3. Special case of carbon-free heat-treated steels

These are iron alloys known as steels, although they do not contain the deliberate addition of carbon. These steels are hardened by precipitation of intermetallic compounds (which replace carbides), which requires them to be fairly rich in the necessary alloying elements. These are essentially :

• precipitation-hardened stainless steels, which will not be discussed here;

• maraging" steels, which contain virtually no carbon that can be brought into solution, and are hardened by precipitation of Ni ₃ Mo, Ni ₃ Ti and Fe ₂ Mo intermetallic compounds. It is the heat treatment of these steels that will be discussed below.

As maraging steel is hardened...