Characterization of physico-mechanical properties of Z-phase strengthened ferritic steels using internal friction measurements in the range 25 ÷ 750@C

The present research is dealing with the comparative study of inelastic/elastic behavior of reference ~12%Cr steel ZL3 and three new trial steels ZU1, ZU2, ZU3, with different ratio of alloying elements and equal content of Cr, using internal friction measurements. The samples were examined in as-received condition and after additional electric current tempering at 700@C under different fixed external mechanical tensions. The measurements of internal friction Q-1(T,Ɛ) and shear modulus G ~ f2(T,Ɛ) spectra were conducted in a vacuum (10-4 torr) in the temperature range 25÷750@C, using the relaxometer at the frequencies 1÷5Hz and amplitudes of deformation 10-5 ÷ 10-3. The values of deformation critical amplitudes for dislocation breakaway (first critical amplitude Ɛ ;1) and for microplastic deformation beginning (second critical amplitude Ɛ2) were determined in addition to the activation energies of relaxation processes in the investigated steels. It is shown that all the three trial steel samples in as-received condition exhibit considerably higher values of Ɛ2 in comparison to those of reference ZL3 steel. Among them the ZU3 steel has the highest values of Ɛ1 and Ɛ2, and demonstrates the visible (~40%) increase in strength characteristics at elevated temperatures (600÷750@C), achieved by the additional electric current tempering under mechanical tension.