JPH06347457A - Structure spalling test method for refractories, evaluation method for crack caused by sintering, and its test device - Google Patents

Abstract

PURPOSE:To enable effect of sintering, the depth of slag penetration and cracks caused by slag penetration to be simulated to a case of actual furnace utilization by raising and lowering the temperature of a furnace after slag has been molten over the refractory specimen rested on the bottom section of the furnace. CONSTITUTION:After slag 7 has been molten over the upper surface of a refractory specimen 6, the temperature of a furnace is raised and lowered. In this case, when the specimen 6 which is 100 to 400mm long, as thin as 50 to 20mm, is used, the same result as the case of an actual furnace can be obtained. Furthermore, temperature for heating on the refractory specimen surface is made equal to or more than 1200 deg.C, temperature gradient within the specimen is made 2 to 10 deg.C/mm, and slag 7 equal to or more than 0.3g/cm<2> on the upper surface of the refractory specimen is made to be molten on the aforesaid surface, and the slag is heated for more than four hours at the highest temperature range after the slag has been molten. In this case, when an AE sensor 4 is installed on the specimen 6, an AE signal is detected corresponding to a heating condition, and material to be poured in, so that it is possible to make judgement more accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slag permeation spalling test method, a method for evaluating cracks caused by firing, and a testing apparatus, which are used for evaluation and analysis in the development of irregular refractory materials, especially refractory materials for casting.

[0002]

2. Description of the Related Art Hitherto, refractory materials such as silica stone, lozenge, alumina, zircon and magnesia have been used as pouring refractory materials for ladle linings. In recent years, due to advances in ladle refining technology for producing high-purity steel, the environment in which ladle refractories are used has become more severe, such as rising molten steel temperature and extending molten steel residence time. Therefore, with conventional refractory materials,
Corrosion resistance and spalling resistance are becoming unusable.

So far, zircon, high alumina,
Various improvements have been made in terms of the material properties of the refractory material such as alumina-spinel and the durability has been improved. And
Due to these improvements, high durability is realized in the steel bath. With this improvement, it has been attempted to expand the application to the slag line portion where durability is further required, but the durability at the process implementation level has not yet been obtained. In order to be applicable to the slag line part, further improvement in material is required.

It is considered that there is a limit to the improvement of zircon, which is an acidic material, because the main form of wear is erosion due to chemical reaction. Further, in the case of the alumina-spinel material which is a neutral material, the occurrence of structural spalling due to the penetration of slag has become a problem, and various studies have been made to solve this problem. Regarding magnesia, which is a basic material, although there are few problems with melting resistance, the problem of spalling due to its thermal expansion has not yet been solved. Conventionally, one of the reasons why such a spalling problem is not sufficiently solved is that there is no evaluation / test method capable of reproducing the structural spalling that occurs in actual use.

The conventional refractory evaluation / testing methods are: (1) slag rotation erosion method (2) high-frequency melting furnace lining method (3) AE measurement method by Kumagai et al.
259-296 (1979) etc.) (4) Evaluation of peeling resistance by Suekawa et al.
l. 1 (1992), 250 and the like.

[0006]

With respect to the above (1) and (2), it is impossible to obtain a sample of a size necessary for evaluating the spalling phenomenon, and it is necessary to provide an appropriate temperature gradient in the sample. There was a problem such as not being. Regarding (3) above, there was a problem that the effect of slag penetration could not be evaluated. Also, the casting material is a non-fired product,
Since sintering starts from one side only after receiving molten steel, spalling resistance evaluation by an AE sensor has not been attempted.
In (4) above, because the retention time after slag penetration is short,
There was a problem that the slag penetration depth and crack initiation depth did not match the actual furnace results.

With respect to various cracks generated by these slag penetration test and spalling test, some trials (for example, JP-A-60-60985 and JP-A-4-42868) are excluded. However, the present situation is limited to visual observation on the cut surface, and no attempt has been made to correlate it with changes in physical properties such as stress distribution, elastic modulus, and strength that cause cracks.

Due to the above problems, in the development of refractory materials, particularly in the development of amorphous refractory materials and casting materials,
At the development stage, there was no evaluation method or test method that sufficiently reflects actual use. In the present invention, in the material development of the casting material refractory that is a non-fired product, the influence of sintering, the slag penetration depth, and the crack generation caused by the slag penetration amount, the actual furnace use, especially the operating conditions of the molten steel ladle It is an object of the present invention to provide an evaluation method, a test method and a device therefor which can be reproduced. It is another object of the present invention to provide a method for evaluating spalling resistance which correlates with nonuniformity of changes in physical properties caused by progress of sintering from one surface.

