MECANISMOS DE ENDURECIMENTO EM AÇO MICROLIGADO Nb-Ti-V

Yield strength of Nb-Ti-V microalloyed steel has been investigated as a function of its microstructure obtained after industrial rolling on a hot strip mill. Optical (OM) and transmission electron microscopy (TEM) were used to reveal the ferrite grain structure, fine carbonitride precipitation and dislocation substructures. It was found that the effects of solid solution and grain size hardening were not sufficient to justify the results of tensile testing. Additional strengthening was attributed to carbonitride precipitation in austenite, interphase precipitation during transformation, and the formation of dislocations. All contributions of these microstructural features on mechanical property were estimated from empirical models available from literature. A global effect of both austenite and interphase carbonitride precipitation hardening was proposed. It was verified that yield strength calculated from cumulative effect of different strengthening mechanisms has presented good fitting with experimental tensile test.