A method for decarburization of a high carbon steel protection slag

Abstract

The application discloses a carbon burning method of high-carbon steel protection slag and belongs to the technical field of high-carbon steel. The method realizes efficient decarburization of the high-carbon steel protection slag by adopting a three-stage heating carbon burning method. The high-carbon steel protection slag is layered and placed in a stainless steel container to ensure sufficient contact between oxygen and the protection slag, and then enters a muffle furnace to be oxidized and decarburized in three heating stages. The heating rate, target temperature and holding time in the heating carbon burning process are reasonably set, the high-iron protection slag is uniformly subjected to the heating oxidation reaction, the total carbon burning time is controlled, and the sintering of low-melting-point substances caused by partial melting is avoided. The protection slag is intermittently stirred to prevent caking, the decarburization efficiency is improved, the carbon residual amount of the high-carbon protection slag is reduced after the three-stage heating carbon burning, and the result accuracy is improved during subsequent performance detection.

Description

Technical Field

[0001] This invention belongs to the field of high carbon steel technology, and specifically relates to a method for carbonizing high carbon steel protective slag. Background Technology

[0002] Before testing properties such as viscosity and melting temperature, continuous casting mold flux needs to be decarburized. Incomplete decarburization can cause bubbling during melting point measurement, affecting the accuracy of the measurement. In viscosity measurement, carbon rises to the surface of the molten slag, affecting the viscosity reading. Therefore, maximum decarburization is essential to ensure the accuracy of continuous casting mold flux performance testing.

[0003] The principle of decarbonization is to oxidize the carbonaceous materials in the protective slag into CO or CO2 at high temperatures. The muffle furnace is an important piece of equipment for removing carbonaceous materials from continuous casting protective slag. Its specific working process is as follows: First, the continuous casting protective slag (granular) is placed in a crucible. When the sample is heated to a certain temperature and stirring is required, the sample is taken out of the muffle furnace and stirred manually with an iron rod. Then, the crucible is put back into the muffle furnace for decarbonization. While heating, air (oxygen) is introduced into the furnace. When the continuous casting protective slag sample in the crucible is heated to the carbon reaction temperature, the sufficient oxygen in the furnace reacts with the continuous casting protective slag sample in the crucible to carry out a carbon oxidation reaction, thereby removing the carbon from the continuous casting protective slag.

[0004] High-carbon steel protective slag has a low melting point, low viscosity, and low basicity. It contains many low-melting-point substances. One crucial condition for decarburization is high temperature, typically 600–1000℃. Too low a temperature results in a slow reaction rate and insufficient decarburization. Too rapid a temperature increase causes the low-melting-point substances to partially melt first, easily leading to sintering. Too high a temperature, especially for high-carbon steel protective slag, easily causes the formation of 20–50 mm slag clumps during the carbonization process. The carbon content within these clumps cannot be burned off, leading to slag agglomeration and making further carbon removal from the slag clumps difficult. Summary of the Invention

[0005] The purpose of this invention is to provide a carbonization method for high-carbon steel protective slag to solve the problem of insufficient carbon removal caused by agglomeration in the decarbonization process of high-carbon steel protective slag.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] This invention provides a method for carbonizing high-carbon steel protective slag, employing a three-stage carbonization process. During this process, iron rods are used to agitate the protective slag to prevent clumping and to ensure sufficient contact between the raw slag and air, thereby guaranteeing thorough carbon removal. The three-stage heating carbonization method includes the following steps:

[0008] (1) Place the high carbon steel protective slag in a stainless steel container and spread it evenly in two layers. Stainless steel is used for carbon burning because it conducts heat quickly, which facilitates the rapid carbon burning of the protective slag. Place the stainless steel container into the muffle furnace.

[0009] (2) First heating stage: Set the muffle furnace heating rate to 20-30℃ / min to heat up to 200-300℃, and set the holding time to 5-20min.

[0010] (3) Second heating stage: Set the heating rate of the muffle furnace to 20℃ / min, heat to 400-500℃, and set the holding time to 10-25min;

[0011] (4) Third heating stage: Set the heating rate of the muffle furnace to 10℃ / min, heat to 600-700℃, and set the holding time to 20-30min to obtain decarbonized protective slag.

[0012] The heating rate varies in each stage, and each stage has a heat preservation section to prevent the heating rate from being too fast and the carbon burning rate from being too fast, which would cause the protective slag to clump together, resulting in incomplete carbon burning and clumping, thus affecting subsequent measurements.

[0013] Furthermore, the high-carbon steel protective slag has a melting point of 850-900℃, a basicity of 0.85-0.95, a viscosity of 0.08-0.15 Pa·s, and a total carbon content of 6%-8% by mass.

[0014] Furthermore, the thickness of each layer of the high-carbon steel protective slag in the stainless steel vessel is ≤20mm.

