Austenitic Stainless Steel Weld Research Articles

Prevention of weld decay in TIG welded AISI 304 steel pipes

Weld decay due to chromium carbide precipitation at grain boundaries in the heat affected zone (HAZ) during TIG welding of austenitic stainless steels. This issue is particularly significant concerning the welding of AISI 304 steels, commonly used in the food industry. Although this problem can be overcome with different methods, there are some restrictions. A novel technique for welding AISI 304 steel pipes is introduced to reduce weld decay and improve the mechanical properties. The use of this technique, which includes faster cooling after welding, significantly minimizes the time of precipitation of chromium carbide. Temperature measurements and microstructural analyses monitor precipitation and the impact of the technique on the mechanical characteristics of AISI 304 steel pipes was assessed through hardness and hoop tensile tests. There was a 6% increase in hardness values observed in the HAZ region. Furthermore, a 16.7% increase in maximum load and a 127.4% increase in elongation. The reduction in chromium carbide precipitation observed in the microstructural analysis was confirmed through the double loop electropotentiokinetic reactivation (DLEPR) test, specifically for assessing intergranular corrosion. With the novel method, there was a 25% increase in corrosion resistance in the HAZ and a 40% increase in the weld zone.

Modelling, Simulation and Thermo-Mechanical FEA of Gas Tungten Arc Welding of Austenitic Stainless Steel

Modelling, Simulation and Thermo-Mechanical FEA of Gas Tungten Arc Welding of Austenitic Stainless Steel

Evaluation of Sensitization Behaviors on the Heat-Affected Zone of Austenitic Stainless Steel Weld by Thermal Cycles of Actual Multi-pass Welding

AbstractThe sensitization behavior of the welding heat affected zone (HAZ) in austenitic stainless steels (SSs) was investigated through simulated thermal cycles emulating actual multi-pass welding processes using the Gleeble simulator. The tests were performed with austenitic SSs, considering carbon contents, heat input, and distance from the fusion line to determine the thermal cycle conditions of the HAZ. Higher carbon content led to increased sensitization (degree of sensitization, DOS) values, while the influence of the thermal cycle in the final weld pass was that even though it was rapidly heated to over 1000 °C and cooled at a rapid rate, the DOS value decreased due to partial carbide dissolution and chromium diffusion. Therefore, effective management of the final thermal cycle in the HAZ contributes to improved intergranular stress corrosion cracking resistance. Even with prolonged exposure of the HAZ to the sensitization region, the discovery that corrosion resistance improves when the final heating cycle reaches 1000 °C underscores the importance of HAZ heat cycle management and provides valuable insights for materials engineering and industrial applications. Graphical abstract

Influence of inconel interlayer on microstructural, mechanical and electrochemical characteristics in single-pass ATIG welding of dissimilar austenitic and duplex stainless steel

This study investigates the impact of Inconel 625 interlayer on dissimilar welded low nickel austenitic stainless steel (LNiASS) and super duplex stainless steel (S32760) using activated tungsten inert gas (ATIG) welding. Two weldments were prepared: with and without (autogenous) interlayer. Geometrical investigation of the weld cross sections revealed that interlayer-based welding significantly increased the depth of penetration and decreased weld width as compared to autogenous welding at the same welding current. The dual microstructure was observed in the weld zone (WZ) of autogenous weldment while fully austenitic structure with few intermetallics was observed in the WZ of interlayer-based weldment. Mechanical properties, particularly impact strength observed to be improved in the case of interlayer-based weldment (91 ± 2 J) compared to autogenous weldment (68 ± 2 J). Lower microhardness was noticed for the WZ of interlayer-based weldment (258 ± 3 HV0.2) than WZ of autogenous (279 ± 2 HV0.2) weldment due to the presence of higher content of Ni. However, UTS of interlayer-based weldment (654 MPa), falls short in comparison to the autogenous weldment (693 MPa), indicating a compromised joint efficiency of 5.96%. The corrosion resistance was observed to be higher for the WZ of interlayer-based weldment attributed to the higher content of Ni and Mo. The sensitization study revealed 47.33% degree of sensitization in the WZ of autogenous weldments due to dual microstructure, while interlayer-based weldments showed no sensitization.

