Amount Of Non-metallic Inclusions Research Articles

Deoxidation of electric steel in arc steelmaking furnaces using complex silicon-aluminum ferroalloys

The article presents the results of studies on the effect of deoxidation by complex silicon-aluminum alloys (including with barium) on the chemical composition, the degree of assimilation of the leading elements, the quality, structure of the electrical steel, the nature and quantity of non-metallic inclusions in comparison with similar indicators of steel deoxidized in the traditional way using ferrosilicon and secondary aluminum

Analysis of defects and non-metallic inclusions distribution in high-strength TWIP steel Fe-25Mn-12Al-1.5C after electroslag remelting

TWIP steels belong to the list of the most innovative materials of our time due to the combination of a high mechanical characteristics level and low density. The most high-strength alloys usually contain about 25-30 wt. % manganese and about 10 wt. % aluminum. Production of such steels is complicated by the peculiarities of their chemical composition. Due to the high content of manganese and aluminum, they are prone to components liquation by density, have a greater number of shrinkage defects and an increased number of sulfides, nitrides and oxides non-metallic impurities. This determines the use of effective refining methods, which include electroslag remelting (ESR). The paper shows a comparison of Fe-25Mn-12Al-1.5C alloy structure, type and amount of non-metallic inclusions after induction melting and after refining electroslag remelting. Electron microscopy of the samples and local chemical analysis of the phases showed a large number of non-metallic inclusions — sulfides, phosphides, and oxynitrides. After refining process, it was shown that electroslag remelting contributes to a noticeable decrease of nitrogen and sulfur content, and as the result — it lowers the number of related of non-metallic inclusions. However, it seems to be an insufficiently effective method of refining materials like TWIP-steels. Relatively large size of the non-metallic inclusions, low phosphides refining ability and the crystallization conditions under which a directionally crystallized structure forms, may be noticed among the disadvantages of the ESR method. It was also established that in crystallizer zones, close to the bottom and walls, metal refines worse than its central volumes. Upper part of the ingot has shrinkage and sub-shrinkage zones enriched with gas-shrinkage defects, so it can be called a problem zone. In general, it is shown that the ESR method is not capable to solve a problem of refining high-manganese TWIP steels with a high aluminum content to the required extent.

Вплив термічної обробки на механічні властивості модифікованих неіржавіючих сталей

The paper presents the results of the study of the influence of structure on the mechanical properties of microalloyed and modified austenitic stainless steels. It is shown that the mechanical properties of cast austenitic stainless steels with a probability of 95 % and an error of 0.46 to 13.2 % are determined by such structural parameters as austenite grain size, carbide phase and ferrite content in austenite after quenching, quantity, size and distance between oxide, titanium sulfides and carbonitrides particles. Mathematical models of the structure influence on the yield strength, reduction of area and toughness of stainless steels are built. The structure parameter effectiveness is shown and it is shown that to increase the efficiency of strength, reduction of area and toughness of stainless steels at normal temperature structural factors affect in the following sequence: austenite grain size, volume fraction, size and distribution of titanium carbonitrides and sulfides, the total quantity of non-metallic inclusions, carbides and ferrite in austenite after hardening of stainless steel, as well as the volume fraction, size and distribution of oxide inclusions. Keywords: steel, structure, mechanical properties, strength, ductility, toughness.

Reserves for Improving the Quality of Metal Layers of the 450Kh30M and 500Kh22B7 Types by Regulation of Silicon Content in Hard-Facing Consumables

An effective way to improve quality of metal layers of the 450Kh30M and 500Kh22B7 types by controlling the silicon content in hard-facing consumables is shown. The influence of silicon and aluminum content in hard-facing consumables on content of silicon, aluminum, chromium and carbon in the hard-faced layer as well as the amount of non-metallic inclusions of silicate type was studied to develop mathematical models and to derive corresponding dependencies. As a result some corrections to the composition of the hard-facing consumables were proposed to improve quality of metal layers of high-alloyed white cast irons of the investigated types.

