Stainless Steel Gas Tungsten Arc Research Articles

Comparative Study of the Mechanical Property of AISI630 Stainless Steel Gas Tungsten Arc Welds with Different Filler Wires under Room and Cryogenic Temperature

Comparative Study of the Mechanical Property of AISI630 Stainless Steel Gas Tungsten Arc Welds with Different Filler Wires under Room and Cryogenic Temperature

Corrosion Resistance of Dissimilar GTA Welds for Offshore Applications

The pitting corrosion resistance of dissimilar pipeline steel API X70 and Super Duplex 2507 Stainless Steel gas tungsten arc (GTA) welds was studied. The GTA welds were fabricated using Super Duplex 2594 Filler Metal or austenitic 309L Filler Metal. The specimens extracted from the base metal, weld fusion zone, fusion boundary, and heat-affected zones (HAZs) were subjected to a potentiodynamic corrosion test in a 3.5% NaCl water solution. The weld made using the 309L Filler Metal was found to have a smaller pitting resistance equivalent number (PREN) difference between ferrite and austenite, making it more corrosion resistant than the weld fabricated using the 2594 Filler Metal. The HAZ on the X70 side was the most susceptible to pitting and galvanic corrosion for both filler metals.

Investigations on the effect of surface coatings on the weldment properties on chromium manganese stainless steel gas tungsten arc welded plates

This paper reports the enhancements for the effects of specific fluxes such as Tungsten Carbide and Chromium Oxide on the weldment properties such as micro hardness, weld bead geometry and tensile strength obtained with Gas Tungsten Arc Welding Process (GTAW) applied to 6 mm thick Chromium Manganese stainless steel plates. The significant expense of Nickel has made Chromium Manganese stainless steel as an option for conventional 300 arrangement stainless steel. The two fluxes tungsten carbide and chromium oxide were utilized in powdered structure. The tensile test, micro hardness test and corrosion resistance test was conducted to reveal the effect of fluxes on the weldment properties. Results of tensile shows that considerable enhancement in tensile strength and elongation of about 20% increase in case of Chromium Oxide coated samples and 10% increase in case of Tungsten Carbide samples when compared to uncoated specimen. In case of microhardness, 10% increase is exhibited for coated samples compared with uncoated samples. The corrosion rate of coated samples found to be highly resistant for coated samples, which sums to be 300% more than that of uncoated samples. The effect of corrosion rate on the specimens was seen by conducting SEM analysis after the corrosion test. The SEM analysis uncovered that the coating covers the limits encompassing the inclusions and encloses dendrites which reduce the pitting corrosion of the parent metal.

Effect of Heat Input and Shielding Gas on the Performance of 316 Stainless Steel Gas Tungsten Arc Welding

The effect of nitrogen addition and heat input on weld metal microstructure and mechanical properties of alloy 316 is studied. Autogenous gas tungsten arc welding (GTAW) is employed by adding up to 2 vol‌.% N2 in Ar. Welding speed and heat input rate are measured as functions of gas composition. Weld defects are examined by radiographic testing, and weld metal microstructure is studied by optical microscopy. Mechanical properties of welds are determined by uniaxial testing, hardness measurements, and bending test. Weld dendritic structure is refined by increasing N2 content in Ar. The mechanical properties and cooling rate are lower with increasing heat input. Besides, adding nitrogen to argon shielding gas leads to higher values of the ultimate tensile strength and hardness. The tensile strength, yield stress and elongation percent of welds depends strongly on the heat input and nitrogen content of shielding gas. This is discussed on the basis of microstructural characterization. Moreover, the weld nugget area, cooling time and solidification time increase with increasing heat input and nitrogen content. Finally, after applying the bending test up to 180o no cracks, tearing or surface defects could be observed on welded samples.

