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Microstructural features and creep-rupture behaviour of a dissimilar weld joint (DWJ) between Grade 91 (G91) steel and 316LN stainless steel prepared by Electron beam (EB) welding are investigated. The SEM-EDAX and EBSD observations in the fusion zone revealed compositional variations and distinct microstructural features, depending on the extent of mixing of both base metals. Further, at the interface between the fusion zone and G91 steel, nickel enrichment was observed, which lowered the Ac1 temperature, resulting in fresh martensite and higher hardness upon PWHT. In the creep-rupture tests conducted at 873 K and 110 to 175 MPa, failure location shifted from G91 base metal to intercritical HAZ of G91 steel above 2500 hours of creep exposure. As against the interface failures, which are considered the life-limiting factor in DWJs, the ruptured specimens in the present study revealed better interface stability with insignificant cavitation even after creep exposure of over 10,000 hours. The composition at the ferritic–weld interface exhibits almost equivalent carbon activity to G91 steel which improved the interface stability by resisting the coarsening of carbides. It is important to highlight that the EB weld joint exhibited higher rupture life and weld strength reduction factor than the joints made by conventional multi-pass arc welding. [ABSTRACT FROM AUTHOR]

This study presents new findings on the underlying failure mechanism of thick dissimilar electron-beam (EB) welds through a study on the AA 2219-AA 5083 pair. Contrary to the prior studies on EB welding of thin Al alloys, where liquation in the grain boundaries (GBs) in the partially melted zone (PMZ) was not observed, the present investigation for thick EB welds reports both liquation and increased segregation of Cu in the PMZ. The work is thus directed towards understanding the unusual observation in the PMZ of thick EB weld through investigation of the microstructural variation across the various regions of the produced weld. The microstructural results are correlated with the mechanical properties of the weld, i.e., hardness variation and tensile response. Results of this investigation suggest that unlike the convention that EB welding produces sound dissimilar Al welds, the weld performance for thick EB Al welds is affected by the heat input, the associated cooling rates, and most importantly by the base material thickness. Extensive liquation and Cu segregation induced failure in the PMZ on the AA 2219 side of the dissimilar weld. The underlying failure mechanism is explained through a heat-transfer analysis. Beyond a certain plate thickness, the heat transfer changes from two to three-dimensional. As a result, retarded cooling promotes liquation and Cu segregation in thick EB welds. [ABSTRACT FROM AUTHOR]

The tensile properties of modified 9Cr-1Mo steel clad tube to end plug TIG weld joint have been studied in as-welded, after post-weld heat treatment (PWHT), at 760 °C and second heat treatment (2HT, at 550 °C) conditions at temperatures 27-550 °C. Heat-affected zone (HAZ) grain size varied from 6 to 28 µm, with coarse grains toward weld and finer grains toward base metal. Weld metal also showed coarse grains (up to 45 µm) after PWHT and PWHT+2HT, with high hardness (367-340 HV0.2) near weld center beyond which hardness gradually decreased through HAZ and attained 210-235 HV0.2 in base metal. Small fraction of polygonal delta ferrite is observed in weld metal. The yield strength (YS) and ultimate tensile strength (UTS), of weld joint at 27 and 550 °C, exhibited increase of 11 MPa and decrease of 20 MPa, respectively, in as-welded condition and showed minimum strength properties after PWHT. However, PWHT+2HT treatment has increased strength values above PWHT condition. The weld joint after PWHT+2HT retains sufficient total elongation over 10% and possess sufficient strength properties (YS: 442-263 MPa and UTS: 639-276 MPa) at 27 and 550 °C. All the weld joint tensile samples failed in base metal by transgranular ductile fracture, irrespective of test temperature and weld joint condition (as-welded, PWHT, 2HT). [ABSTRACT FROM AUTHOR]

