JP2021012053A - Hydration expansion behavior evaluation method of steel making slag and steam aging device - Google Patents

Abstract

To obtain information effective to evaluate and improve the hydration expansion property of slag having a possibility of containing free lime and/or free magnesia by quantitatively gasping aging time dependency in a hydration expansion behavior of steel making slag.SOLUTION: According to the present invention, a hydration expansion behavior evaluation method of steel making slag comprises: installing a plurality of sample materials created from steel making slag containing free lime and/or free magnesia and having a hydration expansion property in an observable container; observing appearance change and/or measuring mass change at a preset time interval in performing steam aging treatment under an atmospheric pressure; calculating a cumulative change frequency and/or a collapse mass ratio of the sample materials in each lapsed time of steam aging; and evaluating aging time dependency in the hydration expansion behavior of the steel making slag on the basis of the calculation result.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for evaluating hydration and expansion behavior of steelmaking slag and a steam aging apparatus.

In the steelmaking process of steel production, refining agents containing calcium oxide and magnesium oxide such as quicklime and dolomite are used, and free lime and free magnesia remain in the steelmaking slag, which is a refining by-product (residue). There are many.
Free lime and free magnesia are solid solutions of calcium oxide, magnesium oxide alone, or oxides such as silicon oxide, aluminum oxide, and iron oxide dissolved in calcium oxide and magnesium oxide, respectively, and are often hydrated and expandable. have.

There are several types of free lime contained in steelmaking slag depending on the cause of its formation, and their hydration and expansion behavior also differ.

Most of the quicklime added as a refining agent fuses (slags) with oxides such as silicon, phosphorus, and manganese contained in the raw materials for refining and oxides of iron itself to form molten slag. However, in the case of high-grade steel with a low phosphorus concentration, a large amount of quicklime may be added in order to enhance the degree of refining. In such a case, not all of the added quicklime is slagged during refining, and some of the added quicklime may remain in the slag as undissolved and unreacted lime particles. This is a type of free lime called unslag lime.
This unslagged lime is generally large and often brownish, often found on the surface of slag masses and fractured surfaces of expansive fractures. The amount of unpolluted lime changes depending on the amount of quicklime added and the refining conditions.

Most of the added quicklime becomes molten slag during refining, as described above, unless it is unusually high. Steelmaking slag is uniformly melted at a high temperature of about 1600 ° C in the slag furnace, but depending on the slag composition, the calcium oxide component is subject to the thermodynamic solubility limit during cooling and solidification, and crystallizes. Produces a free lime phase. This is a type of free lime called crystallized lime.
The generation of crystallized lime is unavoidable as long as basic slag with a high calcium oxide ratio is used. Crystallized lime is generally a fine structure, and it is considered that the hydration and expansion behavior of slag caused by crystallized lime is different from the hydration and expansion behavior of slag caused by unslagged lime.

When the oblong column-shaped tricalcium silicate (3CaO-SiO ₂ ) produced in the 1700 ° C. to 1400 ° C. range is decomposed at 1300 ° C. or lower in the process of cooling the highly basic molten slag, the dicalcium silicate (2CaO-SiO ₂ ) is decomposed. _The free lime produced together with ₂ ) is precipitated lime, which is formed in stripes in the long columnar tricalcium silicate (3CaO-SiO ₂ ) mineral phase. The hydration and expansion behavior of slag caused by precipitated lime is considered to be different from the hydration and expansion behavior of slag caused by unslagged lime and crystallized lime.

It is well known that lime is used in the steelmaking process, but dolomite is also closely related to the steelmaking process and is generally used as an auxiliary raw material to be put into a converter. The dolomite used in the steelmaking process is called light-baked dolomite (CaO-MgO). The CaO content removes impurities in the molten steel, and the MgO content contains refractories in the furnace walls of converters and ladle. Protect and extend the life of converters and ladles. Like CaO, this MgO becomes mostly molten slag during refining, but free magnesia and unpolluted dolomite may be found during the cooling process. The free magnesia There are two types, one M _rim the particle outer edge rich _wustite, another is magnesiowustite mouse Tight (MW). MW is a solid solution of FeO and MgO, and CaO and MnO are in a solid solution. Since a considerable amount of FeO and MnO are dissolved in both _Mrim and MW, it is said that the hydration reaction is remarkably suppressed.

