Control of slag and inclusions in traditional Japanese iron- and steelmaking

Abstract

In traditional Japanese smelting and forging, three characteristic technologies can be identified that may provide a basis for a new process concept in the production of iron and steel. First, ironsand, the use of which is problematic in modern ironmaking, was used instead of ironstone. The titanium oxide present was effective for keeping the slag fluid and increasing the carbon content of the product, thereby decreasing the activity coefficient of FeO in the slag. Second, two types of operation were carried out with almost the same type of furnace. In one of the operations, mainly molten pig iron was produced and, in the other, steel bloom (>50 wt-% of total product) and molten pig iron. The main controlling factors were the type of raw material (titanium content of ironsand) and the oxidising potential in the furnace, which influenced the degree of carburisation and decarburisation of the iron. Third, it is thought that traditional Japanese steel is the best material for Japanese swordmaking. This was confirmed by an experiment with different materials. In the case of traditional Japanese steel, both the homogeneity of the carbon distribution and the inclusion content in the original material can be improved by the forging process, since the degree of contamination during forging is less. With modern steel, weldability in forging is adversely affected by contamination during forging. This means that the complex combination of material and total process is important for producing the particular product.