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Research and application of forsterite-containing tundish coating materials

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Table of Contents

In order to reduce the raw material cost of tundish coating materials, forsterite particles were used as aggregates, and the effect of partially replacing magnesia particles with 1 ~ 3 mm forsterite particles on the performance of tundish coating materials was studied. The results show that compared with magnesia tundish coating materials, the coating product developed by partially replacing magnesia particles with 10% forsterite particles (1~3 mm) is more suitable as a substitute for tundish magnesia coating materials. The strength of the sample added with 5% waste magnesia chromium brick particles is not obvious, and the high temperature performance is reduced.

Keywords: forsterite; magnesia; magnesia chrome brick; tundish coating

In recent years, the pressure on steel smelting costs, the protection of magnesia resources and the increasingly severe environmental protection situation have caused the price of magnesia raw materials to continue to rise. In order to reduce costs and save magnesia resources, many refractory material manufacturers generally use lower-priced forsterite to partially replace magnesia. my country’s natural forsterite mineral resources are extremely rich. However, due to the large number of impurities and low melting points in the forsterite raw material, the performance of tundish coatings produced using forsterite is unstable, and its high-temperature performance is significantly reduced.

Therefore, forsterite particles were used to partially replace magnesia particles, and the effects of waste magnesia chromium brick particles and silica micropowder additions on the physical properties of the tundish coating were studied, and field application research was conducted based on the test results. It aims to provide a feasible idea for reducing the cost of tundish coating materials.

Test

Raw materials

The waste magnesia chromium brick particles in this test were taken from the waste magnesia chromium bricks used in steel plants. They were selected and crushed to produce waste magnesia chromium brick particles ≤3 mm. Use 95# mid-grade magnesia particles (3~5 mm, 1~3 mm and ≤1 mm). Waste magnesia chrome brick particles (≤3 mm). Forsterite particles (1 ~ 3 mm). 97# magnesia fine powder (≤0. 088 mm) and 90# silica fume (≤0. 088 mm) are used as raw materials. The tundish coating material was prepared using Guangxi white mud as the binding agent and sodium tripolyphosphate water-reducing agent. The chemical composition of the main raw materials used in the test is listed in Table 1.

Sample preparation and performance testing

The current magnesium tundish coating with two different binders added is used as the reference formula (marked A1 and B1). The magnesia particles in the reference formula were replaced with 5%, 10%, and 15% forsterite particles (1~3 mm) respectively to obtain a forsterite-magnesia tundish coating material. The specific formula is listed in Table 2.

Table 1 Chemical composition of main raw materials %

projectSiO2MgOAl2O3Fe2O3CaOCr2O3
95# magnesia particles1 . 4595 . 260 . 590 . 701 . 04
97# magnesia fine powder1 . 0297 . 020 . 140 . 231 . 01
Forsterite particles40 . 3046 . 211 . 657 . 831 . 33
Waste magnesia chrome brick particles1 . 3166 . 753 . 215 . 822 . 1512 . 31
90# silica fume90 . 801 . 100 . 640 . 570 . 62
Guangxi white clay46 . 820 . 3534 . 791 . 300 . 20

Accurately weigh the ingredients according to the formula in Table 2, mix the prepared aggregates and powders in a small mixer, and after the materials are evenly mixed, vibrate the materials on a vibrating table to form. Long strip samples of 40mm*40mm*160mm were prepared respectively. The samples were cured at regular temperature for 24 hours, then demoulded and cured for another 24 hours, and then placed in an oven to dry at 110°C for 24 hours. One part of the dried long strip sample was directly used to test its various physical properties after drying, and the other part was heat-treated at 1550°C for 3 hours and then its various physical properties after heat treatment were tested.

Table 2 Test formula

Sample NoA1A2A3A4B1B2B3B4
95# mid-grade magnesia (> 1 mm)6858535363635348
Forsterite (1~3 mm)0101515001015
Waste magnesia chrome brick particles (≤3 mm)00005555
97# Magnesia Fine Powder2626262626262626
Guangxi white clay2.52.52.512.5111
90# silica fume1113.513.53.53.5
sodium tripolyphosphate1.51.51.50.31.50.30.30.3
Others1.01.01.01.211.21.21.2
Amount of water added/%17.618.318.318.317.81818.418.4

Results and analysis

The compressive strength of each castable sample is shown in Figure 1. It can be seen from the figure that as the content of forsterite and silica fume increases, the normal temperature compressive strength of the sample has an increasing trend. The normal temperature compressive strength of the A4 and B2 samples is greater than that of A3 and B1 respectively, which is related to the content of silica fume. Increasing the amount of silica fume added can improve the normal temperature compressive strength of the sample, but judging from the strength of each sample after sintering at 1550°C for 3 hours, the addition of forsterite and silica fume reduces the strength of the coating.

