Effect of purity on the structure and properties of molybdenum

Conclusions

• 1. With reduction of the melting rate in a vacuum are furnace from 99 to 6 kg/h (hearth 100 mm in diameter) and an increase in the number of passes in zone refining from two to five (speed of refining 4 mm/min) the oxygen concentration in molybdenum decreases from 29·10⁻³ to 1·10⁻³ wt. % and from 1·10⁻³ to 0.6·10⁻³ wt. % respectively. At the same time, the molybdenum is also notably freer of other impurities.

• 2. It was found that the ductile and strength characteristics of molybdenum in the deformed condition and also the strength characteristics in the recrystallized condition are independent of the oxygen concentration within limits of 0.001–0.029%; the ductile characteristics of recrystallized molybdenum improve with increasing purity and reach values of δ=29% and ψ=36% at 20°C in the purest molybdenum (0.001% O₂).

• 3. The precipitates of second phase in the cast and recrystallized molybdenum of a compound of molybdenum and oxygen that is distributed as separate inclusions primarily in the grain boundaries. An increase in the purity of molybdenum reduces the number and changes the shape of the inclusions in the grain boundaries.