Method for controlling content of element B of ppm-grade alloy structural steel

Abstract

The invention discloses a method for controlling the content of an element B of ppm-grade alloy structural steel. The technical problem that the element B is difficult to uniformly diffuse in molten steel is solved. The control method comprises the following steps: S1, adding 37-80kg of an aluminum deoxidizing agent before tapping after a blowing end point is reached in the later smelting period of molten steel, and deoxidizing after fully stirring; s2, preparing a steel ladle; s3, the molten steel is poured into a steel ladle, the type of the steel ladle is recorded, 10-30 kg of an aluminum deoxidizing agent is added in the steel tapping process, and the steel ladle is transferred to a refining station; s4, the molten steel is refined, and the content of the B element in other metallurgical auxiliary materials in the smelting process is controlled to be smaller than 0.01%; in the step S2, the steel ladle material contains borax fine powder, and in the process of transferring the molten steel through the steel ladle, the molten steel in the steel ladle and the borax fine powder are subjected to a replacement reaction, so that the B element is diffused into the molten steel. According to the method, the content of the element B in the alloy structural steel is controlled at the ppm level, the element B is evenly diffused and distributed in molten steel, and the problem of water gap blockage of the alloy structural steel can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and particularly relates to a method for controlling the content of element B in ppm-level alloy structural steel. Background Art

[0002] In alloy structural steel, it is necessary to add element B at the ppm level (0.001% - 0.005%) to improve the hardenability of the steel, while having little impact on other properties. Specifically, trace element B dissolves in the solid solution, making the crystal lattice larger and the strength higher. Element B in the grain boundary has the effect of preventing recrystallization diffusion, which can increase the thermal strength of the steel, and element B has little impact on the quenching crack sensitivity of the steel.

[0003] Element B in structural steel will reduce the impact value of the steel after normalizing, but good impact value can be obtained after quenching + low-temperature tempering. Low-carbon boron steel has good carburizing performance, the surface carbon concentration is not easily increased excessively, and it can be directly quenched after carburizing, and it also has little notch sensitivity. Therefore, high strength and fatigue strength performance can be obtained. However, when the content of element B in the steel exceeds a certain limit (such as 0.007%), it will cause adverse effects such as increased brittleness of the steel. Therefore, when adding element B to alloy steel, its content needs to be strictly controlled.

[0004] In the related art, the method for adding element B in alloy structural steel is to add ferrosilicon boron. Since element B in ferrosilicon boron has strong oxidability, it is difficult to diffuse evenly and the recovery rate is only about 38.16%. The remaining element B will enter the LF refining slag, changing the slag system properties and affecting the composition of alloy structural steel. Moreover, due to the addition of alloying elements in alloy structural steel, it is easy to cause the problem of nozzle blockage, which needs to be improved. Summary of the Invention

[0005] In order to solve all or part of the above problems, the purpose of the present invention is to provide a method for controlling the content of element B in ppm-level alloy structural steel, so that the content of element B in alloy structural steel is controlled at the ppm level, ferrosilicon boron is not required, the properties of the refining slag are not changed, and element B diffuses and distributes evenly in the molten steel, while also improving the problem of nozzle blockage in alloy structural steel.

[0006] The present invention provides a method for controlling the content of element B in ppm-level alloy structural steel, including the following steps:

[0007] S1, after the molten steel reaches the blowing end in the later stage of electric furnace or converter smelting, 37 - 80 kg of aluminum deoxidizer is added before tapping, and after sufficient stirring, deoxidation is carried out;

[0008] S2, prepare a ladle for transporting molten steel;

[0009] S3. Pour the molten steel into the ladle, record the ladle type, add 10 - 30 kg of aluminum deoxidizer during tapping, and transfer it to the refining station;

[0010] S4. Refine the molten steel and control the content of element B in other metallurgical auxiliaries during the smelting process to be less than 0.01%;

[0011] In S2: The material of the ladle contains borax fine powder. During the process of transferring the molten steel by the ladle, a displacement reaction occurs between the molten steel and the borax fine powder, so that element B diffuses into the molten steel to achieve the addition of element B in the molten steel.

[0012] Optionally, in S2:

[0013] If the ladle is a recycled ladle, the molten steel can be directly transferred;

[0014] If the ladle is an idle ladle, place the ladle under the ladle dryer for baking, and keep the baking temperature at 1000 - 1400 °C. When the ladle is in use, increase the baking intensity of the ladle dryer to raise the ladle temperature to 1520 - 1580 °C and then transfer the molten steel.

