TEMPERATURE AND STRAIN-RATE DEPENDENCE OF THE TENSILE FLOW-STRESS OF HIGH-PURITY ALPHA-IRON BELOW 250-K .2. STRESS TEMPERATURE REGIME-II AND ITS TRANSITIONS TO REGIME-I AND REGIME-III

Successive tensile measurements at different temperatures with correlated stress-relaxation tests on high-purity alpha-iron monocrystals reveal as one of the characteristic features of stress/temperature regime II of the flow stress, between about 130 and 240 K, violations of a simple Arrhenius relation for the strain rate at the transitions from regime I at higher and to regime III at lower temperature. Mainly for this reason a new interpretation is suggested for regime II, which is based on the results of Part I, according to which kink-pair formation on a {110} plane can be regarded as the elementary step of screw-dislocation motion in regime III. But screw dislocations due to their polarity can move on by repeating this elementary step only, if intermittently a second, polarity reversing process occurs. Regime II as well as regime III are, therefore, accounted for by assuming two alternating, thermally activated processes to take place consecutively in both regimes. A successful data analysis along this line provides rather detailed information on the second process.