Content Of Nonmetallic Inclusions Research Articles

Experimental studies of the influence of hydrogen and sulfur on sulfide-corrosion destruction under tension of pipelines

For the first time, comprehensive experimental studies of the influence of hydrogen and sulfur on sulphide stress corrosion cracking (SCR) of pipe steels in a corrosive-aggressive environment of NACE were carried out. In the research, experimental steels of the 06G2BA and 08KHMCHA brands, which are widely used in the construction of pipelines for various purposes, were used an analytical system (analyzer of non-stationary processes – ANP) was developed and tested in laboratory conditions, into which the installation for tests on corrosion-mechanical cracking under stress was integrated. For the first time, comprehensive experimental studies of pipe steel samples of grades 06G2BA and 08KHMCHA under the influence of sulfur and hydrogen were carried out, which made it possible to develop an understanding of the mechanisms of SCDS (sulphide-corrosion destruction under stress) and HID (hydrogen-initiated destruction). For the first time, experimental studies of the corrosion kinetics of 06G2BA and 08KHMCHA steels were carried out depending on the duration of the tests in the NACE model environment, while three periods of the formation of corrosion products were determined. It was found that sulfur and hydrogen, which are dissolved in test pipe steels, have a strong influence on the growth rate of corrosion cracks of SCDS, which made it possible to determine the optimal content of sulfur and hydrogen in steel 06G2BA. It is shown on the basis of the results of experimental studies that to ensure high crack resistance of pipe steels under conditions of static and cyclic loads both in air and in conditions of corrosive-aggressive environments, the sulfur content should not exceed 0.015-0.020%, and the dissolved hydrogen content should not exceed 2-3 ppm . The obtained results make it possible to improve pipe steels in the process of their smelting at metallurgical enterprises thanks to the use of economical modification with niobium, chromium, cerium and other impurities, which contribute to the fragmentation of the structure and reduce the content of non-metallic inclusions and harmful impurities.

Quantitative and Qualitative Evaluation of Non-Metallic Inclusions in High-Silicon Steel after Hot Rolling

This paper presents an analysis of non-metallic inclusions occurring in high-silicon steels containing about 3% Si of terms of their type, volume fraction and morphology. The inclusions were divided into 3 main groups: oxides, sulfides, nitrides which together can also form complex. The work was based on numerous metallographic observations in two sections (longitudinal and transverse to the rolling direction). The study was performed on three casts differing in chemical composition. The analyzed casts were characterized by a different content of non-metallic inclusions, which can be associated with slight differences in chemical composition. The analyzed results showed that the most common inclusions were oxides and nitrides. Sulfides occurred sporadically.

ОСОБЛИВОСТІ НЕОДНОРІДНОСТІ ПЛАСТИЧНОЇ ДЕФОРМАЦІЇ ГЕТЕРОФАЗНИХ НЕМЕТАЛЕВИХ ВКЛЮЧЕНЬ В СТАЛЯХ

The nature and level of plasticity of microcomposite heterophase inclusions in steels under pressure treatment condition was investigated. Plastic phases in heterophase inclusions of various types under the conditions of hot and cold deformation of steels were investigated. It is shown that each type of inclusions, which are microcomposite formations in steels, is characterized by its own laws of the development of deformation processes, which are determined by their chemical and phase composition, structure, deformation capacity of inclusion phases. The generalized of the plastic behavior of heterophase inclusions of various types with a complex structure have been established and inhibitory effect of non-deformable inclusion phases on the behavior of plastic phases in a wide range of deformation temperatures of steels has been established. The peculiarities of the nature of plasticity of heterophase inclusions with different compositions and structures are discussed. The use of the obtained results will make it possible to develop technologies for obtaining steels with a regulated content and types of heterophase non-metallic inclusions, which will significantly increase their technological plasticity, as well as prevent the formation of various types of defects during pressure treatment of steels.

