Papers - Theoretical Metallurgy - Influence of Gases on Metals and Influence of Melting in Vacuo (Abstract with Discussion. See also A.I.M.E. Tech. Pub. 470.)

When a metal solidifies, gas, initially present in solution, may be concentrated at the grain boundaries, leading to brittleness, or it may form solid compounds which, if localized at the grain boundaries, impair the properties. On the other hand, the solid compounds formed sometimes distribute themselves more or less uniformly, and hence may be relatively harmless. If metallic oxides are heated under a partial oxygen pressure less than that corresponding to the dissociation pressure of the oxide in solution in the melt, they will decompose and oxygen will tend to be eliminated from the melt. This paper presents data on the partial oxygen pressures of copper and nickel oxides over a wide range of temperatures; it also presents data regarding the amount and nature of the gases evolved in the vacuum melting of a 3500-kg. charge of nickel-chromium alloy and gives test values indicating the improvement in impact values ascribed to vacuum melting. The results of commercial experience with a 4-ton vacuum melting and casting furnace indicate that this method entails an increase in cost of about 10 cents per pound of ingot over orthodox practice, which may be justified for special products and may be lowered if hot metal is charged into the vacuum furnace. DISCUSSION (Howard Scott presiding) J. H. ScafF, New York, N. Y. (written discussion).—In the section of Dr. Rohn's paper describing the effect of melting -metals in vacuo, he says, "In this way plain copper, nickel and iron may be easily purified. For example, vacuum-melted copper does not contain any oxygen and for this reason it is never sensitive to hydrogen embrittlement." This statement is contrary to the results of our experiments at the Bell Telephone Laboratories on the effect of vacuum melting on the properties of copper. Several 150-gram samples of tough-pitch copper were melted in a vacuum of the order of 1 X 10-5 to 1 X 10-6 mm. Hg for 2 hr. Portions of the ingots obtained were swaged to 0.100 in., then drawn to wire 0.050 in. in diameter for physical and