Effect of superplastic deformation using different stress modes on the structure of high-speed steels

Abstract

1. During superplastic deformation (SPD) of steel R6M by tension, up setting, and direct extrusion a more dispersed structure develops as a result of refinement and spheroidizing of the carbide phases and an increase in the uniformity of their distribution. This effect occurs to a greater extent during tension loading. 2. In powdered steel 10R6M5-MP, which possesses a greater degree of initial dispersion and uniform distribution of the carbide phases than in steel R6M5, there also occurs an increase in the dispersion and uniform distribution of the carbide phases. However, this effect is only observed during SPD by tension and upsetting. During direct extrusion of steel 10R6M5-MP the dispersion and uniform distribution of the carbide phases remain at the same level they were in the initial condition or become less so with increase in the compressive stress level. 3. The greatest degree of increased dispersion and uniform distribution of the carbide phases in high-speed steels R6M5 and 10R6M5-MP occurs during SPD by tension loading. 4. The more dispersed the initial structure, than the more strongly do compressive stresses inhibit diffusion processes. 5. Changes in the superplastic indices during transfer from tension to compression loading may be associated with a change in the contribution of diffusion creep to the superplastic process. 6. The increased dispersion and uniform distribution of the carbide phases in high-speed steels R6M5 and 10R6M5-MP due to SPD is a function of the initial dispersion and uniform distribution of the carbides and of the type of stress scheme used.