Generalized estimates for thermal expansion of oxide scale in the range from 0C to 1300C with account for movability of phase transitions in its components
Abstract
The thermophysical properties of oxide scale, in the general case, are affected by the variation of the temperature of phase transitions (either magnetic or polymorphic) in its components due to impurities, lattice defects, grain sizes, etc. In this case, since the phase transition is usually accompanied by a sharp change in properties, even a small shift of such a critical temperature can lead to large changes in properties in its vicinity. In order to account for this effect, data known from various sources on the true coefficient of linear thermal expansion (CLTE) of wüstite , magnetite , hematite , and metallic iron are generalized by approximating functions that include critical temperatures as variable parameters. It is shown that the true CLTE of magnetite at the same rated temperature can differ by up to 30% depending on the position of the Curie point within the limits of its possible "movability". The proposed methods allow to take into account the critical temperatures as adaptation parameters in engineering calculations of thermal expansion of oxide scale. Generalized formulas for each scale component are also given in a particular form for fixed (basic) values of critical temperatures. The dependence of the true CLTE of oxide scale as a whole ({\alpha}sc) on the volume fraction of each component is proposed. It is shown by model computations that there are temperatures at which {\alpha}sc is almost independent of the scale composition, as well as areas of instability, where {\alpha}sc depends significantly on the percentage of components. The results of the work are recommended to be used when mathematical modeling of production and processing of steel products in the presence of oxide scale on their surface.
 Publication:

arXiv eprints
 Pub Date:
 October 2021
 arXiv:
 arXiv:2110.08528
 Bibcode:
 2021arXiv211008528B
 Keywords:

 Condensed Matter  Materials Science
 EPrint:
 10 pages, 9 figures