This paper assesses the metallurgical characteristics and mechanical properties of multi-pass gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) of micro-alloyed steel DMR 249-A. The prime objective was to carry out a comparative study of the microstructure and mechanical properties of the joints produced by the two types of welding. A high volume of larger sized inclusions in GMAW contributed to inferior mechanical properties. The coarse-grained part of the heat-affected zone (CGHAZ) showed a lower microhardness. Fracture always occurred in the heat-affected zone, and it is believed that it is associated with CGHAZ. GTAW joints showed low tensile residual stress, higher hardness, and tensile strength. GTA weldment also showed superior impact toughness at sub-zero temperature (–60 °C). Mn-containing inclusions were seen in GTA weldments; it is believed that they promote the formation of acicular ferrite. This is believed to be responsible for the superior mechanical properties of GTA weldments. The microstructural analysis of the two weldments revealed the presence of a higher volume fraction of acicular ferrite in the GTAW. All in all, GTAW joint was found to perform better than GMAW joint. [ABSTRACT FROM AUTHOR]

The austenitic stainless steel weld metal fabricated by multipass welding exhibits a composite microstructure. Microstructural characterization of the weld metal revealed that there are two distinct regions on either side of the weld-pass interface. The variations in dislocation substructure and delta ferrite morphology are the two microstructural attributes which delineate these regions. The generation of subsequent thermal cycles during the fabrication of multipass weld joint is the paramount factor influencing the formation of the composite microstructure. During creep exposure, the extent of creep cavitation and propagation varies substantially in these two regions due to differences in their microstructures. This results in preferential damage during creep exposure of austenitic stainless steel weld metal. [ABSTRACT FROM AUTHOR]

Effects of electron beam oscillation techniques (sinusoidal, square, triangular, ramp, circle, and elliptical) in controlling Nb segregation, Laves formation, and tensile behavior of Inconel 718 electron beam welds were studied. Effects of various postweld heat treatments on tensile behavior were compared. Elliptical beam oscillation technique resulted in less Nb segregation and discontinuous finer Laves in the interdendritic regions compared to that of unoscillated beam weld. Response to aging was better for welds made with elliptical oscillated beam compared with welds made with unoscillated beam. Oscillated beam welds exhibited better mechanical properties than unoscillated beam welds in both solution-treated and aged and directly aged conditions. [ABSTRACT FROM AUTHOR]

Nickel based superalloy Inconel 718 and low alloy steel EN24 are welded by continuous drive friction welding in annealed condition and then post-weld heat treated (PWHT). The welds exhibit low strength and high toughness in the as welded condition. Post-weld heat treatment applicable to either Inconel 718 or EN24, led to reduction in toughness and increase in strength. Toughness degradation after PWHT as per Inconel 718 was predominant. The observed trends in mechanical properties are explained on the basis of observed microstructure, fracture behaviour, electron probe microanalysis and X-ray diffraction. [ABSTRACT FROM AUTHOR]

Quenched and tempered (Q&T) steels are prone to hydrogen-induced cracking in the HAZ after welding. Austenitic stainless steel (ASS) welding consumables are traditionally used for welding of high hardness Q&T steels as they have higher solubility for hydrogen. The use of stainless steel consumables for a non-stainless steel base metal is not economical. In recent years, the developments of low hydrogen ferritic steel (LHF) consumables that contain no hygroscopic compounds are utilized for welding of Q&T steels The use of ASS and LHF consumables for armour grade Q&T steel will lead to formation of distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence in the dynamic fracture toughness of the armour grade Q&T steel welds. Hence, an attempt was made in this paper to study the influence of flux-cored arc welding consumables on dynamic fracture toughness ( J1d) of armour grade Q&T steel joints. The flux-cored arc welding consumables have a significant effect on the dynamic fracture toughness of the armour grade Q&T steel welds. The joints fabricated using ASS flux-cored wires showed superior J1d values than the joints fabricated using LHF consumables and the base metal. [ABSTRACT FROM AUTHOR]

