Cr2O3 Al2O3 Research Articles

Combating Cl− and SO42−-induced molten salt corrosion by laser cladding FeCrNiMoAl high-entropy alloy coating

FeCrNiMoAl high entropy alloy coating was successfully prepared by laser cladding method with phases of dominant face-centered cubic (FCC) and minor intermetallics (AlFe and AlNi). After 144 h of corrosion in the molten salt mixture of 40 % NaCl + 40 % KCl + 10 % Na2SO4 + 10 % K2SO4 at 600 °C, FeCrNiMoAl exhibited a much lower corrosion rate than conventional Inconel 625 by a reduction of 34 %. XRD and SEM were used to characterize the corroded samples. To combat Cl-induced active corrosion and S-induced sulfidation, Inconel 625 develops a single Cr2O3 layer while FeCrNiMoAl developed dual layers of outer Cr2O3 and inner Al2O3, which effectively prevents penetration of Cl and S.

Microstructure evolution and tribological properties over a wide temperature range of Ni-based composite coatings with Ti3AlC2 addition

Ni60A alloy powders doped with varying concentrations (0, 10 wt% and 20 wt%) of Ti3AlC2 MAX phase were coated on S31008 NiCr stainless steel substrate using atmosphere plasma spraying technique in this work. Comparative investigation was conducted to examine the effects of Ti3AlC2 additions on the microstructure evolution, microhardness, and wide temperature range (room temperature to 800 oC) tribological performance of the composite coatings. The findings demonstrated that the composite coatings were composed of γ-Ni, intermetallic hard metal borides, Ti3AlC2 and TiC phases, without any noticeable oxide phases. The 20 wt% Ti3AlC2 additions to the Ni60A alloy coating exhibited minimum imperfections in microstructure with a porosity drop of 65.8 %, and the highest microhardness which was enhanced by 64 % to 924 HV0.515. After introducing of Ti3AlC2, the coefficient of friction decreased and appeared to distinguish itself by remaining minimal and stable at low-medium temperatures compared with an increase of more than 70 % at high temperatures. Ni60A-10 wt% Ti3AlC2 coating resulted in the lowest friction coefficient of approximately 0.45 from room temperature to 400 oC and it peaked to 0.78 at 800 oC, reducing by 19.6 % and 6 % compared to non-composite coating, respectively. The wear resistance of the composite coating was considerably improved with the increment of Ti3AlC2, and the coating with 20 wt% Ti3AlC2 showed the most significant reduction in wear rate: 18.5 % at room temperature, 45.2 % at 200 oC, 37.2 % at 400 oC, 60 % at 600 oC, 90.8 % at 800 oC. The lubricate layered Ti3AlC2 phases and the tribo-oxide film predominate composed of derivative NiO, Cr2O3 Al2O3 and TiO2 played a critical role in antifriction and wear resistance. The wear mechanisms were accordingly conducted as abrasion and adhesion wear at low-medium temperature and transferred into tribo-oxidation wear at elevated temperature.

Synergistic enhancement of hot corrosion resistance and mechanical properties of IN738LC alloy prepared by selective laser melting

The present study investigates the synergistic enhancement of hot corrosion resistance (900 °C, 75%Na2SO4+25%NaCl) and mechanical properties of IN738LC alloy prepared by selective laser melting after heat treatment. The results indicate that the M23C6 precipitation at the grain boundaries coupled with smaller-sized γ′ phase distribution in the inner grain is conducive to the formation of thicker Cr2O3 outer layer and Al2O3 inner layer for the samples, which effectively hinders the diffusion of S and Cl elements penetrate to the matrix, enhancing the hot corrosion resistance. Additionally, the presence of small-sized γ′ phase and re-crystallization-induced grain refinement contribute to an increase in yield strength (σYS = 1261 MPa) and ultimate tensile strength (σUTS = 1360 MPa) for the alloy.

