Mass Pct Research Articles

Metastable Phases of Dross Particles Formed in a Molten Zinc Bath and Prediction of Soluble Aluminum During Galvannealing Processes

The morphology, chemistry, and crystallographic characteristics of metastable dross particles were identified. These particles are formed during the initial stage of precipitation. The particles had aluminum concentrations of 15 to 80 mass pct, with values that decreased gradually as particle size increased. These metastable dross particles were a mixture of the crystalline phase of FeZn10, which is called the “delta phase,” and the high-aluminum amorphous phase, which covered the surface of the crystalline phase. The new “meta Q” concept was proposed to predict the amount of soluble aluminum in the zinc bath by considering nucleation kinetics and particle growth. The results calculated using the “meta Q” concept were compared with the values measured by the aluminum sensor, which were taken during the same period at the commercial galvanizing line. The mean of the absolute values of the differences between the calculated and measured values was 9.7 ppm.

Growth Kinetics of Proeutectoid Ferrite in Fe-0.1C-1.5Mn-1Si Quaternary and Fe-0.1C-1.5Mn-1Si-0.2Al Quinary Alloys

The growth kinetics of proeutectoid ferrite in the early stages of transformation were studied in Fe-0.1C-1.5Mn-1Si (mass pct) quaternary and Fe-0.1C-1.5Mn-1Si-0.2Al quinary alloys. The observed kinetic transition temperatures from partitioned slow growth to unpartitioned fast growth of ferrite in both alloys are in good agreement with predictions using a local equilibrium model for multicomponent systems. The measured parabolic growth rate constants were smaller than those calculated assuming paraequilibrium in the unpartitioned growth region, but the difference between the measured and the calculated growth rate constants gradually diminished with a decreasing reaction temperature. The dissipation of driving force, derived from the diffusion of the substitutional solute within the transformation interface, possibly constitutes a major part of the discrepancy between the measured and the calculated growth kinetics.

Experimental Investigation of the Viscosities of High Titanium Containing Slags with Low Mass Ratio of CaO to SiO<sub>2</sub>

This present paper focuses on the viscosities of high titanium containing slags in the process of titanomagnetite smelting by taking the TiO2-Al2O3-CaO-SiO2 quaternary system as the object. Experimental determinations of the viscosities were carried out in the temperature range from 1573 to 1773K using the rotation cylinder method. The measurements were conducted in the composition range from 23 to 33 mass pct TiO2, 3 to 9 mass pct Al2O3, and 0.3 to 0.7 basicity (mass ratio of CaO to SiO2). The effects of TiO2, Al2O3, basicity, and temperature on viscosity were studied. The experimental results indicated that the viscosities decreased with increasing TiO2 content and basicity, and increased with increasing Al2O3 content, above the liquidus temperature. Based on the experimental data, the liquidus temperatures of the slags were evaluated using the second derivatives of the activation energies for viscous flow with respect to temperature.

Study on Microstructure and Mechanical Properties of Newly Developed High Carbon Fe-Mn-Cu-C TWIP Steels

The effects of high carbon content on the microstructure and tensile properties of Fe-20Mn-3Cu-xC TWIP steels were studied by OM, XRD, SEM analysis. The experimental results indicate that the amount of carbide and micro-porosity increased with the increasing of carbon content. The microstructures in the undeformed and deformed region of Fe-20Mn-3Cu-xC steels exhibit fully austenitic phase. The fractography of tensile samples reveals typical tough fracture microstructure with isometric dimples. The number of carbide in the as-cast structure, the yield strength and the tensile strength increase with the increasing of carbon addition, but the elongation rate increases at first and then decreases. TWIP steel has the optimum property when the carbon addition is 1.3 mass pct, of which the tensile strength is 1040.59 MPa, the elongation percentage is 98.08% and the strength-elongation product achieves 102061.07MPa•%. Fe-20Mn-3Cu-xC steels have high strain hardening capacity, and strain hardening rate (θ) and strain hardening index (n) both increase with the increasing of C addition.