Quenched and Tempered (Q&T) steels are widely used in the construction of military vehicles due to their high strength-to-weight ratio and high hardness. These steels are prone to hydrogen-induced cracking in the heat affected zone (HAZ) after welding. The use of austenitic stainless steel consumables to weld the above steel was the only remedy because of higher solubility for hydrogen in austenitic phase. Recent studies proved that high nickel steel and low hydrogen ferritic steel consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. In this investigation an attempt has been made to study the effect of welding consumables on high cycle fatigue properties of high strength, Q&T steel joints. Three different consumables namely (i) austenitic stainless steel, (ii) low hydrogen ferritic steel, and (iii) high nickel steel have been used to fabricate the joints by shielded metal arc (SMAW) welding process. The joints fabricated using low hydrogen ferritic steel electrodes showed superior fatigue properties than other joints. [ABSTRACT FROM AUTHOR]

Understanding the behavior of weldment at elevated temperatures and especially their corrosion behavior has recently become an object of scientific investigation. Investigation has been carried out on friction-welded AISI 4140 and AISI 304 under Na2SO4 + V2O5 (60%) environment at 500 to 600°C under cyclic condition. The resulting oxide scales in the weldment have been characterized systematically using surface analytical techniques. Scale thickness on the low alloy steel side was found to be higher and was also prone to spalling. Weld area was found to be more susceptible to degradation than in base metals. The influences of welding parameters on the hot corrosion are discussed. [ABSTRACT FROM AUTHOR]

Pitting Corrosion behaviour of similar and dissimilar metal welds of three classes of stainless steels, namely, austenitic stainless steel (AISI 304), ferritic stainless steel (AISI 430) and duplex stainless steel (AISI 2205), has been studied. Three regions of the weldment, i.e. fusion zone, heat affected zone and unaffected parent metal, were subjected to corrosion studies. Electron beam and friction welds have been compared. Optical, scanning electron microscopy and electron probe analysis were carried out to determine the mechanism of corrosion behaviour. Dissimilar metal electron beam welds of austenitic–ferritic (A–F), ferritic–duplex (F–D) and austenitic–duplex stainless steel (A–D) welds contained coarse grains which are predominantly equiaxed on austenitic and duplex stainless steel side while they were columnar on the ferritic stainless steel side. Microstructural features in the central region of dissimilar stainless steel friction welds exhibit fine equiaxed grains due to dynamic recrystallisation as a result of thermomechanical working during welding and is confined to ferritic stainless steel side in the case of A–F, D–F welds and duplex stainless steel side in the case of D–A welds. Beside this region bent and elongated grains were observed on ferritic stainless steel side in the case of A–F, D–F welds and duplex stainless steel side in the case of D–A welds. Interdiffusion of elements was significant in electron beam welding and insignificant in friction welds. Pitting corrosion has been observed to be predominantly confined to heat affected zone (HAZ) close to fusion boundary of ferritic stainless steel interface of A–F electron beam and D–F electron beam and friction weldments. The pitting resistance of stainless steel electron beam weldments was found to be lower than that of parent metal as a result of segregation and partitioning of alloying elements. In general, friction weldments exhibited better pitting corrosion resistance due to lower incidence of carbides in the microstructure. [ABSTRACT FROM AUTHOR]

The distribution of residual stresses due to welding has been studied in maraging steel welds. Gas tungsten arc welding process was used and the effect of filler metal composition on the nature of residual stress distribution has been investigated using X-ray diffraction technique with Cr Kα radiation. Three types of filler materials were used, they include: maraging filler, austenitic stainless steel and medium alloy medium carbon steel filler metal. In the case of maraging steel weld, medium alloy medium carbon filler, the residual stress at the centre of the weld zone was more compressive while, less compressive stresses have been identified in the heat affected zone of the parent metal adjacent to the weld metal. But, in the case of austenitic stainless steel filler the residual stresses at the centre of the weld and heat affected zone were tensile. Post-weld aging treatment reduced the magnitude of stresses. The observed residual stress distribution across the weldments has been correlated with microstructure and hardness distribution across the weld. [ABSTRACT FROM AUTHOR]

