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Experiment And Simulation Study Of Mixed Grain Of Heavy Forging In The Hot Forming Process

Posted on:2014-01-16Degree:MasterType:Thesis
Country:ChinaCandidate:C W HuangFull Text:PDF
GTID:2251330392464607Subject:Mechanical engineering
Abstract/Summary:PDF Full Text Request
As the core components of large equipment, heavy forgings play a very importantrole in the national economic construction, national defense equipment development andthe major installations of the modern advanced science and technology. However, themixed grain appears easily if forging process is unreasonable. When mixed grain is serious,the yield strength declines, the impact toughness reduces and the fracture appearancetransition temperature rises, which bring serious hidden troubles to the operation ofworkpieces. The size of heavy forgings is large, and its production cycle is too long,studying the formation law of mixed grain by field test is slow and not economic, so it hasimportantly theoretical significance and engineering practical value that create themicroscopic organization model of heavy forging materials in high temperaturedeformation and then study the influence of strain, deformation temperature and strain rateon the mixed grain by simulation to get the formation law of mixed grain.In order to make the numerical simulation react practice more truthfully and advancesimulation precision, the influence of initial grain size on dynamic recrystallization of35CrMo steel has been considered. The paper studied the influence of initial grain size,strain, deformation temperature and strain rate on the deformation resistance and dynamicrecrystallization. At first, different degrees of grains were created through heating test.Then, thermal compression tests of35CrMo steel were completed using thermodynamicanalogy testing machine Gleeble-3500to get the true stress-strain curve and create itsdeformation resistance model. The austenite grain morphology in the samples withdifferent hot compression process was gained by metallographic analysis. And themathematical models describing austenite dynamic recrystallization of35CrMo steel wereestablished.The DEFORM-3D software was redeveloped to embed the deformation resistanceand microscopic organization models in it. And the single pass hot compressionexperiment was simulated using DEFORM-3D software to verify the reliability of themodels. With reference to the forging process of13500t large marine propeller shaftforging, the state of mixed grain under the different strain, deformation temperature and strain rate was studied by simulation, which gives us a conclusion that increasing strain,raising deformation temperature or decreasing strain rate could decrease mixed graindegree. This provides the basis for optimizing mixed grain.
Keywords/Search Tags:heavy forging, mixed grain, microstructure evolution, numerical simulation, grain size
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