Al2O3 Inclusions Research Articles

A Thermodynamic and Experimental Analysis of Inclusions Modification in AH36 Liquid Steel by Calcium and Magnesium Treatment

The influence of calcium and magnesium treatment under different molten steel conditions, as well as that of the alloy proportion and addition sequence of calcium and magnesium in composite treatment, on the evolution of inclusions in AH36 liquid steel was analyzed systematically based on thermodynamic calculations. The results show that the inclusions in molten steel are mainly Al2O3, which gradually transform into a liquid phase after calcium treatment with a wide range of calcium contents, indicating that calcium treatment has a significant effect on inclusion modification. Magnesium treatment mainly converts Al2O3 into MgO·Al2O3 inclusions in molten steel; however, it is not suitable to modify inclusions with magnesium treatment alone since it does not produce a significant liquid phase. The effect of calcium and magnesium composite treatment varies with the alloy content composition and the order of alloy addition. The liquid phase range of inclusions follows the order of 80%Ca + 20%Mg composite treatment > calcium treatment > 50%Ca + 50%Mg composite treatment > 20%Ca + 80%Mg composite treatment. Combining the thermodynamic and experimental analysis results, it can be concluded that the composite treatment of magnesium followed by calcium is the best. Specifically, a small amount of magnesium should be added first as the nucleating particle to promote the fine dispersion of the inclusions, thus reducing their impact on steel performance. Then, calcium should be added to modify the surface of the inclusions into a liquid phase, which can effectively reduce nozzle clogging.

Reinforced High-Entropy Fluorite Oxide Ceramic Composites for Thermal Barrier Coating Application.

High-entropy ceramics hold promise for application as thermal barrier coating materials. However, a key challenge in practical applications lies in the low fracture toughness compared to that of yttria-stabilized zirconia (YSZ). Herein, we designed (Hf,Zr,Ce,M)O2-δ-Al2O3 (M = Y, Ca, and Gd) ceramic composites by following a set of fundamental guidelines. First-principles calculations predicted that the inclusion of Al2O3 in compositions containing the other four binary oxides decreased the propensity for single high-entropy phase formation. Instead, it increased the potential for Al2O3 to form a second phase within the high-entropy ceramic matrix, compared to compositions without Al2O3. Ceramic composites consisting of the Al2O3 second phase in a high-entropy fluorite oxide (Hf,Zr,Ce,M)O2-δ matrix were synthesized in situ via conventional solid-state reactions from the five constituent binary oxides. Both the hardness and fracture toughness of the ceramic composites were enhanced due to toughening mechanisms from the discrete Al2O3 particles, microcracks, and crack deflections. Additionally, the ceramic composites exhibited coefficients of thermal expansion and thermal conductivities comparable with those of YSZ. Our findings demonstrated the potential of the high-entropy (Hf,Zr,Ce,M)O2-δ-Al2O3 ceramic composites for advanced thermal barrier coating materials and offered a possible approach to reinforce other high-entropy oxide-based ceramic systems.

Effect of slag composition and refractory material on the formation and modification behaviour of inclusions in Al-killed steel

ABSTRACT In this study, to investigate the effects of CaO-SiO2-Al2O3-MgO slag with CaO/SiO2 (C/S) ratios of 3.81 to 7.65 and CaO/Al2O3 (C/A) ratios of 0.89 to 3.14 on the interactions amongst ‘refractory-molten steel-inclusions’, a series of thermodynamic calculations and laboratory experiments were conducted. The results show that the number density of inclusions exhibits a decreasing trend when the basicity of slag ranges from 3.81 to 7.67. Furthermore, as the C/A ratio of the slag increases, the number density of inclusions initially decreases and then increases. This trend is consistent with the behaviour of the total oxygen (T.[O]) content in the steel. Tests with MgO crucible reveal that the main inclusions in steel are MgAl2O4 (MA) spinel with MgO levels exceeding the stoichiometric ratio of MA compound. When using Al2O3 crucibles, the steel primarily contains Al2O3 inclusions, accompanied by a proportion of Mg-modified Al2O3 inclusions. The MgO crucible exhibits a stronger ability to transfer Mg to molten steel compared to the slag containing 5 wt.% MgO under the conditions of this study. Additionally, the composition of the ladle slag has a significant influence on the formation and modification behaviour of MA inclusions.