This article reports the effect of postweld aging treatment on fatigue behavior of pulsed current welded AA 7075 aluminum alloy joints. AA7075 aluminum alloy (Al-Zn-Mg-Cu alloy) has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers, and railway transport systems. The preferred welding processes of AA7075 aluminum alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Rolled plates of 10 mm thickness have been used as the base material for preparing multipass welded joints. Single V butt joint configuration has been prepared for joining the plates. The filler metal used for joining the plates is AA 5356 (Al-5Mg (wt.%)) grade aluminum alloy. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW), and (iv) pulsed current GMAW(PCGMAW) processes. Argon (99.99% pure) has been used as the shielding gas. Rotary bending fatigue testing machine has been used to evaluate fatigue behavior of the welded joints. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. Grain refinement is accompanied by an increase in fatigue life and endurance limit. Simple postweld aging treatment applied to the joints is found to be beneficial to enhance the fatigue performance of the welded joints. [ABSTRACT FROM AUTHOR]

Aluminium alloy AA2219 is a high strength alloy widely used for aerospace application. One of the drawbacks of most of the high strength aluminium alloys is that they suffer from poor weldability. However, AA2219 is an exception due to the presence of more copper that helps in healing cracks by providing extra eutectics. Although AA2219 has excellent weldability, the strength of a welded joint is only 35–45% of the base metal. The loss of strength is due to the dissolution of the strengthening precipitates during melting. Therefore, there is a need to improve the fusion zone strength of AA2219 welds. In this study, an attempt was made experimentally to use different gas tungsten arc welding (GTAW) techniques and modify the filler chemistry with addition of scandium (Sc) and zirconium (Zr) in order to improve the mechanical properties of the AA2219 weld joints. The application of the GTAW DCEN with Sc and Zr to the filler wire proved to be the most economical and perhaps the optimal choice for welding AA2219 aluminium alloys. Addition of Sc and Zr to the fusion zone during welding enhanced grain refinement in the GTAW welds leading to better mechanical properties when compared to welding with conventional AA2319 filler. [ABSTRACT FROM AUTHOR]

Quenched and tempered (Q&T) steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking in the heat affected zone (HAZ) after welding and HAZ softening. The use of austenitic stainless steel (ASS) consumables to weld the above steel was the only remedy because of higher solubility for hydrogen in austenitic phase. Recent studies proved that high nickel steel (HNS) and low hydrogen ferritic (LHF) steel consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. In this investigation an attempt has been made to study the effect of welding consumables on tensile and impact properties of high strength, Q&T steel joints. Three different consumables, namely ASS, LHF steel and HNS have been used to fabricate the joints by shielded metal arc welding (SMAW) process. The joints fabricated using LHF steel electrodes showed superior transverse tensile properties than other joints. The joints fabricated using HNS electrodes exhibited better impact properties than other joints. The joints fabricated by LHF steel electrodes exhibited lesser degree of HAZ softening, while HNS joints exhibited the maximum HAZ softening due to the difference in weld thermal cycle. [ABSTRACT FROM AUTHOR]

High strength aluminum alloys (Al-Zn-Mg-Cu alloys) have gathered wide acceptance in the fabrication of lightweight structures requiring high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding processes of high strength aluminum alloy are frequently the gas tungsten arc welding (GTAW) process and the gas metal arc welding (GMAW) process due to their comparatively easy applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results in inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying a pulsed current welding technique. Rolled plates of 6 mm thickness were used as the base material for preparing single pass welded joints. A single ‘V’ butt joint configuration was prepared for joining the plates. The filler metal used for joining the plates was AA 5356 (Al-5Mg (wt%)) grade aluminum alloy. Four different welding techniques were used to fabricate the joints: (1) continuous current GTAW (CCGTAW), (2) pulsed current GTAW (PCGTAW), (3) continuous current GMAW (CCGMAW) and (4) pulsed current GMAW (PCGMAW). Argon (99.99% pure) was used as the shielding gas. Tensile properties of the welded joints were evaluated by conducting tensile tests using a 100 kN electro-mechanical controlled universal testing machine. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. In contrast, conventional continuous current welding resulted in predominantly columnar grain structures. Grain refinement is accompanied by an increase in tensile strength and tensile ductility. [ABSTRACT FROM AUTHOR]

