Hong Xia Li

Properties of ZrO2-C Materials with Anti-Oxidants

Submerged Entry nozzle is one of the key functional refractories for continuous casting and the safe and efficiency of the continuous casting is directly influenced by the properties of ZrO2-C materials located at the slag line of the submerged entry nozzle. In general, a little anti-oxidants such as SiC, Si or B4C will be introudced into ZrO2-C materials and anti-oxidants also influence the corrosion resistance of ZrO2-C materials. So this paper researched the properties especially the corrosion resistance of ZrO2-C materials with SiC, Si or B4C additions. The results show that the properties of ZrO2-C materials are relate to the composition of ZrO2-C materials and the corrosion resistance of ZrO2-C materials have no obvious relationship with other properties such as apparent porosity, bulk density, et al. The addition of anti-oxidants will all decrease the corrosion resistance of ZrO2-C material. The decreasing degree of corrosion resistance by Si is the most and the decreasing degree of corrosion resistance by SiC is the least. The corrosion resistance of ZrO2-C material with B4C addition is relate to the kind of the mold slag. To obtain the ZrO2-C material with excellent corrosion resistance antioxidants should not be added into ZrO2-C materials.

Numerical Simulation of Flow Field in the Tundish with Two Outlets

According to the operating parameters of continuous casting tundish in a steel mill, the flow patterns of liquid steel in tundish were studied by the method of numerical simulation. Changing the flow orifice area of slag wall, to simulate and calculate the influence of slag wall on the flow field in tundish. Through calculating the steel flow vector, to analyze the uniformity of steel flow in tundish, by calculating the inclusions distribution to analyze the effect of blocking slag wall holding inclusions. The simulation results show that: the slag wall can obviously deduce the short circuit flow of steel liquid in tundish bottom. With the flow orifice area is reduced, and the turbulence brisk between two slag walls, and liquid surface is easy to roll; the ability of slag wall holding inclusions enhances, but too small flow orifice area will prompt inclusions passing the slag wall.

Numerical Calculation for Temperature Field in Two Exits Tundish

According to the operating parameters of a tundish for continuous casting in a steel mill, the temperature distribution of molten steel in tundish was studied by the method of numerical calculation. Change the flow orifice area of slag wall, simulation calculation for the effect of various slag walls on the temperature distribution of molten steel in tundish was done. Through the calculation and analysis of tundish longitudinal section and the surface temperature distribution, temperature uniformity of molten steel in tundish was determined. The calculation results show that: the slag wall can obviously deduce temperature difference between the top and the bottom of molten steel in tundish; small flow orifice area of slag wall can promote the temperature uniformity of molten steel after slag wall.

Effect of Furfural on Structure and Charring Properties of Phenolic Resins

In order to improve the coke residue of phenolic resins (PF), different solvents were used in the present work. The research indicates that in comparison with other solvents, such as ethylene glycol (EG) and ethyl silicate (ES), furfural (FF) can enhance crosslinking density and increase residual coke yield of phenolic resins (PF). The results demonstrate that the residual coke yield of PF with furfural is 68 % higher than that with other solvents. In addition, pyrolysis peak temperature of PF with furfural is relatively high and pyrolysis process is more smoothly. FTIR results show that new bonds formed in PF when take furfural as solvent, and furfural changed the structure of phenolic resins. Raman spectra analysis results show that the order degree of the carbonized products (treated at 800 °C) is higher than that in other solvents, and stability of the carbonized products is improved. The research concludes that the type of solvent has great influence on the structure and coke residue.

Effect of Sheet Nanocarbon on Properties of Low Carbon Al 2 O 3 -C Refractories

Sheet nanocarbon-Al2O3 composite powders were produced by vibratory milling using expanded graphite and Al2O3 powders as raw materials. The effect of different vibratory milling time on phase compositions and microstructure of the composite powders were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM). Then sheet nanocarbon-Al2O3 composite powders were used as additives to produce low carbon Al2O3-C refractories which had a carbon content of 6%. The results showed that about 50nm thickness sheet nanocarbon and Al2O3 composite powders were produced via 15h milling with expanded graphite to Al2O3 powders weight ratio of 1:2. With the increasing of milling time, the (002) diffraction peaks of graphite wear off gradually and nanosheet was desquamated from expanded graphite; It is beneficial to improve the bulk density, cold modulus of rupture (CMOR) and thermal shock resistance of Al2O3-C refractories when adding certain sheet nanocarbon-Al2O3 composite powders. The sample containing 0.5% sheet nanocarbon had a CMOR of 18.51MPa after 1000 °C heat processing in N2 atmosphere, while sample without adding any sheet nanocarbon was only 12.35MPa; The residual cold modulus of rupture (CMORTS) of sample containing 1% sheet nanocarbon was 4.22MPa after thermal shock test, while that of sample without nanocarbon was only 2.18MPa.

