Composite Inclusions Research Articles

Characterization and 3D Reconstruction of the Crushing Behavior of SiO2–CaO–Al2O3–MgO Complex Inclusions in Spring Steel with High Basicity Slag Treatment

This article mainly studies the element content, phase composition, and fragmentation mechanism of SiO2–CaO–Al2O3–MgO composite inclusions that cause fatigue fracture of spring steel. The study found that the SiO2–CaO–Al2O3–MgO composite inclusions in the wire rod are not a homogeneous phase. According to the electron microscopy energy spectrum analysis results, although the SiO2–CaO–Al2O3–MgO composite inclusion is in the low‐melting‐point area of the phase diagram according to the component content ratio. However, field‐emission transmission electron microscopy analysis reveals that this type of composite inclusions includes MgAl2O4, CaAl2Si2O8, CaSiO3, MgSiO3, and a small amount of CaS. The Zeiss Crossbeam 550 electron microscope is used to conduct a three‐dimensional reconstruction analysis of this type of composite inclusions, which once again verified that the composition of this type of inclusions includes calcium silicate, MgAl2O4, MgO, and other phases. It is also found that there is a certain gap between the inclusions and the matrix, and the gap between the inclusions with high‐melting‐points such as MgAl2O4 and MgO and the matrix is more obvious. During the rolling process of SiO2–CaO–Al2O3–MgO composite inclusions, due to differences in hardness and deformation rate between different phases, the rolling process is deformed and fragmented for extended periods.

Effect of magnesium on primary carbides in GCr15 bearing steel

GCr15 bearing steel has higher carbon and chromium content, large-size primary carbides tend to be easily precipitated during the solidification, which is harmful for the performance of steel. Hence, magnesium treatment was applied to refine primary carbides and the influence of magnesium on the size, distribution and morphology of primary carbides in GCr15 bearing steel was studied in this paper. The results indicated that M3C, M3C2, and M7C3 were precipitated during the solidification of GCr15 bearing steel. When magnesium was added into the steel, the area ratio and maximum size of primary carbide were decreased with the increase of magnesium content. The refinement of primary carbides was the most obvious when the magnesium content was 27 ppm. Compared with the steel without magnesium, the area ratio and maximum size of primary carbides were reduced by 2.41 % and 11.16μm respectively. In addition, for the steel without magnesium, MnS were likely to be attached with primary carbides. Once magnesium was added, smaller and two-layer structured composite inclusions (the inner layer was Mg-Al-O, and the outer layer was MnS) were formed and provided the preferred nucleation site for primary carbides, which ultimately promoted the refinement of primary carbides.

Role of Te-RE alloying on the passive film and pitting corrosion behavior of 316L stainless steel

This work reports the mechanism of corrosion resistance enhancement of 316 L stainless steel after Te-RE alloying. The individual MnS inclusions are replaced by composite inclusions, resulting in a reduced risk of pitting corrosion. The decrease of inclusion amount and Volta potential difference between inclusion and matrix induced by the addition of Te/La promoted the stability of the inclusions and lessened the active sites for pitting corrosion. TeO2 formed in the passive film with Te treatment could be easily reduced by Cr and Mo, and resulting in a significant increasing of MoO2 and Cr2O3 content in the passive film. This enhanced the stability of the passive film. Te and RE exhibited a synergistic effect on the increase of Cr and Mo in the passive film, resulting in a further improvement of the passive film. However, RE could not exist in the passive film stably due to its poor thermodynamic stability of the rare earth oxides, and only acted as a bridge for the formation of Cr and Mo oxides.

Heterogeneous nucleation mechanism of CaS and TiN on spinel combining DFT calculations and experiments

The characteristics of composite inclusions between atomic interfaces has been investigated by combining high-angle annular dark field (HAADF) with first-principles computations. The characteristics of the composite inclusions reveal a core of Ca2Al2O5, with CaS and TiN adhering to its surface. According to mismatch degree theory and SEM characterization, the nucleation rate increases with a decreasing degree of mismatch. Notably, the adhesion work of the Ca2Al2O5/CaS interface is greater than that of the Ca2Al2O5/TiN interface, demonstrating the stronger bond strength of the Ca2Al2O5/CaS interface. The prediction of the lowest interfacial energy shows that a stable interface can form between Ca2Al2O5 and MX. Hence, Ca2Al2O5 can be effectively utilized as a nucleation side for CaS (TiN). The present work provides valuable theoretical and technical information for knowledge-based design and prediction of composite inclusion regulation for structural steels, especially for marine engineering steels.

