JPS647026B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a refractory having excellent erosion resistance, thermal shock resistance, and structural spalling resistance characterized by spinel-dispersed periclase aggregate grains. Originally, magnesia is very advantageous as a refractory material for steel manufacturing due to its high melting point and high chemical stability. The problem is that they have poor resistance to In order to improve this drawback, there are MAG-KURO bricks produced by adding chromite to magnesia, and MAG-carbon bricks made by combining magnesia grains and graphite. However, with advances in steelmaking technology, the conditions for these furnace materials are becoming increasingly severe, and furthermore, restrictions are beginning to appear on the components contained in furnace materials for use in special steel refining. In particular, under the processing conditions of low chromium, extremely low sulfur, extremely low carbon steel, etc. aimed at producing clean steel, the mag-black and mag-carbon materials themselves pose a problem. A magnesia-spinel based material can be considered as a material that meets the above points. However, although attempts have been made to develop magnesia-spinel refractory bricks, which are theoretically expected to be superior, there have been no examples of successful practical use. The main reason for this is thought to be that the form in which spinel exists is not suitable for improving its properties. That is, simply dispersing spinel uniformly in MgO does not completely prevent structural spalling due to slag infiltration, and it is difficult to obtain sufficient hot strength. Therefore, the effective form of existence of spinel is at the periclase grain boundaries, which contributes to improving hot strength and protecting periclase.
It exists as a uniform layer with a thickness of 1μ to 10μ, and a 0.5μ layer within the periclase grains suppresses excessive growth of periclase and disperses and absorbs internal stress caused by expansion and contraction of periclase.
Requires presence as microcrystalline grains less than ~3μ. If spinel does not characteristically exist at the periclase grain boundaries with a thickness of 1μ to 10μ, the hot strength will be poor and structural spalling will easily occur, and if spinel does not exist within the periclase grain boundaries with a thickness of 0.5μ
If there are no microcrystals of ~3μ, the thermal shock resistance is poor. This invention was invented as a result of various studies based on the above-mentioned findings, and the gist thereof is that MgO 85-95%, Al ₂ O ₃ 15-5%,
It has a component ratio of 1.0 to 2.0% CaO and 2% or less of other components, and has a microstructure in which spinel fills the periclase grain boundaries with a thickness of 1μ to 10μ, and spinel crystals within the periclase grains. Grains are 0.5~3μ
Spinel-dispersed periclase aggregate grains obtained by rapid cooling treatment after hot melting so that they are deposited and dispersed in the size of
or more, and contains 50% or more in the fine part, with the remainder being
This is a magnesia-based fired refractory characterized by having excellent erosion resistance, thermal shock resistance, and structural spalling resistance due to its composition of MgO of 80% or more and Al ₂ O ₃ fine particles of 20% or less. This invention will be explained in detail below. The microstructure of spinel-dispersed periclase aggregate grains, which is characteristic of the magnesia-based fired refractory of this invention, is formed by the amount of Al ₂ O ₃ and the amount of CaO contained as a trace component, and by the appropriate rapid cooling treatment after hot melting. It is assumed that the That is, MgO85~
95%, Al ₂ O ₃ 15-5%, CaO 1.0-2.0%, and other components adjusted to 2% or less after thermal melting at 2000℃~
By rapidly cooling to around 1700℃, spinel uniformly fills the periclase grain boundaries with a thickness of 1μ to 10μ, and 0.5μ within the periclase grains.
Spinel-dispersed periclase aggregate grains in which spinel microcrystal grains with a size of ~3μ are deposited and dispersed are obtained. Below this heat melting and quenching treatment,
The ranges of 15 to 5% Al ₂ O ₃ and 1.0 to 2.0% CaO were obtained from the results of several experiments by the inventor and others. 1750℃~1850℃ while having the above prescribed ingredients
The clinker obtained by firing at 0.degree. C. does not have the desired microstructure, but has a structure in which periclase and spinel are simply mixed uniformly. In this structure, most of the bonds between crystals are periclase-periclase bonds, resulting in a structure similar to that of magnesia bricks, so it is thought that the thermal shock resistance and structural spalling resistance are inferior. Also
Structures formed under firing temperatures of approximately 1750℃ to 1850℃ are likely to undergo structural changes when exposed to high temperatures for long periods of time as bricks, causing structural spalling. tissue stability is required. On the other hand, when a given compound is thermally melted and then slowly cooled, the amount of spinel microcrystals dispersed in the periclase crystals is small and the thermal shock resistance is poor. Appropriate quenching treatment is required. When the amount of CaO is 2.0% or more, MgO-CaO-Al ₂ O ₃ low-melting substances are excessively produced at the periclase grain boundaries, resulting in a decrease in hot strength and a decrease in the size of spinel microcrystals to 3μ. Grow more than that. Furthermore, if CaO is 1.0% or less, the filling of spinel at the vericlace grain boundaries becomes non-uniform. Next, regarding the amount of Al ₂ O ₃ , if it is less than 5%, the amount of spinel filling in the periclase grain boundaries will be insufficient, and the amount of dispersion of spinel microcrystal grains within the periclase grains will be small. Spallability is impaired. Also, the amount of Al ₂ O ₃ is 15
If it exceeds %, the corrosion resistance decreases. The content of the spinel-dispersed periclase aggregate grains in the refractory is 80% or more in the aggregate and 50% or more in the joints because of the excellent thermal shock resistance and structural strength of the spinel-dispersed periclase aggregates. This is to make the refractory exhibit sufficient poling properties.
The reason why the remainder is set to be 80% or more of MgO and 20% or less of Al ₂ O ₃ is that if the content is 80% or less of MgO and 20% or more of Al ₂ O ₃ , the erosion resistance decreases. Examples of the fired magnesia refractories according to the present invention will be described below together with comparative examples, and the effects of the present invention will be explained. Table 1 shows the existence form of spinel in the clinker produced under various conditions. In the clinkers of A and above that are removed according to the present invention, spinel does not have a predetermined existing form.

