Pieces of α-brass (Cu 70, Zn 30) wire of l mm in diameter are cold-worked to various degrees by rolling and twisting, and annealed at a constant rising rate of 1.7°C/min from the room temperature to 4600°C. The rigidity is measured by means of a torsion pendulum at various temperatures during the annealing.
(1) The rigidity of annealed specimen decreases slowly in a linear manner with rising temperature up to about 240°C, and departs rapidly from this linear relation at this temperaJture.
(2) There is a marked difference in the aspect of the temperature change of rigidity :according to either the specimens are cold-rolled or cold-twisted. In cold-twisted specimens the rigidity recovers rapidly at first up to about 60°C, but in cold-rolled specimens this is not observed. In cold-twisted specimens the rigidity increases gradually from this temperature, up to a certain temperature θ
1, but as the temperature rises higher than this value, the rigidity becomes almost constant up to a certain temperature θ
2. On the other hand, in cold-rolled specimens the rigidity increases gradually from the beginning of measurement up to θ
1 and within the temperature range of θ
1 and θ
2 the rigidity increases at a moderate rate with rising temperature. In either case, the rigidity begins to increase at the temperature θ
2 at which the recrystallization begins.
(3) For all specimens tested, the rigidity decreases at first and reaches a minimum, after which it increases gradually as the degree of cold-working steadily advances. But the mode of change is different for cold-rolled and cold-twisted specimens.
(4) The change of the rigidity caused by cold-working may be explained as the combined, effect of three factors, that are, lattice distortion and rotation of crystal grains, both of which make the rigidity decrease, as well as the fragmentation of the grains which increases the rigidity.
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