Chhibber, Rahul

Variation in dynamic contact resistance with the change in welding process parameters such as weld current, weld time and electrode force were taken into account for establishing the range of adequate nugget formation parameters. Influence of the welding process parameters on the shear – tensile strength, nugget diameter and the observed failure mode was analysed. The adequate resistance spot welding process parameters for galvannealed high strength interstitial free steel sheets of 1.6 mm thickness were estimated as 8 kA weld current, 250 ms weld time and 3.5 kN electrode force. Increase in the mean dynamic contact resistance led to a significant reduction in nugget diameter. A critical nugget diameter distinguishing between the IF and PF mode was experimentally determined by failure mode analysis. Different numerical models for estimation of critical nugget diameter were evaluated.

The dissimilar joint between aluminium alloy 6063 and aluminium has been made using the friction stir welding process. Three input parameters: Tool rotational speed, feed rate and dwell time have been varied and their effect of the mechanical properties has been studied. Obtained weld joints have been characterized for tensile properties, hardness, and corrosion behavior. Effort has been made to study the in process force acting on the joint and establishing its dependence on the welding parameter. The use of full factorial design methodology brings out the contribution of input parameters and their effect on the output mechanical properties.

This paper investigates the high-temperature wettability property of the mineral waste red ochre added CaO–CaF2–SiO2 and CaO–TiO2–SiO2-based electrode coating mixture for offshore welding. The extreme vertices design method was applied to formulate 21 coating compositions. The pellets made from developed electrode coating compositions were exposed to a high temperature of 1250℃ on the substrate of super duplex stainless steel of 2507 grade. The molten flux has been characterized for contact angle, surface tension, adhesion energy and spreadability. The regression analysis has been used to estimate the effect of individual components and their interactions on the wettability property parameters. The developed regression models have been optimized using multiresponse optimization to achieve optimum flux composition. Structural analysis of flux mixture has been done using X-ray diffraction and Fourier transformation spectroscopy.

Linepipes above 16″ diameter are often submerged arc welded. Weld mechanical as well as metallurgical properties are widely affected by the flux composition. Flux composition and welding parameters play an important role in determining the good bead quality and mechanical properties of the welded joint. In present study submerged arc welding fluxes were formulated using constrained mixture design approach. Twenty one submerged arc welding flux compositions based on CaF2–CaO–SiO2 and Al2O3–CaO–SiO2 flux system were designed using extreme vertices design approach. Regression models were developed in terms of individual, binary and ternary mixture flux constituents for submerged arc series of bead on plate weld deposits (API 5 L X70 pipeline steel). By using F-test regression mathematical models have been checked for 95% significance level. Effect of formulated fluxes on silicon, copper, molybdenum, titanium and chromium content was studied using a multi-layer weld deposits. All binary mixtures C·Al, S·CF, S·Al and C·Al have significant increasing effect on silicon content in a bead on plate weld deposits while S·Al is the most effective synergistic binary mixture. Individual and binary flux mixtures tend to decrease the copper content in a bead on plate weld deposits.

The present paper aims to study the thermophysical and physicochemical properties of CaO-CaF2-SiO2-22.5% TiO2 based electrode coating for welding the components of advanced ultra-supercritical power plants. The mixture design methodology was used to formulate thirteen coating mixtures to explore the effect of flux coating properties, i.e., density, change in enthalpy, weight loss, thermal conductivity, specific heat, and thermal diffusivity. Flux coating properties play an essential role in achieving better weldments. Fourier transformation and X-ray diffraction were used to analyze electrode coating composition structural behavior. The coating composition was also characterized by using a thermogravimetric analyzer and hot disc apparatus, and after that, a regression model analysis was carried out to study individual, and their interaction effects on the thermophysical and physicochemical properties. CaO.CaF2, CaO.SiO2, and CaF2.SiO2 is the most effective binary mixture which has an increasing effect on density. The weight loss of coating observed during thermogravimetric analysis is affected by individual constituents significantly. The binary interaction of SiO2.CaO and CaF2.SiO2 is the most favorable and has an increasing effect on weight loss. Individual components affect change in enthalpy significantly. The binary interaction of CaO.SiO2 and CaF2.SiO2 is the most effective and has an increasing effect on change in enthalpy. The thermal properties of coating composition observed during hot disc are affected by individual and binary mixture constituents. Binary mixture CaF2.CaO and CaF2.SiO2 is having an increasing effect on thermal conductivity. Binary mixture SiO2.CaO shows a decreasing impact on thermal diffusivity. Binary mixture constituents CaF2.CaO, SiO2.CaO is the most effective and has an increasing effect on specific heat.

