Paul K. Dickman wrote:
Judging by the rust and the grind, the inserts are most likely High speed
steel.

Okay. I thought for a bit that they may be carbide. Is the rust a giveaway
that they are not? i.e. does carbide not rust or rust differently?
I haven't gotten around to spark testing the inserts.

The bodies are probably hardened alloy steel. They have to be hard enough
to keep the saw tooth area (that locks in the insert) from getting dinged.

Any idea what type of steel or steels are used in these applications?
Ned suggested that it was likely a tougher rather than harder steel.

These are enormous stagger tooth horizontal milling cutters used to hog
off enormous amounts of metal.

What might the application(s) or industrial process be? The big cutters
have 2 keyways in the center. I can only imagine the forces acting then
these are doing their job.

The inserts are there for several reasons.
#1 it's cheaper,
#2 if you chip a tooth it doesn't trash the whole cutter, and
#3 Each resharpening makes the cutter slightly smaller. With this type of
insert, when they get ground too small for the job, the teeth can be
moved out one notch and reground to spec.

That's a really cool design as I think about it.

Thanks very much for your insight, Paul. And thanks to the others who have
also responded to my question.

Jeff