The following is a cut and paste from the NOC forum, Posted by
Charles Bovington at September 09. 2013and recently resurrected.
Cast iron is a suitable material for low cost mass production of camshafts for low stressed camshafts. The chilling gives a hard white iron layer on the surface which is relatively wear resistant.
For small volume production and for high performance engines camshafts manufactured from steel billet are preferable. Accurate manufacture by CNC grinding machines allows for the production of a superior product, albeit at a higher cost.
In both cases cast iron and steel, careful control of chilling or heat treatment is essential as is the difference in hardness between cam and follower.
The cam/follower interface is the most highly stressed part of the engine. With chilled cast iron, the tensile stresses caused by the cyclic loading experienced at the interface and/or by lack of rigidity in the camshaft can cause sub-surface cracking which, when a grain boundary in the structure, cause lumps to fall out (pitting). Heat treated steel does not suffer this problem because of its higher tensile strength.
There are many pitfalls waiting for the maker of steel cams, the induction hardening process for steel camshafts must be carefully controlled, I know of at least one manufacture who found that he was getting lots of warranty claims on new cars soon after delivery.
We found that the cam hardness varied greatly along the cam shaft and showed them that this was a result of the induction hardening and quenching process. We also supplied a special cam lubricant to help them while they got their heat treatment right.
Flatness of the cam in the transverse direction is also a cause of problems. I chaired the working group which developed the valve train scuffing test which is used in the ACEA engine oil approval system. This uses a Peugeot engine and we found that, using the 'good' reference oil, we could get failing results for cam wear and scuffing on some cam lobes and followers and good passing results on others. Careful measurements showed that inaccuracies in grinding lead to slopes across some lobes such that the oil was squeezed out of the side of the contact causing starved lubrication and scuffing. Peugeot installed a state of the art cam grinder and produced 1000 perfect cams. The problem went away.