Effects of electron beam oscillation techniques (sinusoidal, square, triangular, ramp, circle and elliptical) in controlling Nb segregation, Laves formation and stress rupture behaviour of Inconel 718 electron beam welds are studied. Effects of various post-weld heat treatments on stress rupture behaviour are compared. Elliptical beam oscillation technique resulted in less Nb segregation and discontinuous and fine Laves in the interdendritic regions compared with other welds and unoscillated beam weld. Response to aging was better for welds made with elliptical oscillated beam compared with welds made with unoscillated beam. Oscillated beam welds exhibited longer rupture life than unoscillated beam welds in both solution treated and aged and directly aged conditions. [ABSTRACT FROM AUTHOR]

The present study deals with the effect of beam oscillation patterns on the structure and mechanical properties of Ti–6Al–4V electron beam weldments. Electron beam welding of Ti–6Al–4V sheets was done with beam oscillation in various patterns (sinusoidal, square, triangular and elliptical). Welding without beam oscillation was also done for comparison. Room temperature hardness and tensile properties at different temperatures (room temperature, 150, 300 and 450°C) of the weldments in both as welded and post-welding heat treated conditions were observed and their correlations with the microstructure studied. The beam oscillated weldments showed higher ductility and lower strength (hardness) compared with those without being beam oscillated. This was attributed to wider diffusional α plates in the beam oscillated welds owing to slower cooling rates. Elliptical oscillation pattern produced weldments possessing the highest ductility and lowest strength values compared with other oscillation patterns. The oscillating patterns of sinusoidal, square or triangular forms resulted in weldments with almost the same structure and properties. [ABSTRACT FROM AUTHOR]

Abstract: Effect of three arc manipulation processes pulsed current welding, magnetic arc oscillation and the simultaneous application of pulsed current and arc oscillation, on the weld metal grain structure and tensile properties of the welds were investigated. Initial studies were conducted on autogenous welds made on 3.5mm thick 2219-T6 plates, to identify and optimize, welding parameters resulting in fine equiaxed grains in the weld metal. Welds were made on 8.5mm thick 2219-T87 plates using the optimized parameters and tested for tensile properties. All three techniques resulted in fine equiaxed grains in weld metals and optimum parameters were suggested based on the extent of refinement. Fine-grained weld metals exhibited better yield and ultimate tensile strengths and significant improvement in percent elongation. The reasons for the same were explained with the help of TEM and EPMA studies. [Copyright &y& Elsevier]

The effect of scandium additions to 2219 aluminium alloy weld metal has been investigated. At low levels (0·16%) of scandium, in spite of grain refinement in the weld metal, improvement in the mechanical properties has been nominal. At higher levels of scandium (0·37%), a substantial improvement in the tensile properties has been obtained. Further improvement in mechanical properties has been achieved by adding small amounts of magnesium. Transmission electron microscopy revealed the presence of fine precipitate particles in the scandium containing weld metals. Electron probe microanalysis (EPMA) and SEM–EDX revealed extensive copper segregation to grain and subgrain boundaries. The presence of scandium reduces the severity of segregation by producing fine equiaxed grains in the weld metals and also by refining the grain substructure. The morphology and size of the high copper eutectic phase at grain boundaries and sub-boundaries have been found to be finer and well distributed in the case of scandium containing weld metals. EPMA linescans and quantitative analyses proved that the depletion of copper in the matrix is minimised as a result of the fine grained structure. [ABSTRACT FROM AUTHOR]

