A refining method for controlling the rephosphorization of molten steel

Abstract

The present invention relates to a refining method for controlling the rephosphorization of molten steel, which is implemented using a refining device consisting of a hydraulic lifting device, an immersion tube, a furnace cover, electrodes, a silo, and a ladle. The specific steps are as follows: 1) weakly deoxidizing the molten steel during tapping from the converter into the ladle, and adopting a slag blocking operation during tapping; 2) refining after tapping is completed; 3) the upper edge of the upper groove of the immersion tube is 10 to 20 mm away from the molten steel liquid level; 4) refining slag is added to the interior of the immersion tube, and light-burned dolomite and lime are added to the exterior of the immersion tube; 5) the electrodes are lowered to increase the temperature; 6) aluminum wire segments are added to the liquid slag surface inside the immersion tube for deoxidation and reduction. The method of the present invention can effectively control the amount of rephosphorization in molten steel, while also being beneficial in improving the cleanliness of the molten steel and reducing the temperature drop of the molten steel. It also has the advantages of simple operation and low production cost.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, in particular to a refining method for controlling the rephosphorization of molten steel. Background Art

[0002] Phosphorus is a harmful element in steel. A high phosphorus content will cause the steel to become "cold brittle", reduce the low-temperature plasticity and impact toughness of high-value steel, and worsen the welding and cold bending properties of the steel. Phosphorus is also an element that reduces the surface tension of molten steel. As the phosphorus content increases, the surface tension of molten steel decreases significantly, thereby reducing the steel's crack resistance. Phosphorus has a high degree of segregation in continuous casting billets and a very low diffusion rate in the iron solid solution, making segregation difficult to eliminate. All of the above factors will have an adverse effect on the quality of steel.

[0003] During the converter smelting process, the molten steel is in an oxidizing state, which is conducive to the dephosphorization of the molten steel; during LF refining, the slag changes from oxidizing to reducing, which easily causes the molten steel to return to phosphorus; especially for ultra-low sulfur steel grades, the smelting difficulty will be further increased.

[0004] Chinese patent application number 202210246136.5 discloses a "method for reducing rephosphorization during converter tapping and after slagging." The method involves pouring out some slag, rocking the converter to zero, adding lime (a1 weight) to the converter based on the temperature, and then rocking the converter to tap steel. Based on the tapping temperature and endpoint composition, a slag-forming deoxidizer (a2 weight) is added to the ladle. Based on the converter's endpoint phosphorus content and whether the converter is slagging, a slag-forming deoxidizer (a3 weight) and lime powder (a4 weight) are added to the molten steel. The argon gas inlet flow rate parameters in the molten steel tank are adjusted. This method reduces rephosphorization by adding different weights of lime and slag-forming deoxidizer to the converter multiple times. However, the process is complex and time-consuming, and it does not fundamentally address the rephosphorization issue of converter slag during refining and reduction.

[0005] Chinese patent application number 201510753468.2 discloses a "method for reducing rephosphorization in semi-steelmaking." This method effectively blocks the early slag, slag generated by the vortex effect during tapping, and late slag during the converter steelmaking process, reducing slag discharge and thus rephosphorization. The method comprises the following steps: A. First, a gate valve is installed at the converter's tapping port; B. During converter smelting, the gate valve is controlled to keep the tapping port open; C. Upon completion of converter smelting, the gate valve is controlled to keep the tapping port closed during the converter tilting process until the molten steel in the converter submerges the tapping port; D. When the converter tilts to the point where the molten steel in the converter submerges the tapping port, the gate valve is controlled to open, and the converter tilts vertically downward; E. When the AMEPA system at the tapping port detects molten slag, the gate valve is controlled to close; F. Then, the converter is controlled to tilt in the opposite direction of the tilting in step C to a vertical position, and the gate valve is controlled to open. This method can reduce slag discharge, minimize rephosphorization, and lower costs. However, this method still uses the traditional slag blocking device - the gate valve. When the AMEPA system at the steel outlet detects molten slag, the gate valve is opened, but at this time a part of the slag has already flowed out of the converter. Therefore, the amount of slag cannot be effectively reduced, the slag cannot be fundamentally suppressed, and the problem of phosphorus reversion caused by refining and reduction after slag discharge cannot be solved.

