Non-metallic Inclusions In Steel Research Articles

Modelling of non-metallic inclusions in steel

ABSTRACTIn the current paper, extensive studies of the current authors on the modelling of non-metallic inclusions were summarised. Kinetic studies included the nucleation, collision and agglomeration of inclusions, the interaction between inclusion and bubble in the molten steel, the motion, collision, and removal of inclusions in the molten steel during refining and continuous casting and the entrapment of inclusions in a continuous casting slab strand. Thermodynamic studies included the deoxidation of steel and precise calcium treatment of Al-killed steels. The variation in the composition of inclusions during heating treatment of stainless steels was summarised. The studies ranged from nanoscale of molecules to sub-mili meter scale of inclusions within a meter scale metallurgical vessels, over 10 order in size, and clarified mechanisms for the generation, growth, motion and removal of inclusions in steel.

New Type of Corrosion-Active Nonmetallic Inclusions and their Influence on the Corrosion of 38KHN3МFА Steel

We study the influence of corrosion-active nonmetallic inclusions on the corrosion of 38KhN3MFA steel. A new type of fluorine-containing inclusions of this kind with a size 2–30 μm is discovered. These inclusions are responsible for anomalously rapid damage of drill pipes made of the indicated type of steel. It is difficult to identify them with the help of metallographic analysis. They do not affect the general chemical composition of steel, the characteristics of strength and impact toughness at room and lowered (– 50°С) temperatures. We propose a new approach to the detection of corrosion-active nonmetallic inclusions in steels reduced to the investigation of the fracture surfaces of specimens instead of their microsections. Unlike the existing methods, this approach enables one to determine the chemical composition and correctly reproduces the shape of inclusions.

Dušik in nitridni nekovinski vključki v jeklu

Dušik in nitridni nekovinski vključki v jeklu

Cathodoluminescence Analysis of Nonmetallic Inclusions in Steel Deoxidized and Desulfurized by Rare-Earth Metals (La, Ce, Nd)

The injection of misch metal, which primarily consists of La, Ce, and Nd, into molten steel can reduce the size of nonmetallic inclusions, suppress the formation of harmful nonmetallic inclusions, and reduce the content of oxygen and sulfur in steel. To investigate the impact of misch metal on these effects, we propose a method for identifying inclusions in steel that has been deoxidized and desulfurized by misch metal using cathodoluminescence (CL) analysis within 1 minute. Based on the CL images and spectra of model steel samples that were deoxidized and desulfurized by La, Ce, or Nd metal, we demonstrate that La2O3, La2O2S, CeO2, Ce2O2S, Nd2O3, and Nd2O2S inclusions can be identified by the emitted luminescence color using cameras with sensitivity ranges of 420 to 680 and 350 to 1000 nm. La2O3, La2O2S, CeO2, Ce2O2S, Nd2O3, and Nd2O2S inclusions emitted blue-green, yellow-orange, yellow-orange, violet, blue-violet, and red luminescence, respectively when observed by a camera with a sensitivity range of 420 to 680 nm. CeO2 and Nd2O3 inclusions emitted red-orange and red-violet luminescence, respectively when observed by a camera with a sensitivity range of 350 to 1000 nm.

Algorithm for detecting rounding measures for digital image analysis

The urgency of the paper is to develop a new approach for quantifying the shape of non-metallic inclusions in steel, in particular sulfides. The aim of the article is to develop an algorithm for detecting a rounding measure for analyzing digital images of the macrostructure of metal templates, namely sulfuric prints. Method. According to the proposed algorithm, the object in the image - a non-metallic inclusion is considered to be close to a circular shape, if the ratio of the circumference of a circle equal in area to a non-metallic inclusion to the length of its contour approaches unity. Results. Testing of the developed algorithm for detecting rounding measures for digital image analysis was carried out using the developed application software. To study the image it must first be converted to binary. Next, the image is processed, as a result of which the user receives information about the number of inclusions and their degree of rounding. The application of the developed algorithm to the array of test images showed the adequacy of the proposed algorithm. The developed algorithm is included in the form of a processor in the ASImprints software for analyzing sulfuric prints. Conclusions. The developed algorithm for detecting the rounding measure for analyzing digital images is based on an intuitive approach. Its application to digital images of the macrostructure of metal templates will allow researchers to obtain microstructural and macrostructural phenomena in the melt to obtain their quantitative estimates.

