HIGH TEMPERATURE DEFORMATION AND THERMOMECHANICAL TREATMENT OF LOW CARBON STEEL AND VANADIUM-NIOBIUM MICROALLOYED STEEL.

A low carbon steel and a vanadium and niobium microalloyed steel were deformed by torsion with the true strain rates from about 10** minus **3 to 10 s** minus **1 in the temperature range from 900 to 1,200 degree C. Through the determination of their flow behavior and th obervation of the deformed microstructure, dynamic recrystallization behavior was analyzed. Austenite grain refinement by dynamic recrystallization and final ferrite grain refinement due to microalloying elements in the course of thermomechanical treatments were simulated by using a torsion machine. The final grain size in air-cooled specimen was much reduced in the schedule including only one stage deformation at 800 degree C particularly in the microalloyed steel. The microstructures in the thermomechanical processes revealed the characteristic feature of dynamic restoration process in the two phases region of steels.