Saturn manufacturing technology for welding methods and techniques
Evaluation of various power supplies for gas tungsten arc welding of aluminum
Cushman, E. H.↗
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Automatic orbital GTAW welding: Highest quality welds for tomorrow's high-performance systems
Automatic orbital gas tungsten arc welding (GTAW) or TIG welding is certain to play an increasingly prominent role in tomorrow's technology. The welds are of the highest quality and the repeatability of automatic weldings is vastly superior to that of manual welding. Since less heat is applied to the weld during automatic welding than manual welding, there is less change in the metallurgical properties of the parent material. The possibility of accurate control and the cleanliness of the automatic GTAW welding process make it highly suitable to the welding of the more exotic and expensive materials which are now widely used in the aerospace and hydrospace industries. Titanium, stainless steel, Inconel, and Incoloy, as well as, aluminum can all be welded to the highest quality specifications automatically. Automatic orbital GTAW equipment is available for the fusion butt welding of tube-to-tube, as well as, tube to autobuttweld fittings. The same equipment can also be used for the fusion butt welding of up to 6 inch pipe with a wall thickness of up to 0.154 inches.
Henon, B. K.↗
Effect of Shielding Gas on the Properties of AW 5083 Aluminum Alloy Laser Weld Joints
The paper deals with the evaluation of the shielding gas influence on the properties of AW 5083 aluminum alloy weld joints produced with disk laser. Butt weld joints were produced under different shielding gas types, namely Ar, He, Ar + 5 vol.% He, Ar + 30 vol.% He and without shielding weld pool. Light and electron microscopy, computed tomography, microhardness measurements and tensile testing were used for evaluation of weld joint properties. He-shielded weld joints were the narrowest ones. On the other hand, Ar-shielded weld joints exhibited largest weld width. The choice of shielding gas had significant influence on the porosity level of welds. The lowest porosity was observed in weld joint produced in Ar with the addition of 5 vol.% He shielding atmosphere (only 0.03%), while the highest level of porosity was detected in weld joint produced in pure He (0.24%). Except unshielded aluminum alloy weld joint, the lowest tensile strength was recorded in He-shielded weld joints. On the contrary, the highest average microhardness was measured in He-shielded weld joints.
36 MATERIALS SCIENCE↗
Gas Contamination In Plasma-Arc-Welded Aluminum
Document describes experimental investigation on visible and tactile effects of gaseous contaminants in variable-polarity plasma arc (VPPA) welding of 2219 T-87 aluminum alloy. Contaminant gases (nitrogen, methane, oxygen, and hydrogen) introduced in argon arc and in helium shield gas in various controlled concentrations. Report represents results of experiments in form of photographs of fronts, backs, polished cross sections, and etched cross sections of welds made with various contaminants at various concentrations. Provides detailed discussion of conditions under which welds made.
Mcclure, John C.↗
Isothermal Calorimetric Observations of the Affect of Welding on Compatibility of Stainless Steels with High-Test Hydrogen Peroxide Propellant
Compatibility is determined by the surface area, the chemical constituency and the surface finish of a material. In this investigation exposed area is obviously not a factor as the welded samples had a slightly smaller surface than the unwelded, but were more reactive. The chemical makeup of welded CRES 316L and welded CRES 304L have been observed in the literature to change from the parent material as chromium and iron are segregated in zones. In particular, the ratio of chromium to iron in CRES 316L increased from 0.260 to 0.79 in the heat affected zone (HAZ) of the weld and to 1.52 in the weld bead itself. In CRES 304L the ratio of chromium to iron increased from 0.280 to 0.44 in the HAZ and to 0.33 in the weld bead. It is possible that the increased reactivity of the welded samples and of those welded without purge gas is due to this segregation phenomenon. Likewise the reactivity increased in keeping with the greater roughness of the welded and welded without purge gas samples. Therefore enhanced roughness may also be responsible for the increased reactivity.
