I'm a rank amateur, but I have taken a semester-long welding class, and this was my experience with welding cast iron. It might explain why you hear both answers about whether cast iron can be welded
One of the guys in our class brought in a clincher breaker, which had been sitting at the botton of a coal forge for 50 years. That's probably a worst-case scenario, but the instructor asked me how I would weld it. By that point, I was getting pretty good at TIG, so I pickup up an nickel rod, sharpened a 1/8" electrode, and went at it. Instantly, the electrode popped from all the crap in the cast iron. I tried this three times before I realized the instructor was grinning.
The "trick"was to use a stick welder with nickel rod, but I've got to tell you, it looked like sh!t when I was done: I'd grind out the cracks, pre-heat the casting, skip weld in the cracks, and then repeat. But you'd get little fine hairline cracks all around the nickel bead. So I'd grind some more, fill it in with more nickel, etc, etc. When it got to the point where I thought the clinker was solid nickel, I gave up, but the welding instructor said that's about as good as it was going to get.
The welds held, but it sure didn't look pretty, and I sure wouldn't want to use it on a piece that had any load on it (like a piece from a machine tool).
I found that brazing cast iron, by contrast, is way easier. The bronze braze is flexible/malleable, so it doesn't pull the cast iron apart.
This is the cast iron nose piece of an old drill press that I MIG brazed with Aluminum Bronze. The piece is a heck of a lot cleaner than the clinker breaker, but it's not virgin either:
For cast my dad uses Lincoln 91K2H dual shield mig wire. V the joint out. Weld about 1". Stop and when it cools to a cherry red use a descaler to "peen" the weld. Not too hard though. Weld another inch or so, repeat. If there are any pinholes grind it out and reweld.
He has done quite a bit with this method and has yet to have something breal. All the head covers on my 10EE were cracked or broken when I got it and we welded it up this way. He has welded up bell supports and all sorts of things like this.
If you have something like a crack in a block look in metal stitching. Also when doing cracks get some penetrating dye. The crack usually travels quite a bit further than you thing. Then drill at the end.
There is the nickel rods. Machinable and non machinable. Also there is Super Missle Rod. Works really good but is REALLY expensive. I tigged up a compound from one of my old lathes that the T slot was totally rounded out on the bottom edge of the slot. Darned stuff was so hard that I could not even cut it with carbide. Ended up grinding it smooth.
Last resort for cast is brazing with a torch or tig. Dont do this if you ever plan on trying to weld it in the future. The bronze gets into the metal and makes welding darned near impossible.
Originally Posted by macona
That is a steel wire and is totally incompatible with any kind of cast iron. Never ever attempt to weld cast iron with steel filler, it may seem to hold ok but the transition area between the weld bead and the base metal will be EXTREMELY hard and brittle and have very little strength. Welding cast iron with duel-shield steel wire is a real no-no! The big problem here is that once the base metal is contaminated with the steel it will have to all be removed (the contaminated area) before it can be welded with the proper material because that area will be completely destroyed from a strength standpoint. NEVER attempt to weld cast iron with steel filler!!!
Dont knock it till you try it.
Originally Posted by radkins
If the pieces break they dont break at or near the weld.
Last edited by macona; 12-03-2008 at 09:24 PM.
After over 40 years I have seen a little of everything including people trying to repair cast iron with steel and I simply know better than that, as does anyone else who knows anything about welding! That not only goes against all common welding logic and every welding manual in print it is just commonly known that it will not work. Just because you may have gotten some pieces of cast iron to stick together does not mean they are properly welded and anything welded in this manner will simply be cobbled at best. NEVER use any kind of carbon steel rod or wire on cast iron. Try this little test, run a bead of steel filler on a piece of cast iron and then try cutting into the transition area with a chisel, WEAR SAFETY GLASSES because the chisel is going to chip! This area running along the edge of the weld and the base metal will be extremely hard and brittle and will break very easily on the base metal side of the weld. I don't care how good someone claims to be at welding this is just a physical characteristic of these incompatible materials and it will be the same for anyone who does it.
