Wiki-Yakimodoshi

Tempering is a crucial heat treatment process in the manufacturing of knives, which follows the hardening process. The purpose of tempering is to improve the toughness of the steel and stabilize its internal structure. Below is a detailed explanation of the purpose, methods, and significance of tempering in knife making.

Purpose of Tempering

  • Improving Toughness: After hardening, steel becomes very hard but also brittle. Tempering adds a degree of softness to the steel, reducing the risk of cracking or chipping.
  • Stabilizing the Structure: Hardening can leave residual austenite in the steel, an unstable form of steel. Tempering helps stabilize this structure, preventing dimensional or shape changes in the steel.
  • Enhancing Wear Resistance: Along with improving toughness, tempering can also enhance the steel’s wear resistance, thereby improving the performance of knives.

Methods of Tempering

There are primarily two methods of tempering:

  • Low-Temperature Tempering: This method involves heating the steel to around 150–200°C for about an hour. It maintains some hardness while improving toughness, making it suitable for knives and other products where sharpness is important.
  • High-Temperature Tempering: Performed at higher temperatures (approximately 500–650°C), this method focuses more on toughness than hardness. It is commonly used for springs, shafts, and high-end cutting tools.

Considerations

  • Tempering Brittle Point: One important factor to consider during tempering is the phenomenon known as "tempering brittleness." If the temperature is not controlled properly, it can result in a decline in the mechanical properties of the steel. This is especially a concern in low-temperature tempering, where the steel could soften around 300–400°C, so careful temperature management is essential.

Summary

Tempering is an essential process to maximize the performance of a knife. Through this process, a balance of hardness and toughness is achieved, allowing knives to maintain their performance over long periods of use. Understanding tempering is important when selecting or maintaining a knife, as it directly influences the knife's durability, sharpness, and overall functionality.

Related websites
The Art of Making Japanese Knives: Detailed Process | KIREAJI