The purpose of this investigation was to quantify the effects of intermetallic and secondary phases on the sliding wear behavior of super duplex stainless steel 2507 against bearing steel type EN-31 under both dry and wet contact conditions. Phases were precipitated by suitable heat treatment in the range of 475–875 °C. A pin-on-disc technique was used to investigate the wear characteristics in the wet environment of 3.5% NaCl solution, 1 M HCl solution, 10−2 M sodium thiosulfate solution, and artificial ocean water. These media were chosen to closely match the actual service environment of super duplex stainless steel 2507. Pins were slid against a disc of EN-31 steel for distances of 1,000, 1,500, 2,000, 2,500, and 3,000 m. Results indicate that precipitation of the sigma phase gives the best wear resistivity, followed by precipitation of chi and R phases and then precipitation of the α′ phase. The experimental investigations reveal that hydrogen in acidic medium accelerates the reaction kinetic compared to the neutral medium because of the different cathodic reactions. Progressive wear was closely observed using the change in the sliding pin’s contact face profile and corresponding weight loss data. Scanning electron microscopy was used to study the wear mechanism.

High carbon steels are more difficult to weld than low and medium carbon steels due to its high hardness because of the presence of the high carbon content in it which results in crack formation during the cold working. The present work aims at studying the mechanical behavior of high carbon steel welds with a variation of welding parameters and surface heat treatment processes and relating their effects on the mechanical properties of the material In this work, high carbon steel with 0.90 wt pet C is used as the specimen material. The specimens are prepared using different arc welding parameters followed by heat treatment in the furnace for 700°C, 800°C for 60 and 120 minutes. The mechanical properties of these specimens are measured and analyzed to estimate the effect of variation of process parameters.

The present research focuses on investigating the changes in microstructure–mechanical integrity of the dissimilar joint between X-70 pipeline steel and super duplex stainless steel (sDSS 2507). Gas tungsten arc welding with ER 309L austenitic filler at 0.73 and 1.4 kJ/mm heat inputs was employed. The microstructure was characterized using a scanning electron microscope with energy-dispersive spectroscopy and an optical microscope. The weld joint’s mechanical characteristics and overall integrity were evaluated through microhardness, cross-weld tensile, and impact toughness tests. Oil and gas pipelines and hydrocarbon drilling risers use this type of dissimilar joint. The filler material ER309L solidifies into a ferrite–austenite microstructure with skeletal and lathy ferrites and interdendritic austenite. The study revealed that the weld zone and heat-affected zone (HAZ) microstructure displayed Type II boundaries and macro-segregation for lower heat input (LHI) and higher heat input (HHI) welding conditions. Additionally, three distinct types of HAZs were identified in the X-70 base metal, each associated with a different thermal peak temperature during welding: coarse grain, fine grain, and inter-critical. The hardness values ranged from 190 to 290 Hv0.5, with an average of 205 ± 6 Hv0.5 for LHI and 225 ± 4 Hv0.5 for HHI weldment. The tensile strength and elongation of the LHI samples were found to be 609.4 MPa and 25.3%, while the HHI samples were 601.7 MPa and 30.8%. The impact toughness was 195 ± 5 J and 185 ± 2 J for the cap and root sections of the LHI weldment, compared to 180 ± 4 J and 200 ± 3 J for the HHI weldment. As a result, the investigation sheds insight into the evolution of welding processes and microstructural evolution in the weld zone and HAZ, variations in mechanical characteristics, and changes in residual stresses for the sDSS 2507/X-70 DWJ.

The objective of this study is to develop and examine coating fluxes for SMAW electrodes intended for use in nuclear power plant steel welding. A set of 21 unique flux compositions is created using the extreme vertices design methodology. These compositions predominantly consist of SrO-CaO-Al2O3-CaF2 fluxes. At a temperature of 1373 K, an in-depth investigation is carried out to assess key properties, including the work of adhesion, spread area, contact angle and floatation coefficient. Additionally, the surface tension of these flux compositions is estimated. XRD and FTIR analysis methodologies have been employed for the purpose of examining and identifying the phases that exist within both the flux and slag. Furthermore, structural analysis of the molten material is conducted through the examination of quenched slag powder. Results reveal that the individual components CaO, CaF2 and binary interaction of Al2O3 × SrO have a significant effect on the contact angle and floatation coefficient. Individual interactions of CaO, SrO, Al2O3 and CaF2 exert a positive impact on the spread area. The individual components Al2O3 and SrO were found to have a significant effect on the work of adhesion.

Thermal emittance is an important parameter for the solar thermal collectors as thermal radiative losses from the solar thermal collector increase to the fourth power of temperature. This should be minimized using infrared reflectors in designing spectrally selective absorber coatings for solar thermal applications. The thermal emittance of zirconium (Zr) film as an infrared reflector has been investigated for the use in the spectrally selective absorber. The Zr metallic films are deposited using DC magnetron sputtering process on stainless steel and glass substrates and the deposition process has been optimized to achieve the minimum thermal emittance. The effect of structural, microstructural and surface morphological properties of Zr films is investigated on the emittance of fabricated structures. The X-ray diffraction analysis revealed that the Zr film coatings consist of both cubic and hexagonal Zr crystallographic phase. The optimized deposition time and temperature showed 0.12 and 0.14 emittance values for Zr film coatings on stainless steel and glass substrates respectively.