THE TENSILE DUCTILITY-TRANSITION IN MOLYBDENUM
Rept. for 30 Apr 1963-30 Apr 1964
MANLABS INC CAMBRIDGE MA
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An investigation was carried out to determine the nature of the tensile ductility transition in recrystallized molybdenum strip of three interstitialal contents. For a fine grain size, the tensile ductility transition temperature T sub d and the brittleness transition temperature T sub b were found to approximately coincide whereas with increase in grain size T sub d is raised and T sub b is lowered. The occurrence of a minimum in the fracture stress sigma sub F at T sub d appears to be associated with the temperature dependence of the necking stress Sigma sub n. Prestraining above T sub d, was found to result in as much as a 20 increase in sigma sub F as determined at temperature below T sub d. In general, the mode of fracture initiation was found to be intergranular at T sub d or below and cleavage above T sub d. For a test temperature above as well as below T sub d, crack initiation appears to be the controlling step in fracture. Considering sigma sub F as a flow stress corresponding to the fracture strain epsilon sub F, the variation of sigma sub F with temperature above T sub d was predicted within about 15. Based on a modification of the Cottrell relation for crack initiation, the increase in sigma sub F above T sub d is associated with a decrease in both the flow locking parameter k sub f and the effective grain size.