Tungsten Inert Gas Arc Research Articles

A mathematical model of TIG electric arcs operating in the hyperbaric range

In a recent paper Ducharme et al presented a model for a free-burning tungsten inert gas (TIG) electric arc with non-consumable electrodes using a flat anode and argon shielding gas. The model evaluates the laminar gas flow, temperature distribution and electric field in the arc column by treating the current carrying region of the arc as a partially ionized plasma in local thermodynamic equilibrium. The dependence of transport coefficients on temperature is taken into account, as is the entrained shielding gas flow entering the arc from around the cathode. This model is extended here to investigate both 5 mm long 200 A and 10 mm long 100 A electric arcs at elevated pressures in the ranges 1 - 5 and 1 - 14.8 bar respectively. The results of the electric arc model are found to be in satisfactory agreement with a range of experimental data including spectroscopic temperature maps, electric field distributions, voltage drops, arc radii and total radiative emissions. It has been shown by Allum et al that short arcs length < 4 mm) become unstable once a critical Reynolds number has been reached, signifying the onset of turbulence for the flow emerging from the arc nozzle. This analysis, however, does not explain the inherent instability of longer arcs, which may be present even in a still argon atmosphere. It is proposed here that these are caused by the onset of turbulence in the entrained shielding gas. Two seperate Reynolds numbers, therefore, come into play in the physics of the TIG arc in connection with instabilities and these are estimated in the paper.

Weldability of neutron-irradiated type 316 stainless steel

Abstract The post-irradiation weldability of neutron-irradiated type 316 stainless steel has been examined. The tungsten inert-gas arc welded joints were made of type 316 stainless steel used as wrapper tube in the JOYO fast reactor at 668–683 K to a maximum dose and helium content of about 22 dpa and 9 appm respectively. Large loss of tensile ductility was observed in welded joints made of the irradiated steels, being accompanied with intergranular brittle fracture in the heat affected zone at ambient temperature (about 293 K) and at 773 K, although ductile fracture of unirradiated specimens was observed in the weld metal region. The brittle fracture is closely related to helium bubble formation on grain boundaries during the welding.

Mechanical and Corrosion Properties of High Strength 18% Cr Austenitic Stainless Steel Weldment for Boiler.

The properties of weld metal of 18Cr heat resistant austenitic steel containing high copper, niobium and nitrogen were investigated to obtain the matching filler metal for an austenitic stainless steel of 18Cr-9Ni-3Cu-Nb-N steel. This 18Cu-9Ni-3Cu-Nb-N steel tube has been registered as KA-SUS304HJ1TB in the Japanese official standard for fired power plant materials. This steel tube has a high temperature strength 1.4 times as high as the conventional 18Cr steel ASME TP347H. Welding material applicable to this steel is necessary in the fabrication. However, the weld metal consisting of the same chemistries as the base metal had a lower strength than that of the base metal. In this work, the effect of chemistries of molybdenum and nitrogen on the strength of weld metal was investigated. The addition of molybdenum up to 1 mass% was effective for improving the strength without a deterioration of the corrosion resistance. The nitrogen was also effective for improving the strength, but the nitrogen can be decreased by vaporizing during tungsten inert gas arc welding. For improving the solubility of nitrogen in the molten pool, the addition of manganese was effective. From these findings, the chemistry of welding material was determined as 18Cr-16Ni-3Cu-1Mo-3Mn-0.6Nb-0.2N and the tube weldment with that welding material was evaluated in terms of mechanical properties including creep rupture property. It was confirmed that the weldment had comparable properties to the base metal.

Spectroscopic determination of temperature distributions for a TIG arc

The Fowler-Milne or normalized spectroscopic method is used to measure the temperature distribution of a tungsten inert gas (TIG) arc with a number of different spectral lines. The results highlight some of the limitations of this method and provide evidence for departures from LTE in the arc. The paper describes the apparatus and data inversion procedures, and compares the results with those from other groups.

Formation of stainless steel layer on mild steel by welding arc cladding

The discrete microstructural characterization and the formation of stainless steel layer on mild steel where produced in cladding deposits, and fusion boundary region were investigated using tungsten inert gas (TIG) arc, high current pulsed arc and constricted plasma arc. The experimental procedure involved making bead-on-plate method for controlled travel speed, employing filler metal by using tungsten inert gas arc, pulsed current gas tungsten arc and transferred plasma arc, with subsequent sectioning and examination of the reaction interface. For TIG arc cladding, using filler metal of small diameter the deposit does not become stainless steel, but on using 3.2 mm diameter filler metal it becomes stainless steel with less than 50% dilution. For pulsed arc cladding, the complete stainless steel is not obtained on account of the existence of an incomplete mixture, particularly at the fusion boundary region. However, on using a large diameter filler metal at a pulse frequency of 500 Hz, the complete stainless steel microstructure has been accomplished. The plasma arc cladding can be achieved in such a way that the conversion into stainless steel on the mild steel surface — which is the microstructures of cellular austenite in cladding deposit and cellular dendritic austenite containing δ or σ-phase in fusion boundary region — is possible irrespective of the melt penetration and the dilution. The following conditions were found to be beneficial for the formation of stainless steel microstructure layer on the mild steel: using large diameter filler metal, below 50% dilution, and further rendering arc localized and constricted.