Effects of Aging at 550 °C on α′-Martensitic Transformation of High Si-Bearing Metastable Austenitic Stainless Steel Weld Metal

Effects of Aging at 550 °C on α′-Martensitic Transformation of High Si-Bearing Metastable Austenitic Stainless Steel Weld Metal

The strengthening role of post-welded cryogenic treatment on the performance and microstructure of 304 austenitic stainless steel weldments

The metallurgical changes and micro defects after welding can influence the mechanical property, corrosion resistance and dimensional stability of the stainless steel wielding joints. It is necessary to explore an effective post-welded method to improve the service performance for stainless steel welding joints. Furthermore, the essential mechanism between microstructure changes and macro-property variation during this process needs deep reveal. Therefore, this paper aims at investigating the effects of different post-weld treatments including naturally aging, artificial aging and cryogenic treatment on the residual stress and mechanical properties of 304 stainless steel weldments. The microstructure evolution was also studied to reveal and establish the microstructure-performance relationship. The results showed that the distribution of residual stress was most uniform with lowest magnitude (decreased by up to 49%) after cryogenic treatment. At room temperature, weldments subjected to the three post treatments showed similar mechanical properties. At cryogenic temperature, cryogenic treatment exhibited an outstanding role on maintaining the mechanical properties of weldments. By contrast, the mechanical properties were obviously reduced by artificial aging. The transformation of δ-ferrite and the carbide precipitation in grain boundaries are the main reasons for the decrease of mechanical properties after artificially aging. Welding process was able to cause the transfer of the alloying elements and decrease the stability of austenite. Consequently, martensitic transformation can be induced during cryogenic treatment. The new formed martensite resulted in the refined microstructure and high mechanical properties of weldments, and also the release of residual stress after welding.

Application research on ultrasonic phased array detection algorithm for austenitic stainless steel with V-groove weld

Conventional ultrasonic detection methods are commonly used for detecting austenitic stainless steel weld structure. The anisotropy and inhomogeneity of the weld produces a strong scattering and energy attenuation effect on the acoustic wave. Controlling the accurate focusing of synthetic beams by ultrasonic transducer with multi-array element can be challenging, and difficult in detecting internal defects. A multi-group sequence grain model was established according to the distribution of grain orientation (DGO) in the weld, and then the “Velocity Coefficient K” algorithm was explored and developed, which is capable of quickly determining the acoustic wave propagation in the austenitic stainless steel weld with V-groove weld. By establishing an acoustic ray-tracing model with its analysis, the focusing law can be obtained quickly. The experimental results showed that the proposed algorithm has great effectiveness in detecting the signal-to-noise ratio (SNR) and imaging quality of defects.

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

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

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

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

Effect of Heat Input on Microstructure and Properties of Laser-Welded 316L/In601 Dissimilar Overlap Joints in High-Temperature Thermocouple.

Heat input, a crucial factor in the optimization of high-temperature thermocouple laser welding, has a significant impact on the appearance and mechanical properties of dissimilar welded joints involving stainless-steel- and nickel-based alloys. This study focuses on laser overlay welding of austenitic stainless steels and nickel-based alloys. The findings indicate that an increase in heat input has a more pronounced effect on the penetration depth and dilution rate. Under high heat input, the weld has cracks, spatter, and other defects. Additionally, considerable amounts of chromium (Cr) and nickel (Ni) elements are observed outside the grain near the crack, and their presence increases with higher heat input levels. Phase analysis reveals the presence of numerous Cr2Fe14C and Fe3Ni2 phases within the weld. The heat input increases to the range of 30-35 J/mm, and the weld changes from shear fracture to tensile fracture. In the center of the molten pool, the Vickers hardness is greater than that of the base metal, while in the fusion zone, the Vickers hardness is lower than that of the base metal. The overall hardness is in a downward trend with the increase of heat input, and the minimum hardness is only 159 HV0.3 at 40 J/mm. The heat input falls within the range of 28-30 J/mm, and the temperature shock resistance is at its peak.

Understanding the microstructural evolution and tensile characteristics of low nickel austenitic stainless-steel welds fabricated by diode LASER

In the present investigation, the utilization of diode laser welding in both continuous wave (CW) and pulse wave (PW) modes was applied to weld sections of 4 mm thick low nickel austenitic stainless steel (LNiASS) material. Subsequently, a comprehensive examination of the microstructural attributes of these welds was conducted by X-ray diffraction, electron backscatter diffraction (EBSD), and electron channeling contrast imaging (ECCI). The microstructural assessment was performed at both as-welded state and after the tensile deformation at three discrete strain rates ranging from 3.3 × 10−4 to 1.0 × 10−2. Furthermore, an investigation into the influence of strain rate variations on the tensile behavior of the two aforementioned types of welded joints, along with an exploration of the occurrence of strain-induced martensitic transformation, was carried out. The outcomes revealed that the PW welds yielded finer grain sizes in comparison to CW welds. It was observed that the martensite content within both CW and PW welds exhibited an augmentation with increasing strain rates. Furthermore, the PW welds exhibited a higher martensite content when compared to the CW welds under all examined strain rates. The PW welds consistently demonstrated higher UTS and total elongation across all three strain rates, while the CW welds exhibited a higher YS. Furthermore, as the strain rates increased, a decline in the strength ratio was observed for both weld types, accompanied by an increasing disparity between UTS and YS, indicative of work hardening phenomena.

