Jump to content
I Forge Iron

Help With Weak Forge Welds


Recommended Posts

I did a search on old posts, but I did not find a post that solved this, forgive me if I missed the one(s) The quick and dirty is that my welds are very weak, The long details are below:

I have been struggling with forge welds being very weak. I am welding in a gas forge (single Venturi burner, side entry 3x4 cross section about 12” long), I think the flame is very close to neutral based on the color of the flame being right on the edge of transitioning from green to blue when I adjust the choke. (maybe there is a way I can test that better?)

The weld I am working on is a faggot weld of 3/8" square bar to itself. Either bent back in a loop and scarfed or two together (ends aligned and not scarfed). Hot rolled Mild steel (whatever comes from the steel yard) I have tried this about a dozen times and usually get the same result.
I grind off the mill scale so that the steel is bare and shiny, then I heat to red and flux with borax. Then I bring up the heat until all the borax is bubbling vigorously. I would describe the color as a bright yellow. If I take a pointed piece of the mild steel and press it to the bars at this temp in the forge, it welds instantly and I can lift the piece with the pointed piece and need to twist to get it off.
I pull it out and weld it on the anvil with 3 light, quick blows and the pieces are stuck together. The anvil is very close to the forge (within 2 feet) and I make sure to waste no time. I always get them to stick.
 I take a second heat and go over the weld again from the other side. I then take another welding heat and focus on blending the scarf with the pein. Next I go over one edge and blend it and then the other. By now, the two pieces look completely blended, when they heat I can see no seam and the scale forms uniformly. I sometimes forge it down again at welding heat.

Then I let it air cool to room temp and test the weld by bending it in a vice by pulling on piece away from the other. Every time the weld pops open with not much effort, maybe 10 or 15 lbs of force on a 6 in piece .
The surfaces look shiny, sometimes a small section tears out, but I can never get that level of adhesion over the entire surface. (See image of two attempts, both were loops that I bent back on themselves and then split after welding and tested
I have tried this a lot of time with varied strength of the blows, normalization cycles, using new 1045 (instead of mild) that I forge to 3/8”, forging the section down more, fluxing cold, not fluxing.

I even took out my oxypropane torch and tried it with borax and got the weld to stick, but then had the same failure in testing.
Could I have a contaminate in my flux? Is my forge more oxidizing than I think (I tried going richer, but then I struggle getting to temp)?
I really feel stuck and would really appreciate some help
Thank you,



Link to comment
Share on other sites

What size is the burner? Who's forge plans did you follow? I recommend you find someone else's and either build another forge or make more burners. 

I don't do simple arithmetic to calculate other folk's forges anymore but 3 x 4 x 12 frankly doesn't take any brain sweat. It's 144 cu/in and is about center range for a 1/2" naturally aspirated propane burner. 

Mounting ONE burner is going to make a very unevenly heated chamber and if it's near the center you probably can't tell how well tuned it is on a good day, it's too far away.

Try learning with thicker stock, say 1/2" sq. or similar. Shine up the joint surfaces and flux BEFORE you heat it to red. I know heating to orange is common old school practice but flux melts way sooner so why wait.

You can close the joint cold so it holds itself closed by it's own tension (springiness). sprinkle a LITTLE borax, preferably anhydrous so it doesn't foam up but 20 mule team works okay. You can wipe the joint with a drop of light oil like 3 in 1 so the borax sticks. Oil won't hurt the weld. If you have to pry the joint open to flux it, Perfect.

Slowly bring it to red heat and reflux it to prevent air infiltrating the joint. The flux you put in the joint will have melted and formed a prophylactic layer preventing air contact, more from the outside won't hurt and might help. 

When it's at temp and soaked set the weld with a heavy hammer and dead blows, fast taps are as or more likely to bounce the joint surfaces apart or shear them as weld them. Don't get crazy, a 2lb. hammer is plenty on 3/8" or 1/2" stock, more is. 

Set weld, brush, reflux, refine, repeat. Test later.

That's just how I do it, though I use a commercial, anhydrous borax welding flux available at any welding supply for way cheaper than "forge" welding flux. I'm not pleased to pay 3x more for a name that has zero effect on the results.  Lots of folk forge weld successfully differently. Many at surprisingly low temps.

Frosty The Lucky.

Link to comment
Share on other sites

Your process sounds pretty good, but I would suggest you get the thin edge of your scarf tacked down as early as possible (either the first tap or second), and don't make it a long thin scarf either).  Because it is so much thinner than the parent stock it will tend to cool past the forge welding temperature very quickly, which will eventually give you a failure initiation point for peeling the weld apart when you later test it.  