Studies on microstructure, mechanical and pitting corrosion behaviour of similar and dissimilar stainless steel gas tungsten arc welds

In the present study, an attempt has been made to weld dissimilar alloys of 5mm thick plates i.e., austenitic stainless steel (316L) and duplex stainless steel (2205) and compared with that of similar welds. Welds are made with conventional gas tungsten arc welding (GTAW) process with two different filler wires namely i.e., 309L and 2209. Welds were characterized using optical microscopy to observe the microstructural changes and correlate with mechanical properties using hardness, tensile and impact testing. Potentio-dynamic polarization studies were carried out to observe the pitting corrosion behaviour in different regions of the welds. Results of the present study established that change in filler wire composition resulted in microstructural variation in all the welds with different morphology of ferrite and austenite. Welds made with 2209 filler showed plate like widmanstatten austenite (WA) nucleated at grain boundaries. Compared to similar stainless steel welds inferior mechanical properties was observed in dissimilar stainless steel welds. Pitting corrosion resistance is observed to be low for dissimilar stainless steel welds when compared to similar stainless steel welds. Overall study showed that similar duplex stainless steel welds having favorable microstructure and resulted in better mechanical properties and corrosion resistance. Relatively dissimilar stainless steel welds made with 309L filler obtained optimum combination of mechanical properties and pitting corrosion resistance when compared to 2209 filler and is recommended for industrial practice.

Effect of Microstructure on Stress Corrosion Cracking Behaviour of High Nitrogen Stainless Steel Gas Tungsten Arc Welds

Present work is aimed to improve stress corrosion cracking resistance of high nitrogen steel and its welds. An attempt to weld high nitrogen steel of 5 mm thick plate using gas tungsten arc welding (GTAW) with three high strength age hardenable fillers i.e., 11-10 PH filler, PH 13- 8Mo and maraging grade of MDN 250 filler is made. Welds were characterized by optical microscopy and scanning electron microscopy. Vickers hardness testing of the welds was carried out to study the mechanical behaviour of welds. Potentio-dynamic polarization studies were done to determine pitting corrosion resistance in aerated 3.5% NaCl solution. Stress corrosion cracking (SCC) testing was carried out using constant load type machine with applied stress of 50% yield strength and in 45% MgCl2 solution boiling at 155°C. The results of the present investigation established that improvement in resistance to stress corrosion cracking was observed for PH 13- 8Mo GTA welds when compared to 11-10 PH and MDN 250 GTA welds. However, All GTA welds failed in the weld interface region. This may be attributed to relatively lower pitting potential in weld interface which acts as active site and the initiation source of pitting.

Si-bronze to 304 stainless steel GTA weld fusion zone microstructure and mechanical properties

Si-bronze and 304 stainless steel were joined using gas tungsten arc (GTA) welding with two different welding (filler) rods matching the base metals. Cross-sections of the welds were analyzed using light optical microscopy (LOM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and hardness testing. Mechanical testing was performed for welds from each of the two filler metals using cross-weld tensile bars. For (1) the Si-bronze filler weld, partial mixing resulted in (a) copper-based regions with enhanced hardness due to iron-based islands and (b) iron-based regions with elevated hardness due to Si enrichment. Joint strength was ~ 90% that of the base Si-bronze strength of 340MPa, and elongation was ~ 48%, as compared to the base Si-bronze elongation of 55%. For (2) the stainless steel filler rod (a) primary austenite solidification and (b) micro-fissures were identified in the fusion zone. Thermodynamics calculation software was used to model solidification mode, demonstrating that the Cu (contributed by the Si-bronze) stabilized primary austenite solidification, which led to solidification micro-cracking or micro-fissuring. Micro-fissuring caused low ductility in the transverse weld tensile specimens. Fractography was performed to characterize the fracture mechanisms. For the stainless filler weld, a Cu film formed in interdendritic spaces between primary austenite grains.

Prediction of ferrite number in stainless steel gas tungsten arc welded plates using artificial neural networks

The quality of stainless steel weld is highly influenced by delta ferrite content expressed in terms of ferrite number. The quantity of delta ferrite content formed is controlled by the process parameters. This paper discusses the development of artificial neural network model for predicting the ferrite number in 202 grade stainless steel gas tungsten arc welded plates (GTAW). The process parameters chosen for study are welding gun angle, welding speed, plate length, welding current and shielding gas flow rate. The experiments were conducted based on design of experiments – fractional factorial with 125 runs. Using the experimental data, feed forward, back propagation neural models were developed and trained using Levenberg Marquardt algorithm. The training, learning, performance and transfer functions used are trainlm, learningdm, mean square error and tansig respectively. Five networks were developed with five neurons in the input layer, 1 neuron in the output layer and different nodes in the hidden layer. They are 5-3-1, 5-5-1, 5-10-1, 5-11-1 and 5-15-1. It was found that the artificial neural network (ANN) model based on network 5-5-1 predicted ferrite number more accurately than other networks. The prediction helps in identifying the recommended combination of process parameters to achieve a desired ferrite number in GTAW of stainless steel 202 grade plates.

