The improvement of surface cracks on leaded free-cutting steel bloom

This study was carried out in order to prevent surface cracks on continuous cast of leaded free-cutting steel. As the leaded steel is likely to suffer from surface cracks, prevention of the cracks is necessary for higher reliability of products. The majority of surface cracks of billets of this steel were found out to be bloom cracks originated due to not uniform cooling at the initial solidification of bloom. Consequently, this improvement of bloom surface cracks is important for the decrease of surface cracks of billets of this steel. From the view point of the uniform initial solidification near meniscus, mold powder was optimized. Three types of mold powder with different viscosity and different carbon content were evaluated through commercial production processes. Uniform initial solidification was realized by use of the mold powder with higher viscosity and higher carbon content. Consequently, surface cracks of the blooms cast continuously and the rolled billets were decreased.