Analysis of V(C, N|) nanoparticles in a medium carbon bainitic microalloyed steel and their influence on strengthening

Abstract Continuous cooling transformation diagrams were plotted for a microalloyed steel in dilatometric tests at different cooling rates, and maximum and minimum cooling rates for bainite formation were determined. Austenite grain and bainite packet sizes were measured in three bainitic microstructures obtained by continuous cooling from austenitisation temperatures of 950, 1 050 and 1 150 °C, respectively. The results show that bainitic packet growth cannot exceed the austenite grain boundaries where it has nucleated. V(C, N) particle size was measured using field emission gun scanning electron microscopy and transmission electron microscopy, respectively. Both techniques yielded very similar values, but transmission electron microscopy is preferable due to its higher resolution and the possibility to carry out electron diffraction and dispersive X-ray analyses. The presence of precipitates has contributed to raising the yield strength, which can be predicted by Orowan's expression.