Effect of carbon and nitrogen content on microstructure of V-N-Ti microalloyed steel

The microstructure of V-N-Ti microalloyed steels with 0.26wt%-0.42wt% C and 0.0041wt%-0.021wt% N was studied by quantitative metallographic analysis. The results show that the carbon and nitrogen content has a strong impact on the distribution and amount of the proeutectoid ferrite in a medium carbon V-N-Ti microalloyed steel. So nitrogen does. When the nitrogen contents keeps no change, more of intragranular ferrite (IGF) and more uniform and finer microstructure is available in the steel with 0.33wt% or 0.34wt% C. When the carbon content is Q.33wt% or 0.34wt%, the amount of proeutectoid ferrite increases slightly with increasing nitrogen content. And the results also show that the influence of the nitrogen content on the amount of proeutectoid ferrite in the as-forged microstructure is smaller than that of the carbon content. Finally, the computer calculations of precipitation kinetics of vanadium based on the classic nucleation and the growth theory can well explain the experimental results.