Computer simulation of microstructures evolution for three-high cross-rolling of hollow steels
Based on the rigid-plastic finite element method (FEM), an investigation on three-high cross-rolling of hollow steels was carried out in this study. The numerical model coupled thermal, mechanical and microstructural phenomena, in which some empirical recrystallization mode were obtained using the Gleeble-3500 thermomechanical simulator. The distributions of different field-variables, including temperature, strain and grain size, were obtained by FEM simulation. After different mandrel diameters were calculated, the investigation obtained the effect of microstructures evolution and compared the grain size between no mandrel and different mandrel diameters.
The static and metadynamic recrystallization behaviour of an X60 Nb microalloyed steel
A rapid method has been developed to determine recrystallization kinetics of Nb microalloyed steels by interrupted hot torsion test. The softening behaviour was achieved as a function of different processing parameters. The method clearly identified three regions, where the strain dependency of the recrystallization rate varied. Firstly, at large strains the rate of recrystallization was not a function of strain; this is generally ascribed to metadynamic recrystallization. At lower strains the time to 50% recrystallization showed a power low relationship with strain, characteristic of static recrystallization. A further break point exists on the time for 50% softening curve when strain induced precipitation occurs in the material. The onset of strain induced precipitation was at strains below the strain to the peak stress at temperatures below 900°C. The experimental results were used to estimate the time for 50% softening and to anticipate the onset of the strain induced precipitation for the alloy of this study. Grain refinement of the recrystallized austenite continued to strains significantly beyond the peak stress and beyond the static to metadynamic recrystallization rate transition.
Microstructural evolution of Inconel* 718 during ingot breakdown: process modelling and validation
Abstract A computer model is presented that describes microstructural evolution during the ingot breakdown of nickel base superalloy Inconel 718 via the open die cogging operation. To support the development of the model, a compression testing programme has been carried out which covers the ranges of temperatures, strains, and strain rates experienced during thermomechanical processing. Analysis of the flow curves has allowed the identification of the regimes in which the various deformation mechanisms take place. Logic based rules have been incorporated into the model, and this has allowed predictions of the microstructural evolution to be made. Where possible, the results have been compared with the available experimental data and it is shown that theory and experiment are in reasonable agreement. A number of computational experiments have been carried out, to study the effects of changing the forging procedure.