Microstructure evolution, mechanical characteristics and erosion behavior of Cr2O3–Al2O3–MgO–ZrO2 refractories in molten reduction slag

In order to overcome the serious corrosion problem of furnace hearth refractory materials for smelting reduction ironmaking, the Cr2O3–Al2O3–MgO–ZrO2 refractories were synthesized, and the phase component, microstructure, mechanical characteristics, and slag erosion behavior of composite refractories were investigated and evaluated. The results indicate that the composite refractories mainly consist of Mg(Al, Cr)2O4 spinel phase, (Al, Cr)2O3 solid solution and ZrO2. The content of Mg (Al, Cr)2O4 spinel significantly increases with the increasing MgO content, while the content of (Al, Cr)2O3 obviously decreases. Furthermore, the comprehensive mechanical properties of the MgO modified composite refractories can be obviously enhanced by increasing the MgO content, and sample S4 presents the best mechanical characteristics when the MgO addition is 10 wt%. The corresponding hardness, compressive strength and bending strength are 14.22 GPa, 267.14 MPa and 80.0 MPa, respectively. This is mainly because the formation of Mg(Al, Cr)2O4 significantly improves the densification of composite refractories, and a large number of high-strength Mg (Al, Cr)2O4 spinel “bridge” formed between the large-sized (Al, Cr)2O3 grains. The erosion test results indicate that increasing the MgO content can significantly improve the slag infiltration resistance of composite refractories, because the formation of Mg (Al, Cr)2O4 spinel layer significantly improves the densification of MgO reinforced composite refractories. Although the slag corrosion resistance of Mg(Al, Cr)2O4 is lower than that of (Al, Cr)2O3, the Cr2O3–Al2O3–MgO–ZrO2 refractories still presents good erosion resistance, permeability resistance, and excellent mechanical characteristics.

The synergy effect of elements on the oxidation resistance of a high-purity directionally solidification nickel-based superalloy

A study on the film characteristics of a Cr2O3-forming nickel-based superalloy is conducted. A triplex structure is observed, in which Ta–Ti layer is developed between the external Cr2O3 and inner Al2O3 layer. When the exposure time increased, Ti atoms are divorced from the Ta–Ti layer, filling the voids inside the Cr2O3 layer, which improve the density of the external Cr2O3 layer and retard the inward penetration of the nitrogen. As a result, the degree of internal nitrides is reduced. Consequently, the synergy effect of Ta and Ti in the Cr2O3 forming alloy is beneficial to improve the oxidation resistance.

Effects of TiO2 addition on phase, mechanical properties, and microstructure of Cr2O3–Al2O3 ceramic composite

TiO2 is a sintering additive that can significantly improve the sintering and mechanical properties of Cr2O3–Al2O3 refractory materials with high Cr2O3 contents. In this study, TiO2-reinforced Cr2O3–Al2O3 composite refractories were prepared using a reaction-sintering process. The microstructure, phase composition, mechanical properties, and strengthening mechanism of the TiO2-reinforced Cr2O3–Al2O3 composite refractories were investigated. The results indicated that the Al2O3–Cr2O3–TiO2 composite refractory with a TiO2 content of 3.0–4.5 wt% had good compactness (porosity of 5.89%), hardness (17.21 GPa), wear resistance (wear rate of 0.4 mm3/Nm), flexural strength (101.10 MPa), and compressive strength (420.90 MPa). This is mainly because when the added amount of TiO2 was <3.0 wt%, TiO2 was solidly soluble in the matrix, forming a Ti3+-doped (Cr, Al)2O3 solid solution, inhibiting abnormal grain growth, rapidly increasing the sintering shrinkage of the sample, rapidly increasing the bulk density, rapidly decreasing the apparent porosity, and improving the sintering and mechanical properties of the composite resistant material. When the TiO2 addition exceeded 4.5 wt%, a large amount of (Cr, Al)2TiO5 phase was distributed between the grain boundaries of the solid solution, and its bulk density started to decrease. The sintering shrinkage and apparent porosity did not change significantly, and the bonding between the solid solution was not improved. Thus, the sintering and mechanical properties of the composite resistant material deteriorated. Taking into account the slag resistance and mechanical properties of the material, Al2O3–Cr2O3–TiO2 with a TiO2 content of 3.0–4.5 wt% can meet the service requirements for mechanical properties of the lining of smelting reduction ironmaking furnaces.

Role of Nb in promoting protective scale formation on Al2O3-forming austenitic alloys

The high-temperature oxidation behavior of Fe–25Ni–17Cr–7.7Al–0.03Zr alloys with and without 0.5 or 1 at% Nb addition was investigated at 800 °C in air. Nb addition was found to promote the formation of an external Al2O3 scale. The Nb-free alloy formed a scale consisting of a thick Fe/Ni-rich oxide layer and a Cr2O3 layer, beneath which Al was internally oxidized. However, a continuous protective Al2O3 scale was developed below a thin Cr2O3 layer on the 1 Nb alloy, which significantly decreased the oxidation rate. Examination of the initial oxidation process during heating to 800 °C revealed that all of the alloys formed a Cr2O3 layer and an amorphous Al2O3 layer upon heating to 650 °C, but these layers became discontinuous upon further heating to 800 °C for the Nb-free alloy. The beneficial role of Nb was ascribed to its ability to maintain the initially formed thin Cr2O3 layer by the formation of a Nb-containing Cr-rich oxide layer at the interface between the Cr2O3 and amorphous Al2O3 layers. This Nb-containing Cr-rich layer prevented the breakdown of the transient amorphous Al2O3 layer until its transition to a protective crystalline Al2O3 scale.

