Austenitic Stainless Steel Joints Research Articles

Evaluations of nanomechanical and indentation creep of diffusion-bonded aluminum and austenitic stainless steel joint interface

Diffusion bonding of aluminum alloy (AA-7075) with austenitic stainless steel (AISI 304L) was performed in the environment of Argon inert gas. The resultant bonding interface was investigated for its mechanical, nanomechanical, microstructural, and compositional characteristics using lap shear tests, nanoindentation and indentation creep, as well as optical (OM) and scanning electron microscopy (SEM), with energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results revealed that intermetallic compounds (IMCs) of FeAl3, FeAl2, FeNi3, and Fe3Ni2 were formed at the bonding interface. Similarly, a nano hardness of 3.5 GPa occurred at the bonding interface which was 15% and 454% higher as compared to base metal (BM) of AISI 304 and AA-7075 respectively. Additionally, indentation creep showed that the bonding interface has higher creep resistance compared to other bonding zones (BZ). Lastly, an average shear strength of 67 MPa was achieved with a joint efficiency of 58%.

Pitting behavior of austenitic stainless-steel welded joints with dense inclusions and methods to enhance pitting resistance

PurposeThis study aims to assess the pitting resistance of austenitic stainless steel welded joints fusion zone (FZ) with high density of inclusions before and after surface treatment, including potentiostatic pulse technique (PPT) and pickling.Design/methodology/approachThe potentiodynamic polarization tests and critical pitting temperature tests were carried out for estimating pitting resistance. The PPT and pickling were performed as surface treatment. Scanning electron microscope (SEM) and energy dispersive spectrometer were used for characterize the microstructure and elemental distribution. Electron back-scattered diffraction (EBSD) was used to assess the portion of phases and morphology of grains.FindingsThe weld metal exhibits a higher degree of alloying compared to the base metal, and it contains d-phase and sulfur-containing inclusions. Sulfur-containing inclusions serve as initiation sites for pitting, and they diminish the pitting resistance of weld metal. Both PPT and pickling can remove sulfur-containing inclusions, but PPT causes localized dissolution of the weld metal matrix around the inclusions, while pickling does not. Because of the high density of inclusions, certain pits initiated by PPT are significantly deeper, which makes the formation of stable pitting easier. Because of the high density of inclusions, certain pits initiated by the PPT are deeper. This characteristic facilitates the progression of these initial defects into fully developed, stable pits.Originality/valueAnalysis of pitting initiation in shielded metal arc welding FZ with PPT and ex situ SEM tracking observation. Explanation of why the PPT surface treatment is not able to enhance the pitting resistance of stainless steel with a high inclusion density.

Interfacial microstructure and mechanical properties in diffusion bonded Inconel 718 to austenitic stainless-steel joints

Diffusion bonding (DB) of Inconel (IN718) with Austenitic Stainless Steel (SS-304L) was conducted by varying the bonding temperatures and times at 5 MPa of pressure under vacuum. The optimized joint interface was evaluated for its mechanical, nanomechanical, microstructural, and compositional analyses using shear and Vickers hardness tests, optical and scanning electron microscopy (OM & SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and nanoindentation. The results showed that the optimized bonding parameters for achieving a stable joint interface were 950 °C for 90 min of holding time. It was observed that the joint interface was comprised of NbC, Cr23C7, Fe2Nb, and δ-Ni3Nb. The maximum nanohardness of 3.5 GPa occurred in the joint interface which was 10% and 35% higher as compared to the base metals (BM) of IN718 and SS-304L, respectively. Lastly, maximum joint strength of 143 MPa was achieved with a joint efficiency of 37%.

Comparative analysis of filler metals on microstructure and mechanical performance of TIG-welded AISI 201 austenitic stainless steel joints

In this study, 4-mm thick AISI 201 austenitic stainless steel butt joints were fabricated using the tungsten inert gas (TIG) process with ER309L, ER316L and ER2209 filler rods. TIG welding was performed using a current of 100 A, voltage of 14 V, with pure argon as the shielding gas at a flow rate of 10 L/min, and filler rod diameters of 2.4 mm. The microstructural and mechanical properties were analysed. ER2209 and ER316L promote an austenitic structure in the fusion zone. ER316L filler produced the finest grain structure (9.39 μm) and the lowest δ-ferrite content (25.85%) in the weld zone. Welds made of ER316L exhibited the highest hardness (314 HV), ultimate tensile strength (857 MPa) and yield strength (448 MPa). ER316L welds also demonstrated superior strain-hardening capacity (0.91) and impact toughness (19.8 GPa). Fracture analysis revealed finer dimples in the ER316L welds, indicating improved ductility and strength compared to other welded joints.

