Abstract
It is well known that the maximum prior austenite grain size after carburizing heat treatment is approximately positively correlated with the maximum shear strain in the case of simple deformation of pre process as cold working treatment. On the other hand, it is generally known that the maximum shear strain and the maximum grain size do not correspond when complex cold working is performed, but the reason of these phenomena is not well known. Then, it is necessary to investigate the relationship between the applied strain during cold working with multiple steps and prior austenite grain size after heat treatment(GG). In this study, we used a processing method called HPT processing, which introduces shear strain by torsion deformation under applying high hydrostatic pressure to the top and bottom of a disk-shaped sample using a die, and investigated how GG changes due to the accumulation of dislocations by focusing on the strain amount | ± Δ ε| given in one pass controlled by a processing path called Cyclic-HPT (c-HPT) (4) and the total strain amount 𝛴| ± Δ ε| given to the sample by the accumulation of one pass. As a result, when finer strain is applied, the grain size does not necessarily become smaller, but rather there are boundary conditions that indicate the positive and negative grain size with respect to the number of strains. Similarly, for the grain size distribution, an increase and decrease in grain size was observed with respect to radial distance, so there are boundary conditions that indicate the positive and negative grain size with respect to distance. From these results, it is believed that this may be the mechanism for grain growth behavior in the case of cold working, which involves complex deformation.
