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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

A Reaction Between High Mn–High Al Steel and CaO-SiO{sub 2}-Type Molten Mold Flux: Reduction of Additive Oxide Components in Mold Flux by Al in Steel

The interfacial reaction between high-Mn–high-Al steel and CaO-SiO{sub 2}-type mold flux was investigated, with particular emphasis on the reduction of additive oxide components by Al. Typical additive oxide components (B{sub 2}O{sub 3}, Na{sub 2}O) could be reduced by Al, thereby losing their initial role in the flux. It is proposed to consider the chemical stability of the additive components in the flux in addition to the physico-chemical properties of the flux when developing the mold flux chemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Dynamic Wetting of High-Al Steel by CaO-SiO{sub 2}- and CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes

Wetting of steel by mold fluxes affects the surface quality of steel products. Reaction between [Al] and mold fluxes in the continuous casting of high-Al steel leads to a dynamic interfacial phenomenon. This work investigated the wetting of the high-Al steel substrate by CaO-SiO{sub 2}-based and CaO-Al{sub 2}O{sub 3}-based mold fluxes. The interfacial tensions were estimated and related to their high-temperature structures. The interface morphology revealed that CaO-SiO{sub 2}-based mold flux and CaO-Al{sub 2}O{sub 3}-based mold flux with CaO/Al{sub 2}O{sub 3} = 1 exhibited deep reaction zones in the steel substrates and irregular flux/steel interfaces, while CaO-Al{sub 2}O{sub 3}-based mold fluxes with CaO/Al{sub 2}O{sub 3} = 2 and 3 showed smooth interfaces and superficial reaction zones. The sedation of dynamic wetting behavior in Samples 3 and 4 was related to the high viscosity in the flux droplet after the initial composition change, which led to the stabilization of the interface.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Temperature and Structure Dependence of Surface Tension of CaO-SiO{sub 2}-Na{sub 2}O-CaF{sub 2} Mold Fluxes

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO{sub 2}-Na{sub 2}O-CaF{sub 2} mold-flux melts with different CaO/SiO{sub 2} mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO{sub 2} mass ratios, and agreed with the modification of melt structure. When the CaO/SiO{sub 2} mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO{sub 2} mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Fluorine on Solidification, Viscosity, Structure, and Heat Transfer of CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes

To mitigate the chemical reaction between mold fluxes and high-Al steel, CaO-Al{sub 2}O{sub 3}-based mold fluxes were proposed to replace the conventional CaO-SiO{sub 2}-based mold fluxes. However, the high viscosity of CaO-Al{sub 2}O{sub 3}-based mold fluxes is harmful to the lubrication to the strand. In this article, the effects of fluorine on solidification, viscosity, structure, and heat transfer of CaO-Al{sub 2}O{sub 3}-based mold fluxes were evaluated. The addition of fluorine increased the break temperature and decreased the heat transfer rate of mold fluxes. It also reduced the flux viscosity at 1673 K (1400 °C) when fluorine content increased from 4.0 to 6.9 mass pct; but a further increase of fluorine to 12.5 mass pct did not notably change the flux viscosity. This phenomenon was correlated to the synergic effects of the dissociation of flux network and the increased potential of nucleation at high temperature with the fluorine addition.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Al{sub 2}O{sub 3}/(B{sub 2}O{sub 3 }+ Na{sub 2}O) Ratio on CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes: Melting Property, Viscosity, Heat Transfer, and Structure

CaO-Al{sub 2}O{sub 3}-based mold fluxes, which are under development for the continuous casting of high-Al steel, contain fluxing compounds, such as Na{sub 2}O and B{sub 2}O{sub 3}. The reaction between [Al] and the fluxing agents in mold fluxes leads to an increase in Al{sub 2}O{sub 3} and a decrease in B{sub 2}O{sub 3} and Na{sub 2}O concentrations, changing the properties of mold fluxes. The effect of the Al{sub 2}O{sub 3}/(B{sub 2}O{sub 3 }+ Na{sub 2}O) ratio on the melting properties, viscosity, heat transfer, and structure of the CaO-Al{sub 2}O{sub 3}-based mold fluxes is presented in this work. The increase of the Al{sub 2}O{sub 3}/(B{sub 2}O{sub 3 }+ Na{sub 2}O) ratio in the fluxes raised the melting temperature and high-temperature viscosity of mold fluxes but decreased the heat transfer rate across the flux disks. It also enhanced the degree of polymerization by promoting the formation of 3-D aluminate structure, which accounted for the change of the viscous behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of B{sub 2}O{sub 3} on Crystallization, Structure, and Heat Transfer of CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes

The reaction between traditional CaO-SiO{sub 2}-based mold fluxes and high-Al steel inevitably changes flux composition, and, consequently, flux properties. This problem can be mitigated by using CaO-Al{sub 2}O{sub 3}-based mold fluxes. To maintain appropriate melting properties, CaO-Al{sub 2}O{sub 3}-based mold fluxes contain B{sub 2}O{sub 3}, which is an effective fluxing agent that decreases the liquidus temperature. In this article, the effects of B{sub 2}O{sub 3} on crystallization behavior, structure, and heat transfer of CaO-Al{sub 2}O{sub 3}-based mold fluxes were studied using single/double hot thermocouple technique, Raman spectroscopy, and infrared emitter technique. The increase of B{sub 2}O{sub 3} content from 7.6 to 13.1 mass pct suppressed the crystallization tendency of mold fluxes in continuous cooling experiments and isothermal experiments conducted over 1273 K (1000 °C). The isothermal crystallization below 1273 K (1000 °C) was also inhibited when B{sub 2}O{sub 3} content increased from 7.6 to 9.6 mass pct; but a further increase of B{sub 2}O{sub 3} content to 13.1 mass pct did not show a visible effect on the crystallization tendency. The increase of B{sub 2}O{sub 3} content from 9.6 to 13.1 mass pct improved the heat fluxes under an incident thermal radiation of 1.6 MW/m{sup 2}; however, the increase of B{sub 2}O{sub 3} content from 7.6 to 9.6 mass pct slightly decreased the heat transfer rate. Crystallization of fluxes and heat transfer were discussed in relation to flux structure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Nonisothermal Crystallization Kinetics of Glassy Mold Fluxes

Crystallization of the solid glassy mold flux film occurring in the gap between the initial shell and mold wall is important, as it determines the in-mold heat transfer and mold lubrication during the process of continuous casting. In order to study the nonisothermal crystallization behavior of the glassy mold flux film in the continuous casting mold, the continuous heating transformation diagram, crystallization mechanism, and precipitate phases were investigated using the single hot thermocouple technique, kinetic models, a scanning electron microscope, and an energy-dispersive spectrometer (EDS). The results show that the initial crystallization temperature for CaO-SiO{sub 2} based flux A ranges from [1086 K to 1147 K (813 °C to 874 °C)], which is lower than the case of CaO-Al{sub 2}O{sub 3} based flux B ranging from [1205 K to 1245 K (932 °C to 972 °C)]. The crystallization kinetics for flux A are constant nucleation rate, two-dimensional growth, and control by diffusion. For flux B, they are constant nucleation rate, three-dimensional growth, and control by interface reaction. Besides, the EDS results indicate that the precipitate crystals in fluxes A and B are CaSiO{sub 3} and Ca{sub 2}AlSiO{sub 4}, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of MgO on Crystallization and Heat Transfer of Fluoride-Free Mold Fluxes

The effect of MgO on crystallization and heat transfer of fluoride-free mold fluxes was studied using single/double-hot thermocouple technique (SHTT/DHTT) and infrared emitter technique (IET), respectively. SHTT experiments demonstrated that the increase of MgO concentration promoted the crystallization tendency of mold fluxes. XRD analysis showed that the dominant phases changed from CaSiO{sub 3} to CaSiO{sub 3}/Ca{sub 2}MgSi{sub 2}O{sub 7}/Ca{sub 11}Si{sub 4}B{sub 2}O{sub 22}, and to Ca{sub 2}MgSi{sub 2}O{sub 7} as the MgO content was increased. The heat flux across mold flux disks was reduced from 671 to 615 kW/m{sup 2} in IET experiments when MgO concentration was increased from 0.9 to 4.9 mass pct.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optimization of Mold Flux for the Continuous Casting of Cr-Contained Steels

