INFLUENCE OF VANADIUM ON HOT DUCTILITY OF STEEL

The hot ductility of V + N steels has been examined and compared with that obtained from a Nb containing steel. When tensile samples from ho t rolled plates were solution treated and cooled to test-temperatures in the range 700-1000-degrees-C, the V containing steels exhibited hig her hot ductility than the Nb (0-03 wt-%) steel. Increasing the V and N contents caused both the depth and the width of the low ductility tr ough to increase, due to increasing precipitation of VN. In accordance with this, there was a good relationship between the product of the t otal V and N concentrations and the ductility. This product had to be as high as 1.2 x 10(-3) (corresponding to 0.1 %V, 0.01 2%N) for ductil ity levels to approach the low values of reduction of area exhibited b y the Nb containing steel. Furthermore, with precipitation being the f actor that controls the hot ductility of the steels, marked fine dynam ic precipitation was found to be present in the Nb and the highest V a nd N containing steel examined (0.1 %V, 0.01 1 %N), whereas little pre cipitation was observed in samples taken from a 0-05%V, 0.005%N steel. Recovery of ductility at the high temperature end of the trough corre sponded to when dynamic recrystallisation occurred, and the greater th e degree of precipitation, the higher this temperature. In view of the close relationship observed between the hot ductility behaviour in th e trough and the likelihood of transverse cracking, it is recommended that, where transverse cracking is a problem, V should be considered a s a replacement for Nb.