Cast iron and dissimilar metal welding discussion

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Building a sculpture for a customer. Not even sure what all the materials involved are. Some brass, bronze, cast steel, cast iron and other misc metals.The problem is cracking on a lot of it.It's all antique stuff, gears and stuff like that. All the parts were soaked in vinegar overnight or for a few days prior to him bringing them to me.Today I had to take the cast iron base to a gear that I would assume was cast iron or cast steel. I believe it was cast iron.The issue is cracking every time.Here is what I have tried309LSupermissleDavbro eztig for cast iron -http://www.davbroinc.com/Er70sAl bronzeThe 309, supermissle and even the davebro tig ALL crack right away. I had high expectations for this Davbro wire since it requires no pre/post heat. It had the smallest crack when compared to the rest but still as soon as you lifted the torch there was a crack. Even a weld as short has 1/4". Didn't matter if I had longer post flow to cool it either.The only thing that didn't crack was aluminum bronze. I had to over the other ones with that.Never have I seen 312/supermissle crack before, but sure as ****, every time I lifted the torch it was cracked.Anyone have any good advice for doing stuff like this? Without having to pre/post heat? The customer is paying for my time and is here the entire time as he can't let the piece out of his site, and no pictures since he hasn't gone public with it yet.Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Gamble,If all of the cracking is happening during or immediately following welding; those materials may be "Hot-short". That's what it sounds like to be from your description of the problem.  I've never really understood where this expression comes from.  That said, But it means that the weld puddle is freezing(tranforming from liquid to solid) over a broad range of temperatures.  At a microscopic level, part of the weld solidifies while some remains liquid.  As the freezing puddle shrinks, the weld cracks through the areas that are still liquid.  Normally steel freezes over a narrow range of temperature; < about 10°F. But these cast alloys you're working with may have a much wider freezing range.  This kind of behavior is much more commonly seen when welding aluminum.  But it can happen with old cast irons, and free machining steels.Typically this type of behavior is seen where contamination from elements like sulfur, phosphorus, lead, antimony.  These are much more common in old cast iron; made when foundry techniques weren't advanced enough to remove these contaminants from the pig iron used.  These elements join with Iron to form compounds with much lower freezing temps than the surrounding iron matrix.typically using 309/312/321/347 alloy filler metals, or Nickel based filler metals can help with this problem.  These alloys are more 'tolerant' of some contamination.  But if you're still seeing issues using these alloys you might be in a situation where the materials aren't weldable.I suggest switching to brazing the parts together, rather than welding them.Last thought:It could also be due to an extremely high carbon content in the cast materials as well.  In that case the metal is just too brittle to tolerate rapid cooling created by the welding  process.  If you haven't already tried it, you could use some pre-heat and insulation to control the cooling of the finished welds.  But I think this is a long shot...Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:10/4 on what he said ^^^^^^^^^^^ try tig brazing it with Si Bronze and walk your puddle off as youre backing off on your amperage onto your base metal. That should cure it for ya.I hate being bi-polar it's awsomeMy Heroes Have Always Been Cowboys
Reply:Silver solder might also be an option since you don't actually melt the base material..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 know you don't want to pre-heat but... you should probably pre-heat! Sculpture fabrication is most of what I do, and if someone brings me cast iron or tool steel pieces I tell them it's going to be mo' time and mo' money due to the necessity of pre-heat and slow cooling.Any alloy that is high in carbon is going to get very hard and brittle if subject to rapid heating and cooling. The heavier section you are welding, the worse it will be since the thick metal acts like a heat sink and cools the weld area rapidly. Stick welding and O/A brazing are better than MIG or TIG because the higher heat input of the former methods results in slower cooling. There are many threads on here about welding cast iron, and the advice mostly boils down to plenty of preheat and cooling as slowly as possible. Probably not what your client wants to hear but better than having his sculpture break into pieces. I generally use nickel 55 for cast iron, 309L or 312 for high-carbon steel, with a minimum preheat of 350F. Some have had success welding without preheat by making a small weld (less than 1" long), peening, and allowing the base metal to cool to the touch before making the next weld. This is also, as you can guess, quite time consuming. I have also run into castings that are simply unweldable even with higher preheat temperatures, either white iron or simply crappy metal.Since the bronze seems to be the best of the options you have tried, that may be the direction to go. Torch brazing would be best for reasons stated above. TIG brazing can work but get it as warm as possible first.JohnA few weldersA lot of hammersA whole lot of C-clamps
Reply:Thanks. Never heard of white iron before. The issue is he doesn't even know what he is building exactly, I mean he has an idea. So it's basically like putting legos together until what he likes and then he will hold it and i'll tack then weld it in place. The first time we put maybe 8 pieces together took 2 hours. If i had to pre heat it every time, I'm sure he wouldn't like the bill. I was really disappointed in that over priced ez tig cast iron rod. Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Originally Posted by GambleThanks. Never heard of white iron before.