Inclusions In Steel Research Articles

In-Situ Observation of Steel/Slag/Inclusion Interaction by Means of High-Temperature Confocal Scanning Laser Microscopy

Non-metallic inclusions (NMIs) in steels have been the focus of various experimental studies due to their detrimental character. While isolated processes, such as agglomeration or dissolution, have been well investigated, holistic in-situ views with high-temperature confocal scanning laser microscopy (HT-CSLM) have been rare. In this work a novel and suitable method is presented to simultaneously observe agglomeration, movement, detachment, and dissolution of non-metallic inclusions by combined the melting of steel and slag with a dual-crucible approach. Therefore, different steel/slag combinations were tested. It is shown that, with transparent that does not become tarnished by the ions stemming from the steel, the steel’s surface and non-metallic inclusions are observable. Furthermore, technological limitations are discussed, including restrictions regarding the melting point of steels and certain steel/slag combinations.

Local corrosion characteristics of CaS/CaO–MgO–Al2O3 inclusions in low-alloy steel under multi-factor mechanisms

The influence of inclusions corrosion behavior under multi-factor local corrosion mechanisms was researched by SKPFM, TOF-SIMS, EBSD, and in-situ corrosion tests. The model of the local corrosion behavior of CaO/CaS–MgO–Al2O3 inclusion under the multifactor mechanism was established. The structural defect area at the boundary of the inclusions acted as the anodic phase where corrosion occurs preferentially, and the CaS of the inclusion underwent a chemical dissolution process. TiN, TiS2 and TiO2 were gradually shed, and the MgO, Al2O3 and CaO inside the local corrosion area were not completely shed. The gap defect of inclusion was the preferred condition to induce local corrosion when the matrix contains galvanic corrosion effect, dislocation region and the gap defect, and the process of anodic dissolution occurred in the dislocation region. There was no gap defect, the environment could not completely provide the driving force for local corrosion, and the possibility of non-local corrosion existed. The existence of gap defect provided the condition for the existence of solution, and provided the double layer contribution of potential difference of inclusion/matrix and solution.

Study on the effect of Al2O3 on the crystallization behaviour of MnO–SiO2–MgO inclusions in tire cord steel

ABSTRACT Aiming at avoiding the formation of high melting point inclusions containing Al2O3 and reducing the wire breakage rate of the tire cord steel. MnO–SiO2–10wt.%MgO–(5wt.%, 10wt.%, 15wt.%, 20wt.%) Al2O3 system were designed to investigate the crystallization behaviour by XRD, SEM-EDS, FactSage 8.0. The results indicate that the Mn/Mg element ratio of the Mg-Mn olivine phase precipitated from the system varies. Mg–Mn olivine phase is formed by the interaction of the components in the melt or by the occurrence of homogeneity and the liquidus temperature of the system decreases with the increase of Al2O3 content. Al2O3 lowers the melting point of the whole system by forming the low melting point phase Mn3Al2Si3O12. To obtain low melting point plasticized inclusions, the Al2O3 content of the system needs to be controlled in the range of 15–20 wt.%.

Study on the formation mechanism of clogging layer of rare earth microalloyed Q355 steel’s submerged entry nozzle and process optimization

ABSTRACT The formation mechanism of the clogging layer of the alumina-carbon submerged entry nozzle in the smelting process of rare earth Q355 steel was investigated in this paper. First, the inclusions in the molten steel were discovered to be primarily composed of CaAl2O4, MgO, CaS, and CeAlO3. The mass fraction of solid inclusions increases as the rare earth content increases, and the proportion of inclusions, primarily CaAl2O4, changes. Calcium titanate and cerium aluminate formation can be inhibited by high [Ca] content. XRD and scanning electron microscopy were then used to examine the phase composition and morphology of the inner and outer arcs of the clogging nodules. The clogging was found to be divided into three layers: the nozzle matrix, the reaction layer, and the steel layer. Finally, it is concluded that the dissolution of C element in refractory material is the cause of nozzle blockage, and the core cause of nozzle blockage is the deposition of Al2O3, CaAl2O4, and rare earth compounds. Meanwhile, solutions to nozzle blockage are provided from the perspectives of top slag optimization, the deoxidization process, the calcium treatment process, and protective pouring.

