What can you do with 440C, one of the hardest stainless steels available? You can make some seriously durable knives, that’s what!

440C stainless steel is a popular material with knifemakers and other metalworking hobbyists. But optimizing 440C’s renowned properties does take some attention and care in heat treatment.

Get all the fundamental info hobbyists need for heat treating 440C stainless steel right here.

What Is 440C Stainless Steel?

440C is a high-carbon, martensitic stainless steel that’s widely used to make knives and other cutting tools that hold a sharp edge for a long time.

Important Properties

• High hardness – Rockwell C 58 - 60 after heat treatment
• Good wear resistance – Due to its high carbon content
• Good corrosion resistance – Particularly compared to other high-carbon steels, due to the presence of chromium, which helps to prevent rust
• Toughness – After tempering, shows resistance to cracking and chipping

Composition

Common Applications

440C’s high strength, hardness, and wear resistance make it great for:

1. Knives of many kinds – Hunting, pocket, chef’s and more
2. Bearings – High-speed and high-load applications in aerospace and automotive
3. Valve parts – For ball, check, and gate valves
4. Surgical instruments – For precision cutting and long-lasting sharpness, such as scalpels and forceps
5. Tooling – Punches, dies, and molds

440C Heat Treatments

Various 440C steel treatments can make it easier to machine as well as max out its hardness and edge retention. Here's a look at the key processes.

Annealing

Reduce internal stresses and improve machinability.

1. Heat in furnace to 1650°F and hold for six hours.
2. Shut furnace off and allow metal to cool inside.

Or, for smaller parts, you can save a bit of time by cycling the annealing process:

1. Heat to 1600°F. Hold for two hours.
2. Cool in furnace to 1300°F. Hold for four hours.
3. Remove from furnace and air cool.

Hardening

Increase wear resistance.

1. Preheat in furnace. First to between 1100 - 1250°F.
2. Raise the temperature to 1400 - 1450°F and allow to equalize.
3. After these preheating steps, raise to 1850 - 1950°F. Hold for 30 - 45 minutes.
4. Quench in oil or air cool to 125°F. Temper immediately afterward.

Tempering

Reduce brittleness and improve toughness and ductility.

1. Reheat the metal to 400 - 800°F. This will leave you with a hardness in the range of Rockwell C55 - 56. Don’t go over 800°F at this step, as studies show a decrease in toughness and corrosion resistance caused by higher-temperature tempering. 
2. Hold for at least two hours, plus 1 hour per inch of thickness over 2 inches.
3. To help improve dimensional stability, consider cryogenic treatment.
4. Allow to return to room temperature after refrigeration. Repeat tempering.

Key Considerations & Best Practices

Here are some things to keep in mind when heat treating 440C:

1. Control your temperature. Getting temperature right is vital for cycle annealing, preheating before hardening, and other steps. It helps to have programmable furnace controls, such as the user-friendly control options available on Hot Shot Ovens' heat treat furnaces.
2. Temper carefully. Going too high with your tempering temperature can not only greatly reduce hardness but, as noted above, also can reduce corrosion resistance.
3. Keep your workpiece clean. Ensure the metal is clean and free from any contaminants before heat treating. Even small amounts of dirt, oil, or other debris can affect the final properties of the steel.
4. Take safety precautions. We’re working with very high heat. Wear protective clothing and use proper ventilation to minimize the risk of injury.

Now that you’ve sharpened your knowledge of 440C heat treatment, it’s time to apply what you know to get an edge as a knife maker. Anyway you slice it, 440C stainless steel is an excellent metal for making cutting tools of all types.