Search

The high temperature corrosion at 650°C in the presence of NaCl at atmospheric pressure of AISI 304L, AISI 309, AISI 310S, AISI 314 and AISI 321 austenitic stainless steel was studied. The specimens were cyclically heated in the furnace and immersed in a 3.5% aqueous NaCl solution after cooling for 15 min. After each cycle, the change in mass of the samples was measured. The corroded samples were analysed by SEM /EDX, and the corrosion products were analysed by XRD. The chloride ions react with the steel surface to form porous and poorly adherent oxides and metal chlorides. After the mass increase during the first exposure cycles, spalling of the oxides occurred. The high temperature austenitic stainless steels (AISI 309, AISI 310S, AISI 314) showed less mass loss than conventional austenitic steels (AISI 304L). Surprisingly, the stainless steel AISI 321 showed a similar low weight loss after the cyclic test as AISI 309, but a detailed analysis of the exposed surfaces after the test showed a similar corrosion attack as for AISI 304. After the cyclic test at high temperature in the presence of NaCl, a higher concentration of Cr and Ni definitely improves the corrosion resistance under the present conditions, but a certain addition of Si is even more obvious. Graphical Abstract

Arc welding is a widely applied process in the fabrication of stainless steel structures. Various difficulties may arise in joining of these steels, particularly if high heat input is used. The main aim of this study is to evaluate the influence of heat input on microstructure of the joint region and thus on the mechanical behavior of gas metal arc welded AISI 304 L austenitic plates. To this end, AISI 304 L plates with a thickness of 5 mm were butt-welded by employing two different heat input values. Detailed microstructural and mechanical characterization were carried out. In addition, the influence of heat input on the microstructure and joint performance values was also determined. The higher heat input resulted in a complete recrystallization at the heat affected zone whereas the base metal microstructure was maintained in the lower heat input joint. Both joints displayed strength matching within the weld region, thus exhibited slightly higher tensile strength than that of the base plate (102 %).

This paper reports failure of elbow from side cut piping after three years of refinery gasoil service and piping metallurgy was SS316L austenitic stainless steel. Systematic investigations including visual inspection coupled with laboratory studies were carried out to determine the cause of failure. The samples from failure location were examined for chemical analysis, hardness, fractography, elemental analysis and metallographic evaluation. Further, crude feedstock was evaluated as well. Various characterization studies concluded that presence of material defect encapsulated in elbow prior to start of initial distillation column (side cut piping) operation was the root cause of failure. Localized stresses induced from internal pressure act on remaining wall thickness have lead to brittle fracture and resulted in gasoil leakage. The existence of material defect in failed elbow prior to initial operation had revealed poor pre-commissioning inspection practice. The origination of detected material defect was discussed and similar leakages shall be avoided by defect free piping components provided with proper support system at critical piping locations. The results in this article intended for petroleum refinery piping/energy pipeline operators for use of qualified piping components at critical locations especially during plant/piping commissioning stage.

The pre-compressed CT technique was used to quantitatively investigate the formation of stress relaxation cracks under different tensile residual stresses and aging time in Super304H austenitic stainless steel weld metal. The statistical results revealed that intergranular cracks could occur within 2000 h under 650 °C when the residual stress was applied with greater than 18 KN pre-compression force. Detailed grain interior and boundary analyses showed that the growth of intragranular Cu-rich particles could induce a strong grain interior, and the intergranular Nb(C, N) carbides were one of the causes to crack under short-term aging time. For long-term aging time conditions, the intergranular M23C6 carbides were more susceptible to crack than intergranular Nb(C, N) carbides. Finally, the mechanism responsible for stress relaxation cracking formation was carefully illustrated for the weld metals after short-term aging and long-term aging, respectively.

This work presents a new approach based on the Crack Tip Opening Displacement (CTOD) for studying the fatigue crack growth. The plastic component of the CTOD is employed for predicting the crack propagation on austenitic stainless steel. This is in contrast to Linear Elastic Fracture Mechanics analysis based on the Stress Intensity Factor (SIF) (Ewalds and Wanhill 1984). The current method is also valid beyond Small Scale Yielding (Antunes et al. 2016)(Antunes et al. 2017a)(Borges et al. 2020) as it incorporates naturally the plasticity effects taking place at the crack tip (Lopez-Crespo et al. 2018). The approach is based on post-processing the full-field displacement information generated by Digital Image Correlation technique (Chernyatin et al. 2018). Such technique is used to monitor the crack advance throughout the test (Cruces et al. 2020). The post-processing procedure employed for extracting the plastic component of the CTOD is described in detail. The results on steel CT specimens appear very promising.

Erosion is a multifarious phenomenon and observed to be the major cause of failure of many engineering systems including aircraft engines, power generation units and industrial equipment. In the current study, erosion tests were carried out on SS-304 steel by utilizing an air jet erosion testing rig. The erosion behaviour of austenitic stainless steel (SS-304) at different temperatures (room temperature, 200 °C and 400 °C) was evaluated. The effect of impingement angle of erodent particles on erosion mechanism was also determined. It was observed that the erosion rate of steel was higher at room temperature and decreased gradually with increase in temperature up to 400 °C. The erosion rate was also observed to be high at oblique impact angle (30°) as compared to normal impact angle (90°) indicating the ductile mode of erosion. Further scanning electron microscopy with Energy Dispersive Spectroscopy (SEM-EDS) attachment was utilized for surface characterization of eroded samples. The eroded samples show the development of lips and craters which results in plastic deformation of material.

