A study of the 500 to 900°C tensile deformation behaviour of spheroidal graphite cast iron

Abstract

The general characteristics of the 500 to 900°C tensile deformation behaviour of spheroidal graphite cast iron are reported. The effects of silicon content and strain rate are also included. Three SG cast irons (3.5 wt%C) with 2.1 wt%Si, 2.8wt%Si and 3.9 wt%Si were used to perform the tensile tests. The strain rates were chosen within the same range from 3.3 × 10−4 to 2.7 × 10−2 s−1.At temperatures below 700°C, the flow stress decreases and the elongation increases with temperature. Because of the solid solution strengthening effect, the flow stress increases while the elongation decreases with silicon content. At temperatures above 700°C, there is a reversion of temperature dependence for the flow stress, and the elongation then deteriorates. The temperature of reversion increases with increasing silicon content, a result which can be attributed to the increase in the eutectoid transformation temperature. Because of the higher eutectoid transformation temperature, 3.9%Si alloy has shown good ductility. From the wavy flow in the flow curves and the recrystallization structure, dynamic recrystallization takes place at the temperatures above 700°C. Furthermore, the strain rate sensitivity m value increases with temperature, and has a maximum near the eutectoid transformation temperature. The specimens of higher silicon content have higher m values when deformed at higher temperatures.