If you enjoy making knives, heat treating is crucial to maximizing the quality and durability of your creations.

The heat treating process, which involves controlled heating and cooling of the blade, alters the metal microstructure. As a result, you can improve hardness, corrosion resistance and other properties. (For more info, here’s an overview of heat treating basics.)

To help you get started, follow these 5 essential steps and expert tips on how to heat treat a knife.

Materials Needed

• Your shaped knife blade —Be sure it’s made of a steel suitable for heat treating
• Heat source - We recommend a dedicated heat treating oven with precise temperature control
• Quenching medium - Oil, water, or a specialized solution to cool the heated blade
• Hardness tester - To verify your blade properties after treatment
• Personal protective equipment (PPE) - Gloves, safety glasses, and a face shield

Nice-to-haves:

• A scribe to mark blade for focused heat treating
• Steel wool for cleaning
• Thermometer for temperature checks
• Sharpening stone or grinder for finishing

Step 1. Consider the Needs for Your Knife

Here are a few things to keep in mind to determine your heat treatment approach.

What Kind of Steel Are You Using?

Different steels have different heat treatment requirements. Depending on your steel, you might have different goals for the treatment. For high carbon steels, you might need to normalize, which relieves internal stresses to improve toughness and stability. Other steels need annealing, which softens the metal to make it easier to machine.

You also might need to hold your blade at different temperatures and durations. Or cool it using different methods. We’ll get into a few common knife heat treating recipes below.

What Are the Most Important Physical Properties for Your Knife?

Here are a few properties that heat treating can help with:

• Edge retention - Hardening through heat treatment can improve the blade’s ability to maintain a sharp edge.
• Toughness - Heat treating can reduce internal stresses, so that your blade is less likely to crack.
• Corrosion resistance - Heat treating can help form protective oxide layers.

What Are the Blade Shape Characteristics?

The shape of a blade can have a significant impact on the heat treatment process:

• Cross section - A thick cross section may need longer heating and cooling times to ensure even heat distribution; a thin cross section may be more prone to warping or cracking.
• Edge geometry - A blade with a full flat grind may need different heat treatment than a blade with a hollow grind, due to the different distribution of stress in the blade.
• Spine thickness - A thick spine may need longer heating and cooling times for even heat distribution; a thin spine may be more prone to warping or cracking.
• Blade length - Longer blades may require longer heating and cooling.

Step 2. Prepare the Blade

You want your blade to be as close to your finished product as possible before heat treating. That means grinding and shaping as required.

Make sure you clean the knife so that it’s free from dirt, grease, oil, or any other contaminants that can get in the way of heat treat success.

If you’re isolating parts of the knife for treatment—for example, to focus on the sharp/business side of the blade—you also need to mark those areas at this step.

Step 3. Heat the Blade

Now it’s time for the money steps.

Using your reliable heat source, heat the blade evenly to the temperature prescribed for your heat treatment and steel type. Typical heat treating temperatures range from 1400°F (760°C) to 1650°F (900°C).

Once the blade has reached the right temperature (verified with a thermometer if necessary), hold it at that temperature for the time dictated by your recipe. Twenty to 30 minutes is common.

Step 4. Cool / Quench

This critical step involves rapidly cooling the blade. Remove the hot blade from the heat source and immerse immediately in your quenching medium. Cover the blade entirely.

Keep the blade there for a set time. How long depends on how hard you want your blade. For many carbon steels, 10 to 30 seconds should do the trick. Others may need longer. For your best results, follow the manufacturer guidelines for the specific type of steel you’re working with.

Then remove the blade from the quenching medium and let the blade cool to room temperature.

Step 5. Temper the Blade

Quenching can introduce excess hardness and undesirable brittleness to your knife. So, to relieve internal stresses and improve toughness, heat the blade up again.

This process, called tempering, is slower (up to 2 hours) and at much lower temperatures (around 400°F / 200°C) than your initial heat treatment. Then allow the blade to air cool.

Step 6. Don’t Forget These Key Post-Heat Treat Actions

After tempering, there are a few things you still need to do, including:

Test the Hardness

Did your heat treatment work? It’s time to verify the hardness of your blade with a Rockwell hardness tester. It’s a specialized tool that measures hardness by determining the depth of indentation created by a penetrator with a known force.

Use your tester to look for 55 to 62 on the Rockwell scale for most knives. Harder blades tend to hold a sharper edge, but are more brittle and prone to chipping. Softer blades are more resistant to chipping, but are more difficult to sharpen and may dull more quickly.

If you haven’t used a Rockwell tester before, try it out on other materials first or consult an expert. Be careful not to damage the blade while testing!

Finish the Blade

Get your blade ready for slicing and dicing via:

• Grinding to its final shape and edge geometry using your grinding equipment of choice.
• Sanding to further refine the surface and remove any grinding marks.
• Sharpening as necessary using a combination of stones, honing guides, and other sharpening tools.
• Polishing to a mirror finish using progressively finer abrasives.
• Cleaning to remove any residual abrasives or oil, and to prepare it for handle installation or other final assembly.

Tips & Best Practices to Help Ensure Your Success

Common Knife Heat Treating Recipes

Keeping in mind that every knife will have its own requirements, here are a few basic recipes:

1095 Carbon Steel

• Heat to 1500-1550°F (815-845°C)
• Hold for 20-30 minutes
• Quench in oil

O1 Tool Steel

• Heat to 1400-1450°F (760-790°C)
• Hold for 30-45 minutes
• Quench in oil

440C Stainless Steel - Known for its good edge retention, corrosion resistance, and ease of sharpening

• Heat to 1600-1650°F (870-900°C)
• Hold for 20-30 minutes
• Quench in oil

154CM Stainless Steel - Ideal for high-end kitchen knives and hunting knives

• Heat to 1500-1550°F (815-845°C)
• Hold for 20-30 minutes
• Quench in oil

Temperature Control

Precision in temperature control is key to effective heat treating.

Start with a heat source that can maintain an exact temperature for long periods. Any of these Hot Shot Ovens would be a good choice.

Careful Quenching

Since quenching locks in the hardness for your knife, it’s important to nail this step. Choose the appropriate medium for your steel. Move swiftly but carefully to avoid over-quenching or under-quenching, which can weaken the final properties of the blade.

Staying Safe

Use proper protective equipment at all times, particularly when transferring your knife to quench. The high heat can cause serious burns.

Also consider using a heat source that insulates you from the high heat inside, such as Hot Shot’s Cool-Touch technology.

Happy Heat Treating!

Hope this how-to guide helps you complete heat treating processes for your knives. Heat treating is a tricky discipline, so take your time and enjoy the learning journey.