65Mn CK67 high carbon cold rolled spring steel strip Hardened and Tempered Steel Strip Hardened and Tempered is a thermal process that strengthens steel strips through a controlled heating and cooling process. The hardening process involves heating the steel strip to above the rapidly cooling. The steel strip in this condition is extremely brittle and requires further treatment in the tempering. Then strips are reheated to a lower temperature and holding it at the given temperature for a given period of time. This process is done in an inert atmosphere to avoid oxidation. This type of steel strip has big degree of toughness and has excellent spring properties