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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 %).

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.

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.

A fine granular area, FGA, is a typical phenomenon observed at the very high cycle fatigue fracture crack origin with a subsurface defect in the material. The FGA has been widely investigated, and different mechanisms have been proposed. In this paper, the formation of FGA in a non-defect matrix of one austenitic steel during very high cycle fatigue was studied using a progressive stepwise load-increasing method and electron scanning microscopy/electron channeling contrast imaging (ECCI) technique. A nano rough surface area or FGA at the fatigue crack origin has been observed in the subsurface matrix without any defect. It is a new phenomenon. A mechanism was proposed using the dislocation plasticity theory. The formation of FGA in a non-defect matrix is a localized plasticity exhausting process by strain localization, grain fragmentation, stress concentration and nano crack initiation and propagation along low-angle grain boundaries.

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.

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.

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.

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.

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.

Two different alloys were developed from the mixtures of pre-alloyed powders consisting of ferroalloys to get the required composition of austenitic stainless steel via the powder metallurgy techni...

It is still a big challenge to calculate the probability of defect detection for inspecting pits on austenitic stainless steel welding using traditional POD models. Because we determine the decision threshold, the POD curve has a lot of changes as the decision threshold changes, there is no clear reason to insist which threshold is reasonable. This study proposes a new probability of detection (POD) model to quantitatively assess the detection capability of eddy current probes for inspecting pits on austenitic stainless steel welding. The experimental results show that the proposed model is more reasonable than traditional ones. The novel POD model was employed to analyze three eddy current probes, uniform, TR, plus-point probes on austenitic stainless steel welding. The results reveal that the uniform eddy current probe has the best detection capability for inspecting pits on among the three probes.

Mechanical components are frequently subjected to severe cyclic pressure and/or temperature loadings. Therefore, numerical and analytical low cycle fatigue methods become widely used in the field of engineering to estimate the design fatigue lives. The primary aim of this work is to evaluate the accuracy of the most commonly used numerical and analytical low cycle fatigue life methods for specimens made of 316 LN austenitic stainless steel and subjected to fully reversed uniaxial tension–compression loading, in the room temperature condition. It was found that both maximum shear strain and Brown–Miller criterions result in a very conservative estimation for uniaxially loaded specimens. However, maximum shear strain criteria provide better results compared to the Brown–Miller criteria. The total strain energy density approach was also used, and both the Masing and non-Masing analysis were adopted in this study. It is found that the Masing model provides conservative fatigue lives, and non-Masing model results in a more realistic fatigue life prediction for 316 LN stainless steel for both low and high strain amplitudes. The fatigue design curves obtained from the commonly used analytical low cycle fatigue equations were reexamined for 316 LN SS. The obtained design curves from Langer model and its modified versions are nonconservative for this type of material. Consequently, the authors suggest new optimized parameters to fit the given test data. The obtained curve using the currently suggested parameters is in better agreement with the experimental data for 316 LN SS.

Wire plus arc additive manufacturing (WAAM) technology with higher deposition rate and efficient material utilization was employed to fabricate a stainless steel 321 (SS 321) wall for the first time. In this work, the microstructural characteristics, mechanical properties and corrosion performance of as-built SS 321 were evaluated. The micrographs confirmed the presence of columnar and equiaxed dendrites along the building direction, and recrystallization of grains was noticed due to the re-melting of former layers. The microstructure was dominantly austenite with a small fraction of ferrite within the austenitic matrix. Better tensile properties were noticed for as-printed SS 321 WAAM samples in-comparison to wrought counterpart. This is corroborated to the equiaxed and columnar dendritic microstructure with small fraction of ferrite (FN). The hardness decreased from bottom (247 HV) to top (196 HV) region in SS 321 WAAM plate and is attributed to the microstructural difference with varying amount of ferrite (6.3 to 3.7 FN). The impact strength of samples in the horizontal and vertical direction was 116 ± 2 J and 114 ± 2.5 J respectively, and is comparable with the wrought AISI 321 (123 ± 1.5 J). The reduction in impact toughness is attributed to the ferrite (

