Method for efficiently increasing nitrogen and removing inclusions in RH refining

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a method for efficiently increasing nitrogen and removing inclusions in RH refining, in the RH refining process, nitrogen is blown into an ascending pipe, nitrogen is blown into the side part and / or the bottom of a vacuum chamber, and nitrogen is blown into molten steel in a descending pipe; through composite nitrogen blowing, a good nitrogen increasing effect is achieved; under the action of torrential steel flow and inclusions in steel in the refining process, blowing-in nitrogen is promoted to generate fine dispersed nitrogen bubbles, and dissolution of the nitrogen in molten steel is promoted; part of tiny nitrogen bubbles enter the steel ladle along with the steel flow through the downcomer, and under the action of the static pressure of the molten steel, the bubbles are smaller in size, higher in internal pressure and easier to dissolve; more and smaller fine dispersed nitrogen bubbles are generated to adhere to inclusions in the molten steel, and efficient removal of the inclusions in the molten steel is promoted. The method is easy to operate, low in production cost, high in efficiency and beneficial to industrial large-scale production, popularization and application.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for RH refining with high efficiency nitrogen addition and inclusion removal. Background Art

[0002] High nitrogen steel and nitrogen-controlled steel can use nitrogen to promote the formation of austenite and precipitates in steel to achieve excellent organizational control and performance control goals. Nitrogen-added steel production can generally be nitrogen-added to molten steel by blowing nitrogen from the bottom of the converter, blowing nitrogen from the side of AOD, and blowing nitrogen from the bottom of the LF refining ladle. However, a large amount of CO gas is generated during converter steelmaking and AOD steelmaking, and CO bubbles have a denitrification effect. However, the nitrogen-added effect of the bottom blowing of the LF refining ladle is limited due to the limited amount of nitrogen blown in and the large size of the nitrogen bubbles generated. There are also literature reports on nitrogen-added steel liquid by blowing nitrogen in the RH riser, but due to the large flow rate of nitrogen blown into the riser and the large diameter of the blowing hole, the nitrogen bubbles generated by the nitrogen blown in are large in size, and the contact time with the molten steel is short. In addition, the subsequent vacuum treatment effect has a very limited nitrogen-added effect. Nitrogen-added steel production can also be nitrogen-added to molten steel by adding nitrided alloys, but there are reasons such as high alloy cost and the easy decomposition of some alloys at high temperatures, and the nitrogen-added effect and benefits are not ideal. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a method for RH refining with high efficiency of nitrogen addition and inclusion removal.

[0004] According to one aspect of the present invention, the present invention provides the following technical solution:

[0005] The invention discloses a method for removing inclusions by high-efficiency nitrogen addition in RH refining. In the RH refining process, nitrogen is blown into an ascending pipe, into a side and / or bottom of a vacuum chamber, and into a downcomer into molten steel. The turbulent steel flow and inclusions in the steel during the refining process are utilized to promote the blown nitrogen to generate fine dispersed nitrogen bubbles, thereby promoting the dissolution of nitrogen in the molten steel. Meanwhile, part of the dissolved nitrogen in the molten steel in the vacuum chamber is precipitated to generate dispersed tiny nitrogen bubbles. The tiny nitrogen bubbles precipitated in the molten steel and the generated tiny dispersed nitrogen bubbles adhere to inclusions in the molten steel, thereby promoting the efficient removal of inclusions in the molten steel.

[0006] As a preferred embodiment of the method for RH refining and efficient nitrogen addition and inclusion removal described in the present invention, after the RH immersion tube is inserted into the ladle, nitrogen is blown into the riser as a lifting gas, and nitrogen is blown into the molten steel at the side and / or bottom of the vacuum chamber to achieve nitrogen addition to the molten steel; after the riser is blown for 0.5-1.0 min and the flow rate of the molten steel in the downcomer is ≥0.3 m / s, nitrogen is blown into the molten steel through the downcomer blowing element.

[0007] As a preferred embodiment of the RH refining high-efficiency nitrogen addition and inclusion removal method described in the present invention, the downcomer blowing element is one of a metal tube, a straight-through refractory pore, a dispersed air-permeable brick, and a breathable plug; the diameter of the metal tube and the straight-through refractory pore is controlled to be 0.2-3.0 mm, and the average pore size of the dispersed air-permeable brick and the breathable plug is 5-1000 μm.

[0008] As a preferred embodiment of the RH refining high-efficiency nitrogen addition and inclusion removal method described in the present invention, the blowing element at the bottom of the vacuum chamber adopts a dispersed air-permeable brick or an air-permeable plug, and the average pore size of the dispersed air-permeable brick and the air-permeable plug is 5-1000 μm; the blowing element on the side of the vacuum chamber is a high-speed nozzle.

