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Resistance Upset Welding of ODS Steel Fuel Claddings—Evaluation of a Process Parameter Range Based on Metallurgical Observations
Received: 18 July 2017 / Accepted: 8 August 2017 / Published: 29 August 2017
Resistance upset welding is successfully applied to Oxide Dispersion Strengthened (ODS) steel fuel cladding. Due to the strong correlation between the mechanical properties and the microstructure of the ODS steel, this study focuses on the consequences of the welding process on the metallurgical state of the PM2000 ODS steel. A range of process parameters is identified to achieve operative welding. Characterizations of the microstructure are correlated to measurements recorded during the welding process. The thinness of the clad is responsible for a thermal unbalance, leading to a higher temperature reached. Its deformation is important and may lead to a lack of joining between the faying surfaces located on the outer part of the join which can be avoided by increasing the dissipated energy or by limiting the clad stick-out. The deformation and the temperature reached trigger a recrystallization phenomenon in the welded area, usually combined with a modification of the yttrium dispersion, i.e., oxide dispersion, which can damage the long-life resistance of the fuel cladding. The process parameters are optimized to limit the deformation of the clad, preventing the compactness defect and the modification of the nanoscale oxide dispersion.
ODS steel; PM2000; oxide dispersion strengthened; welding; resistance welding; fuel cladding; sodium fast reactor; dynamical recrystallization
This work is part of PhD between the Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB) and the Commissariat à l’énergie atomique et aux énergies alternatives (CEA-Saclay). The PhD is part of a research program for materials suitable for Sodium Fast Reactor (SFR) financed by CEA, Areva NP (Areva Nuclear Power) and EDF (Électricité De France).
Fabien Corpace is the Ph.D. student. He wrote the paper, Arnaud Monnier, Jean-Pierre Manaud and Angeline Poulon-Quintin directed his work. Michel Lahaye performed the WDS experiments; Jacques Grall contributed to sample preparation.
Conflicts of Interest
The authors declare no conflict of interest.
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Pieces to be welded: end plug and clad.
Schematic scenario of the resistance upset welding steps.
Schematic view of the welding device (Fw = welding force; Iw: welding current intensity; 1: end plug; 2: clad; 3: pneumatic jack; 4 and 5: electrodes).
Wavelength-dispersive spectroscopy (WDS) analysis of a welded zone with (Fw; Iw; tw; Cs) = (1800 N; 14 kA; 15 ms; 0.8 mm): (a) Back Scattering Electron (BSE) picture; (b) Corresponding yttrium distribution.
Evidence of the material deformation with the selected parameters (Fw; Iw; tw; Cs) = (2600 N; 14 kA; 10 ms; 0.8 mm).
Collapse value as a function of the dissipated energy for 32 experiments.
Example of a lack of joining (Mirror polish without etching) for a sample welded with the selected parameters (Fw; Iw; tw; Cs) = (2600 N; 14 kA; 10 ms; 0.8 mm).
Not welded length as a function of the dissipated energy for 32 experiments.
Evidence of modification of the metallurgical state of the sample welded using the parameters (Fw; Iw; tw; Cs) = (2600 N; 18 kA; 10 ms; 0.8 mm). (a) Optical micrograph of an etched sample; (b) WDS Yttrium distribution.
Yttrium modification (arbitrary unit defined in Table 3
) as a function of collapse value.
Range of the allowable dissipated energy to achieve welds with no lack of joining and no yttrium modifications (Cs = 0.2 mm).
WDS yttrium distribution for a weld within the working area with the selected parameters (Fw; Iw; tw; Cs) = (2400 N; 14 kA; 15 ms; 0.2 mm).
PM2000 nominal composition (wt %).
Process parameter range.
|Iw||Current intensity (kA)||14||18|
|tw||Welding time (ms)||10||15|
|Cs||Clad stick-out (mm)||0.2||0.8|
Classification used for the yttrium distribution modification.
|Arbitrary Unit||Shape and Extent|
|0||No yttrium modifications|
|1||Modification localised in the outer part of the joint with possible extension to the outer upset|
|2||Modification in the clad near the electrode piece contact|
|3||2 + spreading to the interface|
|4||3 + spreading through the interface to the inner upset|
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