Chemical Composition Of Non-metallic Inclusions Research Articles

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.

Цифровые измерения неметаллических включений в стали

The experience of many-year research has shown that optimizing the steel chemical composition and microstructural characteristics, as well as reducing its contamination with non-metallic inclusions (NMI), it is possible to significantly increase the corrosion resistance of oilfield pipeline steels and increase the time of their trouble-free operation. The influence of complex NMIs on the steel corrosion resistance is determined by both the chemical composition of NMIs and their quantitative ratios. Therefore, obtaining metal products of the required quality is possible only when using the “control by structure” principle. In the work, based on the analysis of brightness fields of images (on a sample scale) in 256 shades of gray, the authors proposed digital, metrologically supported procedures for measuring the NMI heterogeneity of low-carbon oilfield steels: eliminating the heterogeneity of field illumination, justifying the criteria for binarization and noise filtering. For low-carbon steels of various types of melting, the authors identified the key role of dispersed non-metallic inclusions ranging in size from 5–10 μm2 to 2 nm2 in the formation of the corrosion resistance of steels. This may explain why, in some cases, there is no interrelation between the corrosion rate and the fracture resistance of steels, the formation of which is determined by larger particles. When representing the NMI as a set of random points on the plane, the distribution of distances between the nearest ones is estimated based on Voronoi polyhedra statistics. The study shows that an increase in the kurtosis coefficient of distributions of polyhedra areas is accompanied by an increase in the corrosion rate of the steels under study. This indicates the negative impact of heterogeneity in the arrangement of dispersed NMIs on the corrosion resistance of steels.

Soderzhanie obshchego kisloroda v zhidkoy stali kak kriteriy otsenki nemetallicheskikh vklyucheniy v trubnykh stalyakh

A statistical analysis of the total oxygen content in samples of pipe steels at the stage of continuous casting at the continuous-casting machines of the casting and rolling complex of JSC “Vyksa Metallurgical Plant” was carried out. The microstructures of rolled samples were studied, and the chemical composition of non-metallic inclusions was determined by X-ray spectral microanalysis. A laboratory analysis of liquid steel samples and hot-rolled steel products of the casting and rolling complex was carried out using the method of reduction melting in an inert gas flow. Relationships have been constructed between the duration of metal presence in a steel-pouring ladle and the magnesium content in non-metallic inclusions, as well as between the average score of non-metallic inclusions in rolled metal and the total oxygen content in liquid steel at the stage of continuous steel casting.

Analysis of Ancient Slag Inclusion-Metal Systems as a Method to Disclose Processing Thermo-chemical Parameters: The Case Study of a Medieval Lombard Steel Bar from Northern Italy

An archaeometallurgical characterization of a VI to VII century Lombard steel bar from Ponte di Val Gabbia I site (northern Italy) was performed to reconstruct its manufacturing process and extract processing thermochemical parameters (i.e., temperature and oxygen chemical potential) from the slag inclusion-metal systems. Metallographic observations by optical microscopy and Vickers microhardness measurements indicated that the steel bar was forged from a heterogeneous steel lump, most probably an iron bloom, which was cooled in the air after the forging process. The chemical composition of non-metallic inclusions was determined by scanning electron microscopy coupled with X-ray dispersive spectroscopy. A multivariate statistical analysis of the smelting-derived non-metallic inclusions chemistry allowed to conclude that the steel bar was obtained by the direct or bloomery method. Under the hypothesis of local near-equilibrium conditions for the slag inclusion-metal systems, a thermodynamic-based strategy was adopted to estimate the firing conditions in the bloomery furnace in terms of both temperature and oxygen chemical potential of the reducing gas atmosphere. In particular, the computed temperatures are in the range of 1003 °C to 1171 °C, whereas the values of oxygen chemical potential vary between − 447.47 and − 385.79 kJ/mol.

