Argon Shielding Research Articles

EFFECT OF VARIOUS DRIVING FORCES ON HEAT AND MASS TRANSFER IN ARC WELDING

In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure, and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered: self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc forces. Furthermore, the effect of surface depression due to the arc pressure acting on the molten pool surface was considered. Because the fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model was applied to AISI304 stainless steel and compared with the experimental results.

Influence of shielding medium on deposition rate in arc welding

The aim of this paper was to determine the influence of the shielding medium and the type of welding flux on the deposition rate in arc welding. Previous studies have stated that the shielding medium has no influence on deposition rate and a number of mathematical models derived by previous authors confirm this. In the present work it was found that a larger quantity of material was deposited when using helium, argon, or CO2 as shielding. With constant wire feedrate and constant power, arc current was lowest with helium shielding and highest with argon shielding; with just wire feedrate constant, arc power was lowest with helium and CO2 shielding and highest with basic flux. It was also found that arc welding efficiency was highest for helium shielding and lowest for submerged arc welding with basic flux.

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.

A mathematical model of the arc in electric arc welding including shielding gas flow and cathode spot location

A mathematical model of a free-burning TIG electric arc with non-consumable electrodes using a flat anode and argon shielding gas is presented. Differential equations describing the conservation of mass, momentum and energy are solved together with Maxwell's equations describing the electromagnetic field. The dependence of transport coefficients on temperature is taken into account. The gas flow is assumed to be laminar and the partially ionized plasma is assumed to be in local thermodynamic equilibrium. The mathematical model can cope with a broad range of operating conditions. The model is used to demonstrate the strong influence that the velocity and temperature of the flow of gas entering the top of the electric arc in the region of the cathode can have on the arc column. In particular, it is shown that cathode flows of strength sufficient to produce a significant constriction of the electric arc need to be assumed in order to account for experimentally measured electric fields in the arc column as well as the total voltage drop for 10 mm arcs. The use of this model also shows the part played by the cathode spot and its location in the nature of the electric arc column. In particular, two complementary techniques for studying the arc column are highlighted. In the first, a strictly stable static arc is needed in order to employ the spectroscopic technique of temperature measurement. In contrast, when the position of the arc is less stable, a rapid measurement with an electric probe is indicated in order to measure the electric field. The arc model described by Ducharme et al (1993) will then yield the temperature field. The model presented here produces the results for the temperature distribution and for the electric field based on the use of appropriate boundary conditions.

アルミニウム合金の硬化肉盛溶接 第２報 アルミニウム‐銅複合ワイヤによるアルミニウム合金のガスタングステンアーク肉盛溶接法

The authors have investigated on surfacing technique on aluminum alloys by using gas tungsten arc welding (GTAW) process. The used filler metals were composite cored wire of seamless tube type and 1.2 mm in diameter. They were of Al-Cu composition with varied copper contents of 60, 70 and 80%. Each wire consisted of a copper tube sheath and an aluminum solid wire enclosed.The authors investigated the effects of arc current and weld cooling rate on microstructure, hardness distribution and porosity formation. They studied through chemical analysis the oxide film that covered the surfacing weld metal. They also analyzed the gases evolved in vacuum from machine cut porosities.The hardness in cross section of Al-70%Cu surfacing weld metal decreased from 270 HV to 170 HV with an increase of surfacing current in the case of helium shielding. Helium shielding drastically reduced the porosities that existed in the case of argon shielding. The remaining porosities became smaller than 0.2 mm in diameter. Moreover, the dual shielding by argon-helium gases was found to eliminate perfectly the porosity formation in the surfacing weld metal. Chromatography analysis revealed that the gas in porosities was dominantly hydrogen. The thickness of oxide film on the argon shielded weld metal surface was found to be remarkably greater than that of helium shielded weld metal, and thereby it might have caused more porosities in the case of argon shielding.

静止ＴＩＧアークによる溶込み形態の検討 低速ＤＣ‐ＴＩＧ溶接法の研究 第１報

Generally, in TIG arc welding method, the ratio of penetration depth (D) to bead width (W) is small and the deep penetration cannot be obtained comparatively. But in the case of using the stationary TIG arc when the welding conditions were set to the suitable range, the value of D/W is closer to unity and the penetration depth becomes deep. Paying attention to the above mentioned phenomenon, the authors have made researches into the practical application of the stationary TIG arc.In this paper, the welding conditions which we obtained from the above mentioned penetration forms were investigated using SUS304. It was found out that when suffer (S) content of the base metal is more than 0.005 mass%, both the method of using the electrode with at vertex angle above 60° or with in argon shielding gas and the method of using helium to shielding gas are successful to increase the penetration depth.In the case of using the base metal which contains sulfer about 0.001 mass%, the method of using the tip-cutting electrode in argon shielding gas is more effective for same purpose.

