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The presented study intends to analyze the microstructure and corresponding mechanical characteristics of P91 and Incoloy 800HT dissimilar welded joint (DWJ). The thermo-physical property differences between P91 and Incoloy 800HT arise due to their complex alloying composition, making their weldability difficult. Incoloy 800HT is difficult to weld due to its high susceptibility to solidification cracking. The recommended nickel-based filler metals for welding Incoloy 800HT were employed to weld P91 and Incoloy 800HT using conventional gas tungsten arc welding (GTAW). The welded joint morphology and characteristics were analyzed in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The PWHT was performed to observe changes in microstructural inhomogeneity and residual stress relaxation in weld after the heat treatment. An electron probe microanalyzer (EPMA) was utilized to observe the distribution and segregation of elements in different weld regions. The deep hole drill technique was employed to find the distribution of bi-axial residual stresses in the weld fusion zone (WFZ) and heat-affected zone (HAZ) of base metals in both AW and PWHT conditions. The two nickel-based fillers, ERNiCr-3 and ERNiCrMo-3, were employed, and their weld characteristics were compared. The mechanical strength of ERNiCr-3 filler-based DWJ was found superior to ERNiCrMo-3 filler-based DWJ. The standard AW and PWHT ERNiCr-3 filler-based DWJ tensile specimen failed from Incoloy 800HT base metal with an ultimate tensile strength (UTS) of 570 ± 4 MPa and 650 ± 4 MPa, respectively. The ERNiCrMo-3 filler-based DWJ obtained the highest UTS of 679 MPa after PWHT in a subsize specimen. The microhardness for ERNiCrMo-3 WFZ was found to be higher than ERNiCr-3 WFZ microhardness, and PWHT successfully tempered the P91 HAZ. Further, the impact toughness for the ERNiCr-3 WFZ in AW condition was 86 ± 3 J and PWHT did not provide any significant improvements, while ERNiCrMo-3 WFZ had an impact toughness of 47 ± 10 J in AW state and 41 ± 10 J in PWHT state. Thus, a successful weld characteristic study of defect-free P91 and Incoloy 800HT DWJ was completed, and ERNiCr-3 filler was concluded to be an optimum choice of filler to make the DWJ between P91 and Incoloy 800HT. • Dissimilar weld joints of P91 steel and Incoloy 800HT alloy were investigated for microstructure and mechanical properties. • Through thickness residual stress measurement along the weldments ware performed using the deep hole drilling method (DHD). • Gradient microstructure at the ErNiCr-3 filler welds and P91 steel interface was clarified using the SEM and EPMA methods. • Effect of the post-weld heat treatment (PWHT) on microstructure, mechanical properties, and residual stress variation along the weldments were performed. [ABSTRACT FROM AUTHOR]

Inconel alloys are used for high temperature applications due to their excellent properties at elevated temperatures. The joining of Inconel alloys with other alloys is challenging due to the formation of cracks and interface microstructural segregation of alloying elements. In the present investigation Inconel 718 alloy was joined with high tensile steel using laser welding. In order to attain the quality joints, welding parameters were studied and identified their range. The microstructural characteristics of the welds at the fusion zone and heat-affected zone were analyzed. The microhardness variations across the fusion zone and other zones were observed. The mechanical properties of the joints were evaluated and found that the strength of the joints was related to laser power. The elemental analysis across the fusion zone was revealed the formation of segregation of the elements which has an influence on the strength of the joints. [ABSTRACT FROM AUTHOR]

