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Thread: Can you weld cast iron and mild steel ?

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    Opens RealizE's Avatar
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    Can you weld cast iron and mild steel ?

    As above, we want to weld a flange onto the end of a standard cast iron exhaust manifold. Can this actually be done and if so, do I need any special welding gear to do it?

    I just wanted to check before we wrecked the manifold by trying to weld stuff to it only to find it wont hold together.

    The other alternative would be to bolt an adaptor to the manifold, but that seems like too much effort for what we are trying to achieve.

    Thanks!

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    Have seen it done before, many times in fact (changing turbo flanges, external wastegate onto exhaust housing).... not sure on how to do though.

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    That's what we're trying to do - stick a turbo flange on the end of a standard N/A exhaust manifold.

    I've got access to a stick welder and a gasless mig.

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    not a cunt suzuki dave's Avatar
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    ive welded cast and mild together before using a mig and heating up the cast with an oxy prior to welding , but i do believe that a tig would be the go

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    Ready... Take aim... oldcorollas's Avatar
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    the main issue is that you are going from very high carbon to low carbon, and in the weld pool will have high cooling rates, resulting in brittle phases forming...
    i'm not sure of the exact procedure (you should be able to find it searching) but i vaguely remember it had something to do with burning out some of the carbon from the cast iron first... not sure what filler you should use...
    "I'm a retarded Doctor, not a retarded Mechanic"

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    Losferwords probably has it in that you really need to get the cast part very hot then weld it then I would be wanting to drop the temperature fairly quickly afterwards, but you have to be careful with this to as water might crack it. You need to try and avoid getting a Heat Affected Zone right near the weld from cause by the heat from welding. Basically the heat will cause the material near the weld to go brittle and crack easily, especially on something that will get fatigued like an exhaust manifold. Personally I think an adapter plate is a "better" solution. You would be better off paying 30 bucks to get a welding shop to do it for you.

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    needs boost... morerevsm3's Avatar
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    find a flat bit of cast from an old heater or something, and make flange from it, weld cast to cast
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    I've done this in another application but I brazed rather than welded. Welding is probably possible but IMO would be very tricky. Problem would be cracking next to the weld. Brazing keeps the temperatures down and is a more "flexible" weld.

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    brazing is a far better idea. Strength might not be great but should be alright.

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    Ready... Take aim... oldcorollas's Avatar
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    you are going to go from ferrite to pearlite and maybe martensite, then probably a few chunks of cementite before you get to the cast iron... cooling fast might even be worse for the martensite..
    either way, it's ugly and adaptor plate ftw
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    is unplugging your matrix aaron_hogan's Avatar
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    bigmuz covered this in his turbo deisel van conversion thread.
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    Opens RealizE's Avatar
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    I reckon I'll move this to the too-hard basket, it sounds like far too much effort when I can just go with an adapter.

    Thanks for the help!

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    Surf's Up! bigmuz's Avatar
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    Stainless rods and your stick welder and preheat it all first. Works fine (but the chemists and material scientists will tell you it is bad) My van has 7000 kays with a turbo hanging off the welded cast iron manifold and it has not a single crack. The manifold has done 550 000 kays.

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    Ready... Take aim... oldcorollas's Avatar
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    Quote Originally Posted by bigmuz
    Stainless rods and your stick welder and preheat it all first. Works fine (but the chemists and material scientists will tell you it is bad)


    so you are using chromium as a carbon getter then?

    sheel bee roight
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    Surf's Up! bigmuz's Avatar
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    I dunno what I am using as a whatsit thingo, but the CIG Weldall (which incidentally aren't recommended for cast iron) do the job beautifully. You can't argue with results






    HTH

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    Registered User Asteroid's Avatar
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    That's some nice work Muz. How hot does the cast need to be before welding?

    I've been pondering over jamming an SC14 and front mount into mine
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    Fists with your toes Sturmovik's Avatar
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    Cast iron has to be completely red hot to weld.

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    Quote Originally Posted by Asteroid
    That's some nice work Muz.
    Nah mate, that is rough as guts. But like I say 12 months and 7000 kays with a t25 hangin off it plus the exhaust system has no hangers up the front.. Must be OK. I promise I will post if it cracks.

    I heated it up with an LPG torch because I had no oxy then, nothing like red hot, just really hot, if you know what I mean. Probably 300 degrees.

    In the railways they used to repair cast iron cracks by preheating dull red, welding (not sure what rod, but maybe powdered iron?) and then peening it to within an inch of it's life with ball peen hammers. Apparently this is to transfer the carbon into the weld pool and try and keep the structure uniform through the weld zone.

    So don't get me wrong oldcorollas, I am not suggesting it is a perfect solution or even the right thing to do, but I have done it a few times and had no problems. Can you explain the metallurgy more throughly for us to understand the limitations? Thanks
    Last edited by bigmuz; 09-11-06 at 06:55 AM.

