User Omega

Good info! I had no idea they were doing this with exhaust.

I am well aware of aluminizing stainless. It is just a coating. I had no idea that it was done to exhaust was all. I work in food grade process engineer land. It can be applied to any metal really. I had several classes in college where we learned about the composition of metals at the molecular level. If you wanted a fix all exhaust that would never rust or need repaired you would want 304 stainless. 409 is a garbage metal that is (if made correctly) over 10% chromium (maybe why my resonator pipe rotted so badly if it was stainless). There are many that are far worse in the land of stainless but it sure isn't going to last like 304 or 316. I suppose it would make sense to aluminize it but I wouldn't have expected it to rot off of a vehicle before you saw rust on body steel. Especially underbody with as many plugs they put in these things.

tiapetra

I was responding to your first post above where you stated you had never heard of aluminizing stainless steel.
Sorry for you experiences with 409, but I've had the stellar results as everyone else I know. Work trucks as old as 1994 have yet to even have any surface rust on the 409 exhausts, but of course I am in the deep south and see no salt roads, just some salt air being less than a mile from the ocean.
BTW, besides cost, 304 isn't the best choice for exhaust as it is prone to cracking, but headers do look nice in polished ss.

sleeper

Yes I'm in the deep south myself, & my '08 HHR pipes still look like new.
I did paint the muffler with satin black BBQ paint to make it almost invisible from behind.

This was a popular mod back in the day.

User Omega

My apologies. I was speaking to specifically exhaust components when referencing alumnizing. I bet there are 14 pages of the ALRO catalog full of it in sheets, tubing, piping, and stock.

As far as which stainless is best for corrosion resistance/longevity on an automotive application I suppose we aren't going to agree. I guess the ultra premium exhaust companies are making some mistakes by using the 304 or 316. Maybe they just haven't done their research because they sure aren't using it for polishing or because it's lighter. As for me I've never seen it crack unless it was wrapped in header wrap and fatigued or was welded with poor penetration. All of the process piping we spec in the factory is 304. It is constantly under the stress of vibrations that cars cannot produce and shaking and heating and cooling and so on. No cracks or issues there. We do lose gaskets though.

Also 409 is much cheaper than 304.

User Omega

I thought about doing that myself. It does sort of stand out from the back.

sleeper

Yes it does stand out, & most modders here painted them. I painted mine back in about '09 or '10 & it's still holding up well.

tiapetra

It's all good.
You can easily find plenty references to 304 headers cracking in a google search. And no, they don't all crack.
304 is more brittle and much less ductile than 400 series and suffers readily from work hardening (ie forming and flexing), gauge is an important factor.
As I said before 409 is plenty for me, I can weld, bend or form any of it, not a big deal. You can even polish 409 to a high degree for exhaust tips.
We are not new to ss, we work mostly on mega yachts and use polished 316L almost exclusively, but these people can well afford it.
Where utmost corrosion resistance is needed and appearance isn't a factor, they are now even switching to titanium.

I'm surprised you use so much 304, 420 and 440c ss is used a lot in food processing, but there are a lot of choices.