Method for heat cyclic utilization of medium-carbon aluminum killed steel casting residual steel slag

Abstract

The invention relates to the technical field of steelmaking, and discloses a method for heat recycling of medium-carbon aluminum killed steel casting residual steel slag. According to the thermal recycling method for the medium-carbon aluminum killed steel casting residual steel slag, the continuous casting residual steel slag is recycled on line and recycled for three times. The method is reasonable in design and simple and convenient to operate, and in the production process of the medium-carbon aluminum killed steel, more than 300 kg of molten steel and refining furnace smelting final slag still having the desulfurization capacity are always left at the bottom of a steel ladle after continuous casting pouring is finished; according to a traditional method, the processing cost is high in the treatment process, alloy elements are completely lost in the process of re-smelting in a furnace, and about 10% of iron elements contained in iron-containing material residual tailings are also wasted; compared with other methods, the method has the advantages that the implementation process is not tedious, the casting residual steel slag can be fully recycled under the condition that on-site logistics links are not obviously increased, consumption of alloy and refining slag is reduced, and good economic and social benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, in particular to a method for thermal recycling of medium-carbon aluminum killed steel casting slag. Background Art

[0002] When a steel mill continuously casts medium-carbon aluminum-killed steel, the ladle slag will mix the pure molten steel and ladle slag in the continuous casting tundish. Various substances in the slag will be drawn into the molten steel and become inclusions in the steel, affecting the purity of the molten steel. In severe cases, the castability of the molten steel will be deteriorated, causing the nozzle to be blocked and causing the continuous casting to stop. Therefore, in the actual production process, in order to avoid a large amount of slag in the ladle, the steel mill adopts the ladle slag retention operation during the continuous casting of medium-carbon aluminum-killed steel. The slag retention requirements for different steel grades are different, but the most basic requirement is that the ladle slide must be closed when ladle slag flows out of the large ladle nozzle. However, the ladle slag at this time is affected by the vortex of steel flow. There is still a layer of molten steel and ladle slag in the actual ladle. In addition, the shape of the ladle bottom will also increase the amount of residual slag. The residual molten steel and ladle slag in the ladle are referred to as residual slag. In the existing production process, more than 300 kg of residual slag will often remain at the bottom of the ladle at the end of continuous casting. Casting slag affects the yield of molten steel and increases production costs. The slag also requires special treatment, which increases processing costs. For this reason, many steel mills have studied the heat recovery method of casting slag.

[0003] Patent 1 with publication number CN101956043A discloses a method for recycling steelmaking residues. After the molten steel is poured, 2 to 3 tons of molten steel are first placed in a recycling bag, and then 2 tons of residues are poured into the recycling ladle, and 50 kg of covering agent is added. The recycling ladle is transported to the electric furnace process by a transport vehicle, and the residue and molten iron are poured into the electric furnace together. Since the residue is still rich in CaO, Al2O3, etc. and is in liquid state, it can be poured into the electric furnace to replace lime dephosphorization and desulfurization, reducing lime consumption. At the same time, the heat in the residue is also effectively recycled, reducing the consumption of the electric furnace and avoiding pollution to the environment.

[0004] Patent 2 with publication number CN101403021A proposes a method for utilizing steel slag produced by an electric furnace → LF refining (VD vacuum degassing) → mold casting production process, wherein slag-making material is added to the LF ladle refining furnace and refined, 20kg-50kg of slag-making material is added per ton of molten steel, and then cast, and the ladle furnace slag and remaining molten steel after casting are returned to the electric furnace for smelting, and slag-making material is added to the electric furnace, 50kg-70kg of slag is added per ton of molten steel. The addition of slag-making material lime is reduced during the electric furnace smelting process, and the power supply of the electric furnace is reduced. For steel types that need to be degassed, slag-making material is added to the LF ladle refining furnace after refining, and after slag making, the molten steel is sent to the VD vacuum degassing furnace for degassing, and then cast, and the ladle furnace slag and remaining molten steel after casting are returned to the electric furnace for smelting.

