Distribution of the heat and current fluxes in gas tungsten arcs

The distribution of heat flux on a water-cooled copper anode as a function of welding process parameters has been determined experimentally following an experimental technique developed previously. The results indicate that arc length is the primary variable governing heat distribution and that the distribution is closely approximated by a gaussian function. The half width of the heat flux is defined by a distribution parameter, σ, which was determined from the experimental data and is expressed as a function of arc length, current, and electrode tip angle. The distribution parameter, σ, increases from 1.5 mm to 3.6 mm as the arc length increases from 2 mm to 9 mm for a 100 A arc. The experimental data also show that arc energy transfer efficiency is greater than 80 pct on the water-cooled anode which is much higher than has been measured in the presence of a molten metal pool. For this reason, it is believed that the distribution of the heat flux and not the magnitude is the most useful information obtained in this study. The effect of helium additions to the argon on the heat distribution is also reported. Formerly Research Assistant, is with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA     

The interaction of a DC transferred arc with a melting metal: Experimental measurements and mathematical description

Experimental measurements are reported on the transient development of temperature profiles in a hemispherical metal anode onto which a DC plasma jet is impinging. The main process variables were the arc current, the electrode separation, and the argon flow rate. These experimental measurements were compared with the predictions of a mathematical model, which involved the statement of the turbulent heat and fluid flow equations in the plasma, coupled to the heat flow in the testpiece through the boundary conditions. The experimental measurements were in reasonable agreement with the predictions, and convective heat transfer was found to be dominant in the heat exchange between the plasma and the anode.     

Pressures produced by gas tungsten arcs

The pressure of gas tungsten welding arcs has been measured for currents from 300 to 600 amperes using argon and helium gases. Although the measurements are generally consistent with previous results at lower currents, the present work shows that the pressure exerted by helium is a strong function of arc length. Several different scaling laws for the maximum pressure as a function of arc current and electrode tip angle are discussed.     

SUS410S铁素体不锈钢焊接性能研究

在不锈钢加工工艺中,焊接是最主要的必不可少的加工技术之一。本文以SUS410S铁素体不锈钢为原料,采用手工钨极氩弧焊方法,选用日本生产的交直流氩弧焊机,以ER30gL焊丝为焊接填充金属材料。研究其焊接性能。试验结果表明：在选定的焊接工艺参数条件下,焊接接头性能满足要求;无损检测焊接接头内不存在裂纹、未熔合、未焊透和条形缺陷,抗拉强度、面弯和背弯弯曲检验结果良好,宏观检查受检面焊缝均未发现任何焊接缺陷,耐晶间腐蚀试验未发现明显的裂纹,焊缝为细长的条状奥氏体加少量的8铁素体组织,热影响区为铁素体加马氏体组织。     

Effects of metal vapor on electron temperature in helium gas tungsten arcs

In order to investigate the effects of metal vapor on the thermodynamic property of arc plasma in the welding process, electron temperatures in the pure helium plasma and in the helium plasma during welding in gas tungsten arcs (GTAs) were measured by using the laser scattering method. The experimental results showed that metal vapor led to a significant decrease in the electron temperature compared with that of pure helium GTA plasma. The temperature difference reached 6000 K in the arc fringe at the maximum.     

Metal transfer during vacuum consumable arc remelting

An investigation was conducted to determine how metal is transferred during vacuum consumable arc remelting. The transfer mode was found to be dependent on arc length for the electrode sizes (0.10 to 0.20 m diam) and electrical parameters studied (1.9 to 3 kA and 25 V). At short arc lengths ≤0.03 m, metal transfer was found to occur when liquid metal spikes hanging from the cathode form a low resistance bridge (drop short) by touching the anode and then subsequently rupture. The formation and rupture of these molten metal bridges was confirmed with electrical resistance measurements. During the bridge lifetime (0.0003 to 0.020 s) the arc was extinguished and all of the electrical power was directed through the molten bridge. At long arc lengths (>0.1 m) the spikes separate before touching the anode. Experimental observations concerning the coalescence of molten material at the cathode tip were made and they were found to be in agreement with theories on liquid instabilities. A review of pertinent literature concerning vacuum arcs was conducted and this along with general information on vacuum consumable arc re-melting are included as background information.     

