How do I weld cast iron to steel?

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Building my gate and I have cast iron toppers for each vertical of my gate. But I'm not so sure if I can just grab my mig and go to town. It really just needs to stay on the gate and not be easily taken off, and I was going to use it to seal the tubes to prevent rusting from inside out a bit.
Reply:Most of the finials you buy from places like King metals are cast steel, not really iron. As such they weld just like normal A36 steel does. If it's true cast iron, it can be welded, usually using a high nickle alloy to prevent cracking, but many times it's just brazed on. The brass brazing can add an interesting look..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:http://euroforgings.com/index.php?ro...roduct_id=1209I think it's actual cast iron. It'll all be painted and I'm not sure how to braze, lol. Could I tack it on with my normal mig and then seal it with solder?Or maybe just jb weld?
Reply:I'd contact them and ask what they recommend to attach these. I'm betting they tell you normal mig or 7018. Even though they say "cast iron" in the catalog, I'm betting it's low end cast steel. If they tell you to weld it with either mig/FC or 7018, I'd bet it's some sort of low grade steel. True "cast iron" was made back when true "steel" was an expensive and labor intensive process. Wrought iron fell some where between the two. Ever since they started to mass produce steel the use of true iron has dropped off.I know the local company I get parts from lists stuff as "cast iron" However if you read thru their catalog literature, it says to weld with 7018 or mig/FC. No special requirements like if you are welding true cast iron. They use "cast iron" like most people use "kleenex". It's simply an easily understood term and isn't really connected to the final product, sort of like the term "wrought iron" fencing is used today. There hasn't been a commercial manufacturer of true wrought iron stock in the US in years, and I think over in Europe there's only one maybe two specialty mills that occasionally produce it. Almost anything made of true wrought iron today is made from salvaged materials that were made decades ago and have now been recycled..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I welded all my cast iron spear heads to 1/2" smooth rod for my fence with nickel rod and a stick welder using opposed spot welds.  Took about 10 seconds per piece.Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:Could probably use 309L as well.
Reply:312 tig rod.....................Of all the things I lost I miss my mind the most...I know just enough about everything to be dangerous......You cant cure stupid..only kill it...
Reply:When making handrail or mailbox posts, I MIG weld cast iron caps on them all the time. Done lots of finials also.GraysOrnamentalIron.com
Reply:I used 7018 on some post caps that came from King Metals years ago. They all cracked, some worse than others. It was a rush job and I was working for someone so they just wanted it done and out the door.Finally got the welds to take by doing very small sections just enough to tack them on. Preened them a bit, and they didn't break off.It's a mixed bag. TIG stainless rod would be an option as others have said. It works great on mystery metals and stuff with out gassing and cracking problems. For junk iron, it'll do the trick fine.IMHO of courseExpert Garage Hack....https://www.facebook.com/steven.webber.948
Reply:Originally Posted by roadkillbobb312 tig rod.....................
Reply:312 goes in the puddle like butter.... I get it for 8$ a pound  I welded a 1/2" bead on cast to steel the other day and it cracked pretty bad right after. I did a couple tacks and they did ok, I could here the cast crackleing really bad after the tacks. I preheat to 650 and welded it and it didnt have any visible cracks but I'm gona megnaflux it. Cast iron is very ridged and doesn't like to be pulled around.Last edited by motolife313; 05-09-2015 at 12:10 AM.
Reply:Quick test for cast iron is to file it then rub the filings between your fingers.  The excess carbon (graphite) in the CI will show as black.  Steel filings do not turn finger tips black.   If it is cast iron and the welds are not critical as you describe preheat and weld as mentioned.  If you heat the toppers until the bare metal turns blue which is around 4 to 500 degrees F you are pretty safe.  The steel side will look after itself.   If you decide to use something like a 312 or 309 stainless rod a little preheat still would help.