[0006] In summary, when using existing technologies to produce ultra-low sulfur and low-phosphorus aluminum-killed steel, there are still deficiencies in controlling the phosphorus content. It is urgent to develop a refining method that can achieve ultra-low sulfur in molten steel during LF refining, while controlling the amount of phosphorus return in molten steel, reducing and alloying the molten steel, removing inclusions in the steel, and reducing the temperature drop of the molten steel. Summary of the Invention

[0007] The present invention provides a refining method for controlling the rephosphorization of molten steel, which can effectively control the amount of rephosphorization of molten steel, while being beneficial to improving the cleanliness of molten steel and reducing the temperature drop of molten steel. In addition, it has the advantages of simple operation and low production cost.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A refining method for controlling the rephosphorization of molten steel is implemented using a refining device consisting of a hydraulic lifting device, an immersion tube, a furnace cover, electrodes, a silo, and a ladle. The specific steps are as follows:

[0010] 1) During the process of tapping from converter to ladle, the molten steel is weakly deoxidized and the oxygen content is controlled at 90~150×10 -6 The tapping temperature of the converter is controlled at 1620-1650℃. Slag blocking is adopted during tapping, and the slag layer thickness is controlled at 30-60mm.

[0011] 2) After the steel is tapped, refining is carried out, and the bottom blowing argon flow rate is 0.40~0.50Nm 3 / h·t;

[0012] 3) Use the hydraulic lifting device to lower the immersion tube and furnace cover so that the lower end of the immersion tube is immersed below the molten steel liquid level. The lower end of the immersion tube is provided with a through groove to allow the molten steel in the ladle to flow fully and eliminate the dead zone in the molten steel circulation process; the upper edge of the through groove is 10 to 20 mm away from the molten steel liquid level;

[0013] 4) Add refined slag to the inside of the dip tube through the silo, and add light-burned dolomite and lime to the outside of the dip tube to make the basicity of the steel slag outside the dip tube reach 6.0-7.2;

[0014] 5) Maintain the bottom blowing argon flow rate at 0.27~0.35Nm 3 / h·t; after adding refined slag, light-burned dolomite and lime, lower the electrode to carry out temperature raising operation to achieve the purpose of refining and slag reduction;

[0015] 6) Add aluminum wire segments to the liquid slag surface inside the immersion tube for deoxidation and reduction. After a good reduction slag is formed, keep it for 9 to 12 minutes and reduce the argon flow rate to 0.060 to 0.080 Nm 3 / h·t soft blowing is carried out to make the slag liquid surface move slightly and the molten steel is not exposed. After maintaining this for 8 to 10 minutes, the furnace cover and immersion tube are raised, and the ladle is transferred to the continuous casting process for casting.

[0016] Furthermore, the immersion tube is preheated to 980-1030° C. before use.

[0017] Furthermore, the components of the refined slag are as follows by weight: CaO 46% to 50%; Al2O3 32% to 37%; SiO2 7% to 10%; MgO 6% to 9%, and the remainder is inevitable impurities.

[0018] Furthermore, the amount of the refined slag added is 0.9-1.1 kg / ton of steel, added in 2-3 times.

[0019] Furthermore, the light-burned dolomite has a MgO content of ≥30% and a CaO content of ≥45% by weight.

[0020] Furthermore, the lime contains CaO≥90% by weight.

[0021] Furthermore, the continuous casting process adopts full-process protective casting.

[0022] Furthermore, a plurality of through grooves are evenly arranged along the circumferential direction at the bottom end of the immersion tube.

