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UBC Theses and Dissertations

Characterization of the cooling and transformation of steels on a run-out table of hot-strip mill McCulloch, Craig Allen


A mathematical model has been developed to predict the thermal history of strip during cooling on the run-out table of a hot strip mill. The model incorporates phase transformation kinetics and accounts for the heat of transformation. To characterize the cooling by laminar water sprays, in-plant trials were conducted at the Stelco Lake Erie Works hot strip mill. The temperature data was used in the thermal model to calculate an overall heat transfer coefficient for a laminar water bank of 1 kW/m²°C. Isothermal diametral dilatometer testing was used to generate phase transformation kinetics for a 0.34 weight percent plain carbon steel. Continuous cooling dilatometer testing was used to calculate the transformation start time as a function of the cooling rate. The high cooling rates of 40 °C/s to 50°C/s, experienced on the run-out table had the effect of depressing the transformation start temperature by over 100°C. The phase transformation kinetics were incorporated in a phase transformation model and employed to predict thermal profiles for a 0.34 carbon plain-carbon steel. The temperature predictions were within 25"C of the plant pyrometer readings using the calculated overall heat transfer coefficient and within 35°C of the plant pyrometer values using literature derived heat transfer coefficients. A simulation of the model predicted cooling conditions on a Gleeble high temperature testing machine showed that the transformation was occurring at approximately 730°C. The empirical transformation start time, obtained from cooling rate versus transformation start time tests, which was used in the phase transformation portion of the model, and the Gleeble simulation gave excellent agreement with the model thermal profile predictions.

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