Weld Filler Metal Research Articles

Characterizing Phase Transformations and Their Effects on Ferritic Weld Residual Stresses with X-Rays and Neutrons

Weld residual stresses often approach, or exceed, the yield strength of the material, with serious implications for the integrity of engineering structures. It is not always feasible to measure residual stresses, so integrity assessments often rely heavily on numerical models. In ferritic steels, the credibility of such models depends on their ability to account for solid-state phase transformations, which can have a controlling effect on the final residual stress state. Furthermore, a better understanding of weld transformations provides an opportunity to engineer the weld stress state and microstructure for improved life. In this article, the complementary merits of synchrotron X-ray and neutron diffraction are exploited both to verify and refine weld models and to inspire the development of weld filler metals to control weld stresses. In terms of weld filler metal design, X-ray diffraction is used to characterize phase transformations in real time during realistic weld cooling cycles, for understanding small-scale behavior and identifying features that need to be incorporated into finite-element models. Meanwhile, neutron diffraction is used to elucidate the practical consequences of solid-state phase transformations on the macroscopic scale, thereby providing crucial validatory structural integrity data.

Effect of electromagnetic vibration on the unmixed zone formation in 25Cr–35Ni heat resistant steel/Alloy 800 dissimilar welds

Electromagnetic vibration was applied to molten weld metal during welding of dissimilar welds between 25Cr–35Ni heat resistant steel and Alloy 800 superalloy. It was observed that the unmixed zone in the interface between the 25Cr–35Ni heat resistant steel and (the Alloy 82) weld filler metal was completely eliminated by high-frequency electromagnetic vibration. A complete mixing of the molten filler metal and base metal due to agitation of molten weld metal has caused the unmixed zone to be eliminated.

Crystal Growth in Laser Surface Melting and Cladding of Ni-Base Single Crystal Superalloy

Crystal growth behaviours in the laser surface-melted region and overlay weld metal of/on Ni-base single crystal superalloy CMSX-4 has been investigated. The Ni-base superalloy Rene 142 was used as the filler metal for overlay welding. Surfaces of the specimens were prepared as to be coincident with the (001) plane. The surface melting and overlay welding were conducted using a 2 kW diode laser along the [100] direction. Electron back scattering analysis for the crystal orientation revealed that, under low heat input conditions, the surface-melted region solidified as a single crystal with unidirectional dendrites which grew from the base metal epitaxially along the [001] direction. For intermediate heat input conditions, the surface-melted region was also found to be single-crystalline; however, it consisted of orthogonal dendrites along the [001], [010] and [100] directions. In contrast, under high heat input conditions, stray crystals were observed in some parts of the surface-melted region resulting in the melted region becoming polycrystalline. A numerical analysis of the dendritic growth direction and the constitutional supercooling at solidification front indicated that the overlay weld metal grew epitaxially on the substrate and stray crystals tended to form under conditions of higher laser power and (V f / V w) ratio (V f: wire feeding speed, V w: laser scanning speed), which agreed with the metallographic observation. A numerical calculation combining CET (columnar to equiaxed transition) theory with an inverse heat conduction analysis allowed us prediction of the conditions needed to suppress the formation of stray crystals and to promote single-crystal production in the overlay welded region with epitaxial dendritic growth of [001] orientation and/or dendritic growth of [100] and [010] orientations. Using these predictions, a single crystalline layer of 3 mm thickness on a single crystal substrate could be achieved by laser overlay welding with ten passes. Furthermore, creep rupture properties of single-crystalline surface-melted region were comparable or slightly better than that of the CMSX-4 base metal.

Ni基単結晶超合金のレーザー肉盛溶接部の結晶成長挙動

Crystal growth behavior in the overlay welded regions of Ni-base single crystal superalloy CMSX-4 has been investigated. The Ni-base superalloy René142 was used as the filler metal for overlay welding. The surface of the specimens was prepared as to be coincident with the (001) plane. The overlay welding was conducted using a 2kW diode laser along the [100] direction. Microstructural observation revealed that the overlay weld metal grew epitaxially on the substrate and stray crystal tended to form in the conditions of higher power and (Vf /Vw) ratio (Vf : wire feeding speed, Vw : laser scanning speed). Furthermore, the dendritic growth direction and the single-crystallized condition were analyzed by the theoretical model with combining the geometric model, CET (columnar to equiaxed transition) model and CFD (computational fluid dynamics) analysis. The predicted results of the dendritic growth direction and the stray crystal formation in the overlaid regions corresponded approximately with the experimental ones, which indicated that the current theoretical calculation can be used to predict the conditions to suppress the formation of stray crystals and to promote single-crystal production in the overlay welded region with epitaxial dendritic growth of [001] orientation and/or the dedritic growth of [100] and [010] orientations. On the basis of the condition by the theoretical prediction, a single crystalline layer of 3 mm thickness on a single crystal substrate could be achieved by laser overlay welding with ten passes.