ＡＺ３１マグネシウム合金の摩擦圧接

Magnesium alloy AZ31 was friction welded using a brake type friction welding machine under argon shielding. Microstructures and mechanical properties of the friction welded joints were investigated. The fine grain structure resulting from disappearance of fibrous one is observed closely near the weld interface. The hardness of both the weld interface and heat affected zone are nearly equal to those of the base metal. The tensile strength of welded joints are improved with increasing friction time, but it is lower than that of the base metals. In case of friction pressure of 50MPa and friction time of 6 seconds the elongation of the joint shows the highest value, but it is inferior to that of the base metal. All the impact specimens with the notch into the weld interface showed impact strength inferior to that of the base metals, but impact strength increases with increasing notch distance from the weld interface. There is no trouble in flaming during the welding process.

Hydrogen cracking in duplex stainless steel weldments

The restraint weld cracking test was conducted to investigate the hydrogen cracking in duplex stainless steels which contain various ferrite/austenite ratio. The gas tungsten arc (GTA) welding was applied with the argon shielding gas containing 10% hydrogen. The effects of preheating or post weld heat treatment (PWHT) on the hydrogen cracking were also tested.The hydrogen cracking occurred in the weld metal with the ferrite ratio higher than 60% using the 10% hydrogen containing shielding gas under the severe restraint condition. The higher ferrite ratio of weld metal produced larger amount of diffusible hydrogen bacause the hydrogen can dissolve in the austenite phase. It was effective for the prevention of cracking to apply the preheating at 473K of the solution treatment at 1373K or to reduce the ferrite ratio by the adjusting the nickel and nitrogen content in the weld metal.

二相ステンレス鋼の溶接部の水素割れ

The restraint weld cracking test was conducted to investigate the hydrogen cracking in duplex stainless steels which contain various ferrite/austenite ratio. The gas tungsten arc (GTA) welding was applied with the argon shielding gas containing 10% hydrogen. The effects of preheating or post weld heat treatment (PWHT) on the hydrogen cracking were also tested.The hydrogen cracking occurred in the weld metal with the ferrite ratio higher than 60% using the 10% hydrogen containing shielding gas under the severe restraint condition. The higher ferrite ratio of weld metal produced larger amount of diffusible hydrogen bacause the hydrogen can dissolve in the austenite phase. It was effective for the prevention of cracking to apply the preheating at 473K of the solution treatment at 1373K or to reduce the ferrite ratio by the adjusting the nickel and nitrogen content in the weld metal.

チタンとＳＵＳ３０４Ｌとの摩擦圧接に関する研究

It is well known that fusion welding between titanium and foreign materials is almost impossible because of occurring brittle intermetallic compound in its weld metal. From this reason, there are few research reported for the welding titanium to other steels up to date. And also, there are a few investigations reported for it by using other welding process except fusion welding.In this study, to establish the welding process between titanium and SUS 304L austenitic stainless steel by using friction welding process with argon shielding, the effect of welding conditions on the tensile strength and metallurgical characteristics of the weld joint was evaluated. The results obtained are as follows:(1) There was little or no deformation observed in SUS 304L after weld.(2) The welding conditions, which increase the tensile strength, are, a. low rotational speed, b. high upsetting pressure andc. polishing of the faying surface of SUS 304L before welding.(3) Upsetting pressure was the most effective to tnesile strength than the other factors.(4) The tensile strengths of the joints, which were welded by using conditions described in (2), were from 348MPa to 378MPa.(5) The characteristics of the faying surface of SUS 304L before joining affected the tensile strength of the joint. That is, the roughness and foreign materials on the faying surface decrease the degree of metal bonding.

