Well Gary, I guess some may be disappointed if I didn't give a shot at this so here it goes-

Most of the world thinks of fusion welding when you say the word “weld”. This is where the mating surfaces of the two metals are heated to the melting temperature and are allowed to flow together forming one piece; obviously this is not what happens in a forge weld or the individual layers of would simply mix to form a new alloy and there would be no pattern. Instead in forge welding we perform what is called a “solid state” weld.

For solid state welding we can thank the fact that metals are held to together by metallic type bonding and typically not other covalent type bonds; this is why we don’t use the words “molecular” or “molecules” very often when discussing metals. The iron in your steel is held together by the sharing of free electrons between the iron atoms in the crystalline array (repeating and orderly rows and columns). This sharing is why metals conduct electricity so well.

And interesting side effect is that when two pieces of metal are brought into VERY close contact they will also begin to share free electrons. Steel that is polished very flat and smooth can be made to stick together at room temperature so this you almost need to slide the pieces apart rather than pull them directly apart. And scientists have done experiments where they clamped two different metals together for several years and then found that under microscopic examination the surfaces of the two metals began to swap atoms. But the problem is that even the best polished surface will still have irregularities that we can’t see but are practically miles apart at the atomic scale. But…

If we heat the iron not only are the atoms more energized and mobile, we can also apply enough pressure to squeeze these gaps closed and make enough contact across the surface for the metallic bonding to be permanent (with enough pressure one could do solid state welding at room temperature, but it is just easier to heat the steel rather than deal with those tonnages, or a strip of C-4 can do the trick <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' />). So for forge welding the pressure vs. heat thing is kind of inverse, the more heat the less pressure is needed, the less heat the more pressure is needed, this is why old time, hand hammering, blacksmiths liked white hot while guys with power hammers can go cooler and guys with presses can stick that stuff like crazy!

But in case you thought it would be as simple as the pressure vs. heat thing (life will never let you off that easy), here comes the catch- chemistry. Iron oxides are not pure metals with those convenient metallic bonds so they don’t stick like the parent metal will. The higher you go in temperature the greater the rate and extent of oxidation, so the temperatures that allow us to get the iron atoms to shake hands also locks them up in oxidation. This is why we need to shield the steel from oxygen (there is around 21% all around us at all times) in order to forge weld. This is the idea behind flux, a molton substance that shields the surface from oxygen and can also break up oxides and carry them away in the welding process.

But our main line of defense is our forge atmosphere. That 21% oxygen that is all around us would be in our forge as well except that it gets used up in the combustion process and converted to carbon monoxide and carbon dioxide. Essentially what we are doing is using the oxygen up in an oxidizing process that O2 likes even more that iron so when we put the iron in that mix there is little oxygen left to bond with it. The cool part is that we have very good control over this other oxidizing reaction- all we have to do is introduce more fuel to use up all the oxygen.

So once we have eliminated the oxygen/iron reaction we are now free to squeeze the steel together until the iron atoms shake hands and the pieces become one.

Thanks, Kevin. I appreciate it. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' /> Sorry to make you go through such a lengthy answer.

Smarter minds than mine tried to explain how two pieces could weld at room temperature if you could get them smooth enough while we were in Little Rock recently but I was having a hard time grasping the concept. This helps.

Gary

So for forge welding the pressure vs. heat thing is kind of inverse, the more heat the less pressure is needed, the less heat the more pressure is needed, this is why old time, hand hammering, blacksmiths liked white hot while guys with power hammers can go cooler and guys with presses can stick that stuff like crazy!

But in case you thought it would be as simple as the pressure vs. heat thing (life will never let you off that easy), here comes the catch- chemistry. Iron oxides are not pure metals with those convenient metallic bonds so they don’t stick like the parent metal will. The higher you go in temperature the greater the rate and extent of oxidation, so the temperatures that allow us to get the iron atoms to shake hands also locks them up in oxidation. This is why we need to shield the steel from oxygen (there is around 21% all around us at all times) in order to forge weld. This is the idea behind flux, a molton substance that shields the surface from oxygen and can also break up oxides and carry them away in the welding process.

But our main line of defense is our forge atmosphere. That 21% oxygen that is all around us would be in our forge as well except that it gets used up in the combustion process and converted to carbon monoxide and carbon dioxide. Essentially what we are doing is using the oxygen up in an oxidizing process that O2 likes even more that iron so when we put the iron in that mix there is little oxygen left to bond with it. The cool part is that we have very good control over this other oxidizing reaction- all we have to do is introduce more fuel to use up all the oxygen.

So once we have eliminated the oxygen/iron reaction we are now free to squeeze the steel together until the iron atoms shake hands and the pieces become one.