Roles of Nb on the oxidation characteristics and oxide scale evolution of Fe‐25Cr‐35Ni‐2.5Al‐XNb alloys at 1000°C and 1100°C

AbstractThe oxidation characteristics of Fe‐25Cr‐35Ni‐2.5Al‐XNb (0, 0.6, and 1.2 wt%) alumina‐forming austenitic alloys at 1000°C and 1100°C in air were investigated. Results show that Nb has an important effect on the high‐temperature oxidation resistance. A bilayer oxide scale with a Cr2O3‐rich outer layer and Al2O3‐rich internal layer forms on the surface of the Nb‐free alloy and exhibits a poor oxidation resistance at 1000°C and 1100°C. With Nb addition, both the 0.6Nb‐addition and 1.2Nb‐addition alloys exhibit better oxidation resistance at 1000°C. Because of the third element effect, Nb addition reduces the critical Al content and forms a single external protective Al2O3 scale, which greatly improves the oxidation resistance. After oxidation at 1100°C, niobium oxides (mainly Nb2O5) are formed on the surface of the 1.2Nb‐addition alloy and destroy the integrity of the Al2O3 scale, which causes the formation of Cr‐rich oxide nodules and eventually develops to be a loose bilayer oxide scale with NiCr2O4, Cr2O3, and Fe2O3 outer layers and Al2O3 inner layer.

Microstructure and corrosion behavior of Al2O3–Cr2O3 composites with various Cr2O3 content in Al2O3–SiO2–CaO–FeO slag

The corrosion of refractory materials by high-temperature slag has caused severe technical challenges and economic losses to the metallurgical industry. In this study, the microstructure and mechanical properties of Al2O3–Cr2O3 composites were investigated. The static crucible method was used to investigate the corrosion and infiltration behavior of a typical smelting reduction ironmaking slag for the Al2O3–Cr2O3 refractory. Corrosion test results indicate that the corrosion region of Cr2O3–Al2O3 composites is mainly composed of a corrosion and infiltration layer, and the thickness of the corrosion layer decreases significantly with increasing Cr2O3 content in the sample, whereas the thickness of the infiltration layer increases gradually. The dissolution of Al2O3 into the slag is the main reason for the severe erosion of Al2O3–Cr2O3 composites with a low Cr2O3 content. Increasing the amount of Cr2O3 can significantly improve the slag corrosion resistance of Cr2O3–Al2O3 composites, however will have a negative effect on the slag infiltration resistance, which is mainly owing to the increase in porosity of the composite refractory. The formation of the (Al, Cr)2O3 solid solution effectively inhibited the dissolution of alumina in the slag. In addition, excessive Cr2O3 content can also consume Al2O3 in the slag and form an (Al, Cr)2O3 solid solution, which improves the slag corrosion resistance of the aluminum chromium composite refractory.

Corrosion Behavior of Aluminum-Forming Alloy 310S for Application in Molten Chloride Salt CSP Thermal Storage Tank

The key to the new generation of solar thermal power plants is to increase the operating temperature of molten salt to 800°C, and change the heat transfer medium from nitric acid mixed salt to chlorine mixed salt, so as to significantly reduce the cost of power generation. Therefore, the alloy material’s resistance to high temperatures and fusible chloride salt is one of the core technologies for the successful implementation of concentrated solar power (CSP) technology. In this study, the aluminum-forming alloy (AFA) 310S for the heat storage tank was prepared by the aluminum-thermal reaction casting method. The hot corrosion behavior and mechanism of AFA 310S in chloride molten salt at 800°C were studied by static immersion etching for 600 h. AFA 310S exhibits good thermal corrosion properties in KCl 20.4 wt% + MgCl2-55.1 wt% + NaCl 24.5 wt%. The results indicate that compared with commercial 310S, AFA 310S has better oxidation resistance at 800°C. At the initial stage of corrosion, dense Cr2O3 and continuous Al2O3 passivation films are formed. At the same time, MgO-rich oxidation products were produced in the outermost layers of the two alloys during the 600 h process. Over time, however, the damage caused by chlorine became more apparent, mainly due to the “oxidation-chlorination” process of the metal. A large number of cavities and cracks on the surface are formed, and the oxide layer has obvious spalling. When the Al element was added into the alloy, the dense passivation film could be formed after 120 h of corrosion with the stronger corrosion resistance. The experiment simulated the corrosion behavior in the worst environment, such as air, unoxidized alloy, molten salt without corrosion inhibitor, etc. By weight loss calculation, commercial 310S plate is completely unsuitable for CSP plant. The corrosion rates of the two alloys are compared as follows: commercial 310S &amp;gt; AFA 310S. To sum up, AFA 310S has a good application prospect in concentrated solar power.

