Characterization Of Non-metallic Inclusions Research Articles

Characterization of Nonmetallic Inclusions in Different Ferroalloys used in the Steelmaking Processes

Ferroalloys are one of the most important raw materials widely used in the steelmaking processes. Depending on the cleanliness of used ferroalloys, they can be an inevitable source of impurities and nonmetallic inclusions (NMIs) in steelmaking products. Herein, the inclusions in five different industrial ferroalloys (FeTi, FeMo, FeW, MnN, and FeCrN) are investigated. This is done using 2D investigations on polished cross sections of ferroalloy samples and using 3D investigations of NMIs on film filters and metal surfaces after electrolytic extraction (EE) using scanning electron microscopy in combination with energy‐dispersive spectroscopy (SEM‐EDS). Moreover, the characteristics of the main types of inclusions presented on film filters and metal surfaces after EE are compared and their possible transformations in Al‐killed steel are evaluated. The results show that the main inclusions are more likely the oxidization products of the reductant and some unreduced ore during the ferroalloy production process. The 3D investigations of inclusions on metal surfaces after extraction are found to be very useful in detection and evaluation of larger‐sized inclusions. Overall, this study helps to better understand the impurities in different ferroalloys and their possible effect on the steel cleanliness.

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.

Separation of non-metallic inclusions from high strength low alloy steel by electromagnetic stirring

Non-metallic inclusions are the impurities that solidified during steel continuous casting. The compositions, sizes and shapes of inclusions significantly affect the steels’ mechanical properties such as ductility, formability and toughness. This paper mainly focuses on the observation and characterization of non-metallic inclusions in high strength low alloy steels, and especially is devoted to the homogenization of molten steel within the copper mold of continuous casters, as the primary purpose of this project is to discover the optimum operation parameters for electro-magnetic stirrers surrounding the copper mold. In this paper, non-metallic inclusions in high strength low alloy steel were observed and characterized, and separation of non-metallic inclusions from high strength low alloy steel by electromagnetic stirring was specifically studied. The nonmetallic inclusions in the billet can be greatly reduced when the electromagnetic stirring parameters of the mold are 300 A current and 3 Hz EMS frequency.

Application of Some Modern Analytical Techniques for Characterization of Non-Metallic Inclusions in a Fe-10mass%Ni Alloy Deoxidized by Ti/Zr and Ti/Mg

In this study, a complete and comprehensive analysis of non-metallic inclusions (NMI) in an Fe-10%Ni alloy was done by using two modern analytical methods that complement each other: Electrolytic Extraction (EE) of inclusions from metal samples followed by investigations by using Scanning Electron Microscopy (SEM) and Fractional Gas Analysis (FGA). The composition, morphology, size and number of different NMIs and clusters were investigated in metal samples taken after deoxidation by additions of Ti, Ti/Zr and Ti/Mg. The obtained results were discussed with respect to formation, modification and removal of NMIs and clusters depending on the type of deoxidations and the holding time. It was found that the peaks of oxygen reduced from different oxide inclusions obtained by the FGA measurements corresponded well to the main types of inclusions and clusters observed by using the EE + SEM method. More specifically, the total O content in oxide inclusions (ONMI) increases by 10% after a Zr addition and then decreases linearly by 40% during 5 min of holding due to flotation of NMIs and clusters. However, after a Mg addition in the melt deoxidized by Ti, the ONMI content decreases drastically by 63% during 5 min of holding, due to a fast floatation of NMIs caused by bubbles of vaporized Mg.

Characterization of Non-metallic Inclusions and Clusters during Production of Low-carbon IF Steel

Characterization of Non-metallic Inclusions and Clusters during Production of Low-carbon IF Steel

Characterization of non-metallic inclusions in corrosion -resistance nickel - based EP718 and 718 alloys by using electrolytic extraction method

It is known that non-metallic inclusions (NMI) that are formed during steel production and heat treatment can significantly affect the properties of final steel products. Therefore, it is very important to be able to determine the content of harmful NMI in steels. Nickel-based alloys are widely used in the oil and gas recovery industry, due to a good combination of strength and corrosion properties. Earlier studies have shown that the corrosion properties in immersion test and electrochemical tests for Ni-based EP718 alloys are slightly lower than that for 718 alloys. The focus in this study was the influence of different NMI on the corrosion resistance of these alloys. The characteristics of inclusions (such as size, morphology, and chemical composition) were analysed by using the electrolytic extraction method followed by three-dimensional investigations using SEM in combination with EDS. It was found that some non-metallic inclusions in EP718 alloys significantly reduce its corrosion resistance. It was also shown that a primary dissolution of the metal matrix occurs around certain inclusions during electrolytic extraction. Based on obtained results, the corrosion active non-metallic inclusions can be determined in these Nickel-base alloys and some recommendations for optimization of their production technology can be formulated.

