JP7323747B2 - Method for evaluating hydration expansion behavior of steelmaking slag and steam aging apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for evaluating hydration 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 steelmaking slag, which is a refining byproduct (residue). There are many.
Free lime and free magnesia are calcium oxide and magnesium oxide, respectively, or solid solutions in which oxides such as silicon oxide, aluminum oxide, and iron oxide are dissolved in calcium oxide and magnesium oxide. have.

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

Most of the quicklime added as a refining agent fuses (residues) with oxides of silicon, phosphorus, manganese, etc. contained in the raw materials for refining, and oxides of iron itself, and becomes molten slag. However, in high-grade steels with low phosphorus concentrations, a large amount of quicklime may be added to strengthen the degree of refining. In such a case, not all of the added quicklime turns into slag during refining, and some may remain in the slag as undissolved and unreacted lime particles. This is the type of free lime called unrefined lime.
This unrefined lime is generally large and brown in color, and is often found on the surface of slag masses and fracture surfaces of expansion fractures. The amount of unrefined lime varies depending on the amount of quick lime added and the refining conditions.

Unless the added quicklime is unusually high, most of it becomes molten slag during refining, as described above. Steelmaking slag is uniformly melted at a high temperature of about 1600°C in a refining furnace. Forms a free lime phase. This is the type of free lime called crystallized lime.
The formation of crystallized lime is unavoidable as long as basic slag with a high calcium oxide ratio is used. Crystallized lime generally has a fine structure, and it is believed that the hydration expansion behavior of slag caused by crystallized lime is different from the hydration expansion behavior of slag caused by unrefined lime.

When the long columnar tricalcium silicate (3CaO—SiO ₂ ) generated in the range of 1700° C. to 1400° C. in the process of cooling the high basicity molten slag decomposes at 1300° C. or less, dicalcium silicate (2CaO—SiO ₂ ) is precipitated lime, and forms streaks in the tricalcium silicate (3CaO--SiO ₂ ) mineral phase of long columnar shape. It is believed that the hydration expansion behavior of slag caused by precipitated lime is different from that of slag caused by unrefined 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 charged into the converter. The dolomite used in the steelmaking process is called light-burned dolomite (CaO-MgO). The CaO content removes impurities in the molten steel, and the MgO content strengthens the furnace wall refractories of converters and ladles. Protect and extend the life of converters and ladles. Like CaO, most of this MgO becomes molten slag during refining, but free magnesia and unsloughed dolomite may be seen during the cooling process. There are two types of free magnesia, one is M _rim with wustite-rich outer grain edges, and the other is magnesio-wustite (MW). MW is a solid solution of FeO and MgO, and CaO and MnO are in solid solution. Since considerable amounts of FeO and MnO are solid-dissolved in both M _rim and MW, it is said that the hydration reaction is remarkably suppressed.

When steelmaking slag is used as a roadbed material, etc., the hydration reaction of free lime and free magnesia in the slag occurs over time, causing cracks, partial exfoliation, and pulverization of individual slags. As a result, macroscopic volumetric expansion occurs as an aggregate (bulk) of slag and slag-using products.

Therefore, as a measure to reduce the expansion of slag, some kind of stable aging such as natural aging (atmospheric aging) by long-term accumulation, steam aging by steam permeation to piled slag, or steam aging by high pressure and high temperature in a pressurized tank. It is often treated with a heat treatment. The stabilization treatment is a treatment for reacting free lime and free magnesia with moisture and carbon dioxide to convert them into hydroxides and carbonates, respectively.

Produced slag or slag after stabilization treatment is often subjected to expandability evaluation to ensure quality during use.
JIS A5015 (Non-Patent Document 1) defines the upper limit of the expansion rate of steelmaking slag applied to roadbed materials and the like, and Annex B specifically defines the test method.
This test method is widely used as a macro hydration expandability evaluation method for steelmaking slag, not only for roadbed materials, but also for other uses.

In addition to the water immersion expansion test in accordance with 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 in slag products Various expansibility evaluation methods are used for cause investigation and the like.

