Shielded metal arc welding

About: Shielded metal arc welding is a research topic. Over the lifetime, 4462 publications have been published within this topic receiving 40560 citations. The topic is also known as: manual metal arc welding & flux shielded arc welding.

Relationship between the weldability and the process parameters for laser-TIG hybrid welding of galvanized steel sheets

Abstract: In the lap welding of zinc-coated steel, porosity formation is one of most significant weld defects. It is caused by zinc vapor generated between the steel sheets. Various solutions have been proposed in the past but development of more effective method remains a valuable subject to be investigated. In this study, laser-TIG hybrid welding was applied to the lap welding of zinc-coated steel without a gap. The weld defects could be eliminated by laser-TIG hybrid welding, as the leading TIG arc partially melted the upper sheet, and the coated zinc on the lapped surfaces were vaporized or oxidized before the trailing laser irradiated on the specimen. Optimization of the process parameters for laser-arc hybrid welding process is intrinsically sophisticated because the process has three types of parameters-arc, laser and hybrid welding parameters. In this paper, the relationship between weldability and the process parameters of the laser beam-arc distance, welding current and welding speed were investigated using a full factorial experimental design. Weld quality was evaluated using the weight of the spatter, as porosity formation is a major weld defect in the lap welding of zinc-coated steel sheets. It was found that the weld quality was increased as the laser beam-arc distance and welding current increased, and that this decreased as welding speed increased.

Toward a unified model to prevent humping defects in gas tungsten arc welding

Abstract: During gas tungsten arc (GTA) welding, high welding speed and current can lead to a serious weld defect with a bead-like appearance known as humping. Currently, there is no unified model to predict the formation of humping defects in GTA welding. Here we propose and test a new comprehensive computational model that can predict and prevent the formation of humping defects considering the values of arc current, welding speed, nature of the shielding gas, electrode geometry, ambient pressure, torch angle, and external magnetic field during gas tungsten arc (GTA) welding. The model considers stability of the waves on the weld pool surface due to relative motion between the shielding gas and the liquid metal based on the Kelvin-Helmholtz instability theory. The main factors for the instability were found to be the velocities of the shielding gas and the weld metal, densities of the molten metal and shielding gas, weld pool size, and surface tension of the molten weld metal. The weld pool size and weld metal velocities were calculated by a numerical heat transfer and fluid flow model, and the shielding gas velocity was calculated from an analytical relation. Good agreement between the model predictions of humping and the independent experimental results from various sources show that the model can be used to prevent humping considering the effects of arc current, welding speed, nature of the shielding gas, electrode geometry, ambient pressure, torch angle, and external magnetic field during GTA welding. Recommendations are provided for the use of special electrodes and an external magnetic field and, where practical, controlled pressure and careful selection of shielding gas to prevent humping under conditions when high welding speed and current are needed to sustain productivity goals.

Hot wire-assisted gas metal arc welding of hypereutectic FeCrC hardfacing alloys: Microstructure and wear properties

Abstract: The deposition welding of hypereutectic FeCrC hardfacing alloys requires low dilution rates in order to ensure the specified chemical composition and thus the precipitation of primary M7C3 (M = Fe, Cr) carbides, which affect the abrasive wear resistance of the hardfacing. Because dilution is critical in determining the above mentioned criteria during surfacing, the development of deposition welding processes with reduced thermal impact and hence reduced dilution of the base material is a main focus of current research. For the purpose of improving the processing properties of gas metal arc welding (GMAW) in hardfacing applications, the potential of an additional hot wire (HW-GMAW) was investigated. The application of a hot wire enabled the independent adjustment of the deposition and dilution rates. Furthermore, the dilution and microstructural properties could be adjusted independently of the deposition rate. HW-GMAW enabled hypereutectic solidification in the first layer, even at very high deposition rates of 9 kg/h. In this manner, a primary M7C3 carbide content reaching 17% by area (A%) was achieved in the first layer. In comparison to single-layer GMAW overlays the wear properties were improved.

The interface below stainless steel and nickel-alloy claddings

Abstract: The formation of microstructures across cladding interfaces was examined with an emphasis on the fused region as-welded and after postweld heat treatment (PWHT). The strip submerged arc and shielded metal arc welding processes were used to deposit austenitic stainless steel and nickel-alloy consumables on to 2 1/4 Cr-1 Mo steel. Optical and electron microscopy were employed, with energy dispersive x-ray and electron probe microanalysis for examining major alloying elements and carbon. The observations were related to the results of hardness, bend and crack tip opening displacement (CTOD) toughness testing

Influence of peak temperature during in-service welding of API X70 pipeline steels on microstructure and fracture energy of the reheated coarse grain heat-affected zones

Abstract: In this investigation, thermal simulated specimens were used to investigate the effect of second peak temperature during in-service welding on characteristic fracture energy and microstructure feature of the subcritically (SC), intercritically (IC), supercritically (SCR), and unaltered (UA) reheated coarse grain heat-affected zones (CGHAZs). The API X70 high-strength pipeline micro-alloyed steel was subjected to processing during in-service welding by applying double thermal cycle shielded metal arc welding process with heat input of 9.3 kJ/cm and thermal cycles to simulate microstructure of reheated CGHAZs. This consisted of first thermal cycle with a peak temperature of 1350 °C, then reheating to different second peak temperatures of 600, 800, 1000, and 1200 °C with a constant cooling rate of 60 °C/s. Toughness of the simulated reheated CGHAZs were assessed using Charpy impact testing at −20 °C, and the corresponding fractographs, optical micrographs, and electron micrographs have been examined. It is found that accelerating cooling rate during in-service welding has an improving effect on the microstructure of CGHAZs. Owing to small heat-input and accelerating cooling, the grain size in reheated CGHAZs is relatively small and the brittle microphases are eliminated or minimized. The Charpy impact results show that the CGHAZ fracture energy is improved after the second thermal cycle. The SC CGHAZ showed higher absorbed impact energy and the IR CGHAZ had less absorbed energy, but the phenomenon of embrittlement in IR CGHAZ is not serious. Therefore, it can be concluded that the fracture energy of CGHAZ and IR CGHAZ can be improved by accelerating cooling with appropriate cooling rate.