Austenitic Stainless Steel Plates Research Articles

A new experimental methodology for investigating the impact of subsequent welding passes on the properties of the austenitic stainless clad steel plates welded joint: part I – a substrate case study

In this study, the influence of the applying repeated thermal cycling during welding on the microstructural transformations and mechanical properties in Austenitic Stainless Clad-Steel Plates (ASCSP) has been investigated, particularly in the substrate. For this purpose, a novel methodology was used, by filling the entire groove length and gradually shortening the subsequent passes. Afterwards, microstructural characterization of different zones in the welded joint was conducted using optical microscope. Results showed a decrease in acicular ferrite (AF) in the Weld Metal Substrate (WM-S) from the root pass (10 kJ/cm) to the second pass (13.5 kJ/cm). This decrease continued until a total disappearance by the third pass due to a heat input of 17.8 kJ/cm. Vickers micro-hardness test was used to investigate the effect of the subsequent passes on the mechanical properties of the joint. Micro-hardness examination confirms the metallurgical results. It was revealed that micro-hardness variations are influenced by AF percentage and pro-eutectoid ferrite levels.

Behavior of wire arc additively manufactured 316L austenitic stainless steel single shear bolted connections

This paper aims to investigate the behavior of single shear bolted connections made of wire arc additively manufactured 316L austenitic stainless steel. A set of 44 wire arc additive manufacturing (WAAM) 316L austenitic stainless steel single shear bolted connections were included with consideration of various bolt positions, surface conditions and loading orientations respective to the printing layer direction. The geometric dimensions of the WAAM austenitic stainless steel plates were measured with the assistance of non-contact 3D laser scanning prior to tensile testing. Monotonic tensile tests were carried out to investigate the load-deformation responses, failure patterns and resistances determined by both the deformation and strength criteria of the single shear bolted connections. The effects of geometric and printing parameters on the single shear bolted connections were analyzed. Due to the absence of codified design provisions for WAAM austenitic stainless steel bolted connections, the suitability of the existing design rules originally developed for traditionally manufactured carbon steel and stainless steel bolted connections was examined. Design resistances calculated by the Eurocode 3 (prEN 1993-1-8 and prEN 1993-1-4), the American Specification (ANSI/AISC 370-21) as well as the prevalent design recommendations proposed in existing literature were compared with the obtained experimental results. It is shown that the abovementioned design methods offer conservative predictions for the resistances of WAAM 316L austenitic stainless steel single shear bolted connections. Further study is needed to improve the accuracy of design resistance predictions.

Development of Hot-Wire Laser Additive Manufacturing for Dissimilar Materials of Stainless Steel/Aluminum Alloys

The formation of brittle intermetallic compounds (IMCs) at the interface between dissimilar materials causes considerable problems. In this study, a multi-material additive manufacturing technique that employs a diode laser and the hot-wire method was developed for stainless steel/aluminum alloys. An Al-Mg aluminum alloy filler wire (JIS 5183-WY) was fed on an austenitic stainless-steel plate (JIS SUS304) while varying the laser power and process speed and using paste-type flux and flux-cored wire. The effects of laser power and process speed on phenomena during manufacturing and IMC formation were investigated. Finally, the wall-type multilayer specimens were fabricated under optimized conditions. The suppression of IMC formation to a thickness of less than 2 μm was achieved in the specimens, along with a high interfacial strength of over 120 MPa on average.

