Simulation Of Hot Forming Process For 300M Steel Super Large Forging Billet

300M steel is widely used in key bearing structures such as aircraft landing gear.owing to its high strength,high fracture toughness and good fatigue resistance.The coarse and mixed grains result from the microstructural segregation of the initial ingot and the unevenness of forging can seriously affect the final performance of large forgings.At present,there are few reports on the plastic deformation mechanism and microstructure evolution of as-cast 300M steel during hot deformation,and the ingot forging is an important process during the process of forming large forgings.The main purpose is to break and eliminate the coarse as-cast microstructure in order to obtain the uniform structure.As the forming process parameters are difficult to control when the blank is forged,therefore,this paper studies the thermal deformation behavior of as-cast 300M steel at different deformation temperatures and multi-range strain rates,and constructs the constitutive equation of the material and the dynamic recrystallization model.In addition,this thesis introduces the finite element simulation software DEFORM based on the constitutive model and the dynamic recrystallization model of the as-cast 300M steel,and simulates the forging of the as-cast300M steel double-cone speciment.The simulation results of strain field,temperature field and average grain size of the s compressed sample were obtained,and the accuracy of the finite element material model was verified by experiments.The main research contents and results of the thesis are as follows:?1?The hot compression test of as-cast 300M steel was carried out.The hotl deformation behavior and microstructure evolution of the materials were reseached,and the corresponding constitutive equations,thermal processing map and dynamic recrystallization models were constructed.The microstructure is analyzed combined with the thermal processing map.The suitable parameters of the hot deformation process of the as-cast 300M steel are as follows:the deformation temperature is 1080?¹200?,and the strain rate is 0.01 s^-10.8 s^-1.?2?In order to verify the accuracy of the material model,the hot compression experiment of as-cast 300M steel double-cone specimen was carried out.The microstructure of the typical region of the specimen was analyzed.The thermal deformation process was simulated by DEFORM software.It was found that the double cone hot-compression specimens showed different degrees of dynamic recrystallization in different regions.With the increase of the strain,the dynamic recrystallization volume fraction increased gradually,and the strain-dynamic recrystallization volume fraction relationship showed an"S"shape.Dynamic recrystallization first nucleates at the grain boundary,and as the strain increases,dynamic recrystallization extends into the inner grain.The coMParison between the experimental results and the simulation results shows that the finite element simulation has a good predictability for the hot deformation process.?3?Numerical simulation of the cogging process of the as-cast 300M steel was carried out,and the hot deformation process of cogging was determined.The cogging process consisted of five upsetting and drawing-out.The reduction of the each upset is 50%,and the feed amount of each drawing-out is 600 mm.Applying this process to actual production,and dissecting the 300M steel billet forgings after the cogging,the results show that the forging process meets the grain size requirements of 300M steel forging.