Inclusions In Steel Research Articles

Impact of niobium addition and non-metallic inclusions’ characteristics on the microstructure and mechanical properties of low-carbon CrNiMnMoB ultrahigh-strength steel: A comprehensive investigation

The effect of cooling rate and Nb addition on the phase transformation, microstructures, and mechanical properties of thermomechanically controlled hot-rolled low-carbon CrNiMnMoB ultrahigh-strength steel were studied. The aspects impeding Nb's benefits on hardenability, phase transformation, and mechanical properties were investigated. The hot rolling process was simulated, and a continuous cooling transformation diagram was constructed for the studied steels. Microstructures were analysed using laser scanning confocal microscopy and field emission scanning electron microscopy, with the latter also used for in-depth investigations of the non-metallic inclusions. Transmission electron microscopy was employed to investigate the precipitate characteristics. The concentrations of Nb in the solution and precipitates were quantified for the martensitic and granular bainitic structures. The effect of Nb in solution on phase transformation and strengthening is diminished, and the hardness is reduced by Nb precipitation at an early processing stage. Decreasing the cooling rate promotes the formation of granular bainitic structures rather than martensite. After being subjected to hot rolling followed by water quenching and air cooling, the microstructures are autotempered martensite and fully granular bainite, respectively. Various non-metallic inclusions, including Al2O3, MnS, and Al2O3–MnS, MnS·BN, Al2O3·BN and MnS·Al2O3·BN were observed. The number density and area fraction of non-metallic inclusions in the Nb-containing steel and the air-cooled samples are higher than those observed in the Nb-free and water-quenched samples. Adding 0.04 wt% of Nb slightly increased the strength, but the toughness properties dropped, mainly due to the higher number density and area fraction of non-metallic inclusions and primary large precipitates.

Crystallization Behavior, Viscosity and Structure of CaO–SiO2–MgO–(15~30 Mass Pct) Al2O3 Melts Representing the Oxide Inclusions in Si-Killed Steel

Crystallization Behavior, Viscosity and Structure of CaO–SiO2–MgO–(15~30 Mass Pct) Al2O3 Melts Representing the Oxide Inclusions in Si-Killed Steel

Impact of functional coatings on microstructure and properties of periclase-magnesium aluminate spinel ceramic filter and its purification capacity on molten steel

Reticulated ceramic filters play an important role in the reduction of non-metallic inclusions in molten steel, which can improve the quality of steel products. In this work, periclase-magnesium aluminate spinel ceramic filters with Al2O3 and TiO2 functional coatings were fabricated by using microporous MgO powder, respectively. The effects of the functional coatings on their microstructure, properties and purification capacity on molten steel were studied. The filter with Al2O3 functional coating exhibited the best mechanical properties owing to the good rheological properties of the coating slurry, as well as the formation of in-situ spinel layer connection between the Al2O3 functional coating and the microporous MgO layer of the filter substrate. Compared with the filters without functional coating or with TiO2 functional coating, the filter with Al2O3 functional coating made more Al2O3 inclusions deposit on the filter surface by physical adsorption due to the same chemical composition between the functional coating and inclusions, which significantly improved the adsorption capacity of filter for Al2O3 inclusions in molten steel. Overall, the filter with Al2O3 functional coating had the highest cold compressive strength of 1.4 MPa, a residual retention of cold compressive strength after thermal shock of 65.71 % and an efficiency of 36.56 % in reducing the total oxygen content of the steel.

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 MgO content in refining slag on the non-metallic inclusions in tire cord steel

In order to weaken the corrosion of refractory during the refining process of tire cord steel, the MgO content in the low basicity (w(CaO)/w(SiO2)≈1.0) slags was increased from 7.9% to 12.6% in industrial experiments. The evolution and removal of inclusions during the refining process were investigated, and the slag properties were also measured in laboratory. It is found that during the refining process, the contents of Al2O3 and CaO generally climb in the inclusions, and SiO2 and MnO contents drop accordingly. Even though, the increase of MgO contents in the refining slag has no obvious effect on the evolution trend and the final composition of inclusions. Therefore, the plasticity of inclusions would not be evidently influenced. On the other hand, with the increase of MgO content in slags, the viscosity and surface tension of the refining slags decrease, while the melting point and the melting rate increase. Due to the lower viscosity and surface tension, a higher MgO content in the slag is beneficial for the removal of inclusions in steel. So, a suitable increase of MgO content in the refining slags is suggested considering the melting point of the slag.

