A Review on Experimental Investigation of Welding of Superalloys (original) (raw)
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Welding of Ultra High Strength Steels
The ongoing need to reduce the weight of products while increasing strength has resulted in new generation steel manufacturing using special heat treatments to produce High Strength Steels (HSS) and Ultra High Strength Steels (UHSS) with up to 1700 MPa tensile strength. The high strength level of these steels makes it possible to produce structures with a considerable weight and cost reduction, and such steels have been adopted in the automotive industry and for mobile heavy equipment. Welding of UHSS is, however, not without its complications and welding processes for these steels need careful attention. For instance, their high susceptibility to cracking and Heat Affected Zone (HAZ) softening are risks that need to be borne in mind when choosing welding parameters. This research work discusses the difficulties and challenges of successful welding of UHSS. Common welding methods used in welding of UHSS are briefly reviewed to gain a better understanding of the effects of different welding parameters and methods. The paper finds that UHSS can be satisfactorily welded with laser welding, electron beam welding, resistance welding, and conventional arc welding methods, but the quality of the weld is dependent on appropriate control of several parameters and variables of the welding processes.
Welding Metallurgy of Corrosion-Resistant Superalloy C-276
Superalloys, 2015
Microsegregation occurs during solidification of fusion zone in alloy C-276. The concomitant precipitation of topologically close-packed phases P and μ has been reported to be responsible for the hot cracking observed in this alloy during welding. The clue to preventing hot cracking hence lies in suppressing microsegregation in the fusion zone. An important avenue towards this is the introduction of current pulsing during gas tungsten arc welding. Current pulsing was found to be effective in mitigating microsegregation; it was also found to refine the microstructure in the weld zone and improve the mechanical behavior of weld joints. Judicious choice of filler wire is of paramount importance to get weld joints free from segregation and with a good combination of mechanical properties. Joints made using arc welding methods were found to be highly resistant to corrosion in salt spray tests. Non-arc-based methods-laser welding and electron beam welding-were found to be effective in largely keeping the microsegregation at bay. This chapter elaborates on these issues.
Today getting high thermal efficiency in thermal and nuclear power plant is a big challenge. Many new material are developed. SA 335 grade 91 steel is modified high chrome-moly martenstitic steel. This material is having excellent toughness and high temperature creep strength. During welding, this material is having tremendous change in its microstructure and hence mechanical property. Many research works were done in this area. This paper discusses weld ability of P91 material. Effect of different welding process, type of filler wire, its chemical composition and type of flux is discussed in this paper. PWHT is necessary after welding of P91 steel. PWHT temperature and its duration affects phase transformation and mechanical properties of weld metal, HAZ and parent metal. Major focus is given on hardness, creep resistance and notch toughness.
ASME 2014 Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries, 2014
Boiler and steam piping components in power plants are fabricated using creep strength enhanced ferritic (CSEF) steels, which often operate at temperatures above 550°C. Modification of alloy content within these steels has produced better creep performance and higher operating temperatures, which increases the process efficiency of power plants. The improved materials, however, are susceptible to type IV cracking at the welded regions. A better understanding of type IV cracking in these materials is required and is the basis of the Technology Strategy Board (TSB) UK funded VALID (Verified Approaches to Life Management & Improved Design of High Temperature Steels for Advanced Steam Plants) project. In order to study the relationship between creep performance and heat input during welding, several welds with varying amounts of heat input and resultant HAZ widths were produced using the electron beam welding process. The welding parameters were developed with the aid of weld process modeling using the finite element (FE) method, in which the welding parameters were optimized to produce low, medium and high heat input welds. In this paper, the modeling approach and the development of electron beam welds in ASTM A387 grade P92 pipe material are presented. Creep specimens were extracted from the welded pipes and testing is ongoing.