Also try to avoid putting the surfaces to be welded directly at the exit of the forge burner flame (or air supply on a coal forge for that matter).  These are oxidizing zones and any oxide that builds up on the surface will make it much more difficult to weld.

I've also had similar experience as Thomas with salvaged steel of unknown composition.

Last, there are some different flux formulas that appear to lower the temperature needed for forge welding, or stick better to the steel without foaming off like conventional borax.  I like the Black Magic flux, but have heard good things about Iron Mountain and the Alaskan? flux mix.

Link to comment
Share on other sites

I think you just need to refine the weld a little more. It seems you have successfully tacked the two pieces together, but haven't worked them together sufficiently to get rid of the visible seam between the two pieces. I just use that as an indicator, you don't necessarily have to go so far as to get a (nearly) seamless weld, but if you're just going for strength it doesn't hurt. 

Just looking at the pictures, the spots you were trying to weld still seem to be pretty close to the same thickness as when you started, which suggests they haven't been worked together enough (at a welding heat) after your initial weld.

All of the advise above still applies.

Link to comment
Share on other sites

On 2/7/2021 at 2:36 PM, ThomasPowers said:

The question I have is was all your trials with the same piece of metal?  I've run into some pieces of A-36 that don't like welding to itself and my first forge weld was in 1983.


I did try once with brand new from the steel dealer cold rolled AISI 1045, forged it into 3/8" square, clean the scale off to shiny steel. The weld could be broken just as easily as the other pieces


23 hours ago, Latticino said:

Your process sounds pretty good, but I would suggest you get the thin edge of your scarf tacked down as early as possible

I make my scarves about as long as the parent material, maybe a bit longer so about a 3/8-1/2" long. The remnants in the photos above look about double that because they get elongated when refining the material. I will try a bit shorter. I will also try welding the scarf first next time, that sounds like a good idea, because i do have trouble blending that in sometimes.

I think your comment about being too near the forge burner is probably the root of my problem. I was reading about why you cannot weld steel with Oxypropane torches, and it looks like the main issue is that it is too oxidizing of an environment even if regions are reducing.

I think my forge may just not be a good forge design for welding, because the only region that is hot enough to weld is about a 2" length of the chamber right around the outlet of the burner

I am a bit surprised that I can can get it to stick together, or weld a pointed rod in the forge with it being too oxidizing (I thought the flux was giving me some more margin here), but i guess just because it sticks initially doesn't mean it is going to be a good weld?

I also tried adding some powder metal (1095 powder) into the flux to see if it helps (maybe a 50-50 mix), and it seems worse, like the weld was very crust when i broke it apart and barely holding together which might indicate that the oxidizing issue really is the main one

9 hours ago, Frazer said:

I think you just need to refine the weld a little more.

Sorry, my photos could have been clearer, the photos are after i split apart the two pieces and are showing the weld plane. The do not show the side view. The cross section started as two 3/8" pieces (3/8" x 3/4"), and i usually forge until it is 3/8" in height. so I reduce the height of the weld by about half.

Perhaps my technique for refining the weld is poor? After the pieces are tacked together with the light blows and stuck, i usually progress to a medium blow (think straightening a slight bend in a 3/8" bar) with a 1.5 lb hammer and then full hard blows with the 1.5 lb hammer. Maybe I am working the sides too soon? Maybe i need to do harder blows sooner?


Thank you all for the comments, I will see if I can use a friends propane forge that I know gets much hotter than mine (he can melt steel using it) and see if I can get better welds.

One more comment: I have been reading up on this issue and I saw some posts about axe making with wrapped eye construction where people were warning about eyes splitting easily if you drift too aggressively indicating to me that the parent material is significantly stronger than the weld.

This was surprising to me, because looking at my post vice, there are a lot of forge welds on it, like the two plates that create the lower pivot connecting the two legs together. These welds have no scarfing and minimal apparent drawing out after the weld and the joint has predominantly shear stresses on the welding plane, but it has held up to a lot of abuse .

I wonder how many people actually test their mild steel forge welds made in a propane forge in this way? Perhaps this weakness is more common, but a lot of people are unaware that their welds are weak because they look fine are not tested?



Link to comment
Share on other sites

Try to avoid quoting complete posts by others.  Only highlight the line you specifically want to reference:

1 hour ago, JYForge said:

a bit longer so about a 3/8-1/2" long

I wasn't talking about the entire scarf, just the thinned tail.  I can't really read your photos all that well to be honest, so can't tell where the scarfs are, or even the welded joints.  This video may be of some help: 


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...