Microcracking susceptibility in dissimilar multipass welds of alloy 690 to type 316L stainless steel using La added filler metals

The microcracking susceptibility in dissimilar multipass welds of alloy 690 to type 316L stainless steel was investigated by the Varestraint test and the multipass welding test using the four different stainless steels varying the amounts of impurity elements such as P and S, and using the nine different filler metals of alloy 690 varying the La content. In order to simulate the dissimilar weld metals, stainless steels were gas tungsten arc (GTA) welded using alloy 690 filler metals with varying the dilution ratio. Microcracks occurring in the reheated weld metals were classified into ductility dip, liquation and solidification cracks. The ductility dip cracking susceptibility decreased with increasing the La content in the weld metal, while the liquation and solidification cracking susceptibilities increased contrarily when the La content in the weld metal exceeded ∼0·03 mass-%. The relation among the microcracking susceptibility, the (P + S) and La contents in every weld pass of the multipass welding was investigated. Ductility dip cracks occurred in the compositional range (atomic ratio) of La/(P + S)<0·17 and solidification/liquation cracks occurred in that of La/(P + S)>0·76, while any cracks did not occur at La/(P + S) being between 0·17–0·76. The ductility dip cracking susceptibility could be improved by adding La due to the scavenging of the impurity elements. The excessive La addition to the weld metal resulted in the solidification/liquation cracking alternatively attributed to the formation of Ni–La intermetallic compounds with low eutectic point. The optimal filler metal for the dissimilar multipass welding of alloy 690 to stainless steel was selected as La/(P + S) would be 0·17–0·76 for every weld pass. Microcracking could be completely prevented in the dissimilar multipass weld metal of alloy 690 to type 316L stainless steel by using two kinds of filler metals containing 0·03 mass-%La for the weld passes adjacent to the stainless steel base metal and containing 0·01 mass-%La for other weld passes.

Impact of Small Chemistry Variations in Plate and Weld Filler Metal on the Corrosion Performance of Ni-Cr-Mo Alloys2

Abstract The ASTM standard B 575 provides the requirements for the chemical composition of Nickel-Chromium-Molybdenum (Ni-Cr-Mo) alloys such as Alloy 22 (N06022) and Alloy 686 (N06686). The compositions of each element are given in a range. For example, the content of Mo is specified from 12.5 to 14.5 weight percent for Alloy 22 and from 15.0 to 17.0 weight percent for Alloy 686. It is important to determine how the corrosion rate of welded plates of Alloy 22 using Alloy 686 weld filler metal would change if heats of these alloys were prepared using several variations in the composition of the elements even though still in the range specified in B 575. Seven heats of plate were welded with seven heats of wire. Immersion corrosion tests were conducted in a boiling solution of sulfuric acid plus ferric sulfate (ASTM G28 A) using both as-welded (ASW) coupons and solution heat-treated (SHT) coupons. Results show that, for practical purposes, the corrosion rate was not affected by the chemistry of the materials in the range specified in the standard B 575.

Study of Underwater Laser Welding Repair Technology

IHI developed underwater welding process by using YAG laser and qualified the process to repair a thin wall stainless steel tank in a power plant in Japan. Important features of YAG laser welding are less welding distortion, and a small heat-affected zone (HAZ) due to the smaller heat input and higher cooling rate than with other conventional welding methods. In this study, we have conducted underwater laser welding of Ni-base alloy and stainless clad materials, such as Alloy 600 and E-309L / E-308L clad materials. Alloy 690 was selected as weld filler metal for a corrosion resistant overlay to prevent corrosion attack by the service environment. Welding trials were conducted on the surface of flat plates with simulated surface cracks, and the trial welds were assessed for soundness of welding. The preliminary results of the trial welds by using high power laser diode, and comparison between YAG laser and high power LD are reported.

