Microstructural features of dissimilar welds between 316LN austenitic stainless steel and alloy 800
15 Nov 2000-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing (Elsevier)-Vol. 292, Iss: 1, pp 74-82
TL;DR: In this article, the weld fusion zones and the interfaces with the base materials were characterised in detail using light and transmission electron microscopy, showing that the stainless steel weld metals solidified dendritically, while the 16-8-2 (16%Cr-8%Ni-2%Mo) weld metal showed a predominantly cellular substructure.
Abstract: For joining type 316LN austenitic stainless steel to modified 9Cr–1Mo steel for power plant application, a trimetallic configuration using an insert piece (such as alloy 800) of intermediate thermal coefficient of expansion (CTE) has been sometimes suggested for bridging the wide gap in CTE between the two steels. Two joints are thus involved and this paper is concerned with the weld between 316LN and alloy 800. These welds were produced using three types of filler materials: austenitic stainless steels corresponding to 316, 16Cr–8Ni–2Mo, and the nickel-base Inconel 182 1 . The weld fusion zones and the interfaces with the base materials were characterised in detail using light and transmission electron microscopy. The 316 and Inconel 182 weld metals solidified dendritically, while the 16–8–2 (16%Cr–8%Ni–2%Mo) weld metal showed a predominantly cellular substructure. The Inconel weld metal contained a large number of inclusions when deposited from flux-coated electrodes, but was relatively inclusion-free under inert gas-shielded welding. Long-term elevated-temperature aging of the weld metals resulted in embrittling sigma phase precipitation in the austenitic stainless steel weld metals, but the nickel-base welds showed no visible precipitation, demonstrating their superior metallurgical stability for high-temperature service.
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TL;DR: In this article, dissimilar welding of stainless steel 15-5PH to a Cobalt-base super alloy KC20WN (UNS R30605/Haynes 25) is attempted for specific purpose in space applications.
Abstract: Many of the components/assemblies used in strategic sectors involve dissimilar metal weld joints and dissimilar welding has always imposed challenges in terms of the weld quality because of the physical and chemical mismatches of the base metals. In the present study, dissimilar welding of stainless steel 15-5PH (UNS S15500) to a Cobalt-base super alloy KC20WN (UNS R30605/ Haynes 25) is attempted for specific purpose in space applications. Gas Tungsten Arc Welding is carried out with two types of filler wires, viz., KC20WN and ER 630 (17-4PH). Visual inspection, Dye Penetrant testing and X-ray radiography testing revealed defect free joints and the joints were also characterized for microstructure. Superior properties were observed when welding was carried out with KC20WN filler wire compared to that with ER630 filler wire.
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28 Jul 2020
TL;DR: In this paper, a Monte Carlo approach based on the McStas software package is proposed to simulate pseudo-strains associated with a gauge volume that is partially filled, or with an inhomogeneous and anisotropic material.
Abstract: Neutron diffraction has been used by the nuclear industry for measuring residual stresses in structures for which integrity safety cases must be made. However measurement of stresses in materials containing large grains, or in anisotropic weld metal, or approaching air-metal interfaces, or metal-metal interfaces using neutron diffraction is particularly challenging. These types of measurements can give rise to errors (often termed “pseudo-strains”) that can be significantly larger than the residual stress actually present. Such errors arise when the gauge volume is partially filled (e.g. air to metal interface for measuring near-surface stresses), or when the gauge volume composition is inhomogeneous (metal to metal interface), or the gauge volume material is anisotropic (welds with bundles of elongated grains). To mitigate such errors several approaches have been proposed using numerical and analytical methods to calculate the magnitude of pseudo-strain. Whether these methods can be applied depends on the instrument used and the type of sample being measured. In this context a different approach based on the Monte-Carlo method, as embedded in the neutron ray tracing software package McStas is proposed.