[0015] Optionally, the ladle dryer uses coke oven or blast furnace gas as the heating gas, and the gas temperature is 1000 ± 100 °C.

[0016] Optionally, in S2:

[0017] The material composition of the ladle by mass percentage includes: 60 - 70% magnesite granules, 8 - 12% graphite, 20 - 32% magnesite fine powder, 2 - 5% thermosetting phenolic resin liquid, 0.1 - 0.5% aluminum powder, 0 - 0.7% borax fine powder, and the particle size of the magnesite granules is 1 - 5 mm, the particle size of the graphite is 0.044 - 3 mm, the particle size of the magnesite fine powder is 0 - 0.088 mm, the particle size of the aluminum powder is 0 - 0.074 mm, and the particle size of the borax fine powder is 0 - 0.074 mm.

[0018] Optionally, the MgO content of the ladle is 72 - 92%, the C content is 7 - 12%, the B content is 0 - 0.6%, and the apparent porosity of the ladle is 3 - 5%, the bulk density is 2.95 - 3.21 g / cm3, and the compressive strength is 30.0 - 85.2 MPa.

[0019] Optionally, in S2:

[0020] The rated capacity of the ladle is 70 - 90 tons, the number of uses is 5 - 25 times, the slag line of the ladle is 10 - 12 layers, the molten pool is 13 - 15 layers, and the content of element B in the slag line is 0.05 - 0.06%, and the content of element B in the molten pool is less than or equal to 0.01% to control the increase of element B content in the alloy structural steel molten steel by 1.00 - 4.11 ppm.

[0021] Optionally, in S1 and S3:

[0022] The material composition of the aluminum deoxidizer includes, by mass percentage: 95 - 98% aluminum powder, 0.5 - 1.0% sodium metaaluminate, 0.1 - 2% albite, 0.1 - 3% recycled soda-lime-silica glass, and the total nitrogen content of the aluminum deoxidizer is less than or equal to 0.0051%, the Al content is 94 - 99%, the Si content is less than or equal to 0.22%, the particle size is 20 - 30 mm, and the moisture content is less than or equal to 0.1%.

[0023] Optionally, in S1:

[0024] The rated capacity of the electric furnace is 75 - 95 tons, and the rated capacity of the converter is 75 - 95 tons.

[0025] Optionally, in S4:

[0026] Other metallurgical auxiliary materials include but are not limited to alloys, electric furnaces, converters, refractory materials for tundishes, continuous casters, ladle covering agents, tundish covering agents, mold powder, refining slag, lime, fluorite, and slag-making agents.

[0027] As can be seen from the above technical solutions, the method for controlling the content of element B in ppm-level alloy structural steel provided by the present invention has the following advantages:

[0028] This control method enables the content of element B in alloy structural steel to be controlled at the ppm level, does not require the use of ferrosilicon boron, does not change the properties of the refining slag, and allows for the uniform diffusion and distribution of element B in the steel. At the same time, it can also improve the problem of nozzle clogging in alloy structural steel.

[0029] Other features and advantages of the present invention will be described in the subsequent specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings are used to provide a further understanding of the technical solutions of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solutions of the present invention, and do not constitute a limitation to the technical solutions of the present invention.

[0031] Figure 1 It is a flowchart of the method for controlling the content of element B in ppm-level alloy structural steel in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the embodiments of the present invention will be described in detail below with reference to the drawings. It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined arbitrarily with each other.

[0033] As Figure 1The following figure shows the flowchart of the method for controlling the content of element B in ppm-level alloy structural steel in the embodiments of the present invention. To avoid repetition, the equipment, materials, etc. involved in the specific implementation manners are uniformly described as follows and will not be repeated in each embodiment:

[0034] The rated capacity of the electric furnace is 75 - 95 tons, and the rated capacity of the converter is 75 - 95 tons.

[0035] After the molten steel reaches the blowing end point in the later stage of smelting in the electric furnace or converter, 37 - 80 kg of aluminum deoxidizer is added before tapping. When the molten steel is poured into the ladle, 10 - 30 kg of aluminum deoxidizer is added during the tapping process.

[0036] The material composition of the aluminum deoxidizer includes, by mass percentage: 95 - 98% aluminum powder, 0.5 - 1.0% sodium metaaluminate, 0.1 - 2% albite, 0.1 - 3% recycled sodium calcium silicate glass, and the total nitrogen content of the aluminum deoxidizer is less than or equal to 0.0051%, the Al content is 94 - 99%, the Si content is less than or equal to 0.22%, the particle size is 20 - 30 mm, and the moisture content is less than or equal to 0.1%.

