Home Capped Steel Capped Steel Semikilled steel cast in a bottle-top mold and covered with a cap fitting into the neck of the mold. The cap causes the top metal to solidify. Pressure is built up in the sealed-in molten metal and results in a surface condition much like that of rimmed steel. The good surface and mechanical properties of capped steel make it ideal for the production of sheet and strip products. Capped steel is one of the four basic forms of deoxidized steel which also includes killed, semi-killed and rimmed steels. < Glossary