Modeling of the Effect of Run-out Table Cooling on the Microstructure of a Thick Walled X70 Skelp

• Author / Creator

  Van Der Laan, Antoine

• This thesis presents work performed to model and measure the effect of run-out table cooling on a thick walled X70 steel. During run-out table cooling, the steel undergoes several phase transformations that will affect its microstructure, and thus, its mechanical properties. To predict the steel microstructure at the end of the run-out table, three different models were developed. The thermal model based on a previous finite element thermal analysis, predicts the temperature history of a thick walled X70 skelp through the run-out table. The validation of the model was done by measuring the coiling interrupt temperature at the surface of the skelp at the end of the run-out table. To model the phase transformation during run-out table cooling, the microstructure of different steels was predicted for constant cooling rate transformation. This metallurgical model proposed a new approach to process dilation curves in order to predict the evolution of the fraction of austenite transformed during continuous cooling. With this technique, the transformation of austenite into ferrite and bainite was considered simultaneous and not sequential, as it is commonly done in the literature, and improved CCT diagrams were built. The model gave a good approximation of the volume fractions, but the results needs to be confirmed through a thorough microstructure analysis. The thermal and metallurgical model were then combined in order to predict the evolution of the volume fractions during run-out table cooling. This thermo-metallurgical model was validated by a microstructure analysis of an X70 pipe sample produced in the run-out table. The model was able to accurately predict the microstructure at the centerline and quarter of the skelp, but cannot be used at the surface due to too high cooling rates. The model was also extended to other steels and run-out table configurations, which showed promising results.

• Subjects / Keywords

  • Ferrite
  • Skelp
  • Bainite
  • Steel
  • Centerline
  • Models
  • Volume fraction
  • Runout table
  • Cooling
  • Phase transformation
  • X70
  • Run-out table
  • Micro-structure
  • Dilation
  • Austenite
  • Modelling

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3668907X

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.