Effect of Phosphorus Content of Nanban-tetsu on Forgeability of Japanese Sword Making

Abstract

Nanban-tetsu is a steel which was imported into Japan by Portuguese or Spanish merchant ships in the end of Muromachi period (1392-1573). The steel was produced in India and called "Wootz steel". Nanban-tetsu steel was shaped in some forms of a gourd called "Hyotan", a oval called "Koban", a square timber called "Saijo", a semi-cylinder called "Tajo" and others. In 1613, one of the Japanese sword smith, Echizen Yasutsugu 1, first produced a sword using Nanban-tetsu steel. Since then, many sword smiths who lived in Echizen area (Fukui Prefecture) had used Nanban-tetsu steel as a material of Japanese swords. The steels produced using the "Nittoho-Tatara" furnace in Shimane prefecture has been examined by forge-welding as a function of phosphor content in the steels. It is concluded that "Hyotan" shaped Nanban-tetsu steel is not good for forging, "Saijo" shaped Nanban-tetsu steel is good for forging, "Koban"-shaped one is difiicult to forgeweld and "Tajo"-shaped one is intermediate.