A remarkable elastic anisotropy in plates of austenitic stainless steel produced by the Wire and Arc Additive Manufacturing process is recently reported. The Young’s modulus depends on the angle of orientation with respect to the material deposition direction. Here, for the first time, this anisotropy is exploited to maximize structural stiffness by simultaneously optimizing the structural design layout and the local deposition path direction for WAAM. The results obtained indicate deposition that is commonly preferred along the load-path directions for WAAM is sub-optimal and stiffness can be increased at least 53 % upon optimizing the deposition directions.

WC-10Co4Cr cladding over an austenitic stainless steel (SS-316) was fabricated by using a cost- effective microwave technique. Cladding was performed with 1.20 kW power and a frequency of 2.45 GHz in an industrial microwave oven. The XRD surveillance reveals a cluster of carbide phases adjunct to W-Cr-Fe based hexagonal matrix. The SEM examination reveals a solid microstructure and a homogeneous reinforced skeleton with porosity measures of less than 1% in the clad specimen. Tungsten (W) distributed equally in matrix and carbides, resulting in bulk hardness and matrix micro hardness increasing gradually and reaching a peak at 750HV, respectively, which is significantly greater than the base metal (SS-316) hardness (about 220HV). The clads erosive wear was measured at various impact angles (30°, 60°, and 90°) by utilizing a solid particle erosion with alumina as the erodent. In addition, corrosion testing found that in the NaCl solution of 3.5 wt% the cladded specimen exhibited the less corrosion resistance than that of the base metal.

Efficient and cost effective utilization of WEDM process is a challenge for leading edge era of manufacturing because of the complex and non-linear behavior of the process. The current study focuses on an experimental inquiry carried out for WEDM of Nitronic-30 to obtain optimum process parameters for improved surface roughness (SR) and material removal rate (MRR), Nitronic-30 is austenitic stainless steel offers high strength with good corrosion resistant property which high potential in applications such as automotive parts, aqueous applications, solid handling equipment. Therefore, multi-response optimization of Nitronic-30 on WEDM is very essential. Experiments were carried out with Taguchi's DoE and a L9 orthogonal series, with machining parameters like pulse on time (Ton), pulse off time (Toff), and peak current (IP). Minitab-17 software was used to evaluate response variables such as material removal rate and surface roughness. Analysis of variance (ANOVA) and SN Ratio plot of GRG indicates that peak current is the most important parameter. Grey Relational Analysis (GRA) provides optimal process parameters like pulse on time 124 machine units, pulse off time 40 machine units and peak current 230A for optimal response variables as 4.019 µm SR and 8.683 mm3/min MRR.

The effect of different types of cleaning solutions (neutral, acidic, and alkaline) on the corrosion of AISI 304 stainless steel were studied. The corrosion resistance was observed based on an accelerated immersion process simulating the pattern of steel corrosion over time at room temperature. A potentiodynamic polarization technique was conducted to estimate general corrosion rates. Various electrochemical parameters including potential corrosion (Ecorr), corrosion current density (icorr) and Tafel slopes were analyzed and discussed. The corrosion products after the immersion process were observed by using an optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The results indicated that there was different corrosion resistance for cleaning solutions with different pH value. The CS-E sample showed the best corrosion resistance due to its alkaline condition. The CS-I sample had the highest corrosion rate due to a decrease in the repassivation of the pit.

Cast austenitic stainless steel grade CF8C of ASTM A351 possesses varying degrees of suitability for services both at high temperatures and in corrosive environments. CF8C contain Nb of 1% max as per ASTM A351, i.e. 8 times the carbon content. Unlike CF8M and CF3M of ASTM A351, CF8C grade has option for stabilization treatment due to Nb present which forms carbides, between 870 and 900 °C after solution annealing in austenite matrix. This prevents depletion of chromium around grain boundary and prevents sensitization of steel. However, this stabilization treatment has been mentioned as supplementary requirement of ASTM A351 Clause 3.1 depending on the end property requirement. In this line, experimentation carried out on solution annealing and solution annealing + stabilization treatment of CF8C grade and testing carried out in order to evaluate properties after both treatments. For other stainless steels like CF8M, and CF3M of ASTM A351 similar experiment carried out.

Although delta ferrite is a very common phase in most austenitic stainless steels, studies about its formation and evolution during slab processing from industrial heats of tens of tons are scarce. The main objective of this research is to study the evolution of delta ferrite (quantity, chemical composition, morphology, and distribution) along the production route from the cast slab to the coil of an industrial heat of 80 tons of 304 stainless steel. Samples were extracted after the following processing steps: continuous casting, first and second hot-rolling pass, and solution-heat-treating, arriving at the final commercial condition. Sample analyses were carried out with several complementary microstructural characterization techniques: optical microscopy, scanning electron microscopy with energy dispersive spectroscopy (EDS), X-ray diffraction, and magnetic measurements of delta ferrite content (feritscope). Thermocalc® indicates that the present continuous cast slab solidifes according to the FA (ferrite-austenite) mode and the final microstructure should be completely austenitic in equilibrium conditions. Nevertheless, delta ferrite is detected along the processing steps, indicating that the steel is out of phase equilibrium. The ferrite content measured after solidification varies significantly across the as-cast slab thickness. Lower values are detected on the surfaces, followed by a gradual increase when moving into the slab, reaching a peak, and finally decreasing at the slab center. This pattern of delta ferrite content is named “M type” distribution. The average content of delta ferrite decreases after each subsequent processing step, namely the two hot-rolling passes and the solution heat-treating.

