Cast iron gmaw shielding gas

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GentlemenWhat is the preferred shielding gas for hardened steel to cast iron? Wire is the equivalent of ni99 rod. I have 100% argon and stargon®cs on hand, but will get whatever is needed. Job will be done using a miller 350p.This "HOT" nightmare was thrown in my lap friday afternoon. The job consists of welding three pressed in 15mm dowel pins to the casting. In my opinion this is a band aid for a bad design.The customer has specified using mig.  I suspect this is because of the number of pieces that need to be done ( a couple hundred at least). I tried getting them to let me stick or tig them but no go.Any and all help is appreciated.Last edited by Rob Garner; 03-25-2012 at 03:33 PM.Darwinian evolution used to fix stupid. Now that humans have mostly removed themselves from the process of natural selection the survival rate of idiots has skyrocketed.
Reply:Can you ask the wire manufacturer for their shielding gas recommendations? Ed Craig (weldreality.com) recommends 60% He, 39% Ar, and 1% CO2 for Nickel alloys, IIRC, but your application seems pretty specialized.Good luck,JohnA few weldersA lot of hammersA whole lot of C-clamps
Reply:Inform the customer that the logical solution would be to tap the holes and then insert threaded studs. (Hell, you could hire a bunch of temp laborers to tap all the holes for  8 bucks an hour. but don't tell them that....) Tell them that welding heat-treated steel is likely to result in a high rate of weld cracks and weld failures. Tell them you will not guarantee your work. It is strictly buyer beware. In any case trying to weld or braze heat-treated parts utterly defeats the purpose of said heat treatment in the first place.If a permanent joint is needed then the best option is probably brazing with nickel silver rather than welding. This would reduce the rate of cracks, though it would still destroy the heat treatment on the pins and they'd be better off to select low carbon low alloy steels.If they still insist on welding I think you'd be wise to order something like 50% nickel flux core wires that are specifically designed for welding carbon steels to cast irons. Pure nickel solid wire may work marginally but it's not ideal, whereas flux core wires are much better suited to the inherent dirtiness of most cast irons. Typical shield gas for these is the common Argon + 20-25% CO2.Note: be sure to use plenty of ventilation and/or wear a respirator when welding stuff with a significant nickel content.
Reply:Originally Posted by Rob GarnerGentlemenWhat is the preferred shielding gas for hardened steel to cast iron? Wire is the equivalent of ni99 rod. I have 100% argon and stargon®cs on hand, but will get whatever is needed. Job will be done using a miller 350p.This "HOT" nightmare was thrown in my lap friday afternoon. The job consists of welding three pressed in 15mm dowel pins to the casting. In my opinion this is a band aid for a bad design.The customer has specified using mig.  I suspect this is because of the number of pieces that need to be done ( a couple hundred at least). I tried getting them to let me stick or tig them but no go.Any and all help is appreciated.
Reply:Weld a (hardened steel) dowel pin to a cast iron piece, after the (hardened steel) dowel pin has been press-fit into the cast iron piece?WTF???Weld the hardened steel dowel pin and it will no longer have the 'proper' metallurgical properties that it used to have.  It will most likely end up with a 'witch's brew' of mechanical properties, ranging from glass-hard and super brittle to softer-than-it-is-supposed-to-be.  All in the same dowel pin.Then we can start thinking about what will happen to that already-stressed (from the press-fit) cast iron when you hit it with a welding arc and start melting metal.  The molten cast iron and the molten filler (high nickel content) and the molten (formerly hardened) steel dowel pins all melting toegther and making a mess of the metals and the properties of the metals.  If you make a small weld puddle, then the former compressive stresses in the cast iron from the press fit in addition to the shrinkage compressive stresses from the cooling weld puddle -could- end up exceeding the material properties of the cast iron and then TING, that oh-so-wonderful sound of cracking cast iron.  Grrr.  Make a great big hot weld puddle and then the dowel pin is just cooked to smithereens (tech term there    ) and the thermal stresses again likely make a TING and cracked cast iron.Heat the casting up nice and hot to say 800F and go and make the weld, and the  cast iron may more likely 'survive', but the steel dowel pins are now in some unknown temper/strength condition.Press-fit the dowel pins into the cast iron is all that should be needed.IMHO, rethink the issue because I don't think welding is the answer there.  The best laid schemes ... Gang oft agley ...