Fatigue Crack Growth Evaluation of Pipeline Steels and Girth Welds

Abstract Fatigue test specimens were prepared and tested with an API 5 L X70 spiral welded pipe steel and girth weld. For a few selected specimens, two unloading compliance techniques (elastic compliance and back-face strain compliance) were applied simultaneously to a single specimen for direct comparisons of in situ crack size estimation. This paper also includes fatigue crack growth rate (FCGR) data of other pipe steels and welds available in the literature. It was observed that most FCGR curves of pipeline steels (X65–X100) remained within the BS 7910 mean and upper bound design curves in the Paris region. It was noted that the FCGR of austenitic stainless pipe steel and girth weld obtained from Arora et al. (2014), “Fatigue Crack Growth Studies on Narrow Gap Pipe Welds of Austenitic Stainless Steel Material,” Procedia Eng., 86, pp. 203–208) showed a very superior fatigue property.

Effects of environmental parameters on chloride-induced stress corrosion cracking behavior of austenitic stainless steel welds for dry storage canister application

This study investigated the chloride-induced stress corrosion cracking (CISCC) behavior expected to occur in welds of austenitic stainless steel, which are considered candidate materials for dry storage containers for spent nuclear fuel. The behavior was studied by varying temperature, relative humidity (RH), and chloride concentration. 304L-ER308L welded plates were processed into U-bend specimens and exposed to a cyclic corrosion chamber for 12 weeks. The CISCC behavior was then analyzed using electron microscopy. A previous study by the authors confirmed that CISCC occurred in ER308L at 60 °C, 30% RH, and 0.6 M NaCl via selective corrosion of δ-ferrite. When the temperature was lowered from 60 °C to 50 °C, CISCC still occurred. However, when the humidity was reduced to 20% RH, CISCC did not happen. This can be attributed to the retardation of the deliquescence of NaCl at lower humidity, which was insufficient to promote CISCC. Furthermore, increased chloride concentration to 1.0 M resulted in the absence of CISCC and widespread surface corrosion with severe pitting corrosion because of the increase in thin film thickness.

Understanding and Controlling the Weld Microstructure of Steels

In this article, selected studies are reviewed with a focus on the analysis of microstructure development in steel weld metals. In the study of austenitic stainless steel weld metals, microstructure development in the primary ferrite solidification mode (FA mode) was clarified and related to why FAmode welds are resistant to hot cracking. In studies of duplex stainless steel weld metals and high-Cr ferritic stainless steel weld metals, nitrogen-driven microstructure development and TiN-assisted grain refinement, respectively, were described, and discussions about the mechanism of equiaxed grain formation in the weld metals were added in the latter. In the study of low-alloy steel weld metals, the roles of titanium oxide and titanium nitride (TiN) inclusions on intragranular ferrite formation and the refinement of weld microstructure were described based on crystallographic analysis and the first principles calculation. At the end, the potential importance of the application of different multiscale, multiphysics simulations to welding research was pointed out.

Modeling Yield Strength of Austenitic Stainless Steel Welds Using Multiple Regression Analysis and Machine Learning

Designing welding filler metals with low cracking susceptibility and high strength is essential in welding low-temperature base metals, such as austenitic stainless steel, which is widely utilized for various applications. A strength model for weld metals using austenitic stainless steel consumables has not yet been developed. In this study, such a model was successfully developed. Two types of models were developed and analyzed: conventional multiple regression and machine-learning-based models. The input variables for these models were the chemical composition and heat input per unit length. Multiple regression analysis utilized five statistically significant input variables at a significance level of 0.05. Among the prediction models using machine learning, the stepwise linear regression model showed the highest coefficient of determination (R2) value and demonstrated practical advantages despite having a slightly higher mean absolute percentage error (MAPE) than the Gaussian process regression models. The conventional multiple regression model exhibited a higher R2 (0.8642) and lower MAPE (3.75%) than the machine-learning-based predictive models. Consequently, the models developed in this study effectively predicted the variation in the yield strength resulting from dilution during the welding of high-manganese steel with stainless-steel-based welding consumables. Furthermore, these models can be instrumental in developing new welding consumables, thereby ensuring the desired yield strength levels.

