MIG welding cast iron

[bagged89s10]

I read a few articles where you can weld cast iron using stainless 308 or 309 wire. I understand you would have to preheat the item you're welding, then allow it to slowly cool after welding by burying it in sand.

Has anyone tried this method? I have some broken cast-iron I'm going to practice on. I only have a mig welder and I'm hoping I can be successful trying this method.

Anyone have experience and or tips using this method?

 

[HCNDM]

I read a few articles where you can weld cast iron using stainless 308 or 309 wire. I understand you would have to preheat the item you're welding, then allow it to slowly cool after welding by burying it in sand.

Has anyone tried this method? I have some broken cast-iron I'm going to practice on. I only have a mig welder and I'm hoping I can be successful trying this method.

Anyone have experience and or tips using this method?

I dont mig my cast iron but tig or stick. That Said the process is similar.

1) preheat
2) weld
3) postheat
4) cool slowly

Slowly heating up and cooling down stops the cast or weld from differential expansion and shrinkage reducing the chance of a crack.

I use my kitchen oven to cool slowly. I make sure it's preheated to the highest temp it will go. As soon as I finish post heating with a torch I stick the piece in the oven. I leave it at max temp for and hour, the half the temp and another hour, then let the oven cool down.

You can get silicon bronze (CuSi) wire for a mig. CuSi requires less heat to flow. Less heat is less stress. Further more CuSi due to the copper content is quite ductile further reducing the chance of a crack.

The end result is closer to a really good braze than a weld but its strong. Biggest downside in my books is the bronze look of the weld. It requires paint to match the welded material.

I use CuSi rod with the tig. Speed is higher than steel and slower than alu welding.

I have tried to tig with steel or stainless rod on cast iron... stubborn I know. Results were not stellar and I have had weld failure. CuSi has yet to disappoint me.

Pic from google:



For stick there are also special rods. Nickel based iirc. I used some last weekend to repair a vise key and that works nicely too. The color match is better but it is stick and it took me a lot of hours of practice to get nice stick welds.... did I mention bird ()$&&...

I have heard of the sand method and never tried it. My experience is that even using a torch and an oven to cool if you go to quick it will crack.

Sand does hold heat nicely though I reckon I'd build a fire over the sand to get it warm. Do my welding ... stick the piece in the hot sand and start another fire on top and let it burn out slowly.

I have annealed and softened old files using that method so reckon it should work...


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[MoonRise]

308 is the 'standard' stainless filler, for welding on the 'common' 302 or 304 (or 18-8, as 304 and 18-8 are both mostly 18% chromium and 8% nickel) stainless steels.

The main difference between 302 and 304 stainless is that 302 has a max carbon content of 0.15% and 304 has a max carbon content of 0.08%. Both of these allows have nominally 18% chromium and 8% nickel (and a few other additions, such as 1% silicon and 2% manganese).

309 is often a go-to filler for welding stainless (304) to carbon steel. Or for welding an 'unknown' stainless. It has a bit more chromium (22%) and nickel (12%) than 308 filler.

But cast iron has ~2-4% carbon. That much carbon is what makes it cast iron and not some sort of steel (to much carbon to actually end up in solution within the alloy's molecules like in steel, and instead the carbon is actually carbon molecules interspersed with iron molecules in cast iron). Different shapes and forms and dispersions of the carbon give slightly different properties to the different cast irons.

But that carbon is the problem if you try and weld cast iron. The heating and cooling of welding can lead to the dreaded 'tink!" noise of cracked cast iron.

And 308 or 309 stainless fillers with that much available carbon from the cast iron will also most likely give you a non-forgiving witches brew of hardened martensitic steel and chromium carbides (good for cutting tools or wear resistant alloys like in hardfacing applications). Both of which can crack from their brittleness upon cooling or even just solidifying after welding.

The 'go to' for welding cast iron is usually a high percent nickel filler. Which is also often rather high $$$$ as well. Ni55 filler if you don't need to machine after welding the cast iron (ends up usually still too hard to machine, grinding is possible though) or Ni99 filler if you need to be able to machine the area afterwards.

http://www.hobartbrothers.com/product-details.html?name=Cast-Alloy™

http://www.hobartbrothers.com/product-details.html?name=Cast-Alloy™+60

You still have to watch out for heat gradients during and after welding, and hence often (usually IMHO) still have to do the cast iron intense preheat and post-weld super slow cooling.

Preheat for welding cast iron often means heating it up near 900F +.

If fusion welding cast iron with some cast iron filler, the necessary preheat level is even higher. More like red hot 1500F.

But short circuit transfer mode GMAW with 308 or 309 filler on cast iron? IMHO, you are really rolling the dice on that. With way too much chance to end up snake eyes. Or in this case, broken and cracked cast iron with broken and cracked 'stainless' filler (which is probably no longer even stainless anymore from all the carbon pick up from the cast iron).

 

[HCNDM]

Silicon bronze wire goes for about 30 bucks a roll

https://www.amazon.com/gp/aw/s/ref=...nze+mig+wire&rh=i:aps&sprefix=silicon+bronze+


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[rsanter]

Part of it also depends on the quality of the cast iron.
I have had good luck with MIG welding cast iron like this...
Put item into BBQ, preheat
When up to tempature, use a torch to add heat to the area to be welded.
MIG weld
Apply torch to area that was just welded for about 5 min
Remove torch and leave in BBQ running for about 30 min
Turn off BBQ and leave it in there till cool to touch. Do not open BBQ, just leave it there for several hours

Bob

 

[marinusdees]

Why stainless filler??

I have welded cast iron pump volutes (**** pumps) and cast iron motor end bells with steel filler wire, no preheating, and no controlled cooling. I am NOT a professional welder, just lucky, I guess. The one volute I preheated with a torch and covered with a blanket fell apart, was taken to the best repair shop in Tacoma, and proved to not be weldable. I ground as much of the cracks away so as to get the maximum of filler.
I have also welded cast iron using nickel fill rod. I prefer wire feed with steel filler.
Until you try it, you'll never know. This is only experiential and not scientific.

Good luck!!

 

[zkling]

Crown Alloy makes a very good CI mig wire, 44-30, it's ~$40 a lb but well worth it.

 

[bon3s]

Last Repair I did (and was out of Silicone Bronze) I was given a newer product to use... (new to me at least)

Royal 11-10 ... still has a preheat and post heat, I also peened as it never hurts... seems to have worked well, also has a higher tensile strength than Silicone bronze.

 

[G-ManBart]

Crown Alloy makes a very good CI mig wire, 44-30, it's ~$40 a lb but well worth it.

I have used Crown Alloy stick high nickel electrodes for welding cast iron with pretty good success. The bonus is they're a Michigan company!

I had a couple of questions and decided to give them a call....super nice people who couldn't have been more helpful. In fact they were quite interested in what I was doing, and the results I was seeing. For the OP, I'd suggest giving them a call and see what they recommend.

 

[dffay]

Silicon Bronze is a good way to go and pure Argon is the best gas to use. So, with the extra expense of the wire, you'll need to change tanks. Good luck with it though, there are many roads that lead to cast iron welding success.

 

[2mJps]

Why stainless filler??

I have welded cast iron pump volutes (**** pumps) and cast iron motor end bells with steel filler wire, no preheating, and no controlled cooling. I am NOT a professional welder, just lucky, I guess. The one volute I preheated with a torch and covered with a blanket fell apart, was taken to the best repair shop in Tacoma, and proved to not be weldable. I ground as much of the cracks away so as to get the maximum of filler.
I have also welded cast iron using nickel fill rod. I prefer wire feed with steel filler.
Until you try it, you'll never know. This is only experiential and not scientific.

Good luck!!

I have welded alot of cast with reguler steel wire also and have had good luck with it.I took some welding classes and some one said they had been doing this also with good results.

 

[04chase]

high nickel based rod for me , heat and slow cool if possible.

i had to do tons of manhole lids where pre heat and slow cool isnt easy but helps with oxy torch and covering with a bucket of sand. has worked good enough that i had to re open it for the guys needing access .

 

[dffay]

I thought of something else......if I were Mig'ing it, I might be more cautious of the wire speed. Too fast, and it might not really cook into the void for a flowing puddle. It might pay to linger a bit as its flowing before moving the gun on the travel speed.

Just a thought. Morning caffeine has kicked yet.

Caffeine helps me do stupid things faster.

 

[04chase]

prolonged heat on cast with rapid fluctuations in temperature (expansion and contraction ) results in what your avoiding in cast metal manipulation. In short less heat with the weld is best unless your material being welded is also at a high enough temperature that it will not expand futher before retracting (slowly ) than the material used to weld it.

 

[dffay]

All true about rapid fluctuations. The preheat and cool slowly thing had already been discussed. The same with V'ing the joint for max penetration and minimum porosity.

 

[tdcisco1]

while on the topic of v,ing the joint; any abrasive wheel used will embed contaminates in the base metal. once you have ground out the v take a rotary grinder with a burr in it to polish the joint there by removing the residual grinding debris. this will give a good clean weld joint. good luck!

