Effect of precipitation of (Ti,V)N and V(C,N) secondary phases on mechanical properties of V and N microalloyed 1Cr steels

The influence of (Ti,V)N- and V(C,N)-type precipitates on the mechanical properties was studied using transmission electron microscopy, energy-filtered transmission electron microscopy, and electron energy-loss spectroscopy for four medium carbon 1Cr steels containing various amounts of vanadium and nitrogen in the hot-rolled and normalized states. (Ti,V)N-type nanoparticles were found only in the proeutectoid ferrite, while V(C,N)-type nanometer precipitates were distributed in ferrite and further promoted the transformation of pearlite. Addition of vanadium and nitrogen refined the size of the precipitates and increased the volume fraction of pearlite, leading to increased strength. A linear arrangement of (Ti,V)N nitrides and V(C,N) carbonitrides was observed after normalization and resulted in an increase of elongation-to-failure from 16% to 22% at the expense of a 103 MPa decrease in the strength. The precipitation mechanism of Ti-rich nitrides and V-rich carbonitrides and their effects on the mechanical properties of the ferrite-pearlite 1Cr steels were discussed.