Introduction
Improving the mechanical properties of metallic materials for structural applications is a permanent preoccupation for manufacturers and users. In general terms we talk of hardening (or strengthening) of materials. From a purely technological standpoint, to harden a material is to increase its yield strength. Mechanically, this is effectively to increase the quantity of distortion energy stored in the material without triggering plastic deformation. A physicist will say that this is to increase the quantity and/or efficiency of obstacles to the movement of dislocations. Depending on the domain of use of the materials and the associated strain modes, increasing performance leads to promoting distinct options, but the key to optimisation of the mechanical properties of materials always lies in the manufacturing processes. Manufacturers can act on the following levers:
appropriate thermo-mechanical treatments
careful choice of alloying elements
heat treatments to form hardening phases
surface treatments for superficial local hardening