[0005] Patent 3 of CN 113088800 A proposes a method for recycling the slag and excess molten steel from the LF furnace of low-carbon aluminum killed steel. When the converter is tapping, 60-70wt% of the slag and excess molten steel from the upper refining furnace are poured into the ladle waiting for tapping, and the remaining 30-40wt% are poured into the slag pot; aluminum wire is fed during argon blowing; (2) the ladle is hoisted to the LF refining furnace for refining, and then aluminum wire and calcium wire are fed; (3) the molten steel that has been treated with LF refining after weak blowing is hoisted to the continuous casting ladle turntable to wait for pouring; (4) after the continuous casting of the ladle is completed, 30%-40% of the LF refining slag in the ladle is poured into the slag pot, and the remaining LF refining slag and excess molten steel enter the next cycle. The present invention enables the ladle to have a sufficient liquid slag layer when the LF refining is in place, shortens the time for making white slag, saves the consumption of slag making materials, and saves one ladle pouring process.

[0006] However, the treatment of the residual slag from continuous casting in both Patents 1 and 2 is basically used in the process links such as converters and electric furnaces. The process is long and the requirements for logistics within the factory are very high, so the applicability is not strong. In the solution proposed by Patent 3, the first step is to pour 60-70wt% of the refined slag and the residual molten steel into the ladle waiting for steel tapping, and then to receive the molten steel, which has a greater safety risk. The reason is that if the waiting time is long, the slag will crust at the bottom of the ladle and block the argon gas in the ladle. At the beginning of the steel tapping process, the argon gas is small, and there is a certain probability of explosive splashing caused by the aggregation reaction of materials such as carburizers. In the second step, the remaining 30-40wt% is poured into the slag pot, which is equivalent to the secondary use of the crane, which greatly affects the driving efficiency. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a method for thermal recycling of medium-carbon aluminum killed steel casting slag, thereby reducing the waste of casting slag and lowering production costs.

[0008] The technical solution adopted by the present invention to solve its technical problem is:

[0009] A method for thermal recycling of medium-carbon aluminum killed steel casting slag, wherein the medium-carbon aluminum killed steel suitable for the method has the following components: C=0.25-0.60wt%, Al=0.010-0.050wt%, Si=0.17-0.37wt%, Mn=0.60-0.80wt%, P≤0.035wt%, S≤0.020wt%, and the rest is Fe and essential impurities; the method is characterized by:

[0010] The continuous casting slag is recovered online and thermally recycled three times, and each thermal recycling includes the following steps:

[0011] (1) Converter endpoint control: endpoint C ≤ 0.15wt%, endpoint temperature ≥ 1600℃;

[0012] (2) When the converter is tapping steel, lime and aluminum blocks are added to the ladle. The amount of lime added is (3.0-nth heat cycle utilization*0.5) kg / t, and the amount of aluminum blocks added is 0.8 kg / t. At the same time, Si and Mn element alloys are added to the ladle based on the calculation of the converter endpoint sample;

[0013] (3) After the steel is tapped, the ladle is opened to the slag return position and waits for the slag to be returned;

[0014] (4) After the continuous casting is completed, the medium carbon aluminum killed steel smelted by conventional process is hoisted to the slag return position by a crane, and the remaining casting is poured into the ladle waiting at the slag return position;

[0015] (5) Hoist the ladle that has received the slag at the slag return position to the refining furnace;

[0016] (6) After the refining furnace is powered on for 5 to 8 minutes, lime and calcium carbide are added. The amount of lime added is (0.9-nth heat cycle utilization*0.3) kg / t, and the amount of calcium carbide added is 0.6 to 0.9 kg / t;

[0017] (7) Add corresponding alloys into the refining furnace according to the target composition of medium carbon aluminum killed steel;

[0018] (8) After the sample is tested and the components are qualified, the refined final slag sample is dipped and soft-blown for more than 15 minutes before being hung for continuous casting;

[0019] In which, n in step (2) and step (6) is the same, n is 1 to 3, and n is an integer.

