Pct Si Research Articles

Effect of Boron on the Interfacial Heat Transfer, Contact Behavior, and Microstructure in the Simulation of Strip Casting of 3.5 Wt Pct Si Non-oriented Silicon Steel

Effect of Boron on the Interfacial Heat Transfer, Contact Behavior, and Microstructure in the Simulation of Strip Casting of 3.5 Wt Pct Si Non-oriented Silicon Steel

CALPHAD-Based Modeling and Experimental Validation of Silicon Effect on the Solidification Behavior of Novel SiNb Cast Irons

The low oxidation resistance of SiMo ductile cast irons used as exhaust manifold material at high temperatures necessitates the development of new generation ductile cast iron compositions. New alloy designs can be made using CALPHAD methodology, and solidification sequence, segregation and critical phase transformation temperatures can be determined, especially for the solidified bulk materials. Thus, in commercial practicality, castable compositions with a raised A1 temperature can be obtained. In this study, novel SiNb cast irons with varying silicon contents were developed as candidate materials for exhaust manifolds. Solidification sequence, microsegregation, phase transformations, equilibrium phases of hypereutectic compositions containing 4 to 7 wt pct Si were calculated by CALPHAD-based modeling. The bulk materials of the studied compositions were cast as Y blocks and metallurgical analyzes were carried out. Studies revealed that; (i) in the ferritic matrix of the cast irons, graphite, Nb-rich carbides and some pearlite existed, (ii) pearlite formation was due to the negative segregation of silicon and positive segregation of manganese during solidification, (iii) as silicon content increased the amount of silicon dissolved in ferrite phase increased in the solidified structure and as a result pearlite formation decreased at the cell boundaries, and amount of vermicular graphite increased, (iv) depending on the silicon content the critical A1 temperature varied between 860 °C to 1013 °C and these values were higher than that of SiMo cast iron. All these findings revealed that SiNb cast irons had phase stability at higher temperatures compared to SiMo cast iron.

The Growth of {1 1 h}〈1 2 1/h〉 (α*-Fiber) Grains and the Evanesce of {001}〈100〉 (Cube) Grains During the Recrystallization of Warm Rolled Fe-6.5 Wt Pct Si Non-oriented Electrical Steel

The Growth of {1 1 h}〈1 2 1/h〉 (α*-Fiber) Grains and the Evanesce of {001}〈100〉 (Cube) Grains During the Recrystallization of Warm Rolled Fe-6.5 Wt Pct Si Non-oriented Electrical Steel

Effect of Superheat on the Initial Solidification Behaviors of 3.5 wt pct Si Non-oriented Electrical Steel During Strip Casting

Effect of Superheat on the Initial Solidification Behaviors of 3.5 wt pct Si Non-oriented Electrical Steel During Strip Casting

Investigation of Cracking Behavior of Fe–6.7 Wt Pct Si Manufactured Using Laser Powder Bed Fusion

Investigation of Cracking Behavior of Fe–6.7 Wt Pct Si Manufactured Using Laser Powder Bed Fusion

Improving Oxidation Resistance of Low Fe-Si Alloys by Preheating Treatment

In this work, attempts have been made to improve the oxidation resistance of Fe-Si alloys with 0.5, 1.0 and 2.0 mass pct Si by a preheating treatment, which was carried out at 1073 K for 24 hours in high purity hydrogen atmosphere. Compared with pure Fe and untreated Fe-Si alloys, the oxidation resistance of the preheated Fe-Si alloys at 673 K in O2 is drastically increased, in the case of 2 mass pct Si by two orders of magnitude. The improvement is attributed to a uniform, dense and continuous 25 nm pure SiO2 layer formed on the alloy surface during the preheating treatment in hydrogen atmosphere hindering the diffusion of Fe and O.

