Grain refinement in hypereutectoid steel by semi-solid processing followed by mechanical working

Research into new forming methods has yielded new techniques of altering the microstructure in hypereutectoid steels. An innovative approach to processing can lead to improved mechanical properties thanks to elimination of problematic and undesirable sharp-edged carbides which are very difficult to dissolve. This paper explores an unconventional method of refining the grain in and removing primary sharp-edged chromium carbides from X210Cr12 hypereutectoid tool steel. The process route applied to input stock comprised semi-solid processing followed by forming below the solidus temperature. The goal of the study was to determine the impact of the applied strain on microstructural evolution and grain refinement. In these experiments, the material was heated to above the solidus temperature and then either cooled without any other intervention or cooled to a forming temperature and then formed using five to ten deformation steps. Higher number of deformation steps led to much finer microstructure and higher hardness which increased from the initial 673 HV10 to 873 HV10. This procedure produced a very fine microstructure with grains of approximately 1 µm and a fine dispersion of chromium carbides. Since the resulting material was very hard and brittle, it had to be tempered. Tempering was performed once at 300°C for 1 hour or twice at 530°C, for 1 hour in each operation.