Lamellar Spacing Characteristics of Eutectoids in Oxide Scale Formed on Iron After Holding at 300–500℃

Abstract

The eutectoid reaction in FeO scale was examined by thermogravimetric analysis. The oxidized specimens were held isothermally from 100 s to 50,000 s in the temperature range from 300 to 550 ℃. Under a variety of temperature and temporal circumstances, experiments were conducted and the results analyzed using an electron probe micro-analyzer. The findings demonstrate that FeO forms an eutectoid consisting of Fe₃O₄ and Fe at 300–500 ℃. An experimentally derived TTT diagram of the evolution of the FeO phase change shows eutectoid C-curves with nose temperatures of roughly 425 ℃. The primary factor in the formation of eutectoid product is the local position of Fe supersaturation, which is not directly related to the Fe₃O₄ seam layer that forms. There exists a “white area” in the front of eutectoid phase transformation before stable eutectoid structure layered formed. Rods of Fe can be formed in eutectoid transformation. The lamellar spacing in the eutectoid product at different temperatures was obtained by calculation and verified by experimental results.