AN ANALYSIS OF CREEP BEHAVIOUR OF IRON-MOLYBDENUM SOLID SOLUTIONS

Specimens of iron base alloys with up to 4.3 at. % molybdenum have been strained between 500 and 1000°C at constant load corresponding to 0.5-20 kp/mm2 tensile stress. Stress and temperature dependence of the stationary creep rate have been determined using a technique of repeated load and temperature changes with an appropriate evaluation. A single function, {greater-than with dot}3 ~ σ3 sinh ( Vσ kT), represents in good approximation all creep rate data over the whole stress range, including literature data for pure iron. V is independent of strain, but decreases with increasing Mo content. Within narrow stress intervals, the above function may be approximated by simple power laws with stress exponents varying from 4 (low stress) to about 20 (high stress). The activation energy for creep, after proper correction, shows a pronounced peak at the Curie temperature, and approaches 65 kcal/mole above 850°C, but 100 kcal/mole below 650°C. Further results are given on the stress dependence of the sub-structure parameters as well as on the nature of transient creep within different stress regions. © 1969.