Distribution Of Non-metallic Inclusions Research Articles

Features of the Distribution of Nonmetallic Inclusions in Continuously Cast Billets Made of Sulfur-Containing Steel C45E

Features of the Distribution of Nonmetallic Inclusions in Continuously Cast Billets Made of Sulfur-Containing Steel C45E

Particular Features of the Distribution of Nonmetallic Inclusions in a Continuously Cast Low-Alloy Steel Ingot

Particular Features of the Distribution of Nonmetallic Inclusions in a Continuously Cast Low-Alloy Steel Ingot

ОСОБЕННОСТИ СТРОЕНИЯ НЕПРЕРЫВНОЛИТОЙ ЗАГОТОВКИ ИЗ СТАЛИ МАРКИ С45Е

The paper presents the results of identification and features of the distribution of non-metallic inclusions (NMI) along the cross-section of a continuously cast blank (CCB) with a square cross-section of 360x360 mm made of C45E grade steel. Identification of inclusions by optical and electron microscopy showed that three main groups of NMI prevail in the CCB metal: oxides, sulfides and oxysulfides. Oxide inclusions are represented by inclusions of two types (alumagnesial spinel in a shell of calcium aluminate type CaO∙Al2O3, silicates of type 3MnO∙Al2O3∙3SiO2), sulfide inclusions are represented by sulfides MnS and CaS, oxysulfide inclusions (oxides in a shell of sulfides). The distribution of inclusions across the cross-section is uneven, the surface and central layers of the CCB have the maximum contamination. The paper shows that the reason for the increase in the number of inclusions in the center of CCB is caused by an increase in the number of sulfide inclusions (tertiary NMI), the high content of inclusions in the surface layers of CCB, caused by a high content of oxide and oxysulfide inclusions (primary and secondary NMI).

Evolution mechanism of inclusions during refining and continuous casting process of 321H stainless steel

ABSTRACT The evolution of inclusions during the refining and casting process was investigated on an industrial scale to clarify the quantity and distribution of non-metallic inclusions for 321H stainless steel. The analyses showed that Al2O3-SiO2-MnO-CaO and Al2O3 as the main types of inclusions at the late of AOD and VOD, respectively. Pure titanium nitride and titanium nitride with oxide as the nuclei dominated the inclusions at the late of LF. The types of inclusions in mold and slab were similar to those obtained at the late of LF, while titanium nitride inclusions in slab were higher in numbers and larger in size. The titanium nitride inclusions precipitating with MgO-Al2O3-CaO-(TiO2) nuclei showed a higher number density and area fraction than other oxide inclusions. The calcium treatment of molten steel was optimized by FactSage software and it was necessary to accurately control the calcium content in molten steel before titanium addition.

Influence of the nature of distribution of non-metallic inclusions on the mechanical properties of weld metal of low-alloy steels

Influence of the nature of distribution of non-metallic inclusions on the mechanical properties of weld metal of low-alloy steels

REPAIR TECHNOLOGY OF PRODUCT PIPELINES OPERATED IN A HYDROGEN SULFIDE ENVIRONMENT

Introduction. The article discusses the improved repair technologies of pipeline material saturated with hydrogen sulfide, which should replace conventional repair methods that ignore operational features in a hydrogen sulfide environment.The aim of this work is to develop a technology for repairing pipelines operated in a hydrogen sulfide environment by manual arc welding using a consumable electrode.Materials and methods. Full-scale experiments were carried out to achieve the goals. A section of an industrial pipeline was selected as a test sample, whose service life in a hydrogen sulfide environment at the hydrocracking unit of an oil refinery equals about 10 years. Degassing, i.e., the removal of diffusion atomic hydrogen from the metal in the repairing area, was carried out using electric heating devices. The surfacing of the pipe edges using a layer of austenitic or ferritic metal was carried out by manual arc welding.Results. The developed technology for repairing pipelines operated in a hydrogen sulfide environment by manual arc welding using a consumable electrode involves degassing and surfacing the edges with metal having the same composition as the parent material. Here, the positive effect of surfacing lies in the fine distribution of non-metallic inclusions in the remolten metal and a favorable change in their shape and chemical composition.Conclusions. The efficiency of the repair technology of industrial pipelines using welding is achieved by taking into account the properties of a transported product and its influence on the welding process. When developing the welding technology of industrial pipelines operated in the hydrogen sulfide environment, such basic measures as preliminary degassing of pipe metal, preliminary surfacing, and heat treatment of pipe edges are substantiated.