Further, it is an object of the present invention to provide a quantification method necessary for associating with stress distribution which causes crack generation and changes in physical properties such as elastic modulus and strength of refractory material.

[0010]

[Means for Solving the Problems] The inventors investigated the relationship between the depth of slag penetration into the pouring material and time, and under a sufficiently long use condition such as when considering the use in a ladle. That the depth of slag penetration is determined only by temperature,
We have found that there is a close relationship between the amount of slag and the occurrence of cracks, and have developed an evaluation method, test method and equipment that can reproduce the use of an actual furnace.

That is, the first invention of the present invention is characterized in that after the slag is melted on the upper surface of the refractory sample installed at the bottom of the furnace, the temperature of the furnace is raised and lowered. This is a structural spalling test method, in which one side has a length of 100 to 400 mm and a thickness of 50 to 200 m.
By using a refractory sample having m, it is possible to obtain the same result as in the actual furnace. Further, the heating temperature on the upper surface of the refractory sample is set to 1200 ° C. or higher, and the temperature gradient in the sample is set to 2
At 10 ° C./mm, 0.3 g or more of slag is melted on the upper surface of the refractory sample per 1 cm ^{2 of the} upper surface of the refractory sample, and heated in the maximum temperature range after melting the slag for 4 hours or more.

Next, the inventors of the present invention have found that the spalling resistance of the casting material, which is an unfired product, is mainly due to changes in the mineral phase, strength, elastic modulus, etc. caused by heating on one side. It was By observing how the casting material is cracked by one-sided heating in real time using an AE sensor, we have discovered what the casting material composition such as the binder and chemical components should be.

That is, the second aspect of the present invention is that the inside of the sample produced by raising and lowering the temperature of the furnace by the AE sensor mounted on the cooling surface side of the pouring material refractory sample installed at the bottom of the furnace. The crack is evaluated. An apparatus of the present invention capable of suitably carrying out the above-mentioned invention is a refractory sample installation unit installed at the bottom of a furnace, an acoustic emission (AE) sensor attached to the refractory sample, and a refractory sample of the refractory sample. A heating element that heats from the top side,
A structural spalling test device for a refractory, which is provided with a device for raising and lowering the furnace temperature.

The inventors of the present invention conducted a spalling test by changing the amount of slag permeated into the casting material, the melt permeation time, the heat load condition, etc., and quantified the cracks generated by this test. Regarding the slag permeation spalling test, which is closely related to the present invention, the relationship between the slag permeation (amount and depth) and the heating conditions was investigated, and the sufficiently long use conditions such as when considering the use in a ladle were also investigated. We found that the depth of slag penetration in and was determined only by temperature, and that there was a close relationship between the amount of slag and the occurrence of cracks, and we used the evaluation method and test method that can reproduce the actual furnace use.

[0015]

[Function] In order to confirm the occurrence of structural spalling due to slag infiltration, a sufficient amount of slag is melted, given a temperature gradient similar to that of an actual furnace, and held for a sufficient time.
The slag needs to penetrate the test piece sufficiently. By placing the test piece on the bottom of the furnace and heating the test piece from above, it becomes possible to melt the slag on the heating surface side. Further, this makes it possible to create a temperature gradient in which the temperature decreases from the top to the bottom.

As a test method, heating is performed from the upper surface of the test piece and the temperature is maintained until a sufficient temperature reaches equilibrium, and the slag is melted and penetrated into the test piece. In this state, it is possible to reproduce the actual furnace by applying a temperature change close to that of the actual furnace and checking for the occurrence of cracks. In addition, it is possible to create non-uniformity due to firing within an irregularly shaped refractory that is an unfired product, and by adjusting the thickness of the sample shape to actual use, the turbidity change close to that of an actual furnace can be achieved. give.

FIG. 1 shows a schematic sectional view of the test apparatus of the present invention. A heat insulating material 2 is packed in a steel shell 3, a refractory sample 6 is placed, and a heating element 1 is provided above it. The refractory sample 6 is provided with an AE sensor 4 and a thermocouple 5, and the slag 7 is placed on the refractory sample 6. Refractory sample 6
It is preferable that one side has a length of 100 to 400 mm and a thickness of 50 to 200 mm. The length of one side is 1
If it is less than 00 mm, cracks cannot be reproduced in an actual furnace.
If it exceeds 400 mm, there is no change in the state of crack generation, and the device becomes too large for testing, which is not economical. The length of one side is preferably in the range of 150 to 300 mm. If the thickness is less than 50 mm, it is too thin and cracks are less likely to occur.
If it exceeds 200 mm, it is too thick and different types of cracks are generated. It is preferably 80 to 150 mm.