Surface modification strategies of 304 austenitic stainless steel plate with different micromorphology and composition for improved mechanical interlocking and chemical bonding in metal–epoxy joints

304 austenitic stainless-steel (SS) strip-based carbon fiber metal laminates (CFMLs) have raised significant concerns, in terms of their mechanical performance. On top of that, the hybrid laminates’ interlamination performance is vital in regulating their failure patterns. Along these lines, in this work, SS strips with regulatable micromorphology and composition were obtained by using physical and chemical surface modification strategies, including polishing, acid etching, anodization, and thermal treatment. The shear strength of the treated-SS/epoxy single lap joints (two treated-SS strips bonded by the epoxy resin via hot curing process) was systematically explored, and the origins of the enhancement mechanism were attributed to the resulting surface microstructure, as well as the possible chemical reactions between the treated surface and the curing agent. The etching-anodizing-thermally treated-SS (EAT-SS)/epoxy joint exhibited the maximum shear strength (16.04 MPa) and work of fracture (5.85 kJ·m−2) due to the substantial cohesive failure pattern of the epoxy. The encouraging enhancement was mainly attributed to the synergistic effect of the micro-annular pit and the nanoporous array structure of the EAT-SS surface. These effects induced a significant mechanical interlock and a plausible chemical reaction at the interface, which led to improved bonding strength between the epoxy and treated-SS surface. Overall, in this work, it was demonstrated that the combination of the anodization and thermal treatment can effectively improve the interlamination bonding properties between the SS strip and the epoxy resin due to the combination effect of mechanical interlocking and chemical bonding.

Effect of welding electrode variation on microstructure and mechanical properties of AISI 204 stainless steel plates joined using shielded metal arc welding

The current study investigates the effect of some welding electrodes and post-weld heat treatment on the micro-structure, tensile strength, and hardness of austenitic stainless steel (AISI 204) weldments using the shielded metal arc welding (SMAW) technique. Four different electrode specifications were used in this study, these include stainless steel electrodes (E308L and E308L-16) and mild steel electrodes (E6013 and E7018). Samples of the austenitic stainless steel plate of 5 mm thickness were first sectioned and welded across the width using the four electrodes. Following the welding operations, a post-weld heat treatment was carried out at 1100 oC, soaked for 60 minutes, and then allowed to cool naturally in the open air. Both the heat-treated and the as-welded samples were then subjected to tensile and hardness tests. The hardness and ultimate tensile strength of the weldments with mild steel electrodes are higher than those of stainless-steel electrodes. However, heat treatment after the welding results in even higher hardness and ultimate tensile strength values for all the weldments except for the E6013 electrode. It is, therefore, not advisable to use inappropriate electrodes to weld austenitic stainless steel. Also, the high difference in mechanical properties between the weldments and the base metal will introduce stresses to the material, resulting in solidification cracking. The microstructures of the weldments show distinct dark and bright features, which indicates the depletion of elements like Cr in the steel.

Bayesian data fusion of eddy current testing for flaw characterization with uncertainty evaluation

This study proposed a data fusion method based on Bayesian estimation for flaw characterization using eddy current signals and evaluated its applicability using measured signals. The proposed method can fuse several measured data to define the likelihood function as multiplication of probabilistic distributions of eddy current signals and calculate posterior distribution based on the assumption that all signals are independent. Rectangular slits on austenitic stainless-steel plates were measured by plus-point and uniform eddy current probes with three frequencies: 50 kHz, 200 kHz, and 400 kHz. All combinations of probes and frequencies were utilized to estimate flaw size distribution. The results indicate that the proposed method can accurately evaluate the flaw size from the eddy current signals and probabilistically evaluate the error. Furthermore, variations in the importance of each data were found in the comparison of all combinations of probes and frequencies; therefore, the probabilistic sizing method could be used to determine the proper measurement conditions from the viewpoints of uncertainty of the evaluation.

Mitigating Stress Corrosion Cracking of 304L and 316L Laser Welds in a Salt Spray through Micro-Shot Peening

