The Influence Of Thickness And Micro Alloying Elements On The Toughness Of Ti Bearing High Strength Steel

With the increasing requirement of energy saving of iron and steel corporation,it is a trend for the developement of new steel product to reduce the cost of production by adding plenty and cheap Ti to microalloying steels instead of the expensive elements of Nb,Cr and Ni.However,the high strength structure steel with a high containing of Ti element(>0.10%)has a large fluctuation of low temperature impact toughness due to the effect of plate thickness(? 10mm).The morphology of fracture,inclusion and microstructure of the Ti bearing high strength steels are analysed by scanning electron microscope(SEM)and transmission electron microscope(TEM).The temperature field and cooling rate of laminar cooling process of the steel is simulated and calculated by the software of ANSYS and the CCT curve is calculated by J-mat-pro software.In this paper,The effect of plate thickness and microalloying elements of Mo,N on low temperature impact toughness of the steel are investigated to provide a reference for the thick Ti bearing steel production.Comparing to thin plate(6mm),thick plate(12mm)has a 80? difference between surface and core.The final cooling temperature of the core is closed to the pearlite transformation zone and which lead to the formation of pearlite and polygon ferrite if the cooling rate is not controlled well in the large-scale production,which leads to the fluctuation of low temperature impact toughness of the thickness plates.The hardening increase of the plate with the adding of element of Mo and the transformation of pearlite is inhibited in the core and the bainite is obtained at the same cooling rate.The microstructure become more homogeneity and the precipitates of(Ti,Mo)C are relatively small which improve the impact toughness of the steel.The large size TiN inclusion is the main factor which influence the low temperature impact toughness of the steel.The result show that when the Ti content is 0.12%,even the N content is 92 ppm,the impact toughness at-40? of the Ti bearing high strength steel is still 142 J·cm-2,the process window of N content is wide.