Effect of austempering temperature and manganese content on the impact energy of austempered ductile iron

Abstract

Austempered ductile iron (ADI) is a revolutionary material that has the ability to replace some of the commonly used steel forgings. ADI is being used in wide range of products because of the availability of this material with relatively lesser cost and its higher strength to weight ratio. Manganese is an important alloying element added to ductile iron for improving the hardenability. However, the amount of manganese has to be carefully selected to avoid any adverse effect on the mechanical properties. In this study, impact energy and tensile properties are determined for the various austempering temperatures and manganese content. Statistical analysis is carried out to determine the relative contribution of each factors on the results. Higher impact energy is observed at the higher austempering temperature of 420°C. No adverse effect on impact energy is observed for the addition manganese up to 1 wt%. Response surface methodology is used to optimize the parameters for obtaining the superior combination of ultimate tensile strength and impact energy. Regression equations are fit to predict the impact energy and ductility of manganese alloyed ADI.

An Analysis of the Amount of Retained Austenite in Manganese Alloyed Austempered Ductile Iron

“…These reduction in hardness and strength may be attributed to the coarser grains obtained at higher austempering temperature. From the microstructure study and XRD analysis, it may be seen that, increase in the amount of retained austenite has resulted in the improved impact energy and ductility which is previously reported by the authors 13 . Also, it is seen that by selecting the appropriate austempering parameters, amount of retained austenite obtained at the lower austempering temperature of 320°C is nearly 24 vol %.…”

“…This helps in obtaining the relatively higher impact properties. Further, this analysis is proven to be helpful to achieve the superior combination of strength and toughness by having high amount of retained austenite with finer grains 13,17 .…”

“…The values selected for the heat treatment parameters are based on the literature survey. The mechanical properties such as ductility and toughness are assessed and reported in the previously published report of the authors 13 .…”

“…Knowing the limit of manganese, which could be added without compromising the required mechanical properties could be beneficial, as it helps improving the hardenability. The authors have previously studied and published about the toughness and ductility of the manganese alloyed ADI 13 . Hence, in this study, an effort is made to assess the effect of manganese addition on the volume fraction of retained austenite.…”