Modeling of Heat Transfer and Phase Transformation Phenomena During Runout Table Cooling

摘要

Run-out-table laminar cooling is one of the key metallurgical components at many modern steel hot rolling mills. Optimization of laminar cooling is essential for achieving the desired microstructure and mechanical properties of hot rolled steel products. At SSAB Iowa, a Steckel mill with a run-out-table laminar cooling system is used to produce both strip and plate products. The mill is capable of manufacturing strip products as thin as 0.126" and plate products as thick as 3". The mill produces wide strip/plate products for some key market segments, such as bridge, shipbuilding, tanks, construction machinery and wind energy. A large number of these products are produced through thermo-mechanical controlled processing (TMCP), which often employs on-line accelerated cooling. The run-out-table laminar cooling system at the Iowa mill has a total of 9 cooling banks on the top and bottom and 11 side-sprays, as shown in Figure 1. Each top bank consists of 4 headers and each bottom bank consists of 10 headers. Most of the headers can be controlled individually on/off, but the water flow rate is fixed. Therefore, it is very important to have an optimized header selection and top/bottom header ratio to achieve a specific cooling strategy. Although this could be done by trial and error, a reliable mathematical model would be beneficial for reducing the cost of mill trials and accelerating product development. This paper presents the development of a mathematical model, incorporating both heat transfer and phase transformation for the run-out-table laminar cooling at the Iowa mill. The model was validated by comparing the predicted finish cooling temperatures and microstructures with the temperatures measured by in-line pyrometers and microstructures from metallography performed on as-rolled products.