Morphology Of Non-metallic Inclusions Research Articles

Relation of nonmetallic inclusions to the cyclic properties of steel 42CrMo4 after steel melt cleaning by filtration and related processes

Nonmetallic inclusions (NMIs) detrimentally influence the steel properties. The application of metal melt filter systems promises to reduce NMIs in steel. In the current work, NMIs are analyzed from metallographic sections after metal melt filtration or cleaning by a related process of the steel 42CrMo4 using immersion filtration, flow-through filtration as well as filters floating on top of the melt. Analyses by automated scanning electron microscopy (ASPEX) as well as light optical microcopy (LOM) revealed the chemistry, size distribution, and morphology of NMIs. The filter systems had a significant effect on these characteristics of NMIs. The threshold value ΔKth against fatigue crack propagation was found to depend on the amount of NMIs within the steel. A higher amount of NMIs caused less crack deflection leading to less roughness-induced crack closure and in turn resulted in lower threshold values at a stress ratio of R = 0.1. The comparison of the present analysis of NMIs with fatigue data from previous work indicated that the analysis of NMIs from metallographic sections can be used to approximate the fatigue strength of a batch in the same way as the analysis of NMIs from fatigue fracture surfaces for single specimens, as suggested by Murakami.

Control of the Composition and Morphology of Non-Metallic Inclusions in Superduplex Stainless Steel

Duplex stainless steel is a unique material for cast products, the use of which is possible in various fields. With the same chemical composition, melting, casting and heat treatment technology, pitting and crevice corrosion were observed at the interphase boundaries of non-metallic inclusions and the steel matrix. To increase the cleanliness of steel, it is necessary to carefully select the technology for deoxidizing with titanium or aluminum, as the most common deoxidizers, and the technology for modifying with rare earth metals. In this work, a comprehensive analysis of the thermodynamic data in the literature on the behavior of oxides and sulfides in this highly alloyed system under consideration was performed. Based on this analysis, a thermodynamic model was developed to describe their behavior in liquid and solidified duplex stainless steels. The critical concentrations at which the existence of certain phases is possible during the deoxidation of DSS with titanium, aluminum and modification by rare earth metals, including the simultaneous contribution of lanthanum and cerium, was determined. Experimental ingots were produced, the cleanliness of experimental steels was assessed, and the key metric parameters of non-metallic inclusions were described. In steels deoxidized using titanium, clusters of inclusions with a diameter of 84 microns with a volume fraction of 0.066% were formed, the volume fraction of which was decreased to 0.01% with the subsequent addition of aluminum. The clusters completely disappeared when REMs were added. The reason for this behavior of inclusions was interpreted using thermodynamic modeling and explained by the difference in temperature at which specific types of NMIs begin to form. A comparison of experimental and calculated results showed that the proposed model adequately describes the process of formation of non-metallic inclusions in the steel under consideration and can be used for the development of industrial technology.

Analysis of the effect of cerium on the formation of non-metallic inclusions in low-carbon steel

The research focused on the influence of cerium on the chemical composition and morphology of non-metallic inclusions in pre-oxidised steel to which Al, Ca, and Ce was added in different amount and order. Calculations were carried out using our own computer program. The simulation results obtained according to two calculation models helped identify precipitates from the Ce–O–S system. The possibility of CeN formation was also identified. The trace amounts of these inclusions were also found in the results. Consideration of the physicochemical phenomena at the boundary, as well as the interfacial partitioning and the sulfur partition coefficient, influences the favourable chemical composition of the inclusions, limiting it mainly to compounds from the Al2O3, Ce2O3, and CaS systems. It was found that the addition of Ce before Ca causes the elimination of MnS precipitates and Ca-containing inclusions in the steel.