Thermal Desorption Analysis of Hydrogen in High Strength Martensitic Steels

Thermal desorption analyses (TDA) were conducted in high strength martensitic steels containing carbon from 0.33 to 1.0 mass pct, which were charged with hydrogen at 1223 K (950 °C) under hydrogen of one atmospheric pressure and quenched to room temperature. In 0.33C steel, which had the highest Ms temperature, only one desorption peak was observed around 373 K (100 °C), whereas two peaks, one at a similar temperature and the other around and above 573 K (300 °C), were observed in the other steels, the height of the second peak increasing with carbon content. In 0.82C steel, both peaks disappeared during exposure at room temperature in 1 week, whereas the peak heights decreased gradually over 2 weeks in specimens electrolytically charged with hydrogen and aged for varying times at room temperature. From computer simulation, by means of the McNabb–Foster theory coupled with theories of carbon segregation, these peaks are likely to be due to trapping of hydrogen in the strain fields and cores of dislocations, and presumably to a lesser extent in prior austenite grain boundaries. The results also indicate that carbon atoms prevent and even expel hydrogen from trapping sites during quenching and aging in these steels.

Solubility of Nitrogen in High Manganese Steel (HMnS) Melts: Interaction Parameter between Mn and N

Nitrogen solubility in Fe-Mn melts was measured using a N2 bubbling and sampling method at temperatures from 1823 K to 1923 K (1550 °C to 1650 °C) for manganese content to about 25 mass pct. The effect of temperature on the nitrogen solubility was well described based on the thermodynamic behavior of Fe-Mn system. Furthermore, the interaction parameter between Mn and N was evaluated as a function of temperature. The present results can be used in thermodynamic analyses of the formation of nitride compounds such as AlN or TiN in high manganese steel melts for example, transformation induced plasticity (TRIP) and twin induced plasticity (TWIP) aided steels as well as high Mn-N alloyed stainless steels.

Eutectoid Transformations in 4.12 Mass Pct Cr 0.88 Mass Pct C Steel

The sequence of eutectoid microstructures, obtained by lowering the temperature of the isothermal transformation, was studied in synthetic steel with 4.12 mass pct Cr 0.88 mass pct C. The results were compared with observations on plain carbon steels with 1.65 and 1.67 mass pct C. In both cases, the main features can be explained as an effect of a lowered temperature on the increasing supersaturation of cementite in austenite and an even stronger effect on that of ferrite. One distinction was a continuous change in the pearlite structure toward a more acicular structure. This structure is named acicular pearlite.

Influence of Aluminum on the Formation Behavior of Zn-Al-Fe Intermetallic Particles in a Zinc Bath

The shape, size, and composition of dross particles as a function of aluminum content at a fixed temperature were investigated for aluminum added to the premelted Zn-Fe melt simulating the hot-dip galvanizing bath by a sampling methodology. In the early stage, less than 30 minutes after Al addition, local supersaturation and depletion of the aluminum concentration occurred simultaneously in the bath, resulting in the nucleation and growth of both Fe2Al5Zn x and FeZn13. However, the aluminum was homogenized continuously as the reaction proceeded, and fine and stable FeZn10Al x formed after 30 minutes. An Al-depleted zone (ADZ) mechanism was newly proposed for the “η→η+ζ→δ” phase transformations. The ζ phase bottom dross partly survived for a relatively long period, i.e., 2 hours in this work, whereas the η phase disappeared after 30 minutes. In the early stage of dross formation, both Al-free large particles as well as high-Al tiny particles were formed. The dross particle size decreased slightly with increased reaction time before reaching a plateau. The opposite tendency was observed when the Al content was 0.130 mass pct; with a relatively high Al content, the nucleation of tiny η phase dross was significantly enhanced because of the high degree of supersaturation. This unstable η phase dissolved continuously and underwent simple transformation to the stable δ phase. The relationship between nucleation potential and supersaturation ratio of species is discussed based on the thermodynamics of classical nucleation theory.