Friction and wear characteristics of in-situ Cr+(Cr,Al)2O3 composite coating fabricated by plasma spraying

The [Cr+(Cr, Al)2O3] nanocomposite coating was synthesized in situ by reactive plasma spraying Al–Cr2O3–Al2O3 composite powder, and its friction and wear properties were studied at room temperature. Studies have shown that the microstructure and structure of the composite coating can be optimized by adding a certain amount of additives (aAl2O3+bCr2O3). The metallic Cr particles distributed in the matrix can significantly hinder the crack propagation. The eutectic composite coatings all below 10 nm show the best plastic toughness and friction and wear properties. The microhardness reaches 1899HV0.3, and the wear resistance is 3.28 times that of the Al2O3 ceramic coating. The wear mechanism is fatigue wear and slight adhesion wear.

Influence of Al content on the oxidation behavior of CrAl coating on Zry-4 alloys in 1200 °C steam

The oxidation behavior of CrAl coatings with three representative compositions deposited on Zircaloy-4 in 1200 °C steam environment has been studied. The Cr0.90Al0.10 coating shows bettter performance than the other CrAl coatings due to the protectiveness of both the outer Cr2O3 oxide layer and the internal Al2O3 oxide layer. The Cr0.95Al0.05 coating shows partial-protective performance, exhibiting a continuous Cr2O3 oxide layer and Al2O3 oxide islands. However, the oxidation resistance of the Cr0.68Al0.32 coating is poor, exhibiting a discontinuous Al2O3 layer on the surface and cracks in the coating. The effect of Al concentration on the oxidation resistance of CrAl coatings is discussed in detail.

Chrome-diopside Xenocrysts Entrained in a Neoproterozoic Lamprophyre Dyke from the Mysuru Area: Their Origin and Implications for Lithospheric Thickness Beneath the Western Dharwar Craton, Southern India

Abstract In comparison to the eastern Dharwar Craton, the mantle-derived xenocrysts/xenoliths are extremely rare or even unreported from the western Dharwar Craton, southern India. A Neoproterozoic (ca. 800-900 Ma) lamprophyre cropping out in the Mysuru area of southern India contains chrome-diopside xenocrysts (Cr2O3 content varying from 0.2 – 1.23 wt%) which provide important evidence about the pressure-temperature conditions and lithospheric thickness beneath the western Dharwar Craton. Studied chrome-diopsides show compositional zoning which is lacking in the liquidus phases (amphiboles and feldspars) of the lamprophyre which additionally favors a non-cognate origin of the former. Based on the compositional zoning, all the chrome-diopside xenocrysts can be divided into three groups: (i) Group I- which are euhedral and show reverse zoning with increasing Cr-content from core to rim; (ii) Group II- which are characterized by fractures and resorption textures, show complex reverse zoning and display up to three distinct compositional layers, and (iii) Group III- which evidence the reaction of chrome-diopsides with lamprophyric melt and are marked by alteration phases, such as actinolite and chlorite, together with relicts of some unaltered xenocrysts. High Cr2O3, moderate MgO and low Al2O3 content of all the three varieties of chrome-diopside suggest them to represent disaggregated xenocrysts of mantle-derived garnet peridotite. Temperature-pressure estimates for chrome-diopside xenocrysts ranges from 895 - 1026 °C (± 30 °C) and 32 – 38 kbar respectively and correspond to depth range of 106 – 127 km. The study reveals that lithospheric thickness during the Neoproterozoic beneath the western Dharwar craton was at least ~115 km and is similar in composition to that of the cratonic lithosphere found in the other cratonic domains.