STRUCTURE AND PROPERTIES OF STEEL GRADE 7ХНМФБ FOR MANUFACTURING WOOD CUTTING SAWS

The article covers issues related to the development of a new domestic tool alloy steel of the 7ХНМФБ brand for the manufacture of wood-cutting saws. It is noted that the aforementioned saws were previously made from alloyed tool steels of the 9ХФ and 9ХФМ grades, which were smelted in the Russian Federation (RF), and wood-cutting saws were also made from them in the Russian Federation. With the acquisition of independence, these saws became scarce, and the question arose of developing domestic tool alloy steel for the manufacture of these saws. The purpose of the research is to determine the structure and properties of steel grade 7ХНМФБ. Well-known alloyed tool steels were taken as a basis and such elements as niobium, calcium, aluminum and rare earth elements were added to their chemical composition. We received a new domestic alloyed tool steel of the 7ХНМФБ brand, which, in comparison with known steels, has a number of significant advantages. These include a significant reduction in the content of harmful sulfur and phosphorus impurities, which is achieved both by smelting technology and by introducing additional elements into the steel composition. The introduction of aluminum leads to a change in the quality and shape of the distribution of non-metallic inclusions, which increases the plastic characteristics and increases the resistance to fracture viscosity. The steel of the new brand is distinguished by a higher value of impact strength (especially at negative temperatures), resistance to the occurrence and propagation of cracks. Steel 7ХНМФБ also surpasses the indicators of steels 9ХФ and 9ХФМ in terms of fracture toughness and durability during cyclic bending with rotation. The choice of the alloying scheme ensures that the new brand of steel, with the same hardness, has almost the same strength and yield strength as 9ХФ and 9ХФМ steels.

Influence of Pulse Current on Inclusion Properties of Alumina in Molten Steel

In the process of metal purification, the study of controlling the morphology and size distribution of non-metallic inclusions in steel based on electric fields has attracted extensive attention. However, the action mechanism of electric fields on inclusions in liquid steel has not been clearly identified. In this paper, the influence of pulse current on the quantity, size, and distribution of alumina inclusions in liquid steel was explored through a high-temperature energization experiment, and the action mechanism of pulse current was expounded based on the angle of interface free energy. The results show that the number of small alumina inclusions in the steel after electric pulse treatment (the pulse current density was 0.1–3 A/cm2, the frequency was 100 Hz, and the pulse waveform was a square wave) was significantly increased compared with the sample without electric pulse treatment, and the particle size was concentrated at 2–5 μm, and the inclusions were concentrated in the upper and lower parts of the sample. However, in the samples without electrification treatment, the large particles of inclusions are the majority, the particle size was concentrated at about 10 μm, and the inclusions were concentrated in the upper and middle parts of the samples. When the pulse current was applied to the molten steel, the interfacial free energy of the internal system of liquid steel alumina inclusion was reduced, the nucleation of alumina inclusion was promoted, the aggregation growth between alumina particles was inhibited, and then the migration and distribution of inclusions were also affected. The experimental results could provide technical support for high-quality steel smelting production to a certain extent.

Effect of non-metallic inclusions on AISI 4140 fatigue strength

In the present paper, a procedure for fatigue strength assessment of high strength steel (AISI 4140) containing non-metallic inclusions (NMIs) is proposed. Such a procedure implements: (i) a defect content analysis, (ii) the area-parameter model, and (iii) the multiaxial critical plane-based criterion by Carpinteri at al. According to the defect content analysis, the distribution of NMIs is determined in two cross-sections perpendicular to the maximum principal stress directions under normal and shear uniaxial cyclic loadings. The return periods, obtained optimising the accuracy of the procedure in terms of fatigue strength estimation, are determined by taking into account five different prediction volumes. The results achieved through the proposed procedure are compared with both the experimental data and the results obtained employing the Carpinteri et al. criterion without optimisation.

