Spring Steel Strip and Wire, Hardened and Tempered

A spring must bend and come back. Mild steel bends and stays bent; high-carbon steel, hardened and then tempered to a blue colour, springs back. The strip or wire is shaped soft, heated until a magnet no longer sticks to it, quenched in warm oil to harden it, then tempered: cleaned bright and heated gently until the colour runs to blue. It starts from high-carbon crucible steel. Wire is drawn while the steel is still annealed.