Can Cast Iron be Welded

[macona]

Just because the method is not in a manual does not mean that it does not work.

Using the 91K2-H the weld and the parent metal is quite machinable. It can be turned, drilled and tapped.

And has yet had anyone come back because it broke again. And this is on parts like printing presses where there is repeated impact loads.

It comes down to there are as many recipes to weld cast as there are days in the year. Some cast just wont weld with just about anything, some will weld with 7018.

Harris SuperMissleRod is recommended for cast iron and it is basically 347 stainless.

[torker]

Radkins...those trucks prolly came from an hour down the road from me.
I've worked on a lot of BIG coal mining equipment from there.
Those mines have been owned by various companies over the years so who knows.
Big big stuff anyway...you gotta chuckle when you think of taking 3 days just to gouge out a crack in something that huge (that one was a boom stick)
then take 4 days to fill it back up.
As for the cast welding...I guess we are both on the same page.
I hear lots of "good" advice on these boards...lotta times from people who have no real world experience. Glad to see you are not one of these.
All this reminds me of a small logging town where I used to race my blown alcohol mud rail.
There is a guy there who has been the only weldor around for years.
He welds cast all the time...with 7018.
I got into a big argument with him once....a mud rail had wollaped a water filled 45 gallon barrel full of water used as a safety barrier.
The front axle tube got broken right out of the diff. Tore a big chunk of the cast iron diff out.
The guy wanted me to weld it up for him but i never brought any equipment.
So they got hold of the local weldor.
He pulls out his 7018 and I had to question that.
These "cars" make close to 3000 hp and are very violent.
The crowd is always way too close so there where serious safety issues.
Anyway.. I got outvoted..
I watched the guy....he put a PILE of 7018 on there. Spread the weld out over a large area.
The weld held up...in fact the guy ran the car for the rest of the summer thru some very rough mud pits.
Was it right? Nope...
Would I do that? Not very likely....
But it worked...the guy had developed his own method over the years and it worked for him and all his welding customers.

I've done the "proper" repairs before...in a facility that had all the bells. The monster controlled preheat...the gas welded cast iron rod etc. Beautiful way to repair cast IF you have the facilities.
I've also studied metallurgy...taken extra classes in it and am aware of all the songs and dances about welding cast.
All that stuff has little to do with small shop..."try to get it fixed" real world repairs.
I've developed my own methods for Ni-rod repairs. They work for me.
I do not like brazing cast...yes it works...but IF it doesn't,,,you are in a serious pickle.
I bet half of my cast work comes from failed braze repairs. And we all know what a mess that is to clean up. Some is impossible so I end up brazing it again and hoping for the best.
Anyway..I'm glad you have been on the mountain... you know what it's like..
Russ

[radkins]

Radkins...those trucks prolly came from an hour down the road from me.
I've worked on a lot of BIG coal mining equipment from there.
Those mines have been owned by various companies over the years so who knows.
Big big stuff anyway...you gotta chuckle when you think of taking 3 days just to gouge out a crack in something that huge (that one was a boom stick)
then take 4 days to fill it back up.

That boom stick was a 295 BE maybe? Those things were notorious to crack and sometimes even break in half right in the middle! We had the welding maintenance contract with the mine that bought those 170 ton trucks and had to assemble them when they arrived. That company up there that sold them did so because they were replacing them with even bigger trucks (240 ton) so I would say yes you are familiar with large equipment and heavy welding. In addition to those 170 ton Eucs we also had a fleet of 12 240 ton 830E rock trucks, 2 56 yd electric power shovels, a 110 yd dragline with a 320 ft boom and various caterpillar equipment ranging from D11 bulldozers to some of the very rare 994 loaders and about every thing between, it has been an interesting career and I truly miss it since I retired.



That axle tube is a pretty good example of what I was talking about with unusual loading, how much of that kind of shock could it take now? That is the point, something like that could hold quite a bit even with the wrong filler depending on how well it is supported but nowhere near what it would if it had of been repaired with the right rod.

Also now that I think about it a lot, if not most, of those housings are cast steel (look at the factory plug welds) so in that case a 7018 would have been a good choice. This too accounts for some of the "successful" steel on cast welds, I have had a bunch of steel castings brought in with the owner assuming that because it was a casting it was cast iron.

