On Mon, 04 Jan 2016 08:24:56 +0700, John B.
wrote:

On Sun, 3 Jan 2016 11:56:25 -0600, "Terry Coombs"
wrote:

I have decided to give up and admit those wood stove grates have defeated
me . I have done a lot of research in addition to the excellent advice y'all
have given me and this just ain't happening .
These grates have been repeatedly overheated in a high-carbon environment
, and have apparently absorbed so much carbon as to render them unrepairable
.
First I tried preheat to 500-600° F and TIG welding the cracks with both
cast strips and with the Invar 42 . The problem is that the surface of the
CI just ablates , it will not puddle . I did get some very small "beads"
molten , but the filler would not fuse and puddle .
Next was preheat and brazing rod , it refused to wet the surface and stick
. When I did get it to stick on some places , it cracked as the part cooled
.
Today I tried some new brazing rod with preheat , same deal , it refuses
to wet the surface . Since nothing else has worked I figured I had nothing
to lose so fired up the MIG and tried a short bead with heavy peening as the
weld cooled . And it won't stick either . I'm figuring that with nothing
else working it's pretty much futile to try with stick .
So tomorrow I get to call the guy and tell him the bad news ... but for
some reason I don't think he's going to mind too much . The stove (I got to
see it the other day when I delivered the other piece I repaired) is much
older than mine , and has been cobbled on some before . And he's got another
stove installed where he had this one ... I suspect he was kind of expecting
these to be unrepairable , I pretty sure I'm not the first guy he's asked to
fix them . The others apparently had the good sense to say no .

I might add that most "muffler shops" say that they won't weld to
existing used exhaust pipe for the same reason.

I have successfully welded to old exhaust many times, but there IS a
limit - and aluminized steel is a bit more tricky. With AMC's old
ceramic coated exhaust it was a total exercise in futility..

When it comes to manifolds,I have welded a lot of cracked cast - but
if you get "burned cast" - forget it. It just falls apart when you hit
it with torch or rod.

High nickel (steel) castings seam to stand up to the heat a lot better
than simple grey iron