Fracture Energy of Refractories

This paper introduce the relationship between fracture energy of refractories and its thermal shock resistance, and research status about fracture energy of refractories. It shows that investigation on fracture energy of refractories at high temperature is positive significance for evaluation of thermal shock resistance, and wedge splitting method for fracture energy of refractories is an effective method.

Influence of Ladle Purging Plug Airway on Flow Properties of Liquid Steel

The influence of the different airway structure on mixing time of molten steel are studied through using water model experiments. The bubble volume and velocity have been investigated through the PIV for different airway structure in the flow of 1m3/h. Results showed that with the slit distribution same, the smaller the slit width, the greater the volume percentage of the large bubbles and the average velocity of the bubbles in rising, but the shorter the mixing time. Reduce the number of the slit can lead to the volume percentage of the large bubbles and the average velocity of the bubbles in rising decreases, the mixing time extended, and it is more obvious to the mixing time to reduce the number of the inner slit. Inflatable volume<1.1m3/h, with the slit in the outer ring only and the number of slit same, the volume percentage and the average velocity of the large bubbles in rising is larger, the mixing time is reduced. Inflatable volume≥1.1m3/h, the slit evenly distribution is better for mixing.

The Properties of MgO-C Materials with Different Graphite Size Distributions

Monolithic stopper is one of the functional refractories. The security and continuity of the continuous casting maybe irrupted by the abnormal condition of monolithic stopper. MgO-C material composite monolithic stopper is often used to cast Ca-treated steel. But the thermal expansion of MgO-C materials is relatively large and there is a poor thermal matching between rod part and body part. To improve thermal shock resistance of MgO-C materials, the properties of MgO-C materials with different graphite size distributions are researched. The results show that 1000 mesh graphite addition will decrease thermal shock resistance, fracture energy and thermal expansion will increase. MgO-C materials with combined addition of 595 and 199 graphite present good thermal shock resistance. The trends of thermal shock resistance for MgO-C refractories by immerging molten steel methods agree with that of Rst.

Influence of Additive on High Temperature Performance of Glaze

Using SiO2 – Al2O3 – B2O3 – K2O – Na2O system glaze as base material, adding silicon powder or alumina powder with grain size 15μm by the mass percent of 10%, 20%, 30%, respectively, melting properties of glaze were investigated. Slilica solution as binder, the anti-oxidation coating were prepared. Oxidation resistance was determined by coating to the surface of the Al2O3-C specimens. The results show that additives can raise flow temperature prominently, but has little influence on softening point and semi-sphere point; Glazing temperature ranges are obtained with different additive contents; Glazing temperature rises with addition of silicon; Glazing temperature range widens with silicon adding; Glazing temperature ranges were not strictly corresponding with softening temperature point and flow temperature point; But differences were not tremendous; glazing temperature ranges can be estimated from softening temperature point and flow temperature point. Alumina has not prominent influence on glazing temperature, but glaze forms smoothly with alumina, and oxidation resistance was good.

Formation of Decarbonization Layer and its Effect on Corrosion Resistance of Zirconia Graphite Materials

The effect of graphite content on formation of decarbonization layer and corrosion resistance of zirconia graphite materials were studied by the corrosion test in induction furnace, and the effect of decarbonization layer on corrosion of zirconia graphite materials was also analysed by the kinetic models for the corrosion of SEN in mold, the result show that: (1) Thickness of decarbonization layer of slag line is decreasing with the increase of graphite content. When the mold fluxes for high carbon steel is used, decarbonization layer is thin and graphite content has little effect on corrosion resistance of zirconia graphite materials, and 10wt%graphite is better. When the mold fluxes for low carbon steel is used, decarbonization layer is thick and 14wt% graphite is the best. (2) Corrosion of zirconia graphite materials in mold is characterized by the features of consecutive reaction:original layer (k1) decarbonization layer (k2) corrosion layer . If k1<<k2, there is no decarbonization layer forming and decarbonization is the key step for the corrosion; If k1>>k2, there is decarbonization layer on the hot surface of zirconia graphite materials and the corrosion of the layer is the key step. Graphite content is too high or too low is all harmful for the corrosion resistance of zirconia graphite materials.