Welding Cast Iron

[bob w]

Last night I cut up the exhaust manifold for the 292 Chevy 6 going in the Reo project. Gotta have duals on the beast. Dual Smitty's on a Chevy six are pretty impressive. I've been reading and watching Youtube videos of different techniques for welding cast iron. In this case mild steel will be welded to the manifold both as end plugs and outlets. I have some experience stick welding with Nickel rod. I didn't preheat or slow cool and got by with it. It was probably dumb luck.
Interestingly, the Lincoln site explains how to stick weld with Nickel rod without preheating.

My choices are using the Nickel rod with my Miller stick welder or Oxy-Acetylene Brazing. Preheat or no preheat.

So if any of you have experience please let me know the best, least problematic route to take.

 

[26Troadster]

i have never done what your going to do. i have welded cast iron before, and as many people as there is that has welded it, is about as many ways to do it. i believe you would be better off using stainless steel rether then mild steel. had a buddy that worked for a pump repair shop and they used stainless steel welded to cast iron. i myself have never tried to weld anything to cast. i use castalloy rods when i have to work cast and i try to keep it as cool as i can, another thing i do is sharpen my chipping hammer to a good sharp point and do like a shot ping to try to keep it from cracking. you can use stainless rods on cast iron too.

 

[Old Iron]

I've always just used a wire brush on an angle grinder to clean it then start welding with Nichol rod.
I've never had any trouble doing it that way.
If it were an engine block, to repair a crack, I'd drill a small hole at each end of the crack and preheat.
Weld from the holes to the center and only weld an inch at a time to keep from building too much heat.
I'm sure there's several methods.

 

[Dirtyrat]

I've tig welded quite a few cast iron manifolds using the high nickel rod, and no pre heat.
Might have to clean out the carbon from the inside to help it not get in your weld...

As long as the castings are not complete junk material, I would think you would be good to go.

 

[choppinczech]

Don't touch it with an electric arc! Cast iron has a very high carbon content. And rapid heating creates hardening.

Brazing (depending on where the crack or break is), oven brazing, metal stitching, or fusion welding are the only ways to properly repair cast iron.


http://www.locknstitch.com/CastIronWelding.htm

Lock-N-Stitch
The most important thing for you to understand is that electric welding on cast iron is actually the very worst decision you could make to attempt to repair your cracked cast iron part. If you want to make a complete mess of your part, go ahead and arc weld it with nickel rod. Cast iron cannot stretch and withstand the contraction and hardening caused by cast welding with preheating below 1200 deg. F. The brand of welding rod does not make a very big difference. It's the heat that causes the changes to the cast iron itself. Sure the nickel weld is machineable but the cast iron will become as hard as a drill bit or tap and therefore will prevent the proper machining that is often required. 50% of the casting repairs we see have been arc welded on with disastrous results often costing the owner at least twice as much to repair properly. Cast iron welding should not be attempted even by experienced welders without years of high temperature oven welding training. Cast iron requires preheat of at least 900 deg. F. for brazing and 1300 deg. F. for fusion welding.

 

[Dirtyrat]

Interesting quote, however I've done it, on both turbo and non turbo cast, perhaps these were newer pieces which don't fall under the composition of the days of old castings

 

[tattoodfreak]

Gonna have to go with old iron and dr on this one. I've done it quite a bit at work on things that I had no choice but to try and fix and most of the time I didn't have any problems. Going slow seems to help.

 

[choppinczech]

I'm not saying it can't be done. People all over the world stick weld their cast iron.

Then, we get called to repair their repair.

And let me tell you, nothing screws up cast iron like stick welding it. The surrounding material turns rock hard and usually fails again. You can't see the stresses you just put in it. I looks great. But you've just made the problem worse.

I've repaired hundreds of castings used in industrial and auto. There isn't a single case where we would even consider stick welding.[

If it's a part that's no big deal, then weld it.

If it's an irreplaceable, rare or expensive part I'm just suggesting having it professionally repaired.

 

[bob w]

Contrary to the advice of some but in keeping with the experience of others, I welded the mild steel down tubes to the manifold using 55% Nickel/Stainless electrodes and a Miller AC welder. I never let the heat get very high in the manifold by laying very short beads and letting it cool between shots. It took a long time and the welds looked like crap. Took lots of grinding with a die grinder.

Time will tell if fractures develop in the future.

