Fabrication of Lotus-Type Porous Carbon Steel Slabs by Continuous Casting Technique in Nitrogen Atmosphere

Lotus-type porous carbon steel slabs with long cylindrical pores aligned in one direction were fabricated by the continuous casting technique in a mixture gas of N-2 0.8 MPa and Ar 1.7 MPa or in N-2 2.5 MPa at various transfer velocities from 2.5 mm.min(-1) to 20 mm.min(-1). The pore size in lotus carbon steel fabricated in the mixture gas of nitrogen and argon was small and homogeneous, whereas the pore size in nitrogen had bimodal distribution depending on the transfer velocity. The large pores were observed mainly at the edge of the slab, which are considered to be merged of several inclined pores. The porosity depended on nitrogen partial pressure, which is explained by Sieverts' law. The hardness of lotus carbon steel matrix increased, which was attributed to the solid-solution of nitrogen.