The commercial 7000 series aluminium alloys are based on medium strength Al–Zn–Mg and high strength Al–Zn–Mg–Cu systems. The medium strength alloys are weldable, whereas the high strength alloys are non-weldable. This is because the amount of copper present in these alloys gives rise to hot cracking during solidification of welds. As a result, the high strength Al–Zn–Mg– Cu base alloys are not used for applications where joining of components by welding is an essential step. In the present study, using a combination of qualitative Houldcroft test and quantitative Varestraint test, it is shown that a small addition of scandium to the commercial 7010 alloy reduces the hot cracking susceptibility during solidification of welds produced by the gas tungsten arc welding process. The improvement in weldability is found to be the result of the considerable grain refinement in the weld structure following the scandium addition. The results of microhardness and tensile tests are further described within the context of the present work to demonstrate that the 7010+Sc welds also exhibit a combination of improved strength and ductility. [ABSTRACT FROM AUTHOR]

Continuous drive friction welding studies on austenitic–ferritic stainless steel combination has been attempted in this investigation. Parameter optimization, microstructure–mechanical property correlation and fracture behaviour is a major contribution of the study. Sound welds are obtained at certain weld parameter combinations only. The mechanical properties of dissimilar metal welds are comparable to those of ferritic stainless steel welds. Evaluation of the joints for resistance to pitting corrosion revealed that the dissimilar welds exhibit lower resistance to pitting corrosion compared to the ferritic and austenitic stainless steel welds. Interface on the austenitic stainless steel side exhibited higher residual stress possibly due to its higher flow stress and higher coefficient of thermal expansion. [Copyright &y& Elsevier]

Dissimilar metal welding of austenitic (AISI 304)-ferritic (AISI 430) stainless steel has been taken up to understand the influence of the welding process on microstructure and mechanical properties. Fusion welding processes, namely, gas tungsten arc welding (GTAW), electron beam welding (EBW), and friction welding, have been employed. The GTAW and EBW processes were selected to understand the heat input effects, while friction welding was included to compare fusion and solid-state welding processes. The material used for fusion welding studies is 20-mm-thick, hot-rolled, and annealed plate. Rods of 18 mm diameter machined from the same plate material were used for friction welding studies. In GTAW, ER 430 filler material was employed for dissimilar metal combination, while other welds are autogenous. Gas tungsten arc welds consisted of coarse columnar grains. In electron beam welds, the microstructure consisted of predominantely equiaxed grains on the austenitic stainless steel side, while columnar grains were observed on the ferritic stainless steel side. Epitaxial solidification was noted on the ferritic stainless steel side, while no such features were evident on the austenitic stainless steel side. Electron probe micro analysis (EPMA) revealed that inter diffusion of elements was significant in GTAW, intermediate in EBW, and insignificant in friction welds. Notch tensile and impact properties of ferritic stainless steel and dissimilar metal combination of austenitic-ferritic stainless steel friction welds are superior to gas tungsten arc welds and electron beam welds. Electron beam welds of austenitic stainless steel exhibited superior notch tensile and impact toughness compared to friction welds. Gas tungsten arc welds exihibited the lowest pitting corrosion resistance, while friction welds possessed the highest pitting corrosion resistance. In general, pitting was confined to Cr-depleted regions adjacent to the carbide precipitates. [ABSTRACT FROM AUTHOR]

The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties. [ABSTRACT FROM AUTHOR]

An attempt has been made to study the continuous drive friction welding characteristics of AISI 430 ferritic stainless steel. All the welds exhibited fine equiaxed ferritic grains. Parameters that result in marginally coarse grain size in the bond zone led to low hardness and high toughness. Welds having a fine grain size exhibited higher hardness and superior notch tensile strength. An inverse relationship was observed between impact toughness and notch tensile strength. Regression analysis of the data revealed a high degree of correlation. It was concluded that the selection of parameters would depend on the property of interest. [ABSTRACT FROM AUTHOR]

