Spring washers bent up ~DIN 127 form A-spring steel black 4

Spring steel is a steel that has a higher strength compared to other steels, but with very high elasticity. Tension discs and disc springs are made of spring steel so that the spring forces defined in the standard can be achieved.

The tempering process of screws and nuts (heating - holding - quenching - tempering) results in a thin baked oxide layer, which is referred to as tempered black. This surface condition is not a surface coating and therefore offers no corrosion protection.