JP7180340B2 - Test method for side wall brick of molten steel ladle for LF treatment, LF treatment method for molten steel, and molten steel ladle for LF treatment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a test method for a molten steel ladle side wall brick used for LF treatment, a method for LF treatment of molten steel, and a molten steel ladle for LF treatment.

LF treatment is a process for refining molten steel produced from molten pig iron, scrap, reduced iron, and iron-containing dust. LF treatment involves immersing a graphite electrode in molten slag floating in molten steel in a molten steel ladle, heating the molten slag by arc discharge, and heating the molten steel to a temperature of 1600 ° C or higher through the heated slag. It is a process of refining molten steel with flux added to molten slag or molten steel while heating.

In the LF process, molten steel at a temperature of 1600 ° C. or higher is refined using flux in a molten steel ladle, so the lining furnace material used for the molten steel ladle, especially the molten slag, and the sidewalls that frequently come into contact with the molten steel. The erosion of the bricks becomes significantly larger.

Therefore, the slag line part in contact with the molten slag in the side wall part of the molten steel ladle for LF processing is magnesia-carbon brick with excellent corrosion resistance described in Patent Documents 1 to 3, and the metal line part in contact with the molten steel is patented Carbon-containing bricks with excellent corrosion resistance, such as the magnesia-alumina-carbon brick described in Document 4 and the alumina-magnesia-carbonaceous refractory described in Patent Document 5, have come to be used.

The slag line contacting the molten slag is lined with magnesia-carbon bricks, and the metal line contacting with the molten steel is lined with carbon-containing bricks. Erosion of the side wall bricks was suppressed in the side walls of the molten steel ladle for LF processing. However, a new problem has arisen that the joint erosion of the magnesia-carbon bricks lined in the slag line portion is significantly increased.

JP-A-59-107962 Japanese Patent No. 2517377 Japanese Patent No. 6194257 JP-A-56-92160 JP-A-3-205355

The mechanism of joint erosion of magnesia-carbon bricks lining the slag line is considered as follows. Since the metal line part located at the lower part of the slag line part is lined with carbon-containing bricks with a high coefficient of thermal expansion, on the side wall part of the molten steel ladle where the molten steel is stagnant, from the lower metal line part to the upper part A large thermal stress is generated over the slag line portion of the Since the thermal stress applied to the slag line portion concentrates on the joint portion between the magnesia and carbon bricks lining the slag line portion, the corner portion of the brick constituting the joint is destroyed by the thermal stress, As a result of the chipping of the corner portion, joint erosion progresses.

Therefore, in order to suppress the joint erosion of the magnesia-carbon brick lined in the slag line portion, the inventors of the present invention reduce the thermal expansion of the carbon-containing brick in the metal line portion lined in the lower stage of the slag line portion. However, we thought that it would be an effective countermeasure to prevent damage to the corners of the magnesia-carbon bricks due to thermal stress (compressive stress).

Therefore, in the molten steel ladle for LF treatment, the present invention suppresses the erosion of the side wall bricks, and the magnesia-carbon bricks lined in the slag line part. It is an object of the present invention to provide a testing method for a molten steel ladle side wall brick, a method for LF treatment of molten steel, and a molten steel ladle for LF treatment.

As a result of intensive studies by the present inventors, it was found that the degree of cracking at the corners of the magnesia-carbon bricks lined in the slag line, which causes joint erosion, depends on the degree of cracking at the corners of the bricks that has been subjected to heat treatment. Then, it was found that it can be grasped by the amount of deformation of the brick when the stress is unloaded. Furthermore, it was found that the thermal stress of the carbon-containing brick lined in the metal line part can be grasped from the thermal expansion coefficient curve at temperatures up to 1600 ° C. under a compressive stress of 0.2 MPa for the heat-treated brick. , which led to the present invention.

