How to Choose Refractories for Metallurgical Heating Furnace

Refractories are the lining of high-temperature kilns, which play a protective role in blast furnace hot blast stoves, ladles, and other equipment in the metallurgical industry. It can be said that without refractories, smelting equipment cannot operate. Refractories can prevent ladles from contacting molten steel and prolong The service life of the ladle is also very necessary to use refractory materials in the metallurgical industry. There are also many types of refractory materials used in the metallurgical industry. How to choose refractory materials used in metallurgical heating furnaces is also a science. Today I will take you to understand.

When choosing bricks, we should pay attention to the following issues: First, we should be tailor-made, self-sufficient, pay attention to the characteristics of regional resources, and choose bricks reasonably. Secondly, consider the working characteristics of the furnace masonry to achieve the correct technology.

Different styles of heating furnaces and different parts of the furnace body have different working conditions. Therefore, when using bricklaying materials, the characteristics of masonry work should be fully considered.

The working temperature of different parts of the heating furnace is different, and the selection of masonry materials should choose products of different varieties and grades. For the furnace body or parts with high-temperature stress, the data with better thermal stability should be selected. Data with high compressive strength should be selected for data with high compressive strength, and the load softening point should be considered when selecting.

For some block materials, such as the bottom of the vibration heat treatment furnace, in order to withstand mechanical shock and workpiece collision, the integral tamping structure of alum cement refractory concrete can be selected. The bottom of the annular furnace should consider the collision and conflict of the workpiece during loading and unloading and can be knotted with high alumina bricks or chrome ore. For some parts with particularly serious mechanical damage, the convenience of partial replacement or repair should be considered.

The part of the masonry exposed to corrosive media should choose refractory materials according to the nature of the chemical reaction, such as the bottom of the soaking furnace, the soaking bed of the pushing steel connection heating furnace, the hearth of the reverberatory furnace, etc., because they are corroded by iron oxide slag. Magnesia bricks are recommended. Furnace materials are only visible if they are resistant to chemical attack.

Refractories are widely used in the metallurgical industry. The interaction between refractory materials and molten steel and its influence on molten steel and steel quality: mixing molten steel with steel; the effect of carbonization of refractory materials on molten steel and steel quality; desulfurization of refractory materials is beneficial to improve the quality of molten steel and steel; refractory materials Dephosphorization is beneficial to improve the quality of molten steel and steel.

Refractory materials can generally be divided into acidic refractory materials (quartz silica bricks); semi-acidic refractory materials (semi-silicon bricks); neutral refractory materials (chrome bricks, clay bricks, high alumina bricks); basic refractory materials (magnesia bricks, Chrome-magnesia bricks, magnesia-alumina bricks, dolomite bricks, magnesia, dolomite, magnesia refractory clay), etc. Basic refractories are widely used in smelting equipment because of their high refractoriness, good thermal stability, and good slag resistance.

During the steelmaking process of the converter and electric furnace, the molten steel will mechanically flush the lining refractory material, and the elements of the refractory material will dissolve in the molten steel and react chemically with the molten steel. Mechanical corrosion of steel structure lining and its chemical reaction: On the one hand, the damage and corrosion of the lining; on the other hand, it will affect the quality of steel and water. The interaction between molten steel and refractory materials in the molten pool during steelmaking has five main effects on molten steel and steel quality:

1. The shedding of the refractory material will cause the molten steel to mix with the non-metal in the steel.
During the smelting process, after the furnace lining refractory bricks are eroded, due to structural changes, the decarburization layer and reaction layer of the bricks become loose. Add molten steel, slag, furnace gas, molten iron, and bulk materials. The mechanical scouring of scrap steel makes the refractory material fall off and get involved in the steel solution, forming non-metallic inclusions. The properties of non-metallic inclusions in steel are quite different from those of steel itself.

From a mechanical point of view, the presence of non-metallic inclusions is the stress concentration point of steel, which has a great influence on the strength, stiffness, and durability of steel. Therefore, non-metallic inclusions are one of the serious defects that affect the quality of steel.

