Influence of Manganese and chromium on the segregation kinetics of carbon and nitrogen to the dislocations in heavily de
- PDF / 331,706 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 38 Downloads / 144 Views
ecent works, it was shown that the measurement of thermoelectric power (TEP)[4] can be used to study the segregation of the interstitial atoms to the dislocations during an isothermal static strain aging performed after cold-rolling and to evaluate quantitatively the amount of segregated atoms in ferritic steels. The principle is to measure the TEP variation, noted DSa, between each strainaged state and the cold-rolled state of the steel. As was shown in Reference 2, if the conditions of measurements are such that DSa is representative only of the segregation of the interstitial atoms and does not take into account recovery effects, this TEP variation is directly proportional to the interstitial content that segregated to the dislocations ([Iseg]). If only one type of interstitial atom (C or N) segregates, DSa can be written as: [1–3]
DSa ¼ jPI j ½Iseg
[1]
where PI 5 the coefficient reflecting the influence of the interstitial atom on the TEP of pure iron. When the dislocation density introduced in the steel by cold-rolling is high and when the aging time is long enough to reach the end of the segregation process, all the interstitial atoms in solution can leave the solid solution and segregate to the dislocations. In these conditions, one can write: DSa ¼ jPI j ½Iss
[2]
where [Iss] 5 the interstitial content in solution in the initial state of the steel (before cold-rolling). The TEP technique can thus be used to evaluate quantitatively the interstitial content in solution in a given steel. The procedure used for this quantitative evaluation was well defined in the case of Fe-C-Mn steels with 0.2 wt pct Mn.[2] It consists of introducing a high dislocation density (corresponding to a reduction ratio* .70 pct) in the investigated steel and in treating *Reduction ratio 5 (e0 – e)/e0 where e0 and e are the initial and final thickness of the steel sheet. D. COLAS, Postdoctoral Student, V. MASSARDIER, Assistant Professor, and J. MERLIN, Professor, are with GEMPPM, National Institute of Applied Sciences of Lyon, UMR 5510, Baˆt. B. Pascal, 69621 Villeurbanne Cedex, France. Contact e-mail: [email protected] Manuscript submitted July 29, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
the steel at 120 °C for 30 minutes, as this treatment time is necessary to reach the end of the segregation. The presence of substitutional atoms (such as Mn or Cr) may modify the segregation kinetics of the interstitial atoms (C or N) to the dislocations obtained after a strong deformation by cold-rolling and thus the conditions required to quantify the interstitial content in solution. As a consequence, the aim of the present work is to determine the segregation kinetics of the interstitials (C or N) to the dislocations by TEP when substitutional atoms (Mn or Cr) are present simultaneously in solution. This work should allow us to show the influence of the type of substitutional atom and of its content in solution on the kinetics and thus on the time corresponding to the end of the segregation process, which has to be
Data Loading...
