Microanalysis of Oxide Layers of Steels

Abstract

The scales formed on the steels are examined through the electron probe microanalysis. Examined steels are low carbon rimmed steel, silicon killed steel, weather-resistance steel, high strength steel, sulfer free-cutting steel, ferritic and austenitic stainless steels.
Specimens were oxidized in air at 1000 to 1350°C for various periods. The results obtained in the present investigations are as follows.
(1) Low carbon rimmed steel: three well-known types of iron oxides (hematite, magnetite and wustite) are determined and any other oxides is not observed.
(2) Silicon killed steel: under the iron oxide layers, manganese-iron-silicates exist together with dendritic wustite.
(3) Low alloy steels (weather-resistance steel and high strength steel): the scales consist of hematite, spinel type oxides, wustite, silicate and metallic particles in which nickel and copper are condensed due to preferred oxidation of steel.
(4) Sulfer free-cutting steel: iron sulfide is detected in the oxide scale and theinternal oxidation of manganese sulfide inclusions are also observed.
(5) Ferritic stainless steel: main part of the inner oxide layer is the spinel type oxide of Fe, Cr, Mn and thin layers of Cr₂O₃ and SiO₁ exist between the spinel and the steel substrate.
(6) Austenitic stainless steel: the scale formed at high temperature consists of hematite, spinel type oxide, silicates and metallic particles similar to the case of low alloy steels.