After quenching and treated by a controlled cooling system, the yield strength and tensile strength of the steel plate are improved, while the plasticity and toughness remain unchanged or slightly decrease. For instance, the ferrite and pearlite type steel Q345E, after normalizing and controlled cooling, shows a tensile strength increase of 30 to 50 MPa and a yield strength increase of 20 to 35 MPa compared to the conventional normalizing process. There is a slight decrease in toughness and plasticity, resulting in an overall improved performance, which provides a favorable condition for reducing the alloy content of normalized steel plates. The低碳bainite type Q460E steel plate, after normalization and controlled cooling, achieves a yield strength of 420 to 460 MPa and a tensile strength of 570 to 620 MPa, with a strength ratio of 0.7 to 0.75, elongation of 25% to 30%, and Z-directional reduction of area of 40% to 60%. This system is applied in the 4200 rolling mill's heat treatment line at Wuyang Iron and Steel Co., Ltd., and the production of 110mm steel plates using this system has been successfully applied to the "Bird's Nest" project for the Beijing Olympics main venue. At a medium plate factory, the product pass rate was approximately 82% to 88% when using conventional normalizing for heat treatment, but after the controlled cooling system was introduced, the pass rate increased to over 96%. The controlled cooling system after the normalizing furnace is of great significance in enhancing the performance of medium and thick plates and improving product quality, with broad application prospects. It can produce ship plate steel, container steel, bridge steel, boiler steel, low-alloy high-strength steel, construction structural steel plates, shipbuilding and offshore platform steel plates, etc. As the steel plate head passes through the temperature measuring instrument installed at the entrance, the process computer of the controlled cooling system dynamically sets and calculates based on the measured initial cooling temperature of the steel plate and the actual data transmitted from the second-level server of the normalizing furnace. After the steel plate exits the controlled cooling system and passes through the temperature measuring instruments installed at the exit and later positions, the process computer records the actual values such as the cooling water volume, steel plate speed, operating mode, final cooling temperature, and reheat temperature, and uses these actual values for model self-learning. The coefficients of the self-learned model are then applied to the setting calculation for the next steel plate of the same specification and steel type.
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