Welding a Cast Iron Frying Pan

[Don52]

My mother in law dropped her favorite cast iron frying pan and it landed on the handle and broke it off. I could have brazed it but I didn't like the look of a brazed joint so I TIG welded it with a Ni-Cast rod, which is 99% nickel, which I had left over from another project. According to Lock-n-stitch, which is my favorite site for cast iron welding, you should preheat to 900°F for brazing and 1300°F for fusion welding.

http://www.locknstitch.com/cast-iron-welding.html

I didn't want to destroy the coating on the inside of the pan or the enamel on the outside so I kept the preheat to below 550°F. I heated up several steel plates of metal to 550°F in the oven and placed them on top of fire bricks. I welded the frying pan on top of these hot metal plates. I kept the frying pan and the metal plates at a temperature of 550°F during the welding process with an oxyacetylene torch with a rosebud tip. When I was finished welding, I put the frying pan back in the oven and shut the oven off, to allow the pan to cool down with the oven. I figured that I could get away with the lower preheat because the break was in an area that isn't constrained and was caused by dropping not internal stresses.

Don

[Don52]

Here are some close ups of the welds.

[aametalmaster]

Nice fix. I had never tried Tig cast welding then I bought a small antique wood lathe and the tool holder was broke. So I took it to work and knocked some flux off a piece of Crown Alloys 255 rod and Tig welded it. Since I have a Tig torch in my hand almost everyday welding SS figured I would try it. I don't call myself a Tig welder at all but few guys quit and I got the short end of the torch LOL...Bob

[ryanjones2150]

I'm glad to see the use of a Carbide burr instead of a grinder to clear out the metal for the bevel. I bet that old cast was porous as **** in the puddle. How did it look flowing in? I have only tig brazed and stick welded cast iron. It's cool you were able to fix that for her. Huge style points

[Don52]

I bet that old cast was porous as **** in the puddle. How did it look flowing in?

The crack in the casting was actually clean because the outside was protected by the porcelain enamel and the crack was fresh.
I ground off the porcelain enamel with a carbide burr and I wire brushed it with a stainless steel wire brush.
The puddle was very clean and looked like mild steel except it wasn't really melting the parent Cast Iron metal.
The arc was so dim that I had to lighten my Jackson auto darkening helmet and bump up the sensitivity one notch so that the sensors could see the arc.

[Don52]

I took it to work and knocked some flux off a piece of Crown Alloys 255 rod and Tig welded it. Since I have a Tig torch in my hand almost everyday welding SS figured I would try it.

I used Radnor Cast 99 alloy for Cast Iron. It is similar to the crown 295 alloy, which is 99% Nickel. The Crown 255 alloy that you used is 45 to 60% nickel with 27 to 42% iron. Like you, I knocked the flux off the stick electrode and TIG welded with bare electrode. I could have used a bare wire but the local welding supply didn't have any when I bought these. The Cast 99 rods are pricey because it contains more Nickel, which is expensive.

Don

[ryanjones2150]

Do you think 309 would have done the job just as well? I have never used a stainless alloy for joining cast iron, but I've heard of and seen past repairs using it in stick welding. What about for tig?

[Don52]

Do you think 309 would have done the job just as well? I have never used a stainless alloy for joining cast iron, but I've heard of and seen past repairs using it in stick welding. What about for tig?

My understanding is that ER309 was designed to weld stainless steel to carbon steel. It also is more tolerant to contamination, so it can weld dirty or hot rolled steel without porosity, if one is desperate. The problem with using a mild steel rod to weld cast iron is that it absorbs carbon from the cast iron and becomes high carbon steel. If the weld is cooled too quickly it forms martensite, which is brittle and can crack due to the tension stress, which is due to shrinkage of the weld area during cooling. Nickel and 309 Stainless Steel avoid this problem because they don't form martensite. I have always TIG welded with either a 99% or a 55% nickel rod but I believe that 309 would also work. Below is a quote from another forum.

Don

[Don52]

