Microstructure and Mechanical Properties of Fully Annealed Compacted Graphite Cast Iron for Automotive Applications

The work was conducted to determine the mechanical properties of heat-treated (full annealing) compacted graphite cast irons (CGI) of different microstructures suitable for automotive applications. Six types of CGI were selected from numerous available samples based on their chemical compositions. The six CGI were tagged A1, A2, A3, A4, A5, and A6. Full annealing heat-treated was carried out on A1-A6, they were austenized at 920°C. Chemical analysis and carbon equivalent were done, and the results showed that A1-A6 were hypereutectic CGI with different alloying elements. SEM analysis was equally carried out on A1 to A6. The result from the microstructural analysis indicated that A1 and A2 have structures close to gray cast iron, A3 and A4 have a pure CGI microstructure, and A5 and A6 have structures close to ductile cast iron. Mechanical properties (hardness, impact, and wear resistance) were tested on A1-A6. A1 with 209 Brinell hardness number (HBN) has the highest hardness value and A6 with 112HBN has the least hardness number. Similarly, the result from ultimate tensile strength (UTS) shows that A5 has the highest UTS value of 140 megapascal (MPa) and A2 has the lowest value of 38MPa. 38.8J for A1 is the highest impact energy recorded for the series. Lastly, 67% recorded for A6 was the highest wear loss for the series. A1-A6 is suitable for the production of automotive parts especially exhaust system parts and engine blocks.