TENSILE TEST ON IN-SITU SOLIDIFIED NOTCHED SPECIMENS - EFFECTS OF TEMPERATURE HISTORY AND STRAIN-RATE ON THE HOT DUCTILITY OF NB AND NB-V MICROALLOYED STEELS

Hot steel ductility in continuous casting processes is determined by t ensile tests of notched cylindrical specimens which are obtained by me lting and solidification and then tested after rate-controlled cooling with a new specific device available for any standard test machine. H ot ductility is proposed to be related to ultimate area reduction in t he notched zone of the specimens. Experiments in the range of 700-1000 -degrees-C are achieved on two types of niobium-vanadium microalloyed steels which only differ by their vanadium content. Ultimate area redu ctions are determinate by using in situ solidified specimens and rehea ted ones from room temperature, 10(-3) and 0.5 s-1 mean strain rate be ing considered. The change of ultimate area reductions mainly depends on austenitic grain size, segregation's distribution, dynamic precipit ation of niobium-vanadium carbonitrides and so far the recrystallizati on occurrence of austenite.