recarburizer

from The Century Dictionary.

• noun In the manufacture of steel by the Bessemer process, a material rich in carbon (usually spiegeleisen) which is added to the still molten product from blowing air through fused cast-iron, in order to remove any traces of oxygen which the iron itself may have taken up. The result of this addition is practically not only the removal of oxygen but the reintroduction of a little carbon, producing the so-called mild steel, which differs little from wrought-iron rendered homogeneous by fusion.