Austenitic grain evolution of 23Co13Ni11Cr3Mo ultrahigh strength steel during high temperature deformation

High-strain isothermal compression tests of 23Co13Ni11Cr3Mo ultrahigh strength steel were carried out on a Gleeble 1500 simulator. Influences of deformation temperature and strain rate on austenitic grain size were examined. The results show that austenitic grain size of the steel has a linear relationship with the reciprocal of deformation temperature (T-1) in the semi-logarithmic coordinate, and it has a linear relationship with strain rate and Z parameter in natural logarithmic coordinate. Small size and uniform distribution of grains are obtained for the steel deformed at lower temperature, higher strain rate and higher Z parameter. The ranges of deformation temperature and strain rate of 23Co13Ni11Cr3Mo ultrahigh strength steel are optimized based on the experiments and austenitic grain size model is established for forging process. The predicted values of the model agree well with those of experiment.