More on Forge Welding

Forge Welding Tricks and Temperatures

Hello Mr. Robertson:

I very much enjoy your website (www.ArtistBlacksmith.com) as I am new to blacksmithing and value the articles as a learning resource.

My two questions deal with technique to follow when hand forge welding:

Q#1) I have used both a gas forge and an oxy/acetylene torch to heat small parts when I need to shape and forge weld tool steels (D2) to mild steels. From my research, I understand that the best forge welding occurs when steel temperatures are both above 2400F and when both surfaces are well cleaned. I have a very difficult time seeing the difference in color between dull yellow/orange, bright yellow and yellow/white to know when the materials are both hot enough to effectively weld. I have tried using "Tempsil crayons" to measure surface temperatures, but these crayons only indicate when surface conditions are above 1850F.
What trick or tool do you use to insure that both steel parts are adequately heated to guarantee a good quality forge weld?

There is a lot going on with a forge weld. You certainly need a high temperature and scrupulously clean all helps. At these temperature it is very hard to see and judge the colors of the steel. I usually tell people to look for a lemon yellow or melted butter color or the same color as the interior of the gas forge running at max. But there are some tricks that can be used.

The first one and will gain you the most success is to use special shade 2 welders glasses. Click Here for selection of Amazon Infra-dura safety glasses. I use either the infra-dura shade 2 or rose dydmium glasses for the forge welding. The infra-dura lens actually filters out more of the harsh light than the dydimium. Both of these lenses allow you to see the surface of the steel at high temperatures. The shade 2 lens is green and you have to get use to the color shift but with a little practice this is not a problem. I would suggest wearing them for all forge work.

When using these glasses I am looking for a surface that has a bright greasy look to it. It should also have a look like it is almost slithering around. This is not liquid but getting close to it. The whole weld area should be the same color with no shadows. If it is an uneven heat turn the bar over in the fire and soak it from all sides. It should be an uniform temperature all the way through.

Another trick to try when starting out is forge a 1/4 inch round bar to a point and bend the point over a 90 degrees. Bring the bar that you want to weld up to temperature with the 1/4 round pointed one beside it. When you think it is right touch the point to the part that you think is at welding temperature in the fore fire. It should stick. If it doesn't stick it is too cold. Soak it longer.

If it sticks ( you should be able to pull it apart) take the weld. Start with simple fold over welds such as handles or even 1/4 by 1 inch flat bars just folded over on itself to learn the temperatures required.

Remember in gas forges this is working right at the top of what they are capable of. A high altitude makes a big difference as well. Above 4000 feet you may need a blower to provide extra air.

Q#2) I have heard that some blacksmith's prefer flux when forge welding while others strictly refrain from using flux because flux introduces contamination to the weld site. If flux is preferred, what are the best flux formulas for forge welding steels, stainless steels and wrought iron?

Flux is a bit of contentious issue. If using no flux your joints and fire have to be as clean as possible. Flux keeps the scale from forming on the bar. Scale does not weld. Some fluxes contain a ground metalic ingredient that lowers the welding temperature and increases the surface area at the joint. All these are good things when joining mild steel. I have used these compounds and they do work well. Trade names that come to mind are EZ-weld, Cherry heat, Antiborax, There are others. The problem comes when you are welding damascus billets as this metallic grains introduce a new layer into the billet and it can muddy the sharp transition between the layers.

20 Mule Team Borax found in the laundry isle has been used for years and works well for all general forge welding. It introduces no metallic contaminate. However there is a downside to using 20 Mule Team Borax. On regular joints it leaves a residue of borax that is very hard to clean off. It can be ground or sand blasted off. The problem with this residue is that it will start to turn white as it is exposed to moisture. So you may have this lovely forge welded piece then it starts to get this frosted appearance at the joints after a couple of years. Not pleasant

Different fluxes for different steels.
I have not forge welded stainless steel, but I understand you require a special flux with a Fluoride component to clean the stainless. Wrought iron should have enough slag in the matrix of the bar that you don't need flux but Borax wouldn't hurt.

