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The Hyper Duplex Stainless Steel HDSS enhanced corrosion resistance and toughness relies upon high alloying to obtain a balanced ferrite and austenite volume and pitting resistance equivalent number PREn. However, during welding, sigma phase precipitates might form, hindering corrosion and mechanical performance. Therefore, a kinetics model is developed to avoid the sigma phase's formation during welding and validated using physical simulation, finite element analysis (FEA), welding, and SEM characterisation. The sigma phase kinetics model produced calculated and validated temperature-time-transformation (TTT) and continuous-cooling-transformation (CCT) curves from which a 4°C/s cooling rate was found as a cooling rate threshold for sigma phase formation in this new material. Three-layered gas tungsten arc welding GTAW cladded mockup with 53 beads produced 24°C/s minimum cooling rate. Moreover, microscopy, mechanical, and corrosion testing attested it as a sigma-free weld.
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Effect of sigma phase on CVN impact toughness in HDSS weld metal
This work uses kinetics calculation and a thermomechanical physical simulator to evaluate the sigma phase precipitation in Hyper Duplex Stainless Steel (HDSS) as-welded microstructure for impact toughness evaluation. Precipitation bars were machined out of a HDSS deposited clad mockup and submitted through aging on the thermomechanical physical simulator. Bars with sigma phase volumes of 0 %, 0.16 %, 0.52 %, 0.9 % and 4.3 % were created and machined to sub-size CVN specimens. Through impact CVN testing, complete ductile-to-brittletransition- temperature (DBTT) curves were developed based on absorbed energy (kV), lateral expansion (LE), and shear fracture appearance (SFA) criteria for each sigma phase volume. It was seen that sigma phase presence provides drastic reduction on toughness the HDSS. The DBTT increased from −52.29oC to 38.32oC while the upper shelf energy (USE) is reduced from 68.85J to 11.66J with the increase sigma phase volume. Both the DBTT and USE presented a behavior well fitted through a sigmoidal curve. While very low sigma phase volumes caused little change on the DBTT and USE values, a saturation effect could be inferred on the USE at 4.3 % vol of sigma phase. CVN samples’ secondary cracks high-resolution images suggest that the ferrite and austenite arrest crack propagation while the brittle sigma grains, depending on size and orientation propagate the cracks.
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- PAR ID:
- 10591321
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Materials Science and Engineering: A
- Volume:
- 912
- Issue:
- C
- ISSN:
- 0921-5093
- Page Range / eLocation ID:
- 146948
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/J.MSEA.2024.146948