[0009] As a preferred embodiment of the RH refining high-efficiency nitrogen addition and inclusion removal method described in the present invention, the total blowing flow rate at the side and / or bottom of the vacuum chamber is 20-100% of the blowing flow rate of the riser, and the blowing flow rate of the downcomer is 1-18% of the blowing flow rate of the riser.

[0010] As a preferred embodiment of the RH refining high-efficiency nitrogen addition and inclusion removal method described in the present invention, the RH vacuum refining process controls the ultimate vacuum pressure of the vacuum chamber and the deep vacuum treatment time, the ultimate vacuum pressure of the vacuum chamber is greater than 50Pa, and the deep vacuum treatment time of the vacuum chamber at the late stage of nitrogen addition is ≤100Pa ≤5min.

[0011] The beneficial effects of the present invention are as follows:

[0012] The present invention proposes a method for RH refining to efficiently increase nitrogen and remove inclusions. During the RH refining process, nitrogen is blown into the riser, into the side and / or bottom of the vacuum chamber, and into the molten steel through the downcomer; a good nitrogen increase effect is achieved through composite nitrogen blowing; the turbulent steel flow and inclusions in the steel during the refining process are utilized to promote the blowing of nitrogen to generate fine diffuse nitrogen bubbles, thereby promoting the dissolution of nitrogen in the molten steel; some tiny nitrogen bubbles enter the ladle along with the steel flow through the downcomer, and under the static pressure of the molten steel, the bubble size is smaller, the internal pressure of the bubble is greater, and it is easier to dissolve; more and smaller fine diffuse nitrogen bubbles are generated, adhere to inclusions in the molten steel, and promote the efficient removal of inclusions in the molten steel. The present invention is simple to operate, has low production cost, high efficiency, and is conducive to large-scale industrial production and popularization. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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 the structures shown in these drawings without paying creative work.

[0014] Figure 1 It is a schematic diagram of the method for RH refining with high efficiency of nitrogen addition and inclusion removal according to the present invention.

[0015] In the figure, 1-vacuum chamber, 2-riser pipe, 3-blowing element on the side of the vacuum chamber, 4-ladle, 5-down pipe.

[0016] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0017] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] The present invention proposes a method for RH refining with high efficiency of nitrogen addition and inclusion removal, such as Figure 1 As shown, during the RH refining process, nitrogen is blown into the riser 2, into the side or bottom of the vacuum chamber 1, and into the molten steel through the downcomer 5; the turbulent steel flow and the inclusions in the steel during the refining process are utilized to promote the blowing of nitrogen to generate fine diffuse nitrogen bubbles, thereby promoting the dissolution of nitrogen in the molten steel; at the same time, the fine diffuse nitrogen bubbles generated in the molten steel adhere to the inclusions in the molten steel, thereby promoting the efficient removal of the inclusions in the molten steel; the ultimate vacuum pressure and deep vacuum treatment time of the RH vacuum refining process are controlled, the ultimate vacuum pressure of the vacuum chamber is greater than 50Pa, and the deep vacuum treatment time of the vacuum chamber at the late stage of nitrogen addition is ≤100Pa is ≤5min.

