RH refining device and deep decarburization method

Abstract

The invention relates to the field of metallurgy, and discloses an RH refining device and a deep decarburization method. The RH refining device comprises a vacuum chamber, the side wall of the lower portion of the vacuum chamber forms an inverted circular truncated cone structure, and the upper portion of the vacuum chamber is used for being connected with vacuumizing equipment; the upper ends of the ascending pipe and the descending pipe are communicated with the vacuum chamber, and the lower ends of the ascending pipe and the descending pipe are inserted into molten steel in a steel ladle; the first air blowing pipe is communicated with the ascending pipe; the second air blowing pipe is communicated with the area, close to the ascending pipe, of the inverted circular truncated cone structure in the circumferential direction. According to the method, the RH decarburization reaction rate after the carbon content in the molten steel is smaller than 20 ppm can be increased.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to an RH refining device and a deep decarburization method. Background Art

[0002] RH refining is a method of refining molten steel outside the furnace jointly designed and developed by Ruhrstahl and Hereaeus. It can dehydrogenate, denitrify, deoxidize, decarbonize, desulfurize, make the composition of molten steel uniform, and improve the cleanliness of molten steel. Its advantages are: easy operation, good refining effect, short processing time and large production capacity. Therefore, RH refining is an indispensable process for clean steel smelting. However, when the carbon content in molten steel is less than 20ppm, the decarbonization rate of RH refining is very slow. Therefore, improving the deep decarbonization ability of RH is of great significance to the development of variety steel. Summary of the invention

[0003] The main purpose of the present invention is to provide an RH refining device and a deep decarburization method to solve the problem that the decarburization rate of RH refining is very slow when the carbon content in molten steel is less than 20ppm.

[0004] According to one aspect of the present invention, a RH refining device is provided, comprising: A vacuum chamber, wherein the lower side wall of the vacuum chamber forms an inverted truncated cone structure, and the upper part of the vacuum chamber is used to connect a vacuum pumping device; The upper ends of the riser and the downcomer are connected to the vacuum chamber and the lower ends are used to be inserted into the molten steel in the ladle; A first air blowing pipe, the first air blowing pipe is connected to the rising pipe; The second air blowing pipe is connected to a region of the inverted truncated cone structure close to the riser in the circumferential direction.

[0005] According to one embodiment of the present invention, the angle between the generatrix of the inverted truncated cone structure and the horizontal plane is 45-60°.

[0006] According to one embodiment of the present invention, the height of the inverted truncated cone structure is 500-700 mm.

[0007] According to one embodiment of the present invention, the RH refining device comprises a plurality of second air blowing pipes, and the plurality of second air blowing pipes are evenly arranged around the axis of the riser.

[0008] According to one embodiment of the present invention, the exhaust end of the second air blowing pipe is inclined upward by 25-35 degrees relative to the intake end.

[0009] According to another aspect of the present invention, a deep decarburization method is proposed, comprising: performing RH refining on molten steel using the RH refining device as described above; wherein, during the entire RH refining process, lifting gas is blown in via a first blowing pipe, and the lifting gas flow rate in the early stage of RH refining is smaller than the lifting gas flow rate in the middle and late stages of RH refining; supplementary blowing gas is blown in via the second blowing pipe only in the late stage of RH refining.

[0010] According to one embodiment of the present invention, the early stage of RH refining is within 5 minutes after the start of vacuuming, the middle stage of RH refining is during 5 to 10 minutes after the start of vacuuming, and the late stage of RH refining is during 10 to 15 minutes after the start of vacuuming.

[0011] According to one embodiment of the present invention, the lifting gas flow rate in the early stage of RH refining is 9.5~11NL / min / ton of steel, and the lifting gas flow rate in the middle and late stages of RH refining is 12.5~14NL / min / ton of steel; the total flow rate of the supplementary blowing gas is 600~1000NL / min.