Structural characteristics and properties of heat-resistant nickel β-alloys produced via the centrifugal SHS-casting method

Employing centrifugal self-propagating high-temperature synthesis (SHS) metallurgy, complemented by advanced metallurgical processes such as vacuum induction melting (VIM) and vacuum arc remelting (VAR), yielded the alloy formulation denoted as base–2.5Mo–1.5Re–1.5Ta–0.2Ti. This study investigates the effects of various technological modes and additional metallurgical treatments on the alloy's impurity and non-metallic inclusion content, structural characteristics, mechanical behavior under compression, and its oxidation mechanisms and kinetics when exposed to temperatures of 1150 °C for 30 h. With increasing centrifugal acceleration, the proportion of non-metallic inclusions (number of points) drops from 5 to 1–2 points. The best combination mechanical properties, including σucs = 1640 ± 20 MPa, σys = 1518 ± 10 MPa, and residual deformation were observed in alloys processed under conditions of increased gravitational force (g = 50). Within a centrifugal force range of g = 20÷300, the composition of the synthesis products aligned with the theoretical expectations. The total content of impurities is 0.15 ± 0.02 %, with a decrease in gas impurities–oxygen and nitrogen levels reduced to 0.018 % and 0.0011 %, respectively. The structural analysis of the alloys revealed the presence of globular and streaked inclusions of a chromium-based solid solution embedded within the matrix. Inclusions with thickness of 2–8 μm are present in the intergranular space: (Cr)Ni,Mo,Co, (Cr)Mo,Re and (Cr)Re,Mo. The formation of the Ni(Al,Ti) phase at grain boundaries was identified, contributing to an enhancement in plastic resistance and overall strength of the alloy. Oxidation mechanisms varied across different processing modes, with the size of structural components significantly influencing oxidation kinetics. The weight gain observed in SHS samples was 70 ± 10 g/m2 with oxidation predominantly occurring along the NiAl interphase boundaries and penetrating into the depth of the sample. TEM facilitated the identification of phases enriched with Ti microadditions, reducing the levels of dissolved nitrogen and oxygen within the intermetallic phase to a combined weight percentage (ΣO,N) of 0.0223 wt.%.

Features of the distribution of non-metallic inclusions during electroslag surfacing with a high sulfur content

Today, the question of the quality of parts is quite acute in mechanical engineering. As a rule, most parts are made from castings obtained by various methods. The main task facing the foundry industry in our country is to significantly improve the overall quality of castings, which is expressed in reducing the thickness of the walls, reducing the allowances for mechanical processing and for pouring and feeding systems while maintaining the necessary operational properties of the products. The final result of this work should be to provide the increased needs of mechanical engineering with the required number of cast blanks without a significant increase in the total production of castings by mass. The high operational characteristics of castings depend significantly on the purity of the alloys in terms of the content of harmful impurities and non-metallic inclusions. Sulfur is a very harmful impurity for steel, which, even in small amounts, significantly reduces its mechanical properties. This is especially relevant for parts that work in difficult working conditions (variable loads, high temperature, etc.). This article presents the results of the study of the distribution of non-metallic inclusions and sulfur in the fusion zone, the transition zone and the base metal during electroslag welding of chemically heterogeneous steels with a high sulfur content. It is shown that the amount of sulfur in the metal, even at high concentrations, does not affect the purity of the fusion zone in terms of the content of non-metallic inclusions. Intensive cleaning of the fusion zone and the first portions of the deposited metal occurs due to the large reaction surface with the highly active liquid fluoride flux and the high temperature of the slag bath. As a result of these processes, non-metallic inclusions are crushed, their number decreases and they are evenly distributed throughout the volume of the metal. Accordingly, non-metallic inclusions in the fusion zone have a favorable globular shape, they are small in size and evenly distributed in the volume of the metal, which helps to increase the level of mechanical properties of steels, because their size does not exceed the so-called “critical” sizes of inclusions.

A new approach to the development of an efficient technology for production of steel with a low content of non-metallic inclusions

A new approach to the development of an efficient technology for production of steel with a low content of non-metallic inclusions

Study of the properties of the metal deposited with flux-cored wire of the Fe‒C‒Si‒Мn‒Сr‒W‒V system.

