1. Special-Steel Making iu Japan
In Japan special steel makin was started in 1882 by means of the crucible furnace melting, and since 1914 the electric arc furnace steel-making has been studied. The production of arcfurnace steel increased year by year, and subsequently in 1938 crucible-furnace steel was wholly replaced by electric furnace steel.
In 1931 steel making by means of induction furnace was. started.
At first the capacity of the arc furnace was, as small as, not over 3t. However., towards 1932 it was developed to 5t-10t, and a few 15t and 30t furnaces were erected. About 1937 many furnaces rated 10t-15t were erected. Accordingly the promotion reached to the maximum amount of 2,258,000t, of which the electric furnace steel occupied 75%, in 1944.
After the war the production suddenly decreased to only 80,000t, but during the Korean war it increased to 300,000t.
In 1954, Japan had 142 arc furnaces, whose total capacity was 1,100,000t, and 75 induction furnaces, whose capacity 140,000t.
Owing to the investigation of the Research Institute for Ion, Steel and Other Metals and the 19th Sub-Committee of the Japan Society for the Production of Science, the practice of Special-Steel making of Japan was remarkably improved and steels of good quality are now made by overcoming the bad conditions of raw materials and refractory materials.
2. Development of Electric Furnaces
The range of the transformer capacity, was 300-400 KVA/t, but the recent practice tends towards utilizing higher voltage and larger transformer capacity aiming at quick melting. In order to control electric fluctuation, the “Amplidine” system is in use.
An electric induction stirrer is now studied for stirring the bath in order to obtain both the uniform chemical composition and good quality.
3. Basic Arc Furnace Process (referring constructional steel and case-hardening steel)
(a) Oxidizing Period:
In the early stage until about 1945, active boiling by adding the ore was not in practice. But between 1936 and 1940 some light boiling practice was introduced, and after 1940 the violent boiling was carried out adding ore 20-30kg/t. Since 1951 the oxygen lancing has been applied to the melting resulting in a success to produce low-hydrogen content, good steel and Iow-carbon stainless steel.
(b) Reducing Period:
In the early stage until about 1935, reducing was controlled only by the carbide slag process. From about 1936 the white slag process was adopted. Since about 1940, the practice has changed to the following: After refining the oxidizing slags, a few deoxidizing materials such as ferro-silicon, calcium-silicide and aluminium are added in order to force the active deoxidizing reaction, then the slag was controlled to be white one of weak diffusion, thereby to refine the steel. It is important to lower the content of hydrogen in steel to obtain sound ingots.
It should be noted that the quick method of hydrogen analysis was invented by Japan Special Steel Co., Ltd. By this method they control the furnace pactice in order to lower the hydrogen content under 7cc/100g for medium-and low-carbon or alloy steel and 11cc/100g for 13%Cr stainless steel. They are now obtaining gpod, sound ingots by the method.
4. Ingot Making
Exothermic hot-topping mixtures are used for the purpose of obtaining larger yield, and recently the electric arc hot-topping process is applied.
The continuous casting process, comprising William's process and Rossi-yunghan's process, is now planned in some works in Japan.
It is important to eliminate the hair cracks or sand marks from steel. As it was found that the process of casting the ingots was partly responsible for this failure, the method of teaming practi is now studied.