Aluminum Cast Alloys Based on the Al–Ce–Si–Mg System: An Influence of Silicon on Crystallization, Phase Composition, and Tensile Properties

An attempt at strengthening the aluminum-cerium-based alloys through additions of silicon was assessed using the experimental Al5Ce3Si0.5Mg (wt. pct) cast hypoeutectic composition, designed based on the commercial A356 (Al–7Si–0.3Mg, wt pct) grade by substituting a portion of Si with Ce. To determine a role of Si, the Al5Ce0.5Mg (wt. pct) reference was cast and tested under identical conditions. An addition of 3 wt. pct Si to the Al5Ce0.5Mg base increased the room temperature yield stress almost three times, from 47 to 135 MPa, but reduced its elongation by an order of magnitude from 8 pct to that below 1 pct. A presence of Si led also to essential changes in the alloy crystallization with the melting range widened substantially from 10 °C to 91 °C mainly due to a reduction in the solidus level. As-cast microstructure of the Al5Ce0.5Mg base consisting the primary αAl along with 44 pct of the αAl + Al11Ce3 eutectic was replaced in the Al5Ce3Si0.5Mg alloy with the αAl + AlCeSi2 coarse lamellae ternary eutectic, bulky compounds having the Ce-rich core of AlCe2Si with external shell of Al2CeSi2 along with the quaternary eutectic of fine αAl, Si, Al2MgSi/Al2Mg2Si, and Al–Si–Mg-Ce phases. The fractographic analysis revealed that additions of Si caused a transition from largely ductile fracture to the predominantly brittle mode with crack paths propagating mainly along the interface between the coarse AlCeSi2 lamellae and Al(Si, Mg) solid solution, which explains the measured drastic reduction in the alloy elongation.Graphical

Preparation of C54-TiSi2 by the Electromagnetic Directional Solidification of Hypoeutectic Ti-53.98 Wt Pct Si Alloy Melt

Preparation of C54-TiSi2 by the Electromagnetic Directional Solidification of Hypoeutectic Ti-53.98 Wt Pct Si Alloy Melt

Mechanical Properties of Ausformed Carbide-Free Bainite

In this study, the effect of ausforming temperature and strain on the bainite transformation in a model alloy containing 0.39 pct C, 2.0 pct Mn, 1.9 pct Si, and 0.5 pct Cr (mass percent) was investigated. Samples were deformed at 300 °C, followed by isothermal holding to monitor the phase transformation kinetics. Dilatometry results confirm the acceleration of transformation kinetics when the material is deformed to small strains (0.05 to 0.20). Tensile testing results show that, for long isothermal holding times, no improvement in strength or ductility is achieved as a result of ausforming in comparison with the non-deformed state. However, the benefit of ausforming lies in its ability to accelerate the bainite transformation kinetics and to reduce the isothermal holding time needed to avoid premature fracture due to the presence of a high volume-fracture of fresh martensite. Fracture analysis reveals ductile fracture, with cracks along martensitic regions within the microstructure. The distribution of martensite in the final microstructure was associated with bands of Mn segregation. This banding effect was less visible within the ausformed microstructure because bainite was able to nucleate within both the high- and low-Mn regions. A second advantage of ausforming is, therefore, to reduce the microstructure heterogeneity associated with compositional banding within the steel sheets and, by so doing, eliminate crack propagation within the bands. In spite of the fact that ausforming accelerates the bainite transformation kinetics, the required transformation times for the present steel are still too long for use within industrial continuous annealing lines.

Microstructure and Magnetic Properties of 6.5 Wt Pct Si Steel Strip Produced by Simulated Strip Casting Process

An improved dip test apparatus was used to simulate the strip casting of 6.5 wt pct Si steel in this study. The results showed that the interfacial heat flux between melt and substrate could reach maximum value of 8.2 MW/m2, with > 4350 kJ/m2 heat being removed in the first 1.0 s. The as-cast strip mainly consisted of large columnar grains hundreds of microns in length. The high cooling rate of the as-cast strip suppressed the formation of ordered phases and the precipitation of elements. Only several complex particles of MnS-TiN of a few nanometers were found. After annealing at 1273 K (1000 °C) for 30 minutes, a large number of small particles such as TiN precipitated from the ferrite matrix. Within the testing frequency and magnetic field strength, the three strip samples obtained at different conditions showed the lowest iron loss at the frequency of 20 kHz and the magnetic field strength of 0.07 T, which were 22, 18 and 17 W/kg, respectively. The coercive force and iron loss decreased with increasing heat treatment temperature, while the magnetic permeability showed the opposite pattern. The magnetic permeability and iron loss of the silicon steel strip produced by strip casting are comparable to those of the silicon steel products produced by other techniques such as melt spinning and conventional rolling.