Gostowski, Rudy C.↗
Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by super duplex filler metal
In the present paper, microstructural changes across an as-welded dissimilar austenitic/duplex stainless steel couple welded by a super duplex stainless steel filler metal using gas tungsten arc welding process is characterized with optical microscopy and electron back-scattered diffraction techniques. Accordingly, variations of microstructure, texture, and grain boundary character distribution of base metals, heat affected zones, and weld metal were investigated. The results showed that the weld metal, which was composed of Widmanstätten austenite side-plates and allotriomorphic grain boundary austenite morphologies, had the weakest texture and was dominated by low angle boundaries. The welding process increased the ferrite content but decreased the texture intensity at the heat affected zone of the super duplex stainless steel base metal. In addition, through partial ferritization, it changed the morphology of elongated grains of the rolled microstructure to twinned partially transformed austenite plateaus scattered between ferrite textured colonies. However, the texture of the austenitic stainless steel heat affected zone was strengthened via encouraging recrystallization and formation of annealing twins. At both interfaces, an increase in the special character coincident site lattice boundaries of the primary phase as well as a strong texture with <100> orientation, mainly of Goss component, was observed. - Graphical abstract: Display Omitted - Highlights: • Weld metal showed local orientation at microscale but random texture at macroscale. • Intensification of <100> orientated grains was observed adjacent to the fusion lines. • The austenite texture was weaker than that of the ferrite in all duplex regions. • Welding caused twinned partially transformed austenites to form at SDSS HAZ. • At both interfaces, the ratio of special CSL boundaries of the primary phase increased.
36 MATERIALS SCIENCE↗
The Effect of Weld Metal Composition on Microstructural and Mechanical Properties of Dissimilar Welds Between Monel 400 and Inconel 600
The current work was carried out to characterize welding of Inconel 600 superalloy and Monel 400. In the present study, gas tungsten arc welding (GTAW) with four types of filler metals (ENiCu, ENiCu-7, ENiCr-3 and ENiCrFe-3) was utilized. The filler metals were categorized into two groups based on the presence of Cr and Nb in their chemical composition. This paper describes the selection and application of welding consumables in manufacturing dissimilar metal combinations. It was found that (Nb/Cr) ratio and Fe content can affect on the size and amount of carbides. During solidification of ENiCr-3 and ENiCrFe-3 filler metals, Nb leaves dendritic cores and is rejected to inter-dendritic regions because of its high tendency for segregation. However, No brittle Laves phase was detected in the welds. The interface between weld metal and base metal and gradual changes in alloying elements were also investigated by scanning electron microscopy. EDX analysis was also applied for different samples. Microhardness measurements and tensile test were performed on the joints. The average hardness value in the weld metal obtained from ENiCrFe-3 is higher than the other welds. ENiCu-7 weld exhibited the highest tensile strength of 540 MPa and percent elongation of 53% in contrast to ENiCrFe-3 weld with the lowest tensile strength (518 MPa) and percent elongation (39%).
36 MATERIALS SCIENCE↗
Characterization of as-welded microstructure of heat-affected zone in modified 9Cr–1Mo–V–Nb steel weldment
Non-equilibrium microstructure of the heat-affected zone (HAZ) in the as-welded modified 9Cr–1Mo–V–Nb pipe steel (P91) weldment deposited by gas tungsten arc welding (GTAW) and flux core arc welding (FCAW) has been characterized by field-emission scanning electron microscope (FESEM) and electron backscatter diffraction (EBSD). The heterogeneous structures in the sub-layers of the as-welded HAZ are attributable to phase transformations caused by the welding thermal cycles and the local structure variations in the as-received base metal. Coarse-grained heat-affected zone (CGHAZ) has a prior austenite grain (PAG) size of 20 μm. Fine uniformly-distributed precipitates and a higher fraction of MX carbonitrides are observed in the CGHAZ. Fine-grained heat-affected zone (FGHAZ) consists of the finest grains (1.22 μm measured by EBSD, 5 μm PAG size), coarse undissolved M{sub 23}C{sub 6} carbides within the PAG boundaries and fine nucleated M{sub 23}C{sub 6} particles within the martensite laths. Inter-critical heat-affected zone (ICHAZ) consists of partially austenitized grains and over-tempered martensite laths. EBSD kernel average misorientation (KAM) map in the FGHAZ close to the ICHAZ illustrates the greatest local strain variations with a moderate normalized KAM value of 0.92°. The majority (88.1%) of the matrix grains in the CGHAZ are classified as deformed grains by EBSD grain average misorientation (GAM) evaluation. The FGHAZ close to the ICHAZ has the most recrystallized grains with an area fraction of 14.4%. The highest density variation of precipitates within grains in the FGHAZ originates from the inhomogeneous chemistry in the base metal. - Highlights: •A comprehensive characterization of the as-welded HAZ of P91 weldment is conducted. •Structural features in the each layer of the HAZ are quantified by EBSD. •Structural heterogenities in HAZ are due to welding cycle and base metal structure. •FGHAZ contains the finest grain structure and largest precipitate density variation.
