TiN Inclusions Research Articles

Dissolution of TiO2 and TiN inclusions in CaO–SiO2–B2O3-based fluorine-free mold flux

Dissolution of TiO2 and TiN inclusions in CaO–SiO2–B2O3-based fluorine-free mold flux

Mechanism for TiN refinement and resultant heterogeneous nucleation of δ-Fe in magnesium-rare earth-treated ultrapure ferritic stainless steel

The effect of magnesium rare-earth (Mg-RE) treatments on TiN epitaxial nucleation to refine the as-cast structure of ultrapure ferritic stainless steel was investigated. Four samples with different melt treatments were prepared, namely an initial sample, a low-RE-treated sample, a high-RE-treated sample, and a Mg-RE-treated sample. The results reveal that TiN can be refined after the RE/Mg-RE treatment because of the co-crystallization of TiN and RE-Mg-Al-O. Moreover, the size of the inclusions increased with the RE content owing to the decreasing number of oxides. Compared to the low-RE treated sample, the average inclusion size of the Mg-RE-treated sample was further reduced because of the presence of more oxides. These results suggest that the number of oxides is a key factor in TiN refinement. However, few changes were observed in the 3D morphology of the composite TiN under such circumstances. In addition, compared with the Initial sample, the RE/Mg-RE treatment yielded finer solidification structures, indicating that the addition of RE/Mg-RE modifiers decreased the nucleation barrier. The solidification structure coarsened with increasing RE content because of the decrease in the inclusion number density, particularly for TiN. The Mg-RE treatment yielded the finest solidification structure with completely equiaxed grains. In addition, high temperature laser confocal microscopy was successfully applied to observe the in-situ nucleation-growth of δ-Fe, showing that the average grain size after Mg-RE treatment decreased by 38.09%. To reveal these phenomena, a new interfacial wetting-lattice mismatch heterogeneous nucleation model is established, accounting for the high-temperature wetting angle (θ1). Using differential scanning calorimetry, the upper limit of the heterogeneous nucleation rate (Iheter.) of δ-Fe was determined from the number density of all the TiN inclusions. Crystallization of primary δ-Fe and Iheter. depend on the critical degree of undercooling (∆Tc∗).

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.

Study on the Influences of Adding Rare Earth Ce on the Precipitation Behaviors of TiN Inclusions in 20CrMnTi.

The morphologies and sizes of TiN inclusions in gear steel 20CrMnTi have a significant impact on its service performance. This paper selects rare earth Ce to modify TiN inclusions in 20CrMnTi. The inclusions are analyzed by SEM (scanning electron microscope), EBSD (electron back-scattered diffraction), EDS (energy disperse spectroscopy), and OTS statistical software, and Thermo-Calc software is used to calculate the inclusion formations. The inclusions of MgAlO4-Ce and CeAlO3 can be formed when rare earth Ce is added into 20CrMnTi, which becomes TiN nucleation core after precipitation. Without the addition of rare earth Ce, square TiN inclusions ranging from 2 to 5 μm account for 60% of the total inclusions in 20CrMnTi. After adding rare earth Ce, the TiN inclusions in 20CrMnTiCe account for 36.7% of the total inclusions. Due to the new phase formations of MgAlO4-TiN and CeAlO3-TiN with sizes less than 2 μm, the titanium-containing inclusions are refined. Fatigue tests are conducted on the steels before and after the addition of Ce. The average fatigue lives of 20CrMnTi do not reach 107 times, and the deviations between the maximum and minimum fatigue lives are great. Large-sized TiN are the main inclusions that affect the fatigue performance of 20CrMnTi. The average fatigue lives of 20CrMnTiCe exceed 107 times, and the deviations of the fatigue lives are smaller than those of 20CrMnTi.

Thermodynamics on compositional design of slag for the Ti content control in bearing steel

The control of low Ti content is vital to reducing the adverse effects of TiN inclusions on fatigue life of bearing steel. Compared with the strict Ti content control of raw materials, the Ti content control by interaction between refining slag and bearing steel costs less. The effect of interaction between slag and steel on the Ti content of bearing steel was explored by equilibrium tests and the thermodynamic calculation based on the ion and molecule coexistence theory. The results show that the driving force for the reaction of the Ti and Al in steel and the SiO2 in slag increases with the decrease of the slag basicity, but the driving force for the reduction of TiO2 in slag by Al in steel also increases. Therefore, low Ti content in bearing steel can be obtained by appropriately reducing the basicity and TiO2 content of refining slag and Al content in steel, and properly increasing the Al2O3 content in the slag. For the compositional design of CaO–SiO2–Al2O3-0.1wt%TiO2-1wt%MgO refining slag used for low Ti bearing steel, the slag basicity should be less than 2 and Al2O3 content is 30–50%, or the slag basicity is 3 and Al2O3 content is decreased to 30-40wt%.

