Best steel for turbo header?

[Victor1620]

I can't seem to find a straight on answer, if there is one. Opinions?

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[Dirty25RS]

Inconel 625

its not steel, but it IS best.

Inconel alloys are oxidation and corrosion resistant materials well suited for service in extreme environments. When heated, Inconel forms a thick, stable, passivating oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high temperature applications where aluminum and steel would succumb to creep as a result of thermally-induced crystal vacancies (see Arrhenius equation). Inconel's high temperature strength is developed by solid solution strengthening or precipitation strengthening, depending on the alloy. In age hardening or precipitation strengthening varieties, small amounts of niobium combine with nickel to form the intermetallic compound Ni3Nb or gamma prime (γ'). Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures.

[Victor1620]

Wow. Steel is more in my price range.

[Dirty25RS]

T304 although I'm sure about the heat range.

http://www.matweb.com/search/DataShe...37098da&ckck=1

[Victor1620]

That site wants to feed my computer cookies, however, thanks.

[Dirty25RS]

matweb is an unmatched resource for material property and sourcing information.

Its no BS.

[Victor1620]

Absolutely. Very informative site, thanks again.

[FourOnTheFloor65]

304 really isn't a good choice at all, even though most turbo headers are made from it. They use it because it is cheaper than a proper material. This is one of the biggest reasons, that even name brand turbo headers have a bad reputation for cracking. I'd rather use mild steel and have it Swain Tech coated than use 304. For an NA header it is not bad. The added exhaust temperature in a turbo application causes the issues. The problem with 304 is Chromium precipitation. At high temperatures, like during welding, or use as a turbo header the Chromium (what makes stainless steel, stainless) starts to precipitate out of the material. Over time this allows the stainless to corrode. Sometimes it pits, sometimes it causes intergranular stress corrosion cracking. Anyways 304 is not good unless your bottom line is more important than the product.

321 stainless is a much better material for high heat applications. It is much less prone to Chromium precipitation. It's not quite as good as some of the different Inconel alloys, but it's much cheaper.

[kharris4]

Originally Posted by FourOnTheFloor65

304 really isn't a good choice at all, even though most turbo headers are made from it. They use it because it is cheaper than a proper material. This is one of the biggest reasons, that even name brand turbo headers have a bad reputation for cracking. I'd rather use mild steel and have it Swain Tech coated than use 304. For an NA header it is not bad. The added exhaust temperature in a turbo application causes the issues. The problem with 304 is Chromium precipitation. At high temperatures, like during welding, or use as a turbo header the Chromium (what makes stainless steel, stainless) starts to precipitate out of the material. Over time this allows the stainless to corrode. Sometimes it pits, sometimes it causes intergranular stress corrosion cracking. Anyways 304 is not good unless your bottom line is more important than the product.

321 stainless is a much better material for high heat applications. It is much less prone to Chromium precipitation. It's not quite as good as some of the different Inconel alloys, but it's much cheaper.

+1 for 321 S.S. if you can source everything that you need.

[Darcros]

http://www.burnsstainless.com/ there should be no more post after this one

[Token-Negro]

Simple, 321 and if you can afford 625 do that.

[stispeedwagon]

321 with a nice ceramic coating shuld suit you just fine. howdy token

[downest]

I've built a lot of turbo manifolds with 304 stainless with no issues. Yes, 321 is better, but 304 is more than enough for manifold duty when properly welded and backpurged. Honda guys have been using it for years without problems, it's pretty much the standard. I have personally never seen any kind of precipitation or breakdown of 304 due to use, only from improper welding.

[sofiagonza]

wow..........very nice explanation.............thanks a lot

Originally Posted by FourOnTheFloor65

304 really isn't a good choice at all, even though most turbo headers are made from it. They use it because it is cheaper than a proper material. This is one of the biggest reasons, that even name brand turbo headers have a bad reputation for cracking. I'd rather use mild steel and have it Swain Tech coated than use 304. For an NA header it is not bad. The added exhaust temperature in a turbo application causes the issues. The problem with 304 is Chromium precipitation. At high temperatures, like during welding, or use as a turbo header the Chromium (what makes stainless steel, stainless) starts to precipitate out of the material. Over time this allows the stainless to corrode. Sometimes it pits, sometimes it causes intergranular stress corrosion cracking. Anyways 304 is not good unless your bottom line is more important than the product.

