The term hagane (kanji: 鋼) means "steel" in English. It is written はがね in hiragana. It's pronounced roughly like "hah-gah-neh".
This is one way of saying steel; that is, iron with a carbon content between 0.04 and 2 percent. The word for iron is tetsu (鉄). Sometimes steel is called kotetsu (鋼鉄), which simply combines this hagane kanji for steel, pronounced in the Chinese reading ko, and iron. Sometimes, the Japanese will refer to hagane by the English loanword steel (スチール, rendered in romaji as suchiiru).
Hagane can be used figuratively in the phrase hagane no seishin (鋼の精神, literally “spirit of steel”) to describe a tough and disciplined character.