Characterization of Nonmetallic Inclusions in 18CrNiMo7-6

The detrimental effect of nonmetallic inclusions (NMIs) in steels on, e.g., fatigue lifetime is well known. In order to increase the durability and safety of materials and components, inclusion control and a deep understanding of inclusion formation are essential. The present study examines the formation of inclusions as well as their content, type, morphology, and size distribution for different batches of the steel alloy 18CrNiMo7-6 (AISI 4317), which was processed with various refractory crucible materials. To this end, extensive metallographic investigations were carried out including fracture surface analyses, metallographic sections, and the chemical extraction of inclusions. Scanning electron microscopy supported by energy-dispersive X-ray spectroscopy was used alongside electron backscatter diffraction for the qualitative and quantitative analysis of the NMIs. Oxide contents were found to have a significant effect on sulfide precipitation behavior, and had a strong impact on the resulting sizes and numbers of inclusions. The formation and growth of sulfides and oxide-sulfides featuring different morphologies is discussed on the basis of these experimental results.

Characterization of non-metallic inclusions and their influence on the mechanical properties of a FCC single-phase high-entropy alloy

The characteristics of non-metallic inclusions (NMI) that precipitated in an equiatomic CoCrFeMnNi high-entropy alloy (HEA) were investigated in order to understand their effect on the mechanical properties of the HEA. As the existence of NMI could degrade the mechanical properties, improved information concerning NMI could hold key importance in controlling the promising applications of HEA. An equiatomic HEA composed of CoCrFeMnNi was manufactured using vacuum induction melting (VIM) method. A thermodynamic computation program (FactSage™7.0) was used to investigate the solidification process of the HEA at both equilibrium and non-equilibrium states. Furthermore, the computational program also predicted the type of inclusions that would precipitate. Through an electrolytic extraction process and scanning electron microscopy - energy dispersive spectroscopy (SEM-EDS) observations, the actual compositions of the precipitated inclusions were observed and classified as (a) Mn-Cr-Al oxide, (b) Mn(S,Se), and (c) mixed type; a Mn-Cr-Al oxide core with a Mn(S,Se) shell. Mn-Cr-Al oxide, in a brittle spinel-structured phase with high melting temperature, was also observed in dimples on the fracture surface. The relationship between the tensile properties of HEA and the characteristics of NMI were discussed by comparing two CoCrFeMnNi specimens with the same structure and composition. Overall, the present results indicate that the tensile properties of the HEA were significantly degraded as the area fraction (AF) and number density (ND) of NMI increased.

Characterization of Non-Metallic Inclusions in API Steel Grades Using Automated Energy Dispersive X-Ray

Non-metallic inclusions in API steel grades deteriorate steels’ mechanical properties and their resistance to hydrogen induced cracking. The formation and evolution of inclusion during liquid steel processing was investigated by analyzing samples taken from different stages of the steel making process in API X52 and X60 steel grades. Scanning electron microscope (SEM) with automated feature EDX analyzer (INCAF 250) was used to identify each inclusion in terms of its size, area and composition. It was found that non-metallic inclusions in API X52 and X60 grades from steelmaking and casting samples were mainly Al2O3, Ca–Al and Ca-Mg-Al. In this work changes in inclusion composition, size and area fraction from ladle processing to casting were mapped and this information was used to improve steel cleanness and product quality.

Characterization and Analysis of Non-Metallic Inclusions in Low-Carbon Fe-Mn-Si-Al TWIP Steels

A characterization of non-metallic inclusions in Fe–Mn–Si–Al twinning-induced plasticity (TWIP) steels during argon oxygen decarburization–electroslag remelting–forging (AOD–ESR–forging) process has been performed. The two main kinds of inclusions found in TWIP–AOD ingots are single Al(O)N and MnS(Se)–Al(O)N aggregates. After the ESR process, Al(O)N and MnS(Se) inclusions in all size ranges significantly decrease while other kinds of inclusions show only minor changes. In the present study, the precipitation, growth, and dissolution of AlN and MnS inclusions have been analyzed by thermodynamics and kinetics. It is found that AlN inclusions in TWIP steels can already precipitate in the liquid. Furthermore, AlN inclusions precipitated in the liquid TWIP steels can act as the heterogeneous nuclei of MnS inclusions, and thus forming Al(O)N and MnS(Se) · Al(O)N clusters. After ESR refining, the precipitation temperature of AlN and MnS inclusions will be significantly decreased, and AlN inclusions cannot be formed in the liquid TWIP steels in particular. The kinetic analysis show that the growth of AlN inclusions will be difficult during the ESR process, because their growth rate decreases significantly, while the dissolution rate increases.

Application of Different Extraction Methods for Investigation of Nonmetallic Inclusions and Clusters in Steels and Alloys

The characterization of nonmetallic inclusions is of importance for the production of clean steel in order to improve the mechanical properties. In this respect, a three-dimensional (3D) investigation is considered to be useful for an accurate evaluation of size, number, morphology of inclusions, and elementary distribution in each inclusion particle. In this study, the application of various extraction methods (chemical extraction/etching by acid or halogen-alcohol solutions, electrolysis, sputtering with glow discharge, and so on) for 3D estimation of nonmetallic Al2O3inclusions and clusters in high-alloyed steels was examined and discussed using an Fe-10 mass% Ni alloy and an 18/8 stainless steel deoxidized with Al. Advantages and limitations of different extraction methods for 3D investigations of inclusions and clusters were discussed in comparison to conventional two-dimensional (2D) observations on a polished cross section of metal samples.

