Complete Guide to Heat Treatment

Whether you’re making knives, blades, jewelry, or overseeing industrial processes that involve changes in temperature, heat treatment is an essential part of turning raw materials into finished products.

What Is Heat Treatment?

Heat treatment is the process of exposing material to specific changes in temperature. These temperature changes alter the material’s molecular structure, altering its physical (and sometimes chemical) properties. While heat treatment typically refers to metal alloys, it can also be used in a variety of processes: from roasting coffee beans, to manufacturing plastic, glass, or ceramic objects.

However, for the sake of brevity, this guide will focus on heat treatment for metal alloys!

What You’ll Need for Heat Treatment

The specific equipment you’ll need will vary depending on your project. For example, for making knives you’ll need a file and sandpaper and probably a drill. Additionally, you can find more DIY alternatives, like using a fire pit or BBQ pit instead of an actual oven. For this article, we’ll be sticking to the standard equipment and types of ovens most artists will need!

Below is the general equipment you’ll need for heat treatment:

• Metal or Alloy Material: You’ll need the material that you’ll be heat treating cut into the appropriate shape prior to heat treatment. You should select an alloy that will have the qualities you want for the finished ware.
• Heat Treat Oven or Kiln: A heat treat oven will be necessary for bringing your ware to the necessary temperature(s).
• Heat Treat Oven Controller: You will need a heat treat oven controller to manage the temperature of your oven.
• Tongs or Vice Grips: For most heat treating processes, you’ll need to transfer the ware from the oven to the quenching medium while it’s still hot.
• Quenching Medium and Container: Many heat treatment techniques require you to cool the ware outside of the heat treat oven. Unless your project calls for air cooling, you will need a quenching oil or brine stored in a fireproof container.
• Tempering Oven: If you plan to temper your ware after doing a hardening or normalizing firing schedule, then you’ll need a second tempering oven since it will be impossible for your primary oven to cool down in time. Some artists just use their kitchen oven – but if you heat treat on the regular, it might be worthwhile to invest in a tempering oven!
• Safety Equipment: Investing in proper kiln safety equipment – like protective gloves, eyewear, and a reliable fire extinguisher – helps protect you, your oven, and your property.

Types of Heat Treatments

Heat treatment consists of several different types of processes, depending on the qualities you want for your final ware. These are listed below:

• Normalizing: The metal is heated to an extremely high temperature for a defined time period and then air-cooled. Normalizing relieves internal stress and ensures uniformity, resulting in harder, stronger metals.
• Annealing: The metal is heated beyond the upper critical temperature and then slowly cooled to soften it and increase its workability. Annealing increases ductility and toughness, while relieving stress, making the metal more resistant to fractures.
• Hardening: The metal alloy is heated until it forms an even solution and then allowed to cool to increase its hardness.
• Case Hardening: Only the outside of the metal is hardened, creating a durable outer layer while ensuring the metal retains flexibility and doesn’t become brittle.
• Quench Hardening: After heating, the metal is cooled rapidly by dipping it into an oil, polymer, or water, resulting in very hard, very brittle metal.
• Tempering: After hardening, the metal is heated to a lower temperature to reduce excessive hardness and relieve internal stress. Tempering makes metals less brittle.

While you can apply multiple types of heat treatments to a single project, the order matters. For example, normalizing or annealing should be done before hardening, and tempering should always be done after hardening.

Planning Your Heat Treatment

Before starting your project, a little bit of planning can go a long way to ensuring you get the desired result. You will want to think what qualities you will need for the finished ware – whether that’s hardness, material strength, malleability, temperature resistance, or other qualities. You’ll need to select an alloy that will be workable while exhibiting these characteristics – while having a critical temperature that’s within your oven’s maximum temperature.

From there, you will want to plan out which heat treatment processes you will need – whether that’s normalizing, quench hardening, annealing, or tempering – as well as the order in which they need to occur. Then, you’ll want to collect those firing schedules. If you’re an artist who prefers to do things manually (or your kiln controller limits the number of schedules you can have saved at one time), you can write these down in your kiln notebook so you have them on-hand to program your oven. Or, if you’re using a TAP Kiln Controller, you can easily enter each firing schedule into your controller with a custom title, so that you can easily access them whenever you need them.

Starting Your Project

First, you’ll want to make sure that your studio or workspace is ready for heat treatment. Check to ensure that your heat oven is clean without anything on top of it or beside it, and that your tongs and quenching medium are near your oven (but not inside! Done that; not fun). You’ll also want to make sure that you have a surface ready if you need to air cool your ware.

Finally, before starting your project, you’ll want to make sure that you’ve fully prepared your ware – including defining the final shape, drilling any holes, and applying the desired finish. All of these things will be far more difficult (or impossible!) to do after heat treatment.

Using Your Heat Treat Oven

Now, it’s time to start your project! Place your ware in your heat treat oven. You will want to place your ware as close to the center of the oven as possible to ensure it heats up evenly. Next, securely close the oven door.

Now, it’s time to start your firing! If you’re using TAP, you can easily select or create your desired schedule with a few presses of your finger and press Start to begin your firing. Otherwise, carefully program your kiln controller with the appropriate firing schedule from your notebook.