Some Theoretical and Practical Aspects of Gases in Metals

S I N C E Thomas Graham 1 discovered in 1866 t h a t a piece of meteoric iron heated in vacuum yielded 2.8 times its volume of gas, 2 the solubility of gases in metals has been the subject of a large number of investigations. While these studies have not as yet afforded more than a partial understanding of the nature of the processes by which gases are dissolved in metals, they have yielded considerable knowledge of those factors which determine the extent of such solubility, and thus of the methods by which the amount of dissolved gas can be increased or diminished. At the same time they have shown the importance of dissolved gases in determining not merely the behavior of metals in casting processes, but also the magnetic, mechanical, and chemical properties of metallic materials. It is proposed to discuss, in this paper, theories of the absorption of gases by metals and to review important work on this subject. T H E E F F E C T OF GASES ON THE PROPERTIES OF M E T A L S The importance of producing sound metals should interest every metal founder in the effects of dissolved gases. Any gas whose solubility is greater in the liquid than in the solid metal may cause the formation of blowholes. The formation of these blowholes, however, can be reduced or prevented by cooling the metal slowly enough through its freezing range to permit the escape of liberated gases. Iron saturated with hydrogen, for instance, will yield a sound ingot if cooled very slowly through its freezing point, while chill casting not only will make the metal porous but may cause an evolution of gas violent enough to throw metal from the mold.