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Journal ArticleDOI

Microstructural features of dissimilar welds between 316LN austenitic stainless steel and alloy 800

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.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a finite element method (FEM) based numerical simulation has been used to exactly evaluate the grain structure of a given asymmetric DMW component with specified scatterers.

3 citations

Dissertation
01 Aug 2017
TL;DR: In this paper, the effects of weld metals and long-period thermal aging in operating PWRs on the integrity of the fusion boundary were investigated by a program of microstructural characterization, mechanical evaluations, corrosion testing and crack growth rate measurements was performed.
Abstract: In the primary coolant system of the pressurized water reactor, austenitic Ni-base weld metals are deposited on low-alloy steel to form dissimilar metal weld joints. An example is the weld joint between head penetration nozzle (austenitic Ni-base alloy) and reactor pressure vessel (low-alloy steel). Leakage issues from Alloy 82/182 Ni-base weld metal have frequently been reported since 2000. In addition, the cumulative number of cracked welds increased with the operation time of the pressurized water reactors. Recently, the Ni-base weld metal was replaced from Alloy 82/182 (about 15 wt.% of Cr) into Alloy 52/152 (about 30 wt.% of Cr), and the incident of cracking in Alloy 52/152 has not been reported since the replacement. Recently, the cracks, which approach fusion boundary of Ni-base weld metal / lowalloy steel, were reported. To investigate the effects of (1) weld metals and (2) long-period thermal aging in operating PWRs on the integrity of the fusion boundary, a program of microstructural characterization, mechanical evaluations, corrosion testing and crack growth rate measurements was performed. Two different weld metals were compared: (a) Alloy 182, Ni-base weld metal, and (b) Alloy 152, Ni-base weld metal with a higher chromium content than the Alloy 182. The effect of thermal aging on microstructure evolution, mechanical property and resistances on corrosion and cracking was studied by applying heat treatments to the as-welded mock-up samples. Corrosion testing and crack growth rate measurements, in a simulated primary coolant environment of pressurized water reactors, were performed to rank the resistances to corrosion and cracking. Microstructural examination represents several M23C6 precipitates formed at the fusion boundary of Ni-base weld metal / low-alloy steel at the as-welded state because of the high solubility of C in the low-alloy steel. Nucleation and growth of the precipitates occurred with thermal aging heat treatments. Alloy 152, which has the higher Cr content compared to Alloy 182, had more Cr rich precipitates at the fusion boundary, compared to the one of Alloy 182. Based on the results of corrosion testing and crack growth rate measurements, the corrosion rates and crack growth rates were dependent on the number of the precipitates. The fusion boundary of the Alloy 152 / low-alloy steel is highly susceptible to cracking compared to the one of the Alloy 182 / low-alloy steel and can be weakened with thermal aging heat treatment. In addition, the fusion boundary showed lower resistance to cracking than Ni-base weld metals of Alloy 182 and Alloy 152.

3 citations

Journal ArticleDOI
TL;DR: In this article, a bead on plate welding of AISI 316L welded with continuous laser beam welding (LBW) was presented to find a process parameter for a full penetration weld bead profile; with less segregation effect.

3 citations

Journal ArticleDOI
TL;DR: In this article, the effect of two different filler metals (ERNiCr-3 and ER308) on microstructure and corrosion resistance of gas tungsten arc welded AISI 304 has been investigated.
Abstract: In this study, the effect of two different filler metals (ERNiCr-3 and ER308) on microstructure and corrosion resistance of gas tungsten arc welded AISI 304 has been investigated. The microstructure of the joints was investigated by optical and scanning electron microscope. The microhardness of samples was investigated to determine the mechanical properties of the welds. Also, the electrochemical corrosion resistance of the samples was studied by Tafel polarization and impedance analysis in 1 M hydrochloric acid. The results showed the niobium-rich carbides in the welded specimen by ERNiCr-3 filler, also this sample exhibited a higher hardness and corrosion resistance. The exchange current density and the polarization radius of the ERNiCr-3 filler metal were 0.069 mA and 244 Ω, and those of ER308 filler metal were 0.121 mA and 66 Ω, respectively. The higher hardness and corrosion resistance is attributed to the formation of hard niobium-rich carbides in the weld zone, which eliminates the formation of chromium carbides.

2 citations

References
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Book
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

Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
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