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A New Approach to the Study of Multi-Pass Welds–Microstructure and Properties of Welded 20-mm-Thick Superduplex Stainless Steel
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0003-3374-6282
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0002-0234-3168
Outokumpu Stainless AB, Avesta R&D Center, 774 41 Avesta, Sweden.
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0001-8822-2705
2019 (English)In: Applied Sciences, ISSN 2076-3417, Vol. 9, no 6, article id 1050Article in journal (Refereed) Published
Abstract [en]

Type 2507 superduplex stainless steel 20 mm in thickness was multi-pass-welded with Gas Metal Arc Welding (GMAW) and Flux-Cored Arc Welding (FCAW) processes. Recommended and higher arc energies and inter-pass temperatures were used. Thermal cycles were monitored using a recently developed procedure involving the successive instrumentation of the multi-pass welds, pass by pass, by addition of thermocouples in each weld pass. The repeatability of temperature measurements and survival rate of more than 90% of thermocouples confirmed the reliability of the procedure. Reheating by subsequent passes caused a progressive increase in the austenite content of the weld metal. The as-deposited GMAW passes with higher-than-recommended arc energy showed the lowest presence of nitrides. Therefore, the cooling rate—and not the time exposed at the critical temperature range—seems to be the key factor for nitride formation. The welding sequence layout also plays an important role in the distribution of secondary phases. A larger amount and concentration of secondary austenite and σ-phase was found for a larger number of subsequent passes in the immediate vicinity of a specific weld pass. The impact toughness exceeded requirements for all welds. Differences in absorbed energies were related to the amount of micro-inclusions found with the FCAW weld showing the lowest absorbed energies and highest amount of micro-inclusions. Pitting corrosion preferentially initiated in locations with secondary austenite and σ-phase. However, in the absence of these secondary phases, the HAZ containing nitrides was the weakest location where pitting initiated. The results of this work have implications on practical welding for superduplex stainless steels: the current recommendations on maximum arc energy should be revised for large thickness weldments, and the importance of the welding sequence layout on the formation of secondary phases should be considered.

Place, publisher, year, edition, pages
MDPI, 2019. Vol. 9, no 6, article id 1050
Keywords [en]
multi-pass welding, nitrides, secondary austenite, superduplex stainless steel, thermal cycles, welding, sigma-phase
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-13730DOI: 10.3390/app9061050ISI: 000465017200015OAI: oai:DiVA.org:hv-13730DiVA, id: diva2:1297743
Funder
Knowledge Foundation, 20140046Available from: 2019-03-20 Created: 2019-03-20 Last updated: 2019-05-16

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Valiente Bermejo, María AsunciónHurtig, KjellKarlsson, Leif

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