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J.Leon_Szesny

how to forge weld, "good?"

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I've been through most of the basic standard explanations of forge welding,
like, more carbon = lower forge weld temp, slow build up of heat, reducing non oxidizing fire, clean steel, fluxes, etc
but questions I couldn't find answers for:

1. why doesn't the high carbon steel burn and crumble at the temps it takes for the low carbon steel to become weldable?
(I know that it works but...how exactly?) 

2. Is it possible to forge weld low carbon steel at low temps where it wont spark up?
(cause so far, I really tried and it wouldn't work...I had to get it really sparking hot to be weldable at all!)

I'd appreciate any extra thoughts or advice,
im currently learning how to forge weld "good," since material limitations mean I'll need to make my own stock.

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A surprising amount of information on welding was discussed in this thread: 

To answer your questions, 

1. It's because the high carbon will weld to the low carbon just fine at its own welding temperature, even if the low carbon won't stick to itself at that heat.  This is why, when steeling a wrapped-construction  axe, you weld up the body leaving just enough open space at the edge for the steel to be inserted to fill up the available space. 

2. Yes, but it's so close to sparking hot it's just a matter of very carefully watching the heats.  It's so close that I threw off my eye for it when I switched from soft white to daylight spectrum fluorescent lights.  Took me a month to relearn what to look for.   Plus there's mild and then there's mild.  See the linked thread for examples.

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1. still don't understand why it high carbon can weld to low carbon, at temps where the low carbon wont weld to itself...does the high carbon get hot faster so it, via transferred heat, turns the contacting low carbon steel surface liquid/weldable?

2. yikes, a month? it'll take me a whole bit longer then...and the price of charcoal has currently doubled...

thanks Alan,
puts things into perspective, it means I can relax and not worry so much for why I cant find find the sweet spot/temp for welding low carbon steel, yet!
the linked thread seems promising :')

 

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6 minutes ago, J.Leon_Szesny said:

still don't understand why it high carbon can weld to low carbon, at temps where the low carbon wont weld to itself...does the high carbon get hot faster so it, via transferred heat, turns the contacting low carbon steel surface liquid/weldable?

Not exactly the same thing, but think about brazing.  You only have to get the brass to flow, not the base material.  In the same way (kind of) you don't need to get the low C material to a welding heat, because the high C will weld to it on its own.  They are the same temperature.  This is just a rough analogy.  

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...I have not gotten around to learning much about brazing or soldering.
found a video though that talks about "capillary action" during brazing/soldering, very interesting to have it visualized.
I wonder if the same effect has some influence during forge welding?
like, the molten steel evenly sucking itself along the joining line of a folded bar?(probably not but asking is free?)
 

 

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37 minutes ago, J.Leon_Szesny said:

I wonder if the same effect has some influence during forge welding?
like, the molten steel evenly sucking itself along the joining line of a folded bar?(probably not but asking is free?)

No.  Forge welding is a solid state process, no liquid.  Perhaps it was a bad analogy.  

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Forge welding is forming ionic bonds between the atoms. All you need is one of the materials to have enough energy in its atoms to form those bonds with the atoms around it. Job done.

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Posted (edited)

 You dont need to be a metalurgist to know what you're doing. But if you want to understand why instead of just how I can't help. 

I would suggest you get some borax, get your forge set hot enough to leave vision spots with some dragon's breath, get your steel (that was very clean and well fitting) to a dull red, sprinkle borax on the cracks, and pop it back in until the flux bubbles and dances around the steel frantically (that's a little on the hot side). 

Then, take it out (note the borax fumes coming off) and to your anvil in one swift movement. You ought to be working a large hammer with a wide face as soon as it touches the anvil. Gentle taps first from the back of the billet to the front, working the flux out similar to how you would get that last drop of toothpaste from the tube (just really fast and with a hammer). Wire brush quickly the cracks and get any hard scale off with the side of a junk file or other scraping tool. Flux. Repeat twice more with slightly harder blows each time. Once those are done, I take another welding heat and hit it from the side to weld any possible future coldshuts down and test the welds. 

Time is oxidation. No lolligagging. Be swift. 

