Investigations Of Laws Of Contorlling Shape And Performance For High Quality Large Forgings And Linkage Trajectory For Manipulator-Press

Large forgings are the key parts for heavy machines and equipments which are widely used in metallurgy, ship-building, petrochemical engineering, power generation, and nuclear power industries. Due to the extreme service conditions, the quality of large forgings becomes more and more important. However, the defects, such as coarse grains, slag inclusions, heating cracks, segregations, porosities and voids, inevitably appear when the steel ingots are casted. The mian goals of hot forging are to eliminate metallurgy defects inside large ingots, including breaking dendrites, refining grains, eliminating segregations, compacting porosities, closing voids, and so on. In this dissertation, the flow behaviors, void and microstructure evolution of a typical material for large forgings are investigated. The methods to plan and optimize linkage trajectory of the manipulator-press are put forwarded. The main contents of this dissertation are shown as following.The flow behaviors of42CrMo steel are investigated by on one-pass hot compression tests. Based on experimental results, a revised model describing the relationships of the flow stress, strain rate and forming temperature of42CrMo steel at elevated temperatures is proposed by the compensation of strain and strain rate. The stress-strain values of42CrMo steel predicted by the proposed model well agree with experimental results. The errors and the standard deviation between the preicted and experimental stress is only-4.36%and2.36%.The dynamic, static and metadynamic recrystallization behaviors of42CrMo steel are investigated by hot compression and metallographic tests. Based on the experimental results, the kinetic models and grain size models of three kinds of recrystallization phenomena for42CrMo steel are proposed. Results show that:(1) When the initial austenitic grain size is decreased, both the dynamic and static recrystallization will easily occur, and then the dynamic and static recrystallization grain sizes will decrease. Also, decreasing the initial austenitic grain size will result in the fine metadynamic recrystallization grain size;(2) With the increase of the deformation temperature, the rate of dynamic, static and metadynamic recrystalli-zation will become fast, and the coarse grain size appear;(3) With the increase of strain rate, the dynamic, static and metadynamic recrystallization grain sizes become fine;(4) With the increase of deformation degree, the dynamic recrystallization fraction increases, and the dynamic and static recrystallization grain sizes become more fine;(5) The effects of holding temperature on the grain growth are significant. However, the effects of the holding time on the grain growth are slight;(6) The predictions of the kinetic models and grain size models for three kinds of recrystallization phenomena are well in agreement with the experimental results.Based on the mesoscopic damage mechanics, the representative volume element (RVE) model for elliptic cylinder void (include cylindrical void) inside large viscous mateial forgings is put forward. The variational functions for the soluting the local velocity field are deduced. The laws for void evolution at different remote stress fields were obtained. Results show that:(1) For the remote shear stress field, the relationships between the changing rate of void aspect ratio and void aspect ratio, material Norton exponent can be represented as the parabolic function and first order exponential function, respectively;(2) For the remote uniaxial compression stress field, the relationships between the changing rate of void aspect ratio and void aspect ratio, material Norton exponent can be represented as the linear function and first order exponential function, respectively;(3) For the remote biaxial compression stress field, the relationships between the changing rate of void aspect ratio and void aspect ratio can be represented as the parabolic function;(4) For the remote uniaxial compression stress field, the changing rate of void orintation is relate to its aspect ratio, its orintation, and material Norton exponent.The mechanism of spherical or spheroidal void evolution is studied by thermo-mechanical coupled finite element model. A void aspect ratio evaluation index is proposed to consider the effects of stress and strain on the evolution of the void aspect ratio. The model between the void aspect ratio evaluation index and the void aspect ratio is established. Then, the effects of stretching processing parameters on the void aspect ratio evaluation index are studied, and the predicted results from FEM are verified by the experments.By integrating laws for high quality large forgings abtained in this dissertation, the methods to plan linkage trajectory of manipulator-press is put forward, and the modules for producing the linkage trajectory of manipulator-press is developed. Also, the judging rules for the linkage trajectory are established. Taking the strecthing process of300MW generator as an example, the industrial application of the modules to produce the linkage trajectory of manipulator-press is given.