Effect of preheating and preplaced filler wire on microstructure and toughness in laser-arc hybrid welding of thick steel

Acicular ferrite (AF) is the most important microstructural constituent to achieve high toughness at low temperatures in weld metal of steels. This is due to the relatively small grain size and large misorientation angles. AF is known to form at non-metallic inclusions (NMIs), but under high cooling rates, as in deep and narrow laser-arc hybrid welding (LAHW), this phenomenon is scarcely studied. In deep and narrow LAHW, insufficient transportation of filler wire to the root results in low amount of NMIs, thus bainite-martensite mainly forms due to fast cooling. In this work, a 45 mm thick high strength low alloy steel was welded by double-sided LAHW using different groove preparations. The effect of different cooling times on the microstructure in the weld metal and the heat-affected zone was studied. A low fraction of AF and high hardness were achieved in the root of weld metal when using standard LAHW. This was related to a rapid cooling time (Δt8/5 < 1.0 s) and a low population of NMIs due to lack of filler wire. Micro X-ray computed tomography revealed centerline solidification cracks and porosity. Two external methods were conducted to assist the formation of AF and to reduce hardness, base plate preheating and preplaced metal-cored filler wire into the weld groove prior to welding. Preheating reduced hardness and increased the AF fraction due to increased cooling time. In addition, preheating showed to mitigate porosity. Preplaced filler wire provided an enhanced population of NMIs in the root thus significantly increased the fraction of AF. It was found that the diameter and chemical composition of NMIs has a strong correlation with the cooling time Δt8/5. High impact toughness (> 35 J) was achieved at −50 °C by combining preheating and preplaced filler wire, and up to 45 % fraction content of AF was reached. However, many NMIs were still inactive due to a small diameter (< 200 nm) and unfavorable chemical composition related to the high cooling rate. The external methods had no influence on the occurrence of weld centerline cracks in the root, which will require further attention to secure mechanical properties and integrity.

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.

On the Chemical Composition of Non-Metallic Inclusions in Ultra-Clean Gear Steels

Abstract Fisheye failures due to non-metallic inclusions can lead to the reduced endurance fatigue limit of case-hardened, shot-peened gears. Various approaches for preventing crack initiation at non-metallic inclusions are conceivable. As one approach, steel manufacturers have invested much effort in the steelmaking process to produce ultra-clean gear steels. Such ultra-clean gear steels were investigated in a gear research project. For each steel batch, different measures were taken during steel production to avoid or bind off non-metallic inclusions in order to reduce or even suppress the harmful effect of the non-metallic inclusions. However, the influence of the measures taken on the chemical composition of non-metallic inclusions in such ultra-clean gear steels is not investigated in the gear industry in detail so far. Therefore, in the framework of this publication, the chemical composition of non-metallic inclusions in ultra-clean gear steels is investigated. Furthermore, a comparison of the chemical analysis with the crack-initiating inclusions from the experimental investigations is performed.

PROPERTIES OF AUSTENITE STAINLESS STEEL MICROALLOYED WITH TELLURIUM AND ZIRCONIUM

Stainless steel X8CrNiS18-9 (standard EN 10088-3: 2005) is the most commonly used austenitic stainless steel due to its good machinability. This steel has high mechanical and working properties thanks to complex alloying, primarily with the elements such as chromium and nickel. The content of sulfur present in the steel from 0.15 to 0.35% improves machinability. Microalloying with tellurium and zirconium (individually and in combination) in most cases leads to improved properties of this stainless steel, compared to melt without alloying additives, e.g. the melt microalloyed with tellurium and especially melt microalloyed with zirconium and tellurium has significantly better machinability compared to the melt without alloying elements. The addition of sulfur, which is the cheapest available additive for free machining, will impair not only the transverse strength and toughness but also the corrosion resistance. However, while sulfur improves machinability at the same time decreases the mechanical properties, particularly toughness. This work aims to test the machinability, corrosion resistance, and mechanical properties of the mentioned steel, as well as the chemical composition of non-metallic inclusions.

Compositional modification of nonmetallic inclusions in bloomery iron during post‐smelting treatments and its implication

AbstractThe chemical composition of nonmetallic inclusions in finished iron artifacts often holds key information on the smelting and post‐smelting processes applied during their production. This possibility was tested with special iron objects deemed product intermediaries from a royal tomb constructed at Gyongju, the former capital of the Silla state during the Korean Three Kingdoms period (c. 300–668 ce). Metallographic examination identified two distinct groups of inclusions with features unique to slags derived from smelting in (a) bloomery furnaces and (b) blast furnaces. Clear evidence was also noted that type ‘a’ inclusions, when subjected to an environment of high carbon activity as in a carburization process, underwent a significant change in chemical composition and microstructure to emulate the other type. This observation is expected to remove significant ambiguities encountered in connecting slag compositions to pertinent engineering processes.