I hope this helps
David Robertson
Artist Blacksmith

Tips For Forge Welding Above 4000 Feet

Forge Welding at Higher Altitude

By the way I am at 4000 ft. I am told that it is very hard to weld with a propane forge. Is there something you can share with me on what I can use or do before I start to try this????

Most of the trouble with higher elevations is the thin air. You just need more air to compensate for the fuel required to get enough heat for the forge weld. Some people are successful with an atmospheric forge forge welding at 4000 feet. Above that it seems that they need to add a blower to increase the air (oxygen / fuel ratio) . I would try just normally but run your forge hot as possible. Higher pressure. This depends on what type of forge you have.

For forge welding here I use 20 to 25 psi although I am not very high. This does depend on your particular forge though.

If you find you do not get the temperatures required (lemon yellow at least) then you will probably have to look at adding a blower to the system, if your forge doesn't already have one.

The other thing is to put a piece of scrap plate steel down (1/8 th is fine) to cover your forge bottom to catch any drips of flux as it will eat into the ceramic fire brick or the insulation. I use 20 Mule Team Borax and that works fine for me. If you buy "Cherry Heat" or "Anti-Borax" or "EZ Weld" or other trade name flux from either Centaur forge or Pieh tool company or Blacksmith Depot (addresses in the resource section on the website, members area) this type of flux will help lower the temperature for mild steel.

I hope this helps.
David Robertson
Artist Blacksmith

Blacksmithing : Forge Welding Cable Damascus

I' m interested in trying the steel cable damascus knife, any advice?

Cable is actually really nice stuff to weld. There are a couple of tricks that people forget that help a lot.
The alloy in the cable has a good success of welding even at fairly low temperatures. Having said that use a full welding heat until you are comfortable with it.

Crane cable is better than elevator cable. Elevator cable has an inner core twisted one direction and an out sleeve twisted the other direction. This is called counter rotating cable. That is the cable doesn't twist as it spools off the drum.

Regular crane cable has inner and outer strand twisting in the same direction.

What this means and this is the important step, when you first heat the cable up, clamp it in the vise and twist it as tight as you can get without it buckling. This helps close up the air spaces for better weld. The elevator cable won't twist tight as the inside is expanding when the outer sleeve is being twisted tight, causing spaces to open up.

Back into the fire and take up to a nice orange.
Gently wire brush it, and add flux.
Back into the forge to take the welding heat.

The next trick is instead of welding flat on the anvil (although this does work) use a U shaped bottom swage tool or swage block to help support the sides of the cable when you weld.

As you make the actual forge weld rotate the cable with the direction of the strands. That is each hammer stroke is actually tightening the twist.

You will find that once the cable strands are weld the feeling of the metal changes from the floppy cable to a hard bar. Once it is well stuck together as a bar take a series of refining welds on all edges to make sure any loose strands are tacked down.

When you are completely satisfied that it is well welded then stretch out as normal and make your knife etc. as usual. Once completed, ground, hardened, then sanded again then you can etch in acid to reveal the pattern. You can use vinegar warmed up on the stove. Takes along time but will give you a bit of the pattern, and is the safest acid.

I use more aggressive acids such as sulfuric or nitric or some times ferric chloride. Follow all acid precautions with these strong acids.

Neutralize and take a look at your knife.

David Robertson
Artist Blacksmith

What Flux to Use For Forge Welding Damascus Steel?

What Flux is right for making Damascus Steel?

One of my family-members asks me right away if I could make a knife for him, made of damast-steel.
This is the reason why I'm coming with another question:
What product do you need for welding pieces together, or making damast-steel? In other words: what works best?
I've been looking on www.angele.de and they offer borax, magi-weld and something they call "Flutsch". The last one is black and looks like tar. Magi-weld is the most expensive but does that mean it works best?


I am not familiar with those products except the borax.
Some of the smithing fluxes have iron filings in them that help the steel stick, but this can muddy the layers in the pattern. Most of us use a product called 20 Mule Team Borax. It is laundry borax. Cheap and works well. Found in the laundry isle in the grocery store. Some people use borax ( boric acid) from the pharmacy which is more expensive but is more pure.

I strongly suggest practicing welding mild steel together many times before trying damascus steel. It is a very tricky process and requires a good deal of practice.