HOT DUCTILITY OF NB-V CONTAINING MICROALLOYED STEEL DURING SOLIDIFICATION

Hot ductility of Nb-V-containing steel has been studied by theoretical calculation and thermal simulation experiment. Meanwhile, microsegregation and precipitates were analyzed. The results showed that segregation degree of elements S, P, O is greater in mushy zone, while, the hot ductility was deteriorated by inclusions of Fe(S,O), (Fe,Mn,Si,Al)(S,O) in the interdendritic region. At the temperature 1100 degrees C, a few NbN particles, 60-70nm, have little effect on mechanical property. In the temperature range 1000 degrees C to 975 degrees C, R.A declined rapidly from 82.36% to 69.61% with the diameters decreasing from 20 to 10nm and quantity of particles increased 23 to 45inds/mu m(2), respectively. In the temperature range from 900 degrees C to 850 degrees C, R.A reduced unobviously from 34.27 % to 30.01% with ferric films thickening gradually. The critical stress, 52.38MPa, was equal to tensile strength at 975 degrees C. Intergranular fracture was easy to occur with higher critical stress below 975 degrees C.