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Varmduktilitet vid stränggjutning av duplexa rostfria stål
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2017 (Swedish)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Abstract

Hot ductility during continuous casting of duplex stainless steels

In the continuous casting of the duplex stainless steel, longitudinal corner cracks in the first casted bloom of SAF 2507 have been discovered by Sandvik. SAF 2205 contains the same alloying substances as SAF 2507, but with some difference in the concentration of the elements. Despite this similarity, the occurrence of corner cracks in SAF 2205 is minimal and thus is not considered to be a significant problem. The reason for the appearance of hot cracks in SAF 2507 may be due to reduced ductility and due to stress variations in the material that occurs during casting. An earlier research for mapping longitudinal corner cracks in SAF 2507 and SAF 2205 proved to occur due to thermal stresses created by shrinkage of the shell in the mold. A reduced ductility can be obtained by embrittlement of grain boundaries that may arise with a brittle phase. The high amount of alloy elements in duplex stainless steels can result in precipitation of intermetallic phase, which is a brittle phase. Through a mapping of microstructure of continuous casted SAF 2507 and SAF 2205, intermetallic phase was observed in samples from SAF 2507.In order to gain an understanding of the appearance of hot cracks in SAF 2507, in situ hot tensile tests were performed. The hot tensile tests were performed in order to compare and analyze the ductile behavior of SAF 2507 with SAF 2205. The purpose of the tensile tests was to simulate continuous casting process at Sandvik.The results from the tensile tests show that SAF 2507 and SAF 2205 are not sensitive to hot cracking at temperatures near solidus. However, intermetallic phases were found in SAF 2507 during hot tensile testing at 800 ° C. But no intermetallic phase could be found in SAF 2205. Temperature measurements and calculations by CFD during continuously casting of SAF 2507 showed that intermetallic phases could possibly precipitate in the mold. In a previous research done by Sandvik Materials Technology, shows how thermal stresses can occur on the corners of a cast inside the mold, during continuous casting of SAF 2205 and SAF 2507.The conclusion of this work is that longitudinal corner crackers in SAF 2507 can be initiated in the mold, because of a combination of thermal stresses and intermetallic phases.

Keywords ∙ Duplex rostfritt stålVarmsprickkänslighet SAF 2507 SAF 2205 Stränggjutning Duktilitet Sigma Kromnitrider

Place, publisher, year, edition, pages
2017. , p. 103
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-219751OAI: oai:DiVA.org:kth-219751DiVA, id: diva2:1164782
External cooperation
Sandvik Materials Technology
Educational program
Master of Science in Engineering - Materials Design and Engineering
Supervisors
Examiners
Available from: 2017-12-13 Created: 2017-12-12 Last updated: 2017-12-13Bibliographically approved

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