Number Of Non-metallic Inclusions Research Articles

Особливості формування неоднорідних структур у вуглецевих сталях

Obtaining a homogeneous structure and uniform-phase distribution is critical to a high set of mechanical and operational properties of rolled metal. However, in practice it is not always possible to create metal products with the specified characteristics. In order to determine the morphological features of the structure of rolled carbon steel, a comparative study of carbon steel samples with a carbon content of 0.49 % C and 0.2 % C selected from hot-rolled billets was carried out. The billets of each group were produced under the conditions of the same enterprise, with close temperature-time modes of deformation processing. The main difference was in manufacturing processes of the output continuous cast steel billets. This research shows that with identical normalized chemical composition of steel and the same thermomechanical treatment, the formation of the morphological structure features of hot-rolled steel occurs in a different way. Therefore, we can assume that the liquation, the diffusive mobility of elements is particularly influenced by the content of impurity elements and gases in steel, which leads to a different type of structures in the finished rolled metal. At the same time, these differences are observed in carbon steels with different carbon content. A sample of non-vacuumed OC grade axle steel (0.49 % C) from converter steelmaking has a more homogeneous structure without local areas of pearlite or ferrite accumulation. It was shown that the formation of ferrite rim in the microsegregation areas occurs not only in manganous sulfides, but also arises on the background of the smallest oxide inclusions. There is significant structural heterogeneity in the samples of electric steel, despite the lower sulfur content and gassiness of steel; at the same time, a dense perlite layer is formed around the sulfides. There is also a difference in steel grade 20 (0.2 % C) of different manufacturing processes. The structure is more homogeneous in qualitatively deoxidized vacuum degassed steel; no local areas with different dimensional characteristics were detected. The size of the structural elements is much larger and the structure has mostly large sections of the Widmanstatten ferrite. Since a large number of non-metallic inclusions and gassiness of steel is not a positive factor for providing a high set of properties of metal products, the modes of thermomechanical treatment used today require adjustments depending on the characteristics of steel melting. Keywords: microstructural heterogeneity, ferritic-pearlitic banding, mechanical properties, manganous sulfides.

Classification of Hot-Rolled Plates Using the Mahalanobis Distance of NMIs in Ti-Stabilized Austenitic Stainless-Steel Produced by Secondary Metallurgy.

Three charges of scrap-based, Ti-stabilized, Cr-Ni-Mo austenitic stainless steel in the form of hot-rolled steel plates were characterized. Based on automated metallographic analyses of representative microstructures, a quality characterization in terms of cleanliness of the hot-rolled steel plates was performed. Elevated contents of impurities, especially Pb, Bi, and oxygen, which affect the hot workability of stainless steels, were detected. The recycled FeTi-cored wire was the main source of the elevated levels of impurities detected in the hot-rolled, Ti-stabilized, stainless-steel plates. Related to this, elevated levels of nonmetallic inclusions (NMIs) and segregations were formed. The three charges were classified based on calculations of the Mahalanobis distance (MD) between the inclusions. The charge with the smallest number of nonmetallic inclusions was set as the reference class. The selection of outlier inclusions based on their MDs and their back-representation into ternary diagrams gave relevant metallurgical information about the abnormalities. The advantage of this technique is that the calculations of the MD and the threshold can be fully automated.

Investigation of an oxygen-converter semifabricate deoxidation possibility by lump silicon carbide for the purpose of improving production quality index

The most important operation in steelmaking is rational deoxidation of metal and slag, including deoxidation technology and the choice of deoxidizers. This action directly influences the number of non-metallic inclusions and their properties. The choice of both the deoxidizer type and deoxidation technology is tackled by each metallurgical enterprise in its own way. Nowadays, various metallic and nonmetallic materials used for metal deoxidation have found widespread use. These include the traditional ones – ferroalloys, pig-iron and powdered aluminum, and the wastes from metallurgical industries: aluminum, vanadium and abrasive slags, silicon carbide that have found wide application of late. At present, it has become quite obvious that the use of various types and techniques of deoxidation and out-of-furnace treatment of metal melt makes it possible to solve many problems in each specific production. In doing so,it is possible to solve the following tasks: to regulate the number and composition of non-metallic inclusions; to reduce the cost of steel due to the optimization of metallurgical processing, in relation to specific production conditions; to ensure the required quality of the products. Therefore, work aimed at further improving the methods of out-of-furnace processing in each specific production is, of course, promising and relevant. The prerequisite for the choice of deoxidation methods and the choice of deoxidizers as well as after-furnace treatment should be a comprehensive study of the metal at various stages of the metallurgical redistribution. This paper presents the results of the study of the steel production process using silicon carbide as a deoxidizer in the production of converter steel, smelted in 350 t converters with top blowing of Azovstal Iron and Steel Works. Based on the data on the chemical composition and temperature of the metal melt obtained in the conditions of oxygen conversion, using the StatSoft Statistica 10.0 application software package, the analysis of silicon carbide effect on the significance of the difference in the average chemical converter melt composition has been made