[0015] Furthermore, the distance between the upper and lower layers is 5-10cm.

[0016] Furthermore, the protective slag is turned over with an iron rod every 10 minutes.

[0017] Furthermore, during the insulation section, iron rods are used to turn over the protective slag.

[0018] Furthermore, the total carbon burning time of the three-stage heating carbon burning method is the sum of the times of each heating stage. The total carbon burning time of the carbon burning method is ≤2h. If the time is too long, over-burning and sintering are likely to occur, and the protective slag will be severely agglomerated. If the time is too short, carbon removal will be incomplete.

[0019] Furthermore, the diameter of the agglomerated slag lumps after the high-carbon steel protective slag undergoes carbonization treatment is ≤10mm.

[0020] The beneficial effects of this invention are:

[0021] By adopting a three-stage heating and carbon removal method, different heating rates, holding times, and target temperatures are set for each stage. This effectively avoids the agglomeration of protective slag caused by excessively rapid heating and excessively high temperatures, promotes the full oxidation of residual carbon in high-carbon steel protective slag, achieves efficient carbon removal from high-carbon steel protective slag, and ensures the accuracy of performance testing of high-carbon steel protective slag. Attached Figure Description

[0022] The invention will now be further described with reference to the accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the slag particles after the high-carbon steel protective slag is carbonized in Embodiment 3 of the present invention;

[0024] Figure 2 This is a schematic diagram of the slag particles after carbonization of the high-carbon steel protective slag in Comparative Example 1 of the present invention.

[0025] Figure 3 This is a schematic diagram of the slag particles after the high-carbon steel protective slag of Comparative Example 2 of the present invention has been carbonized. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] Place 250g of high-carbon steel protective slag with a carbon content of 6% in two layers in a stainless steel container, spread them evenly, with a 6cm gap between the two layers and a thickness of 20mm for each layer of protective slag. Then place the stainless steel container into a muffle furnace.

[0029] The muffle furnace was heated at a rate of 20℃ / min to 300℃, held for 20 minutes, then heated at a rate of 20℃ / min to 500℃, held for 25 minutes, and finally heated at a rate of 10℃ / min to 600℃, held for 25 minutes. During the holding period, the protective slag was turned over with an iron rod every 10 minutes to obtain the decarbonized protective slag.

[0030] The total carbon burning time was 104 minutes. After carbon burning, the carbon-removing protective slag particles were grayish-white, the agglomerated slag particles accounted for 7%, the diameter of the agglomerated slag particles was ≤10mm, and the carbon residue of the high-carbon steel protective slag was 0.7%.

[0031] Example 2

[0032] Place 250g of high-carbon steel protective slag with a carbon content of 6% in two layers in a stainless steel container, spread them evenly, with a 6cm gap between the two layers and a thickness of 20mm for each layer of protective slag. Then place the stainless steel container into a muffle furnace.

[0033] The muffle furnace was heated at a rate of 25°C / min to 250°C and held for 20 minutes. Then, the temperature was increased to 450°C at a rate of 20°C / min and held for 25 minutes. Finally, the temperature was increased to 650°C at a rate of 10°C / min and held for 30 minutes. During the holding period, the protective slag was turned over with an iron rod every 10 minutes to obtain the decarbonized protective slag.

[0034] The total carbon burning time was 114 minutes. After carbon burning, the carbon-removing protective slag particles were grayish-white, the agglomerated slag particles accounted for 5% of the total, the diameter of the agglomerated slag particles was ≤10mm, and the carbon residue of the high-carbon steel protective slag was 0.3%.

[0035] Example 3

[0036] Place 250g of high-carbon steel protective slag with a carbon content of 6% in two layers in a stainless steel container, spread them evenly, with a 6cm gap between the two layers and a thickness of 20mm for each layer of protective slag. Then place the stainless steel container into a muffle furnace.

[0037] The muffle furnace was heated at a rate of 20℃ / min to 200℃, held for 15 minutes, then heated at a rate of 20℃ / min to 400℃, held for 20 minutes, and finally heated at a rate of 10℃ / min to 700℃, held for 30 minutes. During the holding period, the protective slag was turned over with an iron rod every 10 minutes to obtain the decarbonized protective slag.

[0038] The total carbonization time was 114 minutes. After carbonization, the decarbonized protective slag particles of the high-carbon steel protective slag were grayish-white, with a 3% agglomerated slag particles and a diameter ≤10mm. The carbon residue in the high-carbon steel protective slag was 0.1%. A schematic diagram of the slag particles after carbonization of the high-carbon steel protective slag is shown below. Figure 1 .

[0039] Comparative Example 1

[0040] Compared to Example 3, no different heating ranges were set, and a one-step heating and charcoal burning method was adopted.

