THE BRITTLE FRACTURE OF METALS AT ATMOSPHERIC AND SUB-ZERO TEMPERATURES

Abstract

Brittleness is a quality of a solid which cannot be considered apart from fracture, because fracture is always implied. A material is described as brittle when it breaks while undergoing elastic deformation. Very few industrially useful metals fall into this category; most exhibit some degree of ductility, the antithesis of brittleness. Yet, as will be demonstrated, a metal may deform plastically and break in a brittle manner. Brittleness is not a specific property of any solid, nor is a low temperature the only factor which may cause a ductile metal to break in a brittle manner. While an endeavour has been made to limit the scope of this review to a discussion of the effect of atmospheric and subzero temperatures upon brittleness, it is neither possible nor desirable to exclude reference to other known causes. Absence of ductility, due to composition, heat-treatment, previous cold work, &c., can usually be detected by well-established mechanical tests. A phase or allotropic change, or precipitation, which takes place at low temperatures and produces permanent changes in structure and physical and mechanical properties can be controlled by the same methods. Brittleness which manifests itself only under certain conditions of stress and temperature must be investigated by special methods of testing. Moreover, unlike the more usual forms of brittleness just enumerated, it is transient; it disappears when the temperature is raised.