Vacuum degassing impact on non-metallic inclusions during clean steelmaking

ABSTRACT The objective of this article was to study the impact of duration of vacuum degassing process on the type and morphology of non-metallic inclusions which are undesired & unavoidable by product of steelmaking process. During the vacuum degassing stage five top slag and steel samples were taken. All sample occasions measured chemical composition of the molten steel and top slag, and SEM analysis of the non-metallic inclusions. It was seen that during vacuum degassing process the chemistry, dispersions as well as the morphology of the non-metallic inclusions is constantly changing. The Alumina content of the top slag is increased while CaO content is reduced. The percentage share of calcium aluminate type of inclusions verses spinel is increased. In the beginning of the vacuum degassing wt-% of Al in non-metallic inclusions is the highest however as the time passes this wt-% is reduced at the same time inclusions with larger ECDs appear.

Взаимодействие празеодима и диспрозия с кислородом в расплавах никеля при РAr = 0,1 MПa и анализ неметаллических включений

The interaction of Pr/Dy with oxygen in nickel melts at РAr = 0.1 MPa and constant temperature was studied by the method of instantaneous EMF fixation using a Mo[Cr/Cr2O3//ZrO2(MgO)//O(NiL)]Mo cell and certified sensors. Dependences a[O] = f[Pr/Dy, %] were expressed as logarithmic equations, which made it possible to compare them with each other in the concentration range of 0.001 – 0.2 % of each deoxidizer and determine that the deoxidizing capacity of Pr is 1.7 times higher in terms of compared to Dy. Calculated a[O] in Ni – O – Al – (Pr/Dy) melts compared to Al at a concentration of 0.05 % elements and showed a seven-fold decrease for the first deoxidizer and an eleven-fold decrease for the second. The morphology of non-metallic inclusions in metallographic sections of Ni – O – Pr/Dy alloys indicates that the inclusions are located along grain boundaries and have different configurations and complex heterophase composition. The analysis of non-metallic inclusions with the maximum content of the deoxidizing element proved the existence of Pr/Dy oxygen compounds, which confirms the data of thermodynamic and mass spectrometric studies. The average content of Zr in non-metallic inclusions during the deoxidation of Pr is twice as high as in the experiments during the deoxidation of Dy, which indicates the interaction of Pr/Dy with ZrO2 of the EMF sensor and the predominant interaction of Pr compared to Dy and correlates with the data on the determination of a[O].

Role of Synthetic Slag Treatment on the Morphology of Non-Metallic Inclusions and Subsequent Cold Drawability of the High Carbon Wire Rod Steel

Role of Synthetic Slag Treatment on the Morphology of Non-Metallic Inclusions and Subsequent Cold Drawability of the High Carbon Wire Rod Steel

The effect of the impurities spaces on the quality of structural steel working at variable loads

Abstract The quality of carbon steels working at variable loads mainly depend of microstructure, but also of impurities. The quantity and morphology of non-metallic inclusions and spaces between impurities are correlated with the content of admixtures in the alloy, while their phase composition and structure, in particular shape, dimensions and dispersion, are determined by the course of metallurgical processes. Non-metallic inclusions as impurities found in steel can affect its performance characteristics. Their impact depends not only on their quality, but also, among others, on their size and distribution in the steel volume. The literature mainly describes the results of tests on hard steels. The article discusses the results of a study investigating the effect of the number of large non-metallic inclusions (over 10 μm in size) on the fatigue strength of structural steel during rotary bending. The study was performed on 6 heats produced in an industrial plant. Fourteen heats were produced in 140 ton electric furnaces. All heats were desulfurized and refined with argon. The experimental variants were compared in view of the tempering the research steel. The fatigue strength of steel with an impurity spaces was determined during rotary bending: the results revealed that fatigue strength is determined by the impurity spaces and tempering temperature.

