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Research and application of magnesium-aluminum-carbon sliding plate for ladle

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Table of Contents

This article describes the research and use of magnesium-aluminum-carbon slide gate plate.

Key words: steel ladle; magnesium-aluminum-carbon slide plate

Background

With the promotion of new steelmaking technology and continuous casting technology, the competition in the steel market is becoming more and more fierce. Many steel mills have begun to produce high-quality clean steel, special steel and alloy steel, which makes the skateboard in a very harsh environment. In the process, especially when the molten steel is treated with calcium, the erosion of the refractory material is intensified, which seriously affects the service life and effect of the slide. Ordinary Al2O3-C and Al2O3-ZrO2-C slides have severe melting loss and reduced durability, which cannot meet the requirements of continuous use in steel mills. Therefore, in ordinary alkaline slides, it is necessary to study to improve its thermal shock resistance, oxidation resistance and high temperature strength, so as to increase the service life of the slides.

Slide gate plates damage mechanism

The melting point of calcium (850°C) is much lower than that of iron, and it has a high vapor pressure at a pouring temperature of about 1600°C. The calcium vapor volatilized from the molten steel forms active CaO in the negative pressure zone, which intensifies the melting loss of the slide. When casting high-calcium steel with an ordinary aluminum-carbon slide plate, Ca and CaO severely erode the hole’s periphery. This erosion forms a special melting loss on the upper slide plate’s surface. The shape resembles a horseshoe, hence called horseshoe melting loss. Long-term flow control during steel pouring aggravates calcium corrosion on the slide plate (Figure 1). The [Ca] reaction mechanism is as follows:

The generated CaO continues to react with Al2O3 to generate 12CaO·7Al2O3 (melting point 1392°C).

Development and Research of Magnesium Aluminum Carbon Skateboard

Slide gate plate performance requirements and raw material selection

According to the erosion mechanism, the slide plate should have the following characteristics:

(1) Reduce the components that can react with CaO, FeO, MnO, reduce the formation of low melting point compounds, and enhance their corrosion resistance;

(2) Reduce the size of the pores, make the pores finer, and reduce the penetration of CaO, FeO, MnO, and oxygen;

(3) Reduce the carbon content and reduce the oxidation of carbon on the sliding working face;

(4) It has high wear resistance, so that it can be used for many times, and the high temperature strength of the material is required;

(5) High thermal shock resistance, reducing the occurrence of cracks in the use and production of skateboards.

Figure 1 Schematic diagram of melting loss of aluminum-carbon slide plate and photos after use

Based on the characteristics of the above slide gate plates, we select high-quality fused magnesia particles with well-developed crystals as aggregates. We introduce spinel aggregates with smaller particle sizes as the main raw material to address the large thermal expansion coefficients of fused magnesia. In the matrix, we add a small amount of metal additives, an appropriate amount of carbon, and low expansion raw materials. We use different treatment processes to compare performance and develop high-grade alkaline slide gate plates.

We use the excellent slag resistance and chemical corrosion resistance of magnesia and spinel raw materials. According to market demand and our factory’s production process, we develop a slide plate with high strength, low expansion, and high thermal shock resistance. Our magnesium-aluminum-carbon slide plate targets calcium-treated steel to meet steel mills’ production needs.

Comparative analysis of tests and indicators

We list the chemical composition of the main raw materials in Table 1. The test formulas of the four samples are in Table 2. We compare various indicators in Table 3. Figures 2 and 3 show the flexural strength and linear expansion of the four samples.

Table 1 Chemical composition of main raw materials

Raw material nameMgOCaOSiO2Al2O3SiCFe2O3C
Fused magnesia particles97.20.850.91  0.59 
Fused magnesia fine powder97.50.790.89  0.65 
Spinel particles22.5  75.8   
Silicon carbide    98.090.12 
Carbon      95.19

Table 2 Experimental comparison formula

Raw material nameSpecification1#sample2#sample3#sample4#sample
Fused magnesia particles3~1mm65656565
Fused magnesia fine powder-200head13121212
Spinel particles-18head10101010
Metal additives A-325head3353
Metal additives B-325head1021
Carbon-100head3333
SiC-18head5553
B4C-325head0.50.50.50.5
Modified resin (additional) 3.53.53.53.5

Table 3 Index comparison

Sample NoCompressive strength/MPaPorosity/%Bulk density/(g.cm3)
200℃800℃1400℃200℃800℃1400℃200℃800℃1400℃
1#10178816.25.75.92.962.972.97
2#9882856.45.85.62.972.992.98
3#9775796.86.16.32.952.972.97
4#10079776.75.95.52.952.932.97

According to the analysis results of the above indicators, the following conclusions can be drawn:

(1) The increase of metal additive A is conducive to the increase of the strength of the slide gate plate.

(2) Increasing metal additive B causes cracks in the fired slide plate due to excessive volume expansion during firing.

(3) After high-temperature firing, the sliding plates of the four samples all had cracks in different degrees, and the volume expansion was large.

(4) There is little difference in the compressive strength, slag resistance and oxidation resistance of the four samples.

(5) The flexural strength of the 4# sample has obvious advantages, and the linear expansion is relatively low.

Fig.2 Comparison of flexural strength of four samples

Fig.3 Comparison of linear expansion of four samples

In view of the above conclusions, it was decided to select the 4# sample slide plate for field test.

Field use of magnesium aluminum carbon slide gate plate

In a domestic steel factory, we used the 4# sample magnesium-aluminum-carbon slide plate for comparison. The pouring time ranged from 30 to 50 minutes. The steel types included calcium-treated steel, high-oxygen steel, and high-manganese steel. On-site use showed it meets the needs of steel mills for 4 consecutive slides. Some slide gate plates can be used for 5 consecutive slides. After use, the board’s surface did not fall or peel off. The board’s surface remained good without obvious oxidation or calcium erosion. The slide plate hole widened to about 5 mm. Figures 4, 5, and 6 show the status photos of the slide plate after 2, 3, and 4 uses.

Figure 4 The condition of the magnesium-aluminum-carbon slide gate plate after being used twice

Figure 5 The condition of the magnesium-aluminum-carbon slide gate plate after being used for 3 times

Figure 6 shows the condition of the magnesium-aluminum-carbon slide gate plate after 4 uses.

In conclusion

(1) The flexural strength of magnesium-aluminum-carbon materials increases with the increase of silicon carbide content in the composition. Silicon carbide is a refractory non-oxide with strong covalent bonds. The bond energy between atoms is relatively large. Compared to MgO, it has a higher elastic modulus and strength. Adding silicon carbide improves the material’s strength. Increasing silicon carbide content decreases the thermal expansion coefficient. Although silicon carbide increases the elastic modulus, the increase is less than the decrease in thermal expansion coefficient. Overall, this improves the material’s resistance to thermal shock.

(2) Adding graphite is easier to improve the strength, density and oxidation resistance of the slide than carbon black.

(3) Appropriate addition of metal additive B is beneficial to improve the thermal shock resistance of the slide gate plate.

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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