This study examines the effect of heat input on the weld bead profile, microstructure and mechanical properties of single V- joint welded carbon and stainless-steel plates. The as-received sample steel plates were sectioned into eight pieces; dimension 75 X 30 X 10 mm thicknesses. Shielded metal arc welding (SMAW) of heat inputs 1250 and 2030 J/mm was used to produce full penetration bead on the plates. Although visual inspection indicated that some of the welds were macro defect free, austenitic stainless steel exhibited more weld distortions than the carbon steel and this was partially attributed to its lower carbon content and the width to depth aspect ratio of the weld profile aside the magnitude of the induced stress. For the carbon steel, as the heat input increased, the hardness value of both the heat affected zone and fusion zone increased. In contrast, for stainless steel, the hardness values were reasonably comparable within same weld region (HAZ or FZ) irrespective of heat input. Furthermore, the ultimate tensile strength of the stainless steel decreased as heat input increased while the ductility increased with an increase in heat input, in contrast to carbon steel, where both ductility and ultimate tensile strength generally decreased.

The heterogeneous and homogeneous nanostructured 316LN austenitic stainless steel with tensile strengths of approximately 1.8 and 2.0 GPa were fabricated by 92% heavy cold rolling and high-pressure torsion straining, respectively. The influence of heterogeneous and homogenous nanostructures on the resistance to hydrogen embrittlement was investigated. Thermal desorption spectroscopy of the electrochemical hydrogen-charged specimen showed that both nanostructures exhibited almost the same concentration of diffusible hydrogen. While the tensile properties of the homogenous nanostructure were severely affected by the diffusible hydrogen, it had less impact on the tensile properties of the heterogeneous nanostructure. The difference in the embrittlement behavior between the heterogeneous and homogeneous nanostructures is attributed to the mechanism of crack growth observed by tensile fractography. Hydrogen embrittlement is suppressed in the heterogeneous nanostructure because crack growth is hindered by twin domains. The crack easily initiates in the homogeneous nanostructure and the resistance to crack growth is low.

Shaped metal deposition (SMD) using metal inert gas welding plus externally cold wire is a relatively new technology of additive manufacturing, which fabricates near-net shaped parts. It is performed by depositing a main wire plus a cold feed wire melted by the electric arc heat. In the present work, a new experimental set-up was developed, which consists of a MIG-welding source and an external cold wire feed unit plus a 3-axis machine. The main intent of the current paper is to investigate the microstructural and mechanical properties of austenitic stainless steel grade 309L deposited parts. The result showed that the value of the wire feed ratio (WR) plays an important role in both microstructure and mechanical properties. The microstructure mainly consists of two phases ferrite and austenite as predominant phases throughout the parts. Widmansttaten austenite structure that is denoted as (W) this appears in the white region, and Vermicular delta ferrite (V) appears as the dark-etching phase. The tensile test results showed the UTS value increased by 17.36% in the longitudinal direction when using cold feeding, while it increased by 4.39% in the vertical direction. The hardness test results showed that the hardness value increased by 36.23% when using cold feeding. Also, cold wire feeding reduces interpass temperature into the workpiece by 10%.

Ti-stabilized austenitic stainless steel SS321 is a creep resistance material commonly used in hot sections of aircraft, boilers, and pressure vessel applications. Various factors such as chemical composition, second phase particles, grain size, microstructure influence the creep life significantly. In this study, stress rupture tests were carried out in temperature range 600 to 800°C and stress magnitudes, 100-300 MPa, to understand the microstructure and damage evolution. At elevated temperature, 800°C and 100 MPa, stress-rupture life was as low as 14 h. The rupture life increases with decreasing temperature and stress magnitude. Larson-Miller parameter predicted the $$5.6\times {10}^{5}$$ h of creep life at 600°C and 100 MPa, and therefore, the test terminated after 10080 h. The higher creep life is attributed to the suppression of the grain boundary sliding (GBS) phenomenon by the well-developed Cr23C6 and Cr3C2 phase and the microstructural evolution such as low-angle boundary, subgrains, and special boundary ( $$\sum 3$$ ) formations. The $$\sum 3$$ boundary formations at the grain boundary are possibly due to stress concentration caused by well-developed second phase particles. The lower rupture life at elevated temperatures and higher stresses is due to considerable GBS, leading to highly elongated grains with intergranular cracking.