36 MATERIALS SCIENCE↗
Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by austenitic filler metal
The evolution of microstructure and texture across an as-welded dissimilar UNS S32750 super duplex/UNS S30403 austenitic stainless steel joint welded by UNS S30986 (AWS A5.9 ER309LMo) austenitic stainless steel filler metal using gas tungsten arc welding process was evaluated by optical micrography and EBSD techniques. Due to their fabrication through rolling process, both parent metals had texture components resulted from deformation and recrystallization. The weld metal showed the highest amount of residual strain and had large austenite grain colonies of similar orientations with little amounts of skeletal ferrite, both oriented preferentially in the < 001 > direction with cub-on-cube orientation relationship. While the super duplex stainless steel's heat affected zone contained higher ferrite than its parent metal, an excessive grain growth was observed at the austenitic stainless steel's counterpart. At both heat affected zones, austenite underwent some recrystallization and formed twin boundaries which led to an increase in the fraction of high angle boundaries as compared with the respective base metals. These regions showed the least amount of residual strain and highest amount of recrystallized austenite grains. Due to the static recrystallization, the fraction of low degree of fit (Σ) coincident site lattice boundaries, especially Σ3 boundaries, was increased in the austenitic stainless steel heat affected zone, while the formation of subgrains in the ferrite phase increased the content of < 5° low angle boundaries at that of the super duplex stainless steel. - Graphical abstract: Display Omitted - Highlights: • Extensive grain growth in the HAZ of austenitic stainless steel was observed. • Intensification of < 100 > orientated grains was observed adjacent to both fusion lines. • Annealing twins with Σ3 CSL boundaries were formed in the austenite of both HAZ. • Cub-on-cube OR was observed between austenite and ferrite in the weld metal. • Weld metal had the lowest texture intensity and ratio of low angle and CSL boundaries.
36 MATERIALS SCIENCE↗
Multi-Pass Hybrid Laser Arc Welding of Alloy 740H
The presentation reviews the progress made toward reducing the joining time of an advanced nickel-based alloy, Alloy 740H by a factor of two using a novel two step fusion welding approach. In the first step, a high powered laser is used to rapidly join thick weld groove lands (~10-12 mm thick) during a single pass. Hybrid laser arc welding (HLAW) is then used to fill the remaining weld groove and complete the joint. This sequential process also utilizes laser wobble in both steps to reduce welding defects and refine the weld microstructure to obtain improved properties compared to conventional gas tungsten or gas metal arc welds, GTAW and GMAW, respectively. The creep behavior of laser-only thick weld groove land welds and HLAW welds were found to be the same or slightly improved compared to conventional GMAW or GTAW welds in this alloy. Creep tests have been started to verify the long-term creep behavior (~10,000 hrs) of these welds. Modeling results on deep penetration laser welding are presented and the initial simulations of laser welding with laser wobble are shown. The next phase of the project will combine the two processes to make complete welds - deep penetration laser welds of thick weld groove lands followed by rapid filling of the remaining weld groove by HLAW - in thick plates (32 mm thick) Alloy 740H plate and entails development of narrow weld groove welding to further decrease the joining time of this alloy.
