A Study on Temperature and Strain Rate Dependences of Yield Stress at Low Temperatures in Pure Iron and Fe-Cr Alloys
1971 Volume 57 Issue 6 Pages 954-964
Details
1971 Volume 57 Issue 6 Pages 954-964
Temperature and strain rate dependences of yield stress in purified pure iron and Fe-Cr alloys, were studied mainly by compression tests in the ranges of -196-300°C of temperature and 10-5-10-2sec-1 of strain rate.
Relations between temperature (T), strain rate (ε) and frictional stress (σt), were established in the following manner:
ε=Cσnt exp(-E/RT)
This is applicable when at is in the range of 5-28kg/mm2. Activation energy E is hardly dependent on temperature, stress and chromium concentration, being about 15 kcal/mol. Strain rate exponent n, however, increases with increasing chromium content. It may be said that solid solutioning of chromium affects mainly n and C in the above equation, and further, that stress is chiefly attributable to entropy term rather than to enthalpy.
Softening effect by solid solutioning is presumed to be mainly due to the increase of the strain rate exponent with increasing chromium concentration, in other words, to the increase of activation volume.