  19. #19
    Ready... Take aim... oldcorollas's Avatar
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    there's no question it works and many people do it, but of course a metallurgist will say it's not good
    after writing the stuff below.. i think it is actualyl a good way to do it

    i will try to explain, but i am a bit rusty on iron/carbon ( )


    main phases to think about are ferrite (ductile, soft), cementite (hard, brittle), pearlite (a plywood looking structure of ferrite and cementite)... and for cast iron, the carbon can be free carbon, like graphite, either as round blobs (SG, speheroidal graphite), or as flakes (grey cast iron), or can be part of the compound cementite (Fe3C) (white cast iron.. which is brittle and nasty and often is found in brake components of certain aussie and american cars )

    so.. your low carbon steel (0.1, 0.2 carbon) is way to the left of the diagram, mostly ferrite with a bit of pearlite... and your cast iron is way on the right side, around 4% carbon (cos it melts at lower temp and is cheaper :P ) which will be probably SG or grey cast iron

    disregarding fast cooling effects.... when you melt mild and cast iron together with a weld pool, you suddenly get the full spectrum of phases, from the soft ferrite in the mild, thru pearlite (strong, hard, not toooo brittle)... but between here are cast iron, you start to get more and more cementite forming, which is brittle and weakens the structure, especially against impact (iirc )

    but to make matters worse, when you go from liquid to solid, the first phase to form is austenite... austenite is ok in itself (but only stable at high temps) but when you cool it quickly, you form stuff like martensite and bainite etc, which are .. well... harder and more brittle... (they form from a mechanical change to the austenite, as opposed to a chemical change when it goes to ferrite/peralite etc)...(think of the brittle but hard surface of gear teeth and hammers) (look up TTT curves, time temperature transformation curves)

    so basically..... the join between the two metals has a lot of stuff going on, but the general trend is for it to become much more brittle.

    when you use a stainless steel filler rod, this usually contains low carbon, but lots of chromium and nickel..
    hmm, here is a tidbit http://www.key-to-steel.com/default....Article&NM=151
    nickel basically makes the austenite more stable.
    however, chromium makes it less stable

    but chromium will also react with the carbon, to form chromium carbides, like Cr3C2, Cr7C3, Cr23C6... these can be brittle, but can also increase strength. it also takes some of the chromium and carbon out of the equation, with the result that you are less likely to form as much martensite, since the nickle is now stabilising austenite....

    so basically... the chromium reduces the carbon problem
    the nickel reduces the martensite/bainite problem...

    kinda nifty really

    although it is still not ideal, and very hard to control the structure forming after the weld pool cools, it is probably better than just using a mild or high carbon filler.

    preheating is needed cos the cast iron parts are heavy and they have a high heat capacity.. no pre-heating = little penetration, and also, a smaller heat affected zone.. which can make matters worse by having a more concentrated/abrupt change in structure...

    when cast iron is repaired, a high carbon filler might be used, combined with slow cooling, to try and preserve the grey or SG structure of the iron...

    anyway.. this could all be wrong as i'm just winging it, and it's been a decade since i learnt it :P

    edit: oh, and changing the carbon content and other compositions can change the coefficients of thermal expansion, and combined with a brittle interface, can cause cracking... similar to the cheap stainless steel manifolds, which have a sensitised heat affected zone at their welds which is brittle...
    Last edited by oldcorollas; 09-11-06 at 12:51 PM.
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    Like I said, brazings safe!!!!

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    Ready... Take aim... oldcorollas's Avatar
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    heh heh, manifolds are like rugby league players,
    make them big enough and thick enough, and they can withstand almost anything
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    Fists with your toes Sturmovik's Avatar
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    Brazing is limited to temperatures of no more of 260 degrees. Not sure what a turbo manifold gets to but I imagine on the dyno or the track it would reach up to and above that.

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    2JZ EL Fairmont tandy ass's Avatar
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    Muz, what size rods and how much current did you use for that weld? That's bloody clean for iron to mild, I tried this once before in a non-automotive app and I was only using mild steel rods and didn't heat up the iron, combined with my (lack of) welding talents made one hell of a mess....
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    Surf's Up! bigmuz's Avatar
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    Thanks heaps oldcorollas- that is kinda how I thought it was, only with more words that I have shunned from my memory since materials science

    The key, imho, is to make the joint as long as possible. 100 mils of fillet will be better than 10mils. I know that is obvious, but it seems to work.

    I have an inverter power supply for stick/ dc tig. DC works WAY better than a choke welder which is 50hz ac..

