My bet is the zinc is acting like an anode and absorbing all of the
oxygen that would do the rusting. Just like an anode on your boat to
keep it from melting away. It melts away.

Martin

On 10/9/2015 8:11 AM, Lloyd E. Sponenburgh wrote:
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