According to one aspect of the present invention, LF treatment for selecting magnesia-carbon bricks lined on the slag line portion of the side wall portion of the molten steel ladle for LF processing and carbon-containing bricks lined on the metal line portion of the side wall portion A method for selecting the side wall bricks of a molten steel ladle for ladle, wherein magnesia-carbon bricks containing 10% by mass or more of carbon and 80% by mass or more of magnesia are fired at 1600 ° C. for 3 hours or more in a reducing atmosphere, and after firing A step of applying a compressive stress of 1/3 of the compressive strength to the brick and selecting the brick under the condition that the distortion of the brick when the compressive stress is unloaded is 0.5% or less, 5% by mass or more of carbon, A carbon-containing brick containing 80% by mass or more of a refractory raw material containing at least two kinds of alumina, magnesia, and spinel is fired at 1600 ° C. for 3 hours or more in a reducing atmosphere, and the brick after firing has a pressure of 0.2 MPa. A step of measuring the thermal expansion coefficient up to 1600 ° C. while applying a compressive stress of , and selecting on the condition that the maximum value of the thermal expansion coefficient in the thermal expansion coefficient measurement is in the temperature range of 1400 ° C. or more and less than 1600 ° C. A method for sorting molten steel ladle sidewall bricks for LF processing is provided.

According to another aspect of the present invention, the magnesia-carbon bricks and carbon-containing bricks selected by the method for selecting the bricks on the side wall of the molten steel ladle for LF processing are separated into slag lines and metal lines on the side walls of the molten steel ladle. a step of lining each part, a step of immersing a graphite electrode in the molten slag floating in the molten steel in a molten steel ladle and heating the molten slag by arc discharge, and a step of heating the molten steel through the heated slag. and refining the molten steel with molten slag or flux added to the molten steel while heating to a temperature of 0° C. or above.

According to yet another aspect of the present invention, a compression of 1/3 of the compressive strength applied after sintering at 1600 ° C. for 3 hours or more in a reducing atmosphere containing 10% by mass or more of carbon and 80% by mass or more of magnesia The lining of the slag line portion of the side wall formed of magnesia-carbon bricks having a strain of 0.5% or less when the stress is released, 5% by mass or more of carbon, and alumina, magnesia, and spinel Refractory raw material containing 80% by mass or more containing at least two types of refractory materials, sintered at 1600 ° C. for 3 hours or more in a reducing atmosphere, and then subjected to thermal expansion coefficient measurement up to 1600 ° C. while applying a compressive stress of 0.2 MPa A molten steel ladle for LF processing is provided, comprising a lining of a metal line portion of a side wall portion formed of a carbon-containing brick having a maximum coefficient of thermal expansion in a temperature range of 1400°C or higher and less than 1600°C.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to more efficiently and effectively obtain sidewall bricks for suppressing joint erosion of magnesia-carbon bricks lined in the slag line part of the sidewall of a molten steel ladle for LF processing.

It is a cross-sectional view of a molten steel ladle for LF processing. 4 is a graph showing changes in the coefficient of thermal expansion of alumina-magnesia-carbon bricks that satisfy the conditions of the carbon-containing brick sorting process according to one embodiment of the present invention. 3 is a graph showing the results of measuring the coefficient of thermal expansion of the same alumina-magnesia-carbon brick as in FIG. 2 under atmospheric pressure without applying compressive stress after sintering. 4 is a graph showing changes in the coefficient of thermal expansion of alumina-magnesia-carbon bricks that do not satisfy the conditions of the carbon-containing brick sorting process according to one embodiment of the present invention.

FIG. 1 is a cross-sectional view of a molten steel ladle for LF processing according to one embodiment of the present invention. In the molten steel ladle 1 for LF processing, the side wall inside the shell 2 is lined with refractory bricks. Specifically, the slag line portion 3 of the side wall is lined with magnesia-carbon brick, and the metal line portion 4 of the side wall is lined with carbon-containing brick. Here, the slag line part 3 is a part that mainly contacts the slag when the molten steel ladle 1 for LF treatment is used, and the metal line part 4 mainly contacts molten steel when the molten steel ladle 1 for LF treatment is used. This is the part to do. In this embodiment, the magnesia-carbon bricks lining the slag line portion 3 and the carbon-containing bricks lining the metal line portion 4 are sorted by a sorting process as described below.

(Magnesia-carbon brick sorting process)
The step of selecting magnesia-carbon bricks in one embodiment of the present invention includes a heat treatment step of firing the magnesia-carbon bricks at 1600 ° C. for 3 hours in a reducing atmosphere, and Then, a compressive stress of 1/3 of the compressive strength of the brick after heat treatment is applied, and then this compressive stress is unloaded. Evaluating the degree of chipping of the corner portion when lined with the slug line portion of the part. In this embodiment, from the viewpoint of corrosion resistance and heat spalling resistance, the brick for the slag line portion of the side wall of the molten steel ladle for LF treatment has a carbon content of 10% by mass or more, and contains magnesia. Magnesia-carbon bricks with an amount of 80% by mass or more are selected.

First, the heat treatment process is performed in order to reflect the phenomenon that the brick structure is weakened when the magnesia-carbon brick is exposed to the working environment in the molten steel ladle for LF treatment.

In the magnesia-carbon bricks before use, the magnesia particles, the carbon particles, and the magnesia particles and the carbon particles are bound by carbon bonds formed by the polycondensation reaction of the phenol resin used as the binder. forms an organization. When the magnesia-carbon bricks forming a structure in such a bonding form are subjected to heat treatment in a reducing atmosphere, the carbon bonds are partially cut and the structure of the magnesia-carbon bricks becomes brittle. By this heat treatment, it is possible to reproduce the structural change that occurs in the brick being used in the molten steel ladle for LF processing.

The sintering of the magnesia-carbon bricks is carried out in a reducing atmosphere. The reason why the reducing atmosphere is used is to suppress the oxidation of the carbon contained in the magnesia-carbon bricks. A non-oxidizing gas such as Ar gas can also be used. A reducing atmosphere may be created by inserting magnesia-carbon bricks and filling with coke powder.

The firing temperature is 1600° C., which is the same as the temperature used in the molten steel ladle for LF treatment. Service temperature is the brick temperature during the LF treatment. The holding time is preferably 3 hours, and the heating rate is preferably 5° C./min, but is not limited thereto.

Next, the process of applying a compressive stress of 1/3 of the compressive strength of the brick after heat treatment and then unloading this compressive stress is performed from the metal line part to the upper slag line when used in a molten steel ladle for LF treatment. This is done to evaluate the fracture resistance of the corners of magnesia-carbon bricks due to thermal stress applied to the part.

As a result of intensive studies, the present inventor found that, in order to simulate the thermal stress applied from the metal line to the upper slag line when used in a molten steel ladle for LF treatment, after heat treatment, It was found that the cracking degree of the corner portion of the brick can be evaluated by applying a compressive stress of 1/3 of the compressive strength of the brick and then by straining the brick after the stress is removed.

As a method of applying compressive stress, for example, a method conforming to JIS A 1149 "Concrete static elastic modulus test method" is preferable because it can remarkably reflect the degree of chipping at the corners of magnesia-carbon bricks. It is not limited.

In the application of compressive stress to bricks after heat treatment in this embodiment, as the maximum load stress when applying the JIS method, at least one or more bricks having the same dimensions and the same heat treatment were prepared, and the compressive strength was measured in advance. Then, let the stress that is 1/3 of the compressive strength be the maximum load stress.

According to the findings of the present inventors, when the compressive stress applied to the brick after heat treatment is less than approximately 1/3 of the compressive strength of the brick after heat treatment, the brick undergoes elastic deformation, and as a result, deformation does not remain after unloading. Therefore, it is difficult to appropriately evaluate the degree of chipping at the corner portion of the brick. On the other hand, if the compressive stress applied to the brick after heat treatment exceeds about 1/3 of the compressive strength of the brick after heat treatment, the deformation after unloading becomes significantly large, and as a result, the amount of deformation is the same regardless of the type of brick. Therefore, it is still difficult to appropriately evaluate the degree of chipping of the corner portion of the brick.

Next, the degree of chipping of the corner portion of the brick when used in a molten steel ladle for LF treatment is evaluated based on the strain of the brick after unloading the compressive stress.

In this embodiment, a compressive stress of 1/3 of the compressive strength is applied to the brick after heat treatment, and then the deformation of the brick after unloading the compressive stress is magnesia-carbon brick with weakened structure. It expresses the susceptibility to breakage due to thermal stress. In other words, it is considered that the larger the amount of deformation, the more likely the magnesia-carbon brick after heat treatment will break due to compressive stress (thermal stress). Since there is a correlation between this amount of deformation and the degree of chipping at the corner of the brick, the degree of chipping at the corner of the brick, which causes joint erosion of the magnesia-carbon brick, can be evaluated based on the amount of deformation.

As a result of intensive studies by the inventors, a compressive stress of 1/3 of the compressive strength of the brick was applied to a magnesia-carbon brick baked at 1600°C for 3 hours in a reducing atmosphere, and then the stress was unloaded. A good correlation is obtained between the amount of deformation of the brick and the presence or absence of joint erosion of the magnesia-carbon brick lined in the slag line part on the side wall of the molten steel ladle for LF treatment, especially when the strain is 0.5%. It has been found that joint erosion of magnesia-carbon bricks is remarkably suppressed in the following cases.

Therefore, in the present embodiment, when the distortion of the brick after unloading is 0.5% or less, the breakage of the corner part is allowable when the magnesia-carbon brick is used in the molten steel ladle for LF processing. range, and select magnesia-carbon bricks that satisfy this condition.

In this embodiment, the magnesia used for the magnesia-carbonaceous brick includes electro-fused magnesia, seawater magnesia, naturally occurring magnesia, and the like. Carbon includes natural scale graphite, earthy graphite, artificial graphite, pitch, mesophase carbon, anthracite, carbon black, and the like. Furthermore, as other components, for example, for the purpose of preventing oxidation of carbon and imparting hot strength to refractories, metals and alloys such as aluminum, silicon, and aluminum-magnesium alloys, and metals such as borides such as boron carbide Intermediate compounds can be added as needed. As long as the magnesia-carbon brick has the following carbon and magnesia contents, the above other components do not affect the effects of the present invention.

(Sorting process for carbon-containing bricks)
Next, the carbon-containing brick sorting step in one embodiment of the present invention includes a heat treatment step of firing the carbon-containing brick at 1600 ° C. for 3 hours in a reducing atmosphere, and , measuring the coefficient of thermal expansion up to 1600° C. under a compressive stress of 0.2 MPa, and evaluating the thermal stress characteristics of the carbon-containing brick from the coefficient of thermal expansion curve.

First, the heat treatment step, like the magnesia-carbon brick sorting step, is performed to reproduce the phenomenon that the brick structure becomes brittle when the carbon-containing brick is exposed to the use environment in the molten steel ladle for LF processing. .

Firing of the carbon-containing bricks is carried out in a reducing atmosphere. The reason why the reducing atmosphere is used is to suppress the oxidation of the carbon contained in the carbon-containing bricks. A non-oxidizing gas such as Ar gas may be used, but in general, the partition box contains carbon. A reducing atmosphere may be created by inserting bricks and filling coke powder.

The firing temperature is 1600° C., which is the same as the temperature used in the molten steel ladle for LF treatment. Service temperature is the brick temperature during the LF treatment. The holding time is preferably 3 hours, and the heating rate is preferably 5° C./min, but is not limited thereto.

In this embodiment, as the brick for the metal line portion of the side wall of the molten steel ladle for LF treatment, at least two types of refractory raw materials out of 5 mass% or more of carbon and three types of refractory raw materials of alumina, magnesia, and spinel are combined. Carbon-containing bricks containing 80% by mass or more are selected. Such carbon-containing bricks specifically correspond to alumina-magnesia-carbon bricks, alumina-spinel-carbon bricks, or magnesia-spinel-carbon bricks.

Among these, carbon-containing bricks containing spinel, such as alumina-spinel-carbon bricks and magnesia-spinel-carbon bricks, are fired at 1600° C. for 3 hours or more in a reducing atmosphere to cause a reduction reaction between spinel and carbon. Voids can form as a result of the evaporation of the spinel. On the other hand, when the alumina-magnesia-carbon brick is fired at 1600° C. for 3 hours or more in a reducing atmosphere, spinel is generated by the reaction between alumina and magnesia, and the generated spinel undergoes a reduction reaction with carbon, resulting in spinel. Voids can form as a result of evaporation. As described above, the carbon-containing bricks to be screened in this embodiment have the possibility of generating voids when fired at 1600° C. for 3 hours or more in a reducing atmosphere. By the heat treatment process as described above, it is possible to reproduce the structural change, that is, the formation of voids, that occurs in the brick being used in the molten steel ladle for LF processing.

As a result of extensive studies, the present inventors found that the thermal stress applied to the upper slag line portion from the carbon-containing brick lining the metal line portion when used in a molten steel ladle for LF processing is 1600 ° C. in a reducing atmosphere. can be estimated from the thermal expansion coefficient curve obtained by measuring the thermal expansion coefficient up to 1600° C. under a compressive stress of 0.2 MPa of a carbon-containing brick fired at 3 hours or more.