Originally Posted by macona
You bet it won't, now stand a piece of steel bar up on a piece of iron casting and weld it on one side with a steel rod. Now pull it over until it breaks, exactly as you said it will not break in the weld but it will come loose with the weld bead attached to the steel bar and a good sized chunk of the cast iron attached to the weld bead. This is the area of the cast iron base metal that was ruined by the carbon steel contamination.
Carbon Steel contamination? Your joking, right?
The primary compositional difference between steel and cast iron is that amount of carbon in the steel versus cast. Cast is typically 2 to 4 percent carbon. Generic steels range from ~.25 percent to .5 percent depending on alloy. High carbon steels reach up to 2% carbon. Cast does have silicon which aids in flow when casting but some carbon steels have silicon as well like 1045. So do the weld wires.
If anything the cast is contaminating the weld, not the other way around. The mixing of the low carbon wire and the high carbon cast essentially creates high carbon steel.
Of course if you welded a rod of steel to cast the cast is going to break under the weld. Where else would it. The steel is malleable and assuming it is heavy enough to not bend under the load the cast will break simply because the cast is more brittle. The same could be seen by drilling a hole into a plate of cast and putting a steel rod in the hole. If the rod dosnt bend the cast will break out.
The only way to prove one way or the other is to have two pieces of cast welded together by different procedures and then the normal shear, bend, and tension tests applied.
My dad has been welding for over 45 years as well and been running his own fab shop for the past 20. He has welded up castings on tractors and trucks and not one has broken.
There's more than one way to skin a cat.
While you were searching for that info you should have looked up some sites dealing with welding cast iron. When I said contaminated I did not mean contaminated with carbon I meant contaminated with whatever alloy steel you are using. I am well aware of the carbon content of steel vs cast iron and that cast iron is quite a bit higher but that is not the primary difference between steel and iron castings, it is how the carbon is contained in the iron casting and in what form. There is no point in you and I arguing about this and if you want to do it go ahead but as I said although it will hold to some degree it is a cobble job at best. I have been doing this for over forty years and I ran a mine machinery repair and welding shop during that time where we maintained some of the largest mining machinery in the world so Don't hand me that decades of experience BS and if you want to compare certs then drag them out. I have a great deal of experience in welding cast iron and besides this is not just my opinion anyway, what you are saying is contrary to every manual written and is just plain non-sense. A warning to anyone who tries this on a small part, once the cast iron is contaminated with the steel ALL of that contaminated and damaged area must be removed before a proper repair can be made. If the part is small or thin then it may very well require so much material be removed that it may become impractical to repair the part, I have seen this happen several times after an amateur repair by someone who did not know better. DON'T anyone take my word for any of this so research it for yourself, go to any of the welding sites or any of the major suppliers sites such as Lincoln or ESAB both of which have excellent info on most any kind of welding. A bit of research at any of these welding sites will quickly expose the folly of trying to weld cast iron with any kind of carbon steel rod. But then maybe I am wrong along every welding manual in print and maybe Lincoln, Hobart consumables, ESAB and a host of others are wrong also.
The whole problem in a nutshell is this:
1-You dont know what the material is exactly. So you dont know what rod is most compatible
2-Anything cast has stresses in it. Cast is brittle, i.e. kinda like welding a china tea cup (not one made in china but a real china tea cup)
3-When you weld it you have to pre heat it to remove the stresses and alow it to cool in a way not to create more stresses. Depending upon its shape and size this may be tough
Last edited by ahidley; 12-04-2008 at 07:19 AM.
Sometimes if you don't know what you can't do, it all turns out well...
Years ago, a construction buddy brought a case of beer and a ram horn exhaust in two pieces.. we cleaned it up with a wire brush, drank some beer, then pre-heated it with a torch, then migged it up, then post heated it and wrapped it up.
I found out later that night I had "stainless" mig wire in the mig. Not tried it since, but the exhaust is still under the truck, even thou I told him it'd fall off again.. the whole muffler system hangs on that exhaust.
His unbroken replacement hangs on the wall. Still unused
Anyways, I think the pre-and post heat have more to do with welding cast than the rods used. Drill a hole at the end of the crack and it will stop right there as the welding heat makes a crack crawl..
Excuse me, I farted.