Characterization of Nonmetallic Inclusions in Low‐Alloyed Steels Using Pulse Distribution Analysis Optical Emission Spectroscopy and Offline Investigation Methods

The characteristics of nonmetallic inclusions (NMIs) in low‐alloyed steel samples taken during ladle treatment before and after Ca treatment are evaluated using the pulse distribution analysis optical emission spectroscopy (PDA/OES) method, INCA‐Feature investigations of inclusions on a polished surface of steel samples, and 3D investigations of NMIs after electrolytic extraction (EE) of steel samples. The investigation results of NMIs using the different methods were compared. The PDA/OES results show a clear tendency of a change in the average composition and quantity of NMIs during ladle treatment, which correlates well with the results obtained from the other two methods. Overall, it is found that the application of the PDA/OES method is appropriate to enable a fast online evaluation of inclusion compositions and their behaviors during steelmaking. This, in turn, provides the means for establishing an online control and correction of technological operations of the ladle treatment to implement necessary modification of NMIs to improve the cleanliness of steels and avoid clogging problems during casting.

Effect of Filtration on the Structure and Properties of an EP-648-VI Nickel Superalloy

The filtration of a melt is known to be an efficient method for decreasing the amount of nonmetallic inclusions. Ceramic foam filters are applied for the filtration refining of an EP-648-VI alloy. Comparative results of experimental melts using ceramic foam filters and melts carried out using a traditional technology show a decrease in dissolved gases and the improvement of the mechanical properties of the EP-648-VI nickel alloy.

Specific Features of Structure Formation in the Course of Modification of the Coatings on Products Made of Dispersion-Hardened Steels

We analyze the technology of hardening and restoration of products made of dispersion-hardened steels and steels containing large amounts of nonmetallic inclusions. For the formation of coatings, we used secondary raw materials obtained as a result of the utilization of a certain collection of ammunition, including nano- and dispersed diamonds. We also study the influence of parameters of the technology of detonation charge modification in the process of surfacing on the metal structure of the restored product. The best results were obtained as a result of introduction of 5.0–7.0% of charge (relative to the mass of the electrode). This guarantees the formation of a homogeneous structure with grains of similar sizes in the coating and increases the wear resistance of the restored product by 25% and of the mating product by up to 37%.

Study of non-metallic inclusions composition in rail joints welded seams, obtained at their contact arc welding

The quality of welded rail joints depends on various factors, in particular, on the type and quantity of non-metallic inclusions, formed at their contact arc welding. To check a hypothesis of the cause-effect of welded joint mechanical properties decrease and composition of non-metallic inclusions in the welded seams, their chemical and metallographic analysis accomplished. To study the non-metallic inclusions, samples of 90×30×10 mm dimensions used, cut of Э76ХФ steel rail head. After contact butt welding at MC-2008 machine, the samples were cut by electro-erosion method perpendicularly to the welding seam into two parts. One part of the sample was used for tensile test, the other – for metallographic analysis for non-metallic inclusions and structure of the welded joint. The microstructure of the welded butts studied after milling and intensive etching in the 50% water solution of hydrochloric acid. The microstructure was studied at the optical microscope OLYMPUS GX71 in the light field at magnification 100–1000 folds after etching in an alcohol solution of nitric acid. The chemical composition of all the revealed inclusions were determined at the scanning electron microscope MIRA 3. It was established, that silicon and manganese oxides were the basic components of inclusions, revealed in the welded seam, as well as oxides of aluminum, iron, titanium, chrome – to a less amount. In the samples seam microstructure the ferrite net, typical for rail butts, was not discovered, which is probably stipulated by their accelerated heating due to the small section of the samples.

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.

INFLUENCE MOLYBDENUM ON THE CORROSION-MECHANICAL PROPERTIES OF CARBON STEEL WELDED JOINTS

The paper studies the impact of molybdenum on the corrosion and mechanical properties of welded joints of steel boiler. Found that the most high and stable toughness values and resistance to cracks and sulfide stress corrosion cracking of the weld metal pipe steels are achieved when the concentration of molybdenum in it from 0.2 to 0.3%, which implemented in electrode input molybdenum powder coating in an amount of 0.5-1.0%. The optimum chemical composition of weld metal provides getting fine-grained structure, holding a small amount of non-metallic inclusions of globular form.

A New Free-Machining Steel Containing Bismuth and Calcium

The paper presents a new environmentally friendly lead-free free-machining structural steel AVTs19KhGN containing bismuth and calcium. The following quality characteristics of the new steel (in as-cast and forged condition) are determined: mechanical properties; austenite grain size; amount of non-metallic inclusions; surface quality. In forged rods (square 20 mm) a tendency towards an increase of bismuth content is observed from bottom to top of the ingot. Calcium distribution along the billet is uniform. Surface quality of billets in heats following the test heats is comparable to that of analog steels. Austenite grain size does not exceed ASTM number 6. Austenite grain is refined with increasing bismuth content. Mechanical properties are at the same level as for the steel without bismuth and calcium.