[0012] According to one embodiment of the present invention, the insertion depth of the riser and the downcomer in the ladle is 500-650 mm.

[0013] According to one embodiment of the present invention, the temperature of the RH inlet steel is 1630-1650°C, the carbon content is 0.025-0.05wt%, and the oxygen content is 0.04-0.07wt%; the vacuum degree drops below 300Pa within 5 minutes after the vacuum pumping starts; oxygen blowing decarburization is performed when the ratio of oxygen content to carbon content of the RH inlet steel is less than 1.4, the oxygen blowing time does not exceed 5 minutes, and the total oxygen consumption does not exceed 0.6m 3 / ton of steel.

[0014] In the technical solution of the present invention, by designing the lower side wall of the vacuum chamber into an inverted truncated cone structure, the surface area and depth of the molten steel in the vacuum chamber can be increased at the same time, and the reaction interface can be expanded. Moreover, by connecting the second blowing pipe to the area of ​​the inverted truncated cone structure circumferentially close to the riser, the molten steel entering the vacuum chamber through the riser can be supplemented with air, thereby increasing the surface decarburization rate of the molten steel and the bubble decarburization rate, which is beneficial to improving the RH decarburization reaction rate when the carbon content in the molten steel is less than 20 ppm. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A schematic diagram showing an RH refining apparatus according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0017] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0018] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. The subsequent embodiments will not explain this one by one.

[0019] As mentioned in the background technology above, the inventors of the present application realize that when the carbon content in molten steel is less than 20 ppm, the decarburization rate of RH refining is very slow. To solve this technical problem, the present application proposes one or more embodiments to be described below.

[0020] Figure 1 A schematic diagram of an RH refining device 100 according to an embodiment of the present invention is shown, referring to Figure 1 The RH refining device 100 includes: a vacuum chamber 10, the lower side wall of the vacuum chamber 10 forms an inverted truncated cone structure 12, and the upper part of the vacuum chamber 10 is used to connect a vacuum pumping device; an ascending pipe 20 and a descending pipe 30, the upper ends of the ascending pipe 20 and the descending pipe 30 are connected to the vacuum chamber 10 and the lower ends are used to be inserted into the molten steel in the ladle; a first blowing pipe 40, the first blowing pipe 40 is connected to the ascending pipe 20; and a second blowing pipe 50, the second blowing pipe 50 is connected to the region of the inverted truncated cone structure 12 close to the ascending pipe 20 in the circumferential direction. The ascending pipe 20 and the descending pipe 30 can be connected to the bottom wall of the vacuum chamber 10. When in use, the molten steel in the ladle rises into the vacuum chamber 10 via the ascending pipe 20, and the molten steel in the vacuum chamber 10 descends through the descending pipe 30 to leave the vacuum chamber 10 and enter the ladle. The first blowing pipe 40 and the second blowing pipe 50 can be used to blow in argon gas.

[0021] During the RH refining process, the immersion pipe (rising pipe 20 and downcomer 30) is inserted into the molten steel in the ladle to be processed. When the vacuum chamber 10 is evacuated to a vacuum state, the molten steel is forced to flow into the vacuum chamber 10 through the immersion pipe due to the atmospheric pressure on its surface. At the same time, gas (such as argon) is continuously blown into the rising pipe 20 through the first blowing pipe 40, so that the rising pipe 20 generates a higher static pressure difference relative to the downcomer 30 without blowing gas, so that the molten steel enters and passes through the lower part of the vacuum chamber 10 from the rising pipe 20, and then flows back to the ladle through the downcomer 30, and this cycle is repeated continuously. In the process of the molten steel circulating through the vacuum chamber 10 in a vacuum state, gases such as argon, hydrogen, and carbon monoxide in the molten steel are extracted, so that the molten steel is purified. In addition, the molten steel entering the vacuum chamber 10 can also undergo a series of smelting reactions, such as carbon oxidation reactions.