Effect of nonmetallic inclusions morphology on destruction of a perspective high strength corrosion-resistant steel 04Х20Н6Г11М2АФБ

Alloying by nitrogen imparts to a steel high strength, viscosity, corrosion resistance and enables to save expensive alloying elements. As a result of theoretical and experimental studies carried out last decades, the problems of composition optimization, plastic deformation and thermomechanical treatment were solved as a whole. The solutions were used at elaboration of new perspective high strength corrosion-resistant steels, in particular, of steel 04 Х 20 Н 6 Г 11 М 2 АФБ . The items of comprehensive hardening of nitrogen-bearing steel of the mentioned composition for plates production were studied quite well. Effect of grain and subgrain metal structure, recrystallization, morphology of secondary phases, their composition and other factors on mechanical and corrosion properties of the steel were studied earlier. However, there are practically no studies dealing with morphology, chemical composition, sulphide and oxide nonmetallic inclusions distribution, evaluation of their influence on deformability and properties of high strength nitrogen-bearing steels, including properties in Z-direction. The aim of this study was revelation of dependence of the steel destruction character at rupture on the type and morphology of nonmetallic inclusions. Study of morphology, chemical composition, sulphide and oxide nonmetallic inclusions distribution density was carried out, as well as evaluation of their influence on properties of hot-rolled sheet, made of experiment high strength steel 04 Х 20 Н 6 Г 11 М 2 АФБ . It was determined, that nonmetallic inclusions of oxides, sulphides and nitrides can locate in a plane, parallel to Z-direction in both ways: evenly and forming stitches, at that one stitch can contain particles of various types. Comparatively low level of plasticity in Z-direction is stipulated both by general contamination of the metal by oxide inclusions and by stitch morphology of accumulation of nonmetallic inclusions of various types. It was shown, that at comparatively low density of nonmetallic inclusions stitches, their length plays the main role in the plasticity decrease in Z direction. In case of many stitch accumulations, the distance between them begins to play the leading role.

Analyzing the Features of Non-Metallic Inclusion Distribution in Ø410 mm Continuously Cast Billets of Low Carbon Steel Grades

The paper reports findings on the morphology of non-metallic inclusions in low carbon pre-peritectic and peritectic steel grades used for the fabrication of seamless pipes. It is demonstrated that the distribution of non-metallic inclusions over the cross section area of continuously cast billets is of a step-like nature conditioned by the features of billet solidification. In all the steels analyzed the non-metallic inclusions are presented by oxides, sulfides and complex oxi-sulfides not larger than 2 μm.

CONTENT MODIFICATION OF DIFFERENT TYPES OF NONMETALLIC INCLUSIONS DURING LOW-CARBON IF STEEL LADLE TREATMENT

Development of advanced materials for the automotive industry allows us to produce a lighter body without losing strength characteristics of the structure. It became possible by the creation and subsequent introduction into the production of such steel grades as IF (Interstitial Free) – steel with no interstitial solute atoms to strain the solid iron lattice and IF-BH (Bake Hardening) – steel with hardening during hot drying. The article provides a brief overview of the history of the emergence of IF steel and the current situation in the production of it in Russia. One of the quality criteria for steels of IF grades is purity of the metal by non-metallic inclusions (NMI), which negatively affect the plastic properties of the material, lead to the formation of surface defects of flat rolled products and reduce the manufacturability due to a decrease in the casting speed of steel, as they cause overgrowing of steel casting nozzles. The article presents investigation results of the content, composition, size and morphology of non-metallic inclusions (NMI) in the metal samples taken at all stages of ladle treatment and casting of IF steel grade production using quantitative metallographic analysis, electrochemical dissolution (ED) followed by X-ray microanalysis of isolated inclusions, Auger electron spectroscopy and fractional gas analysis (FGA). As a result of the analysis of inclusions in the studied samples using a scanning electron microscope, according to morphological features, five characteristic types of inclusions were identified, which reduce the performance properties and strength cha racteristics of the materials produced from them. Results of the analysis of nonmetallic inclusions in metal samples obtained by the ED method are in good agreement with the results of the determination of oxide nonmetallic inclusions by the FGA method. The method of fractional gas analysis shows the dynamics of changes in the content of various types of oxide nonmetallic inclusions during the secondary (ladle) treatment of steel. It is shown that application of the FGA method allows to make analysis of causes of the harmful NMI formation in the metal and to correct operations at ladle treatment.