[0019] During the RH refining process, the molten steel in the vacuum chamber 1 and the downcomer 5 flows at a high speed and has a large turbulent kinetic energy. The fast-flowing molten steel can shear the nitrogen blown into the side or bottom of the vacuum chamber 1 and the downcomer 5, promote the separation of the blown nitrogen and the blowing element, and generate relatively small nitrogen bubbles. The turbulent steel flow can further break the generated nitrogen bubbles, generate even smaller nitrogen bubbles, and make the bubbles dispersed. A large number of dispersed inclusions in the molten steel constantly collide with the bubbles, and some inclusions adhere to the bubbles, reducing the interfacial tension between the bubbles and the molten steel; the irregular movements of the inclusions such as rotation and vibration on the surface of the bubble and nearby pull and break the bubbles; under these effects, the dispersed inclusions in the steel refine the bubbles and promote the generation of small nitrogen bubbles. The nitrogen blown into the downcomer 5 is quickly separated from the blowing element under the shearing effect of the steel flow rapidly downward in the downcomer 5, the collision and traction of inclusions in the steel, and the dissolution of the bubble root in the molten steel, generating relatively fine nitrogen bubbles, which move downward together with the molten steel. During the downward movement of the bubbles, the turbulence of the molten steel, the collision and traction of inclusions, and the compression effect of the static pressure of the molten steel further refine the nitrogen bubbles. These fine nitrogen bubbles are in contact with the molten steel for a long time, and under the action of the static pressure of the molten steel and the surface tension of the bubbles, the nitrogen partial pressure inside the bubbles is high, and they are easy to dissolve in the molten steel, thereby effectively increasing the nitrogen content in the molten steel. The nitrogen gas blown into the side or bottom of the vacuum chamber 1 is quickly separated from the blowing element under the shearing effect of the fast flowing steel flow in the vacuum chamber 1, the collision and traction of the inclusions in the steel, and the dissolution of the bubble root in the molten steel, generating relatively fine nitrogen bubbles. These fine nitrogen bubbles are further refined by the turbulence of the molten steel, the collision and traction of the inclusions in the molten steel; at the same time, these fine bubbles are quickly dissolved in the molten steel, and the content of dissolved nitrogen in the molten steel is increased relatively quickly; some fine bubbles flow into the downcomer 5 with the molten steel, and then enter the ladle 4, and the contact time with the molten steel is longer, which is more conducive to the nitrogen increase of the molten steel. The partially dissolved nitrogen in the molten steel in the vacuum chamber will precipitate inside the molten steel to generate dispersed tiny nitrogen bubbles. The nitrogen gas blown into the side or bottom of the vacuum chamber 1 and the downcomer 5 generates a large number of fine dispersed nitrogen bubbles in the molten steel. The tiny nitrogen bubbles precipitated inside the molten steel in the vacuum chamber can adhere to the inclusions, promote the polymerization and growth of the inclusions, and promote the floating removal of the inclusions in the ladle.

[0020] Preferably, after the RH immersion tube is inserted into the ladle 4, nitrogen is blown into the riser 2 as a lifting gas, and nitrogen is blown into the molten steel at the side or bottom of the vacuum chamber 1 to achieve nitrogen addition to the molten steel; after the riser 2 is blown for 0.5-1.0 min and the flow rate of the molten steel in the downcomer 5 is ≥0.3 m / s, nitrogen is blown into the molten steel through the blowing element of the downcomer 5.

[0021] Preferably, the blowing element of the downcomer 5 is one of a metal tube, a straight-through refractory pore, a diffused air brick, and a breathable plug. The diameter of the metal tube and the straight-through refractory pore is controlled to be 0.2-3.0 mm, and the average pore size of the diffused air brick and the breathable plug is 5-1000 μm.

[0022] Preferably, the blowing element at the bottom of the vacuum chamber is a diffused air-permeable brick or an air-permeable plug, and the average pore size of the diffused air-permeable brick or the air-permeable plug is 5-1000 μm; the blowing element 3 at the side of the vacuum chamber is a high-speed nozzle.

[0023] Preferably, the blowing flow rate at the side or bottom of the vacuum chamber 1 is 20-100% of the blowing flow rate of the riser 2 , and the blowing flow rate of the downcomer 5 is 1-18% of the blowing flow rate of the riser 2 .

[0024] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0025] Example 1

[0026] In a domestic steel plant's 210tRH refining unit, the target nitrogen content of the RH refined molten steel when it leaves the station is 130-150ppm and the oxygen content is 8ppm.

[0027] After the RH refined steel liquid enters the station, the temperature of the steel liquid is measured, and the nitrogen content in the steel is sampled and analyzed. The nitrogen content in the steel is 38ppm; the ladle is lifted and the RH immersion tube is inserted into the ladle; vacuuming begins, and the vacuum chamber pressure is quickly reduced. At the same time, nitrogen is blown into the steel liquid at the bottom of the riser and vacuum chamber; the RH riser has 16 nozzles, and the total flow rate of nitrogen blown into the riser during refining is 4000NL / min; 6 air permeable plugs are installed at the bottom of the RH, and the total flow rate of bottom blowing nitrogen is 2500NL / min; vacuuming 0.5 min later, the flow rate of the molten steel in the downcomer reached 0.4m / s. The downcomer was equipped with 4 stainless steel blowing holes with a hole diameter of 0.8mm. Nitrogen was blown into the molten steel through them, and the total blowing flow rate was 600NL / min. After RH refining treatment for 10min, the pressure in the vacuum chamber was controlled to 60Pa and maintained at this pressure for 3min. It was measured that the nitrogen concentration in the molten steel increased to 148ppm, meeting the nitrogen control requirement for steelmaking, and the refining was ended. The oxygen content in the steel was sampled and analyzed, and the total oxygen in the molten steel was measured to be 7ppm.

[0028] Example 2

[0029] In a domestic steel plant's 210tRH refining unit, the target nitrogen content of the RH refined molten steel leaving the station is 160-180ppm and the oxygen content is 5ppm.