[0041] Place 250g of high-carbon steel protective slag with a carbon content of 6% in two layers in a stainless steel container, spread them evenly, with a 6cm gap between the two layers and a thickness of 20mm for each layer of protective slag. Then place the stainless steel container into a muffle furnace.

[0042] The muffle furnace was set to a heating rate of 20℃ / min, heated to 700℃, and held for 80 minutes. During the holding period, the protective slag was turned over with an iron rod every 10 minutes to obtain decarbonized protective slag.

[0043] The total carbonization time was 114 minutes. After carbonization, the decarbonized protective slag clumps of the high-carbon steel protective slag were blackish-gray, with a clump diameter ≥25mm and a clump weight of 50%, indicating severe agglomeration. The carbon residue in the high-carbon steel protective slag was 3.1%. A schematic diagram of the slag particles after carbonization of the high-carbon steel protective slag is shown below. Figure 2 .

[0044] Comparative Example 2

[0045] Compared to Example 3, the three-stage heating was not set; instead, a two-stage heating process was used for charcoal burning.

[0046] Place 250g of high-carbon steel protective slag with a carbon content of 6% in two layers in a stainless steel container, spread them evenly, with a 6cm gap between the two layers and a thickness of 20mm for each layer of protective slag. Then place the stainless steel container into a muffle furnace.

[0047] The muffle furnace was heated at a rate of 20℃ / min to 350℃ and held for 40 minutes. The heating rate was then increased to 20℃ / min, and the temperature was raised to 700℃ and held for another 40 minutes. During the holding period, the protective slag was turned over with an iron rod every 10 minutes to obtain decarburized protective slag. A schematic diagram of the slag particles after carbonization of the high-carbon steel protective slag is shown below. Figure 3 .

[0048] The total carbon burning time was 114 minutes. After carbon burning, the carbon-removing protective slag clumps were blackish-gray, with a diameter of ≥15mm and a clump weight of 22%, indicating severe agglomeration. The carbon residue in the high-carbon steel protective slag was 2.0%.

[0049] As can be seen from Examples 1-3, with the same three-stage heating and charcoal firing method, extending the charcoal firing time can increase the carbon removal rate. When the total charcoal firing time is the same, different temperature settings in each zone will also affect the carbon removal rate. The slow heating in the first stage of charcoal firing is conducive to uniform heating of the protective slag, preventing agglomeration, and increasing the carbon removal rate. Comparing Example 3, Comparative Example 1 and Comparative Example 2 used one-step heating and charcoal firing and two-stage heating and charcoal firing, respectively. With the same total charcoal firing time, agglomeration was obvious after charcoal firing, and the carbon removal rate was significantly reduced.

[0050] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for carbonizing high-carbon steel protective slag, characterized in that, A three-stage heating and carbonization method is adopted, during which the protective slag is turned over with an iron rod. The three-stage heating and carbonization method includes the following steps: (1) Place the high-carbon steel protective slag in a stainless steel container and spread it evenly in two layers. Place the stainless steel container into the muffle furnace. (2) First heating stage: Set the muffle furnace heating rate to 20-30℃ / min to heat up to 200-300℃, and set the holding time to 5-20min. (3) Second heating stage: Set the heating rate of the muffle furnace to 20℃ / min, heat to 400-500℃, and set the holding time to 10-25min; (4) Third heating stage: Set the heating rate of the muffle furnace to 10℃ / min, heat to 600-700℃, and set the holding time to 20-30min to obtain decarbonized protective slag.

2. The method for carbonizing high-carbon steel protective slag according to claim 1, characterized in that, The high-carbon steel protective slag has a melting point of 850-900℃, a basicity of 0.85-0.95, a viscosity of 0.08-0.15 Pa·s, and a total carbon content of 6%-8% by mass.

3. The method for carbonizing high-carbon steel protective slag according to claim 1, characterized in that, The thickness of each layer of the high-carbon steel protective slag in the stainless steel vessel is ≤20mm.

4. The method for carbonizing high-carbon steel protective slag according to claim 1, characterized in that, The distance between the upper and lower layers is 5-10cm.

5. The method for carbonizing high-carbon steel protective slag according to claim 1, characterized in that, The protective slag should be turned over with an iron rod every 10 minutes.

6. The method for carbonizing high-carbon steel protective slag according to claim 1, characterized in that, Use an iron rod to turn over the protective slag during the insulation section.

7. The method for carbonizing high-carbon steel protective slag according to claim 1, characterized in that, The total charcoal burning time of the three-stage heating and charcoal burning method is the sum of the times of each heating stage, and the total charcoal burning time of the method is ≤2h.

8. The method for carbonizing high-carbon steel protective slag according to claim 1, characterized in that, The diameter of the clumps formed after the high-carbon steel protective slag is ≤10mm after carbonization treatment.

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