Identification of reasons for non-compliance of mechanical properties in boron-containing steel parts

Fasteners are widely used as machine parts, structures and mechanisms. Medium-carbon alloy steels and boron-containing alloy steels are used as materials in production. Boron-containing steels have a good combination of strength and plastic properties, as well as a high level of hardenability. This article describes the research work carried out in the laboratory, and considers the reasons for obtaining low values of physical and mechanical parameters of parts manufactured at competitive enterprises. The qualitative characteristics of the metal are determined. The results of chemical, physical-mechanical and metallographic tests, as well as the results of the chemical composition of non-metallic inclusions are presented. The reasons for the discrepancy of mechanical properties in boron-containing steels are considered. The dependence of the introduction of chemical elements into steel: nitrogen, titanium, aluminum is determined. The possibility of evaluating the content of “effective boron” at OJSC “BSW” – the Management Company of the Holding “BMC” is described. The mathematical model used at OJSC “Oskol electrometallurgical combine”, which allows to carry out a theoretical calculation of the value of “effective” boron, is described. Recommendations for improving the technological process of smelting boron-containing steels are given.

Thermodynamic Model of the Process of Desulfurization of a Black Ferronickel in a Ladle

Goal: Research of the type and chemical composition of non-metallic inclusions in the process of desulfurization of rough ferronickel by compiling of a thermodynamic model of the desulfurization of rough ferronickel process. Methodology. The analysis of the influence of silicon and carbon in a thermodynamic system on the desulfurization process of rough feronickel was carried out. Scientific novelty. For the first time, a thermodynamic model of desulfurization of rough ferronickel in a ladle according to the scheme NiS - FeS - C - Si - Na2CO3 was compiled using data from industrial production in the conditions of Pobuzhsky Ferronickel Plant LLC.

The Impact of the Production Stages of Grade D Steel on its Contamination and the Chemical Composition of Nonmetallic Inclusions

Optical and electronic microscopy methods are used to evaluate the contamination of grade D carbon steel with nonmetallic inclusions in steel samples taken at various stages of steelmaking (electric arc furnace (EAF) discharge -> ladle furnace (LF) -> vacuum deoxidation (VD) -> continuous casting) at an electric furnace melting shop. Steel contamination with nonmetallic inclusions and inclusion chemical composition are assessed. It is demonstrated that the aluminum deoxidation of the semiproduct leads to the formation of corundum nonmetallic inclusions (Al2O3) in molten steel. The total amount of corundum reaches 52% for all the stages of steelmaking process. The identification and evaluation of nonmetallic inclusions demonstrates that deoxidation performed at all the stages of secondary steelmaking reduce the amount of inclusions. After vacuum deoxidation and adding Al and SiCa, corundum inclusions become globular in shape with a particle size less than 6 urn. When the continuously cast billet has solidified, the total amount of nonmetallic inclusions does not change, whereas silicate inclusion content decreases and corundum contamination grows, with corundum inclusions being of an irregular shape. A heavy corundum contamination is caused by aluminum secondary deoxidation during steel casting as well as by the fact that the molten residue in the pouring nozzle is carried into the solidifying continuously cast billet.

CHANGES IN THE COMPOSITION OF NON-METAL INCLUSIONS AND CONTAMINATION STEEL D DURED BY ALUMINUM

Using optical and electron microscopy methods, the pollution of grade D carbon steel by nonmetallic inclusions in samples taken at the stages of metallurgical redistribution (EAF → LF → VOD → Casting). Metal contamination and chemical composition of non-metallic inclusions are determined. It was shown that deoxidation at the stage of production of the intermediate by aluminum leads to the formation of nonmetallic inclusions of corundum (Al2O3) in the metal melt, the proportion of which in total over all redistributions is 52%. Identification and assessment of contamination by non-metallic inclusions showed that subsequent stages of out-of-furnace treatment lead to a decrease in total pollution by inclusions. After evacuation and addition of Al and SiCa, corundum inclusions acquire a globular shape with a maximum size of not more than 6 μm. During solidification, the total contamination by non-metallic inclusions does not change, however. Contamination with silicate inclusions decreases, and the inclusion of corundum increases. The inclusions of corundum are irregular in shape, the high contamination with the inclusions of corundum is caused by secondary oxidation of aluminum during casting, as well as the ingress of products by overgrowing of the casting nozzle into the solidified continuously cast billet.

