Study of inelastic/elastic properties and shear modulus of Z-phase strengthened ferritic steels in the range 25 - 750 ° C

This chapter deals with the internal friction study of inelastic/elastic behavior of the reference ~12%Cr steel, ZL3 and three new trial steels, ZU1, ZU2, and ZU3, with different ratio of alloying elements and equal content of Cr. The samples were examined in âas-receivedâ condition and after additional electric current tempering at 700°C, under different fixed external mechanical tensions. The measurements of internal friction Q- 1(T,ε) and shear modulus G ~ f2(T,ε) spectra were conducted in a vacuum (10-4 torr) in the temperature range 25 ÷ 750°C, using the laxometer 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 ε1) and for microplastic deformation beginning (second critical amplitude ε2) 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 âas-receivedâ condition exhibit considerably higher values of ε2 in comparison to those of reference ZL3 steel. Among them the ZU3 steel has the highest values of ε1 and ε2, and demonstrates the visible (~40%) increase in strength characteristics at elevated temperatures (600 deg · 750 deg °C), achieved by the additional electric current tempering under mechanical load.