During dissimilar steel welding, differences in magnetic permeability and thermophysical parameters between materials result in significant disparity in heat distribution on both sides of weld and poor weld formability. To solve the welding quality problems caused by significant disparity in heat distribution, a novel composite magnetic field consisting of longitudinal magnetic field (LMF) and cusp magnetic field (CMF) is applied to dissimilar steel welding. In this study, the influence of novel magnetic field on the mechanical characteristics, microstructure, and weld formation of dissimilar steel gas tungsten arc welding (GTAW) welds was investigated. It was found that arc deflection is influenced by both the material properties and LMF. When longitudinal exciting current (I L) was 0.5A, the weld melting zone tended to be symmetrical. On the premise that I L remained unchanged at 0.5A, as cusp exciting current (I C) increased from 0A to 5A: the weld fusion zone always remained symmetrical; The arc compression degree, weld penetration, melting area of weld and weld penetration/width ratio significantly increased, while the weld width progressively reduced; The heat-affected zone's (HAZ) width of the base metals and the mean grain size in the HAZ are significantly reduced; The mean microhardness of the weld metal (WM) and tensile properties are also significantly improved. The study results enrich the research foundation on heat input regulation in dissimilar steel GTAW, providing experimental evidence and theoretical support for resolving welding quality issues caused by welding conditions with different material properties. • Novel composite magnetic field can regulate heat input distribution and arc heat flow density. • Novel composite magnetic field optimizes weld formation of dissimilar steels. • Novel composite magnetic field promotes grain refinement in HAZ. • Novel composite magnetic field reduces the thickness of the transition zone at WM/BM interface. [ABSTRACT FROM AUTHOR]

The present work reports about the effect of cast scandium doped ER5356 filler rod in Tungsten Inert Gas welding of dissimilar Aluminium Magnesium alloys. The grain refinement effect on weld microstructure by transition metal scandium was investigated with optical and scanning electron microscope. Additionally, XRD analysis, tensile strength (global and component joint) and microhardness were tested on weld samples. The microstructural examination in weld fusion zone observed fine grain size and suppressed dendrite arm spacing. The formation of Al3Sc precipitate in weld fusion zone due to scandium inclusion in filler was identified and resulted in improving the weld strength significantly. The higher joint efficiency of 92.5% was achieved in the global joint of weld samples. The failure location of global joint tensile samples identified the weld fusion zone is stronger than AA5052 base material. Further weld strength was evaluated with component joint by micro tensile test, which results in 70MPa enhancement in UTS values and validating the accurate weld strength. However, the elongation of the tensile test sample reduced marginally for the weld. The fracture mechanism of the weld joint observes decrease in ductility. The significant increase in hardness of the weld fusion zone was evident due to doping of scandium compared to the other zones of the weld. [ABSTRACT FROM AUTHOR]

This study characterizes an electron beam welded dissimilar joint between P91 ferritic/martensitic steel and Incoloy 800HT Nickel-based alloy. Such dissimilar metal welds (DMW) have applications in nuclear and thermal powerplants where steam-carrying pipes lead to header sections operating at around 600–650 °C. The study employed an advanced welding process to obtain a clean, high-quality dissimilar metal. The microstructure characterization of the DMW involving Nickel-based alloys is prone to solidification cracking in the weld fusion zone (WFZ), which affects the overall weld properties and leads to failure. In the present study, the WFZ microstructure revealed a mixed solidification mode with a homogenous presence of equiaxed dendritic and cellular-type structures. Advanced analyses of WFZ microstructure were done to account for microsegregation. Nb, Ti, Cr, and Mo microsegregation was found in the WFZ. The Ti-rich grain boundaries in the WFZ provided the pinning action during plastic deformation. The evolution of Cr, Mo-based carbide phases affected the microhardness distribution. Microsegregation under rapid solidification of the WFZ resulted in the formation of secondary phases in the interdendritic region. The effect of the evolution of precipitates deteriorated the mechanical strength. High and uneven dislocation distribution was observed in the WFZ near the IN 800HT weld interface. Under tensile loading, the DMW failed from the IN 800HT weld interface due to coarsening of precipitated in the IN 800HT HAZ region near the weld interface and grain boundary thickening due to the deposition of Ti over them. The tensile strength of WFZ was 592 MPa. The tensile strength of WFZ was 592 MPa. The post-weld heat treatment (PWHT) homogenized the microhardness across the weld. Impact toughness after PWHT slightly increased from 63 J to 69 J. The dissimilar joint obtained using the EBW process had sufficient mechanical strength to be considered for Generation IV power plants under the American Society for Testing and Materials (ASTM) standards. The study concludes that the dissimilar metal welded joint was highly prone to failure despite sufficient strength, as IN 800HT weld interface was susceptible to grain boundary liquation. • The electron beam welding process successfully produced a clean, distortion-free, and aesthetic dissimilar metal weld of P91 and Incoloy 800HT. • The DMW was characterized for its microstructural and corresponding mechanical properties in AW and PWHT conditions. • PWHT successfully homogenized the microhardness variation observed in the P91 HAZ region and weld metal. [ABSTRACT FROM AUTHOR]

