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Differential heat treatment
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Differential heat treatment is a technique used during heat treating of steel to harden or soften certain areas of an object, creating a difference in hardness between these areas. There are many tech
A differentially hardened sword, showing the hardened edge as the whiter portion of the blade.
A differentially hardened sword, showing the hardened edge as the whiter portion of the blade.
Diagram of a cross section of a katana, showing the typical arrangement of the harder and softer zones.
Diagram of a cross section of a katana, showing the typical arrangement of the harder and softer zones.
The curving of a katana during quenching first begins with a downward bend as the edge cools, followed by an upward bend as the rest of the sword cool
The curving of a katana during quenching first begins with a downward bend as the edge cools, followed by an upward bend as the rest of the sword cools.
A katana, shown at a long angle to reveal the nioi, which is the bright line following the hamon. The inset shows a close up of the nioi, which appear
A katana, shown at a long angle to reveal the nioi, which is the bright line following the hamon. The inset shows a close up of the nioi, which appears as the speckled area between the bright hardened edge and the darker soft zone. The wood-grain appearance is from the folding techniques used during forging.
Hamon (swordsmithing)
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In swordsmithing, hamon is a visible effect created on the blade by the hardening process. The hamon is the outline of the hardened zone which contains the cutting edge. Blades made in this manner are
Differential heat treatment
…between the martensite portion of the blade and the pearlite. This boundary is often called the "temper line", or the commonly used Japanese term, the "hamon". Between the hardened edge and the hamon lies an intermediate zone, called the '"nioi" in Japanese, which is usually only visible at long angles. The…
Example of a hamon. It is not the entire white hadori area, but a fuzzy line within the hadori. It is difficult to photograph, and to appreciate hamon
Example of a hamon. It is not the entire white hadori area, but a fuzzy line within the hadori. It is difficult to photograph, and to appreciate hamon, the viewer must hold the sword in his hand and change the angle of the light on the blade as he views it.
Types of hamon. The first is a straight pattern and the remaining are various irregular patterns (gunome).
Types of hamon. The first is a straight pattern and the remaining are various irregular patterns (gunome).