2. In molten steel, the constituent elements of refractory materials interact with non-metallic elements.
Some elements that produce non-metallic inclusions to form refractory materials are directly dissolved in molten steel, and oxygen, carbon, and other non-metallic elements are added to the molten pool. Under certain conditions, non-metallic elements in molten steel react with each other to produce non-metallic inclusions. Likewise, it can adversely affect the quality of molten steel and steel.

3. The effect of recarburization on molten steel and steel quality.
Carbon composite refractory is a new type of basic refractory developed in the 1980s. Carbon composite refractories usually contain 3% to 30% carbon. The carbon oxidation reaction is an important reaction in the steelmaking process. One of the important tasks of steelmaking is to reduce the carbon oxidation in molten steel to the specification of steelmaking numbers.

When smelting pure and ultra-pure steel, decarburization increases the carbon content of molten steel and changes the composition of the steel. Especially when melting pure steel or ultra-pure steel, decarburization will seriously affect the quality of molten steel. The decarburization mechanism of refractory materials is that there is a certain liquid phase isolation layer between a certain degree of smelting and refractory materials. The reactants form a solid product layer on the surface of the refractory material, through which the elements in the material diffuse into the molten steel.

Some elements and oxides in the steel mainly pass through the refractory brick reaction layer to reach the reaction interface of the decarburization layer in the steel slag, and decarburization reaction occurs at the meeting point. Therefore, the composition of molten steel is affected. Carbon oxidation produces cocoa bubbles, which float when grown and are discharged through the slag layer. Carbon oxidation can affect the content of other components, such as oxygen in molten steel. This will also have a certain impact on the quality of molten steel and steel. However, the floating and discharge of bubbles have a strong stirring effect on the molten metal pool, which makes the composition and temperature of the molten steel uniform and improves the dynamic conditions of the chemical reaction of the molten steel.

4. Desulfurization of refractory materials is beneficial to improve molten steel and quality.
Sulfur exists in steel in the form of sulfides and is harmful to most steels. Its main influence on steel properties: making steel hot and brittle and reducing its mechanical properties and welding properties. Therefore, reducing and controlling the sulfur content in steel is conducive to improving the quality of steel. The test results show that the refractory material produces a certain liquid phase at high temperatures. The liquid phase layer between molten steel and refractory materials is usually silicate melt, whose composition and structure are very similar to slag.

Therefore, it also has redox of slag; desulfurization, phosphorus, and adsorption of impurities in molten steel. The desulfurization mechanism of the molten steel in the molten pool is as follows: the sulfur ions entering the liquid interlayer of the refractory diffuse through the liquid to the refractory layer, react with the CaO particles in the refractory and form a CaS layer on the surface of the CaO particles. The chemical formula (CaO) + [S] = (CaS) + [O] This shows that CaO has a strong desulfurization effect. Calcium carbonate series refractories have a strong desulfurization effect.

5. Dephosphorization of refractory materials is beneficial to the improvement and quality of molten steel.
Phosphorus exists in the form of iron phosphide in steel, and phosphorus is a harmful element in most steels. It has a major impact on the properties of steel: reducing the plasticity, toughness, weld resistance, and cold brittleness of steel. Its phosphorus removal effect is the same as that of slag. The basic principle is that phosphorus oxidation produces P2O5 in molten steel. Since the P2O5 gas is unstable, the liquid level floating on the surface of the slag steel needs to react with the basic oxide in the liquid phase of the refractory material and the phosphate produced is dissolved in the slag, thereby discharging the phosphorus in the steel. Refractory materials can effectively remove certain phosphorus content, which is beneficial to improve the quality of molten steel and steel.

In recent years, with the rapid development of industry, national defense, aerospace, and other fields, the demand for high-quality steel has been increasing. When smelting high-quality steel such as pure steel, it is necessary to attach great importance to and deeply study the influence of the reaction between molten steel and refractory materials on the quality of steel. At the same time, it also provides the basis for the development of new refractory materials that can purify molten steel.