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welding cast iron

does some of the carbon burn during welding of cast iron (gray, ductile)?

It’s not decarb, you get a faint white line at the edge of a gas or arc fusion welding with cast iron rods or mild steel electrodes.

I just used to use whatever worked, cast iron rod, steel/brass/bronze or electrode. Prolly still have 40-60# of Kastweld 111 & some Postile cast$$$. If you gas weld it well you can’t find the fix.:smoking:

An example below


Good luck,
Matt
 
I think there's a big difference between the 99% nickel rods and the 55% nickel rods. The deposits from one are widely considered unmachinable, regardless of your preheat technique.

That hasn't been my experience. 55 is a little tougher. Definitely not anything like what I would call unmachinable if correct procedure is followed.
 
recently i watched a friend of mine with 50 years of experience repair a pretty massive ci frame. he used an electrode of uncertain composition he had around, i strongly assume nickel based. he did stitches cold and peened with a medium sized hammer. you could see the deformation.
 
recently i watched a friend of mine with 50 years of experience repair a pretty massive ci frame. he used an electrode of uncertain composition he had around, i strongly assume nickel based. he did stitches cold and peened with a medium sized hammer. you could see the deformation.

You can do "cold" or short stitch welds and they will hold up if you peen them well, but I wouldn't want to use that technique if you have to machine them afterward. Keeping the heat input as low as possible will work to do a structural weld repair but the stuff will be pretty hard to cut. Seeing the deformation when peening is kind of the idea - you want to put the weld into compression rather than tension.
 
a lot of interesting info. however the question was not how to weld ci.

i had a discussion recently and was told the carbon would partally burn during the process. i somehow doubt this, as its embeded in the melt and
protected by inert gas, so oxygen doesnt get to it. (might be different with o/a torch.) then again if you look up combustion temperature of carbon you get very different results, starting at 300°c.

what do you think?
Sorry. I sort of glossed over your question.

I'm not a metallurgical. My knowledge of welding cast iron is all from first hand experience and a LOT of trial and error. "School of hard knocks" or whatever.

I'll play with some cast iron in the shop tomorrow and try to get back with ya regarding your question :)

I've been cleaning out the shop this week. I'll try to find some of the pieces of scrap cast iron I tossed out.

Sent using Morse code on - .- .--. .- - .- .-.. -.-
 
a lot of interesting info. however the question was not how to weld ci.

i had a discussion recently and was told the carbon would partally burn during the process. i somehow doubt this, as its embeded in the melt and
protected by inert gas, so oxygen doesnt get to it. (might be different with o/a torch.) then again if you look up combustion temperature of carbon you get very different results, starting at 300°c.

what do you think?

I don't think so. I have read that the carbon in the iron can diffuse out of the iron and into the weld deposit if you use a lower carbon mild steel welding rod or filler though. If not slow cooled properly it can also then get hard as hell just as if it were heat treated. That's the good thing about the nickel 99 rod - carbon is not soluble in it.
 
I don't think so. I have read that the carbon in the iron can diffuse out of the iron and into the weld deposit if you use a lower carbon mild steel welding rod or filler though. If not slow cooled properly it can also then get hard as hell just as if it were heat treated. That's the good thing about the nickel 99 rod - carbon is not soluble in it.
The bad thing is the $$$ per rod!

I was welding with some fancy filler that was $5 per rod last week.

I usually burn 6010 and 6011, so basically no prep. For this stuff, I actually wiped down the parts with acetone!

When I weld cast iron, I end up saving every little stub. Heck. Give me a few decades and I'm liable to pay for a case of beer with the scrap weight.

Sent using Morse code on - .- .--. .- - .- .-.. -.-
 
carbon is insoluble in nickel at room temp. but gets up to 3% when hot. so thats kind of wierd, first is sucks out c from the ci and then precipitates it? as what? there is ni3c, but its "unstable" and i know nothing about it.
 
Everyone is trying to get away with something.
Everyone is trying to cheat the system.
But physics and chemistry of the nature are what they are.
No one wants to pre-heat.
They want to short cut it.
They act like it is a momentous effort.
Perhaps they are ignorant of metallurgy and believe only
second hand information from their buddies buddy and salesmen
at the welding shop. Sadly this is more true than it is not true.
Understand both what heat and temperature are and how they are not the same.
Understand what the critical cooling curve is and why it is important.
Learn that peening is more than just tapping the bead with your whimpey
little slag hammer. Understand why brazed repairs are still holding strong
over 80 years later. There are material properties that contribute and
process variables that contribute. It is a syndrome of events that contribute
to a successful cast iron weld. Part shape and geometry also contribute.
There is also the guys who have "some" shortcut technique of cold welding
and claim success because it is still holding. Leave aside the real strength
of the joint and how the repair will last under load. They are fooling themselves.