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

Further, in Patent Document 2, steelmaking slag is finely pulverized and divided into two, one is formed by adding water and the other is formed without contact with water, and both formed bodies are uniaxially expandable. Measure the maximum value of the coefficient of linear expansion when curing is performed while making a part of the compact contact with water and absorb water, and the amount of quicklime estimated from the correlation between the coefficient of linear expansion and the amount of quicklime A method is disclosed for determining the amount of quicklime that affects expansion from the difference between the two compacts.

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 for calculating the area ratio (content ratio) of crystallized lime and precipitated lime to converter slag particles.

JP-A-2005-61863 JP 2014-157019 A JP 2015-105873 A

JIS A5015:2013 Steel slag for roads

As mentioned above, the water immersion expansion test in accordance with the JIS method is widely used as a macroscopic hydration expansion evaluation method for steelmaking slag, including not only for roadbed materials but also for other applications. Using the test material, one point of data is obtained as the average value of the measurement results of three test pieces after 10 days, so the cause of expansion required for measures to reduce slag expansion can be specified, i.e. However, information such as discrimination between free lime and free magnesia and the type and amount of free lime cannot be obtained.

In addition, the evaluation method of 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 necessary for improving the operation from the time of generation. The types of free lime such as lime and crystallized lime are unknown.
Similarly 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 and the amount of quicklime described in Patent Document 2 does not provide 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 and the linear expansion coefficient obtained in advance, and it is said that this correlation does not change for any specimen. No guarantees.
On the other hand, according to the method described in Patent Document 3, although each content of unsloughed lime, crystallized lime, and precipitated lime can be grasped, information on the hydration expansion behavior of slag itself cannot be obtained.

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

The present invention has been made in view of such circumstances, quantitatively grasping the aging time dependence of the hydration expansion behavior of steelmaking slag, The purpose of this study is to obtain useful information for evaluating and improving hydration expandability.

In order to achieve the above object, a method for evaluating hydration expansion behavior of steelmaking slag according to the first invention is provided by: When the test material is placed in an observable container and subjected to steam aging treatment under atmospheric pressure, at preset time intervals , the test material expands, cracks, peels, falls off, breaks, collapses, Observe the change in appearance due to pulverization and / or measure the change in mass, and when expansion, cracking, peeling, falling off, breaking, collapse, pulverization is observed in the test material, each change is counted as one time. The accumulated number of changes and/or the collapse mass ratio of the test material are calculated for each elapsed time of steam aging, and the aging time dependence of the hydration expansion behavior of the steelmaking slag is calculated based on the calculation results. Characterized by evaluation.

"Steelmaking slag" is a general term for converter slag, electric furnace slag, hot metal refining slag, and secondary refining slag.
"Cumulative number of changes in test material" is a numerical value obtained by counting and accumulating the number of changes when expansion, cracking, peeling, falling off, breakage, collapse, and pulverization are observed in the test material. Swelling, cracking, peeling, falling off, cracking, crumbling, and pulverization are each counted as one change.
Also, the "disintegration mass ratio of the test material" is the ratio of the mass of the part peeled from the test material to the mass of the test material before steam aging.

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

Further, in the method for evaluating hydration expansion behavior of steelmaking slag according to the first invention, the mineral phase contained in the portion separated from the test material during the steam aging treatment is specified at preset time intervals. can be

Here, "specification of the mineral phase contained in the part separated from the test material" means that the part separated from the test material contains free lime and/or free magnesia, or that the part separated from the test material contains free lime and/or free magnesia. If lime and/or free magnesia is present, specify whether it is unrefined lime, crystallized lime, precipitated lime, M _rim , MW, unrefined dolomite.

As shown in the examples below, the hydration expansion behavior of slag due to each of unsludged lime, crystallized lime, precipitated lime, M _rim , MW, and unsludged dolomite is different, so that free lime becomes unsludged. It is important to specify whether it is lime, crystallized lime or precipitated lime, and whether the free magnesia is M _rim , MW or unrefined dolomite.

A second invention is a steam aging apparatus used in the method for evaluating hydration expansion behavior of steelmaking slag according to the first invention,
A steam generator that generates steam, an aging treatment container that stores a 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 comprising

According to the method for evaluating the hydration expansion behavior of steelmaking slag according to the present invention, it is possible to quantitatively grasp the aging time dependence of the hydration expansion behavior of steelmaking slag. It is possible to obtain useful information for evaluating and improving the hydration expandability of slag that may be damaged.

