Size Of Non-metallic Inclusions Research Articles

Analysis of Thermophysical Properties of Electro Slag Remelting and Evaluation of Metallographic Cleanliness of Steel.

Improving the competitiveness of steel companies is linked to sustainable, quality-compliant steel production. Therefore, new steel production technologies contributing to increased cleanliness of steel are continuously being developed and optimized. One way to achieve a high steel quality is to use electro slag remelting (ESR) technology. In this paper, the principle of ESR technology and the importance of fused slags for optimizing the process are outlined. The aim of this work was to analyze the main thermophysical properties of steel and fused slags used in the ESR process. Determination of the properties of steel and slags was performed using the FactSage calculation software, which involved the calculation of the liquid and solid temperature of steel and slags, the calculation and construction of quaternary diagrams, and the calculation of viscosity. The resulting quaternary diagrams revealed the substantial influence of chemical composition on melting temperatures of slags. In order to validate the acquired results, a CrNiMoV-type steel was subjected to investigation of its metallographic cleanliness and evaluation of its mechanical properties; the ESR process was shown to significantly improve the cleanliness of the steel and improve the mechanical properties of the steel compared to its cleanliness and quality when produced via vacuum degassing (VD) technology. During the ESR process, the average size of non-metallic inclusions was reduced from 20 μm to 10 μm, and the maximum size of non-metallic inclusions was reduced from 50 μm to 28 μm. The mechanical properties of the steel produced using ESR technology were impacted as follows: the ductility increased by 10%, contraction increased by 18%, notched toughness at 20 °C increased by 46%, and at -40 °C (respectively -50 °C) it increased by 30%.

Effects of Typical Inclusions on the As‐Cast Microstructure and Recrystallization of Low‐Density Steel

Herein, the effect of nonmetallic inclusions (NMIs) on the microstructure and dynamic recrystallization (DRX) of Fe–23Mn–6Al–0.7C low‐density steel is studied. The specimens are separately added sulfur (S) and nitrogen (N) to change the characteristics of NMIs. As a result, the addition of S significantly increases the number of MnS inclusions and AlN–MnS complex inclusions in low‐density steel. The addition of N results in a significant increase in the size of NMIs. In the results, NMIs act as the heterogeneous nucleation sites for austenite and refine the as‐cast grains in low‐density steel. In addition, the treated specimens are subjected to a thermal compression simulation experiment. During the thermal compression process, discontinuous DRX is considered to be the main recrystallization method in the experimental low‐density steels. Meanwhile, the typical NMIs significantly accelerate the DRX within grains in low‐density steel through the mechanism of particle‐stimulated nucleation and continuous DRX.

DOCOL 1100M WELDING IN THE CONSTRUCTION OF ELECTRIC MEANS OF TRANSPORT

Advanced high-strength steels are important for the automotive sector. Metal active gas (MAG) is the most popular method for joining grades of steel. The goal of the paper is to analyze the mechanical properties of the MAG welding joint made of high-strength DOCOL 1100M intended for the construction of electric vehicles. The manuscript shows a basic understanding of the properties of DOCOL joints. This type of material is characterized by a martensitic microstructure, which makes it difficult to make a proper joint. The tensile strength, metallographic structure, and type of non-metallic inclusions were analyzed as a function of the oxygen amount in the protective gas mixture. Investigations of oxide non-metallic inclusions were carried out using scanning electron microscopy. This article attempts to obtain high joint strength of the electric vehicle structure by controlling the average size of non-metallic inclusions in the weld, which is influenced by shielding gas in the MAG welding process. The solution has application potential for the automotive industry, especially for electric vehicles.