Bravo Kevin! That information needs to be a "sticky" at the top of the forums! I've tried so many times to explain the relationship of heat and pressure to those who ask about forge welding....and usually all I see is a pair of glassy eyes looking back at me! <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

Okay, so I'm going to pick some minds here even further. I've been able to pull off my fair share of consistently good welds, and I've gotten to where I don't often fail using kerosene as a soak and nothing more before welding up, but it sounds like the chances are greater for successful welds if a full coating oxygen barrier(borax flux) is used, but my welds are better using the kerosene. ? I am also wondering about the depth of weld using hand hammer vs powerhammer vs press. Is this a huge factor? The reason I'm asking is to determine from those with the equipment and experience whether there is greater risk of weld shearing from twisting or forging on the bias when using one method over another when "sticking" your billets together. I'm aware that the temperature at which your stressing the welds has much to do with this, but is there a depth of weld factor here? Thanks, Wes

Wes, what is your most frequently used method of setting your initial weld?

Press, power hammer, hand hammer, etc.?

I generally do a light tacking with an 8lb sledge hammer, meaning I just let the hammer weight do the work, and then I'll bring it back up to welding heat and put it under the 50lb little giant, but I won't go real hard on it until the third high heat(not welding) where I'll start drawing it out. I forge by feel of the plasticity of the billet more than trusting my eye. I'm hoping to sell one of my powerhammers sometime to buy a press, but I'm getting real interested in salt bath heat treating too, boy, the cost!

|quoted:

Okay, so I'm going to pick some minds here even further. I've been able to pull off my fair share of consistently good welds, and I've gotten to where I don't often fail using kerosene as a soak and nothing more before welding up, but it sounds like the chances are greater for successful welds if a full coating oxygen barrier(borax flux) is used, but my welds are better using the kerosene. ? I am also wondering about the depth of weld using hand hammer vs powerhammer vs press. Is this a huge factor? The reason I'm asking is to determine from those with the equipment and experience whether there is greater risk of weld shearing from twisting or forging on the bias when using one method over another when "sticking" your billets together. I'm aware that the temperature at which your stressing the welds has much to do with this, but is there a depth of weld factor here? Thanks, Wes

Wes, the thing that is battling the O2 the most is your forge atmosphere itself. The kerosene is actually burning off and leaving a thin carbon layer on the weld surfaces by the time you reach 1000F and that carbon layer is burned off, with a little bit being absorbed into the metal by the time you reach welding temp; its effects on the forge atmosphere are negated by that atmosphere rather quickly. I don't use kerosene but instead I spray the surfaces with Pam cooking spray before tack welding to keep the slag residue and spatter from the SMAW rod from gunking up my weld surfaces. I got the idea since welders will use that spray to cut down on spatter and keeping MIG tips clean, and it is the only good use I have for it since I hate that crap for cooking (my wife likes it and is always angry to find her cans in my shop).

Borax became a mainstay of forge welding when blacksmiths were doing a lot of welding outside of the coal fire with lap welds, and drop tong type welds where it was unavoidable to have those weld surfaces exposed to that 21% O2 until they could get them hammered down. Our style of welding, i.e. stacks of clean metal tacked and ready to be squeezed, is pretty safe during the short time it takes to seal them down.

There was a discussion on this forum last year about the need for flux and what some have called “dry welding”, and I did a study of it with a good deal of metallographic examination of the weld areas of the different types of welds which I put on my website here- http://www.cashenblades.com/dryweld.html

Borax will not give you a better weld per say, but it will give you a different weld, the kerosene and dry welding will have some of its own concerns but in different areas. But the real key is the forge atmosphere and how well the weld surfaces are prepared. The flatter they are and the better they can come in contact the tighter will be the weld. In the solid state welding process it is not the “depth” of weld, but that is how we think of welding if we have any training in the various methods of fusion welding, that it is all about the penetration. In solid state welding it is less about penetration and more about surface area, the more atoms that link up along the surface the tighter will be the weld.

|quoted:

Wes, the thing that is battling the O2 the most is your forge atmosphere itself. The kerosene is actually burning off and leaving a thin carbon layer on the weld surfaces by the time you reach 1000F and that carbon layer is burned off, with a little bit being absorbed into the metal by the time you reach welding temp; its effects on the forge atmosphere are negated by that atmosphere rather quickly. I don't use kerosene but instead I spray the surfaces with Pam cooking spray before tack welding to keep the slag residue and spatter from the SMAW rod from gunking up my weld surfaces. I got the idea since welders will use that spray to cut down on spatter and keeping MIG tips clean, and it is the only good use I have for it since I hate that crap for cooking (my wife likes it and is always angry to find her cans in my shop).