In situ characterisation of MnS precipitation in high carbon steel

Manganese sulphide (MnS) is one of the major non-metallic inclusions in steel with huge impact on steel property. In the case of high carbon steel, due to higher sulphur content and its brittleness, controlling MnS formation is one of the main issues. MnS has a complicated precipitation mechanism during solidification in liquid and solid steel and at the interface with oxide inclusions. Higher sulphur content, lower melting point and different oxide inclusions in high carbon steel will cause MnS precipitation at different stages. In this study, different stages of MnS precipitation from liquid and/or solid in high carbon steel and at the interface with oxide inclusion were investigated comprehensively via two different types of High Temperature Confocal Scanning Laser Microscope (HTCSLM). Samples were analysed further using SEM-EDS for better understanding the pertaining mechanisms. MnS precipitation on the surface of liquid steel was observed in situ in a HTCSLM by the use of a concentric solidification technique. Additionally, formation of MnS following solidification and at the interfaces of oxide inclusions, was investigated in situ in a HTCSLM, which has a uniform temperature profile across the specimen. These comprehensive descriptions about different stages of MnS precipitation in high carbon steel have been conducted for the first time and provide crucial information for controlling MnS morphology in high carbon steel.

Transformations of Nonmetallic Inclusions in Steels Subjected to High-Temperature Heating

We study the mechanism of dissolution of nonmetallic inclusions under the conditions of high-temperature heating. It is shown that the dispersion of inclusions is associated with several processes (dissociation and partial dissolution of the inclusions, their diffusion fragmentation in the course of selective dissolution and the formation of dispersed “satellite” particles). We also discuss the specific features of the formation of microcomposite zones near inclusions.

Material defects as cause for the fatigue failure of metallic components

The paper provides an overview on material defects which may serve as fatigue crack initiation sites and can cause final fatigue failure of a component. These comprise non-metallic inclusions in steel and aluminum alloys, cavities such as pores, micro-shrinkages and un-welded regions in cast, sinter and additively manufactured alloys, graphite nodules, shrinkages and other items in nodular cast iron, regions of defective microstructure, microcracks and secondary notches such as undercuts and surface roughness. Besides their origin, the effect and mechanisms on fatigue crack initiation and propagation are discussed. The considerations are proceeded and accompanied by a brief discussion of some basic aspects such as the stages of crack propagation along their length scale, the overcoming of crack arrest and the question when a secondary notch can be treated as a crack.

Types and structure of heterophase inclusions in steels

Purpose. The problem of the influence of heterophase nonmetallic inclusions on the properties of steels is actual. The goal of the work was to study the main types and structures of heterophase nonmetallic inclusions in steels. Methods. Comprehensive methods for the study of heterophase non-metallic inclusions (metallographic, petrographic, X-ray microanalysis methods) were used. Results. It has been established that heterophase inclusions have different structure and phase composition. The features of various combinations of phases in microcomposite inclusions are shown. The main types of hetero-phase inclusions in steels are established. Scientific novelty. The structural features of heterophase inclusions in steels are established. A classification of microcomposite heterophasic inclusions is proposed: inclusions of the first type “high-melting phase surrounding with low-melting cover”; the inclusion of the second type of “phases are beside”; the inclusion of the third type of “eutectics”; Inclusions of the fourth type “dispersed phases in a non-metallic matrix”; inclusions of the fifth type "eutectics inclusion-matrix". Practical significance. The use of the obtained results will make it possible to develop technologies for the production of steels with regulated content and types of heterophase non-metallic inclusions, which will significantly improve their technological, mechanical and operational properties.

Modification of Non-Metallic Inclusions in Oil-Pipeline Steels by Ca-Treatment

Corrosion rate in different steel grades (including oilfield pipeline steels) is determined by the presence of non-metallic inclusions (NMI) in steels. Specifically, the effect of different inclusions on the quality of steels depends on their characteristics such as size, number, morphology, composition, and physical properties, as well as their location in the steel matrix. Therefore, the optimization and control of NMI in steels are very important today to obtain an improvement of the material properties of the final steel products. It is well known that a Ca-treatment of liquid steels in ladle before casting is an effective method for modification of non-metallic inclusions for improvement of the steel properties. Therefore, the NMI characteristics were evaluated in industrial steel samples of low carbon Ca-treated steel used for production of oil-pipelines. An electrolytic extraction technique was used for extraction of NMI from the steel samples followed by three-dimensional investigations of different inclusions and clusters by using SEM in combination with EDS. Moreover, the number and compositions of corrosion active non-metallic inclusions were estimated in hot rolled steel samples from two different heats. Finally, the corrosion resistance of these steels can be discussed depending on the characteristics of non-metallic inclusions present in the steel.

