Types Of Nonmetallic Inclusions Research Articles

METALLOGRAPHIC ANALYSIS OF NON-METALLIC INCLUSIONS IN SEMI-KILLED STEEL (GRADE 25G2S) DEOXIDIZED WITH A COMPLEX ALLOY Fe-Si-Mn-Al

This study presents a metallographic analysis of non-metallic inclusions in steel samples obtained from six different heats of the oxygen converter shop at JSC «Qarmet» and under laboratory conditions at the Karaganda Industrial University. The investigation focused on semi-killed steel samples deoxidized using traditional technology under industrial conditions and with a complex alloy containing Fe-Si-Mn-Al under laboratory conditions, aiming to identify the types and assess the level of contamination by non-metallic inclusions. The results revealed the presence of various types of non-metallic inclusions, such as corundum, chromite spinel, chromium oxides, as well as titanium nitrides and carbonitrides. The degree of contamination by non-metallic inclusions ranged from 2 to 3 points. The analysis showed that the use of a complex Fe-Si-Mn-Al alloy instead of traditional deoxidizers can affect the quantitative and qualitative composition of non-metallic inclusions. It was established that the complex alloy promotes the formation of more stable inclusion phases, which can positively impact the mechanical properties of the steel. It was also found that different production technologies and the use of deoxidizers can significantly influence the quantity and types of non-metallic inclusions, requiring further study and optimization of technological processes. Therefore, the results of this study can be valuable for metallurgical enterprises in selecting optimal steel deoxidation methods and improving steel quality, as well as for further scientific research in the fields of metallurgy and materials science.

ON COMPETING PROCESSES AT THE INCLUSION – MATRIX BOUNDARIES DURING STEEL ROLLING

Purpose of the work – to study of the processes that determine the interaction of non-metallic inclusions and the steel matrix during steel rolling. Methods. The behavior of inclusions was studied during hot rolling of steels 08Yu, 08T, 08kp, NB-57, 08GSYUTF in the temperature range of 1 200...900 °C and cold rolling with degrees of deformation of 35...75 %. The study of hot slipping along the boundaries of the inclusion − matrix was observed during high-temperature (900...1 200 °C) deformation by stretching in a vacuum on the IMASH-5S installation with a gripper movement speed of 1 680 mm/min. According to the study of slipping, steel samples were stretched in a vacuum at temperatures of 25...900 °С on the IMASH-5S installation with a gripper movement speed of 2 000 mm/min. On the surface of the samples, using the PMT-3 device, reference points were applied near the 0° and 90° inclusion poles on both sides of the inclusion − matrix boundary. Research methods are given in works [10; 11]. Identification of inclusions was carried out by metallographic (Neophot-31), petrographic and micro-X-ray spectral (MS-46 Cameca) methods. Results. It is shown that during plastic deformation, there is an interaction between non-metallic inclusions and the steel matrix, which determines their joint plastic shape change and is associated with the development of competing processes at the inclusion − matrix interphase boundaries: interphase friction and slipping (hot or cold depending on the deformation temperature). The mechanisms of these processes are determined depending on the deformation conditions and the level of plasticity of non-metallic inclusions and the steel matrix. Scientific novelty. The peculiarities of interphase friction and hot and cold slipping along the inclusion − matrix interphase boundaries of steel under different conditions of plastic deformation have been established. It is shown that the mechanisms of each of these processes depend on the temperature regime of deformation, the level of plasticity of the inclusions and the steel matrix, as well as on the structure of the inclusion − matrix boundaries, which determines the possibilities of movement and interaction of interfacial defects. It is shown that the specified processes determine the level of plasticity of the inclusion − matrix boundaries and significantly affect the nature of the change in shape of the inclusions and their redistribution in the steel matrix during steel rolling, which inevitably affects the technological plasticity of steels. Practical significance. The use of the results obtained will make it possible to develop technologies for producing steels with regulated types of nonmetallic inclusions, which will significantly increase their technological characteristics, as well as prevent the formation of various kinds of defects during the processing of steels by pressure of products.

