Grain refinement limit during hot radial ring rolling of as-cast GCr15 steel

Using hot radial ring rolling to process as-cast blank is a new ring manufacturing technology of high efficiency, high material utilization and low energy consumption. It was customarily considered that larger deformation amount is needed in the new process to obtain smaller average grain size. However, in our work, no further refinement of the average grain size has been found at a certain sufficient deformation amount. Hot radial ring rolling of as-cast GCr15 steel at elevated forging temperature has a grain limit, further deformation produced by this technology does not help overcome this limit. The key explanation to this phenomenon lies in the balance of dynamic recrystallization-induced grain reduction and thermal-induced grain growth occurred during this process. The minimum strain to reach grain limit has been defined and quantified based on the empirical dynamic recrystallization models. The effects of strain and Z parameter on grain limit have been carried out. The optimizing selections of rolling parameters based on grain limit have been discussed. These results obtained provide guidance for grain size controlling and performance improving in the new technology of manufacturing rings.