Precipitation behaviour of carbonitrides in ti-nb-c-n microalloyed steels and an engineering application with homogenously precipitated nano-particles

Abstract

A thermodynamic model enabling calculation of equilibrium carbonitride composition and relative amounts as a function of steel composition and temperature has been developed previously based on the chemical equilibrium method. In the present work, actual carbonitride precipitation behaviour has been verified in the Ti-Nb-C-N microalloyed steels. The Ti microalloyed steel after refining with 0.012% Nb exhibited highly improved tensile strength without sacrificing ductility. According to further detailed SEM and TEM analysis, the improved mechanical properties of Ti/Nb microalloyed steel could be attributed to the larger solubility of Nb and Ti, inducing fine dispersion of the carbonitrides with particle size of 2–10 nm in the ferrite matrix.