THE EFFECT OF WELDING HEAT INPUT AND WELDING SPEED ON MICROSTRUCTURE OF CHROMIUM – MANGANESE STAINLESS STEEL GAS TUNGSTEN ARC WELDED PLATES

The quality of any weld joint is highly influenced by the microstructure of the weldment. The quality of the weldment gets deteriorated due to metallurgical changes such as micro-segregation, precipitation of secondary phases, presence of porosities, grain growth in the heat affected zone and loss of material by vaporization. This paper presents study on the effect of welding process parameters such as welding current, welding speed, on the metallography of AISI202 grade chromium manganese stainless steel Gas Tungsten Arc Welded Plates. Experiments were conducted using bead on plate method keeping one parameter at the minimum and maximum levels and keeping the other parameters constant. The metallographic study concentrated on the grain structure, presence of carbides and formation of ferrite, austenite and martensite in the weldment. The obtained results help in selecting quickly the required process parameters to achieve the desired weld quality.

The Effect of Welding Process Parameters on Pitting Corrosion and Microstructure of Chromium-manganese Stainless Steel Gas Tungsten Arc Welded Plates

In this paper, the effect of gas tungsten arc welding (GTAW) parameters on the pitting corrosion on AISI 202 chromium manganese stainless steel was investigated. An empirical mathematical equation correlating pitting resistance equivalent number (PREN) with the welding parameters such as welding current, welding speed, welding gun angle and gas flow rate was developed. Central composite response surface methodology with four parameter and five levels was employed for conducting the experiments. The adequacy of the developed model was checked using ANOVA. The main effects of the process parameters on PREN of the welded joints were studied using surface and contour plots. The quality of the weld joint is also highly influenced by the microstructure of the weldment. The quality of the weldment gets deteriorated due to metallurgical changes such as micro-segregation, precipitation of secondary phases, presence of porosities, grain growth in the heat affected zone and loss of material by vaporization. This paper also investigates the influence of welding gun angle on the microstructure examination of the weldment. The microstructure study concentrated on the grain structure, presence of carbides and formation of ferrite, austenite and martensite in the weldment. The results obtained from the present investigation helps in quickly selecting the required process parameters to achieve the desired PREN and weld quality.

Effect of copper and aluminium addition on mechanical properties and corrosion behaviour of AISI 430 ferritic stainless steel gas tungsten arc welds

The influence of grain refining elements such as copper (Cu) and aluminium (Al) on mechanical properties of AISI 430 ferritic stainless steel welds through gas tungsten arc welding process was studied. Cu (foil form) and Al powder of −100μm mesh was added in the range from 1 to 3g between the butt joint of ferritic stainless steel. In order to investigate the influence of post-weld heat treatment on the microstructure and mechanical properties of welds, post-weld annealing was adopted at 830°C, 30min holding followed by water quenching. Corrosion behaviour of ferritic stainless steel welds was also studied. From this investigation, it is observed that the joints made by the addition of 2g Al (2.4wt.%) in post-weld annealed condition led to improved strength. There is a marginal improvement in the ductility and pitting corrosion resistance of ferritic stainless steel welds by the addition of 2g Cu (0.18wt.%) in post-weld annealed condition. The observed mechanical properties have been correlated with microstructure, fracture features and corrosion behaviour of ferritic stainless steel weldments.

Prediction of Weld Bead Geometry in Chromium-Manganese Stainless Steel Gas Tungsten Arc Welded Plates Using Artificial Neural Networks

