Welding failure

[kdog]

Hi
For the welders or metallurgists out there, can someone explain to me what process causes this.
I welded up a repair in my sons cheap vice that looked like cast iron judging but the grainy structure of the metal. The section for the weld was about 5mm thick and was the extension arm near the head of the vice.
My weld looked good, and I put it back together. This next day it failed with little pressure. The fracture was longitudinally through the middle of the bead of the weld, with half the weld bead still stuck to each broken part.
The weld was grainy like the metal (which I've never seen before) and had shattered in a similar manner to the base metal. My welds are usually tough and flexible but this was like halvah (the dessert), sort of grainy and stringy and brittle
I'm thinking that the base metal (maybe very in high carbon) has diffused into the filler during the welding and affected the structure resulting in a ultra brittle weld...
Is this right?

 

[Hillhater]

How did you weld it ?,.. gas, arc, mig, etc ???
Welding cast iron is a very tricky process , often unsuccessful. Due to the high free carbon content.

 

[stan.distortion]

Can you post a pic? Hosting somewhere like imagur and posting the provided link is the easiest way I've found of doing it.

Yeah, welding cast iron is very tricky, phosphor bronze tig brazing is probably the best "universal" option but it's almost a science in its self, often it's simply impossible to repair. Steel alloys also come with a host of issues, spring steel is never going to work without a very accurately matched filler and post weld heat treatment for example. Imo your best cost effective option is to grind away all traces of your weld and try (regual, ie. brass) brazing, if your problem is an unusual steel alloy then braze could be ok with a bit of reinforcement but if it's cast iron then the braze won't stick, better to either go to a specialist of replace the part.

 

[amberwolf]

i've never been able to repair a cast iron item like a vise (or a pan). tried a number of times and ways....

welding was the worst failure, though, destroying parts pretty completely.


i've never tried "smithing" a fix, basically re-casting it, but i'm pretty sure that would work.

 

[kdog]

It hard to get a reasonable pic of it... Looks like rubbish on screen.
I guess it's probably as discussed, an unfixable failure. Good thing it's only a cheap vice but annoying that it's now useless. Mostly I fix stuff and use till its final death.

 

[stan.distortion]

Ahh, it's the vice you're trying to weld, sorry! Duh, I thought it was a part you where welding in the vice. Yeah, cheap vices are usually pretty much the lowest grade of cast iron you can get, not worth even trying to weld imo, the cost of replacement is less than the headache is worth. The cheap steel ones are usually pretty good, about the same price and not all that rigid but they take abuse pretty well. If you keep an eye on classified adds you can usually pick up a decent used Record or other good brand for next to nothing that will last a lifetime.

 

[speedmd]

Broken vice did him a favor. Chuck it!

From understanding the repair failure standpoint, it is as said before, pooling of carbon and other elements into high concentrations- weak spots. These in relatively stiff cast structures will yield cracks forming on weld cooling alone many times. Several things can be done to minimize the possibility but without knowing the metals, it is a guess if it will yield reliable results.

What has worked well for me in the past is the following.
*Best is to use cast iron rod or if possible gas weld using exact metal from a like part if that method can work (depending on thickness- size of part). Works great on really old -burnt cast stove parts.
*Pre and post heat the work.
*Do not weld a continuous bead.

Best to weld smaller sections (stagger weld) at a time. Weld a 10mm section, followed by a 20 mm gap and repeat pattern of welding across the part. Fill weld into the gaps in like fashion to complete the repair prior to it going cold. Keep purple hot a few extra minutes to allow even cooling. If you notice (if it looks like a crack, it most likely is) cracking on the initial pass, reduce the 10mm spots a bit and try again once you clean out the cracks.

 

[markz]

Could be that you needed way more amperage to get deeper into the material, and for that a home welder wouldnt cut it.