Application of Plasma FIB to Analyze a Single Oxide Inclusion in Steel

We demonstrate that Plasma Dual Beam focused ion beam (PFIB) milling can be used for high-resolution three-dimensional chemical study of a single non-metallic inclusion in steel. A CaO-Al2O3-MgO inclusion (~ 10 μm) on a polished cross-section of steel sample was located and milled using a Xe+ ion beam. A secondary electron image and EDS map of every section were recorded and subsequently processed to show the 3D chemistry and morphology of the inclusion.

Изучение микроструктуры и механических свойств низкоуглеродистой стали, микролегированной бором

The paper presents the results of the study of non-metallic inclusions, the structure and mechanical properties of low carbon steel, microalloying by boron. The study of the amount and composition of nonmetallic inclusions showed that with the introduction of boron the volume fraction of oxide and oxysulfide inclusions increases and the volume fraction of sulfide inclusions significantly decreases. At the same time, the alloying of steel with boron increases to 99.7% the proportion of inclusions with a size of no more than 5 microns against 80.6% in the metal without boron. In the metal with boron, nonmetallic inclusions larger than 10 μm are absent, while in the metal without boron their share is 13.6%. Studies have shown that in a metal containing 0.011% boron, independent boron-containing inclusions were not detected. Boron was not detected in the composition of the studied nonmetallic inclusions. In all samples, steel nonmetallic inclusions are represented mainly by oxide, oxysulfide and sulfide inclusions. In the boron-free steel, a small amount of perlite is present along with the ferritic phase. Steel microalloying by boron is accompanied by the formation of a dispersed ferrite-bainite structure, which consists of fine-grained ferrite with bainite sites with a tendency to form bainite strips along the rolling direction. The microhardness of ferrite and perlite in steel without boron does not exceed an average of 180 and 214 HV10, respectively. It is noted that the presence of boron in steel in an amount of 0.011% increases the microhardness of ferrite to 260 HV10 and bainite to 335 HV10. The mechanical properties of hot-rolled steel with a thickness of 10 mm from boron-containing low-alloyed steel, due to the predominant formation of small rounded inclusions with a size of no more than 5 microns and the formation of a fine ferrite-bainite structure, are characterized by enhanced strength properties with preservation of plastic characteristics. The absolute values of the yield strength and temporary resistance of steel with boron reach 575 and 650 MPa, respectively. With such strength properties of metal, high plastic characteristics are preserved. Rolled steel without boron is characterized by reduced to 540 and 610 MPa tensile strength and temporary resistance, respectively.

Characterization of non-metallic inclusions in corrosion -resistance nickel - based EP718 and 718 alloys by using electrolytic extraction method

It is known that non-metallic inclusions (NMI) that are formed during steel production and heat treatment can significantly affect the properties of final steel products. Therefore, it is very important to be able to determine the content of harmful NMI in steels. Nickel-based alloys are widely used in the oil and gas recovery industry, due to a good combination of strength and corrosion properties. Earlier studies have shown that the corrosion properties in immersion test and electrochemical tests for Ni-based EP718 alloys are slightly lower than that for 718 alloys. The focus in this study was the influence of different NMI on the corrosion resistance of these alloys. The characteristics of inclusions (such as size, morphology, and chemical composition) were analysed by using the electrolytic extraction method followed by three-dimensional investigations using SEM in combination with EDS. It was found that some non-metallic inclusions in EP718 alloys significantly reduce its corrosion resistance. It was also shown that a primary dissolution of the metal matrix occurs around certain inclusions during electrolytic extraction. Based on obtained results, the corrosion active non-metallic inclusions can be determined in these Nickel-base alloys and some recommendations for optimization of their production technology can be formulated.

Assessment and interpretation of nonmetallic inclusions in steel

Assessment and interpretation of nonmetallic inclusions in steel

Effect of Sulfur Content on the Properties and MnS Morphologies of DH36 Structural Steel

The behavior of MnS, a significant non-metallic inclusion in steel with low sulfur content, is poorly understood, in particular, how the MnS inclusion becomes a favorable secondary phase. To clarify how the sulfur content in DH36 structural steel affects the behaviors of MnS, and the steel properties, samples containing 20–380 ppm sulfur were melted, and the ingots were rolled in a semi-industrial single-roll mill. According to experiments using optical microscopy (OM), scanning electron microscopy (SEM), an automatic inclusion analysis system, and transmission electron microscopy (TEM), the morphology of MnS inclusions changed from thread-shaped to spherical- or spindle-shaped with decreasing sulfur content, and their size and number also decreased. The steel with 20 ppm S contained much more nanoscale MnS, whose pinning effect created a fine grain size in the steel. The reason is that the temperatures of maximum nucleation rate and fastest precipitation of MnS in this sample (900 °C and 920 °C, respectively) are much lower than the soaking temperature. Compared to samples with 70–380 ppm sulfur, the sample with 20 ppm sulfur content demonstrated the highest yield strength, tensile strength, and impact energy. Finally, the industrially produced DH36 samples were analyzed, and the steel with the lower S content had a higher stability and yield strength, in agreement with our laboratory results.