While conventional Gibson–Ashby models provide a general insight into how elastic modulus and yield strength degrade with increasing overall porosity in materials, very limited work has investigated the effects of pore size and distribution on the mechanical properties of metals. One key question is whether and how pores can be utilized for improved mechanical properties rather than being eliminated or minimized for full densification. To fill in this gap, austenitic stainless steel 316L samples with intentional pores of varying diameters and distributions were fabricated by spark plasma sintering using starting powders with different morphologies. Characterization of pore features was not limited to the total volume percentage but also addressed the pore size, shape, interpore spacing, and pore surface area. The mechanical properties of those samples were investigated at multiple length scales to investigate the effect of pore characteristics, including macro-scale compression testing, Vickers micro-indentation, nanoindentation, and nanoscratch. Results suggested incorporating submicron pores improved both the yield strength and strength to weight ratio. The sample containing submicron pores represented an outlier in the classical Hall–Petch relation between yield strength and grain size, and it achieved a yield strength of 482 MPa, compressive strength of ~ 1.4GPa at a strain of 0.3 without fracture, and a specific yield strength of 67.7 MPa cm3/g. The mechanism was attributed to local stiffening and (Cr, Mn)-rich precipitates surrounding the submicron pores. It was discovered, for the first time, the specific yield strength and the pore diameter followed a Hall–Petch type correlation.

During wire and arc additive manufacturing (WAAM) of high nitrogen austenitic stainless steel (HNASS), the explosion of droplets with high-content nitrogen will induce grievous spatters, causing incomplete fusion, cracks and inclusions. In this study, the formation, characteristics and influence of spatters on cold metal transfer + pulse (CMT+P)-based WAAM of HNASS were investigated. The droplets exploded violently due to the sharp decrease of nitrogen solubility in liquid steel, which produced abundant spatters at the pulse stage. The spatter particles were a mixture of manganese oxides (MnO and Mn3O4) and molten metals of the wire. The overall particle size followed normal distribution. The majority of particles were spherically shaped in diameter of 20–150 µm, and over 80% of spatters were below 200 µm in diameter. Inclusion of manganese oxide spatter particles appeared in the deposition metals of single-pass single layer. The spatters at the root of the deposited metal can be hardly removed, which produced interpass defects in overlapping deposition. For multi-pass multilayer deposition, interlayer tearing occurred to reduce the mechanical properties of HNASS. The interlayer tearing was caused jointly by the incomplete fusion caused by spatter particles of manganese oxide and the large thermal stress. Hence, the spatters generated in the droplet transition for WAAM of HNASS must be controlled.

This study investigates the fatigue performance of wire arc additive manufactured (WAAM) SS 347 in different orientations. WAAM processed SS 347 plate features with grains mostly oriented in and crystallographic texture along the building direction (BD). Microstructure was mainly austenitic with a smaller fraction of ferrite. Tensile properties of the as-built SS 347 specimens were evaluated to understand the effect of orientation in regard to BD. Stress controlled fatigue tests were conducted at different stress amplitudes for samples in the horizontal direction (HD) and vertical direction (VD). The fatigue strength of as-built samples after sustaining 2×106 cycles were 135 MPa and 128 MPa for VD and HD specimens, respectively. Fatigue strength was less for both the samples in different orientation than the wrought counterpart (~40%). The increase in tensile strength and decrease in fatigue strength is attributed to the presence of austenitic columnar grains with a smaller ferrite fraction less than 5% and noticed phase transformation along with local recrystallization as a result of remelting the former layers along the BD during deposition. The higher kernel average misorientation values confirm the degree of grain misorientation along the BD. The fatigue failure mode was ductile for HD and VD specimens with striations in the crack propagation region and micro-voids coalescence in the final fracture region.