This work deals with studying staging and macroscopic strain localization in austenitic stainless steel 12Kh18N9T within a temperature range of 143 K < T < 420 K. The visualization and evolution of macroscopic localized plastic deformation bands at different stages of work hardening were carried out by the method of the double-exposure speckle photography (DESP), which allows registering displacement fields with a high accuracy by tracing changes on the surface of the material under study and then comparing the specklograms recorded during uniaxial tension. The shape of the tensile curves σ(ε) undergoes a significant change with a decreasing temperature due to the γ-α'-phase transformation induced by plastic deformation. The processing of the deformation curves of the steel samples made it possible to distinguish the following stages of strain hardening, i.e. the stage of linear hardening and jerky flow stage. A comparative analysis of the design diagrams (with the introduction of additional parameters of the Ludwigson equation) and experimental diagrams of tension of steel 12Kh18N9T for different temperatures is carried out. The analysis of local strains distributions showed that at the stage of linear work hardening, a mobile system of plastic strain localization centers is observed. The temperature dependence of the parameters of plastic deformation localization at the stages of linear work hardening has been established. Unlike the linear hardening, the jerky flow possesses the propagation of single plastic strain fronts that occur one after another through the sample due to the γ-α' phase transition and the Portevin-Le Chatelier effect. It was found that at the jerky flow stage, which is the final stage before the destruction of the sample, the centers of deformation localization do not merge, leading to the neck formation.

The prediction of M-shaped δ-ferrite content along the thickness direction of continuously cast 304 austenitic stainless steel slab was performed using a diffusion-controlled phase transformation module of Thermo-Calc software. The surface and center of the slab, which solidified with different cooling rates and secondary dendrite arm spacing, were used for kinetic calculations. Comparison between observations and calculations for slab specimens demonstrated that the moving-boundary model could predict retained δ-ferrite content according to various thermal histories. After this validation, the effects of different cooling rates at liquid and solid-state were analyzed to understand the importance of each stage on the diffusion-controlled δ $$\to \gamma$$ phase transformation. Decrease in solid-state cooling rate generally had a larger effect on the reduction of δ-ferrite during cooling when the solidification rate was fast (27.75 °C/s) than when it was slow (0.075 °C/s). This model can be used to predict and control δ-ferrite behavior under different thermal histories during slab casting and welding practices.

Stainless steel (SS) is increasingly used for structural applications in the construction industry as its beneficial properties outweigh initial material costs when sustainability aspects and the whole life cycle of structures are appropriately accounted for in the structural design. Despite the well-recognised significance of connections in bare metallic construction, experimental research on SS beam-to-column connections, especially full-scale test results, are scarce. This paper presents a full-scale experimental investigation on the semi-rigid behaviour of top-seat bolted connection (also known as ‘flange cleat’ connection) made from austenitic SS. Deformation characteristics of various elements of the connection were carefully investigated and subsequently used to calibrate nonlinear FE models for parametric analysis. Obtained numerical results were used to develop a four-parameter power model that relies on simplified expressions for key input parameters to predict the semi-rigid behaviour of bolted top-seat connections. Results predicted using the proposed model and those obtained using currently available techniques based on carbon steel behaviour were compared. Outcomes of the current research highlighted the significance of appropriate inclusion of stain hardening offered by austenitic grade to capture the semi-rigid response of such connections.

A new kind of high strength sorbite stainless steel named S600E was developed recently, which has the 65% corrosion resistance, but three times higher yield strength than commonly used austenitic stainless steel S30408. In addition, the price of S600E is only 70% of S30408 owning to the low nickel content of 1.5–2.5%. Fundamental investigations on the mechanical behaviours of S600E were presented in this study. Two monotonic and seventeen cyclic material tests were conducted subjected to different strain-controlled loading protocols including the constant strain amplitude ranging from 0.25% to 2.5%, as well as the varied strain amplitudes. Monotonic test results show that S600E presents the typical feature of rounded nonlinear strain hardening, but the 0.2% proof stress is extremely high, up to 750 MPa, and the elongation after fracture is over 20%. In the cyclic tests, little cyclic hardening was occurred in the initial few cycles, while cyclic softening tended to appear at the remaining cycles. Based on the test results, the isotropic component in the constitute model was neglected, key material parameters for the nonlinear kinematic hardening model with two pairs of backstresses were obtained and validated using the numerical analysis in ABAQUS. At last, the cyclic material properties were compared with commonly used stainless steel to reveal the advantages of S600E. The results of this study could be used in finite element modeling of members, joints and structures of S600E.