Diagnosis of the microstructural and mechanical properties of over century-old steel railway bridge components

The mechanical and microstructural properties as well as durability of more than century-old steel railway bridges that are still widely in use, among others in Poland, have not been well recognized. Ignoring the effect of material and mechanical properties on the operation of an old-steel bridge may eventually lead to the structure’s failure. This study investigates the reliability of a 100-year-old bridge made of wrought (puddled) iron. The aim of this study is to identify the microstructural and mechanical properties of over century-old steel bridge components in relation to the requirements for modern mild steel grades. The paper presents an analysis of the material and mechanical behaviour of a truss railway bridge that had been in operation for over a century. Laboratory tests were performed on samples taken from the component parts of a dismantled railway bridge, i.e. stringers, crossbars, lower belts, stringer bracings and wind bracing. Fatigue, fracture, hardness and tensile tests are performed to estimate the mechanical properties of the investigated steel bridge component parts. Spectroscopy is used to examine the chemical composition of every element. Light optical microscopy and scanning electron microscopy are employed to examine the microstructure of the steel component parts and its non-uniformities. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are used to obtain data about the fracture mechanism and the chemical composition of non-metallic inclusions. Microstructural and mechanical results are discussed in relation to modern mild steel grades S355 and S235, which are widely used structural ferrous alloys. Based on the chemical composition analysis, the possibilities of increasing the strength of the bridge by welding methods and the application of fibre-reinforced polymer (FRP) composite materials are discussed. Obtained results add to the body of knowledge about the maintenance, reinforcement and demolition of bridge structures, which is crucial for preventing failure of over 100-year-old steel structures. This research is an introduction to the study on reinforcing old steel structures by FRP composite materials.

Influence of Selected Deoxidizers on Chemical Composition of Molten Inclusions in Liquid Steel

The conditions of nonmetallic inclusions formation by using manganese, silicon, and aluminum deoxidizers in a steel bath (four steel grades) are reviewed in the presented paper. The changes in the chemical composition of nonmetallic inclusions were calculated under thermodynamic equilibrium conditions between liquid steel containing Mn, Si, O, Al and the formed liquid oxide phase, applying a non-commercial (author’s) computer program. The impact of the order of dispensing alloy additions, and the initial manganese content in steel on the final oxygen concentration, as well as the evolution of the chemical composition of nonmetallic inclusions were considered. The acquired results indicate that the proposed calculation procedure can be used to design the desired chemical composition of steel with a controlled value and chemical composition of nonmetallic inclusions.

IMPROVING METHODOLOGY FOR DETERMINING METALLURGICAL VALUE OF AGGLOMERATED WASTE

The results critical analysis standard methods determining the contamination coagulated iron-containing wastes, used as metal additives in steelmaking processes, impurities, are presented. The advanced method determination content harmful and harmful impurities and estimation metallurgical value steel chips briquettes is proposed, which is based on the use techniques high-temperature experiments and provisions theory of metallurgical processes for the processing results.Complex high-temperature experiments with the use induction crucible furnace with the selection samples of metallic melt and slag for further chemical analysis. In order to prevent the secondary oxidation iron briquettes, in the working space of the furnace formed a neutral gas medium (by injecting argon with a flow of 0.05...0.15 m3/min). In order to work out the evaluation method, the bunches of steel chips from different grades of steel were used.The influence chemical composition of steel chips and nonmetallic inclusions briquettes on the process melting, the degree iron removal, yield and properties slag from non-metallic inclusions of briquettes are investigated. The differences and features melting of briquettes from different types steel shavings are determined.When the investigated briquettes are matched to the requirements standards, density and strength indicators have established a wide range of fluctuations pollution indicators and the possibility iron extraction in steelmaking from briquettes from 2.47 to 7.33% and from 92.67 to 97.53% respectively.The classification types of briquettes destruction during heating is proposed, which includes: deformation briquettes without breaking with peripheral melting; formation cracks in the central part with the destruction briquettes without peripheral melting; сombination, with different ratios, cracking processes and melting of cake. The temperature beginning destruction or melting briquettes was in the range from 1380 to 14700С.The proposed integral indicator briquettes contamination (KZ). Due to the use of an improved method for assessing the metallurgical value briquettes, it is possible to determine the KZ, which takes into account all types mass loss briquettes and the presence different types contaminants: iron losses due to the transition to slag during the melting briquettes, the degree loss, the presence and removal of moisture, residues of lubricants, composition and amount of harmful impurities and non-metallic inclusions in briquettes, etc.It has been shown that without reliable data on the mass loss briquettes with lethal components, the amount and chemical composition of non-metallic inclusions, as well as the metal produced by the melting of briquettes, the determination metallurgical value of this type metal additive is a difficult task.