Microstructure Evolution of Dissimilar Graded Joints of Ferritic P91 and Austenitic 347H Stainless Steels Manufactured with Directed Energy Deposition

Microstructure Evolution of Dissimilar Graded Joints of Ferritic P91 and Austenitic 347H Stainless Steels Manufactured with Directed Energy Deposition

Mechanical and Corrosion Properties of Super Austenitic Stainless Steel Joint for Double‐Sided Synchronous TIP TIG Arc Butt Welding

Super austenitic stainless steel 254SMO (254SMO SASS) plates are joined by double‐sided double‐arc synchronous TIP TIG butt welding (DSSTTABW) using ER NiCrMo3 wire, and the micro‐structure, mechanical and corrosion properties of 254SMO SASS joints are investigated subsequently. Results show that solidification grain boundary and solidification sub‐grain boundary can be observed in fusion zone. A small amount of σ phase precipitates in the weld, while χ phase is found in the transition zone, but no solidification crack occurs in weld and heat affected zone (HAZ). 254SMO SASS joint has higher micro‐hardness and lower tensile strength and elongation compared to base metal. During transverse tensile process, 254SMO SASS joints fail in the weld zone in a ductile mode. Electrochemical corrosion performance tests indicate that 254SMO SASS joint achieve equivalent pitting corrosion resistance and similar passive mechanism to base metal in 3.5 wt% NaCl solution. The passivation film on the surface of both joint and base metal display as n‐p semi‐conductive character, but the film stability of 254SMO joint surface is slightly poorer compared to base material. The surface passivation film of 254SMO joint primarily consists of oxides of Fe, Cr, and Mo before potentiodynamic polarization, while hydroxides of Fe and Cr are also observed after polarization.

The dissimilar joint of 316L austenitic stainless steel to 5083 aluminum alloy by friction stir welding and investigation of its microstructure and mechanical properties

The dissimilar joint of 316L austenitic stainless steel to 5083 aluminum alloy by friction stir welding and investigation of its microstructure and mechanical properties

Corrosion behavior of austenitic stainless steel and nickel-based welded joints in underwater wet welding

Marine structures such as ports, bridges, pipelines, vessels, and platforms are an essential part of modern infrastructure, where the use of higher-strength steel provides savings in logistics and construction. However, the repair of higher-strength steels can be challenging, especially underwater. Wet shielded metal arc welding is the most widely used and least expensive method for underwater welding repairs, but is very susceptible to hydrogen-induced cracking. Thus, researchers and welding engineers aim to reduce the amount of hydrogen in the weld material. Recent success has been achieved through the use of austenitic welding consumables, such as austenitic stainless steel and nickel-based electrodes. The use of these consumables drastically reduces the amount of diffusible hydrogen in the weld metal. However, these austenitic materials usually have different corrosion potential as compared to the structural steel the weld beads are applied to. This creates the risk of severe galvanic corrosion. In the presented study, the corrosion behavior of welds created with austenitic stainless steel and nickel-based electrodes were studied. Samples were aged for 1.5 years in the Baltic Sea. Simultaneously, the effectiveness of corrosion protection systems such as coating and Impressed Current Cathodic Protection (ICCP) were evaluated. Localized corrosion occurred in the heat-affected zone when austenitic electrodes were used in the corrosive environment. The localized corrosion depth after 1.5 years in the Baltic Sea and in the salt spray layer was approximately 250 µm and 390 µm, respectively. The ICCP system and the use of a coating were effective in preventing localized corrosion. The low pitting corrosion density of 2.5 × 103 m−2 corresponds to grade A1 according to the standard and was found to be negligible as compared to the localized corrosion in the heat-affect zone.