In the self-assembly process of β-Si3N4 (SN)/316L stainless-steel (SUS316L) composite materials tailored via sintering of powder mixtures, the formation of a SN agglomerate resulting from condensation–dispersion reactions during the stirring of SN/SUS316L was found to play an important role in improving the thermal conductivity. Moreover, the obtained SN secondary particle groups connected to form a network through diffusion-limited aggregation. In particular, it was shown that the sample prepared at the milling speed of 150 r/min has a similar particle group area (about 1.38 μm2) to that at 120 r/min, but a higher κ (increased from 9.5 W m−1 K−1 to 11.5 W m−1 K−1). To quantitatively evaluate the microstructural morphology of the texture of the self-assembled composite material, global parameters τ( q) and D q and local parameters α( q) and f( α) were determined via multifractal analysis. These characteristics of the anisotropy, dispersion, and cohesiveness of the particle network in the material texture could be analyzed together with the capacity dimension D0, information dimension D1 (configuration entropy), correlation dimension D2, and α( q) (related to internal energy). The results suggest that α( q) reflects the differences in the cohesion of the additive particle agglomeration that constitutes the self-assembly process under the solid-state reaction.

This study evaluates the effects of temperature, H2S, and Cl− concentration on the onset of localized corrosion, in UNS S31603 stainless steel by evaluating the changes in the behavior of the passi...

Effect of active screen plasma nitriding (ASPN) on microstructure, hardness, and wear loss of 347H austenitic stainless steel (AuSS) was studied at various processing parameters. Scanning electron microscopy, x-ray diffraction (XRD), hardness, and wear tests were performed on samples. The XRD analysis showed the presence of S-phase (γN-expanded austenite) in samples nitrided at 350 °C and 400 °C. In contrast, samples nitrided at higher temperatures ranging from 450 to 550 °C showed the presence of various types of nitride phases in the nitrogen-enriched layer. The case depth and mass of nitrided samples increased with the increase in nitriding temperatures owing to the increase in diffusivity of nitrogen at a higher temperature. The wear loss of samples nitrided at higher temperatures was lower than those nitrided at lower temperatures due to the formation of a higher amount of hard nitride phase(s) in the nitrogen-enriched layer at temperature ≥ 450 °C.

In this study, room temperature tensile properties of type 304, a metastable austenitic stainless steel, prior rolled above Md temperature (200 °C and 300 °C) are compared with mill-annealed and material prior rolled at room temperature (25 °C). Strain-induced martensite that formed during the tensile tests, followed using in-situ using magnetic measurements, display kinetics that vary with prior deformation temperature and strain. Scanning Electron Microscopy and Electron Backscattered Diffraction studies provided direct evidence for shear band formation during prior deformation. Kinetics of strain-induced martensite is found to fit the Olson–Cohen equation modified to include the prior deformation strain and martensite formed during prior deformation. The systematic changes observed in the model parameters of the modified Olson–Cohen equation are explained. The strain hardening in the material is analyzed and correlated with changes in the rate of formation of strain-induced martensite with respect to strain.

To study and understand the solidification behavior of super austenitic stainless steel under different cooling rates and segregation laws of alloying elements is of great significance to optimize the subsequent diffusion annealing homogenization treatment process and improve product quality. According to Thermo-Calc thermodynamic simulation results and combined with high temperature laser confocal scanning electron microscope (HT-CSLM), the tissue morphology of 904L super austenitic stainless steel was observed in-situ during solidification. The solidification path of the test steel was determined via calculation with the Scheil-Gulliver model. Microscopy techniques, including true color microscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and electron probe microanalyzer (EPMA) were used to analyze the influence of different cooling rates (6 ℃/min, 50 ℃/min, and 100 ℃/min) on the solidification structure and determine the main distribution law of alloying elements. This analysis determined that the solute distribution coefficient (K) of Cr, Mn, Mo, Cu, and Si elements is less than 1 during the solidification process, which means that they will accumulate in the liquid phase. Among them, elemental Mo segregation is the most severe, while elemental Ni hardly segregates. As the cooling rate increases, the crystallization temperature of the test steel decreases, and the secondary dendrite arm spacing λ2 decreases, the concentration of Mo in the residual liquid phase increases.

Recent developments in the 3D printing of austenitic stainless steels have led to the need for standardization of electrochemical techniques used to assess the corrosion performance of these alloys. Currently, ASTM standards for austenitic stainless focus on assessing their resistance to different modes of corrosion such as pitting, crevice, and intergranular corrosion. Due to the complexity of the additive process, selective corrosion occurs in microstructural features such as cellular structures and melt pool boundaries. Standardized corrosion testing needs to incorporate these microstructural features. This study characterizes the corrosion behavior of laser powder bed fusion stainless steel in a variety of ASTM standards with special attention to melt pool boundary dissolution, cellular structures, and intergranular corrosion.

This study proposes to characterize through analysis of wettability and surface energy of Al59Cu25.5Fe12.5B3 and Al65Co18Cu17 quasicrystalline (QC) coatings produced by high-velocity oxygen-fuel (HVOF). Other materials such as polytetrafluoroethylene, bronze and austenitic stainless steel were also analyzed. For this, the sessile drop method was used to measure the static contact angle, as well as the experimental model proposed by Owens–Wendt–Rabel–Kaelble. The results were analyzed in terms of the polar and dispersive components of the total surface energy. The results showed that the quasicrystalline coatings showed low surface energy, in the order of magnitude of polytetrafluoroethylene.

