The new year sparks a renewed passion for craftsmanship among knife makers worldwide, with a focus on precision and perfection. Among all the steps in knife making, few are as transformative, or misunderstood, as heat treating.
This process defines a blade’s strength, toughness, and cutting ability. This month, KMTS takes a closer look at how heat treatment works, why it matters, and how you can achieve professional results in your own workshop.
What Is Heat Treating and Why Does It Matter
Heat treating is a controlled process of heating and cooling steel to alter its internal structure. It’s the step that turns a soft, easily shaped blank into a functional cutting tool capable of holding an edge.
The process typically involves three main stages:
1. Hardening: Heating steel to a specific temperature (the austenitizing point) and then quenching it in oil or air to lock in hardness.
2. Tempering: Reheating at a lower temperature to reduce brittleness and restore toughness.
3. Testing: Verifying hardness and flexibility to ensure performance balance.
Without proper heat treatment, even the best-designed knife will dull quickly or chip under stress.
Tools and Equipment for Heat Treating
For small workshops, a propane forge, heat-treating oven, and quench tank with the correct oil are sufficient to reach target temperatures. Other helpful gear includes fire-resistant gloves, eye protection, and a tempering oven or kitchen oven capable of maintaining consistent low temperatures.
Tip: KMTS stocks various steels with detailed temperature guidelines, making it easier to match your process to the material’s properties.
The Hardening Process
Different steels have different heat ranges, typically between 780°C and 850°C for high carbon steels and 1030°C to 1080°C for martensitic stainless steels. Heat your blade evenly until it reaches the correct temperature, indicated by a bright orange hue or verified with a thermometer or magnet.
Once heated to the desired temperature, quickly quench the blade in oil while maintaining a vertical position to prevent warping and ensure optimal hardening. This rapid cooling changes the steel’s crystalline structure, locking in hardness.
After quenching, your blade will be tough but brittle. Avoid dropping or flexing it until tempering is complete.
Tempering for Toughness
Tempering restores balance. Reheat your hardened blade at 180°C–220°C for 1–2 hours, depending on steel type and desired performance. The process relieves internal stresses and improves flexibility.
After tempering, test your edge with a file; it should glide over the hardened surface rather than bite in. This indicates a successful heat treatment.
Common Challenges and How to Avoid Them:
● Warping: Ensure even heating and use proper quenching orientation.
● Overheating: Avoid exceeding recommended temperatures to prevent grain growth.
● Inconsistent hardness: Maintain steady temperatures and allow the steel to soak adequately before quenching to ensure consistent hardness.
Pro Tip: Keep detailed notes for each batch of steel, including time, temperature, and quench type, to refine your process over time.
Final Thoughts
Heat treating is the pivotal step that transforms a knife from a shaped piece of metal into a finely tuned instrument, marking a knife maker’s ascent to mastery.
At KMTS, we provide the materials, tools, and knowledge to help you succeed. We can also heat treat the blade on your behalf. From premium steels and heat-treating gear to abrasives and handle supplies, everything you need is available right here in South Africa.
Start your year by sharpening your skills. Visit kmts.co.za and take your knife-making to the next level.
New year, sharper knives.