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Thread: Identifying steel type for rod selection

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    Identifying steel type for rod selection

    Iím thinking about projects for my new TIG which should arrive this week (refer TIG thread).

    One candidate is the bastard DPF in the towing rig. The exit has a 90 degree elbow, so one member of the Brains Trust suggested cutting the end off it, applying a pressure washer to clean it out, then weld it back together. Being thin, itís a good candidate for TIG welding.

    How do I identify the steel type and therefore the rod selection?

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    Registered User bang chong's Avatar
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    Identifying steel type for rod selection

    Er70s2 for mild steel, 316 for most stainless, 309 for joining dissimilar metals(stainless to mild),4043 for most aluminium. Thatís just a rough idea of filler wire I use. Welding supply stores usually can guide you in the right direction if you arenít sure(well good ones should).

    See if a magnet will stick first
    Last edited by bang chong; 22-01-18 at 05:01 PM.

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    For mild steels, use ER70-S2, or CuSi brazing rod. Will have that familiar bluish tint to it, even if polished. Magnetic, rusts quickly when polished and wiped with vinegar.

    For stainless steels, the rule of thumb is use a filler rod with a number equal to or greater than the base alloy you're welding-so if welding 303 free machining stainless, use ER308L rod. For 304L, use 308L rod. (N/A stainless headers and exhaust flanges/v-band rings) For 316 stainless, use ER316L rod. (Stainless high-heat N/A, rotary, or nitrous headers) For 321 Ti-stablized stainless, use ER347 rod. (stainless turbo header, nitrous rotary header) For 409 stainless, use ER409Cb rod. (this is very common in OE stainless exhausts these days.) You can use ER309L in a pinch and it'll be OK with 409, too, but it's going to be more prone to cracking.

    On thin tubing like exhaust tubing, you will not be using rod for butt joints. Your joint must fit perfectly flush, there can be absolutely no gap, and you will have to use either a backing flux or back purge for stainless joints. Don't use a backing flux upstream of a turbo or a filter. It turns to glass and flakes off a little after a while at heat-but it's tough as nails so it will take a long time to flake out.

    When tig welding thin exhaust tube to thick flanges, don't aim for a fillet weld between the tube and the back of the flange, do a tiny fusion weld with no rod, on the inside of the flange. This helps prevent a LOT of warpage, and the on the back side where you'd put a fillet weld, get some ER-CuSI silicon bronze TIG rod. NOT REGULAR BRAZING ROD! The CuSi filler has no zinc or tin, so it won't fume out when you start welding and blow smut all over your electrode and cup.

    By brazing the backside, you've supported the tubing and since the brazing occurs at a much lower temperature and has a lower coefficient of expansion, the flange will warp MUCH less, often times not even enough to need to be surfaced. As a bonus, the bronze is soft and so it resists vibration cracking better, as well as quieting the "header ping" you get sometimes. You still have the stainless fusion weld on the inside of the tube to seal it all up, so you can leave a gap in the fillet braze near bolt holes so that bolts/nuts will still set flush on the flange.

    If you have a hard time making the fusion-only butt weld on stainless, more than likely it's dirty, you have a gap in the joint fitup, or you're burning through. For 308L 1.2mm wall thickness tubing, I run 6-8A DC, use a 1.2mm 2% cerium oxide electrode, ground to a needle point, a gas lens and a 12 or 14 cup on diameters over 2" and a 12 or 10 cup for under 2" tubing, unless I have to get into a super tight spot. Pure argon cover gas always, and if it's non-turbo, Solarflux B backing flux, and if it's turbo, backpurge with argon or nitrogen, depending on grade of stainless and size of tube-the nitrogen works fine as a backing shield, you just have to keep the oxygen out of it. On Ti-stablized grades like 321, 347, and 409, though, you MUST use argon inside and out. You'll have a nice titanium nitride coated exhaust on the inside, and a weak weld, if you try to backpurge with nitrogen.

    Usually the best way to ID stainless alloys is by the numbers printed on the tubing-other than that you'll find 409 is magnetic and 300-series stainless is not, and beyond that it's pretty tough to ID them. If you are stuck with non-marked tube and no way to know what it is, and you gotta get it done, then use the higher-rod-number rule of thumb and get the greatest-number rod you have in the shop.