Effect of Mg-treatment on transformation of oxide inclusions in X80 pipeline steel

Effect of Mg-treatment on transformation of oxide inclusions in X80 pipeline steel

Quantitative and Qualitative Evaluation of Non-Metallic Inclusions in High-Silicon Steel after Hot Rolling

This paper presents an analysis of non-metallic inclusions occurring in high-silicon steels containing about 3% Si of terms of their type, volume fraction and morphology. The inclusions were divided into 3 main groups: oxides, sulfides, nitrides which together can also form complex. The work was based on numerous metallographic observations in two sections (longitudinal and transverse to the rolling direction). The study was performed on three casts differing in chemical composition. The analyzed casts were characterized by a different content of non-metallic inclusions, which can be associated with slight differences in chemical composition. The analyzed results showed that the most common inclusions were oxides and nitrides. Sulfides occurred sporadically.

Effect of Silicon–Manganese Deoxidation on Oxygen Content and Inclusions in Molten Steel

In order to improve the cleanliness of steel, non-aluminum deoxidation processes have begun to replace aluminum deoxidation processes. Although the aluminum deoxidation process can reduce the oxygen content in steel to <10 × 10−6, this deoxidation method causes fatigue failure resulting from the formation of large-grained spherical (Ds-type) inclusions composed of calcium–aluminate. It also tends to lead to nozzle blockage during casting. Given the above problems, this study conducted an in-depth investigation of silicon–manganese deoxidation. Thermal experiments and thermodynamic calculations were used to assess the impact of different Mn–Si ratios on the oxygen content and inclusion characteristics during the deoxidation process of molten steel with different initial oxygen contents. The experimental samples were analyzed using an oxygen–nitrogen–hydrogen analyzer, a direct reading spectrometer, and an automatic scanning electron microscope. After that, the samples were electrolyzed to observe the 2D morphology and 3D morphology of the inclusions using scanning electron microscopy. Finally, thermodynamic calculations were carried out using FactSage to verify the experimental results. The results indicated that, regardless of the initial oxygen content, silicon–manganese deoxidation maintained the total oxygen content at 35 × 10−6. It effectively managed the plasticization of inclusions in molten steel, predominantly yielding spherical silicates while minimizing Al-containing inclusions. Nevertheless, as the initial content of [O] increased, the size and density of the silicate inclusions in the steel also increased. An optimal point in the number and size of inclusions was observed with an increased Mn–Si ratio. Moreover, the combined utilization of silicon–manganese deoxidation, diffusion deoxidation, and vacuum deoxidation enabled ultra-low oxygen content control of molten steel.

Overview of application of automated SEM/EDS measurements for inclusion characterization in steelmaking

AbstractThe scanning electron microscope equipped with an energy dispersive spectroscopy (SEM/EDS) is considered as a state‐of‐the‐art characterization tool to determine the morphological features and the chemical composition of non‐metallic inclusions in steel. Such a characterization is pivotal to assessing the steel quality, which influences the properties of end products. This paper offers a comprehensive review of the SEM/EDS system, tracing its historical developments and methodological advancements by various research groups which have contributed to non‐metallic inclusion analysis. Then the discussions transition to developments that have matured the SEM/EDS platform. The paper highlights selected examples utilizing the SEM/EDS to examine inclusions across various steel grades and at different stages of the metallurgical process. Finally, latest advancements in integrating machine learning techniques to expedite the analysis process were discussed.

Estimation of probable maximum aspect ratio of MnS inclusions in non-quenched and tempered steel after isothermal compression

Estimation of probable maximum aspect ratio of MnS inclusions in non-quenched and tempered steel after isothermal compression

ОСОБЛИВОСТІ НЕОДНОРІДНОСТІ ПЛАСТИЧНОЇ ДЕФОРМАЦІЇ ГЕТЕРОФАЗНИХ НЕМЕТАЛЕВИХ ВКЛЮЧЕНЬ В СТАЛЯХ

The nature and level of plasticity of microcomposite heterophase inclusions in steels under pressure treatment condition was investigated. Plastic phases in heterophase inclusions of various types under the conditions of hot and cold deformation of steels were investigated. It is shown that each type of inclusions, which are microcomposite formations in steels, is characterized by its own laws of the development of deformation processes, which are determined by their chemical and phase composition, structure, deformation capacity of inclusion phases. The generalized of the plastic behavior of heterophase inclusions of various types with a complex structure have been established and inhibitory effect of non-deformable inclusion phases on the behavior of plastic phases in a wide range of deformation temperatures of steels has been established. The peculiarities of the nature of plasticity of heterophase inclusions with different compositions and structures are discussed. The use of the obtained results will make it possible to develop technologies for obtaining steels with a regulated content and types of heterophase non-metallic inclusions, which will significantly increase their technological plasticity, as well as prevent the formation of various types of defects during pressure treatment of steels.