--Doozer
 
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Everyone is trying to get away with something.
Everyone is trying to cheat the system.
But physics and chemistry of the nature are what they are.
No one wants to pre-heat.
They want to short cut it.
They act like it is a momentous effort.
Perhaps they are ignorant of metallurgy and believe only
second hand information from their buddies buddy and salesmen
at the welding shop. Sadly this is more true than it is not true.
Understand both what heat and temperature are and how they are not the same.
Understand what the critical cooling curve is and why it is important.
Learn that preening is more than just tapping the bead with your whimpey
little slag hammer. Understand why brazed repairs are still holding strong
over 80 years later. There are material properties that contribute and
process variables that contribute. It is a syndrome of events that contribute
to a successful cast iron weld. Part shape and geometry also contribute.
There is also the guys who have "some" shortcut technique of cold welding
and claim success because it is still holding. Leave aside the real strength
of the joint and how the repair will last under load. They are fooling themselves.

--Doozer
Application makes a big difference. I've had good luck with those "cold welds" holding. They probably aren't as strong as a weld that had the proper pre/post heating. I've done a fair amount of them and they are all holding up just fine and I'm not worried about them breaking.

They're on VERY IMPORTANT, high stress, parts, too. Like a cast iron stew pot and a tiny cast iron bench in the garden that has a garden gnome on it. :)

Of course you shouldn't pein with your chipping hammer.

I like a bunt point in an air hammer if I have the option.

Sent using Morse code on - .- .--. .- - .- .-.. -.-
 
By the way "cold welding" isn't a thing. Minimizing heat input and consequently HAZ and temperature differential in the part is what I'm going after on those small repairs. Try it.

Sent using Morse code on - .- .--. .- - .- .-.. -.-
 
To me all this talk of preheating/postheating peening is sending up a red flag that your process has flaws? Sure it works good enough to get you by, and because all the old timers did it makes it seem like that's the way to do it, because that's the way it's always been done, but maybe it's time to examine what's happening and how we can make things easier or solve some of the issues? The purpose of preheating is to get your piece closer to the temperature of the haz so the shock of the weld is less and I think we can agree that when a weld cools the bead shrinks causing stress which peening is supposed to help alleviate? The same thing happens when "cold welding" is done, you get in strike a quick arc run a short bead and stop to let it cool and repeat. Do this until done. Both can work. At one time or another at some point we have all warped the shit out of something by welding on it! Did we learn anything? I was lucky when I was young I had a mentor that told me "Question everything, believe nothing!" He experimented with all kinds of unconventional methods and tried things you guys would find laughable? He would use piston rings to weld cast iron because he said "Your filler needs to be as near to the original metal as you can get? He hated grinding wheels and only used files? Yeah, he was strange, but he could do amazing work and fix anything. He died before you tube was invented and learned it all on his own.
 
Cast iron is correctly welded with oxyacetylene using cast iron filler rods. Preheat and postcool are critical. Done by a skilled craftsman, the color match is almost perfect. I know a guy in his mid-80s who has gas welded cast iron professionally since 1972 and is extremely good at it. I think they should put up statues of guys like that.

metalmagpie
 
To me all this talk of preheating/postheating peening is sending up a red flag that your process has flaws? Sure it works good enough to get you by, and because all the old timers did it makes it seem like that's the way to do it, because that's the way it's always been done, but maybe it's time to examine what's happening and how we can make things easier or solve some of the issues? The purpose of preheating is to get your piece closer to the temperature of the haz so the shock of the weld is less and I think we can agree that when a weld cools the bead shrinks causing stress which peening is supposed to help alleviate? ......................

I was under the impression that pre-heating was to reduce the differential shrinkage. After all, welding results in melting and re-freezing of the material. As soon as it solidifies, it starts shrinkage that puts stresses in the material. Explained to me as the following:

If all the material is at a similar (or not "too" different) temperature, then it all shrinks at the same time and close to the same amount. That's why all the fuss about thickness changes in molding...thin spots cool faster, and so they set up stresses that can exceed the tensile stress the material can take.

Since you are only heating a small area when you weld, and you are starting the whole shrinkage thing again from the temperature of solidification, there can be a very high stress set up right at the weld.

If you pre-heat, the shrinkage is closer to even all over the part, and the stresses set up are less. They are related to the difference between the pre-heat and the melting point of the welded area.

That made sense to me. I know you can tighten up sheet metal panels that have a "can" in them by quick spot heating and then cooling the spots quickly. The heating deforms the metal against the surrounding cold metal, and the fast cooling shrinks the deformed area creating a pull on the surrounding metal. Welding would do that also.
 
There are opinions from some here who don't know what they're talking about. Looking at Servicar Rider on this one. Cast iron has very low ductility, which is why it needs to be preheated and slow cooled to be correctly welded and maintain some of the ductility. Spreading the heat thoroughly through the part spreads the growth and shrinkage over a much larger area, preventing concentrations of stress at or near the weld area. Putting a buttload of heat into the part at the weld then letting it cool and shrink rapidly back down is a shortcut to weld failure in iron.