Alloys of the Fe‒C‒Si‒Мn‒Сr‒W‒V system widely used for hot-rolling roll repairs provide high resistance of the deposited layer against abrasion, but its thermal endurance is relatively low. It is shown that in order to ensure the quality of roll repair, it is necessary to improve the composition of the flux-cored wire charge and the technology of their use. It is proposed to reduce the structural heterogeneity of the deposited metal the use of flux-cored wire of the type PP-Np-35V9X3SF. The influence of the introduction of carbon-fluorinated elements and titanium on hydrogen concentration, microstructure, level of pollution by non-metallic inclusions, grain size, hardness and rate of wear of the deposited metal layer was evaluated. The data on the chemical composition of the deposited layer, the content of non-metallic inclusions in it, the microstructure of the deposited metal, depending on the content of titanium in the flux-cored wire, are presented. It was found that an increase the concentration of titanium increases the hardness of the deposited layer and reduces the rate of wear (abrasion) of samples. The effect on the level of contamination of the studied fused layers with oxide inclusions was not revealed. Increasing the hydrogen content in the deposited layer re-duces its hardness and increases the rate of wear of the deposited layer. Increasing the content of titanium in the depos-ited layer helps to reduce the size of the martensite needles, as well as the size of the former austenite grain. The de-pendencies of HRC hardness and wear resistance on the content of titanium and hydrogen in the deposited layer were established

Calcium-Treated Steel Cleanliness Prediction Using High-Dimensional Steelmaking Process Data

Control of calcium treatment in steel is challenging due to the reactivity of Ca and difficulty of measuring total oxygen of steel in-process to make actionable decisions. In this work, a method combining statistics and process engineering are developed using partial least squares regression (PLS) to predict non-metallic inclusion content (oxides and CaS) and composition at the end of ladle treatment and in the tundish using extensive process data and SEM/EDS-based non-metallic inclusion analysis. Total oxygen at the end of the ladle treatment can be predicted to an accuracy of 7 ppm, and the Mg/(Mg+Al) ratio in inclusions to an accuracy of 3at% providing enough data to recommend Ca addition based on a thermodynamic calculation for the Ca liquid window. Alternatively, the model can predict total inclusion fraction to 20 ppm accuracy, and accurately predict average CaS content and Ca/Al ratio of inclusions in the tundish. Model interpretability is hindered by high dimensionality and multicollinearity of the data. Non-metallic inclusion compositions correspond to the expected composition at the onset of CaS formation based on steel composition.

Hot Tearing in an Investment Cast Burner Swirler

Abstract The damage case dealt with in the present work relates to a generally less common manufacturing defect that was discovered during its installation. The part was sourced from a supplier. An installation of the defective part in a large gas turbine engine used for energy generation could thus be prevented. The defect, a solidification crack, could have been repaired by welding and the component could have been used for operation. Instead, it was subjected to destructive examinations aiming at identifying what caused the crack. As the component could not possibly perform its function prior to being repaired by welding we are, in any event, talking about a damage case. The solidification crack initiated at a site of oxide infiltration. It was thus clearly a casting defect. The respective supplier was advised to reduce the content of non-metallic inclusions by the use of ceramic filters when the material is poured into the shell mold and a better control of the vacuum in the casting furnace.

Electroslag heating and additional melt feed of steel ingots of semi-continuous casting