When steelmaking slag is used as a roadbed material or the like, the hydration reaction of these free lime and free magnesia in the slag occurs with the passage of time, and cracks, partial exfoliation, and pulverization collapse of individual slag occur. As a result, macroscopic volume expansion occurs as an aggregate (bulk) of slag and products using slag.

Therefore, as measures to reduce the expansion of slag, some kind of stability such as natural aging by long-term piles (atmospheric aging), steam aging by steam steaming to piles of slag, or steam aging by high pressure and high temperature in a pressurized tank, etc. Often subjected to chemical processing. The stabilization treatment is a treatment in which free lime and free magnesia are reacted with water and carbon dioxide to be converted into hydroxides and carbon dioxide, respectively.

The generated slag or the slag after the stabilization treatment is often evaluated for expandability in order to guarantee the quality at the time of use.
For steelmaking slag applied to roadbed materials and the like, the upper limit of the expansion coefficient is set in JIS A5015 (Non-Patent Document 1), and the test method is specifically defined in Annex B.
This test method is widely used as a macroscopic evaluation method for hydrated expansion of steelmaking slag not only for roadbed materials but also for other applications.

In addition to the water immersion expansion test conforming to the above JIS method, in addition to regular quality control work, operation management and improvement studies of refining and slag treatment processes, quality improvement of slag products, etc., or when trouble occurs with slag products Various expansiveness evaluation methods are used for investigating the cause and the like.

For example, in Patent Document 1, the infrared absorption spectra of a sample obtained by crushing and pulverizing steelmaking slag containing calcium and / or magnesium are measured before and after the hydration treatment, and calcium hydroxide and / or water in the sample is measured. A method of estimating the amount of magnesium oxide and evaluating the difference between the amount of calcium hydroxide and / or the amount of magnesium hydroxide in the sample before and after the hydration treatment as the degree of hydration of steelmaking slag is disclosed.

Further, in Patent Document 2, steelmaking slag is finely pulverized and divided into two, one is molded by adding water, and the other is molded without contact with water, and both molded bodies can be uniaxially expanded. The maximum value of the coefficient of linear expansion when curing is performed while bringing a part of the molded body into contact with water to absorb water is measured, and the amount of quicklime estimated from the correlation between the coefficient of linear expansion and the amount of quicklime. A method for determining the amount of quicklime that affects expansion from the difference between the two molded bodies is disclosed.

Furthermore, in Patent Document 3, the area ratio of the crystallized lime and the precipitated lime in the observation field is multiplied by the area ratio of the phase containing the crystallized lime and / or the precipitated lime in the converter slag particles. , A method of calculating the area ratio (content rate) of crystallized lime and precipitated lime to converter slag particles is disclosed.

Japanese Unexamined Patent Publication No. 2005-61863 Japanese Unexamined Patent Publication No. 2014-157019 JP 2015-105873

JIS A5015: 2013 Road steel slag

As mentioned above, the water immersion expansion test based on the JIS method is widely used as a macroscopic hydration expansion evaluation method for steelmaking slag not only for roadbed materials but also for other applications, but in units of several kilograms. Since it is a method to obtain one point of data as the average value of the measurement results of three specimens after 10 days using the test material of the above, the cause of expansion necessary for measures to reduce the expansion of slag, that is, , Information such as the distinction between free lime and free magnesia and the type and amount of free lime cannot be obtained.

In addition, the method for evaluating calcium hydroxide and / or magnesium hydroxide by measuring the infrared absorption spectrum before and after the hydration treatment described in Patent Document 1 is also required to improve the operation from the time of occurrence. The type of free lime such as lime and crystallized lime is unknown.
Similar to the method described in Patent Document 1, the method of estimating the amount of quicklime that truly contributes to expansion from the correlation between the linear expansion coefficient in uniaxial expansion described in Patent Document 2 and the amount of quicklime cannot obtain information on free lime. .. Furthermore, it is not a direct evaluation from the measurement data, but includes an error factor of using the correlation between the amount of quicklime obtained in advance and the coefficient of linear expansion, and this correlation does not change for any of the specimens. There is no guarantee.
On the other hand, according to the method described in Patent Document 3, the contents of unslagged lime, crystallized lime, and precipitated lime can be grasped, but information on the hydration and expansion behavior of slag itself cannot be obtained.