Influence of Refractory Metal Oxide Ultrafine Particles on the Structure and Mechanical Properties of High-Manganese Steel

The study examines the influence of the modifier based on refractory metal ultrafine oxides on the structure and properties of frogs made of 110Г13Л (Russian grade) high-manganese steel. It is established that the introduction of the modifying mixture leads to the samples grain size refining by 1.5 times, significant reduction in the amount of nonmetallic inclusions in the grain body and along its boundaries, and enhancement of mechanical properties.

Evaluation of Degradation Causes of the Forged Rotors Made of NiCrMo Steel Grade

Contamination of steel by excessive amount of non metallic inclusions leads tosignificant deterioration of its quality and consequent degradation. Cause of degradation of forgedrotors for steam turbines made of NiCrMoV steel grade is examined in this paper. Metallographicand electron-microscopic analyses were performed, including X-ray microanalysis for detecting thepurity of the forging being examinated. Concurrently, the consequence of failed technologicalproduction process, namely the influence of broken brick for argon blowing at the casting ladle, wasalso examined.

Fast Characterization of Fatigue Properties of an Anisotropic Metallic Material: Application to a Puddled Iron from a Nineteenth Century French Railway Bridge

Largely used as main material in railway riveted bridges during the second half of the nineteenth century, the puddled iron characterizes for having an anisotropic behaviour due to the large amount of non metallic inclusions that it posses. Its mechanical characterization is thus difficult. Since these ancient structures have supported variable cyclic loadings at least for a century, the determination of the puddled iron's fatigue properties becomes crucial to their maintenance. The self-heating method is proposed in this paper to accomplish this task. The obtained experimental self-heating curves show dispersion non observed in homogeneous materials, this phenomenon is explained by the lack of determination of the representative elementary volume of the puddled iron. However, this data gives us important information such as the minimum and maximum boundaries of the mean fatigue limit for several orientations. A two-scale probabilistic model for high cycle fatigue is also used to represent the dispersion on the experimental data by using Weibull's distribution law to describe several characteristics of each site where the microplasticity occurs. The influence of such parameters and the limitations of the model are also studied.

Connections of the Microstructure of the Fe-Al (25-33%wt.) with its Composition and Cooling Rate from the Liquid State

Laboratory researches of cooling rate influence on matrix structure, composition and quantity of nonmetallic inclusions in iron-aluminum alloys, containing 25-33%Al, are conducted. Thermodynamic modeling of composition and quantity of phases, which were formed in alloy system, containing Fe-Al-Si-C-O, for equilibrium conditions by means of the program complex ASTRA-4 (TERRA) is carried out. It is established, that irrespective of cooling rate the matrix has structure of intermetallic Fe-Al, and nonmetallic inclusions have platelet shape and composite of iron and aluminum oxy-carbides. It is confirmed, that ferroalloy with the optimal structure, necessary for receiving the high heat-resistance cast iron, should be cooled after smelting with the highest speed in these condition.

Structural and corrosion characterisation of pulse plated Zn and Zn–Ni alloy coatings

The effects of pulse plating on the phase and chemical composition, preferred orientation and surface morphology of Zn and Zn–Ni (12 wt-%) electrodeposited coatings have been investigated using atomic force microscopy, scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy and electrochemical techniques. It has been established that pulse current plating with respect to direct current (dc) conditions resulted in ∼50% reduction in the grain size dimensions and in fourfold and twofold reduction in the corrosion current densities of Zn and Zn–Ni coatings respectively. Under all the pulse plating conditions applied the deposited alloy consisted of the single γ-Zn21Ni5 phase, while, according to the XRD measurements both coatings possessed inclusions of the oxide phase. The analysis of the protective properties and the thickness of the oxide films formed on the surface of investigated coatings revealed the fact that the surfaces of pulse plated samples were favourable for the formation of thinner oxide films which at the same time exhibited higher protective properties. Pulse plating increased the amount of non-metallic inclusions in Zn and Zn–Ni coatings, however, these amounts were not high, as the O concentration in the deposits did not exceed 1·5 and 0·2 wt-% for Zn and Zn–Ni respectively.

