JP6014574B2 - Determination of free lime in converter slag - Google Patents

Description

  The present invention relates to a method for evaluating the expansibility of converter slag, and more particularly to a method for determining free lime, which is an expansion factor of converter slag.

Converter slag is steel slag generated in a steelmaking process using a converter, and is used for road materials such as roadbed materials because it is hard and has high bulk specific gravity.
The converter slag contains free lime (f-CaO) derived from quicklime added during refining. When free lime comes into contact with moisture or rainwater in the air, it causes a hydration reaction represented by the formula (1), and the volume expands about twice.
CaO + H ₂ O → Ca (OH) ₂ (1)
Therefore, if the converter slag containing a lot of free lime is used as it is as a road material, problems such as cracks and bumps on the road surface are caused. For this reason, when converter slag is used for road materials, steam aging treatment of converter slag is usually performed in advance to complete the hydration reaction of free lime.

  The steam aging treatment is a method in which steam is blown into a pile of slag to promote the hydration reaction, and the hydration reaction of free lime is completed within a few days. For example, Patent Document 1 discloses that hydration reaction of free lime in steelmaking slag by blowing steam at 80 to 100 ° C. into piled steelmaking slag crushed to a predetermined particle size and exposing it to the atmosphere for 48 hours or more. It is described that the aging process can be stably performed in a short time.

  However, since the steelmaking process by the converter is a batch process, the properties of the converter slag are likely to vary, and the free lime content varies greatly depending on the refining conditions. For this reason, the steam aging process is inevitably forced to operate on the safe side, and the present situation is that a process longer than the 48-hour exposure described in Patent Document 1 is performed.

  On the other hand, if a method capable of quickly detecting the content of free lime contained in converter slag is established, the steam aging treatment should be optimized by grasping the content of free lime before the steam aging treatment. It is possible to reduce costs. Therefore, various methods for quantifying free lime contained in converter slag have been proposed so far. The ethylene glycol method is one of the most widely known methods.

In the ethylene glycol method, the converter slag is dissolved at a predetermined temperature for a predetermined time using an ethylene glycol reagent, and the content of calcium in the solution is measured. A neutralization titration method, an atomic absorption analysis method, or a conductivity measurement method is used to measure the calcium content in the solution. It should be noted that calcium hydroxide (Ca (OH) ₂ ) is dissolved in the ethylene glycol reagent in addition to calcium oxide (CaO). Thermogravimetric analysis is used to measure the content of calcium hydroxide. Non-Patent Document 1 includes “a method for determining f-CaO and Ca (OH) ₂ in steel slag (= ethylene glycol method)” and “a method for determining Ca (OH) _{2 in} steel slag (= thermogravimetric analysis). "Method)" describes an analysis method that aims to improve the accuracy of the analysis and has reviewed the conditions.

JP-A-61-101441

“Standardization of characterization technology for free CaO in steel slag”, Analytical Technology Subcommittee, Japan Iron and Steel Association, March 2013, p. 88-94

Free lime contained in converter slag is roughly classified into the following three types based on the generation behavior.
(A) Undegraded lime: Free lime in which a portion of quicklime added during refining remains in the slag in an undissolved state. It is in the form of brown particles and can be confirmed visually.
(B) Crystallized lime: Free lime that is melted once during refining and is produced as excess lime at the end of the process in which various minerals are produced by cooling the slag. Since it is formed at the end of the process in which various mineral phases are formed, it has a shape that fills the gap between other mineral phases.
(C) precipitation of lime: in the course of molten slag of high basicity cools the die when the 1700 ° C. to 1400 tricalcium silicate long columnar generated in ° C. zone (3CaO-SiO ₂₎ was decomposed at 1300 ° C. or less it is a free lime to produce with calcium silicate (2CaO-SiO _2). It forms in stripes in the long columnar mineral phase.

These three types of free lime have different effects on the hydration expansion of converter slag from the location and form of converter slag. For example, crystallized lime and precipitated lime are present between the crystals and inside the crystal, and therefore contribute to the expansion of the converter slag depending on the content, and exhibit long-term expansion behavior.
Therefore, in order to accurately grasp the expansion behavior of converter slag, it is important to understand how much uncontained lime, crystallized lime, and precipitated lime are contained in the converter slag. It becomes.