After all, in the methods described in Patent Documents 1 to 3, only the result information at a specific time such as after the slag stabilization treatment can be obtained, and the aging time dependence in the hydration expansion behavior of slag, which is necessary for the time evaluation of steam aging, No information is available.

The present invention has been made in view of the above circumstances, and quantitatively grasps the aging time dependence of the hydration and expansion behavior of steelmaking slag, and the slag which may contain free lime and / or free magnesia. The purpose is to obtain useful information for evaluation and improvement of hydration swelling.

In order to achieve the above object, the method for evaluating the hydration and expansion behavior of steelmaking slag according to the first invention is a plurality of test materials prepared from steelmaking slag containing free lime and / or free magnesia and having hydration and expansion. When the steam aging treatment is performed under atmospheric pressure, the appearance change is observed and / or the mass change is measured at preset time intervals, and the cumulative number of changes of the test material and the cumulative number of changes and the mass change are measured. / Or the decay mass ratio is calculated for each elapsed time of steam aging, and the aging time dependence of the hydration and expansion behavior of the steelmaking slag is evaluated based on the calculation result.

"Steelmaking slag" is a general term for converter slag, electric furnace slag, hot metal refining slag, and secondary refining slag.
The "cumulative number of changes in the test material" is a numerical value accumulated by counting the number of changes when expansion, cracking, peeling, falling off, circumcision, collapse, and pulverization are recognized in the test material. Expansion, cracking, peeling, falling off, circumcision, collapse, and pulverization are counted as one change.
The "disintegration mass ratio of the test material" is the ratio of the mass of the portion peeled from the test material to the mass of the test material before the steam aging is performed.

In the first invention, the hydration expansion of the steelmaking slag is steam-aged by grasping how the cumulative number of changes of the test material and the decay mass ratio change according to the elapsed time of steam aging. It can be determined whether the process has completed or has not yet completed.

Further, in the method for evaluating the hydration / expansion behavior of steelmaking slag according to the first invention, the structure of the portion peeled from the test material during the steam aging treatment may be specified at preset time intervals. Good.

Here, "identification of the structure of the portion peeled from the test material" means that the portion peeled from the test material contains free lime and / or free magnesia, and the peeled portion contains free lime and /. Or, if free magnesia is contained, it is to identify whether it is desquamated lime, crystallized lime, precipitated lime, _rim , MW, or desquamated dolomite.

As will be shown in Examples described later, the hydration and expansion behavior of slag caused by each of unstained lime, crystallized lime, precipitated lime, _Mill , MW, and unstained dolomite is different, so that free lime is unstained. It is important to identify whether it is lime, crystallized lime or precipitated lime and whether the free magnesia is _rim , MW or unstained dolomite.

The second invention is a steam aging apparatus used in the method for evaluating the hydration and expansion behavior of steelmaking slag according to the first invention.
A steam generator that generates steam, an aging treatment container that stores the test material and performs steam aging of the stored test material, and a pipe that supplies the steam generated by the steam generator to the aging treatment container. It is characterized by having.

According to the method for evaluating the hydration and expansion behavior of steelmaking slag according to the present invention, the aging time dependence of the hydration and expansion behavior of steelmaking slag can be quantitatively grasped, and thus free lime and / or free magnesia is included. It is possible to obtain useful information for evaluating and improving the hydration-expandability of slag that may be present.

It is a flow chart which showed the procedure of the hydration expansion behavior evaluation method of the steelmaking slag which concerns on one Embodiment of this invention. It is a schematic diagram which showed the structure of the steam aging apparatus which concerns on one Embodiment of this invention. It is a graph which showed the cumulative number of changes of the test material for each elapsed time of steam aging. It is a graph which showed the decay mass ratio of each of unslagged lime and crystallized lime contained in the part exfoliated from the test material for each elapsed time of steam aging.

Subsequently, an embodiment embodying the present invention will be described with reference to the attached drawings, and the present invention will be understood.

The present invention exhibits the hydration-expansion behavior of a test material produced from steelmaking slag containing free lime and / or free magnesia and having hydration-expandability when steam-aged under atmospheric pressure. , A method of evaluation in relation to the elapsed time of steam aging.