Microstructural observations of discrete regions of mild steel surface produced by the tungsten-inert gas arc bead-on-plate method

Microstructural observations of discrete regions of mild steel surface produced by the tungsten-inert gas arc bead-on-plate method

Characterization of the morphological properties of welding fume particles by transmission electron microscopy and digital image analysis.

The morphological characteristics of welding fume particles have been determined using transmission electron microscopy (TEM) and automatic image analysis (AIA). Two personal samples and one background sample were collected using a new, easy to handle sampling method, during tungsten inert gas (TIG) and manual metal arc (MMA) welding on Inconel in the same shop. The collection method gave samples which were suitable for TEM and AIA. Electron micrographs were taken in a transmission electron microscope and further analyzed using an image analysis unit. Aggregates composed of many individual particles were analyzed both for the parameters of the aggregate and for the parameters of the individual particles by using an algorithm based on a grain boundary reconstruction technique. The morphological parameters allowed the welding fume's particulate matter to be divided into three types - here called small, medium, and large - with a somewhat unclear distinction between medium and large. Medium and large particles occur either as individual particles or as clusters of approximately spherical particles with average diameters of 0.07 and 0.15 microm, respectively. Small particles occur almost exclusively as long chains or lace-like structures of aggregates of particles, often in the range of 5-10 microm. The aggregates have an average projected area of 2.6 x 10-3 microm2 and are composed of several hundred individual particles.

Stress corrosion cracking of weldments of AISI Type 316 stainless steel

AbstractThe weldments of AISI Type 316 stainless steel prepared by the tungsten inert gas (TIG) and manual metal arc (MMA) welding processes, were tested in a boiling solution of 5 M NaCl + 0.15 M Na2SO4 (pH = 1.3) at an initial stress level of 200 MPa under the open circuit potential (OCP) and the impressed potential (IP) conditions using the constant load technique. Anodic polarisation above the critical cracking potential (CCP) which was determined by the OCP test, accelerated the stress corrosion cracking of both the weldments whereas slight cathodic polarisation below the CCP prevented it. The cracks initiated through pits in both the types of weldments under open circuit as well as impressed potential conditions. The TIG weldments cracked in the heat affected zone whereas the MMA weldments failed in the fusion zone at all potentials. At open circuit potential, the MMA weldments failed by the stress assisted dissolution of delta ferrite, while the TIG weldments failed by the TGSCC of austenite. On anodic polarisation, the MMA weldment failed by the dissolution of delta ferrite and intergranular SCC of austenite, while in the TIG weldments the cracks initiated and propagated in the intergranular mode in the austenite.

Spectroscopic analysis of the plasma created by a double-flux tungsten inert gas (TIG) arc plasma torch

Measurements of population densities and temperature distributions have been performed in a double-flux tungsten inert gas (TIG) arc plasma column using high-resolution spectroscopy. The experimental conditions have been chosen to mimic typical welding conditions with argon gas. The results show that the plasma is dominated by metallic vapour species in the vicinity of the molten anode, while a nearly pure argon plasma is observed in the cathodic region.

Welding Zircaloy Thin Tubes to End Plugs

This work aimed at optimizing parameters while welding Zircaloy-2 tubes with end plugs, as a simulation of a part of the fabrication of the nuclear fuel pins. Samples were welded by Tungsten Inert Gas arc welding (TIG) process under controlled atmosphere of pure argon. Some samples were welded using Electron Beam (EB) welding process. For samples welded using TIG process both the design of the welding chamber (size and tightness), and the purity of the shielding atmosphere were found to have appreciable effect on the quality of the welded joint. Increasing the arc length and/or the welding current increases grain growth and extends both fusion and heat-affected zones. However, heat input (arc length and welding current) must be high enough to give complete penetration welds. Optimum arc length of 1.2 mm was found to give good welds with the smallest possible heat-affected zones. Optimum parameters of EB welding process (vacuum, welding current and EB amplitude) were determined. Welds prepared by EB welding were found to have finer grain size and less extended fusion and heat-affected zones. Welds prepared by both TIG and EB processes were inspected visually, metallographically and by using X-ray radiography. Welds integrity were tested using helium leak and pressure tests.

Weldability and Weld Performance of a Special Grade Hastelloy-X Modified for High-Temperature Gas-Cooled Reactors

The characteristics of weld defects in the electron beam (EB) welding and the tungsten inert gas (TIG) arc welding for Hastelloy-XR, a modified version of Hastelloy-X, are clarified through the bead-on-plate test and the Trans-Varestraint test. Based on the results, weldabilities on EB and TIG weldings for Hastelloy-XR are discussed and found to be almost the same as Hastelloy-X. The creep rupture behaviors of the welded joints are evaluated by employing data on creep properties of the base and the weld metals. According to the evaluation, the creep rupture strength of the EB-welded joint may be superior to that of the TIG-welded joint. The corrosion test in helium containing certain impurities is conducted for the weld metals. There is no significant difference of such corrosion characteristics as weight gain, internal oxidation, depleted zone, and so on between the base and the weld metals. Those are superior to Hastelloy-X.

