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Swords, Cutting and Military History

Metallurgical analysis of Japanese gunto by US War Department, 1946

Metallurgical analysis of Japanese gunto by US War Department, 1946

photo by Keith Putnam

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Declassified in 1997, this report The Metallurgical Analysis of a Japanese Samurai Sword (a digital copy of a mimeographed copy of the original) was the analysis of a Japanese officer’s “saber”, requested by the US War Department, Office of the Chief of Ordinance, and conducted at the Watertown Arsenal Laboratory.

The major interest expressed was in how the cutting edge was hardened and sharpened “so that it holds its cutting edge”.  Apparently it had been noted that these swords held their edges much better than standard issue bladed weaponry.

 

 

War Department Order

 

The actual order accompanying the delivery of the gunto — a Japanese military sword made specifically during this time period — shows that some people understood that there may have been a difference in quality between antique nihonto (Japanese swords) and gunto, but wanted the item checked to make sure.

 

Report order

 

How the blade was tested

The sword was slated to undergo destructive testing.  This process included:

  1. The sword being photographed, dismantled and the blade cut into sections.
  2. Hardness tests, using the Vickers scale, were performed at points on the exterior as well as on the interior of the various sections.
  3. The interior of each section was inspected for microstructures.
  4. Two longitudinal sections taken from the back of the blade were submitted to tensile strength testing.
  5. Finally, to test temper, three small sections were heated to 1800 degrees F.;  one was air cooled, one quenched in water and the last in oil, then the hardness of all three were compared to the original.

 

Results

1) Inspection and photography:  When the blade was disassembled, an inscription was found on the tang (nakago).  Unfortunately, as with many photographs in this mimeographed report, the images are so dark and obscured as to be unreadable.

2) Hardness:  When the hardness tests were completed, it was found the blade was softest in the tang (as low as 348 Vickers) with hardness increasing towards the longitudinal middle of the blade (550 Vickers), and dropping off slightly as the tip was neared.  Edge hardness was fairly consistent for the entire length of the blade:  between 442 and 446 Vickers.  The following chart shows precise hardness ratings in a large number of locations.

 

Hardness table

Click to enlarge

3) Microstructures: The edge of the blade was made up of tempered martensite, while the interior and back were mostly fine to very fine grained perlite.  The Carbon rating of the blade was 1.05.  A chemical analysis showed the steel had many non-ferrous inclusions, indicating very poor quality steel.

4) Tensile Strength:  The tensile strength of the blade was 191,000 psi, yield strength 120,000 psi.  Their analysis showed that there were internal stresses which might have caused fractuing in the blade which a milder temper would have prevented.

5) Temper:  Tests showed the blade had been air quenched from a temperature of approximately 1600 degrees F.

This makes an interesting historical read and gives some information on the manufacture of Japanese wartime officer’s swords.

 

Source

The Metallurgical Analysis of a Japanese Samurai Sword: Watertown Arsenal Laboratory Memorandum Report No. WAL 739/87,  Problem #R-1.6 September 1946, declassified 1997

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