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Coating weld cavitation erosion resistance using austenitic stainless steel and cobalt alloys deposited by GMAW and CW-GMAW

The repair processes more utilized in hydraulic turbines are welding, the Cold-Wire-Gas Metal Arc Welding (CW-GMAW) process, which adds a non-energized wire to the welding pool and presents an advantageous proposal to the conventional welding techniques. This work evaluates the coating weld cavitati...

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Bibliographic Details
Published in:Journal of the Brazilian Society of Mechanical Sciences and Engineering 2022-11, Vol.44 (11), Article 569
Main Authors: da Silva, Fabio Gonçalves, Braga, Eduardo M., Ferraresi, Valtair A., Ferreira Filho, Demostenes
Format: Article
Language:English
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Summary:The repair processes more utilized in hydraulic turbines are welding, the Cold-Wire-Gas Metal Arc Welding (CW-GMAW) process, which adds a non-energized wire to the welding pool and presents an advantageous proposal to the conventional welding techniques. This work evaluates the coating weld cavitation erosion resistance of the austenitic stainless steel (309LSi) and cobalt alloys (Stellites 21 (CoCrMo) and Stellite 6 alloys (CoCrW)) deposited by GMAW and CW-GMAW on a carbon steel substrate with one buttery layer 309LSi. Cavitation erosive laboratory tests were conducted according to the ASTM G32-92 standard. Wear evaluation was made via mass loss. Cavitation erosion resistance was correlated with the phase characterization analysis using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and chemical composition by optical emission spectrometry. It was found that the coatings presented good weldability, without discontinuities or defects, and had a good surface finish, indicating that the CW-GMAW process can reduce the cost of production. Austenitic alloys presented two phases, with the presence of ferrite spines or laths in the austenitic matrix. For the cobalt alloys, interdendritic and grain boundary carbides were founded in the dendrite form. The microhardness values were by the type of alloy used, with those of 309LSi with values close to or 200 HV, while for the Stellite 21 and Stellite 6 alloys these values reach approximately 300 HV and 350 HV, respectively. Cobalt alloys showed a decrease of approximately 90% of rates and accumulated mass losses with better cavitation resistance performance compared to 309LSi austenitic alloys. Aiming to reduce the cobalt content in the coating, the alloys manufactured using CW-GMAW with Stellite 21 and 309LSi (as cold wire) and with Stellite 6 and 309LSi (as cold wire) showed good cavitation resistance performance at similar levels of roughness and hardness when compared to Stellites 21 and Stellite 6 coatings manufactured using the conventional GMAW process. This research has great potential for turbine repairs and coating applications, and the novelty is the CW-GMAW process usage for development of formulation and deposition of new alloys from commercial wires relating the resistance to erosion by cavitation.
ISSN:1678-5878
1806-3691
DOI:10.1007/s40430-022-03845-9