Two austenitic stainless steel (ASS) plates, 304L and 316L, were cold-rolled (304R and 316R) with a 10% reduction in thickness and then subjected to laser welding. Cold rolling caused slight surface hardening and introduced residual tensile stress into the ASS plates. The susceptibility to stress corrosion cracking (SCC) of the welds (304RW and 316RW) was determined using the U-bend test pieces in a salt spray. To highlight the stress concentration at the weld’s fusion boundary (FB), the top weld reinforcement was not ground off before bending. Moreover, micro-shot peening (MSP) was performed to mitigate the SCC of the welds by imposing high residual compressive stress and forming a fine-grained structure. Cold rolling increased the susceptibility of the 304R specimen to pitting corrosion and intergranular (IG) microcracking. Moreover, pitting corrosion and SCC were found more often at the FBs of the 304RW. The corrosion pits of the peened 304RW (304RWSP) were finer but greater in amount than the those of the un-peened one. The results also indicated that the 316L ASS welds with MSP were resistant to the incidence of pitting corrosion and SCC in a salt spray. The better reliability and longer service life of dry storage canisters could be achieved by using 316L ASS for the construction and application of MSP on it.

An experimental study on shear resistance of austenitic and duplex stainless steel plate girders with perforated webs

Stainless steel is increasingly being used in the field of engineering as building construction materials, as it has an inherent ability to resist corrosion, as well as other environmental benefits. When used as plate girders, web perforations are often required to accommodate building services. In the literature, no experimental study has been reported that investigates the shear resistance of austenitic and duplex stainless steel plate girders with perforated webs. This issue is addressed herein. A detailed experimental program is described comprising eight stainless steel plate girders. The plates are austenitic grade EN 1.4301 and duplex grade EN 1.4462, and the depth of web is fixed as 500 mm and 700 mm. For comparison, specimens with perforated webs and solid webs were tested. Prior to shear tests, the distribution of initial geometrical imperfections was determined through three-dimensional (3D) scanning. Finite element (FE) models incorporating the material non-linearity and initial geometric imperfections were then developed. The results of FE models were validated against the experimental results. Using the validated FE models, a parametric study comprising 182 FE models was then undertaken, and variables which were examined included local geometrical imperfections, aspect ratio, end conditions, hole ratio and stainless steel grades. The results suggested that for those members with a hole diameter - web height ratio of 0.6, the shear resistance was reduced by 52% on average due to the web perforation. The design rules given in Eurocodes, American Specification and those design recommendations proposed by Chen et al. (2023) were evaluated.

Study of contact melting of plate bundles by molten material in severe reactor accidents

In a severe reactor accident, a crust will form on the surface of the molten material during the core melting process. The crust will have a contact melting with the internal components of the reactor. In this paper, the contact melting process of the molten material on the austenitic stainless steel plate bundles is studied. The contact melting model of parabolic molten material on the plate bundles is proposed, and the rule and main effect factors of the contact melting are analyzed. The results show that the melting velocity is proportional to the slope of the paraboloid, the heat flux and the distance between two plates D. The influence of melt gravity and the plate width on melting velocity is negligible. The thickness of the molten liquid film is proportional to the heat flux and plate width, and it is inversely proportional to the gravity. With the increase of D, the liquid film thickness decreases at first and then increases gradually. The liquid film thickness has a minimum against D. When the width of the plate is small, the width of the plate is the main factor affecting the thickness of the liquid film. The parameters are coupled with each other. In a severe reactor accident, the wider internal components of reactor, which can increase the thickness of the melting liquid film and reduce the net input heat flux from the molten material to the components, are the effective measures to delay the melting process.

Detection of flaws in austenitic stainless steel plate using eddy current testing

This study proposes an eddy current testing (ECT) probe to detect flaws in finite thickness austenitic stainless-steel plates. In order to obtain the spatial magnetic field distribution and the detection sensitivity of the probe in different scanning directions, a 3D model of ECT is simulated. The detection ability of ECT probe is verified by experiment. To detect surface flaws and subsurface flaws, 2.0 kHz and 1.0 kHz are chosen as excitation frequencies respectively. In addition, the pick-up signal goes through the amplification circuit and the signal conditioning module to improve the signal-to-noise ratio. Finally, the experimental results are compared with those from numerical simulation. Both results show the ability of the probe to detect flaws in the austenitic stainless-steel plate.