Effect of composition and morphology of non-metallic inclusions on fracture toughness in as-cast AHSS

A set of water-cooling copper-chill mold equipment is designed to study the precipitation behavior of different inclusion types in test steel under different cooling conditions, as well as its effects on the steel mechanical properties. As the results reveal, slow cooling treatment near the solidus temperature of test steel is conducive to forming more MnS + Al2O3 composite inclusions. The impact energy (−16 °C) of slow-cooled cast ingots at the core position is 28% higher than that of the air-cooled ingots. Scanning electron microscopy analysis of the specimens shows that small cracks are formed around single Al2O3 inclusions, but no cracks were found around composite inclusions. A calculation model of the tessellated stress of composite inclusions in steel is introduced to verify this phenomenon. The calculation demonstrates that, with a cover of ductile MnS, stress concentration around the composite inclusion is significantly decreased as compared with the single Al2O3 inclusion in the test steel.

Microstructure Examinations in Corners of the Low-Carbon Steel Slabs from Continuos Caster Machine

Abstract The exposed selvedge layers in slabs cast by the continuous process should be free from surface defects, which in most cases appear in the form of cracks on the casting surface and run to its interior. In addition to the parameters of the casting process, the occurrence of such defects depends on the chemical composition of cast steel, on the segregation of surface active elements and formation of the precipitates of carbides, nitrides and other phases. Due to the frequent occurrence of defects in corners of the slabs, non-destructive testing was performed on the mechanically cleaned surfaces of slabs. The test material was low-carbon API(American Petroleum Institute API 5L standard) steel micro alloyed with Nb and Ti designed for the production of pipes to handle gas, oil and other liquid and gaseous fuels. Despite the use of different methods of inspection, i.e. ultrasonic, magnetic particle and penetrant, cracks were not traced in the examined material. Then, from the corners of the examined slabs, specimens were cut out for metallographic examinations. The main purpose of these examinations was to disclose the presence of possible cracks and micro cracks on the surfaces transversal and longitudinal to the direction of casting. At the same time, studies were conducted to establish the number and morphology of non-metallic inclusions in selvedge layers of the slab corners and axis. Additionally, hardness of the slabs was measured. The conducted studies revealed only some minor differences in the slab hardness along its axis (130 ÷ 135 HB) and in selvedge layers (120 ÷ 123 HB).

Features of Nonmetallic Inclusion Formation and Evolution During Ladle Treatment and Continuous Casting of Special Alloy Steels

Features of nonmetallic inclusion formation and evolution in special alloy steels during ladle treatment and continuous casting are studied for special alloy steel 40Kh. The main differences in types, sizes, and morphology of nonmetallic inclusions in relation to steel deoxidation scheme are analyzed. It is established that the composition of more than 97% of oxide inclusions present belongs to CaO–Al2O3–SiO2, Al2O3–MgO–SiO2, CaO–Al2O3–MgO, CaO–Al2O3–MgO~5% SiO2, Al2O3–MnO–SiO2 systems. The main factors that affect the formation of aluminum-magnesium spinel are determined. It is shown that a non-optimal slag regime in a tundish leads to formation of silicate inclusions with cross section of more than 1000 μm2, even with a steel aluminum content more than 0.015 wt.%.

Effect of Structure Factor on High-Temperature Ductility of Pipe Steels

Effects of various factors such as the grain size, the morphology of nonmetallic inclusions, and joint microalloying with boron and titanium on the high-temperature ductility of pipe steels are studied. Physical modeling of the conditions of cooling of the skin of a continuous-cast preform in the zone of secondary cooling in a Gleeble facility is performed. Technical recommendations are given for raising the hot ductility of steels under industrial conditions.