[0020] In the first thermal cycle, n is 1; in the second thermal cycle, n is 2; and in the third thermal cycle, n is 3.

[0021] Furthermore, in the step (8), the composition of the slag sample after each thermal cycle is: CaO = 50-55wt%, SiO2 = 13-15wt%, FeO≤0.8wt%, Al2O3 = 18-22wt%, MgO = 6-8wt%, and the rest is S and unavoidable impurities.

[0022] Furthermore, in the steps (2) and (6), the lime content is CaO ≥ 85wt%, and the rest is CaCO3, Al2O3, water and essential impurities; in the step (6), the calcium carbide content is CaC2 = 70-78wt%, CaO = 18-22wt%, and the rest is Al2O3, water and essential impurities. Lime is used to increase CaO; calcium carbide is used for deoxidation to reduce FeO content and increase CaO content.

[0023] Furthermore, the amount of lime added decreases in the three thermal cycles. Since part of the silicon in the added silicon-containing alloy is oxidized into SiO2 and enters the slag, lime needs to be added to adjust the composition of the slag. At the same time, since the thickness of the slag layer increases after each cycle, if the amount of lime added remains unchanged, the thickness of the slag layer increases too fast. In the third thermal cycle, the slag layer may be too thick and foaming may occur, causing the slag to overflow from the ladle mouth. Therefore, the amount of lime added needs to be decreased in sequence.

[0024] The beneficial effects of the present invention are as follows: the present invention has reasonable design and is easy to operate. During the production process of medium-carbon aluminum-killed steel, more than 300 kg of molten steel and final slag from the refining furnace that still has desulfurization capacity often remain at the bottom of the ladle at the end of continuous casting. The traditional method has high processing costs, and alloy elements are completely lost during re-smelting in the furnace. About 10% of the iron elements contained in the residual tailings of the iron-containing material are also wasted. The present invention is superior to other methods in that the implementation process is not cumbersome, and the casting slag can be fully recovered without significantly increasing the on-site logistics links, thereby reducing the consumption of alloys and refining slag and having good economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 This is a flow chart of the thermal recycling of the residual slag from the casting of medium carbon aluminum killed steel in Example 1. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this description, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment uses a 100-ton converter in conjunction with a 100-ton LF refining furnace to specifically illustrate the method for thermal recycling of medium-carbon aluminum killed steel casting slag.

[0032] like Figure 1 A method for thermal recycling of medium carbon aluminum killed steel casting slag is shown, specifically:

[0033] 1. First thermal cycle

[0034] (1) Converter endpoint control: endpoint C is 0.11%, endpoint temperature is 1630°C;

[0035] (2) When the converter is tapping steel, lime and aluminum blocks are added to the ladle 2, with the lime input amount being 250 kg and the aluminum block input amount being 80 kg; at the same time, Si and Mn element alloys are added to the ladle 2 based on the calculation of the converter endpoint sample;

[0036] (3) After the steel is tapped, ladle 2 is opened to the slag return position and waits for slag return;

[0037] (4) Ladle 1 is filled with medium carbon aluminum killed steel smelted according to conventional processes. After the continuous casting is completed, ladle 1 is lifted to the slag return position by a crane, and the casting residue is poured from ladle 1 into ladle 2 waiting at the slag return position;

[0038] (5) hoisting the ladle 2, which has been subjected to conventional slag return process at the slag return position, to the refining furnace;

[0039] (6) After the refining furnace is powered on for 6 minutes, lime and calcium carbide are added. The amount of lime added is 60 kg and the amount of calcium carbide added is 80 kg.