Interactions of Cr2O3–Al2O3–ZrO2 refractory with slags in an entrained-flow coal-water slurry gasifier

The corroded microstructures of the Cr 2 O 3 –Al 2 O 3 –ZrO 2 refractory brick in an industrial opposed multi-burner (OMB) coal water slurry gasifier were investigated. It was found that the chromite spinel isolation layer rich in iron and magnesium was formed on the surface of the corroded brick body. By comparing and analyzing the corrosion of different zones in the gasifier, the results indicated that the molten slag entered the brick through the gaps and generated the spinel layer along the edge of the gaps, causing the dense structures of the refractory surface destroyed. In addition, in the high chrome brick corrosion experiment conducted by HTSM, 3 μm sized spinel were observed covering on the surface. The FactSage calculation results showed that the amount of spinel produced would drop significantly as the slag penetrated.

Effect of Basicity and Boron Oxide in Slags of the AOD Process on the Equilibrium Interphase Distribution of Sulfur and Boron

The use of fluorspar in modern metallurgical slags, incl. slags of the argon-oxygen decarburization (AOD) process, as a fluxing agent, is associated with many disadvantages. Those disadvantages can be solved by using boron oxide as an alternative, which also provides conditions for direct microalloying of steel with boron. The paper presents the results of thermodynamic modeling of the effect of basicity and boron oxide content in slags of the CaO–SiO2–B2O3–Cr2O3–Al2O3–MgO system on the equilibrium interphase distribution of sulfur and boron, and their equilibrium content in the metal. Modeling was carried out using the HSC 8.03 Chemistry software package (Outokumpu). Slag from the desulfurization period of the AOD-process was used as the oxide phase. As a result, it was shown that, in the range of basicities 2.0-2.5 and a content of 2-4% B2O3, it is possible to carry out desulfurization of the metal, providing a sulfur content of 0.001-0.007%, and simultaneous microalloying of steel with boron in an amount of up to 0.0103%.

Thermal shock resistance of Cr2O3–Al2O3–ZrO2 bricks with the microstructure of Cr2O3 aggregates coated by ZrO2

Zirconia-coated Cr2O3 aggregates synthesized by mixing ZrO2 powders and Cr2O3 aggregates with a phenolic resin binder followed by thermosetting treatment were employed as modified Cr2O3 aggregates to obtain Cr2O3–Al2O3–ZrO2 bricks (high-chromia bricks). The elastic modulus (E) and cold modulus of rupture (CMOR) of these high-chromia bricks before and after thermal shock cycles were systematically investigated, and the residual ratios of CMOR and E were calculated. The thermal shock resistance of the high-chromia bricks was significantly improved by the factor of modification of Cr2O3 aggregates. The mechanism of the improved thermal shock resistance of these high-chromia bricks was studied via microstructure analysis, and the crack propagation behavior was analyzed by scanning electron microscopy (SEM). The fracture work (γWOF), thermal shock damage factor (R′′′′), and thermal stress crack stability parameter (Rst) were measured and calculated using the wedge splitting test (WST). The results indicate that the porous ZrO2 coating layer wrapped the Cr2O3 aggregates, forming modified Cr2O3 aggregates that can increase crack deflection, free path of crack propagation, and fracture work, thus improving the thermal shock resistance of high-chromia bricks. The thermal shock resistance of the fabricated high-chromia bricks was highly correlated with the thickness of the ZrO2 coating layer surrounding the Cr2O3 aggregates. The variation trend of Rst is well consistent with the experimental results, which is suitable to evaluate the thermal shock resistance of high-chromia bricks.

Tribological properties of plasma sprayed Cr2O3, Cr2O3–TiO2, Cr2O3–Al2O3 and Cr2O3–ZrO2 coatings

