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 paper, microstructural variation across the dissimilar weld joint between modified 9Cr-1Mo ferritic steel and 316LN stainless steel with nickel-based filler metal was fabricated and analyzed.
Abstract: In this investigation, microstructural variation across the dissimilar weld joint between modified 9Cr-1Mo ferritic steel and 316LN stainless steel with nickel-based filler metal was fabricated and...
4 citations
TL;DR: In this paper, the microstructure evolution and microhardness changes in the heat-affected zone of the substrate and the cladding layer near the laser cladding interface were studied in detail by using optical microscopy, electron backscatter diffraction and micro-hardness tests.
Abstract: Laser hot wire cladding is an efficient and energy-saving additive manufacturing process, which is used in coating, repair, and 3D printing. In this study, 308L stainless steel wire was deposited on the low carbon steel substrate using Laser hot wire cladding technology. The microstructure evolution and microhardness changes in the heat-affected zone of the substrate and the cladding layer near the laser cladding interface were studied in detail by using optical microscopy, electron backscatter diffraction and microhardness tests. The phase transformations and the relationship between microstructure and mechanical properties of the cladding layer were discussed. Owing to the dual effect of temperature gradient and cooling rate, the grain morphology in the central region of the cladding layer is equiaxed, while the edge region is mostly columnar dendritic morphology along the structural direction. There is a dilution zone composed of single austenite near the interface of the cladding layer. In the cladding layer, the ferrite-austenite solidification mode is dominant, and the austenite-ferrite solidification mode is also found in local areas. The carbon migration process from the substrate to the cladding layer promotes the austenite-ferrite mode. The heat-affected zone microstructure consists mainly of ferrite and tempered bainite, and slatted martensite can be observed near the interface. The electron backscatter diffraction results demonstrate the existence of martensite in the heat-affected zone. The texture is more apparent in the cladding layer, while the heat-affected zone contains more residual strain and higher dislocation density. The average grain size in the heat-affected zone region is about 4 μm, while the average grain size in the cladding layer is above 14 μm. The hardness of the heat-affected zone near the interface is the highest due to numerous factors, such as grain size, microstructure transformation and dislocation density. The yield strength increases with the decrease of grain size and texture strength, demonstrating the correlation between microstructure and mechanical properties.
4 citations
TL;DR: In this paper, the precipitate evolution and its correlation with mechanical properties were investigated during post-weld heat treatment (PWHT) at 690 °C for up to 12h.
Abstract: A 16Cr-25Ni superaustenitic stainless steel weld metal for austenitic stainless steel/ferrite heat-resistance steel dissimilar metal weld was designed and prepared through tungsten inert-gas welding. The precipitate evolution and its correlation with mechanical properties were investigated during post-weld heat treatment (PWHT) at 690 °C for up to 12 h. The primary precipitates in the as-welded weld metal were identified as Mo-rich M6C carbides in the interdendritic region and semicontinuous fine-sized M23C6 carbides along grain boundary. After PWHT, three types of precipitates coexisted in the interdendritic region: primary M6C carbides, newly precipitated Mo-rich M2X carbonitrides and some of the secondary M23C6 carbides. Additionally, mass secondary M23C6 carbides formed and coarsened along grain boundary. No undesirable intermetallic phases formed during the whole period. The M2X and interdendritic M23C6 improved the strength of the weld metal after PWHT, but the elongation and impact toughness degraded, which were mainly owing to the intergranular M23C6 carbides that changed the fracture mode from ductile transgranular mode to mixed mode of transgranular and intergranular fracture. Meanwhile, the coarsening of M2X carbonitrides may lead to the elongation loss during 8 h to 12 h. Evolution of impact toughness was also related to the M2X carbonitrides, which made the crack easier to propagate compared with austenitic matrix and contributed to the decline of impact toughness. However, due to the sluggish precipitation of M2X carbonitrides with longer holding time, the decreasing trend became slow from 4 to 12 h. The results showed that PWHT should be controlled within 8 h to obtain better combination of strength and ductility.
4 citations
TL;DR: In this article, the microstructural growth and the effect of precipitation due to elemental variation across the fusion boundary is analyzed for PCGTA welding between two different metals using ERNiCrCoMo-1 (enriched Ni-CrMo-Mo) fillers.
4 citations
01 Jan 2014
TL;DR: In this paper, the authors present an acknowledgment of the authorship of the author's work........................................................................................................................................................ iii Acknowledgements and acknowledgements of the acknowledgements are given.
Abstract: ....................................................................................................................................................... iii Acknowledgements ...................................................................................................................................... iv
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Cites background from "Microstructural features of dissimi..."
...The unmixed zone (UZ) is a laminar region where some of the base metal has melted and re-solidified without undergoing filler metal dilution [2], [3], [4]....
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...The inclusions were also confirmed by Sireesha in [4]....
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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
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
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
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
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