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This study focuses on the effect of tungsten as a Laves phase forming element on the steam oxidation behavior of the Fe-9Cr alloy. Steam oxidation tests of the Fe-9Cr alloys with different tungsten concentrations were conducted in an Ar-15%H2O gas mixture at 923 K for up to 345.6 ks. The results showed that tungsten addition significantly improved the oxidation resistance of the Fe-9Cr alloy. By forming FeWO4 in the internal oxidation zone (IOZ) during oxidation, the oxygen partial pressure in this zone corresponded to Fe(W)/Fe2W/FeWO4 equilibrium, which is slightly lower than the Fe/FeO equilibrium. Therefore, the matrix of the IOZ was not being oxidized to form the inner scale, resulting in an improvement in oxidation resistance. A finer and higher fraction of the Fe2W phase produced by rapid cooling provided better Cr enrichment and improved the oxidation resistance of the alloys. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of microstructure change due to the addition of alloying elements (W or Ti) on steam oxidation behavior of the Fe–20Cr–35Ni–2.5Nb (at.%) steel at 1073 K. Steam oxidation behavior of the steels strongly depended on the formation of continuous Cr2O3 layer. Microstructure of the steels was changed by the addition of alloying elements. A high density of fine precipitates in the steels gave a better steam oxidation resistance. Heterogeneous interface between IMCs and the matrix may play important role of nucleation and diffusion in the matrix, resulting in the rapid formation of the continuous Cr2O3 layer. [ABSTRACT FROM AUTHOR]

The effect of water vapor on the transition from internal to external oxidation of austenitic alloys has been conducted at 1,073 K under the equilibrium oxygen partial pressure for the coexistence of Fe and FeO. Critical Cr concentrations in the Fe-Cr-30Ni (at.%) austenitic alloys were determined to be 30 at.% in dry atmosphere and 37 at.% in humid atmosphere. Thus, water vapor significantly affected the transition from internal to external oxidation of austenitic alloys. Two oxides of CrO and FeCrO precipitated in the Fe-5Cr-30Ni (at.%) alloy and solid state reaction for the formation of FeCrO may be influenced by water vapor. Oxygen permeability, which was estimated by considering the effective stoichiometric ratio, was also enhanced by water vapor. [ABSTRACT FROM AUTHOR]

Silicon-containing steel forms an oxide layer within the scale during hot rolling. This layer comprising oxides such as Fe2SiO4 and FeO adversely affect the surface quality of steel owing to strong adhesion between Fe2SiO4 and the steel substrate. A method to melt this silicon-containing oxide layer through the oxidation reaction of iron plates by applying SiO2 powder to the surface is proposed. The aim of this study is to understand the reaction mechanism and identify the optimal conditions for this process. Application of SiO2 coating to the surface of an iron plate at 6.67 × 10–4 g·mm−2 and maintaining the plate at 1423 K, just below the eutectic temperature of Fe2SiO4–FeO system (1450 K), cause the surface oxide scale to melt when exposed to oxidation in an atmospheric environment. Notably, reducing the electric furnace temperature hinders the melting process, whereas excessive application of SiO2 hampers the formation of sufficient liquid phase. On the surface of the iron plate, primarily FeO and Fe2SiO4 are formed. Heat generation is mainly due to the formation of FeO, which leads to the rapid generation of Fe2SiO4. Eutectic reactions within SiO2–Fe2SiO4 or FeO–Fe2SiO4 systems drive the formation of the liquid phase. Once the liquid phase was established, rapid diffusion of iron ions within it resulted in rapid iron oxidation and additional heat generation. Ultimately, a liquid phase in equilibrium with FeO is formed across the entire surface of the iron plate. [ABSTRACT FROM AUTHOR]

This study investigated the effects of oxygen addition on the microstructure, phase transformations, and oxidation resistance of TiAl alloys at 1023 K. The addition of oxygen stabilized the α (α 2) phase at the expense of the γ phase and reduced the oxidation mass gains of the TiAl alloys by more than 20%. Oxide scales composed of external scattered Ti-rich oxide particles/Al-rich/Ti-rich mixed Ti/Al oxides, and internal affected zones with Al-rich precipitates were observed in all oxidized samples. The results showed that the microstructure and phase transformations of the alloys were altered by adding 1 at% oxygen. The addition of O accelerated the α → α 2 chemical ordering reaction and partly suppressed the α → γ massive phase transformation. The oxidation resistance of the TiAl alloys in air at 1023 K was not significantly affected by the addition of oxygen. • Oxygen induces α→α 2 ordering reaction at the expense of the α→γ massive phase transformation. • α→α 2 ordering phase transformation occurs within 1373–1473 K. • Oxygen addition expands the α(α 2) + γ two-phase region in TiAl alloys. • The dissolved oxygen level in the TiAl alloy increased by α→α 2 phase transformation. • Oxygen addition reduces the oxidation mass gain of TiAl. [ABSTRACT FROM AUTHOR]

Effect of grain refinement from 370 to 34 μm on oxidation of transition Fe–13Cr–5Ni alloy at 973 K in Ar–21 vol%O 2 was investigated. The measured weight gains were fitted taking into account a mixed kinetic model with an initial linear and subsequent parabolic growth behaviour. Different scale microstructural evolution was discussed. Contribution of grain refinement to the oxidation is predominantly due to its effect on the inward oxidation process. Decreasing grain size promoted intergranular oxidation, accelerated formation of the Cr-containing inner scale, contributed to the faster transition to the steady state oxidation and correspondingly slightly improved the oxidation resistance. [ABSTRACT FROM AUTHOR]