Reaction mechanism between MgO and MgO–C lining refractories and an ultra-low-carbon Al-killed steel

In the current study, effects of the carbon in MgO-based refractory rod on the cleanliness of an ultra-low-carbon Al-killed steel and on the corrosion degree of the refractory were investigated using laboratory experiments, thermodynamic calculation and a kinetic modeling. After a 90-minute reaction between the MgO refractory rod and the steel, the penetration of the molten steel into the MgO refractory was quite small and an about 20 µm thick interfacial layer containing the liquid slag phase and the spinel was generated at the interface. The liquid slag phase was mainly composed of Ti3O5, CaO, MgO, and Al2O3, while the spinel was mainly composed of Al2O3 and MgO. The composition of inclusions in the steel varied little due to the dense interfacial layer at the steel/refractory interface hindering the mass transfer between the steel and the MgO refractory. When the steel reacted with the MgO–C refractory for 90 min, the molten steel penetrated 1 mm into the MgO–C refractory through grain boundaries, forming channels due to the graphite consumption. A new 20 µm thick interfacial layer containing CaS and MgO was formed between the steel and the refractory. The formation of CaS was favored at the steel/MgO-C refractory interface and was rarely existed at the ssteel/MgO refractory interface during cooling process. The average content of MgO in inclusions increased from 10.29 wt.% to 46.55 wt.% while that of Al2O3 in inclusions decreased from 89.71 wt.% to 53.45 wt.% reacting for 90 min. The experimental result agreed well with the current kinetic model combined with thermodynamic calculation results. The influence of different content of T.O and T.Al in the steel on the composition of the steel and inclusions were also investigated using the current model. It is indicated that the content of MgO in inclusions increased with the decreasing T.O content and the increasing T.Al content in the molten steel.

Competition and Precipitation Mechanism of Inclusions in the Al–Ti–Mg Complex Deoxidized Steel

In this work, the competitive precipitation mechanism of inclusions in Al–Ti–Mg complex deoxidized steel is investigated by experimental observation and thermodynamic analysis. Many types of inclusions are observed in steel, and the two and multi‐layer structural inclusions are composed of the single‐particle inclusions of TiS, TiN, TixOy, MnS, Al2O3, and MgAl2O4. Thermodynamic calculation results suggest that the transformation order of Al2O3 contains two pathways: one is Al2O3 → MgAl2O4 → MgTi2O4 → MgO and the second is Al2O3 → Ti2O3 → MgTi2O4. However, the transformation reaction of Al2O3 into MgAl2O4 or Ti2O3 has not completely ended, and no MgTi2O4 and MgO inclusions are found in the steel sample. The precipitation order of Ti2O3, TiN, TiS, and MnS in present steel is Ti2O3 → TiS → TiN → MnS. MnS only precipitated in solid steel, TiS, and TiN precipitated in the solid–liquid interface at T < 1794 K and T < 1796.5 K, respectively. The actual transformation and precipitation order of inclusion in the present Al followed by Ti–Mg deoxidized steel is Al2O3 → MgAl2O4 → Ti2O3 → TiN → TiS → MnS or Al2O3 → Ti2O3 → TiN → TiS → MnS.

Influence of different introduction methods of graphene on the mechanical properties and cutting performance of Al2O3/TiB2 ceramic tool materials

Influence of different introduction methods of graphene on the mechanical properties and cutting performance of Al2O3/TiB2 ceramic tool materials

Al Alloy Melting Behavior and Interfacial Reactions with Steel Under Natural Convection.

The Al alloy melting behavior and interfacial reactions during the steelmaking process of high-Al automotive steel were investigated in this study. The total dissolution time of Al bars (20 × 20 × 80 mm) in molten steel was quite short, decreasing from 21.4 s to 10.0 s with an increase in bath temperature from 1580 to 1620 °C. The Al alloy melting process at the molten steel temperature of 1600 °C included the formation of a solidified steel layer, the latter's rapid melting, and Al alloy normal melting, while at 1600 °C, the process included a second increase in the thickness of the solidified layer. Because steel elements such as [Fe], [C], [O], and [N] could diffuse during the whole Al alloy melting process, an Fe (Al)-FeAl-FeAl2-Fe2Al5-Al diffusion layer along the direction of the Al-rich matrix could be found at the Fe-Al interface. Moreover, FexO, Al2O3, and unstable AlN inclusions could be observed in the FeAl layer. This study also investigated how to reduce the number of these easily formed inclusions. Decreasing the pre-heating process time and dissolved oxygen content could be useful in decreasing FexO and Al2O3 inclusion formation. Some small-sized AlN inclusions formed in the center of the Al bars where they could not come into contact with the molten steel directly during the melting process; even for the immersion time of only 1 second, these inclusions were not stable in molten steel at the refining temperature and disappeared during the melting process.