[0037] The ladle can be a turnover ladle or an idle ladle. If it is a turnover ladle, the molten steel can be directly transported. If it is an idle ladle, the ladle is placed under the ladle dryer for baking, and the baking temperature is maintained at 1000 - 1400 °C. When the ladle is in use, the baking intensity of the ladle dryer is increased to raise the ladle temperature to 1520 - 1580 °C before transporting the molten steel.

[0038] The rated capacity of the ladle is 70 - 90 tons, and the number of uses is 5 - 25 times. The slag line of the ladle is 10 - 12 layers, and the molten pool is 13 - 15 layers. The B element content in the slag line is 0.05 - 0.06%, and the B element content in the molten pool is less than or equal to 0.01% to control the increase of the B element content in the alloy structural steel water by 1.00 - 4.11 ppm.

[0039] The material composition of the ladle includes, by mass percentage: 60 - 70% magnesia particles, 8 - 12% graphite, 20 - 32% magnesia fine powder, 2 - 5% thermosetting phenolic resin liquid, 0.1 - 0.5% aluminum powder, 0 - 0.7% borax fine powder. The particle size of the magnesia particles is 1 - 5 mm, the particle size of the graphite is 0.044 - 3 mm, the particle size of the magnesia fine powder is 0 - 0.088 mm, the particle size of the aluminum powder is 0 - 0.074 mm, and the particle size of the borax fine powder is 0 - 0.074 mm. At the same time, the MgO content of the ladle is 72 - 92%, the C content is 7 - 12%, the B content is 0 - 0.6%, and the apparent porosity of the ladle is 3 - 5%, the bulk density is 2.95 - 3.21 g / cm3, and the compressive strength is 30.0 - 85.2 MPa.

[0040] The ladle dryer uses coke oven gas or blast furnace gas as the heating gas, and the gas temperature is 1000 ± 100 °C.

[0041] Other metallurgical auxiliary materials include but are not limited to alloys, electric furnaces, converters, refractory materials for tundishes, continuous casters, ladle covering agents, tundish covering agents, mold powder, refining slag, lime, fluorite, and slag melting agents.

[0042] Example 1

[0043] This example discloses a method for controlling the content of element B in ppm-level alloy structural steel, including the following steps:

[0044] S1. After the molten steel reaches the blowing end in the later stage of smelting in an electric furnace or converter, 58 kg of aluminum deoxidizer is added before tapping, and after sufficient stirring, deoxidation is carried out.

[0045] S2. A turnover ladle is selected to transfer the molten steel.

[0046] S3. The molten steel is poured into the ladle, and the ladle is recorded as a turnover ladle. 15 kg of aluminum deoxidizer is added during tapping, and it is transferred to the refining station.

[0047] S4. The molten steel is refined, and the content of element B in other metallurgical auxiliary materials during the smelting process is controlled to be less than 0.01%.

[0048] In this example, the ladle is used 12 times, the slag line of the ladle is 10 layers, the molten pool is 15 layers, the content of element B in the slag line is 0.06%, and the content of element B in the molten pool is less than or equal to 0.01%. The detected content of element B in the alloy structural steel prepared in this example increases from 3 ppm to 4 ppm, that is, the content of element B increases by 1 ppm.

[0049] Example 2

[0050] This example discloses a method for controlling the content of element B in ppm-level alloy structural steel, including the following steps:

[0051] S1. After the molten steel reaches the blowing end in the later stage of smelting in an electric furnace or converter, 51 kg of aluminum deoxidizer is added before tapping, and after sufficient stirring, deoxidation is carried out.

[0052] S2. An idle ladle is selected to transfer the molten steel. The ladle is placed under the ladle dryer for baking, and the baking temperature is maintained at 1000 - 1400 °C. When the ladle is used, the baking intensity of the ladle dryer is increased to raise the ladle temperature to 1540 °C, and then the molten steel is transferred through the ladle.

[0053] S3. The molten steel is poured into the ladle, and the ladle is recorded as an idle ladle. 20 kg of aluminum deoxidizer is added during tapping, and it is transferred to the refining station.

[0054] S4, refining the molten steel, and controlling the content of B element in other metallurgical auxiliary materials in the smelting process to be less than 0.01%.

[0055] In this embodiment, the ladle is used 6 times, the slag line of the ladle is 12 layers, the molten pool is 13 layers, the B element content in the slag line is 0.06%, and the B element content in the molten pool is less than or equal to 0.01%. The B element content of the alloy structural steel prepared in this embodiment is increased from 3ppm to 5ppm, that is, the B element content increases by 2ppm.

