Austenitic grain refinement in as cast HSLA steels by dynamic recrystallization

Grain refinement of as cast austenite by dynamic recrystallization in HSLA steels was studied by using a hot working simulator. The hot compression and tensile specimens were prepared from 0.14%C-1.45%Mn and 0.018%Ti or 0.078%Zr bearing steels. Variations of the true stress-true strain curve and dynamically recrystallized grain size with the deformation temperature, strain rate and the initial γ grain size were investigated by hot compression test. The direct hot deformation experiment after levitation melting and solidification was conducted by using the tensile specimens, where the C-Mn and 0.018%Ti-bearing steels were reheated in the temperature range from 1743 K to 1773 K, cooled by various cooling rates, and then hot deformed by tensile strain at 1423 K to 1523 K. It was confirmed that dynamically recrystallized grain size was determined simply by steady state flow stress or Zener-Hollomon parameter, but was not influenced by the initial grain size. The very coarse γ grain size with an order of mm was much refined down to 90 to 150 μm by dynamic recrystallization.