Autogenous Tungsten Inert Gas Research Articles

Effect of Activated Flux on the Microstructure, Mechanical Properties, and Residual Stresses of Modified 9Cr-1Mo Steel Weld Joints

A novel variant of tungsten inert gas (TIG) welding called activated-TIG (A-TIG) welding, which uses a thin layer of activated flux coating applied on the joint area prior to welding, is known to enhance the depth of penetration during autogenous TIG welding and overcomes the limitation associated with TIG welding of modified 9Cr-1Mo steels. Therefore, it is necessary to develop a specific activated flux for enhancing the depth of penetration during autogeneous TIG welding of modified 9Cr-1Mo steel. In the current work, activated flux composition is optimized to achieve 6 mm depth of penetration in single-pass TIG welding at minimum heat input possible. Then square butt weld joints are made for 6-mm-thick and 10-mm-thick plates using the optimized flux. The effect of flux on the microstructure, mechanical properties, and residual stresses of the A-TIG weld joint is studied by comparing it with that of the weld joints made by conventional multipass TIG welding process using matching filler wire. Welded microstructure in the A-TIG weld joint is coarser because of the higher peak temperature in A-TIG welding process compared with that of multipass TIG weld joint made by a conventional TIG welding process. Transverse strength properties of the modified 9Cr-1Mo steel weld produced by A-TIG welding exceeded the minimum specified strength values of the base materials. The average toughness values of A-TIG weld joints are lower compared with that of the base metal and multipass weld joints due to the presence of δ-ferrite and inclusions in the weld metal caused by the flux. Compressive residual stresses are observed in the fusion zone of A-TIG weld joint, whereas tensile residual stresses are observed in the multipass TIG weld joint.

Advances in Fusion Welding Technique of Austenitic Stainless Steels

Activated flux assisted tungsten inert gas (TIG) welding of austenitic 316L stainless steel was investigated. Autogenous TIG welding was used to produce a bead-on-plate weld. The FeO, FeS, and FeF2 were selected as the flux powders. The results showed that the FeS and FeO fluxes produced high aspect ratio welds, while the FeF2 flux produced a relatively low aspect ratio weld. The undercut defect was produced with use of the FeS flux. An experimental result suggested the constriction of arc column as a mechanism in improving activated TIG penetration. In addition, activated TIG process can increase the delta-ferrite content in austenitic stainless steel weld metal.

Study of the characteristics of duplex stainless steel activated tungsten inert gas welds

The purpose of this study is to investigate the effects of the specific fluxes used in the tungsten inert gas (TIG) process on surface appearance, weld morphology, angular distortion, mechanical properties, and microstructures when welding 6 mm thick duplex stainless steel. This study applies a novel variant of the autogenous TIG welding, using oxide powders (TiO 2, MnO 2, SiO 2, MoO 3, and Cr 2O 3), to grade 2205 stainless steel through a thin layer of the flux to produce a bead-on-plate joint. Experimental results indicate that using SiO 2, MoO 3, and Cr 2O 3 fluxes leads to a significant increase in the penetration capability of TIG welds. The activated TIG process can increase the joint penetration and the weld depth-to-width ratio, and tends to reduce the angular distortion of grade 2205 stainless steel weldment. The welded joint also exhibited greater mechanical strength. These results suggest that the plasma column and the anode root are a mechanism for determining the morphology of activated TIG welds.

Algorithmic optimisation of parameters in tungsten inert gas welding of stainless steel sheet

The present paper considers algorithmic optimisation of autogenous manual tungsten inert gas (TIG) welding of four different types of joint using stainless steel sheet of varying thickness from 0.9 to 2.0 mm. First a literature survey is presented, experimental work and the equipment used are described, welding conditions are stated, and the welded joints are represented. Then, experimental results are analysed, assessed, and presented in tables and graphs. Mathematical modelling for the calculation of maximum, minimum, and optimum values of welding current and welding voltage as functions of sheet thickness is described for the four joints. Finally, algorithmic optimisation is described for a particular case, namely, a T joint with a fillet weld. The entire algorithm for optimisation of TIG welding is represented.

