Abstract
Chunky graphite appears easily in heavy-section spheroidal graphite cast irons and is known to affect their mechanical properties. A dedicated experiment has been developed to study the effect of the most important chemical variables reported to change the amount of chunky graphite, namely the content in silicon and in rare earths. Quite unexpectedly, controlled rare earths contents appear beneficial for decreasing chunky graphite when using standard charge materials. Tin is shown to decrease chunky graphite appearance and it is evidenced that this effect is not related to rare earths. Finally, the effect of tin and antimony are compared and it is noticed that both suppress chunky graphite but also lead to some spiky graphite when no rare earth is added. Chunky graphite negatively affects the room temperature mechanical properties, though much more in the case of low silicon spheroidal graphite cast irons than in high silicon ones. Spiky graphite has been found to be much more detrimental and should thus be avoided.
Highlights
Spheroidal graphite cast iron has rapidly become one of the most important engineering materials after its discovery some 70 years ago [1]
To explain the maximum in chunky graphite fraction at location T4 in castings P3 and P7, the correlation that we found is that these are the two alloys with the lowest carbon equivalent (CE) values of the series, only correlation that we found is that these are the two alloys with the lowest CE values of the series, 4.11 and 4.05 wt.% respectively
Quite unexpectedly, controlled rare appear beneficial for decreasing chunky graphite when using standard charge materials
Summary
Spheroidal graphite cast iron has rapidly become one of the most important engineering materials after its discovery some 70 years ago [1]. It is of prime interest to stress that these trace elements are otherwise considered as promoting degeneracy of spheroidal graphite when present above a critical level and should be balanced by RE addition in that case This ambivalent role of trace elements and RE is quite striking and would lead to the conclusion that chunky graphite should not appear if pure charge materials and no RE were used for melt preparation. That this is so has been recently reported by Jia-xin Bai [27] for low-silicon cast irons prepared with high-purity charge materials, but such a way certainly leads to a dramatic cost increase It remains unclear if an optimum addition of elements such as Sb and Sn could be found that would be below the critical limit for graphite degeneracy when no RE are present, but high enough for eliminating the risk of chunky graphite. Si as compared to standard Si content, and the effect of a low level of RE and Sb on chunky graphite occurrence; (iii) documenting the effect of Sn in eliminating chunky graphite and confronting it to that of Sb; (iv) characterizing the impact of chunky graphite on mechanical properties of low and high silicon spheroidal graphite iron
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