How To Heat Treat Steel, Knives and Blades

Heat treating your steel, knife or blade is an integral process to ensure its hardness, longevity and suitability for its purpose. The heat treatment alters the property of the steel from a soft workable metal to a hardened steel suitable as a knife or blade.

The main consideration when heating a steel is to consider the temperature to heat it to, and this depends on the amount of carbon present in the base metal. The amount of carbon essentially determines the type of heat treatment that can be carried out on it.

The three main stages of heat treating

There are essentially 3 main stages of the heat treat process, which are broadly covered as follows:

• Heating the metal slowly to ensure that the metal reaches a consistent temperature 
• Soaking, or holding, the metal at a specific temperature for a certain amount of time
• Cooling the metal back to room temperature 

It’s important before you start to heat treat your steel that you have the appropriate equipment in place in order to carry out the process effectively. For consistent temperature you will need an appropriate furnace or oven and you will also need a suitable material to help quench and cool the steel effectively.

Stage 1 - Heating

The vital element during the heating stage is to ensure that your steel is heated consistently and uniformly across its entire area. Failure to do so will cause parts of the metal to remain soft or too brittle if overheated, or one area of the metal may expand too fast leading to cracking or distorting. A slow and steady rise in temperature is best and can be achieved effectively using a pre-programmed option with a heat treating oven.

Choosing the correct rate of heating can depend on a number of factors, which include

• The conductivity of the metal. The higher the conductivity of the metal, the faster it will heat up
• If a metal has been treated previously then it will require a gentler heat increase in order to maintain its integrity
• Thicker or larger pieces of metal need to be heated over a longer and slower period so that all parts of the metal are heated to the same temperature (i.e. if the metal is thick, it may take longer to heat the core of the metal than the face)

Stage 2 - Soaking or Holding

This is a vital stage of the process. Metal needs to be held at a temperature for a certain amount of time in order to ensure that its internal structure changes to the desired state. ‘Soaking’ is the period at which your metal is held at this appropriate temperature. 

It’s important to consider some of the same factors as at the heating stage, particularly considering the mass of the metal, when thinking about how long the soaking stage should last. It’s also important to reach this temperature gradually to ensure that the entire metal structure has reached the soaking temperature required.

This is important because uneven heat areas can cause warping of the metal and a poor finished product.

Stage 3 - Cooling

There are a number of ways to get your metal back to room temperature and the method really depends on what you are trying to achieve as an end result. The rate of cooling also really depends on the medium that you use.

One of the main methods of cooling steel is to use quenching, which can be processed by using a material such as air, oil, water or brine. Quenching is an effective method of hardening metal, as once it has soaked for its designated period of time, the cooling is rapid and maintains the structure of the metal.

Not all metals are suitable for quenching. Quenching can crack or warp some metals. Generally, brine or water can rapidly cool metal, while oil mixtures are better for a slower cooling. The general rule is that water can be used to harden carbon based steels, oil to harden alloy based steels, and water to quench nonferrous metals. The basis of your decision should be based around the structure and desired end use of your metal.

Read more: Oil Quenching vs Water Quenching: Differences, Pros and Cons.

As with any process, it will take time as a beginner for you to achieve the desired results. It is best to practice with different types of steel before using the process to complete a knife or blade project. You should also consider the heat treat equipment that you will be using for your project. Alongside the obvious safety equipment that is required such as heat resistant gloves and tongs and the quenching materials of choice, you will also need to consider the vital component - the oven or kiln that you will use to carry out the heat treatment.

At Soul Ceramics, we provide an extensive range of heat treat ovens, which have the advantage of programming the heating and timing settings to ensure a consistent and even heat of your steel, knife or blade. Unlike other methods such as blow torches or furnaces, the heat can be controlled in a heat treat oven and can be adjusted accurately depending on the metal.

Please view our range of heat treat ovens and our guide to heat treat ovens to see if there is a model that is suited to your heat treat needs.

Additional resources on knife making

• How to make a knife: a step by step guide
• An overview of supplies and tools you need for knife making
• What steel to choose for knife making