Thank you everyone for offering your opinions and experience.

There's more info and pics in the build thread.

 

[hoggyrubber]

sounds like you got it. chances are it would have cracked if it is going to. i read the thread about brazing and i know most don't seem to like it but i have really had the best luck with brazing cast iron. it doesn't have to get near as hot, and if cooled slow seems to work good most of the time.
i have done some great welds on cast with specilty cast rods, one i even ground down and you could hardly see the weld. at least have the time they crack and it almost always toward the end or when it's cooling. i would hate to bet on it. maybe others are just more patient or better welders. either way glad it worked!
you should give your self a pat on the back, i think these manifolds are a little tricky to weld. i have heard the metal gets contaninated with the fuel. sounds like you made the right choice on method.

 

[Torch]

if it cracks it wont be along the weld but somewhere near.
I had a ford 460 block that had a hidden crack show up after it had already had the #1 main cap re-fitted and the crank line honed and the block bored and honed.
It was a tiny little crack in the drivers side upper water pump bolt hole. that's what happens when someone who just doesn't care runs a bolt into a blind hole full of dirt and grease.
The cost for a section repair was throw it away and get another one. there was no-one to do it here and I think the guys I called either didn't want to mess with it or they really were worth $500 an hour.
I have a friend who was a maintenance engineer at Loziers. he told me they have to weld castings on drop hammer forges. he told me heat it up as much as I can, grind it all out. get a good root, and don't weld more than an inch before you ping it as it cools to relieve the stresses.

I did notice the carbon when I was fishing for some good steel to weld to. It was in granular inclusions in the grain you just had to burn it out and back off before you melted in deep enough to hit the next pocket.

when I started grinding into the crack it spider webbed into the block requiring half the water pump boss to be ground away leaving a golfball sized hole in the block you could see the cylinder lining through.
It took some long and tedious welding to build it back up but as far as machining goes i just worked it out with a couple small grinders and finished off the gasket face with a hand file.
The welding arc is hot but the block is not. the key is to not let that weld heat get into the block, let it dissipate while you ping the weld.

Another thing that might have helped is i did not weld along a straight line.
The area I ground out looked like I was going to do a fiberglass section repair to a fiberglass body part.


Cast iron manifolds routinely get to 1200, 1400 degrees. turbo manifolds require a special alloy.
I had a mack truck that had burned the carbon out of the dividing web between the 2 turbo ports and what was left looked like steel sponge.
The quality of the cast makes a big difference just because something was cast doesn't dictate whether it's iron or steel

The carbon content dictates if it's iron or steel.
once the carbon content in steel reaches a certain point it is classified as cast.
Don't let the term carbon steel fool you, steel has lower carbon than iron.
Some parts like steering knuckles and some connecting rods are actually cast steel
Somewhere on here I posted a detailed article on the different types of ferrous alloys

What he said about doing a cast iron section repair is correct. the suppliers of new parts to the automobile industry do section repairs on brand new parts with casting flaws.
But if there's no-one around to do it or the guy you do find wants to drink beer for a year off the job what else are you going to do?

 

[29Abone]

I always used to split 6 cylinder manifolds by brazing them. I never had any problems with cracking, or any thing else. I guess I did it this way because that's all I had to work with, but it worked. In later years I've tried to arc weld cast iron & it got real brittle and cracked. Hope this helps!

 

[choppinczech]

I always used to split 6 cylinder manifolds by brazing them. I never had any problems with cracking, or any thing else. I guess I did it this way because that's all I had to work with, but it worked. In later years I've tried to arc weld cast iron & it got real brittle and cracked. Hope this helps!

BINGO!

If you can slowly soak heat into the part, and it's shape allows for uniform expansion, there's not a thing wrong with brazing. And then slowly cooling the part for even contraction.

Stick welding cast iron super heats an isolated spot and cools too fast.

When oven brazing, we would often heat up a part over an hour or two, increasing the saturation temp slowly. And cool back down over a similar time period.



Hell, I've seen cool down periods of 6 hours for fusion welding with cast iron rod. There, you're talking a 2000 degree pre-heat.

 

[bob w]

http://www.lincolnelectric.com/en-us/support/welding-how-to/Pages/welding-cast-iron-detail.aspx

See the part about welding without preheat. No doubt not the best technique, but I gave it a try and so far, so good. The proof will be in the driving. That won't be for quite a while yet.