3. How to harden iron

To increase the mechanical performance of iron near room temperature, it is necessary to reduce its plastic deformation potential (article L'état métallique. Plastic deformation in this treatise): since these depend on the mobility of dislocations, obstacles will have to be placed in their path.

These obstacles can be :

• other dislocations generated by strain-hardening or quenching;

• foreign atoms introduced into solid solution ;

• precipitates ;

• grain boundaries.