Introduction to Japanese Kitchen Knives Part 3

How a Japanese Knife is made - Heat treatment

The Heat Treatment Process for Japanese Knives


This is a general summation of the knifemaking process.

Many aspects can vary depending on a variety of factors such as style type ( Stainless Steel , Carbon Steel or Damascus Steel ) ,steel thickness and size, forging method ( Mono-Steel, Multi-layered Steel).

The heating temperatures, time frames and even ambient temperature can all vary and influence the blade smithing process.

What is Heat Treatment?

Heat treatment includes Normalizing, Quenching and Tempering.

What is Normalizing?

During the forging process, the steel structure can become uneven, so most craftsmen will conduct a normalizing process where the steel will be evenly heated above 1400 degrees Celsius and then allowed to cool slowly. This balances out the steels structure, reducing the risk of weak points in the metal.

What is Quenching?

However, once the rough final shape of the blade has been made, and the bevels hammered in. The craftsman will conduct a hardening process.

In simplest terms, the steel is heated to one thousand degrees centigrade (can vary depending on steel type), once at the right temperate, the steel usually has a bright glow to it. It is then “quenched”. Quenching is driving the red-hot blade into oil or water to rapidly cool it.

The Traditional Japanese style used in high quality Japanese knives and Japanese cutlery involves quenching in water and sometime with a clay coating over the steel blades.

The rapid cooling changes the steel structure, making it hard. If the steel were to stay soft, then it would not hold an edge and would be a terrible kitchen knife.

A side effect of the blades rapid cooling is the increase in overall brittleness. If left in this state, the knife could shatter at first use. Thus, we proceed to the tempering process.

What is Tempering?

After the Blade has been quenched and hardened as a result, it is very brittle and needs to be tempered.

The tempering process removes stress from the blade making it more durable. Firs the blade is allowed to cool further, close to room temperature, then it is placed in an oven with precise temperature and time control.

How hot the oven is will determine whether the blade is more durability optimized or optimized for edge retention and of course will remove most of the brittleness from the steel if done correctly

making high quality chef knife.

Stainless Steel and High Carbon Steel will react differently to the forging process.

After Tempering

After the tempering process, the knife is ready for cleanup, final sharpening and polishing.