Originally Posted by ski

They both contain iron. 409 SS has approx. 85% Fe, 304 SS has approx 70% Fe.
409 SS contains Ti, 304 SS does not.
Intergranular corrosion of ferritic stainless steels occurs due to the precipitation of chromium-carbonitride (Cr-C/N) particles at the grain boundaries leading to Cr-depleted regions. Cr-depletion of grain boundaries in 12Cr alloys(409 SS) occurs due to the formation of mixed Ti/Cr-C in the form MC.

http://www.suppliersonline.com/prope....asp#chemistry

http://www.suppliersonline.com/Resea...1&Mechanical=1

Originally Posted by 4LiterSonic

Everything exhaust system (headers, midpipe, O/As, etc) -minus the tips, of course- is made of T409 steel....
The tips are made of T304 stainless steel, which is designed to resist rusting.

Originally Posted by jbt56

I stand corrected. Thanks for the info!