Thermomechanical Processing Map in Retaining {100}//ND texture via Strain-Induced Boundary Migration Recrystallization Mechanism

The feasibility of establishing thermomechanical conditions to promote {100}//ND fiber texture via strain-induced boundary migration (SIBM) recrystallization mechanism in a non-grain oriented (NGO) electrical steel was investigated. Single-hit uniaxial compression at various temperatures and strains has been applied on Fe-6 wt pct Si to establish the relationship between stored energy and the softening mechanisms. Recovery only and recrystallization by SIBM or by subgrain growth (SGG) have been observed depending on the stored energy level. A strong {100}//ND fiber recrystallization texture, i.e., 45 pct area fraction, was seen in the sample which was deformed to 0.2 strain at 650 °C and then annealed at 1000 °C for 15 minutes, whereas only 13 pct {100}//ND fiber component was observed after 0.4 strain at 500 °C followed by the same annealing treatment. By examining the same microstructural region before and after annealing via EBSD, it has been shown that {100}//ND textured recrystallized grains were formed adjacent to the {100}// ND textured deformed matrix. Low stored energy has been shown to favor the formation of {100}//ND texture recrystallized grains via SIBM recrystallization mechanism attributed to its slow recrystallization nucleation rate. The results from the deformation studies have been used to suggest a processing window map concept to define the recovery, SIBM, and SGG regions for the starting as-cast columnar microstructure.

Effect of Si Addition on Flow Behavior in Al-Mg and Al-Mg-Si Molten Alloys

This study investigates the fluidity change of Al-Mg binary alloys with the addition of Si and examines the factors that determine flow length in these binary and ternary alloys. Fluidity tests for Al-6Mg-xSi (all compositions in mass percent; x = 0, 3, 5, or 7) alloys were carried out using a spiral-type steel mold. The results show a decrease in both the rate of oxidation and the freezing range, as well as an increase in the heat of fusion of Al-Mg-Si ternary alloys with increasing Si content. Nevertheless, at constant superheating of 60 °C, a lower fluidity was achieved in ternary alloys of ≤ 5 pct Si content than in Al-6Mg alloy. However, further increase to 7 pct Si content yielded a flow length 25 pct higher than for Al-6Mg alloy. Further superheating above the liquidus temperature resulted in increased flow length for Al-Mg-Si ternary alloys, with a flow length increase of about 1 cm per 5 °C temperature increase. Instead of solidification range, Tα–Te range (the temperature difference between the start of the pro-eutectic α-Al phase (Tα) and eutectic phases (Te)), was used in this study, as it was found to be a more suitable criterion for predicting flow length for Al-Mg-Si ternary alloys. The key variables for predicting flow length were found to differ based on alloy composition. In the ternary alloys, total heat content and (Tα–Te) range were found to be the most influential factors driving flow behavior, while the poor fluidity of Al-6Mg binary alloys was found to be driven primarily by high oxidation tendency and low latent heat of fusion.