BRIEF DESCRIPTION OF THE DRAWINGS It is the flowchart which showed the procedure of the hydration expansion behavior evaluation method of the steelmaking slag which concerns on one embodiment of this invention. 1 is a schematic diagram showing the configuration of a steam aging device according to an embodiment of the present invention; FIG. 4 is a graph showing the cumulative number of changes in a test material for each elapsed time of steam aging. 4 is a graph showing the collapsed mass ratio of unrefined lime and crystallized lime contained in a portion peeled from a test material for each elapsed time of steam aging.

Next, an embodiment embodying the present invention will be described with reference to the attached drawings for understanding of the present invention.

The present invention relates to the hydration expansion behavior of a test material produced from steelmaking slag containing free lime and/or free magnesia and having hydration expandability, when the test material is subjected to steam aging treatment under atmospheric pressure. , in relation to the elapsed time of steam aging.

A method for evaluating the hydration expansion behavior of steelmaking slag according to one embodiment of the present invention will be described below with reference to the flowchart of FIG.
[STEP1]
Steelmaking slag containing free lime and/or free magnesia and having hydration expandability is crushed, magnetically separated, and sieved to prepare a plurality of test materials (see ST1).
The amount of test material to be subjected to one test, that is, the number of lumps/granules, can be appropriately selected according to the purpose of the test, constraint conditions, and the like. Unless there are at least 10 lumps/grains, it is difficult to statistically evaluate the behavior of the test material as a group. In addition, as the amount of test material increases, the statistical evaluation accuracy improves, but the load of the test increases. Therefore, it should be judged comprehensively from the purpose of the test, the type of test material, the ability of the evaluation equipment, etc. Although it is difficult to uniquely define the number of samples and the absolute value of the mass, it is desirable to test with a small amount as long as the purpose of the test is satisfied. For example, about 20 to 100 lumps/granules are recommended as a scale that substantially achieves a good balance between test efficiency and accuracy of results, based on the experience of the inventors.

The particle size and dimensions of the test material before testing 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 grain size regulation for each type of various roadbed materials defined in JIS A 5015. If the particle size is too fine, it becomes difficult to observe and measure cracks, expansion, and collapse, so a size that allows easy observation 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, from the viewpoint of the gist of the present invention, ``evaluation of expansion behavior as a slag group from the behavior of many lumps and grains,'' and the heat capacity and heat transfer rate (reaction rate to temperature change), the upper limit size of the test material is also determined. limited to some extent. Specifically, 30 mm or less is preferable. Considering JIS A 5015, which specifies the particle size of roadbed materials, such as "26.5 mm sieve ratio is 0 to 5%", there is little demand for investigation of the behavior of slag larger than this size.

[STEP2]
A steam aging apparatus is used to subject a plurality of specimens to steam aging treatment under atmospheric pressure (see ST3) until a predetermined aging time is reached (see ST2).
The steam aging apparatus 10 used is shown in FIG. The steam aging apparatus 10 includes a steam generator 11 that generates steam, an aging treatment container 12 that stores the test material S and performs steam aging of the stored test material S, and steam generated by the steam generator 11. to the aging treatment container 12 and a pipe 13 for supplying the aging treatment container 12 as a main component.

The aging processing container 12 includes 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 sensor for monitoring the temperature in the container so that the pressure in the container does not rise. A total of 20 are provided. A plurality of sample shelves 19 on which the test materials S are placed are arranged in the container, and the container itself is provided with a transparent window through which the test materials S can be observed from the outside.

In the middle of the pipe 13, there are a safety valve 14 for automatically releasing water vapor when the internal pressure rises abnormally, a mist separator 15 for removing water droplets from the water vapor, and a pressure gauge 16 for monitoring the pressure of the water vapor. A shut-off valve 17 for shutting off the supply of steam to the aging treatment container 12 and a flow control valve 18 for adjusting the amount of steam supplied are installed during observation and measurement of the test material.

