Inclusions In Steel Research Articles

Characterization of Inclusion Size Distributions in a Large Forged Shaft Using X‐ray Micro‐Computed Tomography Imaging

The presence of nonmetallic inclusions in steel considerably affects the material's properties. This study investigates these effects by sampling six locations along the radial direction of a large forged shaft to analyze the distribution characteristics of inclusions. Scanning electron microscopy and optical microscopy are used to identify the types and morphologies of the inclusions. X‐ray micro‐computed tomography scanning provides detailed distribution data, including the length, width, equivalent diameter, and shape of the inclusions. This approach allows for a comprehensive understanding of the radial distribution characteristics of inclusions in the forged shaft. The results reveal that both the quantity and size of inclusions in the large forged shaft increase progressively from the edge toward the center. Additionally, the fatigue strength is estimated based on the inclusion distribution at various locations. The prediction shows a relative error exceeding 15%, indicating that the heterogeneity of the components considerably affects their fatigue performance. Finally, a novel method for predicting the maximum inclusion size within the heterogeneous large forged shaft is introduced.

Effect of Magnesium Modification on Inclusions and Carbide in As‐Cast 21‐4N Valve Steel

To investigate the impact of magnesium on the inclusions, carbides, and microstructure of the 21‐4N valve steel, the magnesium modification industrial experiment is carried out. Optical microscope, a scanning electron microscope with an energy‐dispersive spectrometer, thermodynamic calculation, and a 3D etching method are used. In the results, it is shown that the oxide inclusions in steel modifies from Al2O3–MnO to MgO–MnO–SiO2 after magnesium modification, which presents a more dispersed size distribution. The primary precipitates in the steel remain as massive carbide M23C6 and lamellar precipitate γ + M23C6, and the maximum size of large carbides and lamellar precipitates in the magnesium‐modified steel decreases from 15.1 to 13.4 μm and from 98.8 to 68.8 μm, respectively. Furthermore, Mg‐containing inclusions act as more heterogeneous nucleation cores for austenite precipitation, resulting in the refinement of austenite grain and a reduction in the last‐to‐solidify region. The reduction in the last‐to‐solidify region limits the growth space of carbides and contributes to their size refinement.

Coupled Precipitation Behavior of MnS–Nb(C, N) Composite Inclusion in Medium Carbon Micro-alloyed Steel

Coupled Precipitation Behavior of MnS–Nb(C, N) Composite Inclusion in Medium Carbon Micro-alloyed Steel

Evolution of Al-Ti Complex Oxide Inclusions in Interstitial-Free Steel Analyzed Using CALPHAD, SEM, EDS, EBSD, and CSLM

Evolution of Al-Ti Complex Oxide Inclusions in Interstitial-Free Steel Analyzed Using CALPHAD, SEM, EDS, EBSD, and CSLM

Theoretical precipitation modeling and multidimensional characterization of sulfide inclusions in tellurium-containing steels

This study investigates the precipitation characteristics of sulfide inclusions during the solidification of alloy steels under the combined influence of sulfur (S), manganese (Mn), and tellurium (Te). A multidimensional characterization and comparison of sulfide inclusions in Te-containing steels with varying sulfur content and cooling conditions were performed using X-ray Micro-CT, Raman spectroscopy, and field emission scanning electron microscopy (FE-SEM). Both 2D and 3D analyses confirmed that increasing the S content in Te-containing steels leads to a higher overall number of sulfide inclusions. In particular, the rise in the proportion of small-sized inclusions was analyzed from the perspectives of interfacial dynamics and equilibrium thermodynamics. Regarding inclusion morphology, 2D characterization exhibited significant inaccuracies in assessing large inclusions in high-S, Te-containing steels, while X-ray Micro-CT proved advantageous for evaluating both the spatial distribution and morphology of inclusions. In addition, X-ray Micro-CT was used for the first time in this study to perform a non-destructive analysis of the layered MnS-MnTe structure, expanding the method's application in the metallurgical field. A predictive model based on inter-element activity interaction coefficients was employed to determine the first-order activity interaction coefficient of Te for Mn. Furthermore, a thermodynamic model for sulfide precipitation in Te-containing steels was developed. This study lays a theoretical foundation for better control of sulfide inclusions in future Te-containing specialty steels.