Effects of Rare Earth La–Ce Alloying Treatment on Modification of Inclusions and Magnetic Properties of W350 Non-Oriented Silicon Steel

In order to study the effects of rare earth La–Ce alloying treatment on the characteristics of inclusions in non-oriented silicon steels, industrial experiments were conducted studying the composition, morphology, size and quantity of inclusions in W350 non-oriented silicon steel during the RH (Ruhrstahl-Hereaeus) refining process and tundish process, after rare earth treatment. The products were analyzed by means of ICP-MS (inductively coupled plasma mass spectrometry), SEM/EDS (scanning electron microscope-energy dispersive spectrometry), and ASPEX (automated SEM/EDS inclusion analysis). The research results showed that the types of inclusions in experimental steel changed significantly after rare earth treatment. The types of inclusions after RE (rare earth) treatment are typically rare earth composite inclusions that are mainly composed of (La, Ce)Al2O3, and conventional inclusions. The addition of rare earth promotes the agglomeration of inclusions; the morphologies of the inclusions are mostly blocky, and some are distributed in long strips. After rare earth treatment during the RH refining process, the number of inclusions with sizes of 1.0~3.5 μm in the experimental steel is increased, and the average size of the inclusions is 2.66 μm. In addition, the number of inclusions larger than 4 μm in the specimens increases due to the collision and growth of inclusions caused by the RH circulation. After rare earth treatment during the tundish process, the number of micro inclusions with sizes of 1.0~2.5 μm in the specimen steels decreases, while the number of inclusions larger than 5 μm increases. The size distribution of micro inclusions in hot-rolled sheets after rare earth treatment was studied using TEM (transmission electron microscopy). In the specimens without rare earth, the content of micro inclusions (≤1 μm) is 51,458.2/mm2 and the average size is 0.388 μm. In the specimens with rare earth added, the content of micro inclusions (≤1 μm) is 24,230.2/mm2 and the average size is 0.427 μm. Compared to sheet produced by the original process, the iron loss of the 0.35 mm finished experimental sheet is reduced by 0.068 W/kg, and the magnetic induction is increased by 0.007 T. The iron loss of the 0.50 mm finished experimental sheet is reduced by 0.008 W/kg, and the magnetic induction is increased by 0.004 T. After rare earth treatment, the average size of micro inclusions increases and the magnetic properties are obviously improved.

Efficient mitigation of railway induced vibrations using seismic metamaterials

The fast growth of railway transport pushed by its sustainability requires all railway stakeholders to work together to minimise any possible drawbacks that might slow down this positive trend. Among these, the induced vibrations generated at the wheel–rail interaction during train passage are the most significant, especially in urban areas where in the form of ground-borne vibrations and/or noise negatively affects the daily life of the residents. In this direction, the innovative concept of seismic metamaterial can enhance the vibration attenuation levels of existing mitigation measures and, at the same time, ensure a straightforward application in the railway environment. This paper uses a combined vehicle/track/soil prediction dynamic model of the T2000 LRV (Light Rail Vehicle) tram operating in Brussels, based on a two-step approach already validated in the past, to analyse the effects that the inclusion of seismic metamaterials within the transmission path has in terms of vibration attenuation. In particular, a four-by-four group of piles is examined with different material proprieties for the inclusions, considering a range of velocities and distances from the track in order to quantify the achievable Insertion Loss (IL) for each configuration depending on the distances and the tram speed, attaining ILs up to 10 [dB]. The study is then extended to other possible arrangements of the group of piles, providing a direct relationship between the repetitiveness of each row of the primitive unit cell of the metamaterial and the gained levels of attenuation, in order to give a base for the costs of this type of mitigation measure. Furthermore, the influence on the attenuation levels of the soil characteristics, is evaluated by considering an ideal uniform underground, extending the IL to 18 [dB] in the case of steel inclusion. Finally, the paper gives insights into the use of metamaterials as mitigation measures for railway-induced vibration in order to understand and evaluate the potential of this novel concept and its benefits.

