welding cast to stainless

I'd like to weld stainless(304) v-band flanges on the exhaust manifolds of the 2-stroke saabs I work on for better sealing and easier disconnect. I've only welded mild to cast iron or cast iron to itself, any thoughts? because 'cast' rod is mostly nickel anyway (55 or 99%) I can't see much of a problem using a high-nickel stick rod, but I figure I'll solicit opinions anyway.

this is also probably thick enough that I can TIG it with the I-MIG, though, so if anyone has a dynamite TIG filler for welding 304 stainless to highly carbon-impregnated cast iron, I'm all for it :)

Wouldn't it be easy to just make a stainless exhaust manifold for it ?

yes and no. we have upwards of 40 cast manifolds(stainless is expensive, boss is cheap) and re-designing 2-stroke exhaust ahead of the expansion chamber is a big headache that I'm not ready to tackle yet, so factoring those things in it's much easier to weld a new modern flange on the mani and the downpipe. when I do get around to redoing the manifold in stainless, I'll probably move the joint down outside the belly pan closer to the expansion chamber so the exhaust is easier to handle.

worse case I can use mild steel flanges, I was going to use stainless to the sealing surface wouldn't corrode and start leaking.

Expansion differential is so different, I'd imagine something would crack even if the weld was solid.

Although I have never attempted welding stainless to cast, my gut tells me: stick or TIG weld with nickel rod (and I only have experience with "Nickel 55", which seems suitable) for this.

The reason nickel rod is good for welding cast iron when cold, is that it doesn't contract from heat as much as other alloys, so it limits the contraction stresses that are applied to the brittle cast parent metal from the cooling weld bead.

I don't know how much I like the idea of austenitic stainless welded to cast iron, however, due to the differences in thermal expansion of the two materials, combined with the brittleness of cast iron - as already mentioned by Mark. (Even if you got it welded without cracking, it might crack subsequently upon usage - normal heat cycling of an exhaust manifold.

Mild steel to cast iron would have less potential problems with cracking in this manner (because the thermal expansion coefficients of the materials are a lot closer.)

You might have a better chance if you build up a ledge out of nickel, say 1/4 to 3/8 and then welded the stainless to the nickel ledge, a thought for you to think about.

I'm glad I asked, I hadn't thought about the difference in thermal expansion. I'm pretty sure these manifolds are plain grey iron, so figure 5.7 ppm/F. 304&308 are 9.3, 309 is 8.2*
410, on the other hand, is 6.1. too bad no one makes V-band flanges in 410.

mild I'm seeing listed at 7.3, and I'm seeing 5.5 for 410 on another reference.

http://cp.literature.agilent.com/lit...5517-90143.pdf
http://www.engineeringtoolbox.com/li...ents-d_95.html

I guess I'll use mild flanges. my other option is to fab a new downpipe and move the v-band under the bellypan.


*this explains why 309 does well welding 304/308 to mild.

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Originally Posted by geezer

You might have a better chance if you build up a ledge out of nickel, say 1/4 to 3/8 and then welded the stainless to the nickel ledge, a thought for you to think about.

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you're probably right on that one. nickel is ductile enough to disperse enough of the stresses from the stainless' higher coefficient of expansion before they reach the brittle cast iron to keep it from cracking.

3/8" deposit is probably what, 5-6 passes with 1/8" ni55? should be able to get that out of a lb. I'd like to not have to buy more than a lb for experimentation. that stuff ain't cheap.

That's interesting that the 4xx series stainless steel is closer to grey cast iron in terms of thermal expansion rate than mild steel is.

I thought so too. I think that might explain it's prevalence in exhaust, too. although, I don't think I've ever seen headers out of 410, where the benefit would be greatest.

400 series stainless doesn't have nickle in it only chromium. That is why it is not a corrosion resistant as 300 series.

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Originally Posted by Cippee

400 series stainless doesn't have nickle in it only chromium. That is why it is not a corrosion resistant as 300 series.

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400 series do contain nickle, just not in the high amounts as 300 series.

Sorry no it doesn't look. "There are several "types" of stainless steel. The 300 series (which contains nickel) is NOT magnetic. The 400 series (which just contains chromium and no nickel) ARE magnetic."

Look it up.

Hears a link to a chart of different stainless alloy compositions.

http://www.scotforge.com/charts/sf_s...ainless_ns.htm

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Originally Posted by Cippee

Sorry no it doesn't look. "There are several "types" of stainless steel. The 300 series (which contains nickel) is NOT magnetic. The 400 series (which just contains chromium and no nickel) ARE magnetic."

Look it up.

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maybe i should have been more specific... ferritic ss dont have nickle. martensetic ones do. 403 408 414 431 to name a few.

If you weld cast iron in small runs and let it cool in between runs you can weld it without preheat. Some pieces are too big for me to preheat evenly. Also I tend to be on the lazy side at times. Sorry jerky I didn't mean to sound rude or snotty about the 400 series. I didn't realize how my post sounded until I read it.

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Originally Posted by Cippee

If you weld cast iron in small runs and let it cool in between runs you can weld it without preheat. Some pieces are too big for me to preheat evenly. Also I tend to be on the lazy side at times. Sorry jerky I didn't mean to sound rude or snotty about the 400 series. I didn't realize how my post sounded until I read it.

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its ok, i was just trying to get across that some 400's do have nickle, but most dont. as for cast, you also need to "peen" the weld, witch is hitting it with a hammer to allow the deposited weldment to "stretch" so it wont crack when cooling.

I did leave out the most important part, thanks. All the fumes I have inhaled are starting to affect my brain. Someone would have been cursing when the weld cracked. Thanks guys.

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Originally Posted by Cippee

I did leave out the most important part, thanks. All the fumes I have inhaled are starting to affect my brain. Someone would have been cursing when the weld cracked. Thanks guys.

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sounds like a 309 filler is in order considering that what it is used for

You can 'butter' the cast with a real stretchy nickel rod, then weld 312 or 308L to it, but compatibility problems could be very high and carbon monoxide danger very real in case of a crack. Best not.