[0040] (7) Add corresponding alloys into the refining furnace according to the target composition of medium carbon aluminum killed steel;

[0041] (8) After the sample is tested and the components are qualified, the refined final slag sample is dipped and soft-blown for more than 15 minutes before being hung for continuous casting;

[0042] (9) The composition of the final slag of the first refining by thermal recycling is as follows: CaO = 54.3wt%, SiO2 = 13.2wt%, FeO = 0.56wt%, Al2O3 = 20.6wt%, MgO = 6.3wt%, and the rest is S and unavoidable impurities;

[0043] 2. Second thermal cycle

[0044] (1) Converter endpoint control: endpoint C is 0.09%, endpoint temperature is 1626°C;

[0045] (2) When the converter is tapping steel, lime and aluminum blocks are added to the ladle 3, with the lime input amount being 200 kg and the aluminum block input amount being 80 kg; at the same time, Si and Mn element alloys are added to the ladle 3 based on the calculation of the converter endpoint sample;

[0046] (3) After the steel is tapped, ladle 3 is opened to the slag return position to wait for slag return;

[0047] (4) Ladle 2 is filled with medium carbon aluminum killed steel after the first heat cycle casting. After the continuous casting is completed, ladle 2 is lifted to the slag return position by a crane, and the remaining casting is poured from ladle 2 into ladle 3 waiting at the slag return position;

[0048] (5) hoisting the ladle 3, which has received the first heat cycle slag return at the slag return position, to the refining furnace;

[0049] (6) After the refining furnace is powered on for 7 minutes, lime and calcium carbide are added. The amount of lime added is 30 kg and the amount of calcium carbide added is 70 kg.

[0050] (7) Add corresponding alloys into the refining furnace according to the target composition of medium carbon aluminum killed steel;

[0051] (8) After the sample is tested and the components are qualified, the refined final slag sample is dipped and soft-blown for more than 15 minutes before being hung for continuous casting;

[0052] (9) The final slag composition of the second refining using thermal recycling is as follows: CaO = 53.9wt%, SiO2 = 13.6wt%, FeO = 0.59wt%, Al2O3 = 19.6wt%, MgO = 6.2wt%, and the rest is S and unavoidable impurities;

[0053] 3. The third thermal cycle

[0054] (1) Converter endpoint control: endpoint C is 0.08%, endpoint temperature is 1631°C;

[0055] (2) When the converter is tapping steel, lime and aluminum blocks are added to the ladle 4, with the lime input amount being 150 kg and the aluminum block input amount being 80 kg; at the same time, Si and Mn element alloys are added to the ladle 4 based on the calculation of the converter endpoint sample;

[0056] (3) After the steel is tapped, ladle 4 is opened to the slag return position to wait for slag return;

[0057] (4) Ladle 3 is filled with medium carbon aluminum killed steel after the second heat cycle casting. After the continuous casting is completed, ladle 3 is lifted to the slag return position by a crane, and the casting residue is poured from ladle 3 into ladle 4 waiting at the slag return position;

[0058] (5) hoisting the ladle 4 which has received the second heat cycle slag at the slag return position to the refining furnace;

[0059] (6) After the refining furnace is powered on for 5 to 8 minutes, add calcium carbide, the amount of calcium carbide added is 75 kg;

[0060] (7) Add corresponding alloys into the refining furnace according to the target composition of medium carbon aluminum killed steel;

[0061] (8) After the sample is tested and the components are qualified, the refined final slag sample is dipped and soft-blown for more than 15 minutes before being hung for continuous casting;

[0062] (9) The composition of the final slag of the third refining using thermal recycling is as follows: CaO = 52.8wt%, SiO2 = 14.7wt%, FeO = 0.67wt%, Al2O3 = 18.7wt%, MgO = 6.8wt%, and the rest is S and unavoidable impurities.

[0063] In this embodiment, the thickness of foamed slag in the ladle using conventional process and three heat cycles is shown in Table 1.

[0064] Table 1 Slag thickness of foam slag in ladle with conventional process and three-time thermal cycle

[0065]

[0066]

[0067] Comparative Example 1

[0068] Compared with Example 1, this comparative example uses conventional processes to treat the heat recycling of medium carbon aluminum killed steel casting slag. In conventional processes, the casting slag is generally cooled by methods such as hot stewing and hot pouring, and then transported to the slag treatment process to recover iron-containing materials by crushing, magnetic separation and other processes. The residual tailings after screening are generally sent to a building material specialty factory for making general-purpose building materials.