The temperature gradient in the refractory sample is 2 to 10 ° C./m.
It is preferably m. This value is close to the temperature gradient in the refractory in the actual furnace, but the inventors found that the slag penetration depth is determined only by the temperature, so if the temperature gradient changes, the slag penetration depth changes. It will be done and it will not be a reproduction of the actual furnace. It is preferably 3 to 7 ° C / mm. Cooling side of refractory sample (bottom surface) to obtain a prescribed temperature gradient
Insulation may be put in or air-cooled.

The maximum temperature is preferably 1200 ° C. or higher. 1
If it is less than 200 ° C, the slag is not melted. The actual furnace temperature is preferably 1450 to 1600 ° C. The heating time in the maximum temperature range after melting the slag is preferably 4 hours or more.
If it is less than 4 hours, the penetration of slag is not sufficient and cracks occur at a shallower position than originally expected. The time is preferably 10 hours or more, more preferably 15 hours or more. Four
Even if heated for 5 hours or more, the result is not so different and it is not economical.

The amount of slag to be melted on the refractory sample is 0.
It is preferably 3 g / cm ² or more. Below this, the amount of slag is not sufficient, and cracks may not occur. Desirably, it is 0.8 g / cm ² or more. By attaching the AE sensor to the refractory sample under test, the AE signal according to the heating conditions and the material of the casting material is detected, and more accurate determination is possible. In the conventional method, cracks were observed from the cut surface after cooling, so it was not possible to determine whether the cracks occurred during the temperature change or during cooling. By attaching an AE sensor and evaluating the amount of cracks, the time of occurrence, and the position of occurrence, more accurate judgment can be made.

The refractory sample is judged by the method of the present invention as shown in FIG. 2 by the size and number of cracks (vertical cracks) perpendicular to the heating surface and cracks (transverse cracks) parallel to the heating surface, which are generated in the sample. It evaluated by various methods. The maximum crack width is 0.1 mm
The above items were measured. Figure 2 shows the procedure for crack quantification
Will be described with reference to. (1) The Y axis 12 is taken in the depth direction from the heating surface 8. (2) Heating surface 8 by cutting the Y-axis 12 at 10 mm pitch 14
A large number of parallel measuring lines 13 are drawn between the and the back surface 9. (3) Count the intersections 10 of the measurement lines 13 and the vertical cracks 11. (4) The horizontal axis is the distance from the heating surface 8 of the measuring line 13,
The number of intersections 10 is taken on the vertical axis and graphed. An example of the graph thus formed is shown in FIG. The area of the hatched part is defined as the damage amount.

Similarly, for cracks parallel to the heating surface, (a) the Y axis is taken from one side surface of the sample to the other side surface along the heating surface. (B) The Y axis is carved at a pitch of 5 mm and a measurement line perpendicular to the heating surface is drawn. (C) Count the intersection of the measurement line and the lateral crack. (D) The horizontal axis represents the distance of the measurement line from the heating surface, and the vertical axis represents the number of intersections, which are graphed.

An example of a graph is shown in FIG. In this way, the lateral cracks can be graphed in the same manner, and the crack amount can be quantified. The crack generation pattern shown in FIG. 3 is obtained by the above-described spalling test method based on actual use.
It was found to have a strong correlation with the results of computer-aided thermal stress simulations. Specifically, the heating surface side (1
The thermal stress was calculated by changing the elastic modulus from 500 ° C.) to the cooling surface side (900 ° C.) as shown by the curve 50 in FIG. 9, and the thermal stress distribution generated in the sample was found to be in good agreement. saw. FIG. 11 shows a stress component parallel to the heating surface (lateral crack generation factor), and FIG. 12 shows a stress component perpendicular to the heating surface (vertical crack generation factor).

The method of the present invention can be applied not only to a test of a ladle pouring material, but also to an evaluation and a test in the case of developing an unshaped refractory such as a gutter, an RH device, a converter or a tundish.

[0025]

【Example】

Example-1 The relationship between the use results of the alumina-based casting materials (sample names A to H) in the 230t molten steel ladle and the results of the slag infiltration spalling test according to the present invention was investigated. It has been found from the results of observation and analysis that the damage to the 230-ton ladle is mainly structural spalling due to slag infiltration.