[0022] In the embodiment of the present invention, by designing the lower side wall of the vacuum chamber 10 into an inverted truncated cone structure 12, compared with the conventional cylindrical structure, the surface area and depth of the molten steel in the vacuum chamber 10 can be increased at the same time, the reaction interface can be expanded, and the RH decarburization reaction rate can be increased when the carbon content in the molten steel is less than 20ppm; and by connecting the second blowing pipe 50 to the area of ​​the inverted truncated cone structure 12 close to the riser 20 in the circumferential direction, the molten steel entering the vacuum chamber 10 through the riser 20 can be supplemented with air blowing, the surface decarburization rate of the molten steel and the bubble decarburization rate can be increased, thereby further increasing the decarburization reaction rate below 20ppm. Through the technical solution of the present invention, the carbon content of the molten steel after VCD (vacuum carbon deoxidation) can be less than or equal to 13ppm, and the decarburization time can be shortened to about 15min.

[0023] In some embodiments, the lower base diameter of the inverted truncated cone structure 12 is 200 mm smaller than the diameter of the conventional cylindrical lower trough, and the upper base diameter of the inverted truncated cone structure 12 is 800-1000 mm larger than the diameter of the conventional cylindrical lower trough.

[0024] In some embodiments, the angle θ between the generatrix of the inverted truncated cone structure 12 and the horizontal plane is 45-60°. If the angle is too small, the volume of the vacuum chamber increases too much, affecting the rate of vacuum degree decrease; if the angle is too large, the surface area of ​​the molten steel does not change significantly. This preferred angle range can achieve a better effect of increasing the decarburization rate.

[0025] In some embodiments, the height of the inverted truncated cone structure 12 is 500-700 mm.

[0026] In some embodiments, there is a gap between the lower bottom of the inverted truncated cone structure 12 and the pipe openings of the ascending tube 20 and the descending tube 30 , and the gap may be the straight bottom wall of the vacuum chamber 10 .

[0027] refer to Figure 1 In some embodiments, the RH refining device 100 includes a plurality of second air blowing pipes 50, and the plurality of second air blowing pipes 50 are evenly arranged around the axis of the riser 20. Thus, the molten steel flowing in through the riser 20 can be supplemented with air blowing in all directions and comprehensively, and the flow rate of the molten steel can be more effectively increased. For example, five second air blowing pipes 50 with an inner diameter of 5 mm can be evenly arranged on the inverted truncated cone structure 12 with the axis of the riser 20 as the center. The exhaust ends of the plurality of second air blowing pipes 50 can be set at the middle position of the inverted truncated cone structure 12 in height, which is conducive to increasing the bubble decarburization effect.

[0028] In some embodiments, the exhaust end of the second blowing pipe 50 is tilted upward by 25-35° relative to the intake end, that is, the angle α between the second blowing pipe 50 and the horizontal plane is 25-35°. A suitable tilt angle is conducive to further improving the decarburization rate of the molten steel.

[0029] refer to Figure 1 In some embodiments, the first blowing pipe 40 includes a main pipe 42 and a plurality of branch pipes 44 connected to the main pipe 42, and the plurality of branch pipes 44 are connected to the riser 20. The plurality of branch pipes 44 may be arranged in a staggered manner, for example, the exhaust ends of different branch pipes 44 are arranged at different heights of the riser 20, and / or angles are formed between different branch pipes 44. By staggering the plurality of branch pipes 44, the gas blown in through the plurality of branch pipes 44 may have a stronger disturbance to the molten steel, and the movement path of the gas in the vacuum chamber 10 may be lengthened, so that the contact time between the gas and the molten steel may be lengthened, which is beneficial to improving the decarburization efficiency.

[0030] The present invention also proposes a deep decarburization method, comprising: using the RH refining device 100 as described above to perform RH refining on molten steel; wherein, during the entire RH refining process, lifting gas is blown in through the first blowing pipe 40, and the lifting gas flow rate in the early stage of RH refining is smaller than the lifting gas flow rate in the middle and late stages of RH refining; supplementary blowing gas is blown in through the second blowing pipe 50 only in the late stage of RH refining.

