Cooling Condition to Prevent Thermal Stress Cracking during Slag Casting

Steel Slag Hydrated Matrix was developed by mixing steelmaking slag as an aggregate with ground granulated blast furnace slag as a binder. In this study, a direct casting process from molten slag was investigated as an alternative to the complicated and expensive Matrix manufacturing process. However, cracks that occur during casting can reduce strength. To prevent crack formation, the mechanism of thermal stress crack initiation and the appropriate conditions for casting molten slag in rock form were investigated by casting experiments, sound measurements, and thermal stress analysis. Compared with slag cooled in the mold, the slag cast under the optimum cooling condition suppressed cracks and did not cause cracks inside the slag. The crack sound was measured by sound measurements. To suppress cracks, it was suggested that a uniform temperature in the slag should be achieved quickly within 10 min after slag injection. The required solidification shell thickness could be estimated based on the tensile stress that occurred on the slag surface. The casting experiments and thermal stress analysis revealed the cooling conditions for suppressing thermal stress cracks in slag casting. Specifically, it was found that thermal stress cracks can be avoided when the molten slag is poured into the mold and then is demolded at the stage where the solidification shell thickness sufficiently exceeds the strength of the slag surface against tensile stress applied to the solidification shell. The solidified slag is thermally insulated, and the temperature inside the slag is uniform and cools while remaining uniform.