Hereinafter, a method for evaluating the hydration and expansion behavior of steelmaking slag according to an embodiment of the present invention will be described with reference to the flow chart of FIG.
[STEP1]
Steelmaking slag containing free lime and / or free magnesia and having hydration expansion property is crushed, magnetically separated, and sieved to prepare a plurality of test materials (see ST1).
The amount of test material to be used in one test, that is, the number of lumps / grains, can be appropriately selected depending on the purpose of the test, constraints, and the like. It is difficult to statistically evaluate the behavior of the test material as a group unless there are at least 10 lumps / grains. In addition, the larger the amount of the test material, the higher the statistical evaluation accuracy, but the higher the test execution load. Therefore, it should be judged comprehensively from the purpose of the test, the type of test material, the ability of the evaluation device, and so on. Although it is difficult to uniquely specify the number and absolute mass value, it is desirable to test with a small amount as long as the test purpose is satisfied. For example, from the experience of the inventors, about 20 to 100 lumps / grains are recommended as a scale with a substantially good balance between test efficiency and accuracy of results.

The particle size and dimensions of the test material before the test can be appropriately selected according to the material to which this measurement is applied and the purpose. For example, there is also a method of selecting in consideration of the particle size regulation for each type of various roadbed materials specified in JIS A 5015. If the particle size is too fine, it will be difficult to observe and measure cracks, expansion and collapse, so a size that can be easily observed should be selected. According to the findings of the present inventors, for example, about 2 mm is considered to be a substantial lower limit size.
In addition, the upper limit size of the test material is also set from the viewpoint of the gist of the present invention, "evaluation of expansion behavior as a slag group from a large number of lump / grain behaviors", and from the viewpoint of heat capacity and heat transfer rate (reaction rate to temperature change). Limited to some extent. Specifically, it is preferably 30 mm or less. Considering the particle size regulation of JIS A 5015, such as "the ratio on the 26.5 mm sieve is 0 to 5%", there is little demand for behavioral surveys of slags of larger sizes.

[STEP2]
A plurality of test materials are steam-aged under atmospheric pressure using a steam aging apparatus until a predetermined aging time is reached (see ST2) (see ST3).
The steam aging device 10 used is shown in FIG. The steam aging device 10 includes a steam generator 11 that generates steam, an aging processing container 12 that houses the test material S and performs steam aging of the stored test material S, and steam generated by the steam generator 11. Is the main component of the pipe 13 that supplies the steam to the aging treatment container 12.

The aging treatment container 12 has an exhaust port 21 for releasing water vapor in the container, a water droplet discharge valve 22 for discharging water droplets in the container, and a temperature for monitoring the temperature in the container so that the pressure in the container does not rise. It has a total of 20. The sample shelves 19 on which the test material S is placed are arranged in a plurality of stages in the container, and the container itself is provided with a transparent window in which the test material S can be observed from the outside.

In the middle of the pipe 13, there are a safety valve 14 that automatically releases water vapor when the internal pressure rises abnormally, a mist separator 15 that removes water droplets from the water vapor, and a pressure gauge 16 for monitoring the pressure of water vapor. A shutoff valve 17 that shuts off the supply of water vapor to the aging treatment container 12 and a flow control valve 18 that adjusts the amount of water vapor supplied are installed when observing and measuring the test material.

In the present invention, when a plurality of test materials prepared from steelmaking slag containing free lime and / or free magnesia and having hydration expansion property are subjected to steam aging treatment under atmospheric pressure, the hydration expansion exhibited by the test materials. This is a method of evaluating the behavior in relation to the elapsed time of steam aging. In steam aging, slag is generally loaded on a steam pipe, covered with a heat insulating sheet, and cured for about 1 week to 10 days. In this method, the temperature inside the sheet does not reach 100 ° C.
An object of the present invention is to evaluate the expansion behavior over time in general steam aging, and it is desirable that the conditions do not deviate significantly from the conditions of actual operation.

Even if the atmospheric pressure steam is continuously blown into the aging treatment container 12, the temperature inside the container does not strictly reach 100 ° C., and it differs slightly depending on the meteorological relationship between the atmospheric pressure and the heat input / output balance. Generally, the temperature is about 95 to 100 ° C., and in many cases, the temperature is about 97 to 99 ° C. Even this temperature is sufficient for evaluation purposes.
The amount of water vapor generated by the steam generator 11 varies depending on the size of the aging treatment container 12, the amount of the test material mounted in the container, the atmospheric temperature, etc., but the point is that excess water vapor is constantly discharged from the exhaust port 21. It suffices if the temperature inside the container can be maintained at 95 to 100 ° C.

