2014 Volume 54 Issue 5 Pages 1059-1066
In Tatara process, steel “kera” and pig iron “zuku” were produced. Pig iron and low quality of steel “Bugera” in these products were decarburized with air by hand blowing to produce steel plates with low carbon content, called “Hochotetu” or “Waritetsu”. The decarburization in pre-modern refining process was called “Okaji” and composed of two processes of “Sageba” and “Honba”. In the Sageba process, pig iron was decarburized to steel with about 0.7 mass%C, called “Sagegane” and the yield was almost 100%. In the Honba process, the Sagegane was decarburized to steel with about 0.1 mass%C, called “Oroshigane”, without deoxidation and the yield was 60 to 70%. The Orosigane was promptly forged to make plates. Thus, the contents of oxygen in Hochotetsu was about 0.2 mass%. The Okaji process has been examined in the present work. In the Sageba process, pig iron was decarburized by FeO slag, called “Noro”, with CO gas bubbling at about 1400°C. In the Honba process, the temperature in furnace was kept about 1450°C. Sagegane was oxidized by oxygen gas in air to generate heat and the temperature of Oroshigane increased to near 1528°C. The temperature of furnace during Okaji process was carefully controlled by blowing rate and keeping moisture in hearth of wet charcoal bed. Water was sometimes poured during operation.