Effect of Cr content on microstructure and mechanical properties of carbidic austempered ductile iron

Abstract The effect of Cr content on the microstructure and mechanical properties of carbidic austempered ductile iron (CADI) was studied by means of optical microscopy (OM), X-ray diffractometry (XRD), scanning electron microscopy (SEM), Rockwell hardness testing, pendulum impact testing machine and ring-on-block wear tester. The results show that with the increase of Cr content the volume fraction of graphite and nodularity rate of as-cast ductile iron decrease gradually, but carbide content increases, and the diameter of graphite reaches the maximum followed by decrease. Then, the specimens were austenitized at 900 °C for 100 min and austempered at 300 °C for 100 min. The hardness and wear resistance of CADI reach maximum when Cr content is 1.42 wt.-% and then decrease with the increase of Cr content, and the impact toughness decreases gradually. Taking the impact toughness into consideration, the comprehensive mechanical property is best when Cr content is 0.96 wt.-%.