Plasma sprayed Cr2O3 is widely used to protect industrial components against wear. The present study seeks to clarify how its properties can be modified by alloying with other oxides. Therefore, pure Cr2O3 and Cr2O3–25%TiO2, Cr2O3–16%Al2O3, Cr2O3–35%Al2O3, Cr2O3–10%ZrO2 and Cr2O3–20%ZrO2 coatings were studied. All samples were obtained from pre-alloyed feedstock, resulting in rather homogeneous solid solutions.Compared with pure Cr2O3 and Cr2O3–Al2O3 coatings, the Cr2O3–25%TiO2 and Cr2O3–ZrO2 ones exhibit lower indentation hardness (HIT) but higher toughness, qualitatively assessed by scratch testing. Cr2O3 and Cr2O3–16%Al2O3 also exhibit higher hardness/elastic modulus ratios (HIT/E*, HIT3/E*2) than all other samples.The sliding wear resistance of the coatings against Al2O3 and ZrO2 balls is most closely correlated to indentation hardness and, secondarily, to the hardness/modulus ratios. Pure Cr2O3 is therefore the most sliding wear resistant of all samples, whilst Cr2O3–25%TiO2 suffers very severe wear. However, ZrO2 counterparts cause systematically more severe wear than do Al2O3 ones.Dry particles' abrasion, which proceeds through flake formation, is controlled by toughness. The resistance to abrasive wear is, therefore, predicted by scratch testing. The various coatings rank almost the opposite as they did in sliding wear tests, with comparatively lower wear losses for Cr2O3–25%TiO2 and (most of all) Cr2O3–ZrO2 samples.

Synthesis of Cr2O3–Al2O3 powders with various Cr2O3/Al2O3 molar ratios and their applications as support for the preparation of nickel catalysts in CO2 methanation reaction

The Methanation of CO2 to CH4 is a significant route to save energy and reduce CO2 emission. In this work, a series of Cr2O3–Al2O3 powders were synthesized by a novel and simple solid-state method and considered as the carrier for the nickel catalysts in CO2 methanation. The BET area and pore volume of the supports decreased with the decrease in Al2O3/Cr2O3 molar ratio. The results indicated that the increase in Cr2O3 content improved the catalytic performance and 15 wt%Ni/Cr2O3 catalyst exhibited the highest CO2 conversion of 80.51%, and 100% CH4 selectivity at 350 °C. The results indicated that the CO2 conversion improved with the increment in H2/CO2 molar ratio from 2 to 5. The improvement in CO2 conversion was also observed with decreasing GHSV due to the longer residence time of the reactants on the catalyst surface. Also, the results showed that increasing calcination temperature led to a decrease in CO2 conversion. The 15 wt%Ni/Cr2O3 catalyst exhibited high stability in carbon dioxide methanation reaction.

High temperature oxidation of NiCrAlY coated Alloy 625 manufactured by selective laser melting

The high temperature oxidation of fully SLM-processed NiCrAlY coated Alloy 625 parts was investigated between 800 °C and 1000 °C. For comparison, bulk NiCrAlY and bulk Alloy 625 were also fabricated using SLM. Two thin layers of NiCrAlY powder were lasered at the surface of Alloy 625 to form the bi-materials. Bulk NiCrAlY and bi-materials showed an improved oxidation behavior compared to Alloy 625. The oxidation of the NiCrAlY coating results in regions with a dense and continuous external Al2O3 layer and regions composed of a mixture of external Cr2O3 and internal Al2O3. Large EDS maps at the surface and cross-sections of the bi-material highlighted a heterogeneous distribution of constitutive elements of the NiCrAlY coating, resulting in some regions with an Al activity lower than the one required for the formation of a continuous and dense Al2O3 layer (≤10 atomic percent). Low Al activity and high Al activity regions were related to the topography of the SLMed surface and correspond to hill and valley regions, respectively. In addition, cracks, mainly occurring in high Al activity regions, were observed across NiCrAlY specimens. The fabrication of coated but small components with a brittle coating by SLM is not trivial and needs further investigations.

Evolution of oxide inclusions in stainless steel containing yttrium during thermo-mechanical treatment

To get more fundamental information on the control of rare earth inclusions in solid steel, the evolution behavior of oxide inclusions during thermo-mechanical treatment of stainless steel containing yttrium at 1423K (1150°C) was investigated in detail. Homogeneous spherical SiO2–MnO–Al2O3–Y2O3 inclusions were observed in the as-cast steel. After thermo-mechanical treatment, the homogeneous oxide inclusions changed to heterogeneous ones with gray-colored (SiO2–Y2O3)-rich phase and dark-colored MnO–Cr2O3–Al2O3 spinel phase owing to the mutual effects of (i) crystallization of the glassy oxide and (ii) reaction between inclusions and steel matrix. In addition, the oxide inclusions were elongated along the deforming direction of steel during hot deformation process. With increasing reduction of the steel, the MnO–Cr2O3–Al2O3 spinel phase (dark phase) were crushed into small pieces. And the two phases (gray and dark phases) in inclusions gradually became separated from each other due to different deformability. The deformation index of inclusions gradually decreased with an increase in the deformation degree of the steel, indicating that the deformability of inclusions got worse.