noun
steel industry
Refers to the industrial sector that produces steel and steel products.
鉄鋼業は日本の重要な基幹産業だ。
The steel industry is an important key industry in Japan.
鉄鋼 means 'steel' as a material, while 鉄鋼業 refers specifically to the industry that produces it.
Compound of 鉄鋼 (てっこう, 'steel') and 業 (ぎょう, 'industry').