Influence of electrode current on mechanical and metallurgical characteristics of hot wire TIG welded SS304HCu austenitic stainless steel and P91 ferritic steel dissimilar joints

Influence of electrode current on mechanical and metallurgical characteristics of hot wire TIG welded SS304HCu austenitic stainless steel and P91 ferritic steel dissimilar joints

The possible solidification modes of austenitic stainless steels joints according to different chemical compositions and cooling rates

The microstructures of four welded joints of austenitic stainless steel were studied to better understand the effect of different cooling rates on the volume fraction of δ-ferrite phase, in overlay deposits obtained by SMAW process. The weld pads were carried out using E316L and E347 electrodes and adjusting welding parameters to provide high and low heat. The weld pads produced were submitted to different cooling rates, being one produced by applying higher heat input and cooling in air, and another by applying lower heat input and cooling in water. Complementary techniques of microstructural analysis were applied, such as optical emission spectrometry, optical microscopy, and quantitative image analysis. There was an increase in the volume fraction of δ-ferrite in the weld pads, executed using the welding electrode E347, as the cooling rate increased. On the other hand, it was observed the opposite effect in the weld pads manufactured with the E316L welding electrode. The results suggest that the solidification mode of E347 is ferritic-austenitic and it is austenitic-ferritic in the case of E316L.

Evaluation of welded joints of austenitic stainless steels at high temperatures in the presence of SO2, SO3, and O2

This study undertakes a comprehensive examination of crack formation in welded joints of austenitic stainless steel 304, particularly in high-temperature corrosive environments prevalent in sulfuric acid production units. Initially, an investigation was conducted on a steam superheater that had been operational for about 19 years, where a crack formation was discovered. This unit, subjected to a working temperature of approximately 620 °C and exposure to gases composed of SO2, SO3, and O2, allowed for the analysis of corrosion products formed during the crack propagation. Building on the initial findings, a more controlled study was undertaken, focusing on the cracks formed in welded joints using the coated electrode E308L for joining 304H stainless steel plates under similar corrosive conditions. The specimens, constructed using materials typically utilized in sulfuric acid production units, were designed based on the double-beam principle, enabling exposure to both tensile stresses and a corrosive environment at high temperatures. Over a span of 122 days, or roughly 3000 h, microstructural analyses were conducted, revealing that the formation and propagation of cracks preferentially occurred through fragile microconstituents, notably the sigma phase. These findings mirrored the sigma phase formation observed in the initial superheater study and point to a stress corrosion process acting synergistically with sigma phase development, and consequently seen as a probable cause of failure. This comprehensive evaluation, therefore, indicates a significant role of the sigma phase and corrosive environments in influencing crack formation and propagation in welded joints of austenitic stainless steels, which require further studies for preventative strategies in industrial setups.

Microstructural study of microwave welded austenitic stainless steel

The joining of austenitic stainless steels through microwave hybrid heating has gained much attention due to its advantages, like uniform and volumetric heating. However, to establish a microwave joining process for promising applications, a microstructural study of the welded joint is still an area to explore. In the present study, microstructural analysis of austenitic stainless steel (SS304) joints is explained through optical microscopy, scanning electron microscopy (SEM), elemental mapping, X-ray diffraction (XRD) and Vickers' micro-hardness tester. Further, detailed microstructural analysis of interlayer and heat-affected zone (HAZ) is studied through electron back-scattered diffraction (EBSD). XRD results reveal the development of various Ni, Cr and the M23C6 type carbides at the joint interlayer region. SEM results point toward non-epitaxial grain evolution along the fusion zone. The mean microhardness of 350 ± 20 HV was determined at the joint interlayer region. A relatively fine grain structure was observed along the fusion boundary. However, moving away from the joint, two different forms of coarse grain heat-affected zone (CGHAZ) were observed. The presence of two different forms of CGHAZ is confirmed through inverse pole figure maps and grain size plots. The presence of high-angle boundaries (HABs) at 60° rotation describes the twin boundaries characterized along the <111> axis. The existence of improved fractions of HABs in the microwave-joined specimen of SS will favor the microstructure to retard bulk deformation. The joint specimen endures a maximum force of 6.98 kN, and the ultimate tensile strength of 613 MPa with 4.75% of elongation. It is observed that microhardness observations and the microstructural studies in the research help establish a solid microstructure-property correlation for the joined material.

