Sy nopsis H igh tem/Jerature tellsile deformatioll of a 0. / 6°o C steel was st1ldied over a wide rallge of straill rates from 18 to 2.73 x /0-• sec-I ill the austellite ral/ge. From metallographic obsenatiol/s al/d flow stress measuremel/ls it was revealed that the first flow stress maximum, a~I' the shape of the a-e curves, alld tne deformed structure ill high strail/s were unique .functiolls of the Z eller-Hollom on parameter, Z, which was calculated 01/ all activatioll energy for deformation (68.5 kcal/mol). The distillct structural challges occurred ill the initial hardenil/g stage below tlte strain at aM, al/d the r grain structures for high strail/s were of a mixture of fill e grains alld comparatively coarse graills, and the grain boul/daries of the latter were wavy on the whole regardless of z. 1t was cOl/sidered then that the deformatioll if a 0. 1 6~o C steel ill the r ral/ge was cOl/trolled ~Y the dynamic recrystallization p rocess assiJted by the migration of vacal/cies. al/d that this fact was closely related to the shape of the a-e curves, I/otably a sharp stress maximum or stress oscillatiol/s in low strain region followed by steady-state deformatioll in high strain region. I,Vhether a a-e curve was the stress peak type or the stress oscillation type depel/ded critica lljl 01/ the relative difference between tlze il/itial r grain size b~rore d,!/ormaliol/ al/d that dynamically rerrystallized under a high strain.
The effect of annealing on stress-strain curves of an Al-3% Li alloy which had been overaged and then cold-rolled was studied, by comparing with the changes in lattice constant and electrical resistivity and also in the transmission electron micrographs. A sharp yield drop followed by the propagation of Luders bands was observed when the Al-3% Li alloy wasThe above results were discussed in terms of general requirements for the yielding.It was concluded that the decomposition of the precipitates, AlLi, was not always necessary for the occurrence of the sharp yielding but promoted the pinning of dislocation sources near the boundaries.
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