Inclusions In Steel Research Articles

Effect of Al–Ti Concentration on Alumina Inclusions Aggregation Floating Behavior in Molten IF Steel

Understanding the aggregation‐floating behavior of alumina inclusions, which is influenced by the interface properties between inclusions and molten steel, is crucial to control the purity of interstitial‐free (IF) steel in the refining process. In this work, it is attempted to investigate the effect of aluminum and titanium concentrations on the aggregation‐floating behavior of alumina inclusions in the interior of IF molten steel based on the interface properties between molten steel and alumina inclusions. The interface properties between the molten steel and alumina inclusions are measured using an improved sessile drop method. And, the aggregation‐floating behavior of inclusions in the interior of molten steel is quantitatively discussed by an aggregation model based on the attractive force between alumina inclusions, which was combined with the interface properties. In the results, it is shown that the attractive forces between alumina inclusions, ranging from 6.96 × 10−6 to 5.41 × 10−5 N, increase and decrease, respectively, with increasing aluminum and titanium concentrations. Furthermore, the terminal floating speeds of alumina inclusions, ranging from 0.0510 to 0.0873 m s−1, increase and decrease, respectively, with increasing aluminum and titanium concentrations.

Recyclate-containing magnesia-carbon refractories – Influence on the non-metallic inclusions in steel

The fabrication of MgO–C refractories containing MgO–C recyclates is a current approach for saving resources and energy. However, it must be ensured that the steel quality is not adversely affected, particularly with regard to non-metallic inclusions. The present study investigates MgO–C refractories containing different proportions of MgO–C recyclates (up to 83%) in contact with 16MnCr5 steel melt and a slag. A recyclate-free MgO–C material served as a reference. The tests were performed in a steel-casting simulator. By an automated feature analysis of the solidified steel, manganese sulfide and complex alumina-manganese sulfide inclusions were found to be the predominant ones in all steel samples. No negative influence of the recyclate on the inclusion count and the size distribution of the inclusions, the latter being determined for the sum of alumina and alumina-manganese sulfide as well as for the manganese sulfide inclusions, was observed.

Formation and aggregation behavior of inclusions in Ni-based alloys with different Mg contents

Large non-metallic inclusions affect the mechanical properties and service life of nickel-based superalloys. This study investigates the effects of magnesium elements on non-metallic inclusions in K4169 nickel-based superalloys, exploring the formation mechanisms and aggregation relationships of the inclusions. Four gradients of the magnesium content were used to simulate the erosion of MgO refractories on inclusions in the vacuum induction melting of nickel-based superalloys. The observed inclusions mainly comprised MgO, TiN, MgAl2O4, and MgAl2O4–TiN composites. To study the formation mechanism of inclusions in Ni-based alloys with different Mg contents, the predominance diagram of Mg–Al–Ti–O inclusions in nickel-based superalloy systems was calculated using Factsage thermodynamics software and classical thermodynamics separately. The aggregation behavior of MgAl2O4 and MgO inclusions on the surface of molten nickel-based superalloys was observed in situ under a high-temperature confocal laser scan microscope. The capillary force acting on inclusions in nickel-based superalloys was calculated using the Kralchevsky–Paunov model (K–P model), the calculation was verified with experimental results, and the influencing factors were analyzed. The capillary force acting on inclusions on the surface of molten nickel-based superalloys weakened in the order of MgAl2O4 > MgO > Al2O3, which is the opposite of the order for the force acting on inclusions in molten steel. Minimizing the magnesium content in the alloy is crucial to preventing the formation of large inclusions in nickel-based superalloys, and the use of magnesium-containing materials in the smelting process should thus be avoided.