[0023] Furthermore, two through grooves are symmetrically provided at the bottom end of the immersion tube, and the height of the through grooves is 30 to 80 mm.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) The refining method of the present invention can fully achieve the purpose of controlling the rephosphorization of molten steel. The small-sized furnace cover reduces the chance of contact between molten steel and slag during converter slagging. At the beginning of refining, the bottom blowing argon gas flow rate is large, and most of the initial slag is pushed to the vicinity of the ladle wall, further reducing the possibility of rephosphorization of molten steel by converter slag. Compared with conventional LF refining, the amount of rephosphorization of molten steel by the converter slag remaining in the immersion tube does not exceed 5×10 -6 , the impact can be basically ignored.

[0026] 2) The refining method of the present invention can effectively reduce the temperature drop of molten steel during the treatment process. Compared with conventional LF refining, the temperature loss is reduced by about 33%.

[0027] 3) When refining by the method of the present invention, inclusions in molten steel can be effectively removed by the refining slag, so that the inclusions fully float and are adsorbed by the slag, thereby improving the cleanliness of the molten steel. The amount of refining slag used is 40% of that in conventional operations, thereby reducing production costs.

[0028] 4) The through groove provided at the bottom of the immersion tube can not only prevent the slag from affecting the immersion tube, but also enable the molten steel in the ladle to flow fully, eliminate the dead zone in the molten steel during refining treatment, enable the molten steel to fully participate in the reaction, ensure the refining and desulfurization effect, and improve the refining efficiency.

[0029] 5) The refining device of the present invention has a simple structure, is easy to operate, requires little investment, and does not affect the normal operation of other equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of the refining device of the present invention.

[0031] Figure 2 It is a structural diagram of the immersion tube.

[0032] Figure: 1. Hydraulic lift 2. Immersion tube 3. Furnace cover 4. Refined slag 5. Electrode 6. Silo 7. Calcined dolomite and lime 8. Molten steel 9. Ladle 10. Air bricks 11. Channel DETAILED DESCRIPTION

[0033] The refining method for controlling the rephosphorization of molten steel described in the present invention is implemented by using a refining device consisting of a hydraulic lifting device 1, an immersion tube 2, a furnace cover 3, an electrode 5, a silo 6 and a ladle 9. The specific steps are as follows:

[0034] 1) During the process of tapping from the converter to the ladle 9, the molten steel is weakly deoxidized and the oxygen content is controlled at 90-150×10 -6The tapping temperature of the converter is controlled at 1620-1650℃. Slag blocking is adopted during tapping, and the slag layer thickness is controlled at 30-60mm.

[0035] 2) After the steel is tapped, refining is carried out, and the bottom blowing argon flow rate is 0.40~0.50Nm 3 / h·t;

[0036] 3) The immersion tube 2 and the furnace cover 3 are lowered using the hydraulic lifting device 1 so that the lower end of the immersion tube 2 is immersed below the molten steel surface. A through groove 11 is provided at the lower end of the immersion tube 2 to allow the molten steel in the ladle 9 to flow fully and eliminate dead zones in the molten steel circulation process; the upper edge of the through groove 11 is 10 to 20 mm above the molten steel surface;

[0037] 4) adding refined slag 4 to the interior of the dip tube 2 through the hopper 6, and adding light-burned dolomite and lime 7 to the exterior of the dip tube 2, so that the basicity of the steel slag outside the dip tube 2 reaches 6.0-7.2;

[0038] 5) Maintain the bottom blowing argon flow rate at 0.27~0.35Nm 3 / h·t; after adding refined slag, light-burned dolomite and lime, lower the electrode to carry out temperature raising operation to achieve the purpose of refining and slag reduction;

[0039] 6) Add aluminum wire segments to the liquid slag surface inside the immersion tube 2 for deoxidation and reduction. After a good reduction slag is formed, keep it for 9 to 12 minutes and reduce the argon flow rate to 0.060 to 0.080 Nm 3 / h·t soft blowing is performed to make the slag liquid surface move slightly and the molten steel is not exposed. After maintaining this for 8 to 10 minutes, the furnace cover 3 and the immersion tube 2 are raised, and the ladle 9 is transferred to the continuous casting process for casting.