Evaluation and Analysis of the Influence of Rare-Earth Ce on Inclusions in Heavy Rail Steel

The effect of rare-earth Ce on the evolution behaviour of inclusions in heavy rail steel was studied. The addition of Ce can significantly reduce the number and size of class A, B, D, and Ds inclusions in the heavy rail steel smelting process. According to the statistical analysis of the size of inclusions in steel, the number and size of A and B inclusions in steel tend to decrease significantly, while D and Ds inclusions disappear. Ce splits the aluminium inclusion into several small-sized inclusions and improves the morphology of the large-size aluminium inclusion, thereby making aggregation and growth difficult while facilitating easy floating and removal. Because the addition of Ce reduces the concentration of S element in steel, MnS inclusions are difficult to grow. The decrease in the number and size of core inclusions required for MnS growth leads to a corresponding decrease in the number and size of MnS inclusions. Meanwhile, the S element also easily gathers on the surface of CaO–MgO–Al2O3–SiO2–CeO inclusions, forming composite inclusions that are more easily removed, thus reducing the quantity and size of MnS inclusions.

Influence of various thermal conditions on the composition of high‑temperature diffusion oxides (satellite inclusions) in solid steel

The main goal of any modern production of long products is to ensure the required quality of finished products. One of the important quality indicators, along with mechanical and technological properties, is the quality of the rolled metal surface. The article presents the results of experimental studies of the composition of high‑temperature diffusion oxides formed on the surface of artificially deposited defects under various conditions of temperature exposure using the microrentgenospectral method on a scanning electron microscope with an energy dispersive microanalyzer. The characteristic features in terms of the percentage and presence of certain chemical elements in the scale of various steel grades have been established.

Effect of Nitrogen Content on the High Cycle Fatigue Properties of Titanium Microalloyed Steel

The high cycle fatigue properties of three industrial 0.12% Ti microalloyed steels with different nitrogen contents (56, 40, and 30 ppm in molten steel of tundish) are investigated. The results show that <20% of the fatigue crack initiation sites are oxide inclusions of size in 16.8 μm ≈ 55.9 μm, while the rest 80% are surface defects. No TiN inclusions cause fatigue failure and the fatigue limit strength slightly decreases with increasing N contents as the yield strength decreases with a coarser ferrite grain. Inclusions characterization in the section near the fracture shows that the average sizes of TiN inclusions in H56, M40, and L30 steels are 3.50, 3.22, and 2.89 μm, and the maximum sizes are 6.92, 6.67, and 6.23 μm, respectively. Calculating for a cooling rate of 0.2 K s−1 using ChemAppPy precipitation model, the size of TiN inclusions will increase from 6.1 to 7.1 μm, when increasing N content from 30 to 60 ppm. The relationships between nitrogen content, TiN inclusions, and fatigue failure quantified by experimental test and modeling show that the nitrogen content in steel can be relaxed up to 60 ppm when considering economical denitrogenization and fatigue safety.

Properties of typical non-metallic inclusions in steel: First-principles calculations

Properties of typical non-metallic inclusions in steel: First-principles calculations

Effect of Bismuth and Telluride on the Inclusions of Sulfur Free-Cutting Steel

The development of free-cutting steel is inseparable from the development of environmentally friendly alloy elements and the control of inclusions shape. Alloying elements can affect the composition, morphology, size, and distribution of inclusion, which are the main factors affecting the machinability of free-cutting steel. This study selected sulfur free-cutting steel with different chemical compositions as the research object to examine the effects of bismuth and bismuth tellurium on sulfur-containing free-cutting steel through electrolytic corrosion experiments, metallographic microscopy, scanning electron microscopy, energy spectrum, and electron backscattering analyzer. The results showed that the microstructures of free-cutting-steel containing sulfur, free-cutting steel containing sulfur bismuth, and free-cutting steel containing sulfur bismuth tellurium are composed of ferrite, pearlite, and inclusions. The inclusions in sulfur-containing free-cutting steel are chain, cluster, and a few dotted MnS. The inclusions in sulfur-bismuth free-cutting steel are point and a few dotted MnS. After the addition of Te, the number of dotted inclusions is reduced, while the number of chain and cluster inclusions is increased. Most of the inclusions in bismuth-containing free-cutting steel are flake inclusions, and the class II MnS change into class III MnS, which is beneficial for improving the free-cutting property of steel and to reduce anisotropy. With the addition of Te, MnS of other shapes, such as heart, water drop, butterfly, etc. of a length–width ratio of less than 4 also appeared as MnS and MnTe complex inclusions, and the fusiform manganese sulfide accounted for most of the steel. Both Bi and Te had modification effects on MnS.

