Well you won't have any success welding cast Iron to mild steel but one doesn't have to look much farther than the rear axle of most pickup trucks of the 70's and 80's to find Iron joined to steel. If I am not mistaken a lot of the housings are Nodular Iron and the tubes are usually welded to them, 4x4 enthuiasts build reinforcement trusses for them all the time and many other mods. My choice would be MIG or Stick 7018. I used to do a lot of welding on pile driving hammers, many parts were ductile Iron I think and we used to weld the picking eyes on them, that has to be right or someone gets hurt, never had one let go. That was stick with 70 or 8018. What parts are you wanting to join?

 

Building chassis for a street rod. Installing triangulated 4 link for air ride. One of the upper arms sits right on top of housing (iron). There will be some stress on that connection, but this is not a race car so it won't be that bad .Like you said, the steel axle tubes are welded into the iron case.

 

TIG, preheat the bejesus out of the housing then run 309 filler on the joint, it should flow in like butter. Why can't you weld the brackets to the axle tubes like everyone else, slight angle change on the frame brackets and you will be all set. To be practical, I have built Dana axles and used 7018 on the tubes with no ill effects.

 

I am welding to tube on right side. Like many Ford housings, the center is offset to left and therin lies my problem.

I'm sitting right at 30 deg. now. Any less might cause the housing to rack. I've seen a lot of off road trucks and buggies do it, never tried it myself. I had a rock crawler that had early Dada 60's in it and they had welded supports on them.

If I don't have access to a TIG, can I MIG it? What wire, heat?

 

I wasn't far off , heh. Panhard bar?

 

I wasn't far off , heh. ?

Panhard bar>>>>Can't. The body of that 39 sets right down on the frame and I would have no room for exhaust.

 

Preheat the housing, and run the bracket on with your MIG, post heat and let it cool real slow. Wrap a welding blanket around it and you should be ok.

 

OK...hope I don't sound too dumb here, but heat the housing with my O/A torch, weld the brackets on, then re-heat and let it cool slow. What's the blanket for:help:

 

Yes, the blanket keeps the heat in and let's it cool slow. If you have or can get a junk pumpkin, do a trial so you know what your getting in to.

 

tozz what about nickel rod

 

As far as I was aware, diffs are steel, not iron and are very weldable. They even have two plug welds on each side from the factory to hold he axle tubes in. Plug welds are one of the most crack prone welds. So, if the factory can get away with plug welding you can get away with whatever type of welding you want.

Be careful preheating the housing because if you get it too hot everything will shrink as it cools and none of your bearings will fit anymore.

Otherwise, I prefer brazing even for steel to iron connections:

 

Bought an old Moncrief Coal Furnace the other day. The top 4 inches was cracked off of it. I could have just ground the area flat and added more sheet metal for the outside shroud but I instead decided to try to weld it back in place. Took the pieces as the part that was cracked off was also broken in half and ground the edges to a 45 angle then welded the top section together by using a MIG welder and tacking it together about every inch or so. Then proceeded to weld it between the tacks no more the 3/4 inch at a time and going from side to side to allow cooling so it would not crack on me. Finally got it all welded up and the top section was ready to put back on the furnace. Followed the same procedure by tacking it about every couple inches from side to side then center etc. Then welded up the gaps and started grinding it to make it look good. My grinding wheel wore out so have to get another couple of them tomorrow and finish the grinding. It never cracked and I think it is as strong as if it never did crack off at all. So yes you can weld Cast Iron with a MIG and Argon/ C02 mixed shielding gas and it will come out fine as long as you do not try to make a full pass. Jump and skip around with the tacks and 3/4 inch welds to keep it cooling equally and you should be fine. Will post a photo of finished job after the grinding is done on it to let you all see how it came out.

 

Here is the photos of the furnace. The red line in the one photo shows where the pieces broke off the top of the furnace.

The photo without the red line shows how it looks now.

No Cracky!!!

:drinkup::drinkup:

 

WOW--if I could weld like that then I probably need to ask these questions..VERY NICE!

 

So--tried a little mild steel to cast iron yesterday and was a little supprised. I'm welding a piece of 1/4" to the top of a Ford housing. The axel tubes are steel but the housing itself is iron. Using MM 250 with ER70S-6 .030 75/25 AR/CO2. There was a lot of popping and spiting when I hit the iron. Normal, not normal, too much heat????

 

Pretty normal for cast iron. It does not like being welded in general. If I KNOW it's cast iron, I nickel/ bronze braze those joints. And I am not shy with the filler!!!:dizzy: It's a softer junction, so a little extra does not hurt to get a better web on the joint.

 

If the parts you're welding are nodular or ductile cast iron, the the popping and spitting are normal. Low quality castings may have pores or non-metallic inclusions inside them that don't react well when the welding arc makes contact. If you didn't aggressively clean the surface, you can also get some bad reactions from sand and/or mold release compounds imbedded in the surface of the casting.

I'll add my opinion to the advice already given and say that brazing is the best way to go, but welding with slow cooling is possible also. Brazing has two advantages.. The first is flux to float out impurities. The second is that the base metal isn't actually melted.

Nodular iron is very similar in chemistry to gray cast iron, with special control over some alloying additives; Magnesium being the most important. The molten gray cast iron is innoculated with a controlled amount of magnesium. This element, plus a controlled cooling rate in the molds causes the excess carbon in the cast iron to form microscopic round nodules, rather than any of the half a dozen structures that are possible. The round nodule shape of the graphite is part of what gives ductile iron it's toughness.

Magnesium melts at a much lower temperature than iron or steel. So if you're welding on nodular cast iron it's important to get in, fuse the material, and get out again in a quick, efficient manner. Pouring a lot of excess heat into the material can boil away some of the magnesium in the weld puddle and nearby material. This causes the material to no longer form ductile iron when the liquid base metal re-solidifies. These microscopic changes in the structures formed by the excess carbon can also cause the material to expand or contract at a different rate then the surrounding material; which causes cracking. Slow cooling helps minimize these thermal stresses.

Welding with a filler metal containing a high amount of Nickel can avoid cracking as well, because the dilution of nickel into the weld and surrounding base metal makes the cast iron more tolerant of shrinkage during cooling. But, there's no guarantee with anything. You've got to hit the Nickel dilution and cooling rates just right. Adding Nickel just makes cooling rate window bigger, if you will.

I'm not saying you cannot weld ductile iron. but I am saying that if you've tried and it's cracked here are some possible reasons why.

Like a couple of others I think brazing is still the most reliable solution, and because the cast iron doesn't get hot enough to melt you avoid all the problems associated with welding.

 

WELL GOOD GREIF!!

I've been puttin off welding this steel bracket to this center section on a Ford 8.8 rear for about 3 weeks because-----well, I just don't know what I'm doing. So I come here and read--read--read and ask questions and get a ton of great advice, which I truly appreciate.

NOW I find that the center section is probably CAST STEEL!??

Can somebody please tell me if there is a way for me to determine what metal this is?

Thanks so much,
Pat

 

Grinding and looking at the sparks is one way. Lanse and the folks at Longevity have videos out just in the past few days that show the spark patterns and colors. That's about the cheapest and quickest, not very scientific though. You can find other videos on youtube with spark patterns and then there's Wiki.