Papers by Keyword: Metadynamic Recrystallisation

Abstract: The present work concerns the simulation of metallurgical evolutions in 3D multi-pass forming processes. In this context, the analyzed problem is twofold. One point refers to the management of the microstructure evolution during each pass or each inter-pass period and the other point concerns the management of the multi-pass aspects (different grain categories, data structure). In this framework, a model is developed and deals with both aspects. The model considers the microstructure as a composite made of a given (discretized) number of phases which have their own specific properties. The grain size distribution and the recrystallized volume fraction distribution of the different phases evolve continuously during a pass or inter-pass period. With this approach it is possible to deal with the heterogeneity of the microstructure and its evolution in multi-pass conditions. Both dynamic and static recrystallization phenomena are taken into account, with typical Avrami-type equations. The present model is implemented in the Finite Element code FORGE2005®. 3D numerical simulation results for a multi-pass process are presented.

Abstract: The static and metadynamic recrystallisation characteristics of a 9SMn28 (EN 1.0715) free cutting steel have been evaluated by employing the stress relaxation technique. In the steel, the sulphur was bound in the form of numerous MnS inclusions. Fractional softening laws stating the kinetics of static and metadynamic softening behaviour were experimentally determined and compared with the existing literature data for C/C-Mn steels. The analysis of the static recrystallisation data suggested the powers of the strain and strain rate to be -2.7 and -0.13, respectively, and the apparent activation energy was estimated as 177 kJ/mol. The power of grain size was taken from a regression model developed previously that is able to predict the static recrystallisation kinetics of vast number of carbon and microalloyed steel grades. Even though a fraction of Mn was out of the solid solution in the form of sulphides, the predictions by the regression model as accounting the balance Mn in the solid solution were quite close to the experimental data, confirming the applicability of the model. As expected, the metadynamic recrystallisation behaviour showed a strong dependence on the strain rate, the power being -0.78 and the apparent activation energy 57 kJ/mol.

Abstract: The post-dynamic softening of Nb micro-alloyed steel and plain carbon steel was investigated through stress relaxation method. Meanwhile, By comparison with C-Mn steel, the effect of deformation temperature and strain on post dynamic recrystallization of Nb steel was studied . The result shows that element Nb in solution state can dramatically improve the apparent activation energy of static recrystallization. At lower temperature, the recrystallization can be retarded and precipitation of Nb(C, N) occured. If strain is more than the critical strain of dynamic recrystallization, the metadynamic recrystallization takes place. If fully metadynamic recrystallization takes place, the kinetics is no longer dependent on strain of the kind of steels.