Modification of Rare Earth Ce on Inclusions in W350 Non-Oriented Silicon Steel

In this paper, the effect of rare earth Ce content on the morphology, composition, type and size distribution of inclusions in W350 non-oriented silicon steel was investigated by means of ICP-MS (inductively coupled plasma mass spectrometry), SEM/EDS (scanning electron microscope-energy Dispersive Spectrometer), and ASPEX (automated SEM/EDS inclusion analysis). The results showed that with the increase of Ce content in the steel, the modification sequence of inclusions was CeAlO3→Ce2O2S→CexSy. The type and size distribution of inclusions in the steel obviously changed with the difference in added Ce content. When the added Ce content in the steel was 10 ppm, 14 ppm, 20 ppm and 30 ppm respectively, the rare earth inclusions were mainly CeAlO3-Ce2O2S. Furthermore, when the added Ce content increased to 60 ppm, the rare earth inclusions were mainly Ce2O2S with a small amount of CeAlO3 contained in part inclusions. When the added Ce content increased continually to 95 ppm, the rare earth inclusions were mainly CexSy-Ce2O2S. The critical Ce content for the conversion between CeAlO3 and Ce2O2S was 41 ppm. To ensure that inclusions transform from CeAlO3 to Ce2O2S, the Ce content in the steel should be greater than 41 ppm. Under the current experimental conditions, it was found that when the Ce content was 20 ppm, the number density and proportion of inclusions in the steel were lower, and their average size was larger. When the added Ce content increased to 95 ppm, the number density of inclusions in the steel significantly increased, which deteriorated the steel cleanliness.

Research on Intelligent Identification and Grading of Nonmetallic Inclusions in Steels Based on Deep Learning.

Non-metallic inclusions are unavoidable defects in steel, and their type, quantity, size, and distribution have a great impact on the quality of steel. At present, non-metallic inclusions are mainly detected manually, which features high work intensity, low efficiency, proneness to misjudgment, and low consistency of results. In this paper, based on deep neural network algorithm, a small number of manually labeled, low-resolution metallographic images collected by optical microscopes are used as the dataset for intelligent boundary extraction, classification, and rating of non-metallic inclusions. The training datasets are cropped into those containing only a single non-metallic inclusion to reduce the interference of background information and improve the accuracy. To deal with the unbalanced distribution of each category of inclusions, the reweighting cross entropy loss and focal loss are respectively used as the category prediction loss and boundary prediction loss of the DeepLabv3+ semantic segmentation model. Finally, the length and width of the minimum enclosing rectangle of the segmented inclusions are measured to calculate the grade of inclusions. The resulting accuracy is 90.34% in segmentation and 90.35% in classification. As is verified, the model-based rating results are consistent with those of manual labeling. For a single sample, the detection time is reduced from 30 min to 15 s, significantly improving the detection efficiency.

Formation Mechanisms and Three-dimensional Characterization of Composite Inclusions in Low Aluminum Steel Deoxidized by Silicon

Silicon deoxidized steel takes a large proportion in addition to aluminum deoxidized steel, since aluminum deoxidation may cause many problems, such as nozzle clogging and low toughness. In this paper, a low aluminum silicon deoxidized steel was prepared in the laboratory. The inclusions in steel mainly include MnS and composite inclusions made of MnS and oxides. The formation of MnS and composite inclusion was discussed based on the thermodynamic calculations. It was clarified that the MnS precipitate during the solidification process of steel. In addition, the formation mechanism of the composite inclusions was illustrated from the perspective of thermodynamics and lattice mismatch. The composite inclusions in steel were reconstructed by Micro-CT and the three-dimensional (3D) morphologies were analyzed in details. This method avoids artifacts and misleading of the two-dimensional observation on the cross sections of the steel samples. Meanwhile, the 3D observation by Micro-CT is an innovation way to characterize the different phases of the inclusion simultaneously, which paved a way for the analysis of the composite inclusions in the steel.

