Influence of Vanadium on Hot Ductility of Steels
The hot ductility of V + N steels has been examined and compared with that obtained from a Nb containing steel. When tensile samples from hot rolled plates were solution treated and cooled to test temperatures in the range 700-1000°C, the V containing steels exhibited higher 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 trough to increase, due to increasing precipitation of VN. In accordance with this, there was a good relationship between the product of the total 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, 0·012%N) for ductility levels to approach the low values of reduction of area exhibited by the Nb containing steel. Furthermore, with precipitation being the factor that controls the hot ductility of the steels, marked fine dynamic precipitation was found to be present in the Nb and the highest V and N containing steel examined (0·1 %V, 0·011 %N), whereas little precipitation 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 corresponded to when dynamic recrystallization occurred, and the greater the degree of precipitation, the higher this temperature. In view of the close relationship observed between the hot ductility behaviour in the trough and the likelihood of transverse cracking, it is recommended that, where transverse cracking is a problem, V should be considered as a replacement for Nb.
B. Mintz and R. Abushosha
Department of Mechanical Engineering and Aeronautics, City University, London.
Ironmaking and Steelmaking,Vol. 20, No. 6, 1993, pp. 445-452