Effect of vacuum smelting method on the quality of pipe steel of northern application

Pipe metal of Northern application must meet increased requirements of strength properties, low-temperature ductility, cold resistance and weldability. Cracks, skins, flaws, roll-ins and other defect are not allowed on the surface of pipes. The fulfillment of the requirements substantially can be provided by the process of steel smelting by a vacuum remelting method. Study of the effect of 03ХГ grade pipe steel smelting in vacuum and without vacuum on its contamination by nonmetallic inclusions and resistance against hydrogen cracking was accomplished. The smelting of ingots of adjusted chemical composition was carried out in a vacuum induction furnace ZG-0.06L. To imitate the process of hot roughing rolling, hydraulic press П6334 of 250 t force was used. Finishing rolling was carried out at reversible hot rolling mill 500 duo, combined with a controlled cooling facility. It was determined, that the samples, smelted in vacuum, had insignificant number of nonmetallic inclusions and withstand the test of resistance against hydrogen cracking; cracks were not detected on them. After testing on resistance against hydrogen cracking of the samples smelted without vacuum, cracks were discovered, located on both the surface and central layers amounting to 600 mm and 1700 mm length correspondently. It was shown, that steel smelting in vacuum allows to reach a high degree of the steel purity, results in increased crack growth resistance and in decreased number of nonmetallic inclusions in the pipe steel of Northern application.

Refi ning of nickel alloys using foam ceramic fi lters

It is shown that fi ltration of nickel alloy by ceramic foam fi lters is effective way to reduce the number of non-metallic inclusions. Features of fi ltration refi ning of KhN45MVTYuBR alloy are studied. The effect of fi ltration refi ning on the microstructure and the chemical composition of the alloy is studied. The prospects for application of ceramic foam fi lters to improve the microstructure of the alloy KhN45MVTYuBR are shown.

Effect of Nonmetallic Inclusions on Fatigue Properties of Superelastic Ti-Ni Fine Wire

This study investigated the effects of the types and length of nonmetallic inclusions on fatigue properties in rotating bending fatigue testing of Ti-Ni alloy fine wire. It was fabricated to include titanium carbides Ti(C,O) and titanium oxides Ti4Ni2Ox as either single phases or a mixture of both phases as nonmetallic inclusions in Ti-Ni alloy. The fatigue strength of Ti-Ni alloy depended on the number of nonmetallic inclusions of a length of ≥2 μm. Compared with Ti(C,O), Ti4Ni2Ox is coarse. It also exhibited a trend of readily forming particles and void assemblies, which are a defect morphology that originates from nonmetallic inclusions and readily act as crack origins of fatigue fractures.

Determining the temperature dependent fracture toughness of carbon-bonded alumina using chevron-notched specimens

Open cell ceramic foam filters are used for metal melt filtration. The aim is to reduce the number of non-metallic inclusions and therefore to enhance the quality of the cast product. A new generation of multifunctional filters, which is investigated within the collaborative research center CRC920, is made of fine grained carbon-bonded alumina. The filter manufacturing process leads to hollow struts with sharp edge cavities, which could act as a crack tip. To evaluate the integrity of the filter, a fracture mechanical characterization of the bulk material at different temperatures is necessary. In the applied chevron-notched beam method (CNB) the small specimens (5 x 6 x 25 mm3) are loaded with a four-point bending test set-up until failure occurs. The test set-up offers the possibility of testing at temperatures up to 1000°C. With the help of the measured load-displacement curve the fracture toughness is calculated. Additionally, an analysis of the microstructure of the fracture surface of the specimens is presented.

Application of Integrated Methods to Improve the Technological Properties of Steel

Getting a new generation of materials, advancing by its qualities world counterparts, among the most important objectives of the creation of scientific and technical groundwork in various fields of science and technology. Particular attention is paid to technological metals and their alloys; materials having the fine and ultrafine structure, single crystal, amorphous and powder materials. The preparation of such materials is possible thanks to new production technologies, modern equipment and the use of costly additives or use of technologies with application of complex measures for these materials. One way to obtain the desired technological properties is the use of complex natural materials. This method is cheaper compared to other costs, and requires no additional equipment, as well as lower costs of preparatory. For more efficient use of these components is necessary to preliminary processing, which will improve the effect of the use of steel in the modification. The type of treatment can be varied by mechanical activation powder to extract individual components. As a result of a series of studies on the impact modifiers to change the structure and properties of steel were detected changes in the structure; in particular the number of non-metallic inclusions was reduced.Heat treatment allows improving effect of modifying the structure of steel and the items received.

