INFLUENCE OF THE NITROGEN CONTENT ON THE INTERNAL FRICTION OF Fe-16.6 wt % Cr ALLOYS

Abstract
Using N₂-H₂ mixtures, controlled quantities of nitrogen were introduced in pure iron-chromium alloys. The internal friction was measured during heating and cooling on a 1100°C as quenched sample between room temperature and 400°C. A maximum Q^-1_max was detected as soon as the nitrogen content was in the 130-200.10^-4 wt % range. At a frequency ν = 0.9 Hz, the temperature of this maximum T_m was slightly decreased from 270°C to 250°C when the nitrogen content was increasing. A martensitic phase appeared in the 1100°C as quenched alloy for a nitrogen content between 480 and 580.10^-4 %. Then an increase of the height of the maximum and a modification of T_m were detected. Below a 580.10^-4 wt % nitrogen content, the maximum was broad and a small reversible peak was detected during cooling. Comparing these results with those obtained on similar alloys containing carbon, the behaviour of these two interstitials in ferritic iron-chromium are discussed.