Introduction to Welding of Metallic Materials.: Methods, Metallurgy and Performance
Elsevier, 2023
Welding of Metallic Materials: Methods, Metallurgy and Performance looks at technical welding methods used based on different principles and sources, such as heat, with or without pressure, electrical, plasma, laser and cold-based welding. The metallurgical aspects associated with the welding processes, specifically those associated with metallic alloys, are explained, alongside the advantages and welding features that are associated with specific welding processes. In addition, the performance of metallic weldments under specific conditions and environments such as offshore, oil industry, radiation and high-temperature services are discussed. This book will a vital resource for researchers, practicing engineers and undergraduate and graduate students in the field of materials science and engineering.
Metals
Heat-affected zones (HAZs) of Inconel 939 (IN-939) superalloy are susceptible to cracking during welding process. Preventing cracking during the repair welding of turbine components is important. In this study, the effects of heat input and pre-welding heat treatment on the microstructure, mechanical properties and crack formation in tungsten inert gas welding of IN-939 were investigated. The whole specimens were welded using Inconel 625 filler in an Ar atmosphere and characterised by metallographic examinations and hardness measurements. Results showed that the microstructures of IN-939 HAZs were highly susceptible to cracking during welding due to increasing of γ′ volume fraction. All of these cracks appeared in the HAZs and grew perpendicular to the melting zone along the grain boundaries. In this survey, the pre-welding heat treatment and heat input strongly affected the HAZ microstructure and hardness. However, the pre-welding heat treatment with 67% impact was more effective t...
Weld development for Incoloy alloy 908, a low thermal expansion superalloy
In this thesis, an systematic approach was taken to: (1) understand the fundamental processes operative in welding alloy 908 and (2) development of appropriate filler wire compositions based on (1). Improvement of fracture toughness was achieved in two ways: By reducing the concentration of niobium in weld filler wire, By homogenizing the weld prior to aging heat treatment. Both methods reduced or eliminated Laves phase and/or the size of surrounding brittle area. Solidification characteristics of alloy 908 welds is that: * During the weld solidification, niobium segregates into interdendritic zone and precipitated in the formation of cubic MC carbides and hexagonal Laves phases. i The area surrounding these secondary phases is enriched with niobium and become brittle after aging heat treatment. Fractography analysis of welds revealed that: Fracture occurs by a typical ductile dimple rupture mechanism, voids initiating at MC carbides and Laves phases. Voids grows, first by the failure of surrounding brittle area, then by plastic deformation of ductile matrix. Thus, the segregation of niobium was identified as a primary cause of weld degradation.
Welding of Large Thickness Super Duplex Stainless Steel: Microstructure and Properties
Metals, 2021
In this study, Submerged Arc Welding (SAW) and Gas Metal Arc Welding (GMAW) processes were used in multi-pass welding of 33 mm thickness super duplex stainless steel plates. Recommended and higher than recommended arc energy and interpass temperatures were used. Both GMAW and SAW processes were able to produce large thickness weldments meeting the microstructural, mechanical, and corrosion resistance requirements, and also when using higher than recommended arc energy and interpass temperature. It was possible to reduce the number of welding passes by half when using higher than recommended arc energy and interpass temperature. The SAW process needed only half of the welding time required for the GMAW process to produce a weldment with nearly the same number of weld passes, when using recommended arc energy and interpass temperature. Based on the results of this investigation, the practical recommendations for welding large thicknesses should be revised and updated.
Welding Characteristics of Ultrahigh Strength Steel in Annealed and Quench-Tempered Conditions
Journal of Materials Engineering and Performance, 2010
In this research, the welding characteristics of a new UHSLA steel, 35NiCrMoV123, have been studied in two general conditions (annealed and quench-tempered). Carbon equivalent value of 35NiCrMoV123 steel is near 0.9 which classifies it as a ''very difficult to weld'' steel. The effects of welding heat treatment cycle (preheat, interpass, and postheat) on metallurgical and mechanical properties of weldments have been investigated by tensile, impact toughness, and hardness tests, as well as optical microscopy observations. It has been observed that by employing high-temperature stress relief (600°C), welding could be performed in annealed condition successfully. Also, the results indicate that by applying precise welding heat treating cycle (preheat, interpass, and postheat temperature at 310°C) in order to obtain lower bainitic microstructure in HAZ, also employing high-temperature stress relief (600°C), welding in quench-tempered condition could be successfully performed.