The issues related to the continuous compensation of metal shrinkage during its crystallization are studied. Based on the evaluation of ways to reduce the size of the shrinkage shell, aimed at maintaining the liquid phase for a long time, the most effective ways to reduce the size of the shrinkage shell and reduce the head trim are selected. The influence of electroslag heating and recharge technology on the length of the shrinkage shell and the quality of the metal of the sub-shrinkage area of semi-continuously cast ingots has been studied. The study was carried out on ingots with a diameter of 500 mm weighing 3.5 tons of carbon and alloy steels. The installation consisted of 3 electrodes with a diameter of 75–100 mm, connected to the transformer TSH-3000-3. The transformer power was 570 kVA, the current per phase was 1000–3000 A, the voltage on the electrodes was 40–60 V. Temperature measurements were carried out in the copper sleeve of the mold. For comparison, the temperatures in the walls of the mold were recorded during the cooling of the ingot in the mold without heating. The cooling curves showed that the process of electroslag heating does not cause overheating of the mold walls. This is explained by the appearance of a side metal crust in the upper part of the ingot, which does not melt with liquid slag and protects the walls of the mold. The surface of the ingots had no visible defects (crust inversions, film and slag inclusions). Additional surface treatment (stripping, stripping) was not required. The macrostructure of the ingots is dense, without visible defects, including in the axial zone. Sulfur liquation on sulfur prints according to Bauman was not detected. Electroslag heating had a significant impact on the length and shape of the shrinkage shell. The results obtained show that electroslag heating with graphite electrodes, feeding with consumable steel electrodes of the same composition with the resulting ingot and electroslag casting of steel can improve the structure, density and chemical homogeneity of cast metal, reduce the content of non-metallic and gas inclusions and significantly increase the yield of usable compared to conventional casting.

Complex refining of aluminum alloys in mould casting process

It is shown that the service properties of aluminum alloy castings are largely determined by the content of nonmetallic inclusions in the melt. The effect of such inclusions of various origins on the service properties of castings is analyzed. The process of chill mould casting is studied and means for complex in-mould purification of the casting material from oxide spots and their fragments formed when filling channels and cavities of the mould are proposed.

In-mould refining of cast aluminum alloys

Methods for preventing of castings contamination or their critical parts by using filters of various types and concentration of non-metallic inclusions in washers or unloaded parts of castings are considered. The possibility of increasing in service properties of power castings and economic parameters of their manufacturing process by using washers on the example of industrial casting with weight of 0.38 kg AK9 alloy.

Effect of low aluminum additions in the microstructure and mechanical properties of hot forged high-manganese steels

In the present work, the effect of low aluminum additions and the hot forging process on the microstructure and non-metallic inclusions of high manganese steels is analyzed. Four high-manganese steels (HMnS) were prepared by adding low aluminum contents of 1.1 and 1.5 wt. % to four carbon austenitic steels with medium carbon content (0.3 - 0.4 wt% C) and manganese contents of 17 and 22 wt. Samples of the as-cast steels were hot forged to 1100?C to obtain an overall reduction of 70 %. Microstructural evolution was studied using microscopy techniques (OM, and SEM-EDS) and X-ray diffraction measurements for the as-cast and hot forged steels. A typical grain columnar zone formed during solidification of a cast ingot was obtained in the as-cast condition, where the microstructure consisted of nonmetallic inclusions in a fully austenitic matrix. The non-metallic inclusions were identified as Al2O3 and MnS particles. Thermomechanical treatment allows the formation of an austenitic microstructure characterized by twins in steels with high manganese content, while an austenitic-martensitic duplex microstructure was obtained in HMnS, which contained the lowest manganese contents. The highest tensile strength values were obtained for 17Mn-1Al steel, which had the smallest grain size and higher content of non-metallic inclusions. The hardness values were similar to those obtained in the as-cast condition.

Mastering the production of special types of pipes made of ferritic-martensitic steels, taking into account the peculiarities of the microstructure and properties

The main results of the development of a technology for the production of special types of pipe products, carried out taking into account the features of the microstructure, the laws of phase and structural transformations, as well as the resistance to plastic deformation in a wide temperature range of steels of the ferritic-martensitic class of grades EP450-Sh and EP823-Sh, are presented. The microstructure was studied with determination of the grain size, the content of non-metallic inclusions and fraction of the main structural components depending on the heating temperature for quenching. Using the Gleeble 3800 multifunctional complex, the resistance to fracture deformation at high temperatures was determined. In the laboratory of JSC RusNITI, physical modeling of the cold rolling process in a two-roll stand was carried out according to the oval-oval calibration scheme in the mode of successive increase in reduction. On the basis of the studies carried out for the steel grades under study, were developed the modes for pressing stock hot-pressed pipes with dimensions of 133.0×14.0 and 89.0×7.0 mm; cold rolling of both large-scale samples of round pipes and stock pipes intended for subsequent production of hexagonal pipes; final heat treatment of pipes of round and hexagonal sections, ensuring compliance with the requirements of technical specifications. As part of the project direction, PJSC TMK developed and implemented, through inter-plant cooperation with JSC VTZ, TMK-INOKS Ltd. and JSC RusNITI, a new technology for manufacturing hexagonal pipes according to the hot pressing – cold deformation scheme (rolling, profiling), whereby large-scale samples of new types of pipes for special purposes were obtained from EP450-Sh and EP823-Sh steel grades. The results obtained are used to form a set of technical requirements for the new type of high-tech pipe products, presented in technical specifications TU 420-2021, TU 422-2021, TU 423–2021.