  However, the ethylene glycol method mentioned above treats unexpansion lime, crystallized lime, and precipitated lime as a combined value without distinction, so it is difficult to accurately grasp the expansion behavior of the converter slag. For example, even if the converter slag has the same value of calcium oxide, if one is mainly composed of undegraded lime and the other is mainly composed of crystallized lime and precipitated lime, both exhibit different expansion behaviors.

  The present invention has been made in view of such circumstances, and in order to accurately evaluate the expansion behavior of the converter slag and optimize the steam aging treatment, uncontained lime, crystallization contained in the converter slag It aims at providing the fixed_quantity | quantitative_assay method of the free lime in converter slag which can grasp | ascertain each content rate of lime and precipitated lime.

In order to achieve the above object, the present invention is a method for calculating the content of each lime by classifying free lime contained in the converter slag into uncontained lime, crystallized lime, and precipitated lime, The following steps are provided.
(1) A sample piece containing converter slag particles is prepared.
(2) The converter slag particles in the sample piece are observed with a microscope at a first magnification to photograph a first observation field.
(3) The number of cells occupied by the phase containing crystallized lime and / or precipitated lime by attaching a grid line having the first cell width to the image of the first observation visual field taken in the second step And measuring the number of squares occupied by the phase of undehydrated lime and the number of squares occupied by the converter slag particles, and calculating the area ratio (content ratio) of the phases occupied by the converter slag particles. .
(4) The phase containing the crystallized lime and / or precipitated lime is observed with a microscope at a second magnification having a magnification higher than the first magnification, and a second observation visual field is photographed.
(5) A grid line having a second grid width finer than the first grid width is attached to the image of the second observation visual field photographed in the fourth step, and crystallized lime is formed. The number of squares occupied, the number of squares occupied by precipitated lime, and the number of squares occupied by the second observation visual field are measured, and the area ratio of crystallized lime and precipitated lime in the second observation visual field is determined. calculate.
(6) Multiplying the area ratio of crystallized lime and precipitated lime in the second observation field, respectively, and the area ratio of the phase containing the crystallized lime and / or precipitated lime in the converter slag particles Then, the area ratio (content ratio) occupied by crystallized lime and precipitated lime with respect to the converter slag particles is calculated.

The present invention provides a pre-process for calculating the area ratio of each phase by attaching a grid line having a coarse mesh width to the observation visual field image of converter slag particles, and a phase containing crystallized lime and / or precipitated lime. This is generally composed of a post-process for calculating the area ratio of crystallized lime and precipitated lime with a grid line having a fine mesh width.
First, a low-magnification observation visual field image obtained by photographing converter slag particles is attached with a grid line having a coarse mesh width, and a phase containing crystallized lime and / or precipitated lime and a phase of undehydrated lime are respectively present. The area ratio of the converter slag particles is calculated. Next, a high-magnification observation visual field image of a phase containing crystallized lime and / or precipitated lime is attached with a grid line having a fine mesh width, and crystallized lime and precipitates on converter slag particles The area ratio which each lime occupies is calculated.

  In the present invention, unmagnified lime and crystallized lime and precipitated lime having a small mineral phase compared to unhatched lime are efficiently measured. ) And high magnification (second magnification). Although each magnification depends on the resolution of the microscope to be used, the first magnification is about 50 times and the second magnification is about 200 times.

  Moreover, in the determination method of the free lime in the converter slag according to the present invention, it is preferable that the first mesh width is 0.3 mm to 0.5 mm and the second mesh width is 10 μm to 15 μm. .

When the first magnification is about 50 times, if the first cell width is less than 0.3 mm, the number of cells included in the phase becomes too large and the measurement becomes complicated, while the first cell width If it exceeds 0.5 mm, the mesh is too rough and the error from the actual shape of each phase becomes too large.
In addition, when the second magnification is about 200 times, if the second mesh width is less than 10 μm, the number of meshes contained in the crystallized lime and the precipitated lime becomes too large, and the measurement becomes complicated. If the second mesh width is more than 15 μm, the mesh is too coarse and the error from the actual shapes of crystallized lime and precipitated lime becomes too large.

