Open Collections

Sztanko, Matthew

University of British Columbia

High performance steels are increasingly in demand to meet societal challenges in a wide range of sectors including transportation, energy, and construction. As a result, thermo-mechanically controlled processing (TMCP) including accelerated cooling (ACC) of hot rolled steel sheets and plates has become a key technology to reach the required performance criteria. The phase transformations that occur during ACC are the primary metallurgical mechanisms that can be optimized to tailor the mechanical properties of the steels. An important additional aim of ACC is to obtain the desired performance criteria by reducing the alloying content of the steels, thereby decreasing cost and demands on natural resources. Thus, the focus of this study is to develop a new generation of process models to accurately predict the evolution of these phase transformations and the resulting mechanical properties. In this work, the phase transformations of two low carbon microalloyed steels were studied with continuous cooling tests in a Gleeble 3500 thermomechanical process simulator. Various thermal paths were investigated to determine the effect different processing parameters have on austenite decomposition. These include prior austenite grain size’s (PAGS) of 10 and 40μm, cooling rates of 3, 10, and 30°C/s, and retained strains of 0.2 and 0.4. The resulting microstructures were characterized using optical microscopy and electron backscattered diffraction (EBSD). The mechanical properties were studied using Vickers hardness. It was observed that an increase in PAGS and cooling rate and decrease in retained strain resulted in lower transformation temperatures. For PAGS of 10μm, the microstructure ranged from ferrite-pearlite to a refined irregular ferrite or bainitic microstructure. A mixed ferrite-bainite to fully bainitic structure was seen for PAGS of 40μm. As cooling rate increases and transformation temperature decreased, an increase in Vickers hardness was measured. Based on these experimental studies, a phase transformation model has been applied for the investigated steels that can be incorporated into a process model for ACC on a runout table in a hot strip mill.

Text

2024-04-19

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87892

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/