Dissimilar Welding of AISI 304 and AISI 310 Steels Using Metal Inert Gas Welding

Thermal, mechanical and chemical properties decides the quality of welding dissimilar metals, as controlling of welding variables is difficult to achieve the desired output of weld joint. Welding of dissimilar metals is a difficult task, as one has to take care of the metallurgical changes taking place in both the metals due to heat produced during welding. Proper selection of welding variables plays an important role in obtaining sound weld joint. Austenitic stainless steel plates of AISI 304 and AISI 310 are welded by MIG welding. Three factors namely filler wire feed rate, welding current and edge included angle are taken as input variables of welding. Grain size and hardness are the output variables. Fifteen combinations of experiments are conducted by considering Box Benhken Design for three factors and three levels. The effect of welding variables on grain size and hardness of the welded joint was studied. The welding variables were optimised using Response optimizer for minimum grain size and maximum hardness of weld joint.

Microstructural Evolution and Mechanical Performance of Two Joints of Medium-Mn Stainless Steel with Low- and High-Alloyed Steels

In this work, 2 mm thick medium-Mn austenitic stainless steel (MMn-SS) plates were joined with austenitic NiCr stainless steel (NiCr-SS) and low-carbon steel (LCS) using the gas tungsten arc welding technique. A precise adjustment of the welding process parameters was conducted to achieve high-quality dissimilar joints of MMn-SS with NiCr-SS and LCS. The microstructural evolution was studied using laser scanning confocal and electron microscopes. Secondary electron imaging and electron backscatter diffraction (EBSD) techniques were intensively employed to analyze the fine features of the weld structures. The mechanical properties of the joints were evaluated by uniaxial tensile tests and micro-indentation hardness (HIT). The microstructure of the fusion zone (FZ) in the MMn-SS joints exhibited an austenitic matrix with a small fraction of δ-ferrite, ~6%. The tensile strength (TS) of the MMn-SS/NiCr-SS joint is significantly higher than that of the MMn-SS/LCS joint. For instance, the TSs of MMn-SS joints with NiCr-SS and LCS are 610 and 340 MPa, respectively. The tensile properties of MMn-SS/LCS joints are similar to those of BM LCS, since the deformation behavior and shape of the tensile flow curve for that joint are comparable with the flow curve of LCS. The HIT measurements show that the MMn-SS/NiCr-SS joint is significantly stronger than the MMn-SS/LCS joint since the HIT values are 2.18 and 1.85 GPa, respectively.

Local buckling behaviour of longitudinally stiffened stainless steel plate girders under combined bending and shear

This paper presents a comprehensive experimental and numerical investigation into the local buckling behaviour of longitudinally stiffened stainless steel plate girders under combined bending moment and shear force. Five plate girders configurated with longitudinal stiffeners with different geometrical proportions and vertical positions were fabricated from austenitic and duplex stainless steel plates. Initial geometric imperfections and material properties were measured, and all plate girders were tested to failure under a three-point loading configuration. The critical buckling strengths, ultimate capacities and failure modes were carefully analysed. Elaborate finite element (FE) models were developed and validated against the test results, and were then used to conduct parametric studies to generate further structural performance data over a wide range of cross-sectional properties, including various geometrical proportions and positions of longitudinal stiffeners, and loading combinations. The obtained test and FE results were utilised to assess the applicability of existing M–V interaction design methods in EN 1993-1-5 and that proposed by Jáger et al. for longitudinally stiffened plate girders. It was indicated that these two M–V interaction curves coupled with the design provisions in EN 1993-1-4 for determining the bending and shear endpoints, offer safe-sided predictions with a good level of consistency and accuracy, for longitudinally stiffened stainless steel plate girders under combined bending and shear. The reliability of these design approaches was further confirmed by statistical analysis.