钽钢复合板钽覆层的焊接工艺研究

对钽钢复合板的钽覆层采用敷设盖板的方式焊接，研究了直流氩弧焊与交流脉冲氩弧焊两种焊接工艺对钽钢复合板焊接质量的影响。结果表明，直流氩弧焊的焊接热影响区较宽，焊接熔深为1～1．5mm，在钢与过渡金属层之间形成了中间夹层；交流脉冲氩弧焊的焊接热影响区较窄，焊接熔深为0．5～1mm，复合板焊接质量较好。与直流氩弧焊相比，交流脉冲氩弧焊焊接参数范围较宽，对焊工技能的要求相对较低，可实现连续化生产，因此更适合用于钽钢复合板钽覆层的焊接。     

Effect of rare earth metal oxide additions to tungsten electrodes

A comparative study has been made on the operating characteristics of gas-tungsten arc (GTA) welding for several types of electrodes. The work was carried out with a pure tungsten electrode and tungsten electrodes activated with a small quantity of the rare earth metal oxides, La₂O₃, Y₂O₃, CeO₂, and with ZrO₂, ThO₂, and MgO. Their behaviors during arcing were analyzed and compared from the points of view of arc starting characteristics, electrode consumption, change in shape due to long-term operation, and incompleteness of insert gas shielding and electrode temperature. The results indicated that W-La₂O₃ electrodes have superior characteristics among those tested. Metallographic studies of the electrodes indicate that the superiority of operating characteristics strongly depends on the behavior of the rare earth metal oxides during arc burning. It is observed that the rare earth metal oxides form tungstate or oxytungstate during arc burning. These newly formed compounds have low melting points and migrate from the low temperature zones to the high temperature zones throughout the electrode tip, while ThO₂ reacts with tungsten, forming pure Th. Also, the investigation demonstrates good stability of La₂O₃ during arc burning compared with the other oxides. Particular attention was also paid to the electrode temperature measurement and the important phenomena concerning the emissivity of a particular surface as one of the thermal properties. The investigation reveals the effects of temperature and oxide distribution on the spectral emissivity of the electrode in addition to the main different effect of oxides added to tungsten. Observations of the cathode tip microstructure during and after arc burning were made, and important phenomena concerning the formation of a tungsten “rim” at the periphery of the cathode area, which governs the durability of the electrode and the stability of the arc, are discussed theoretically and experimentally based on the temperature measurement of the tip and the oxidation of tungsten. ALBER A. SADEK, formerly with the Welding Research Institute, Osaka University     

脉冲熔融-飞行时间质谱法测定钛中氦和氩

应用气体分析仪开展脉冲熔融-飞行时间质谱法定氦的方法研究和定氩的应用研究,采用气标标定,标定曲线线性良好。选择脉冲-热导法作为参比方法,文中公布的实验结果均为两种方法对比数据。建立了质谱定氦和氩的方法,分析测定科研用充氦钛膜中氦,实际应用于测定粉末冶金钛合金中氩。试验表明脉冲熔融-飞行时间质谱法可以准确测定金属中氦和氩,定量分析结果与现有的脉冲-热导法基本一致。     

Microstructural damage and residual mechanical properties in helium-bearing gas metal Arc weldments

The influence of entrapped helium on microstructural damage and residual mechanical properties subsequent to applying low-penetration gas metal arc (GMA) weld overlays was examined for an AISI Type 304 stainless steel. Two helium levels were examined: 22.5 and 85.0 atomic parts per million (appm) He. Detailed scanning electron microscopy (SEM) revealed the presence of intergranular cracks in the weld heat-affected zone (HAZ). The crack surfaces exhibited a dimple structure that was characteristic of a gas bubble embrittled material. Transmission electron microscopy (TEM) revealed that the size and spacing of the grain boundary helium gas bubbles remained virtually unchanged (relative to that established by the charging and aging procedure) at distances greater than 1 mm from the fusion line. Within this first millimeter, the diameter of the bubbles increased rapidly, and the bubble spacing increased to the characteristic spacing of the dimples that decorated weld-induced cracks. Mechanical testing revealed a loss in strain-to-fracture and ultimate tensile strength (UTS) at the higher helium level. While the majority of the fracture occurred in a transgranular, ductile manner, some deformation-induced intergranular cracking was observed. This cracking occurred over a very narrow region localized to the HAZ of the weldment. At the lower helium level, ductility and strength were unaffected compared to helium-free specimens.     