  According to the method for quantifying free lime in the converter slag according to the present invention, it is possible to detect the respective contents of uncontained lime, crystallized lime, and precipitated lime contained in the converter slag. The steam aging process can be optimized by accurately evaluating the expansion behavior of the converter slag.

It is a flowchart which shows the procedure of the determination method of the free lime in the converter slag which concerns on one embodiment of this invention. It is the schematic diagram which showed the preparation procedures of the sample piece. It is a schematic diagram of the microscope observation surface of a sample piece. (A) is a schematic view of an image obtained by photographing converter slag particles in a sample piece at a first magnification, and (B) is an image obtained by attaching a grid line having a grid width of 0.3 mm to 0.5 mm to the image. FIG. (A) is a schematic diagram of an observation visual field image obtained by imaging a phase containing crystallized lime and / or precipitated lime at a second magnification, and (B) is a grid line having a grid width of 10 μm to 15 μm in the observation visual field image. It is a schematic diagram of the attached image.

  Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

  With reference to the flowchart of FIG. 1, a procedure of a method for quantifying free lime in converter slag according to an embodiment of the present invention will be described.

[STEP-1]
A sample piece containing converter slag particles is prepared (ST1). The procedure for preparing the sample piece is as follows.
(1) The converter slag particles 10 having a particle size of about 5 mm to 30 mm are cut (see FIG. 2).
(2) The cut converter slag particles 10 and the resin 11 (for example, epoxy resin) are put in a vacuum vessel and evacuated to impregnate the converter slag particles 10 with the resin 11.
(3) The converter slag particles 10 infiltrated with the resin 11 are placed in a cylindrical mold 13 and the resin 11 is poured into the mold 13 (see FIG. 2). At that time, the converter slag particles 10 are arranged in the mold 13 so that the cut surface of the converter slag particles 10 is on the lower side.
(4) Remove the specimen 12 cured at room temperature from the mold 13.
(5) The microscope observation surface of the sample piece 12 (the surface on the cut surface side of the converter slag particles 10) is roughly polished with abrasive paper and then finish-polished with diamond paste. The microscope observation surface of the sample piece 12 is shown in FIG.

[STEP-2]
The converter slag particles 10 in the sample piece are observed with a microscope at a first magnification (for example, 50 times) to photograph an observation field (first observation field) (ST2). At that time, the entire view of the converter slag particles 10 is included in the observation visual field.
[STEP-3]
An observation visual field image photographed at the first magnification is taken into a personal computer, and a grid 15 having a size of 0.3 mm to 0.5 mm square (first grid width) is superimposed on the observation visual field image on the image editing software (see FIG. 4). ). And about the observation visual field image which overlapped 0.3 mm-0.5 mm square grid 15, based on the characteristic of each mineral phase contained in converter slag particle 10, it classifies into the following five types of phases (ST3). .

(A) Phase not containing crystallized lime and precipitated lime: Mineral phases with no expansibility such as magnesia wustite and dicalcium silicate appear clearly and do not contain crystallized lime and precipitated lime. It may contain MgO-based inclusions and metals and is not expandable.
(B) Phase containing crystallized lime and / or precipitated lime: Crystallized lime and / or precipitated lime is included together with a non-expandable mineral phase such as magnesia wustite or dicalcium silicate. Depending on the concentration of crystallized lime and precipitated lime, it contributes to the expansibility of converter slag.
(C) Phase in which the crystal is unclear: a phase in which the crystal is not sufficiently grown by solidification and solidified. The boundary between minerals is unclear, and dendrite growth (primary crystals) is also seen. There is no expansibility.
(D) Undehydrated lime phase: Undehydrated lime phase remaining undissolved. Hydration proceeds promptly when left indoors. Has expandability.
(E) Pore phase: Pore in converter slag.

  An image of the converter slag particles 10 taken at the first magnification is shown in FIG. 4A, and an image obtained by adding grid lines having a grid width of 0.3 mm to 0.5 mm to the image is shown in FIG. 4B. Show. In the figure, reference numeral 20 is a phase containing crystallized lime and / or precipitated lime, reference numeral 21 is a phase of undehydrated lime, and reference numeral 22 is a phase not containing crystallized lime and precipitated lime. The converter slag particles 10 do not contain a phase in which crystals are unclear and a phase of pores.