Check out www.weld.com forums

I like this web site too

http://www.weldingtipsandtricks.com/tig-welding-cast-iron-vise.html

 

[kdog]

Here a section of a weld I did on it a while ago. We (my son mostly :lol: ) smashed it up with a mallet, and had a look at its composition.
In this section the weld is the lighter top most metal and a few mm below is the base metal. This one didn't fail like the one in question (well until the mallet got it!) as it was very low stress area. But it shows a similar grainy structure.. I guess it's the carbon diffusing in with the heat.
(sorry it's a bit blurry after resizing)

 

[speedmd]

Looks like a good weld. I don't think your seeing anything other than two very different materials in that section photo. Steel over grey iron. With regards to "Cast Iron" as a group, I would tread carefully. Good quality tools would use a more "ductile" iron (near steel) casting alloy which is much finer grain. Cast steel would be best. What your showing, just going by the grain is a much more brittle "grey" iron. Great in compression but terrible in tensile or bending loads which is why it most likely failed in the first place. It looks like your dealing with material that has virtually the same elongation capability as glass. Big group of materials and process issues also add greatly to the variability. Some good points on the topic in this article. http://info.cpm-industries.com/blog/bid/226682/Housing-Material-Cast-Iron-vs-Ductile-Iron

 

[torker]

I welded the base of my vice and it has held.

I heated the part in the oven. I cranked up my ac arc welder to max and I covered the part with a weld blanket after welding.

Or maybe I just got lucky.

Oh. I ground a deep v / or chamfered the parts.
And I welded both sides. Looked like in the pic you welded one side?

 

[speedmd]

Something like a Wilton will weld like most normal steels. These cheap "grey" cast ones are not easy or worth the trouble in most cases. I found turning up the current on grainy iron only burns away a bunch of metal and always leaves a significant sink at boundary zone. Its a fine line, getting filler to attach well and not just drill away- go too deep with this stuff. When you get into trouble, I have gone to smaller rod diameters, pre heat more than normal, and yes cover or torch it for a bit on cooling.

If you don't have a blanket and are a wood burner, just bury in some wood ash to greatly slow cooling.

 

[DogDipstick]

You need to tig it with a cast rod and rosebud it glowing red first.

I've welded hundreds of old castings. From thin to thick, you will never get the whole of the original strength back in properties.... Brass and iron. Even some brand new ones..hot out the cope & drag, dont drop that, it cost 10,000$ for the first.... ( dont tell the boss either, Ok? ).....

 

[DogDipstick]

See this table? We repro'ed them for about 3000$ each off. The original ( in the photos, painted by me,...) was broken, both the long stringers where they attached, and the decorative "JRT" on the ends. The "JRT" was in about 6 pieces when It was given to me. I welded it up and we had the pattern made. The pictures are of the original that we fixxed. Can you see where I welded the "JRT"? I know where it is welded. Lol. I have before and after pictures, let me see if we can find them.

The ones we sell are solid brass. But we still needed the original for the pattern. Original still stands to this day in the Mill the old man owns that hires me. Its a very heavy table. Lol. About 700 lbs.

Link t table: https://www.ebay.com/itm/Solid-Cast...-T-Robinson-Model-Casting-Legs-/282558739618

Used a 400A (? I think) designed-to-build battleships tig Miller on 3ph. Shook the whole building.

THIS is absolutely correct. I also have fixed a few stoves. Let it cool slowly too...

What has worked well for me in the past is the following.
*Best is to use cast iron rod or if possible gas weld using exact metal from a like part if that method can work (depending on thickness- size of part). Works great on really old -burnt cast stove parts.
*Pre and post heat the work.
*Do not weld a continuous bead.

Best to weld smaller sections (stagger weld) at a time. Weld a 10mm section, followed by a 20 mm gap and repeat pattern of welding across the part. Fill weld into the gaps in like fashion to complete the repair prior to it going cold. Keep purple hot a few extra minutes to allow even cooling. If you notice (if it looks like a crack, it most likely is) cracking on the initial pass, reduce the 10mm spots a bit and try again once you clean out the cracks.
Last edited by speedmd on Feb 05 2020

 

[speedmd]

Nice work. Painter hid it well. :lol: