Microstructure and Mechanical Property Change During FSW and GTAW of Al6061 Alloy

The variation of morphology and mechanical properties of Al6061 automotive aluminum alloy due to friction stir welding (FSW) and gas tungsten arc welding (GTAW) was investigated by optical metallography, scanning electron microscopy, microhardness measurement, X-ray diffraction, tensile testing, and fractography. The center-line dendrite emergence and microhardness reduction in the heat-affected zone were observed in the GTAW process. Although similar microhardness reduction with respect to the base metal was observed in the FSW samples, higher HVs were obtained for the FSW rather than the GTAW process at almost all heat-affected locations. Ultimate tensile strengths of the FSW and the GTAW samples in the transverse direction were ~0.57 and ~0.35 of the base metal, respectively. Post-weld aging improved the strength, but reduced the ductility of the welding.     

Optimising process parameters for gas tungsten arc welding of an austenitic stainless steel using genetic algorithm

Automated Gas Tungsten Arc Welding (GTAW) with filler wire addition using a wire feeder is a candidate process for welding of 316LN austenitic stainless steel, which is the major structural material for the Indian 500 MWe Fast Breeder Reactors. In GTAW, the quality of the weld is characterized by the weld-bead geometry as it influences the mechanical properties and its performance during service. This paper discusses the development of computational model using genetic algorithm for determining the optimum/near-optimum GTAW process parameters for obtaining the target weld-bead profile during automatic welding of 316LN stainless steel. Using the experimental data generated on the influence of process variables on weld-bead geometry, regression models correlating the weld-bead shape parameters with the process parameters were developed for determining the objective function in genetic algorithm. Close agreement was achieved between the target weld-bead profile and the model-computed weld-bead profile. This study has shown that use of genetic algorithm is an appropriate methodology for optimising process parameters to obtain target weld-bead profile in GTAW with wire feeder of 316LN stainless steel.     

Microstructural and Mechanical Characterization of as Weld and Aged Conditions of AA2219 Aluminium Alloy by Gas Tungsten Arc Welding Process

In this article, Welding of AA2219 aluminium alloy using Gas tungsten arc welding process (GTAW) and evaluation of metallurgical, mechanical and corrosion properties of the joints are discussed. The weld samples were subjected to ageing process at the temperature range of 195°C for a period of 5 h to improve the properties. AA2219 aluminium plates of thickness of 25 mm were welded using gas tungsten arc welding (GTAW) process in double V butt joint configuration. The input parameters considered in this work are welding current, voltage and welding speed. Tensile strength and hardness were measured as performance characteristics. The variation in the properties were justified with the help of microstructures. The same procedures were repeated for post weld heat treated samples and a comparison was made between as weld condition and age treated conditions. The post weld heat samples had better tensile strength and hardness values on comparing with the as weld samples. Fracture surface obtained from the tensile tested specimen revealed ductile mode of failure.     

Influence of Activating Flux and Helium Shielding Gas on an Austenitic Stainless Steel Weldment

Activating flux-assisted gas tungsten arc welding (GTAW) is a well-established method for enhancing weld penetration. In GTAW, steel is usually welded with a shielding gas that contains mostly argon. However, pure argon does not provide enough weld penetration. Argon-helium mixtures are inert and a greater concentration of helium would increase the arc voltage and the weld depth-to-width (D/W) ratio. There is a significant level of interest in the interaction between activating flux and shielding gas composition. Weld morphology, arc profile, retained δ ferrite content, angular distortion, and microstructure are extremely important in applying the activating flux combination argon-helium in GTAW; therefore, in this work, all these were studied.     

Argon-Hydrogen Shielding Gas Mixtures for Activating Flux-Assisted Gas Tungsten Arc Welding

Using activating flux for gas tungsten arc welding (GTAW) to improve penetration capability is a well-established technique. Argon is an inert gas and the one most widely used as a shielding gas for GTAW. For the most austenitic stainless steels, pure argon does not provide adequate weld penetration. Argon–hydrogen mixtures give a more even heat input to the workpiece, increasing the arc voltage, which tends to increase the volume of molten material in the weld pool as well as the weld depth-to-width ratio. Great interest has been shown in the interaction between activating flux and the hydrogen concentration in an argon-based shielding gas. In this study, the weld morphology, the arc profile, the retained delta ferrite content, the angular distortion, and the microstructures were examined. The application of an activating flux combining argon and hydrogen for GTAW is important in the industry. The results of this study are presented here.     