[STEP-4]
The number of grids occupied by the phase 20 containing crystallized lime and / or precipitated lime, the number of grids occupied by the phase 21 of un-hatched lime, and the number of grids occupied by the converter slag particles 10 are measured, and each phase is measured. Calculates the area ratio (content ratio) of the converter slag particles 10 (ST4).

[STEP-5]
The phase 20 containing crystallized lime and / or precipitated lime is microscopically observed at a second magnification (for example, 200 times) having a magnification higher than the first magnification to photograph an observation field (second observation field) ( ST5). The number of field of view is about 10 per one converter slag particle 10 in which the phase 20 containing crystallized lime and / or precipitated lime is observed. An observation visual field image obtained by photographing the phase 20 containing crystallized lime and / or precipitated lime at the second magnification is shown in FIG. In the figure, reference numeral 25 denotes crystallized lime, reference numeral 26 denotes precipitated lime, and reference numeral 27 denotes a mineral phase such as magnesiowite or dicalcium silicate.

[STEP-6]
The entire observation visual field image photographed at the second magnification is taken into a personal computer, and a grid 16 of 10 μm to 15 μm square (second grid width) is superimposed on each observation visual field image on the image editing software (FIG. 5B). reference). And about each observation visual field image which piled up 10 micrometers-15 micrometers square grid 16, the number of cells which crystallized lime 25 occupies, the number of cells which precipitation lime 26 occupies, and the number of cells which observation field occupies are measured. Then, the area ratios of the crystallized lime 25 and the precipitated lime 26 in the observation visual field are obtained, and the average value of the area ratios obtained for each observation visual field is calculated (ST6).

[STEP-7]
The converter slag particles are obtained by multiplying the area ratio of the crystallized lime 25 and the precipitated lime 26 in the observation field by the area ratio of the phase 20 containing the crystallized lime and / or precipitated lime in the converter slag particles 10. The area ratio (content ratio) occupied by the crystallized lime 25 and the precipitated lime 26 with respect to 10 is calculated (ST7).

According to the method for quantifying free lime in converter slag according to the present embodiment, the free lime contained in converter slag is classified into uncontained lime, crystallized lime, and precipitated lime, and Since the content rate can be detected, it is possible to accurately evaluate the expansion behavior of the converter slag and optimize the steam aging treatment.
For example, converter slag containing a certain amount or more of undecomposed lime is not subject to steam aging treatment, or the steam aging period is shortened, and converter slag containing a large amount of crystallized lime and precipitated lime is long-term It is possible to determine in advance that a material having high expansibility is not used as a road material, that is, a steam aging treatment is not performed.

  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 matters described in the claims. Other possible embodiments and modifications are also included.

  The converter slag particles are discharged from the converter, transported in a receiving pan, cooled in the discharge field, and then recovered in metal and adjusted in particle size (processing amount: about 1000 tons, processing time: about 5 What was discharged from time) was used. At that time, in order to prevent the sample from being biased, samples of 5 kg to 10 kg were taken 5 times every 1 hour. The particle diameter of the collected converter slag particles is 5 mm to 30 mm.

  In accordance with JIS Z8815 “General Rules for Screening Test Method”, the collected converter slag particles were reduced by the conical quadrant method, and one sample piece was produced for each sample collection. The sample piece had a diameter of 32 mm, and four converter slag particles were embedded per sample piece (see FIG. 3).

The converter slag particles of the sample pieces were observed with a microscope at a magnification of 50 times, and an observation field was photographed. The shooting range was a full view of the converter slag particles. Next, the captured observation visual field image was taken into a personal computer, and a 0.5 mm square was superimposed on the captured observation visual field image on the image editing software, and classified into the five phases described above.
And the number of cells was measured about each classified phase, and the area ratio of each phase was computed. The results are shown in Table 1. The number in the table indicates the number of cells.

