Arc-melted molybdenum, in which the main impurity is carbon, and high purity molybdenum were fully recrystallized and annealed below 1100 K under various atmospheres. They were tested by bending. The ductile-brittle transition temperature (DBTT) of the arc-melted molybdenum is reduced markedly by the annealing, while that of the high purity molybdenum is not affected. Auger electron spectroscopy (AES) of the fractured surface reveals grain boundary segregation of carbon in the arc-melted molybdenum. The ductility improvement is due to carbon segregated at grain boundaries. AES measurement does not reveal any segregation of impurities in the high purity molybdenum, which fractures along grain boundaries. The DBTT is rather high, about 280 K. Purification of molybdenum to a level of 1 at.ppm of interstitial impurities does not prevent the intergranular fracture.
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