Dilution in single pass arc welds

A study was conducted on dilution of single pass arc welds of type 308 stainless steel filler metal deposited onto A36 carbon steel by the plasma arc welding (PAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and submerged are welding (SAW) processes. Knowledge of the arc and melting efficiency was used in a simple energy balance to develop an expression for dilution as a function of welding variables and thermophysical properties of the filler metal and substrate. Comparison of calculated and experimentally determined dilution values shows the approach provides reasonable predictions of dilution when the melting efficiency can be accurately predicted. The conditions under which such accuracy is obtained are discussed. A diagram is developed from the dilution equation which readily reveals the effect of processing parameters on dilution to aid in parameter optimization.     

Service Reliability Assessment of Weld Repaired CrMoV Steel Rotors

This research deals with the service evaluation of a retired CrMoV steel rotor that has been repaired using deep groove multi‐pass submerged arc welding (SAW) and gas tungsten arc welding (GTAW). Accelerated creep tests were conducted at several elevated temperatures and extrapolated to the service temperatures. The coalescence of carbides and cavity growth during creep were evaluated. For the CrMoV‐GTAW samples, it was found that the creep life depended on the location of the crossweld in the welded specimen. The service lives of the weldments were extrapolated.     

T91/Super304H异种钢管焊接工艺研究

研究了具有良好高温蠕变强度和抗氧化性的T91和Super304H异种钢管的焊接试验材料、焊接参数、焊缝两侧力学性能及冲击韧性,焊接组织转变等,最终确定了T91及Super304H的最佳焊接工艺。     

Effect of GTAW Parameters on Structure and Mechanical Properties of C86300 Weld Joint

In this study, the effects of heat input variation in gas tungsten arc welding (GTAW), on structure and mechanical properties of commercially C86300 (containing addition of 0.6 wt% silicon) weld joint were investigated. Following microstructural characterization of Base metal, GTAW has been performed at welding currents 50 and 60 A and flow rates of argon shielding gas (10, 14 and 18 l/min) using the same filler metal composition. Therefore six GTAW samples were performed with various welding specifications. By structural investigations and hardness profiles, effects of increasing heat input on increasing average grain size in weld zone, heat affected zone width, penetration depth and alloying element losses were indicated. However increasing heat input increases penetration depth and has a positive effect on hardness and strength of the joint. In considering wear application of this alloy castings and probable GTAW for them, pin-on-disc wear test was performed and revealed better wear resistance of weld metal in comparison with base metal. Hence the optimum values of welding current and argon flow rates (in GTAW with the same composition filler) was determined for this alloy.     

The effect of Ti addition on equiaxed grain formation in ferritic stainless steel welds

This study examines mechanisms for providing nuclei to equiaxed grains in the welds of pure ferritic stainless steel(FSS).The addition of the alloy element Ti to pure FSS 439 causes the precipitation of TiN,which can benefit the columnar-to-equiaxed transition(CET) of gas tungsten arc welding(GTAW).Meanwhile,the initial morphology of the precipitates,the concentration multiplications of Ti,N,etc.of FSS 439 should be controlled to induce the formation of CET during the short welding process.     

Microstructure and Mechanical Properties of TWIP Steel Joints

As a new type of high manganese steel, the twinning induced plasticity （TWIP） steels have attracted a growing interest in the automotive industry due to their good performance. Thin plates of TWIP steel were welded by laser beam welding （LBW） and gas tungsten arc welding （GTAW）. The microstructure result shows that GTAW joint has obvious heat-affected zone （HAZ）, while the HAZ of LBW joint is almost invisible. The X-ray diffraction result shows that the phase compositions of both joints are austenitic and no phase transition occurs. Energy disper- sive spectrometry result shows that there is violent evaporation of Mn element in LBW joint, while the proportion of Mn element in GTAW joint is almost unchanged. Tensile tests and micro-hardness measurements were performed to take into account the mechanical properties of joints manufactured by the two different processes. The micro-hard- ness profiles of both joints present a typical saddle distribution, and the hardness of GTAW seam is lower than that of LBW seam. The failure positions of LBW joints are all located in base metal while the GTAW joints are all at the weld toe due to the softening of HAZ. By means of scanning electron microscopy, a typical ductile fracture is observed in LBW joint, while a brittle fracture with quasi-cleavage fracture characteristic is observed in GTAW joint.     