[0031] The inventors of the present application recognize that as the decarburization reaction proceeds, the reaction rate will gradually decrease. When the carbon content in the molten steel is less than 20ppm, the effect of the vacuum on the decarburization reaction decreases, the effect of the static pressure of the molten steel increases, the reaction only occurs in the reaction layer on the surface of the molten steel, the reaction rate is greatly reduced, and the decarburization reaction is close to stagnation. Therefore, in an embodiment of the present invention, the lifting gas flow rate in the middle and late stages of RH refining is made greater than the lifting gas flow rate in the early stages of RH refining to promote the decarburization reaction. At the same time, in the late stage of RH refining, supplementary blowing gas is blown in through the second blowing pipe 50 to increase the surface decarburization rate of the molten steel and the bubble decarburization rate, thereby further improving the decarburization reaction rate below 20ppm of carbon content. Considering that the reaction in the early and middle stages of RH refining is more intense, if supplementary blowing gas is blown in during this period, it may cause splashing of the molten steel on the one hand, and affect the reduction of vacuum on the other hand. Therefore, the present invention does not blow supplementary blowing gas in the early and middle stages of RH refining, but only blows supplementary blowing gas in the late stage of RH refining through the second blowing pipe 50.

[0032] In some embodiments, the early stage of RH refining is within 5 minutes after the start of vacuuming, the middle stage of RH refining is during 5 to 10 minutes after the start of vacuuming, and the late stage of RH refining is during 10 to 15 minutes after the start of vacuuming.

[0033] In some embodiments, the lifting gas flow rate in the early stage of RH refining is 9.5~11NL / min / ton of steel, and the lifting gas flow rate in the middle and late stages of RH refining is 12.5~14NL / min / ton of steel; the total flow rate of the supplementary gas is 600~1000NL / min. If the lifting gas flow rate is too large, splashing is likely to occur and the vacuum degree will be reduced. If the lifting gas flow rate is too small, the circulation speed of the molten steel will be slow, both of which will reduce the decarburization rate. On the basis of the RH refining device 100 designed as above, the present invention has correspondingly improved and designed the relevant process parameters of the RH refining process to ensure that the RH refining process can be adapted to the RH refining device 100, and to synergistically achieve the improvement of the decarburization reaction rate from the structural and methodological aspects. In an embodiment of the present invention, the lifting gas flow rate in the early stage of RH refining can be, for example, 9.5, 10, 10.5 or 11 NL / min / ton of steel, and the lifting gas flow rate in the middle and late stages of RH refining can be, for example, 12.5, 13, 13.5, 14 NL / min / ton of steel; the total flow rate of the supplementary blowing gas can be, for example, 600, 700, 800, 900, 1000 NL / min.

[0034] In some embodiments, the insertion depth of the riser and the downcomer in the ladle is 500-650 mm. A suitable insertion depth is conducive to ensuring the amount of circulating molten steel and improving the decarburization reaction efficiency to a certain extent.

[0035] In some embodiments, the temperature of the RH inlet steel is 1630-1650°C, the carbon content is 0.025-0.05wt%, and the oxygen content is 0.04-0.07wt%. The vacuum degree drops below 300Pa within 5 minutes after the vacuum pumping starts. When the ratio of the oxygen content to the carbon content ([O] / [C]) of the RH inlet steel is less than 1.4, oxygen blowing decarburization is performed. Oxygen blowing can be performed when the vacuum degree is 15-25kPa, the oxygen blowing time does not exceed 5 minutes, and the total oxygen consumption does not exceed 0.6m 3 / ton of steel; when the ratio of oxygen content to carbon content of RH incoming molten steel is greater than 1.4, natural decarburization is carried out. These parameter settings are conducive to ensuring the decarburization effect and controlling the cleanliness of molten steel.

