How to Temper a Knife -The Ultimate Guide

Getting into the knifemaking world may be frustrating for some people. Learning about work at the anvil, all these different types of metal, forging techniques, tools, and the heat-treating process is sometimes overwhelming for a beginner.

In this article, we will cover everything you need to know about the tempering process of a knife, including:

  • First of all, is tempering actually necessary?
  • Explaining the process of tempering
  • How can you temper a blade at home?
  • Is an oven necessary for the tempering process?
  • How long do you temper a knife?
  • How many times should you temper a knife?

Let’s tackle the first question.

Do You Have to Temper a Knife?

Before answering this question I should first explain this process so you could easily understand its purpose. So, you may already know that hardening or quenching is done prior to tempering. The goal of hardening is as its name suggests, to harden the knife. You harden a knife by heating it to between 1800 and 2000°F and then quickly quenching it in oil or water.

The good news is that your blade is very hard after the quenching. The bad news is that is also very brittle. That is where the tempering process comes in to solve the problem of brittleness. The primary goal of tempering is to reduce the hardness in exchange for greater ductility of the knife. I mean, what’s the point of having a razor-sharp hard knife if it is so brittle that if you accidentally drop it would shatter in million pieces.

In short, yes, you have to temper a knife. Tempering makes your knife slightly less hard but tougher and more durable. Without tempering, your blade is much more likely to crack and therefore become useless. There are rare cases where tempering a knife is not required.

I know a guy who started making knives without even knowing that tempering exists. You may guess how his knives ended only after the first use. He came into my shop and told me about his problem and when I asked him – “Do you temper all these knives?” he said – “No, what is that?”

So, after explaining to him the importance of tempering a blade after quenching, his knives suddenly became durable and finally useful. This is why you should always take enough time to learn and inform yourself before you start anything, including knifemaking.

What Is the Difference Between Tempering and Hardening?

It is not so uncommon for a beginner to get confused about the parts of heat treating and many other terms used in knife making. I noticed that many people are still mixing the tempering and hardening process so let’s get this over with.

In short, hardening involves heating the steel to non-magnetic temperature and then rapidly quenched in oil or water. As its name suggests, the goal is to increase the hardness of the steel. On the other side, tempering is the process of heating the steel below the critical temperature, usually in the oven. Its primary goal is to reduce the hardness in exchange for increased strength and durability.

How Many Times Should You Temper a Knife?

Now when you understand the basics of the tempering process, let’s see how many cycles are required for achieving optimal results. To fully understand this, it is good to know what is going on during temper.

So, in the quenching phase, the austenite is transformed into martensite which usually happens at about 400°F. Note that the steel wants to convert into pearlite at around 1000°F but with proper quenching, it turns back to the martensitic start point. After that, you let the blade cool down to room temperature. Keep in mind that your blade is still useless as it is too brittle. One drop on the floor and it is done.

The goal here is to make the martensite stable and allow the austenite to finish. Now, by heating up the blade to about the martensitic start temperature and keeping it for enough time, martensite loses its brittleness. This typically happens due to the changes in the grain boundaries. At this temperature, the austenite is much more active so it slowly finishes its conversion to martensite (good). Set time and temperature play a crucial role in this process.

The blade is then cooled down to room temperature. The steel now consists of tempered martensite which is good, and untampered martensite which is not good. This is why we need to do another tempering cycle to finish the conversion of leftover austenite.

The amount of tempering needed mainly depends on the intended usage of the material. So if you want to make a nice high-quality knife, it must be hard and tough enough for optimal usage. Know that the higher the temperature used for tempering, the softer the blade is going to be. Contrary, the lower they are the harder but also more brittle they will be.

For instance, a kitchen knife is usually tempered at lower temperatures since it is not intended for heavy use. On the other side, hunting knives are tempered at higher temperatures since they are used for hard cutting. So, to have a good blade at the end, I don’t recommend going above 600°F as it can soften the blade too much. Also, don’t go too low either because you may not decrease the hardness enough.

On the other hand, if the material is used for something else, where high hardness is not required, lower temperatures are recommended.

In most cases, you should do 2 tempering cycles lasting 2 hours at around 400°F. Between cycles, the blade should be cool down to room temperature. After the second tempering cycle, the blade is usually fully tempered and ready to finish into a knife. Note that the temperature must be controlled. In some rare cases, more than 4 hours are required.

