Microstructural evolution during RAP process and deformation behavior of semi-solid SKD61 tool steel

Semi-solid forming technology has several advantages over the conventional metal forming process owing to the unique behavior and characteristic microstructure of metals in the semi-solid state. With the aim of establishing a shorter process chain for manufacturing the high-quality tools required for forming, the microstructural evolution and basic deformation mechanism of the hot-working tool steel SKD61 in the semi-solid-state were studied experimentally. The feasibility of the recrystallization and partial melting (RAP) process for the fabrication of SKD61 stock with a uniform spherical microstructure was validated. The effects of parameters in RAP processing, such as the predeformation temperature and predeformation ratio, on grain refinement were systematically clarified. Finally, the effects of semi-solid forming parameters, such as the forming temperature, forming ratio and strain rate, on the morphology of the microstructure and the flow stress were also investigated.