Research Of Hot-rolled Steel After Ultra-fast Cooling Process

In order to meet the requirements of performance and quality of the steel plate, TMCP technology has been widely used in hot-rolled steel production process, and achieved excellent results. However, for thick hot-rolled steel plate, the cooling rate of the central portion is much lower than that of the surface in the cooling process. The internal and external temperature difference along the steel plate thickness direction is bigger during the cooling process. Ultra-fast cooling technology is a new kind of controlled cooling technology, which can improve the cooling rate of the central portion of plate. Compared with the traditional laminar cooling, the cooling rate of ultra-fast cooling has a breakthrough improvement. For ultra-fast cooling process in multiple phases, simulation studies are launched in this paper, which develop for the actual production process parameters to provide theoretical guidance.First of all, mathematical model of the surface heat transfer coefficient is established. By using the discrete analysis method, surface heat transfer coefficient of the hot-rolled steel is solved in the ultra-fast cooling process, which is obtained as a boundary condition when simulates temperature field of hot-rolled steel with a computer.Secondly, for the plate thickness of less than 40 mm, this paper mainly studies the ultra-fast cooling and slow cooling process of the 20 mm and 30 mm steel after rolling respectively. It analysis the characteristics of temperature distribution and the variation of steel cooling rate in this process, which includes the surface, the center and the fourth position from the surface. It concludes that steel can obtain the expected ideal organization by properly extending ultra-fast cooling time.Finally, for the plate thickness of greater than 40 mm, this paper mainly studies temperature distribution of the 50 mm steel in ultra-fast cooling process after rolling. In order to increase the cooling rate of the central portion of plate, and to obtain the expected ideal organization, the segmented secondary ultra-fast cooling process is adopted in this paper. For thick steel plate, the puzzle of internal cooling difficulty is effectively settled through reasonably allocating the time of water cooling and air cooling. At the same time, each section layer of steel plate meets the requirements, which supercooled austenite transforms to pearlite absolutely, to provide a theoretical and pratical basis for the ultra-fast cooling technology in the thick steel plate production process.