[0036] The following is a description based on specific embodiments.

[0037] Example 1 The RH lower trough is built into an inverted cone shape. The lower bottom diameter of the inverted cone is 200mm smaller than that of the conventional cylindrical lower trough, and the upper bottom diameter of the inverted cone is 1000mm larger than that of the conventional cylindrical lower trough. The inverted cone is 500mm high, and the angle θ between the inverted cone generatrix and the horizontal plane is 45°. With the axis of the riser as the center, 5 Ar blowing pipes with an inner diameter of 5mm are evenly arranged in the middle of the inverted cone. The exhaust end of the Ar blowing pipe is tilted upward relative to the intake end, and the angle α between the Ar blowing pipe and the horizontal plane is 25°. The RH inlet molten steel temperature is 1630~1650℃, the carbon content is 0.025~0.05%, and the oxygen content is 0.04~0.07%. The insertion depth of the immersion pipe (riser and downcomer) is 500mm, and the vacuum degree drops below 300Pa within 5min. If the [O] / [C] ratio is less than 1.4, oxygen decarburization should be carried out. The oxygen should be blown at a vacuum of 15-25 kPa for no more than 5 minutes and the total oxygen consumption should not exceed 0.6 m 3 / ton of steel. If the [O] / [C] ratio is greater than 1.4, natural decarburization is performed. From the start of vacuuming, the gas flow rate is increased to 9.5NL / min / ton of steel for 0-5min, and the gas flow rate is increased to 12.5NL / min / ton of steel for 5-15min. The Ar pipe is opened for 10-15min, and the total flow rate is 600NL / min. After VCD (vacuum carbon deoxidation), the average carbon content of molten steel is 13ppm, and the decarburization time is 15min, which is 4min shorter than before the improvement.

[0038] Example 2 The RH lower trough is built into an inverted cone shape. The lower bottom diameter of the inverted cone is 200mm smaller than that of the conventional cylindrical lower trough, and the upper bottom diameter of the inverted cone is 940 larger than that of the conventional cylindrical lower trough. The inverted cone is 600mm high, and the angle θ between the inverted cone generatrix and the horizontal plane is 52°. With the axis of the riser as the center, 5 Ar blowing pipes with an inner diameter of 5mm are evenly arranged in the middle of the inverted cone. The exhaust end of the Ar blowing pipe is tilted upward relative to the intake end, and the angle α between the Ar blowing pipe and the horizontal plane is 30°. The RH inlet molten steel temperature is 1630~1650℃, the carbon content is 0.025~0.05%, and the oxygen content is 0.04~0.07%. The insertion depth of the immersion tube is 580mm, and the vacuum degree drops below 300Pa within 5min. If the [O] / [C] ratio is less than 1.4, oxygen decarburization should be carried out. The oxygen should be blown at a vacuum of 15-25 kPa for no more than 5 minutes and the total oxygen consumption should not exceed 0.6 m 3 / ton of steel. If the [O] / [C] ratio is greater than 1.4, natural decarburization is performed. From the start of vacuuming, the gas flow rate is increased to 10.2NL / min / ton of steel for 0-5min, and the gas flow rate is increased to 13.2NL / min / ton of steel for 5-15min. The Ar pipe is opened for 10-15min, and the total flow rate is 800 NL / min. After VCD, the average carbon content is 12ppm, and the decarburization time is 15min, which is 5min shorter than before the improvement.