The quality of the weld joint is highly influenced by the welding parameters. Hence accurate prediction of weld bead parameters is highly essential to achieve good quality joint. This paper presents development of neural network models for predicting bead parameters such as depth of penetration, bead width and depth to width ratio for AISI 202 grade stainless steel GTAW plates. The use of this series in certain applications ended in failure of the product as there is no adequate level of user knowledge. Hence it becomes imperative to go for detailed investigations on this grade before recommending it for any application. The process parameters chosen for the study are welding current, welding speed, gas flow rate and welding gun angle. The chosen output parameters were depth of penetration, bead width and depth to width ratio. The experiments were conducted based on design of experiments using fractional factorial with 125 runs. Using the experimental data feed forward back propagation neural net work models were developed and trained using Levenberg Marquardt algorithm. The training, learning, performance and transfer functions used are trainlm, learningdm, MSE and tansig respectively. Four networks were developed with four neurons for the input layer, 3 neurons for the output layer and different nodes for the hidden layer. They are 4 – 2 – 3, 4 – 4 – 3, 4 – 8 – 3 and 4 – 9 – 3. It was found that ANN model based on network 4 – 9 – 3 predicted the bead dimensions more accurately than the other networks. The prediction of weld bead geometry parameters helps in identifying the recommended combination of process parameters to achieve good quality joint.

Modeling and analysis of ferrite number of stainless steel gas tungsten arc welded plates using response surface methodology

The prediction of delta ferrite content expressed in terms of ferrite number in austenitic stainless steel welds is very helpful in assessing its performance. The final ferrite content determines the properties of weldments such as strength, toughness, corrosion resistance, and phase stability. This paper presents a study on the effect of process parameters on ferrite number in 202 grade stainless steel gas tungsten arc welded plates (GTAW). Experiments were conducted based on response surface methodology. The ferrite number was determined by using a ferrite scope and by using DeLong diagram. A mathematical model was developed correlating the important controllable GTAW process parameters like welding gun angle, welding speed, plate length, welding current, and shielding gas flow rate with ferrite number. The adequacy of the model was checked using analysis of variance technique. The developed model is very useful to quantitatively determine the ferrite number. The main and interaction effects of the process parameters are presented in graphical form that helps in selecting quickly the process parameters to achieve the desired results.

Hydrogen-assisted crack propagation in 304L/308L and 21Cr–6Ni–9Mn/308L austenitic stainless steel fusion welds

Elastic–plastic fracture mechanics methods were used to characterize hydrogen-assisted crack propagation in two austenitic stainless steel gas tungsten arc (GTA) welds. Thermally precharged hydrogen (140wppm) degraded fracture initiation toughness and crack growth toughness and altered fracture mechanisms. Fracture initiation toughness in hydrogen-precharged welds represented a reduction of >67% from the estimated toughness of non-charged welds. In hydrogen-precharged welds, microcracks initiated at ferrite, and dendritic microstructure promoted crack propagation along ferrite. Deformation twinning in austenite interacts with ferrite, facilitating microcrack formation. While hydrogen altered fracture mechanisms similarly for both welds, the amount of ferrite governed the severity of hydrogen-assisted crack propagation.

Prediction and optimization of depth of penetration for stainless steel gas tungsten arc welded plates using artificial neural networks and simulated annealing algorithm

The quality of a weld joint is highly influenced by depth of penetration. Hence, accurate prediction and maximization of depth of penetration is highly essential to ensure a good-quality joint. This paper highlights the development of neural network model for predicting depth of penetration and optimizing the process parameters for maximizing depth of penetration using simulated annealing algorithm. The process parameters chosen for the study are welding current, welding speed, gas flow rate and welding gun angle. The chosen output parameter was depth of penetration. The experiments were conducted based on design of experiments using fractional factorial with 125 runs. Using the experimental data, feed-forward backpropagation neural network model was developed and trained using Levenberg–Marquardt algorithm. It was found that ANN model based on network 4-15-1 predicted depth of penetration more accurately. A mathematical model was also developed correlating the process parameters with depth of penetration for doing optimization. A source code was developed in MATLAB to do the optimization. The optimized process parameters gave a value of 3.778 mm for depth of penetration.

Impact properties of 304L stainless steel GTAW joints evaluated by high strain rate of compression tests

This paper presents an investigation into the high velocity impact of 304L stainless steel gas tungsten arc welded (GTAW) joints at strain rates between 10−3 and 7.5×103 s−1 using a compressive split-Hopkinson bar. The results show that the impact properties and fracture characteristics of the tested weldments depend strongly on applied strain rate. This rate-dependent behavior is in good agreement with model predictions using the hybrid Zerilli–Armstrong constitutive law. It is determined that the tested weldments fail as a result of adiabatic shearing. The fracture surfaces of the fusion zone and base metal regions are characterized by the presence of elongated dimples. The variation in the observed dimple features with strain rate is consistent with the results of the impact stress–strain curves.