Effect of Molten Steel Composition on Inclusion Modification by Calcium Treatment in Al-Killed Tinplate Steel

The effects of oxygen, magnesium, and sulfur content in Al-killed tinplate steel on the “liquid zone” of inclusion modification by calcium treatment were clarified through industrial experiments and thermodynamic calculation, and the characteristics of inclusions modification were studied. The results show that the inclusions in molten steel before calcium treatment are mainly Al2O3 inclusions. The inclusions in molten steel are CaO·Al2O3 after calcium treatment with a holding time of 10 min, while the inclusions are mainly 3CaO·Al2O3 with a holding time of 30 min. And 12CaO·7Al2O3 inclusions are observed in molten steel when T.O content increases to 40 ppm after calcium treatment with a holding time of 30 min. As the increase of T.O content from 10 ppm to 40 ppm, the difference between the upper and lower limits of the critical calcium content corresponding to the “liquid zone” increases from 5 ppm to 17 ppm. The increase of T.O content in molten steel will enlarge the “liquid zone” range of inclusion modification by calcium treatment, and increase the critical calcium content. With the increase of magnesium content in molten steel, the liquid phase ratio of inclusions modification by calcium treatment decreases. To obtain the liquid phase ratio of inclusions at least 50% in molten steel, not only the calcium content in steel should be strictly controlled, but also the magnesium content in steel should not be larger than 15 ppm. With the increase of sulfur content in molten steel, the “liquid zone” range of inclusion modification by calcium treatment becomes narrow.

Effect of cold-rolling deformation and rare earth yttrium on microstructure and texture of oriented silicon steel

Abstract In order to study the effect of cold-rolling deformation and rare earth Y on the microstructure and texture of 3.0% Si-oriented silicon steel, the microstructure and texture of cold-rolled oriented silicon steel with 60, 72, and 86% deformation are analyzed using electron backscatter diffraction and image analysis software. The experimental results show that the deformation band becomes narrower and the distribution of shear bands becomes denser with increasing cold-rolling deformation. Compared to the Y-free steel, cold-rolled sheet containing rare earth Y has greater shear bands. The pinning effect of rare earth Y hinders the dislocation movement, which leads to the increase of kernel average misorientation value and shear bands. With the increase of cold-rolling deformation, the texture concentrates on α and λ. This is mainly due to the change from {100} 〈001〉 to {001} 〈110〉, intensifying λ texture, and the change from {111} 〈112〉 to {111} 〈110〉, thus strengthening the α texture. The texture strength of cold-rolled sheets can be decreased by rare earth Y. But the γ texture strength in cold-rolled sheets containing Y is significantly higher than in those without Y. The γ texture strength can reach up to 7.3, and the strong points are mainly {111} 〈112〉. This is because the number of inclusions in steel increases with the addition of rare earth Y. In the process of grain nucleation, the {111} oriented grains nucleate heterogeneously on the inclusions. It forms a large number of {111} oriented grains and improves the γ texture strength.