Effect of Sulfur Content on Precipitation Behavior of Dendrite Sulfide Inclusion in Continuous Casted 20CrMnTi Gear Steel

The effect of sulfur content on sulfide inclusion and dendrite MnS in continuous casted 20CrMnTi gear steel is investigated. There are two main types of sulfides in 20CrMnTi steel: pure MnS and TiN–MnS composite inclusions. The number of TiN–MnS is higher than MnS, especially in the edge of the billet. TiN–MnS is smaller both in area and size than pure MnS. The statistical results of dendrite MnS show that the increase of S content decreases the average size of sulfides, whereas raises the number and the maximum size of sulfides. With the S content increasing, the proportion of large‐sized dendrite MnS in steel decreases, but the amount of large‐sized dendrite MnS increases, which results in the increase of number of large‐sized dendrite MnS. The average area of dendrite MnS inclusions first increased and then decreased from the edge to the center of billet, and the maximum area appeared at about 1/2 radius of the billet. Comparison with the microstructure of the two billets, the proportion of ferrite increased with the increase of S content.

Study on the effect of Al-La composite deoxidation on the modification behaviors of TiN and sulfide inclusions in 20CrMnTi gear steel

This article uses experimental and thermodynamic calculations to study the directional modification behavior of TiN and sulfides in 20CrMnTi steel before and after the addition of rare earth La element. The morphologies (SEM) and elemental distributions (EDS) of TiN and sulfide inclusions in steel are characterized using scanning electron microscopy, and the sizes of the inclusions are statistically analyzed. With the addition of rare earth La, the average sizes of TiN and sulfide inclusions in steel decrease, and the proportions of TiN and sulfide inclusions in all inclusions of the steel decrease. The results show that the addition of La element can promote the formation of LaAlO3 in steel, which can be used as the nucleation core of TiN and MnS inclusions in steel, and then form LaAlO3-TiN and LaAlO3-MnS-TiN composite inclusions, which are smaller in size and more uniform in distribution than TiN and sulfide in steel before La element is added. When La is added alone, the average size of TiN inclusion in steel is 2.2 μm. After the deoxidation of Al-La alloy, the average size of TiN inclusion in the steel is 1.9 μm. After Al-La composite deoxidation, the TiN containing inclusions in the steel will be transformed into smaller LaAlO3-TiN composite inclusions. When adding La alone, the average size of sulfide inclusions in the steel is 2.1 μm. When Al-La composite deoxygenation is used, the average size of sulfide inclusions in steel is 1.1 μm, indicating that the Al-La composite deoxygenation has a better improvement effect on sulfide inclusions in steel than the improvement effect of adding La alone.

Influence of Inclusion Parameter and Depth on the Rotating Bending Fatigue Behavior of Bearing Steel

Inclusions are an important parameter affecting the fatigue life of materials. In this paper, the type, size, and quantity of inclusions in bearing steel were quantitatively analyzed using scanning electron microscopy and automatic scanning electron microscopy with an X-ray energy dispersive spectroscopy function. The effects of the inclusion parameters and positions on the rotating bending fatigue properties were analyzed using the rotating bending fatigue test. The results proved that for samples 1 and 2, the inclusions were mainly sulfides, Ti-containing inclusions, and their composite inclusions. For samples 3 and 4, the inclusions were mainly oxides or sulfide–oxide complexes. The number and maximum size of inclusions in sample 2 were relatively small. This was mainly due to the difference in the content of Al, S, and Ca elements in the different samples. The inclusion distance to the surface and the maximum inclusion size had a larger influence on the rotating bending fatigue life in comparison to the inclusion type. Moreover, nitride–oxides had a more detrimental effect on the rotating bending fatigue life as compared to the sulfide–oxide complex inclusions. A model was established on the basis of the inclusion size, depth, and stress by using the Python software. The simulation demonstrated that using five parameters fit well with the experiment results.