What's really remarkable here is that the guy managed to get that thing back in alignment close enough to make the bearings hold up, now that's something to brag about!

[boslab]

Interesting thread, first off, cast iron, the word CAST is the clue, cast iron cast steel cast brass, everything is cast, a weld is in fact a casting process, you are casting iron with a CI welding rod, or casting steel with a steel one, mig welding is very similar metallurgically to continuous casting in the way the weld solidifies
so there you have it you can weld cast iron, however you cannot hope to have a weld that will have the same mechanical properties as one homogenous block of cast iron, you will have three no matter what, thats two original peices plus the one you made
as radkins post clearly illustrates identification is often wrong, look carefully at lines on the casting if you see flash it aint cast iron as the flash would break away, look at the fracture is it ductile or brittle failure, can you knock bits off with a chipping hammer?
regards
mark

[radkins]

boslab, The problem with welding cast iron using steel MIG wire really has little to do with the mechanical structure of the material, whether it is cast, forged, drawn or what ever, it has to do with the carbon content and how the carbon is contained and in what form. A steel casting is formed in the same way as an iron casting but the make-up of the metal is vastly different. There is a much higher carbon content in an iron casting but it is the form of carbon/graphite and how it is distributed in the metal that makes it impossible to obtain a decent weld on an iron casting with a steel filler. The point at which the steel and iron casting are mixed (the transition area between the weld bead and the base metal) will be contaminated with the carbon to the point that it will be EXTREMELY hard and brittle. It is so hard in fact that years ago it was common to melt chunks of cast iron into a weld bead to be used as hard surfacing! This is still a cheap way to hard face in some instances but it is very crack prone and does not work as good as a rod/wire made for that purpose. There simply is no way to compare welding a steel casting with a steel rod to welding cast iron with that same rod, the base metal is just radically different in composition. I have seen a great many attempts to weld cast iron with steel rod/wire, most of the time because someone simply did not know better other times the casting was mis -identified and sometimes it was done out of desperation, in any case I have also seen the very poor results of doing this. Since the beginning of arc welding various methods have been tried to perform this very tricky procedure of welding cast iron and it is simply ludicrous to think that welding it with a common steel rod or wire has been overlooked, indeed every welding text in print and all commonly accepted standards warn against doing it. Looking at the metallurgical make-up of steel vs cast iron should make it quite clear why this will not and can not work and if it was a viable option it would be accepted as normal welding practice but it is not, for a darn good reason!

[boslab]

i'm sorry rad, i dont think i explained myself, i did not mean weld CI with MS mig process wire, please accept my apology, i was refering to the solidification process that occurs in the weld metal bounded by the HAZ, the initial crystalization of the weld to the base substratr results in a crystal that in foundry practice is a 'chill crystal' after that the weld pool increses in temp so that dendritic growth occurs, between the dendrites equiaxed crystals form, just like casting.
CI as you correctly state has a high carbon content, ferrite can hold 4.7% carbon in solution, the resulting crystaline phase is Cementite [Fe3C] it is as hard as you can get, brittle also, when C>4.7% it endsup inbetween the grains of cementite as free carbon in carbons stable graphite form resulting in a primarily laminar cast form, it can be modified to make ductile iron but thats not the question.
the point is i did not say you can weld cast iron by mig with mild steel wire
i am aware of the structure of steel and iron as i have spent my working life making them [i am a metallurgist]
as a cautionary note it is not advisable to weld unknown matirials by any process, if you dont know what it is seek advice from someone who does, i'm lucky i just slice a bit off and stick it on a spectrometer [OES/Xray] as we have about 12 assorted in the lab.
thank you
mark

[radkins]

I do see what you are saying and I try to make my point without being too technical (Otherwise I tend to get in over my head so to speak ) and your explanation of what separates common steels from iron castings is much better detailed than anything I could have said without doing some serious research on the proper terminology. Also your analogy of a weld bead being a casting (of whatever the filler is composed of) is very interesting and makes a heck of a lot of sense, I had not thought of it quite like that before but I can certainly see it since it was pointed out. There would of course be several other factors come into play in multiple pass welding the biggest of which would be the stress relieving effect on each bead with succeeding passes as they are added.