Welding nodular iron

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I have an off road car based on a landrover with axles ofF a Volvo c303. I have broken off a cast lug which connects the steering linkage to the axle. I cut this lug off completely, heated the whole cast axle housing and welded on some 8mm thick mild steel bar. Lots of gussets were added to make a very strong modification to the steering.During a competition on Sunday, I drove the car hard into a step and the modified lug snapped off. On looking at the area where the weld has "snapped", it has "pulled" out metal from the casing leaving the nodular structure exposed.I preheated the whole casting prior to, during and after welding although I dont know to what temperature.I used a MIG welder to weld the steel to the casting.My question is what should I have done to get a better weld.It definately is nodular iron (a sort of cast steel), it is not cast iron and is very strong under normal condition. I am pushing the limits I know...Hope someone can help.CheersALAN
Reply:Someone just revived an old thread concerning 'ductile iron'. Give it a look over. There's a link there. http://weldingweb.com/vbb/showthread.php?t=24023Lincolns 'Metals and How to' book also has a couple of small sections. There is also a Ductile Iron Pipe association with links out there that give some good reading. I can't find my old link or I'd post it.Last edited by Sandy; 07-28-2009 at 09:59 PM.
Reply:I think this is occurs in welding of many types of castings, but the formation of martensite seems to be a bigger problem in nodular iron.  This is most likley your problem, as the formation of martensite lowers the ductility of the iron and makes it easier for cracks to start.  The metal that pulled out is probably what transformed into martensite.Welding procedure is preheat to 500-600F for stick welding or 900-1000F for gas welding.  Welding should be done with a hi-nickel electrode or filler, buttering the weld surfaces before laying the  beads is preferred.Post heat to 1000-1200F to transform the martensite back into ductile iron.I'm betting that you did not post heat to a high enough temperature, and it also seems that welding with er-70 is not recommended.Have we all gone mad?
Reply:Thanks for the reply. As you say, I did not post heat.  I have read elsewhere that a 309 s/s tig wire is a good filler for this application. Would pre heat to 600, TIG weld with the 309 the post heat all to 1200 do the job, bearing in mind I am welding mild steel to the ductile iron?CheersAlan
Reply:309 is usually the go to filler for welding dissimilar metals, so you should be alright there.  I would suggest since your doing it with TIG take a few passes first and lay down a buttered surface of 309 on the nodular iron, then without letting it cool either use 309 to weld the part on or er-70Have we all gone mad?
Reply:Going to get some Temple Sticks?? today to get the pre heat temp right. My supplier suggests 316L mig wire has 12% nickel compared to 12.5% nickel in 309 filler wire. Could I MIG weld stainless steel bar to the ductile iron using 316L MIG wire with the same pre heating etc. instead of buying the 309 which is quite expensive for the small amount of welding I have to do.
Reply:How about brazing it?
Reply:That should be fine, like I said I would preheat first, then butter the surface of the nodular piece first and then weld to that.Have we all gone mad?
Reply:I have the big test on my welding over the next 2 weekends. I ended up welding 316 stainless bar to the ductile iron casting using 316l stainless mig after pre heating to 600 deg then post heating to 1200 and allowing to cool slowly.
Reply:Nodular Iron is not cast steel; it is cast iron with various alloying materials like Magnesium which cause the excess Carbon to form spheres of nodules rather than long thin flakes. WRT alloys to use when welding, when Nickel is molten, it can dissolve higher levels of Carbon which are rejected as it cools; this both removes some of the excess carbon from cast iron it is welded to, and provides a shrinkage rate similar to the cast iron. It is also ductile enough to deform during the cooling, preventing stress from building in the joint.The amount of Chromium and other alloying elements of the filler also need to be considered due to their effect on the hardening properties.Last edited by Oldiron2; 10-23-2009 at 11:25 AM.