Forge welding is one of the skills that many beginner blacksmiths find very complicated. But, learning how to forge weld will make your work considerably easier and more convenient for various reasons. I see a lot of discussion on the internet about the right choice of flux.
I decided to write this article to inform all current and upcoming blacksmiths more about this topic.
So, what is the best flux for forge welding, you ask?
One of the best and most popular fluxes for forge welding is borax. Borax is historically the most reliable and consistent flux used for this purpose. It is cheap, readily available, and mixed with other additives to produce a better effect. Since borax is a powder, all you need to do is sprinkle it on when the metal is at least red hot.
You can get borax on this Amazon link.
Now, that would be a direct and short answer, but the truth is that there is more than that. Factors like the type of steel, the heat, amount of flux are all things that are crucial for understanding the usage of flux.
Let’s dive into it.
First of All, Is Flux Even Necessary?
You may see some blacksmiths forge weld without any flux usage, especially if you live somewhere in Europe. Nowadays, no flux welding is becoming more and more popular, but the question arises, is it truly necessary?
While using flux for forge welding may not be necessary, it makes the process much easier. Flux is primarily used to keep the welding metal surfaces from oxidizing and therefore reduce the chances of a poor quality weld. However, in recent times, many people stopped using flux as they have access to MIG/TIG welders. To use the no flux method, ensure that the stack is clean and well sealed.
You may have also heard that propane forges cannot produce the heat required for forge welding. While this is often true, propane forges that are properly installed and maintained can produce welding heat. So, don’t fall into this trap just because someone said it.
On the other side, if you are using a coal forge, you need to maintain a fire properly. Make sure to use enough coal to have a nice and deep fire. Also, the coal should be coked as green coal usually ruins a weld under the billet, but if it is on the top, you should be fine.
The chances are that if you are from England, you have never used flux for forge welding. That may be partly due to the higher standards of iron in Britain. Also, the British never lost their blacksmith tradition, which allows them to learn from highly experienced smiths directly.
There are certain cases where the flux is almost inevitable, like welding high-carbon steel to mild steel. The primary reason is that flux lowers the melting point, which matches the melting point of the two types of steel.
On the other side, there is no need to use flux when welding two pieces of mild steel together. Namely, both have the same melting point, so flux is not required. I only use flux on mild types of steel when working on more complex joints.
However, we recommend using flux for forge welding purposes for beginners. After you gain a little experience, then feel free to try the no-flux method. You don’t want to throw away metals just because you wanted to try forge welding without using flux. That would be a foolish beginner mistake.
What Is Borax?
Borax, also called sodium borate, is an alkaline mineral salt with a mostly powdery white look. It is most popular as a laundry washing powder, but it can also be used as a flux for forge welding. It is one of the most popular flux choices, mainly due to price and availability.
The term borax often refers to similar compounds, characterized by their water content. There are a lot of discussions between borax and boric acid, so let’s explain their differences. Namely, borax is not the same thing as boric acid. Borax is a natural component mined from the ground, whereas boric acid is formed after acidifying borax. So, borax is hydrated salt of boric acid.
How to Use Borax for Forge Welding?
Before explaining the usage of borax in forge welding, I should shortly clarify what forge welding is in the first place. Forge welding is heating two pieces of an iron-based material to welding temperatures and fusing them under the hammer or press pressure.
The problem is that when you take out the work from the forge, it usually contains a scale that prevents that fusion. So, you can think of a scale as the enemy of forge welding. That’s where a flux like borax comes in. Borax eats away the original scale and further prevents the air from coming in, which in the end represents a nice sealed weld.
When using borax for forge welding, ensure your material is properly heated. You don’t want to put borax on a cold metal the same way there is no point in sprinkling borax on melted metal. After you take the workpiece out of the forge, place it on the anvil and pour borax on the desired side where you want to make the weld, and put it back in the forge.
Please keep in mind that the welding temperature is usually very subjective. Quite frequently, you may hear that lemon yellow is the color of welding heat. While that is not a bad measure to aim for, note that you don’t see colors the same way as someone else does. For example, someone working outside doesn’t have the same lighting as someone in a gloomy workshop.
One of the easy ways of knowing when you are just near the welding heat is to observe the surface of the metal in the forge. Namely, if the flux on the surface of the metal doesn’t flow, it means that you are near the welding heat.
On the other hand, if you notice sparks coming out of the fire, it is too hot, or you have too much air in the forge. It is better to come to welding heat slower rather than fast.
How Much Flux Do You Actually Need for Forge Welding?
It is not uncommon to see someone pouring two tablespoons of flux on a tiny piece of hot metal. While sometimes that may not be a problem, it is highly unnecessary. Contrarily, some people put too little flux.
How do I know the ideal amount of flux for forge welding?
You need just enough to cover the welding surface when pouring flux on the heated metal. To put a proper amount of flux on the steel, use a teaspoon or your hand and slowly sprinkle it on. When you notice a nice glassy coating on the material’s surface, it means that you put enough. Adding too much flux can prevent the weld from sticking.
I should point out that if you are using the borax, you may notice bubbling as you sprinkle it on. As there is water in borax molecules, it is entirely normal, so you don’t have anything to worry about. Check the video below to see how too much flux looks on the material.
But in the end, the crucial part of learning to forge weld is to find a process that works for you and your setup. You can read as much as you want, but until you do a lot of experiments, you will never find out what works best for you.
