| FV520B martensitic stainless steel has been widely used to the manufacture of impellers for steam turbines.The complex working environment requires good macro and microscopic properties of the blades.The hot forged blades perform better in all aspects than machined blades.The hot deformation behavior and hot workability of FV520B steel play a crucial role in the selection of blade hot forging process parameters.At present,the t hot deformation behavior and hot workability of FV520B steel is still in a blind zone.In view of this situation,this article analyzes the influence of deformation parameters on the hot deformation behavior and hot hot workability of FV520B steel,and deduces the constitutive equation,thermal processing diagram and dynamics of FV520B steel,provides the basis for the selection and optimization of the technological parameters of the hot forging blade of FV520B steel.The specific research results are as follows:Based on the flow stress-strain curve of FV520B steel at deformation temperature of 850-1150°C and strain rate of 0.005-5s-1,the influence of deformation temperature and strain rate on the hot deformation behavior of FV520B steel has been discussed and analyzed.The modified Arrhenius type and modified J-C type constitutive equations for FV520B steel were constructed.The average relative errors between the predicted flow stress and experimental values for the two constitutive equations were 3.012%and 8.408%,respectively.The comparative analysis shows that the modified Arrhenius constitutive equation can more accurately predict the high-temperature flow stress of FV520B steel than the modified J-C constitutive equation.Combined with the dynamic material model?DMM?and the modified Arrhenius constitutive equation of the FV520B steel and the Murty instability criterion,the power dissipation efficiency?and instability parameter???5???of the FV520B steel were calculated to build its processing map.The unstable area of FV520B steel increases gradually with the increase of strain and then decreases slightly.Combining the processing map with microstructure,the optimum region for good workability is designated as the temperature range of 1050-1125?and strain rate range of0.027-0.23 s-1.The dynamic recrystallization characteristic parameters of F520B steel were calculated by flow stress-strain curves,and the mathematical expressions between them and Z parameters were established.The dynamic recrystallization kinetics?volume fraction?model of FV520B steel was deduced,and the dynamic recrystallization volume fraction of FV520B steel at 1000-1150°C/0.005-5s-1 was predicted.The microstructure analysis under the corresponding conditions verified the reliability of the dynamic recrystallization kinetics model established for FV520B steel.The statistical measurement results show that the dynamic recrystallization grain size of FV520B steel increases with the decrease of strain rate,increase of initial grain size,increase of temperature and decrease of deformation.The average relative error between the predicted grain value and the measured value of the FV520B steel dynamic recrystallization grain size model is 7.62%,which can accurately predict the dynamic recrystallization grain size of FV520B steel.Based on the finite element simulation of thermal upsetting microstructure of FV520B steel,the effect of deformation temperature and strain rate on the dynamic recrystallization volume fraction and average grain size distribution of FV520B steel was verified,and the reliability of optimal hot processing parameters 1150-1125?/0.027-0.23s-1 for FV520B steel was verified. |
PDF Full Text Request