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Machinability of Materials
Published in David A. Stephenson, John S. Agapiou, Metal Cutting Theory and Practice, 2018
David A. Stephenson, John S. Agapiou
Compacted graphite iron (CGI) has a structure intermediate between gray and ductile iron and is used especially for diesel engine blocks and heads and for bearing caps, where it provides increased strength. Most data indicates its machinability of CGI is closer to that of nodular rather than gray iron [130,145–150]. This is in part because complex castings nominally made of compacted graphite iron may exhibit a range of microstuctures, including nodular structures in thin sections. In high volume applications, it is normally assumed that CGI components require one third more capital investment than for gray iron due to reduced cutting speeds. As with austempered ductile iron, CGI exhibits increased adhesive and abrasive wear compared to gray iron [148]. Temperatures are also higher in CGI machining, with thermal cracking and other heat-related tool failures being common In drilling, the use of curved, contoured chisel edges rather than standard straight chisels reportedly improves tool life [151]. In face milling, PCBN tooling is often avoided due to oxidation and diffusion reactions between the work material and the binder in the tool [152], although ceramic binder grades may be effective in these applications. The sulfur content of CGI is reported to have a significant effect on machinability through the formation of soft MnS layers at the tool surface (as in gray iron) [149]. However, CGI is produced by adding magnesium to liquid iron to consume both sulfur and oxygen; the presence of Mg in CGI greatly inhibits MnS formation [150]. Increased titanium content also reduces CGI machinability, so that Ti content in CGI should be specified to be less than 0.01% [150]. Other chemical and metallurgical effects are summarized by Dawson et al. [150].
Effects of rare earth elements (Ce, La) on microstructure and mechanical properties in compacted graphite iron
Published in Philosophical Magazine, 2021
Jianan Zhu, Xintong Lian, Hengchang Lu, Qingyi Liu, Ailong Jiang, Duo Fang, Han Dong, Dexiang Xu
Compacted graphite iron (CGI) possesses both excellent casting performance and heat transfer capability as grey cast iron, and high strength and thermal fatigue properties as nodular cast iron. Therefore, CGI is widely used in iron castings of diesel engine such as cylinder block and cylinder head [1–3]. As the power of diesel engine enhances, thermal load and mechanical load increase greatly. As a result, higher requirements are imposed on the structure optimisation, strength improvement and thermal fatigue performance of the cylinder head material.