Hot cracking susceptibility and the formation of brittle martensite phase are the main factors that limit the weldability of a dissimilar joint between carbon steel (CS) and austenitic stainless steel (SS). In this study, the self-constraint finger test was used to correlate the welding thermo-mechanical field with the crack susceptibility of a dissimilar weld between the CS ASTM A36 and SS AISI 304L. The finger test allowed to intercalate fingers (portions) of tested materials in the weld samples to produce dissimilar welds. The heat dissipation and the distortion behavior were related to the crack susceptibility, critical weld regions extension, and chemical species diffusion. Four samples were welded (two similar welds and two dissimilar welds) using the filler metals ER70S-6 and EC410NiMo. Welds were analyzed through light optical microscopy (LOM) and scanning electron microscopy (SEM) to characterize phases, detect cracks, microstructural changes, and element diffusion. A finite element (FE) numerical model was applied to simulate the welding thermo-mechanical field. FE estimations of distortion and residual stress helped to predict induced crack propagation (the initial gap between fingers) towards the fusion zone. Additionally, electrochemical tests were carried out to assess the corrosion susceptibility of the dissimilar welds. The observed cracks were produced due to different factors such as residual stress distribution, the formation of brittle and untempered martensitic phase in the fusion zone (FZ), and hot cracking associated with the weld sample distortion behavior. According to the FE estimations, the high thermal expansion of the SS was responsible for the bending curvature change in welds 2 and 4, which produced a gap between fingers and increased the crack extension in the FZ of weld 4. The dilution contributed to the formation of δ-ferrite in the FZ, which limited the growth of cold and hot cracks. The decarburization and sensitization were not observed in dissimilar welds due to the low element diffusion.

The article discusses the mechanical properties and cold resistance of austenitic stainless steel (analogue 07Cr25Ni13) obtained by 3D printing by electric arc surfacing from ER309LSI welding wire on a CNC machine. These properties were investigated in the process of physical tests of samples cut along and across the layers of 3D printing for tensile and impact bending. Using optical microscopy, the microstructures of steel sections were obtained for various temperature conditions of interlayer exposure, as well as the values ​​of the recommended microhardness. In the process of 3D printing, an intelligent system for monitoring the dynamic stability of the electric arc was applied, which made it possible to guarantee the stability of the structure and properties of the obtained samples throughout the entire process of surfacing. Additional heat treatment of experimental samples (austenitization) was considered as a way to improve mechanical properties and cold resistance. It has been established that the dynamic stability of an electric arc, modes of interlayer temperature holding and subsequent heat treatment largely determine the mechanical properties and cold resistance of ER309LSI steel obtained by 3D printing by electric arc surfacing.

The scarcity of oil and gas resources made High Pressure and High Temperature (HPHT) reservoir attractive to be developed. The sour service environment gives an additional factor in material selection for HPHT reservoir. Austenitic 28 Cr and super duplex stainless steel 2507 (SS 2507) are proposed to be a potential materials candidate for such conditions. C-ring tests were performed to investigate their corrosion behavior, specifically sulfide stress cracking (SSC) and sulfide stress cracking susceptibility. The C-ring tests were done under 2.55 % H2S (31.48 psia) and 50 % CO2 (617.25 psia). The testing was done in static environment conditions. Regardless of good SSC resistance for both materials, different pitting resistance is seen in both materials. The pitting resistance did not follow the general Pitting Resistance Equivalent Number (PREN), since SS 2507 super duplex (PREN > 40) has more pitting density than 28 Cr austenitic stainless steel (PREN < 40). SS 2507 super duplex pit shape tends to be larger but shallower than 28 Cr austenitic stainless steel. 28 Cr austenitic stainless steel has a smaller pit density, yet deeper and isolated.