Experimental-numerical study on ballistic impact behavior of 316L austenitic stainless steel plates against blunt and ogival projectiles

316L austenitic stainless steel (ASS) is the standard reference material in fabricating pressurized hydrogen storage tanks due to its low hydrogen embrittlement sensitivity and excellent corrosion resistance. Ballistic performance of such tanks is of course a concern of safety. In this study, ballistic impact behavior of 316L ASS was studied against blunt and ogival nose shaped projectiles within impact velocity range of 160.3–324.1 m/s. Ballistic impact behavior of 316L ASS is sensitive to nose shapes of projectiles. For targets against blunt projectile, shear plugging with ejected plugs is observed, and target deflection is limited; for targets against ogival projectile, failure mode is ductile hole enlargement, small bulge and some fragments are observed on front and rear sides of targets, respectively. Ballistic limit velocities (BLVs) for two projectiles are respectively 180.9 m/s and 333.5 m/s, indicating better energy absorption against ogival projectile. Numerical simulations of ballistic impact tests were carried out using either the Lode independent MJC or the Lode dependent modified Mohr-Coulomb (MMC) fracture criterion. Numerical prediction by the latter is more accurate than the former as ballistic impact tests are dominated by stress state where Lode parameter is strong enough to cause a big difference between MMC and MJC criteria, and fracture behavior is accurately predicted by the latter but overestimated by the former.

The effect of laser energy density on microstructural evolution and mechanical properties of laser clad 316L stainless steel for repair

Laser energy density can affect the powder forming state in laser metal deposition (LMD), ultimately altering the evolution pattern and mechanical properties of formed structures. This work uses high-speed LMD technology to repair the 316L austenitic stainless steel plate with a trapezoidal groove. By analyzing the microstructural evolution and mechanical properties of repaired specimens under different laser energy densities, we revealed the effects of density on LMD shaping. Results indicated that the microstructure in the repair zone developed alternately in forms of columnar, branch, and isometric crystals in the opposite direction of heat flow. Increased laser energy density could enlarge crystal grains in formed structures. Meanwhile, γ-Fe tended to transform into δ phase that was distributed among crystal grains in γ-Fe. When the density reached its peak, the number of the δ phase plummeted. The average microhardness of specimens first increased and then decreased in the repair zone, with its distribution fluctuating repeatedly, and the values in this zone were 1.5–1.7 times that of the substrate. The mechanical properties of repaired specimens were superior to those of the rolled steel substrate at room temperature, and these specimens' ultimate tensile strength (UTS) and elongation at this temperature were positively correlated with the laser energy density. There were dimples and typical cleavage patterns around the fracture of tensile specimens, indicating that the fracture mechanism at room temperature was of quasi-cleavage type. As the density rose, the UTS first increased and then reduced in a tensile test conducted at 500 °C, during which the strain kept growing. Simultaneously, numerous dimples with congregate micropores but without typical cleavage patterns were observed in the fracture, which revealed that all specimens exhibited ductile fracture at high temperatures.

Austenitic Stainless Steel I‐section Beam‐column Tests and Numerical Modelling

AbstractStainless steel became a relatively common material for load‐bearing structures in corrosive environment or when maintenance is difficult. The existing design rules cover all common cases. However, for some, the experimental or numerical data are very limited. This includes studies on welded I‐section beam‐columns. This paper presents a comprehensive experimental and numerical investigation into the structural performance of welded I‐section members loaded by compression and major axis bending moment. In total, eighteen test specimens were fabricated from grade EN 1.4301 austenitic stainless steel plates using two welding methods, namely conventional and laser welding. The experimental program on pin‐ended long beam‐columns is described in the paper. The loading eccentricities for the tests varied to provide a wide range of bending moment‐to‐axial load ratios. Nonlinear finite element models were developed in ABAQUS software and validated using the test results to simulate the beam‐column behaviour accurately.