Microstructure features induced by fatigue crack initiation up to very-high-cycle regime for an additively manufactured aluminium alloy

Fatigue failure can still occur beyond 107 cycles, i.e. very-high-cycle fatigue (VHCF), in many metallic materials, such as aluminium alloys and high-strength steels. For VHCF of high-strength steels, a fine granular area (FGA) surrounding an inclusion is commonly identified as the characteristic region of crack initiation on the fracture surface. However, no such FGA feature and related crack initiation behaviour were observed in VHCF of conventionally cast or wrought aluminium alloys. Here, we first reported the distinct mechanisms of crack initiation and early growth, namely the microstructure feature and the role of FGA in VHCF performance for an additively manufactured (AM) AlSi10Mg alloy. The AM pores play a key role in fatigue crack initiation similar to that of the inclusions in high-strength steels, resulting in almost identical FGA behaviour for different materials under a range of mean stress with a stress ratio at R < 0 or R > 0. The profile microstructure of FGA is identified as a nanograin layer with Si rearrangement and grain boundary transition. This process consumes a large amount of cyclic plastic energy making FGA undertake a vast majority of VHCF life. These results will deepen the understanding of VHCF nature and shed light on crack initiation mechanism of other aluminium and AM alloys.

Phase diagrams of oxide system FeO–MnO–MgO–SiO2. Report 1. Binary oxide systems MnO–SiO2 and MgO–SiO2

Manganese and silicon are present in almost any steel, and magnesium can enter the metal from the lining and magnesian slags or be introduced in the form of an alloy, so knowledge of the thermodynamics and phase equilibria of liquid and solid silicate solutions allows to predict the appearance of non-metallic inclusions in steel. The FeO–MnO–MgO–SiO2 system includes six double and four triple phase diagrams of oxide systems. The binary phase diagrams of FeO–MnO, FeO–MgO, FeO–SiO2, and MnO–MgO oxide systems were previously studied. In this work, the phase diagrams of the MnO–SiO2 and MgO–SiO2 systems were considered, the liquidus lines and thermodynamic data on the melting of manganese and magnesium silicates – the enthalpies and entropies of melting of ortho- and metasilicates of manganese (Mn2SiO4 and MnSiO3) and magnesium (Mg2SiO4 and MgSiO3) were calculated. The theory of subregular ionic solutions, which takes into account the dependence of the coordination number on the melt composition, is used to calculate the activities of the components of the oxide melt and accurately describes the diagrams with two immiscible liquids and is consistent with the experimental data presented in the literature. The obtained data on the energy parameters of the theory of subregular ionic solutions for the systems MnO–SiO2 and MgO–SiO2, as well as the thermodynamic data on the formation of manganese and magnesium silicates, make it possible to proceed to the study of ternary oxide systems belonging to the FeO–MgO–MnO–SiO2 system.

Phase diagrams of oxide system FeO–MnO–MgO–SiO2. Report 1. Binary oxide systems MnO–SiO2 and MgO–SiO2

Manganese and silicon are present in almost any steel, and magnesium can enter the metal from the lining and magnesian slags or be introduced in the form of an alloy, so knowledge of the thermodynamics and phase equilibria of liquid and solid silicate solutions allows to predict the appearance of non-metallic inclusions in steel. The FeO–MnO–MgO–SiO2 system includes six double and four triple phase diagrams of oxide systems. The binary phase diagrams of FeO–MnO, FeO–MgO, FeO–SiO2, and MnO–MgO oxide systems were previously studied. In this work, the phase diagrams of the MnO–SiO2 and MgO–SiO2 systems were considered, the liquidus lines and thermodynamic data on the melting of manganese and magnesium silicates – the enthalpies and entropies of melting of ortho- and metasilicates of manganese (Mn2SiO4 and MnSiO3) and magnesium (Mg2SiO4 and MgSiO3) were calculated. The theory of subregular ionic solutions, which takes into account the dependence of the coordination number on the melt composition, is used to calculate the activities of the components of the oxide melt and accurately describes the diagrams with two immiscible liquids and is consistent with the experimental data presented in the literature. The obtained data on the energy parameters of the theory of subregular ionic solutions for the systems MnO–SiO2 and MgO–SiO2, as well as the thermodynamic data on the formation of manganese and magnesium silicates, make it possible to proceed to the study of ternary oxide systems belonging to the FeO–MgO–MnO–SiO2 system.

Development of technological solutions to improve the quality of railway rails by improving the technology of smelting, out-of-furnace processing and continuous casting of rail electric steel.