The flexural strength of each castable sample is shown in Figure 2. It can be seen from the figure that as the forsterite content increases, the normal temperature flexural strength of the sample does not change significantly. Increasing the amount of silica fume can increase the normal temperature flexural strength of the sample. Judging from the flexural strength of each sample after sintering at 1550°C for 3 hours, as the addition of forsterite and silica fume increases, the flexural strength of the coating decreases significantly.

Figure 1 Compressive strength of the sample

Figure 2 Flexural strength of the sample

The linear change rate of each castable sample is shown in Figure 3. It can be seen from the figure that after sintering at 1550°C for 3 hours, each castable sample shrinks, which is related to the sintering of the sample at high temperature. At the same time, as the forsterite content increases, the linear shrinkage of the coating tends to increase. According to the chemical composition of each sample, Factsage 6.4 software was used to calculate the amount of liquid phase generated at 1550°C for each sample, as shown in Figure 4.

Figure 3 Linear shrinkage of the sample

Among them, the liquid phase formation amounts of samples A1 ~ A4 at 1550°C are 6.182%, 5.904%, 5.776%, and 5.634%. The liquid phase formation amounts of samples B1 to B4 at 1550°C are 6.527%, 6.192%, 6.070%, and 5.926%, respectively. Therefore, when the amount of silica fume added increases, the forsterite phase formed by it and magnesia fine powder at high temperatures will reduce the low melting point phase produced, resulting in reduced shrinkage after high temperature treatment. The introduction of waste magnesia chrome bricks is not conducive to the high temperature performance of the samples.

Figure 4 Theoretical liquid phase amount of the sample at 1550°C

Industrial tests

From the laboratory research results (Table 3), it can be seen that the high-temperature compressive strength of the A2 sample is slightly worse than that of existing products (11.52 Mpa), but both meet the requirements for field use (=8.0 Mpa). At the same time, the trial safety factor of the A2 proportioned coating material is higher than that of other samples. Therefore, the A2 formula was selected and applied on-site at a steel plant for trial use, and there were no abnormalities during the construction process.

Table 3 Comparison of performance indicators between developed products containing forsterite and existing tundish coating materials

Test items Indicator
Developed product A2 Existing mid-pack coating products Internal Technical Conditions
MgO/%86.2791.82≥86.0
110℃,24h   
Volume Density/(g·cm-³)2.04≤2.5
Compressive strength/MPa4.98≥4.0
1550℃,3h   
Compressive strength/MPa10.7011.52≥8.0
Line change rate/%-2.61-1.6-3~0

The first batch of 50 tons of the developed coating material was produced for trial use. A total of 12 packages were applied. The maximum usage was 8 furnaces, the minimum usage was 5 furnaces, and the average usage was 6.75 furnaces. The trial conditions were normal. The second batch of 150 tons was produced for trial use, and a total of 35 packages were applied. 24 packages have been tried, with a maximum usage of 12 furnaces, a minimum usage of 3 furnaces, and an average usage of 6.08 furnaces. The maximum erosion is 3 ~ 4cm, and the average erosion is about 2cm. The trial conditions are normal. Now it has been fully promoted and used in a certain steel plant, and the coating material can reduce the cost by 50 yuan per ton. The specific trial situation is shown in Figure 5.

Figure 5 On-site trial of coating material

Conclusion

(1) After adding 1 ~ 3 mm forsterite particles, the high-temperature strength of the tundish coating decreases and the linear shrinkage increases. The simultaneous addition of 3.5% silica fume will further reduce the high-temperature strength and linear shrinkage of the specimens.

(2) Compared with on-site smear products, the smear product developed by partially replacing magnesia particles with 10% forsterite particles (1 ~ 3 mm) is more suitable as a substitute for tundish magnesia smear materials. The strength of the sample added with 5% waste magnesia chromium brick particles is not obvious, and the high-temperature performance is reduced.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

Our Product have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time

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