Вплив модифікування на руйнування аустенітних неіржавіючих сталей при динамічних навантаженнях

The paper presents the results of studying the cold resistance of cast stainless steels of austenitic grade and developed mathematical models showing the effect of cerium, boron, vanadium and copper on cold resistance, which is associated with austenite grain size, carbide phase and ferrite content in austenite after quenching, particle volumes, size and distance between particles of oxides, sulfides, titanium carbonitrides and the total content of non-metallic inclusions in cast stainless steel. It was established that with complex microalloying and modification of Ce, B, V and Cu, the impact toughness of stainless steels increases by 2.7-3.1 times, as a result of the increase of nucleation and crack propagation work. It showed that the crack nucleation and their development is associated with non-metallic inclusions, while in the original steels around non-metallic inclusions significant zones of brittle failure are observed, and in the fracture of complex microalloyed and modified steels there are practically no areas of brittle failure around non-metallic inclusions. It was established that the impact toughness and crack initiation and propagation of the investigated stainless steels are determined by the patterns of changes in such structural factors as the size of the austenite grain, the content of the carbide phase and ferrite in the austenite after quenching, the volume fraction, the size and distance between oxide particles, titanium sulfides and carbonitrides, as well as the total content of non-metallic inclusions. Mathematical models of the influence of structural factors have been developed, which show the predominant influence of non-metallic inclusions on the process of destruction of stainless steels under dynamic loads, in comparison with other structure characteristics, in conditions of negative temperatures is shown. It is established that the mechanism of influence of Ce, B, V and Cu on this process is connected, mainly, with dispersion of oxides and their more homogeneous distribution. Keywords: steel, toughness, fracture work, crack formation, crack propagation, modification.

Composition of non-metallic inclusions and microstructure of electric arc coating formed using the flux-cored wire of Fe – C – Si – Mn – Сr – Ni – Mo system

The article considers the study of composition of the non-metallic inclusions and microstructure of the electric arc coating using the flux-cored wire of Fe – C – Si – Mn – Cr – Ni – Mo system. Formation of the electric arc coating was carried out using the ASAW-1250 automatic arc welding machine by the investigated wire. In order to influence the level of contamination of the deposited metal with non-metallic oxide inclusions, aluminum gas purification dust was introduced into the flux-cored wire (instead of amorphous carbon). Composition of the electric arc coating was determined using XRF-1800 spectrometer. Microstructure of the electric arc coatings was studied by optical microscopy. The phase and elemental compositions were studied using scanning electron microscopy on MIRA 3 LMH instrument. Non-metallic inclusions in the electric arc coating consist of oxides of silicon, fluorine, calcium, aluminum and magnesium oxides. The darker component in the inclusion, which looks like rectilinear crystals directed from the surface deep into the inclusion, has a similar phase composition, but differs somewhat in the content of chemical elements. A small dark component of a rounded shape (aluminum and magnesium oxides) is observed in the inclusion. Traces of sulfur are highlighted along the contour of the globules. Metallographic analysis of the deposited surface showed that the microstructure of the deposited layer is a coarse-needle martensite. The structure is uniform, has a dendritic (columnar) structure characteristic for cast metal. The results of the conducted investigations allow measures to be developed to reduce the content of non-metallic inclusions containing elements of fluorine, sodium and aluminum, which in turn may adversely affect the physical and mechanical properties of the deposited layer, for example, by using refining additives to reduce the contamination of the deposited layer with non-metallic inclusions.