[0056] Example 3

[0057] This embodiment discloses a method for controlling the B element content in ppm-level alloy structural steel, comprising the following steps:

[0058] S1, after the molten steel reaches the blowing end point in the later stage of smelting in an electric furnace or a converter, 62kg of aluminum deoxidizer is added before steelmaking, and deoxidation is performed after sufficient stirring.

[0059] S2, select an idle ladle to transfer molten steel, place the ladle under the ladle drying device for baking, and maintain the baking temperature at 1000-1400℃. When the ladle is in use, increase the baking intensity of the ladle drying device to raise the ladle temperature to 1540℃, and then transfer the molten steel through the ladle.

[0060] S3, pour the molten steel into the ladle, record the ladle as an idle ladle, add 17kg of aluminum deoxidizer during the steel tapping process, and transfer it to the refining station.

[0061] S4, refining the molten steel, and controlling the content of B element in other metallurgical auxiliary materials in the smelting process to be less than 0.01%.

[0062] In this embodiment, the ladle is used 21 times, the slag line of the ladle is 12 layers, the molten pool is 13 layers, the B element content in the slag line is 0.05%, and the B element content in the molten pool is less than or equal to 0.04%. The B element content of the alloy structural steel prepared in this embodiment is increased from 3ppm to 6ppm, that is, the B element content increases by 3ppm.

[0063] Example 4

[0064] This embodiment discloses a method for controlling the B element content in ppm-level alloy structural steel, comprising the following steps:

[0065] S1, after the molten steel reaches the blowing end point in the later stage of smelting in an electric furnace or a converter, 79kg of aluminum deoxidizer is added before tapping, and deoxidation is performed after sufficient stirring.

[0066] S2, select an idle ladle to transfer molten steel, place the ladle under the ladle drying device for baking, and maintain the baking temperature at 1000-1400℃. When the ladle is in use, increase the baking intensity of the ladle drying device to raise the ladle temperature to 1540℃, and then transfer the molten steel through the ladle.

[0067] S3, pour the molten steel into the ladle, record the ladle as an idle ladle, add 26kg of aluminum deoxidizer during the steel tapping process, and transfer it to the refining station.

[0068] S4, refining the molten steel, and controlling the content of B element in other metallurgical auxiliary materials in the smelting process to be less than 0.01%.

[0069] In this embodiment, the ladle is used 19 times, the slag line of the ladle is 12 layers, the molten pool is 13 layers, the B content in the slag line is 0.05%, and the B content in the molten pool is 0.06%. The B content of the alloy structural steel prepared in this embodiment is increased from 3ppm to 7ppm, that is, the B content increases by 4ppm.

[0070] As can be seen from the above, by adopting this control method, aluminum deoxidizer is added to the molten steel during the steel tapping process, and the aluminum deoxidizer can fully contact with the molten steel, which is conducive to the diffusion of the aluminum deoxidizer and the reduction of the O element content in the molten steel. The main component of the borax fine powder in the ladle is B2O3, with a melting point of about 450°C. During the drying period, it can improve the medium-temperature strength of the ladle and reduce thermal shock damage.

[0071] During the use of the ladle, the aluminum powder in the ladle is oxidized to form Al2O3, which protects C from oxidation. At the same time, B2O3 reacts with Al2O3 to form 9Al2O3·2B2O3 (melting point 1965℃), so that Al2O3 is consumed in large quantities, and a large amount of liquid B2O3 remains. At this time, since the ladle has been eroded by slag, the C content gradually decreases along the working surface of the ladle, and the ability to resist slag erosion decreases. Driven by the surface energy difference and concentration difference of the ladle, the liquid B2O3 moves toward the working surface of the ladle and undergoes a replacement reaction with the Al element in the aluminum deoxidizer, so that the B element is integrated into the molten steel. Since the B element in the molten steel is a metal structure, it is incompatible with the ionic structure of the ladle, so it will not flow back into the ladle.

[0072] Due to the large contact area between the ladle and the molten steel, the diffusion speed of element B is faster and more uniform than that of adding ferroboron, and the strong stirring in the subsequent refining will further promote the uniform distribution of element B in the molten steel. In addition, the Al2O3 formed by the reaction of liquid B2O3 and aluminum deoxidizer is a high melting point substance, which will cover the graphite surface in the ladle, preventing the problem of graphite oxidation and carbon addition to alloy structural steel.