Evolution of inclusions in Ti-Ce-Mg deoxidized steel and its effect on acicular ferrite transformation in simulated welding HAZ

The characteristics of non-metallic inclusions in Ti-Ce-Mg deoxidized steel and their influence on the microstructure and toughness of welding heat-affected zone (HAZ) were studied. Results showed that Ti-Ce-Mg deoxidation led to a refined inclusion size and an increase in the number of inclusions below 1 μm. The highest acicular ferrite fraction was obtained in the HAZ of Ti-Ce-Mg steel, and the impact toughness was significantly improved. Ti-Ce deoxidation enhanced the stability of Ti-containing oxide, while Mg treatment promoted its fine dispersion. The final formation of composite inclusions of Ti-Ce-Mg oxide with TiN and MnS enhanced the ability to induce acicular ferrite transformation.

Chromitites and associated mineralization of the Akkarga ophiolitic massif in the southeastern Urals (Russia)

The Akkarga ultramafic massif exposed in the Trans-Uralian megazone represents the mantle section of an ophiolite assemblage that was emplaced into the upper crust during the Permian collision. Ultramafic rocks include harzburgites and subordinate dunites that have undergone complete serpentinization and host podiform chromitite bodies typical of the ophiolite complexes worldwide. Numerous lens-shaped and podiform occurrences of massive and densely disseminated chromitites are surrounded by envelopes of serpentinized dunites whereas nodular chromitites and lenticular bodies of banded disseminated ores are of subordinate importance. Three ore zones are distinguished on the massif, including the Western, Central and Eastern, but only the sites of the latter two are currently accessible for study. Chromite from chromitites of the Central Ore Zone has higher Cr# (Cr/Cr + Al) (0.81–0.83) than that of chromitites of the Eastern Ore Zone (Cr# = 0.67–0.80) and accessory chromite of peridotites (Cr# = 0.52–0.75). Chromites contain mineral inclusions, which are distributed unevenly. The most abundant are inclusions of high-Mg high-Ni olivine (Fo94–98 and up to 1.5 wt% NiO) and calcic amphibole, while inclusions of pyroxenes and base metal sulfides are less common. Platinum group minerals (PGMs) in chromitites are represented by alloys, sulfides, and sulfoarsenides, which occur in single-mineral and composite inclusions. Ruthenium and Os disulfides typically compose the euhedral single-mineral inclusions in cores of chromite crystals, whereas the composite inclusions, mostly of irregular shapes, are dominated by Ir compounds. PGMs are regularly associated with OH-bearing silicates such as amphibole and, less frequently, chlorite. The setting, morphology and composition of the inclusions seem to support a leading role of subsolidus solid-state exsolution in the formation of primary laurite-erlichmanite mineralization in Akkarga chromitites. Subsequent hydrothermal reworking of podiform chromitites and their ultramafic hosts, which is likely related to the supra-subduction setting, led to the precipitation of more diverse interstitial assemblages, comprising base-metal sulfides, nickeline, sulfoarsenides of the Ir-subgroup platinum group elements (IPGE), REE phosphates, zircon, barite, and baddeleyite. Later granite intrusions likely provided an additional contribution of fluid-mobile incompatible elements to chromitites.

Influence of refractories on cleanliness in high-purity C96V saw wire steel

ABSTRACT Four kinds of refractories, MgO, Y2O3, ZrO2 and MgO–CaO, were selected to smelt C96V saw wire steel to choose a suitable crucible material. In detail, the effect of refractory on number, size, composition and morphology of inclusions in steel samples has been studied. The results indicated that all of the steel samples can obtain the target composition of all the elements by using these refractories as a crucible. Both Y2O3 and ZrO2 refractory can also produce excellent steel samples; this is mainly because the order of stability of the four oxides from high to low at steelmaking temperature is CaO > Y2O3 > ZrO2 > MgO. In addition, both Y2O3 and ZrO2 have extremely high stability in the steelmaking process and are difficult to be reduced by any elements in molten steel. Nevertheless, MgO–CaO refractory still has obvious advantages in terms of smelting effect, mainly in the following aspects: the steel samples can obtain the lowest content of T. O (total oxygen content in steel), S and [Al]s, and the lowest value of Al2O3 content in composite inclusions. However, the most troublesome for MgO–CaO refractory is its tendency to absorb moisture in air and become invalid.