Effects of Ce-Modified TiN Inclusions on the Fatigue Properties of Gear Steel 20CrMnTi

In this paper, the results of a study on the influences of different morphologies, types, and sizes of inclusions on the fatigue lives of 20CrMnTi are reported. The results show that the addition of the rare earth element Ce can lead to the formation of spherical CeAlO3-TiN inclusions in 20CrMnTi. The fatigue performance of 20CrMnTi-Ce was significantly improved compared to that of 20CrMnTi. Using the “edge-to-edge matching” crystallographic theory, CeAlO3 was validated as a suitable hetero-nucleus core for TiN, and the following best orientation relationships between them were determined: [010]TiN//[21¯1¯1] CeAlO3&(002) TiN//(112¯1)CeAlO3. The fatigue cycle times of 20CrMnTi-Ce range up to 107, and this value is higher than that of 20CrMnTi without Ce. As the size of the TiN inclusions increases, the maximum stress of the steel matrix also increases. Also, the high-stress and low-life regions noticeably increase, thus increasing the possibility of a fatigue fracture. Under the same sizes of inclusions, the high-stress and low-life regions of square TiN are larger than those of circular TiN.

Competitive Precipitation Mechanism Between TixOy and TiN Inclusions Dependent on Nucleation Pathways in Ti-Contained Steel Solidification Process

Competitive Precipitation Mechanism Between TixOy and TiN Inclusions Dependent on Nucleation Pathways in Ti-Contained Steel Solidification Process

The investigation of precipitation behavior of titanium compounds for high titanium steel based on in situ observation.

The effects of cooling rate, Ti content, and casting temperature on titanium compounds for high titanium steel were investigated. In-situ observation of high titanium steel during remelting and solidification was carried out by using a High Temperature Confocal Scanning Laser Microscope (HTCSLM), and the observed results were in good agreement with the thermodynamic and kinetic calculations. The observation and calculation results both show that the inclusions in high titanium steel first precipitate in the form of TiN, followed by TiC precipitates as temperature decreases, eventually forming TiCxN1-x type inclusions at room temperature. The initial precipitation temperature of the inclusions increases with the increase of Ti content in molten steel, whereas casting temperature has little effect on the initial precipitation temperature of inclusions. In addition, the size of TiN inclusions increases with the increase of Ti content in steel but decreases with the increase in cooling rate.

Distribution behavior of inclusions in compact-strip-produced martensitic steel and its influence on mechanical properties

The distribution behavior of inclusions in martensitic steel produced by compact strip production process (CSP-MS) and its influence on mechanical properties were systematically investigated. The inclusions in the CSP-MS specimen are mainly composed of spherical Al2O3-CaO-CaS, MnS with high aspect ratio and small-sized TiN, whereas many coarse cuboidal TiN inclusions do exist in conventional martensitic steel (Con-MS). The high inclusion density of the CSP-MS specimen resulted in lower total elongation and impact toughness, and the MnS inclusions with high aspect ratio led to significantly stronger mechanical anisotropy than that for Con-MS specimen. The in-situ tensile results indicated that when the fracture direction is parallel to MnS direction, the microcracks induced by MnS inclusions tend to propagate into the matrix, leading to the formation of valley-like features, which significantly deteriorate the properties such as the total elongation and impact toughness. The microcracks caused by TiN inclusions are sharper than those caused by spherical Al2O3-CaO-CaS inclusions, and are easy to propagate into the matrix. This work is expected to guide the optimization of the mechanical properties of martensitic steels produced by CSP process and provide a theoretical basis for the CSP process design.

Influence of Microsegregation on the TiN Inclusions Formation Behavior in a K418 Superalloy during the Continuous Unidirectional Solidification Process

Controlling the formation behavior of inclusions during solidification is an effective approach to improve the purity of Ni-based superalloys. In this study, the effects of the microsegregation on the formation behavior of inclusions in the continuous unidirectional solidification (CUS) process were investigated. Three types of inclusions were found in revert and the CUS solidified K418 alloy: nitrides, oxides and SiC, with the nitrides as the dominant inclusions. With the application of the CUS process, the precipitation and growth behaviors of inclusions were significantly suppressed by the larger cooling rate, refinement of microstructure, and a reduction of microsegregation. Compared to the revert K418 alloy, the removal rates of the inclusion index and contents of N and O were 93, 84.1, and 57.7%, respectively in the CUS solidified K418 alloy at the withdrawal velocity of 27 mm/min. Numerical simulations based on a coupled microstructure-microsegregation-nucleation-growth model were carried out in order to verify the experimental results of the formation behaviors of inclusions during solidification. This study provided a theoretical and practical approach to the recovery of the revert K418 alloy.

