I ran into something very similar when I built the exhaust for my subie
conversion.  I wanted to re-use the flanges and Y 's and discovered that I
could not cut the pipe with a torch.
  If you are going to weld it with your MIG, you should look for a wire
alloy that is recommended for joining stainless to ordinary steel.  You
should also check whether you need to use a different shielding gas.
  I ended up welding mine with oxy-acetylene and had a lot of trouble with
cracking.  Now I have found a flux that would have helped perhaps.  Very
educational; still more to learn...

Larry A.

On Tue, Apr 1, 2008 at 5:05 PM, neil N <musomuso@gmail.com> wrote:

> Hi all.
>
> Well, am somewhat embarrassed to say that I didn't check to see what
> kind of metal I was playing with. I was just about to tack it in place
> when I noticed it wasn't attracted to the magnet I use for holding the
> work.
>
> Here's some pics of part. Its' the "Y" I cut from the Jetta downpipe:
>
> http://tubaneil.googlepages.com/temp%22y%22pics
>
> There appears to be corrosion inside, but maybe not the pipe reacting.
>
> It is not attracted to my magnet. (how I found out)
>
> It feels too heavy to be aluminum and doesn't grind/file like it either.
>
> SS?
>
> --
> Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
>
> http://web.mac.com/tubaneil
> http://tubaneil.googlepages.com/
>