Crystallization Behavior and Structure of CaO–SiO2–Al2O3 Melts Representing the Oxide Inclusions in Si‐Mn Deoxidized Steel

For further optimization of the inclusion plasticization control process of Si‐Mn deoxidized steel, the crystallization behavior and structure of CaO–SiO2–Al2O3 system inclusions are investigated. The crystallization behavior of four typical low melting point CaO–SiO2–Al2O3 inclusions at 1000 to 1250 °C is studied by steel crucible isothermal heating experiment. The obtained results reveal that the glassy stability of the inclusions is high when the composition of low melting point inclusion is located in the eutectic region of tridymite, pseudowollastonite, and anorthite in the ternary phase diagram. However, when the composition of the inclusion is located in the eutectic region of melilite, pseudowollastonite, and anorthite, it is easy to undergo glass‐crystallization transformation and precipitate wollastonite and anorthite crystalline phases when isothermal heating at 1100 to 1200 °C. In addition, the crystallization mode of these inclusions is mainly surface crystallization, and the crystallization degree of inclusions increases with the increase of heat treatment temperature and time. The activation energy of crystallization and the content of nonbridging oxygen in the silicate structure NBO/T can be used to predict the crystallization ability of inclusions. The greater the activation energy of crystallization and the smaller the NBO/T value, the higher the glassy stability of the inclusions.

Dynamic interaction between refractory and low‐carbon low‐silicon Al‐killed steel

AbstractTo investigate the dynamic interaction between refining refractory and low‐carbon low‐silicon Al‐killed steel, the “refractory‐molten steel‐inclusion” system was analyzed using dynamic erosion experiments and the FactSage database. This study discussed the formation of interfacial layers between various refining refractories and molten steel, as well as the transformation of nonmetallic inclusions in steel. The findings indicate that the interaction between refractories and molten steel produces a distinct interface layer. The influence of various refining refractories on inclusions varies significantly. MgO‐C refractory promotes the formation of MgO·Al2O3 inclusions in steel, while Al2O3‐MgO refractory leads to the formation of SiO2‐MnO‐Al2O3 inclusions. Both Al2O3‐SiC refractory and Al2O3‐MgO‐C refractory result in Al2O3 inclusions with trace levels of MgO. Steel refined with Al2O3‐MgO‐C refractory has increased MgO content within Al2O3 inclusions but still does not reach the stoichiometric ratio of MgO·Al2O3. As the initial Al content increases, the influence of MgO‐C refractory inclusions becomes increasingly noticeable. The average MgO content within the inclusions rises with the reaction duration, achieving as high as 62.9%. The transition path of Al2O3 inclusions in molten steel follows “Al2O3→MgO·Al2O3→MgO.”

Effect of Trace Rare Earth Element Cerium (Ce) on Microstructure and Mechanical Properties of High Strength Marine Engineering Steel

In this paper, FH460 special steel with rare earth element cerium (Ce) was selected, and the control group without Ce was set up. By changing the content of Ce, the microstructure, phase transition point, and mechanical properties of the test steel were observed to study the effect of trace rare earth element Ce on the microstructure and mechanical properties of high-strength marine engineering steel. The morphology and energy spectrum of inclusions in three kinds of test steels were observed by SEM, and the morphological changes in inclusions in FH460 high-strength marine engineering steel after adding Ce were investigated. The fracture morphology and energy spectrum analysis were carried out by combining the tensile test at room temperature and the gradient low temperature impact toughness test, and the effect of trace Ce on the mechanical properties of the test steel was comprehensively analyzed. The results show that the addition of Ce changes the phase transformation temperature of Ac1 and Ac3, and refines the original microstructure of the test steel. SEM observation showed that the addition of Ce changed the long strip MnS and polygonal irregular Al2O3 inclusions into ellipsoids, which reduced the size of inclusions. The gradient low temperature impact test shows that with the decrease in temperature, the fracture dimple depth of the three test sheets of steel decreases, and the Ce-containing test steel forms a deep dimple centered on rare earth inclusions, which hinders the crack propagation and significantly improves the low temperature impact toughness of the test steel.

