Abstract: Thin wall ductile iron (TWDI) readily finds application in automobile sector as it offers tremendous weight savings without sacrificing functional properties. However its wide application is limited by carbide precipitates and non-nodular graphite in the as-cast microstructure rendering it unsuitable for automobile applications. In this study the mould sand thermal characteristics is modified using rice husk ash (RHA). This is employed to reduce cooling rate, inhibit carbide precipitations, produce good nodule characteristics and mechanical properties in 3 mm TWDIs within ASTM standard. Green sand was blended with 1-6 wt. % RHA to produce the moulds for casting, samples were subjected to microstructure (Optical and SEM) and strength analysis. Results show that TWDI samples cast in sand mould with 4 wt. % RHA have nodule ratings > 90%, nodule count >1000 nodules/mm2 and strength of 575 MPa. Ductility of 5.8 occurred in sand mould containing 6 wt. % RHA.
Authors: E.F. Ochulor and S.O. Adeosun
Keywords:Cooling rate, solidification, microstructure, nodularity, nodule count, strength properties