MECHANICAL PROPERTIES OF HIGH PURITY IRON AT LOW TEMPERATURES.

Abstract

Mechanical properties of high purity irons were investigated by tensile testing at temperatures from room temperature down to 4. 2 K. Specimens with the residual resistivity ratio (RRR**H) of 1800 were brittle and fractured at grain boundaries at 4. 2 K. Specimens with RRR//H of 3600, of which the grain structure was almost of the bamboo type, were deformed by slip and often showed complete ductile fracture even at 4. 2 K. This is the first observation of slip at 4. 2 K without pre-straining at high temperatures in a coarse-grained iron. Specimens with RRR//H of 5000, of which the grain structure was of a well-developed bamboo type, cleaved at 4. 2 K, and never showed grain boundary fracture. Some plastic properties were investigated on specimens with RRR//H of 3600 and 6000.