[STEP3]
When free lime and free magnesia contained in the test material undergo a hydration reaction, the test material changes. The hydration reaction is shown by the following reaction formula, and when the hydration reaction occurs, the volume of the test material increases. In the first formula, the volume is 1.99 times that before the reaction, and in the second formula, the volume is 2.23 times.
CaO + H ₂ O → Ca (OH) ₂ ... (1 set)
MgO + H ₂ O → Mg (OH) ₂ ... (2 formulas)
When volume expansion occurs in a part of the structure of the test material, the test material itself or a part of it expands, surface cracks occur, a part of the surface layer peels off or falls off, the test material itself is broken, and fragments Changes such as disintegration that divides into powder and pulverization that the entire test material becomes powdery occur. What kind of morphological change is exhibited is the metallurgy of the shape and size of the test material, the amount of free lime and free magnesia contained in the test material, the mineral structure of the test material, the progress of hydration, etc. Depends on the factors.

In the present embodiment, the appearance change is observed and / or the mass change is measured at preset time intervals for the test material undergoing the steam aging treatment (see ST4).
When observing changes in the appearance of the test material, visually judge changes in expansion, cracking, peeling, collapse, etc. of each test material, and grasp whether or not there is a change in the test material due to the hydration reaction.
Immediately after the steam aging is interrupted, the test material is moistened with water droplets, and it is often difficult to grasp the color and surface texture. In such a case, if the test material is taken out from the aging treatment container 12 and dried, it may be possible to more clearly grasp the change in color and surface texture.
In addition to visual observation on the spot, it is also a preferable method to take a picture of the condition of the test material. By comparing with the photograph taken before the aging process, it becomes easier to judge the change in the appearance of each test material.

When measuring the mass change of the test material, the mass of each test material is weighed before the aging treatment, and the mass of each test material during the aging treatment is weighed at a preset time interval. Understand the changes.

The total aging treatment time (total treatment time) and the time interval for observing and measuring the change status of the test material differ depending on the evaluation purpose and the type of slag. It may be determined in advance with reference to past knowledge, or it may be selected as appropriate after judging the progress of the evaluation test.
The time during which steam injection is suspended for observation and measurement of the test material is deducted from the cumulative processing time.
Since the hydration and expansion behavior often depends on the logarithm of time, the time interval between observation and measurement of the test material is 5 minutes, 10 minutes, 20 minutes, 50 minutes, 100 minutes, 200 minutes, etc. It is better to choose the intervals to be appropriately distributed in logarithmic display.

Each time the observation and measurement of the test material at each time interval is completed, the test material is returned to the aging treatment container 12, but since the aging treatment is performed on each test material under equal conditions, the test material is used. It is desirable to randomly change the placement position of the test material each time observation and measurement are performed.

[STEP5]
In the observation and / or measurement of the test material at each time interval, in addition to the observation of the appearance change and the measurement of the mass change, the structure of the portion peeled from the test material may be specified (see ST5).
Mineralogical investigations can identify the mineral phase contained in the part exfoliated from the test material. The mineral phase is, for example, an unpolluted lime phase, a crystallized lime phase, a calcium ferritic stable phase, a quenching phase, or the like. In addition, information such as the presence or absence of precipitates in the phase and the presence or absence of cracks can be obtained.
If the range is set and the composition of the mineral phase is quantitatively investigated, quantitative data such as the free lime area ratio can be obtained. The method described in Patent Document 3 and the like can be used for the measurement.

When the micromineral structure is measured by EPMA (Electron Microanalyzer) and SEM (Scanning Electron Microscope), the fine three-dimensional structure, microscopic local component analysis, component distribution within the structure / phase, etc. Information is available.
Using this information, the relationship between the content of unslagged lime and crystallized lime and the hydration / expansion behavior, the component comparison of the hydrated / expanded / collapsed part and the unreacted part, and the degree of hydration progress of each tissue. It is possible to discuss the differences, etc. and the factors involved. Furthermore, it is possible to study operational improvement measures that go back to the slag occurrence stage.

[STEP6]
When the predetermined aging time is reached (see ST2), the cumulative number of changes and / or the decay mass ratio of the test material is vaporized from the observation result of the appearance change of the test material and / or the measurement result of the mass change of the test material. Calculated for each elapsed time of aging. Then, based on these calculation results, the aging time dependence of the hydration and expansion behavior of the steelmaking slag is evaluated (see ST6).

