Welding Wrought Iron

Date 06-24-2003 13:12

I think your right on target with using the nickel rod and the pre/post heat treatments. Check it out first. If it is white cast. From what i can remember in school, you cant fix it. Brazing is another option if in fact you have grey cast. If its wrought iron, 7018 should weld it up nice.

David

By welder_guy2001 (***)

Date 06-24-2003 18:17

i've always heard that it's best to limit the heat input as much as possible. preheat it, stick weld it, then postheat it. they have stick welding rod that contains nickel which helps reduce cracking. check it out at a welding store...they should have it.

By TimGary (****)

Date 06-24-2003 18:38

You might consider looking up your local Blacksmith and learn something new.
I bet it would be interesting.
Just a thought...
Tim

By swellwelder (*)

Date 06-25-2003 02:49

Has anyone else used wire welding on cast iron? I have used standard 70 class .035 wire on lots of cast iron repairs in my welding shop with much more consistent results than any nickel based stick weld. The heat input is much less, slag inclusions is not a worry, each side of the crack can be buttered, then fill welded without worry about excessive heating. On a large piece, preheating to approx 500 degrees and then doing the full length bead is a snap, not having to weld a few inches, peen theweld as it cools, then a few inches more.

By jwright650 (*****)

Date 06-25-2003 12:07

You can check out at these blacksmithing forums.

http://www.keenjunk.com/junkyard.htm (open forum no moderator)

http://www.anvilfire.com/gurusden/index.htm (moderated very closely)

I saw these links in another post by stever and they were talking about successfully welding materials like was asked about.

John Wright

By kam

Date 06-25-2003 12:23

Excellent links John! Have them marked and will read through them. To save some cash (Nickel rods are a bit pricey) I though about trying some stainless steel wire on the project. Since its a low carbon wire it might do the job. What do you guys think? I have plenty of 308 & 309 wire.

Thanks

kam

By billvanderhoof (****)

Date 06-26-2003 06:09

Your fire front ( I think that's what it's called) is cast iron not wrought iron. Wrought iron would have been used for pokers and such where malleability was necessary. It would have been shaped by forging. The cast iron is in all likelyhood grey. White cast iron is usually found in applications where wear resistance is required.

First- this being an antique it is possible that its value may be reduced by repairing it even if the repair is well done.

A large flat (essentially) thin piece of cast iron is difficult to repair. The stresses that warp steel weldments will crack cast iron so you need to manage them very well. Lots of preheat, small stitches, peening as the work cools, and really slow cooling are all helpful.

I have no experience with stainless on cast but have used e70 wire as swellwelder says above. For me always small things, preheated to dull red and welded. Worked ok. Keep in mind that the cast iron has so much carbon that which will diffuse into your weld metal that the deposit is likely to be very hard and brittle. Buttering first will probably help as will all above, preheat etc.

Consider brazing this. Preheat the whole piece then braze from the back. The braze is malleable and can yield a little to releave stress as it cools. Keep the reenforcement small. If the heat is enough it will sweat into the crack which is good. Cool really slowly. In an oven is best but buried in a pile of hot sand or wood ashes may work. Wrapped in insulation may also work.

Following is philosophical- don't go for an invisible repair, the crack is part of the history of the piece. The repair should restore strength, and arrest further damage nothing more.

Good luck

Bill

By kam

Date 06-26-2003 12:32

Thanks Bill
The piece is a fire front. Has been repaired several times already. Last repair appears to have been made by mig. Weld held but crack propogated from toe of crator fill. Part is in 3 pieces now. Think will try 70 wire for starters since you guys have had good luck with it.

Thanks to all for the help!!

kam

By Niekie3 (***)

Date 06-26-2003 17:28

Personally I would not go with the stainless electrodes. You will end up with a high carbon Cr - Ni martensitic steel structure. Very brittle!

Also, if you want to use the C/Steel filler you will need to put a very high pre-heat to end up with a relatively ductile weld. You will need a temperature of around 500°C. - Very high!

For your application, I would go with the Nickel filler and give no pre-heat, as well as using a low heat input. Simple for you and usually gives a serviceable result.