In Situ Observation on the Heterogeneous Nucleation of MnS in Heavy Rail Steels with Varied Aluminum Content

In situ observation, scanning electron microscope/energy‐dispersive spectrometer detection, and lattice disregistry calculation are combined to investigate the evolution mechanism of inclusions in heavy rail steels with varied aluminum contents from SiO2–Al2O3–MnO to SiO2–Al2O3–MnO–MnS at 1323 K and 1393 K. The precipitation of MnS inclusions on SiO2–Al2O3–MnO inclusions in the steel occurs when the Al2O3 content in identical oxide inclusions is 30% at 1393 K and 30%, 40%, and 59% at 1323 K. The MnS outer layer shows visible precipitation from 3 min after heating at experimental temperature. The area fraction of MnS phase in SiO2–Al2O3–MnO–MnS inclusions with varied Al2O3 content at 1323 K decreases in the following order: SiO2–Al2O3 (30%)–MnO > SiO2–Al2O3 (40%) –MnO > SiO2–Al2O3 (59%)–MnO. The precipitation of MnS is prone to occur on the Al2O3‐less region of the SiO2–Al2O3–MnO inclusion. The solubility of Mn and S decreases with decreasing temperature. Lower heating temperature and lower Al2O3 content in SiO2–Al2O3–MnO oxide cores are profitable to the heterogeneous nucleation of MnS due to lower disregistry between MnS with the SiO2–Al2O3–MnO inclusion.

Effect of Complex Inclusions on Localized Corrosion Behavior in Ferritic Steel

The localized corrosion behavior of different inclusions in a simulated solution of coastal industrial pollution is investigated in this study. It is indicated in the results that the Al2O3–MnS composite inclusions of ordinary carbon Q345B steel have microcracks and induce severe lattice distortions in the surrounding matrix. The MnS in the Al2O3–MnS composite inclusions dissolves preferentially to induce pitting corrosion. The microcracks and severe lattice distortion of the surrounding matrix accelerate the corrosion propagation. The preferential dissolution of CeAlO3–Ce2O2S inclusions induces pitting in No. 2 steel. The inherent physical and chemical properties of the inclusions and the chemical corrosion of the simulated fluid are vital in the initiation and expansion of pitting corrosion. The TiN in the test steel exhibits excellent resistance to pitting corrosion, and the double‐layer composite inclusions completely covered by TiN do not form corrosion pits in the simulated solution and do not cause the dissolution of the adjacent matrix. The coordinated addition of Ti–Ce can reduce the size of the inclusions and improve the probability of complete cladding of TiN.

Analysis of the evolution law of oxide inclusions in U75V heavy rail steel during the LF–RH refining process

Abstract The number density, size and composition of inclusions in U75V heavy rail steel during ladle furnace (LF)–RH refining process were studied by an Aztec-Feature inclusion automatic software which equipped with a field emission microscope. The results showed that the MnO–SiO2–Al2O3-type inclusions were the main inclusions at LF start. The MnO–SiO2–Al2O3-type inclusions were transformed into the CaO–SiO2–Al2O3-type inclusions during the LF refining process because of the Ca and Al elements which were brought by ferroalloy. At the RH start stage, the main inclusions were CaO–SiO2–Al2O3-type inclusions with low melting temperature and CaO–MgO–Al2O3-type inclusions with high melting temperature in the sample. And, the CaO–MgO–Al2O3-type inclusions were obviously removed during RH vacuum treatment. The average compositions of CaO–SiO2–Al2O3-type inclusions had no obvious change from RH vacuum holding for 15 min, RH vacuum break to RH soft blowing.

Effect of Oxide Metallurgy Technology on Mechanical Properties and Hydrogen‐Induced Cracking Susceptibility of High‐Strength Low‐Alloy Steel

The oxide metallurgy is used in the fabrication of X80 pipeline steel. The mechanical properties of X80 steel at different tempering temperatures are studied by offline heat treatment process. The hydrogen‐induced cracking (HIC) susceptibility of X80 steel with optimal mechanical properties is studied. The results show that the optimal combinations of mechanical properties are obtained for the X80 pipeline steel under the heat treatment conditions of water quenched at 900 °C and tempered at 630 °C. The yield strength of the X80 steel is 569 MPa and the impact energy is higher than 300 J at −40 °C. After deoxidation by Ti and Zr, the average size of inclusions in X80 steel is 0.23 μm. Among them, the typical spherical composite inclusions are TiOX–Al2O3–ZrO2–MnS, combined with the fine (Nb, V, Ti)C and the formation of Cu2S and Cr2O3 protective layers. X80 steel has excellent HIC resistance.