Annealing and aging of interstitial C in {alpha}-Fe, as measured by internal friction
- Falconbridge Ltd., Ontario (Canada). Metallurgical Technology Centre
- McMaster Univ., Hamilton, Ontario (Canada). Dept. of Materials Science and Engineering
The diffusion of interstitial C in {alpha}-Fe has been studied by the dynamic mechanical relaxation method, and the isothermal aging kinetics of the removal of interstitial C by precipitation from its saturated state has been measured at several temperatures. The height of the Snoek peak is found to decrease according to the relation Q{sub max}{sup {minus}1}(T,t) = Q{sub max}{sup {minus}1}(T,t {yields} {infinity}) + {Delta}Q{sub max}{sup {minus}1}(T) exp {l_brace}{minus}t[k{sub 0} exp (E/RT)]{r_brace}, where t is the aging time, k{sub 0} a time constant, and E the activation energy for the precipitation of C atoms. The anelastic relaxation time is independent of the amount of C in {alpha}-Fe and varies according to {tau} = 3.45 {times} 10{sup {minus}15} exp [80.0 (kJ/mol)/RT]. The diffusion coefficient varies according to D = 6.61 {times} 10{sup {minus}3} exp [{minus}(80.0/RT)] cm{sup 2} s{sup {minus}1}, over the temperature range 303 to 357 K. The effect of chemical composition on k{sub 0} has been determined and a procedure for determining the constant of proportionality between Q{sub max}{sup {minus}1} and the amount of dissolved carbon in steel is described. A concept of accumulated equivalent aging time is introduced and theoretically justified on the bases of time-temperature superposition of aging effects. Calculations and experiments show that a substantial decrease occurs in the C content of steel when it is heated to high temperatures and that this effect alters the shape of the Snoek peak.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 382500
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 27, Issue 9; Other Information: PBD: Sep 1996
- Country of Publication:
- United States
- Language:
- English
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