Secondary Steel Refining for Continuous Sequence Bloom Casting for High Oxide Cleanness Final Products

Secondary Steel Refining for Continuous Sequence Bloom Casting for High Oxide Cleanness Final ProductsSteelmaking and secondary refining process technology of resulphurized liquid steel with low content of total oxygen, assigned for continuous casting of strands for rolled and forged products for automotive industry was developed. The influence of secondary steel refining parameters on total oxygen content as well as amount and morphology of non-metallic inclusions was examined. It was found, that content of total oxygen and amount of non-metallic inclusions in steel decrease as steel refining time in the ladle becomes longer, and the chemical composition of non-metallic inclusions in steel changes from modified calcium aluminates to spinel inclusion of CaO·Al2O3·MgO type. The total oxygen content in steel from continuous casting in four cast sequence ranged from 6 to 25 ppm, with percentage share of non-metallic inclusions from 0.09 to 0.30 per cent and equivalent diameter 0.78 to 1.59 μm.

Investigation of Failure in a Crankpin of a Motorcycle Engine

This study performs a failure analysis of a failed crankpin connecting the crank shaft with the piston rod in a motorcycle engine. The failed crankpin under examination is embedded in a 16NiCrMo12 alloy, a typical steel designed for carburizing treatment. The crankpin experiences a periodic compressive stress associated to the compression stroke featuring the cyclic movement of the piston rod imposed by the rotation of crank shaft. During the failure analysis, such mechanism has been associated to a pulsing fatigue phenomenon. The failure of the crankpin concerns the surface, which is affected by significant spalling phenomena causing the detachment of steel fragments, as the element is subjected to constant friction because of relative rotation. Since not all the produced crankpins undergo the observed damaging phenomena, the aim of the study is to identify the factors governing the failure phenomenon and to provide a working solution to the problem. The employed experimental techniques include microstructure analysis by means of optic microscopy and scanning electron microscopy, and hardness measurements. The combination of the obtained results has allowed us to identify the presence of large amounts of non-metallic inclusions underneath the surface as the cause of the damage.

Mathematical Modeling of Behaviour a Liquid Steel Flow and a Non-Metallic Inclusions in the One Strand Wedge Type Tundish with a Subflux Turbulence Controller and a Low Dam

The numerical modelling technique is successfully used for simulation of liquid metal movement and behaviour of non-metallic inclusions in the continuous casting devices. The CFD (Computational Fluid Dynamic) method allows information on physical, chemical and hydrodynamic phenomenon in the metallurgical processes to be obtained. In the continuous steel casting process, where the tundish performs the function of a device batching steel to the mould, the monitoring especially of non-metallic inclusions is very essential because a quantity of non-metallic inclusions in the liquid steel limit the quality of final steel product. The paper presents the results of computing simulation of behaviour a liquid steel flow and non-metallic inclusions in the one-strand tundish with stopper rod system. The subject of simulation was a one-strand tundish of a nominal capacity of 30 tons. The tundish is used in the polish steel mill to process of continuous casting slabs. In the paper authors analysed two tundish i.e. tundish with a low dam and tundish with a subflux turbulence controller and a low dam. The Ansys-Fluent® program was used for solved mathematical model of casting process. The computer simulations were performed for unsteady and nonisothermal conditions. The population balance model was used to description of non-metallic inclusions growth process. As a result of computations, fields of liquid steel flow, fields of secondary phase volume fraction, fields of volume fraction for particular bins and non-metallic inclusions growth curve were obtained.

Numerical simulation of liquid steel flow and behaviour of non-metallic inclusions in one-strand slab tundish with subflux turbulence controller and gas permeable barrier

The paper presents computation results from the simulation of liquid steel flow in a one-strand slab tundish used in a Polish steel plant. This is a wedge type tundish with a depression in the bottom of the discharge zone. Fluent software was used for solving the mathematical model of the casting process, and Euler–Lagrange description was chosen for the description of interactions between the continuous phase (liquid steel) and the discrete phase (inert gas). To verify the mathematical model and the numerical simulation results, test results obtained from industrial experiments were applied. The internal geometry of the facility under consideration was changed by two types of flow control devices, a subflux turbulence controller and a gas permeable barrier mounted on the tundish bottom. A number of variants were tested including flowrate and position of the argon. For all variants of modification, the quantity of non-metallic inclusions removed from liquid steel has been obtained.