Question

Which of the following cast irons cannot be machined?

(a) White cast iron

(b) Grey cast iron

(c) Malleable cast iron

(d) Spheroidal graphite cast iron

This question was addressed to me in a national level competition.

Enquiry is from Cast Irons in portion Non Ferrous Materials of Engineering Material & Metallurgy

Answer 1

Right option is (a) White cast iron

The explanation is: White cast irons are used where hardness and wear resistance matter, like grinding and crushing. Since it is hard, it cannot be machined. Grey and malleable cast irons, on the other hand, have excellent machinability. Spheroidal graphite cast irons also possess good machinability.