1. Steel constituents

For ease of reading, we use the word constituent to designate both the constituents of steels (such as bainite) and the phases present in the equilibrium diagram (such as austenite or ferrite).

The existence of two allotropic varieties of iron – austenite and ferrite – enables steels to be produced with a wide variety of microstructures, each with its own specific mechanical properties. By acting on the composition and the conditions of thermal and thermomechanical transformation treatments of austenite, the metallurgist can vary, to a large extent, the relative proportions of the different major constituents as well as their respective morphologies. In addition, certain additives can be used to induce the precipitation of second-phase particles within the major constituents, thereby contributing to the hardening of the steel. We now present an overview of the...