321 stainless is a much better material for high heat applications. It is much less prone to Chromium precipitation. It's not quite as good as some of the different Inconel alloys, but it's much cheaper.

[GEE-OTTO]

No to T304SUS and I would only use 16ga. or heavier 321 I would use 625 but it is pricey but I wonder how well T202 would work and never use T409 really for anything hahaha it is bad unless coated.

[PHATsuby]

How does 316 compare to 321? I assume slightly less ideal but is it still better than 304?

Thanks for the help.

Ben

[XplicitRacingDesign]

I agree with using 321 s.s.

I've used 304 in the past, it's usually alright as long as it has some wall thickness to it, and i would def recommend getting everything high temp coated.

[GEE-OTTO]

T202! high nickel content or T321 I have used T308 and T304 they work well and will suffice .16 ga min use a good stainless wire or rod or filler (depending on welding method) mandrel bend everything to maintain true radius in bends

[madmax718]

Most of the time headers I've seen fail are from rust, or thin steel. 304 is fine, but you have to use a minimum thickness to prevent problems. The other part is, things will generally crack at the welds (especially stainless) as the extreme heat at the welding site will migrate the contents of the alloy. Thats why most cracks are at the weld line.

There is no perfect answer- especially if you want to keep things light weight.

[All4bSpinnin]

what about the thickness of the 321? how thick should the piping be?

[GEE-OTTO]

Originally Posted by All4bSpinnin

what about the thickness of the 321? how thick should the piping be?

I would find a good source for 321 i see it a lot in 18 and 16 gauge but for a manifold i would like see something beefier.



If only cast iron wasn't such a bitch!

[madmax718]

You can weld cast iron. Just takes patience and time. No guarenteed results, but a nickle rod works ok.

[smallblock]

The problem with austenitic stainless (300 series) is that chromium carbides precipitate in the sensitization range (~850-1500..hey my EGT's are somewhere in there..). Essentially, the chromium would rather be close friends with carbon than hang out in the alloy, and precipitates into the grain boundaries as chromium carbide. When 304 headers crack, it is primarily because the welder did not solution anneal the part (1900 F for 30 min soak) to re-dissolve the chromium carbides. One alternative is to use "L" grades (304L / 316L...), which have a lower carbon content. The Carbides precipitate into the heat affected zone. Further cycling in the sensitization range just makes this worse. 321, 347, etc. alloys are what are referred to as "stabilized" alloys, where titanium(321), niobium, or tantalum have a greater affinity for carbon, and allow the chromium to remain in solution. A greater nickel/chromium content doesn't hurt, either.

[downest]

Originally Posted by smallblock

The problem with austenitic stainless (300 series) is that chromium carbides precipitate in the sensitization range (~850-1500..hey my EGT's are somewhere in there..). Essentially, the chromium would rather be close friends with carbon than hang out in the alloy, and precipitates into the grain boundaries as chromium carbide. When 304 headers crack, it is primarily because the welder did not solution anneal the part (1900 F for 30 min soak) to re-dissolve the chromium carbides. One alternative is to use "L" grades (304L / 316L...), which have a lower carbon content. The Carbides precipitate into the heat affected zone. Further cycling in the sensitization range just makes this worse. 321, 347, etc. alloys are what are referred to as "stabilized" alloys, where titanium(321), niobium, or tantalum have a greater affinity for carbon, and allow the chromium to remain in solution. A greater nickel/chromium content doesn't hurt, either.

On most of my inline four turbo manifolds, I use sch 10 1.5" 304 with 308L filler, backpurge, two passes with the first being pretty much all fusion welding. There is no sugaring after welding, and I have never seen it develop from high EGTs either. I think this is common practise for many manifold builders for Hondas, DSMs, etc. Obviously for an EJ manifold, sch 10 would be extremely heavy and probably not the best for the job.

[GEE-OTTO]

Originally Posted by madmax718

You can weld cast iron. Just takes patience and time. No guarenteed results, but a nickle rod works ok.

I know it can be welded but finding a person to weld it is the bitch even when you want to pay