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Old 09-15-2004, 05:33 AM   #1 (permalink)
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Welding to cast

I know about pre heating when Mig welding to cast and I know to use a nickle rod when stick welding. My ? is what does the nickle do? Is it more flexible so there is no cracking? Does it have properties that heat the cast to a higher temp than the mild steel?

Plain and simple, how and why does it work??

Thanks.
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Old 09-15-2004, 09:40 AM   #2 (permalink)
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The quick answer is that nickle mixes ideally with the high carbon content in the cast iron so that it doesn't precitptate as iron carbide (cementite). Iron carbide is hard and brittle, which is why the welds crack under the bead and they can't be machined.

You still have to either preheat to above 500F or weld short segments and let it cool down to avoid stress cracking.
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Old 09-15-2004, 10:10 AM   #3 (permalink)
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Thank you. With it being necessary to preheat for both types of welding, is there anything wrong with mig?
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Old 09-15-2004, 12:19 PM   #4 (permalink)
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Quote:
Originally Posted by flexj
Thank you. With it being necessary to preheat for both types of welding, is there anything wrong with mig?
Steel welds on cast iron tend to be brittle even though they may be strong. It depends on what type of cast iron, but generally they have less impact resistance because of problems with brittle iron carbide and martensite formation in the fusion zone.

It would depend on what you are welding and why. If you are simply repairing a crack or mounting a spring perch, then it is no big deal.

If you have weldment that has a high dynamic loading and impact, like a control arm, then welding it may be a problem. Cast iron even without welding doesn't have the ductility and impact resistance that steel does.

The strongest joint you can make in cast iron is to drill, tap and install two rows of 1/8 inch steel screws spaced 3/8 inch apart in the cast iron on either side of the weldment. Weld nickle stringer beads over the screws. Then weld whatever you want onto the nickle-coated cast surface with either MIG or 7018 rod. The cast housing will break before the weld will.
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Old 09-15-2004, 01:10 PM   #5 (permalink)
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i welded to cast. preheated till it was just about red. then welded short 1" weldeds and hammered them as thewy were cooling. no cracking but this was only for a spring perch. nothign with significant stress to it. i would much rather drill and tap into cast then weld it anyday. you never know the quality of the cast material or the cuantity of components comprizing the cast. Most of the axles were wroking on are made 30 years ago in a factory i'd bet did not have the greatest quality control .
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Old 09-15-2004, 02:25 PM   #6 (permalink)
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I'll be welding gussets for my control arm bridge to the cast housing.

Pinhead, your idea of the screws is intriguing. How much nickle would I lay down between the screws?

Another question, I've been told that cast iron is not magnetic but cast steel is. Any truth to that? This housing is magnetic if that makes any difference.
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Old 09-15-2004, 02:44 PM   #7 (permalink)
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Quote:
Originally Posted by flexj
I'll be welding gussets for my control arm bridge to the cast housing.

Pinhead, your idea of the screws is intriguing. How much nickle would I lay down between the screws?

Another question, I've been told that cast iron is not magnetic but cast steel is. Any truth to that? This housing is magnetic if that makes any difference.
You don't have to use nickle rod to butter over the screw pins, but it is the most forgiving rod to use. You can also MIG weld over them, but remember to preheat, cool slowly and peen the beads while hot. The point is to lay down a surface of steel to make it easier to weld the gusset to. The screws embedded in the iron help strengthen the joint so the iron won't crack under the bead (at least that is what they said in welding class). It is a PITA, but so is doing it over again.

Cast iron is mmagnetic, just like steel. Niether is magnetic above the austenitic phase transition temp (~1700F or cherry red).
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Old 09-15-2004, 03:37 PM   #8 (permalink)
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So here's a stupid theoretical question on the subject....

Suppose one were to be cutting and turning their knuckles, and only had a mig gun.

Would it be hugely inappropriate (meaning causing the metal to become brittle) to tack weld the knuckles into place with the mig gun in order to take them to a pro to have them welded on correctly?
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Old 09-15-2004, 03:46 PM   #9 (permalink)
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Sully,
Most all axle "C's" or inner knuckles are forged or cast STEEL. Welding steel to cast STEEL is child's play compared to welding steel to cast IRON.
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Old 09-15-2004, 03:57 PM   #10 (permalink)
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Quote:
Originally Posted by Mechanos
Sully,
Most all axle "C's" or inner knuckles are forged or cast STEEL. Welding steel to cast STEEL is child's play compared to welding steel to cast IRON.
Duhhh. Guess I let myself get ahead of my brain there, huh?
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Old 09-15-2004, 04:21 PM   #11 (permalink)
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flexj , have you thought about fabing a bracket that bolts on to the center section to weld the mounts to ? it may be easier and stronger and removable.
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Old 09-15-2004, 05:27 PM   #12 (permalink)
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Quote:
Originally Posted by peesalot
flexj , have you thought about fabing a bracket that bolts on to the center section to weld the mounts to ? it may be easier and stronger and removable.
maybe incorporate a tab on your diff cover to help as well. something like Poison spider customs offers.
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Old 09-15-2004, 07:51 PM   #13 (permalink)
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Quote:
Originally Posted by flexj
I'll be welding gussets for my control arm bridge to the cast housing..
I for one am in the "don;t do it" camp. I don't believe you (or even a pro welder) can do a good job of welding steel to cast iron in a structurall application. One day, it WILL fail.

