Thermal Diffusivity Measurement of Oxide Scale Formed on Steel during Hot-rolling Process

Abstract

Thermal diffusivity and conductivity of oxide scales formed on steel plates are essential to control the cooling rate of the steel in the hot-rolling process. A flash method was applied to measure the thermal diffusivity of oxide scales. Sample specimens were commercial hot-rolled plates on which about 25 μm-thick oxide scales were formed. The results of the flash measurement with the analysis for two-layered sample provided an average thermal diffusivity value of 7.3 × 10 -7 m 2 s -1 for the oxide scale. This value produces a thermal conductivity value of 3.8 W m -1 K -1 . The future application of this measurement and analysis technique was also discussed to derive the thermal diffusivity and conductivity of oxide scales formed in actual hot-rolling processes.

Temperature Dependence of Thermal Diffusivity and Conductivity of FeO Scale Produced on Iron by Thermal Oxidation

“…For such mathematical simulations, the thermal conductivity and diffusivity of the iron oxide scale are the most important thermophysical properties. 4) To date, to the best of the authors' knowledge, there have been six reports on the thermal conductivity/diffusivity of iron oxide scales; [5][6][7][8][9][10] each has reported that the thermal conductivities/diffusivities of iron oxide scales are smaller than those of steel. Three of these studies have obtained the thermal diffusivities of single-phase samples of sintered iron oxides as functions of temperature.…”

“…In contrast to the sintered iron oxide samples, actual iron oxide scale has a multilayered structure of Fe 2 O 3 , Fe 3 O 4 , and FeO phases, and also contains pores. 8) Even if accurate thermal conductivity/ diffusivity values are known for single-phase iron oxides, it is extremely difficult to predict the values of an actual iron oxide scale. Thus, sintered iron oxide samples are not suitable representatives of an actual iron oxide scale.…”

“…[8][9][10] Taylor et al 9) have measured the thermal diffusivities of iron oxide scales on iron substrates from 450 to 1 250 K using the laser flash method. 11) The scale phase composition and amounts of Fe 3 O 4 and Fe produced by the FeO decomposition are not considered, although they are thermodynamically possible below 843 K. 12) In fact, these form easily and very rapidly at 623 to 723 K in dynamics, as shown in a study of FeO decomposition dynamics by Tanei and Kondo.…”

“…11) The scale phase composition and amounts of Fe 3 O 4 and Fe produced by the FeO decomposition are not considered, although they are thermodynamically possible below 843 K. 12) In fact, these form easily and very rapidly at 623 to 723 K in dynamics, as shown in a study of FeO decomposition dynamics by Tanei and Kondo. 13) Baud et al 14) have also reported that significant numbers of magnetite seams are generated in the temperature range of 648 to 748 K. More recently, Endo et al 8) have measured the thermal diffusivity of an actual oxide scale formed on a steel slab during hot rolling using the laser flash method following the analysis proposed by Baba.…”

A New Method for Apparent Thermal Conductivity Determination for Sheet Samples Utilizing Principle of Bunsen Ice Calorimeter

“…Mu LI, 1) * Rie ENDO, 1) Li Ju WANG, 2) Lei LI 2) and Masahiro SUSA 1) 1) Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8552 Japan.…”