Structure Formation and Corrosion Resistance of Austenitic Steel Treated with High-Temperature Energy Sources

The results obtained in investigations of stress corrosion specimens of 08Cr18Ni10Ti steel, produced by welding with electrodes with basic and rutile coatings, are discussed. We present the results of metallographic analysis of the surface of corrosion failure. Investigation of stress corrosion cracking tests performed by automatic measurement of deflection patterns, depending on the test time, using the displacement sensor. We found that two structural factors – structure homogeneity of weld metal and morphology of non-metallic inclusions – provide high corrosion resistance. The experimental results show that the metal of the welded joints in the high-alloy chromium-nickel austenitic steels produced with the electrodes with a basic coating has higher resistance to corrosion failure in the corrosive medium of chloride salts in comparison with the weld metal produced with the rutile electrodes.

Effect of complex inoculation of a high-strength shipbuilding steel on the composition and morphology of nonmetallic inclusions

The effect of inoculating a high-strength shipbuilding steel with flux-cored wires containing FeCa and FeCa in a complex with rare-earth metals (REMs) on the distribution, composition, and morphology of nonmetallic inclusions is investigated. It is shown that inoculation with both FeCa and FeCa in combination with REMs with the calcium and cerium content of the metal within 0.002–0.003% for each of them allows obtaining a high-strength shipbuilding steel with a low level of contamination by nonmetallic inclusions.

Experimental Study on the Formation of Non-Metallic Inclusions Acting as Nuclei for Acicular Ferrite in HSLA Steels through Specific Deoxidation Practice and Defined Cooling Conditions

Specific types of non-metallic inclusions are known to act as heterogeneous nuclei for the formation of acicular ferrite, which provides excellent toughness. By increasing the amount of acicular ferrite in the microstructure, the properties of HSLA steels can be optimized significantly.Although the formation of acicular ferrite caused by heat treatments (thermomechanical treatments or welding) is quite well described in literature, there is less information to find about the formation of acicular ferrite immediately out of the liquid melt. Within the present study experiments on laboratory scale are carried out simulating the influence of cooling conditions and Ti-content on size, chemical composition and morphology of non-metallic inclusions and consequently on the amount of acicular ferrite. All experiments were carried out with a dipping test simulator enabling very well controllable cooling conditions. Optical microscopy in combination with special etching methods as well as SEM/EDS-analysis was used for microstructure and inclusion characterization.

Wide – Ranging Influence of Mischmetal on Properties of GP240GH Cast Steel

Abstract This paper presents influence of rare earth metals (REM) on the properties of GP240GH cast carbon steel. The research has been performed on successive industrial melts. Each time ca 2000 kg of liquid metal was modified. The rare earth metals were put into the ladle during tapping of heat melt from the furnace. Because of this the amount of sulphur in the cast steel was decreased and the non-metallic inclusion morphology was significantly changed. It was found that non metallic inclusions the cracking mechanism of Charpy specimens and the impact strength were all changed. The following properties were tested: mechanical properties (σy, σUTS), plastic properties (necking, elongation) and impact strength (SCI). In the three-point bend test the KJC stress intensity factor was evaluated.

Modification of Non-Metallic Inclusions by Rare-Earth Elements in Microalloyed Steels

Modification of Non-Metallic Inclusions by Rare-Earth Elements in Microalloyed Steels The modification of the chemical composition of non-metallic inclusions by rare-earth elements in the new-developed microalloyed steels was discussed in the paper. The investigated steels are assigned to production of forged elements by thermo-mechanical treatment. The steels were melted in a vaccum induction furnace and modification of non-metallic inclusions was carried out by the michmetal in the amount of 2.0 g per 1 kg of steel. It was found that using material charge of high purity and a realization of metallurgical process in vacuous conditions result in a low concentration of sulfur (0.004%), phosphorus (from 0.006 to 0.008%) and oxygen (6 ppm). The high metallurgical purity is confirmed by a small fraction of non-metallic inclusions averaging 0.075%. A large majority of non-metallic inclusions are fine, globular oxide-sulfide or sulfide particles with a mean size 17 μm2. The chemical composition and morphology of non-metallic inclusions was modified by Ce, La and Nd, what results a small deformability of non-metallic inclusions during hot-working.

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.