Microstructural and Mechanical Studies of T91/T22 Welded Joints

Comparative studies have been performed to decide an appropriate combination of welding process and filler material by virtue of microstructural evolution, micro-hardness studies, tensile strength and fractographic analysis. Manual arc welding and tungsten inert gas welding processes are used along with different filler materials to manufacture T91/T22 welded joints. Studies with the purpose of comparison and evaluation of different zones of the weldments have been carried out. The highest value of micro-hardness observed on the T91 HAZ of the weldments may be attributed to martensitic structure of the region. The fracture morphology of both the weldments obtained from T22 BM has revealed the ductile fracture. Comparatively higher tensile strength (578 MPa) of T91/T22, GTAW combination is noticed by virtue of lower heat input. The better performance of T91/T22, GTAW weldment can be quoted on the basis of better joint integrity, tensile strength and ductility (26.4%).     

On the calculation of the free surface temperature of gas-tungsten-arc weld pools from first principles: Part I. modeling the welding arc

A mathematical formulation has been developed and computed results are presented describing the temperature profiles in gas tungsten arc welding (GTAW) arcs and, hence, the net heat flux from the welding arc to the weld pool. The formulation consists of the statement of Maxwell's equations, coupled to the Navier-Stokes equations and the differential thermal energy balance equation. The theoretical predictions for the heat flux to the workpiece are in good agreement with experimental measurements — for long arcs. The results of this work provide a fundamental basis for predicting the behavior of arc welding systems from first principles.     

Improvement of Metallurgical and Mechanical Properties of Gas Tungsten arc Weldments of Alloy 686 by Current Pulsing

This research article examines the metallurgical and mechanical behavior of twenty-first-century nickel-based superalloy 686. The weld joints were produced with ERNiCrMo-4 and ERNiCrMo-14 filler wires by continuous current gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) mode. Optical and scanning electron microscope (SEM) analyses were performed to evaluate the microstructure of welded joints. PCGTAW weldments showed refined microstructure, narrower weld bead and minimum heat-affected zone compared to GTAW. SEM analysis revealed the presence of secondary phases in the interdendritic regions of GTA and PCGTA weldments made of ERNiCrMo-4 and GTA ERNiCrMo-14 fillers. Energy-dispersive X-ray spectroscopy examination was also performed to assess the microsegregation of alloying elements in the weldments. The results proved nonexistence of microsegregation in the case of PCGTA weldments made by ERNiCrMo-14 filler. However, segregation of alloying element Mo was noticed in other weldments. Strength and toughness of the weld joints were evaluated by conducting tensile and Charpy impact tests. The refined microstructure with the absence of microsegregation obtained in the PCGTA welding made with ERNiCrMo-14 filler wire resulted in the higher strength and toughness than other weldments.     

Evaluating the Properties of Dissimilar Metal Welding Between Inconel 625 and 316L Stainless Steel by Applying Different Welding Methods and Consumables

The current work was carried out to characterize welding of Inconel 625 superalloy and 316L stainless steel. In the present study, shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) with two types of filler metals (ERNiCrMo-3 and ERSS316L) and an electrode (ENiCrMo-3) were utilized. This paper describes the selection of the proper welding method and welding consumables in dissimilar metal joining. During solidification of ERNiCrMo-3 filler metal, Nb and Mo leave dendritic cores and are rejected to inter-dendritic regions. However, ERSS316L filler metal has small amounts of elements with a high tendency for segregation. So, occurrence of constitutional super-cooling for changing the solidification mode from cellular to dendritic or equiaxed is less probable. Using GTAW with lower heat input results in higher cooling rate and finer microstructure and less Nb segregation. The interface between weld metal and base metal and also unmixed zones was evaluated by scanning electron microscopy and energy dispersive X-ray (EDX) analysis. Microhardness measurements, tensile test, and Charpy impact test were performed to see the effect of these parameters on mechanical properties of the joints.     