Effect of nitrogen contamination on intergranular corrosion of stabilized ferritic stainless steels

AbstractThree different alloys of AISI Type 444 (18Cr–2Mo) ferritic stainless steel, stabilized to different levels with titanium and/or niobium, were melted as welds or weld simulations with deliberate additions of nitrogen to the argon shielding gas in order to simulate the effects of accidental contamination by nitrogen during production welding. The oxalic acid etch test (ASTM A262–A) was used to assess the susceptibility of the melts prepared in this way to intergranular attack, and the extent of attack was quantified. It is shown that a clear correlation exists between the extent of intergranular corrosion and the amount of nitrogen taken up by the steel on melting. The implications of sensitization by nitrogen contamination both for steel design and integrity of production welds are discussed.MST/415

Comparison of the mechanical properties of ESR and directionally solidified AISI 4340 steel

In a previous investigation by two of the present authors the mechanical properties of test specimens cut from directionally solidified AISI 4340 steel castings were determined.I It was found that the yield stress and ultimate tensile stress were essentially constant throughout the casting, independent of dendrite arm spacing. On the other' hand, the elongation and reduction in area were markedly sensitive to dendrite arm spacing, the maximum ductility being obtained with the minimum dendrite arm spacing. In this investigation, the mechanical properties of test specimens cut from AISI 4340 steel ingots, prepared by electroslag remelting, were determined. These results are presented and compared with the corresponding values for the directionally solidified ingots. The procedure used for producing directionally cast ingots is given elsewhere, 1 as well as data concerning the micro segregation of the alloying elements in this material. 2 The electroslag-remelted ingots were prepared on the UBC electroslag unit from air-melt bar stock of the same nominal composition as the directionally cast ingots. The 3 x 10-2 m diameter electrodes were melted using dc power and argon shielding, with the electrode negative and the mould insulated. The slag used was 70wt-%CaF2+30wt-% Ca(AI02h and was fused before melting. The melt rate was 1·5 gs-I, corresponding to an ingot solidification rate of 0·8 x 10-4 ms-I. The volume of metal which is molten at any time is approximately 6 x 10-5 m3 in the configuration used, with a 15kg ingot, and a 7·5 x 10-2m diameter mould. The same conditions were used to prepare two ingots. The dendritic structure across the electro slag-remelted ingots remained essentially constant along the ingot. The spacing of the primary dendrite branches was measured to be about 200 p,m midway between the ingot axis and the outside surface. Test specimens were cut from the ESR ingot both parallel and perpendicular to the ingot axis. They were heat treated and tested in the same manner as the directionally solidified test specimens 1 giving the results listed in Table 1. Two ESR ingots were examined and are indicated as A and B. The transverse and longitudinal test specimens, with respect to the ingot axis, are marked T and L respectively. The corresponding values for the directionally cast 22 kg heat of AISI 4340 steel (which were all transverse specimens) are included in the lower part of the table, as well as the ingot compositions. The results shown in Table 1 indicate that the ultimate tensile stress and the yield stress are highly reproducible for both ESR ingots and are similar to the values obtained for the directionally solidified ingots. The elongation and reduction in area values are not as consistent as the ultimate tensile and yield stresses, with six of the eight specimens in the range of 35-43% and two at low values of 20 and 12% for no apparent reason. There is no significant difference between specimens which were cut either parallel or perpendicular to the ingot axis in the ESR ingots. Comparing the elongation and reduction in area of the ESR specimens with the directionally solidified specimens, the electroslag ingots have appreciably better ductility,

Technical manual RTM 26 64?71 on ?impulse-arc welding of stainless steel chemical and petroleum equipment using consumable electrodes and argon shielding?

Technical manual RTM 26 64?71 on ?impulse-arc welding of stainless steel chemical and petroleum equipment using consumable electrodes and argon shielding?

溶接金属の気孔について

This study was carried out directly to detect the constituent of gas in blowholes of weld metal by a microscopic micro-analysing and a mass spectrometer. Aluminum and its alloy, mild steel, high strength steel and austenitic stainless steel were used as base metals. And a bead - on - plate was deposited by the gas shielded metal arc welding under various shielding gases for each base metal. The diameter of a collected gas bubble from blowholes was measured by the microscope under a thin glass in absorbent step by step. The composition of the gas bubble was determined by calculation from the difference of diameters of the bubble before and after an absorbent solution. The quantity of hydrogen was determined from the loss of explosion by a special explosion pipet. The remainder gas after the microscopic micro-analysing was determined by the mass spectrometer (JMS-OISG).According to the results of analysis for aluminum deposit metal, a blowhole consists of the following gases; hydrogen about 75-85%, oxygen and argon several % and nitrogen 10-20%. In aluminum alloy deposit metal, oxygen could not be measured. Carbon dioxide, hydrogen sulphide, carbon monoxide and metahne were not recognized in both cases. Blowhole in mild steel deposit metal is full of carbon monoxide, hydrogen and nitrogen. Under the carbon dioxide shielding gas with a wire of insufficient deoxydation elements or carbon dioxide shielding gas with excess oxygen, blowholes consist mainly of carbon monoxide over 55% and nitrogen. Blowholes which were formed in a bead on rusted steel or on greased steel contained mainly 40-60% of hydrogen and 30-40% of carbon monoxide. In austenitic stainless steel deposit metal, the gas in blowhole is also carbon monoxide, hydrogen, nitrogen and argon in the case of argon and argon-nitrogen shielding.

