Mechanical Properties of Solid Solution-Strengthened CGI

Despite the increased usage of pearlitic compacted graphite iron (CGI) in heavy vehicle engines, poor machinability of this material remains as one of the main technical challenges as compared to conventional lamellar iron. To minimise machining cost, it is believed that solution strengthened CGI material with a ferritic matrix could bring an advantage. The present study focuses on the effect of solution strengthening of silicon and section thickness on tensile, microstructure and hardness properties of high Si CGI materials. To do so, plates with thicknesses from 7 to 75 mm were cast with three different target silicon levels 3.7, 4.0 and 4.5 wt.%. For all Si levels, the microstructure was ferritic with a very limited pearlite content. The highest nodularity was observed in 7 and 15 mm plate sections, respectively however it decreased as the plate thickness increased. Moreover, increasing Si content to 4.5 wt.% resulted in substantial improvement up to 65% and 50% in proof stress and tensile strength, respectively as compared to pearlitic CGI. However, adding up Si content to such a high level remarkably deteriorated elongation to failure. For each Si level, results showed that Young's modulus and tensile strength are fairly independent of the plate thickness (30 to 75 mm) however a significant increase was observed for thin section plates, particularly 7 mm plate due to the higher nodularity in these sections.