The specific activated flux has been developed for enhancing the penetration performance of TIG welding process for autogenous welding of type 304LN and 316LN stainless steels through systematic ...study. Initially single-component fluxes were used to study their effect on depth of penetration and tensile properties. Then multi-component activated flux was developed which was found to produce a significant increase in penetration of 10-12 mm in single-pass TIG welding of type 304LN and 316LN stainless steels. The significant improvement in penetration achieved using the activated flux developed in the present work has been attributed to the constriction of the arc and as well as reversal of Marangoni flow in the molten weld pool. The use of activated flux has been found to overcome the variable weld penetration observed in 316LN stainless steel with <50 ppm of sulfur. There was no degradation in the microstructure and mechanical properties of the A-TIG welds compared to that of the welds produced by conventional TIG welding on the contrary the transverse strength properties of the 304LN and 316LN stainless steel welds produced by A-TIG welding exceeded the minimum specified strength values of the base metals. Improvement in toughness values were observed in 316LN stainless steel produced by A-TIG welding due to refinement in the weld microstructure in the region close to the weld center. Thus, activated flux developed in the present work has greater potential for use during the TIG welding of structural components made of type 304LN and 316LN stainless steels.
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This study investigates dissimilar metal weldments between P91 steel and AISI 316 L austenitic stainless steel fabricated by activated TIG welding (A-TIG) with and without the use of ...interlayers of Incoloy 800 and Inconel 600. Through thickness penetration in 8 mm thick plates was achieved in a single pass A-TIG welding using a pre-coated mixture of metallic oxides. Hot cracking was eliminated in A-TIG weld joints in contrast to conventional TIG weld joints without flux. Fully martensitic structure was observed in the weld metal developed without the use of interlayer. Microstructural modifications were achieved with the use of interlayers. The weldment with Incoloy 800 interlayer exhibited martensitic-austenitic structure whereas fully austenitic structure was observed with Inconel 600 interlayer. Interlayers improved impact toughness and ductility of the weld joints without significant loss of tensile strength. The effect of interlayers on carbon migration after aging treatment (620 °C/500 h) was evaluated with the help of thermodynamic simulations and it was observed that the use of interlayers reduced the severity of carbon migration.
The effect of laser, Hybrid Laser-Tungsten inert gas (HLT) and Hybrid Laser-Metal inert gas (HLM) welding processes on the microstructure and mechanical properties of 5.6 mm thick 316L(N) stainless ...steel weld joints have been studied. The differences in weld metal microstructure and mechanical properties of the weld joints were evaluated and discussed. Weld bead geometry, ferrite number (FN), solidification mode, secondary dendrite arm spacing, hardness and tensile properties are compared. Laser weld joint showed narrow weld bead profile and a higher cooling rate than the hybrid laser arc weld joints and the weld metal manifested austenitic solidification mode. HLT weld displayed coarser weld metal microstructure due to higher heat input and austenitic ferritic solidification mode. HLM process possesses moderate heat input and cooling rate. The HLM weld metal exhibited ferritic austenitic solidification mode and 2.5 FN. The hardness of weld metal was higher in hybrid welding processes due to the higher ferrite content. HLM weld joint has higher yield strength, ultimate tensile strength and ductility compared to that of the other weld joints. HLM welding process also permits higher gap tolerance with filler metal addition and is recommended for welding of type 316L(N) stainless steel.
The current work investigates activated flux TIG welding of dissimilar steel combination of 8 mm thick plates of Modified 9Cr-1Mo (P91) steel and 2.25Cr-1Mo (P22) steel. The effect of different ...fluxes namely- SiO2, TiO2, Cr2O3, MoO3 and CuO on the weld bead geometry was investigated. The possible mechanism for the increase in depth of penetration has been discussed. The integrity of the weld joint made with MoO3 flux was investigated by evaluating metallurgical and mechanical characteristics in as-welded and post weld heat treated (750 °C/2 h) conditions. The occurrence of carbon migration was confirmed by optical microscopy and elemental redistribution through EPMA analysis. The precipitation of carbides of M23C6 type in the carbon enriched zone was confirmed through TEM analysis. The beneficial effect of A-TIG welding in reducing the widths of carbon enriched/depleted regions at the P22 steel-weld interface after post weld heat treatment has been discussed with the help of DICTRA simulations. The weld joints failed from P22 steel base metal in both as-welded and post weld heat treated conditions during a tensile test. The impact toughness was found to be improved after post weld heat treatment.
The present work discusses the microstructure and mechanical properties of dissimilar metal weld joint between AISI 316L SS-Alloy 800 developed by activated TIG (A-TIG) welding. The evolution of ...fusion zone microstructure and solidification temperature range were investigated through equilibrium calculation and Scheil-Gulliver equation. Electron probe micro-analysis revealed the micro-segregation of Ti and Si in the inter-dendritic arms of the fusion zone. The presence of secondary phases (Ti(C,N) and FeSi2) in the fusion zone was confirmed with X-ray diffraction technique and transmission electron microscopy of electrochemically extracted precipitates. The A-TIG weld joint showed a decent combination of tensile strength and impact toughness. Tensile testing with digital image correlation revealed a transfer of strain localization from Alloy 800 side heat affected zone to the fusion zone due to lower hardening capacity of the fusion zone. During tensile loading, the formation of micro-cracks along the solidification grain boundaries reduces the peak tensile strength of the fusion zone.