Weldability is one of the most important processes for new metallic alloys moving toward engineering applications. In this work, both the laser beam weldability of an equiatomic TiZrHfNbTa refractory high entropy alloy (HEA) and the dissimilar weldability of TiZrHfNbTa to C103 niobium-based alloy are assessed. Single BCC phase maintains stability around both the TiZrHfNbTa welding joint and HEA-C103 dissimilar welding joint. Fine equiaxed grains are obtained within these two types of weld fusion zones with no detectable macro- or microcracks formation. Despite the existence of a small amount of porosity in the fusion zone, the tensile properties of samples containing welding joints are comparable to the corresponding base materials. This work confirms the prototype TiZrHfNbTa refractory HEA has excellent laser weldability and meanwhile exhibits good dissimilar weldability to widely used C103 alloy. • The TiZrHfNbTa alloy exhibits outstanding weldability. • Both the welding joint of TiZrHfNbTa and the dissimilar joint to C103 alloy maintain an original single BCC phase. • There are no micro- or macro-cracks around the weld points both in similar HEA and dissimilar HEA-C103 welding joints. • The mechanical properties of the welding joints are comparable to the base materials. [ABSTRACT FROM AUTHOR]

Si-bronze and 304 stainless steel were joined using gas tungsten arc (GTA) welding with two different welding (filler) rods matching the base metals. Cross-sections of the welds were analyzed using light optical microscopy (LOM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and hardness testing. Mechanical testing was performed for welds from each of the two filler metals using cross-weld tensile bars. For (1) the Si-bronze filler weld, partial mixing resulted in (a) copper-based regions with enhanced hardness due to iron-based islands and (b) iron-based regions with elevated hardness due to Si enrichment. Joint strength was ~ 90% that of the base Si-bronze strength of 340 MPa, and elongation was ~ 48%, as compared to the base Si-bronze elongation of 55%. For (2) the stainless steel filler rod (a) primary austenite solidification and (b) micro-fissures were identified in the fusion zone. Thermodynamics calculation software was used to model solidification mode, demonstrating that the Cu (contributed by the Si-bronze) stabilized primary austenite solidification, which led to solidification micro-cracking or micro-fissuring. Micro-fissuring caused low ductility in the transverse weld tensile specimens. Fractography was performed to characterize the fracture mechanisms. For the stainless filler weld, a Cu film formed in interdendritic spaces between primary austenite grains. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dissimilar laser welding of A516 low carbon steel and duplex stainless steel was conducted. • The laser power had the most notable impact on the weld tensile strength. • The A516 weld fusion zone microstructure was composed of fully martensitic. • The duplex stainless fusion zone microstructure was ferrite–austenite distribution. Laser welding of dissimilar A516 low carbon steel and duplex stainless steel was conducted to evaluate the effect of fiber laser welding parameters (e.g., laser power, welding speed, nozzle distance and beam deviation) on the responses of tensile strength, depth of the melt pool, microstructure, temperature near the melt pool and melt pool hardness. The maximum tensile strength of 500 MPa and 18 percent elongation were obtained at the laser power of 400 W, welding speed of 300 mm/min and the focal point. The absorbed power of laser and linear speed of welding had the most notable impact on the tensile strength of the weld. The fusion zone microstructure was composed of a combination of ferrite–austenite distribution from duplex stainless steel (DSS) based on different cooling and heating cycles. During the nucleation process, ferrite grains were transformed to austenite grains from different areas of the fusion zone. Also, the weld fusion zone microstructure at A516 side was composed of fully martensitic structure, according to the higher heat input upper critical temperature of steel (AC3), thereby leading to rapid cooling. The EDS analysis also showed that the Fe percentage was continually reduced at the fusion line from A516 to DSS, although Ni and Cr were distributed at the fusion zone with some minor changes of weight percentage. Therefore, Cr and Ni had a crucial effect on elemental alloy composition in this laser welding process. The ductility of the A516 fracture surface with bigger and deeper fracture dimples was caused by applying higher laser energy density, which effectively improved the fracture ductility of the welded samples. [ABSTRACT FROM AUTHOR]

