Effect of Cooling Rates after Hot Deformation on Microstructure of Vanadium-nitrogen Non-quenched and Tempered Steel

The microstructure of vanadium-nitrogen steel was observed by using optical microscopy,scanning electron microscopy and transmission electron microscopy after hot deformation of austenite and cooling to room temperature at four different cooling rates on thermal simulation tester Gleeble 1500.Structural constitution and mechanical properties were calculated via JMatPro4.1 software.The results show that the ferrite refined and its amount decreased,the pearlite content increased the amount of bainite increased gradually and martensite appeared with the continuous increasing of cooling rate.The morphology of vanadium and titanium precipitates changed from regular to granular and from (Ti,V)N to (Ti,V)C,the size was also refined.The calculation equilibrium phase constitution results from the software was similar to that of real samples.The yield stress at room temperature was (814±42) MPa at the cooling rate of 3.0 ℃·s-1.