Causes of Increased Number of Non-Metallic Inclusions in Filtered Steel

Common phenomenon observed during steel filtration in laboratory conditions is the increased number non-metallic inclusions. These are the smallest inclusions in the Ferret diameter range from 0.5 to 6 μm. This phenomenon concerns only the number of inclusions. The analysis of literature shows that there is no explanation of this in the previous research, for example [1, 3]. Therefore, this paper attempts to explain the important relationship that was so far overlooked.

A Self-Heating Approach to Characterize Anisotropy Effects in Fatigue Behaviour: Application to a Nineteenth Century Puddled Iron from a French Railway Bridge

The puddled iron is known for its extended use in monumental construction during the second half of the nineteenth century; among the structures built with such material are about half of French railway metallic bridges, most of them with over a century of service life. This scenario rises several concerns about the resistance of this material to cyclic loadings and therefore its fatigue behaviour. However, the puddled iron possesses several properties that make its mechanical characterization particularly difficult. Due to the puddling process this metal contains an important number of non-metallic inclusions that not only will turn out in a heterogeneous material but also (due to the rolling process) into an anisotropic one. In this paper a fast characterization of fatigue properties is proposed by using the self-heating method. The experimental self-heating curves obtained from specimens of the bridge of Toles (Chaumont, France) showed a scatter that was not observed in homogeneous materials (modern steel for example), 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. An anisotropic two-scale probabilistic model for high cycle fatigue is also used to represent the orientation dependency of the results and the scatter found on the experimental data by using Hills elasto-plastic law and Weibulls 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 discussed.

Regarding the efficiency of complex steel deoxidation

The mechanism of carbon removal at the initial stage of processing the chromium steel scrap was considered. The results of thermodynamic analysis of the processes of decarbonization and deoxidation of steel were given. For improving the deoxidation efficiency, physical-chemical analysis of combinations of metals and their interactions with the dissolved in the melt oxygen was made. Complex deoxidizers based on aluminum with silicon and barium are quite effective. Thus, the possibility to increase the efficiency of the complex based on metal with lower affinity for oxygen from the metals with higher affinity for oxygen of a series of affinities was established. Explanation of the obtained results based on the model which takes into account the equilibrium of reactions between the metal-deoxidizer and dissolved oxygen was proposed. The use of complex deoxidizer improves the kinetics of deoxidation and reduces the number of non-metallic inclusions.

Experimental and Numerical Investigations on Non-metallic Inclusions Distribution in Billets Casted at a Multi-strand Continuous Casting Tundish

Modern tundishes plays an important role of refining treatments to improve the quality and purity of casted steel. Purity of steel is defined by the non-metallic inclusions in the steel product, including their size, quantity, distribution, chemical composition and mineralogy. The aim of presented studies was to investigate the number and distribution of non-metallic inclusion in individual billets casted in a six-strand tundish. The industrial measurements, performed during stable production conditions at the continuous steel casting (CSC) plant, were performed for different tundish working space configurations. Analysis of the size and number of non-metallic inclusions has been done on the metallographic samples using light microscope. Experimental studies were supported with numerical simulations using large eddy simulations (LES) method. A modified boundary condition describing inclusion separation at the liquid steel surface was implemented in commercial code AnsysFluent. Experimental results concern size distribution of inclusions in billets for current tundish configuration showed big differences between casted ingots. Numerical results shown the domination in the number of inclusions occurring in the nozzles number 3 and 4 (for basic tundish configuration) and in the nozzles number 2 and 5 (for tundish with turbulence inhibitor). The reason for that is the change in configuration tundish working space, that has an impact on the flow field inside the tundish. Experimental measurements performed for proposed modified tundish configuration (with turbulence inhibitor) shown that those differences are much smaller, which in consequence has an influence in higher quality of continuously casted ingots for individual strand of CSC.