[0039] Example 3 The RH lower trough is built into an inverted cone shape. The lower bottom diameter of the inverted cone is 200mm smaller than that of the conventional cylindrical lower trough, and the upper bottom diameter of the inverted cone is 810mm larger than that of the conventional cylindrical lower trough. The inverted cone is 700mm high, and the angle θ between the inverted cone generatrix and the horizontal plane is 60°. With the axis of the riser as the center, 5 Ar blowing tubes with an inner diameter of 5mm are evenly arranged in the middle of the inverted cone, and the angle α between the Ar blowing tube and the horizontal plane is 35°. The RH inlet molten steel temperature is 1630~1650℃, the carbon content is 0.025~0.05%, and the oxygen content is 0.04~0.07%. The insertion depth of the immersion tube is 650mm, and the vacuum degree drops below 300Pa within 5min. From the start of vacuuming, the gas flow rate is increased to 11NL / min / ton steel for 0~5min. Oxygen decarburization is carried out when the [O] / [C] ratio is less than 1.4. Oxygen is blown when the vacuum degree is 15~25kPa. The time does not exceed 5min. The total oxygen consumption does not exceed 0.6m 3 / ton of steel. The gas flow rate was increased to 14NL / min / ton of steel for 5-15min, and the Ar pipe was opened for 10-15min, with a total flow rate of 1000NL / min. After VCD, the average carbon content was 11ppm, and the decarburization time was 15min, which was 6min shorter than before the improvement.

[0040] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A RH refining device, characterized in that: include: A vacuum chamber, wherein the lower side wall of the vacuum chamber forms an inverted truncated cone structure, and the upper part of the vacuum chamber is used to connect a vacuum pumping device; An ascending pipe and a descending pipe, wherein the upper ends of the ascending pipe and the descending pipe are connected to the vacuum chamber and the lower ends are used to be inserted into the molten steel in the ladle; a first air blowing pipe, the first air blowing pipe being connected to the rising pipe; A second air blowing pipe, wherein the second air blowing pipe is connected to a region of the inverted truncated cone structure close to the riser in the circumferential direction.

2. The device according to claim 1, characterized in that The angle between the generatrix of the inverted truncated cone structure and the horizontal plane is 45-60°.

3. The device according to claim 1, characterized in that The height of the inverted truncated cone structure is 500-700 mm.

4. The device according to claim 1, characterized in that The RH refining device comprises a plurality of the second air blowing pipes, and the plurality of the second air blowing pipes are evenly arranged around the axis of the riser.

5. The device according to claim 1, characterized in that The exhaust end of the second air blowing pipe is inclined upward by 25-35 degrees relative to the intake end.

6. A deep decarburization method, characterized in that: include: The RH refining device as described in any one of claims 1 to 5 is used to carry out RH refining on molten steel; wherein, during the entire RH refining process, lifting gas is blown in through the first blowing pipe, and the lifting gas flow rate in the early stage of RH refining is smaller than the lifting gas flow rate in the middle and late stages of RH refining; supplementary blowing gas is blown in through the second blowing pipe only in the late stage of RH refining.

7. The method according to claim 6, characterized in that The early stage of RH refining is within 5 minutes after the start of vacuuming, the middle stage of RH refining is from 5 to 10 minutes after the start of vacuuming, and the late stage of RH refining is from 10 to 15 minutes after the start of vacuuming.

8. The method according to claim 6, characterized in that The lifting gas flow rate in the early stage of RH refining is 9.5~11NL / min / ton of steel, and the lifting gas flow rate in the middle and late stages of RH refining is 12.5~14NL / min / ton of steel; the total flow rate of the supplementary blowing gas is 600~1000NL / min.

9. The method according to claim 6, characterized in that The insertion depth of the ascending tube and the descending tube in the ladle is 500-650 mm.

10. The method according to claim 6, characterized in that The temperature of the RH inlet steel is 1630~1650℃, the carbon content is 0.025~0.05wt%, and the oxygen content is 0.04~0.07wt%. The vacuum degree drops below 300Pa within 5 minutes after the vacuum pumping starts. When the ratio of oxygen content to carbon content in the RH inlet steel is less than 1.4, oxygen blowing decarburization is carried out. The oxygen blowing time does not exceed 5 minutes, and the total oxygen consumption does not exceed 0.6m 3 / ton of steel.

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