Welding wrought iron

Had an interesting problem today, asked to weld up a broken bit from an iron gate. Set to with a MIG, mild steel wire and CO2 gas. It didn't go well, and the joint didn't flow very well, with much 'slag' being formed on the welding tip.

I am assuming that I was welding wrought iron and not mild steel - The gate was probably 150 years old, definitely not cast iron. Any ideas from the team as to what I should have used ??
BobH

Due to the impurities genuine wrought ca only be forge welded Mike

If all else fails, braze is usually a safe bet

If it is wrought iron and you can't forge weld it for any reason, bronze welding with oxy acetylene will work OK for a structural repair if the surface is cleaned well. Only issue is the weld will be yellowish brassy colour so some flat black paint would be in order to dress up the repair.

If it's a special artefact needing proper restoration type repair I suggest taking it to a blacksmith for forge welding.

They cut down all the wrought iron railings in Edinburgh to help the war effort

They sat in a pile at Carstairs Junction until 1946 when some scrappie heaved them away

You need a forge, an anvil and a big hammer, and some sand for flux. Yes wrought iron is a bit of a beginers trap when it comes to welding.

Ian S C

The Welding Institute gives different advice, and they should know what they are talking about, see **LINK**

You can use Dissimilar welding rods but you need a stick welder.

I use MIG stainless wire and Argon on cast iron. Do you think it would have worked on wrought iron.

I don't know which idiot decided it would be a good idea to cut down all the wrought iron railings for the war effort. Because they are of no good what so ever for making steel!

Probably why they sat in a pile until after the war.

Followed Duncans link to the TWI site and was pleased to see that my usual "difficult iron" MMA, stick, welding method seems to be approved practice.

My Rule 1 is avoid anything taking tensile or anything beyond mild shear stresses like the plague! Usual engineering assessments of what it is and why it broke before agreeing to try. Try being the operative word. Over-engineered "if its stiff enough its strong enough" design and broke 'cos dinkle brain hit it really hard in the wrong place are usually a good start.

If it passes that assessment then decent grind out to give space to weld. Start by buttering on thin layers of weld metal at low current waiting for it to cool properly between layers whist peening with the chipping hammer. Take the grinder to any bits that look bad or are improperly adhered. Four to six buttering passes are usually enough to get a nice clean layer of good weld metal allowing more normal currents and larger rods to be used to finish the join. Still relatively small rods and low current in thin layers followed by peening as it cools ready for the next pass. Can take ages but it works.

But as TWI says wrought iron is very variable and you need to watch what's happening very carefully. I suspect you end up digging pretty much all of the slag inclusions out of the area where you want the weld to adhere. Lord knows what that does to the strength and stress resistance profile in in the joined area. Hence Rule 1.

Doing such repairs on old cast iron with lots of free carbon can leave you looking like a coal miner! Try to avoid architectural stuff. Or at least slap a shower tax on the price.

The relatively inexpensive amateur friendly rods seem to be fine for this sort of work. Probably because they are made to cope with poor technique on a goodly range of materials.

A good inverter welder is much better than the common inexpensive AC buzzbox for this sort of thing.

Best technique is to send them down the road to bother someone else!

Clive.

I don't know which idiot decided it would be a good idea to cut down all the wrought iron railings for the war effort

Lord Beaverbrooks idea

Edinburgh wasn't getting touched by the war (bombing) and he came up with this one as her sacrifice

He ended up being shoved off to Russia

I never knew he became a Canadian citizen before now though

It wasn't only Edinburgh, Glasgow and Paisely lost all their iron railings too. The same thing happened here in NZ, but before WW2, then during WW2 the Japanese tried to give it all back.

Ian S C

So why can't you make steel out of it? I would have thought that as long as you can melt it the inclusions would flot to the top and you'd be left with .

Too many impurities and no-one knows whats in it to start with

So you can't make anything reliable

Some would be cast iron, some wrought iron, some god knows what

Decent metal is like making a decent soup, you've got to know whats going into it to start with, nice fresh ingredients make good soup

Back in the war if they could have used it it would have been gone in a flash

Wrought iron is tough, malleable, ductile, corrosion-resistant and easily welded

From the wrought iron wiki

Probably depends on the "grade" though

Sounds like a suck-it-and-see material to me, every batch is different

The problem is the make up, is a semi laminar construction with all sorts of crap between the layers.

The problem is that wrought iron is as near to pure, carbon free iron as you can get, it's melting point is much higher than carbon steel. In the smelting process the metal never becomes liquid in the furnace (Puddling Furnace), as much slag as possible is removed, the rest gets stirred into the mix. The lumps of iron (blooms) are then forged to shape. There was a Guy Martin program on the subject, they dug up some iron ore, smelted it in a crude furnace, then made something, can't remember what.

Ian S C

Slightly off topic,

ALL towns and cities lost their iron railings. Can remember seeing them being cut with Oxy Acetylene in Hereford and Wolverhampton. No doubt the words were "Don't you know there's a war on?", uttered by some bureaucrat who did not know the difference between cast iron and steel.

Howard