The slag infiltration spalling test was conducted as follows. Refractory sample size is 200 × 200 × 100m
m, and the surface of 200 × 200 mm was heated. The maximum temperature was 1500 ° C, and a temperature gradient of 4.2 ° C / mm was provided in the refractory. After 5 hours from reaching the maximum holding temperature, 400 g (1 g / cm ² ) of converter slag was charged and held for 18 hours, then, a temperature change of 900 to 1500 ° C. was given 6 times and then cooled. Attaching four AE sensors to this refractory sample,
The position and time of occurrence of cracks were recorded. After cooling, the refractory samples were cut and cracks were evaluated in the same manner as shown in FIG.

FIG. 4 shows the relationship between the slag permeation spalling test results according to the present invention and the actual pot use results. Further, for comparison, FIG. 5 shows the relationship between the slag rotary erosion test and the method of Suekawa et al. As is clear from these figures, it can be seen that the method is in best agreement with the actual use result.

Example-2 Alumina-based casting material similar to that of Example 1 (sample name A to
For H), a test piece having the same size was prepared and tested under the following conditions. Maximum temperature: 1550 ° C. Temperature gradient: 5.6 ° C./mm Slag input: Converter slag 800 g (Ig / cm ² ) Holding time: 20 hours Temperature change: (900 to 1550 ° C.) × 8 times The result is substantially as shown in FIG. Were the same.

Example 3 A casting material of magnesia-zircon (using alumina cement), magnesia-alumina (using alumina cement), and alumina-spinel (using silica sol) was used. The slag infiltration spalling test was conducted as follows. The test piece size is 200 × 200 × 100 mm,
The 200 × 200 mm surface was heated. Temperature rising rate is 8 ° C /
The maximum temperature was 1500 ° C., and a temperature gradient of 4 to 5 ° C./mm was applied to the three types of use. In this test, four AE sensors for evaluating the crack position were attached.

FIG. 6 shows the relationship between the heat pattern and the number of AE signals measured (count rate) for each sample. In the magnesia-zircon material shown in FIG. 6 (a),
About 400 minutes after the start of holding at 1500 ° C., the number of measurements increased sharply. The rapid increase continued for about 200 minutes, and then maintained a high count rate for about 600 minutes before entering cooling. The number of measurements decreased drastically from the start of cooling to 800 ° C, and about 1 after cooling
It was almost 0 at 00 minutes. After that, the temperature decreased while measuring three large peaks until the temperature decreased to room temperature. Figure 6
In the magnesia-alumina material shown in (b),
During the holding process, the number of measurements was almost zero. The number of measurements increased rapidly after the start of cooling, and reached a peak at about 100 to 200 minutes after cooling. After that, the temperature decreased to room temperature. In the alumina-spinel material shown in FIG. 6C, a small peak appeared in the temperature rising process and the holding process, but the number of measurements was small. Immediately after the start of cooling, the number of measurements increased sharply, reached the first peak, then decreased again, and reached the second peak about 120 minutes after cooling.

According to the present invention, the detection pattern of the AE signal which differs depending on the material of the casting material can be arranged as follows. (A) Magnesia-zircon material In the magnesia-zircon material, cracks perpendicular to the heating surface were observed in the observation of the cut surface after the test. This crack is shown in Figure 6.
It is known from the results of the two-dimensional position evaluation that the point a shown in (a) starts to occur and the point b continues to grow.
In the case of magnesia-zircon, it was found from the relationship between the firing temperature and the bending strength and elastic modulus at room temperature that sintering proceeds during the temperature rising and temperature holding processes. From the above, it can be said that the magnesia-zircon material is a material having a large non-uniformity in sintering due to heating on one side. (B) Magnesia-alumina material In the magnesia-alumina material shown in FIG. 6 (b), cracks perpendicular to the heating surface were observed in the observation of the cut surface after the test.
In the magnesia-zircon material, due to the relationship between the bending temperature and the bending modulus at room temperature and the elastic modulus, the strength and elastic modulus of the matrix decrease to the extent that cracking does not occur during the temperature rising and temperature holding processes, and the cooling process decreases. It is probable that a crack occurred when it entered. (C) Alumina-spinel In this system using the silica sol shown in FIG. 6 (c) as a binder, the room temperature strength increased remarkably with the firing temperature, but the porosity hardly changed. The modulus increased only slightly with increasing strength. This system can be said to be a material with a small non-uniformity difference between the heating surface side and the cooling surface side.

