a steel to be air - hardened as part of heat treatments such as hardening - and - tempering , induction hardening , carburizing , carbonitriding or nitriding comprising , in weight %: c 0 . 10 - 0 . 55 ; si 0 . 97 - 2 . 03 ; mn 1 . 14 - 1 . 83 ; cr 0 . 00 - 1 . 65 ; mo 0 . 36 - 0 . 58 ; and the balance fe + impurities .