Influence of aluminum content on the characterization of microstructure and inclusions in high-strength steel welds

The present study describes the methods for the characterization of the microstructure of welded joints from test welds. This comprises the analysis of the solidification microstructure (primary and secondary dendrite arm spacing) as well as the former austenite grain size and the final phase distribution. The main focus is the characterization of nonmetallic inclusions by means of SEM/EDX and light microscopy. Based on already-developed prototypes with a weld yield strength of more than 800 MPa, different kinds of inclusions and precipitates have been assessed with respect to grain refinement and the resulting impact on strength and ductility. The effect of aluminum, in the range 90 to 800 ppm, on the microstructure and the mechanical properties of high-strength steel weld metals has been studied and it has been found that at low aluminum contents good values for the tensile strength and the toughness could be obtained. The results of metallographic investigations of test welds with different alloy compositions are presented. The results indicate a significant change of the size distribution, the morphology, and the composition of the inclusions. These results are finally compared with results from literature and discussed with respect to the expected influence on the mechanical properties of the welded joint.

Characterization of Nonmetallic Inclusions in High-Manganese and Aluminum-Alloyed Austenitic Steels

The effects of Al and Mn contents on the size, composition, and three-dimensional morphologies of inclusions formed in Fe-xMn-yAl (x = 10 and 20 mass pct, y = 1, 3, and 6 mass pct) steels were investigated to enhance our understanding of the inclusion formation behavior in high Mn-Al–alloyed steels. By assuming that the alumina is a dominant oxide compound, the volume fraction of inclusions estimated from the chemical analysis, i.e., insoluble Al, in the Fe-Mn-3Al steels was larger than the inclusion volume fractions in the Fe-Mn-1Al and Fe-Mn-6Al steels. A similar tendency was found in the analysis of inclusions from a potentiostatic electrolytic extraction method. This finding could be explained from the terminal velocities of the compounds, which was affected by the thermophysical properties of Fe-Mn-Al steels. The inclusions formed in the Fe-Mn-Al–alloyed steels are classified into seven types according to chemistry and morphology: (1) single Al2O3 particle, (2) single AlN or AlON particle, (3) MnAl2O4 single galaxite spinel particle, (4) Al2O3(-Al(O)N) agglomerate, (5) single Mn(S,Se) particle, (6) oxide core with Mn(S,Se) skin (wrap), and (7) Mn(S,Se) core with Al2O3(-Al(O)N) aggregate (or bump). The Mn(S,Se) compounds were formed by the contamination of the steels by Se from the electrolytic Mn. Therefore, the raw materials (Mn) should be used carefully in the melting and casting processes of Fe-Mn-Al–alloyed steels.

Characterization of Non-Metallic Inclusions in Superelastic NiTi Tubes

Non-metallic inclusions have been shown frequently to lead to crack initiation in superelastic Nitinol fatigue specimens. While prior studies suggested that both carbide (TiC) and oxide (Ti4Ni2Ox) inclusions can develop in superelastic Nitinol alloys, questions remain on whether or how the chemistry and morphology of these non-metallic inclusions are affected by the melting and subsequent tube manufacturing process. In the present study, samples of Ti-55.8wt.%Ni alloy were taken from tubes fabricated from materials of various VIM and VAR melt processes. Additional samples were taken from various stages of the tube drawing process for studying the stringer formation. Our results suggest that both carbide and oxide inclusions are present in VIM/VAR materials and the oxide break-down during tube drawing appears to be the primary mechanism for stringer formation. Carbides in VIM materials generally remain as isolated particles during tube fabrication while the primary inclusion of oxide in the VAR material explains its higher stringer density. In addition, the carbide inclusion has been confirmed to contain a noticeable amount of oxygen; hence, we suggest the “Ti(C, O)” nomenclature. Further study on the role of oxygen on carbide and oxide formation in VIM/VAR materials may be beneficial for improving the future melt quality of NiTi alloys.

Fast Scanning Laser-OES. I. Characterization of Non-metallic Inclusions in Steel

Pulsed laser sources with high repetition rates, high beam quality and pulse-to-pulse stability are available since few years. These sources can be applied to micro-analytical scanning techniques requiring high number of laser pulses in a short time, low signal deviation and good focusability. A scanning laser-induced optical emission spectrometer (Laser-OES) using such a laser source was built up and applied to steel cleanness analysis. This novel analytical technique enables to distinguish between different inclusion types based on their chemical compositions. Coincidences of high intensity peaks for single elements at the same co-ordinates can be connected to specific inclusion types.

Fast Scanning Laser-OES. II. Sample Material Ablation and Depth Profiling in Metals

For the characterization of non-metallic inclusions in steel samples, a fast scanning laser-induced optical emission spectrometer (Laser-OES) was developed. In this second part of the series, the correlation between Laser-OES signal intensities and depth profiles and crater geometries as well, was investigated by scanning electron-beam microscopy (SEM) and confocal microscopy. The influence of the laser pulse energy on the crater topography in the sample surface is described.