Creep and creep strain recovery of a spinel forming refractory castable - measurement and simulation

Behnam Akbari

Research output: ThesisDoctoral Thesis

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Abstract

Spinel forming (SF) and Pre-formed spinel (PS) castables are common materials in refractory linings of steel ladles in secondary steel metallurgy. In service, these materials are affected by thermo-mechanical stresses. At elevated temperatures, this leads to creep of the castables. For the optimum design of the lining, consideration of the creep behaviour is important. In the current study, the castables were characterized in dried and sintered state and compared in bulk and true density, apparent and true porosity, Young’s modulus up to 1500 °C and uniaxial compressive creep behaviour. The microstructure of both castables was investigated using SEM, additionally, mineralogical phases were analysed with XRD. For further investigation, only the SF castable was selected. During the sintering process, the SF castable showed volume expansion and formation of liquid phases. The liquid phase partially counterbalanced the volume expansion caused by the in-situ spinel formation. However, it was observed that the liquid phase formation decreases the castables Young’s modulus at high temperatures and reduces the creep resistance. Uniaxial compressive creep tests were performed at 1300, 1400, and 1500 °C for three loads per temperature. The separation of creep stages was performed with an in-house developed MATLAB code and the three-stage creep parameters were inversely evaluated using the Norton-Baily creep equation. Additionally, a statistical study was carried out to evaluate the creep parameters by different combinations of measurements. Furthermore, the material’s creep behaviour was investigated under loading/unloading (l/u) conditions. For this purpose, the experiments have been performed at 1300 °C under different loads. After defined periods, the load was reduced. In this way, several cycles were performed. It was observed that creep strain recovery occurs after load reduction. The recovery increases with holding time and the degree of unloading. It was identified that the internal stress (back-stress) was the driving force for the creep strain recovery. Finally, a non-linear kinematic hardening model (Chaboche) was applied to simulate the creep strain recovery behaviour. The model fits the experimentally observed creep strain for different creep periods and unloading degrees with one parameter series. However, further work is necessary to automatize the parameter determination.
Translated title of the contributionKriechen und Kriechdehnungsserholung einer spinellbildenden feuerfesten Gießmasse - Messung und Simulation
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Gruber, Dietmar, Supervisor (internal)
  • Christos Aneziris, Habil, Assessor A (external), External person
  • Harmuth, Harald, Assessor A (internal)
  • Bernhard, Christian, Co-Supervisor (internal)
DOIs
Publication statusPublished - 2024

Bibliographical note

no embargo

Keywords

  • Refractory
  • Spinel-forming castable
  • Creep
  • Creep strain recovery

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