ABSTRACT
Analysis of damages on cold chamber shot sleeve of Al high pressure die casting machine (HPDC) was carried out after two industrial tests, namely: after 16.000 shots with use of larger shot sleeve and after 21.000 shots with smaller size shot sleeve. The shot sleeves were characterized and were made from newly developed SiMo cast iron with vermicular graphite shape, alloyed with Cr and with increased amount od Si (SiMoCr CGI) instead of the commonly used hot forged tool steel material (HWTS). New material exhibits improved thermal conductivity and acceptable mechanical properties. The progress of the damages is further revealed and explained in this study. The formation of cracks on the sharp shaped edges on graphite particles and decrease in adhesion between grain boundaries has been identified. Cracks have progressed further locally and resulted in material spalling. This can be attributed to the fatigue nature of thermal (mechanical) loads as a consequence of the mutual effects of thermal stresses (gradient) on the surface layer and the different thermal dilatation properties between graphite particles and matrix material, and the occurrence of stress concentration on the sharp shaped spots of the graphite particles. This approach enables us to make the price of the unit more economical compared to the existing forged one, made from H11 or H13 (HWTS) grade tool steel.
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