A Study of the Viscous Properties with NaF Additions in the CaO-SiO2-12 mass pct Na2O Based Slags

The viscous behavior of the CaO-SiO2-12 mass pct Na2O based slag system with various concentrations of NaF has been studied using the rotating spindle method. NaF additions decreased the viscosity by interacting with bridged oxygens in the complex silicates and depolymerizing the network structure of the molten slag. NaF was particularly effective at lowering the viscosity in small amounts, but beyond 8 mass pct NaF, the effect was not as pronounced. A comparison between additions of NaF and CaF2 revealed NaF to be more effective at decreasing the viscosity for 1523 K and 1573 K (1250 °C and 1300 °C). From the slopes of the Arrhenius relationship for viscosity, the activation energy of viscous flow was found to be between 128 kJ/mol to 115 kJ/mol, which were lower than the values for the same amount of CaF2 additions. Both a temperature effect and a compositional effect on the molten slag structure and subsequently the viscous behavior were observed. The Fourier transformed infrared (FTIR) spectra taken for the CaO-SiO2-12 mass pct Na2O-8 mass pct NaF slag samples quenched from 1623 K to 1773 K (1350 °C to 1500 °C) revealed that the temperature effect on the viscosity was observed at temperatures below 1673 K (1400 °C).

The Effect of Calcium Fluoride on Slag Viscosity

The effect of CaF2 on the viscosity of high-basicity Al2O3-CaO-MgO-SiO2 (-CaF2) slags for secondary steelmaking was studied using a Brookfield digital viscometer. The addition of approximately 3 mass pct CaF2 could decrease the liquidus temperature substantially in the case of high CaO containing slags, leading to good flowability of the slag at the temperature of the ladle treatment. The addition of CaF2 had the strongest effect on the viscosity of liquid slag with high SiO2 content.

Experimental Determination of the Liquidus in the High-Basicity Region in the Al2O3(25 mass pct)-CaO-MgO-SiO2 and Al2O3(35 mass pct)-CaO-MgO-SiO2 Systems

Liquidus in the Al2O3(25 mass pct)-CaO-MgO-SiO2(<20 mass pct) and Al2O3(35 mass pct)-CaO-MgO-SiO2(<20 mass pct) systems were determined experimentally in the high-CaO-containing region at 1873 K (1600 °C). For the Al2O3(35 mass pct)-CaO-MgO-SiO2(<20 mass pct) system, liquidus data were also determined for 1773 K (1500 °C). The equilibrating and quenching technique with subsequent electron probe microanalyzer (EPMA) microanalysis were employed. Based on the data, liquidus lines were constructed for the 25 and 35 mass pct alumina planes at silica contents generally below 20 mass pct. The current results showed a slightly lower solubility of CaO and a higher solubility of MgO at 1873 K (1600 °C) for the 25 mass pct Al2O3 section compared with the existing phase diagram. At 1773 K (1500 °C), the result showed a slightly lower solubility of both CaO and MgO in the 35 mass pct Al2O3 section compared with the existing phase diagram. In addition, the activities of MgO, CaO, and Al2O3 were estimated at 1773 K and 1873 K (1500 °C and 1600 °C) using the phase diagram information.

The Effect of Sulfur Concentration in Liquid Iron on Mineral Layer Formation During Coke Dissolution

The effects of sulfur concentration in liquid iron on mineral layer development between coke and iron as coke dissolves in a 2 mass pct carbon-iron liquid have been investigated at 1773 K (1500 °C). The initial sulfur in iron concentrations used ranged from 0.006 to 0.049 mass pct. Key findings include that the two-stage dissolution behavior exhibited in the carbon transfer from coke to iron, as reported in a previous study by the authors, at low initial sulfur in iron contents, was also apparent at the higher values used in this study. This two-stage behavior was attributed to a change in the mineral layer density as a result of changes in mineral morphology at the interface. In addition to confirming the two-stage behavior of the carbon-transfer kinetics at the higher sulfur concentration in iron levels, after a period of time, a solid calcium sulfide layer formed on the mineral layer. The sulfide layer formed after approximately 40 minutes, and the proportion of sulfide in the mineral layer increased with increased experimental time and initial sulfur concentration in iron. It was usually found at the iron side of the mineral layer and was associated with calcium-enriched calcium aluminates. Thermodynamic analysis of this layer confirmed that the sulfide is stabilized as the mineral layer is enriched by calcium.