Effect of Nitrogen Content on the High Cycle Fatigue Properties of Titanium Microalloyed Steel

The high cycle fatigue properties of three industrial 0.12% Ti microalloyed steels with different nitrogen contents (56, 40, and 30 ppm in molten steel of tundish) are investigated. The results show that <20% of the fatigue crack initiation sites are oxide inclusions of size in 16.8 μm ≈ 55.9 μm, while the rest 80% are surface defects. No TiN inclusions cause fatigue failure and the fatigue limit strength slightly decreases with increasing N contents as the yield strength decreases with a coarser ferrite grain. Inclusions characterization in the section near the fracture shows that the average sizes of TiN inclusions in H56, M40, and L30 steels are 3.50, 3.22, and 2.89 μm, and the maximum sizes are 6.92, 6.67, and 6.23 μm, respectively. Calculating for a cooling rate of 0.2 K s−1 using ChemAppPy precipitation model, the size of TiN inclusions will increase from 6.1 to 7.1 μm, when increasing N content from 30 to 60 ppm. The relationships between nitrogen content, TiN inclusions, and fatigue failure quantified by experimental test and modeling show that the nitrogen content in steel can be relaxed up to 60 ppm when considering economical denitrogenization and fatigue safety.

Effect of TiN inclusions on oxidation behavior of austenitic stainless steels

The effects of TiN inclusions on the oxidation behavior of modified stainless steels have been investigated systematically in this study. It was found that the oxidation rate of steel with TiN stringers is almost seven times faster than the clean one during the homogenized treatment. In the oxidation layers, the TiN stringers induce the spall fracture and facilitate the air permeation. At the oxidation interface, the TiN inclusions act as the nucleation sites for the oxides and promote the internal oxidation. The air permeation and internal oxidation causes the severe oxidation of modified austenitic stainless steels.

Formation of TiN Inclusions During Solidification of Titanium Micro-Alloyed Steel: Modeling With ChemAppPy

Formation of TiN Inclusions During Solidification of Titanium Micro-Alloyed Steel: Modeling With ChemAppPy

Influence of Plasma Treatment Parameters on the Structural-Phase Composition, Hardness, Moisture-Resistance, and Raman-Enhancement Properties of Nitrogen-Containing Titanium Dioxide.

The paper shows, for the first time, the prospects of treatment with a quasi-equilibrium low-temperature nitrogen plasma in an open atmosphere for the formation of super-hard, super-hydrophobic TiN/TiO2 composite coatings with pronounced Raman-enhancement properties. X-ray diffractometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy, as well as the analysis of hardness and moisture-resistance properties, are used as analytical research methods. During plasma treatment of titanium films on sapphire with a mass average temperature of 4-6 kK, an X-ray amorphous hydrophilic titanium oxide film with a low nitrogen content is formed. The nitrogen content in titanium oxide films increases with increasing treatment temperature up to 6-7 kK. In this case, an X-ray amorphous hydrophobic film is formed. With a further increase in temperature to 7-10 kK, a TiN/TiO2 composite structure based on polycrystalline rutile is formed with increased hydrophobicity and pronounced Raman enhancement properties due to the effective excitation of surface plasmon polaritons. The presence of the crystalline phase increases the dephasing time, which determines the quality of the resonance and the achievable amplification of the electromagnetic field near the TiN inclusions. All treated films on sapphire have a super-hardness above 25 GPa (Vickers hardness test) due to high grain size, the presence of nitrogen-containing inclusions concentrated along grain boundaries, and compressive stresses.

Microscopic formation mechanism of Si/Tl5Al1/TiN ohmic contact on non-recessed i-InAlN/GaN heterostructures with ultra-low resistance

In this work, we use Si/Tl5Al1/TiN for a source/drain ohmic contact to demonstrate an ultra-low contact resistance of 0.11 Ω mm (ρc = 2.62 × 10−7 Ω cm2) on non-recessed i-InAlN/GaN heterostructures. The Ti5Al1 alloy was used to suppress the out-diffusion of Al and extract N from the InAlN layer, which aided the formation of ohmic contact by improving the tunneling efficiency of electrons, as we have reported in the past work. A thin Si inter-layer combined with the Ti5Al1 alloy is proposed to further reduce contact resistance. A heavy n-type InAlN layer was obtained through doping with Si atoms to improve the tunneling transport of electrons. Furthermore, the TiN inclusions penetrated into the GaN channel because the in-diffused Si promoted the decomposition of GaN at a high annealing temperature and the in-diffused Ti reacted with GaN. These TiN inclusions provided direct contact with two-dimensional electron gas, offering an additional path for the injection of electrons into the channel. The tunneling and spike mechanism worked alternately to lower the contact resistance at different annealing temperatures (dividing at 900 °C), implying that the joint effect of tunneling and the spike mechanism was initially promoted in the formation of ohmic contact. The mechanism of this Si/Ti5Al1/TiN ohmic contact was fully understood through microscopic and thermodynamic analyses. These results shed light on the mechanism for the formation of ohmic contact in a gold-free metal stack for GaN-based HEMTs.

