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 , the effect of corrosion testing at supercritical water conditions on mechanical properties of Inconel 625 base material (BM) and weldments was investigated using an autoclave at 575°C (848.15 K) and 23.5 MPa for 500 h (1.8 × 106 s).
Abstract:
Inconel 625 is considered one of the candidate materials for fuel cladding in the Canadian supercritical water reactor. Gas tungsten arc welding (GTAW) is being evaluated as a joining technique for SCWR fuel cladding since this method is widely used to join components in the power and nuclear industry. The thermal cycle, during the GTAW process, produces different types of microstructures that affect the material's mechanical properties. The objective of this work was to study the effect of corrosion testing at supercritical water conditions on mechanical properties of Inconel 625 base material (BM) and weldments. Tubular Inconel 625 specimens were welded using a GTAW orbital process. Corrosion testing was conducted in an autoclave at 575 °C (848.15 K) and 23.5 MPa for 500 h (1.8 × 106 s). Weld characterization included mechanical tests, optical microscopy, and scanning electron microscopy-energy dispersive X-ray spectroscopy. The composition of second phase precipitates observed during microstructural characterization was elucidated using equilibrium phase diagrams. Tensile tests showed that both BM and welds displayed an increase in strength and a decrease in ductility after corrosion testing. The ultimate tensile strength increased about 2% and 9% for the BM and the weldment, respectively. The maximum specimen elongation decreased around 35% for the BM and 45% for the weldment. The microstructure showed indications of second phase precipitation and grain morphology changes produced by both welding and corrosion processes. Results show that ductility of Inconel 625 GTAW welds is significantly reduced after exposure to supercritical water for 500 h (1.8 × 106 s).
1 citations
15 Sep 2016
TL;DR: In this article, microstructural features and mechanical properties of Incoloy 825-316L stainless steel dissimilar joints have been investigated using pulsed gas tungsten arc welding method.
Abstract: In this study, microstructural features and mechanical properties of Incoloy 825-316L stainless steel dissimilar joints have been investigated. For this purpose, pulsed gas tungsten arc welding method was employed and 316L, Inconel 82 and Inconel 625 alloys were used as filler metal. First, specimens were cut. Pulsed gas tungsten arc welding was performed using peak and base currents of 220 A and 110 A, respectively. Microstructure of welded joints was studied using metallographic observations and energy dispersive spectroscopy (EDS) analysis. In order to evaluate the mechanical properties, tensile and microhardness measurements were done on the joints. In all specimens, dendritic and equiaxed and/or cellular growth of austenite phase was observed. Incoloy 625 weld metal had the finest dendritic structure. Tensile test results revealed the ductile fracture with a high percent of elongation for all specimens. The highest tensile strength and percent of elongation of 610 MPa and 48% were obtained for specimen welded using Inconel 625 filler metal. Inconel 625 and 316 stainless steel weld metals showed the highest and lowest microhardness with values of 232 HV and 224 HV, respectively.
1 citations
TL;DR: In this article, the effect of post weld heat treatment on microstructures, tensile and corrosion properties of Inconel601 weld seam was investigated and the results indicated that the microstructure of weld metal consisted of coarser columnar grains with (Nb, Ti)-rich precipitations and laves phase distributed in them.
Abstract: The effect of post weld heat treatment on microstructures, tensile and corrosion properties of Inconel601 weld seam was investigated. The results indicated that the microstructure of weld metal consisted of coarser columnar grains with (Nb, Ti)-rich precipitations and laves phase distributed in them. Tensile and corrosion test displayed that the weld seam without any heat treatment exhibit the lowest mechanical and corrosion properties. Solution treatment at 1050°C was found to result in the considerable refinement of grain size and finally the improvement of mechanical and corrosion properties. It was also found that the specimens had the best mechanical and corrosion properties after heat treatment at 1150°C. However, with the treatment temperature increasing to 1200°C, the grain began to grow up, leading to the decrease of tensile strength and corrosion resistance.
1 citations
TL;DR: In this paper, the microstructural features and mechanical properties of dissimilar joints between Hastelloy C276 and AISI 316L by gas tungsten arc welding were characterized.
Abstract: In this study, the microstructural features and mechanical properties of dissimilar joints between Hastelloy C276 and AISI 316L by gas tungsten arc welding were characterized. ERNiCrMo-4, ...
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31 Oct 2016
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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