Cyclic behaviour of diagonally stiffened stainless steel plate shear walls with two-side connections: Experiment, simulation and design

Stainless steel has good ductility and energy dissipation, which is very suitable for steel plate shear walls. However, there is no report on stainless steel plate shear walls. Therefore, based on a completed low cyclic loading test of 6 diagonally stiffened S30408 austenitic stainless steel plate shear walls, a refined finite element model of the test specimens is established using ABAQUS software. Then, a large number of parametric analyses are conducted mainly considering the influence of the aspect ratio α, height-thickness ratio λ, stiffness ratio of the periphery stiffener ηf and stiffness ratio of the diagonal stiffener ηs on the elastic buckling stress. A simplified formula for calculating the elastic buckling stress of diagonally stiffened stainless steel plate shear walls with two-side connections is proposed. Based on the experimental study, parametric analysis and theoretical derivation, a resilience model of diagonally stiffened stainless steel plate shear walls is proposed. Finally, to facilitate the engineering design, a simplified resilience model and design method of stainless steel plate shear walls are proposed. The research herein illustrates the differences of cyclic behaviour between stainless steel plate shear walls and other steel plate shear walls and provides an accurate design method for the first time.

Role of δ-ferrite in fatigue crack growth of AISI 316 austenitic stainless steel

FF sample (nearly free of δ-ferrite) and CF sample (containing ∼4% δ-ferrite) were prepared from the AISI 316 austenitic stainless steel plate to elucidate the role of δ-ferrite in the fatigue crack growth under the solution treated and accelerated aged conditions. It is found that the fatigue crack growth resistance of the CF sample is higher than the FF sample under the solution treated condition. However, a significant deterioration of the fatigue crack growth resistance is observed in the CF sample while little variation is found in the FF sample after accelerated aging treatment at 750 °C for 10 h. In the solution treated condition, deflected crack growth path is present when the main crack encounters the δ-ferrite in the CF sample due to the differences in the fatigue responses between austenite and δ-ferrite. The measured growth rate of the deflected crack is significantly slower than that of the flat crack of the same length. After the accelerated aging treatment, microcracks are produced at the M23C6/δ interface due to the strain incompatibility between M23C6 and retained δ-ferrite when the decomposed δ-ferrite is subject to plastic deformation in the crack tip plastic zone. The preexisting microcracks in the front of crack tip provide a viable path for crack propagation, resulting in the relatively flat crack path.

Al2O3 and TiO2 flux enabling activated tungsten inert gas welding of 304 austenitic stainless steel plates

Gas tungsten arc welding (GTAW) is important in those manufacturing where it is significant to control the mechanical and metallurgical characteristics and its weld bead geometry. This work has been committed to study the influence of oxide fluxes on welding of 4 mm thick 304 austenitic stainless steel plates. The Al2O3 and TiO2 were used as an oxide flux in powder form and are mixed with the acetone. The prepared mixture is applied on bead plate without any joint preparation and without filler wire addition. The Taguchi method with L9 orthogonal array is used to determine the optimal parameters. The current work aims to explore the influence of weld parameters on weld bead geometry (i.e. weld bead width, penetration and angular distortion), and mechanical & metallurgical characteristics for 304 stainless steel welds. The oxide flux seems to narrow the arc and thereby the current density increases at the anode spot, that results in high weld depth.

Friction stir welding of AISI 316LN high strength austenitic stainless steel for cryogenic application

Friction stir welding (FSW) is a solid state joining process that uses the heat generated by the friction of a rotating tool and the base material to join materials together. Due to the fact that the material is never melted, and that extensive plastic deformation is introduced in the weld seam, a unique set of properties is achieved. The technique has been extensively used to join aluminium and aluminium alloys, but very few developments are reported on high strength austenitic stainless steel, which is the material of choice for many high energy physics and fusion magnets. This paper contains a comprehensive microstructural and mechanical characterization, including at cryogenic temperature, of an 8 mm thick high strength austenitic stainless steel plates. The steel grade is the high alloy version of AISI 316LN (identified as 1.4429 or -X2CrNiMoN17-13-3 according to European standards). Special attention was given to cryogenic elastic – plastic J – integral testing of the weld seam. To the authors’ knowledge, this is the first time fracture toughness at cryogenic temperature on friction stir welded 1.4429 has been measured.