[0069] About 20 heats of steel were selected in 15 hours. Taking the production of No. 35 steel in a 100-ton converter for medium-carbon aluminum killed steel as an example, the benefits of the two methods of Example 1 and Comparative Example 1 were tested. The test results are shown in Tables 2 to 4.

[0070] Table 2 Conventional process (Comparative Example 1) Consumption

[0071] Furnace No. Lime for steel tapping (kg) Pre-melted refined slag (kg) LF lime supplement (kg) Amount of molten steel in casting (kg) 1 300 200 90 300 2 300 200 90 300 3 300 200 90 300 4 300 200 90 300 5 300 200 90 300 6 300 200 90 300 7 300 200 90 300 8 300 200 90 300 9 300 200 90 300 10 300 200 90 300 11 300 200 90 300 12 300 200 90 300 13 300 200 90 300 14 300 200 90 300 15 300 200 90 300 16 300 200 90 300 17 300 200 90 300 18 300 200 90 300 19 300 200 90 300 20 300 200 90 300 total 6000 4000 1800 6000

[0072] Table 3 Example 1 Consumption

[0073]

[0074]

[0075] Table 4: Overall benefits of Example 1 and Comparative Example 1

[0076]

[0077] It can be seen from Tables 2 to 4 that, compared with Comparative Example 1, Example 1 reduces the total amount of steel slag by 1500+3000+900+4500=9900kg, of which the direct benefit of reducing the consumption of lime and refined slag is 7200 yuan. At the same time, heat recovery of 4500kg of molten steel reduces alloy consumption and process processing costs by about 4500*0.1=450 yuan, greatly reducing production costs.

[0078] Comparative Example 2

[0079] Compared with Example 1, this comparative example adds a fourth thermal cycle on the basis of three thermal cycles, and the fourth thermal cycle specifically includes the following steps:

[0080] (1) Converter endpoint control: endpoint C: 0.09%, endpoint temperature 1621°C.

[0081] (2) When the converter is tapping steel, lime and aluminum blocks are added to the ladle, with the lime input amount being 100 kg and the aluminum block input amount being 80 kg; at the same time, Si and Mn element alloys are added to the ladle based on the calculation of the converter endpoint sample;

[0082] (3) After the steel is tapped, the ladle opens to the slag return position and waits for the slag to return.

[0083] (4) After the continuous casting is completed, the medium carbon aluminum killed steel that has been poured three times by heat recycling is hoisted to the slag return position by a crane, and the remaining casting is poured into the ladle waiting at the slag return position;

[0084] (5) hoisting the ladle that has received the third heat cycle slag at the slag return position to the refining furnace;

[0085] (6) After the refining furnace is powered on for 5 to 8 minutes, add 60 kg of calcium carbide instead of lime.

[0086] (7) In the refining furnace, add the corresponding alloy according to the target composition of medium carbon aluminum killed steel.

[0087] (8) After refining, soft blow for more than 15 minutes and then hang to continuous casting;

[0088] (9) The composition of the final slag after the fourth refining by thermal recycling is as follows: CaO = 52.8wt%, SiO2 = 14.7wt%, FeO = 0.67wt%, Al2O3 = 18.7wt%, MgO = 6.8wt%, and the rest is S and unavoidable impurities.

[0089] In this comparative example, the thickness of foamed slag in the ladle using the conventional process and four thermal cycles is shown in Table 6.

