Austenite Formation in Low Carbon Microalloyed Pipeline Steels

  • Author / Creator
    Hintze Cesaro, Alejandro
  • A study of the kinetic and microstructural aspects of austenite formation in
    low carbon pipeline steels during continuous heating and a model capable to
    predict the interface velocity are presented in this study. The overall goal of
    this work is to increase the level of understanding concerning the austenite
    reversion in low carbon pipeline steels. This work builds on top of the theory
    of solute drag and a Gibbs energy balance approach, and expands this theory
    to account for the effect of Mn redistribution at slow heating rates.
    Due to the unique characteristics of commercial pipeline steels, given by
    a refined chemical composition and tailored steel processing conditions, the
    initial microstructure previous to the austenite transformation was carefully
    studied to ponder all the relevant transformation conditions during continuous heating. Dilatometry experiments were employed to construct a continuous heating transformation (CHT) diagrams and study the kinetics and
    microstructural aspects of two commercial X80 pipeline steels.
    Experimental results suggested that orthoequilibrium calculations are
    poor predictor of the transformation temperatures and that the mechanisms
    controlling the transformation kinetics are susceptible to the heating rate. To
    obtain a better understanding of the transformation kinetics, a Gibbs free
    energy balance across the interface was employed to calculate the boundary
    migration rate as a function of the available driving force. This energetic approach was supported by an original methodology to calculate the chemical
    driving force under paraequilibrium conditions coupled with a modification
    of the solute drag model. The calculation was applied for continuous heating
    transformation at 1 ◦C/s and 200 ◦C/s.
    The results of this work serve to bring a deeper understanding on how
    austenite is formed during continuous heating. In particular to highlight the
    differences between slow (conventional heat treatments) and fast (welding)
    heating rates.

  • Subjects / Keywords
  • Graduation date
    Fall 2022
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Library 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.