If you think it needs more welding passes, feel free, but after the first 4 or so passes you dont need anymore borax (if your forge is reducing in atmosphere). 

Hope this helps! 

Edit: oops! You said charcoal... 

Charcoal is actually really clean burning stuff, so it's nearly the same procedure. I haven't welded any large billets in it though. Just small stuff and chunks of remelted mild steel. You just need to learn how to play with that fire to get larger areas to heat. Also, how to forge weld in sections of a few inches at a time. That's a little trickier. 

 

Edited by Zeb Camper
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2 hours ago, James Higson said:

Forge welding is forming ionic bonds between the atoms. All you need is one of the materials to have enough energy in its atoms to form those bonds with the atoms around it. Job done.

\engage Dr. Science mode\

Technically it's metallic bonds, but close! ;)  In an ionic bond two atoms share an electron or two.  In a metallic bond they share all their electrons.  That's why electricity works.  With a good conductor, a little amperage added at one end acts like one of these: 450px-Newtons_cradle_animation_book_2.gi

in that the impulse travels the length of the wire via all those shared electrons smacking up against each other.  That's just a rough image, they really "flow" more like water (but not really, it's complicated), but you get the idea.  

To create that bond you need clean surfaces and very close contact.  24 carat gold and fine silver will forge-weld at room temperature, just gently hammer on them.  A pair of optically flat polished steel surfaces will start to weld at room temperature as well.  If they are flat enough and clean enough, the electron transfer starts to take place.  The same thing can happen with threaded or tight-fitting sliding joints if they're clean and very tight, we call it "galling" because when you finally get it to break loose the bits that welded tear off in little "galled" patches.  In a vacuum you can forge weld clean steel at room temperature with enough pressure.  Since we don't live in a vacuum, and our steel is rarely truly flat or truly clean, and most of us don't have the kiloton presses it takes to weld cold, we use heat to get the atoms excited enough to start sharing those electrons. 

The definition of absolute zero is that point where it's so cold all atomic motion stops.  It's not that it can't get colder than that, it's that there is no way to measure it since the very atoms stop moving.  Likewise, if you heat an atom, it starts moving faster and faster and faster, so you go from solids in which the atoms vibrate slowly and don't intermingle much to liquids in which atoms freely circulate, if sluggishly, to gasses in which atoms go where they want, to plasmas in which they disassociate and gain a whole new set of properties.  

So, what we do to get steel to weld in the forge is heat it up until it's on the verge of turning into a liquid to ensure that the atoms are energetic enough to bond, then add pressure via hammering or pressing to close up any gaps.  If we have forges with controlled atmospheres that we can run slightly reducing, which with charcoal means a very deep fire (say 20cm deep with the steel in the top 5cm) to ensure no oxygen is getting to the metal, we don't even need flux.  Since it's hard to maintain a reducing atmosphere for long in a solid-fuel forge, we use flux in the form of borax, boric acid, sand, glass, salt, or clay to scavenge any free oxygen and absorb any oxides on the surface of the steel to ensure a clean surface for welding.  The addition of iron powder to assist has been covered in your iron powder thread.  

This has been a very long-winded way to say it's not magic, it's just messy science that looks like magic.  Oh, and you have to hold your tongue just right or it won't work. :lol:

\end Dr. Science mode\ 

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11 minutes ago, Alan Longmire said:

Technically it's metallic bonds, but close! ;)

As a metallurgist, I wanted to jump in right away and say this, but then I remembered that there is a case to be made that metallic bonds are a form of ionic bond.  

It gets messier than anyone really wants to get into here.  :)

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Well said!  I'm just travelling on business and boredly posting to much information. :lol:

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1 hour ago, Alan Longmire said:

A pair of optically flat polished steel surfaces will start to weld at room temperature as well.  If they are flat enough and clean enough, the electron transfer starts to take place.  

I'm curious as to whether or not I've seen this happen...

I have a few plates at work used to zero micrometers and indicators and such, some are exactly .375" thick, for example, with literally 0 visible deviation in thickness along its length. The realistic deviation is probably around .00001", if I had to guess. They are made of mirror polished and hardened A2 (if memory serves.) 

My point in explaining all of this is this; if you slide two of these plates together, they are just about impossible to separate. Even stacking two on top of each other makes it difficult. 