Effects of Ce addition on inclusion modification in martensitic stainless steel

The control of inclusion features, i.e., chemical composition, distribution, quantity, and size, is in high demand for stainless steels to achieve good surface quality, pitting corrosion resistance, and mechanical properties. In this paper, the effects of rare earth (RE) modification on the inclusions of martensitic stainless steel were explored. Martensitic stainless steels with various contents of Ce were prepared, and the inclusions in the cast billets were characterized by field emission scanning electron microscopy (FE-SEM) and an automatic analysis system for nonmetallic inclusions in steels (OTS). The effect of Ce on the modification of nonmetallic inclusions during solidification was explored with thermodynamic calculations. The results showed that the addition of Ce modified the oxygen and sulfur inclusions by transforming them from irregular elongated inclusions to nearly spherical RE composite inclusions. Compared with those in basic martensitic stainless steel, nine types of RE inclusions were found in the presence of Ce. As the Ce content increased from 0.048 wt% to 0.092 wt%, the CeAlO3 content decreased, whereas the Ce2O2S content increased. Moreover, there were 80% fewer inclusions than in the basic martensitic stainless steel.

Formation mechanism and control of a kind of pit-shaped defect in Cf53 rolled products

Aiming at the frequent issue of pit-shaped surface defects in S-bearing and Al-killed steel products and the related poor castability due to submerged entry nozzle (SEN) clogging, the melting and casting process of a popular auto steel Cf53 has been studied based on in-situ investigation and experimental analysis. To clarify the generation of the pit-shaped defects, the local surface chemistry, evolution of steel inclusions throughout the melting process, SEN clogging substances, and the internal relationship among them were systematically analyzed. The results show that this type of defect in the Cf53 rolled products is caused by the large-sized composite inclusions rich in CaS, which originate from the molten steel during the refining process, gradually accumulate on the inner wall of the SEN during casting, and finally lead to SEN clogging. The loose structure of clogging inclusions makes them prone to fall off into the mold and get trapped by solidifying steel shell. The formation mechanism of the inclusions was studied through FactSage software calculation. The results show that the increase in total sulfur and total calcium content, and the decrease in total oxygen content and temperature in steel will lead to CaS inclusion formation, which agrees reasonably well with experimental results. An optimized refining process to reduce calcium addition into molten steel is proposed accordingly, which achieves a remarkably alleviation in casting SEN clogging and an elimination of the pit-shaped defects on the final rolled products as well.

Formation mechanism of large-sized CaO-SiO2-CaF2-Al2O3-MgO composite inclusions in super 304H stainless steel rods

Employing silicon deoxidation in the production of Super 304H stainless steel, large-sized CaO-SiO2-CaF2-Al2O3-MgO (CSFAM) composite inclusions are frequently observed in the rods, posing a substantial threat to product quality. This study delves into an analysis of the constituent phases of these large-sized inclusions, identifying the coexistence of liquid phase and spinel phase. Leveraging industrial experiments, systematic sampling of Super 304H stainless steel, and a comprehensive analysis involving dynamic and thermodynamic calculations, this study investigates the formation mechanism underlying such inclusions. The composition of inclusions in the sample before AOD tapping mirrors that of the slag, with high CaF2 content, indicating that they come from slag entrapment. Through kinetic calculations, it is indicated that the time of existence of the liquid film during the ascent of these inclusions is significantly longer than the collision time. This suggests that they are not easily removed and tend to persist in the steel. Despite LF refining, the predominant types of inclusions remain unchanged, and the decrease in temperature leads to the precipitation of solid-phase MgO within the inclusions. Solubility calculations for solid-phase MgO show a rising trend with temperature. Post-casting, MgO and Al2O3 content in inclusions increase, the solid-phase MgO region disappears, and in the subsequent cooling process, inclusions precipitate the stable spinel phase (MgAl2O4). Solubility calculations for solid-phase MgAl2O4 show a temperature-dependent increase. After the completion of casting, the steel ingot undergoes a deformation process through rolling, leading to the transformation of inclusions into large-sized, elongated, composite CSFAM inclusions.

Precipitation and growth mechanism of TiN on Y2O3 (110) and (100) surfaces of yttrium-containing T4003 stainless steel

The Y2O3/TiN interface of main complex inclusions in T4003 stainless steel with rare earth element Yttrium (Y) content of 0.014 wt% was studied. The chemical composition and morphology of composite inclusions were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectrometer (EDS), the formation process of Y2O3/TiN composite inclusions was calculated by the first-principles calculations of the Vienna Ab-initio Simulation Package (VASP). Compared with Fe matrix, TiN is more likely to grow in an uneven state, and tends to exist in stainless steel in the form of Y2O3(100)/TiN(110). The main reason for the stability of the interface system is that the p orbitals of the O atoms at the interface forms covalent bonds with the d orbitals of the Ti atoms. It provides a new idea for improving the properties of stainless steel effectively by using heterogeneous nucleation of inclusions in steel.

