Research On Hot Deformation Process And Forming Simulation Of Shield Machine Hob Materials

The mechanical properties of H13-mod steel optimized by composition and heat treatment process can meet the requirements of the hob.Although it has good mechanical properties after heat treatment,the hot working process as a key step before heat treatment will also affect the performance of the tool.Therefore,a series of kinetic models of H13-mod steel was established by heat compression test of Gleeble-3800 at a temperature of 900-1150? and a strain rate of 0.01-10s^-1.Based on the thermal processing map theory of dynamic material model,combined with microstructure analysis,the reasonable processing interval is determined.The dynamic recrystallization behavior of H13-mod steel was simulated and analyzed by finite element software,and its dynamic recrystallization mechanism was analyzed.Combined with the actual production process,the finite element software was used to simulate the forming process of the cutter hob material.The main conclusions drawn are as follows:?1?At the beginning of deformation,the stress rise is mainly caused by work hardening.After reaching the peak stress,the curve decreases,and the flow softening phenomenon is more obvious when the strain rate is low.The flow behavior was predicted by the strain-compensated Arrhenius-type constitutive equation,and the correlation coefficient between the experimental value and the predicted value reached 0.987.A linear relationship between peak stress?strain?,critical stress?strain?,saturation stress,stable stress and Zener–Hollomon parameters was established.Through the thermal compression experiments of different deformation amounts,it was found that the decrease of?causes the recrystallized grains to coarsen.The processing temperature range is determined to be 998?-1026? and 1140?-1150?,and the strain rate is0.01s-1-0.02s^-1 and 0.01s-1-0.057s^-1,and the true strain is determined.Not more than 0.6.In addition,the microstructure is uniform at high temperature and high strain rate,which can be regarded as a safe processing area.?2?The dynamic recrystallization equation of H13-mod steel hot compression process was established.The dynamic recrystallization model and finite element software were used to determine the effect of hot deformation conditions on dynamic recrystallization behavior.It was found that dynamic recrystallization was greatly affected by temperature and strain rate,and obvious dynamic recrystallization behavior occurred at strain rates of 0.01s^-1 and 10s^-1.The thermal compression experiments were carried out under different deformation amounts.The evolution of H13-mod steel was analyzed by EBSD.It was found that the recrystallization mechanism of H-13-mod steel at low strain rate is strain-induced grain boundary migration,ie discontinuous dynamic recrystallization.The rheological curve softening phenomenon is obvious.When the strain rate is high,the continuous dynamic recrystallization is dominant,and the microstructure is uniform.At the same time,there is a significant dynamic recovery at both low strain rates and high strain rates.?3?The simulation was performed according to the reasonable processing interval determined by the hot processing map.It is found that the greater the pressure drop rate of the upper die,the more obvious the temperature rise.However,when the deformation temperature is low and the lower die pressing rate is small,the forging temperature is obviously lowered and the rheological resistance is increased due to the long air heat transfer.The higher the temperature,the smaller the flow stress.The equivalent strain field and the equivalent strain rate distribution are basically the same during the deformation process.When the dynamic recrystallization process is simulated,the dynamic recrystallization volume fraction increases with increasing temperature.At 1000^oC,0.01s^-1,due to the long forming time,the heat dissipation is faster,resulting in a lower dynamic recrystallization volume fraction.At 1150^oC,the dynamic recrystallization volume fraction is high.Combined with the simulation results,the hot processing map has certain reliability.