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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.
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Heat treating furnace at 1,800 °F (980 °C)
Heat treating furnace at 1,800 °F (980 °C)
Photomicrographs of steel. Top: In annealed (slowly cooled) steel, the carbon precipitates forming layers of ferrite (iron) and cementite (carbide). B
Photomicrographs of steel. Top: In annealed (slowly cooled) steel, the carbon precipitates forming layers of ferrite (iron) and cementite (carbide). Bottom: In quenched (quickly cooled) steel, the carbon remains trapped in the iron, creating great internal stresses in the needle or plate-like grains.
Hypereutectoid steel
Hypereutectoid steel
Steel castings after undergoing 12-hour 1,200 °C (2,190 °F) heat treatment.
Steel castings after undergoing 12-hour 1,200 °C (2,190 °F) heat treatment.