36 MATERIALS SCIENCE↗
Microstructure of a safe-end dissimilar metal weld joint (SA508-52-316L) prepared by narrow-gap GTAW
The microstructure, residual strain and interfacial chemical composition distribution of a safe-end dissimilar metal weld joint (DMWJ, SA508-52-316L) prepared by narrow-gap gas-tungsten arc welding (NG-GTAW) were studied by optical microscope (OM) and scanning electron microscope equipped with an energy dispersive X-ray microanalysis (SEM/EDX) and an electron back scattering diffraction (EBSD) system. Complex microstructure and chemical composition distribution are found, especially at the SA508-52 interface and the 52-316L interface. In brief, a complicated microstructure transition exists within the SA508 heat affected zone (HAZ); the residual strain, the fraction of high angle random grain boundaries and low angle boundaries decrease with increasing the distance from the fusion boundary in 316L HAZ; neither typical type II boundary nor obvious carbon-depleted zone is found near the SA508-52 interface; dramatic and complicated changes of the contents of the main elements, Fe, Cr and Ni, are observed at the distinct interfaces, especially at the SA508-52 interface. No carbon concentration is found at the SA508-52 interface. - Highlights: •Residual strain and GBCD change as a function of the distance from FB in 316L HAZ. •Neither type II boundary nor obvious carbon-depleted zone is found in SA508 HAZ. •No carbon concentration is found at the SA508-52 interface. •The middle part of the DMWJ has the highest residual strain.
36 MATERIALS SCIENCE↗
Welding Heat Input Influence on UNS S82441 Lean Duplex Stainless Steel Corrosion Resistance Assessed by Scanning Vibrating Electrode Technique (SVET)
The precipitation of the intermetallic phases can impair mechanical and corrosion properties. In the case of lean duplex stainless steels, they present solidification mode as primary ferrite, with austenite precipitation in the solid state, during cooling. This means the heat-affected zone balanced microstructure can be changed during the welding by the cooling rate, which is associated to the welding heat input, the thickness of the plate and the physical properties of the material. This work intends to present the influence of welding heat input on the corrosion resistance of UNS S82441 lean duplex stainless steel. The gas metal arc welding process was used to make the weld beads, using ER2209 as filler metal, which characterizes a dissimilar welded joint. The corrosion resistance of these specimens was analyzed through scanning vibrating electrode technique. It was observed that welding heat input variation distinctly influences corrosion in different zones of the weld beads over the specimen exposure time. The weld bead under intermediate welding heat input showed the highest corrosion rate and the one under the highest welding heat input, the lowest corrosion rate intensity.
36 MATERIALS SCIENCE↗
Vacuum vapor deposition: A spinoff of space welding development
A vapor deposition process has been defined through a spinoff effort of space welding development. In this development for welding in a space environment, a hollow electrode was used to add gas precisely at the welding arc. This provides gas for ionization which carries the welding arc current. During this welding development metal vapor coatings were observed. These coatings are unique in that they are produced by a new process. Some coatings produced and the potential of this new and innovative vapor deposition process are characterized. Advantages over prior art are discussed.
Poorman, R. M.↗
High temperature aircraft research furnace facilities
Focus is on the design, fabrication, and development of the High Temperature Aircraft Research Furnace Facilities (HTARFF). The HTARFF was developed to process electrically conductive materials with high melting points in a low gravity environment. The basic principle of operation is to accurately translate a high temperature arc-plasma gas front as it orbits around a cylindrical sample, thereby making it possible to precisely traverse the entire surface of a sample. The furnace utilizes the gas-tungsten-arc-welding (GTAW) process, also commonly referred to as Tungsten-Inert-Gas (TIG). The HTARFF was developed to further research efforts in the areas of directional solidification, float-zone processing, welding in a low-gravity environment, and segregation effects in metals. The furnace is intended for use aboard the NASA-JSC Reduced Gravity Program KC-135A Aircraft.
Smith, James E., Jr.↗
Microstructure-Property Correlations in Fiber Laser Welded Nb-Ti Microalloyed C-Mn Steel
Mechanical Performance of traditional gas-shielded arc welded joints of 700 MPa grade microalloyed C-Mn steel cannot meet service requirements. Laser welding, with its characteristic high energy density, is known to improve the welding performance of experimental steels. In the present study, Nb-Ti microalloyed steel with a thickness of 4.5 mm was welded using a 4 kW fiber laser. The microstructure, precipitation, and mechanical properties of the welded joints were studied. The hardness and tensile strength of the welded joints were higher than those of the base metal (BM). The microstructure of the fusion zone (FZ) and coarse grain heat affected zone (CGHAZ) was lath martensite (LM), while the microstructure of the fine grain HAZ and mixed grain HAZ consisted of ferrite and martensite/austenite islands. Although LM was observed in both the FZ and CGHAZ, the hardness and calculated tensile strength of the FZ were lower than those of the CGHAZ, due to a reduction in solid solution strengthening by element loss and the dissolution of high-hardness precipitates in FZ. Most precipitates such as [(Nb,Ti)C and (Nb,Ti)(C,N)] that were present in the BM were dissolved, which led to an increase in C and N in solid solution in the FZ. Thus, the elastic modulus of the FZ was higher than that of the BM. Similarly, the elastic modulus of the CGHAZ was higher than that of the BM due to the segregation of C and N atoms during the welding process. The toughness of the FZ was superior to that of the BM, and the toughness of the HAZ approached 91% of that of the BM. The change in toughness primarily depended on the microstructural refinement, the increase in the fraction of grains with high misorientation, the residual austenite in the FZ and CGHAZ, and the dissolution of coarse precipitates.