Borax became a mainstay of forge welding when blacksmiths were doing a lot of welding outside of the coal fire with lap welds, and drop tong type welds where it was unavoidable to have those weld surfaces exposed to that 21% O2 until they could get them hammered down. Our style of welding, i.e. stacks of clean metal tacked and ready to be squeezed, is pretty safe during the short time it takes to seal them down.

There was a discussion on this forum last year about the need for flux and what some have called “dry welding”, and I did a study of it with a good deal of metallographic examination of the weld areas of the different types of welds which I put on my website here- http://www.cashenblades.com/dryweld.html

Borax will not give you a better weld per say, but it will give you a different weld, the kerosene and dry welding will have some of its own concerns but in different areas. But the real key is the forge atmosphere and how well the weld surfaces are prepared. The flatter they are and the better they can come in contact the tighter will be the weld. In the solid state welding process it is not the “depth” of weld, but that is how we think of welding if we have any training in the various methods of fusion welding, that it is all about the penetration. In solid state welding it is less about penetration and more about surface area, the more atoms that link up along the surface the tighter will be the weld.

Hi Kevin - I'm brand new here, but have previously looked at your website and have lately been following your method (as much as possible) of using thick layers and grinding off the mill scale on the belt grinder before the initial forge weld. Following that method, does grinding the surface of the steel composing the billet at very low grits (I'm using a 36-grit belt) make a significant difference in increasing the surface area that's being bonded during the welding process?

I am still using borax/boric acid flux, but less of it and am welding at lower temps than i previously had been, and seeing very good results -- so thanks for the help you didn't know you were giving <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

Bareback welding or "Dry Welding" is what brought me here. I thank my lucky stars that I discovered that specific thread early in the game. One thing that I keep reading, which is pretty relevant to the topic is the concern surrounding the quality of borax in the U.S.. Is this a ecological fallacy or is the "quality" of our golden go-to flux really diminishing? The billets that I've welded up with boric acid do have inclusions, but I attribute that to my inexperience and lack of process proficiency. A lot of complaints about borax aren't all about inclusions though, as a majority of the issue deals with the cloudy effect that's become more and more apparent between laminations. Bringing this full circle and back on topic, I'm curious about the differences between "Flux" and "Bareback"? I don't mean for you to repeat yourself Mr. Cashen, so I'll be digging through your website tonight...

|quoted:

...Following that method, does grinding the surface of the steel composing the billet at very low grits (I'm using a 36-grit belt) make a significant difference in increasing the surface area that's being bonded during the welding process?

I am still using borax/boric acid flux, but less of it and am welding at lower temps than i previously had been, and seeing very good results -- so thanks for the help you didn't know you were giving <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

The grit should not effect much as far as bonding since at temperature the ridges will not be significant in the pressing action of the hammer or press, but what it can so is give the Damascus a "fuzzier" look as the layer count increases and the 36x scratches are cutting through significant depths of the individual layers.

Oh, and you are very welcome <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//biggrin.gi f' class='bbc_emoticon' alt=':D' />

|quoted:

Bareback welding or "Dry Welding" is what brought me here. I thank my lucky stars that I discovered that specific thread early in the game. One thing that I keep reading, which is pretty relevant to the topic is the concern surrounding the quality of borax in the U.S.. Is this a ecological fallacy or is the "quality" of our golden go-to flux really diminishing? The billets that I've welded up with boric acid do have inclusions, but I attribute that to my inexperience and lack of process proficiency. A lot of complaints about borax aren't all about inclusions though, as a majority of the issue deals with the cloudy effect that's become more and more apparent between laminations. Bringing this full circle and back on topic, I'm curious about the differences between "Flux" and "Bareback"? I don't mean for you to repeat yourself Mr. Cashen, so I'll be digging through your website tonight...

Hello Zach, you can find my findings on the dry weld topic on my site here: http://www.cashenblades.com/dryweld.html

As for the borax quality, it is not like we can shop around, borax, at least in the U.S. is like one of the few surviving total monopolies we still have since it all comes from the same singular mine in the Death Valley area. I have done business directly with the company that run things there. But whether it is being made into detergent or simply pentaborate it all gets shipped out from there in box cars. I think the real question is whether they are changing the formula of 20 Mule Team Detergent or not, after all they are trying to make clothes cleaner, not stick hot metal together. Although I always did enjoy that spring time fresh scent it gave to my Damascus.

Mr. Cashen

You mention a temperature-force dependence in your first response. Now not wanting to have to synthesize C4, that suggests with a big enough press, one can weld at lower temperatures and maybe reduce oxidation (as that is also temperature dependent)? Is there a formula for that or a reference?

Thanks

Kevin