Hot Tearing Behavior in Double Ternary Eutectic Alloy System: Mg-Ce-Al Alloys

The hot tearing behavior of the double ternary eutectic alloy system, Al-6Mg-xSi (0 to 6.0 wt pct Si) alloys, was evaluated by a constrained rod casting mold equipped with a thermocouple and a load cell connected to a data acquisition system. Experimental results were compared with the results calculated by Scheil’s model using Pandat software to predict the occurrence of hot tearing in Al-6Mg-xSi alloys. The curve of hot tearing susceptibility contained two peaks, which were mainly affected by the double ternary eutectic reactions and the solidification phases evolution. And it agreed with the Kou’s hot tearing index precisely. The types and fractions of solidification phases (Al3Mg2, Mg2Si, and eutectic Si) determined by the addition of Si content changed the freezing range and eutectic liquid fraction greatly. In addition, the types, fractions, sizes, and distributions of solidification phases affected the nucleation, propagation, and healing of hot tear cracks. The maximum contraction force value decreased as the reduction of volume shrinkage coefficient due to the addition of Si content. The drop-in force value on the contraction force curve could indicate the occurrence of hot tearing, and predict the hot tearing susceptibility when considering the shrinkage coefficient.

Mechanism for Si Poisoning of Al-Ti-B Grain Refiners in Al Alloys

Al-5Ti-1B is the most widely used grain refiner for Al alloys. However, it is not effective for grain refining Al alloys containing more than 3 wt pct Si. This adverse effect of Si is referred to as Si poisoning. In spite of extensive experimental and theoretical investigations in the past decades, the exact mechanism for Si poisoning is still not clear. In this work, the state-of-the-art electron microscopy was performed to investigate the mechanism for Si poisoning. Our experimental results suggest that Si segregates preferably to the TiB2/Al-Si melt interface and the pre-existing Al3Ti 2-dimensional compound (2DC) layer on TiB2 surface dissolves into the Al-Si melt. Based on the experimental results, we have postulated a new mechanism for Si poisoning: interfacial segregation of Si leads to enrichment of Si at the TiB2/Al-Si melt interface, and this in turn makes the pre-existing Al3Ti 2DC on the TiB2 surface unstable and dissolve gradually in the melt, resulting in a loss of TiB2 nucleation potency and hence a decreased total number of potent TiB2 particles available for heterogeneous nucleation and grain initiation and consequently an increased grain size. This mechanism for Si poisoning can explain consistently the experimentally observed phenomenon reported in the literature.

Unusual Iron Nitride Formation Upon Nitriding Fe-Si Alloy

The influence of Si, substitutionally dissolved in ferritic Fe-2 at. pct Si and Fe-4.5 at. pct Si alloys, on the nucleation and growth of γ′ iron nitride upon controlled gaseous nitriding was investigated. The nitrided specimens were characterized by XRD, light microscopy, TEM, EELS, EPMA and EBSD. The combination of difficult and thus delayed precipitation of (1) silicon nitride, because of a large misfit with the ferrite matrix, and (2) γ′ iron nitride, because of the negligible solubility of Si, was shown to lead to a series of unusual, nonequilibrium phenomena: high nitrogen supersaturation, development of Si-containing metastable γ′ phase of peculiar morphology, precipitation of amorphous silicon nitride in γ′ and development of ε nitride at thermodynamic conditions unlikely to allow its formation.