Characteristics and Formation Mechanism of Complex TiN Inclusions in 20CrMnTi Gear Steel

Characteristics and Formation Mechanism of Complex TiN Inclusions in 20CrMnTi Gear Steel

Distribution and Precipitation Mechanism of TiN in Industrial Pure Iron Bloom

The size and distribution of TiN particles have a great influence on the properties of industrial pure iron. It is necessary to understand TiN precipitation behavior in bloom. Herein, inclusions in industrial pure iron cast billets are observed. The temperatures and conditions for TiN precipitation are calculated using thermodynamics and kinetics. The results show a large number of TiN inclusions in the bloom, and the quantity density is the largest at the inner arc of the bloom. This is caused by the large cooling rate at the inner arc and the homogeneous nucleation of inclusions. According to the thermodynamic calculations, during the solidification of industrial pure iron, TiN begins to precipitate at a solidification fraction greater than 0.82. The amount of TiN precipitated during solidification is 93%, with TiN continuing to precipitate from the solid phase after the solidification is complete. The results of TiN particle growth kinetics reveal that MgO is the most effective in promoting TiN nucleation, followed by δ‐Fe, CaS, and MgAl2O4, the effectiveness of Al2O3 as a heterogeneous nucleation core is relatively poor. The radius of the TiN particles decreases with a decrease in the N and Ti content and an increase in the cooling rate.

New insights into the mechanism of localised corrosion induced by TiN-containing inclusions in high strength low alloy steel

This work investigated the chemical and electrochemical mechanisms of localised corrosion triggered by CaS·xMgO·yAl2O3·TiN complex inclusions in high strength low alloy steel (HSLAS) under a simulated marine environment. Special focus was given to the role of the TiN portion of the inclusion on the initiation and growth of the corrosion pits. The thermodynamic process of pitting initiation was investigated by Gibbs free energy, Pourbaix diagram and first principle calculation. Localised corrosion is mainly induced by inclusions and triggered by dissolution of adjacent distorted matrix. Chemical dissolution of CaS portion in CaS·xMgO·yAl2O3·TiN complex inclusion creates an acidic aggressive environment that accelerates the further dissolution of inclusion and matrix. Galvanic coupling effect between TiN inclusion and matrix is directly verified. TiN covered with a TiO2 film acts as the cathodic phase in galvanic corrosion, although it has a lower Volta potential than the matrix. This is an unusual correlation with the scanning Kelvin probe force microscopy result, which has been explained for this special system.

Roles of different components of complex inclusion in pitting of 321 stainless steel: Induction effect of CaS and inhibition effect of TiN

Pitting behavior of 321 stainless steel (SS) in sodium chloride solution was studied by potentiostatic pulse technique triggering pits. Pure TiN inclusion and complex inclusion with core-shell structure are found in 321 SS. The former has no effect on pitting performance, while CaS in the latter is the exact inducer of pitting. Mechanism of pitting initiation and propagation induced by complex inclusions was proposed. When CaS content differs little, inhibition effect of TiN shell on pitting propagation is the main reason why a complex inclusion with higher TiN content is more resistant to pitting.

Modification of Nonmetallic Inclusions by Ti and La Complex Treatment in High‐Al Transformation‐Induced Plasticity Steel

The effect of Ti and La complex treatment on the formation and evolution of inclusions in high‐Al transformation‐induced plasticity steel is investigated by laboratory experiments and thermodynamic calculations, with consideration given to the amount of La added and the sequence of the addition of Ti. The main inclusions are Al2O3 and AlN inclusions before the Ti and La additions. The AlN inclusions are transformed into TiN inclusions with the addition of 0.1 wt% Ti. After the subsequent addition of 0.007 wt% La, the main inclusions are LaAlO3, La2O2S, and TiN. With the addition of 0.06 wt% La to molten steel, the main inclusions are La2O2S, La2S3, and TiN. La may prevent the precipitation of TiN inclusions. Different addition sequences of Ti and La result in the same types of inclusions, with higher La addition. In the case of La addition before Ti, Ti can restrain the formation of La‐containing inclusions, and the number density of inclusions increases.