江戸時代後期に製造された管打銃の金属組織と非金属介在物

Abstract

The metallurgical microstructure and nonmetallic inclusions in the steel barrel of a Japanese percussion lock gun fabricated in the late Edo period have been investigated. The purpose of this work is to obtain metallographic data of the Japanese percussion lock gun, and to clarify the manufacturing technique and raw material of the barrel. Test pieces are cut from the center and the muzzle of the barrel. The carbon concentration is determined by chemical analysis. The microstructure is observed using an optical microscope and a scanning electron microscope (SEM). The concentration of nonmetallic inclusions is obtained by electron dispersive X-ray analysis (EDS). The carbon concentration is 0.003~0.2 mass% for the center of the barrel and 0.028~0.2 mass% for the muzzle of the barrel. The distribution of the nonmetallic inclusions in the steel shows that the barrel is fabricated from a single steel sheet. Nonmetallic inclusions in the center of the barrel are of a plural phase consisting of FeO, Fe2SiO4 and calcium-and phosphorus-rich matrix oxide. Nonmetallic inclusions in the muzzle of the barrel are classified into two types: a plural phase consisting of FeO and the matrix containing Fe-Si-O grains and glass, and a single phase of glass. The difference in the metallurgical microstructure and nonmetallic inclusions between the center steel and the muzzle steel shows that the barrel is made of different carbon-content steels. Since Ti is detected from the nonmetallic inclusions, it is thought that Japanese iron sand is used as the raw steel to fabricate the barrel.