A dissimilar laser beam welded joint of ferritic/martensitic P92 steel, and 304L austenitic stainless steel (ASS) has been examined in as-weld and post-weld heat treatment (PWHT) at 760 °C for 120 min for microstructure feature and mechanical aspects. The microstructure of the weld metal, interface, and heat-affected zone (HAZ) was characterized in detail, and it was observed that a great level of inhomogeneity exists in a dissimilar joint. In addition, the effect of the inhomogeneity in microstructure on mechanical properties, microhardness, and impact strength of the welded joint was discussed. The welded joint's mechanical properties met the USC boiler requirement for both as-weld and PWHT situations. The welded joint showed a decent combination of tensile strength and impact strength for both as-weld and PWHT conditions. The tensile results showed the failure from the 304L SS base metal, which ensured the acceptable strength of the weld metal for the laser welded joints. The part of the welded joint with relatively poor impact strength was the weld metal. Though, the Charpy impact toughness of the weld metal (89 J) was measured higher than the ASME standard value (>41 J) and EN 1599:1997 standard value (>47 J) in the as-weld situation. The impact strength of the weld fusion zone was 138 J in PWHT condition. • An autogenous laser beam welded dissimilar joint of P92 martensitic and 304L SS austenitic steel was characterized for microstructure and mechanical properties. • Mechanical behavior and microstructural feature were studied for as-welded and post-weld heat treatment conditions. • Studied the effect of the laser beam welding process on the heat-affected zone of P92 steel. • The weld metal was qualified for the USC boiler requirements in as-welded and PWHT conditions. [ABSTRACT FROM AUTHOR]

This investigation attempts to explore the weld characteristics of a laser welded dissimilar joint of ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel and Incoloy 800HT austenitic nickel alloy. This dissimilar joint is essential in power generating nuclear and thermal plants operating at 600–650 °C. In such critical operating conditions, it is essential for a dissimilar joint to preserve its characteristics and be free from any kind of defect. The difference between the physical properties of P91 and Incoloy 800HT makes their weldability challenging. Thus, the need for detailed characterization of this dissimilar weld arises. The present work intends to explore the usage of an unconventional welding process (i.e., laser beam welding) and its effect on the joint's characteristics. The single-pass laser welding technique was employed to obtain maximum penetration through the keyhole mode. The welded joint morphology and mechanical properties were studied in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The macro-optical examination shows the complete penetrations with no inclusion and porosities in the weld. The microstructural study was done in order to observe the precipitation and segregation of elements in dendritic and interface regions. Solidification cracks were observed in the weld fusion zone, confirming the susceptibility of Incoloy 800HT to such cracks due to a mismatch between the melting point and thermal conductivity of the base metals. Failure from base metal was observed in tensile test results of standard AW specimen with a yield stress of 265 MPa, and after PWHT, the value increased to 297 MPa. The peak hardness of 391 HV was observed in the P91 coarse grain heat-affected zone (CGHAZ), and PWHT confirmed the reduction in hardness. The impact toughness results that were obtained were inadequate, as the maximum value of impact toughness was obtained for AW P91 heat-affected zone (HAZ) 108 J and the minimum for PWHT Incoloy 800HT HAZ 45 J. Thus, difficulty in obtaining a dissimilar joint with Incoloy 800HT using the laser beam welding technique was observed due to its susceptibility to solidification cracking. [ABSTRACT FROM AUTHOR]