36 MATERIALS SCIENCE↗
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Highlights: • The formation and spheroidization of the eutectic-like carbides are found in the Hastelloy N alloy during welding and PWHT. • All precipitates in the joints before and after the PWHT are identified as a M{sub 6}C type carbide with different morphology. • The diffusion of main element of Mo leads to the decrease of lattice parameter of the carbide during the welding and PWHT. - Abstract: The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M{sub 6}C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M{sub 6}C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M{sub 6}C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M{sub 6}C carbides, which results in a decrease of the lattice parameter.
36 MATERIALS SCIENCE↗
An evaluation of GTAW-P versus GTA welding of alloy 718
Mechanical properties were evaluated to determine statistically whether the pulsed current gas tungsten arc welding (GTAW-P) process produces welds in alloy 718 with room temperature structural performance equivalent to current Space Shuttle Main Engine (SSME) welds manufactured by the constant current GTAW-P process. Evaluations were conducted on two base metal lots, two filler metal lots, two heat input levels, and two welding processes. The material form was 0.125-inch (3.175-mm) alloy 718 sheet. Prior to welding, sheets were treated to either the ST or STA-1 condition. After welding, panels were left as welded or heat treated to the STA-1 condition, and weld beads were left intact or machined flush. Statistical analyses were performed on yield strength, ultimate tensile strength (UTS), and high cycle fatigue (HCF) properties for all the post welded material conditions. Analyses of variance were performed on the data to determine if there were any significant effects on UTS or HCF life due to variations in base metal, filler metal, heat input level, or welding process. Statistical analyses showed that the GTAW-P process does produce welds with room temperature structural performance equivalent to current SSME welds manufactured by the GTAW process, regardless of prior material condition or post welding condition.
Gamwell, W. R.↗
Comparative study of microstructure and properties of low-alloy-steel/nickel-based-alloy interfaces in dissimilar metal weld joints prepared by different GTAW methods
Highlights: • Number of type I and type II boundaries: H-DMWJ > C-DMWJ > W-DMWJ. • Width carbon depleted zones and carbon enriched zones: H-DMWJ > C-DMWJ > W-DMWJ. • Type I and type II boundaries are susceptible to SCC and cracked during mechanical bending. • C-DMWJ has the best performance while H-DMWJ has the worst one. - Abstract: Low-alloy-steel/buttering (or welding) metal interfaces in safe-end dissimilar metal weld joints (DMWJs) at nuclear power plants are weak parts. To optimize the quality of the safe-end DMWJs used for the construction of domestic nuclear power plants and to improve the welding productivity, a series of DMWJs in full-size have been manufactured by using different gas tungsten arc welding (GTAW) methods. The microstructure, chemical composition distribution and local properties across the SA508/52(M) interfaces in these DMWJs are studied. The high heat input and long high temperature duration during hot-wire GTAW process promote the carbon diffusion and grain boundary migration and hence the DMWJ by hot-wire GTAW has the largest amount of type I and type II boundaries and the widest carbon depleted zones and carbon enriched zones, which resulting in the worst performance among the DMWJs in simulated primary water. Type I and type II boundaries are high angle random grain boundaries (RGBs) and Cr-depleted zones are found along type II boundaries resulting in their high susceptibility to SCC. In addition, these boundaries are prone to be cracked during mechanical bending process.
36 MATERIALS SCIENCE↗