Abkühlung von Stahl mit erhöhten Spurenelementgehalten unter Wasserdampf und Untersuchung der Auswirkung auf die Rissbildung im IMC-Biegeversuch

Translated title of the contribution: Cooling of steel with increased trace element contents under water vapour and investigation of the surface crack formation by IMC bending test

Christoph Lex

Research output: ThesisMaster's Thesis

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Abstract

An increased content of tramp elements like copper, tin and nickel in steel will in the future result from infiltrating the continuously growing use of steel scrap as raw material for steel production due to the ongoing decarbonization of steel production routes. Their removal from the melt is impeded by their low oxygen affinity and low vapour pressure. When cast in the continuous casting process, an enrichment of those tramp elements at the strand surface takes place due to the selective oxidation of iron, whereby low-melting copper phases can be formed at the strand surface and subsequently penetrate austenite grain boundaries, resulting in potential deterioration of the slabs surface quality. This master thesis studies the effects various tramp element contents exhibit on the intergranular fracture of in-situ cast steel samples and their possible cause. The “in-situ material characterization − bending” or IMC−B experiment, developed at the Chair of ferrous-metallurgy at Montanuniversitaet Leoben, was applied to do so. A total of 19 IMC−B samples representing various tramp element contents were examined at two different bending temperatures (900 °C and 1100 °C). Throughout this thesis, the IMC−B experiment was enhanced to conduct the cooling stage under a water vapour-rich atmosphere similar to the prevailing atmosphere in the secondary cooling zone of a continuous casting machine. The tendency of crack formation, assessed by the value of critical strain, exhibits a negative linear relationship to the tramp element content described by an equivalent measure, only if Cu and Sn are both present. When bending is carried out at a temperature of 1100 °C, a considerably higher critical strain is achieved, than at 900 °C bending for the same copper equivalent value. Further investigations of the steel−scale interface by scanning electron microscope reveal the existence of low-melting copper-rich phases, either occluded in the scale, as well as along the austenite grain boundaries. The present findings of this thesis suggest that liquid metal embrittlement LME is a plausible reason for the loss of hot ductility at the surface of tramp element contaminated IMC−B samples, for 900 °C and 1100 °C bending.
Translated title of the contributionCooling of steel with increased trace element contents under water vapour and investigation of the surface crack formation by IMC bending test
Original languageGerman
QualificationDipl.-Ing.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Bernhard, Christian, Supervisor (internal)
Award date15 Dec 2023
DOIs
Publication statusPublished - 2023

Bibliographical note

no embargo

Keywords

  • Tramp Elements
  • Liquid Metal Embrittlement
  • IMC-bending test
  • Surface Crack Formation

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