Investigation Of Behavior Of Dynamic Recrystallization And Strain Induced Precipitation In Hg785Steel

High strength welding structural steels are widely used for large engineeringmachinery and coal machinery because of their excellent weldability and high strength.The production of new-type HG785high strength welding structural steels are towardlow-cost by using cheap element of Ti to substitute expensive element of Nb in order toincrease the market competition. There’s not only important theoretical significance incompleting micro alloying theory, but also actual application value for the industryproduction process in providing experimental basis for the establishment of rollingtechnology by investigating the behavior of dynamic recrystallization and strain inducedprecipitation of HG785steel.In this paper, the effect of experimental parameters of heating temperature and theamount of deformation and strain rate and isothermal relaxation time on behavior ofdynamic recrystallization and strain induced precipitation are investigated by usingGleeble1500thermal simulator with the method of unidirectional compression. Themicrostructure and grains of austenite dynamic recrystallization are observed by OMand SEM, and the dislocation and precipitation particles are observed by TEM and EDS.In addition, the effect of high Ti content on behavior of dynamic recrystallization andstrain induced precipitation are analyzed, and the relationship between dynamicrecrystallization and strain induced precipitation are also discussed.The influence of temperature and strain rate and the amount of deformation onbehavior of dynamic recrystallization in HG785steel has been systematically studied.The results show that the process of austenite dynamic recrystallization is stronglyretarded. This intense suppression leads to only work hardening phenomenon when thesteel undergoes30%defermation amount with the strain rate range of1s-1at850℃to1100℃, and the total recrystallization occurs only if the specimens undergo60%deformation amount or more with the strain rate range of0.01s-1~0.1s-1at1100℃to1150℃。 The hot deformation equation is built on the basis of the Jonas hyperbolic model, which can be used to describe the hot deformation behavior of HG785steel. It’s shown as follows: According to this hot deformation equation, the relationships among temperature, strain rate and stress can be quantitatively calculated.On the basis of Zener-Hollomon theory, the Z factor model is fitted as following: The dynamic recrystallization diagram is drawn and the rolling technology can also be exactly developed with the help of Z factor model.With the results of experiments on the condition of different temperatures, the P-T-T curve which exhibits typical "C" shape is drawn up. The nose temperature of the P-T-T curves is940℃, which shows that precipitation particles have the shortest start time when HG785steel is rolled at940℃. The precipitation kinetics curve is also drawn up and it presents typical "S" shape. According to the precipitation kinetics curve, the volume fraction of precipitation particles which are isothermally heated with different times can be obtained.The impact of deformation and isothermal relaxation on behavior of strain induced precipitation in HG785steel has been researched. The results show that there are more precipitate particles in the steels when the steels undergo60%deformation amount than that in40%deformation amount, and the former has smaller size of precipitate particles than the later. The number of precipitate particles would reduce and the size of precipitate particles increase when the isothermal relaxation time prolong from lmin to16min. A great number of fine (Ti, Nb)(C, N) can be obtained when the steel undergoes60%large deformation amount and1min isothermal relaxation time.