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dang
11-28-2007, 10:09 AM
Hi,

I've got this piece of equipment that is missing a rather difficult to find iron casting. The casting is used to transmit power, so it does bear a bit of load to it. I've found a replacement casting, but it has a crack in it. I'm now wondering if it'd be possible to weld the casting back together without totally destroying it. Anyone ever done anything like this?

From my experience with test welding a bit of another casting, this works. Does anyone know different?

Geof
11-28-2007, 10:36 AM
Are you sure it is steel? No matter what anyone told me if I see a casting with a crack I immediately suspect it is cast iron. The welding technique is different for the two materials and I have never had success with stick welding cast iron but steel is a different matter. I would use stick 7018 and would preheat the casting to several hundred degrees before welding. Probably also vee the crack to get penetration and drill a small hole through at the tip of the crack to help ensure it did not propagate further.

The main problem in welding castings is shrinkage cracks adjacent to the weld and changes in the metal properties in the heat affected zone. You probably do not know the steel composition but when it is a casting it is likely that it is a medium carbon steel, maybe even an alloy steel, so a concern is making it brittle in the heat affected zone.

Realistically you do not have anything to lose because the casting is no use with the crack. Wait and see what other suggestions are posted and then make your decision.

dang
11-28-2007, 11:00 AM
Geof,

Thanks for the reply. It IS cast iron. My mistake. After I typed up that post, I went out and test welded some of the other cast iron I have, and it worked. I have a MIG welder. All I did was clean off a bit of the part and weld it, just to see if the weld stuck, no problem there.

Again, thanks for the reply. That bit about widening the crack to achieve a better weld is gold.

NC Cams
11-28-2007, 09:02 PM
One of the key elementts (no pun intended) in welding cast iron is literally the alloy used to weld with and the "alloy or "alloys" that you create when you melt/fuse the metals together.

A common trick in welding cast iron is to use a high nickel rod. There are some patents wherein iron bodies were welded to steel to affect a bond and they plated the parts with nickel at the fuse point - this provided an alloy that, when the metals melted, created a weld that When subsequently heated and cooled properly after welding, the stuff was could be turned into tempered martensite. You want tempered martensite at the weld as it is hard and tough as opposed to BRITTLE which untempered martensite is/may be.

The 'trick" is surely pre and post heating. The residual stresses that are generated during welding and cooling are not minor. These tend to be the demise of a lot of welds. Poor weld cleanliness leads to weld contamination as well. Both will affect weld integrity andor durability. Properly welded and subsequently annealed welds in cast steel and/or iron have proven to work well when done carefully and properly. The welds are DEFINITELY techniuque sensitive.