STEEL ADDITIVE

PROBLEM TO BE SOLVED: To provide a CaO-Al2 O3 -based steel additive free from a fluorine component, which develops a devulcanization property equivalent to or better than that of additives including fluorine. SOLUTION: The steel additive is characterized by including, by mass%, at least 60% CaO, and 5-40% Al2 O3 as a chemical composition, and 10-90% 3CaO/Al2 O3 , 5-50% 12CaO/7Al2 O3 , and 5-40% CaO/Al2 O3 as a mineral composition, and excluding the fluorine component. The above additive is preferably a granular substance consisting of, by mass percentage content, grains with sizes of more than 15 mm of 10% or less (including 0%), grains with sizes of 10-15 mm of 40-90%, grains with sizes of less than 10 mm but 5 mm or more of 10-60%, and grains with sizes of less than 5 mm of 15% or less (including 0%).