Association of microstructural features and rippling phenomenon in 304 stainless steel gas tungsten arc welds

High speed, high magnification video microscopy has been used to investigate rippling behaviour in autogenous 304 stainless steel gas tungsten arc (GTA) welds. Images of the trailing edge of a weld pool (solid-liquid interface) were collected during the welding process. Weld ripple formation was observed and the associated solid-liquid interface velocity was measured. A distinct sequence of events was observed each time a ripple formed. This sequence of events involved apparent changes in the solid-liquid interface velocity, dendrite morphology, and dendrite growth direction. The microstructures of a group of rippled welds were examined and a number of features associated with the rippling phenomenon were identified. These features included changes in the pattern of the interdendritic constituents and changes in the solute distribution across the ripple feature. This information coupled with the video images was used to explain more fully the weld rippling phenomenon and the origins of microstructural changes associated with it. It is shown that solute redistribution occurs in the weld on a length scale associated with the ripple features.

Dynamic Mechanical Properties and Fracture Behavior of a 304L Stainless Steel GTAW Joint under Shear Conditions

This paper employs the torsional split-Hopkinson bar to investigate the dynamic shear deformation behavior and fracture characteristics of a 304L stainless steel Gas Tungsten Arc Welded (GTAW) joint at room temperature under strain rates in the range of 8 � 10 2 s � 1 to 2:8 � 10 3 s � 1 . The experimental results indicate that the strain rate has a significant influence on the mechanical properties and fracture response of the tested GTAW joints. It is found that the flow stress, total shear strain to failure, work hardening exponent and strain rate sensitivity all increase with increasing strain rate, but that the activation volume decreases. The observed dynamic shear deformation behavior is modeled using the Kobayashi-Dodd constitutive law, and it is shown that the predicted results are in good agreement with the experimental data. Observation of the fractured specimens indicates that the fracture features are closely related to the preceding flow behavior. At all values of strain rate, it is noted that the specimens all fracture within their fusion zones, and that the primary failure mechanism is one of extensive localized shearing. The fracture surfaces are characterized by the presence of many dimples, which suggests a ductile fracture mode. It is shown the strain rate has a significant influence upon the appearance of the dimpled surface. A higher strain rate tends to reduce the size of the dimples and to increase their density. Finally, it is determined that the presence of weld inclusions also influences the appearance of the fracture. These inclusions cause the initiation of micro-voids, which grow and coalesce within the fusion zone, and eventually form a continuous fracture surface.

PWHT effect on the mechanical properties of borated stainless steel GTA weldments for nuclear shield

To improve ductility of the welded joint of B-added austenitic stainless steels, postweld annealing effect has been studied. Gas Tungsten Arc (GTA) welds of AlSI 304-B3 stainless steel plates were annealed either at 700~1100°C for 1 hour or at 1100°C and 1200°C, for 1~7 hours. Bending test of the welds in as-welded and annealed conditions resulted in cracks propagated along the welds’ fusion line except the one annealed at 1200°C, which revealed no cracks. Tensile elongations of the as-welded and annealed welds at the temperature up to 1000°C were only a half value of the base metal, whereas the welds annealed at 1200°C had fully recovered the original elongation of the base metal. Charpy impact test result exhibited the same tendency with annealing temperature. Elongated and accicular morphology ofY-(Cr, Fe)2B eutectic phase at the Partially Melted Heat Affected Zone (P.M.HAZ) of welds seemed to be responsible for the poor ductility of the welds. The welds annealed at 1200°C for various durations, on the other hand, showed fully spheroidized eutectic phases at the P.M.HAZ with its size increased with annealing durations, suggesting that postweld annealing at the temperature as high as 1200°C is required for the welds to have ductility matching that of base metal.

Mechanisms of equiaxed grain formation in ferritic stainless steel gas tungsten arc welds

Mechanisms of providing nuclei for equiaxed grains in gas tungsten arc welds in ferritic stainless steel were examined. Tin-quenching of the solid-liquid interface revealed that TiN particles in commercial steels could act as heterogeneous nucleation sites. Direct additions of TiN also promoted an equiaxed region. However, no evidence for equiaxed grain formation by dendrite fragmentation was observed, despite the fact that titanium additions did produce a more branched dendritic structure.