Effect of Thermal Refining on Mechanical Properties of Annealed SAE 4130 by Multilayer GTAW

 During the first welding process in manufacturing a precise seam container, the steel material must first undergo a full annealing treatment. Multilayer welding operations are conducted and then applied with refining treatment to obtain the goal by hardening. The influence of thermal refining on mechanical properties of annealed SAE 4130 by multilayer GTAW (gas tungsten arc welding) was discussed. The AW (annealing+welding) and AWST (annealing+welding+solution+tempering) occurred with a minimum hardness value at GGHAZ (grain growth heat affected zone) due to coarse grain growth; the hardness occurred with sudden drops between the multilayer welding, but was still larger than the minimum value at HAZ (heat affected zone). The welded joint efficiency of the AWST was 89.9%, with the elongation reduced to 77.2% of AST (annealing+solution+tempering). The cross section of the tensile samples both appeared with a uniform dimple-shaped structure, and however the necking for AST was greater than that for AWST. The impact value for AWST was 166.5% of AST. Moreover, from microstructure observations, it was found that AWST had a greater tendency to ductile failure than AST. These results can be inferred: the process of steady pressure and the initial position of the precision tube breakage HAZ. However, when stress occurs instantly, HAZ can absorb more energy, therefore the initial damage does not occur.     

电弧炉电弧特性与节电可行性分析

为了最优化修正电弧炉现场操作工艺,达到提高效率,降低电弧炉能耗的目的,分析了电弧炉的电弧特性以及电弧炉节电的可行性。     

The chemistry and structure of wear-resistant,iron-base hardfacing alloys

The chemistry and microstructure of iron-base alloys resistant to galling wear were determined by using optical microscopy and scanning electron microscopy (SEM). Castings and weld overlays, deposited by the gas tungsten arc and plasma arc welding (GTAW and PAW, respectively) processes, were evaluated. The microstructure typically consisted of a primary austenitic matrix, eutectic carbides (M₇C₃ type), and noneutectic carbides. Processing techniques that resulted in high cooling rates yielded microstructures with finer features, less complete partitioning of alloying elements to the carbides, and improved resistance to galling wear. Carbon and manganese appeared to improve resistance to galling wear. Nickel was detrimental to galling wear resistance. Formerly with AMAX Materials Research Center Formerly with AMAX Materials Research Center Formerly with AMAX Materials Research Center     

Effects of the Electrodes’ Shape and Graphite Quality on the Arc Stability During Hydrogen Plasma Smelting Reduction of Iron Ores

Reducing greenhouse gases (GHG), especially CO₂, is necessary to counteract climate change. The European steel industry currently corresponds to 5.7% of the total EU emissions and must therefore minimize their GHG fractions in the future. One of the most promising technologies to eliminate CO₂ emissions while directly reducing iron ore to steel in a single step is the hydrogen plasma smelting reduction. The stability of the plasma arc, which is determined by the properties and geometry of the graphite electrode, has a substantial impact on the process’ economic feasibility. To study the arc stability concerning the graphite quality, tip geometry, and electrode gap, a series of experiments is conducted. The results are evaluated to create stability maps and fields to identify stable process parameters. The geometry of the graphite cathode shows the primary influence on arc stability. Tips with a flat end (standard version) offering the most unstable and a machined step on the graphite cathode providing the most stable conditions. However, an additional coating to prevent side arcing leads to the deterioration of the arc. The two graphite grades tested, with different maximum grain sizes and price classes, show no great relevance to the stability of the arc.     

A Feasibility Study on Manufacturing of Functionally Graded Structures Using SiC Ceramic Powder in a Steel‐Based Matrix by Gas Tungsten Arc Welding (GTAW)

The paper presents a feasibility study on application of the gas tungsten arc welding (GTAW) process to obtain metal composite functional coating for advanced tribological application. Silicon carbide (SiC) particles in the form of powder was added to a weld pool in autogenous mode as well as with an additional filler wire. Powder feeding was carried out at different angles and with varying separation distance from the welding torch. The metallurgical characterization of the cladded structure was carried out using optical as well as scanning electron microscopy (SEM). Energy dispersive X‐ray spectroscopy (EDS) was performed to analyze the composition of the deposited weld metal. It has been observed that due to low SiC density it was difficult for particles to penetrate the weld pool. Also the added SiC was found to be dissociated into Si and carbon (C) and the large amount of dissolved C in the weld pool resulted in formation of graphite phases.