On this page
- The Baking Cookies Analogy
- Step 1: Normalizing for Grain Refinement
- Step 2: Annealing for Workability
- Step 3: Quenching for Hardness
- Step 4: Tempering for Toughness
- Final Thoughts and Next Steps
- Watch this lesson
Welcome back to Sword Wolf Forge, everybody. This is Lesson 5 in our Bladesmithing 101 series. Today is the big day. You have been hearing me talk about heat treating in pretty much every single one of these 101 lessons, and today we are finally getting to it. If you are following the stock-removal path from Lesson 4, you already profiled the blade and drilled your tang holes before heat treat—this lesson picks up from that point.
Heat treating involves several different phases or steps that we take to molecularly change the properties of the steel. This is a necessary step in bladesmithing, and it may be the most important. If you mess this up, you essentially just have a paperweight. You need to do this whether you are forging or doing stock removal, and even if your steel comes annealed from the factory, you should do a full anneal and run through every step again. This ensures you know the exact grain structure and helps you build crucial muscle memory. You can heat treat in a forge, in an exact heat treat oven, or by sending it out to a company, but today I am showing you how to do this in a forge since that is likely how you will start.
The Baking Cookies Analogy
Heat treating can feel overwhelming with so many technical terms, but I am going to simplify it. I highly recommend the book by Dr. Larrin Thomas (Knife Steel Nerds), as well as his YouTube channel and site. Dr. Thomas compares starting heat treating to baking cookies for the first time.
If you have a good recipe, you just follow that recipe exactly. You do not need to understand what the baking powder or soda does right away; you just put the ingredients in as spelled out, and you will successfully make a cookie. Later, when you have more experience under your belt, you will understand the learning curve and know exactly what temperatures or times to adjust if something is slightly off. To prove the importance of this process, a piece of raw 8670 steel from the factory will bend and snap under pressure. However, a piece of 8670 from the exact same batch that has been properly heat-treated is incredibly tough and takes serious effort to even bend.
Step 1: Normalizing for Grain Refinement
The first step in the heat treating process is normalizing. Especially after you have forged a blade, all the molecules in the steel are different shapes, sizes, and randomly patterned all over the place. Normalizing makes all those molecules uniform in size and gets them lined up nicely, which gives your blade its strength. It also relaxes the steel from forging stress.
For my 5160 steel recipe, we heat the blade to 1600 degrees Fahrenheit and "soak" it, meaning we leave it at that exact temperature for 15 minutes. Every steel is different, so always check the manufacturer's data sheet for accurate temperatures and times. In the forge, I use a piece of square tubing to distribute the heat evenly and prevent hot spots, using a thermometer probe to monitor the internal temperature. When you pull the blade out after its soak, a magnet will no longer stick to it, meaning it has reached critical temperature. Clamp it straight in a vise and let it air cool.
Step 2: Annealing for Workability
After the steel air cools to the touch, we move on to the anneal. Normalizing refined the grain, but the blade is still a bit too hard. We want to put some softness and workability back into the steel, especially so we can easily drill holes in our tang.
For 5160, I heat the steel up to 1300 degrees for 20 minutes. Then, the blade needs to cool very slowly overnight. I bury the blade in vermiculite, which is a fantastic insulator you can find at nurseries or on Amazon, to let it cool down super slow. Once it sits in there overnight, you have a completely annealed blade.
Step 3: Quenching for Hardness
After annealing, your steel is nice and soft. If you have not drilled your tang holes yet, do it now—you absolutely must drill them before you quench, because after quenching you will need carbide-capable bits to get through that steel. Austenitizing is the high-temperature soak that puts the steel in the right state to harden; quenching is the rapid cool right after that soak, and it is what locks in the hardness.
For my 5160, I heat the forge to 1525 degrees Fahrenheit for a 15-minute soak. I quench my blades in Parks 50, a dedicated quenching oil that I heat to 120 degrees to change its viscosity for better blade coverage. If you are a beginner, canola oil works okay for your first couple of quenches, but it breaks down quickly under extreme heat and will eventually lose its consistency.
When pulling the blade from the forge, plunge it directly into the oil quickly and immediately move it up and down. You want to oscillate it in the oil for at least ten seconds to prevent an air pocket from ruining the quench. Do not just dip it and pull it right back out, or you will ignite the oil and fail the quench. Once finished, clamp the blade straight in a vise to air cool; never lay it flat on an anvil, as the anvil acts as a heat sink and will pull heat from one side quicker, warping your steel.
Step 4: Tempering for Toughness
The quench makes the blade super hard, but also extremely brittle. The final cycle is tempering, which takes out some of that extreme hardness and puts flexibility and workability back into the steel so your knife does not snap or chip the first time you use it.
For 5160, my recipe is 400 degrees for one hour. I pull it out to air cool to room temperature, and then repeat it for a second hour. I use a basic toaster oven out in the shop with a supplemental temperature gauge to ensure accuracy. To prevent the blade from warping and to ensure even heat on both sides, I firmly clamp the blade upright in a simple jig made from angle iron. Once that is done, you have a fully hardened and workable blade.
Final Thoughts and Next Steps
We went through every step—normalization, annealing, quenching, and tempering—and explored why we do each one in that exact order. This was the hardest part for me to learn when I first started, so I heavily recommend making a log book to write everything down. Always remember that every steel is different, so check those temperatures and soak times for your specific material.
Our next lesson in the 101 series will cover grinding, where we will actually be cleaning everything up and putting bevels on our knife. Thank you for joining me, and stay sharp, everybody.
If you have questions about the tools or techniques used today, reach out through the contact form and I will be happy to help.
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