Precipitation Behavior of VN in High Nitrogen and Vanadium Micro-alloyed Low Carbon Weathering Steel

In this study, the high nitrogen and vanadium micro-alloyed low carbon weathering steel (0.0320%N–0.096V) with excellent mechanical properties was produced. TEM and EDS tests of the hot rolled specimens were conducted and it was found that a great number of VN precipitates were generated and the size of VN particles was in the range of 10–300 nm, which exceeded the critical size of 7.89 nm for pinning dislocation line. Thermodynamic calculation results showed that, at high temperature, the precipitation performance of VN remarkably increased due to high nitrogen content. For the experimental steel, the initial precipitation temperature of VN reached 1133 °C and the precipitation rate of V exceeded 90% at the finish rolling temperature of 850 °C. The precipitation temperature time (PTT) curves drawn from kinetic data showed that the fastest precipitation temperature was about 950 °C. The total precipitation time was shortened from 110 to 10 s at 850 °C due to the high dislocation density caused by deformation, and the VN particles could thus be completely precipitated with a brief relaxation process. High nitrogen and vanadium micro-alloying was beneficial for improving the grain refinement and precipitation strengthening effect of vanadium.