Fluidity Of Liquid Phase Research Articles

Refined W-3.5Nb alloy fabricated by electron beam melting via doped carbon

Electron beam melting (EBM) is a promising powder bed fusion additive manufacturing (AM) technology for the preparation of complex refractory components due to the significant advantages of vacuum environment and high level in energy utilization, scanning speed and temperature in the build chamber. However, the fabrication of crack-free and refined W-based alloy remains a challenge. This study aims to address this problem by introducing 0.7 wt% carbon in EBM W-3.5Nb alloy. Results revealed that the as built W-3.5Nb alloy had a typical columnar structure with obvious solidification cracks along the grain boundary. Doping 0.7 wt% carbon generated refined microstructure, which was composed of the initial dendrite of tungsten and the eutectic phase in the dendrites gap. Due to the low distribution coefficient of carbon, the nucleation at the bottom of the molten pool was caused by constitutional supercooling in the front of liquid solidification in a single molten pool, and velocity of the solidification front was reduced by carbon concentration leading increased thermal supercooling. Supercooling (thermal supercooling together with constitutional supercooling) refined the microstructure of W-3.5Nb alloy effectively. Meanwhile, due to the formation of eutectic phase with low melting point, the fluidity of liquid phase at the terminal solidification was improved and the solidification cracks along the grain boundary were reduced. The carbon addition also played a significant role in alloy strengthening. The microhardness of the alloy increased from 382 HV to 696 HV, and the compressive strength increased from 962.89 MPa to 1892.56 MPa. These findings offer a new perspective on the AM fabrication of high-quality W-based alloys.

Effect of B2O3 Content on the Sintering Basic Characteristics of Mixed Ore Powder of Vanadium-Titanium Magnetite and Hematite

The sintering basic characteristics of iron ore play a key role in the process of sintering. In this study, the effects of B2O3 on the assimilation characteristics, softening temperature, fluidity of liquid phase, compressive strength of bonding phase, and microstructure of the mixed fine powder of hematite and vanadium-titanium magnetite (H-VTM) are studied. Results show that B2O3 content from 0%–5% (wt%) could improve the assimilation characteristics of the H-VTM and increase the amount of the liquid phase. The liquidity of the bonding phase index (LBPI) of the H-VTM increases from 3.7 to 24.2. When B2O3 content exceeds 2%, the diameter of the pore in the H-VTM sintered samples enlarges. However, the compressive strength gradually decreases. Boron and calcium-magnesium-aluminium elements are abundant in the bonding phase, which can reduce the formation of calcium silicate and perovskite in H-VTM sintered samples.

Fundamental mechanism of effects of MgO on sinter strength

MgO-containing flux may have a series of effects on the quality of sinter and performances of the blast furnace. Thus, the fundamental mechanism of the effects of MgO on the sinter strength was investigated. Both the chemical reagent and industrial flux were used for preparing the specimens. The experimental results show that the sinter strength decreases with MgO addition. There are three reasons for it. The first reason is diffusion rate. Almost all of the CaO may react with Fe2O3 and generate CaO·Fe2O3, but most of MgO cannot react with Fe2O3, and it still remains in the state of original minerals. The diffusion rate of MgO in iron oxide is only 17.51 μm/min in 30 min. The second reason is the fluidity and ability to generate liquid phase. In the case of Fe2O3 mixed with CaO, there is some liquid phase formed above 1200 °C, while in the case of Fe2O3 mixed with MgO, even at 1200 and 1220 °C, there is still no liquid phase. The third reason is self-strength. In the case of industrial flux, the compression strength of the specimens made of Fe2O3 and limestone is 0.52 and 0.71 kN at 1150 and 1180 °C, respectively, while that of the specimens made of Fe2O3 and magnesite is 0.48 and 0.56 kN, respectively. Therefore, the fundamental mechanism of the effects of MgO additive on sinter strength can be better understood based on the diffusion rate of MgO in iron oxides, the fluidity of liquid phase, and the self-strength of bonding phase.

The correlation between high temperature properties and sintering performance of Australian iron ore fines

ABSTRACT The characteristics of iron ore fines were considered to have tremendous effects on their subsequent sintering performances, but it is difficult to judge their sintering performances only based on their basic physicphysio-chemical properties. In this study, the correlation between the fundamental high temperature properties of seven commercial Australian iron ore fines and their single-ore sintering performance were revealed by measuring the lowest assimilation temperature (LAT), index of fluidity of liquid phase (IFL), strength of bonding phases (SBP) and the percentage of formed silicoferrite of calcium and aluminium (SFCA) of the iron ores and conducting pilot scale sintering pot tests. The results showed that the correlation is very complicated. There is a negative correlation between the tumble index (TI) of sinter products and LAT of iron ore fines. Iron ore fines have better sintering performance within the appropriate range of IFL between 0.17 and 0.88. The correlativity between SBP, percentage of formed SFCA (PFS) and the sintering performance of iron ore fines is complex.

Relationship Between Liquid Fluidity of Iron Ore and Generated Liquid Content During Sintering

The fluidity of sintering liquid phase reflects the effective bonding range of the binder phase in the sintering process of iron ores. In this study, the liquid composition and quantity during sintering was calculated using FactSage 7.0 thermodynamic calculation software. The results show that two liquid phases are formed during sintering. One phase is generated at about 1373 K (1100 °C) and the other is generated at about 1523 K (1250 °C). The liquid fluidity index and the low-temperature liquid phase are closely related. The higher-temperature liquid phase has little influence on the liquid fluidity index. The larger the amount of low-temperature liquid phase generated, the higher the liquid fluidity index is. The alkalinity of the low-temperature liquid phase has insignificant influence on the liquid fluidity index. The content of SiO2 in the iron ore is the main factor that affects the liquid fluidity index during sintering. The liquid fluidity index increases greatly with increasing SiO2 content. In contrast, Al2O3 content has little influence on the liquid fluidity index, with an increase in the Al2O3 content only slightly increasing the liquid fluidity index. An increase in the MgO content of the iron ore can reduce liquid generation, promote the spinel generation, and decrease the liquid fluidity index during sintering.