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Geosynthetic clay liners (GCLs) are mostly used as flow barriers in landfills and waste containments due to their low hydraulic conductivity to prevent the leachate from reaching the environment. The ...self-healing and swell-shrink properties of soft clays (expansive soils) such as bentonite enable them as promising materials for the GCL core layers. However, it is important to modify their physico-chemical properties in order to overcome the functional limitations of GCL under different hydraulic conditions. In the present study, locally available black cotton soil (BCS) is introduced in the presence of an anionic polymer named carboxymethyl cellulose (CMC) as an alternative to bentonite to enhance the hydraulic properties of GCL under different compositions. The modified GCL is prepared by stitching the liner with an optimum percentage of CMC along with various percentages of BCS mixed with bentonite. Hydraulic conductivity tests were performed on the modified GCL using the flexi-wall permeameter. The results suggest that the lowest hydraulic conductivity of 4.58 × 10
m/s is obtained when 25% of BCS is blended with bentonite and an optimum 8% CMC and further addition of BCS results in the reduction of the hydraulic conductivity.
Type 316L(N) stainless steel (SS) weld joints were made by employing advanced welding processes such as laser, hybrid laser-MIG (HLM) and hybrid laser-TIG (HLT). First, the welding parameters were ...identified and full penetration joints were fabricated using 5.6-mm-thick plates. To understand the residual stresses and distortion in weld joints, thermomechanical analysis of advanced welding processes has been performed. The validation of model predictions was carried out experimentally. The hybrid double ellipsoidal heat source coupled with a conical heat source model was used to analyze hybrid welding processes, and the conical model with a cylindrical shell was used for laser welding process. The heat source parameters were fine-tuned by matching the simulated weld profile with the experimentally obtained profile. Thermocouple measurements verified the simulated thermal cycles. Then the predicted temperature distribution was sequentially coupled to the mechanical analysis considering the isotropic hardening model. The simulated residual stresses were confirmed by experimental measurements employing an ultrasonic technique with longitudinally critically refracted (L
CR
) waves. The hybrid heat source model was found to be accurate for the thermomechanical analysis of the laser and hybrid laser welding of 316L(N) SS. Spot analysis showed that the HAZ of the weld joints exhibited higher residual stresses than the weld metal. The longitudinal tensile residual stress values are lower for the TIG/MIG part than the laser part in the through-thickness direction for the hybrid welds. The weld joint’s measured distortion values are generally low and found to correlate with the weld metal volume.
Automated ball indentation (ABI) tests were conducted across the 316LN stainless steel (SS) weld joints at 298 K, and 823 K. Zone wise tensile properties of 316LN SS weld joints such as weld metal, ...heat affected zone (HAZ), and base metal region are evaluated in this work. Uniaxial tensile tests were conducted to assess the effect of welding processes on the tensile properties. The weld joints were initially fabricated using arc based and laser based welding processes. The variations of tensile properties such as yield strength, ultimate tensile strength and strain hardening component values across the heterogeneous microstructure zones of the weld joints were evaluated. The correspondence between the microstructure variations and the tensile properties have been studied. The variations in grain size, secondary dendrite arm spacing (SDAS) and δ-ferrite content are found to be the primary cause of tensile strength variation across the weld joints. The gradient in tensile strength across the weld joints was higher at 298 K than at 823 K which was attributed to the microstructural changes at higher temperature causing material softening. It was noticed that the 316LN stainless steel weld joint made by hybrid laser MIG welding exhibited the highest values of strength and ductility among all the weld joints. It was attributed to the combined effect of higher δ-ferrite content and finer SDAS values. Therefore, the HLM welding process is recommended for welding of 316LN stainless steel components from the point of view of better tensile properties.
•Type 316LN stainless steel weld joints were fabricated by fusion, advanced laser and hybrid-laser welding techniques.•The variations of tensile properties across the different zones in the fabricated weld joints were obtained at 298and 823 K.•The automated ball indentation (ABI) and Uni-axial tensile testing methods were utilised to evaluate the tensile properties.•Influence of secondary dendrite arm spacing and amount of delta ferrite content on the tensile properties are presented.•The 316LN stainless steel weld joint exhibiting the highest strength and ductility is identified.
•The thermo-elasto-plastic analysis of 316L stainless steel during laser welding.•Three different heat sources employed.•Simulated thermal cycles, residual stresses and distortion were ...validated.•Good agreement between the model predictions and experimental measurements.•3D conical with cylindrical shell heat source predicted weld attributes accurately.
The thermo-elasto-plastic analysis of type 316L stainless steel sheets during pulsed Nd-YAG Laser-beam welding was carried out using three different heat sources employing SYSWELD. The three heat sources employed were 3D conical, 3D conical with double ellipsoidal and 3D conical with cylindrical shell. The simulated thermal cycles, residual stresses and distortion were validated by experiments. The simulated thermal cycles were validated by thermal cycles measured using thermocouples at pre-defined positions. The simulated residual stress profiles were validated by residual stress profiles measured using ultrasonic technique (UT). The simulated distortion values were validated by distortion measured using vertical height gauge. There was good agreement between the model predictions and experimental measurements. It was found that the model using 3D conical with cylindrical shell heat source predicted the thermal cycles, residual stresses and distortion more accurately compared to that of the other heat sources.
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