Collision of Micro-sized Non-metallic Inclusions in Liquid Steel Flows: A Computational Study

The quality of steel is limited, among others, by the contained non-metallic inclusions. A key factor in this context is the growth of micro-sized indigenous inclusions. Those are assumed to form larger inclusions or clusters by collision in the turbulent melt flow. In this study, a numerical model is established to investigate the collision probability of spherical and clustered non-metallic inclusions in steel by discrete particle simulations. A strong dependence of the agglomeration probability from the particle sizes, form and shear rate in the process is observed. Larger particles are hampered to coagulate because of the significant influence of the lubrication force. Thus, the maximum particle size of spherical particles is limited, while clustered agglomerates can still grow. From the simulation results, models for the determination of the collision coefficient are deduced for spherical particles and non-spherical particle clusters.

Transformation of Nonmetallic Inclusions in Steel at High Temperatures

The solution of nonmetallic inclusions on heating to high temperatures is analyzed. Dispersion of the inclusions is associated with several processes: dissociation and partial solution of inclusions; diffusional disintegration of inclusions in selective solution; and the formation of disperse satellite particles around the initial inclusions.

Characterizing Non-Metallic Inclusions in Steel by Ultrasonic Spectrum

Characterizing Non-Metallic Inclusions in Steel by Ultrasonic Spectrum

X-Ray Excited Optical Luminescence and Portable Electron Probe Microanalyzer-Cathodoluminescence (EPMA-CL) Analyzers for On-Line and On-Site Analysis of Nonmetallic Inclusions in Steel.

The potential of the application of an X-ray excited optical luminescence (XEOL) analyzer and portable analyzers, composed of a cathodoluminescence (CL) spectrometer and electron probe microanalyzer (EPMA), to the on-line and on-site analysis of nonmetallic inclusions in steel is investigated as the first step leading to their practical use. MgAl2O4 spinel and Al2O3 particles were identified by capturing the luminescence as a result of irradiating X-rays in air on a model sample containing MgAl2O4 spinel and Al2O3 particles in the size range from 20 to 50 μm. We were able to identify the MgAl2O4 spinel and Al2O3 particles in the same sample using the portable CL spectrometer. In both cases, not all of the particles in the sample were identified because the luminescence intensities of the smaller Al2O3 in particular were too low to detect. These problems could be solved by using an X-ray tube with a higher power and increasing the beam current of the portable CL spectrometer. The portable EPMA distinguished between the MgAl2O4 spinel and Al2O3 particles whose luminescent colors were detected using the portable CL spectrometer. Therefore, XEOL analysis has potential for the on-line analysis of nonmetallic inclusions in steel if we have information on the luminescence colors of the nonmetallic inclusions. In addition, a portable EPMA-CL analyzer would be able to perform on-site analysis of nonmetallic inclusions in steel.

Characteristics of Non-metallic Inclusions in Steel Obtained from Different-Sized Samplers

To determine the effect of sampler size on the detection of inclusions in liquid steel, four different-sized samplers were designed for industrial sampling from a continuous casting tundish. The samples were evaluated via scanning electron microscopy and energy-dispersive spectroscopy. With increasing sample size, the cooling rate of the sample and velocity for particle engulfment decreased. The extent of encapsulation of complex inclusions increased from 0 pct with the smallest sampler to 48.2 pct with the largest sampler. In the samplers that cooled at 41.2 and 26.7 K s−1, the major inclusions were calcium aluminates; in the larger samplers, which cooled more slowly at 8.2 and 1.0 K s−1, the complex inclusions predominately comprised Al2O3 + (Ca, Mn)S and Al2O3 + CaS, respectively. The sizes of the sulfides gradually increased with increasing sampler size; for example, the sulfide average diameter increased from 2.5 to 3.5 μm when the sampler inner diameter increased from 50 to 70 mm. The main direction of movement of the inclusions during the sampling process was upward.