Role of Ni content on microstructural and mechanical responses of Nb-stabilized metastable austenitic stainless steel weld metals

Three Nb-stabilized metastable austenitic stainless steel (15Cr–9Ni–Nb steel) weld metals with Ni contents of 8.4 wt%, 9.2 wt%, and 10.2 wt% were designed and prepared by gas tungsten arc welding. The effects of Ni content on the solidification behavior, microstructure, and the mechanism of deformation-induced martensitic transformation in the tensile process were investigated via scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, and high-resolution transmission electron microscopy, and their effects on mechanical properties were also discussed. As the Ni content increased, the solidification mode of weld metals changed from ferrite-austenite mode to austenite-ferrite mode, which made the segregation of Nb and Si at the interdendritic region more obvious and increased the total volume and the average size of primary NbC significantly. The large amount of coarse primary NbC in the AF weld metal damaged the impact toughness and reduction of area by inducing intergranular cracks and intergranular fractures. Moreover, both the three weld metals had poor mechanical stability and the deformation-induced martensitic transformation (DIMT) (γ→α′) occurred during the tensile process, which contributed to increased tensile strength. As the Ni content increased, the mechanical stability of austenite increased, and the strengthing effect of DIMT decreased, while the uniform elongation of weld metals increased.

Microstructure and Hardness Properties of AISI 321 Stainless Steel Welded Joints with Different Filler Metal

Austenitic stainless steel is susceptible to sensitization when exposed to high temperatures. During welding operations, they tend to form chromium depletion zones and thus become susceptible to intergranular corrosion. The microstructure and hardness properties of AISI 321 austenitic stainless steel welds have been studied in this work. The phenomenon of sensitization of AISI 321 stainless steel during GTAW has also been investigated. This experiment observed three welded samples using different filler metals, ER316, ER308, and ER347. Weld sample analysis was studied using an optical microscope and a microhardness tester. The results demonstrated that the type of filler metal significantly affected changes in the microstructure and hardness of the weld joint.

Simulation of wave propagation in austenitic stainless steel welds with solidification structure predicted by Cellular Automaton method

Austenitic stainless steel is widely used in nuclear power plants (NPPs) and a variety of occurrences of stress corrosion cracking (SCC) near its weld have been reported among NPPs. Ultrasonic testing is a critical technique for the detection and depth sizing of SCCs. However, such welds' anisotropic and heterogeneous properties cause difficulties in ultrasonic testing when ultrasonic waves propagate through welds. Deeply understanding the characteristics of ultrasonic waves with wave propagation simulation is effective to improve the accuracy of ultrasonic testing. To this end, it is necessary to take crystal orientation and grain boundary into account simultaneously in the numerical model. In this study, a model was developed so that the Cellular Automaton (CA) method can simulate the solidification structure from multilayer and multipass welding process, then the solidification structure of a 7-layer and 7-pass weld of austenitic stainless steel was predicted based on welding conditions. Finally, the finite element method was used to compute wave propagation in austenitic stainless steel weld with the solidification structure predicted. Numerical results of wave propagation in austenitic stainless steel weld were compared to those obtained by experiment.

Interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening of δ-ferrite in 308L stainless steel weld metal

In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors, the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure vessel suffers from thermal aging and irradiation damage simultaneously, which can induce microstructural evolution and hardening of the material. Since it is quite difficult to achieve this simultaneous process out of the pile, two kinds of combined experiments, i.e., post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work. The interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening of δ-ferrite in 308 L weld metal was investigated by combining atom probe tomography, transmission electron microscopy and nanoindentation tests. The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation, thus enhancing hardening of irradiated δ-ferrite. For the effect of irradiation on the microstructure and hardening of thermally aged δ-ferrite, however, intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spinodal decomposition, leading to a limited effect on hardening of thermally aged δ-ferrite. Furthermore, the interaction of thermal aging and irradiation can promote G-phase precipitation. Meanwhile, the interaction can cause δ-ferrite hardening, which is mainly influenced by spinodal decomposition, followed by G-phase and dislocation loops, where spinodal decomposition and G-phase cause hardening by inducing strain fields.

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.