My purpose was to cut t-slots in cast iron, which I have done and found easier than expected.  These cutters have held up well after repeated use.   

Hard tool steel is required for this application and  SKS-3 JIS (Japanese Industrial Standards) was chosen.

Machining of this material must proceed slowly.  Depth of cut was limited to 0.5 mm, with cutting speeds limited to 1,000 rpm.   The chips were hot and blue, necessitating care to avoid danger to the operator.

After basic machining, the cutters were hardened and the edges sharpened.