The purpose of this lecture is to survey the post-war development of special steels. Special steels are usually melted in an electrical furnace, which has a tendency to become larger and larger in its scale. In the United States the furnace with a capacity of 200 tons is used widely. In Japan also, a furnace with a similar capacity will be constructed in 1961.
In recent years the method has been developed to melt high grade special steel in vacuum; the Consel arc-melting method, in particular, has a prospect to be advanced greatly in the future.
The demand for free cutting steels has increased as a result of using high-speed machine tools, and the study of lead-containing steel has been developed. The remarkable progress of the electric welding method has made it possible to construct buildings,bridges and ships etc. by welding, and various kinds of high-ten steels with high yielding strength have been developed in many countries.
As to the steels for low temperature use, the study has been advanced on steels with low transition temperature. New discoveries have also been made in the field of tool steels, such as high-C high-V high-speed steel, die steel, casting tool, and hobbing steel. The kind, the amount, and the nature of carbides contained in these steels are made clear by academic studies.
The demand for stainless steels has been increasing, and for different uses, different types of stainless steeles are being developed: age-hardening type with high strength, high-C high-Cr type for tools, and high-grade type for chemical industry. For use in an atomic reactor, studies have begun on a special stainless steel with a small absorption cross-section of neutron and the work is progressing successfully.
There is also a progress in the study of heat-resisting metallic materials: steels for turbine blades, high-pressure boilers and engine valves, and alloys with high-temperature heat-resistance for gas turbines.
Finally, the lecture refers to the new development in the case hardening of steels.