Experimental investigation of microstructural, mechanical and corrosion properties of 316L and 202 austenitic stainless steel joints using cold metal transfer welding

The objective of the current experimental study is to investigate influence of dissimilar welding between 316 L Austenitic and 202 Austenitic Stainless Steel. This is achieved through the utilization of Cold Metal Transfer (CMT) Welding in conjunction with the GTAW mode. Various welding approaches are employed, including the use of ER316L and ER309L fillers, as well as a no-filler (autogenous) welding technique. Microstructural observation shows martensitic formation in the interface region. The tensile test was conducted by using Universal Testing Machine for the weldment and found that ER316L filler (721 MPa) has higher strength than ER309L (672 MPa) and autogenous weld (528 MPa). Charpy impact test was used to determine toughness of the weldment and found that ER309L Filler weld has toughness (87 J) which is higher than ER316L filler weld (5 4 J) and autogenous weld (23 J). Vicker's hardness test shows that autogenous weld hardness (avg. 193.34 HV) which is highest than ER309L filler (avg.188 HV) and ER316L filler weld (avg. 184.67 HV). The intergranular corrosion test by double loop electrochemical potentiokinetic reactivation (DLEPR) test shows sensitization at highest degree for autogenous weld (18.25 %) than ER316L filler weld (9.22 %) and ER309L filler weld (7.28 %).

A 2D and 3D segmentation-based microstructure study on the role of brittle phases in diffusion brazed AISI 304L/NiCrSiFeMoB joints

Nickel-based filler metals are frequently used in high temperature vacuum diffusion brazing for austenitic stainless-steel joints when components are subjected to high static or dynamic loads, corrosive environments and elevated temperatures. Due to melting point depressing metalloids such as silicon and boron, hard and brittle intermetallic phases are formed during the brazing process depending on the diffusion mechanisms. These brittle phases significantly affect mechanical and corrosive properties of the compounds. To quantify the influences of their amount, morphology and distribution, deep learning image segmentation was applied to segment these phases of the athermal solidification zone and the diffusion zone. Subsequently, characteristic microstructure parameters were calculated from these. The parameters of six different brazed joint variations were compared with their experimental characterization of mechanical and corrosive properties so that several correlations could be identified. Finally, a layer-by-layer removal of a brazed joint was performed using a focused ion beam, and a 3D model was reconstructed from the generated images to gain a mechanism-based understanding beyond the previous 2D investigations.

Effect of welding current on the microstructural and corrosion behavior of GTA welded austenitic stainless steel joints

In the present study, effect of welding current was analysed on the microstructural and corrosion properties of 316L austenitic stainless steel (ASS) joints welded by gas tungsten arc welding (GTAW). Three welding current were chosen from the GTAW process's operational range and welded joints fabricate using these currents were exposed to microstructural, microhardness as well as corrosion evaluations. Microstructural examination showed the lathy and vermicular morphology of δ-ferrite in the weld metal microstructures while different degrees of grain coarsening in the HAZ microstructures were seen. DLEPR method was used to assess the welds' resistance to corrosion, which depicted that high welding current specimen revealed relatively higher value of DOS (indicate higher amount of corrosion rate) as compared to low welding current specimen. This was due the fact that vermicular morphology of δ-ferrite was present in the high welding current specimens, which promoted the corrosion rate. However, lathy morphology of δ-ferrite was found in the low welding current specimens, which demotes the corrosion rate.

Effect of post-welding sensitisation on the degree of sensitisation of the welding zones of AISI 304 resistance spot welding joints studied by using an electrochemical minicell

ABSTRACT In resistance spot welding (RSW) joints of austenitic stainless steel (ASS), a small-scale electrochemical cell (minicell) was used for assessing individually, on each of the three welding zones, of size less than 1000 µm (fusion zone (FZ), heat affected zone (HAZ) and base metal (BM)), the combined effect of a RSW process and post-welding sensitisation on the degree of sensitisation (DOS). The results show that the three welding zones have different microstructures that make each of them respond differently to post-welding sensitisation. The DOS varies with post-welding sensitisation time in all three welding zones, but it varies at a different rate in each welding zone (the highest rate in the FZ). This variation is due to the fact that when the DOS reaches a certain level, which is observed when plotting the reactivation charge (Qr) versus the post-welding sensitisation time, a microstructural regeneration occurs.

