Publicação: ADDITION OF COBALT IN DUPLEX STEEL FUSION ZONE WELDED WITH PULSED Nd:YAG LASER
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Super duplex stainless steels (SDSS) have a two-phase microstructure, with approximately equal volumetric fractions of ferrite and austenite, giving them excellent mechanical properties and high corrosion resistance. The problem in laser welding of SDSS is to obtain the fusion zone with a balanced microstructure, ensuring their properties and applications. In general, when SDSS is welded with processes involving high cooling rates, as laser welding, a mostly ferritic microstructure is obtained. To balance the microstructure, addition of austenite stabilizing elements or heat treatments are indicated. The Watts bath is one of the most used processes for cobalt electrodeposition, because it is considered an economical and efficient process. Given the importance of phase balance to maintain the properties and applications of SDSS, and considering the suitability of the Watts Bath for the formation of an electrodeposited cobalt layer, the present research studied the use of the Watts bath as a way to promote cobalt enrichment in a UNS S32750 joint welded by pulsed Nd:YAG laser process and, consequently, form a microstructure with approximately equal volumetric fractions of ferrite and austenite. Butt joint faces of UNS S32750 stainless steel were submitted to the Watts bath for different times, forming electro-deposited cobalt layers with different thickness. These joints were welded using a pulsed Nd:YAG laser. The microstructural characterization of the weld beads was carried out by means of LM, SEM and EDS, as well as XRD and the volumetric fractions were obtained with the aid of an Image analysis software and computerized volume fraction computation. The results showed that addition of cobalt in the fusion zone was efficient to avoid the undesirable unbalanced microstructure resulting from Nd:YAG laser welding of the SDSS as the volumetric fractions of austenite increased.
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COBALT ADDITION, DUPLEX STAINLESS STEEL, MICROSTRUCTURE, ND:YAG PULSED LASER WELDING
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Inglês
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ESSC and DUPLEX 2022 - 11th European Stainless Steel Conference - Science and Market and 7th European Duplex Stainless Steel Conference and Exhibition.