The metastable austenitic stainless steel AISI 347 offers the possibility to induce a phase transformation from γ-austenite to ε- and α’-martensite when machining. This knowledge is well understood during cryogenic turning and was already applied to improve the surface morphology of metastable austenitic steel. However, the potential of this in-process hardening method is so far limited to rotationally symmetrical components. The aim of this study is to investigate deformation induced phase transformation during cryogenic milling, aiming at an improved surface morphology and at the resulting beneficial surface properties of the workpiece for parts with complex geometries.

The deposition of austenitic stainless steel coatings on high-strength low-alloy steel surfaces was a common method in engineering. However, excessive dilution of the substrate resulting in degradation of the coating properties is a constant challenge. In this paper, tungsten argon arc welding (TIG) technology was optimized based on the response surface method to produce a very low dilution (4%) stainless steel coating on the surface of Q355 steel. The intergranular corrosion sensitivity of the two coatings was tested by the double-loop electrochemical potentiodynamic reactivation technique. The DOS value of the coating made by the TIG technique (6.83%) is lower than that of the coating made by flux-cored arc welding (9.31%). The improved intergranular corrosion resistance is attributed to the dilution rate, grain size, grain boundary type, and inclusions. A technique of manufacturing low dilution coatings is provided, achieving a 50% savings in welding material.

This research investigates the Z-Phase solubility product of austenitic stainless steel (ASS) ASTM F-1586 used as orthopedic implants under the solubilization procedure. Precipitate extraction by an electrolytic separation technique and analytical thermodynamic calculations as a function of the solubilization temperature and chemical composition were employed. In the first procedure of preferential electrolytic phase dissolution, samples were submitted to a solubilization treatment, followed by quenching. The specimens were subjected to a surface treatment then dissolved in solution. Following the dissolution, the electrolyte was vacuum filtered on a 0.20 μm polyvinylidene difluoride (PVDF) membrane and vacuum dried for 24 h. The microstructures were characterized via scanning electron microscopy (SEM/EDS) and transmission electron microscopy (TEM/EDX) techniques. The results revealed by the Z-phase (Cr2Nb2N2) precipitation potential (Ks) that the precipitates acted as a softening inhibitor agent and retarded the grain growth at lower solubilization temperature conditions (Ts

In this paper, the effect of continuous and pulsed current in the gas tungsten arc welding (GTAW) on the various properties of an AISI 316L stainless steel joints was investigated. 316L austenitic stainless steel sheets with a thickness of 10 mm were used together with ER309L filler. The sheets were welded together by the GTAW technique in two modes of continuous and pulsed currents. Microstructural characterization and phase equilibria were done using optical microscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with electron backscatter diffraction (EBSD) detector, techniques. Charpy impact, uniaxial tensile, and microhardness tests were used to investigate the effect of the type of the welding current on mechanical properties of the joints. The fracture surfaces were evaluated by FE-SEM after tensile and Charpy impact tests. Results showed that the weld metal (WM) microstructure is austenitic-ferritic (AF). It was also consisted of columnar and coaxial structures, in a way that varying the welding current from continuous to the pulsed mode changed the morphology of the grains from elongated columnar to a fine coaxial morphology. In addition, such a change in the welding current reduced the size of the grains in the WM, and the width of the unmixed zone (UMZ) as well. XRD analysis showed that the predominant phase and the preferred crystal plane of the WM are austenite, and (111), respectively. Both joints were broken from the base metal (BM) during the tensile test. Also, the above change of the welding current mode increased hardness and fracture toughness of the WM. Finally, fractography of the joints indicated that both joints experienced a completely ductile fracture.

This paper investigates the machinability of AISI 316L stainless steel without and with NMI treatment, when machined with three different PcBN tool grades: low cBN content (50% vol.), medium (65% vol.) and high (90% vol.). The NMI treatment consisted of resulfurized and Ca-treated steels with two different Si/Al ratio. The tool materials were evaluated in terms of tool life, showing the best performance for the medium cBN content grade. Results showed that the crater wear has a more significant effect on the tool performance than the standard wear criteria of maximum flank wear. The worn tools were examined using scanning electron microscopy (SEM), focused ion beam (FIB) and transmission electron microscopy (TEM). In most cases, the crater exhibited three distinct regions from the edge to the end of the contact zone: the plateau, middle crater, and the upper region. Plateau and crater region displayed tool protective layer (TPL), consisting mostly of Al, Si, Mg and Ca-oxides; and some dimples in the tool from preferential wear of cBN grains. In the upper region of the best performing material, a ~1.5 μm thick TPL of mostly MnCr2O4 spinel was found, a result of the transfer of Mn- and Cr-rich oxide NMIs found in this material or oxidation of workpiece material, during the machining process. (Less)

The nickel-based Colmonoy-5 hardfacing alloy is used to hard-face 316LN austenitic stainless steel components in fast reactors. The nominal composition (in wt%) was listed as follows: 0.01 C, 0.49 Si, 0.87 Mn, 17.09 Cr, 14.04 Ni, 2.56 Mo, 0.14 N, and balance Fe. Hardfacing is a technique of applying hard and wear-resistant materials to substrates that need abrasion resistance. The thickness of hardfacing deposit varies between 0.8 mm and 2 mm based on parameter combinations. In this study, laser hardfacing process parameters including laser power, powder feed rate, travel speed, and defocusing distance were optimized to reduce weight loss of laser hard-faced Ni-based deposit. The tribological characteristics of reactor-grade NiCr-B hard-faced deposits were investigated. The RSM technique was used to identify the most important control variables resulting in the least weight loss of the nickel-based alloy placed on AISI 316LN austenitic stainless steel. Statistical techniques like DoE and ANOVA are utilized. Changing the laser settings may efficiently track the weight loss of laser hard-faced nickel alloy surfaces. These are created using the response surface technique. The deposit produced with a laser power of 1314 W, powder feed rate of 9 g/min, travel speed of 366 mm/min, and defocusing distance of 32 mm had the lowest weight loss of 16.4 mg. Based on the F value, the powder feed rate is the major influencing factor to predict the hardness followed by power, travel speed, and defocusing distance.

