Experimental investigations on the SiO<Subscript>2</Subscript> flux-assisted GTA welding of super-austenitic stainless steels

Analyzed in this paper are barrier properties of wood specimens treated by ball burnishing. For the purpose of experimental investigation, special device was designed which allows continuous monitoring of the volume of water absorbed by specimen within particular time intervals. The device allows water pressurized at 3 bar to efficiently penetrate specimen internal structure over its burnished/non-burnished surface interface. The experimental investigation encompassed six types of wood—beech, acacia, walnut, oak, linden, and ash tree. Comparative analysis was performed to establish relative resistance to water penetration in burnished and non-burnished specimens, as well as the quantities of water volume absorbed over time. The results indicate that ball burnishing is capable of enhancing barrier properties in all of the examined types of wood.     

Leakage current and charge in RTV coated insulators under pollution conditions

Room temperature vulcanizing (RTV) silicone rubber coating has excellent leakage current suppression characteristics. It is used extensively on porcelain and glass insulators in pollution prone areas as an anti-pollution measure. A pollution aging chamber has been fabricated and an on line 4-channel personal computer (PC) based data acquisition system has been developed to conduct tests on RTV coated porcelain samples. A study of the dependence of the leakage current and the charge on the flow rate, conductivity and pressure of the solution forming the fog is reported. It was observed that a higher charge and a higher average leakage current were obtained at a higher flow rate and a higher conductivity. The results with coated HV insulators are consistent with those published in the literature with RTV coated fiber glass reinforced plastic (FRP) rods.     

Division Director's Message

It is believed that room temperature vulcanizing (RTV) silicon rubber coating is not passive but reacts to its environment. The hydrophobicity of the coating is extremely resilient and can recover under all exposure conditions provided there is adequate rest after removal of the stress (voltage, pollution, UV, etc). The present letter deals with the recovery characteristics of the hydrophobicity of the RTV-coated insulator during a combined continuous voltage and a cyclic low conductive fog application.     

Characterization of Microstructure,Strength, and Toughness of Dissimilar Weldments of Inconel 625 and Duplex Stainless Steel SAF 2205

The dissimilar combinations of Inconel 625 and duplex stainless steel SAF 2205 obtained from manual GTA welding process employing ER2209 and ERNi CrMo-3 filler metals have been investigated. Formation of secondary phases at the HAZ of Inconel 625 and grain coarsening at the HAZ of SAF 2205 were witnessed while using these filler wires. The average hardness of ER2209 weldments was found to be greater than ERNi CrMo-3 weld. Tensile fracture was observed at the weld zones for both the fillers. Impact test trials showed brittle mode of fracture on employing ER2209 filler and mixed(ductile–brittle) mode of fracture while using ERNi CrMo-3 filler. Further optical microscopy and SEM/EDS analysis were carried out across the weldments to investigate the structure–property relationships.     

Hot-corrosion resistance of dissimilar AISI 4340 and AISI 304L weldments in the molten salt environment at 600°C

High temperature corrosion resistance of welded components in power plant industry, hot sections of gas turbines, boilers, industrial waste incinerators, metallurgical furnaces and petrochemical installations is one of the serious necessity. The failure of hot sections of welded component is due to the deposition of molten salt which accelerates the hot corrosion reactions in the weld joint. In this research work, the oxy-chlorination of dissimilar weldments between AISI 304L austenitic stainless steel and AISI 4340 alloy steel at 600°C in eutectic mixture of K₂SO₄?+?60% NaCl under molten salt conditions was investigated. Corrosion kinetics for this dissimilar joints calculated from the thermogravimetric charts were represented. Corrosion on the dissimilar joint employing E309L filler in pulsed current gas tungsten arc welding process is found to be very aggressive, due to the fragmented delta ferrites at numerous locations resulting in the formation of the micro electrochemical cells, which act as sites for corrosion initiation and thus leading to higher corrosion rate. However, in the case of continuous current, the joint is able to protect itself better in this environment due to lower amounts of delta ferrites in weld zone, which is attributed to the higher temperature available in continuous mode leading to austenisation of delta ferrites in the multipass welding.     

Hot Corrosion Behavior of Friction Welded AISI 4140 and AISI 304 in K2SO-60% NaCl Mixture

Understanding the behavior of weldment at elevated temperatures and especially the corrosion behavior has become an object of scientific investigation recently.Investigation has been carried out on friction welded AISI 4140 and AISI 304 in molten salt of K 2 SO 4-60% NaCl environment at 550,600 and 650 C under cyclic condition.The resulted oxide scales in the weldment have been characterized systematically by surface analytical techniques.From the results of the experiments,it is observed that the scale thickness on low alloy steel side was higher than that on stainless steel side.Furthermore,weld interface has been found to be more susceptible to degradation than base metals due to inter diffusion of element across the interface and the formation of intermetallic compound.The influences of welding parameters and the temperature of exposure on the hot corrosion behavior of the weldment were discussed in this paper.     

Influence of Filler Metals in the Control of Deleterious Phases During the Multi-pass Welding of Inconel 718 Plates

The present study reported the effect of filler metals on the microstructure and mechanical properties of pulsed current gas tungsten arc-welded Inconel 718 plates. Two different filler metals such as ERNi Cr-3 and ERNi Cr Mo-4 were employed for welding Inconel 718. The primary objective of this study is to suppress or eradicate the deleterious phase such as Laves or d(delta) which is considered to be detrimental to the weld properties. Microstructure examination corroborated the presence of unmixed zone at the HAZ for both the weldments. Tensile test trials envisaged that ERNi Cr Mo-4 weldments offered better tensile properties compared to ERNi Cr-3 weldments, whereas the impact toughness was found to be better for ERNi Cr-3 weldments. Line mapping analysis was carried out to study the elemental migration across the weldments. The structure–property relationships of the weldments were arrived at using the combined techniques of optical and scanning electron microscopy. Optical and SEM/EDAX analysis showed that there is no prominent occurrence of deleterious phases at the weld zone on employing these filler metals.