Characteristics and Formation Mechanism of Oxide–Sulfide Complex Inclusions in High-Speed Railway Wheel Steel

Characteristics and Formation Mechanism of Oxide–Sulfide Complex Inclusions in High-Speed Railway Wheel Steel

Dissociative Adsorption of Hydrogen Molecules at Al2O3 Inclusions in Steels and Its Implications for Gaseous Hydrogen Embrittlement of Pipelines

Hydrogen embrittlement (HE) of steel pipelines in high-pressure gaseous environments is a potential threat to the pipeline integrity. The occurrence of gaseous HE is subjected to associative adsorption of hydrogen molecules (H2) at specific “active sites”, such as grain boundaries and dislocations on the steel surface, to generate hydrogen atoms (H). Non-metallic inclusions are another type of metallurgical defect potentially serving as “active sites” to cause the dissociative adsorption of H2. Al2O3 is a common inclusion contained in pipeline steels. In this work, the dissociative adsorption of hydrogen at the α-Al2O3(0001)/α-Fe(111) interface on the Fe011¯ plane was studied by density functional theory calculations. The impact of gas components of O2 and CH4 on the dissociative adsorption of hydrogen was determined. The occurrence of dissociative adsorption of hydrogen at the Al2O3 inclusion/Fe interface is favored under conditions relevant to pipeline operation. Thermodynamic feasibility was observed for Fe and O atoms, but not for Al atoms. H atoms can form more stable adsorption configurations on the Fe side of the interface, while it is less likely for H atoms to adsorb on the Al2O3 side. There is a greater tendency for the occurrence of dissociative adsorption of O2 and CH4 than of H2, due to the more favorable energetics of the former. In particular, the dissociative adsorption of O2 is preferential over that of CH4. The Al-terminated interface exhibits a higher H binding energy compared to the O-terminated interface, indicating a preference for hydrogen accumulation at the Al-terminated interface.

Structural Behavior of Circular Concrete Columns Reinforced with Longitudinal GFRP Rebars under Axial Load

This paper presents experimental and theoretical assessments of the structural behavior of circular steel fiber-reinforced concrete (SFRC) columns reinforced with glass fiber-reinforced polymer (GFRP) bars subjected to a concentric axial compressive load. Laboratory experiments were planned to evaluate and compare the effect of different design parameters on the structural behavior of column specimens based on experiments and finite element (FE) analysis. The experimental variables were (i) concrete types, i.e., conventional concrete (CC) and fiber-reinforced concrete (FC), (ii) longitudinal reinforcement types, i.e., steel and GFRP bars, and (iii) transverse rebar configurations, i.e., tied and spiral with different pitches. Sixteen column specimens were fabricated and categorized into four groups with respect to rebar configurations and concrete types. The results showed that the failure modes and cracking patterns of those four column groups were comparable, particularly in the pre-peak branches of load-deflection curves. Even though the average ultimate load of the columns with longitudinal GFRP bars was 17.9% less than that with longitudinal steel bars, the ductility index (DI) was 10.2% greater than their counterpart on average. The addition of steel fibers (SF) to concrete increased the axial peak load by up to 3.1% and the DI by up to 6.6% compared to their counterpart CC columns without SFs. The DI of specimens was increased by higher volumetric ratios (up to 12%) and spiral types (up to 5.5%). The concrete damage plastic (CDP) model for FC columns was updated in the finite element software ABAQUS 6.14. Finally, a new simple equation was theoretically proposed to predict the axial capacity of specimens by considering the inclusion of longitudinal GFRP rebars, volumetric ratio, and steel spiral/hoop ties. Good agreement between the proposed model predictions and the experimental/numerical results was observed.