Grain Refinement Mechanism of the δ-Ferrite in Steels Through Cerium Addition

To investigate and clarify the roles and mechanism of Ce addition in grain refinement of primary δ-ferrite during solidification of steels, a Fe-4wt pct Si alloy, which can retain the primary δ-ferrite to room temperature after solidification, was used to evaluate the roles of Ce in refining the δ-ferrite. Experimental results showed that addition of small amount of Ce led to significant reduction in average grain size of the as-cast Fe-4wt pct Si alloy from 1906 ± 160 µm without Ce addition down to 998 ± 70 µm at 0.0260 wt pct Ce addition. For the purpose of investigating the grain refinement mechanism of Ce, the Equilib and Phase Diagram modules in the FactSage Software System were used to simulate the formation sequence and calculate fractions of the Ce-containing inclusions above the liquidus in various Fe-4wt pct Si alloys with different Ce, S and O contents. The predicted formation sequence was Ce2O3 > Ce2O2S > Ce2S3/Ce3S4. However, due to the low fraction of the oxide and sulfides formed, only the oxysulfide, Ce2O2S, was observed and verified in the experimental alloys at room temperature in a transmission electron microscopy and a scanning electron microscope that was equipped with the electron backscatter diffraction and energy-dispersive X-ray spectroscopy. Based on the crystallographic calculations using the edge-to-edge matching model together with previously determined orientation relationships between the δ-ferrite and Ce2O2S, it is considered that the heterogeneous nucleation of δ-ferrite on the in situ-formed Ce2O2S particles in the Fe-4wt pct Si alloy melt played a key role in grain refinement of the δ-ferrite. An inductively coupled plasma mass spectrometry was used to measure the amount of Ce solute in the ferrite after conducting low-temperature electrolysis to separate and filter out the Ce compounds. The calculation of the growth restriction parameter (β) using the Phase Diagram module in FactSage Software System indicated an almost negligible role of the Ce solute in the grain refinement of δ-ferrite. The present work clarifies previous uncleanness in understanding the grain refinement mechanism of δ-ferrite through Ce addition.

Fabrication of the τ5c Intermetallic Compound Monoliths by a Novel Powder Metallurgy and Hot-Dipping Approach

The precipitation of discrete iron-based intermetallic compounds (IMC) is an inevitable phenomenon in a steel strip alloy coating pot due to the continuous supply of iron from the steel strip and temperature perturbations in the pot. These IMC [τ5c: Al20Fe5Si2(Zn) or Al8Fe2Si(Zn)] particles grow by coarsening and agglomeration and are the primary source of coating inclusions for coated steel products. They are further responsible for excessive bottom dross build-up in the alloy coating pot. It is hypothesized that they will re-dissolve into the pot during the heating cycle of the coating bath, but their dissolution kinetics remains unclear. The underlying hold-up is the lack of large IMC samples for quantitative studies of their dissolution kinetics in the molten coating alloy. To quantify and understand the dissolution of the τ5c IMC phase, this study reports the fabrication of monolith samples of the τ5c phase by a novel powder metallurgy and hot-dipping approach. Firstly, τ5c IMC particles were extracted by acid dissolution of the bottom dross collected from a commercial alloy coating pot. A powder metallurgy route was then used to fabricate an intermediate form of the monolithic τ5c IMC disks of 14.80 mm in diameter and 17 mm in height. X-ray diffraction (XRD) and electron transmission microscopy (TEM) analyses revealed that the initial τ5c IMC phase transformed into α-Al8Fe2Si (τ5H) and Al3Fe phases during isothermal sintering at 900 °C due to devolatilization of Zn from the τ5c phase. However, when these intermediate IMC monoliths were immersed in the Zn-concentrated and iron-saturated 55 pct Al-43.4 pct Zn-1.6 pct Si (AZ) alloy coating bath at 595 °C, both the α-Al8Fe2Si (τ5H) and the Al3Fe phases transformed back into the τ5c IMC phase through diffusion of Zn into the as-sintered monoliths. The fabrication of the τ5c monolith samples, which can be shaped in any geometry, provides an essential basis for quantifying and understanding the dissolution of the τ5c intermetallic phase in a commercial steel strip coating pot. Dissolution analysis of the IMC monoliths revealed a mass transfer coefficient (k) of 5.3 × 10−8 m/s in an unsaturated AZ alloy coating bath at 595 ± 2 °C. It is suggested that dissolution kinetic of IMC monoliths is sluggish; therefore, IMC(τ5c) particles precipitated in the AZ alloy bath will unlikely dissolve back at industrial steel strip coating processing conditions.

