Experiment Research Of Physical Simulation On Internal Defect Closing Of Ultra-Heavy Plate Rolling Process And Application

Under the background of taking saving resources as the basic national policy, iron and steel industry in China prevalently requires optimizing structure, improving production efficiency and reducing consumption. Therefore, more and more iron and steel enterprises pay attention to the defect closing to improve production efficiency.This dissertation is combined with the project of "Research on Reduced Rolling Process of High Toughness Low Alloy Heavy Plate", which is supported by a research and development center of wide and heavy steel plate. Laboratory physical simulation of critical condition of internal defect closing of the new developed400mm ultra-heavy continuous cast slab is carried out, and the results have been used as the basis of improving inspection pass rate on-site. Via industrial test, three specifications of hot rolled ultra-heavy plate are developed. They are120mm Q390C with CR+ACC process,160mm non-microalloyed Q235B with RCR+ACC process and190mm Q345C with RCR+ACC process respectively. The matching of strength and toughness of these steels is very good, and their inspection pass rate and are improved greatly.The major achievements of the paper in theory and practice include:(1) Taking Q345steel as the research object, the influence of deforming temperature, deforming degree and deforming rate on deformation resistance of the steel is researched by single pass compression. Activation energy Q=272.32KJ/mol and critical true strain εc=2.9978×10-3Z0.1661of dynamic recrystallization are obtained. The processing map of Q345is also established. In the processing map, the optimized deformation parameters (strain, strain rate and deformation temperature) for hot rolling are given and the instable regions un-suitable for hot rolling are also pointed out. This work provides a theoretical basis for making a reasonable rolling processing.(2) Taking Q235steel as the research object, in order to meet the conditions of defect closing, the rolling process parameters are controlled. Experiment results show that with the increases of rough rolling reduction ratio and compression ratio, the segregation is eliminated better, and Z-direction property is improved. When the compression ratio is greater than2.3, the internal defects can be closed and the result of ultrasonic inspection can satisfy standard requirement with critical reduction by13.9%. The detection test can be used in verifying the critical condition of defect closing and providing a test basis for improving inspection pass rate and quality of production on-site.(3) The industrial production experiments of high strength and low alloy heavy plate are tested by using expanded double stand production line and new developed400mm ultra-heavy continuous cast of one domestic wide and heavy steel plate factory. The goal of rolling of400mm ultra-heavy continuous cast to obtain low-alloy ultra-heavy plates is fulfilled, and the mechanical properties of all plates reach requirements of GB/T1591-2008standard for Q235, Q345, Q390.