Phase determination and microstructure of oxide scales formed on steel at high temperature

Abstract

SummaryEven in simple low-alloy steels the oxide scales that form during hot working processes are often a complex mixture of three iron oxide phases: haematite, magnetite and wüstite. The mechanical properties, and hence descalability, are intimately linked with phase distribution and microstructure, which in turn are sensitive to both steel composition and oxidation conditions. In this study electron backscatter diffraction in the SEM has been used to characterize the microstructures of oxide scales formed on two compositions of low-alloy steel. The technique can unambiguously differentiate between the candidate phases to provide the phase distribution within the scale. This is used to investigate grain orientation relationships both within and between phase layers. It has been found that the strength of the orientational relationship between the magnetite and wüstite layers is dependent on steel composition, and in particular Si content. In a low-Si (0.01 wt%) alloy only a very weak relationship was found to exist for a range of oxidation temperatures (800 -1000 ° C), whereas for the higher Si (0.37 wt%) alloy a strong relationship was observed under the same oxidation conditions. These orientational relationships are particularly important because, in this temperature range, the majority of oxide scale growth occurs at the magnetite/ wüstite interphase boundary.

High-Temperature Oxidation Behavior of Fe–1Cr–0.2Si Steel

“…After adding Cr to the iron-based alloy, the product formed by oxidation is affected by the amount of added Cr [5][6][7]. With the addition of 5% Cr, the Cr-rich and Fe oxides enter the FeO phase to form FeCr 2 O 4 , but the solubility of the spinel structure is also limited owing to the stability of the spinel structure.…”

Optical properties of thin iron oxide films on steel

“…Iron oxides have been studied extensively because of their enormous importance in hot processing of steel, 1 pigments, 2 catalysts, and so on. Iron oxides can be produced in several ways, such as electron beam deposition, 3 electrochemically 4 and also thermally.…”

High temperature oxidation resistance of 1.25cr–0.5mo wt.% steels by zirconia coating

“…The outer layer is formed by hematite (Fe 2 O 3 ). At temperatures below 570°C, the iron would be expected to form a two-layered scale of magnetite (Fe 3 O 4 ) and [13][14][15][16][17][18]. The presence of chromium in the inner layer is due to an internal oxidation of this element that does not form a continuous layer because of its low concentration in the metal.…”