A preliminary study on the role and implication of plate-type iron artifacts in the ancient iron technology of Korea

Special iron objects in the form of a narrow plate with a fan-shaped blade on one or both ends, but with a substantial variation in shape and size, have continually been excavated from ancient historical sites located in the southern part of the Korean peninsula. The frequency and abundance of their excavation imply that they must have played a crucial role in the initial shaping of the Korean iron industry. Little is known, however, of their intended purposes or the exact engineering processes applied in their production. Speculation suggests that they might have been used as currencies or intermediate materials for the making of finished products. This study examined the microstructures of three such iron objects from the Korean Three Kingdoms Period (ca. 300–600 AD). It was determined that they were made of low carbon iron generally containing a number of non-metallic inclusions, with hints of surface carburization particularly at the ends of the plates. These results reveal the likely presence of an iron technology based primarily on the bloomery technique as opposed to the Chinese style of iron-making based on cast iron technology, which was also in use in ancient Korea.

Effect of ladle slag of previous heat on number of non-metallic inclusions in ladle treatment of tool steel

Nine series of industrial trials were carried out using the same ladle in each series to examine the effect of ladle slag on the number of non-metallic inclusions in the next heat. Steel and slag samples were taken after ladle vacuum treatment for chemical composition analysis. Samples of the final steel product were examined to determine the number of non-metallic inclusions. It was found that the number of inclusions increased with SiO2 content of the ladle slag in the previous heat. No clear trends were found for the effects of viscosity and MgO activity of the previous slag on the number of inclusions.Theoretical analysis based on the experimental results suggested that the formation of 2CaO.SiO2 followed, but the dusting of the compound made the refractory more porous, which was reasonable for the number of non-metallic inclusions.

Effect of a pipe-steel killing technology on the composition and number of nonmetallic inclusions

Pipes made from steels 19G, 17GS, 17G1S, 10G2FBYu, 13G1S-U, and 20KT of various manufacturers and technologies are studied. Electron microprobe and fractional gas analyses are used to determine the main types and number of nonmetallic inclusions (NIs). The effect of a modification procedure on the oxidic cleanness of steel 20KT (produced at JSC “Volzhskii Pipe Works”) is studied. The use of a silicocalcium-filled wire is shown to increase the total contamination of the steel by nonmetallic, in particular, calcium aluminate and magnesium spinel inclusions, which are conditionally related to corrosion-active nonmetallic inclusions (CANIs). Fractional gas analysis is shown to allow the number of oxide inclusions of various types to be accurately determined in pipe steels. No correlation is found between the volume fraction of oxide inclusions determined by fractional gas analysis and the number of CANIs determined by a metallo-graphic method.

Effect of the melting conditions on the ductility of nickel-chromium superalloys

The effect of the melting conditions on the ductility of nickel-based superalloys is studied. The experimental results obtained are used to refine the formation mechanism and composition of nonmetallic film inclusions in as-cast nickel-chromium alloys. The magnesite lining of an electric furnace is found to serve as a secondary source for the transition of nonferrous and modifying impurities into a metal, which leads to the formation of a large number of nonmetallic inclusions. Film impurities located along the grain boundaries are shown to cause the low ductility of the metal during deformation.

Behaviour of inclusions in RH vacuum degasser

Vacuum degassing processes are now an integral part of secondary steelmaking operations and besides the more obvious benefits of steel chemistry control to precise specifications, they also reduce the number of non-metallic inclusions. Care has to be taken, however, that the change in steel composition through loss of C, O, Mn, etc. does not result in a deleterious change in the composition of the remaining inclusions. Attempts in the past to determine the effect of vacuum on inclusion compositions have been through the use of thermodynamic models, following the inclusion engineering approach. The calculated inclusion compositions do not, however, compare well with the inclusions as analysed in samples taken from the liquid steel after the degassing operation. Clearly, it is important to take into account time dependent effects during degassing and this has been achieved by the development of a combined fluid flow-thermodynamic model. Using the computational fluid dynamics model, CFX, to establish the temperature, flow and species contours in a two-dimensional steel ladle under the influence of natural convection, the results are transferred as start conditions in a three-dimensional RH degasser model. A body force is then applied to simulate the argon bubbles that are injected into the up-leg of the degasser and changes in flow, temperature and species concentrations are calculated. Allowing for additions made during the process, the composition of the top slag and any local inclusions within the steel is predicted. The influence on top slag and inclusion chemistry of any glaze on the snorkels of the degasser is also taken into account.

Development of high quality bar and rod by applying continuous forging at continuous caster

Kawasaki Steel invented « Continuous Forging Method » and installed a forging machine at No.3 bloom continuous caster in Mizushima works in 1990. This method continuously discharges concentrated molten steel at center portion of blooms by forging them before their solidification are completed. The method can not only eliminate conventional centerline segregation of blooms but also control the chemical composition at center portion of blooms. The application of the method makes it possible to increase the super-heat at the tundish and thus reduce the number of non-metallic inclusions.

