Metallurgical Investigation into Ancient Iron Nails

Abstract

Metallurgical investigation has been carried out on 28 specimens of ancient iron nails used in the famous old wooden, builpings in Japan such as “Kondo” (sanctuary) of “Horyu-ji” temple, “Hoodo” (main hall) of “Byodo-in”, three-storied pagoda of “Meitsu-ji”, five-storied pagoda of “Daigo-ji” and “Haiden” (oratory) of “Otonashi” shrine. The age when these specimens were manufactured are presumed to lie in the years from 607 down to 1800 A. D. Results obtained are summarized as follows.
(1) In general Mn, S and Cu content in steel is very low and probably these ancient nails were manufactured from wrought iron which had been produced from sand iron.
(2) There are a few specimens with nearly the same content of Mn and S as those in steel used at present. Presumably they have been produced from iron ore, not from sand iron.
(3) Even in the same specimen, C content is remarkably different depending upon the position. Consequently, unevenness in hardness is also noticeable. From these facts it is presumed that these specimens were made by forging several, pieces of crude iron which had contained respectively different C contents.
(4) The content of alloying elements are extremely slight therein but the content of iron slag is very high.