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INTERNAL FRICTION CHARACTERISTICS OF INTERSTITIAL CARBON AND NITROGEN IN
α-IRON
T. Gladman, R. Barker
To cite this version:
T. Gladman, R. Barker. INTERNAL FRICTION CHARACTERISTICS OF INTERSTITIAL CAR- BON AND NITROGEN INα-IRON. Journal de Physique Colloques, 1971, 32 (C2), pp.C2-57-C2-58.
�10.1051/jphyscol:1971211�. �jpa-00214537�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 7, tome 32, Juillet 1971, page C2-57
INTERNAL FRICTION CHARACTERISTICS
OF INTERSTITIAL CARBON AND NITROGEN IN a-IRON
by T. GLADMAN Ph. D., F. I. M. and R. L. BARKER, L. I. M.
1. Introduction. - Complex interactions of inter- stitial and substitutional solutes in ferrite are well documented [l-51. The Mn-N interactions have been studied extensively [2-4, 6, 71 and in the present work, the results of Ritchie and Rawlings [3] have been used as a means of interpreting the internal friction curves for mild steels. The Ritchie and Raw- lings model indicates that there are five nitrogen peaks and two carbon peaks in this class of steel. Details of the seven peaks are given in Table I.
Peak No. I I1 I11 I V V VI VII
- -
Tp (OC) at1
c. p. s. - 8.5 3.5 10 24 30.5 40 62 Q cal/mol 15.8 16.7 17.5 18.6 19.3 20.1 21.9
The activation energies of peaks I, 11,111, V and VII were assumed from the Zener relationship. Peaks I to 111 are believed to be associated with pairs of manganese atoms and nitrogen atoms. Peak V is belie- ved to be associated with single manganese atoms and nitrogen atoms. Peaks IV and VI are the normal Snoek peaks for nitrogen and carbon respectively in a-iron. Peak VII is believed to be associated with carbon pairs.
2. The effect of manganese content. - The effect of increasing the manganese content of steels contai- ning
-
0,005 wt % N on the internal friction curves is shown in figure 1. Peak V was dominant at 0.3 % MnINTERSTlTlALS IN FERRITE
0 l I 1 I
- 5 0 0 5 0 100
T E M P E R A T U R E ' C
FIG. 1. - Effect of manganese on the internal friction charac- teristics of low carbon steels.
indicating a strong association between nitrogen and manganese even at this low manganese level. As the manganese content increased above 0.3 %, the contri- bution from peaks 1-111 increased. The aggregate peak temperature was higher than the normal Snoek peak temperature at 0.3 % Mn, but decreased to a temperature well below the Snoek peak temperature at 1.4 % Mn.
The effect of manganese on the damping contri- butions from the nitrogen peaks are illustrated in figure 2. The normal Snoek peak (peak IV) decreased
Proportion of N ~ t r o g e n 0 ' 5 -
Damping
X Peaks 1-3 (Mn-N - M n ) - / ' /
'
1 z e o k 5 ( F e - N - M n )
---
0.5 1.0 1.5
% Manganese
FIG. 2. - Effect of manganese on nitrogen damping.
continuously with increasing manganese content ; peak V increased with increasing manganese content up to -- 0.4 % Mn and then decreased with a further increase in manganese content. The sum of the heights of peaks 1-111 increased continuously with increasing manganese content.
Additiocal peaks have been observed at higher temperatures by Nacken and Kuhlmann [7], but these only occurred at high nitrogen levels and may well be associated with nitrogen pairs.
3. Mechanisms of damping. - Peak V has been attributed to interstitial damping by nitrogen atoms associated with single manganese atoms as shown in figure 3a. As the manganese content is increased above a critical level, then the probability of manganese atoms existing as single atoms decreases, and combi- nations of manganese atoms can be expected, such as are shown in figure 3b and c. This may give rise to peaks 1-111. In figure 3b, the nitrogen atom can vibrate around the manganese pair without changing
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971211
C2-58 T. GLADMAN PH. D., F. I. M. AND R. L, BARKER, L. I. M.
'x
(a) Fe - N - Mn
0 Fe atom
Mn atom
X N site
Mn atoms are nearest neighbours
( c ) Mn - N - Mn Mn atoms are second nearest neighbours
FIG. 3. - Interstitial-substitutional interactions.
its position with respect to the pair. This is an impor- tant point because the relaxation time associated with the pairs peak is shorter than that of the normal Snoek peak and yet manganese retards the long range diffusion of nitrogen. Enrietto [4] and Wolf and Han- Ion [8] have suggested that nitrogen atoms will not jump away from manganese sites during the internal friction experiment even with quite modest binding energies. Nacken and Kuhlmann [7] suggested that nitrogen jumps from Fe-N-Mn sites to Fe-N-Fe sites may cause one peak and the reverse jump may cause another peak, but Nowick [9] has suggested that one lattice defect will give a single relaxation time.
The origins of peaks 1-111 are believed to be asso- ciated with defects involving two or more manganese atoms, such as are shown in figure 3b and c, there
being one relaxation time for each (( defect D, as sugges- ted by Nowick [9]. The centre nitrogen site shown in figure 3c may be unfavourable for the nitrogen atoms because the manganese atoms are larger than iron atoms, and would compress this site. The nitrogen atoms could occupy the outer sites shown in figure 3c and could vibrate around the manganese pair. These are obviously other arrangements of manganese atoms besides those shown in figures 3b and c which could possibly give other peaks.
It is interesting to note that there are no comparable complexities in Fe-Mn-C alloys [lo], which suggests that the association of interstitial nitrogen with man- ganese may not be simply a result of elastic interac- tion but may in part be caused by chemical interaction.
The relationships between peak height and intersti- tial contents associated with each peak are not known precisely. Nacken and Kuhlmann [7] suggested that the proportionality constant for each of their peaks was approximately constant. However, other work [6, 111 has indicated that the proportionality constant for peak V is lower than that for the normal Snoek peak, but that of peak 11, which is generally the domi- nant member of the low temperature peaks, is higher than that of the normal Snoek peak. These observa- tions were all made on alloys with ferrite grains of
N 10-20 pm diameter. As yet, there appears to have been no systematic study of the relaxation strengths and the effect of ferrite grain size on the proportio- nality constants relating the peak height to the intersti- tial content.
References
[I] DIJKSTRA (L. J.) and SLADEK (R. J.), Trans. AIME, [7] NACKEN (M.) and KUHLMANN (U.), Arch. f. d.
1953, 197, 69. Eisenhutt, 1966, 37, 331.
[2] FAsT tJ. D.1, M E I J E R I N ~ tJ. L.) and VERRIJP (Ma Be), [8] WOLF (J. D.) and HANLON (J. E.), Trans. A. S . M, 1961, Mktaux, Corrosion Ind., 1961, 36, 112. 53, 955.
f3] RITCHIE (I' G') and tR')> Met., 1967, [9] N o w I C ~ (A. S.), Internal Friction Conference, Man- 15,491.
[4] ENRIETTO (J. F.), T r m . AIME, 1962, 224, 1. chester, 1965.
[5] PERRY (A. J.), MALONE (M.) and BOON (M. H.), [lo] FAST (J. D.), Iron and Coal ~ r a d e s Review, 1950,
Journ. App. Phys., 1966, 37, 4 . 160, 837.
[6] GLADMAN (T.) and PICKERING (F. B.), Journ. Iron [ l l ] COOPER (G. J.) and KENNEDY (R.), Journ. Iron Steel
Steel Inst., 1965,203, 1 . Inst., 1967, 205, 642.