Effect of rare-earth Ce on the texture of non-oriented silicon steels

Abstract Macroscopic and microscopic textures of non-oriented silicon steel hot rolled sheets with different rare-earth Ce contents were investigated using X-Ray Diffraction, Electron Back Scatter Diffraction, and field emission scanning electron microscopy, and the magnetic properties of the cold-rolled annealed sheets were examined using a silicon steel sheet testing system. The results show that the addition of rare-earth Ce reduces the proportion of unfavorable γ texture intensity and texture {111} and enhances the proportion of favorable η texture intensity and texture {100} and {110} in the steel. Magnetic property tests show that rare-earth Ce favors the reduction in test steel loss and the increase in magnetic susceptibility. The main reason is that rare-earth Ce combines with O and S in steel to form large-size inclusions, which preferentially precipitate in the liquid steel and inhibit the precipitation of fine AlN and MnS inclusions, while denaturing the inclusions to spherical composite inclusions such as Ce2O2S-MnS, CeS-AlN, and CeAlO3, thus exerting a good effect of purifying the liquid steel and denaturing the inclusions.

Effect of Al on the Cleanliness of the x% Al–7CrSiMnMoV Steel Produced by Scrap Steel

It is crucial for recycling scrap steel to effectively remove impurities such as sulfur and oxygen, which directly determine the characteristics of inclusions in steel liquid. This study attempts to investigate the effect of Al concentration on the cleanliness of x% Al–7CrSiMnMoV steel by directly smelting scrap steel. Impurities such as sulfur and oxygen, as well as alloying elements in steel, are investigated. Also, the evolution characteristics of inclusion in the x% Al–7CrSiMnMoV steel are evaluated. The results show that the oxygen concentration in steel liquid gradually decreases; however, the sulfur concentration in steel liquid first increases and then decreases as the aluminum concentration increases from 0.026% to 0.58%. A high‐cleanliness 0.58% Al–7CrSiMnMoV steel with sulfur and oxygen concentrations of 0.0015% and 0.0018%, respectively, can be obtained. Additionally, the high Al–Ca–Mg–O and high Ca–Al–Mg–O contain S composite inclusions, and a small amount of fine Mn(Ca)S inclusions first form the high‐Al–Ca–Mg–O composite inclusions with an aluminum concentration of 0.026%, then form the high‐Al–Mg–O, Al–Mg–O‐wrapped Mn(Ca)S, and a large number of fine MnS inclusions with an aluminum concentration of 0.11%; eventually, it forms Al–Mg–O‐wrapped CaS as the Al concentrations continuously increase.

The Influence of the Second Phase on the Microstructure Evolution of the Welding Heat-Affected Zone of Q690 Steel with High Heat Input.

Q690 steel is widely used as building steel due to its excellent performance. In this paper, the microstructure evolution of the heat-affected zone of Q690 steel under simulated high heat input welding conditions was investigated. The results show that under the heat input of 150-300 kJ/cm, the microstructures of the heat-affected zone are lath bainite and granular bainite. The content of lath bainite gradually decreased with the increase in heat input, while the content of granular bainite steadily increased. The proportion of large-angle grain boundaries decreased from 51.1% to 40.3%. Overall, the average size of original austenite increased, and the precipitates changed from Ti (C, N) to Cr carbides. During the cooling process, the nucleation position of bainitic ferrite was from high to low according to the nucleation temperature, and in order of inclusions at grain boundaries, triple junctions, intragranular inclusions, bainitic ferrite/austenite phase boundaries, twin boundaries, grain boundaries, and intragranular inclusions at the bainitic ferrite/austenite phase interface. The growth rate of bainitic ferrite nucleated at the phase interface, grain boundary, and other plane defects was faster, while it was slow at the inclusions. Moreover, it was noted that the Mg-Al-Ti-O composite inclusions promote the nucleation of lath bainitic ferrite, while the Al-Ca-O inclusions do not facilitate the nucleation of bainitic ferrite.

