Hot Deformation And Dynamic Recrystallization Behavior Of 30CrNi3MoV Steel

As a medium carbon Cr-Ni-Mo-V steel,30CrNi3MoV steel has good comprehensive mechanical properties,and is commonly used to manufacture steam turbine rotors,aircraft spindles,valve boxes and other products.These products are usually forged in production.As the forging is large,it is easy to produce coarse grain and mixed grain,which weakens the performance of the material and greatly reduces the service life of the product.In this paper,through the hot compression experiment of30CrNi3MoV steel,the hot deformation and DRX behavior of 30CrNi3MoV steel are studied,the best range of hot working parameters is obtained,and the forming of the product are controlled,which provides a theoretical basis for the actual production of30CrNi3MoV steel;due to the narrow range of the best hot working parameters,it is difficult to accurately control the hot working parameters of different parts of forgings in a narrow range in the actual forging process,which will lead to coarse grains and mixed grains in some forgings.Therefore,through roughening and normalizing the forged samples of 30CrNi3MoV steel,it is studied whether the normalizing process has a good effect of isolating the microstructure inheritance,eliminating the mixed crystal and refining the grain.The main results of are as follows:(1)The true stress and true strain curve of 30CrNi3MoV steel has three different characteristics:the typical dynamic recrystallization process occurs at high temperature and small strain rate;the dynamic recovery characteristic is observed at low temperature and small strain rate;the stress increases with the increase of strain when the strain rate is large,and there is no obvious peak stress.The strain coupled rheological stress constitutive equation constructed by the fifth order polynomial fitting has high accuracy.The average relative error between the predicted value and the experimental value is 3.2%,and the correlation coefficient R is 0.993.From the hot working diagram,the optimum range of hot working process parameters of test steel is:deformation temperature is 1020?1150?,strain rate is 0.03?0.35 s^-1.(2)30CrNi3MoV steel is more prone to dynamic recrystallization at high temperature and low strain rate,and its hot deformation activation energy is 328.2k J/mol.The critical strain was determined by the inflection point of work hardening rate versus flow stress curve(?-?),and the critical strain was obtained as?_c=0.51?_p.The dynamic recrystallization percentage and its average grain size models were established.The predicted values of the two models were in good agreement with the experimental values,which could well predict the dynamic recrystallization percentage and grain size of the test steel.When the strain rate was 0.1 s^-1 When the deformation temperature is 1050?,the grain size of the steel is 19.9?m.(3)After three times of high temperature normalizing treatment,the grain size of the sample is refined to 8.5 grade,and the grain distribution is very uniform,the inheritance of the structure is restrained,and the coarse and mixed grains are eliminated;after two times of high temperature side normalizing treatment in the critical region,the grain size is 5.5 grade 50%+8.5 grade 40%+10.5 grade 10%,and the grain is greatly refined,but the coarse and mixed grains are still serious,and the effect of blocking tissue heredity is not good.