The present invention relates to the hydration expansion exhibited by a plurality of test materials produced from steelmaking slag containing free lime and/or free magnesia and having hydration expandability when subjected to steam aging treatment under atmospheric pressure. This is a method of evaluating the behavior in relation to the elapsed time of steam aging. Steam aging generally involves loading slag onto a steam pipe, covering it with a heat insulating sheet, and curing it for about a week to 10 days. In this method, the temperature inside the sheet does not reach 100°C.
The purpose of the present invention is to evaluate the expansion behavior with the lapse of time in general steam aging, and it is desirable that there is not much deviation from the actual operation conditions.

Strictly speaking, the temperature inside the container does not reach 100° C. even if the steam of atmospheric pressure is continuously blown into the aging processing container 12, and the temperature varies somewhat depending on the meteorological atmospheric pressure, heat input/output balance, and the like. Generally, the temperature is about 95 to 100°C, and in many cases about 97 to 99°C. Even this temperature is sufficient for evaluation purposes.
The amount of steam generated by the steam generator 11 varies depending on the size of the aging treatment container 12, the amount of test material mounted in the container, the ambient temperature, etc., but in short, excess steam 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 the free lime and free magnesia contained in the test material undergo a hydration reaction, the test material changes. The hydration reaction is represented by the following reaction formula, and when the hydration reaction occurs, the volume of the specimen increases. In formula 1, the volume is 1.99 times that before the reaction, and in formula 2, it is 2.23 times.
CaO+H ₂ O→Ca(OH) ₂ (1 formula)
MgO+H ₂ O→Mg(OH) ₂ (2 formulas)
If volumetric expansion occurs in a part of the structure in the test material, the test material itself or a part of it expands, surface cracks occur, part of the surface layer peels off or falls off, cracking of the test material itself, and small pieces Changes such as collapse into two parts and pulverization of the entire test material occur. 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 a number of factors.

In the present embodiment, changes in appearance and/or changes in mass are observed and/or measured at preset time intervals for the test material during the steam aging treatment (see ST4).
When observing the change in the appearance of the test material, visually judge the changes such as expansion, cracking, peeling, and collapse of each test material, and grasp the presence or absence of changes in the test material due to hydration reaction.
Immediately after stopping the steam aging, the test material is wet 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 of the aging treatment container 12 and dried, the changes in color and surface texture can be grasped more clearly.
In addition to visual observation on the spot, it is also a suitable method to photograph the condition of the test material. By comparing with the photograph taken before aging treatment, it becomes easier to judge the appearance change of each test material.

When measuring the mass change of the test material, the mass of each test material is weighed before the aging process, and the mass of each test material during the aging process is weighed at preset time intervals. Understand change.

The total aging treatment time (total treatment time) and the time interval between observation and measurement of changes in the test material differ depending on the purpose of evaluation and the type of slag. It may be determined in advance by referring to past knowledge, or may be appropriately selected by judging the situation during the evaluation test.
The time during which steam blowing is temporarily suspended for observation and measurement of the test material shall be deducted from the total processing time.
Since the hydration swelling 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. Intervals should be chosen to be appropriately distributed in logarithmic terms.

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. It is desirable to randomly change the arrangement 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 change in appearance and the measurement of the change in mass, the structure of the portion separated from the test material may be identified (see ST5).
By mineralogical investigation, it is possible to identify the mineral phases contained in the part separated from the test material. The mineral phase includes, for example, an unrefined lime phase, a crystallized lime phase, a calcium ferritic stable phase, a quenched phase, and 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.
Quantitative data such as the area ratio of free lime can be obtained by quantitatively investigating the composition of the mineral phase by setting a range. The method described in Patent Document 3 or the like can be used for the measurement.

EPMA (Electron Microanalyzer) and SEM (Scanning Electron Microscope) measurements of microscopic mineral structures can reveal fine three-dimensional structures, component analysis in microscopic local areas, component distributions within structures and phases, etc. information is obtained.
Using this information, we investigated the relationship between the content of unrefined lime and crystallized lime and the behavior of hydration swelling, the compositional comparison of the hydrated swollen/collapsed part and the unreacted part, and the progress of hydration in each structure. It is possible to discuss the differences, etc. and the factors involved. Furthermore, it is possible to examine measures for improving operations by going back to the stage of slag generation.