As I and others said earlier, it CAN be welded in short bursts and kept as cool as possible and that will work with peening, but it will NOT be as strong and ductile as an iron weldment that has been properly preheated and slow cooled. The weld will be hard and fragile, but it will hold for something that's not mission critical. A sharp impact may break that weld though. Gas welding works well also - with correct preheating, in-process heat maintenance, and slow cooling. The same as nickel rod welding. Rapid cooling from too high a heat results in movement beyond the material's ability to accommodate and the result is almost universally brittle failure, cracking, etc. You can get away with it on short welds by limiting heat input because the material doesn't grow and shrink as much.

And no, "cold" welding absolutely does NOT have the same effect as peening. Exactly the opposite in fact. A quick short stitch weld heats and cools rapidly, shrinking and putting the weld bead in tension as it does so - exactly what you don't want. Peening stretches the outer surface of the weld bead, putting it into compression - exactly what you DO want to counter the shrinkage of the bead. Leaving the bead in tension will very frequently result in cracking of the weld bead.
 
I've welded cheap 1800's era cast iron architectural brackets and components having stupid amounts of carbon floating around in it. No pro would touch it but I managed it with patient use of the cold weld and peen technique. Loads of smoke, I ended up looking like a coal miner coming off shift, and dealing with the voids left when the metal collapsed after the "lumps" of carbon evaporated out was challenging. But, fortunately, no fires from burning carbon.

There is no mystery about the proper "cold" welding process for basic cast irons. Just too many folk in hurry up mode trying to apply standard welding techniques and messing about over peening to try and expand the metal to reduce contraction stresses enough that things don't break. As always with hurry-ups folk who know what they are doing and pick their battles can get good reliable results. The less experienced just have to be lucky and not too ambitious.

It has to be recognised that its a field expedient process for when nothing more engineering can be arranged. Its also very slow in its pure version. Which is why so many folk want hurry ups.

Basic rule is to pick a ductile rod and over widen the break to give access to both sides for direct weld deposition. Then using a small rod and lowest current for satisfactory fusion short lengths of minimally thick weld weld metal are laid on the surfaces to be joined and peened whilst cooling. Chipping hammer is fine. The idea is to stretch the metal so no contraction stresses remain. A nice thin layer doesn't want much hitting to stretch. Low current keeps the heat affected zone down. Plenty of waiting time between welds keeps the iron cool. Once you have several thin layers, I usually use 3 to 5 when persuaded into doing this stuff by persistent folk immune to strong language (or pretty girls), you can build up a bit more with larger rods and higher current as the weld proper is now weld metal to weld metal so things are better behaved. Deposition rate still needs to be low enough that the peening can stretch out any attempted contraction stress. Did I say it was a slow old job.

I'm told that the tensile strength of a joint done that way isn't greatly reduced relative to the original iron. How true that is I don't know as I refuse to stick anything in used in tension back together. Also figure that any cast part having been hit hard enough to break will likely have acquired hidden cracks elsewhere.

Most important part comes right at the end. Firstly charge the customer a bit more than he/she thought you could get away with then look him/her straight in the eye and say "That's your one time. Don't ever bring a job like that to me again." and mean it. Life is to short to spend that amount of time futzing about on other peoples jobs.

Clive
 
reading the first paragraph above i get the impression carbon can burn off during welding after all.
 
dian

No visible flames when the carbon was coming off so I reckon it was more like evaporation than burning. You'd expect Carbon Dioxide and Carbon Monoxide if it were burning. Both transparent gases so a proper fire wouldn't smoke so much. Don't forget I was putting as little heat as possible with a minimum weld lay due to the amount of metal collapsing out of position when the carbon went. Pretty much no burn through or blobs of iron on the bench. The iron was just pulling back when the carbon went.

Re-defined my concept of bitch job from hell! Mousetrapped into a freebie too by social connections.

I have had flames when oil contamination was boiled out of somewhat porous cast iron. Very distinct and easily seen behind the arc. Burning continued after welding stopped. That time I did just enough weld to get the flames going, waited them out and did the lay over the burnt area.

Clive
 
Preheat has four purposes in ferrous welding.

One is to reduce thermal stresses both during and after the weld caused by variation of temperature in the workpiece.

Two is to increase ductility so that some of the stress can relieve itself...in-process thermal stress-relief

Three is to cook off contaminants

Four is to slow the cooling of the weld and HAZ. Flame-hardening works by heating the surface rapidly so the undelying metal is still cool. When the heating is removed the hot surface is quenched and hardened by the heat being rapidly conducted away to the underlying cold metal. Just what you do not want, usually, in a weld

Fifth is to roast the weldor by radiant heat, so you are not shy to charge a lot of money for the job.
 
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