Study On Phase Transformation Behavior Of Ti Micro-alloyed Steel During Continuous Cooling After Rolling

Micro-alloyed steel is widely used as engineering structural material.And it developed on the basis of ordinary carbon steel adding micro alloying elements,The Nb,V,Ti,Mo,etc.were used to adding in steel.The content is less than 0.2%in the proportion of components.The addition of different elements leads to a difference in ultimate properties of steel.The dynamic continuous cooling transformation curve?CCT?can directly reflect the phase transition of steel during the continuous cooling process.In order to control the final microstructure and obtain the desired material properties,the cooling systems is guided by CCT.Based on this,in order to deeply understand the phase transformation behavior of steel during high temperature cooling process,the influence of phase change behavior on the comprehensive properties of steel is studied.In this paper,firstly,the Ac of micro-alloyed steel has been studied by thermos-dilatometer;Secondly the hot rolling process and cooling at different cooling rates after rolling are simulated on the Gleeble-1500D thermal simulator.Finally,the phase transition in cooling process was analyzed,and the dynamic continuous cooling transformation curve was drawn.The main work of this paper is summarized as follows:?1?The Ac transformation point of micro-alloyed steel was studied by thermal expansion instrument.It was found that Ac₁=702?,Ac₃=826?,Ar₃=806?,Ar₁=640?,T_f=590?.In order to obtain better rolling cooling performance,the final rolling temperature can be set at about 850?.?2?The hot rolling process in the continuous cooling process was simulated Gleeble-1500D.After the sample was heated to a single phase?A?,the sample experienced two segments of deformation.The microstructure and properties at 9 kinds of cooling rates were studied.?3?The production process can be guided according to CCT.Reasonable production process:high cooling rate above the bainite transformation temperature,the re-reddening temperature is over 650?;cooling rate controlled at 5 to 10?/s in order to ensure that the surface and the heart tissue is uniform;Then air cooling to room temperature to get the fine ferrite+pearlite.This study can provide guidance for the production process.