Vn Micro Alloying On The Microstructure And Properties Of High Strength Hot Rolled Steel Plate

Combining the item "Hot rolling series of automotive structural steels development" of Panzhihua steel, evaluating phase transition temperature , thermal-simulated experiment and hot rolled experiment are carried out in this paper through V steel being contrast to V-N steel. The phase transition temperatures of V-N steel and V steel are compared and microstructures of thermal-simulated samples are observed, this study investigates the influence of different deformated temperatures and different speeds to the tested steels.Adopted the instruments of metallography microscopes, SEM and TEM, the experiment observes the microstructures of the tested steels and analyzes the precipitation of the second phase in steels. Through the stretching and impacting experiments to test the performance of steels, this article studies the effects of vanadium-nitrogen microalloying to microstructures and performance of high intensity hot-rolling steel plates.The result of phase transition temperature evaluated indicates that the complete austenitizing temperature(Ac₃) is raised along with V content being increased whether V-N steel or V steel and the temperature of V-N is higher than V steels. With V content being increased, Ar₃ of V steel is raised that non-crystallization will become narrow and two phase region will become wide;Ar₃ of V-N steel is reduced that non-crystallization will become wide and two phase region ill become narrow.The result of thermal simulation test indicates that the ferrite content rises with deformation temperature being reduced and the ferrite content of V-N is more than that of V steel on the same V content status.The ferrite content of V-N in the deformation rate of 10/s is more than that of V steel in 1/s rate, the ferrite content of V-N is more than that of V steel on the same V content status..The hot-rolling experiment has show that the structures of V-N microalloyed hot-rolling steel plates obtained by controlled rolling and controlled cooling are all "ferrite and pearlite", and the ferrite grain degree level is very high.The ferrite grain size is minished , precipitated particles become thin , many more and the yield strength is raised and toughness-plasticity is lowered slightly with V and N content being increased.In the same V content level, the yield strength and tensile strength israised 5.1MPa and 4.5MPa with 0.001%N being increased. With the end-rolling temperature lowered, more grains which are more dispersible will be appeared and the grain size is changed little, the tested steels have the most obdurability in the temperature of 850°C .The second-phase grains becomes more smalK many more and more modispersible which may markedly improve intensity with coiling temperature being lowered. And the obdurability is optimal in the coiling temperature of 640-600 °C.