Correlation between lab-scale wedge mould castings and slab samples, a method for new alloy development

Abstract

Industrial scale trials to develop new steel grades are energy intensive as well as expensive, therefore it is more efficient to do laboratory scale casting trials of different steel grades in order to evaluate the casting microstructure of a new steel grade. A conventional square ingot, has advantages and disadvantages. On one hand, it has a well-known geometry and the size of the mould can easily be adjusted. On the other hand, the cooling rate and thus heat extraction is not comparable to that during continuous casting of slabs. Therefore, features related to the solidification, such as grain size and segregation are not comparable to a continuously cast product. A wedge mould set-up was developed in-house to study the effect of cooling rate on the as-cast solidification structure and micro segregation at laboratory scale. Different cooling rates were achieved by making five steps of different thicknesses, leading to microstructures, comparable with the continuously cast product. To validate the results of the wedge mould ingots, slab samples with comparable chemistry as the ingots have been ta ken from a conventional slab caster and a thin slab caster. The as-cast microstructure of the ingots and slab samples were compared through the primary and secondary dendrites arm spacing measured along the thickness of all samples. Cooling rates for each step of the wedge mould samples were calculated based on the dendrite arm spacing and compared with the cooling rates based on the thermocouple measurements. The microstructure and cooling rates at two steps of the wedge mould correlate well with the thin and conventional slab samples, making these steps particularly useful for assessment of castability of new steel grades.