[0040] Furthermore, the immersion tube 2 is preheated to 980-1030° C. before use.

[0041] Furthermore, the components of the refined slag 4 are as follows by weight: CaO 46% to 50%; Al2O3 32% to 37%; SiO2 7% to 10%; MgO 6% to 9%, and the remainder is unavoidable impurities.

[0042] Furthermore, the addition amount of the refined slag 4 is 0.9-1.1 kg / ton of steel, added in 2-3 times.

[0043] Furthermore, the light-burned dolomite has a MgO content of ≥30% and a CaO content of ≥45% by weight.

[0044] Furthermore, the lime contains CaO≥90% by weight.

[0045] Furthermore, the continuous casting process adopts full-process protective casting.

[0046] Furthermore, a plurality of through grooves 11 are evenly arranged along the circumferential direction at the bottom end of the immersion tube 2 .

[0047] Furthermore, two through grooves 11 are symmetrically provided at the bottom end of the immersion tube 2 , and the height of the through grooves 11 is 30 to 80 mm.

[0048] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0049] like Figure 1 As shown, the refining device of the present invention (see "A Refining Device and Method for Controlling Nitrogen Content in Molten Steel" disclosed in Chinese patent application publication number CN 105624367 A) includes a hydraulic lifting device, an immersion pipe, a furnace cover, electrodes, a silo and a ladle; the hydraulic lifting device is fixed to the ground, a connecting rod is fixed transversely to the front end of the hydraulic cylinder piston rod in the hydraulic lifting device, one end of the connecting rod is welded to the furnace cover, a plurality of electrodes are provided in the middle of the furnace cover, and a silo is provided above the feed port on one side of the furnace cover; the immersion pipe made of refractory material is fixed to the steel structure below the furnace cover, and the furnace cover is raised and lowered by the hydraulic lifting device and hung above the ladle.

[0050] The diameter of the furnace cover 3 is 1 / 3 to 1 / 2 of the diameter of the ladle 9.

[0051] The immersion tube 2 can be reused; in the present invention, two through grooves 11 (preferably with a depth of 50 mm) are symmetrically opened along the circumferential direction at the bottom end of the immersion tube 2. During the refining treatment, the through grooves 11 can not only prevent the slag from affecting the immersion tube 2, but also allow the molten steel in the ladle to flow fully, eliminating the dead zone in the molten steel during the refining treatment, allowing the molten steel to fully participate in the reaction, and ensuring the refining and desulfurization effect.

[0052] When molten steel is subjected to LF refining, the immersion pipe 2 under the furnace cover is preheated to 980-1030°C before use.

[0053] During the tapping process of the converter, deoxidizers such as silicon and manganese are added for weak deoxidation to control the oxygen content in the molten steel at 90-150ppm. After tapping, the molten steel enters the LF refining process. After the ladle 9 is placed, a height mark is made on the immersion tube 2 to measure the thickness of the slag layer in the ladle 9. A large argon flow rate is used for bottom blowing through the air bricks 10 at the bottom of the ladle. The bottom blowing argon flow rate is 0.40-0.50Nm 3 / h·t, used to blow the slag above the molten steel 8 and make it flow toward the wall of the ladle.

[0054] When the amount of slag remaining above the center of the ladle is low, the hydraulic lift mechanism 1 is used to lower the dip tube 2 and furnace cover 3. Depending on the thickness of the slag layer, the dip tube's slot 11 is adjusted to just pass through the upper surface of the molten steel. The bottom-blowing argon flow rate is then reduced, and refined slag 4 is added to the dip tube 2 through the hopper 6. Lightly calcined dolomite and lime 7 are added to the outside of the dip tube 2 to form a non-flowing slag.

[0055] After adding the slag-forming material, the electrode 5 is lowered to increase the temperature to refine and chemically refine the slag. The liquid slag inside the dip tube 2 is reduced while maintaining bottom argon blowing. After the dip tube 2 is lowered, the bottom-blown argon is discharged only through the dip tube 2 to the molten steel, which helps remove sulfur and oxide inclusions from the molten steel.

