Welding Knives: The Good, the Bad, and the Just Plain Ugly

Can you weld knives?

While it’s certainly possible to weld a knife, it’s not always practical. Consider the value and purpose of the knife in question. An intermediate-to-advanced understanding of metals increases the chances of success; however, welding knives is often left to the experts or simply used as a last resort.

Your broken knife blade sits before you. You may think it’s a lost cause, that you should scrap it and buy a new one, but what if there was a way you could bring it back to life? It’s certainly not for the faint of heart but it is a possibility—if you know what you’re doing.

Many of you may have heard of welding cracked engine blocks back together, but what about knife blades? Because these blades are comprised of metal, they are certainly candidates for welding upon. At the same time, there’s quite a few things to consider if you’re going to take torch to tang.

By NearEMPTiness - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=36804500In this article, we’ll be discussing the good and the bad of welding knives. Whether it’s to repair a crack or to fulfill an individual creation, welding knife blades is a tricky process. In short, it’s not something you should rush into. After reading this article, you should have a better idea whether to scrap the blade you’re attempting to fix or give it a go and see what happens.

Before You Weld, Ask Yourself

A few considerations stand before you if you entertain welding a knife blade as an option. In fact, there are a few questions you should ask yourself before you begin:

  • How imperative is it that I weld this particular knife?
  • Can I buy a replacement knife?
  • Do I have the proper tools and materials to weld this knife?
  • What alloy of metal is this blade?
  • What are the safety risks of welding a knife blade?
  • Will the knife blade be as effective after I’m done welding it?
  • Is the knife worth more to me in pieces as it is or perhaps in worse condition if I can’t successfully weld it?

Most of these questions center upon the value of the knife, both sentimental and retail. Commercially-made knives are typically easy to replace. That’s not denying the fact that some are expensive to replace, which complicates the matter for some. Other knives can never be replaced or duplicated.

At the same time, having the tooling and materials necessary to complete a successful repair is another matter entirely. Knives are made from a variety of metals. “Older knives are usually the same medium to high carbon steel throughout,” notes WeldingWeb.com. However, different “types of knife steel are ideal for different types of knives.” Knife blade technology didn’t stay in the stone age. New knife blades can be made from a variety of alloy material and forged with specific processes for a particular need.

Ultimately, the decision lies with you. Are you willing to take a chance in potentially ruining the blade in an attempt to fix it, albeit with similar chances of successfully repairing the blade? If you’re still not sure, keep reading for the good and bad associated with welding a knife blade.

Knife Blade Welding: The Good

Here are some of the good things that can come out of welding a knife blade:

  • Welding experience
  • Gain knowledge of various metals, quenching methods, and knife-making in general
  • Potential career path
  • Repurposing a blade for continued use
  • Repairing a valuable piece of personal property (such as a family heirloom)
  • Restoration of a blade for show/display
  • Successful repair of the blade

So those are the good things that could come of welding a knife blade. But it’s important to consider the following list. Because bad things do happen to good people, even good welders.

Knife Blade Welding: The Bad

And here’s the not-so-good things that could happen if you weld on a knife:

  • Weaken surrounding blade metal
  • Deface knife blade with blobby weld beads
  • Potentially harm yourself and/or others
  • Render blade unusable
  • Destroy knife blade completely

If you find yourself stopping here and realizing maybe it’s not worth it, that’s fine. It’s better to be safe than sorry when it comes to welding, especially on fine metal such as knife blades. But if you’re of the few and the brave who still want to learn more and potentially weld a knife blade, take note of the next section. Because the filler material you use could mean a world of difference.

Consider This: Base Knife Metals and Filler Material

The basics of welding dictate melting two metal pieces together using intense heat. Nothing new, right? But the filler material you use to supplement the joining of these two metal pieces differentiates between a successful weld and one that won’t hold up to the weight of a feather. This is especially true for knife blades, which are already thin and somewhat brittle in nature.

Most knife blades are forged, cast, or ground out of a single piece of metal. They’re tempered to a specific rating, which you may need to duplicate once more if you weld the blade back together. The majority of knife blades are made from some alloy of steel. It’s this alloy that you’ll want to take note of when picking out your filler material. Your chosen filler rod should match—as close as is possible—the alloy of the blade’s steel. It’s a bit like mixing concrete: you want to make sure the entire mixture is correct in terms of the ratios of each component so that the final product is strong and durable.

If you’d like to learn more about the different types of steel used in making knives, Jantz Knife Supply’s “Blade Steel Reference Chart” is a great resource. Specifically, the “Hardness (HRC)” section could be incredibly useful for figuring out which knives will take well to welding and which won’t. Harder steels, or those with a higher carbon content, are going to be more brittle. A softer steel, measured anywhere from 52-56 HRC, may be easier to weld since it will melt faster. At the same time, achieving the same hardness across the length of the blade could be harder since the metal is softer and therefore more flexible.