Suppressing type IV failure via modification of heat affected zone microstructures using high boron content in 9Cr heat resistant steel welded joints

Creep rupture strength at 923 K and microstructural evolution of welded joints have been investigated for high boron–low nitrogen–9Cr heat resistant steels developed at the National Institute for Materials Science (Japan). Welded joints were prepared from plates containing 47–180 ppm boron using gas tungsten arc welding and Inconel type filler metal, and showed superior creep properties to those of welded joints of conventional high chromium steels such as P92 and P122. No type IV failure was observed in the boron steel welded joints. A large grained microstructure was observed in the heat affected zone heated to Ac3 (Ac3 HAZ) during welding, whereas the grains are refined at the same location in conventional steel welded joints. The simulated Ac3 HAZ structures of the boron steels have a creep life almost equal to that of the base metal. Large grained HAZ microstructures and stabilisation of M23C6 precipitates are probable reasons for suppression of type IV failure and improved creep resistance of the boron steel welded joints.

Development of Filler Metal for Welding of Nickel-Base Superalloy IN738LC by Mathematical Programming Method

There is a great demand for filler metals for high-performance IN738LC Ni-base superalloy, which is widely used for blades in recent advanced gas turbines. These fillers are required to have compatible high temperature properties and hot cracking resistance. This paper reports on investigations made on the weld metal of alloys with a composition similar to that of IN783LC but varying Al, Ti and C contents. Their hot cracking susceptibility was examined by transverse Varestraint tests. The mathematical programming method was used to determine the optimum Al, Ti and C contents in the weld metal with a good balance of hot cracking resistance and mechanical properties at elevated temperatures. The method adopted was a satisficing trade-off method with a neural network model, which enabled to efficiently determine the optimum Al, Ti and C contents in the weld metal: 3%, 2% and 0.26%, respectively. The Varestraint tests indicated that the hot cracking susceptibility in the weld metal with the optimized Al, Ti and C contents was remarkably reduced. Hot tensile tests revealed that the creep rupture strength of the weld metal with that composition was also at a satisfactory level as slightly lower than that in the IN738LC base metal.

In Situ Repair Welding of Steam Turbine Shroud for Replacing a Cracked Blade

A root-cracked blade in a high-pressure steam turbine of a nuclear power plant had to be replaced with a new blade by cutting the shroud to remove the cracked blade. This necessitated in situ welding of a new shroud piece with the existing shroud after the blade replacement. The in situ welding of the shroud, a 12% Cr martensitic stainless steel with tempered martensite microstructure, was carried out using gastungsten arc welding and 316L austenitic stainless steel filler metal followed by localized postweld heat treatment at 873 K for 1 h using a specially designed electrical resistance-heating furnace. Mock-up trials were carried out to ensure that sound welds could be made under the constraints present during the in situ repair welding operation. In situ metallography of the repair weld after postweld heat treatment confirmed the adequate tempering of the martensitic structure in the heat-affected zone. Metallurgical investigations carried out in the laboratory on a shroud test-piece that had been welded using the same procedure as employed in the field confirmed the success of the in situ repair operation. The alternate option available was replacing the cracked blade and the shroud piece to which it is riveted with a new one, reducing the height of all the blades attached to the shroud by machining, riveting the blades with reduced height to the new shroud, and, finally, dynamic balancing of the entire turbine after completion of the repair. This option is both time-consuming and expensive. Hence, the successful completion of this repair welding resulted in enormous savings both in terms of reducing the downtime of the plant and the cost of the repair. The turbine has been put back into service and has been operating satisfactorily since December 2000.

Search for filler metal for welding of ferrous alloys to titanium

The use of a filler metal to facilitate the gas tungsten arc (GTA) welding of ferrous alloys to titanium alloys has been investigated. Semi-empirical rules have been applied to identify alloying elements that would resolve the important problems of brittle intermetallic formation and weld cracking. Vanadium was found appropriate. The GTA welds between a low carbon steel and Ti–15V–3Cr–3Sn–3Al made with a vanadium filler wire resisted cracking better than comparable autogenous welds. However, the presence of a hard, brittle eutectic microconstituent along the ferrous side of the fusion boundary drastically limited the gain in weldability. As anticipated, analysis of GTA welds produced with vanadium filler wire suggested the presence of a ternary (Fe,Ti,V) single phase. Although cracking was reduced with vanadium, the practical benefit of a vanadium filler wire for GTA welding is small because the weld metals remain very hard and brittle.

