PRODUCTION AND PROPERTIES EVALUATION OF ANTIMONY MODIFIED COMPACTED GRAPHITE IRONS

Abstract

In this research, the production of compacted graphite iron (CGI) alloys and the evaluation of their microstructural and mechanical properties were carried out. The CGI samples were produced in a rotary furnace and ladle–treated with alloying addition of predetermined amounts of magnesiumferrosilicon (MgFeSi), cerium-based ferrosilicon (Ce-based FeSi), aluminium (Al), copper (Cu), and antimony (Sb) to produce different alloying compositions. Cylindrical specimens of Ø 25 mm × 200 mm were produced by sandwich method and designated as C1, C2, C3, C4, A1, A2, A3, A4 and A5. Samples C2, C3 and C4 were the unmodified CGI ladle-treated with MgFeSi, Ce-based FeSi + MgFeSi, and Ce-based FeSi + MgFeSi + Al + Cu alloys respectively. Samples A1, A2, A3, A4 and A5 were the antimony (Sb) modified CGI alloys ladle-treated with constant addition of Ce-based FeSi, MgFeSi, Al, Cu and varying Sb addition at 0.003, 0.006, 0.05, 0.1 and 0.13 wt% respectively. Sample C1 had no treatment and served as control sample. The melts were tapped between 1520oC – 1570oC into the treatment ladle and poured at about 1370oC–1420oC into sand moulds. The result of the chemical analysis of the CGI alloys indicated that the alloys solidified as hypoeutectic (for C1 – C4 and A4 samples) and hypereutectic (for samples A1, A2, A3 and A5). The microstructural examinations revealed that increased antimony addition modified the compacted graphite particles from thick, short, and worm–like with round-ended edges to less thick, short, worm and crab–like graphite with needle-like (Kish) edges interspersed in ferrito – pearlitic matrix. The tensile, % elongation and elastic modulus results showed that sample A1 had the highest value of 327 MPa, 4.11% and 34.2 MPa respectively while alloy A5 had the least 32 MPa, and 0 MPa. Sample C1 had the highest average hardness of 90.7 HRA while sample C4 possessed the least value (83.2 HRA). The impact toughness result showed that sample C2 had the highest toughness value of 34.7 J while the lowest toughness value of 5.4J was recorded for sample A5. Therefore, sample A1 had the best overall properties which fall between Grade 300 – 350 according to ASTM A842 – 85.