Localized Deformation in Multiphase, Ultra-Fine-Grained 6 Pct Mn Transformation-Induced Plasticity Steel

Multiphase, ultra-fine-grained transformation-induced plasticity (MP UFG TRIP) steel containing 6 mass pct Mn was obtained by cold rolling and intercritical annealing of an initially fully martensitic microstructure. UFG microstructures with an average grain size less than 300 nm were obtained. The amount of austenite in the microstructures, speculated to be formed by diffusionless transformation, was controlled by changing the intercritical temperature. The tensile properties were strongly influenced by the volume amount and the stability of the reversely transformed austenite. The MP UFG TRIP steel was characterized by pronounced localization of the deformation. The deformation band properties were analyzed in detail.

Hardening and Toughening Mechanisms of Cemented Carbides with Plate-Like WC Grains Prepared by Seeding

WC-10Co (mass pct.) cemented carbides containing plate-like WC grains were prepared by using plate-like WC single crystals as seeds. With the increase of seed addition amount, more and bigger plate-like WC grains are formed, the hardness and transverse rupture strength (TRS) increase first and then decrease. When 2.5 mass% seeds are added in WC-10Co, the density is hardly affected, whereas the hardness and TRS increase simultaneously, especially TRS increases by 12.8%. The hardening and toughening mechanisms of WC-10Co cemented carbides with plate-like WC grains were discussed.

Solid Solution Strengthening for Mg-3.0 Mass Pct (2.71 At. Pct)Al and Mg-0.06 Mass Pct (0.036 At. Pct)Ca Alloys

Tensile tests were carried out at 123 K to 373 K (–150 °C to 100 °C) on pure Mg, Mg-3.0 mass pct (2.71 at. pct) Al alloy, and Mg-0.06 mass pct (0.036 at. pct) Ca alloy. Little decrease occurred in the yield stress of the pure Mg and the Mg-Ca alloy with increasing temperature from 223 K to 373 K (–50 °C to 100 °C). For the Mg-Al alloy, however, its yield stress decreased with increasing temperature from 223 K to 373 K (–50 °C to 100 °C). Analyses based on the existing solid-solution strengthening theories, focusing on the athermal component of stress, revealed that the dominant strengthening mechanism is the shear modulus effect for the Mg-Ca alloy and the chemical interaction for the Mg-Al alloy. It is suggested that the shear modulus effect is dominant at a low concentration and the chemical interaction is dominant at a high concentration for Mg alloys.

Effect of Zr Additions on the Oxidation Kinetics of FeCrAlY Alloys in Low and High pO2 Gases

Alloys of nominal composition Fe-20Cr-5Al-0.05Y (mass pct) with and without a 0.03 pct Zr addition were isothermally oxidized at temperatures of 1473 to 1573 K (1200 to 1300 °C) in both flowing Ar-O2 and Ar-H2-H2O. Continuous thermogravimetric (TG) measurements of oxygen uptake showed the rates to be faster in both gases for Zr-containing than for the Zr-free alloy. Scale growth on the Zr-bearing alloy by inward oxygen diffusion is accelerated by the fine alumina grain size and the formation of elongated zirconia particles in the two-phase scales. Zirconia formation ceases when the supply of metal in the thin alloy substrate is exhausted, and subsequent single-phase alumina growth proceeds at a slower rate. A simple diffusion model is shown to account semiquantitatively for zirconium enrichment in alumina scales. The presence of hydrogen modifies both oxygen transport in the scale and its permeability in the alloy.

Kinetics of Reverse Transformation from Pearlite to Austenite in an Fe-0.6 Mass pct C Alloy and the Effects of Alloying Elements

Substitutional alloying effects on reversion kinetics from pearlite structure at 1073 K (800 °C) in an Fe-0.6 mass pct C binary alloy and Fe-0.6C-1 or 2 mass pct M (M = Mn, Si, Cr) ternary alloys were studied. Reverse transformation in the Fe-0.6C binary alloy at 1073 K (800 °C) was finished after holding for approximately 5.5 seconds. The reversion kinetics was accelerated slightly by the addition of Mn but retarded by the addition of Si or Cr. The difference of acceleration effects by the addition of the 1 and 2 mass pct Mn is small, whereas the retardation effect becomes more significant by increasing the amount of addition of Si or Cr. It is clarified from the thermodynamic viewpoint of carbon diffusion that austenite can grow without partitioning of Mn or Si in the Mn- or Si-added alloys. On the one hand, austenite growth is controlled by the carbon diffusion, whereas the addition of them affects carbon activity gradient, resulting in changes in reversion kinetics. On the other hand, thermodynamic calculation implies that the long-range diffusion of Cr is necessary for austenite growth in the Cr-added alloys. It is proposed that austenite growth from pearlite in the Cr-added alloys is controlled by the diffusion of Cr along austenite/pearlite interface.