Based on a complex of metallographic and X-ray phase studies for the conditions of EVRAZ ZSMK, which is a leading domestic manufacturer of railway rails, the nature of characteristic defects of rails of metallurgical origin has been determined. These defects, which are the cause of rejection of rails during ultrasonic quality control in the flow of rail-block mill, are stratifications, in the localities of which accumulations of silicate, alumina and sulfide non-metallic inclusions are concentrated; at the same time, these defects in the vast majority of cases are located in the neck of the rail profiles. Analysis of contamination with non-metallic inclusions of suitable rails of the current production of EVRAZ ZSMK showed that, unlike the locations of defects in rejected rails, alumina non-metallic inclusions have an extremely low concentration, while manganese sulfides and silicate inclusions have the highest relative concentration. Based on the results obtained, technological measures were developed, pilot-industrial and implemented to improve the production technology of rail steel in the conditions of the electric steelmaking workshop of EVRAZ ZSMK. In order to reduce the concentration of oxide nonmetallic inclusions in rail steel, a new technology of ladle treatment of steel using a low-ash carburizer and calcium carbide for slag deoxidation has been developed. To reduce sulfide inclusions contamination, measures have been implemented to ensure the sulfur content in the finished steel at a level of no more than 0.008%. The optimization of the modes of electromagnetic mixing in the mold and the temperature regimes of continuous casting of steel was carried out, which also had an effect on reducing the concentration of non-metallic inclusions in continuously cast billets of rail steel and finished rails. The introduction of a set of these technological solutions and measures allowed to reduce the rejection of rails for internal defects from 7% to less than 2%

Development of technological solutions to improve the quality of railway rails by improving the technology of smelting, out-of-furnace processing and continuous casting of rail electric steel.

Based on a complex of metallographic and X-ray phase studies for the conditions of EVRAZ ZSMK, which is a leading domestic manufacturer of railway rails, the nature of characteristic defects of rails of metallurgical origin has been determined. These defects, which are the cause of rejection of rails during ultrasonic quality control in the flow of rail-block mill, are stratifications, in the localities of which accumulations of silicate, alumina and sulfide non-metallic inclusions are concentrated; at the same time, these defects in the vast majority of cases are located in the neck of the rail profiles. Analysis of contamination with non-metallic inclusions of suitable rails of the current production of EVRAZ ZSMK showed that, unlike the locations of defects in rejected rails, alumina non-metallic inclusions have an extremely low concentration, while manganese sulfides and silicate inclusions have the highest relative concentration. Based on the results obtained, technological measures were developed, pilot-industrial and implemented to improve the production technology of rail steel in the conditions of the electric steelmaking workshop of EVRAZ ZSMK. In order to reduce the concentration of oxide nonmetallic inclusions in rail steel, a new technology of ladle treatment of steel using a low-ash carburizer and calcium carbide for slag deoxidation has been developed. To reduce sulfide inclusions contamination, measures have been implemented to ensure the sulfur content in the finished steel at a level of no more than 0.008%. The optimization of the modes of electromagnetic mixing in the mold and the temperature regimes of continuous casting of steel was carried out, which also had an effect on reducing the concentration of non-metallic inclusions in continuously cast billets of rail steel and finished rails. The introduction of a set of these technological solutions and measures allowed to reduce the rejection of rails for internal defects from 7% to less than 2%

Investigation of the Precipitation and Solid Solution Behavior of TiN Inclusions in SWRH92A High‐Carbon Tire Cord Steel

TiN, a typical nonmetallic titanium inclusion, is regarded harmful for the quality of hypereutectoid tire cord steel. At present, the effective methods of controlling the TiN inclusions in the high‐carbon tire cord steel are still uncertain. Herein, the precipitation and solid solution behavior of the TiN inclusions in SWRH92A tire cord steel are studied. The main characteristics, e.g., size distribution and morphology, of the TiN inclusions precipitated under different steel remelting conditions (e.g., Ti and N concentrations and cooling rate) are analyzed. The results indicate that the average TiN inclusion size is proportional to the Ti and N concentration product, and Ti shows larger effect on the TiN inclusion size than N. For the samples with heat treatment, the number percentage and average size of larger TiN inclusions decrease compared with reference sample. As heating temperature increases from 1150 to 1250 °C, the total TiN inclusion number decreases, and the number percentage and average size of larger TiN inclusions decrease. After heating, the sample with a higher cooling rate has a higher number percentage of finer inclusions and the average size of larger inclusions is smaller, indicating that increasing cooling rate is helpful to refining the TiN inclusions.