As a method for measuring the coefficient of thermal expansion up to 1600 ° C. under a compressive stress of 0.2 MPa, a method in accordance with JIS R 2209:2207 "Test method for softening point under load of refractory bricks" is effective. It is preferable because it can estimate the thermal stress of , but it is not limited to this. The reason for measuring the coefficient of thermal expansion up to 1600 ° C under a compressive stress of 0.2 MPa is that the carbon-containing brick lined on the metal line part of the side wall of the molten steel ladle for LF processing is used with the upper end restrained. This is because the carbon-containing brick itself is exposed to a temperature of 1600° C. while being subjected to compressive stress as a reaction to the thermal stress generated by the carbon-containing brick itself.

FIG. 2 is a graph showing changes in the coefficient of thermal expansion of alumina-magnesia-carbon bricks that satisfy the conditions of the carbon-containing brick sorting process according to the present embodiment. Specifically, the results of measuring the coefficient of thermal expansion up to 1600° C. under a compressive stress of 0.2 MPa for alumina-magnesia-carbon bricks fired at 1600° C. for 3 hours in a reducing atmosphere are shown. In the graph of FIG. 2, the coefficient of thermal expansion of the alumina-magnesia-carbon brick increases as the temperature rises to about 1450°C, reaches a maximum at about 1450°C, and further increases from about 1450°C to 1600°C. It can be seen that it is decreasing. The reason why the coefficient of thermal expansion decreases at temperatures above about 1450° C. is as follows. At a temperature of about 1450° C. or higher, impurity components inevitably contained in the raw materials of alumina and magnesia dissolve out, forming a liquid phase on the surfaces of the raw material particles of alumina and magnesia. As a result, the carbon bonds formed between the raw material particles of alumina and magnesia and the carbon are completely broken, and the raw material particles of alumina and magnesia become easily movable. Then, if the structure of the alumina-magnesia-carbon brick fired at 1600° C. for 3 hours in a reducing atmosphere contains voids generated by the evaporation of spinel, each raw material particle of alumina or magnesia will have a pressure of 0.2 MPa. Under the action of compressive stress, the spinel migrates into the vaporized voids, causing shrinkage and resulting in a decrease in the coefficient of thermal expansion.

Here, since the thermal stress of the carbon-containing brick is proportional to the product of the coefficient of thermal expansion and the modulus of elasticity, the decrease in the coefficient of thermal expansion at temperatures above about 1450° C. as shown in the graph of FIG. This leads to reduction of stress. Among the voids generated by spinel evaporation, voids that are too small to allow movement of raw material particles of alumina and magnesia remain as voids, contributing to a reduction in elastic modulus and, in turn, a reduction in thermal stress.

FIG. 3 shows the result of measuring the coefficient of thermal expansion up to 1600° C. under atmospheric pressure without applying compressive stress to the same alumina-magnesia-carbon brick as in FIG. 2 after baking it at 1600° C. for 3 hours in a reducing atmosphere. is a graph showing It can be seen in the graph of FIG. 3 that the coefficient of thermal expansion of the alumina-magnesia-carbon brick continues to increase until the temperature reaches 1600.degree. From the examples shown in FIGS. 2 and 3 above, in the evaluation of carbon-containing bricks, under the same mechanically constrained conditions as when used in a molten steel ladle for LF treatment, i.e., as in the present embodiment It can be seen that the effect of thermal stress can be accurately estimated by measuring the coefficient of thermal expansion under compressive stress conditions.

FIG. 4 is a graph showing changes in the coefficient of thermal expansion of alumina-magnesia-carbon bricks that do not satisfy the conditions of the carbon-containing brick sorting process according to the present embodiment. Specifically, the results of measuring the coefficient of thermal expansion up to 1600° C. under a compressive stress of 0.2 MPa for an alumina-magnesia-carbon brick sintered at 1600° C. for 3 hours in a reducing atmosphere are shown. In the graph of FIG. 4, the thermal expansion coefficient of the alumina-magnesia-carbon brick increases as the temperature rises to about 1350°C, reaches a maximum at about 1350°C, and further increases from about 1350°C to 1600°C. It can be seen that it is decreasing. The coefficient of thermal expansion at 1600° C. is approximately the same value as the alumina-magnesia-carbon brick of the example of FIG. Therefore, the alumina-magnesia-carbon brick of the example of FIG. 4 is evaluated as suitable as the brick for the metal line part, if only the maximum value of thermal stress is considered. However, as a result of intensive studies by the inventors, it was found that bricks exhibiting thermal expansion behavior such as the example shown in FIG. 4 are inferior in corrosion resistance. Specifically, the coefficient of thermal expansion of the brick in the example of FIG. 4 decreases as the temperature rises from about 1350° C. The reason for this is inevitably contained in the raw materials of alumina and magnesia. It is considered to be a raw material with a low melting point that is blended in addition to the impurity components. In this way, when the alumina-magnesia-carbon brick is blended with the raw material having a low melting point, the maximum value of the thermal stress is the alumina-magnesia-carbon brick selected by the carbon-containing brick screening process according to the present embodiment. However, since the low-melting raw material is blended, the temperature at which the thermal stress is maximized is too lower than the temperature during use, resulting in poor corrosion resistance.

As described in the above examples, the inventors have made intensive studies, and as a result, measured the coefficient of thermal expansion up to 1600°C under a compressive stress of 0.2 MPa for a carbon-containing brick fired at 1600°C for 3 hours or more in a reducing atmosphere. In the coefficient of thermal expansion curve obtained in , when the maximum value of the coefficient of thermal expansion is in the temperature range of 1400 ° C. or more and less than 1600 ° C., as a carbon-containing brick lining the metal line part of the side wall of the molten steel ladle for LF treatment, It was found that the thermal expansion characteristics and corrosion resistance can be evaluated without problems.

In this embodiment, as the brick for the metal line part of the side wall of the molten steel ladle for LF treatment, the carbon content is 5% by mass or more, and among the three types of refractory raw materials, alumina, magnesia, and spinel The carbon-containing bricks in which the total content of at least two types of refractory raw materials is 80% by mass or more are selected. As described above, the carbon-containing bricks of the present embodiment correspond to any of alumina-magnesia-carbon bricks, alumina-spinel-carbon bricks, and magnesia-spinel-carbon bricks. Alumina used in carbon-containing bricks can be electrofused alumina, sintered alumina, and the like. As magnesia, electro-fused magnesia, seawater magnesia, natural magnesia, etc. are used. A sintered spinel, an electrofused spinel, or the like is used as the spinel, and as the composition of the spinel, alumina-rich spinel and magnesia-rich spinel can be selected in addition to normal spinel. As carbon, natural flake graphite, earthy graphite, artificial graphite, pitch, mesophase carbon, anthracite, carbon black, and the like are used. Furthermore, as other components, for example, for the purpose of preventing oxidation of carbon and imparting hot strength to refractories, metals and alloys such as aluminum, silicon, and aluminum-magnesium alloys, and intermetallic compounds such as borides such as boron carbide Compounds may be added as needed.

Examples of the present invention are shown below.
Table 1 shows examples (Examples 1 to 9) of combinations of magnesia-carbon bricks for the slag line part of the side wall of the molten steel ladle for LF treatment and carbon-containing bricks for the metal line part. In Example 5, the magnesia-carbon brick for the slag line part imitates the brick described in Japanese Patent No. 6194257, and the carbon-containing brick for the metal line part is described in JP-A-3-205355. It imitates a brick.

The test method for each example is described below.
Magnesia-carbon bricks and carbon-containing bricks are fired by embedding each brick cut into a cylindrical shape with a diameter of 50 mm and a height of 100 mm in coke powder filled in a partition box and heating to a predetermined temperature in an electric furnace. I went by

The compressive strength of the magnesia-carbon bricks fired in a reducing atmosphere was measured according to JIS R 2206-1:2007 "Method for testing compressive strength of refractory bricks". Compressive stress was applied to the magnesia-carbon bricks fired in a reducing atmosphere in accordance with JIS A 1149 "Concrete static elastic modulus test method". Strain was calculated from the following equation.
Strain (%) = (Brick height before compressive stress load - Brick height after compressive stress load) / (0.01 x Brick height before compressive stress load)

The thermal expansion coefficient of the carbon-containing brick fired in a reducing atmosphere up to 1600°C under a compressive stress of 0.2 MPa was measured in accordance with JIS R 2209:2207 "Test method for softening point under load of refractory bricks". rice field.