Revealing the kinetics of non-metallic inclusion reactions in steel using in-situ high temperature environmental scanning electron microscopy

The kinetics of solid-state reactions involving non-metallic inclusions (NMIs) in steel is a topic of growing interest due to the need to understand the effects of heat treatments on NMI composition and stability. In this study, a High Temperature Environmental Scanning Electron Microscope (HT-ESEM) is utilized to conduct in-situ observations of various types of NMIs, including calcium aluminate complex, CaS, MgAl2O4-CaS, MnS, and TiN, in steels at temperatures of 800 °C and 900 °C for different holding times. The observed morphological variations in the NMIs indicate a decrease in the fractions of CaS and MnS, promoting void formation and ferrite–austenite phase transformation. To estimate the NMI reactions with the residual atmosphere in the sample chamber during experiments, HT-ESEM-driven thermodynamic calculations have been performed using FactSage 8.2 software. These calculations provide valuable insights into the interpretation of the experimental data, facilitating a better understanding of the complex NMI reactions in steel.

Confirming Debonding of Non-Metallic Inclusions as an Important Factor in Damage Initiation in Bearing Steel

Damage in bearings is closely associated with the presence of microstructural alterations, known as white etching areas (WEAs) and white etching cracks (WECs). One of the main reasons for the creation of these microstructural alterations is the presence of defects in the material, such as non-metallic inclusions. Manganese sulfides and aluminum oxides are widely reported in the literature as the most common types of non-metallic inclusions found in bearing steels. This study classifies 280 non-metallic inclusions in an investigated bearing steel according to several criteria: bonded/debonded with the matrix, size, shape, orientation angle, depth below the raceway surface, and chemical composition. Contrary to the findings in the literature, this investigation reports that the chemical composition of the inclusion (MnS + Al2O3) is of secondary importance when considering factors for damage initiation. The orientation of the microstructural alterations is observed to coincide with the high-stress regions, indicating a relation between the formation of butterfly wings and the white etching crack. In our investigation, butterfly wings typically exhibit a 45-degree pattern originating from the non-metallic inclusions. Conversely, the white etching crack starts from the non-metallic inclusion at a shallower angle in correspondence to the raceway. This can be attributed to the stress state, which corresponds to a region where extensive white etching cracks are formed. In conclusion, the microstructural observations demonstrate that the state of non-metallic inclusion—i.e., whether they are bonded or not to the steel matrix—plays an essential role in initiating rolling contact fatigue damage.

Classification of Nonmetallic Inclusions in Steel by Data‐Driven Machine Learning Methods

Nonmetallic inclusions have strong influence on final steel properties. An important characterization tool to make a comprehensive analysis of nonmetallic inclusions is the scanning electron microscope equipped with energy‐dispersive spectroscopy (SEM‐EDS). A major drawback which prevents its use for online‐steel assessment is the time taken for analysis. Machine learning methods have been previously introduced which circumvents the usage of the EDS for obtaining chemical information of the inclusion by classifying inclusion based on their back scatter electron images. This study introduces a method based on a simpler tabular data input consisting of morphological and mean gray values of inclusions. Naive Bayes and Support Vector Machine classifier models are built using the R statistical programming language. Two steel grades are considered for this study. The prediction results are shown to be satisfactory for both binary (maximum 89%) and 8‐inclusion class (maximum 61%) categorization. The input dataset is further improved by optimizing the image settings to distinguish the different types of nonmetallic inclusions. It is shown that this improvement results in a higher rate of correct predictions for both binary (maximum 98%) and 8‐class categorization (maximum 81%).

Interaction of rail steel melt with refractory lining

The rail steel properties are adversely affected by rigid non-metallic inclusions, containing aluminum oxides. Therefore, aluminum content is limited to 0.004 % wt. in rail steel grades. Aluminum can get into steel from charge materials and refractory lining. In this work, we’ve analyzed how the chemical composition of refractories used in rail steel making influence steel quality on example of one domestic enterprise. To determine the main types of non-metallic inclusions created in E76F rail steels, we have performed fractional gas analysis of the samples taken in various process steps. It was found that the slag composition after degassing changes insignificantly, while the most part of non-metallic inclusions in rail steel is represented by aluminates.

