Scientific analysis for ancient iron plate materials excavated from the Maisaki site

Parts of iron plate materials excavated from the Maisaki site at Tsuruga city of Fukui prefecture were analyzed by scientific methods of the element analysis and the metallographic observation. In the element analysis, a combustion infrared absorption method for determination of carbon and sulfur in iron plates, and a neutron activation analysis (NAA) for determination of 37 trace elements were used. In the metallographic observation, the metal structures were investigated by an optical microscope and an electron probe micro analyzer (EPMA). Carbon concentration in iron samples were low carbon steel or medium carbon steel of about 0.1-0.5%. The existence of ferrite and pearlite structures and non-metallic inclusions were observed in the samples by the optical microscope. An existence of titanium being an index of the origin of Japanese iron sand was not confirmed in these non-metallic inclusions by the EPMA mapping images. As a ratio of arsenic (As) concentration to antimony (Sb) concentration, As/Sb value were less than 1.0, the origin of the samples were estimated, namely, it is concluded that the iron plate materials were brought in Japan from ancient Korea made from iron ore as a raw material. (author)