Variation Characteristics of Microstructures in Non-quenched and Tempered Steel with Vanadium and Nitrogen

The microstructures of non-quenched and tempered steel with different vanadium and nitrogen contents, cooled to room temperature at different cooling rates after being deformed in austenite,were observed and analyzed using optical microscope,scanning and transmission electron microscope.The results indicate the amount of pearlite increases as nitrogen increases or vanadium decreases.A large amount of nano-precipitates with size less than 3 nm were found in both pre-eutectoid and eutectoid ferrite.With cooling rate increasing, ferrite fined and its amount decreased,bainite and martensite appeared as cooling rate increased further, meanwhile,the sizes of vanadium and titanium precipitates fined and main compositions changed from (Ti,V)N to(Ti,V)C.