Localized corrosion induced by MnS inclusions in U71Mn rail steels

To understand the corrosion mechanisms of rail steels, immersion tests were conducted on U71Mn rail steels produced in 1994 and 2021. It was observed that, at the onset of corrosion, only matrix near clustered MnS inclusions dissolved. Further characterization revealed that this was due to the combined effects of lower Volta potential, higher lattice distortion of the surrounding matrix, and strip-shaped carbides in the surrounding matrix induced by the clustered distribution of MnS. Consequently, the U71Mn2021 rail steel, with fewer MnS clusters formed, exhibited better corrosion resistance, as evidenced with electrochemical measurements. These findings suggest that refined processing techniques to control inclusion formation could be effective methods for developing U71Mn rail steels with greater corrosion resistance.

The Effect of La, Ce Rare‐Earth Elements on the MnS Inclusion Precipitation and Distribution in U75V Heavy‐Rail Steel

The quality of heavy rail steel is significantly influenced by the distribution and morphology of MnS inclusions. With the help of experimental methods and thermodynamic predictions, the evolution of inclusions in heavy rail steels with different rare‐earth (RE: La + Ce) additions is investigated, and the relationship between RE inclusions and MnS is better interpreted by the classical two‐dimensional mismatch degree theory. The results show that the deoxidizing ability of RE elements added to the steel is greater than the desulfurizing ability. The best data for physical parameters of inclusions in steel are obtained at a RE addition of 122 ppm. The MnS inclusion particles are roughly spherical around the REAlO3 inclusion particles when the aluminum content in the RE inclusion is high. The MnS inclusion particles are better able to fit flatly around the RE2O2S inclusion particles when the sulfur content of the RE inclusion is high. By computing the two‐dimensional mismatch between the interfaces of different inclusions, it is discovered that the heterogeneous nucleation efficiency is comparatively low between MnS and REAlO3, relatively high between MnS and RE2O2S, and highest between MnS and RE2O3.

Effects of Cold Gas Tungsten Arc Welding on Dissimilar DHP-CW024A Copper/304 SS Thin Lap Joint

Copper and stainless steel possess distinct properties that make them suitable for different applications (i.e. e-mobility, nuclear power plants, etc.). However, the high thermal conductivity of copper presents a significant challenge in welding. In fact, researchers have explored various fusion welding processes for joining copper to steel and concluded that fusion welding is generally difficult or even unsuitable for obtaining sound and defects free joints. The present study investigated the feasibility of dissimilar lap joint between copper and stainless-steel thin plates using Cold Gas Tungsten Arc Welding (CGTAW) without a filler material and with no significant geometrical distortion of welded plates. The weld was created by consecutive partially overlapped spots, whose welding time varied between 100 and 150 ms, in upgraded conventional TIG machine equipped with cold TIG welding function. Samples made with 150 ms welding time showed a near-uniform distribution of equiaxed copper grain microstructure, while those obtained with 100 ms exhibited significant differences in grain size with the presence of steel inclusions in globule and vortex shapes. The joints demonstrated exceptional flexibility, allowing it to be bent up to a 180º angle without any visible damage. The maximum tensile strength of sample obtained with a welding time of 150 ms was 220 MPa with a fracture located in the heat-affected zone. The sample welded with a welding time of 100 ms exhibited 171 MPa of tensile strength with the fracture along the melting spot area due to pronounce mixing of welded materials. All the samples showed ductile behavior in the fracture zone. Eventually, the application of CGTAW resulted in promising at obtaining joint with good mechanical properties.

Comparative study on the cleanliness and compositional change of alloy steels processed by electroslag remelting and vacuum arc remelting

The cleanliness and compositional change of Ni containing alloy steel processed by electroslag remelting (ESR) and vacuum arc remelting (VAR) were studied. The results show that compared with the electrode steel, the total oxygen content increases in the steel processed by ESR. On the contrary, the total oxygen and total nitrogen content in the steel processed by VAR can be significantly decreased due to the vacuum environment. The number and size of inclusions in steel processed by VAR are significantly decreased, which indicates that the VAR is conducive to improving the cleanliness of steel. Single TiN inclusions are found in both steels processed by ESR and VAR, and oxide inclusions in two steels are (Mg,Al,Ca)O and (Mg,Al)O, respectively. The growth time of TiN inclusions is relatively shorter in the steel processed by VAR, which leads to the thinner TiN layer surrounding the oxide inclusions. During the VAR process, the high temperature and high vacuum conditions promote the volatilization of Mn in steel, leading to decrease of the Mn content in steel. Therefore, extra Mn should be added to the electrode steel before VAR.

