1. Meeting two contradictory requirements

Under these conditions, it is necessary (both technically and economically) for their strength characteristics to be raised to maximum values compatible with the levels that ductility characteristics must reach to ensure safe operation in service. This is generally achieved by subjecting steels to a hardening heat treatment involving quenching and tempering.

But mechanical engineers often demand that steels should be easy to work with, i.e. that their properties should be such that machining or cold forming, to take only the most commonly used means of forming, should be feasible under the technical and economic conditions deemed most attractive. This requires that the steel's strength characteristics are more or less close to the minimum values they can assume (and that, correlatively, its ductility characteristics reach their maximum values), and therefore that...