Distribution of Nonmetallic Inclusions in Slab for Tinplate

Tinplate is widely used in food packaging and chemical packaging. Industrial production continues to reduce the thickness of tinplate steel, which puts higher requirements on the control of inclusions. In this study, compared with traditional detection methods, the Ultrasonic Detection method can analyze the distribution of nonmetallic inclusions in larger size samples, which is closer to the actual production process. The numerical simulation model is established to analyze the flow, heat transfer and solidification behavior of molten steel. The results show: There are two nonmetallic inclusion bands in the sample at the edge of the slab, one is the inner and outer arc side of the sample, and the other is the 1/8 to 1/4 slab thickness region of the inner arc side in the sample. The inclusions in the thickness direction of the slab edge within the range of 1/8 to 1/4 are captured in areas 800 mm to 1400 mm below the meniscus. The solidification of the inner and outer arcs is not symmetrical, which leads to the asymmetrical distribution of inclusions in the inner and outer arcs. This study can provide a reference for improving the tinplate production process.

Influence of Non-Metallic Inclusions on Local Deformation and Damage Behavior of Modified 16MnCrS5 Steel

This work investigates a ferrite matrix with multiple non-metallic inclusions to evaluate their influence on the global and local deformation and damage behavior of modified 16MnCrS5 steel. For this purpose, appropriate specimens are prepared and polished. The EBSD technique is used to record local phase and orientation data, then analyze and identify the size and type of inclusions present in the material. The EBSD data are then used to run full phase crystal plasticity simulations using DAMASK-calibrated material model parameters. The qualitative and quantitative analysis of these full phase simulations provides a detailed insight into how the distribution of non-metallic inclusions within the ferrite matrix affects the local stress, strain, and damage behavior. In situ tensile tests are carried out on specially prepared miniature dog-bone-shaped notched specimens in ZEISS Gemini 450 scanning electron microscope with a Kammrath and Weiss tensile test stage. By adopting an optimized scheme, tensile tests are carried out, and local images around one large and several small MnS inclusions are taken at incremental strain values. These images are then processed using VEDDAC, a digital image correlation-based microstrain measurement tool. The damage initiation around several inclusions is recorded during the in situ tensile tests, and damage initiation, propagation, and strain localization are analyzed. The experimental results validate the simulation outcomes, providing deeper insight into the experimentally observed trends.

Calculated-experimental model of distribution of non-metallic inclusions in the metal of welds by sizes

The Paton Welding Journal, 2021, №12. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.

Numerical Simulation on Motion Behavior of Inclusions in the Lab-Scale Electroslag Remelting Process with a Vibrating Electrode

In order to meet the requirement of high-quality ingots, the vibrating electrode technique in the electroslag remelting (ESR) process has been proposed. Non-metallic inclusions in ingots may cause serious defects and deteriorate mechanical properties of final products. Moreover, the dimension, number and distribution of non-metallic inclusions should be strictly controlled during the ESR process in order to produce high-quality ingots. A transient 2-D coupled model is established to analyze the motion behavior of inclusions in the lab-scale ESR process with a vibrating electrode, especially under the influence of the vibration frequency, current, slag layer thickness, and filling ratio, as well as type and diameter of inclusions. Simulation model of inclusions motion behavior is established based on the Euler-Lagrange approach. The continuous phase including metal and slag, is calculated based on the volume of fluid (VOF) method, and the trajectory of inclusions is tracked with the discrete phase model (DPM). The vibrating electrode is simulated by the user-defined function and dynamic mesh. The results show that when the electrode vibration frequency is 0.25 Hz or 1 Hz, the inclusions will gather on one side of the slag layer. When it increases from 0.25 Hz to 1 Hz, the removal ratio of 10 μm and 50 μm inclusions increases by 5% and 4.1%, respectively. When the current increases from 1200 A to 1800 A, the flow following property of inclusions in the slag layer becomes worse. The removal ratio of inclusions reaches the maximum value of 92% with the current of 1500 A. The thickness of slag layer mainly affects the position of inclusions entering the liquid-metal pool. As the slag layer thickens, the inclusions removal ratio increases gradually from 82.73% to 85.91%. As the filling ratio increases, the flow following property of inclusions in the slag layer is enhanced. The removal ratio of 10 μm inclusions increases from 94.82% to 97%. However, for inclusions with a diameter of 50 μm, the maximum removal ratio is 96.04% with a filling ratio of 0.46. The distribution of 50 μm inclusions is significantly different, while the distribution of 10 μm inclusions is almost similar. Because of the influence of a vibrating electrode, 10 μm Al2O3 and MnO have a similar removal ratios of 81.33% and 82.81%, respectively.