The friction stir welds o thick precipitation-hardenable aluminum alloys suffer from reduced joint strength due to dissolution/coarsening of the strengthening precipitates. The article portray hybrid pin profiled tool that enables sound welds at speeds 7-times faster than a conventional tool (a conical threaded tool), without pin breakage. The conical threaded and triangular cross-section in the upper and lower pin half-lengths of the hybrid tool facilitate material flow in a downward direction and shear deformation at a faster rate, respectively. The paper brings out the process mechanism responsible for the enhanced welding speed and mechanical properties obtainable with the hybrid tool through a case of 13-mm thick aluminum alloy AA2219-T6. The hybrid tool facilitates a 26% improvement in weld strength by reducing TMAZ softening, as evidenced by the microhardness and mechanical properties and supported by microstructural investigation and fractography. [ABSTRACT FROM AUTHOR]

Eighteen percent Ni maraging steels are high performance Fe-Ni martensite-based alloys with ultra-high strength and good toughness. They find applications in strategic sectors, joining of thick sections often coming into picture. Welding of thick section involves a longer processing time, more passes, and a higher heat-input. Double-pulsed gas metal arc welding (DP-GMAW) is an emerging welding technique, well suited for joining thick sections. DP-GMAW is capable of controlling the solidification parameters, weld pool geometry, and cooling rate at a reduced heat-input. The major concern regarding the welding of maraging steel is the formation of the reverted austenite (RA) phase in the fusion zone (FZ). The formation of RA deteriorates the mechanical performance of welded joints. The presence of RA can be supressed by the usage of suitable welding techniques and proper post-weld heat treatments (PWHTs). DP-GMAW process was employed to carry out the welding; studies on the joints produced are reported in this research paper. The studies also included the effect of various PWHTs on the metallurgical and mechanical properties of the maraging steel weldments. The research used three distinct PWHTs: direct aging (DA), solutionizing + aging (SA), and homogenizing + solutionizing + aging (HSA). The FZ microstructures under DA and SA conditions show that there is RA at the cell boundaries. However, there was no evidence of RA in FZ following HSA. The energy dispersive spectra (EDS) analysis of the as-welded FZ showed segregation along the grain boundaries (GBs). This led to the premature formation of RA upon subsequent aging. The SA treatments proved inadequate to totally eliminate RA in the microstructure. On the other hand, the HSA treatments were effective in evening out concentration differences and preventing formation of RA. This study demonstrates that DP-GMAW combined with HSA treatment has the best mechanical properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Traditional usage of austenitic stainless steel filler for armour steel welding shows poor ballistic performance. [•] Earlier efforts show dubious success on ballistic resistance of armour steel joints. [•] Comparative evaluation of equal/unequal joint design on ballistic performance. [•] Effect of joint design covers the main aspects of successful bullet stoppage. [Copyright &y& Elsevier]

Abstract: Due to weld thermal cycles and under matching fillers, the armour steel welded joints showed poor ballistic performance compared to the base metal. An attempt was made to enhance the ballistic performance of armour steel welded joints by depositing hardfaced (HF) interlayer between austenitic stainless steel weld metal. Though this method yielded marginal improvements in ballistic performance, cracks were observed in between base metal and HF layers. A novel method was proposed by the same authors to eliminate these cracks by depositing a soft buttering layer using austenitic stainless steel (ASS) consumable in between base metal and HF layer shows additional improvements on ballistic performance. Buttering layer enhanced the ballistic immunity by keeping the weld layer intact successfully at the time of impact, but the bullet was pierced through. In this investigation, an attempt has been made to stop the bullet completely by varying HF interlayer thickness. This paper reveals the effect HF layer thickness on ballistic performance of shielded metal arc welded armour steel welds. A HF interlayer thickness of 0.3 times, the plate thickness is found to be optimum from this investigation. [Copyright &y& Elsevier]

