Book excerpt: There appear to be two ways in which interstitials promote brittle behavior in Groups V-A and VI-A refractory metals: (1) By locating at the grain boundaries in the form of segregates of precipitates, promoting grain-boundary rupture and crack initiation; and (2) In solid solution by inhibiting dislocation movement and reducing the resistance to crack propagation. Both embrittling effects operate in Group VI-A metals; whereas, only the latter is significant in the Group V-A at the levels of purity currently achieved. The problem of reducing the low-temperature brittleness of Group V-A metals is readily solved through the purity route. Purification of Group V-A metals to interstitial levels well below the solubility limits may be readily accomplished either in the initial purification of the base metal or during melting or consolidation. There are three possible routes to solving the problem of the embrittling effect of interstitials on the Group VI-A metals: (1) the purity route, (2) through working, and (3) through alloying (thermodynamically through strong scavengers, by additions which modify the electron bonding, and via grain-refining dispersions). (Author).