The cumulative number of changes in the test material is a numerical value that is accumulated by counting the number of changes when cracks, peeling, collapse, etc. are recognized in the test material. For cracking, peeling, collapse, etc., each change is counted as one time.
The decay mass ratio of the test material is the ratio of the mass of the portion peeled from the test material to the mass of the test material before steam aging is performed.

By grasping how the cumulative number of changes and the decay mass ratio of the test material change according to the elapsed time of steam aging, it is possible to determine whether the hydration expansion of the steelmaking slag was completed by the steam aging process. Or determine if it hasn't been completed yet.

Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and is within the scope of the matters described in the claims. It also includes other possible embodiments and variations.

The verification test carried out for verifying the effect of the present invention will be described.
[Example 1]
Hydration of two types of converter slag, steel type A and steel type B, which are expected to have severe hydration expansion and collapse of the resulting converter slag due to the large amount of quicklime used in the steel type with a large refining load in the converter. The reaction behavior was evaluated by the method described above.
Each ore was crushed, magnetically separated, and sieved on a laboratory scale, and slag lumps under a 31.5 mm mesh sieve and on a 4.75 mm mesh sieve were used as test materials. The number of test materials used for the test was 31 for steel type A and 27 for steel type B. Each test material was numbered so that individual test materials could be managed, and they were placed on a sample shelf in an aging treatment container for steam aging treatment. In order to average the effects of temperature differences and water vapor changes in the aging treatment vessel, the locations of the test materials were changed as appropriate for each observation. The temperature inside the container during the test was 97 to 98 ° C.

The steam aging treatment was carried out for a total of 400 hours. During that time, steaming was interrupted at preset time intervals, and the hydration and expansion status of each test material was observed.
Changes such as cracking, peeling, and disintegration of each test material were visually observed after the surface was dried, and the number of occurrences of the changes was counted. When changes such as partial cracking, peeling, and disintegration were repeated multiple times with the same test material, each was cumulatively counted as one time.

The result of the verification test is shown in FIG. The figure shows the cumulative number of changes in the test material for each elapsed time of steam aging.
It can be seen from the figure that the disintegration and pulverization behavior differs depending on the steel type. Steel type A has a high initial disintegration / pulverization rate, and after about 5 hours, the disintegration / pulverization rate is slower than before. However, it seems that gradual disintegration and pulverization are progressing even after the 5th hour. Therefore, the decay / pulverization rate for each aging time is defined as the slope of the approximate straight line, and this slope is less than 1/10 of the maximum value of 10 to 15 hours excluding the initial stage (up to 5 hours). The time when it became a point of convergence of collapse and pulverization was set. When the aging time exceeds 100 hours, the slope of the approximate straight line becomes 1/10 or less, and it is presumed that the disintegration / pulverization, that is, the hydration reaction is completed.
On the other hand, the decay / pulverization rate of steel type B is slightly stagnant from about 10 hours ago to about 30 hours, but maintains a high rate until the end of 400 hours, and as a result, exceeds steel type A. It is the number of occurrences of cracking, peeling, collapse, etc.

From the above, it is considered that the steel type A has almost completed the hydration reaction in 100 to 150 hours, that is, about 4 to 6 days of steam aging treatment as described above, and is in an industrially practical range as an aging load. It was judged. On the other hand, the steel type B is not sufficient for steam aging treatment for several days, and is still expanding. Therefore, there remains a concern that it will expand after 400 hours when the measurement is completed. Therefore, it was considered that a period of a dozen days or more was required to stabilize the expandability only by the steam aging treatment. Considering productivity and processing cost, it is dangerous to rely only on steam treatment for expansion suppression, and it is judged that it is necessary to use it in combination with other measures (refining measures such as reduction of slag basicity). We examined improvements in terms of refining.

This implementation method will be supplemented to some extent.
It is not necessary to carry out observations at a high frequency as in this embodiment. It may be appropriately selected according to the test purpose and the behavior of the test material, including the test end timing (total test time).
Further, although the purpose of this example is to compare steel type A and steel type B, this method can also be used for investigating variations in hydration reaction behavior for each refining batch of the same steel type. In that case, the slags of the same steel type (slag type) in multiple refinements may be compared. For example, if evaluation is performed by this method for a total of 300 slags for 10 heats from 001 to 010 refining numbers of steel type A, the slag behavior for 10 heats of steel type A is evaluated. The variation can be evaluated.