Three-Dimensional Imaging of Non-metallic Inclusions in Steel Using Ionoluminescence

Obtaining information on the morphology, size, distribution, and chemical composition of non-metallic inclusions in steel helps control the steel production process and the quality of the steel products. Two-dimensional analysis is commonly used to acquire this information; however, more accurate data can be obtained through three-dimensional analysis, leading to a better control of the quality of steel products and their production process. Currently, several techniques are proposed for the three-dimensional analysis of non-metallic inclusions; however, they are time consuming. Herein, the author presented a method to rapidly obtain three-dimensional images of non-metallic inclusions in steel using ionoluminescence (IL). A three-dimensional image of MgO·Al2O3 spinel inclusions was constructed based on two-dimensional IL images obtained every 10 min during argon–ion bombardment. The proposed IL imaging can cover an oval-shaped area of 1.17 mm × 0.26 mm on the semi-major and in the semi-minor axes, respectively, at a single measurement. Three-dimension images of MgO·Al2O3 spinel inclusions with sizes more than 20 μm can be obtained within 4 hours. Therefore, the IL imaging proposed here can provide a precise and rapid account of the effects of non-metallic inclusions on steel products and the steel production process.

Sulfide Inclusions in an Al‐Killed Nonoriented Electrical Steel with Lanthanum Addition

Herein, laboratory experiments are conducted to evaluate the effect of sulfur and lanthanum content in the steel on the modification of inclusions. The amount, composition, morphology, and size of nonmetallic inclusions in the steel are observed using an automatic scanning electron microscope. Results show that as the lanthanum content in the steel increased from 0 to 72 ppm, the inclusions in the steel with 12 ppm sulfur are modified in the following order: Al2O3–CaO–MgO → LaAlO3 → LaAlO3–La2O2S → La2O2S. Similarly, when the sulfur content is 27 ppm, inclusions transformed in the order of Al2O3–CaO–MgO → LaAlO3 → LaAlO3–La2O2S → La2O2S → La2O2S–LaxS → LaxS as the lanthanum content increases from 0 to 150 ppm. Thermodynamic analysis using FactSage based on a private database is employed to reveal the mechanism for the modification of inclusions. Additionally, a kinetic model is established to study the transformation rate of inclusions in the steel after the addition of lanthanum and sulfur. Liquid Al2O3–CaO–MgO inclusions disappear after 800 s when the steel contains 12 ppm sulfur and 12 ppm lanthanum. The composition of inclusions is 53%LaAlO3–47%La2O2S at 1800 s, while it is 100%La2O2S and 80%La2O2S–18%LaxS–2%CaS when the lanthanum content is 33 and 72 ppm, respectively.

Uncovering the origin of critical hydrogen concentration for initiation of hydrogen-induced cracking and its relation to inclusion type and size

This paper presents a theoretical criterion and approach for determining the relationship between the critical hydrogen concentration for hydrogen-induced cracking (HIC) initiation and the type and size of non-metallic inclusions. We used plate-like MnS and sphere-like Al2O3 as representative inclusions for in-depth analyses. Our results indicate that decreasing inclusion size increases the hydrogen concentration required for HIC initiation, particularly in the range of small inclusion sizes. Al2O3 exhibits a higher susceptibility to HIC than MnS. Each type of inclusion has a specific hydrogen concentration below which crack initiation cannot begin. The critical concentration for HIC initiation in the entire steel corresponds to the lowest value among these concentrations. This study provides a quantitative and comprehensive solution to this issue.

Study of the Microstructure of 08PS Steel Deoxidized with Standard Ferroalloys and Prospects for Replacing Them with Complex Deoxidants

The annotation This research work is devoted to the study of the microstructure of 08PS steel deoxidized using standard ferroalloys and the prospect of replacing them with complex deoxidifiers. The purpose of the study was to determine the impact of the deoxidation process on the microstructure of steel and to assess the replacement with complex deoxidants. Research methods included metallographic analysis of steel samples and energy dispersion analysis (EDX) to determine the composition of non-metallic inclusions. The analysis was carried out on steel samples before and after deoxidation, the microstructure, the size of non-metallic inclusions and their composition were studied.