The aim is to validate by neutron measurements the ability of McStas to simulate pseudo strains associated with a gauge volume that is partially filled, or a gauge volume that samples inhomogeneous and anisotropic material. The instrument modelled for this research project is ENGINX a time-of-flight instrument located at ISIS (RAL). To understand and isolate the effects of traversing an interface made up of different materials a stepwise approach was taken. The initial phase involved building a new model of ENGINX in McStas and to validate its correctness by analysing the characteristics of the beam and gauge volume by simulating a steel pin scan. The subsequent phase focussed on virtual experiments to study the pseudo strain arising when measuring strain in an air-to-material interface, a material-to-material interface and when large grains or pores are present as in the vicinity of welds. The results presented are not intended to be used as a quantitative prediction of pseudo strain but to demonstrate how McStas can be used to model virtual experiments to study the pseudo strains occurring. Several virtual sample models have been built to demonstrate how this could be useful/interesting for beamline scientists and users of neutron diffraction. One such virtual sample model is used to demonstrate that the mitigation technique of rotating the sample 180° works when the detector is in transmission but not in reflection, and that it is strongly dependent on the attenuation of the investigated material. Another virtual sample model is used to demonstrate that when the ratio of a cavity (hole, pore, etc) to the gauge volume is more than 2%, then significant pseudo strains can arise. Moreover, this work delivers a new model for ENGINX.
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TL;DR: In this paper, the microstructure-mechanical response relationships in UNS N08825/AISI 316L welds were characterized by means of electron backscatter diffraction analysis.
Abstract: The aim of this work was to characterize the microstructure-mechanical response relationships in UNS N08825/AISI 316L welds by means of electron backscatter diffraction analysis. Welding was conducted by ERNiCrMo-3 and ER308L filler wires. It was indicated that a significant increase in fractions of low Σ coincidence site lattice (CSL) boundaries occurred in UNS N08825 heat-affected zones (HAZs), whereas a small number of the boundaries formed in the AISI 316L HAZs and weld zones were of low ΣCSL types. Abnormal grain growth took place in the HAZs leading to changes in the initial texture components of the alloys. It was also demonstrated that the type of the used filler wire was a factor influencing the microtexture components formed within the HAZs. According to the results of mechanical tests, the weldment employing the ERNiCrMo-3 filler wire exhibited superior hardness, tensile strength, and elongation. Moreover, the occurrence of the abnormal grain growth in UNS N08825 HAZs had no negative effects on the tensile response of the weldments as a result of the activation of texture strengthening mechanism. Based on the obtained results, the ERNiCrMo-3 filler metal was recommended to fabricate the joint.
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TL;DR: In this article, Alloy 52MSS was used in weld surfacing on A508 steel and the results showed that Nb concentrated in the interdendritic region, and Mo gathered around Nb-rich carbide grains.
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06 Mar 2023-Proceedings Of The Institution Of Mechanical Engineers, Part E: Journal Of Process Mechanical Engineering
TL;DR: In this article , the microstructure development and mechanical behavior of dissimilar metal welds between ferritic and austenitic steel, as well as their application in nuclear power plants, are discussed.
Abstract: The microstructure development and mechanical behaviour of dissimilar metal welds between ferritic and austenitic steel, as well as their application in nuclear power plants, are discussed in this review paper. Nuclear reactor components, such as steam generators and pressure vessels, consist primarily of SA508 due to their low cost and high operating temperatures and pressures. The welding of dissimilar metals is crucial due to variations in physical characteristics such as thermal conductivity, thermal expansion coefficient, mechanical properties and chemical compositions. The principal challenges of dissimilar ferritic and austenitic steel welding are the subject of this review work. Weldability issues include a sharp change in mechanical and metallurgical characterization across the fusion line, carbon migration, cyclic thermal stresses and residual stresses, which necessitate a thorough investigation of the welded joint. Generally, austenitic steel and nickel-based fillers are used to join austenitic and ferritic steel materials; however, owing to many weldability concerns, nickel-based consumables are replacing austenitic consumables. Another critical issue in the weld joint is the selection of appropriate welding consumables, and detailed explanations of the benefits of employing a buttering layer on the ferritic side are provided. The effect of heat treatment on the metallurgical and mechanical characteristics of the weld joint, as well as the formation of residual stress, has also been thoroughly explored.
1 citations
References
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01 Oct 1988
TL;DR: In this article, the importance of the Constitution diagram for the understanding of Welding Phenomena is discussed, and a detailed description of the Welding and post-weld surface treatment of Fabrications and Welded Components made from Austenitic Stainless Steels is given.