Effects of Si Content and Forging Pressure on the Microstructural and Mechanical Characteristics in Semi-solid Forging of Al-Si-Mg Alloys

In this study, semi-solid forging (SSF) using electromagnetic stirring of Al-Si-Mg alloys was carried out. To evaluate the acceptability for producing a semi-solid slurry of an alloy with various Si contents, the temperature sensitivity of the solid fraction and solidification range were calculated by Thermo-Calc. The effects of the Si content and forging pressure on the microstructural and mechanical properties, such as tensile strength and elongation, were ascertained. Specimens were taken from two typical positions on the semi-solid-forged products, where one position corresponds to a region of directly applied forging pressure and the other region corresponds to the position of slurry being squeezed and extruded. Microstructural characteristics such as average grain size, volume fraction, and form factor of the α-Al were evaluated as the Si content was changed from 5 to 7 wt pct at 0.5 wt pct intervals. As the Si content increased, the particle size of α-Al and tensile strength increased, while the volume fraction of α-Al and elongation decreased. At lower Si contents, solidification shrinkage was observed, resulting in a decrease in the elongation. At 5 and 6 wt pct Si, α-Al particles were agglomerated, and shrinkage was observed. Uniform, fine, and globular microstructures were obtained at 6 wt pct Si. At 6 and 7 wt pct Si, α-Al particles were coarsened. The forging pressure was changed from 100 to 250 MPa, and at a forging pressure of 250 MPa, shrinkage was observed. As the forging pressure was increased from 100 to 200 MPa, the tensile strength and elongation increased, and the particle size of α-Al decreased. At a forging pressure of 250 MPa, α-Al particles were deformed and agglomerated, which decreased the strength.

Texture Evolution of a 2.8 Wt Pct Si Non-oriented Electrical Steel and the Elimination of the 〈111〉//ND Texture

A 2.8 wt pct Si non-oriented electrical steel was thermomechanically processed using conventional hot rolling, hot band annealing, cold rolling and final annealing routes. The evolution of texture during these processes was investigated using electron backscatter diffraction (EBSD) techniques. The final annealing was conducted at 750 °C for various times (10 to 120 minutes), and it was found that by simply changing the annealing time, the texture shows significantly different features, i.e. depending on the annealing time, the Goss ({011}〈100〉), the θ-fiber (〈001〉//normal direction, ND) or the γ-fiber (〈111〉//ND) may dominate the texture. Annealing for 60 or 90 minutes can essentially eliminate the magnetically unfavorable 〈111〉//ND texture while promoting the desired 〈001〉//ND texture. On the other hand, annealing at the same temperature for 30 or 120 minutes, the 〈111〉//ND texture is strengthened and the favorable 〈001〉//ND texture is weakened. The formation of the typical textures observed in each process was examined with respect to known mechanisms existing in the literature. The formation of the various textures during annealing at different times was discussed against the oriented growth theory based on a statistic analysis of the grain boundary misorientation and grain size. It is seen that during annealing at different times, the grain boundary character (e.g. mobility) and the grain size may determine the growth of certain orientations, which give rise to the different textures after annealing for different times.

A Transition from Fine to Coarse Lamellar Eutectics in the Undercooled Ni-29.8 At. Pct Si Eutectic Alloy: Experiments and Modeling

In contrast to the classical eutectic growth models, according to which the eutectic spacing decreases invariably with undercooling, an anomalous transition from fine to coarse lamellar eutectics was found in the undercooled Ni-29.8 at. pct Si eutectic alloy. In this study, the growth kinetics, recalescence processes, and grain orientations were analyzed. A sharp increase of the growth velocity at an undercooling of about 100 K was found. The recalescence front transited in sequence from a diffuse one with tips, to a diffuse one without tips and then to a sharp one. The microstructures changed from a mixture of directional rod-shaped γ-Ni31Si12 grains and fine lamellar eutectics to solely coarse lamellar eutectics. Coarse lamellar eutectics were found to be formed by rapid solidification of primary directional rod-shaped Ni31Si12 intermetallic compound and subsequent epitaxial growth of secondary Ni2Si intermetallic compound, being consistent with the predictions of eutectic–dendritic and dendritic growth models. Coarse anomalous eutectics at low undercooling were formed by fragmentation of fine lamellar eutectics and their subsequent coarsening. At high undercooling, they were formed by decoupled-eutectic growth.