Fracture Toughness Requirements for ASME Section VIII Vessels for Temperatures Colder Than 77K

Earlier research work conducted at MIT and NIST indicated that CVN specimens with an initial temperature at or near 4K (−452°F) actually fracture at temperatures significantly above 4K due to adiabatic heating. As a result of this work, ASTM E-23 test method on CVN testing was revised to incorporate a restriction that CVN tests are valid only at 77K (−320°F) and warmer. ASME requested PVRC to assess the above CVN issue and provide an appropriate recommendation for the Code change or for a further Code change, if needed for vessels with MDMT colder than 77K. PVRC formed a Task Group under the Committee on Failure Modes. The TG undertook a program which included a review of the existing data and an experimental program to develop new KIcJ data at 4K and 77K and CVN data at 77K. In the experimental program, a total of four 1-in-thick weldments were prepared from SA 240, Type 304 stainless steel plate using the SMAW process and E316L-15 electrodes. The electrodes purchased permitted the preparation of the weldments with four progressively higher levels of ferrite. The PVRC data and existing data were utilized in developing the recommendations to ASME. The recommendations are: use CVN tests (with 316L S.S. weld filler metal with FN⩽5) at 77K with increased acceptance criterion of 21 mils lateral expansion; for welds not meeting the foregoing requirements, use ASTM E1820 JIc tests at MDMT and the acceptance criterion for KIcJ has been set at 120 ksi√in. This paper presents the test data, analysis and technical basis for the PVRC recommendations to ASME.

HAYNES 230-W FILLER WIRE

Abstract Haynes 230-W Filler Wire is a specially formulated welding filler metal designed for the fabrication of Haynes 230 alloy (see Alloy Digest Ni-320, August 1985). This datasheet provides information on composition, physical properties, elasticity, and bend strength. It also includes information on joining. Filing Code: Ni-558. Producer or source: Haynes International Inc.

Evaluation of pre-Northridge steel moment-resisting frame joints

The 1994 Northridge earthquake caused widespread and unexpected damage to steel moment-resisting joints and connections. Shortly following the earthquake, the Federal Emergency Management Agency funded a series of full-scale tests of steel moment-resisting joints and connections to characterize the behavior of pre-earthquake connections and to evaluate the efficacy of a selected number of repair schemes. Twelve pre-earthquake connections were tested. Three of the twelve connections were tested by the authors to failure, and then repaired and re-tested. The response of the pre-earthquake connections was highly variable and uniformly poor. Premature fractures were observed in all twelve connections, and the types of fractures were similar to those observed in the field following the earthquake. The mean beam plastic rotation was 0.005 rad: one-sixth of the target value of 0.03 rad. The response of those moment-resisting connections that were repaired by replacing fractured weld and parent metal with toughness-rated weld filler metal was also poor. On the basis of the studies described in the paper, the rotation capacity of large-size moment-resisting connections built prior to the Northridge earthquake is smaller than the target values established following the earthquake; rehabilitation of earthquake-damaged moment-resisting connections by re-welding only will likely be ineffective; beam-column panel zones should be designed to remain elastic for the forces associated with plastic hinging in the beams; design equations for continuity plates should be revised; and design checks for flange compactness should be based on expected rather than nominal material properties. Copyright © 1998 John Wiley & Sons, Ltd.

Duralumin-stainless steel joint: structure and mechanism of forming by means of electron beam welding and Ag-2Mg filler metal shim

High-alloyed stainless steel of 18-8 type and duralumin are not directly weldable due to significant differences in their properties. The results of structural investigations of the joints between the two materials, obtained by a previously developed method of electron beam welding with an Ag-2 wt% Mg alloy filler metal shim, are presented in this paper. The microstructure of the weld is diphasic, being composed of supersaturated Ag in Al solid solution and also an Ag2Al phase. At the base materials and weld boundaries interstitial layers are crystallized in the form of solid solutions while brittle intermetallic compounds do not appear. On the basis of presented results a mechanism for the joint formation is proposed.

