There are several ways you can heat treat stainless steel knives. One method involves using subcritical annealing. Another is the use of cryogenic treatment. In either case, it’s important to check the hardness of the blade.
Tempering temperatures
Tempering temperatures for stainless steel knives can vary. The higher the temperature, the harder the material. You will want to choose a tempering temperature that is appropriate for the application. Using the wrong tempering temperature could result in brittleness and reduced corrosion resistance.
Heat treating can be done by a forge, an oven or a blowtorch. It is recommended that you use a heat resistant face shield to protect your hands.
Most steels are tempered in the 500-600degF range. This is the same range as the martensite transformation. A temperature below 347degF will produce a brittle blade.
For the best results, it is a good idea to start with a larger block of steel. If possible, you should use a double tempering process. This will allow the hardening process to work its magic.
Subcritical annealing
Subcritical annealing is a heat treatment process that reduces the hardness of a steel through the recrystallisation of the microstructure. It is particularly effective for high carbon steels. The aim of this process is to improve the machinability of a component while ensuring it has a hardness that is suitable for further shaping.
Subcritical annealing is a very low temperature heat treatment that is performed in a furnace, which can range in temperature from 1275F to 1450F. This allows the annealing temperatures to be held for an extended period to ensure the temperature is uniform.
Subcritical annealing is one of several annealing techniques for spheroidising the cementite and austenite phases in a steel. This helps improve the ductility of the material and also enhances the ability of the metal to resist cold working.
Cryo treatment
There are many ways to heat treat stainless steel. The process can vary depending on the type of steel and how you plan to use it.
Cryogenic treatment is another method of hardening stainless. It uses dry ice or liquid nitrogen.
This technique isn’t as expensive as traditional heat treating. You’ll need to find a commercial company that offers it. Also, you’ll need to be sure the price you pay includes the tempering.
Another advantage of cryogenic hardening is that it’s compatible with a variety of metals. Some alloys are particularly well-suited to this process, such as magnesium and copper.
For hobbyists, dry ice is a relatively inexpensive method of hardening stainless. Dry ice can be stored in a small cooler.
Heat treating stainless steel requires a large investment in time and equipment. However, it does provide a great deal of benefits for your knife’s durability and longevity.
Wrapping the blade in stainless steel foil
You can heat treat your stainless steel knife to very high temperatures. The key is to use the right foil. There are two types. One is an aluminum sheet, and the other is made from 309 Stainless Steel.
The best foil for heat treating is the latter. It has a thickness of 0.07mm, and it is cold rolled. This allows it to hold its shape during heat treatment. Also, it is insulated, so it will not burn after it’s heated.
An airtight tool wrap envelope will keep out excess oxygen, which is a problem during heat-treating. In addition to keeping out air, it will also prevent slag from forming.
Several commercial companies offer heat-treating services. They are especially useful if you’re experimenting with stainless steel. Some are more expensive than others, but they are usually much cheaper if you order a lot.
Checking the hardness of the blade
Checking the hardness of a heat treated stainless steel knife can be difficult. In order to ensure that your knives are properly hardened, you need to use a Rockwell hardness tester. The Rockwell hardness test measures the amount of penetration depth that a diamond point can make into a steel sample.
The Rockwell test is the industry standard for testing the hardness of a knife. There are other hardness scales used, depending on the type of material being tested. Some of these scales employ different combinations of test forces.
Checking the hardness of a heat-treated stainless steel knife can be done in four steps. First, you must temper the blade. Tempering increases the toughness and hardness of the metal. This process takes a significant amount of time.