Steel Gas Tungsten Arc Welds 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

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.

Thermo-mechanical analysis in SAE-AISI 1524 carbon steel gas tungsten arc welds

A thermo-mechanical analysis was conducted in SAE-AISI 1524 carbon steel gas tungsten arc welds. The sequentially coupled thermal-mechanical finite element modelling approach was used to simulate the thermal and stress evolution during the GTAW process. The analysis procedure was divided into two major steps. First, a 3D transient nonlinear heat flow analysis was performed to determine the temperature distribution for the entire welding and cooling cycle of the process. In the second step, the thermal history from the heat flow model was included into the mechanical elasto-plastic calculation of the stress and deformation in the weldment. Temperature-dependent material properties and the effect of forced convection due to the flow of the shielding gas were included in the model. It is encouraging to note that the model is sufficiently accurate to predict the FZ and HAZ weld profiles as evidenced for the good agreement observed between numerical cross-sectional and metallographic temperature profiles. The successful in the results can be attributed greatly to the characteristic heat distribution parameter C selected from the complementary experimental work. For further experimental comparison purposes, numerically predicted residual stresses obtained in three different locations of two different weld situations are presented.

Thermo-mechanical analysis in SAE-AISI 1524 carbon steel gas tungsten arc welds

A thermo-mechanical analysis was conducted in SAE-AISI 1524 carbon steel gas tungsten arc welds. The sequentially coupled thermal-mechanical finite element modelling approach was used to simulate the thermal and stress evolution during the GTAW process. The analysis procedure was divided into two major steps. First, a 3D transient nonlinear heat flow analysis was performed to determine the temperature distribution for the entire welding and cooling cycle of the process. In the second step, the thermal history from the heat flow model was included into the mechanical elasto-plastic calculation of the stress and deformation in the weldment. Temperature-dependent material properties and the effect of forced convection due to the flow of the shielding gas were included in the model. It is encouraging to note that the model is sufficiently accurate to predict the FZ and HAZ weld profiles as evidenced for the good agreement observed between numerical cross-sectional and metallographic temperature profiles. The successful in the results can be attributed greatly to the characteristic heat distribution parameter C selected from the complementary experimental work. For further experimental comparison purposes, numerically predicted residual stresses obtained in three different locations of two different weld situations are presented.

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.

Effect of Mechanical Arc Oscillation on the Grain Structure of Mild Steel Weld Metal

The effect of mechanical arc oscillation on the weld metal grain structure in mild steel gas tungsten arc welds has been studied. For welds made without arc oscillation, columnar grains were observed in the weld metal; however, for the same welding parameters, the weld made with arc oscillation had smaller sized relatively equiaxed grains in the weld metal. The strengths for weld made with arc oscillation was higher than that for weld made without arc oscillation, with appreciable increase in ductility; this could be attributed to the reduction in grain size diameter due to arc oscillation. Lower weld metal hardness and increase in heat affected zone hardness was observed in weld made with arc oscillation; this could be attributed to increase in pro-eutectoid ferrite formation with absence of Widmanstatten ferrite structures in the weld metal and less coarsening of grains in the heat affected zone due to increased cooling rate.

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.

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.