[Table] (1) α indicates spinel grains within periclase grains. β indicates a spinel layer at the periclase grain boundary. (2) Test method: 40×40×230mm in high frequency induction furnace
Steel (SS41) and slag were melted in a container lined with a shaped sample, and the erosion rate of the slag line was measured. Basicity of slag: 2.0 (MgO = 5%) Thermal conditions: 1650°C to 1780°C x 4 hours (3) Test method: Slag placed in a graphite crucible was melted in a high frequency induction furnace and preheated above the crucible. 20
A sample with a size of ×20 × 150 mm is immersed in the slag and rotated. After the sample was lifted out of the slag and cooled, the erosion rate of the slag immersion area was measured. Slag basicity: 6.0 (Al ₂ O ₃ = 30%) Thermal conditions: 1680-1730℃ x 20 minutes Sample rotation speed: 10 r.pm (4) Test method: In an electric furnace heated to 1100℃, 50
Insert half of the ×60×114mm sample into 15
After heating for a minute, immediately put into water to cool. Visually observe the cracks that have occurred in the sample.

【table】

[Table] Displayed in degrees. /...Slight cracks, //...2 cracks or less, ///...3 to 5 cracks, ////...5 cracks
(5) Test method; 50 x 60 x 114 squares in a cylindrical drum
A mm-shaped sample was lined and heated to 1700°C with a propane-oxygen flame while rotating the drum, and then slag (C/S = 2.0) was introduced. After increasing the temperature to 1750℃, stop heating and blow air onto the sample surface to rapidly cool it to around 500℃. After repeating this heating and cooling three times, the sample was cut and the state of cracks was visually observed and expressed in degrees. Examples A ₁ , A ₂ , A ₃ , and A ₄ in Table 2 are bricks made by blending within a predetermined range using the clinker A in Table 1; Compared to bricks, it has excellent erosion resistance, thermal shock resistance, and structural spalling resistance. Furthermore, when compared with Maguro Semibond and Maguro Direct Bond bricks, there is a clear difference, and the brick of the present invention is far superior. Generally, magnesia bricks are
Since the content of MgO is high, the corrosion resistance is high, but the thermal shock resistance and structural spalling resistance are significantly inferior. When the same brick as in Example _A1 of the present invention was used for the VOD slag line, it was possible to extend the service life by about four times that of the conventional magcro direct bond brick.

[Brief explanation of the drawing]

The drawing shows an electron micrograph of a brick structure according to the present invention. Magnification: 1000x.

Claims (1)

[Claims] 1 Chemical analysis weight% MgO 85-95%, Al ₂ O ₃ 15
~5%, CaO1.0~2.0%, and other components less than 2%.The microstructure is that spinel fills the periclase grain boundaries with a thickness of 1μ~10μ, and the periclase grain boundaries are filled with spinel with a thickness of 1μ~10μ. Spinel crystal grains with a size of 0.5μ to 3μ are deposited and dispersed, and the spinel-dispersed periclase aggregate grains are coarsely mixed in the refractory.
A magnesia-based fired refractory comprising 80% or more in the medium grain part, 50% or more in the fine grain part, and the balance being 80% or more MgO and 20% or less Al ₂ O ₃ fine grains.