The determination of the residual strains and stresses in a tungsten inert gas welded sheet of IN718 superalloy using neutron diffraction

The residual stress state in a tungsten inert gas (TIG) welded sheet of IN718, a high-strength nickel-based superalloy, has been characterized using neutron diffraction. The measurements were performed using a time-of-flight diffractometer, which allowed lattice strains from the γ-γ′ {111} and γ-γ′ {311} composite peaks to be compared with the Reitveld-refined spectra. Residual stresses were estimated using plane-specific values of Young's modulus and Poisson's ratio for the {311} and {111} peaks, and the macroscopic material response for the Reitveld-refined data. These values were obtained from a theoretical analysis of existing data after Kröner. The weld considered was an autogenous TIG weld 180mm long placed centrally on to a 2mm × 100mm × 200mm solution heat-treated sheet of IN718. The strain was mapped over the central 140mm of the plate; within this region, the measured strains were almost constant along the length, with the peak bulk longitudinal strain of 1700 × 10-6 detected 4mm from the weld centre, in the heat-affected zone. The corresponding peak longitudinal stress was 270 MPa, and the tensile region 11 mm wide, with the longitudinal residual stresses typically up to 2.5 times greater than those in the transverse direction. It was also found that, while in-weld stresses derived from analysis of single peaks may be incorrect due to textural and compositional effects, those derived from Reitveld refinement of the entire spectrum showed reasonable agreement with those obtained from incremental hole drilling measurements made with the Matthar-Soete method.

Sensitization Resistance of AISI 308 Stainless Steel Welds with Widmanstatten Austenite

Abstract Seven autogenous tungsten inert gas (TIG) welds were produced in each of 2 plates of AISI 308 stainless steel (SS). The chromium-to-nickel equivalency ratios [(Cr/Ni)eq] of the plates were...

Effect of travel speed on solidification cracking in autogenous tungsten inert gas arc welding of low-alloy steel sheet

A study has been made of the combined effects of composition and travel speed on solidification cracking in the autogenous tungsten inert gas arc welding of low-alloy steel sheet. Data were obtained using the Huxley cracking test for steels to specifications En 24, SAE 4130, and ASTM A 387 B with a range of carbon, sulphur, phosphorus, and oxygen contents. A strong and complex effect of travel speed on cracking susceptibility was revealed, the form of the relationship being determined by the composition of the steel. At high carbon, high sulphur, high phosphorus, and/or low oxygen contents cracking was severe at low speeds but fell progressively to low values at high speeds. At low carbon, low sulphur, low phosphorus, and/or high oxygen contents cracking was low at both low and high speeds with a maximum at an intermediate speed. It is demonstrated that increased travel speed decreases the transverse crack-promoting forces at the rear of the pool but increases the length of the crack-susceptible zone. These effects are used to account for the reported interaction of composition and speed on cracking behaviour. Consideration is given to the significance of the results for welding production and welding test procedure with these steels.

A quantitative study of the effect of composition on vveld solidification cracking in lovv-alloy steels

A study has been made of the effects of material composition on weld metal soldification cracking in the autogenous tungsten-inert gas arc welding of thin low-alloy steel sheet. Published data obtained for about eighty steels have been examined by regression analysis to produce a linear relationship between cracking susceptibility and composition which is both simpler and superior to earlier complex expressions. Using the Huxley cracking test new data were obtained for a range of steels to specifications En 24, SAE 4130 and ASTM A387B as well as several aircraft compositions. The results confirmed the crack-promoting influences of sulphur, phosphorus, and carbon already identified in the cracking relationship, and also revealed a major crack-inhibiting effect of oxygen. These findings were used to produce the following expression linking cracking and composition for these steels under the standardized conditions of the Huxley weld cracking test, i.e. the crack susceptibility factor (CSF) =42 (wt-%C)+847 (wt-%S)+265 (wt-%P)–10 (wt-%Mo)–3042 (wt-%O)+19. The scope and limitations of this type of formula are discussed in terms of its value in demonstrating and predicting the effects of composition on crack susceptibility.