Forge welding Temperature

[Clayton M.]

I haven't been able to pin down a real definite answer as to the proper temperature of forge welding.

I am assuming that the temperature range is slightly below the melting point by a few hundred degrees, but other than semi molten I don't know anything else. 

 

What is the general rule of thumb on temperature for forge welding; mild steel and high carbon, respectively? I don't want semi molten as an answer, because that doesn't tell me anything more than I already know.

[ThomasPowers]

Forge welding depends on Temperature, Cleanliness and Pressure as such you can do forge welds at room temperature if you max out the other variables---galling a bolt thread is a solid phase welding process!

 

May I commend to your attention "Solid Phase Welding of Metals" Tylecote for in depth information of the process.

[Frank Turley]

Down here on earth as opposed to outer space, we contend with oxygen and other gases (plus dirt) that interfere with cohesion. I am making a guess that for mild steel with a coal forge, the forge welding temperature would be between 2400 and 2500F. The higher the carbon, the lower the welding temperature. High carbon tool steel is welded at a "sweating heat," no sparks. At a sparking heat, it will crumble. Low carbon steel and low carbon wrought iron can withstand a higher welding heat with perhaps a few incipient sparks, not necessarily a big shower of sparks. Realize that at a sparking heat, you're already in the burning range.

 

Thomas' mention of 'solid phase welding' lets us know that the metal is not semi-molten. The metallurgists say that the iron is in a solid phase or solid state. Many smiths think that the surface is molten and that is what causes them to 'stick.' I say "no." It just so happens that iron is one metal that goes into a solid welding phase at a certain temperature and if conditions are right, it will cohere, not adhere. Some other metals seem to go from solidus to liquidus in an brief instant, not so iron. 

 

It seems to a smith that the welding heat doesn't last too long, and from my viewpoint, that is correct. John Allgood in the film, "Hammerman" says, "You hit it a few licks, and you ain't welding anymore."

[Dodge]

It seems, unless one is using a pyrometer, the specific temp would be irrelevant anyway, unless the information is purely for a reference or research document. I have usually gone by eyeball. If it
looks hot enuff, pull it out and give it a couple smacks :D YMMV

[Ric Furrer]

Are you writing a paper on the subject or trying to get your forge to the "right" temp?

 

If you simply wish to hit the mark and not too much lower or higher then try this:

 

Take two small pieces of rod long enough to hold the end while the others are in the fire.

Get them hot

Dip them in borax flux and place back into fire

Rub the ends together in the fire till you feel them get sticky

What you feel is the surfaces trying to weld and your hand pressure breaking those welds.

That is your temp

 

try running the forge cooler and see how cold it can go...do the same for hot.

 

An issue some find is that the fire running too oxygen rich and continuous scale formation is interfering with the weld.

 

Shade #3 welding glasses help with the light in the forge and let you look at the metal.

 

Ric

[Steve Sells]

I feel a desire to throw another curve ball into the mix, you do realize that steel is not technicaly not a soid anyway?  it is a plastic, which is why, when we heat it... it gets softer.

 

The best way to learn how to forge weld is to do it with a person that is there to help guide you,  the harder you hit the billet the less heat you need, it is next to impossible to learn to forge weld on your own. but you can do it in a very short time working with an experianced smith.

[Clayton M.]

Okay, now I know a little more than I did before. This was just a curious post because I wanted to know more so when I attempted to weld I would have a better understanding about how to do it. I'm new to this so you guys are always a great help to me. You always seem to know exactly where to look and what to read. Thanks.

[Glenn]

Okay, now I know a little more than I did before. This was just a curious post because I wanted to know more so when I attempted to weld I would have a better understanding about how to do it. I'm new to this so you guys are always a great help to me. You always seem to know exactly where to look and what to read. Thanks.

 

They speak from books and more importantly from experience having been there and done that.

They spend a lot of time at the forge. (grin)

[ThomasPowers]

I've seen Billy Merritt weld at temps I would consider on the low side for efficient forging.