Increasing the efficiency of refining and modification of aluminum alloys when using electromagnetic factors

Mechanical properties of aluminum alloys and their corrosion resistance are strongly influenced by the content of non-metallic inclusions and hydrogen dissolved in the melt, therefore, the improvement of technologies for refining aluminum alloys is important. The use of electromagnetic factors for this purpose has not yet been studied enough, but theoretical studies and experiments carried out show that this direction is promising. The paper presents the results of testing a new technology in which electromagnetic factors are used to enhance the efficiency of aluminum alloy refining from non-metallic inclusions and hydrogen. A melt flow was initiated through a ceramic foam filter by an electromagnetic pump, through which an electric current with a frequency of 50 Hz passes. At the same time, argon was introduced perpendicular to the flow direction at the crucible bottom. After refining, a modifier was introduced into the liquid metal bath and electromagnetic stirring was started. Metallographic studies of the sample cast from the refined metal have shown a significant quality increase. Cast mechanical properties increased accordingly. Tables 1, Figs 1, Refs 10.

Development of a Mathematical Model and Software for Predicting the Composition and Content of Nonmetallic Oxide Inclusions in Steel in Secondary Steelmaking Processes

Development of a Mathematical Model and Software for Predicting the Composition and Content of Nonmetallic Oxide Inclusions in Steel in Secondary Steelmaking Processes

Challenges in determination of microscopic degree of cleanliness in ultra-clean gear steels

Shot-peened, case-hardened gears can fail in the tooth root due to crack initiation below the surface of the steel matrix. Here, the crack is initiated at a non-metallic inclusion in the center of a so-called fisheye. This failure type can lead to a reduced endurance fatigue limit of the gears. It is for this reason that, over the last decade, much effort has been invested by steel manufacturers to reduce the non-metallic inclusion content of gear steels so as to mitigate or even completely prevent such crack initiation. These ultra-clean gear steels were achieved by various measures in the steel production process. However, as a result, the remaining non-metallic inclusions are inhomogeneously distributed in the steel volume in terms of both size and location. However, due to the inhomogeneity of ultra-clean steels, the question arose if the values derived according to the standards are still representative of ultra-clean steel batches. The results show that the standards can still be applied, but more effort must be applied. To determine the degree of cleanliness, six microsections are currently evaluated according to steel test specification (SEP) 1571, method K. It is shown that an examination of 24 microsections starting from size class 0 seems beneficial to get more reliable and comparable results of the degree of cleanliness of these ultra-clean gear steels. In addition, it is shown that a high degree of cleanliness has been achieved for all steel batches investigated with the measures taken in the steel production process.

Investigation of the Nature of Damage to Welded Flexible Compensating Elements Made of Austenitic Stainless Steels

Welded flexible compensating elements made of austenitic stainless steels, such as metal hoses and bellows expansion joints, operate in a complex stress state; therefore, almost all corrosion damage of these products occurs in a stressed state. In addition, in welded joints, defects are possible associated with elastic-plastic deformations and stresses arising in the manufacturing process. Paper considers the defects of welded joints of multilayer bellows expansion joints made of stainless steels AISI 304 and AISI 316 types. The influence of the parameters of the argon tungsten electrode welding mode, with or without filler wire, on the mechanical characteristics of welded joints was studied. Mechanical tests of samples of welded joints were carried out on a tensile testing machine. The optimal range of variation of the parameters of the welding mode has been established, in which the plastic characteristics of the welded joints have maximum values. A metallographic study of the microstructure of welded joints of metal hoses and bellows expansion joints was carried out. The influence of the content of nonmetallic inclusions in the material of products on the conditions of melting and crystallization of the weld pool, contributing to the appearance of pores and hot cracks in the metal of the weld and the heat affected zone, has been established. To reduce the influence of the content of non-metallic inclusions in the weld metal and the heat-affected zone on the conditions of melting and crystallization of the weld pool, it is recommended to carry out preliminary heat treatment of the austenitic steel strip.