[Example 2]
The effect of the mineral structure, which is the cause of expansion, on the hydration and expansion behavior of the converter slag of steel type C was investigated. Although free magnesia having hydration expansion may be present as the mineral composition of slag, it was confirmed by a preliminary microscopic examination that free magnesia was substantially absent in the slag of steel type C.
Laboratory-like steam aging treatment was performed on 50 test materials sampled from coarse-grained slag (30 mm to 5 mm size slag) that had been crushed, magnetically separated, and sieved at a slag ballas manufacturing plant in the same manner as in Example 1. It was.
In this example, the masses of all the test materials were individually weighed before the start of the test. Steam aging was carried out for a total of 400 hours, but if pulverization or peeling occurred during observation during the process, the mass of that part was also weighed. The hydration and expansion behavior of the test material was arranged according to the mass of these collapsed parts.

Regarding the pulverized / peeled portion, the type of free lime was confirmed by visually observing the fracture surface, embedding the pulverized / peeled portion with resin, and observing with an optical microscope by polishing. The determination of the type of free lime was based on the following criteria based on the metallurgical findings from the literature and the experience of the inventor.
If brown particles are visually observed on the fracture surface of the defective part or peeled part, unstained lime is found in the collapsed slag pieces / powder in the microscopic examination result with an optical microscope, or the collapsed slag If the piece / powder had a rapidly cooled structure, it was judged that it had collapsed due to unslagged lime.
On the other hand, if crystallized lime was found in the collapsed slag pieces / powder, or if the slag mass pulverized and collapsed over a wide area, it was judged to be collapsed by crystallized lime.

The results of the verification test are shown in FIG. The figure shows the decay mass ratio of each of the undepleted lime and the crystallized lime contained in the portion peeled from the test material for each elapsed time of steam aging.
In the drawing using the data for each measurement, the hunting for each measurement is large and it is rather difficult to judge the macro tendency. Therefore, the drawing is performed by the moving average of the measurement data for every three measurements.

It can be seen from the figure that there is a difference between the hydration and expansion behavior due to unslagged lime and the hydration and expansion behavior due to crystallized lime. Cracking and collapse due to unslagged lime mainly occurs on the short-time side, decreases once, and then becomes active again. Even at the end of the 400-hour test, cracks and collapses continue to occur. On the other hand, cracking and disintegration due to crystallized lime occurred violently mainly in the period of several tens of hours from the start of steam aging, and it was found that the steam aging treatment for several days to 10 days almost settled down.

From the above, it was found that measures from the refining aspect are necessary to avoid the steam aging treatment for steel grade C slag for more than 10 days to 20 days. Compared to crystallized lime, the reduction of unslagged lime is easier to reduce the generation of lime while maintaining the refining results such as dephosphorization, so it is blown to promote the dissolution of quicklime in the converter. We examined changing the conditions.

10: Steam aging device, 11: Steam generator, 12: Aging processing container, 13: Piping, 14: Safety valve, 15: Mist separator, 16: Thermometer, 17: Shutoff valve, 18: Flow control valve, 19: Sample Shelf, 20: thermometer, 21: exhaust port, 22: water droplet discharge valve, S: test material

Claims (3)

Set in advance when multiple test materials made from steelmaking slag containing free lime and / or free magnesia and having hydration expansion properties are placed in an observable container and subjected to steam aging treatment under atmospheric pressure. The appearance change was observed and / or the mass change was measured at the time intervals, and the cumulative number of changes and / or the decay mass ratio of the test material was calculated for each elapsed time of steam aging, and the hydration and expansion behavior of the steelmaking slag. A method for evaluating the hydration / expansion behavior of steelmaking slag, which comprises evaluating the aging time dependence in the above based on the calculation result. The method for evaluating the hydration and expansion behavior of steelmaking slag according to claim 1, wherein the structure of the portion peeled off from the test material during the steam aging treatment is specified at a preset time interval. Method for evaluating hydration and expansion behavior. A steam aging apparatus used in the method for evaluating hydration and expansion behavior of steelmaking slag according to claim 1 or 2.
A steam generator that generates steam, an aging treatment container that stores the test material and performs steam aging of the stored test material, and a pipe that supplies the steam generated by the steam generator to the aging treatment container. A steam aging device characterized by comprising.

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