TIG,n Iron....

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OK I've TIG'd for years on ALUM -SS - Mild Steel but never cast iron, or I think thats what it is.I welded up the openings in a rear axle diff to seal it off so to pack it with grease as it was to be used in a Trike axle and open to the world and not sealed in the stock axle houseing.Anyways I cut a bit of steel to the shape of the hole thats kinda kidney shaped, clean it all up with a burr bit and decreased it good, heated it up to 200* and went to welding, well it turned out nice until it cooled a bit and a crack formed all the way around.... grind it out reweld and heat it down slowly over the next hour, still cracked so I MIG'd the inside and built up some on the outside so it couldnt ever work loose and sealed it with JB-Weld from the inside, never see any wetness on the outside so all is sealed and working fine.Next one I weld up what can I do to keep the crack from forming, forget welding it and Braze it ? Use a diff filler rod ?Last edited by mikestrikes; 08-12-2008 at 05:20 PM.
Reply:When welding on cast, you preheat, weld, post heat, then let cool slowly over a long period of time. I have welded numerous cast drill press tables (the major smiley faces) and I have always preheated to near 1100F, weld it up while hot, reheat to at least 1100F or more, then wrap it in something to keep the heat in as long as possible. Typically, I build a big fire, put the piece in the fire until its got a nice deep red glow, then yank it out and weld it up, then stick it back into the fire. Then when the fire is dying down, I cover the piece with several inches of ash and leave it there for a couple of days....it has never failed me yet. I always use O/A with a cast rod. My $.02.
Reply:I did what was needed but not good enough. Next time heat it alot more and cool it alot slower... This beers for you, Thanks.
Reply:To add what was previously said.Instead of making the patch flat, dish it so there's a 1/4" or more flange around the perimeter so it looks something like a frost plug and do your welding to the edge of the flange . This will allow the patch and the piece you're welding the patch into to expand and contract at different rates without adding undue stress into the area. The flange will absorb the movement....Mike**EDIT**I meant to add, floor dry is a good thing to pack it into for slow coolingLast edited by mrmikey; 08-12-2008 at 06:12 PM.