Effect of addition of NiO powder on pore formation in lotus-type porous carbon steel fabricated by continuous casting

Lotus-type porous carbon steel (lotus carbon steel) plates were fabricated by continuous casting technique in a pressurized nitrogen atmosphere. The experiments were done both with adding 0.3wt% of NiO powder in molten carbon steel in a ceramic crucible and without NiO powder. The lotus carbon steel fabricated without NiO powder under nitrogen pressures of 0.1 and 0.5 MPa had single pores which grew independently. On the other hand, the lotus carbon steel fabricated with adding NiO powder had pores which coalesced each other and became in irregular shapes. Under nitrogen pressure of 2.5 MPa, the pores formed with adding NiO powder were smaller than that formed without NiO powder. The porosity increased by adding NiO powder in every pressurized nitrogen atmosphere. From these results, NiO powder in molten carbon steel is considered to act as nucleation sites for pores at the solid-liquid interface and to increase of the pore number.