Redox Equilibrium of Niobium in Calcium Silicate Base Melts

The oxidation state of niobium has been determined at 1873 K (1600 °C) in CaO-SiO2-NbOx melts with CaO/SiO2 ratios (mass pct) of 0.66, 0.93 and 1.10, and 5.72 to 11.44 pct Nb2O5 (initial). The slag samples were equilibrated with gas phases of controlled oxygen pressure, then quenched to room temperature and analyzed chemically. The niobium is mainly pentavalent with small amounts in the tetravalent state. It was found that the Nb5+/Nb4+ ratio increases with oxygen pressure at a constant CaO/SiO2 ratio and constant content of total niobium, closely according to the ideal law of mass action, which is proportional to \( {\text{p}}_{{{\text{O}}_{2} }}^{1/4} . \) The ratio also increases with total niobium content, and it seems to have a maximum at a basicity of about 0.93. The color of the solidified slag samples is described and is explained with the help of transmission spectra.

Oxidation of Fe-V Melts Under CO2-O2 Gas Mixtures

The oxidation mechanism of liquid Fe-V alloys with V content from 5 to 20 mass pct under different oxygen partial pressures using CO2-O2 mixtures with CO2 varying from 80 pct to 100 pct was investigated by thermogravimetric analysis between 1823 K and 1923 K (1550 °C and 1650 °C). The products after oxidation were identified by scanning electron microscopy energy-dispersive spectrograph and X-ray diffraction. The results indicate that the oxidation process can be divided into the following steps: an apparent incubation period, followed by a chemical reaction step with a transition step before the reaction, and diffusion as the last stage. At the initial stage, a period of slow mass increase was observed that could be attributed to possible oxygen dissolution in the liquid iron-vanadium coupled with the vaporization of V2O. The length of this period increased with increasing temperature as well as vanadium content in the melt and decreased with increasing oxygen partial pressure of the oxidant gas. This analysis was followed by a region of chemical oxidation. The oxidation rate increased with the increase of the O2 ratio in the CO2-O2 gas mixtures. During the final stage, the oxidation seemed to proceed with the diffusion of oxygen through the product layer to the reaction front. The Arrhenius activation energies for chemical reaction and diffusion were calculated, and kinetic equations for various steps were setup to describe the experimental results. The transition from one reaction mechanism to the next was described mathematically as mixed-control equations. Thus, uniform kinetic equations have been setup that could simulate the experimental results with good precision.

Effect of Multiwalled Carbon Nanotubes on the Thermal Conductivity and Porosity Characteristics of Blast Furnace Carbon Refractories

Different amounts of carbon nanotubes (CNTs) (0–5 mass pct) containing carbon refractory specimens for a blast furnace were prepared and coked for 3 hours at 1473 K (1200 °C) and 1673 K (1400 °C). The thermal conductivity and porosity characteristics of the coked specimens were evaluated using the flash diffusivity technique and mercury porosimetry, respectively. It was found that CNTs acted as carbon source, and most of them were consumed during coking. With the increase of CNT content, the aggregation of CNTs became more severe, the amount of SiC whiskers formed increased and their aspect ratio became larger, and the SiC whiskers tended to be distributed nonhomogeneously. The thermal conductivity of a 4 mass pct CNT containing a carbon specimen was highest because of the contributions of SiC and residual CNTs. The porosity characteristics of a 0.5 mass pct CNT containing a carbon specimen was best because of the uniform filling of SiC whiskers. The excessive addition of CNTs degraded the porosity characteristics because of the severe aggregation of CNTs.