After tempering, your blade is both hard and tough, meaning it is almost ready for use. All that has left is finishing work. I would also add that the quenching process must be done properly, otherwise, you will run into problems like cracking and edge chipping.

This is why you should always read the recommended tempering temperature and duration of the steel you are working with. Not every steel is the same nor you should treat it like that.

How Do You Temper Steel at Home?

When you look at the tempering, you realize it actually a very simple process. In most cases, everyone can do it in his home. All you need is the kitchen oven and your blade of course. As I have said before, not all steels are the same so each of them will require a different tempering process. In terms of knifemaking, there are 3 relevant steel types:

  • Carbon Steel – these knives are usually made where toughness and durability are a must. Carbon steel knives are very sharp and are easy to sharpen. Due to the low chromium content, they are more prone to corrosion. The most popular steel in this category is 1095.
  • Tool Steel – they are primarily used in cutting tools since they are hard steel alloys. Steels like O1, D2, CPM3V, M4 are some of the most common choices for knife making.
  • Stainless Steel – simply said, these are carbon steel with added chromium. Chromium increases corrosion resistance which is a nice characteristic of any blade. Unfortunately, they are not as tough as other steel types. Some of the most popular stainless steels include AUS, CTS, VG, 154CM, and SxxV series. Keep in mind that there must be at least 13 percent of chromium to be qualified as stainless steel.

Tempering of 1095 high carbon steel knife

This is the most popular high-carbon steel used for knifemaking. After the quenching phase, your knife is around 66Rc which means it is fragile as glass. As soon as it gets to room temperature place it in the oven. Now, depending on the desired hardness do the following:

  • For 62 RC set the temperature at 450°F and temper it twice, each cycle for 2 hours.
  • For 60 RC set the temperature at 500°F and temper it twice, each cycle for 2 hours. This is usually the sweet spot.
  • For 58 RC set the temperature at 600°F and temper it twice, each cycle for 2 hours.

Tempering of 1084 high carbon steel knife

  • For 60-61 RC set the temperature at 400°F and temper it twice, each cycle for 1 hour.
  • For 57-58 RC set the temperature at 450°F and temper it twice, each cycle for 1 hour.
  • For 55-56 RC set the temperature at 500°F and temper it twice, each cycle for 1 hour.

Tempering of 1075 high carbon steel knife

  • For 60 RC set the temperature at 400°F and temper it twice, each cycle for 2 hours.
  • For 57-58 RC set the temperature at 450°F and temper it twice, each cycle for 2 hours.
  • For 56-57 RC set the temperature at 500°F and temper it twice, each cycle for 2 hours.

Tempering of 5160 high carbon steel knife

  • For 60-61 RC set the temperature at 350°F and temper it twice, each cycle for 2 hours.
  • For 58 RC set the temperature at 400°F and temper it twice, each cycle for 2 hours.
  • For 57 RC set the temperature at 450°F and temper it twice, each cycle for 2 hours.

Tempering of O1 tool steel knife

  • For 61 RC set the temperature at 350°F and temper it twice, each cycle for 2 hours.
  • For 60 RC set the temperature at 400°F and temper it twice, each cycle for 2 hours.
  • For 58 RC set the temperature at 450°F and temper it twice, each cycle for 2 hours.

Tempering of D2 tool steel knife

  • For 60 RC set the temperature at 400°F and temper it 2-3 times, each cycle for 1 hour.
  • For 58 RC set the temperature at 500 °F and temper it 2-3 times, each cycle for 1 hour.
  • For 57 RC set the temperature at 900°F and temper it 2-3 times, each cycle for 1 hour.

Tempering of D2 tool steel knife

The tempering process should be done at 566°C (1051°F) to achieve a Rockwell C hardness of 62 to 66. It should be done 2-3 times, each cycle lasting 2 hours.

Can You Temper a Knife With a Propane Torch?

I get this question quite often whether you are surprised or not. It usually comes either from people who are quite skeptical about kitchen ovens or don’t have one. Note that kitchen ovens don’t always produce the temperature you set which can produce a lot of problems for the heat-treating process. I heard about some methods of tempering without using an oven but. The one with the propane torch is usually used.

You can use a propane torch to temper a knife. All you have to do is to hold your blade with tongs and slowly heat it while observing the colors. Make sure you constantly move the torch so you cover the whole blade rather than one spot. You want your edges to be straw color. If the edges become blue, you have gone too hot.

You can get propane torches like Master Appliance PT-2000Si Propane Torch Head on Amazon.

Leave a Reply