THE EFFECT OF BOUNDARY CONDITIONS OF CASTING ON THE SIZE OF MACROSEGREGATION IN HEAVY STEEL INGOTS

The paper builds on the previous work of authors devoted to the verification of casting technology of 90-ton heavy steel ingot using numerical modelling and operational experiment. Numerical modelling was performed with use of the ProCAST software. In the first stage of an extensive modelling research, the conditions of heat transfer used in the setting of calculation of casting and solidification were modified based on experimental thermography measurement. Thermodynamic properties of steel were also verified. The results of numerical modelling of macrosegregation in ingot under standard conditions of casting were continuously compared with the results obtained from the analysis of experimentally-cast ingot. Once the agreement has been reached between the numerical and experimental results of the research, the attention was paid to verification of the effect of boundary conditions of casting on the size of macrosegregation in heavy steel ingots. In the case of casting of steel ingots, the most important and most easily influenced technological boundary conditions include the casting temperature and the speed of the casting. In contrast, the material of the mould or the grade of cast steel cannot be arbitrarily changed. For this reason, the attention was focused on the verification of the extent of ingot volume defects depending on the casting temperature of steel and casting speed. The best appeared to be the variant, in which was used the decrease of casting temperature during filling of the mould and simultaneously the longer casting time up by 15 minutes.