The corrosion resistance of carbon-containing bricks was evaluated by the rotary erosion furnace method using slag after LF treatment as the erosion material. A corrosion-resistant evaluation sample was prepared by cutting from a carbon-containing brick. In the rotary erosion furnace method, the evaluation sample is lined in the rotary erosion furnace, and when the surface temperature of the evaluation sample reaches 1650 ° C., slag is put into the furnace, and after 30 minutes, the molten slag is discharged. The test was carried out by repeating the operation of adding new slag four times. After the test, the samples were cut and corrosion resistance was evaluated by measuring the maximum corrosion depth on the cut surface. The corrosion resistance index is an index based on the maximum corrosion depth of the carbon-containing brick for metal line portion of Example 6 being 100, and the smaller the corrosion resistance index, the better the corrosion resistance.

Regarding the presence or absence of joint erosion of the magnesia-carbon bricks for the slag line, the wear rate of the joints, and the wear rate of the carbon-containing bricks for the metal line, the side wall of the molten steel ladle for LF processing with a capacity of 270 tons. The slag line part and the metal line part were lined with the bricks of Examples 1 to 9, and LF treatment was performed on 30 charges of molten steel. The wear rate was calculated from the remaining thickness of the magnesia-carbon bricks and the carbon-containing bricks.

The magnesia-carbon bricks for the slag line part of Examples 1 to 4 were sintered at 1600° C. for 3 hours in a reducing atmosphere, and then subjected to compressive stress of 1/3 of the compressive strength of the bricks after reducing sintering. is 0.5% or less. In addition, the carbon-containing bricks for metal line portions of Examples 1 to 4 were sintered at 1600° C. for 3 hours in a reducing atmosphere, and then measured under a compressive stress of 0.2 MPa. The value is in the temperature range of 1400°C or more and less than 1600°C. Even if these bricks are used in an actual furnace on the side wall of a molten steel ladle for LF processing, erosion is suppressed and joint erosion in the slag line is eliminated, so the screening method according to the present invention is effective. , it can be seen that the combination of bricks suitable for lining the side wall of the molten steel ladle for LF processing can be correctly selected.

On the other hand, the magnesia-carbon brick for the slag line portion of Example 5 was sintered at 1600° C. for 3 hours in a reducing atmosphere, and then subjected to compressive stress of 1/3 of the compressive strength of the brick after reduction sintering. Does not satisfy the condition of being 0.5% or less. Further, the carbon-containing brick for the metal line portion of Example 5 was fired at 1600°C for 3 hours in a reducing atmosphere, and then measured under a compressive stress of 0.2 MPa. Since the maximum value of the rate is observed, it does not satisfy the conditions of the screening method of the present invention. When these bricks are used in an actual furnace on the side wall of the molten steel ladle for LF treatment, joint erosion damage occurs in the slag line, so the screening method according to the present invention is the side wall of the molten steel ladle for LF treatment. It can be seen that the combination of bricks inappropriate for lining the part can be correctly sorted out.

In Example 6, the magnesia-carbon brick for the slag line portion is the same as in Example 3, but the carbon-containing brick for the metal line portion is fired at 1600° C. for 3 hours in a reducing atmosphere and then subjected to a compressive stress of 0.2 MPa. In the measured coefficient of thermal expansion curve, the maximum value of the coefficient of thermal expansion is observed at a temperature of 1600° C., so the conditions of the screening method of the present invention are not satisfied. When these bricks were used in an actual furnace on the side wall of a molten steel ladle for LF processing, the joint erosion of the slag line was eliminated, but the metal line was heavily eroded and the wear rate was high. From this, it can be seen that the selection method according to the present invention can correctly select combinations of bricks that are inappropriate for lining the side wall of the molten steel ladle for LF processing.

In Example 7, the magnesia-carbon brick for the slag line portion is the same as in Example 4, but the carbon-containing brick for the metal line portion contains sodium silicate, which is a raw material with a low melting point, for the purpose of reducing the coefficient of thermal expansion. Therefore, the thermal expansion coefficient at 1600°C is equivalent to that of the carbon-containing brick of Example 3 in the thermal expansion curve measured under a compressive stress of 0.2 MPa after firing at 1600°C in a reducing atmosphere. However, the temperature at which the maximum value of the coefficient of thermal expansion is observed is 1350° C., which does not satisfy the selection criteria of the present invention. When these bricks were used in an actual furnace on the side wall of a molten steel ladle for LF processing, the joint erosion of the slag line was eliminated, but the metal line was heavily eroded and the wear rate was high. From this, it can be seen that the selection method according to the present invention can correctly select combinations of bricks that are inappropriate for lining the side wall of the molten steel ladle for LF processing.

