Is it really stainless??

[beem]

Hi guys ive been reading on other posts that some of you reckon the 318is has a stainless manifold,is this true? i thought stainless steel didnt rust. a Pic.

[Speedtouch]

Depends on the grade/quality of stainless: cheaper ones are actually closer to mild steel! I bought a cheap s/s exhaust for a car and it's rusted in places too, though nowhere near as bad as a 'normal' exhaust would.

[maxfield]

I wouldn't of thought that's stainless

[DanThe]

Dont look like stainless to me

[fuzzy]

doesnt look like stainless to me either

[WillG]

I think its either 409 which people like powerflow use and that will rust over 4-5 years time even on a back box or 304 which is alot better but where there is alot of heat like that and over 15-20 years I reakon its possible it would rust like that, I doubt a mild steel tube header like that would of lasted that long. I think 308 and 316 is marine grade and wont really ever rust. I think jon volk uses that on his manifolds, the down sides with it is that its expensive and its quite alot more brittle and more likely to crack

[beem]

would stainless really look like that after 15 years?

[Theo]

Put a magnet against it - if the manifold is magnetic it isn't stainless.

[billgatese30]

Put a magnet against it - if the manifold is magnetic it isn't stainless.

not necessarily, some stainless alloys have cobalt content, and as far as i can remember from GSCE science, cobalt is naturally magnetic

it is also added to alot of steels to help resist high temperatures, which in an exhaust manifold has obvious benefits

wether enough is added to make it magnetic enough to detect with a fridge magnet though is another matter

[old_skool]

Put a magnet against it - if the manifold is magnetic it isn't stainless.

"Grade 304 stainless may exhibit quite strong response to a magnet, whereas Grades 310 and 316 will in most instances still be almost totally non-responsive."

[appletree]

i tryd a big strog magnet on mine abit back there wasnt any response if you give it a little polish with a scotch bright pad it will come back shuney min did and it was still shiney in parts anyway.

[WillG]

would stainless really look like that after 15 years?

yeah if there is enuff ferrite in the grain structure then there will be some on the outside of the gains which is what you see has rusted, I think on stainless which has more of different metals in it then it stays inside the grains and that is why it wont ever rust. Its done well tho really imagine if you put mild steel that thickness there, it probly wouldnt last 5 years, that area of the exhaust gets upto 800 C there, im pretty sure some stainless steels change grain structure at that temperature and become ferous/magnetic (possible to rust) but id have to get my college folders out to be sure, its been 4 years and I just get the metal whats on the drawing and weld it now

[kam-325i]

Some of the alloys can migrate to the surface over time, combined with the heat, causing this. Stainless has so many different grades.......it could be anything.....some manufactures will have an alloy made up just for exhaust manifolds that are very good at withstanding heat, but can oxidize over time.....

[E30Mark]

I think there are two basic groups of stainless, austenitic & martensitic. Martensitic has a higher carbon content and can become magnetic due to stress levels..... martensitic stainless is good for tensile stressed components, but can fracture under stress. The exhaust is more than likely austenitic as this is less likely to fracture under heat / vibration, and also has a higher corrosion resistance. Damn materials lessons were sooooo boring, i may have got the above all mixed up!

[buster]

yep ,mark hit the nail on the head there.
There are all types off stainless steels,like duplex.Its very tough,corrosion resistant but is still magnetic.

[billgatese30]

yep ,mark hit the nail on the head there.
There are all types off stainless steels,like duplex.Its very tough,corrosion resistant but is still magnetic.

and is a pain in the arse to machine, same with incanel, although i can't remember if its strcitly classed as a stainless, its more of a super alloy


but its the worst stuff to machine ever, so bloody hard and tough

[buster]

yep ,mark hit the nail on the head there.
There are all types off stainless steels,like duplex.Its very tough,corrosion resistant but is still magnetic.

and is a pain in the arse to machine, same with incanel, although i can't remember if its strcitly classed as a stainless, its more of a super alloy


but its the worst stuff to machine ever, so bloody hard and tough

yeah,its a bit tricky to machine,but not too bad if you know what your doing.

[billgatese30]

yep ,mark hit the nail on the head there.
There are all types off stainless steels,like duplex.Its very tough,corrosion resistant but is still magnetic.

and is a pain in the arse to machine, same with incanel, although i can't remember if its strcitly classed as a stainless, its more of a super alloy


but its the worst stuff to machine ever, so bloody hard and tough

yeah,its a bit tricky to machine,but not too bad if you know what your doing.

we used to do alot of it in my old place, so it wasn't too bad, still can be a pain in the arse though comapred to other things

[buster]

do you work in a machine shop ?