Quote:
Originally Posted by flexj
Another question, I've been told that cast iron is not magnetic but cast steel is. Any truth to that? This housing is magnetic if that makes any difference.
Not true, both are ferrous, meaning containing iron, which is what makes them magnetic. Here's some reading you may enjoy:

https://www.pirate4x4.com/tech/billav...0/index1a.html
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Old 09-15-2004, 10:51 PM   #14 (permalink)
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Walker built the diffs under the rockit five years ago, welding the top links directly to the cast of an old-school, shaved, Dana 60 housing...that car has been BEATEN to death many times over and not once have those welds failed...truly, I cannot think of another car that has taken more abuse on links when I am actually bending 1 3/4" x 3/4"wall DOM links on a regular enough basis.

Done right, they should hold up fine. Though I have no clue how he did em right.


Oh great, now they're gonna break since I opened my mouth!
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Old 09-15-2004, 11:11 PM   #15 (permalink)
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You bend 1.75x.75 wall DOM I only have .25 wall DOM links
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Old 09-15-2004, 11:43 PM   #16 (permalink)
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I've now replaced two lower links of that material simply from falling backwards off big wall in full-throttle reverse and hitting something behind me. Before going to that wall thickness, I was breaking .180 wall chromo that was cut and spined through the stress areas, then heat-treated. Went through about 8 of those before giving up and going HEAVY...still, nothing's DustinProof so I have trouble with the thick stuff too. The current ones are bent from banging up rocks but are still holding up.
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Old 09-16-2004, 04:54 AM   #17 (permalink)
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Quote:
Originally Posted by peesalot
flexj , have you thought about fabing a bracket that bolts on to the center section to weld the mounts to ? it may be easier and stronger and removable.

I did that on my rear diff, along with an "I" beam set up that ties into the tubes. I thought I try something different for the front. It seems, from what I've seen, that the front doesn't take the abuse that the rear does.

Thanks for all the ideas.
Keep them coming.
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Old 09-16-2004, 04:59 AM   #18 (permalink)
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Originally Posted by RedBullJeep
simply from falling backwards off big wall in full-throttle reverse and hitting something behind me.
He says "simply". You're a maniac, man. But fun to watch. Saw you on TV the other day tring to jump off of an 8' wall with you rig. Crazy I tell you.
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Old 09-16-2004, 05:31 AM   #19 (permalink)
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IMO, what your dealing with is cast steel rather than iron. I thought that to be machined meant that it was a higher grade. I was told by an old welder that Lincoln NR-211 innershield was perfect for this application because of its high nickle content rather than mig wire. So, preheat with Lincoln fluxcore and it should work just fine.
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Old 09-16-2004, 07:40 AM   #20 (permalink)
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what are pitman arms made of?? cast iron? because the death wish I have made me weld my own pitman arm with 7018 3 yrs ago and its still together with 30,000 km (18,600miles) on it. so dont get in my way cause I might not be able to avoid you!
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Old 09-16-2004, 08:16 AM   #21 (permalink)
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Quote:
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what are pitman arms made of?? cast iron? because the death wish I have made me weld my own pitman arm with 7018 3 yrs ago and its still together with 30,000 km (18,600miles) on it. so dont get in my way cause I might not be able to avoid you!
I dont know what OEM pitman arms or made of but the aftermarket one are supposed to be forged 4140 and heat treated.
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Old 09-16-2004, 09:00 AM   #22 (permalink)
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Quote:
Originally Posted by MrWillys
IMO, what your dealing with is cast steel rather than iron. I thought that to be machined meant that it was a higher grade. I was told by an old welder that Lincoln NR-211 innershield was perfect for this application because of its high nickle content rather than mig wire. So, preheat with Lincoln fluxcore and it should work just fine.
Someone is probably going to chime in here and say that they are nodular iron. What is the diff?(pun intended)

I am leaning toward the nickle rod and preheating. If it breaks, I'll have to come up with something different. That's part of the fun, not?
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Old 09-16-2004, 10:09 AM   #23 (permalink)
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Nodular is still cast iron, but it is an entirely different class. There is grey cast iron (common just called 'cast iron' here in this forum) and there is nodular cast iron (aka ductile iron). Both of them are iron and both of them are cast, but the material properties are very different.

In plain old grey cast iron, the carbon forms in long ribbon-like structures which is what makes grey iron brittle and prone to cracking. Nodular (or ductile) iron is made by taking molten grey iron and reacting it with magnesium and some other things. The result of this process caused the carbon to form in round bead-like nodules.... hence the name nodular. Compared to grey iron, nodular iron is amazingly malleable and quite ductile... hence it's other name, "ductile iron". Ductile iron will flex, stretch and tear whereas grey iron will just crack and split.

Here is a maginfied pic of the carbon in nodular iron on the left and grey iron on the right:

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Old 09-16-2004, 10:42 AM   #24 (permalink)
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I asked and I got taken to school!!! That's what I call service.
Thanks.
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Old 09-16-2004, 12:41 PM   #25 (permalink)
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Originally Posted by RedBullJeep
I am actually bending 1 3/4" x 3/4"wall DOM links on a regular enough basis.

3/4 + 3/4 = 1.5

Do your 1.75 links only have a 1/4" hole thru them? Why not just use solid?
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