Effect of Nb-V addition (Nb 0 ~0.072%

V 0.09% ~0.12% ) on austenite grain growth behavior of high-carbon steels (0.70% ~0.73%C) in 900 ~ 1200℃ is studied

and the continuously cooled transformed curves of steel are investigated by Gleeble-3800 thermal-mechanical simulator

and the influence of cooling rates on microstructure and hardness of steel is investigated using optical microscope and hardness tester. The results show that with increasing Nb and V content in steel the austenite grain size is fining and grain grown tendency of the steel is smaller

and CCT curves move to the lower right

and the formation and end point of bainite and martensite shift towards low cooling rate

the end point decreases from 8 Y/s to 3 P/s

and the hardness of sample increase with increase of Nb/V content.