In Situ Observation of Precipitation Behavior of MnS during Solidification of Steel Melt Intended for Production of Nonquenched and Tempered Steel

Two heats of steel are melted using a vacuum induction furnace in the laboratory, with one heat undergoing magnesium treatment and the other being subjected to a combined magnesium–calcium treatment. The precipitation and agglomeration behaviors of inclusions of these two steel samples are observed using a high‐temperature confocal laser scanning microscopy. MnS precipitates form around oxide cores and undergo rapid growth during the solidification process of molten steel, and these MnS precipitates with oxide cores react with the cores, resulting in the transformation of the MnS into complex sulfides. In comparison with Al2O3 inclusions, MgO·Al2O3 inclusions have a lower critical velocity (V c), making them more susceptible to being engulfed by the solid–liquid interface. As the size of colliding inclusions increases, the coalescence–collision frequency (E 0) initially decreases until it reaches a minimum value. After that, with further size increments, the frequency starts to increase. During the inclusions growth process through collision, there is a distinct zone where coalescence–collision frequency is low. Inclusions that reach this zone struggle to grow further due to reduced collision coalescence, consequently leading to a predominance of inclusions with diameters in this zone.

Effect of MgO on solidification crystallisation behaviour of high SiO2 content MnO–SiO2–Al2O3-based inclusions in Si–Mn-killed steel

Aiming at avoiding the formation of high-hardness crystalline phase in inclusions, the effect of MgO on the solidification crystallisation behaviour of high SiO2 content MnO–SiO2–Al2O3-based inclusions was investigated. The results showed that the high SiO2 content MnO–SiO2–Al2O3 inclusions precipitated the pure SiO2 phase during the solidification process. With the increase of MgO content in inclusions, the content of the SiO2 phase decreased continuously, while the MgSiO3 phase began to precipitate and the content increased gradually. Besides, 20 wt.% MgO content inclusions first precipitated the Mg2SiO4 phase, and the MgSiO3 phase was formed in the subsequent solidification process. Thermodynamic calculation results indicated that the beginning of crystallisation temperature first decreased and then increased with the increase of MgO content in inclusions. However, the calculation results were partially different from the experiment results, because inclusions became the undercooling system during solidification and led to crystallisation hysteresis. The increase of MgO content in inclusions decreased the content of bridging oxygen and resulted in the depolymerisation of complex network structures, which promoted the crystallisation of inclusions. Moreover, the crystalline phase formed in inclusions transformed along the route of “SiO2 phase–MgSiO3 phase–Mg2SiO4 phase” with the increase of MgO content in inclusions.

Phase evolution at interface between magnesia refractories and low-density steel/slag by Mg/Ca mass transfer

Phase evolution at interface between magnesia refractories and low-density steel/slag by Mg/Ca mass transfer

Effect of MgO on Crystallization Behavior of CaO–SiO2–Al2O3 Inclusions in Si–Mn Deoxidized Steel During Solidification Stage

Effect of MgO on Crystallization Behavior of CaO–SiO2–Al2O3 Inclusions in Si–Mn Deoxidized Steel During Solidification Stage

Mechanism analysis of pitting induced by Al2O3 inclusions: insight from simulation calculation

Mechanism analysis of pitting induced by Al2O3 inclusions: insight from simulation calculation

Effect of Interface Property on the Agglomeration Characteristic of Inclusions in High Al Steel with Different Al Contents

Herein, a 3D stability diagram is established in the AlON system. Based on that, four sets of experiments with different Al contents are designed to prepare different inclusions. Subsequently, the agglomeration behavior of inclusion is observed in situ by using confocal laser scanning microscopy (CLSM) combined with an infrared image furnace. The sample with inclusions is heated to melt and the agglomeration behavior of inclusion is recorded by the CRT monitor of CLSM. The calculated agglomeration force of inclusion shows that when the Al content increases from 0.5 to 3 pct, the agglomeration force of Al2O3 inclusions decreases from 7.2 × 10−16 ≈ 6.0 × 10−14 N to 1.2 × 10−16 ≈ 3.2 × 10−15 N. As the Al content increases from 6.5 to 10 pct, the agglomeration force of AlN inclusions increases from 2.2 × 10−17 ≈ 1.1 × 10−15 N to 1.7 × 10−16 ≈ 7.9 × 10−15 N. The theoretical calculation also shows that the agglomeration force of Al2O3 inclusions decreases and that of AlN inclusions increases with the increasing Al content. When the Al content is >4.7 pct, the agglomeration force of AlN inclusions is larger than that of Al2O3 inclusions.

