HIGH-TEMPERATURE DEFORMATION-BEHAVIOR OF SKD11 DIE STEEL

SKD11 tool steel is one of the steels which contain high compositions of carbon and alloying elements forming a lots of carbides. Major part of these carbides are coarse eutectic carbides which are difficult to be refined through the conventional heat treatment. In order to obtain the refinement of the carbides and the improvement of deformability of SKD11 steel, powder metallurgy method (P/M) of HIP treatment of atomized powder followed by hot forging was utilized and the characteristics of high temperature deformation behaviors of the P/M SKD11 materials and also the effects of the powder particle size and HIP treatment condition were investigated. Maximum elongation of 196% was obtained at the lowest strain rate of 5.6 x 10(-5)s-1 in this work and at the test temperature of 1053K just below Ac, transformation point. HIP temperature and particle size had generally very small effects on such high temperature deformation behavior. Microstructural observation showed the grain growth and directionality along tensile direction during the deformation at lower strain rates and the test temperature just below Ac, point. This is cosidered to indicate that the so called ''superplasticity due to grain boundary sliding'' is not the principal deformation mechanism for the large elongation of the P/M SKD11 steel of the present result.