1. Cast iron welding using stainless steel wire
   
   The basic problem with welding cast iron is that it is, as everyone knows, brittle. It will crack if subjected to tensile forces. As your weld contracts it will tend to crack the iron due to differential thermal contraction. The traditional way to avoid this is to avoid the "differential" bit and to pre-heat the whole thing to as near the melting point of the filler rod used as practicable. This is the approach generally used with cast-iron filler rod.
   There is another issue with cast iron, of a chemo-metallurgical mature. What makes it cast iron rather than steel is the very high carbon content. This tends to diffuse into your filler rod, causing unfortunate metallurgical transformations on cooling. An attempt to use mild steel to weld cast iron will leave you with a fast-quenched, high-carbon steel weld. You will almost certainly end up with Martensite, brittle and unmachinably hard.
   The phase-transformation in which austenite turns to martensite (or pearlite, ferrite, or bainite, depending on carbon content and cooling rate) is at the heart of the problem. This occurs at about 720 degrees. It is also accompanied by a change in volume, which may cause more differential stress cracking issues. Both the austenite-ferrite (hot-cold low carbon) and austenite-martensite (hot-cold high carbon) transformations lead to an increase in volume, so ought to reduce the residual stresses slightly, and under conditions of slow-cooling this is probably true. However this sudden expansion on cooling of the weld pool will tend to crack the already solidified and transformed weld behind it.
   None of this metallurgy happens in Nickel, so nickel rods side-step the problem, as does brazing. I am not sure what sort of bond nickel rods make with iron, but brazing material needs to "wet" the surface to stick properly in just the same way as solder. This might be why your thin-sheet mig-brazing worked well, and your cast iron brazing less so, perhaps the greater section thickness resulted in the material not getting hot enough for the braze to take.
   There is, however, another common mig-welding filler rod which does not go through the austenite phase transformation, and that is stainless steel. As long as the stainless is austenitic (easily checked with a magnet, austenite is non-magnetic) then the phase change on cooling won't happen, and so you can afford a great deal of dissolved carbon without fear of creating a brittle, unmachinable, weld.
   Armed with this theoretical knowledge I attacked the broken guide-arm of a mechanical hacksaw I had been given. Using stainless wire in short bursts (to avoid too much heat input creating thermal stresses elsewhere) I successfully repaired the arm, and it has shown no signs of breaking again yet, after 10 years of irregular use.

Shift_Taste, May 10, 2009
http://www.jalopyjournal.com/forum/threads/welding-question.360441/

[Burnt hands]

Don52,

Well documented repair project.

Went and looked at lockstich's website - wow !

Amazing how technology has improved.

Thought I was a litle bit knowledgeable on cast iron repairs but......................no way

Please excuse me while I hide under a rock and study to get a little more up to date.

[Donald Branscom]

Good job on the prep and welding and choice of filler metal!
309 filler would not have been a good choice. 309 filler is to join steel and stainless steel.
When welding cast iron it is good to bury the weldment in dry sand overnight so it can cool down gradually.

That repair job is what I call a critical job.
If the repair fails your mother could be seriously burned by the contents of the pan or the pan itself.
I am sure you knew that.

[Don52]

Good job on the prep and welding and choice of filler metal!
309 filler would not have been a good choice. 309 filler is to join steel and stainless steel.
When welding cast iron it is good to bury the weldment in dry sand overnight so it can cool down gradually.

That repair job is what I call a critical job.
If the repair fails your mother could be seriously burned by the contents of the pan or the pan itself.
I am sure you knew that.

Thanks, I agree with everything that you said.

[com1]

Amazing work. Wish I had those skills.

[Olivero]

That repair job is what I call a critical job.
If the repair fails your mother could be seriously burned by the contents of the pan or the pan itself.
I am sure you knew that.[/QUOTE]

True right there. Definetley not one to quicky a job like that.

[old jupiter]

Yeah, I was looking at the underside of that handle and thinking I would have hidden (mostly) a piece of reinforcing under there, as long as the pan just had to work and didn't have to look original. Braze in a piece of steel round bar, while brazing the crack. But Don has more and surely better aesthetic sensibility than a Neanderthal like me.

Don't know how this would work with cast iron. But when I was in welding school long ago, it happened that at the same time I had graduated to the TIG booth, I left a cheap uncoated aluminum saucepan on the electric range at home too long. All the water boiled out of it, I smelled something funny from downstairs, ran up to the kitchen and saw smoke and arcing and molten aluminum melted right out of the bottom of the pan.

So okay, now I have another practice project for school. I cut out a piece of 6061 sheet and welded it to my pan, which now actually had a better (somewhat thicker and flatter) bottom than it had originally. But here's the interesting part. Since the re-bottomed pan was rather discolored and ugly, the next time I had to go into my favorite auto machine shop, I used their glass bead blaster to clean up the saucepan, make it look more uniform. Back home, I quickly observed that the glass-beaded inner surface of that pan worked almost as well as a new factory Teflon-coated pan in NOT having cooked food residues stick to it. It was nearly self-cleaning!

Whether glass-beading would do anything for an old uncoated cast iron pan, I have no idea, but it might be worth a try. I know that good cooks have their ways of "conditioning" a cast iron pan, but possibly (?) doing the glass-beading trick first might have some good effect . . . .

Don, let me add my thanks for that link. At a first quick glance, they make a couple of flat assertions that I would have made conditional assertions based on my experiences. But I'm not one to argue with undoubted experts without good reason, and look forward to studying the site.