Boyd’s Bible Dictionary:

Hebrews were not acquainted with carbonized iron, or steel
Wherever the word is found in Scripture, copper is meant (Psa. 18:34).

Concise Bible Dictionary:

The words are nechosheth or nechushah, and are often translated “brass.” Either copper, or some alloy is most probable, not what is now known as steel, though in the first three passages it is “a bow of steel” (2 Sam. 22:35; Job 20:24; Psalm 18:34; Jer. 15:1.2).