アルミニウムのMIG溶接部の気孔におよぼす送給ガスへの窒素または酸素添加の効果

For the purpose of decreasing blowholes in aluminum weld metal, this experiment was carried out under the shielding gas of argon mixed with nitrogen and/or oxygen.Results obtained are as follows:-1) Blowholes in aluminum deposited metal by MIG welding can be decreased by adding nitrogen and/or oxygen to supplied argon gas. Minimum porosity is obtained respectively for mixing ratios of argon 50%+nitrogen 50%, argon 98.5%+oxygen 6.5% (bead on plate) and argon 98.5%+oxygen 1.5% (I-butt weld).2) In case of argon and oxygen shielding gas, same spray transfer is observed by oscillogram as in the case of argon only, but under argon-nitrogen shielding gas metal transfer changes to short circuit type.

Evaluation of Solid Metal Specimens Produced for Spectrographic Analysis by the Inert-Gas dc-Arc Fusion of Wire and Chips

A study has been made of the chemical composition of solid-metal buttons of low-alloy steel, stainless steel, high-temperature alloys, and copper-base and aluminum-base alloys produced by the dc-arc fusion of wire and chips under argon shielding. The effect of fusion on 22 elements commonly encountered in these alloys has been determined quantitatively. A correlation has been shown between boiling points and element losses. With the exception of zirconium, no significant changes in the composition of metallic elements having boiling points greater than manganese (2150° C) were noted while using the recommended procedures for button preparation. Steels showed consistent, slight losses of manganese and occasional loss of zirconium. Losses of lead in copper-base alloys and of magnesium, lead and manganese in aluminum-base alloys, which occur with high currents, may be eliminated by first briquetting the chips, then fusing at relatively low amperage. Consistent and significant losses of zinc were noted. Carbon pickup from the graphite electrode is slight, but inconsequential. Copper pickup from the water-cooled copper cup is usually negligible.

Background Control in Direct Reading Analysis of Stainless Steels

Variable background from alloy to alloy in direct reader analysis of stainless steels affects working curves adversely Spectrographic evidence shows that its effect can be photometrically removed Its influence can be minimized by use of excitation producing a “black burn” using argon shielding of the analytical gap in a point-to-plane arrangement. Automatic dynamic background correction is accomplished with production instruments based on a method of Weekley and Norris.

アルミニウム合金のMIGスポット溶接法の改善

The main problems presently arising with regard to MIG spot welding of aluminium alloys are the variation of weld joint strength and the cracking of weld metal. To solve them, some experiments were conducted on the effects of mixing of a little amount of O2 gas in argon shielding gas, with the following results:1) Depth of penetration and nugget diameter increase considerably by mixing 0.3-2% amount of oxygen in argon which leads to an increase mainly of the penetration into base metal. Conversely, the button diameter was observed to decrease as a result of the mixing.2) It was noted that O2 gas contents could be increased up to 5.0% from a metallurgical viewpoint, although for practical appearance of weld surface the mixing amount of oxygen should be kept below 0.5%.3) Tension-shear strength of weld joint was observed to increase in proportion to the increase of nugget diameter, which in turn increases with the content of oxygen.4) The variation of tension-shear strength could be kept below 40-30% by mixing 0.3-2% amount of oxygen.5) The tendency was observed that both weld cracking and porosity in weld deposit decrease when a little amount of oxygen is added.6) It appears that the improvement of arc concentration as well as arc force and agitation phenomena owing to the mixing of oxygen is the influential factor to the sectional shape of penetration.7) The decrease of cracking can be attributed to the absence of delayed freezing which caused strain concentration.