A feasibility study on nitriding of aluminum by surface melting

In order to establish aluminum alloys as a more reliable material for machine parts, especially for sliding or rolling parts, a feasibility study on nitriding of pure aluminum by surface melting was performed. Simultaneous melting and nitriding was attempted in order to obtain a highly hardened surface layer which would not be spoiled during sliding or rolling. A tungsten inert gas arc (TIG) welder with argon-nitrogen mixed shield gas was used to attain the simultaneous melting and nitriding. It was found that when the nitrogen content in the shield gas was less than 5 pct and the flow rate exceeded 10 1/min, flat surfaces are obtained. Under these conditions, it was also found that lamellar aluminum nitride was formed at the melting area and its hardness was about Hv250, almost four times the hardness of the original aluminum. Furthermore, it was observed that the increase of arc-current caused an increase in depth of the hardened layer but did not affect the hardness.

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.

Steam porosity formation in tungsten inert gas arc welding of copper

AbstractA quantitative study has been made of the effects of welding and material variables on porosity formation in the tungsten inert gas arc welding of copper. It has been confirmed that porosity can result from the occurrence of the steam reaction in the weldpool. The extent of this porosity is increased by increasing water vapour content of the arc atmosphere, increasing oxygen content of the base material, and decreasing welding speed. All three factors interact so that the threshold porosity levelfor eachfactor is strongly influenced by the value of the other two factors. The steam reaction has been investigated during arc melting by determining the oxygen and hydrogen contents of copper buttons which have reacted with argon–water vapour atmospheres. It is shown that hydrogen ispreferentially absorbed from the arc following dissociation of the water vapour. The final levels of the oxygen and hydrogen in the button correspond to the equilibrium for the steam reaction in a high-temperature zone under...

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.

The Design of a Portable Polychromator to Monitor Contaminants in Tungsten Arc—Inert Gas Shields

A small portable spectrometer was developed to monitor oxygen and hydrogen as the free or dissociation products in the tungsten arc–inert gas welding process. The hydrogen (6562.8 Å) and oxygen (7771.9 Å) lines were monitored and the argon (8521.4 Å) line was used for the internal standard. The instrument, a fixed Eagle mount, used a 76×50 mm, 60 cm focal length, concave grating with 610 grooves/mm blazed in the second order. The reciprocal dispersion at 6562 Å was 12 Å/mm. The oxygen triplet was resolved. Optical design requirements included the use of very short arc lengths in the order of 0.5 mm and less, an optical plane of 65° to 75deg; with a large flat plate instead of the conventional 90° with respect to the electrodes, and an arc that does not remain in a fixed optical position in space. The focusing lens-limiting aperture assembly was mounted on the torch head with a fiber optic bundle transmitting the light to the spectrometer. The instrument recorded only the signal above background, including the very high background produced by introducing the electrode tip into the optical path. This was accomplished by the use of an oscillating optical block in the entrance beam which yields an ac signal above the dc signal from background. The direct ratio readout system used a Devar ratio computer in each analytical channel and was essentially instantaneous.

Parameters Involved in the Spectroscopic Monitoring of Atmospheric Contaminants in the Tungsten—Inert Gas Arc Process

The parameters involved in the spectral monitoring of atmospheric contaminants in the tungsten–helium arc process were studied under welding conditions. An internal standard was necessary because small variations in arc length, current, condition of metal surface, alloy, the portion of the arc in the aperture, etc. resulted in relatively large variations in spectral response, proportionally much greater than for those same parameters in conventional low current–graphite electrode spectroscopy. Only the argon line internal standard was satisfactory. Warping of the work metal caused the arc to change in space, so a side arm mount for the torch was designed to carry the entrance optics. The high and varying background that resulted from electrode reflections, glowing oxide particulate, focus on hot metal, and possible radiation from the electrode tip required the use of a rotating circular wedge to oscillate the emission lines across the exit slits. Alternating current electronics amplified the difference in signal levels.

高周波併用電弧熔接に関する基礎的実験について

In recent years, the tungsten inert gas arc welding process superposing the high frequency current is being, more and more, used. According to this, it comes to the problem how the noise in the wireless fields, which is generated by the high frequency current, is decreased.In order to study fundamentally on this problem, we have set a vacuum tube high frequency oscillator. And we have investigatied the relations between the discharging voltage and frequency in the atomospheres of air and argon gas and in use of some shapes of electrode where the gap length is taken as parameter.The works performed are summarrised as follows :(1) Discharging voltage goes down to minimum value at about 800KC and 10MC in both atomospheres.(2) Discharging voltage in the argon atomosphere is about a third of that in air.(3) Remarcable influences of the rate of argon flow upon the discharging voltage are not found.