Evaluation of Cooling Performance in Intensive Cooling with High Water Flow Rate and Effect of Controlled Rolling Just after Cooling on Mechanical Properties

摘要

Laboratory tests were conducted in order to quantify the cooling performance of intensive inter-pass water cooling, which was introduced as an effective method for increasing productivity of high strength steel plates. The range of flow rates was extended to 0.17-0.39 m~3/m~2 s. Pipe nozzles with inner diameters of 3 mm or 6 mm were used in addition to the original hole-type nozzle. The effects of the type of nozzle, the density of the nozzles and the injection distance on cooling performance were investigated. In tests with the φ6 pipe nozzles, temperature drop in the specimens increased with higher water flow rates. The upper limit of cooling performance was found to be around 0.25 m~3/m~2 s in top side cooling, whereas an upper limit was not seen in bottom side cooling. In tests with the φ3 hole nozzles, temperature drop decreased with longer injection distance, and that tendency is larger in bottom side cooling. A nozzle arrangement with a shorter installation pitch results in higher cooling performance. The effect of the inner diameter of the pipe nozzles on cooling performance is small. After water cooling, controlled rolling of specimens of Si-Mn-C steel, which is used widely as a high tensile steel, was performed with a laboratory mill. As results, it was found that total rolling time can be reduced with inter-pass water cooling, and water cooling does not affect the microstructure or mechanical properties. Intensive inter-pass cooling, which has high cooling performance, has the potential to realize efficient production of high-strength steels in controlled rolling.