Dissimilar laser welding has been researched to combine the excellent anticorrosion and high strength properties of Ti and the low weight and cost of Al. However, when welding dissimilar Al and Ti sheets, many kinds of intermetallic compound are easily generated. Therefore, intermetallic compounds and differences in material properties make joining such dissimilar metals very difficult. Previous studies clarified that ultra-high welding speed could suppress the weld defects. To elucidate the mechanism of Al and Ti dissimilar laser welding, material behavior of the weld fusion zone and components of fume generated during the ultra-high speed welding process were observed and analyzed using energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high speed cameras, and a spectrometer. The results show that the atom movement of Al and Ti in the weld plume affects the behavior of elemental components distributed in the weld fusion zone. [ABSTRACT FROM AUTHOR]

• Autogenous Gas Tungsten arc (A-GTA) welded joint of P91 and SS304L Steel is prepared. • The effect of the A-GTA welding process on mechanical behavior (tensile, hardness, Charpy impact toughness) of the dissimilar weldments is studied. • The structure and property relationship for the dissimilar welds joint of P91 and SS304L steel is developed. • The role of the heat-treatment on the structure-property relationship of dissimilar welds joint is studied. The microstructure and mechanical behavior of the Gas Tungsten Arc (GTA) welded joint of ferritic/martensitic (F/M) P91 and austenitic SS304L steel was investigated in as-welded and post-weld heat treatment (PWHT) conditions. The microstructural studies included the particle size and its distribution, grain size, and percentage area fraction of the precipitates (%AFP) in different zones of the weldments. In as-welded condition, weld metal showed untempered martensitic microstructure devoid of carbide precipitates. After the PWHT, weld metal was characterized by tempered martensitic microstructure along with the decoration of the coarse carbide particles at PAGBs and fine carbonitride particles inside the matrix region. The mechanical behavior of the dissimilar weld was analyzed in as-welded and PWHT conditions by performing tensile testing, Charpy impact testing, and microhardness testing. A significant variation in microstructure and mechanical properties was obtained across the dissimilar welded joint (DWJ) for as-welded, which was minimized after the PWHT. The minimum%AFP in the coarse grain heat-affected zone was measured due to the formation of the precipitate-free soft δ ferrite patches, which also showed a negligible response to PWHT. The poor Charpy impact toughness (CIT) of 0.8 ± 1.5 J and high tensile strength of 864 ± 12.5 MPa were measured for the as-welded joint. The combination of high strength and low CIT was obtained mainly due to the untempered martensitic microstructure in the weld fusion zone. The DWJ after the PWHT showed a significant increase in Charpy impact toughness (CIT), and it was measured 70 ± 4 J. Improved mechanical behavior with a good combination of ultimate tensile strength and CIT were obtained after the PWHT. [ABSTRACT FROM AUTHOR]

In this research, the microstructures and mechanical properties of similar and dissimilar autogenous joints of 3 mm thick commercially pure titanium (CP-Ti) and Ti-6Al-4V welded by ytterbium fiber laser (Yb:YAG) were investigated. Two sets of laser power and welding speed were selected in such a way that the heat input remained constant. Microstructural characterization of the joints was investigated by an optical microscope, and mechanical properties were determined by hardness and tensile tests. The only defects found were porosity and underfill, and no signs of lack of penetration and solidification cracks were observed in any of the joints. Microstructural evaluation of the fusion zone (FZ) showed that in similar Ti-6Al-4V joint, a supersaturated nonequilibrium α′ martensite was formed due to rapid cooling associated with laser welding. In similar CP-Ti, coarse equiaxed grains were observed in the FZ. Unlike the similar joints, a clear interface was observed between the heat-affected zone (HAZ) and the FZ in both the CP-Ti and Ti-6Al-4V sides in dissimilar joints. Among all the joints with different weld parameters, similar Ti-6Al-4V showed the highest strength and the lowest ductility. In similar CP-Ti and dissimilar joints, fractures took place in the CP-Ti base metal, but all the Ti-6Al-4V similar joints failed in the FZ. Significant changes in the strength and hardness with varying laser power and welding speed implied that the mechanical properties of the weld fusion zones were not entirely governed by the heat input but were also affected by individual welding parameters. [ABSTRACT FROM AUTHOR]