The ferrite content of austenitic stainless steel welds seriously affects to perform stainless steel welds. Keeping the ferrite content at the lower limit can reduce the thermal crack sensitivity o...

The use of post-processing heat treatments is often considered a necessary approach to relax high-magnitude residual stresses (RS) formed during the layerwise additive manufacturing laser powder bed fusion (LPBF). In this work, three heat treatment strategies using temperatures of 450 °C, 800 °C, and 900 °C are applied to austenitic stainless steel 316L samples manufactured by LPBF. These temperatures encompass the suggested lower and upper bounds of heat treatment temperatures of conventionally processed 316L. The relaxation of the RS is characterized by neutron diffraction (ND), and the associated changes of the microstructure are analyzed using electron backscattered diffraction (EBSD) and scanning electron microscopy (SEM). The lower bound heat treatment variant of 450 °C for 4 hours exhibited high tensile and compressive RS. When applying subsequent heat treatments, we show that stress gradients are still observed after applying 800 °C for 1 hour but almost completely vanish when applying 900 °C for 1 hour. The observed near complete relaxation of the RS appears to be closely related to the evolution of the characteristic subgrain solidification cellular microstructure.

The influence of severe plastic deformation induced by ultrasonic shot peening (USP) on evolution of microstructure and the resulting properties of 316 austenitic stainless steel is evaluated. Microstructural characterization was carried out by using optical, scanning, and transmission electron microscopies in addition to electron backscattered diffraction, x-ray diffraction and x-ray photoelectron spectroscopy. Mechanical properties were evaluated using hardness and sliding wear tests. USP resulted in high dislocation density and refined microstructure that led to significant increase in hardness. Although no strain induced martensite formed after USP at room temperature, USP carried at cryogenic temperatures led to martensite formation indicating the importance of temperature in USP on strain induced martensite development. Contrary to this, sliding wear at room temperature led to martensite development suggesting dominant role of deformation mode on martensite development during sliding wear. Sliding wear mechanism involved abrasion of steel accompanied by plastic deformation. Localized corrosion resistance improved due to nanostructured surface produced after USP enhancing the diffusional transport of chromium to surface. XPS analysis revealed higher Cr: Fe ratio in the oxide film after USP. Simultaneous enhancement of wear and corrosion resistance of stainless steels by the application of USP is discussed.

This article describes the optimization of processing parameters for the surface roughness of AISI316 austenitic stainless steel. While experimenting, parameters in the process like feed rate (fd), speed (vc), and depth of cut (DoC) were used to study the outcome on the surface roughness (Ra) of the workpiece. The experiment was carried out using the design of experiments (DOE) on a computer numerical control (CNC) lathe. The surface roughness is tested for three conditions i.e. Dry, Wet, and cryogenic conditions after the turning process. Samples are step turned on CNC Lathe for all three conditions with a set of experiments designed. The response surface methodology is implemented, and mathematical models are built for all three conditions. The nature-inspired algorithm is the best way to get the optimal value. For the discussed problem in the paper, nature-inspired techniques are used for obtaining the optimum parameter values to get minimum surface roughness for all set conditions. The Grasshopper optimization algorithm (GOA) is the technique that is the most effective method for real-life applications. In this research, GOA is used to get optimum values for the surface roughness (Ra) at Dry, Wet and cryogenic conditions. Finally, results are compared, and it's observed that the values obtained from GOA are minimum in surface roughness value.

Welding fumes have been found to be carcinogenic and stainless steel welders may be at higher risk due to increased formation of hexavalent chromium (Cr(VI)). The slag-shielded methods, identified to generate most airborne particles and Cr(VI), would potentially be most harmful. With ever-stricter limits set to protect workers, measures to minimize human exposure become crucial. Austenitic stainless steel flux-cored wires of 316L type have been developed with the aim to reduce the toxicity of the welding fume without compromised usability. Collected particles were compared with fumes formed using solid, metal-cored, and standard flux-cored wires. In part 1, the new wires were concluded to have improved weldability, to generate even less Cr(VI) in wt.-% than with solid wire and to be less acute toxic in cultured human bronchial epithelial cells as compared to standard flux-cored wires. In part 2, two additional institutes created fume emission datasheets for the same wires for correlation with the fume data obtained in part 1. The reported values showed large variations between the three laboratories, having a significant effect on the standard deviation. This is suggested to be the result of different welding parameters and various ways to collect and analyze the fume. More stringent specifications on parameter settings and fume collection would be required to increase the accuracy. This means that at present, it may not be possible to compare fume data on datasheets from two different wire producers and care should be taken in interpretation of values given in the available literature. Nevertheless, the laboratories confirmed the same trends for Cr(VI) as presented in part 1.