[0056] During the slag reduction process, phosphorus in the slag released from the converter during tapping inside the immersion tube is reduced and released into the molten steel. Argon protects the molten steel. Once the slag is fully reduced and the molten steel temperature meets the required requirements, electrode 5 is raised. Bottom argon blowing is maintained for 9-12 minutes. The argon flow rate is then reduced, and soft argon blowing is employed for 8-10 minutes. Finally, the furnace lid 3 and immersion tube 2 are raised, and the ladle is transferred to the continuous casting process for casting.

[0057] In the refining method for controlling the rephosphorization of molten steel described in the present invention, the reasons for selecting the various process parameters are as follows:

[0058] a. During the tapping process of the converter, the molten steel is weakly deoxidized and the oxygen content is controlled at 90~150×10 -6 By weak deoxidation, the phosphorus in the slag is suppressed from returning to the molten steel. The tapping temperature of the slag converter is controlled at 1620-1650℃. The lower tapping temperature is beneficial to reducing the phosphorus content in the molten steel.

[0059] b. During the steel-making process, slag blocking operation is adopted and the thickness of the slag layer is controlled at 30-60 mm.

[0060] c. The through groove 11 of the immersion tube 2 is immersed in the depth of 10 to 20 mm below the liquid surface of the molten steel, which is beneficial to the flow of the molten steel in the ladle, thereby improving the desulfurization effect of the molten steel.

[0061] d. Refining slag 4 is added to the interior of the immersion tube 2. Refining slag has a low melting point and is highly adsorbent of inclusions. The space inside the immersion tube 2 is relatively small, so the slag deposited by the converter during steelmaking is minimal, effectively suppressing the amount of rephosphorization in the molten steel. This significantly reduces the required heating time of the molten steel (approximately half that of conventional refining processes), minimizing temperature losses and ultimately lowering production costs.

[0062] e. Adding light-burned dolomite and lime to the outside of the immersion tube 2 to increase the basicity of the external steel slag to 6.0-7.2; this high-basicity steel slag has the characteristics of a high melting point and poor fluidity, which does not provide the steel slag with sufficient thermodynamic and kinetic conditions to participate in the reaction. Therefore, the steel slag in this area will not be stirred, and the reaction of 10[Al]+3P2O5=6[P]+5(A12O3) will not occur, thereby achieving the effect of reducing phosphorus reversion during the refining process and improving the qualified rate of low-phosphorus steel.

[0063] f. After adding refined slag 4, light-burned dolomite and lime 7, maintain the bottom blowing argon flow rate at 0.27~0.35Nm 3 / h·t, add aluminum wire segments to the liquid slag surface inside the immersion tube 2 for deoxidation and reduction. After forming a good reduced slag, keep it for 9 to 12 minutes and reduce the argon flow rate to 0.060 to 0.080 Nm 3 / h·t soft blowing is carried out to make the slag liquid surface move slightly without exposing the molten steel. After maintaining this for 8 to 10 minutes, the continuous casting process can be started. During the continuous casting process, protective casting is adopted to reduce air absorption by the molten steel.

[0064] It should be noted that, unless there is a conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The described embodiments are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative work are within the scope of protection of the present invention.

[0065] [Example]

[0066] The refining device of the present invention was used to conduct tests in a 120-ton LF furnace. The preheating temperature of the immersion tube 2 before use was 980-1030°C. The steel type to be smelted was ultra-low sulfur and low-phosphorus aluminum-killed steel. A total of 12 groups of tests were conducted, of which 2 groups were comparative tests. The comparative tests were conducted in a conventional LF furnace. Refining slag was added to perform slag reduction desulfurization. The slag on the entire molten steel surface was uniform, and then the steel was put into casting machine.

[0067] The refining process parameters and control results of each embodiment are shown in Table 1, and the amount of refined slag added and its composition are shown in Table 2.

