Influence of specimen geometry of hot torsion test on temperature distribution during reheating treatment of API-X70

The commercial finite element package ANSYS™ was utilized for prediction of temperature distribution during reheating treatment of hot torsion test (HTT) samples with different geometries for API-X70 microalloyed steel. Simulation results show that an inappropriate choice of test specimen geometry and reheating conditions before deformation could lead to non-uniform temperature distribution within the gauge section of specimen. Therefore, assumptions of isothermal experimental conditions and zero temperature gradient within the specimen cross section appear unjustified and led to uncertainties of flow curve obtained. Recommendations on finding proper specimen geometry for reducing temperature gradient along the gauge part of specimen will be given to create homogeneous initial microstructure as much as possible before deformation in order to avoid uncertainty in consequent results of HTT.