δ-ferrite was formed in the weld metal when the melted metal solidified to the room temperature. The δ-ferrite morphology depended on the composition, temperature gradient and growth rate. Research on the influence of heat treatment temperature (400°C, 600°C, 900°C) on the morphology changes and the δ-ferrite content is presented in this paper using optical microscopy, SEM, TEM. The δ-ferrite concentration reduced continuously in increasing temperature (from 23.5% after welding to 11% at 900°C for 10 hours). Besides, the formation of sigma phase and carbides at 600°C were the main cause of increasing hardness values in the fusion zone. However, the heat treatment at a temperature of 900°C eliminated both the sigma phase and brittleness.

In recent years, the need for eco-friendly machining processes has increased dramatically in order to limit the excessive use of conventional cutting fluids, thereby reducing their negative effects on both the environment and the operator’s health. In this context, environmental alternatives such as dry cutting, minimum quantity lubrication (MQL), and nanofluid-assisted MQL have been demonstrated to be effective in overcoming this problem. In the present work, an attempt was made to improve the machining characteristics performance in turning of AISI 304 austenitic stainless steel (ASS) under dry, MQL and nanofluids, and hybrid nanofluid-assisted MQL conditions, with respect to surface roughness (Ra), main cutting force (Fc), and cutting temperature (T). The main purpose of this experimental study is to evaluate and compare the effect of dispersed nano-additives into the vegetable cutting fluid on the responses under consideration. As nano-additives, multi-walled carbon nanotube (MWCNT), nano molybdenum disulfide (MoS2), and nano graphene particles have been used. Additionally, the effects of lubricating conditions on flank wear (VB) were investigated. In the end, statistical analysis, regression modeling, and multi-criteria optimization based on desirability function were performed. The results revealed that the Ra, Fc, and T as well as VB were found to be lower with the use of nano graphene-reinforced nanofluid-assisted MQL followed by nano graphene/MoS2-reinforced hybrid nanofluid-assisted MQL, MWCNT/MoS2-reinforced hybrid nanofluid-assisted MQL, MWCNT-reinforced nanofluid-assisted MQL, nano MoS2-reinforced nanofluid-assisted MQL, and MQL, respectively, as compared to dry condition. Finally, it is worth mentioning that the nano graphene has the capability to perform as a lubricant/coolant, thus contributing positively to the turning process.

Hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800–1200°C and constant strain rates of 0.001, 0.01, 0.1, and 1 s−1. Hot flow curves were used to determine the strain hardening exponent and the strain rate sensitivity exponent, and to construct the processing maps. Variations of the strain hardening exponent with strain were used to predict the microstructural evolutions during the hot deformation. Four variations were distinguished reflecting the different microstructural changes. Based on the analysis of the strain hardening exponent versus strain curves, the microstructural evolutions were dynamic recovery, single and multiple peak dynamic recrystallization, and interactions between dynamic recrystallization and precipitation. The strain rate sensitivity variations at an applied strain of 0.8 and strain rate of 0.1 s−1 were compared with the microstructural evolutions. The results demonstrate the existence of a reliable correlation between the strain rate sensitivity values and evolved microstructures. Additionally, the power dissipation map at the applied strain of 0.8 was compared with the resultant microstructures at predetermined deformation conditions. The microstructural evolutions strongly correlated to the power dissipation ratio, and dynamic recrystallization occurred completely at lower power dissipation ratios.

In this work the feasibility test of friction stir processing (FSP) of 1.5 mm thick austenitic stainless steel cold spray coating deposited on 304L stainless steel substrate was performed using tungsten carbide tool. Applied FSP parameters (advance speed 50 mm/min, rotation speed 300 rpm, axial force 20 kN, tilt angle 1.5°) allowed to perform FSP treatment with a higher depth than the coating thickness. As a result, the material mixing at the coating/substrate interface was observed. The microstructure observation revealed that the coating microstructure in the stir zone was significantly modified. EBSD analysis confirmed that full material recrystallization during FSP allowed to formation of dense and uniform fine-grain structure with the mean grain size 1.9 mm. Average coating microhardness was decreased from 406 HV to 299 HV. Further FSP parameters optimization should be carried out in order to improve the process reliability and avoid any coating failure during treatment.