Microstructure and Pitting Corrosion Characteristics of Tig Welded Joints of Super 304HCu Austenitic Stainless Steel

Abstract Super 304HCu is an advanced ultra-super critical (A-USC) boiler grade austenitic stainless steel with the distinct addition of 3 wt.-% of Copper. A-USC power plants intended to operate in chloride rich environments (sea shore, feed water residues, etc.) are susceptible to chloride assisted corrosion failures. In this study, the pitting corrosion behaviour of the Super 304HCu parent material and tungsten inert gas weld joints was studied using a potentiodynamic cyclic polarization test in 3.5 % NaCl solution at three different pH levels (pH = 3, pH = 7, and pH = 11). The Epit values of the parent material is found to be much nobler than that of the weld joints. The micrographs of the pitted weld joints and the oxalic acid etched structure of Super 304HCu joints are presented. From the micrographs it is revealed that the heat affected zone is the most susceptible region to pitting corrosion.

Corrosion behaviors of super austenitic stainless steel weldment by GTAW welding for ships desulfurization system

This study aims to clarify how filler-typed metals which were ERNiCrMo-3 and ERNiCrMo-4 affect corrosion resistance characteristics in the weldment of super austenitic stainless steel joints under the simulated desulfurization environment for ships. The desulfurization environment includes high temperature, chlorides, and acidic conditions, which, inevitably, can cause severe corrosion to great extent. For exact clarification, the variations of microstructure and the composition distribution in the weldment before and after welding was examined by using scanning electron microscope and energy dispersive X-ray spectroscopy. Then, the corrosion resistance characteristics were comparatively evaluated through the cyclic potentiodynamic polarization test together with potential measurement under the desulfurization simulated environments. In addition, the correlation between passive film and corrosion resistance characteristics was investigated after identifying the formed features of the passive film through the X-ray photoelectron spectroscopy analysis. Through these studies, it made certain, ERNiCrMo-4 filler metal with high Mo content is advantageous for the formation of MoO3 oxide on the surface, which belongs to form a stable passive film and maintains the corrosion resistance characteristics under the simulated desulfurization environment.

Process parameters, structure and mechanical properties of dissimilar Nimonic 80 A/AISI 316 L resistance welded joints

Abstract The effects of welding current and welding time on the shear resistance of spot welded joints of dissimilar Ni-base superalloys and austenitic stainless steels are investigated for expanding the limits of their use in automotive, naval and aerospace industries. The macro- and micro-structural characteristics, microhardness, and shear strength of the welded joints were examined in order to characterize the resulting joints. It was found that the shear resistance of the heterogeneous welded joints reaches values of 742–849 MPa, much higher than the one specific of the weaker material, which is the austenitic stainless steel with low carbon content, AISI 316 L. The diameter of the welded cores increased for higher current and welding time. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) were used to evaluate the microstructure of the welded joints from the two dissimilar materials.

Effect of incident angle on weld microstructure and mechanical properties of laser beam welded nitronic −50 austenitic stainless steel joints

3 mm thick nitronic-50 stainless steel sheets were successfully butt-joined using a 2 kW fiber laser beam welding. Three weld joints were fabricated for different incident angles, namely, 70°, 80° and 90° for the other constant welding process parameters. The effect of incident angle on the weld bead geometry, microstructure evolution, and strength of the laser beam welded joints was studied in detail. The incident angle significantly affected the bead geometry and its orientation. Lowering the incident angle beyond a limit caused the beam shift near the weld root of the joint, where the bead was formed away from the joint line resulting in improper fusion and a defective weld occurred. The microstructure transformed from columnar to an equiaxed dendritic structure at the center of the weld nugget for lower incident angles. Skeletal and lathy ferrite was observed in the joints' weld zone. However, the fraction of lathy ferrite was higher at lower incident angles due to a faster cooling rate. A higher weld joint strength of 1010 MPa (97% of the base metal UTS) was achieved at an 80° incident angle, owing to the formation of more equiaxed dendritic grains and the absence of the secondary phases. All of the tensile test samples showed evidence of ductile failure, and overall, an acceptable level of elongation was achieved.