On the metallurgy and manufacture of cast metallic heat resistant alloys as components for powder processing applications

摘要

The reduction of oxides of refractory metals is usually carried out at high temperatures using a reducing furnace consisting of pusher tubes, which serve as a containment for the boats comprising the powder. Indirectly fired rotary kilns are also employed in high temperature materials processing of metallic and ceramic powders. These applications demand the usage of heat resistant alloys for such components. Material property requirements for these components are essentially a combination of creep strength and oxidation resistance. Cast heat resistant Ni-Cr-Fe alloys with austenitic matrix and strengthened by strong carbide formers provide the necessary creep resistance. Microalloying additions lead to high temperature strength enhancement. Oxidation resistance is provided by chromia (Cr_2O_3) scale. For even higher temperature applications, a new metallurgy with alumina (Al_2O_3) oxide scale has been developed. This contribution shall focus on the metallurgy necessary for the attainment of desired properties and the manufacture of such components using the horizontal centrifugal casting process.