Stability of structure and mechanical properties of molybdenum under prolonged influence of temperature and stress

Abstract

1. In the investigated range of temperatures (800\2-1000\dgC) the variation in the mechanical properties of deformed low-alloy molybdenum as a result of annealing is determined mainly by the annealing temperature. Further increase in the annealing time from 10 to 500 h and the application of a load reaching 0.75 σ500 during the annealing process and little effect on the mechanical properties of molybdenum. 2. If the annealing of deformed molybdenum is carried out in a range of temperature in which primary recrystallization occurs, the additional application of a load during the annealing process somewhat increases the recrystallization rate and reduces the strength characteristics. 3. Under the influence of the applied load a cellular structure is again formed in part of the recrystallized grains, and a dynamic equilibrium is established between the deformation and recrystallization processes. With the selected level of stresses (σ≤0.75σ500) the hardening resulting from the formation of substructure under the influence of a load during the annealing process is small, since together with the grains in which the cellular structure is formed a large amount (50% or more) of recrystallized grains without the cellular structure remains. 4. The influence of a load during the annealing of deformed molybdenum does not give rise to a significant increase in the temperature corresponding to the transition to the brittle state. 5. By introducing disperse particles of a second phase it is possible to reliably stabilize the cellular structure in molybdenum at 1000\dgC under conditions involving the action of considerable loads for prolonged periods. Under these conditions the stress-rupture strength increases by several times.