    WELDALL
    TYPICAL ALL WELD METAL MECHANICAL
    PROPERTIES:
    0.2% Proof Stress 630 MPa
    Tensile Strength 780 MPa
    Elongation 25%
    CVN Impact Values 30 J av @ +20C.
    TYPICAL ALL WELD METAL ANALYSIS:
    C: 0.11% Mn: 0.60% Si: 0.88%
    Cr: 27.0% Ni: 9.10% S: 0.011%
    P: 0.020%
    COMPARABLE CIGWELD PRODUCTS:
    Murex Speedex 312-16
    AWS A5.4: E312-16
     Easy-to-Use Rutile Type, High Alloy Electrode.
     Outstanding Operator Appeal!
     WELDS ALL Steels!
     Ideal for Repair & Maintenance jobs.
     Easy Arc Starting and Excellent Stability on Low O.C.V.Welding Machines.
     Not Recommended for Welding Cast Irons.
    Classifications:
    AS/NZS 1553.3 E312-17.
    AWS/ASME-SFA A5.4: E312-17.
    Packaging and Operating Data:
    AC (minimum 45 O.C.V.), DC+ polarity.
    Electrode Approx No. Current Packet Carton Easyweld Part No
    Size mm Length mm Rods/kg Range (amps) Handipaks
    2.5 300 57 40 80 2.5kg 15kg 6 x 2.5kg 611702
    2.5 300 57 40 80 1kg 12kg 12 x 1kg 610702
    2.5 300 57 40 80 20 rod 322101
    3.2 350 30 75 110 2.5kg 15kg 6 x 2.5kg 611703
    3.2 350 30 75 110 1kg 12kg 12 x 1kg 610703
    3.2 350 30 75 110 15 rod 322102
    4.0 350 20 110 150 2.5kg 15kg 6 x 2.5kg 611704
    I used 2.5 and 3.2 mil weldalls. Like i said, they are really for welding tool steel to mild steel, or cromo to mild. Not sure exactly why they recommend against use on cast iron, as they are the best electrode I have used on it. I assume it is because it is too fraught with danger, and people might rely on it for critical applications, like welding crankshafts together

    They say 40 to 80 amps, I would say as hot as you can control, and weave as wide as possible to give the weld as wide a transition from steel to cast as possible.

  25. #25
    Surf's Up! bigmuz's Avatar
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    http://www.lincolnelectric.com/knowl...ronpreheat.asp
    To Heat, or not to Heat

    In general, it is preferred to weld cast iron with preheat--and lots of it. But, another way to successfully weld cast iron is to keep it cool--not cold, but cool. Below, both methods will be described. However, once you select a method, stick with it. Keep it hot, or keep it cool, but don't change horses in the middle of the stream!
    Interesting. they also recommend Lincoln softweld 55 for structural welds.

    http://www.mylincolnelectric.com/Cat...et.asp?p=16771

    A versatile, all-purpose electrode for repairing and reclaiming gray cast iron. It is recommended for repairing heavy sections and phosphorous bearing castings. Welds made with this electrode are strong and ductile. Mulit-pass welds are typically machinable. Operational characteristics are excellent.

    Advantage Lincoln

    • For repairing and reclaiming gray cast iron.
    • Designed for single and multiple pass stick welding.
    • Multi-pass welds are typically machinable.
    • Manufactured under a quality system certified to ISO 9001 requirements.
    That sounds even better than the weldall to me.

  26. #26
    dangerous fugitive
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    Only tid-bit I can add - if using the stainless rods (or possibly the ones made for cast) - if you can't get it to stick well, you might find it easier to first run a bead of weld all around the cast exhaust and _then_ later try to weld the new flange to the welded up section of the exhaust, rather than mating both together with one weld. If you can get it to stick, fine, if not try the above to get you out of a jam.
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  27. #27
    Ready... Take aim... oldcorollas's Avatar
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    the lincoln stuff sounds more like high carbon... and the weldall has shiteloads of chromium....

    if i was in Aus, i would offer to do some cross-sections and analysis of a weld for the heck of it

    hmm.. or i could simulate the weld in a vac arc furnace here (yes yes, nerd alert....)
    "I'm a retarded Doctor, not a retarded Mechanic"

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    Registered User GSRman's Avatar
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    I'm just subscribing to this thread so i can read what corollas said sometime when im awake
    This is a post i wrote by mistake, which is nice...

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    Registered User RB30-POWER's Avatar
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    a few posts in here by 6boost if they help at all

    http://www.calaisturbo.com.au/showth...egate+manifold

  30. #30
    sleepr
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    Quote Originally Posted by oldcorollas
    when cast iron is repaired, a high carbon filler might be used, combined with slow cooling, to try and preserve the grey or SG structure of the iron...
    Correct - having studied this only last year - I would recommend slow cooling as this tends to form longer more aligned crystal structures with less chance of shear dislocations.

    Quenching - if applied properly could result in good properties but this is usually done at sub-zero temps and just dunking it in a bucket of water would most likely result in a very unstable - brittle martensite..
    Last edited by jett; 11-11-06 at 09:40 AM.
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