How to Temper a Knife the Right Way – Step-by-Step GuideGreg
Knife hardening is a critical process usually carried out by manufacturers during the forging process. It ensures that your knife is strong and solid. As a result, the knife has a good balance between toughness and sharpness retention.
The heat treating processes involved in hardening steel are carried out at certain recommended temperatures ranging between 300- and 650-degrees Fahrenheit depending on the knife’s purpose.
For instance, a camping or survival knife is usually tempered at about 650 degrees Fahrenheit to make it tough but also malleable enough to handle rugged use without becoming damaged. A kitchen knife, on the other hand, is usually tempered at about 350 degrees Fahrenheit to enhance edge retention.
This article provides an overview of the heat treatment processes that knives undergo during forging and a step-by-step guide for tempering your knife steel at home.
Heat Treating Procedures for Knives
Most manufacturers incorporate a 3-step heat treatment process when making knives. The 3-step process involves normalizing, quenching, and tempering.
Normalizing is the first step and is aimed at stabilizing the structure of the metal. This process minimizes warping during the quenching stage.
Normalizing involves exposing the unhardened knife blade to heat at critical temperatures several times. A magnet is attached to the blade to test for the critical temperatures to normalize the blade effectively.
Once the blade reaches the critical temperatures, the magnet drops. This is because most steel is magnetic up to the critical temperature, where it loses its magnetism.
After reaching the critical temperatures, the blade is removed from the heat and allowed to cool at room temperature. The heating and cooling normalizing process is then repeated two more times.
After the final normalizing cycle, quenching is done by once again heating the knife to critical temperatures and then promptly dipping the full blade in warm quenching oil until the bubbling and hissing stop. The blade is then removed from the oil and left to cool at room temperature. The main purpose of quenching is to harden the blade.
The final stage of the heat treatment process is tempering. Tempering is a heat treatment method employed to improve the characteristics of metal, particularly steel and iron cast alloys. It is done by heating the metal at a high temperature, just below the melting point, then allowing it to cool in the air. As a result, the metal becomes less brittle.
The right temperature to temper steel varies from one type of steel to another but generally ranges between 350- and 500-degrees Fahrenheit. The higher the tempering temperature, the more malleable the metal. The lower the temperature, the harder the metal. This means that metals tempered at a lower temperature are more brittle than those tempered at a higher temperature.
A DIY Step-by-Step Guide for Tempering Your Knife
Although blacksmiths and knife manufacturers primarily do the tempering as part of an elaborate blade production process, you can heat treat your kitchen knife, camping knife, or survival knife at home with your oven to improve its durability. If you notice that your steel knife has become brittle and hardly retains sharpness, heat treating may be the solution.
Below is a step-by-step guide for tempering your knife:
What You Need
- Kitchen oven
- Dull or brittle kitchen knife
- Grip pliers or tongs
- Heat resistant gloves
- Wire brush
- Soap or gentle detergent
- Prepare the knife for tempering.
Scrub the knife using a wire brush, warm water, and soap. Rinse thoroughly, and then dry the knife.
Cleaning the knife is a crucial tempering preparatory step as it removes any steel scraps and excess oil that may be on the blade. If you skip this step, your oven is likely to smoke during the tempering process as the oil gets burned.
Depending on the handle material, you may need to dismantle the handle from the blade. Materials such as wood and plastic are likely to burn or melt. However, if the handle is metal, you can leave it on as it can withstand high temperatures.
- Preheat the oven to the recommended tempering temperature.
If you know the exact type of steel your knife’s blade is made of, search online to determine the correct temperature. Otherwise, temperatures ranging between 350- and 400-degrees Fahrenheit will do.
- Place the knife in the oven for tempering.
Place the oven rack in the middle to ensure that the blade gets an equal amount of heat from the bottom and the top. Then, place the knife on the rack and leave it in the oven for one hour.
- Air-cool the knife.
Wear your heat-resistant gloves and use grip pliers or tongs to grasp the hot knife. Remove the knife from the oven and let it cool at room temperature for one hour.
- Return the knife into the oven for another tempering cycle.
Once again, let the knife heat in the oven for one hour at the previously set temperature. Then, remove it from the oven and let it cool at room temperature.
- Repeat the tempering cycle for a third and final time.
- Clean the knife.
Once the knife is fully tempered, clean the blade with a soft cloth, warm water, and soap. Dry it and sharpen the cutting edge either using a whetstone, file, or electric sharpener. If you had disassembled the handle, re-install it, and store your knife.
All good-quality knives go through a heat treatment process when being made. Normalizing, quenching, and tempering knives reduces the brittleness of the metal and makes it tough. Ultimately, the hardening of the knife ensures better sharpness retention and longer durability.
Heat treatment is not reserved for professional knife manufacturers and blacksmiths only. If you notice your steel knife is becoming brittle and losing its sharpness too often, tempering it by following the DIY step-by-step process above will make it tougher and more efficient.