Abstract: Contents: Significance of Constitution Diagrams for the Understanding of Welding Phenomena * Metallurgical Processes During Solidification and Cooling in Stainless Steel Weld Metal * Metallurgical Phenomena in Secondary Crystallization of Stainless Steels and Weld Metals * Precipitation Phenomena in Stainless Steel and Weld Metals * Hot Cracking Resistance During the Welding of Austenitic Stainless Steels * Welding Metallurgy of Ferritic Stainless Chromium Steels with Carbon Contents Below 0.15 per cent * Welding Metallurgy of Low Carbon Chromium-Nickel Martensitic Stainless Steels (Soft Martensitic Steels) * Welding Metallurgy of Duplex Austenitic-Ferritic Stainless Steels * Welding Metallurgy of Austenitic Stainless Steels * General Instructions for the Welding and Post-Weld Surface Treatments of Fabrications and Welded Components Made from Austenitic Stainless Steel * Welding Metallurgy of Heat Resisting Steels * Welding Metallurgy of Austenitic-Ferritic Dissimilar Joints * Appendix: Abbreviations and Short Designations * References * Author Index * Subject Index.
394 citations
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TL;DR: In this article, a trimetallic joint involving modified 9Cr-1Mo steel and 316LN austenitic stainless steel as the base materials and Alloy 800 as the intermediate piece was investigated.
150 citations
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TL;DR: In this paper, a wide range of fundamental knowledge of solidification processes is applied to the study of fusion-weld solidification, including inoculants, stimulated surface nucleation, dynamic grain refinement, and arc modulation.
Abstract: To an increasing extent the wide range of fundamental knowledge of solidification processes is being applied to the study of fusion-weld solidification. Initially this fundamental knowledge is surveyed concisely and those areas of particular importance to weld-pool solidification are indentified. This is followed by an examination of phenomenological studies of the solidification behaviour of fusion welds in which particular attention is given to factors influencing the development of the fusion-zone structure. Then, the ways in which the metallurgical structure of the fusion zone influences the mechanical properties of the weldment are reviewed. Attention is then given to methods of controlling the fusion-zone structure by using inoculants, stimulated surface nucleation, dynamic grain refinement, and arc modulation. The gains and advantages which accrue from the way in which structure control affects properties are then considered. The review concludes with a discussion of likely future developme...
119 citations
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TL;DR: In this paper, a ternary system composed of a pure iron substrate and a 70Ni-30Cu filler metal was used to determine the nature and evolution of boundaries and structure in dissimilar metal welds.
Abstract: Cracking, or disbonding, along the fusion boundary in dissimilar metal welds has been a persistent problem, particularly in applications where austenitic alloys are clad on to structural steels for corrosion protection. Many failures in dissimilar metal welds occur as a result of cracking along a boundary that runs parallel to the fusion boundary in the adjacent weld metal. A preliminary investigation was undertaken to determine the nature and evolution of boundaries and structure in dissimilar metal welds using a simple ternary system composed of a pure iron substrate and a 70Ni–30Cu (Monel) filler metal. Changes in base metal dilution were found to alter the evolution of boundaries and structures near the fusion boundary dramatically. Optical metallography and electron microanalysis reveal that the resulting weld microstructures and boundaries are similar to those observed in engineering materials used for cladding and corrosion resistant overlay. Transmission electron diffraction analysis revea...
63 citations
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TL;DR: In this article, a series of laser and gas tungsten arc welds traversing stainless steels of different chemical compositions has been studied, to elucidate the role of austenite or ferrite nucleation and cooling rate on solidification behaviour.
Abstract: A series of laser and gas tungsten arc welds traversing stainless steels of different chemical compositions has been studied, to elucidate the role of austenite or ferrite nucleation and cooling rate on solidification behaviour. It has been found that a steel with a high CrEQ/NiEQ ratio can be induced to solidify as metastable austenite by initiating the weld in a steel with a lower CrEQ/NiEQ ratio in which the thermodynamically stable solidification mode is austenitic. The austenite dendrites are then found to continue growth across the weld junction into the undiluted regions of the high CrEQ/NiEQ ratio material. By providing austenite particles in this way, nucleation is rendered unnecessary and it is found that solidification to metastable austenite can be induced at cooling rates significantly lower than previously encountered. The results of these and other experiments in which the welding speed was changed during the experiment are interpreted to yield new information about the mechanisms o...
37 citations