Regards
Niekie Jooste
Fabristruct Solutions

By DavidP66 (*)

Date 06-26-2003 17:31

From my understanding and what i have learned. You always preheat cast iron. Preheat and Post heat. And let is slowly cool down. Its never failed for me.

David

By Niekie3 (***)

Date 06-27-2003 18:23

Hi David

You are correct that using adequate pre-heats, post heats and slow cooling will give you good results most of the time. The problem comes when you are welding something that is either impractical to pre-heat adequately or you do not have the necessary facilities to do this.

To explain my approach, I will give you a run-down on the reasoning:

When welding cast iron, you have two potential areas for problems to develop. The weld metal itself, and the HAZ. When using a filler that will form a hard brittle weld metal (e.g. E7018) you have to take steps to reduce the cooling rate significantly. This can really only be done with very high pre-heats. As mentioned before, we are talking of around 500°C or so. You can however get around this problem by using a filler that will not form a hard weld. (e.g. ENi-CI filler) This does however bring us to our second problem area, namely the HAZ.

Due to the high carbon content of the cast iron, the HAZ will always form martensite and carbides, unless a very high pre-heat is once again used. Once again, if this is not practical, a different approach is required. Seldom will a "low temperature" pre-heat give much benefits in terms of reducing the HAZ hardness. What it will however do is form a wider HAZ, because with an increase in pre-heat, a greater area around the weld will move above the lower critical temperature during welding, resulting in the martensitic phase change upon cooling. (And carbide precipitation) The wider the HAZ, the bigger your chances of getting a crack forming. The other alternative is to accept that the HAZ will be hard and brittle, but to try and reduce the size of the HAZ. This will ultimately lead to a lower probability of cracking. This is the approach that I think is best here.

The only other problem that remains are the cooling stresses that are greater, the faster the cooling rate. To overcome these, you need to deposit small amounts of weld metal at a time. This means small string beads of a short length deposited at a time, and then "staggering" the welds. I believe that the job being described here would typically lend itself to this approach, because of it's ornamental nature.

Hope this makes sense.

Regards
Niekie Jooste
Fabristruct Solutions

By Michael Sherman (***)

Date 06-26-2003 17:33

I weld a fair amount of cast iron and over the years I have researched it here and there. Often I find most people know one or two tricks. I have tried to put together here most of what I have learned.
E70S wire or E7018 will give you a hard, brittle repair. They are generally used for cosmetic repair in nonstructural applications where machining is not needed and cracking is not a major concern. You will have a weld metal carbon content around .8 to 1.5% and with rapid cooling can produce a crack sensitive martensitic microstructure. You can minimize this by using preheat, slow cooling and postweld annealing. ESt electrodes are steel electrodes made for cast iron. They are DIFFERENT than regular carbon steel electrodes. They are primarily used for small pits, cracks, and other defects in castings that do not require machining. Stainless steel electrodes are generally not used for welding cast irons. This is due to the formation of chromium carbides which give you a brittle microstructure. You are also more likely to get cracking in the HAZ due to the differences in tensile strength and the coefficient of expansion between stainless and cast. Nickel based electrodes are the best, they do not form carbides and have low solubility for carbon. I also use powder flame spray quite often.

Mike Sherman

By stever

Date 07-01-2003 01:08

There is also "cold welding". This technique is simple. Make a one inch weld on one end of the crack, then make a one inch weld at the other end of the crack. Remember to weld toward the crack from the start of the crack. Pein and clean to help stress relief. Make a one inch weld in the middle of the crack. Depending on crack length, allow any weld to cool to "No Heat" to the touch. Never allow the heat to accumulate. Only enough heat to make a one inch weld should be input to the cast iron. Continue the pattern of one inch welds until the welds connect and completed. Again, never allow the want to finish and make big welds get you. To make big welds, you'll need to do the preheat and post heat as stated in the other posts.

I've made several GTAW(tig) repairs on small cast iron parts.

Cast iron will have a fine grain appearance on a broken edge. Real wrought iron will look fibrous if bent in a broken area. Real wrought iron is simply "iron" with an insignificant amount of carbon. This means that it could be welded with E-60xx, E-70xx, mig/tig 70 series. It will forge weld easily with the proper preparation. I do not know of anyone that has forge welded cast iron.(grin)