Evaluation of Weldment Creep and Fatigue Strength-Reduction Factors for Elevated-Temperature Design

New explicit weldment strength criteria in the form of creep and fatigue strength-reduction factors were recently introduced into the American Society of Mechanical Engineers Code Case N-47, which governs the design of elevated-temperature nuclear plant components in the United States. This paper provides some of the background and logic for these factors and their use, and it describes the results of a series of confirmatory creep-rupture and fatigue tests of simple welded structures. The structures (welded plates and tubes) were made of 316 stainless steel base metal and 16-8-2 weld filler metal. Overall, the results provide further substantiation of the validity of the strength-reduction factor approach for ensuring adequate life in elevated-temperature nuclear component weldments.

Microscopical evaluation of low temperature aging of type 308 stainless steel weldments

AbstractType 308 stainless steel is often used as weld filler metal in light water reactor piping systems. In similar cast CF8 type steels, the ferrite phase has been shown to be responsible for the reported degradation in properties after long term aging at temperatures between 300 and 400°C. Despite the relatively low volume fraction of ferrite in the type 308 materials, long term aging at the maximum operating temperature (343°C) results in a significant loss of impact toughness. Using TEM, G phase precipitation was detected in the ferrite matrix of the aged welds both in the matrix and on dislocations. Composition modulations in the aged ferrite consistent with spinodal decomposition were detected in atom probe composition profiles. A variety of statistical techniques was used to analyse the atom probe composition profiles. The spinodal decomposition of the ferrite into iron rich and chromium enriched regions is the most likely cause of the mechanical property degradation of these materials during agi...

Grain boundary segregation in the Ni-base alloy 182

Grain boundary segregation is often considered to play a role in the various types of intergranular failures observed in austenitic alloys. However, there has been little direct study of this segregation because it is usually very difficult to obtain intergranular fracture in these alloys in the high vacuum required for surface analysis. This paper reports an Auger electron spectroscopy study of grain boundary segregation in the nickel-base Alloy 182. This alloy was used because it would easily fracture along its grain boundaries in high vacuum and because it has a very complex microstructure, as do many nickel-base alloys used in engineering applications. Furthermore, the alloy is widely used as a weld filler metal to join nickel-base alloys to one another or to stainless steels. Phosphorus was found to be the only impurity element that segregated to the grain boundaries. There was considerable variability in segregation from grain boundary to grain boundary and also on a single grain facet. It is suggested that these variations arise primarily from variations in grain boundary structure, in the density and types of precipitates in a grain boundary, and in the consequent variety of precipitate matrix interfaces present at the grain boundary. It is also suggested that quantitative Auger analysis on such a material would be very difficult.

Dissimilar Metal Weld and Boiler Creep Damage Evaluation for Plant Life Extension

The basic causes of dissimilar metal weld (DMW) failures in boilers are now well understood. Guidelines have emerged for achieving significantly improved DMW life, in terms of operational parameters, weld filler metals, and weld designs. Analytical, as well as experimental, nondestructive techniques have been developed that enable assessment of the condition of DMWs in service so that intelligent run-replace decisions can be made. Techniques for assessing the remaining life of superheater/reheater (SH/RH) tubes are under development. The techniques utilize information on steamside oxide scale growth and dimensional changes on the fireside due to corrosion to compile the temperature–stress profile of operation in the tubes. This information is then combined with standard creep data to estimate the remaining life of the tubes more accurately than was possible heretofore. The potential of a replication technique that allows nondestructive monitoring of creep damage in heavy section pipes has been successfully demonstrated at several utility sites. It has been possible to detect early stages of incipient creep damage and to recommend specific courses of action to affected utilities. Laboratory and field studies currently in progress are expected to result in metallographic and miniature test specimen techniques that would further augment the capabilities of the replication technique, and render it into a more quantitative tool for life assessment of heavy section components.

The Room Temperature Ductility of Molybdenum-Base Weldments

This study evaluates the tensile properties and behavior of three commercially available and two experimental vacuum arc cast molybdenum base alloys that have been GTA welded. Exceptionally low applied strain rates were required to produce significant elongation in the commercial specimens tested. Strain localization in the narrow HAZ results in high effective strain rates in that area. The experimental alloys exhibited more than five times greater elongation compared with the commercial material at practical strain rate levels. In commercial alloys, the fracture location was influenced by the weld filler metal, with TZM causing fracture in the fusion zone whereas Mo-50Re caused fracture in the HAZ.