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Your application requires a lengthy response. Please forgive that. The biggest problem with brazing (using a Cu based filler metal) would stem from vibration and thermal cycling, Robert. It probably cracked through the bolt holes as result of these two influences already. Common brazing filler metals aren't that well suited to these type environments when compared to other options. I wouldn't be afraid to use Ni welding powder on it. I don't imagine you have that equipment though. In that case, the M.I.G. wire we call #925 would be beneficial. It welds pretty good with contaminants present in the base metal and operates with an economical CO2 shielding gas. (75/25 would be the cadillac gas here.) It is available on 5# spools for those who occasionally require an alloy for cast-iron repair or for welding cast iron to carbon steel. The procedure would be to remove the part and prep it by grinding a "U" groove on both sides. Grind the top clean about 1/4" on both sides in the transition zone. This will allow the edges of the weld to blend in as the deposit flows out onto the surface of the part. (If you have an airless gouging electrode..... .those are ideal for creating the "U" shaped groove. They also provide some preheat, create more of an anchor profile for the weld deposit, partially fuse the root, and seal off contaminants. They don't leave behind contaminants either like a grinding wheel does or a carbon arc will. Wire brush afterwards.) If the crack does not extend completely across the part, terminate it by drilling a 1/4" hole at the end or by tacking a small 1/8" thick piece of square or rectangular carbon steel at the end of the crack. Make your tack welds a bit longer than you usually would and place them parallel with the crack on both sides. Once the part is prepped, preheat to around 300�F..... .if you weren't able to prep with the gouging electrode. On parts that are over 1/2" in thickness and more than about 6" in length..... you have two choices for weld procedure. (Provided you intend to keep the part temp in the 300�F range during the entire pprocess.) You can skip weld or use the backstep method. The skip weld technique is self explanatory. The backstep method consists of making a 1/2" deposit at one end of the joint....then one at the opposite end....then one in the middle. Continue that pattern until welding is completed. Stress relieve by peening aggressively between passes. If the part is only about three to four inches in length and 1/4" to 1/2" thick, I would just preheat to between 500�F and 800�F and weld it from one end to the other. Then bury it immediately in dry sand, vermiculite, cat litter, KAO wool, etc. The #925 will provide a narrow band of heat input to the substrate as opposed to stick welding or an oxy-fuel process. It can also be used as a T.I.G. welding electode to reduce the width of the heat input zone even further. If you decide to go with it, be sure to ask for a data sheet to be sent with your order so you'll have all the welding parameters. I will make a phone call to a U.S. Alloys customer who needs help with any application. It may be possible to get face to face, hands on, assistance in some cases. Thanks for the inquiry. Hope you've been helped out here. Feel free to field any other questions you may have regarding this application or alloys mentioned.
Cordially,
Steve
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