The role of inclusion-matrix boundaries in steels fracture processes

The features of the fracture of the interphase inclusion-matrix boundaries under various thermal-deformation and aggressive actions are investigated. The reasons and conditions for the formation of cracks as a result of decohesion of the inclusion-matrix boundaries associated with the concentration of interfacial thermal and deformation stresses are discussed. It was found that the character of decohesion of the inclusion-matrix boundaries (rupture of interatomic bonds of a nonmetallic inclusion and a steel matrix) caused by interphase thermal stresses is due to the conditions of heating and cooling, depending on the type of processing (conventional heating, laser or electromagnetic treatment), which determines the possibility of passing relaxation processes associated with the redistribution of interfacial defects within the specified boundaries. The mechanisms and features of decohesion of the interphase inclusion-matrix boundaries at different methods and temperatures of deformation are discussed. It is shown that the decomposition of the inclusion-matrix boundaries upon deformation occurs in cases of certain types of nonmetallic inclusions (oxides, spinels, some sulfides). For different types of inclusions and steels, parameters have been determined that characterize the cohesive strength of the inclusion-matrix interface depending on the loading conditions. It is shown that decohesion (fracture) of the inclusion-matrix boundary into two free surfaces can be considered as the transformation of interphase misfit dislocations into surface steps as a result of loss of conjugation. The role of inclusion-matrix boundaries in the formation of cracks of fatigue and fatigue-corrosion origin is considered. It is shown that under the influence of aggressive media and cyclic stresses, the structure of the inclusion-matrix interphase boundaries degrades, which is associated not only with the accumulation of interfacial stresses, but also with the facilitation of the penetration of surfactant atoms from the environment along these boundaries. As a result, fatigue-corrosion destruction of the inclusion-matrix boundaries occurs, and the effect of an adsorptive decrease in their strength is manifested.

Characteristics and Transformation Mechanism of Nonmetallic Inclusions in 304 Stainless Steel during Heat Treatment at 1250 °C.

Evolutions of two typical types of nonmetallic inclusions, i.e., inclusions based on CaO-SiO2-Al2O3 and MnO-SiO2-Al2O3 of 304 stainless steel were investigated in laboratory-scale experiments under isothermal heat treatment at 1250 °C for 0, 30, 60 and 120 min. Results show inclusion population density increases at the first stage and then decreases while their average size decreases and then increases. Moreover, almost no Cr2O3 content within the inclusion before the heat treatment, but Cr2O3 content increases gradually along with increasing heat treatment time. Furthermore, the increasing of Cr2O3 content in the inclusions would increase their melting points and reduce their plasticities. The experimental results and thermodynamic analysis indicate that there are three steps for inclusion evolution during the heat treatment process, in which Ostwald ripening plays an important role in inclusion evolution, i.e., inclusions grow by absorbing the newly formed small-size MnO-Cr2O3 inclusions.

Effect of Non-Metallic Inclusion Chemical and Phase Composition on Corrosion Resistance of Carbon and Low Alloy Steels in Water Media Typical for Oilfield Pipeline Operating Conditions

Results of studying the effect of the chemical and phase composition of non-metallic inclusions on the corrosion resistance of carbon and low-alloy steels in neutral aqueous media characteristic of the operating conditions of oilfield pipelines are presented. It is shown that the corrosivity of complex nonmetallic inclusions present in modern steels depends on their chemical and phase composition, the optimization of which can prevent an unfavorable effect of these inclusions on steel corrosion resistance under oilfield pipeline operating conditions. A method for reducing the corrosivity of non-metallic inclusions based on aluminum-magnesium spinel is its oxide component modification with calcium and/or titanium, which contribute to its conversion into a globular form. An increase in corrosivity of complex non-metallic inclusions, the oxide component of which consists of various components, and correspondingly a large amount of corundum among oxide components, results in a reduction of steel corrosion resistance. An increase in the content of calcium and magnesium oxides leads to a reduction in the corrosivity of complex inclusions. In producing steels with increased corrosion resistance for oil field pipelines it is advisable to provide production methods aimed at preventing formation of adverse types of non-metallic inclusions.

Agglomeration Mechanism of Complex Ti-Al Oxides in Liquid Ferrous Alloys Considering High-Temperature Interfacial Phenomenon

This work presents the agglomeration mechanism of complex Ti-Al oxides in the liquid ferrous alloy. Cluster characteristics were investigated using Al and Ti/Al-complex deoxidation method in lab scale. The time-dependent size distribution, total number per volume, average size, and circularity of the clusters were quantitatively analyzed. Furthermore, high-temperature confocal laser scanning microscopy was utilized to directly observe the cluster formation of Ti-Al oxides. A capillary force model including wettability parameters was applied to compare the agglomeration capabilities of different types of non-metallic inclusions. When a low Ti is added into melt, the agglomeration of TiOx·FeO liquid inclusions is one of the key factors to decrease the frequency of cluster formation. When the Al is added into melt, the heterogeneous precipitation on TiOx·FeO surfaces is the main reaction process. Ti-Al oxides have lower agglomeration ability than that of Al2O3, which in turn, contribute to a low agglomeration frequency as well.