Selecting conditions of preparation of copper-based melts for spraying

The chemical heterogeneity of copper and its alloys in respect of certain elements in relation to the thermal and time conditions of melting and the effect of the type of deoxidizing agent on the content of oxygen and nonmetallic inclusions were examined on rapidly cooled cylindrical specimens 4-6 mm in diameter produced by sucking the liquid metal into quartz tubes at specific periods in melting, followed by rapid cooling in water. Metal samples were taken from laboratory and industrial melts of copper and its alloys in induction furnaces with a capacity of 65-1000 kg using graphite crucibles. The charge was represented by M0 grade copper (cathodes, waste from elctrotechnical industry: pressings, conductors, powder blanks, etc.), grade TsO zinc (Tsl), grade SO (SI) lead, grade Ol (02) tin. Deoxidation was carried out with a 0.02-0.10% copper--phosphorus (MF-10) and copper-boron (2% boron) master alloy. To reduce the extent of gas absorption, all the melts were covered with a dried charcoal layer 60-120 mm thick. The deoxidizing agent was added after melting copper. This was followed by adding alloying elements, with tin added last. Samples of the melts to be used for further dispersion by water to produce nonspherical powders were taken at temperatures of 1180-1280 (copper), 1100-1220 (L80 brass), and I080-I150°C (BrOTsS bronze) in 20 deg intervals. The holding time at each temperature was 10-30 min. Sections were prepared from the cylindrical specimens. The degree of homogeneity of the distribution of the solute and alloying elements was analyzed in Superprobe-733 equipment, the oxygen content was estimated in a device manufactured by Balzers Company, the number of nonmetallic inclusions in Quantimet equipment, and the volume fraction of the inclusions was calculated in measuring 500 fields of view on each section. The results show that the degree of chemical heterogeneity of the copper melt greatly decreases after thermal treatment at 1250°C with holding for 20 min, and that of the melts of brass and bronze decreases after treatment at 1180 and I130°C and holding for 15 and 20 min, respectively. Figure 1 shows the concentration curves of the maximum and minimum values of microheterogeneities in respect of the solid and alloying elements for copper, brass, and bronze. As an example, Tables 1 and 2 give the average results of examination of the effect of the oxidizing agents (phosphorus and boron) on the content of oxygen and nonmetallic inclusions in OTsS 5-5-5 bronze. It can be seen that boron results in lower oxygen concentration than phosphorus. When the boron concentration is increased to 0.06% the amount of oxygen rapidly decreases. A further increase of the boron concentration is less effective and the fraction of spherical powder particles increases. This impairs the technological processes of the powder. Subsequent addition of zinc to the melt results in an additional reduction of the oxygen concentration. The content of the nonmetallic inclusions decreases on adding both deoxidizing agents, but in deoxidation with boron a subsequent addition of zinc to the melt is not accompanied by an increase of the volume fraction of the inclusions.

Lamellar, lamellar-brittle, and lamellar-ductile failure of welded joints

1. The low parameters of the static, dynamic, and cyclic fracture toughness of rolled metal in the z-direction are one of the reasons for formation of lamellar cracks in welded structures characterized by the presence of macro- and microsteps and ledges. It is shown that lamellar fracture takes place in various loading conditions both in the pure form and in the form of mixed lamellar-ductile, lamellar-brittle, or lamellar-fatigue cracks. 2. The occurrence of two types of lamellar cracking was confirmed: high-temperature lamellar cracking in materials contaminated with nonmetallic inclusions, and low-temperature lamellar cracking in the so-called clean steels with a very small number of nonmetallic inclusions. In high-temperature lamellar tearing, the reduction of the fracture toughness of the metal in tests in the z-direction takes place both at high and at low temperatures and, consequently, the formation of lamellar, lamellar-ductile and lamellar-brittle cracks may take place in welding, assembling, and service of structures. In low-temperature lamellar cracking, the fracture toughness decreases mainly at low temperature. This must be taken into account in using steels produced by controlled rolling for welded structures where the metal of members and welded joints is subjected directly to tensile loading in the z-direction. 3. To prevent lamellar, lamellar-ductile, and lamellar-brittle cracks, additional requirements ensuring satisfactory ductility and fracture toughness in the z-direction should be imposed on the materials used for welded structures; this relates mainly to the members and welded joints in which the metal works in the z-direction.