[STEP6]
When the predetermined aging time is reached (see ST2), the total number of changes in the test material and/or the collapse mass ratio are calculated from the observation results of the appearance change of the test material and/or the measurement results 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 expansion behavior of the steelmaking slag is evaluated (see ST6).

The cumulative number of changes in the test material is a numerical value obtained by counting and accumulating the number of changes when cracks, delamination, collapse, etc. are found in the test material. Cracking, peeling, disintegration, etc. are counted as one change.
The disintegration mass ratio of the test material is the ratio of the mass of the part detached from the test material to the mass of the test material before steam aging.

By grasping how the cumulative number of changes and the collapsed 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 has been completed by the steam aging treatment. Or judge whether it is not yet completed.

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. Other possible embodiments and modifications are also included.

Verification tests conducted to verify the effects of the present invention will be described.
[Example 1]
Hydration of two types of converter slag, steel type A and steel type B, which were expected to have a large refining load in the converter and a large amount of quicklime, and as a result, the hydration expansion and collapse of the resulting converter slag were expected to be severe. Reaction behavior was evaluated by the method described above.
Each raw ore was crushed, magnetically separated, and sieved on a laboratory scale, and slag lumps under the 31.5 mm mesh screen and above the 4.75 mm mesh screen were used as test materials. The number of specimens subjected to the test was 31 for steel type A and 27 for steel type B. In order to manage individual test materials, a number was given to each test material, and they were placed on a sample shelf in an aging treatment container and subjected to steam aging treatment. In order to average out the effects of temperature difference and steam flow change in the aging treatment vessel, the location of the test material was appropriately changed for each observation. The temperature inside the container during the test was 97-98°C.

Steam aging treatment was performed for a total of 400 hours. During this time, steaming was interrupted at preset time intervals to observe the hydration swelling of each test material.
Changes such as cracks, peeling, and collapse of each test material were visually observed after surface drying, and the number of occurrences of such changes was counted. When partial cracking, peeling, collapse, etc. were repeated multiple times in the same test material, each occurrence was counted cumulatively.

The results of the verification test are shown in FIG. This figure shows the cumulative number of changes in the test material for each elapsed time of steam aging.
The figure shows 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 the gradual disintegration and pulverization progress even after 5 hours. Therefore, the disintegration/powder rate for each aging time is assumed to be the slope of the approximate straight line, and this slope is less than 1/10 of the maximum value at 10 to 15 hours, except for the initial period (up to 5 hours). The point of time when it became the convergence point of the collapse and pulverization was taken. When the aging time exceeds 100 hours, the slope of the approximation straight line becomes 1/10 or less, and it is presumed that the disintegration and pulverization, that is, the hydration reaction is completed.
On the other hand, with steel type B, the rate of disintegration and pulverization is slightly stagnant from the first 10 hours to about 30 hours, but it maintains a high rate until the end of 400 hours, and as a result surpasses steel type A. It is the number of occurrences of cracks, peeling, collapse, etc.

From the above, it can be concluded that the hydration reaction of steel type A is almost completed by steam aging treatment for 100 to 150 hours, that is, about 4 to 6 days, and the aging load is within the industrially practical range. It was judged. On the other hand, the steam aging treatment for steel type B for about several days is insufficient, and it still continues to expand. Therefore, there remains a concern that expansion will occur after 400 hours when the current measurement is completed. Therefore, it was thought that a period of ten and several days or longer would be required to stabilize the expansibility only by the steam aging treatment. Considering productivity and treatment costs, it is dangerous to rely solely on steam treatment to suppress expansion. Improvements from the refining aspect were considered.

Some supplementary information will be given regarding this implementation method.
It is not necessary to always perform observations at a high frequency as in the present embodiment. It may be appropriately selected according to the purpose of the test and the behavior of the test material, including the test end timing (total test time).
In addition, although the purpose of this example is to compare steel grades A and B, this method can also be used to investigate variations in hydration reaction behavior for each refining batch of the same steel grade. In that case, it is sufficient to compare the slag in refining of the same steel type (slag type) multiple times. For example, if a total of 300 pieces, 30 each of 10 heats of refining numbers 001 to 010 of steel type A, are evaluated by this method, the slag behavior of 10 heats of refining of steel type A can be evaluated.

