1. A few reminders about steels

Iron has two allotropic varieties: austenite (face-centered cubic crystallographic structure) and ferrite (face-centered cubic crystallographic structure). This specificity gives rise to a wide variety of microstructures, each with its own specific properties. By modifying the austenite's composition and the conditions of its thermal and thermomechanical transformation, the metallurgist can vary, to a large extent, the relative proportions of the various constituents, as well as their respective morphologies. In addition, certain additives can be used to induce the precipitation of second-phase particles within the constituents, which contribute to the hardening of the steel.