Ok, Harold, you're right and I'm wrong. Hot iron dissolves
diamond. It doesn't say that in any of my chemistry books
and it doesn't say that in a chemical engineering book, it
doesn't say that in my CRC handbook, although it says
graphite is soluble in liquid iron. It says diamond melts
above 3550 degrees C, but a reference on the net indicates
that diamond breaks down at a much lower temperature. So
maybe it breaks down to graphite and then dissolves into the
steel.

In any case, there appear to be plenty of references in the
tooling industry that iron and diamond don't work together.

As I already admitted in another reply, I was wrong about
the silicon carbide wheels on small grinders. To answer
your question, nope, I can't tell the composition of a wheel
at a glance. The dry ones mostly look gray and the water or
oil soaked ones just look dark. Although silicon carbide
ones come in black and green, mine are black, just like
silicon carbide wet/dry paper. I don't have a clue what the
red wheels are as they aren't marked. I have sharpening
stones, but of the two that retain their packaging, one says
carborundum and the other says silicon carbide (unopened).
Both are the same (of course) and are essentially the same
color as my aluminum oxide grinding wheels. My packaged
grits are silicon carbide and they also have the same dark
grey color.

Well, it's been an interesting thread, and I learned
something.

Harold & Susan Vordos wrote:

"George E. Cawthon" wrote in message
...
big snip-------

If silicon carbide is so bad on steel, how come most small
bench grinders come with silicon carbide wheels?

What reason do you have to believe they do? In almost all instances
(tungsten carbide sharpening grinders excepted, those come with green wheels
or diamond), they do NOT!
Do you have any idea what constitutes a silicon carbide wheel? Can you
identify one at a glance?

Harold