In order to obtain the local buckling capacity of lipped C-section stainless steel beams under weak axis bending, local buckling tests were carried out on 6 stainless steel beams under weak axis bending made of Austenitic stainless steel S30408 (AISI304), revealing the mechanical properties and failure mechanism when local buckling occurred, and the failure phenomenon, load–displacement curves, load–strain curves and local buckling capacity of the specimens were obtained. The test results showed that the failure mode of the specimen was local buckling located in the mid-span web, showing a convex or concave mode. The wave peak was near the mid-span section, and the local buckling of the web along the longitudinal direction occurred in multi-wave buckling mode. The refined finite element model of lipped C-section stainless steel beam specimens under weak axis bending was established. The mechanical properties and local buckling bearing capacity of each specimen were simulated and analysed. The accuracy of the refined model was verified by comparing the finite element results with the test results. In order to simplify the finite element simulation analysis, the refined finite element simulation was simplified. Then 4 kinds of imperfection simplification models were established considering different initial imperfections, and 8 kinds of length simplification models were built based on different lengths and support constraints. Detailed comparison and analysis were performed on results of simplified model refined finite element model and tests to verify the accuracy of the simplified model.

This paper proposes a deep-learning framework, specifically, a Deep Belief Network (DBN), for studying the web crippling performance of cold-formed stainless steel channel sections (lipped and unlipped as well as fastened and unfastened) with centered and offset web holes under the end-two-flange loading condition. G430 ferritic, S32205 duplex and 304 austenitic stainless steel grades are considered. A total of 17,281 data points for training the DBN are generated from an elasto plastic finite element model, validated from 69 experimental results reported in the literature. When a comparison was made against a further 53 experimental results reported in the literature, the DBN predictions were found to be conservative by around 10%. When compared with Backpropagation Neural Network (a typical shallow artificial neural network) and linear regression model based on PaddlePaddle, it was found that the proposed DBN outperformed these two methods, using the same big training data generated in this study. Using the DBN predictions, a parametric study is then conducted to investigate the effect of web holes, from which unified strength reduction factor equations are proposed. Finally, a reliability analysis is conducted, which shown that the proposed equations can predict the web crippling strength of cold-formed stainless steel channel sections under the end-two-flange loading condition.

A TC4 titanium alloy plate was lap joined to a 304 austenitic stainless steel plate via friction stir welding. The microstructures at the lap joint interface were intensively examined by means of energy dispersive X-ray spectroscopy and transmission electron microscopy analysis, and the mechanical properties of the lap joint were evaluated by a microhardness and shear tensile test. The results show swirling-like stir zones of TC4 and 304 SS are formed along the interface, where an aprox. 200 nm interface layer composed of TiFe and TiFe2 intermetallic compound is dispersed at the high rotating speed of the tool. In addition, the high hardness value is discontinuous distribution at the interface, and the shear strength of the commercially TC4 plate and 304 SS FSW lap joint can reach 7507 N at a rotational speed of 600 rpm, a welding speed of 30 mm/min, and a press amount of 0.4 mm.

There are several possibilities for establishing a cohesion joint between dissimilar metals. In the case of thin sheets, the ultrasonic welding process is suitable. This process can establish a cohesion joint rapidly, with a low heat input between the thin sheets. The authors have tried to determine the optimal ultrasonic welding parameters for copper and austenite stainless steel joining by using an experimental method of joining. Suitable results were obtained by welding tests due dissimilarities in the chemical, physical and mechanical properties of the copper and stainless steel. A standard size sheet thickness and test sample was used for the welding by different parameters. The parameters were refined based on the theoretical and practical knowledge during the experiments. The experimental welding was made by a Branson L20 type welder machine. The joint made by the different parameters was inspected by shearing-tensile tests (maximal force level).

Steel (St) and aluminum (Al) have a high affinity to each other and form intermetallic compounds (IMCs) when bonded by friction stir welding (FSW). Understanding the effect of alloying elements of steel on the formation of IMCs will help to design joints in which the formation of IMCs is controlled. In this study, two kinds of steel, carbon steel (CS) and austenitic stainless steel (SS) with 3 mm thickness, were selected to be welded to aluminum by FSW under similar conditions. The effect of the rotation speed of the FSW tool was also examined in the range of 850–1300 RPM. The morphology, thickness, and composition of IMCs in the interfaces were studied by various characterization techniques. It was observed that the IMC layers in the SS/Al joints were much thinner than the ones in CS/Al joints (0.1–0.7 µm in SS/Al and 2–6 µm in CS/Al). Moreover, the thickness of IMC layer in CS/Al joints increased with increasing the rotation speed while in SS/Al joints it began to decline by exceeding a certain rotation speed. In order to explain these differences, diffusion-based equations were used to calculate the interdiffusion coefficients in both SS/Al and CS/Al couples. It was found that the interdiffusion coefficient in SS/Al was lower than CS/Al. This was attributed to the alloying elements of SS such as Ni and Cr which can diffuse to IMC layer and hinder the growth rate of IMCs. It was also observed that some form of liquation occurred in SS/Al joints at high rotation speed of FSW due to the formation of a low-melting multielement compound of Al–Fe–Cr–Ni. The decline of IMC thickness in SS/Al joints at high rotation speed was attributed to this multielement compound which was melted during FSW and reduced the nucleation rate of Al–Fe IMCs. Finally, the fracture of the specimens and the effect of IMC formation on the joint establishment were elaborated. It was concluded that the alloying elements of steel have a beneficial effect on controlling the growth of IMCs.