Example 4 A slag permeation spalling test was conducted as follows. The sample used is magnesia. The test piece size is 200
It was set to × 200 × 100 mm, and the surface of 200 × 200 mm was heated. Maximum temperature is 1500 ° C, and refractory is 4.
A temperature gradient of 2 ° C / mm was applied. 5 hours after reaching the maximum holding temperature, 400 g (0-2 g / cm ² ) of converter slag
After being charged and held for 18 hours, a temperature change of 900 to 1500 ° C. was applied 6 times and then cooled. Four AE sensors were attached to this test piece, and the crack generation position and time were recorded.
After cooling, the test piece was cut and evaluated for cracks by the same method as shown in FIGS.

FIG. 7 and FIG. 8 show a part of the results of graphing the generated cracks according to the present invention. Curve 40 is slag 400
The curve 41 indicates the number of intersections of the slag 800g. The distance from the heated surface is 14 mm for 400 g of slag and 18 mm for 800 g of slag, and it can be seen that lateral cracks have occurred at a deeper depth as the amount of slag added increases. Further, the elastic modulus (room temperature value) from the heating surface side to the cooling surface side is, as shown in FIG. 9, a curve 51 when slag is not charged and a curve 50 when ² g / cm ² is charged. . From the thermal stress calculation based on this, the stress (factor of occurrence of lateral crack) in the direction perpendicular to the heating surface generated in the center of the sample is calculated by the elastic modulus curve 5 respectively.
Curves 60 and 61 shown in FIG. 10 were obtained according to 0 and 51, and good agreement was seen with the result of graphing the lateral cracks shown in FIG.

[0034]

The slag infiltration spalling test method according to the present invention is in good agreement with the result of using the developed actual pot, and can be said to be effective in determining the application to the actual pot. In addition, cracks due to non-firing which are inherently non-firing of cast refractory can be observed in real time during heating, and the degree of non-uniformity of physical properties caused by heating from one side can be evaluated.

Further, the slag permeation spalling test method according to the present invention and the quantification of cracks generated by the slag permeation spalling test are evaluated by associating the crack evaluation which has been limited to visual observation with physical property values such as change in elastic modulus. Made it possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a slag permeation spalling test apparatus.

FIG. 2 is an explanatory diagram illustrating a crack quantification procedure.

FIG. 3 is a diagram showing quantification of cracks.

FIG. 4 is a graph showing test results by a slag infiltration spalling test device and actual pot usage results.

FIG. 5 is a graph showing the relationship between the test results by the slag rotary erosion method and the method of Suekawa et al.

FIG. 6 is a graph of a count rate of an AE signal.

FIG. 7 is a graph showing the relationship between the distance from the heating surface and the number of intersections.

FIG. 8 is a graph showing the relationship between the distance from the heating surface and the number of intersections.

FIG. 9 is a graph showing the values of the elastic modulus and the distance from the heating surface.

FIG. 10 is a graph showing the relationship between the distance from the heating surface and the stress.

FIG. 11 is a quantitative stress distribution diagram by thermal stress calculation.

FIG. 12 is a quantitative stress distribution diagram by thermal stress calculation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Heating element 2 Heat insulating material 3 Iron skin 4 AE sensor 5 Thermocouple 6 Refractory sample 7 Slag 8 Heating surface 9 Back surface 10 Intersection point 11 Vertical crack 12 Y axis 13 Measuring line 14 Pitch

Claims (5)

[Claims] 1. A structural spalling test method for a refractory, which comprises melting the slag on the upper surface of a refractory sample installed at the bottom of the furnace and then raising or lowering the temperature of the furnace. 2. The test method according to claim 1, wherein a refractory sample having a side length of 100 to 400 mm and a thickness of 50 to 200 mm is used. 3. The heating temperature on the upper surface of the refractory sample is set to 12
The temperature within the sample is set to 00 ° C or more, the temperature gradient in the sample is set to 2 to 10 ° C / mm, and 0.3 g or more of slag is melted on the upper surface of the refractory sample per 1 cm ^{2 of the} upper surface of the refractory sample, and the maximum temperature range after slag melting The test method according to claim 1, wherein heating is performed for 4 hours or more. 4. An amorphous refractory sample is placed in a furnace with one surface exposed, the temperature of the furnace is raised and lowered, and the amorphous refractory is detected from acoustic information detected on the cooling surface side of the amorphous refractory. A method for evaluating cracks caused by firing of an irregular-shaped refractory, characterized by judging and evaluating cracks that have occurred in a material sample. 5. A refractory sample installation section installed at the bottom of the furnace, an acoustic emission sensor attached to the refractory sample, a heating element for heating from the upper surface side of the refractory sample, and a furnace temperature rise and fall. A device for testing a refractory material, comprising: