welding cast iron

[dian]

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

 

[boslab]

I read there is a decarb around the HAZ, I know there’s a massive shrink due to a peritectic transformation that causes cracks without preheat
Mark

 

[52 Ford]

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

Yes.

What type of cast iron welding do you need to do?

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[52 Ford]

I read there is a decarb around the HAZ, I know there’s a massive shrink due to a peritectic transformation that causes cracks without preheat
Mark

Yes and no. Preheat/postheat is just one common way of preventing cracks. Keeping the cast from getting hot is another. I've had luck with that on very thin castings.

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[john.k]

Filler rods for gray cast iron are high silicon content to compensate for property changes in the iron..........malleable/ductile/SG iron should not be melted,but joined using nickle or bronze filler .

 

[Servicar rider]

I have tried most all the usual ways to weld cast iron. What I have found works the best for me is Tig with a cheap soft iron baling wire from the farm store for filler, or tig with silicon bronze filler. I have had far less problems with cracking, warping, machining, etc. I don't spend alot of time preheating or post heating, just warm things up a little before you start and keep it from cooling fast when you are done. I have tried nickel rods, some stuff called EZ WELD for cast iron, and had problems with them.

 

[john.k]

Nickle rods work ,but need a special technique......couldnt imagine what they cost now.....anyhoo,using a bronze is easy ,because the bronze has a soft transformation around 400C ,which is where iron has a brittle transformation.....the bronze can easily yield as it cools......ive seen many bronze welds on old engines that are over 80 years old,and havent shown any signs of the electrolytic corrosion often predicted .......I have an old Mack 711 diesel motor in the yard,which has the whole back of the block welded back on with nickle deposit......this was a common repair when B61 s were plentiful,the 3/4 ton gearbox would break the back off the block on rough roads......nothing but rough roads here in the 1960s.

 

[john.k]

Ductile /SG irons appear to weld very nicely using stick or mig....but there is a very brittle heat affected zone ,which will break under a fraction of the load the SG iron is designed for.....Seen accidents with everthing from box trailer couplers to the door on a landing barge fail due to welding SG components.

 

[52 Ford]

Nickle rods work ,but need a special technique......couldnt imagine what they cost now.....anyhoo,using a bronze is easy ,because the bronze has a soft transformation around 400C ,which is where iron has a brittle transformation.....the bronze can easily yield as it cools......ive seen many bronze welds on old engines that are over 80 years old,and havent shown any signs of the electrolytic corrosion often predicted .......I have an old Mack 711 diesel motor in the yard,which has the whole back of the block welded back on with nickle deposit......this was a common repair when B61 s were plentiful,the 3/4 ton gearbox would break the back off the block on rough roads......nothing but rough roads here in the 1960s.

I want to say last time I looked at nickel 99 rods was a few months ago and a 10 pound can was about $300 or maybe a bit more.

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[Big B]

Yes and no. Preheat/postheat is just one common way of preventing cracks. Keeping the cast from getting hot is another. I've had luck with that on very thin castings.

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How do you weld something without getting it hot?

 

[52 Ford]

How do you weld something without getting it hot?

Water.

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[52 Ford]

Obviously it still gets hot, but the heat is pulled back out very rapidly. So the HAZ is very small.

You can argue that it doesn't work or it's a bad idea... I'm just going off of what I know from first hand experience welding cast iron. Stuff that I learned "the hard way". Lots of trial and error.



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[Big B]

Water.

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I've never had any luck getting filler rod to stick unless I melt the parent metal and that requires getting it hot.

 

[Big B]

Obviously it still gets hot, but the heat is pulled back out very rapidly. So the HAZ is very small.

You can argue that it doesn't work or it's a bad idea... I'm just going off of what I know from first hand experience welding cast iron. Stuff that I learned "the hard way". Lots of trial and error.



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So it appears that what you meant was not getting the whole piece hot. Kind of like stitch welding cast iron with a arc welder and alloy rod. Lots of small stich welds.

 

[52 Ford]

I've never had any luck getting filler rod to stick unless I melt the parent metal and that requires getting it hot.

Nah, usually when I weld, I mix up part A and part B and slap it on. Works GREAT.

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[52 Ford]

So it appears that what you meant was not getting the whole piece hot. Kind of like stitch welding cast iron with a arc welder and alloy rod. Lots of small stich welds.

Right. I suppose "going to extremes" to minimize the HAZ would be a good way of putting it.

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[Servicar rider]

When I used nickel rod the end result was so hard you couldn't machine it. If you don't need to drill tap or resurface your part it's probably fine?

 

[eKretz]

When I used nickel rod the end result was so hard you couldn't machine it. If you don't need to drill tap or resurface your part it's probably fine?

Then you did it wrong. You need to use a good high preheat (I like 700°-800° F if it's feasible, but at least 450° F) and keep the part up to temp while welding with the nickel rod. Peening the welds thoroughly is also a Very Good Idea™. After the welding is finished, make sure the part is fully up to temperature again/still and then cool as slowly as possible - preferably over 12 or more hours. With that method the nickel deposit will be readily machined, only a little tougher than the base metal.

If you don't do the pre-heat/in-process heat/post-heat and slow cool you are going to get brittle hard weld/iron that will fail, possibly even during too-rapid cooling. If you don't do the peening you will likely get eventual welds cracking.

 

[sfriedberg]

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.

 

[dian]

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?