How to Weld a Knife Blade

Now that you’ve decided you want to weld on your knife blade, there are a few things you’ll want to do in order to prepare yourself for success. Each knife will be different, just like each welder has his or her own style. What follows is simply a guide, but it should put you on the path to a whole knife blade once more.

Preparation

Begin by setting up your welder. TIG is perhaps the best welding method for fusing knife blade pieces together because it allows you to control heat. You can easily pinpoint an area where you want to concentrate the weld and be quick and direct about setting down a weld bead. Tack, or stitch welds as they are sometimes known, are best for getting the blade in place first before you complete your first pass.

Adjust the settings to accommodate the type of metal you’re welding. Make sure that you’ve got plenty of filler rod. Your filler rod should be sharpened to a point, which will allow for more precise welding. If you plan on quenching the knife blade once you’ve melted it, you’ll want to have that quenching liquid ready as well. There are a variety of quenching methods available, from air and water to (diesel) oil or brine. Diesel oil is a great alternative quenching liquid if you want a higher carbon content in the blade.

You’ll also want to clamp down the pieces you’re welding together. This might be difficult with smaller knife blades. However, the more secure you can keep each piece, the better your welds will be. Just make sure that the way in which you secure the knife blade pieces still allows you to move around the joint to weld it.

Practice

If you’re not sure about welding on your knife blade and want a little practice first, purchase a pack of thin razor blades at your local hardware store. These razor blades mimic the thickness and size of many knife blades. Most razor blades are made from some alloy of steel as well.

Practice tack welding the blades together in a variety of positions. Though you’ll of course be welding your knife blade in a flat position, practicing with the razor blades will allow you to see how much penetration you’re achieving, as well as how the thin steel reacts in terms of heat. Because though TIG welding allows you to control heat, welding on thin material like a knife blade requires a delicate touch.

Process

The first step in welding a knife blade is to tack it together. Depending on the break in the blade, you can tack weld on either side of the blade where the cracks occur. Alternatively, weld a short distance inwards from the edge of the knife blade on either side. The idea here is to put less stress on your clamps and outline where you’ll be welding.

Once you’ve achieved suitable tack welds, make your first pass across the blade. Some blades may not require a lot of filler rod, but others may. Depending on the length of the crack and the width of the overall blade, you may need to complete another pass as well. Note that as you move towards the fine edge of the blade—just as you might have learned with the razor blade practice—you won’t need as much power to melt the metals together.

That’s the trickiest part about welding knife blades, other than the fact that they are so small and sometimes brittle. Knife blades tend to start out relatively thick at the top edge of the blade and thin out to a sharp edge that gives the knife its purpose. As you weld, you’ll be moving across a waning thickness. Often it’s best to start at the thick edge and move towards the sharp edge, decreasing amperage as the thickness of the blade decreases.

Post-Treatment

After you’ve successfully welded the knife blade pieces back together, there are quite a few steps you’ll want to take in order to make sure the blade can still function. First, the spot in which you welded could be softer or harder than the surrounding metal. One way to combat this is to anneal the area that you welded and then re-harden, or temper, the entire blade. A uniform temper will give the blade strength across the entire surface in such a way that further breaks or cracks can be prevented.

Re-hardening the blade often requires you to heat the blade up and then quench it to seal in the carbon content. Some of you may want to get crazy and use a purge environment to remove any oxygen still left in the blade. While this could ensure better end results, it’s not always necessary. At the same time, it may be a good idea to heat-treat your blade to re-harden it. You can easily do this with a torch, heat-treating oven, or furnace, if you have access to one.

After you’ve completed the heat-treatment process, you’ll likely want to bring your knife back to the shiny standard it once was. You can easily grind and sand the welds down to bring out the nice finish. Polish the entire blade however you see fit. Finally, you may need to sharpen the edge of the blade once more, depending on where you welded. There are a variety of knife sharpeners available but you can also have your knife professionally sharpened as well. It all depends on your budget.    

To Weld or Not to Weld

There are a lot of factors to consider when pondering whether or not you should weld your knife blade back together. You have to think about your skill as a welder, how valuable the blade is to you, how you’re going to use it after you weld it back together (if you can weld it, that is), and what risks are involved in the entire process.

At the same time, repairing a knife blade via welding can be a welcome challenge for some. It’s a test of your welding knowledge and a way to prove that you can control your welds well enough to restore something as delicate as a knife blade.

Whether you choose to weld knife blades back together or not, we hope you’ve learned something from this article. Welding opens up a whole new world of possibilities. And though it make take a bit of trial and error in some cases, the results are almost always incredibly rewarding. Happy welding!

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