Optimization of the Composition and Amount of Nonmetallic Inclusions in a Continuously Cast Billet Based on the Deoxidation of the Melt with Aluminum and Calcium Carbide

The methods of optical and electron microscopies are used to estimate the degree of contamination of D carbon steel with nonmetallic inclusions in samples taken in all stages of steelmaking at the electrosmelting workshop of the Volzhskii Piping Factory. The procedure of smelting was carried out by using the following technology: production of semifinished products in the electric arc furnace → processing of the melt in devices for out-of-furnace treatment → continuous casting. We determine the degree of contamination of steel and the chemical composition of nonmetallic inclusions in the samples for two different procedures of deoxidation: with the AB-87 aluminum and CaC2 deoxidizers. It is shown that calcium carbide positively affects the chemical composition of steel and the process of formation of nonmetallic inclusions and leads to the modification of corundum inclusions, and their globularization in the initial stages of steelmaking. The favorable shape of the inclusions formed in the initial stages of the out-of-furnace treatment is preserved in the subsequent stages, which facilitates their efficient removal. The application of CaC2 as a deoxidizer makes it possible to produce continuously casted billets with a twice lower degree of contamination with nonmetallic inclusions.

Experimental precision study of types and of the chemical composition of nonmetallic inclusions in radial section of the railway axis by the method of the electronic microscopy and x-ray spectral microanalysis

Purpose. Investigation of the structure and composition of non-metallic inclusions in the radial section of the draft railway axis obtained from continuously cast billets. Methodology. Studies were conducted on samples of steel EA1N using electron microscopy of X-ray spectroscopy analysis. Results. It has been established that during cooling of the melt and crystallization of the metal of a continuously cast billet, inclusions close in composition to quasi-equilibrium states of binary and ternary oxide systems are formed. Originality. The structures and composition of heterophase inclusions formed in the central part by spinel MgO * Al2O3 with the (Ca, Mn) S sulfide phase shell are identified. Practical value. The results of the study determine the modes of deoxidation and alloying of the axial metal during out-of-furnace treatment at LF and VD.

Electron microscopy and x-ray spectral microanalysis of types and chemical propeties inclusions of the railway axis from a continuous billet

Purpose. Analysis of status and chemical composition of non-metallic inclusions of raw railway truck axle shafts steel using electron microscopy and X-ray spectral microanalysis for the improvement of the throughout technology of the axles production. Methodology. Study of phase composition and type of non-metallic inclusions in axles shaft steel was carried out with modern equipment and method of X-ray spectral microanalysis for quantitative and qualitative data. Findings. The analysis of the elements on chemical composition on EA1N steel and of non-metallic inclusions on physical and mechanical properties of railway axles made by rolling of continuous cast billt of 470 mm diameter. The types and composition of non-metallic inclusions were studied with electron microscopy and X-ray spectral microanalysis. Results can be applied for improvement of steel refining and alloying technology for railway wheel axles production. Originality. There were discovered the original data about the types and chemical compositions of nonmetallic heterophasic inclusions in railway axis metal using the electronic microscopy and X-ray microanalysis. The obtained research results about formations of multiphase inclusions were proved using the phase equilibrium charts consiolering oxide, oxide-sulphide mineral phases. Practical value. The results of electron microscopy and X-ray spectral microanalysis are important to understand and improve the throughput technology of refining and alloying of EA1N steel for railway axle shafts. Keywords: railway axle, railway truck, axle shaft, steel chemical composition, continuous casting billet, mechanical properties, non-metallic inclusions

Ways to Improve the Quality of Die Steel 5KhNM

There was performed an analysis of influence of the deoxidation technology, hydrogen content and high concentration of titanium in steel 5KhNM (Rus. “5XHM”) on quality of die blanks, evaluated based on the results of the ultrasonic test.The fractographic examinations of fractures and the X-ray microprobe analysis of chemical composition of non-metallic inclusions were conducted, the evaluation of macro- and micro-structure of a die blank with high titanium content was performed.It is demonstrated that defects of dies from steel 5KhNM (Rus. “5XHM”) are cracks from merged flakes and micro-flakes; in most cases large concentrations of sulphides appeared to be hydrogen collectors for formation of flakes and micro-flakes.