Thermodynamic analysis of processes in the high-temperature polycomponent Fe–Y–Si–O–C system

In the production of low-carbon and high-quality steels, it is recommended to use special complex alloys of rare earth metals for deoxidation, microalloying and modification. To elucidate the mechanism of action of each of the components of the alloy, it is necessary to differentiate the action of each individual element. Yttrium is usually classified as a rare earth metal, but its deoxidizing and modifying ability deficiency studies. The use of yttrium applica-tion is known to increase in density, ductility, scale resistance, resistance to high-temperature corrosion of steel, effec-tively affects the shape, size and distribution of non-metallic inclusions. This paper consider the interaction of yttrium, silicon, and carbon with oxygen dissolved in liquid iron. Nonmetallic inclusions formed in this case can be identified on the state diagram of the FeO–Y2O3–SiO2 oxide system. This diagram is absent in the literature; therefore, it was mod-eled on the basis of the available binary phase diagrams of the FeO–Y2O3, FeO–SiO2, and Y2O3–SiO2 systems. Com-plex deoxidation by yttrium and silicon is possible only at yttrium concentrations in liquid iron less than 0.0001% (ox-ide melt or yttrium silicates are formed as non-metallic inclusions). If the concentration of yttrium is higher than this value, then it is the only deoxidizer. In the presence of carbon, liquid non-metallic inclusions can form in a very narrow range of liquid metal compositions, and the main oxide non-metallic inclusion is yttrium oxide. At yttrium concentra-tions below 0.0001% and silicon concentrations up to 1%, only carbon is the deoxidizer. Taking into account the previ-ously studied Fe–Y–Me–O–C (Me–Ca, Mg, Al, Cr) systems, a thermodynamic data base was created for designing the compositions of complex yttrium-containing ligatures.

Влияние термической обработки на образование соединения MNS в низкоуглеродистой конструкционной стали 09Г2С

Introduction. The properties of steels are determined by many factors, including the manufacturing process and subsequent treatment. Some features of these processes lead to the fact that in steel, apart from alloying elements added to obtain a certain level of physical and mechanical properties, there are also foreign impurities that enter it at various stages. Foreign elements can not only dissolve in the matrix, but also participate in the formation of particles of nonmetallic inclusions acting as defects. Its presence significantly affects the performance characteristics of the material. That is why it is necessary to understand the processes that lead to the appearance of nonmetallic inclusions and affect its shape. Purpose: to consider the effect of heat treatment, leading to the appearance of a ferrite-martensitic structure, on the shape and size of nonmetallic inclusions; to determine its influence on the physical and mechanical properties of the material. In the work, samples of rolled steel 09Mn2Si after heat treatment are studied. Research methods. To study the properties and structure of steel 09Mn2Si, the following methods were used: scanning electron microscopy – to study the structure of the material, chemical composition in the local area and the site under study and to determine the accumulation of impurities; SIAMS 800 software and hardware complex – to compare the structure of the material with the atlas of microstructures, to determine the score of the grain structure, differences in the structural and phase composition occurring during heat treatment; portable X-ray fluorescence analyzer of metals and alloys X-MET 7000 - to determine the chemical composition of the samples under study in percentage terms; Vickers hardness tester with a preload of 20 kg – to measure the hardness of the samples under study. Results and discussions. It is found that in the low-alloy low-carbon structural steel 09Mn2Si in most cases there are nonmetallic inclusions of the type of manganese sulfide formed during its manufacture. When this steel is heated to the temperatures of the intercritical transition, this compound is formed in the area of grain boundaries in the form of spherical inclusions. The presence of these inclusions significantly affects the strength and corrosion properties. Manganese sulfide acts as the point of the corrosion process initiation.

Fatigue life assessment of low carbon API 5L X52 pipeline steels retired from long-term service

The fatigue lifetime of two API 5L X52 steels retired from long-term service was investigated. Both steels presented pearlite fragmentation, fine precipitate particles and spheroidized cementite at the grain boundaries, which is associated to microstructural degradation due to natural aging. Neither tensile strength nor hardness properties have significant variations respect to the design specifications; however, lower ductility was observed in the most degraded steel. Fatigue characterization was carried out by axial force-controlled tests, finding that the fatigue life is 77 % lower in the steel with the lowest ductility and highest microstructural degradation. Results indicate that the fatigue lifetime of a ferrite-pearlite microstructure is more affected by the microstructural degradation due to long-term service of the steel, in spite of traditional considerations as non-metallic inclusion or grain size. Hence, the natural aging effect is a main factor to be considered in the fatigue life of long-term exposure low carbon steels.

High-Pressure Die Casting: A Review of Progress from the EPSRC Future LiME Hub

This article provides an overview of high-pressure die casting (HPDC)-related research undertaken at the EPSRC Future LiME Hub between 2015–2022. The project aimed to identify the cause of variability in the tensile ductility of die-cast structures, and to develop novel processing techniques to address this issue. Variability in tensile ductility was related to the size of large pores and non-metallic inclusions. It was proposed that these non-metallic inclusions formed during the pyrolysis of commercial plunger lubricants in the shot sleeve, and that these large pores derived from dilatational strains introduced during semi-solid deformation. Processing parameters and die design were found to significantly influence the microstructure of die-cast products, and the subsequent variability in tensile ductility. To close, recent progress on the application of intensive melt shearing to HPDC is reviewed. Intensive melt shearing was found to induce significant grain refinement in both Al and Mg alloys due to the effective dispersion of native oxide particles, and the use of these particles as heterogeneous nucleation substrates. The presence of native oxide particles also enabled the use of novel heat treatment procedures that avoided conventional issues such as surface blistering and geometrical distortion.

Modeling of Tensile Test Results for Low Alloy Steels by Linear Regression and Genetic Programming Taking into Account the Non-Metallic Inclusions

Štore Steel Ltd. is one of the biggest flat spring steel producers in Europe. The main motive for this study was to study the influences of non-metallic inclusions on mechanical properties obtained by tensile testing. From January 2016 to December 2021, all available tensile strength data (472 cases–472 test pieces) of 17 low alloy steel grades, which were ordered and used by the final user in rolled condition, were gathered. Based on the geometry of rolled bars, selected chemical composition, and average size of worst fields non-metallic inclusions (sulfur, silicate, aluminium and globular oxides), determined based on ASTM E45, several models for tensile strength, yield strength, percentage elongation, and percentage reduction area were obtained using linear regression and genetic programming. Based on modeling results in the period from January 2022 to April 2022, five successively cast batches of 30MnVS6 were produced with a statistically significant reduction of content of silicon (t-test, p < 0.05). The content of silicate type of inclusions, yield, and tensile strength also changed statistically significantly (t-test, p < 0.05). The average yield and tensile strength increased from 458.5 MPa to 525.4 MPa and from 672.7 MPa to 754.0 MPa, respectively. It is necessary to emphasize that there were no statistically significant changes in other monitored parameters.

On the comparative inclusion analysis in steels: Spark-DAT, ASCAT and optical microscopy

In the last decades, the control of amount, size, morphology, and chemical composition of non-metallic inclusions in steel has been investigated, particularly at the stage of steel refining, where endogenous and exogenous inclusions can affect the castability and the mechanical properties of the material, thus affecting the quality and performance of the process and final product. In this way, identifying the origin of inclusions and the steelmaking stages where they are formed is essential. The purpose of this study was to compare the results of methodologies for inclusions characterization and analysis using Spark-DAT, ASCAT and optical microscope systems, aiming to validate these systems for inclusions amount and size measuring control during steelmaking. Samplings of ultra-low (ULC) and medium (MC) carbon steels were carried out and both steels killed with silicon and/or aluminum. The MC steel presented higher concentration of inclusions with size in a range between 1 and 5 μm and this behavior is associated with calcium treatment. The total amount of inclusions per square area, presents significant difference between the measurement systems, however correlations could be noted. Spark-DAT and ASCAT showed better correlations. The study also showed the predominancy of oxide inclusions type. For sulfide inclusions there are a discrepancy between Spark-DAT and ASCAT, so that inclusions such as CaS and MnS are revealed but only ASCAT system showed the TiS inclusion type.

Effects of Non-Metallic Inclusions and Mean Stress on Axial and Torsion Very High Cycle Fatigue of SWOSC-V Spring Steel

Inclusion-initiated fracture in high-strength spring steel is studied for axial and torsion very high cycle fatigue (VHCF) loading at load ratios of R = −1, 0.1 and 0.35. Ultrasonic S-N tests are performed with SWOSC-V steel featuring intentionally increased numbers and sizes of non-metallic inclusions. The fatigue limit for axial and torsion loading is considered the threshold for mode I cracks starting at internal inclusions. The influence of inclusion size and Vickers hardness on cyclic strength is well predicted with Murakami and Endo’s area parameter model. In the presence of similarly sized inclusions, stress biaxiality is considered by a ratio of torsion to axial fatigue strength of 0.86. Load ratio sensitivity is accounted for by the factor ((1 − R)/2)α, with α being 0.41 for axial and 0.55 for torsion loading. VHCF properties under torsion loading cannot appropriately be deduced from axial data. In contrast to axial loading, the defect sensitivity for torsion loading increases significantly with superimposed static mean load, and no inclusion-initiated fracture is found at R = −1. Size effects and the stress gradient effective under torsion loading are considered to explain smaller crack initiating inclusions found in torsion ultrasonic fatigue tests.

Numerical Investigation of Outflow of Non-Metallic Inclusions during Steel Refining in the Ladle.

The article presents the results of numerical simulations of liquid steel flow in the main steelmaking ladle. The paper analyses the mechanism of the outflow of non-metallic Al2O3 and MnS inclusions with diameters in the range of 4–27 µm. The simulations were performed with ANSYS Fluent software. In order to determine the shape and size of non-metallic inclusions formed in the main ladle during steel refining, the collected samples of liquid metal were analysed using a scanning microscope with SEM/EDS and LM (light microscopy). Simulation tests and calculations were carried out for the case of steel refining under the conditions of the Cognor SA HSJ Department in Stalowa Wola (Poland). The presented method of using simulation tests to optimize the technology of steel refining in the ladle is an example. The analysis of the results shows that the gas flow in the metal volume has the greatest impact on the outflow of non-metallic inclusions in the steelmaking ladle.

Key factors affecting hydrogen trapping at the inclusions in steels: A combined study using microprint technique and theoretical modeling

The factors affecting hydrogen trapping at the non-metallic inclusions (NMIs) are identified by a combined experimental and theoretical study. The calculated results based on the proposed models show that the hydrogen trapping capacities at the NMIs decrease in the order of EbTiC>EbTiN>EbAl2O3>EbFeO>EbMnS. The interfacial sinking of hydrogen leads to the formation of a silver particle-denuded zone around the NMIs. The elastic property of NMIs is more important for hydrogen trapping than the misfit strain. This work unveils the hydrogen trapping-dependent mechanism on the composition, the misfit strain, the elastic properties, the shape and the size of NMIs.

Microstructure and crystallographic structure of ferritic steel subjected to stress-corrosion cracking

The article presents the results of studies on the microstructure and crystallographic texture of ferritic steel under stress-corrosion cracking (SCC). Using scanning electron microscopy (SEM), the size and type of non-metallic inclusions, the elemental composition of corrosion products, and the cracking mode in the SCC zone were determined. As a part of X-ray diffraction (XRD) analysis, during which the shape and size of grains-crystallites, crystallographic texture, atomic displacements, the Debye-Waller factor and instrumental broadening of lines using the Caliotti function for LaB6 were taken into account, parameters of the microstructure in the SCC zone were assessed. It is shown that the SCC zone is characterized by high density of introduced edge-type dislocations, strong elastic microdistortions of the crystalline lattice and a relatively small size of coherent scattering domains (CSD). It is found that the processes of texture formation in the pipeline during SCC are characterized by a set of Cube {001}<100>, Brass {110}<11¯1>, Copper {112}<1¯11¯>, rotated copper H {001}<11¯0>, Goss {001}<110> and СН {001}<21¯0> orientations. It is shown that when approaching the zone where there are no SCC traces, orientations of Goss {001}<110>, Copper {112}<1¯11¯> and Rot G {011}<01¯1> type increase and orientations of Cube {001}<100>, H {001}<11¯0> and СН {001}<21¯0> type decrease.

