The authors measured resistances to deformation, “Kf”, of low carbon steels, with contained 0.02-0.09% carbon, nickel and 0.0-1.5% chromium, and of an ultra low carbon 2% Al iron at various temperatures i. e. from room temperature to 1, 000°C. The order of strain rate was of 102/sec. Deformation was done by a “Counter-blowing” type forging tester.
The results are as follows.
(1) Below 500°C., the strain-rate and temperature dependence of the “Kf” are large. The value of log Kf/ log ε is about 0.2. The difference of “Kf” between at room temperature and at 500°C. reaches 25-30kg/mm2. It is concluded that this phenomenon has the same nature as that of yield and flow stress of iron below room temperature at low strain rate i. e. 10-4-10-3/sec. It is also found that thetemperature dependence of “Kf” of some 0.05% carbon steels containing nickel, 0.02% carbon steel and 2% Al iron decreases between 100°C and room temperature. However, the reason is yet unknown.
(2) From 500°C to 600°C, “Kf”-temperature curves show a peak in the case of carbon steel. It is concluded that at this strain rate and temperature the velocity of moving dislocations is favourable for the dislocations to be dynamically locked by Cottrell atmosphere, the need of dislocation multiplication increases, and therefore, work hardening rate is much larger than at other temperature. It is also found that the strain-rate dependence becomes 1/3 smaller.
(3) This phenomenon is disscussed from the point of view of the interaction between interstitials and dislocations, whereas the dragging mechanism does not seem to explain it well.
(4) At γ-α coexisting temperature range, no peak of “Kf”-temperature curves is found at strain ratt -102/sec., but a peak is found at lower strain rate. It is concluded that as the strain-rate dependence of “Kr” of α-phase is 2-3 times larger than that of γ-phase, any peak is not found at the higher strain rate.
(5) The strain-rate and temperature dependence of “Kf” of the 2% Al iron are very small between 500°C and 900°C. Above 900°C., they become larger, and it seems reasonable to think that self-diffusion or recovery becomes effective for deformation process.