Previous studies, including ASME and RCC-MR standards, did not consider the influence of environmental factors on the ratcheting boundary of the material, and only a unified ratcheting boundary was proposed. In this paper, thermal aging was taken into consideration, and the effect of thermal aging time on the ratcheting boundary of 316LN austenitic stainless steel was characterized by the efficiency diagram rule. The results show that, when the secondary ratio U is small, there is no significant difference in ratcheting boundary between the original material and the thermal aged material. When the secondary ratio U is large, the ratcheting boundary of the material presents a slight upward trend with the increase of thermal aging time. Compared with ASME and RCC-MR standards, it is found that RCC-MR is conservative. Based on the evolution of the efficiency index V with the number of cycles, it is more conservative and reasonable to choose the stage when the efficiency index V develops into a constant.

Purpose Effect of grain size on degree of sensitization (DOS) was been evaluated in Nickel free steel. Manganese and nitrogen contained alloy is a Ni-free austenitic stainless steels (ASS) having type 202 grade. The main purpose of this investigation is to find the effect of recrystallization on the DOS of stainless steel after the thermo-mechanical processing (cold work and thermal aging). Design/methodology/approach In the present investigation, the deformation of 202 grade analyzed using X-ray diffraction (XRD) and microstructural testing. Optical microstructure of Ni-free ASS has been done for cold worked samples with thermally aged at 900°C_6 h. Double loop electrochemical potentiodynamic reactivation test used for findings of degree of sensitization. Findings Ni-free ASS appears to be deformed more rapidly due to its higher stacking fault energy which gave results in rapid transformation from strain induced martensite to austenite in form of recrystallized grains, i.e. it concluded that as cold work percentage increases more rapidly recrystallization occurs. XRD results also indicate that more fraction of martensite formed as percentage of CW increases but as thermal aging reverted those all martensite to austenite. So investigation gives the conclusion which suggests that with high deformation at higher temperature and duration gives very less DOS. Originality/value Various literatures available for 300 series steel related to the effect of cold work on mechanical properties and sensitization mechanism. However, no one has investigated the effect of recrystallization through thermomechanical processing on the sensitization of nickel-free steel.

The welding of dissimilar armor-grade steels is always challenging due to their carbon equivalent (CE) differences. In this investigation, dissimilar armor-grade steels (rolled homogenous armor (RHA) steels and ultra-high hard armor (UHA) steel) are welded using three electrodes, namely low hydrogen ferritic (LHF), austenitic stainless steel (ASS), and duplex stainless steel (DSS) by shielded metal arc welding (SMAW) process. All the three joints were tested against the 7.62 × 54 mm armor-piercing (AP) projectile. The projectile was wholly stopped at the Weld Metal (WM). Three modes of failures were observed in WM (1) wear debris (WD), (2) wear debris + continuous cracks (WDCC), and (3) fine wear debris + microcracks (FWDMC). The joint fabricated using ASS electrode with the level of failure of WDCC performs better than other joints with the lowest area density of 70 kg/m2 due to the high energy absorption capability of the austenite phase and higher strain hardening properties. At the interface, the martensitic band (MB) increases the hardness and has a vital role in determining ballistic resistance. The impact toughness and ductility of the weld metal play a significant role in deciding the ballistic performance more than hardness and strength properties.

In order to determine the deformation process window and inquire the cause of internal cracks and voids, three-roll planetary rolling process was modeled by three-dimensional finite element method, and internal cracks and voids were investigated by real rolling of a bismuth-containing austenitic stainless steel bar. It shows that improper process parameters will lead to cracks and voids in the rolled bar. The Brozzo ductile fracture criteria revised can be used to determine the damage factor. The deformation process window to avoid internal cracks and voids can be described by rolling elongation and temperature. The three positive principal stresses in the center of the rolled bar, the alternating stress caused by periodically discontinuous contact between the rolls and the rolled piece, and the uneven radial strain distribution can be counted to be the main reasons for internal cracks and voids in the rolled bar. This study shows that the elongation has an upper limitation for avoiding internal cracks and voids in the bismuth-containing austenitic stainless steel bar rolled by three-roll planetary mill.

The low nickel austenitic stainless steel (LNiASS) is more economical than the conventional 300-series austenitic stainless steels as 60% (approx.) of the Ni is replaced by manganese; it exhibits similar mechanical properties but inferior corrosion resistance. In this work, low nickel austenitic stainless steel samples were coated with Ni-based metallic powders using a thermal spray coating technique. The microstructures, phase composition and properties of coatings were examined using SEM, EDS, XRD and Vickers’s microhardness. The corrosion behavior was investigated by potentiodynamic polarization test in 0.5 M H2SO4 solution and 3.5 wt.% NaCl solution both for the uncoated and coated specimen. In both test solutions, the coatings that contained molybdenum and more chromium showed better corrosion resistance. The coated low nickel austenitic stainless steel can, therefore, be a cost-effective alternative to replace the widely used austenitic stainless steel in commercial as well as industrial applications.