To compensate the negative effect caused by the absorption of chromium oxide inclusions during the casting process of Cr-contained steels, a new mold flux system has been designed and investigated. The melting temperature range of the newly designed mold flux system is from [1124 K to 1395 K (851 °C to 1122 °C)]. The viscosity at 1573 K (1300 °C) and the break temperature increase with the addition of MnO and Cr{sub 2}O{sub 3} but decrease with the addition of B{sub 2}O{sub 3}. The crystalline fraction of mold flux decreases from 81 to 42.1 pct with the addition of MnO and Cr{sub 2}O{sub 3}, and then further decreases to 25.3 pct with the addition of B{sub 2}O{sub 3}; however, it improves from 54.4 to 81.5 pct when the basicity increases. Besides, the heat-transfer ability of mold flux is inverse to the crystallization ratio of the slag. The comprehensive study of the properties for the four designed mold fluxes suggests that the mold flux with 1.15 basicity-3.01 pct B{sub 2}O{sub 3}-1.10 pct MnO-2.10 pct Cr{sub 2}O{sub 3} shows the best properties for the continuous casting of Cr-contained steels.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Li{sub 2}O on the Behavior of Melting, Crystallization, and Structure for CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes

The effect of Li{sub 2}O content on the behavior of melting, crystallization, and molten structure for CaO-Al{sub 2}O{sub 3}-based mold fluxes was investigated in this article, through use of single hot thermocouple technology (SHTT), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction (XRD). The SHTT results showed that the melting temperature range of the designed mold fluxes decreases and the crystallization of mold fluxes is inhibited first and then becomes enhanced when the Li{sub 2}O content increases from 1 to 6 mass pct. The FTIR and Raman spectroscopy results suggested that Li{sub 2}O could release O{sup 2−} ions to break the complex Al-O-Al structural unit into Al-O{sup −} structure. Meanwhile, Li{sub 2}O could also stabilize the structural unit of Si-O-Al by link aluminate and Q{sub 0}{sup Si} structure through providing Li{sup +} ions to merge into the network and compensate for the charges between Al{sup 3+} and Si{sup 4+}. Besides, the XRD results indicated that the precipitation of LiAlO{sub 2} in molten slag would enhance the crystallization behavior of mold flux when Li{sub 2}O content is over 4.5 mass pct.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interfacial Reaction Between High-Al Steel and CaO-Al{sub 2}O{sub 3}-Based Mold Fluxes with Different CaO/Al{sub 2}O{sub 3} Ratios at 1773 K (1500 °C)

The reaction between high-Al steel and CaO-Al{sub 2}O{sub 3}-based mold fluxes with different CaO/Al{sub 2}O{sub 3} ratios was investigated at 1773 K (1500 °C). The increase of CaO/Al{sub 2}O{sub 3} ratio from 1 to 3 accelerated the accumulation of Al{sub 2}O{sub 3} in the flux and reduction of Na{sub 2}O, but had no significant effect on the reduction of SiO{sub 2} and B{sub 2}O{sub 3}. The microstructure of flux-steel interfaces showed that emulsification occurred in the reaction between steel and mold flux. The emulsification was affected by the precipitation of crystals in the flux after the change of flux composition due to the interfacial reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Radiation–Conduction Heat-Transfer Study for Mold Flux by Thermoviewer-Enhanced Infrared Emitter Technique

A thermoviewer-enhanced infrared emitter technique was developed in this article to study the heat-transfer behavior of mold flux in the continuous casting mold. Then, a radiation–conduction heat-transfer model was built to determine the radiative/conductive heat flux, thermal conductivity, and optical properties of slag. The results showed that the mold/slag interfacial thermal resistance decreases with the increasing temperature of slag surface at the mold side, and then reaches the minimum when the slag surface is the hottest, and finally increases slightly with further increase in slag crystallization. In addition, the radiative heat flux decreases with the increasing depth of radiation propagating into the slag. While the amount of heat of radiation lost is being converted to produce an additional radiative heat source to heat the slag, the increase in the conductive heat flux in the slag is realized. Furthermore, the apparent transmittivity is obtained as 0.63 for the glassy slag disk and as 0.41 for the partially crystallized slag disk. Besides, when mold heat flux decreases from the maximum to a saturation value due to the further slag crystallization, the corresponding apparent transmittivity of slag disk decreases from 0.58 to 0.41, and the ratio of the heat across the slag disk by radiation decreases from 67.3 to 50.0 pct.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Slag-Steel Reaction on the Initial Solidification of Molten Steel during Continuous Casting