OTOH I welded up a billet at an "Open Air Museum" in Germany and the 80+ year old smith kept saying "too cold" as it welded up beautifully---he thought my borax flux must be magic.---I asked what he used: clean quartz sand; the old real wrought iron flux. He was also used to forge welding mild or wrought iron so the high carbon billet did weld at a cooler temp than he was used to. I left him the little "sample box" of borax so he could try to find it in Germany. (and yes, I did travel to Germany on a business trip with a billet and borax in my luggage...)

Near my house they do quite a bit of explosive welding where they max out pressure and so weld metals together.

[Ric Furrer]

mmmm..explosion welding........ ^_^

[Frosty]

Lil' dog" As a new guy to a craft wanting all the data is a normal feeling and isn't terribly important in reality. There are too many variables to say X is the single factor to attain to be sure of good welds or anything else for that matter. The secret to good welds is two fold. A little knowledge and two a LOT of practice.

 

The problem with the knowledge part is all the variables and knowing which apply, how they interact, etc. Nope the best way to ensure good welds is experience, you have to build a fire and start trying till you get it right.

 

With enough experience we can adjust to variables reflexively, these things can change far too fast to think through.

 

Here are a few factors that work for me: Clean. The cleaner the join surfaces the better the chance. Matched, the closer the joint faces match, the better the chance.

 

The less oxy the better your chances, flux's primary purpose is NOT to flush out: dirt, scale and other crud you should've cleaned out first. It's to keep oxy out of the joint. This is why I don't flux at orange heat. The higher the temperature the faster chemical reactions take place so iron/steel at orange heat will scale almost instantly. Your typical borax based flux melts just below 200f. iron/steel doesn't oxidize terribly quickly at 200f if you don't dawdle. Just a light dusting of flux, the stuff isn't glue it's just a prophylactic(barrier) glaze to keep oxy off the stock.

 

If those factors are good enough heat isn't such a factor though flux would only get in the way if taken far enough. For instance, Thomas is talking about vacuum welding where metals are cleaned and polished to as perfect matching faces as possible, placed in contact and evacuated of air so oxidization can't take place.

 

My Father was a metal spinner and machinist and did a lot of aerospace work so he had to have everything calibrated to the mil. His gauge (joe) blocks were tools you'd better keep your hands OFF. Each joe block was individually wrapped in oil paper and in it's own little box. They were so perfectly finished that letting them touch face to face meant they'd weld together inseparably after maybe 15 seconds and Dad sent you to the office for your pink slip.

 

It's the same action that makes Mokume Gane work. The thing that makes metals conductors is the loosely bonded electrons in the valence shells if the atoms get close enough together they begin exchanging electrons and before long nucleii start swapping positions and violA it's ONE piece of metal of two distinctly different flavors.

 

The only people realistically concerned with exact welding temperatures are folk doing it on a production basis where a couple degrees too hot is wasted fuel/money and failed welds is wasted materials/money. It's not such a big deal on lour scale where good seat of the pants navigation is what does the trick.

 

Frosty The Lucky.

[EricJergensen]

...

The less oxy the better your chances, flux's primary purpose is NOT to flush out: dirt, scale and other crud you should've cleaned out first. It's to keep oxy out of the joint. This is why I don't flux at orange heat. The higher the temperature the faster chemical reactions take place so iron/steel at orange heat will scale almost instantly. Your typical borax based flux melts just below 200f. iron/steel doesn't oxidize terribly quickly at 200f if you don't dawdle. Just a light dusting of flux, the stuff isn't glue it's just a prophylactic(barrier) glaze to keep oxy off the stock.

...

 

I use regular 20 mule team borax (laundry booster) for my flux. In that form it is hydrous (is chemically bonded with water). Putting it on hot metal (orange heat) quickly drives out the water and melts the now anhydrous borax (melting point: 1,369°F). With that flux, I can't use Frosty's low-temp approach. So, I clean the piece (sometimes by grinding), heat it to orange, give it a quick clean-off on the welding surface (don't waste time with any other surfaces) with my butcher block brush, get flux on it quickly and then get it back in the low O2 environment of the fire.

 

If you have a commercial flux, it will probably be borax based with other ingredients like boric acid (melting point: 339.6°F, boiling point: 572°F). Not sure what else might be used for lower melting point or coverage between 572°F and 1,369°F.