Clean the steel, first with a stainless steel brush and then with a degreaser to remove surface debris and oils.
Weld each end of the steel in a series of short passes. As the steel heats, be vigilant to detect sand holes or other defects. Use the flame to bring these defects to the surface of the steel.
Work the defects over to the edge of the welding pool using the welding tool. Weld in the same direction each time.
Run a weld bead over any holes in the cast steel to eliminate them.
Allow the steel to cool to room temperature by covering it in dry sand or wrapping it in a fireproof blanket.