Modelling of electrovortex and heat flows in dc arc furnaces with bottom electrode

Abstract

The article is devoted to the investigation of interaction between electrovortex and heat flows of liquid metal in dc arc furnaces with a bottom electrode. A mathematical model of liquid steel flows in a dc arc furnace with a bottom electrode was developed, and an algorithm of a three-stage solution was produced based on standard software packages. The results of electromagnetic, heat transfer and hydrodynamic analysis in industrial dc arc furnaces are given. It is shown that the Lorentz force makes up ～30% of the volumetric gravity force and makes the main contribution to vortex flow of liquid metal in a dc arc furnace. The convection flows with the maximum heat power of furnace make a significant contribution to the vortex flow of liquid metal, and the maximum value of the vortex flow velocity is ～1·5 times more than the movement without convection. The verification of results has been carried out by comparing them with general electrovortex flows theory, experimental data and results of similar software packages.     

金属中气体元素分析典型案例

金属中气体元素分析已经存在60余年,其检测方法不同于其他化学元素.论文列举5个典型案例(铝中氢、金属中氩、金属中氦、稀土钢中氢、(铝)镁中氧),以进行技术交流和讨论.铝中氢作为金属中气体分析之最难当之无愧,有研究尝试简化铝中氢分析方法,期望像钢样那样快速准确地得到结果,比如应用现有通用的脉冲熔融法反复试验上百次,未能成...     

金属中气体分析现状与未来

综述了金属中气体分析概况, 提及元素周期表中所有气体元素以及碳和硫。提出常规气体分析已经从氧氮氢碳硫扩大至氦和氩。气体分析所涉及材料种类不断增加, 从金属及合金扩大至冶金炉料、金属氧化物和陶瓷材料等等。气体分析检测极限不断被刷新, 向着更低和更高方向发展。脉冲熔融-质谱新方法应用于金属中气体分析, 可做到氧氮氢氩4元素同时测定, 有可能助推改变气体分析现状。火花源原子发射光谱仪和X射线荧光光谱仪等其他非气体分析专业仪器也正交叉渗入。诸如, 二次离子质谱(SIMS), 离子探针(IM)和电子探针(EP)等微观分析手段一直作为金属中气体分析的辅助手段, 随着未来发展可能转变为主要手段。     

10t AOD冶炼Inconel 690合金的工艺实践

目前Inconel 690合金广泛用于核电站蒸汽发生器传热管。其通常采用真空感应炉冶炼自耗电极,冶炼成本较高。本研究通过对Inconel 690合金熔体的热力学分析和还原过程的讨论,认为采用电弧炉+氩氧精炼炉冶炼工艺路线,可以生产出满足标准要求的自耗电极。通过实践,表明此工艺可行,生产的自耗电极化学成分满足要求,气体含量低。为该产品的生产开辟了一条低成本、高效率的冶炼工艺路线。     

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.     

Optimal concentration of nanostructured powder in protective gas

In the present work, a method is developed for determining the optimal concentration of nanostructured powder in the protective gas in welding by a floating electrode in argon. The theoretical analysis is confirmed by experiments with molybdenum nanopowder, which is introduced in the welding bath through a special device. The apparatus used for surfacing of the sample includes a GSP-2 welding head combined with the specially developed device and a VS-300B power source. In surfacing 12Kh18N10T steel samples, 12Kh18N19T steel welding wire (diameter 1.2 mm) is employed. To ensure a satisfactory weld joint, the dendrite dimensions must be minimized. Stable welding is ensured by transfer of a droplet of electrode metal from the end of the welding wire to the welding bath. Hence, the droplet volume must also be minimized. Before optimizing the concentration of nanostructured powder in the protective gas, the influence of the welding parameters on the microstructure of the surfaced metal is established. The results show that the grain size is smallest with a current of 240–260 A and an arc voltage of 28–30 V. In those conditions, the optimal concentration of nanostructured powder in the protective gas is determined. It is found that the optimal concentration is 20 mg per 1 m of weld seam. The use of different concentrations of nanostructured powder in the protective gas results in different microstructure of the applied metal. When the concentration of nanostructured powder in the protective gas is 20 mg per 1 m of weld seam, the branching of the dendrites is least and the dendrite size corresponds to equilibrium structure. On adding nanostructured powder to the liquid bath, the mechanical properties of the weld joints are increased by 7.5% at +20°C and by 6.5% at +500°C.     

