Machining weld bead

John_Dennis

John_Dennis

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I welded a piece of unknown cast steel or iron to a piece of ductile iron pipe using a mig welder. The resulting area was very hard to machine even with a carbide tool. The chips were hot and glowing bright yellow.

Is this normal, I don't understand why this material or weld bead would be hard.

Thanks
John
 
Welds, even on mild steel, can get hard because of the rapid cooling from the surrounding metal. Add some additional carbon from cast to the mix and they can be extremely hard, and frequently brittle. It's just one of those things you have to anticipate and work around. I'm impressed that you were able to MIG that without difficulty. If needed, annealing with an O/A torch would help machinability.
 
You can MIG weld cast material, insofar as you can get a bead into it. However, as Twirpunky mentioned, the high carbon content will lead to brittle, hard welds and area around the weld as it turns into something like a poor tool steel that's been heated and quenched. Machining it will be horrid and it'll likely fail due to cracking fairly soon anyway. Brazing is a much better process for cast.
 
As @Lo-Fi says, cast iron should be brazed not welded. Welding the metal, in other words melting the base metal will cause it to become very hard and brittle. Brazing will only take about 1400 degrees to flow into the cast iron pours. Preheating the metal to about 600 degrees is important
Do not attempt to weld a hair line crack or joint, you really need to open the joint up with a grinder to create a U shaped channel to fill and create the bond. Use lots of flux before attempting to flow the rod, you want to create a shiny surface on the metal as the flux melts before you attempt to flow.
 
I like to prepare the joint as stated above, then liberally butter it up with silver solder flux, then preheat and proceed to heat the point of brazing to a very low red heat, and use a generous amount of flux; I like Anti Borax EZ #3, it is black colored and much superior to any other cast iron brazing flux that I have ever used, with its use, bronze will wet out on the iron similarly to silver solder. It is important to not overheat the iron so that the flux cannot clean the scale off that was caused by the overheating.
 
Ductile iron is basically cast iron once it has been remelted. The bead with any standard welding rod is considered non-machinable. If I don't care, I will usually TIG weld with inconel. It doesn't crack, but it is definitely not machinable. You could try Ni99, or braze as the above suggestions say. If the weld just needs a little shaping, you could try a die grinder. This works really well with this kind of junk weld.
 
on a dare,
i was able to successfully mig weld a steel jaw to a cast iron vise by v slotting both pieces and a preheat with a rosebud.
 
Ulma Doctor said:
on a dare,
i was able to successfully mig weld a steel jaw to a cast iron vise by v slotting both pieces and a preheat with a rosebud.
Click to expand...

Good job. Did you do any peening after the weld? That often helps too. But it won't make the weld machinable.
 
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