Improving the corrosion resistance of steels intended for use in seawater

The results of study of influence of the chemical composition of steel, the structural condition and contamination of nonmetallic inclusions of various types on its corrosion resistance in seawater are presented in the paper. The requirements for increased-corrosion-resistance steel for marine conditions and oilfield pipelines have been compared. It has been shown that a mandatory requirement for ensuring high corrosion resistance of steels is to ensure the purity of steels from unfavorable types of nonmetallic inclusions. It has also been shown that reducing the carbon content and alloying with nickel lead to an increase in the corrosion resistance of steel.

Effect of New Types of Nonmetallic Inclusions on Continuously-Cast Billets and the Quality of High-Strength Low-Alloy Steel Rolled Product

The nature of new types of nonmetallic inclusions (NI) facilitating improvement of a continuously-cast billet (CCB) and rolled product of high-strength low-alloy steels is studied. Contemporary approaches are considered for improving hot-rolled product. It is noted that apart from chemical composition and hot rolling regimes its properties are affected by CCB quality and the degree of different liquation processes. Results are analyzed for previous studies pointing to the fact that liquation inhomogeneity is suppressed in the case when in the concluding stage of steel treatment in a ladle and/or during crystallization there is formation of oxide NI of complex composition, presumably glassy. NI composition, and macro- and microstructure of CCB whose rolled product has a different level of mechanical properties and an axial zone with a different degree of structural inhomogeneity, are studied. It is shown that rolled product with a high level of properties and uniform structure of the axial zone is obtained from a CCB within whose structure there are compound NI of complex composition containing oxides of silicon, iron, and other elements, and also dendrite-like precipitates of carbonitrides (carbides).

Developing a Technological Means of Obtaining Superior Properties and Quality for Quenched and Forged Structural Steels

In order to establish the scientific principles of a technology for the production and ladle treatment of new steels that can be quenched at forming, steels which were made in factory and laboratory heats and had different carbon contents were analyzed to explore the key factors and processes that determine both their total content of nonmetallic inclusions (NIs) and their content of certain types of NIs – particularly the types that are harmful. It was found that the most important factors in producing steel which is clean based on its content of all types of inclusions (which has an NI rating no higher than 1.5 in the government standard GOST 1778) are the slag regime and the ratio of the weights of the lime and aluminum added to the steel-pouring ladle during tapping. The optimum ranges of values for these parameters are determined. The existing requirements on the slag-regime parameters are observed to ensure a low content of harmful corrosion-active nonmetallic inclusions (CANIs) in the steel. However, it is essential to maintain a low (at or below the lower limit of 0.02% specified for the grade of steel) aluminum content for the duration of the ladle treatment. Aluminum content can be increased during the final stages, if necessary. A study was made of the effect of the MgO content of the covering slag on the possibility and rate of formation of CANIs based on alumomagnesian spinel. it was found that the steel’s content of such inclusions rises sharply when the concentration of MgO in the covering slag is greater than 14.1%. An MgO content of up to 8% guarantees that the steel will be clean based on its content of all types of inclusions. The results obtained for the metal of two trial heats confirmed the adequacy of the key parameters that were identified and the ranges of values for those parameters which were determined to be optimum for obtaining a low CANI content and high resistance to local corrosion.

Advancement of the Properties of Structural Steels by Creating an Optimum Form of Existence of Impurities and Nonmetallic Inclusions

Special features of a recent metallurgical process for structural steels are considered. The types of nonmetallic inclusions, precipitates of excess phases and impurities are described, and the effect of their content, size, morphology and volume distribution on the production, operational and quality characteristics of the steel is determined. Specific examples are used to show the perspectives of the formulated principle for advancing the combination of properties of structural steels of various types at substantial decrease in the expenses.