This is a known and common phenomena in the machining world, but is this an actual bond happening or is just a vacuum holding them together?

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Damn, my primary school science teaching has let me down again! Cheers Alan, loads of new stuff to me there.

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6 hours ago, Alan Longmire said:

The definition of absolute zero is that point where it's so cold all atomic motion stops.  It's not that it can't get colder than that, it's that there is no way to measure it since the very atoms stop moving. 

The last part isn't true. It can't get colder, as temperature is defined by the vibrational motion of atoms, rather then the motion being a result of temperature. So zero vibrational motion of atoms is the absolute lowest possible temperature. It's not the lowest enthalpy state however, but that is not temperature. 

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5 hours ago, Will W. said:

I'm curious as to whether or not I've seen this happen...

I have a few plates at work used to zero micrometers and indicators and such, some are exactly .375" thick, for example, with literally 0 visible deviation in thickness along its length. The realistic deviation is probably around .00001", if I had to guess. They are made of mirror polished and hardened A2 (if memory serves.) 

My point in explaining all of this is this; if you slide two of these plates together, they are just about impossible to separate. Even stacking two on top of each other makes it difficult. 

This is a known and common phenomena in the machining world, but is this an actual bond happening or is just a vacuum holding them together?

What you experience is the van der Waals force between the two plates. If you get the atoms close enough, they start to attract eachother. But for them to bond, they have flat at the atomic level. At that point, the plates would become one by simply touching them together. You may experience that some spots do weld together, which need to be broken apart though, particularly if you press them together. 

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2 hours ago, Jeroen Zuiderwijk said:

The last part isn't true. It can't get colder, as temperature is defined by the vibrational motion of atoms, rather then the motion being a result of temperature. So zero vibrational motion of atoms is the absolute lowest possible temperature. It's not the lowest enthalpy state however, but that is not temperature. 

I knew someone would catch that. :lol:

That's what happens when I try to oversimplify stuff after a beer or two...

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6 hours ago, Jeroen Zuiderwijk said:

What you experience is the van der Waals force between the two plates. If you get the atoms close enough, they start to attract eachother. But for them to bond, they have flat at the atomic level. At that point, the plates would become one by simply touching them together. You may experience that some spots do weld together, which need to be broken apart though, particularly if you press them together. 

Thank you for the answer, Jeroen. I'll have to look into Van Der Waals force further. 

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14 hours ago, Will W. said:

This is a known and common phenomena in the machining world, but is this an actual bond happening or is just a vacuum holding them together?

Also, if you were to pull them apart after bonds formed, they would no longer be perfectly smooth.  See the galling description above.  

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11 hours ago, Jerrod Miller said:

Also, if you were to pull them apart after bonds formed, they would no longer be perfectly smooth.  See the galling description above.  

Good point. I have only accidentally set plates like this on top of one another, but have heard stories of some that were practically welded and required hammering to separate. And yes, they required re-surfacing, from what I'm told. 

An interesting effect, for sure. 

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Ask a simple question around here :lol:

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yea absolutely love this!

I can barely keep up with this level of science but I think/hope I got some of it.

On 10/4/2019 at 3:16 AM, Alan Longmire said:

what we do to get steel to weld in the forge is heat it up until it's on the verge of turning into a liquid to ensure that the atoms are energetic enough to bond, then add pressure via hammering or pressing to close up any gaps. 

what that means, is...
but that would mean...
if you have two bars of LC steel, you can weld LC steel to LC steel with only one of the two bars having reached full welding heat and vice versa with HC steel?!
am I stupid or did I reach the enlightenment moment? 

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Not really.  With LC steels they like to be at the same temperature, or at least very close.  Since the welding heat of HC steel is lower, it will stick to LC when it is at its heat AND the LC is at that same heat, which would be too cold to do an all-LC weld.

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In the extreame heat of arc welding where the epicenter can reach temps of 30,000°F, the liquid spatter balls that come out of the arc latch on to clean cold steel pretty easily. In some cases fully fused where a chisel has to cut them off instead of just breaking the slight galling. 

But, I think that's the only way to fuse hot metal with colder metal. Drop some extreamely molten stuff on it. 

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