Effect of rare earth element on H13 microscopic structure and mechanical properties

In view of the phenomenon that irregular inclusions are easy to use as crack sources, rare earth H13 steel with different gradients is designed. The results showed that ellipsoidal rare earth inclusions (Ce2O3, CeAlO3 and Ce2O2S) were formed from irregular Al2O3 inclusions with the assistance of rare earths. The carbides that precipitated from liquid phases were arranged in a network along the grain boundary, forming composite carbides that are rich in Mo and V. Along the grain boundary, the morphology of the composite carbides got finer, and MC-type carbides enclosed the modified inclusions into nuclei, facilitating their precipitation. After annealing, the microstructure revealed that the carbides were dispersed in black segregated patches along the grain boundary and were discontinuous. The average diameter of carbides decreased from 109.7 to 79.2 nm in the same region according to a statistical comparison of the number of carbides before and after the addition of rare earth elements. The carbides were distributed alongside primary carbides as tiny particles of M7C3 and M23C6 secondary carbides. Especially when the rare earth content was 0.032 wt-%, the impact toughness increased to 34%. This work offers a reference value for the practical application of rare earth in hot work die steel in addition to revealing the strengthening mechanism of ultra-high strength RE-13 steel.

Effect of ladle slag composition on the cleanliness of Al-Ti deoxidized interstitial-free steel

The effect of slag composition on the cleanliness of Al-Ti deoxidized interstitial-free steel produced via basic oxygen furnace (BOF)-ladle furnace (LF)-Ruhrstahl-Heraeus (RH)-continuous casting (CC) process was investigated by the systematic samplings and analyses for four heats in a steel plant in China. Oxygen/nitrogen analyzer, automatic scanning electron microscope, field-emission scanning electron microscope, and energy spectroscopy analysis were used to analyze the variations of number, size, type, and morphology of inclusions in molten steel from RH to tundish, and X-ray fluorescence was used to analyze the slag composition. The relationship between slag composition and inclusion characteristics in molten steel was investigated. The effect of slag composition on the oxygen mass transfer from the slag–metal interface to liquid steel was also studied through a theoretical calculation. The results showed that the cleanliness of molten steel was greatly affected by the slag composition. The deterioration of steel cleanliness was mainly arisen from a serious reoxidation of molten steel by oxidizing components like (T.Fe + MnO) in top slag during RH refining process. A weak ability to absorb inclusions of top slag with high CaO/Al2O3 and CaO/SiO2 mass ratios was confirmed from the inclusions analyses. The size and number of Al2O3 inclusion clusters were larger, and Ti content in Al2O3-TiO x inclusions was higher from RH to tundish in the case of serious reoxidation. The reduction of FeO content and keeping the CaO/Al2O3 and CaO/SiO2 ratios at about 1.6 and 4–7, respectively, in top slag during RH refining process was beneficial to minimize the reoxidation of Al and Ti and increase the inclusion absorption ability of top slag.

Periclase-magnesium aluminate spinel ceramics filter with excellent purification efficiency on molten steel prepared from Mg(OH)2: Effect of fused MgO content

Periclase-magnesium aluminate spinel ceramics filter with excellent purification efficiency on molten steel prepared from Mg(OH)2: Effect of fused MgO content

Inclusion Removal Process of Homogeneous CuCr50 Alloy In-Situ Synthesized by Al-Mg Composite Strengthening Reduction Coupling Slagging.

To overcome the problem of Cr2O3 and Al2O3 inclusions in CuCr50 alloy prepared by aluminothermic reduction method, in this paper, a novel methodology for strengthening metal-slag separation through in situ slagging is proposed. CuCr50 alloys were prepared by metallothermic reduction using Al and Al-Mg as reducing agents, and the physical properties of the slag, such as viscosity, density, and surface tension, were adjusted by controlling the proportion of CaO in the slagging agent in the raw material to achieve good separation of the slag-metal. The results show that with the ratio of CaO increased, CaO and MgO were coupled to make slag, which combined with Cr2O3 and Al2O3 to form CaCr2O4, MgCr2O4, and CaAl4O7 in the slag, thus reducing the content of impurities in the alloy. When RCaO/(CaO + Al2O3 + MgO) = 20%, the Cr content ranged from 46.61% to 47.09%, the inclusions accounted for 1.60%, the Cr particle size was refined to 20 µm, the number of Cr spherical crystals accounted for 9.88%, the conductivity reached 14.96 MS/m, and the hardness reached 100.23 HB. After heat treatment, the Cr phase was refined in the alloy, the conductivity increased from 14.96 MS/m to 18.27 MS/m, and the hardness increased from 100.23 HB to 103.1 HB. This method is expected to provide an effective method for the preparation of CuCr50 contact materials.