Assessment of unusual failure in crankshaft of heavy-duty truck engine

The unusual premature failure of a heavy-duty truck engine crankshaft has been the subject of a rigorous study, and this manuscript describes it in detail. The failure was happened to begin with the growth of the crack from the surface defects, in the form of the clusters of non-metallic inclusions, in the lubrication hole zone of ​​the first main journal, which was the stress concentration zone. A series of experiments including chemical composition, microstructure, mechanical properties, hardness, toughness, and fractography were performed on the failed crankshaft. In addition, the stress analysis was performed on the crankshaft. Careful fractographic study with scanning electron microscopy equipped with energy dispersive spectroscopy revealed that failure with cluster inclusions MnS (r=S/Mn=0∙024>0∙01) was more than the standard amount. Besides, stress analysis showed that the stress field in stress concentration zones with the lubricating hole is much less than the web-crankpin fillet but the presence of cluster impurities, low hardness (>600 HV0.1 proposed standard), downshifting has caused the growth of primary cracks. It is recommended to first increase the hardness by about 43% and then, decrease the size of non-metallic inclusions so that primary crack growth does not initiate from the worst clusters of inclusions.

Research of Microstructure of Molybden Doped Weldings of Oil and Gas Pipelines

Abstract Still existing scientific, technical and technological developments to improve the quality of welded joints of metal pipe structures contain contradictions and uncertainty about the effects of alloying elements, such as molybdenum, mechanical and visco-plastic properties, as well as metallographic component joints. All this indicates the need for a systematic study of these problems for the development of rational metallurgical and technological measures to significantly improve the technological and corrosion-mechanical properties of weld metal. Metallographic studies, using laboratory equipment with high identifying ability, found that the doping of weld metal with molybdenum in the amount of 0.2-0.4% causes fragmentation of ferrite-pearlite structure, including carbides Mn and Fe, and also reduces the number and size of non-metallic inclusions – sulfides, oxides and silicates. Moreover, non-metallic inclusions have a dispersed appearance, which promotes plasticization of the structure, which directly increases the viscous-plastic characteristics and resistance of the metal joints to crack formation. Based on the results of metallographic research, the optimum content in the weld metal of the alloyed element – molybdenum, which is 0.2-0.4%, is determined.

Database Clustering after Automatic Feature Analysis of Nonmetallic Inclusions in Steel

Non-metallic inclusions (NMIs) in steel have a negative impact on the properties of steel, so the problem of producing clean steels is actual. The existing metallographic methods for evaluating and analyzing nonmetallic inclusions make it possible to determine the composition and type of NMIs, but do not determine their real composition. The analysis of single NMIs using scanning electron microscope (SEM), fractional gas analysis (FGA), or electrolytic extraction (EE) of NMIs is too complicated. Therefore, in this work, a technique based on the automatic feature analysis (AFA) of a large number of particles by SEM was used. This method allows to obtain statistically reliable information about the amount, composition, and size of NMIs. To analyze the obtained databases of compositions and sizes of NMIs, clustering was carried out by the hierarchical method by constructing tree diagrams, as well as by the k-means method. This made it possible to identify the groups of NMIs of similar chemical composition (clusters) in the steel and to compare them with specific stages of the steelmaking process. Using this method, samples of steels produced at different steel plants and using different technologies were studied. The analysis of the features of melting of each steel is carried out and the features of the formation of NMIs in each considered case are revealed. It is shown that in all the studied samples of different steels, produced at different steel plants, similar clusters of NMIs were found. Due to this, the proposed method can become the basis for creating a modern universal classification of NMIs, which adequately describes the current state of steelmaking.