Cold-Shortness

cold-shortness

Brittleness in metal at room temperatures.

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Cold-Shortness 

in metals, the tendency of brittleness to appear or to increase substantially with a reduction in temperature. Cold-shortness is associated with a substantially increased yield point, caused by difficulty in the movement of dislocations; starting at a specific temperature (the brittle temperature), brittle failure occurs before the onset of plastic flow. Cold-shortness is inherent in low-alloy steels, tantalum, tungsten, chromium, molybdenum, and some other metals having body-centered cubic lattices, as well as in alloys of such metals. It is promoted by the introduction of admixtures, which, in conjunction with the compression of the crystal lattices, causes internal stresses to increase as the temperature is lowered. The transition temperature from ductile fracture to brittle fracture depends on the heat-treatment conditions, the grain size, the loading rate, and the magnitude of the stress concentrations.

Cold-shortness is most often evaluated by tensile impact tests of notched, prismatic specimens, which determine strain energy and failure energy. The tendency toward cold-shortness can also be evaluated from the temperature at which ductility is sharply reduced or from the surface area of a fibrous fracture. Cold-shortness is of particular importance for structures used under the temperature conditions characteristic of northern regions, equipment used in space, lunar vehicles, and hydrogen engines. It can be reduced by the elimination of harmful impurities, heat treatment, and alloying.

S. I. KISHKINA