N. Arivazhagan

Improvement of Microstructure and Mechanical Behavior of Gas Tungsten Arc Weldments of Alloy C-276 by Current Pulsing

Superalloy C-276 is known to be prone to hot cracking during fusion welding by Gas Tungsten Arc method. Microsegregation occurring during cooling of fusion zone with consequent appearance of topologically close-packed phases P and µ has been held responsible for the observed hot cracking. The present work investigated the possibility of suppressing the microsegregation in weldments by resorting to current pulse. Weldments were made by continuous current gas tungsten arc welding and pulsed current gas tungsten arc welding using ERNiCrMo-4 filler wire. The weld joints were studied with respect to microstructure, microsegregation, and mechanical properties. Optical microscopy and scanning electron microscopy were employed to study the microstructure. Energy-Dispersive X-ray Spectroscopy was carried out to evaluate the extent of microsegregation. Tensile testing was carried out to determine the strength and ductility. The results show that the joints fabricated with pulsed current gave rise to narrower welds with practically no heat affected zone, a refined microstructure in the fusion zone, reduced microsegregation, and superior combination of mechanical properties.

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 ERNiCrMo-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 ERNiCrMo-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 ERNiCrMo-3 filler. Further optical microscopy and SEM/EDS analysis were carried out across the weldments to investigate the structure–property relationships.

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 K2SO4–60% 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.

Hot corrosion studies on dissimilar friction welded low alloy steel and austenitic stainless steel under chlorine containing salt deposits under cyclic conditions

Abstract High temperature corrosion tests were performed on dissimilar friction weldment of low alloy steel and austenitic stainless steel. Test conditions simulated the environment of a biofuel fired boiler. The samples were exposed to synthetic salt containing 40 wt-%K2SO4, 40 wt-%Na2SO4, 10 wt-%KCl and 10 wt-%NaCl. In the present paper, hot corrosion behaviour of friction welded AISI 4140 and AISI 304 dissimilar materials in molten salt environments at 500, 550 and 600°C was studied. Corrosion was extremely severe on the interface of the dissimilar weldment in molten salt environment. Comparative evaluation was based on the effect of burn-off length and temperature of exposure on hot corrosion behaviour of the dissimilar weldment. Even the interface was attacked through chromium rich phases in hot corrosion environment. The metals formed on the weldment were non-protective.

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 ERNiCr-3 and ERNiCrMo-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 δ (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 ERNiCrMo-4 weldments offered better tensile properties compared to ERNiCr-3 weldments, whereas the impact toughness was found to be better for ERNiCr-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.

Effect of Filler Metals on the Structure–Property Relationships of Continuous and Pulsed Current GTA Welds of AISI 430 and AISI 904L

This research article reports the effect of filler metals on the weldability, microstructure, tensile strength, and impact toughness of bimetallic joints involving ferritic stainless steel (AISI 430) and super-austenitic stainless steel (AISI 904L). These dissimilar combinations were obtained using continuous current (CC) and pulsed current (PC) gas tungsten arc-welding (GTAW) processes, employing duplex stainless steel (ER2553) and Inconel 625 (ERNiCrMo-3) fillers. Microstructure studies revealed the presence of grain boundary martensite and a slight grain coarsening effect in the HAZ of AISI 430 for all the cases. The study also inferred that both CCGTA and PCGTA welding employing these fillers resulted in better joint strength by observing failure at the parent metal of AISI 430 in all the trials. Impact toughness was found to be better for the PCGTA weldments employing ERNiCrMo-3 filler due to the refinement of grains. The impact studies showed that the root pass corroborated higher toughness values than the cap zone for all the cases. Based on the structure–property relationships, this study recommends the use of PCGTA employing ERNiCrMo-3 for joining AISI 430 and AISI 904L.

Investigations on the microstructure and mechanical properties of multi-pass PCGTA welding of super-duplex stainless steel

This paper addresses the weldability, microstructure and mechanical properties of the multi-pass welding of super-duplex stainless steel (SDSS). Pulsed current gas tungsten arc welding (PCGTAW) was carried out employing ER2553 and ERNiCrMo-4 fillers. Microstructure examination showed the presence of austenite in different forms at the weld zone of ER2553 whereas multi-directional grain growth was observed for ERNiCrMo-4 welds. Tensile and impact studies corroborated that the weldments employing ER2553 exhibited better results compared with ERNiCrMo-4 weldments. Detailed structure–property relationships of the weldments have been reported in the present study. The results corroborated that the enhanced properties could be achieved with the matching filler wire compared with the over-alloyed filler.

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

ABSTRACT 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.

Effect of Filler Metals on the Weldability and Mechanical Properties of Multi-pass PCGTA Weldments of AISI 316L

The influence of filler metals on the microstructure, mechanical properties, and corrosion behavior of AISI 316L welds was investigated. Pulsed current gas tungsten arc welding was employed to join the AISI 316L plates using two different fillers ER2553 and ERNiCr-3. Microstructures studies showed the presence of different forms of austenite on employing ER2553 filler and formation of migrated grain boundaries at the weld zone while using ERNiCr-3 filler. Tensile studies corroborated that the tensile strength was greater for the weldments employing ER2553 filler. Charpy V-notch studies ascertained that the impact toughness was greater for ER2553 weldments as compared to the parent metal. Potentiodynamic polarization curves clearly inferred that the weld zone of ER2553 exhibited better corrosion resistance among the various coupons tested. It was concluded from the study that ER2553 exhibited better mechanical and corrosion properties and could be adopted to achieve optimal properties compared to over-alloyed filler.

Microstructural evolution and precipitation behavior in heat affected zone of Inconel 625 and AISI 904L dissimilar welds

In the present investigation an attempt has been made to join the dissimilar combination of Inconel 625 super alloy and super austenitic stainless steel (AISI 904L) using manual multi-pass continuous current gas tungsten arc (CCGTA) welding processes. Two different filler wires such as ERNiCrMo-4 and ERNiCrCoMo-1 have been used to compare the metallurgical properties of these welded joints. Both optical microscopy and scanning electron microscopy techniques were adopted to disseminate the microstructure traits of these weldments. Formation of secondary phases at the HAZ and weld interface of AISI 904L was witnessed while using the ERNiCrCoMo-1 filler, along with Solidification Grain Boundary (SGB) and Migrated Grain Boundary (MGB) were also observed at the weld zone.