Investigation of Evolution of Inclusions in 15-5PH Stainless Steel During Hot Compression Using 3D X-Ray Microscopy

Investigation of Evolution of Inclusions in 15-5PH Stainless Steel During Hot Compression Using 3D X-Ray Microscopy

Eddy Current False Indications in Austenitic Steel and Titanium Alloys Heat Exchanger Tubes Activated by Stress

Eddy current non-destructive examination with the internal bobbin type probes is a mandatory test for heat exchanger tube manufacturing due to its high sensitivity to the different type discontinuities. In this paper, we want to highlight the problems related to the false indications in the nonmagnetic austenitic steel and titanium alloys due to magnetic inclusions. There are known origins for magnetic inclusions in stainless steel like chips or filings as a result of ferrous tool application, alloy depletion concerned with oxidation or corrosion, and magnetite deposits. The little-known origin of magnetic inclusions is concerned with stress induced martensitic transformation is shortly analyzed in this report as a possible mechanism for the creation of the magnetic inclusion in austenitic steel as in titanium alloy tubes. The phase transformation and as the result the presence of magnetic inclusions is generated by the activation of the spin magnetic moments of the free electrons under stress influence. These inclusions can radically influence the eddy current signal due to quite large difference in relative magnetic permeability but can be differentiated from real defects by re-inspection of the suspicious tubes at reduced operational frequency. During the eddy current examinations of stainless steel and titanium tubes by an internal probe, the false indications in tubes have been detected. The presence of these isolated indications is located always in the same length of the tested tube. The indications were detected in each tube and the signal amplitude was estimated in the range of 40-50% of the acceptance reference level. In stainless steels, the false indications generated are higher than in titanium alloys.

MECHANICAL AND DURABILITY STUDY ON STEEL AND GLASS FIBERS BASED CEMENTITIOUS COMPOSITE

The study targets the utilization of steel and glass fibers in developing engineered cementitious composite. Compressive strength (CS) tests, split tensile strength (ST) tests, and static flexure tests were conducted to comment on the mechanical behavior of the composites. The durability properties of the designed mixes are commented on using rapid chloride penetration (RCPT) and sulfate tests. The CS of the conventional mix C-40 is compared with the S-ECC and G-ECC. The tested G-ECC specimens were more ductile than the S-ECC specimens and their respective variants. The S-ECC produced better results for both the CS and ST tests than the S-ECC and its variants. The conventional mixes of C-40 resulted in high penetration values than the composites prepared with steel and glass fiber inclusion. The destruction of the aluminosilicate skeleton, which leads to the liberation of silicic acid and sodium ions, is responsible for the deterioration caused during sulfate attack tests.

Effects of Na2O, K2O and B2O3 on Deformability of SiO2-MnO-Al2O3 Inclusion in High-Carbon Steel

Cord steel is used for making tire frames and wire saws for cutting silicon wafers. The diameter of mainstream cutting wire has been developed to be lower than 100 μm. The size and deformation ability of inclusions are very important to the wire breaking rate of cord steel during the drawing process. In order to improve the deformation ability of the inclusions in cord steel, alkali metal oxide was added into the molten steel to improve the inclusions in the steel so as to obtain good, plastic, low-melting-point inclusions. Mass fractions of 0.3%, 0.5% and 1.0% K2CO3, Na2CO3 and B2O3 were added into cord steel, which were melted in 10 furnaces (including 0% alkali metal oxides, mass fractions of 0.3%/0.5%/1.0% K2CO3, Na2CO3 and B2O3). The morphology and composition of inclusions were observed by SEM-EDS. Factsage phase diagram calculations and experimental results show that, with the increase in Na2CO3 content in cord steel, the aluminum content in the inclusions gradually decreased. When the mass fraction of Na2CO3 was 0.5% per ton, most of the inclusions in the steel fell in the low melting point region (less than 1300 °C). With the increase in K2CO3 content in cord steel, the silicon content in the inclusions decreased gradually. When the mass fraction of K2CO3 was 0.5% per ton, most of the inclusions in the steel fell in the low melting point region. The deformation ability of the inclusions added with 0.5% Na2CO3 in the steel during forging was better than that of the inclusions added with 0.5% K2CO3. After adding B2O3, the inclusions in the steel were SiO2-MnO-Al2O3 inclusions or inclusions with SiO2-MnO-Al2O3 as the core and BN wrapped around. Boron could not be dissolved into the inclusions for plastic modification.

