TENSILE PROPERTIES OF A THERMOMECHANICALLY PROCESSED DUCTILE IRON

A ductile cast iron was continuously hot-and-warm-rolled or one-step-f orged from a temperature in the austenite range (900 degrees C to 1100 degrees C) to a temperature below the A(1) temperature. Various amoun ts of reduction were used (from 60 to more than 90 pct). Tensile prope rties including tensile strength and total elongation were measured al ong the directions parallel and transverse to the rolling direction an d along the direction transverse to the forging direction. The tensile ductility and strength both increase with a decrease in the amount of hot-and-warm working (HWW). Compared with the results obtained by oth er investigators, the present results showed higher strengths and duct ilities over the same range of reduction in thickness. The improvement in properties is related to the lower temperature of the postprocessi ng heat treatment given in this study (600 degrees C) compared to othe r studies (900 degrees C). The low temperature of heat treatment leads to a structure of fine graphite in a matrix of ferrite and carbides, whereas the high temperature of heat treatment leads to coarse graphit e in a matrix of carbide-free ferrite. The delay in failure from the p resence of the small graphite constituent results in an increase in te nsile ductility with an accompanying increase in tensile strength.