Research On Microstructure Evolution Process Of Die Forging Blade Based On Monte Carlo

Metals in thermoplastic deforming process exists hardening and softening mechanisms atthe same time. Dynamic recrystallization is one of the most important softening mechanisms.The dynamic recrystallization can change the grain structure of deforming metal; fully orpartly eliminate the work hardening caused by plastic deformation through transforming thedistorted grains into the fine intact grains, thereby improving or enhancing the capacity ofmetal continuous thermoplastic deformation. Therefore, it has an important practicalsignificance to deep study and master the microstructure evolution in metal hot processing, inorder to understand and predict effectively the effects of deformation temperature,deformation rate, deformation force and other process parameters on the ultimatemicrostructure thermoformed parts.In this paper, according to the metal thermoplastic deformation theory and Monte Carlo(for short MC) random statistical theory, a microstructure evolution model in dynamicrecrystallization based on the non-uniform distribution of stored energy was established, anapplication system for simulating the microstructure evolution in the blade hammer forgingwas developed by used of Matlab software, and the influence of thermodynamic parameterssuch as deformation temperature, strain rate and flow stress on the microstructure evolution ofdie forging blade was studied by means of the system. The results show that:(1) The non-uniform storage distribution and variation can determine the transformationalprobabilities of the orientation selected node in MC-Potts model, which simulate thephenomena of recrystallization nucleation and grain growth in the metal deformation.(2) The recrystallization model established by the theory of uneven storage energydistribution can better reflect the potential sites of recrystallization nucleation and the growthof recrystallized grains.(3) The applications of the theory and technique, which relate to the criticality storagecriterion of recrystallization nuclear, the recrystallization nucleation rate and the allocation ofnucleation number at a MC step determined by material macro and micro parameters, themigration direction of large-angle grain boundary determined by the relative change of energy,recrystallization nucleation and grain growth coexisted in one MC step，make the establishedmicrostructure evolution mode in the paper more close to practical engineering.(4) The main calculation program developed in the paper ensured that the system revealedtruthfully basic features and evolution process of dynamic recrystallization in a certain extent ，because some technical problems were solved such as creating initial microstructure, loadingincrementally thermodynamic parameters, allocating dynamically storage energy, associatingMCS time with physical time, showing microstructure, statistic grain information, and so on.(5) The number of initial nucleation in dynamic recrystallization has a great relationshipwith the equivalent plastic strain and equivalent strain rate, following by the equivalent stress.But the deformation temperature has a little influence on the nucleation number. In differentdeformation zone thermodynamic parameters unevenly distributed and dynamically changedwith time step, the blow count and deformation amount resulted in the grain size differenceafter the forging end, which there was a smaller grain size in large amount of plasticdeformation zone.(6) At each time step of the blade formation, the linear relationship in logarithmic existedin the recrystallization fraction and Monte-Carlo calculation step indicated it meets therecrystallization kinetics but the Avrami index slightly lower than theoretical value.