Effect of Rare Earth on the Occurrence Characteristics of Inclusions in High-strength Wheel Steel

Effect of Rare Earth on the Occurrence Characteristics of Inclusions in High-strength Wheel Steel

Improving HIC resistance of pipe-steel by Ti/Mg treatment with insights into hydrogen migration

The presence of inclusions in steels is responsible for hydrogen-induced cracking (HIC), which necessitates control over their size and distribution. The aims of this study are to investigate the effects of different inclusion-modifying elements on steels, as well as reveal the impact of inclusions on hydrogen migration. Various methods, including HIC evaluation, electrochemical hydrogen permeation, silver microprint, and in-situ hydrogen escape observation, are utilized. The results indicate that steel with a Ti/Mg content ratio of 4:1 exhibits favorable comprehensive resistance against HIC. Moreover, the observation of in-situ hydrogen escape observations reveals that steels with a higher number of hydrogen bubbles and a higher ratio of bubbles related to the inclusions demonstrate better HIC resistance. The refined, dispersed, and multi-compounded inclusions facilitate the formation of more complex trapping sites, ultimately improving the dispersion and pinning of dissociative hydrogen atoms. Consequently, employing a multicomponent inclusion modification strategy holds promise for the development of hydrogen-resistant pipeline steel.

Study on the Cleanliness of SWRS82B Hard Wire Steel Refined by Fluorine‐Free Slag with Medium and High Basicity

In order to apply and develop fluorine‐free slag in steelmaking, it is of great significance to study the effect of composition for fluorine‐free refining slag on the cleanliness of molten steel which affects its performance directly. The effect of composition of fluorine‐free refining slag with medium and high basicity on the contents of impurity elements for sulfur and oxygen, and characteristics of inclusions in SWRS82B hard wire steel, are investigated systematically. Sulfide capacity of refining slag is estimated based on the Royal Swedish Institute of Technology model. Dissolved oxygen content in molten steel equilibrated by refining slag is calculated based on Factsage software and classical thermodynamics. The calculated results are in good agreement with experimental results. The plasticity of inclusions at high temperature and low temperature is analyzed by phase diagram and Young's modulus calculation. The best cleanliness and inclusions of SWRS82B steel are obtained with slag composition of 53%CaO–19%SiO2–19%Al2O3–7%MgO, which has good melting characteristics. The impurity elements sulfur and oxygen in steel can be controlled for 26 and 19 ppm, respectively, and the average size of inclusions is 2.84 μm.

Electrochemical properties of MnSe inclusions and improving the pitting corrosion resistance of stainless steel via Se microalloying

Controlling the electrochemical properties of non-metallic inclusions is of substantial interest in the design of corrosion-resistant alloys. To the best of our knowledge, the dissolution and pitting corrosion behavior of selenide inclusions in stainless steels and the improvement of the pitting corrosion resistance of type 304 stainless steels via Se microalloying have not been investigated. In this study, stainless steel specimens containing artificial MnS and MnSe inclusions were fabricated via spark plasma sintering to systematically investigate their electrochemical properties. The superior pitting corrosion resistance and dissolution resistance of MnSe to those of MnS were demonstrated. The results obtained from the sintered specimens were applied to improve the pitting corrosion resistance of type 304 stainless steels via Se microalloying. Adding a trace amount of Se (0.005 mass%) altered the readily soluble sulfide inclusions to dissolution-resistant selenide-type inclusions, resulting in improved pitting corrosion resistance of type 304 stainless steel.

Study on the Evolution of Inclusions in Ce-Modified M50NiL Steel Through the CALPHAD Approach and a Novel Inclusion Prediction Condition

Study on the Evolution of Inclusions in Ce-Modified M50NiL Steel Through the CALPHAD Approach and a Novel Inclusion Prediction Condition

Effect of ladle-lining materials on inclusion evolution in Al-killed steel during LF refining

Abstract The effect of lining materials (Al2O3 and Al2O3–MgO·Al2O3) of ladle on evolution of non-metallic inclusions in aluminum-killed (Al-killed) steel during ladle furnace refining without Ca treatment was investigated through industrial experiments. The results showed that non-metallic inclusions experienced the changes from Al2O3 → MgO–Al2O3 → CaO–Al2O3. During the refining process using either of the two ladle lining materials, for all non-metallic inclusions, the vast majority are distributed in the high Al2O3 area of the CaO–Al2O3–MgO phase diagram, with very little or none in the low melting point zone. Non-metallic inclusions are mainly smaller than 3 μm, while those larger than 3 μm consisted primarily of MgO·Al2O3 and CaO–Al2O3 inclusions. The use of an Al2O3–MgO·Al2O3-lining ladle is more effective in reducing the number density of inclusions in the steel. However, during the refining process, the Al2O3-lining ladle does not have a significant impact on the presence of MgO–Al2O3 and CaO–Al2O3 inclusions in the molten steel. The Al2O3–MgO·Al2O3-lining ladle does not have a significant effect on MgO–Al2O3 inclusions, but it does promote the formation of CaO–Al2O3 and CaS inclusions in the molten steel.