What are Hardening, Annealing and Annealing and why do we do it? Heat treatment of steel!

Would you like a brief introduction to heat treatment of steel? The goal is for you to quickly gain an introduction and some knowledge that will be useful later.

When we talk about hardening, we often have several processes in mind, which fall under a larger concept that we call heat treatment. Included in this are the main processes:

• Annealing
• Hardening
• Tempering

We will go into these in more detail, but first you need to know that to get results in these processes you should know the material you are working with. If you find a random piece of steel in the garage, it is not certain that it can be hardened. You can roughly find out if it can be hardened by test hardening it, or using the spark test . Since it takes time and energy to make a good knife, and the result is entirely dependent on a blade that is hardened in the right way, it is very important that you know what alloy the steel has or that you have enough of the steel to use for testing and error until you find a good method.

What is annealing?

Usually when you buy a steel for knife making you get it delivered in an annealed state, that is, the soft state of the steel. It is soft enough to drill, file, shape and polish with relatively little resistance. The annealing process is somewhat different depending on the steel in question, but in most beginners' cases it involves heating the steel to a certain temperature, for example 790C, and cooling it slowly. Cooling can be done by insulating the hot steel well or leaving it in a furnace that slowly but surely cools down over time. By using this technique you can take a hardened steel and make it soft enough that you can drill holes and use a file without damaging either the drill or the file!

What is hardening?

Hardening is when you take a soft steel with an alloy that is hardenable, and change the structure to a structure with high hardness. Hardenable steel means that the content of the steel, mainly carbon and iron, is in the right proportion to each other. A steel that can be hardened often has recommended hardening temperatures based on the content of the specific steel, and it is therefore a great advantage to know the steel you are working with. Once the steel has reached the temperature, and has been at the temperature for the desired number of seconds or minutes, it is removed from the heat and cooled quickly. Common cooling agents are oil, aluminum sheets and water. In simple carbon steels, it is often good enough to follow a simple recipe that involves heating until a magnet no longer sticks to the blade, and then quickly cooling the blade in heated rapeseed oil. When you have had the steel at the right temperature for the right number of minutes, and cooled at a satisfactory rate, you have a knife blade that is now too hard to be a good knife. This is where tempering comes in.

What is tarnishing?

In order to get a knife that doesn't break with the slightest effort, you have to give up some of the hardness you gained through hardening. Tempering is about adding toughness to the steel through a heat treatment process that involves heating the steel, but not as much as during hardening. How high you go depends on how tough you want the steel to be, but for regular smaller knives in good single carbon steel, around 200C is often recommended. You can often use 225-250C for slightly larger knives that you often want a little tougher. As mentioned, the temperatures and processes will vary somewhat depending on which steel you use. If in doubt, get in touch.

Multiple processes

In addition to these and more advanced versions of these, you have several other procedures such as normalization, deep cooling and cryotherapy, which we will discuss at a later time.

Summary:

Annealing: Done at high temperature and slow cooling. Produces soft steel.
Hardening: Done at high temperature and rapid cooling. Produces hard steel
Tempering: Performed on hard steel at a lower temperature. Produces tougher steel.

Now you have a basic understanding of these three central processes in the work of blacksmiths and knifemakers, and if you have any questions, remember to get in touch anytime for anything!

We hope and believe you will find everything you need in our online store here at Storbua!

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