Welding Cast Iron


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The following comes from a recent topic on SmokStak, which can be found on the Internet at: smokstak.cgi. As ever, various individuals started, commented on and concluded the following bulletin board thread.

A lot has been said on this site about welding cast iron. I'll admit right off that I have no experience doing this. However, last week in the shop where I work a cast iron part broke in an automatic cutoff machine. To keep things going and to avoid down time, I took the broken part, 'V'-grooved the two broken sections and MIG (metal inert gas) welded them together. I then ground and filed the excess, and got the machine running again. A week later, it's still holding up! Mind you, I wasn't a bit fussy about doing all this because time was of the essence. I had mild steel wire in the MIG welder, using a ratio of 75:25 argon/CO2 gas. So, for what it's worth, it worked for me. - Al

I have had several cast iron parts break a second time at the point that I had brazed the repair correctly. Out of need, I welded them with 0.023 diameter mild steel wire and 100 percent CO2 gas. Working under the same conditions, the parts have not broken again - and I am quite pleased with the looks of the MIG weld on the cast iron. I have no doubt that your MIG weld repairs are holding up fine. - Marty

How would MIG welding a flywheel hub work? - Dave

Based on the experiences I have had welding cast iron with my MIG, I would do it. - Marty

I am a welder by trade, and the best product I know of for welding cast iron is a stick rod called Certanium. It is a very good rod and you don't have to be a pro to use it. - Rod

Rod, is that the #889? If so, I have also had very good results using it. - John

While digging through reference books about iron for a magneto charger, I learned that the recipe for cast iron is as varied as a Sunday dinner. This helped me understand why some of my welds have been good and some have failed. - Ralph

Ralph, I was so glad to read your post. Maybe it has been said before, but I don't recall reading it. There have been so many threads concerning the methods of welding cast iron, and for a very simple reason. Your statement of, 'the recipe for cast iron is as varied as Sunday dinner' is so true. It's the same thing concerning the removal of a stuck piston. For every stuck piston, there is a 'best' method to free THAT PARTICULAR piston. For nearly every situation there is a different set of circumstances, so generally a different method of 'fix' applies.

I think the reason is because we call what is in essence an entire group or family of metals 'cast iron.' Like the generic term 'steel,' the name simply doesn't convey much useful information beyond an average carbon content. Metallurgy has advanced enough that we can manipulate 'cast iron' to have all sorts of properties, some that even defy what the average fellow thinks he knows about the material. On the other hand, there are still quite a few places that simply make a Mulligan stew-type of cast iron by throwing just about anything into the pot. They don't control cooling rates, either, so the physical and structural properties end up differing from batch to batch. - Allen

I have been on a soapbox for years about welding cast iron with a MIG welder. I found out by welding exhaust manifolds on automobiles. It is not a very strong weld and I don't know how much I would trust it on a flywheel, but as far as welding up a crack in the water hopper or welding a bracket back on, it seems to work just fine. Also, it is a very hard weld. You can't machine it because it will break your tools. All you can do is grind it back to size or shape with a disc grinder. - David

I went out to the shop and got a stick of Certanium rod, and here is what it said: 889sp p/n 12003 AC/DC all position rod, 1/8, 90 to 125 amps for cast iron. I agree with the person who said he doesn't weld up flywheels. Cast iron combined with rpm g-force is very scary! - Rod

The reason MIG works fairly well, at least some of the time, is because you have a lower heat input, therefore there is less thermal shock in the heat-affected zone than with conventional arc welding. Running a cooler weld (essentially a localized re-casting) means less penetration, and a weaker joint. If you tried to run it hot - into transition or metal spray - you'd find that the end result would be subject to the same problems as a conventionally welded repair. - Allen

I weld a lot of cast iron. I use Ni-cad rods or cold weld rods made of almost pure nickel. These are not cheap, but really do the job. I have welded flywheels, but I would never do it for someone else. I want to keep my farm. - Kevin

The 'smooth' rod I use on cast iron works really well. I think most of the cast iron before World War II is a much better quality cast iron than what came later. The guy that sells me the rods I use won't tell me the company name or the numbers for the rod. There isn't any thing printed on the flux and I only buy them about a pound at a time, so there isn't a box with writing on it. I guess he wants me to just buy them from him. I think I pay about $1.50 each for them, and they are well worth it. The smooth rod welds this old cast iron like mild steel. I don't know what it's made out of, but they are a lot better than any nickel rods I have ever used. I have bought the most expensive nickel rods I could find, as well as the cheaper ones, and they don't hold a candle to the smooth rod. The weld is soft enough to file, as well. - Don

I agree with Don on Ni-cad rod, which is too hard, can't be machined and doesn't blend with the cast iron, appearance wise. I use Palco 808 and 827 cast iron alloy machinable rod. - Brian

The above messages and many more can be found by visiting SmokStak on the Internet world wide Web at SmokStak is an engine conversation bulletin board and is part of the Old Engine series of Web sites that started in 1995 as 'Harry's Old Engine.' This past month, we passed our 20,000th ad on the Big Engine Classified Ad board and our 50,000th message here on SmokStak!

Harry Matthews is a retired electronic engineer and gas engine collector from Oswego, N.Y., now residing in Sarasota, Fla.

Additional Thoughts on Welding Cast Iron

In Procedure Handbook of Arc Welding Design and Practice (11th Edition, Cleveland, Ohio, 1957), the Lincoln Electric Co., publishers, make various comments on welding cast iron. It's worth noting that only arc welding procedures are discussed. This is because Lincoln Electric is in the business of selling arc welding equipment and consumables. Their remarks on the carbon arc process largely apply to oxy-fuel welding, as well.

I am not familiar with the mild steel electrodes for welding cast iron. I have used nickel 'Mi-rod' cast iron filler with oxy-acetylene, and, in very limited applications, with mild steel mig wire. 1 often braze cast iron. Brazing and oxyacetylene welding give preheating almost automatically because the O2-C2H2 flame is much cooler than the electric arc and you have to heat longer to bring the iron to welding/brazing temperature. Also, brass and nickel both yield deposits more ductile than the parent metal, giving a small measure of stress relief. The tensile strength of the brass is comparable to that of the cast (though less than that of steel), and a good brass is better than a bad weld anytime.

In one passage the handbook says:

'As contrasted with the use of steel rod, non-ferrous alloys do not harden appreciably when deposited on cast iron base metal. The weld deposits so made are therefore machinable. However, the hardening of cast iron in the casting adjacent to the line of fusion, due to the quenching action of the mass of cold metal back of it, remains much the same as in the case of welding with a steel electrode.' The old guys say; any preheat is better than none - at least 'take the chill off.' More than you ever wanted to know ....

Walt Hull

Walt Hull Iron Work Lawrence, KS

'While digging through reference books about iron for a magneto charger, I learned that the recipe for cast iron is as varied as a Sunday dinner.'

I have bought the most expensive nickel rods I could find, as well as the cheaper ones, and they don't hold a candle to the smooth rod.'