[0090] Table 6 Thickness of foam slag in ladle with conventional process and four thermal cycles

[0091] Cycle times Foam slag thickness (mm) Conventional process 80 Thermal Cycle First Time 120 Thermal cycle 2 180 Thermal cycle 3 280 Thermal cycle 4 400

[0092] As shown in Table 6, the thickness of foam slag in the ladle of the fourth thermal cycle reaches the maximum value. After analysis, the main reason is that the slag layer is too thick, and the carbon powder floats on the slag layer and cannot enter the molten steel through argon stirring in a short time. The carbon powder floating on the slag layer is partially burned during the power transmission process, resulting in a decrease in the yield. In addition, the foam slag layer is too thick and easily overflows the ladle mouth, which does not meet the safety control requirements. Therefore, three thermal cycles are the optimal operation.

[0093] In summary, the present invention is reasonably designed and easy to operate. During the production process of medium-carbon aluminum-killed steel, more than 300 kg of molten steel and the final slag from the refining furnace that still has desulfurization capacity often remain at the bottom of the ladle at the end of continuous casting. The traditional method has high processing costs, and the alloy elements are completely lost during the re-smelting in the furnace. About 10% of the iron elements contained in the residual tailings of the iron-containing material are also wasted. The present invention is superior to other methods in that the implementation process is not cumbersome, and the casting slag can be fully recovered without significantly increasing the on-site logistics links, thereby reducing the consumption of alloy and refining slag and having good economic and social benefits.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for thermal recycling of medium-carbon aluminum-killed steel casting slag, wherein the medium-carbon aluminum-killed steel composition applicable to the method is: C = 0.25-0.60wt%, Al = 0.010-0.050wt%, Si = 0.17-0.37wt%, Mn = 0.60-0.80wt%, P ≤ 0.035wt%, S ≤ 0.020wt%, and the rest is Fe and essential impurities; characterized in that: The continuous casting slag is recovered online and thermally recycled three times, and each thermal recycling includes the following steps: (1) Converter endpoint control: endpoint C ≤ 0.15wt%, endpoint temperature ≥ 1600℃; (2) When the converter is tapping steel, lime and aluminum blocks are added to the ladle. The amount of lime added is (3.0-nth heat cycle utilization*0.5) kg / t, and the amount of aluminum blocks added is 0.8 kg / t. At the same time, Si and Mn element alloys are added to the ladle based on the calculation of the converter endpoint sample; (3) After the steel is tapped, the ladle is opened to the slag return position and waits for the slag to be returned; (4) After the continuous casting is completed, the medium carbon aluminum killed steel smelted by conventional process is hoisted to the slag return position by a crane, and the remaining casting is poured into the ladle waiting at the slag return position; (5) Hoist the ladle that has received the slag at the slag return position to the refining furnace; (6) After the refining furnace is powered on for 5 to 8 minutes, lime and calcium carbide are added. The amount of lime added is (0.9-nth heat cycle utilization*0.3) kg / t, and the amount of calcium carbide added is 0.6 to 0.9 kg / t; (7) Add corresponding alloys into the refining furnace according to the target composition of medium carbon aluminum killed steel; (8) After the sample is tested and the components are qualified, the refined final slag sample is dipped and soft-blown for more than 15 minutes before being hung for continuous casting; In which, n in step (2) and step (6) is the same, n is 1 to 3, and n is an integer.

2. The method for thermal recycling of medium carbon aluminum killed steel casting slag according to claim 1, characterized in that: In the step (8), the composition of the slag sample after each thermal cycle is: CaO = 50 ~ 55wt%, SiO2 = 13 ~ 15wt%, FeO ≤ 0.8wt%, Al2O3 = 18 ~ 22wt%, MgO = 6 ~ 8wt%, and the rest is S and unavoidable impurities.

3. The method for thermal recycling of medium carbon aluminum killed steel casting slag according to claim 1, characterized in that: In the steps (2) and (6), the lime content is CaO ≥ 85wt%, and the rest is CaCO3, Al2O3, moisture and essential impurities; in the step (6), the calcium carbide content is CaC2 = 70-78wt%, CaO = 18-22wt%, and the rest is Al2O3, moisture and essential impurities.

4. The method for thermal recycling of medium carbon aluminum killed steel casting slag according to claim 1, characterized in that: In the three heat cycles, the input amount of lime decreases successively.

Images