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Dissimilar metal welds (DMWs) between P91 steel and Incoloy 800HT® using shielded metal arc welding (SMAW) with ENiCrCoMo-1 filler electrode were characterized in detail. The impact of multiple weld passes on microstructure in the heat-affected zone (HAZ) and weld fusion zone (WFZ) was thoroughly investigated. Postweld heat treatment (PWHT) impacts on mechanical characteristics and microstructure were also observed. The DMW was observed with heavy C, Cr, and Mo microsegregation in the WFZ, which deteriorated mechanical strength. The microstructural changes directly affected the mechanical behavior of the DMW. The ultimate tensile strength of the weld fusion zone was low at 576 MPa compared to the base metals’ strength. The tensile specimens failed in the IN 800HT base metal and WFZ. The WFZ had significant microsegregation near the solidified grain boundaries (SGBs). The metallurgical heterogeneity in the WFZ caused the formation of localized stress zones, which directly affected the mechanical behavior of the WFZ. The carbide particles influenced the microhardness in the WFZ and P91 HAZ regions. The PWHT successfully homogenized the microhardness in the WFZ and P91 HAZ regions. The impact toughness decreased to 64 J from 82 J after PWHT due to precipitation at SGBs and its coarsening. The SMAW process involves multiple thermal cycles during welding. The deposition of filler metal in multiple welding passes created uncontrolled variations in the solidification behavior of the WFZ. Microsegregation had a detrimental impact on the microstructure and mechanical properties of the P91 and IN 800HT dissimilar metal welds. [ABSTRACT FROM AUTHOR]

Shape the Future of Space This is a call to action for the welding community to proactively embrace the challenges and opportunities presented by the new space economy. Lockheed Martin was recently awarded a NASA Tipping Point proposal to develop and demonstrate welding and inspection technologies for in-space assembly of structural, electrical, and fluid systems (Refs. FEATURES Space is an inhospitable environment with extreme temperatures that will freeze nitrogen in the shade and boil water in the sunlight. Welding in the Space Environment The uniqueness of the space environment poses distinct physics-related challenges for welding (and other joining) processes. [Extracted from the article]

The pitting corrosion resistance of dissimilar pipeline steel API X70 and Super Duplex 2507 Stainless Steel gas tungsten arc (GTA) welds was studied. The GTA welds were fabricated using Super Duplex 2594 Filler Metal or austenitic 309L Filler Metal. The specimens extracted from the base metal, weld fusion zone, fusion boundary, and heat-affected zones (HAZs) were subjected to a potentiodynamic corrosion test in a 3.5% NaCl water solution. The weld made using the 309L Filler Metal was found to have a smaller pitting resistance equivalent number (PREN) difference between ferrite and austenite, making it more corrosion resistant than the weld fabricated using the 2594 Filler Metal. The HAZ on the X70 side was the most susceptible to pitting and galvanic corrosion for both filler metals. [ABSTRACT FROM AUTHOR]

During laser welding of an Al-Si coated 22MnB5 steel to produce tailor-welded blanks, the Al-Si coating mixes into the weld and causes the formation of the lower strength ferrite phase dispersed in an otherwise martensitic matrix. It has been shown that the presence of the ferrite phase is the principal reason for premature failure of hot-stamped laser-welded joints. Currently, the Al-Si coating is removed prior to welding, which can be time consuming and costly. This work showed that adding Ni to the fusion zone of laser welded Al-Si coated 22MnB5 steel by welding through a pure Ni coating of a specified thickness, ferrite formation can be suppressed, whereby improving the weld strength and successfully shifting failure from the fusion zone, where it normally occurs, to the base material to achieve 100% joint strength. This work also showed that laser welding Al-Si coated 22MnB5 steel through a Ni coating eliminated the need to mechanically or chemically remove the Al-Si coating prior to welding. [ABSTRACT FROM AUTHOR]

Microstructure, hardness, tensile and high cycle fatigue (HCF) properties of the welded dissimilar joints of Ti60 and TC17 titanium alloys had been investigated in this study. A significant microstructural change was observed to occur after welding, with rod-like α and β phases in the fusion zone (FZ), equiaxed α phases, fine α laths and β phases in the heat-affected zone (HAZ) of TC17 side and acicular martensite α' phases+“ghost” α phases in the HAZ of Ti60 side. The microhardness across the joints exhibited an inhomogeneous distribution with the highest hardness of ∼404 HV in FZ and the lowest hardness of ∼304 HV in base material (BM) of Ti60. All the joints tested in tension fractured at BM of Ti60 side. Fatigue limits of the joints at 10 7 cycles were 425 MPa at room temperature and 380 MPa at 400 °C, respectively. Welding micropores were found to be the main source of fatigue crack initiation. [ABSTRACT FROM AUTHOR]

Low-carbon steel Q235B was successfully joined by plasma-pulsed gas metal arc welding (plasma-GMAW-P) with an external magnetic field. The arc profile, temperature field, electrical signal, microstructure, and mechanical properties of this method were analyzed. The results indicated that the coupling degree of the two arcs increased with the strengthening of the magnetic field current. However, when the magnetic field current was greater than 1 A, the arc profile changed slightly with the increase of the magnetic field current. Fixed on the magnetic field current, the coupling degree first increased and then decreased with the increase of the plasma welding current, GMAW-P welding current, plasma gas flow rate, and nozzle height, respectively. The maximum temperature had no obvious influence on joint penetration at different magnetic field currents. However, the average temperature had an inverse effect on joint penetration at different magnetic field currents. The weld fusion zone joint tensile test results showed that the ratio of depth to width increased with the application of magnetic field currents. Moreover, tensile strength on the upper and lower part of the tensile samples were 521 and 488 MPa, respectively, which were 4.6% and 3.2% higher than those without the magnetic field. The microhardness of the weld joints was higher than that without the magnetic field. [ABSTRACT FROM AUTHOR]

Selective laser melting was used to produce an aluminum alloy Al-8.5Fe-1.3V-1.7Si (wt%). The effects of heat treatment on microstructure evolution and phase stability during long-term thermal exposure of the deposits were investigated. Results show that the microquasi-crystalline phase, Al 12 (Fe,V) 3 Si and Al m Fe metastable phases coexisted with α-Al in the as-produced alloy. Annealing at 400 °C resulted in decomposition of microquasi-crystalline phase and supersaturated α-Al into Al 12 (Fe, V) 3 Si phase in the fusion zone, accompanied by the decrease in alloy hardness. The activation energy of this decomposition process was 115 kJ/mol. A more homogenous microstructure was obtained after annealing at 400 °C for 60 min, which was resistant to coarsening exposed at 425 °C up to 500 h. The Al 12 (Fe,V) 3 Si and Al m Fe phases were coarsened at 475 and 525 °C with increasing the exposure time. Coarsening of Al 12 (Fe,V) 3 Si phase was attributed to a combination of volume diffusion and grain boundary diffusion mechanism of Fe. Heat treatment at 600 °C resulted in accelerated microstructure coarsening and formation of large-sized equilibrium phases, which significantly degraded the room temperature microhardness. [ABSTRACT FROM AUTHOR]

If the specimen breaks in the weld and below the SMTS of the pipe material, the weld shall be set aside and a new test weld shall be made. Failures like the ones described are often attributed to the weld - "It was a weld that failed" - which negatively impacts the welding community. The use of welding procedures that result in matching or overmatching strength girth welds and are resistant to softening in the HAZ will prevent axial strains from accumulating at understrength girth welds. [Extracted from the article]