Study on Transformation of Glassy and Crystalline Inclusions in Cord Steel during Heat Treatment at 1100 °C

Study on Transformation of Glassy and Crystalline Inclusions in Cord Steel during Heat Treatment at 1100 °C

On the formation of oxide inclusions in the high nitrogen chromium-manganese steel produced by the Wire and Arc Additive Manufacturing

Oxide inclusions significantly impeded the mechanical properties of the Wire and Arc Additive Manufacturing (WAAM) made high nitrogen Cr–Mn austenite stainless steels (HNSs). This paper focused on the inclusions' component, crystallization characteristics and formation mechanism. Results revealed that there are two types of inclusions: the round-shape nano-size inclusion (Type-I) and the micron-size island-shape inclusion (Type-II). The Type-I inclusion usually consists of the MnO particle or the combination of the MnO, Si-oxides and precipitations (MnS or Cr2N). Most of the Type-I oxide inclusion is located in the range between 300 nm and 700 nm,the number of Type-I oxide inclusion takes the main part of 69.7%.With higher content, smaller size and more even distributions, the isolated Type-I oxide inclusions would be beneficial to the mechanical properties owing to the Orowan strengthening mechanism. The Type-II inclusion is mostly composed of the MnO matrix and the coherent chromite spinel (MnCr2O4). In general, the larger the size, the more serious the negative impact on mechanical properties. And there was a strong negative correlation between the size and quantity of type II oxide inclusions. After heat treatment, abundant phase transformations occurred in the Type-II inclusions and some harmful phases (Sigma, MnS et cl.) were often found in or around the inclusions with specific orientation relationships. During deposition, the unstable droplet transformation and the trapped residual slag were the main causes for the inclusions in the molten pool.

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 Gadolinium on Inclusions in a High-Sulfur Free-Cutting Steel and Converting Two-Dimensional to Three-Dimensional Morphology of Inclusions Through Matlab Programming

Effect of Gadolinium on Inclusions in a High-Sulfur Free-Cutting Steel and Converting Two-Dimensional to Three-Dimensional Morphology of Inclusions Through Matlab Programming

Study on the effect of rare earth Ce on the modification of sulfide inclusions in U71Mn heavy rail steel

In this paper, the directional modification behavior of rare earth Ce on sulfide inclusions in steel is studied by thermodynamic calculation and experiment methods, and the mechanism of directional modification of rare earth Ce on sulfide inclusions in U71Mn heavy rail steel is proved. The results show that U71Mn heavy rail steel contained more large-sized inclusions and their distribution is more concentrated without the addition of rare earth Ce element. After the addition of rare earth Ce element, the average size of sulfur-containing inclusions in the steel decrease from 5.22 μm to 1.85 μm, and the number density of sulfur-containing inclusions in the steel increase from 83.65 mm-2 to 217.68 mm-2, indicating that the number of sulfur-containing inclusions in the steel increases after the addition of Ce element, and more small-sized sulfur-containing inclusions will form in the steel. The addition of rare earth Ce element can effectively reduce the existence of large-sized inclusions in the steel and modify large-sized inclusions into small-sized inclusions.

First-principles study on atomic formation and manganese diffusion in MnS/Mg-Ti-oxide complex inclusions in steel

Mg-Ti oxide/MnS complex inclusions effectively serve as nucleation sites for intragranular ferrite. This study employs first-principles calculation methods to investigate the inducing properties of complex inclusions, including the growth of MnS on Ti oxide, the absorption of Mn atoms by Ti oxide, and the diffusion behavior of Mn atoms within Ti oxide, both untreated and Mg-treated. Ti2O3 indicates the untreated group, while MgTiO3 indicates the Mg-treated group. Computational analysis indicated that MnS is more likely to adsorb and grow on MgTiO3 than on Ti2O3. MnS vertically grows on the O-Mg-Mg surface of MgTiO3. By calculating the dissociation energy, it can be determined that the Mn in the oxide of the MnS/oxide complex inclusions originates from the steel matrix rather than from MnS. By analyzing the diffusion behavior of vacancies and Mn atoms through energy barrier calculations, it is evident that the addition of Mg alters the diffusion pathways of Mn atoms in Ti oxide and confirms that the bonding between Mn and O is the limiting step for Mn atom diffusion within the oxides. The diffusion path of Mn atoms in MgTiO3 is Path I → Path II → Path I. Path I: Mn atoms diffuse within the cationic layer. Path II: Mn atoms diffuse by traversing across two layers of O atoms.

