Study On Strain-induced Precipitation And Properties Of Titanium Micro-alloyed Steel

With the rapid development of the application industry and the extreme environment of using,the comprehensive performance of steel materials is put forward with higher requirements,not only higher strength,but also good toughness.The strain-induced precipitation of TiC particles in titanium micro-alloyed steel can significantly strengthen fine grains and improve toughness.During the isothermal processing,the TiC of isothermal precipitation can play a significant role in precipitation enhancement.In this paper,Gleeble-3800 thermal simulator was used to simulate the rolling process of titanium microalloy steels.The relationship between induced precipitation and recrystallization of titanium microalloy steels was studied by controlling the deformation temperature,deformation and holding time.Combined with isothermal treatment,the relationship between strain-induced precipitation and isothermal precipitation of titanium micro-alloyed steel was studied.The main research contents and results are as follows:(1)The strain-induced precipitation of titanium microalloy steel was studied.The stress relaxation curve under different experimental parameters can be roughly divided into three stages,and the recrystallization process will be inhibited under the influence of the strain-induced precipitation,which is shown as a section of stress platform on the curve.The PTT of strain-induced precipitation are typical of the "C" shape,with increase of deformation,the precipitation is the fastest the reduction temperature from 910 ? to 900 ? of the tip,the start time of precipitation reduced from 65 s to 50 s,the precipitation incubation time decreased,the end time of the fastest precipitation from 790 s to 1180 s.(2)The strain-induced precipitation kinetics curve of titanium microalloy steel is typical of the "S" shape,precipitated phase at 900 ? had the shortest nucleation incubation period.The strain-induced precipitation process and recrystallization process of titanium microalloy steel exist simultaneously and compete with each other.The austenite grain obviously refined after the strain-induced precipitation,and the austenite grain size is reduced under large deformation.(3)Isothermal treatment was used to study the relationship between the strain-induced precipitation and isothermal precipitation of titanium microalloy steel.The microstructure of titanium microalloy steel at room temperature before and afterisothermal treatment is mainly composed of quasi-polygon ferrite(PF)and granular bainite(GB).(4)EDS analysis shows that TiC is the precipitated phase in the thermal deformation process of titanium microalloy steel.There are two sizes of TiC particles in the experimental steel after isothermal treatment.The size of TiC particles induced by deformation is larger than 10 nm.The size of isothermal TiC particles is small,about 3~6 nm.(5)The testing and analysis of mechanical properties.The yield strength of un-isothermal steel increases first and then decreases with the increase of holding time after deformation.After Isothermal treatment,the yield strengthof steel is obviously higher than that of un-isothermal treatment experiment of steel,isothermal treatment experiment of steel,the experiment of steel yield strength decreases with the increase of the preservation time presented a decrease trend,it shows that the TiC of strain-induced precipitation in austenite and its isothermal precipitation in ferrite area exist obvious competitive relationship,and the strain-induced precipitation more fully,the TiC of isothermal precipitation caused less precipitation strengthening effect.(6)The application of the strain-induced precipitation controlling in industrial production.the titanium micro-alloy steel production can be used in a two phases control rolling technology,as far as possible by using large deformation and the appropriate rolling temperature,rolling temperature suggested control in 900-920 ?,isothermal temperature should be controlled at about 600 ?.In order to realize the fit of strength and toughness of the titanium microalloy steel,the reasonable rolling process and isothermal treatment process were developed to promote the good fit between the strain-induced precipitation and isothermal precipitation,and the fine crystal strengthening and precipitation strengthening effects of TiC were effectively played.