What Is Forge Welding? Here’s What You Need To Know.

This article will provide background on a technical blacksmithing skill known as forge welding. If you're interested in blacksmithing and want to find out some specifics about what it entails, this is for you. Not only will we explain what forge welding is and how it is performed, but when you're done reading you should feel confident that you have just what you need to know. Whether you're thinking about this as a possible career opportunity or you're simply interested in getting started with forge welding as a hobby, you will find it equally helpful. So let's get down to business.

What Is Forge Welding?

If you don't know much about forge welding yet, it is simply the process of taking two pieces of metal and joining them through the use of extreme heat. Forge welding is one of the oldest welding techniques in existence, dating back to ancient times. Back then, it used to be performed manually, specifically using hot coals and a hand-held hammer. Today, forge welding is an automated process commonly used by steel manufacturing companies that seek to join similar or different types of metals into a singular piece.

Common Examples of Forge Welded Items

  • Bicycles
  • Crankshaft
  • Airplanes
  • Farming Equipment

Materials That Can Be Forge Welded 

So what types of metals are we talking about? With forge welding, we can use a range of materials. From iron, aluminum, and copper to brass and, of course, steel, there is a wide range of options. In most cases, however, the metal used most often is steel. The steel can come in the form of a bar, flat sheet, or other varieties of steel thickness. In fact, the steel can be high or low-carbon as long as it can be heated to a high enough temperature to be malleable or moldable.

What You'll Need to Forge Weld Steel

  • Metals of your choice - same or different types of metals can be used
  • Heat Source - hot coals are commonly used
  • Hardy Tool - a tool that is used to assist in bending your metal once it has achieved the necessary temperature
  • Flux Material - helps with removing oxidation and creating a sticky surface
  • Power Hammer or hydraulic press - used to flatten and shape your hot metal

Forge Welding Temperature

hot and burning coal used for forge welding

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So, what is a high enough temperature to make this process work? In most cases, steel temperatures will range from 3,000 to 20,000 °C. Other sources describe the range as 50 to 90 percent of the metal's melting temperature. There's actually quite a bit of science behind this topic that will not be explored here, but if you're into physics, you should definitely conduct additional research. For our purposes in this article, we simply want you to understand there are a few variables that determine the appropriate temperature which include: strength, porosity, hardness, oxygen absorption, and critical temperature of the selected metal.

How Does Steel Melt? 

So, what is a high enough temperature to make this process work? In most cases, steel temperatures will range from 3,000 to 20,000 °C. Other sources describe the range as 50 to 90 percent of the metal's melting temperature. There's actually quite a bit of science behind this topic that will not be explored here, but if you're into physics, you should definitely conduct additional research. For our purposes in this article, we simply want you to understand there are a few variables that determine the appropriate temperature which include: strength, porosity, hardness, oxygen absorption, and critical temperature of the selected metal.

Heat Color Chart 

This color change is significant. In fact, there is a color chart that helps you identify the necessary color level when forge welding is possible for different metals. The range of colors goes from a fiery reddish-orange at the lowest temperatures to a bright yellow at the maximum heat levels. These color changes are visible to the naked eye, so no specialized viewing tools are necessary. Red iron metal is on the low end, silver and copper are in the middle range, while wrought iron and stainless steel require the highest level of heat — thus, a bright yellow color change must be achieved. Once the proper heat level is achieved, the metal is primed for fusion.

Welding Flux 

a jar of borax, used as flux agent for forge welding

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In order for fusion to occur, a welding flux is required. Welding flux is a chemical agent used in the welding process to remove impurities and achieve a smooth and seamless result. It serves as a chemical catalyst that helps in joining or fusing two metals by preventing oxidation during the forging process. Oxidation can cause bubbling or unsightly and undesirable blemishes. More importantly, oxidation can prevent two metals from sticking together. The welding flux prevents metal oxide formation. It works by dissolving or cleaning the oxides on the base and filler materials. The welding flux coats the metal and keeps air from getting in.

What Flux Is Used for Forge Welding? 

There are different types of welding flux agents. Some commonly used flux products include borax, zinc chloride, hydrochloric acid, and ammonium chloride. Choosing the best one depends on a few factors. These factors can include the type of forge welding being performed, the necessary heat level, or how fine or delicate the nature of the product is. In addition to considering these elements, it is always important to run a sample test of the welding flux before committing because some flux agents can have the opposite effect and cause erosion of the welded material.

Can You Use Borax for Flux? 

Borax can most definitely be used as a welding flux, and it is commonly done. In its powdery state, borax can be poured directly onto the heated metal where you can visibly see a caramel-looking goo form which sticks to the metal. When this happens, the metal is now in a state where it can fuse with another metal. Borax is a viable oxidizer for forge welding but its use does raise a few concerns. Borax can be harmful to the user if inhaled, exposed to skin or eyes, or ingested. It is a poison that must be used with care. Some recommend cooking it down before using borax in this process.

Fusion vs Diffusion Welding 

a welder shaping the metal while the metal is still hot

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Just as there are different flux agents, there are different techniques commonly used in forge welding for joining metals. We'll take a look at two specific types — fusion and diffusion welding. Before this article, you may have believed the only way to join or fuse two metals was through the application of heat. We're going to share the truth on this matter, so you will understand your options.

Fusion Welding

The first technique, fusion welding, is what you are probably most familiar with. This process involves joining two separate pieces of metal by applying a certain degree of heat which enables you to shape or meld the pieces together. Up to this point, everything we have mentioned has been centered around fusion welding. In this process, pressure is not necessary. Fusion is commonly used in arc welding, gas welding, and resistance welding. It is particularly useful when fusing different types of metal materials together.

Diffusion Welding 

On the other hand, there are instances where heat is not required. In fact, the temperature of the metals involved always remains below the critical temperature. This is known as diffusion welding or solid state welding. The key to this process is not heat, but pressure. Common examples of diffusion welding include forge welding, roll welding, and friction welding.

Tips for Forge Welding 

a man connecting two metals through forge welding

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Forge Welding Can Be Tricky 

Although forge welding seems like a cut and dry process, there are some key factors to which you must adhere:

  • Good hand-eye-coordination is important when working in an environment that exposes you to high levels of heat
  • Caution and patience are necessary to avoid accidents
  • Speed and accuracy are essential to managing efficient timing of each step

Temperature Is Key 

As we discussed, the temperature requirements vary based on the materials you forge weld. Therefore, you must understand the different materials and adhere to the appropriate standards for the material you have selected. There's no getting away from the fact that the metal has to get hot enough to fuse.

Flux Makes a Difference 

Choosing the best welding flux for your project type and materials makes a difference. Knowing which one coats a specific material best and is acidic enough to oxidize the metal will simplify your effort.

Safety

Last, but certainly not least, adhering to proper safety measures is of the utmost importance. Hot things are dangerous, chemicals can be poisonous, and sharp things cut. Putting all these hazardous elements into one room could be a recipe for disaster. However, being aware is the first step and keeping your space organized and clutter-free can also make a difference.

Conclusion 

Whether you're seeking to become a professional blacksmith or just begin forge welding in your garage for fun, this article has given you just about everything you should know to get started. With continued practice and the knowledge base we have provided, you can become very skilled at forge welding. Best wishes on your forge welding project!

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