Well... got out to the shop this a.m. to find something different.

Last night, I sparked out a piece, and it looked for all the world like
just ordinary structural steel. A piece of A36 next to it made the same
sparks... BUT... for a long time (a couple of seconds of grinding...) no
sparks.

So today, I took it back in the shop, mic'd a flange, then ground lightly
just until I saw the first sparks, and mic'd it again. There's darned-
near 15 mils of zinc on this stuff!

Further, I had treated a cut end last night with potassium nitrate/water
slurry. This a.m. there WAS some visible rust on the cut surface. The
untreated cutoffs I left out in the dew, now, for two nights are still
pristine.

So, even though these flanges are about 3/8" thick, I guess I'll have to
go with Ed's surmise that the 'galvanic cell' process is keeping the cut
edges from rusting, unless otherwise accelerated to do so.

Huh! I guess I just got a lesson in how good at its job GOOD galvanizing
can be!

LLoyd