[Example 2]
The effect of the mineral structure, which is the cause of the expansion, on the hydration expansion behavior of steel type C converter slag was investigated. Free magnesia having hydration expandability may be present in the mineral composition of the slag, but it was confirmed by a preliminary microscopic examination that the slag of steel grade C had substantially no free magnesia.
50 test materials sampled from coarse-grained slag (30 mm to 5 mm size ballast) that were crushed, magnetically separated, and sieved at a slag ballast manufacturing plant were subjected to laboratory steam aging treatment in the same manner as in Example 1. rice field.
In this example, the mass of all test materials was individually weighed before the start of the test. Steam aging was carried out for a total of 400 hours, and if pulverization or peeling occurred during observation, the mass of that portion was also weighed. The hydration expansion behavior of the test material was organized by the mass of these collapsed parts.

The type of free lime was confirmed by visual observation of the fracture surface of the powdered/peeled portion, embedding of the powdered/peeled portion with resin, and observation with an optical microscope by polishing. The type of free lime was determined according to the following criteria based on metallurgical knowledge based on literature and the inventor's experience.
If brown particles are visually observed on the broken surface of the defect or peeled part, if unrefined lime is found in the collapsed slag pieces or powder as a result of microscopic examination with an optical microscope, or collapsed slag If the piece/powder was a quenched structure, it was determined that the collapse was due to unrefined lime.
On the other hand, when crystallized lime was found in the collapsed slag pieces/powder, or when slag lumps were extensively pulverized and collapsed, it was determined that the collapse was caused by crystallized lime.

The results of the verification test are shown in FIG. The figure shows the collapsed mass ratio of unslagified lime and crystallized lime contained in the portion separated 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 trend. Therefore, the moving average of the measurement data for every three measurements was drawn.

It can be seen from the figure that there is a difference between the hydration expansion behavior due to unrefined lime and the hydration expansion behavior due to crystallized lime. Cracks and collapses due to unsloughed lime mainly occur in a short period of time, decrease once, and then become active again. Even after 400 hours of testing, cracks and collapses continue to occur. On the other hand, cracks and collapses due to crystallized lime mainly occur severely in the period of about several tens of hours from the start of steam aging, and it was found that the cracks and collapses are almost settled after steam aging treatment for several days to 10 days.

From the above, it was clarified that countermeasures from the refining aspect are necessary in order to avoid the steam aging treatment of steel type C slag for ten and several days to twenty days or more. Compared to crystallized lime, it is easier to reduce the occurrence of unrefined lime while maintaining the results of refining such as dephosphorization. A study was conducted to change the conditions.

10: steam aging device, 11: steam generator, 12: aging treatment container, 13: piping, 14: safety valve, 15: mist separator, 16: pressure gauge, 17: cutoff valve, 18: flow control valve, 19: sample Shelf, 20: Thermometer, 21: Exhaust port, 22: Droplet discharge valve, S: Test material

Claims (3)

When a plurality of test materials of slag lumps made from steelmaking slag containing free lime and/or free magnesia and having hydration expandability are placed in an observable container and subjected to steam aging treatment under atmospheric pressure , At preset time intervals , expansion, cracking, peeling, falling off, breakage, collapse, pulverization of the test material is observed and / or mass change is measured, expansion, cracking, peeling, falling off, The cumulative number of changes, which is a numerical value accumulated by counting each change as one time at the time when cracking, collapse, and pulverization is observed in the test material, and / or the collapse mass ratio of the test material, is the progress of steam aging . A method for evaluating hydration and expansion behavior of steelmaking slag, wherein the hydration and expansion behavior of steelmaking slag is calculated for each time, and aging time dependence of the hydration and expansion behavior of steelmaking slag is evaluated based on the calculation results. 2. The method for evaluating hydration expansion behavior of steelmaking slag according to claim 1, wherein the mineral phase contained in the portion separated from the test material during the steam aging treatment is specified at preset time intervals. method for evaluating hydration expansion behavior of steelmaking slag. A steam aging apparatus used in the method for evaluating hydration expansion behavior of steelmaking slag according to claim 1 or 2,
A steam generator that generates steam, an aging treatment container that stores a 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 comprising:

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