Determination of total nitrogen in solution in Fe-Mn-N alloys by internal friction
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The internal friction of 22 Fe-Mn-N alloys with 0 to 2 pet Mn and 23 to 170 ppm N was measured at 1 Hz and temperatures between 220 and 525 K. The Snoek spectra were r e solved into sets of Debye peaks of height Pi. This resolution was accomplished with five independent sets of Debye p a r a m e t e r s (number of peaks, activation energies, and peak temperatures), which were obtained from the literature. The five resulting sets of Pi were correlated with the chemically determined nitrogen (Nch) by multiple r e g r e s s i o n analyses. A high degree of correlation was obtained with all five sets of p a r a m e t e r s . For ease of calculation, we recommend resolving the spectra into the three Debye peaks d e t e r mined by Couper and Kennedy. The r e g r e s s i o n equation obtained by applying these p a r a m eters was Nch (ppm) = 11.9 + 2.33pt + 0.83p2 + 0.75Ps with a standard e r r o r of estimate of 6.8 ppm. The first t e r m on the right-hand side was interpreted as nitrogen precipitated by t r a c e s of r e f r a c t o r y metals. The sum of the last three t e r m s on the right was interpreted as the total nitrogen in solution. A procedure for determining total nitrogen in solution in Fe-Mn-N alloys is recommended and described in detail.
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quantitative determination of nitrogen and carbon in solution in steel has been one of the more challenging applications of internal friction. Although internal f r i c tion has been used for over two decades to measure dissolved nitrogen and carbon in binary Fe-N and Fe-C alloys,* the interaction between manganese and nitrogen atoms a-" has Interfered with the quantitative determination of nitrogen in solution in the common grades of steel. For thl8 reason, a procedure for measuring dissolved nitrogen tn Fe-Mn-N alloys can also be applied to many steels. The theory of substitutional-interstitial (such as Mn-N) Interactions has been discussed by others. ~-7 Our purpose here is to consider, from a purely emptrleal standpoint, the determination of the total nitrogen in solution (N) in Fe-Mn-N alloys, Two approaches have been applied to t h e m e a s u r e ment of N in Fe-Mn-N alloys. The f i r s t approach is based on the resolution of the complex internal f r i c tion spectra of such alloys. Several investigators have resolved those spectra into a series of perfect Debye peaks, i.e., by the equation 4,a,9 Q-*(T) • 10' = ~ P i sech
x 10' = ~ P i ', T / seth
where Q-* (T) is the measured internal friction above background at temperature T, Pi is the height of the i-th Debye peak in t e r m s of Q-*• 10 4, Hi is the activation energy of t h e i-th Debye peak, T is the t e m p e r a ture in degrees Kelvin, T i is the peak temperature of the i-th Debye peak, and R is the gas constant. These E. T. STEPHENSON is Senior Research Engineer in the Research Department o f the Bethlehem Steel Corporation, Bethlehem, Pa. 18016. Manuscript submitted March 4, 1974. METALLURGICAL TRANSACTIONS
mann a 7
/=t
while according to Couper and Kennedy'*
Table I. Reported Parameter
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