Abstract
This study investigated the characteristics of the surface modification layer of SG cast irons using the electro-discharge machining (EDM). Experimental results indicated that the EDMed surface shows a continuous ridge appearance and the ridge density increases with higher graphite area fraction or nodule count. The modified layer with the high hardness of about Hv 1000 possesses a similar composition to the base material with near-eutectic composition. Microstructural analysis results showed that this rapidly solidified layer comprises mainly cellular γ Fe and intercellular metastable HCP ε phase. Micro-twins can be observed within the γ cells and their formation can be attributed to the residual tensile stress caused by thermal impact.