Creep deformation and rupture behavior of nitrogen-alloyed (0.14 wt.%) nuclear grade 316LN austenitic stainless steel were investigated for the varying stress levels at 873 K and 923 K. The power-law dependency of creep properties such as steady-state creep rate and rupture life on applied stress was observed. For a given applied stress condition, a systematic increase in strain to failure was noticed with increasing temperature from 873 K to 923 K. Irrespective of test temperatures, creep rupture elongation of the steel increased with the increase in rupture lifetime ( $t_{r}$ ) for $t_{r} > 1000$ h. Analysis indicated that the interdependency between creep properties could be well described by the modified Monkman-Grant relationship. The predominance of inter-granular fracture arising from the triple point cracks and/or coalescence of cavities was observed at all the tested conditions for the steel. The enhanced tendency for wedge cracking was noticed for high stress levels at 873 K and 923 K. The evaluated damage tolerance factor $(\lambda ) < 5$ and the calculated ratio between time to reach the Monkman-Grant strain and creep rupture lifetime in the range of 0.69 to 0.80 indicated the accumulation of Monkman-Grant strain for the major fraction of lifetime during creep deformation of 316LN steel.

The present work investigates the effect of rolling (90% thickness reduction) on phase transformation, mechanical properties, and corrosion behaviour of 304L-austenitic stainless steel through cryorolling and room temperature rolling. The processed steel sheets were characterised through X-ray diffraction (XRD), electron backscattered diffraction (EBSD), and vibrating sample magnetometer (VSM). The analysis of XRD patterns, EBSD scan, and vibrating sample magnetometer results confirmed the transformation of the austenitic phase to the martensitic phase during rolling. Cryorolling resulted in improved tensile strength and microhardness of 1808 MPa and 538 VHN, respectively, as compared to 1566 MPa and 504 VHN for room temperature rolling. The enhancement in properties of cryorolled steel is attributed to its higher dislocation density compared to room temperature rolled steel. The corrosion behaviour was assessed via linear polarisation corrosion tests. Corrosion resistance was found to decrease with increasing rolling reduction in both room temperature rolled and cryorolled specimens.

Nickel‐free high‐nitrogen‐alloyed stainless steels like the P2000 (X13CrMnMoN18‐14‐3) were developed to enhance the strength and corrosion resistance of austenitic stainless steels like 304 and 316 while keeping the typical high ductility. The mechanical and corrosive properties of P2000 were investigated and compared with 304 and 316 to highlight the application opportunities of this new alloy. The microstructure of the solution‐annealed condition was characterised by electron backscatter diffraction and the mechanical properties were studied by uniaxial tensile tests, Charpy impact tests and hardness measurements. The passivation behaviour was analysed using the electrochemical potentiodynamic reactivation, whereas the pitting corrosion resistance was compared by pitting potentials and pitting temperatures. However, secondary thermal influences or suboptimal heat treatment can impair the corrosion resistance due to the precipitation of secondary phases and the resulting sensitisation. Thermodynamic calculations and artificial ageing treatment in the range of 500–900°C for up to 100 h were used to determine critical time–temperature parameters for sensitisation. The microstructure of the various aged states was evaluated by scanning electron microscopy and compared with the degrading corrosion resistance characterised by the KorroPad method.

The friction and wear behavior of electrode rod nickel chromium (ER NiCr) nickel-based hardfacing alloys ER NiCr-A, ER NiCr-B, and ER NiCr-C deposited over austenitic stainless steel was studied ag...