Shape of fragments cloud behind heterogeneous screen by a space debris particle impact

Technogenic pollution of near-Earth space poses a threat to the functioning of spacecraft. Collisions between space debris (SD) and spacecraft (SC) structures can have catastrophic consequences or cause localized damage, leading to the loss of SC operability or the failure of certain functions. The SC body must effectively protect the internal equipment from various external impacts, be technologically feasible to manufacture, and have as little mass as possible. As a result, the task of designing spacecraft bodies and protective screens for low-orbit SC is particularly relevant due to the large concentration of SD in low Earth orbits.A comparative numerical study was conducted to evaluate the effectiveness of various thin shields in protecting against impacts from space debris particles. The study examined homogeneous shields made of A356 aluminum alloy and 316L stainless steel, as well as volumetrically reinforced composite shields produced using additive manufacturing with steel inclusions, and shields with a gradient distribution of steel throughout the thickness of an aluminum matrix, all with the same areal density. In all the heterogeneous plates considered, the volumetric concentration of steel was 36 %. The study covered an interaction velocity range of 2–9 km/s. Numerical modeling results indicated that the structure of the thin heterogeneous plate does not affect the shape of the debris cloud formed behind the protective shield. The findings of this study can serve as a basis for selecting materials for the development of more effective protection for spacecraft against high-velocity impacts.

Development and properties of cost-effective self-sensing Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) incorporating steel slags

This study examined the electrical and self-sensing capacities of ultra-high performance fiber-reinforced concrete （UHPFRC） with and without steel slag powder. The inclusion of steel slags provides a reliable way to enhance the electrically conductive and self-sensing capabilities of UHPFRC, which is composed of cement, silica fume, and steel fiber. The conductibility of UHPFRC and its response to external loading were investigated. Additionally, through 3D analysis of fiber structure and pore distribution, the conductive mechanisms were revealed. The results show that the addition of steel slags powder (SSP) can improve both mechanical properties and flowability. The maximum fractional change in electrical resistivity under compressive and flexural loads reached 37.6 % and 54.1 %, respectively. However, the conductive model under compressive loading differs from that under flexural loading. Furthermore, an analysis of carbon emissions and material costs revealed that using SSP reduced carbon emissions by 45.2–96.4 % and lowered costs by 41.8–88.8 %, making this approach both economically and environmentally advantageous.

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.

Residual stress induced granular bright facets around inclusions in high-strength steels under high-cycle fatigue

Granular bright facets (GBFs) are frequently observed adjacent to inclusions and within fish-eye areas in the fatigue fractures of high-strength steels under very-high-cycle fatigue (VHCF), considered as a characteristic fracture feature of VHCF. Previous understanding on GBF formation emphasizes the occurrence of nanocystallization in microstructure. In this study, however, the same morphology can also be observed under high-cycle fatigue (HCF). GBF, although closer to fatigue crack initiator and experiencing more stress cycles than the peripheral part of fish-eye (PPFE), exhibits rougher surface morphology in the absence of accumulated plastic strain in microstructure, manifesting relieved crack surface wear. This indicates that the traditional theories on GBF formation for VHCF becomes invalid for HCF. The root cause for GBF formation under HCF is analyzed to be the presence of residual stress around inclusions, which reduces the contact pressure of fatigue crack surfaces inducing wear relief. Accordingly, an analytical model capable of predicting GBF thickness with the effects of HCF conditions and steel properties taken into consideration is established. The model yields accurate predictions of GBF thickness with various loading stresses and inclusion diameters, validated by experimental observations. This study provides theoretical guidance for HCF fracture analysis and fatigue life prediction.

Effect of CaO–Al2O3–SiO2–MgO(–CaF2) refining slag system on inclusions in silicon–manganese deoxidized spring steel

In order to make the refined slag match various grades of spring steel, high-temperature equilibrium experiments were conducted in the laboratory to study the effect of CaO–Al2O3–SiO2–MgO refining slag with varying basicity, Al2O3 content, and CaF2 additives on inclusions containing Al (Al2O3) in silicon–manganese-deoxidised steel. The results show that the control effect of low basicity refining slag on inclusions is better than that of high basicity slag. The soluble aluminium increases with the increase of the basicity of steel slag and the Al2O3 content in inclusions is positively correlated with the Al2O3 content in slag. When the relative adsorption capacity of the refined slag is 6 × 10−3, the area density of Al-containing inclusions in steel is at a low level. Low basicity slag with low Al2O3 is good, and it is more suitable for producing high-end spring steel. To produce middle- and low-end spring steel, the refining slag system with a basicity of about 2–2.5, Al2O3, MgO, and CaF2 content is about 10% can be used. Among them, a small amount of CaF2 improves the liquidity of steel liquid, improves its relative adsorption capacity to Al-containing inclusions, and can control the production of Al-containing inclusions in the steel.