  As shown in the table, the converter slag particles employed in this test have 7255 0.5 mm squares in total, a phase not containing crystallized lime and precipitated lime, crystallized lime and / or precipitated lime. , 3658, 2615, 65, 571 and the area ratio are 4.77 in this order. %, 50.4%, 36.0%, 0.90%, and 7.87%.

Next, the phase containing crystallized lime and / or precipitated lime was observed with a microscope at a magnification of 200 times, and an observation visual field was photographed. The number of field of view was about 10 per one converter slag particle including a phase containing crystallized lime and / or precipitated lime. Next, the captured entire observation visual field image is taken into a personal computer, and on the image editing software, a 13 μm square is superimposed on each captured observation visual field image, and each area ratio of crystallized lime and precipitated lime is set to a 13 μm square grid. It calculated | required from number and the average value of 10 visual fields was computed about each area ratio of the obtained crystallization lime and precipitation lime.
Then, the average value is multiplied by the area ratio of the phase containing crystallized lime and / or precipitated lime obtained from the 50 times image to calculate each area ratio of crystallized lime and precipitated lime with respect to the converter slag particles. did. Table 2 shows the calculation results. In the table, the left column of crystallized lime and precipitated lime represents the area ratio of crystallized lime and precipitated lime in the observation field, and the right column includes crystallized lime and / or precipitated lime. The number of phase cells is multiplied by the area ratio of the left column, and converted to the number of crystallized lime and precipitated lime per 0.5 mm square.

  As shown in the table, crystallized lime and / or precipitated lime was confirmed in 10 of the 20 converter slag particles, and the number of grids of crystallized lime was 134 in terms of a 0.5 mm square. The number of grids of precipitated lime was 389, and the area ratio to converter slag particles was 1.86% for crystallized lime and 5.34% for precipitated lime.

  From the above operation, the unsaturated lime, the crystallized lime and the precipitated lime contained in the converter slag were each quantified by the area ratio. The area ratio of each mineral phase obtained from this example is 4.8% for a phase not containing crystallized lime and precipitated lime, and 50.4% for a phase containing crystallized lime and / or precipitated lime, 1.86% crystallized lime, 5.34% precipitated lime, 36.0% phase with unclear crystal, 0.90% undehydrated lime phase, 7.87% pore phase Met.

10: Converter slag particles, 11: Resin, 12: Sample piece, 13: Mold, 15, 16: Grid, 20: Phase containing crystallized lime and / or precipitated lime, 21: Phase of unfoamed lime, 22 : Phase not containing crystallized lime and precipitated lime, 25: crystallized lime, 26: precipitated lime, 27: mineral phase

Claims (2)

It is a method of classifying free lime contained in converter slag into unzaturated lime, crystallized lime, and precipitated lime, and calculating the content of each lime,
A first step of producing a sample piece containing converter slag particles;
A second step of observing the converter slag particles in the sample piece under a microscope at a first magnification and photographing the first observation field;
A grid line having a first grid width is attached to the image of the first observation visual field taken in the second step, and the number of grids occupied by the phase containing crystallized lime and / or precipitated lime is not A third step of measuring the number of squares occupied by the phase of hatched lime and the number of squares occupied by the converter slag particles, and calculating the area ratio of each phase in the converter slag particles;
A fourth step of observing the phase containing the crystallized lime and / or precipitated lime with a second magnification having a magnification higher than the first magnification and photographing a second observation field;
A grid having a second grid width finer than the first grid width is attached to the image of the second observation visual field taken in the fourth step, and the grids occupied by crystallized lime The number, the number of grids occupied by the precipitated lime, and the number of grids occupied by the second observation visual field are measured, and the area ratio of the crystallized lime and the precipitated lime in the second observation visual field is calculated. 5 steps,
The ratio of the area occupied by crystallized lime and precipitated lime in the second observation visual field is multiplied by the area ratio occupied by the phase including the crystallized lime and / or precipitated lime in the converter slag particles, and A sixth method for calculating an area ratio of crystallized lime and precipitated lime with respect to the furnace slag particles, and a method for quantifying free lime in converter slag.   2. The method for determining free lime in converter slag according to claim 1, wherein the first mesh width is 0.3 mm to 0.5 mm, and the second mesh width is 10 μm to 15 μm. A method for quantifying free lime in furnace slag.

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