Effects of refining slag basicity and vacuum treatment on the cleanliness of bearing steel

The effect of vacuum treatment on the cleanliness of low Ti steel treated with low basicity refining slag was studied by analyzing the change of oxygen content and inclusions characteristics in the steel after the interaction between different basicity slags and GCr15 bearing steels and after vacuum treatment. The results show that the oxide inclusions in the steel are mainly MgO·Al2O3 after slag-steel interaction. The low basicity slag refining is beneficial for decreasing the harm of TiN inclusions due to the better low Ti content control. However, the oxygen content and the number of inclusions in the steel increase with the decrease of slag basicity (CaO/SiO2 mass ratio), which means that the decrease in the basicity is disadvantageous to the cleanliness of steel. Typical inclusions in the steel transform into smaller MgO inclusions and MgS–MgO-(MnS) composite inclusions after vacuum treatment, and the oxygen content of steel is decreased to the same level. Furthermore, the size and number density of inclusions are significantly decreased after the vacuum treatment. It indicates that the combined process of low basicity slag refining and vacuum carbon deoxidation can realize the TiN inclusion control and cleanliness improvement of GCr15 bearing steel.

Influence mechanism of rare earth (RE) on inclusion modification in non-oriented silicon steel

Effects of rare earth (La+Ce) on inclusions in hot-rolled band of 3.0∼3.3%Si-0.8∼1.0%Al non-oriented silicon steel was studied using industrial trials, scanning electron microscope (SEM) and thermodynamic analysis. Furthermore, combining Heterogeneous Nucleation Theory with Edge-to-Edge Matching (E2EM) model, the formation mechanism of complex inclusions was also investigated. Rare earth (La+Ce) would promote the spheroidization and coarsening of inclusions, and then transform into regular and near circle morphology composite inclusions of rare earth. The low content of rare earth (21 ppm) mainly deoxidized and modified Al2O3 inclusions, and formed (La,Ce)AlO3 inclusions. Increasing of rare earth (29–45 ppm) would promote the formation of (La,Ce)AlO3-(La,Ce)2O2S and (La,Ce)2O2S inclusions, reduce the sulfide precipitation, and promote a gradual transformation of the core of composite inclusions from (La,Ce)AlO3 to (La,Ce)AlO3-(La,Ce)2O2S and (La,Ce)2O2S, which agreed well with the thermodynamic analysis. However, rare earth (29–45 ppm) had a weak metamorphic effect on Al2O3 inclusions generated by temperature drop and secondary oxidation. LaAlO3, CeAlO3, La2O2S and Ce2O2S could be the heterogeneous nucleation core of AlN, Al2O3, MgO-Al2O3, typical composite inclusions with (La,Ce)AlO3 and (La,Ce)2O2S as the core would ultimately form.

Investigation on the formation mechanism of composite inclusions by multi-scale characterization in high manganese steel with yttrium addition

The rare earth modification of inclusions is an effective method to solve the critical issue of brittle inclusions leading to the failure of high manganese steel railway frog as one of the most essential assemble units of the railway operating system. The high manganese steel with rare earth yttrium was produced using a vacuum induction furnace. The multi-dimensional structural analysis of composite inclusions in the high manganese steel was performed to clarify the composition, crystal structure, and interface structure of the composite inclusions at multi-scales ranging from micrometers and nanometers to atoms and electrons. The chemical composition and morphology of composite inclusions were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy. After modification with rare earth yttrium, the MnS-Al2O3 composite inclusions in the steel transform into Y2S3-Y2O2S composite inclusions with smaller dimensions and approximately spherical shapes. The interface structure and crystallographic orientation of the Y2S3-Y2O2S composite inclusions were revealed as Y2O2S (100) // Y2S3 (5 0 3) by the focused ion beams scanning electron microscopy and the high-resolution transmission electron microscopy analysis. Moreover, the first-principles calculations were performed to obtain the adsorption energies and electronic structures of Y and S atoms at various positions on different terminations of the three low-index surfaces ((1 0 0), (110), and (111)) of Y2O2S, which reveals the adsorption pathway of Y and S atoms and formation mechanism of enclosed phase Y2S3 on the core phase Y2O2S that the adsorbate Y and S atoms grew parallel to the Y2O2S (1 0 0) surface and formed specific hexagonal ring structures of Y2S3 crystal.