In Example 8, the magnesia-carbon brick for the slag line portion is the same as in Example 5, and the carbon-containing brick for the metal line portion is the same as in Example 3. In Example 8, the sintering temperature of the magnesia-carbon brick in a reducing atmosphere was 1500°C instead of 1600°C. In this case, even with the same magnesia-carbon brick as in Example 5, that is, unsuitable for the slag line, the strain after applying a compressive stress of 1/3 of the compressive strength of the brick after reduction firing is Since it is 0.5% or less, it is determined that the condition is satisfied. As a result, when the side wall of the molten steel ladle for LF processing is used in an actual furnace, the joint erosion of the slag line occurs. In Example 8, if the conditions of the sorting method according to the present invention are deviated, the degree of chipping at the corner of the brick that causes joint erosion in the slag line cannot be accurately evaluated, so the side wall of the molten steel ladle for LF treatment is lined. This indicates that it becomes impossible to correctly sort out inappropriate combinations of bricks because of the

In Example 9, both the magnesia-carbon brick for the slag line portion and the carbon-containing brick for the metal line portion are the same as in Example 1. In Example 9, the compressive stress applied to the magnesia-carbon brick sintered in a reducing atmosphere was set to 2/3 of the compressive strength of the sintered brick instead of 1/3. In this case, even if the magnesia-carbon brick is the same as in Example 1, that is, suitable for the slag line, the strain after unloading exceeds 0.5%, so it is determined that the condition is not satisfied. In Example 9, if the conditions of the sorting method according to the present invention are deviated, the degree of chipping at the corner of the brick that causes joint erosion in the slag line cannot be accurately evaluated, so the side wall of the molten steel ladle for LF treatment is lined. This indicates that it becomes impossible to correctly sort out suitable combinations of bricks due to

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1... Molten steel ladle for LF processing, 2... Steel shell, 3... Slag line part, 4... Metal line part.

Claims (3)

A test method for magnesia-carbon bricks for lining the slag line part of the side wall of the molten steel ladle for LF processing and carbon-containing bricks for lining the metal line part of the side wall,
For the magnesia-carbon brick,
Containing 10% by mass or more of carbon and 80% by mass or more of magnesia, and
Firing at 1600° C. for 3 hours or more in a reducing atmosphere, applying a compressive stress of 1/3 of the compressive strength to the brick after firing, and straining the brick when the compressive stress is removed is 0.5% or less. to be
subject to
Regarding the carbon-containing brick,
Containing 5% by mass or more of carbon and 80% by mass or more of a refractory raw material containing at least two kinds of alumina, magnesia, and spinel, and
Firing at 1600 ° C. for 3 hours or more in a reducing atmosphere, thermal expansion coefficient measurement up to 1600 ° C. while applying a compressive stress of 0.2 MPa to the brick after firing, and the maximum thermal expansion coefficient in the thermal expansion coefficient measurement A test method provided that the value is in the temperature range of 1400°C or more and less than 1600°C. a step of lining the slag-line portion and the metal-line portion of the side wall of the molten steel ladle with magnesia-carbon bricks and carbon-containing bricks, which have been determined to satisfy the conditions by the test method according to claim 1;
A step of heating the molten slag by immersing a graphite electrode in the molten slag floating in the molten steel in the molten steel ladle and performing arc discharge;
and refining the molten steel with flux added to the molten slag or molten steel while heating the molten steel to a temperature of 1600° C. or higher via the heated slag. A molten steel ladle for LF processing comprising a slag line portion lining on a side wall portion and a metal line portion lining on the side wall portion,
The lining of the slag line part of the side wall contains 10% by mass or more of carbon and 80% by mass or more of magnesia, and in the test , it is 1/3 of the compressive strength applied after firing at 1600 ° C. for 3 hours or more in a reducing atmosphere. Formed of magnesia-carbon brick having a strain of 0.5% or less when compressive stress is unloaded ,
The lining of the metal line part contains 5% by mass or more of carbon and 80% by mass or more of a refractory raw material containing at least two kinds of alumina, magnesia, and spinel, and is tested at 1600° C. for 3 hours in a reducing atmosphere. The maximum value of the thermal expansion coefficient in the thermal expansion coefficient measurement up to 1600 ° C. performed while applying a compressive stress of 0.2 MPa after firing is in the temperature range of 1400 ° C. or more and less than 1600 ° C. It is formed of a carbon-containing brick. Molten steel ladle for LF processing.

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