[0068] Table 1 Refining process parameters and control results

[0069]

[0070]

[0071] Table 2: Refined slag addition amount and composition

[0072]

[0073] As shown in Table 1, the refining apparatus described herein significantly reduces rephosphorization during molten steel refining, with the amount of rephosphorization in the Example being no more than 1 / 10 of that in the Comparative Example. Furthermore, the desulfurization rates in the Example and Comparative Example during LF refining were comparable, improving overall steel quality. The heating time required for molten steel during refining was significantly reduced, with the Example being approximately two-thirds of that in the Comparative Example, minimizing temperature loss and contributing to lower production costs. The amount of refining slag added in the Example was also reduced compared to the Comparative Example, further reducing production costs.

[0074] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 refining method for controlling the rephosphorization of molten steel, characterized in that: This is achieved using a refining device consisting of a hydraulic lifting device, an immersion tube, a furnace cover, electrodes, a silo, and a ladle. The specific steps are as follows: 1) During the process of tapping from converter to ladle, the molten steel is weakly deoxidized and the oxygen content is controlled at 90~150×10 -6 The tapping temperature of the converter is controlled at 1620-1650℃. Slag blocking is adopted during tapping, and the slag layer thickness is controlled at 30-60mm. 2) After the steel is tapped, refining is carried out, and the bottom blowing argon flow rate is 0.40~0.50Nm 3 / h·t; 3) Use the hydraulic lifting device to lower the immersion tube and furnace cover so that the lower end of the immersion tube is immersed below the molten steel liquid level. The lower end of the immersion tube is provided with a through groove to allow the molten steel in the ladle to flow fully and eliminate the dead zone in the molten steel circulation process; the upper edge of the through groove is 10 to 20 mm away from the molten steel liquid level; 4) Add refined slag to the inside of the dip tube through the silo, and add light-burned dolomite and lime to the outside of the dip tube to make the basicity of the steel slag outside the dip tube reach 6.0-7.2; 5) Maintain the bottom blowing argon flow rate at 0.27~0.35Nm 3 / h·t; after adding refined slag, light-burned dolomite and lime, lower the electrode to carry out temperature raising operation to achieve the purpose of refining and slag reduction; 6) Add aluminum wire segments to the liquid slag surface inside the immersion tube for deoxidation and reduction. After a good reduction slag is formed, keep it for 9 to 12 minutes and reduce the argon flow rate to 0.060 to 0.080 Nm 3 / h·t soft blowing is carried out to make the slag liquid surface move slightly and the molten steel is not exposed. After maintaining this for 8 to 10 minutes, the furnace cover and immersion tube are raised, and the ladle is transferred to the continuous casting process for casting.

2. A refining method for controlling rephosphorization of molten steel according to claim 1, characterized in that: The immersion tube is preheated to 980-1030° C. before use.

3. A refining method for controlling rephosphorization of molten steel according to claim 1, characterized in that: The components of the refined slag are as follows by weight: CaO 46% to 50%; Al2O3 32% to 37%; SiO2 7% to 10%; MgO 6% to 9%, and the remainder is inevitable impurities.

4. A refining method for controlling the rephosphorization of molten steel according to claim 1 or 2, characterized in that, The amount of the refined slag added is 0.9-1.1 kg per ton of steel, added in 2-3 times.

5. A refining method for controlling rephosphorization of molten steel according to claim 1, characterized in that: The light-burned dolomite has a MgO content of ≥30% and a CaO content of ≥45% by weight.

6. A refining method for controlling rephosphorization of molten steel according to claim 1, characterized in that: The lime contains CaO≥90% by weight.

7. A refining method for controlling rephosphorization of molten steel according to claim 1, characterized in that: The continuous casting process adopts full-process protection casting.

8. A refining method for controlling rephosphorization of molten steel according to claim 1, characterized in that: The bottom end of the immersion tube is evenly provided with a plurality of through grooves along the circumferential direction.

9. A refining method for controlling rephosphorization of molten steel according to claim 1 or 8, characterized in that: The bottom end of the immersion tube is symmetrically provided with two through grooves, and the height of the through grooves is 30 to 80 mm.

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