Droplet formation,detachment, and impingement on the molten pool in gas metal arc welding

A mathematical model is developed to describe the globular transfer in gas metal arc welding (GMAW). This work is both theoretical and experimental. Using the volume-of-fluid (VOF) method, the fluid-flow and heat-transfer phenomena are dynamically studied during the following processes: droplet formation and detachment, impingement of a droplet on a solid substrate, impingement of multiple droplets on the molten pool, and solidification after the arc extinguishes. A He-Ne laser, in conjunction with the shadow graphing technique, is used to observe the metal transfer processes. Theoretical predictions and experimental results are in close agreement, suggesting that the theoretical treatment of the model is good.     

A Model of Liquid Metal Droplet Vaporization in Arc Heated Gas Streams

A model of simultaneous heat and mass transfer has been constructed to describe vaporization of liquid metal droplets in arc heated gas streams. The major assumptions of the model include 1) plug flow, 2) negligible pressure drop, 3) no droplet-droplet interactions, 4) negligible gas radiation, natural convection, thermal diffusion, diffusion-thermo transport and axial conduction and diffusion, and 5) no interfacial discontinuities in temperature or concentration. The latter assumption is discussed in detail in a separate appendix. The analysis is limited to binary, nonreacting gas mixtures. The mathematical formulation results in five nonlinear, first order differential equations with temperature and compositional dependent properties. The model is applied to the vaporization of sodium and magnesium droplets injected into arc heated argon flowing in a cylindrical reactor. The effect of parameters such as initial droplet radius, reactor diameter, and liquid metal flowrate on the reactor length required to achieve a specified degree of vaporization is calculated.     

Nitrogen transfer into plasma heated steel melts as a function of arc polarity

Heating liquid steel in the tundish with argon stabilized plasma arcs is one example of the increasing importance of mobile and inert heating systems in metallurgy. Unwanted nitrogen pick-up caused by infiltrated air, and possibly aggravated by the activating effect of plasma, should be minimized by selecting the optimum current mode and torch polarity. With this aim in mind, the nitrogen transfer kinetics have been investigated on 150-kg low carbon steel melts at different nitrogen partial pressures as a function of arc polarity. The experimental plasma plant was equipped with a 2000-A torch, housing a thoria stabilized tungsten electrode, and a counter electrode located at the bottom of the crucible. The torch could be operated with DC of either polarity or with AC. Kinetic models of nitrogen transfer have been developed, which show good agreement with experimental results. Arc polarity has a significant effect both on the rate of nitrogen pick-up in the arc area (pumping effect) and on the mass transport in the melt (stirring effect). Of all configurations tested, the torch as cathode is the most suitable arc configuration for inert heating, since the particularly active N⁺ ions in the plasma are repelled by the melt surface. Furthermore, the relatively strong stirring effect of the plasma jet leads to the highest heat transfer efficiency. On the other hand, where controlled nitrogen pick-up is required, the highest nitrogen transfer rates are obtained with the torch poled as anode.     

Numerical analysis of metal transfer in gas metal arc welding

The present article describes a numerical procedure to simulate metal transfer and the model will be used to analyze the transport processes involved in gas metal arc welding (GMAW). Advanced Computational fluid dynamics (CFD) techniques used in this model include a two-step projection method for solving the incompressible fluid flow; a volume of fluid (VOF) method for capturing free surface; and a continuum surface force (CSF) model for calculating surface tension. The electromagnetic force due to the welding current is estimated by assuming several different types of current density distribution on the free surface of the drop. The simulations based on the assumption of Gaussian current density distribution show that the transition from globular to spray transfer mode occurs over a narrow current range and the size of detached drops is nonuniform in this transition zone. The analysis of the calculation results gives a better understanding of this physical procedure. Comparisons between calculated results and experimental results are presented. It is found that the results computed from the Gaussian assumption agree well with those observed in experiments.