Study On Precipitation Behavior In Bainite Region And Properties Of V-N Microalloyed Steel

In this paper,based on two kinds of V-N microalloyed steel with different nitrogen content,The deformation behaviors of experimental steels at high temperature,the contiuous cooling transformation behavior of austenite and the precipitation behavior of V(C,N)in the bainite region were studied.The vanadium microalloyed bainite experiment steels were trial-produced in laboratory based on above results.The main works and results of this paper are as follows:(1)By conducting single-pass compression tests,we studied the deformation behaviors of experimental steels under high temperature,drawn strain-stress curves.The dynamic recrystallization activation energy of V-N1,V-N2 are 336.59kJ/mol,370.92kJ/mol,respectively.the rising of vanadium content increased dynamic recrystallization activation energy.(2)By austenite continuous cooling transformation experiment,static/dynamic CCT curves were drawn and the precipitation law in continuous cooling transformation was analyzed.Deformation is benefit to the transformation of austenitc to ferrite or pearlitc,In the static CCT experiment,Ferrite,pearlite and bainite transformation can occur when the cooling rate is less than 2?/s;when the cooling rate is more than 10?/s,ferrite transformation disappeared and whole bainite can be obtained.In the dynamic CCT experiment,the ferrite organization be obtained in the whole process when the cooling speed is less than 25?/s.(3)The isothermal precipitation experiment in bainite region was done by thermomechanical simulator and the results showed that:isothermal treatment at 500? could get single phase of bainite;When the experimental steel in 600/700 ? degrees for insulation,The mixed organization of bainite and ferrite was obtained.The volume of precipitation increased with the extension of heat preservation time and the organization became more dispersion.Within the isothermal scope of 500?700?,there was the maximum volume fraction of V(C,N)at 600?.600? was the best temperature of precipitation.(4)Based on two kinds of V-N microalloyed steels with different nitrogen content,The hot rolling experiments were conducted to analyze the effect of technological parameter and N content on microstructure and properties of experimental steels on?450 mill.We could conclude as follows:the experimental steels can get ferrite and bainite after coiling at 500??550?.Due to V(C,N),the strength would be increased when the amount of N increased at approximately the same condition of rolling technology.When the final coiling temperature was low,yield strength 629MPa and tensile strength 716MPa were obtained by V-N2 experimental steel.Results of experiment steels in impact experiment and cold bend experiment were judged as qualified.