Study on the Evolution Law of Inclusions in the Whole Process and Evaluation of Cleanliness in Start and End of Casting Billets of 42CrMo-S Steel

To investigate the evolution law of inclusions in 42CrMo-S steel, this paper samples and analyzes the steel during its refining process as well as the head and tail billets. An oxygen and nitrogen analyzer, a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectrometry (EDS), and an ASPEX automatic inclusion scanning electron microscope are employed to analyze the cleanliness level of the molten steel in the refining stage and the head and tail billets. The results demonstrate that the total oxygen content at the end of LF slagging is 10.2 ppm, indicating that the refining slag has an excellent deoxygenation effect. During the RH refining process, the total oxygen content of the molten steel diminishes to less than 10 ppm and reaches 6.3 ppm at end-RH. The nitrogen content in the molten steel gradually increases during the smelting process and attains 65 ppm at end-RH. Upon arrival at LF, pure Al2O3 plays the role of the primary inclusions in the molten steel. Afterwards, the pure Al2O3 inclusions transform into Mg-Al spinel-type inclusions, Al2O3-MgO-CaO inclusions, and Al2O3-CaO inclusions. The number of CaS-type inclusions in the steel reaches the maximum after feeding the S wire. In the RH refining stage, the percentage of inclusions with a size less than 5 μm is maintained above 90%. Finally, the cleanliness level of the head and tail billets (the start and end of a casting sequence) is analyzed, and it is recommended that the cut scrap length for the head billet is 0.3 m and the reasonable cutting scrap length for the tail billet is 1 m.

Effects of Mn Content on the Formation of Inclusions in High Aluminum Steel

Effects of Mn Content on the Formation of Inclusions in High Aluminum Steel

Refinement and Modification of Al2O3 Inclusions in High-Carbon Hard Wire Steel via Rare Earth Lanthanum.

In this paper, an experimental protocol of adding rare earth lanthanum (La) was used to refine and modify inclusions (Al2O3) in aluminum-deoxidized steel. An optical microscope (OM), a scanning electron microscope (SEM), and an energy dispersive spectrometer (EDS) were used to study the impact of size distribution, number density, distribution uniformity, interfacial distance, area density, and so on of rare earth La on high-carbon hard wire steel inclusions. As indicated by the findings when the addition amount of La is 0.063%, the refining and homogenizing effect of Al2O3 inclusions in steel is the best. The average diameter of the inclusions is 1.75 μm, the uniformity is 0.84, the proportion of the interfacial spacing greater than 10 μm is 48.4%, and the area density of inclusions is set at 0.014. Based on classical thermodynamics and Factsage software, the effect of La activity on inclusion formation was computed. As indicated by the findings, the addition of rare earth La mainly combines with O and S in the liquid steel, and the La-containing inclusions wrap around the Al2O3 inclusions, hindering the Al2O3 inclusions. Through the evolution of inclusions during solidification, the modification of Al2O3 inclusions via rare earth La and the types of inclusions are discussed. The experimental results and theoretical calculations verify that the optimal treatment plan is to add 0.063% La.