    For welding cast iron and turbine housings, use ER309 or the ER309/ER310 combo, it's just easier these days to use the ER309 rod and not fuss with keeping two wire alloys around. You can weld stainless to cast, mild to cast, cast to cast, with these rods and normally it'll be OK. Ocassionally you'll need to use Ni-Rod, which is just straight nickel, no alloy, and it stays soft. Not really needed in exhaust work, but for repairing blocks when the customer doesn't want a braze or you need to paint it to hide the repair, Ni-Rod works. (bronzes and brasses won't hold paint as well, and will start to flake first.)

    Hope that helps. Grab some cheap stainless tubing to cut up and weld back together before you tackle the truck. Don't be scared of ruining practice tube to get the motion into your bones-welding is 80% muscle memory and 18% planning and knowledge. The last 2% is just blind fucking luck, some days...

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    Registered User StanM3's Avatar
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    Xnke: I would happily pay to subscribe to your newsletter!


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    Quote Originally Posted by StanM3 View Post
    Xnke: I would happily pay to subscribe to your newsletter!


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    If you had seen some of his welds you would be amazed.
    Radical SR3
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    Quote Originally Posted by StanM3 View Post
    Xnke: I would happily pay to subscribe to your newsletter!


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    Xnke, thatís a big +2! You have gone to a lot of trouble to comprehensively answer my question, thank you!!!

    Serious question, do you have a newsletter? Or YouTube channel?

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    I might by tomorrow, it's 5AM and I haven't slept in two days so shit like that is starting to sound like a good idea.

    Youtube might be filmed in finest potatovision. And my welds look like shit half the time, I'm not a sexy welder.

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    Arrogant wankeler Slides's Avatar
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    Thanks for the details.

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    tryhard snelens's Avatar
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    As a sparky I have lots of respect for the metal artisans of the world.

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    Circling back on this thread, I'm going to pull out the DPF over Easter and cut it open and have a go at cleaning it.

    I have not been able to identify the grade of stainless steel the DPF is made of, beyond it being magnetic. Based on that scant information, what filler rod should I get? Or does anyone know what grade of SS is typically used on DPFs?

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    Non Compos Mentos Gammaboy's Avatar
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    Quote Originally Posted by Xnke View Post
    Usually the best way to ID stainless alloys is by the numbers printed on the tubing-other than that you'll find 409 is magnetic and 300-series stainless is not, and beyond that it's pretty tough to ID them. If you are stuck with non-marked tube and no way to know what it is, and you gotta get it done, then use the higher-rod-number rule of thumb and get the greatest-number rod you have in the shop.
    .
    Quote Originally Posted by Xnke View Post
    For stainless steels, the rule of thumb is use a filler rod with a number equal to or greater than the base alloy you're welding-so if welding 303 free machining stainless, use ER308L rod. For 304L, use 308L rod. (N/A stainless headers and exhaust flanges/v-band rings) For 316 stainless, use ER316L rod. (Stainless high-heat N/A, rotary, or nitrous headers) For 321 Ti-stablized stainless, use ER347 rod. (stainless turbo header, nitrous rotary header) For 409 stainless, use ER409Cb rod. (this is very common in OE stainless exhausts these days.) You can use ER309L in a pinch and it'll be OK with 409, too, but it's going to be more prone to cracking.
    It's all there.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

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    Quote Originally Posted by Gammaboy View Post
    It's all there.
    Thanks Gamma, so we are assuming it's 409? There's no markings on it, and as you know there are other grades of SS that are magnetic.

    If that's the Brains Trust's best guess, then I'll get ER409 rods and give them a run.

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    ER409 is the cheapest grade of exhaust tubing that's still stainless, and it'll "corrode" to a brownish dirty looking color wheras most other stainless won't get that dirty brown look going on. The other magnetic grades of stainless are mostly 400 series as well, and weld like garbage so it's very unlikely to be a different grade of magnetic stainless. Combo of being cheap, dirty brown, and magnetic stainless, along with the big 3 using 409 (ford, GM, Chrysler), means that's what I'd treat it as. Besides, follow the rule of thumb re:numbers and you'll be OK, you can pretty much weld any steel to any steel or cast iron with a 309 rod, with generally "OK" results regarding cracking issues.

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    Thanks Xnke, it's definitely got that brownish dirty colour about it, so we'll run with 409.

    I've got my supplier trying to find me some rods, and a back purge setup for my reg. Worst case, he's got 309L.

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