The identity of the mechanical properties of ductile iron (QP) and cast iron with compact forms of graphite, in particular, with nodular and vermicular graphite (CSWG). Given the fundamental differences in techniques of obtaining QP and CSUG in terms of their labor, material and energy intensity at virtually the identical strength properties shown to be technically and economically preferable for the manufacture of castings of CSWG and other cast iron with a compact form of graphite.