Effects of Cu Content on Inclusions and Pitting Corrosion in S32205 Duplex Stainless Steel

Cu is an austenite‐forming element in duplex stainless steel, and the precipitation of Cu‐rich phase can improve the strength of the alloy. However, the role of Cu element in the corrosion resistance of stainless steel is widely controversial. Herein, the effects of different Cu content on the formation of inclusions and the pitting resistance of duplex stainless steel are studied by using potentiodynamic anodic polarization test, immersion corrosion, scanning electron microscope, and electron probe microanalysis. The results show that the pitting potential decreases significantly with the increase of Cu content, which greatly reduces its ability to resist Cl− corrosion. The reason is that Cu increases the driving force for the formation of Al‐containing oxides, which increases the number and size of Al‐containing inclusions formed in the process of melting and solidification. At the same time, Cu promotes the formation of Cr‐depleted zone, which promotes the formation of microcracks and pitting corrosion between steel matrix and inclusions in duplex stainless steel.

Correlation Between Nonmetallic Inclusions and Localized Corrosion of a Low‐Nickel Stainless Steel with Cerium Treatment

The localized corrosion induced by different kinds of inclusions in low‐nickel stainless steel is studied through immersion tests and first‐principles calculations. The galvanic corrosion between the steel matrix and different kinds of inclusions occurs in the corrosive environment due to the difference in the electron work function of the steel matrix and inclusions. The electron work function of MnS, CeS, and Ce‐O‐S is smaller than that of the steel matrix, thus, these inclusions first dissolve as the anode. However, the electron work function of cerium‐containing oxides is bigger than that of the steel matrix, and the steel matrix dissolves prior to cerium‐containing oxides. The order of the volume expansion rate of pits induced by inclusions is CeS &gt; Si‐Mn(‐Al)‐O &gt; MnS &gt; Ce‐C‐O‐S &gt; Ce‐Si‐Mn(‐Al)‐O &gt; Ce‐O‐S. For cerium‐containing inclusions, the electron work function of inclusions increases with the increase of the O/Ce ratio and the S/Ce ratio of inclusions. The order of the electron work function of cerium‐containing inclusions is cerium oxides &gt; cerium sulfides &gt; cerium oxysulfide.

Study on the high cycle fatigue behavior of titanium microalloyed high strength beam steel by magnesium treatment

Non-metallic inclusions, which was mainly modified by magnesium treatment process in this work, played a decisive role in controlling the high cycle fatigue behavior of titanium microalloyed high strength beam steel. Magnesium treatment process profoundly reduces the large-sized inclusions in experimental steels, leading to a high fatigue strength and crack growth resistance simultaneously. The magnesium treatment process improved fatigue strength by 5.1% despite a 7.3% decrease in tensile strength of 6-Mg steel. In addition, Generalized Pareto Distribution (GPD) statistical method is used to evaluate the maximum inclusion size, which decreases by 25.3% through magnesium treatment process. These findings provide a new strategy to develop a titanium microalloyed beam steel with outstanding fatigue resistance.

Effect of Mg-Ce Treatment on Inclusion Characteristics and Pitting Corrosion Behavior in EH420 Marine Steel

Reasonable regulation of nonmetallic inclusions in steel can significantly improve its strength, toughness, and corrosion resistance. In this paper, EH420 marine steel was treated with Mg, Ce, and Mg-Ce to modify the inclusions. The effects of different treatments on the morphology, composition, size distribution, induced intragranular ferrite (IGF) nucleation, and pitting resistance of inclusions were systematically analyzed using various methods. The results show that the Mg-Ce composite treatment can modify irregular MgAl2O4 inclusions into spherical Mg-Ce-O composite inclusions and MgO-dominated inclusions. The density of inclusions is increased from 74.8/mm2 to 186.0/mm2, and the average size of inclusions is decreased from 2.60 μm to 1.07 μm. The Mg-Ce-O composite inclusions are effective inclusions for inducing IGF. Furthermore, the pitting potential is increased from −503 mV to −487 mV, and the corrosion rate is decreased. The order of average electronic work function is ΦMgO &lt; ΦCe2O3 &lt; Φα-Fe &lt; ΦAl2O3. Ce2O3 is hard to induce pitting corrosion due to its similar electronic work function to the steel matrix. Thus, the Mg-Ce composite treatment is better than that for Mg and Ce treatment alone, and has better application prospects.