High yield strength steels (HSLA) are microalloyed niobium, vanadium and titanium steels. They are known as dispersoidal steels with respect to elements forming stable insertion phases. The main structural constituents of these steels are: ferrite, perlite and secondary phases (carbides, nitrides). These steels are used in the as-rolled state or in the improved state for welded constructions and pipelines. Their intrinsic properties after thermomechanical rolling are obtained by hardening of precipitation and by refining. These compounds prevent any growth of grains during heating giving rise to fine grain structure. However, thermal and/or thermomechanical treatments applied to maximize the mechanical properties of these alloys can sensitize them to various modes of structural corrosion.For this reason, we will follow the evolution of the metallurgical and electrochemical behavior of L485Q grade steel (Quenched and tempered) in relation to the effect of precipitation after thermal improvement treatments. We will do a final comparative study with the same grade of L485M Thermomechanical rolled steel according to the ISO3183 standard.Thus, knowledge of the mixed influence of precipitation hardening and microstructural modifications resulting from heat treatments on the corrosion resistance is necessary to allow the desensitization of these alloys to this mode of damage, by introducing in particular a normative notion. imitates elasticity /corrosion resistance "among the many requirements.