With the mold simulator technique, the effect of slag-steel reaction on the initial shell solidification as well as the heat transfer and lubrication behavior of the infiltrated mold/shell slag film was studied in this article. The results showed that the Al{sub 2}O{sub 3} content, the CaO/SiO{sub 2} ratio, and the viscosity of mold flux were increased with the progress of the slag-steel reaction during casting. The slag-steel reaction has two major effects on the initial shell solidification: one is increasing the mold heat flux and shell thickness by the decrease of slag film thickness. The other is the reduction of mold heat flux by the increase of crystal fraction in slag film. Mold flux with a lower basicity, viscosity, and crystallization temperature would result in a larger liquid slag consumption and the uneven infiltration of slag into the mold and shell gap that eventually leads to the irregular solidification of initial shell with a poor surface quality, such as slag entrapment and depressions as well as glaciation marks. Conversely, mold flux with a higher viscosity, basicity, and crystallization temperature would result in a smaller liquid slag consumption, which would cause the poor mold lubrication, the longitudinal shell surface defects, and drag marks.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Nozzle Port Angle on Transient Flow and Surface Slag Behavior During Continuous Steel-Slab Casting

Undesirable flow variations can cause severe instabilities at the interface between liquid mold flux and molten steel across the mold top-region during continuous steel casting, resulting in surface defects in the final products. A three-dimensional Large Eddy Simulation (LES) model using the volume of fluid method for the slag and molten steel phases is validated with plant measurements, and applied to gain new insights into the effects of nozzle port angle on transient flow, top slag/steel interface movement, and slag behavior during continuous slab casting under nominally steady conditions. Upward-angled ports produce a single-roll flow pattern with lower surface velocity, due to rapid momentum dissipation of the spreading jet. However, strong jet wobbling from the port leads to greater interface variations. Severe level drops allow easy entrapment of liquid flux by the solidifying steel shell at the meniscus. Sudden level rises may also be detrimental, leading to overflow of the solidified meniscus region. Downward-angled ports produce a classic double-roll pattern with less jet turbulence and a more stable interface everywhere except near the narrow faces. Finally, the flow patterns, surface velocity, and level predicted from the validated LES model are compared with steady-state standard k-ε model predictions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Structural analysis of molten materials by a remote fiber optic Raman sensor

This study presents a novel in situ high-temperature fiber optic Raman probe that enables the study of the physical properties and structure of molten samples at temperatures up to 1400 °C. To demonstrate the functionality of the high-temperature fiber optic Raman probe, different composition mold fluxes were evaluated in this report. The Raman spectra at flux molten temperature were successfully collected and analyzed. A deconvolution algorithm was employed to identify peaks in the spectra associated with the molecular structure of the components in each sample. Here, the experimental results demonstrate that the composition-dependent Raman signal shift can be detected at high temperatures, indicating that molten materials analysis using a high-temperature Raman system shows significant promise. This flexible and reliable high-temperature Raman measurement method has great potential for various applications, such as materials development, composition and structure monitoring during high-temperature processing, chemical identification, and process monitoring in industrial production.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Effects of Simultaneous Static and Traveling Magnetic Fields on the Molten Steel Flow in a Continuous Casting Mold

The drawback of steel fluid flow phenomena for a continuous casting mold under an electromagnetic stirrer with a traveling magnetic field is the resulting severe meniscus fluctuations due to the high-velocity and excessive downward flow in the casting direction. This can result in slab surface defects due to mold flux or inclusion entrainment. To inhibit these defects in the as-cast steel products, the implementation of braking forces using static magnetic fields in combination with a traveling magnetic field was studied in the current study. The numerical results of the fluid flow in the mold under a combined traveling and static magnetic field operation show not only 50 pct lower downward flow speed, but also more enhanced rotational flow to improve washing effects. The numerical results were validated in commercial-scale operations. The results suggest the optimized range of the ratio between the traveling and static magnetic flux densities is 65 to 75 pct to ensure steel quality improvements; this range maintains a balance between the fluid forces from the jet flow and the magnetic forces in the mold.

36 MATERIALS SCIENCE↗