Molten Steel Flow, Heat Transfer and Inclusion Distribution in a Single-Strand Continuous Casting Tundish with Induction Heating

The electrical magnetic field plays an important role in controlling the molten steel flow, heat transfer and migration of inclusions. However, industrial tests for inclusion distribution in a single-strand tundish under the electromagnetic field have never been reported before. The distribution of non-metallic inclusions in steel is still uncertain in an induction-heating (IH) tundish. In the present study, therefore, using numerical simulation methods, we simulate the flow and heat transfer characteristics of molten steel in the channel-type IH tundish, especially in the channel. At the same time, industrial trials were carried out on the channel-type IH tundish, and the temperature distribution of the tundish with or without IH under different pouring ladle furnace was analyzed. The method of scanning electron microscopy was employed to obtain the distribution of inclusions on different channel sections. The flow characteristics of molten steel in the channel change with flow time, and the single vortex and double vortex alternately occur under the electromagnetic field. The heat loss of molten steel can be compensated in a tundish with IH. As heating for 145 s, the temperature of the molten steel in the channel increases by 31.8 K. It demonstrates that the temperature of the molten steel in the tundish can be kept at the target value of around 1813 K, fluctuating up and down 3 K after using electromagnetic IH. In the IH channel, the large inclusions with diameters greater than 9 μm are more concentrated at the edge of the channel, and the effect of IH on the inclusion with diameters less than 9 μm has little effect.

Three-Dimensional Spatial Distribution of Non-metallic Inclusions on the Entire Cross Section of a Steel Continuous Casting Slab

Three-Dimensional Spatial Distribution of Non-metallic Inclusions on the Entire Cross Section of a Steel Continuous Casting Slab

Improvement of wear-resistant properties of steel 30Н3MF with additional microalloying

One of the directions of wear resistance improvement is microalloying of improved steels. In the studies conducted, the feasibility of adjusting the composition of steel 30Н3MF was determined by additional microalloying of V + Nb in order to give it wear-resistant properties. Microstructural studies of the experimental alloy were carried out. The microstructure is fairly uniform, represented by a matrix and inclusions. Matrix is represented by doped solution, which includes nickel. It is determined that in a chemically and structurally inhomogeneous ingot, even after heat treatment, structural components will remain. Characteristics such as the amount, morphology and distribution of non-metallic inclusions in the metal matrix are mainly laid at the stage of metal discharge from the steelmaking unit, as well as in the process of deoxidation and modification of steel during its off-furnace treatment.

Comparative analysis of the structure of solid and hollow steel cast billets

This paper presents the research results of solid structure and hollow steel billets obtained by continuous casting. To substantiate the feasibility of using a hollow billet as an initial one in the production of seamless hot-rolled pipes, a comparative analysis of the distribution of non-metallic inclusions, macro- and microstructure, as well as segregation by structural zones was carried out. When analyzing the macrostructure of a hollow billet, two distinct zones were revealed: equiaxed small and columnar crystals, which distinguishes it, compared with a solid billet, by the absence of a zone of misoriented crystals. This, in turn, helps to eliminate defects such as axial porosity and segregation. The improved quality of the macrostructure during casting of a hollow billet is explained by more favourable conditions for heat removal and a higher rate of solid-phase advance due to bilateral cooling, and less shrinkage of the melt due to its cross-sectional geometry. The distribution of nonmetallic inclusions, consisting of oxide, sulfide and oxysulfide compounds, and liquidation elements, showed that they are concentrated mainly at the boundaries of crystalline zones, and for a solid billet and in the central part. This fact is caused by the development of a zone of intense heat removal. When research the microstructures of solid and hollow workpieces, a ferrite-pearlite mixture is observed in both cases. The microstructure of the hollow billet is more dispersed, which is confirmed by durometric measurements.

