EFFECT OF RAW METALS AND MELTING METHOD ON Ni-Cr ALLOYS

Abstract

Ni-Cr alloys and Nimonic 80-alloys were prepared by using raw metals of various purities by melting rapidly or slowly in a Tammann furnace. Some mechanical and metallographical tests were made on the alloys. The results obtained are as follows.
(1) Even in a Tammann furnace, rapid melting enables C-content in Ni-Cr alloys prepared from raw etals of high purity to be lower than that in commercial Nichrome-alloys melted in a high frequency induction furnace. In case of slow melting or high Cr-content, for instance 40% Cr, in alloys, the preparation of alloys in the Tammann furnace is inadequate because of the carburizing action of the atmosphere in the furnace.
(2) The lower the purity of raw metals becomes, the more both the C-content and the amount of inclusions in alloys increase. (3) It is found in Ni-Cr alloys prepared from low grade chromium that both the hardness and the recrystallization temperature are raised and that precipitation hardening may occur at 500-550°C.
(4) The creep property of Nimonic 80-alloys is superior in the case of the alloy prepared from high purity metals, which is lower in C-content, lower in hardness at solution-treated state, less in amount of inclusions and coarser in grain size than in those of alloys prepared from low grade metals.