 

[mustange70]

For mig welding, if using stainless (and it does work, i've done it a few times on ductile cast iron, never grey cast iron though), use 309L, which is the low carbon varient of the wire, which is a must with cast iron, the other wires are a waste of time.

As mentioned, if want to MIG cast iron, crown alloys 44-30 is on of the best I've used, and works on a variety of materials, plus uses standard C25 or 100% CO2 vs. tri mix with the 309L.

With the heating and cooling being mentioned, while the minimizing differential expansion reduces internal weld stresses, it's as much for achieving the proper gain structure within the weld to reduce initial hot cracking, and later to reduce cold cracking.

 

[bagged89s10]

For mig welding, if using stainless (and it does work, i've done it a few times on ductile cast iron, never grey cast iron though), use 309L, which is the low carbon varient of the wire, which is a must with cast iron, the other wires are a waste of time.

As mentioned, if want to MIG cast iron, crown alloys 44-30 is on of the best I've used, and works on a variety of materials, plus uses standard C25 or 100% CO2 vs. tri mix with the 309L.

With the heating and cooling being mentioned, while the minimizing differential expansion reduces internal weld stresses, it's as much for achieving the proper gain structure within the weld to reduce initial hot cracking, and later to reduce cold cracking.

How hot would you need to preheat the metal? Is heating at 400-500F in an oven for an hour, depending on the size of the piece, hot enough?

 

[dffay]

Yes indeed. Keep it in a hover at that temp while you do your work. Then, bring it down as slowly as you can. Good luck with it.

It's good to be good, but it's better to be lucky. (Paraphrased by many)

 

[HCNDM]

How hot would you need to preheat the metal? Is heating at 400-500F in an oven for an hour, depending on the size of the piece, hot enough?

No an oven won't be enough. Even with silicon bronze which needs the least heat you are going to to need a propane torch.

Being a hobbyist I do my color by eye

Silicon bronze just on dull red

Nickel rod or filler you need to go to bright red.

With silicon bronze you can do afterheat with the torch and then do the rest of the cool down in the oven.


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[MoonRise]

Preheat for welding cast iron often means heating it up near 900F +.

How hot would you need to preheat the metal? Is heating at 400-500F in an oven for an hour, depending on the size of the piece, hot enough?

See where I quoted myself from earlier in this thread?

No, 400F is nowhere near enough preheat.

Usually, you want some sort of red-hot. As in the metal is actually glowing red hot.

And regarding time, it's however long it takes for whatever size and thickness of cast iron you are dealing with to uniformly come all the way up to the desired preheat temperature.

And for cool down, shoot for about 100F/hour of cooling rate. So, about 12+ hours from 'hot' back to room temperature.

Or you can ignore all that and try the Callahan method.

As in "Do you feel lucky?"

 

[mustange70]

No, do not preheat cast iron red hot prior to welding it, you are nearing the transformation temperature which will completely mess up the grain structure of the material (I can't remember the exact details as it's been a while since I went through it, but I can look it up and post back if needed), and will also allow hot cracking to occur when arc welding it.

for preheat, follow whatever the consumable data sheet says to use, otherwise a minimum of 250*F (this is what you use with the crown alloys 44-30), but a 3-400*F is plenty, but make sure the whole part is at this temperature.

 

[MoonRise]

Yes, preheat to 'red hot'.

Transformation temperatures for 'cast iron' will depend a bit on the exact alloy (yes, cast iron has different alloys. There is no 'one' cast iron.)

As a reference point, austempering of ductile iron would require a heating temperature of about 1545F to 1745F and then a 'rapid' quench down to 450F to 750F and then a dwell time at that temperature.

Full-up carbon-iron transition temperature is up at 2100F.

Another carbon-iron transition temperature would be at 1360F.

A "normalizing" or "stress relieving" temperature for most cast irons would be in the range of 800F to 1100F and a soak time of 30 minutes to 5 hours, depending on size and thickness and exact temperature used, and then a slow cooling back to room temperature. No real grain or other changes (other than the desired stress relieving) would occur in this temperature range.

Annealing of cast iron would be done up at 1300F to 1500F or so, other heat treatments with desirable microstructure changes (such as a spheroidizing treatment) would be done up at 1600F to 1700F for 1-5 hours and then a slow cool down to 1275F and hold for another 3 to 5 hours and then final cooling would give you a ferritic nodular iron.

And none of those temperatures would be achievable with a home cooking oven. They would need a kiln or actual heat treat oven.

Heat red hot. Or go Callahan on it. Your call.