Evolution of the Numerical Model Describing the Distribution of Non-Metallic Inclusions in the Tundish

Continuous casting is one of the steel production stages, during which the improvement in the metallurgical purity of steel can be additionally affected by removing nonmetallic inclusions (NMIs). This can be achieved by means of various types of flow controllers, installed in the working space of the tundish. The change in the steel flow structure, caused by those flow controllers, should lead to an intensification of NMIs removal from the liquid metal to the slag. Therefore, it is crucial to understand the behavior of nonmetallic inclusions during the flow of liquid steel through the tundish, and particularly during their distribution. The presented paper reports the results of the modeling studies of NMI distribution in liquid steel, flowing through the tundish. CFD modeling methods—using different models and computation variants—were employed in the study. The obtained CFD results were compared with the results of laboratory tests (using a tundish water model). The results of the performed investigations allow us to compare both methods of modeling; the investigated phenomena were microparticle distribution and mass microparticle concentration in the model fluid. The validation of the CFD results verified the analyzed computation variants. The aim of the research was to determine which numerical model is the best for describing the studied phenomenon. This will be used as the first phase of a larger research program which will provide for a comprehensive study of the distribution of NMIs flowing through tundish steel.

New insight into the role of inclusions in hydrogen-induced degradation of fracture toughness: three-dimensional imaging and modeling

ABSTRACT An in-depth understanding of the role of non-metallic inclusions (NMIs) in the hydrogen-induced failure of structural materials is important in the manufacture and application of steels. In this paper we investigated the type, the amount and the distribution of NMIs in pipeline steels and their relation to the susceptibility to hydrogen-induced cracking (HIC). Scanning Electron Microscope (SEM) observation confirmed the interlinking of the microcracks formed at the inclusion-matrix interfaces. By combining with the nondestructive three-dimensional (3D) mapping of crack propagation paths, based on the synchrotron tomography technique, we obtained direct evidence that the cracking initiation at the NMIs and then interlinking on the (nearly) same plane are the main mechanism of HIC failure in X70 steels. We built an elastic-energy-based model, which can be applied to quantitatively predict the HIC-induced dependence of the fracture toughness on NMIs, based on statistical information of the NMIs. The theoretical results show a good agreement with the experimental observation. We proposed a criterion to determine the susceptibility to HIC by the observation of NMIs. We also developed a thermodynamics-based model to analyze the hydrogen trapping at the inclusion-matrix interface and its dependence on the strength of the steel matrix. For the first time, the direct relationship between NMIs and HIC-induced degradation of fracture toughness is obtained.

Хімічна і фізична неоднорідності та гази у великому сталевому зливку

For creation of the high-tech equipment that is used in energy, heavy engineering, chemistry and transport, the unique large-sized steel products are required. In the manufacture of such products, large forging ingots in the mass to 600 tons are used. However, an increase in the mass of the ingots leads to the formation of chemical and physical heterogeneity, enlargement and unfavorable distribution of non-metallic inclusions, of the development of segregation defects in them, which reduce the strength and exploitation characteristics of the metal. In this connection, the quality forgings and finished parts are not always meet the producing demands and the loss of metal, in the form of technological waste and rejects are reaching significant values. It is known that eccentric zonal segregation, especially it’s the most dangerous variety - cords, significantly reduce the quality and properties of products from large steel ingots. In connection with the continuous expansion of the production of large ingots, the problem of creating optimal technologies for their formation, which reduce or exclude the possibility of the formation of chemical heterogeneity and cords in steel during crystallization, it is currently important and relevant. In this paper it are presented the results of studies of the structure, gas distribution, physical and chemical heterogeneities in the cross section and height of an ingot in the mass of 140 tons, which was casted in vacuum from steel 25KHN3MFA. It is shown that depending on the temperature and time conditions of ingot hardening, among which the crystallization interval (due to the chemical composition of steels), cooling intensity in different volumes in height and cross section of ingot, temperature gradient before the crystallization front, solubility of alloying elements and gas content in the melt, etc. Based on this, when developing technology for large ingots to ensure their quality, optimal structure and properties should take into account not only their dimensions, but also the combination of these thermokinetic parameters on the crystallization process, dendritic structure formation, manifestations of liquation in different ingot volumes. Keywords: ingot, segregation strip and inclusions, dendrites, structure, oxygen, oxides, sulfides.