Influence of gangue existing states in iron ores on the formation and flow of liquid phase during sintering

Abstract Gangue existing states largely affect the high-temperature characteristics of iron ores. Using a micro-sintering method and scanning electron microscopy, the effects of gangue content, gangue type, and gangue size on the assimilation characteristics and fluidity of liquid phase of five different iron ores were analyzed in this study. Next, the mechanism based on the reaction between gangues and sintering materials was unraveled. The results show that, as the SiO2 levels increase in the iron ores, the lowest assimilation temperature (LAT) decreases, whereas the index of fluidity of liquid phase (IFL) increases. Below 1.5wt%, Al2O3 benefits the assimilation reaction, but higher concentrations proved detrimental. Larger quartz particles increase the SiO2 levels at the local reaction interface between the iron ore and CaO, thereby reducing the LAT. Quartz-gibbsite is more conductive to assimilation than kaolin. Quartz-gibbsite and kaolin gangues encourage the formation of liquid-phase low-Al2O3-SFCA with high IFL and high-Al2O3-SFCA with low IFL, respectively.

Influencing Factors and Effects of Assimilation Characteristic of Iron Ores in Sintering Process

Iron ore’s assimilation characteristic reflecting the beginning formation temperature of liquid phase in sintering process plays very important role on the fluidity of liquid phase and bonding strength of sinter body. Experimental study of assimilation characteristics of 12 kinds of iron ores were conducted using micro-sinter equipment, and pure reagent simulating tests of assimilation characteristic were also carried out for the purpose of achieving the influence of chemical composition on the assimilation characteristic. In addition, effects of assimilation characteristic of iron ore on the fluidity and bonding capacity of bonding phase were also researched. This study showed that SiO2 and LOI promoted the assimilation of iron ore, low Al2O3 (<1.5 mass%) was good to the assimilation, but high Al2O3 (≥1.5 mass%) was bad, MgO was adverse to assimilation of magnetite concentrate. In addition, lower assimilation temperature of iron ore led to higher superheat degree of liquid phase at a certain sintering temperature, then higher liquid fluidity and bonding strength.

Research on Influence Law of Fuel Structure for Low-FeO Sintering

Micro–sintering equipment was applied to simulate sintering process of iron ore. FeO content of sinter-samples under different fuel structures was measured, and then the effect of fuel structure on fluidity of liquid phase and strength of bonding phase were analyzed in this paper. The proper fuel structure was finally discussed under low FeO sintering condition. The results show that: when anthracite was adopted as partial substitution of coke breeze as part of solid fuel, FeO of sinter reduces and self-strength of bonding phase increases. Although fluidity of liquid phase reduces, the fluidity index it is still above 0.8, which can meet the liquid volume needed for sintering. When CDQ powder is used as part of solid fuel, FeO of sinter also reduces, but fluidity of liquid phase and self-strength of bonding phase reduce a little due to its low combustibility. Taking experimental results and practical production together into account, it can be concluded that proper fuel structure that meets low FeO sintering should be “70% coke+30% anthracite”.

Research on High-Temperature Properties of Typical Iron Ores Used in China and its Blending Optimization

High-temperature properties of 10 samples of iron ore from Brazil, Australia and China were measured. Several conclusions were made based on these experimental results. Assimilability of Brazilian ore, Australian ore and Chinese ore concentrate were low, high and medium, respectively. Optimal fluidity of liquid phase was observed in 2 types of Brazilian ores (BR-B, BR-C), 1 type of Australian ore (AU-C) and 1 type of Chinese ore (CH-D). For self-strength of the bonding phase, Australian ore presented low levels, while Brazilian and Chinese ore presented high levels. According to the experimental results of high-temperature properties of iron ore, schemes of ore blending optimization were designed and sinter pot test using these blends were performed. The results indicated that ore blends composed of 30~45% Brazilian ores + 25~50% Australian ores + 20~30% Chinese concentrates presented excellent sintering results, considering both the performance of the processing and quality of the sinter. Therefore this experiment has proved that ore blending optimization combining high temperature properties can lead to more efficient sintering mixes.

Mechanisms of composite agglomeration of fluoric iron concentrate

The effect of composite agglomeration process (CAP) on fluoric iron concentrates sintering was investigated. The yield and quality of the sinter are greatly improved when using CAP assisted with heat airflow and enhancing magnesium oxide (MgO) contents. For conventional sintering of fluoric iron concentrate, due to lower viscosity of binding phase and higher fluidity of liquid phase, the sinter is formed with large thin-walled holes and the strength of the sinter is deteriorated consequently. The novel process forms composite agglomerate in which acid pellets are embedded in basic sinter. The pellets are solid with interconnecting crystals of hematite (Fe2O3) and magnetic (Fe3O4). For basic sintering, after adding MgO, the viscosity of the melting phase increases and the fluidity decreases; and calcium and aluminum silico-ferrites and magnesium ferrite are formed with perfect crystals and good sintering microstructure.