[0073] This control method does not use ferroboron, and the properties of the refined slag system will not change due to the change of B. The slag system can be stabilized, and the inclusions and components of the alloy structural steel will be more stable. The aluminum deoxidizer contains a certain amount of Na2O, which will react with Al2O3 to form Na2O·11Al2O3 during the deoxidation process. When it enters the refined slag, it will convert the aluminum oxide hexahedron in the slag into aluminum oxide tetrahedron, stabilizing the refined slag while preventing B from entering the refined slag. Due to the reduction of aluminum oxide hexahedron in the slag, the probability of aluminum oxide hexahedron sticking to the inner wall of the invasive nozzle during the continuous casting process is reduced, and the nozzle blockage phenomenon of smelting alloy structural steel is significantly improved.

[0074] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present invention should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0075] In addition, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the present invention, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0076] 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 them; 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 by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A method for controlling the content of element B in ppm-level alloy structural steel, characterized in that, It includes the following steps: S1. After the molten steel reaches the blowing end in the later stage of smelting in an electric furnace or a converter, 37 - 80 kg of aluminum deoxidizer is added before tapping. After sufficient stirring, deoxidation is carried out. S2. Prepare a ladle for transporting molten steel. S3. Pour the molten steel into the ladle, record the ladle type, add 10 - 30 kg of aluminum deoxidizer during tapping, and transport it to the refining station. S4. Refine the molten steel, and control the content of element B in other metallurgical auxiliaries during the smelting process to be less than 0.01%. In S2: The ladle material contains borax fine powder. During the process of transporting molten steel by the ladle, a displacement reaction occurs between the molten steel and the borax fine powder, so that element B diffuses into the molten steel to achieve the addition of element B in the molten steel.

2. The control method according to claim 1, characterized in that In S2: If the ladle is a recycled ladle, the molten steel can be directly transported. If the ladle is an idle ladle, place the ladle under a ladle dryer for baking, and keep the baking temperature at 1000 - 1400 °C. When the ladle is used, increase the baking intensity of the ladle dryer to raise the ladle temperature to 1520 - 1580 °C and then transport the molten steel.

3. The control method according to claim 2, wherein The ladle dryer uses coke oven gas or blast furnace gas as the heating gas, and the gas temperature is 1000 ± 100 °C.

4. The control method according to claim 1, characterized in that, In S2: The material composition of the ladle includes, by mass percentage: 60 - 70% magnesite granules, 8 - 12% graphite, 20 - 32% magnesite fine powder, 2 - 5% thermosetting phenolic resin liquid, 0.1 - 0.5% aluminum powder, 0 - 0.7% borax fine powder, and the particle size of the magnesite granules is 1 - 5 mm, the particle size of the graphite is 0.044 - 3 mm, the particle size of the magnesite fine powder is 0 - 0.088 mm, the particle size of the aluminum powder is 0 - 0.074 mm, and the particle size of the borax fine powder is 0 - 0.074 mm.

5. The control method according to claim 4, characterized in that The MgO content of the ladle is 72 - 92%, the C content is 7 - 12%, the B content is 0 - 0.6%, and the apparent porosity of the ladle is 3 - 5%, and the bulk density is 2.95 - 3.21 g / cm 3 , and the compressive strength is 30.0 - 85.2 MPa.

6. The control method according to claim 1, characterized in that, In S2: The rated capacity of the ladle is 70 - 90 tons, the number of uses is 5 - 25 times, the slag line of the ladle is 10 - 12 layers, the molten pool is 13 - 15 layers, and the content of element B in the slag line is 0.05 - 0.06%, and the content of element B in the molten pool is less than or equal to 0.01% to control the increase of element B content in the alloy structural steel molten steel by 1.00 - 4.11 ppm.

7. The control method according to claim 1, characterized in that In S1 and S3: The material composition of the aluminum deoxidizer includes, by mass percentage: 95 - 98% aluminum powder, 0.5 - 1.0% sodium metaaluminate, 0.1 - 2% albite, 0.1 - 3% recycled sodium calcium silicate glass, and the total nitrogen content of the aluminum deoxidizer is less than or equal to 0.0051%, the Al content is 94 - 99%, the Si content is less than or equal to 0.22%, the particle size is 20 - 30 mm, and the moisture content is less than or equal to 0.1%.

8. The control method according to claim 1, characterized in that, In S1: The rated capacity of the electric furnace is 75 - 95 tons, and the rated capacity of the converter is 75 - 95 tons.

9. The control method according to claim 1, wherein In S4: Other metallurgical auxiliaries include but are not limited to alloys, electric furnaces, converters, refractory materials for tundishes, continuous casting machines, ladle covering agents, tundish covering agents, mold fluxes, refining slags, lime, fluorite, slag - melting agents.

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