

Classification and ultimate capacity of duplex stainless steel H-section under cyclic loading

Stainless steel materials are high ductility and strain hardening under cyclic loading, which is promising in seismic design. However, the current European stainless steel structure design code prEN 1993-1-4(EC3) ignores this favorable effect in the cross-section classification, as well as the lack of prediction formulas for the ultimate capacity of H-section under cyclic loading. In this paper, parametric analysis was carried out for H-section to extend the database based on the existing test results after calibration of the finite element model. The cross-section classification criteria of duplex stainless steel beams and beam-columns around major-axis under cyclic loading were investigated, and the EC3 classification of stainless steel H-section was evaluated. The predicted results for EC3 are conservative due to not considering the constraints of the cross-section component plates and the favorable conditions for the material strengthening of stainless steel under cyclic loading. Based on this, classification criteria for stainless steel H-section under cyclic loading were proposed and summarized. Subsequently, the method of calculating the ultimate capacity methods under cyclic loading suggested by EC3, Chen and Zhou et al. were evaluated. The results show that EC3 is on the conservative side, with actual results being generally 1.5 times higher than the predictions. In contrast, Chen and Zhou et al.'s method is on the unsafe side of the prediction. Finally, improvement suggestions are given for EC3 and the continuous strength method by considering the over-strength factor under cyclic loading, respectively, with results exhibiting high accuracy.