Research on transformation mechanism and microstructure evolution rule of vanadium–nitrogen microalloyed steels

In order to design microalloyed steels with various contents of vanadium and nitrogen, the experimental steels are firstly melted in the intermediate frequency vacuum induction furnace. Aiming to research the dynamic transformation rule of RCR + ACC, the thermal–mechanical simulation tests are carried out on GLEEBLE 3800 thermal simulator and the static transformation temperature and dynamic CCT diagrams are then obtained. It is found that contents of Neff and V have no obvious influence on transformation temperatures of Ac1 and Ac3. However, when their contents increased, transformation temperatures of Ar1 and Ar3 is decrease during RCR + ACC process. When cooling velocity drops down to 4 °C/s, all microalloyed steels microstructures are composed of ferrite and pearlite at room temperature. when cooling increases above to 4 °C/s, Bainite begins to appear and would replaced by pearlite after 9 °C/s. Hardness of microalloyed steels is also increased with increasing of cooling velocity and effective contents of N during the same cooling rate.