Experimental Study on the Formation of Non-Metallic Inclusions Acting as Nuclei for Acicular Ferrite in HSLA Steels through Specific Deoxidation Practice and Defined Cooling Conditions

Specific types of non-metallic inclusions are known to act as heterogeneous nuclei for the formation of acicular ferrite, which provides excellent toughness. By increasing the amount of acicular ferrite in the microstructure, the properties of HSLA steels can be optimized significantly.Although the formation of acicular ferrite caused by heat treatments (thermomechanical treatments or welding) is quite well described in literature, there is less information to find about the formation of acicular ferrite immediately out of the liquid melt. Within the present study experiments on laboratory scale are carried out simulating the influence of cooling conditions and Ti-content on size, chemical composition and morphology of non-metallic inclusions and consequently on the amount of acicular ferrite. All experiments were carried out with a dipping test simulator enabling very well controllable cooling conditions. Optical microscopy in combination with special etching methods as well as SEM/EDS-analysis was used for microstructure and inclusion characterization.

Laws governing the transformation of undesirable types of nonmetallic inclusions during the treatment of steel 20-Kt in the solid state

A study is made of the effect of the regimes used for heating, hot-rolling, and heat-treating seamless pipes of steel 20-KT on their content of corrosion-active nonmetallic inclusions (CANIs). Technological measures are developed to ensure that the low CANI content which is required is obtained and that the steel thus has high indices for resistance to local corrosion in aqueous chlorine-bearing media.

Analysis of various versions of the deoxidation of rail steel at OAO NTMK

The deoxidation of steel melted using various types of deoxidizers during out-of-furnace treatment is studied. The total oxygen and nitrogen content and the oxygen contents in the main types of oxide nonmetallic inclusions are determined by fractional gas analysis of steel samples taken from heats performed by various schedules. The main types of nonmetallic inclusions and their size distributions are found with qualitative and quantitative metallography. The oxygen content in the rail steel is minimal (5 ppm) when calcium carbide CaC2 is introduced into the metal in tapping of a converter. When the metal is deoxidized using a steel wire filled with calcium or a steel wire filled with silicocalcium, the oxygen content in rail steel is ≈8 and ≈11 ppm, respectively. A comparison of various processes of rail steel deoxidation under the OAO NTMK conditions shows that the limitation of the aluminum content (no more than 30 ppm) or the use of a wire with a calcium or calcium carbide filler is more effective than the use of a wire filled with silicocalcium.

Physicochemical prediction of the types of nonmetallic inclusions: Complex deoxidation of steel with aluminum and calcium

The complex deoxidation of steel with aluminum and calcium is used as an example to analyze the state of the art in the methods of physicochemical prediction of the types of nonmetallic inclusions forming during ladle treatment of steel. The uncertainty existing in the thermodynamic description of the simplest object of metallurgical technologies, i.e., iron-based dilute liquid solutions, is shown to lead to radically different versions of the oxide-precipitation diagram of the Fe-Ca-Al-O system. The physical causes of this discrepancy are revealed. It is demonstrated that the concentration and temperature dependences of the thermodynamic properties of iron melts can be well approximated using an approach based on the concept of associated solutions. This approach has been used to adequately interpret the reactivity of calcium in iron-based solutions for the first time. The modern methods of physicochemical prediction of the types of nonmetallic inclusions in steel are noted to require detailed theoretical and experimental grounds.

Nonmetallic Inclusions in Low-Alloy Tube Steel

Study of the nonmetallic phase of unalloyed tube steel 10G2FB has shown that the steel contains four types of nonmetallic inclusions. Relatively fine (no coarser than 12 µm) calcium aluminates of variable composition are the main type of nonmetallic inclusion (NI) in such steel. It was established that a decrease in the point rating for NI contamination of the steel from 3.5 to 1.5 leads to an increase in the steel’s impact toughness from 235 to 318 J/cm2.

The electromagnetic filtration of molten aluminum using an induced-current separator

The production of clean metal, free from oxides and other types of nonmetallic inclusions, is central to product quality and performance. Toward this end, electromagnetic filtration is an emerging technology for the purification of molten metals. This paper reviews the theory and the mechanism of the electromagnetic separation of inclusions from molten metal and describes the induced-current electromagnetic separator developed at the University of Alabama. The results of laboratory and large-scale experiments on the purification of molten aluminum demonstrate the capability of the system for producing super clean metals.