Niloy Kumar Nath

Abstract:

Reheating of steel ingots in batch furnace such as soaking pit and box furnace, and Concast steel products like bar, billets and slabs in continuous furnace such as walking beam, and pusher type furnace is an important step for further thermo-mechanical processing like forging and rolling operations.  Concast Steel and ingots are heated up to 1100 – 1250 C, and since this is a high temperature and energy intensive process, excess heating time will cause productivity and energy loss, as well as oxidation or scale loss. On the other hand, if it is heated very fast causing high thermal variation between the surface and core temperature, will lead to thermal stress, distortion and crack formation. Furthermore, rapid heating without thermal homogenization can cause problems during hot rolling or forging operations, which may lead to, roll stuck, cracking and forging problems. Therefore, the aim of the heating process is to avoid any excessive thermal stress, particularly in the vulnerable ferrite to austenite phase transformation range, and also to achieve thermal homogenization with optimum time and energy efficiency.

To numerically simulate the process, a detailed two dimensional finite difference model is developed by using generalized axisymmetric equation, and Crank-Nicholson technique. To accurately simulate the process. The model also has to consider all the complexities of the process like anomalous behaviour of thermal conductivity of steel and latent heat of phase transformation. The model has been validated with limited number of Lab-experiments in a muffle furnace. Model based Process Control system have been developed for both batch and continuous reheating process, with Graphical User Interface (GUI) for plant application.