 The most important material properties for the dies are thermal shock resistance and softening at elevated temperature ; other important properties include hardenability , machinability , heat checking resistance , weldability , availability ( especially for larger dies ) , and cost . The longevity of a die is directly dependent on the temperature of the molten metal and the cycle time . The dies used in die casting are usually made out of hardened tool steels , because cast iron cannot withstand the high pressures involved , therefore the dies are very expensive , resulting in high start @-@ up costs . Metals that are cast at higher temperatures require dies made from higher alloy steels . 
