The behavior of magnesium vapor injected in the molten steel and the potential of magnesium vapor for the miniaturization of TiN were evaluated via continuous casting experiments. The position where ...magnesium vapor should be injected was determined through a non-steady state three-dimensional numerical simulation for molten steel flow in a tundish. The yield of magnesium in the molten steel was changed by the injection position. A high additive yield was achieved when magnesium vapor was injected between the immersion nozzle and the narrow wall of the tundish. The concentration of the soluble magnesium was maintained using a novel method that continuously added magnesium vapor into the molten steel in the tundish, which also ensured stable miniaturization of TiN.
It is important to understand the solidification behavior of titanium alloys for optimizing the casting conditions. In this study, to evaluate the solidification behavior of the Ti-6Al-4V alloy, an ...experiment was conducted using a lab-scale electron beam furnace. After melting the surface layer of the ingot through electron beam heating, the surface layer was allowed to solidify. Based on the measurement results of the cooling curve of the surface of the ingots, it was observed that the solid was subject to undercooling during its formation. The cooling rate of the ingot could be predicted through numerical simulation, for the melting and solidification of the ingot. The primary and the secondary dendrite arm spacing were examined with respect to the cooling rate. The concentrations of Al and V in the dendritic region were analyzed using electron probe microanalysis (EPMA). It is clarified that the Al is segregated into the dendrite core during solidification, and that V is segregated into the interdendritic region.
This study examines the evaporation of Al from a molten commercial Ti alloy with different Al concentrations after partial melting in a small electron beam furnace. Electron probe micro analysis ...confirmed that the Al concentration in the molten region was uniform. The movement of Al in the molten region was not found to be the rate determining step. The Al concentration in the molten region consistently decreased with an increasing melting time but in a non-linear manner. The activity of Al in the molten alloy was calculated using thermodynamic data, which indicated that it increased with an increasing Al concentration in the ingot. However, the activity of Al in the molten alloy did not increase linearly under the influence of the other alloying elements. The overall mass transfer coefficient of Al from molten alloy during evaporation increased with an increasing initial Al concentration with the mass transfer coefficient of Al depending on the activity of Al. An evaporation model was constructed by considering the mutual interaction between Al and the other alloying elements. This evaporation model was able to predict the amount of Al evaporation from the multi-component Ti alloy melt.
The occurrence of longitudinal surface cracks in hypo-peritectic carbon steel slabs depends largely on the cooling capacity of the mold and the flow velocity of molten steel below the meniscus. The ...influence of both flow velocity of the molten steel below the meniscus and the heat flux in the copper mold were examined using continuous casting tests and numerical simulation of the molten steel flow. The casting speed was fixed, and the meniscus flow velocity was controlled by adjusting the port size of the submerged entry nozzle. The molten steel flow velocity was predicted by a three-dimensional unsteady-state numerical simulation. Heat flux in the copper mold was calculated based on temperature readings from thermocouples arranged in the direction of both the mold width and mold length. When the difference in flow velocity of molten steel in the mold width direction became large, longitudinal surface cracks occurred in the central region of the slab. In these cases, the heat flux below the meniscus in the mold width direction was not constant. Small holes were drilled along the central region of the mold width. This decreased both the heat flux and tensile strength of the central region of the slab width, and successfully reduced the occurrence of longitudinal surface cracks.
For multi-component titanium alloy ingots that contain evaporable solute elements, the evaporation behavior of these elements is very important for optimizing the casting conditions. This study ...examined the evaporation of Al and Sn from molten Ti-6242, an alloy used for aircraft engines, after partial melting in a small electron beam furnace. The amount of Al and Sn evaporation depended on the melting time, and there equilibrium vapor pressure of the elements and activity in the molten alloy. The concentration of Al changed in proportion to that of Sn in the molten alloy during evaporation process and the amount of evaporation of Al was twice as Sn. The rate control step of evaporation of Al and Sn were limited by evaporation from the molten alloy surface to the vacuum phase. The liquidus temperature of the alloy melt also changed with the evaporation of Al and Sn. These findings will help predict the amount of solute evaporation from molten titanium alloys and maintain the surface and internal quality of the ingots.
The nitriding behavior of titanium sponges with nitrogen gas and the dissolution behavior of titanium nitride titanium sponges in titanium alloy melt were examined.A titanium nitride sponge was ...produced using nitrogen gas. A high nitriding temperature corresponded to a longer nitriding time, and thus to a higher nitrogen concentration in the sponge. Both the titanium sponge and titanium nitride sponge featured a porous structure. Porous structures at both the surface layer and inside were formed at intervals of about 5.0 × 10−5 m. When the titanium nitride sponge was immersed into a titanium alloy melt, the melt permeated into the pores. The nominal dissolution rate of the titanium nitride sponge in the titanium alloy melt depends on the temperature of the melt. Higher melt temperatures corresponded to higher nominal dissolution rates. However, the concentration of nitrogen in the titanium nitride sponge had no influence on the nominal dissolution rate. Nitriding models of the titanium sponge with nitrogen gas, and the dissolution model of the titanium nitride sponge into the titanium alloy melt were proposed. These models considered the structure of the sponge; thus, the behavior of both the nitriding and dissolution sponges was predicted and confirmed.
The behavior for injection of magnesium vapor into molten steel and the potential of magnesium vapor for miniaturization of TiN size were evaluated by the experiment in tammann furnace and the ...experiment in vacuum furnace. From the results of these experiments, the partial pressure of magnesium reacting with molten steel could be increased, and the both high concentration in molten steel and high additive yield of magnesium into molten steel could be done together. It was confirmed that spinel MgO·Al2O3 was formed as a heterogeneous nucleus of TiN. The dissolved magnesium concentration governed the heterogeneous nucleus for TiN. The injection of magnesium vapor into molten steel could control the generation of heterogeneous nucleus during solidification.
The dissolution behaviors of titanium nitride titanium sponges in titanium alloy melt were examined. A titanium nitride sponge was produced using nitrogen gas. The titanium nitride sponge featured a ...porous structure. Porous structures at both the surface layer and inside were formed at intervals of about 5.0 × 10-5 m. When the titanium nitride sponge was immersed into a titanium alloy melt, the melt permeated into the pores. The dissolution rate of the titanium nitride sponge in the titanium alloy melt depends on the temperature of the melt. Higher melt temperatures corresponded to higher dissolution rates. However, the concentration of nitrogen in the titanium nitride sponge had no influence on the dissolution rate. Dissolution model of the titanium nitride sponge into the titanium alloy melt were proposed. These models considered the structure of the sponge; thus, the behavior of the dissolution sponges was predicted and confirmed.
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