Abstract: This investigation describes about improving the ballistic immunity of armour steel joints which are fabricated by sandwiching of plasma transferred arc (PTA) hardfaced interlayers in between soft austenitic stainless steel (ASS) welds. From the results, the welds with sandwiched interlayer stopped all the projectiles successfully, irrespective of processes used, whereas welds without sandwiched interlayer were failed. In order to know the cause of failure, a detailed metallographic examination was carried out. The variation in microstructure and hardness at various zones of the weld are discussed. For the first time, it was found that the armour steel could be hardfaced by the PTA process with tungsten carbide powder. [Copyright &y& Elsevier]

Abstract: Austenitic stainless steel (ASS) welding consumables are traditionally used for welding quenched and tempered steels as they have higher solubility for hydrogen in austenitic phase. An attempt was made in this investigation to explore an alternate consumable to replace expensive ASS consumables. Austenitic stainless steel and low hydrogen ferritic steel were used to fabricate the joints by shielded metal arc welding and flux cored arc welding processes. The joints fabricated using low hydrogen ferritic steel consumables showed superior fatigue performance than the joints fabricated using ASS consumables. [Copyright &y& Elsevier]

Abstract: This paper reports the influences of pulsed current welding and post weld aging treatment on fatigue crack growth behaviour of AA7075 aluminium alloy (Al–Zn–Mg–Cu alloy). The preferred welding processes for this alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. In this alloy, the weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Rolled plates of 6mm thickness have been used as the base material for preparing single pass butt welded joints. The filler metal used for joining the plates is AA5356 (Al–5Mg (wt.%)) grade aluminium alloy. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW) and (iv) pulsed current GMAW (PCGMAW) processes. Argon (99.99% pure) has been used as the shielding gas. Fatigue crack growth behaviour of the welded joints has been evaluated by conducting the test using servo hydraulic controlled fatigue testing machine. Current pulsing leads to relatively finer and equi-axed grain structure in GTA welds. Grain refinement is accompanied by an increase in fatigue crack growth resistance and fatigue life. Simple post weld aging treatment applied to the joints is found to be beneficial to enhance the fatigue crack growth resistance of the welded joints. [Copyright &y& Elsevier]

• A low heat-input welding technique for the fabrication of rocket motor casing was devised and implemented. • The novel DP-GMAW reduced heat-input by 67% and RA by 49% compared to conventional GMAW. • DP-GMAW improved weld properties compared to GMAW. Maraging steels are ultra-high strength steels, which are most widely used in different strategic sectors. These steels are well-suited for the fabrication of rocket motor casings, which involves welding as one of the critical manufacturing processes. The major concern regarding welding of maraging steel is the formation of reverted austenite (RA) phase, which deteriorates the mechanical performance of the joints. The conventional arc welding processes involve higher heat-input during welding; the available literature indicates that segregation of alloying elements and the resultant formation of RA are promoted by high heat-input. The present study adopted a novel dual-pulse gas metal arc welding (DP-GMAW) technique, which reduces the heat-input during welding by current pulsing approach. The Dual pulsing approach was capable of 67% reduction of heat-input and 49% reduction of RA when compared to conventional gas metal arc welding (GMAW). [ABSTRACT FROM AUTHOR]

Abstract: The present study deals with the effect of beam oscillation technique using elliptical waveform on fatigue life of Ti–6Al–4V electron beam weldments. Autogenous full penetration bead-on-plate electron beam welds were made with and without beam oscillation. Some welds were subjected to post-weld heat treatment (PWHT) at two different temperatures (700 and 900°C). Room temperature hardness, tensile properties and fatigue life of the weldments in the as-welded and PWHT conditions were studied and correlated with the microstructure. The beam oscillated weldments exhibited lower strength (hardness) compared to those made without beam oscillation. This was attributed to wider diffusional α plates in the beam oscillated welds due to lower cooling rates. The beam oscillated weldments exhibited inferior fatigue lives compared with unoscillated weldments owing to the presence of wider α platelets in the former. As the width of α platelets in the weldments subjected to PWHT at 700°C was smaller than that in the weldments subjected to PWHT at 900°C, they exhibited longer fatigue lives. [Copyright &y& Elsevier]