The laser micro-spot welding process was studied to implement a sheet lamination process-based methodology for the fabrication of austenitic stainless steel scaffolds. AISI 302 sheets with a thickness of 254 μm were laser cut and laser welded. Experimental tests were carried out with different values of average laser power (i.e., 180, 200, and 220 W) and different exposure times (25, 50, 75, 100, 125 ms). The micro-spot welds were visually inspected according to the ISO 13919-1 Class B requirements. Spot welds were qualitatively characterized, and weld dimensions were measured (i.e., penetration depth, top, middle, and bottom width and the heat-affected zone (HAZ)) to identify the cross-sectional shape. Furthermore, process efficiencies (i.e., coupling, melting, and process) were studied. A seam welding model was adapted to calculate the required exposure time and was used to obtain a micro-spot weld to accomplish the quality requirements of the scaffold. A scaffold prototype was designed and manufactured using the selected parameters by experimental trials and using the mathematical model (i.e., a laser power of 220 W and an exposure time of 45 ms).

Bimetallic additively manufactured structures (BAMSs) can replace traditionally-fabricated functionally-graded-components through fusion welding processes and can eliminate locally-deteriorated mechanical properties arising from post-processing. The present work fabricates a BAMS by sequentially depositing the austenitic stainless-steel and Inconel625 using a gas-metal-arc-welding (GMAW)-based wire + arc additive manufacturing (WAAM) system. Elemental mapping shows a smooth compositional transition at the interface without any segregation. Both materials being the face-center-cubic (FCC) austenite, the electron backscattered diffraction (EBSD) analysis of the interface shows the smooth and cross-interface-crystallographic growth of long-elongated grains in the direction. The hardness values were within the range of 220–240 HV for both materials without a large deviation at the interface. Due to the controlled thermal history, mechanical testing yielded a consistent result with the ultimate tensile strength and elongation of 600 MPa and 40 %, respectively, with the failure location on the stainless-steel side. This study demonstrates that WAAM has the potential to fabricate BAMS with controlled properties.

Cold extruded components are characterized by residual stresses, which originate from the experienced manufacturing process. For industrial applications, reproducibility and homogeneity of the final components are key aspects for an optimized quality control. Although striving to obtain identical deformation and surface conditions, fluctuation in the manufacturing parameters and contact shear conditions during the forming process may lead to variations of the spatial residual stress distribution in the final product. This could lead to a dependency of the residual stress measurement results on the relative axial and circumferential position on the sample. An attempt to examine this problem is made by the employment of design of experiments (DoE) methods. A statistical analysis of the residual stress results generated through X-Ray diffraction is performed. Additionally, the ability of cold extrusion processes to generate uniform stress states is analyzed on specimens of austenitic stainless steel 1.4404 and possible correlations with the pre-deformed condition are statistically examined. Moreover, the influence of the coating, consisting of oxalate and a MoS2 based lubricant, on the X-Ray diffraction measurements of the surface is investigated.

Fiber laser welding experiments are conducted on SS316L austenitic stainless steel plates based on the statistical design of experiments technique. A special kind of fixture is designed and fabricated with a facility to provide argon gas and is made up for bead protection. The influence of beam power, welding speed, and defocused position on fusion zone width, fusion zone area, and tensile strength of weldments is studied and discussed briefly. The most influencing factors and their percentage contribution on output responses are identified by analysis of variance technique. Beam power directly influences the bead features, whereas welding speed inversely affects it. However, the defocused position shows an insignificant effect on the fusion zone area within the selected range. The tensile strength increases with an increase in both beam power and welding speed up to a particular optimum value, and beyond that, it starts reducing. The highest hardness value is observed in the fusion zone at ‘1’ mm defocused position below the workpiece surface due to a decrease in grain size and interdendritic spacing. Ductile mode of fracture failure is found in both base material and weldment. The optimum welding condition obtained in this study yields full penetration, narrower weld width, lesser fusion zone area, minimal weld defects, and acceptable tensile strength of weldments.