[0030] After the RH refined steel liquid enters the station, the temperature of the steel liquid is measured, and the nitrogen content in the steel is sampled and analyzed. The nitrogen content in the steel is 40ppm; the ladle is lifted and the RH immersion tube is inserted into the ladle; vacuuming begins, and the vacuum chamber pressure is quickly reduced. At the same time, nitrogen is blown into the steel liquid at the bottom of the riser and vacuum chamber; the RH riser has 16 nozzles, and the total flow rate of nitrogen blown into the riser during refining is 3800NL / min; 10 air permeable plugs are installed at the bottom of the RH, and the total flow rate of bottom blowing nitrogen is 3000NL / min; vacuuming 0.5 min later, the flow rate of the molten steel in the downcomer reached 0.3m / s. The downcomer was equipped with 5 stainless steel blowing holes with a hole diameter of 0.5mm. Nitrogen was blown into the molten steel through them, and the total blowing flow rate was 600NL / min. After RH refining treatment for 12min, the pressure in the vacuum chamber was controlled to 100Pa and maintained at this pressure for 5min. The nitrogen concentration in the molten steel was measured to reach 178ppm, which met the nitrogen control requirements for steelmaking, and the refining was ended. The oxygen content in the steel was sampled and analyzed, and the total oxygen in the molten steel was measured to be 4.7ppm.

[0031] In the RH refining process, the present invention blows nitrogen into the ascending pipe, blows nitrogen into the side and / or bottom of the vacuum chamber, and blows nitrogen into the molten steel through the descending pipe; a good nitrogen-increasing effect is achieved through composite nitrogen blowing; the turbulent steel flow and the inclusions in the steel during the refining process are utilized to promote the blowing of nitrogen to generate fine diffuse nitrogen bubbles, and promote the dissolution of nitrogen in the molten steel; some tiny nitrogen bubbles enter the ladle with the steel flow through the descending pipe, and under the static pressure of the molten steel, the bubble size is smaller, the internal pressure of the bubble is greater, and it is easier to dissolve; more and smaller fine diffuse nitrogen bubbles are generated, adhere to the inclusions in the molten steel, and promote the efficient removal of the inclusions in the molten steel. The present invention is simple to operate, low in production cost, high in efficiency, and is conducive to industrial large-scale production and popularization.

[0032] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for RH refining with high efficiency nitrogen addition and inclusion removal, characterized in that: During the RH refining process, nitrogen is blown into the riser, into the side and / or bottom of the vacuum chamber, and into the molten steel in the downcomer; the turbulent steel flow and inclusions in the steel during the refining process are utilized to promote the blown nitrogen to generate fine dispersed nitrogen bubbles, thereby promoting the dissolution of nitrogen in the molten steel; at the same time, dispersed tiny nitrogen bubbles are precipitated in the molten steel in the vacuum chamber; the precipitated tiny nitrogen bubbles and the generated tiny dispersed nitrogen bubbles adhere to inclusions in the molten steel, thereby promoting the efficient removal of inclusions in the molten steel.

2. The method for RH refining and efficient nitrogen addition and inclusion removal according to claim 1, characterized in that: After the RH immersion tube is inserted into the ladle, nitrogen is blown into the riser as lifting gas, and nitrogen is blown into the molten steel at the side and / or bottom of the vacuum chamber to achieve nitrogen addition to the molten steel; the riser is blown for 0.5-1.0min, and after the flow rate of the molten steel in the downcomer is ≥0.3m / s, nitrogen is blown into the molten steel through the downcomer blowing element.

3. The method for RH refining and efficient nitrogen addition and inclusion removal according to claim 1, characterized in that: The downcomer blowing element is one of a metal tube, a straight-through refractory air hole, a diffused air brick, and an air plug.

4. The method for RH refining and efficient nitrogen addition and inclusion removal according to claim 3, characterized in that: The diameter of the pores of metal tubes and straight-through refractory materials is controlled to be 0.2-3.0mm.

5. The method for RH refining and efficient nitrogen addition and inclusion removal according to claim 3, characterized in that: The average pore size of diffused air bricks and air plugs is 5-1000μm.

6. The method for RH refining and efficient nitrogen addition and inclusion removal according to claim 1, characterized in that: The blowing element at the bottom of the vacuum chamber adopts a diffused air brick or an air plug, and the average pore size of the diffused air brick and the air plug is 5-1000μm.

7. The method for RH refining and efficient nitrogen addition and inclusion removal according to claim 1, characterized in that: The blowing element on the side of the vacuum chamber is a high-speed nozzle.

8. The method for RH refining and efficient nitrogen addition and inclusion removal according to claim 1, characterized in that: The blowing flow rate at the side and / or bottom of the vacuum chamber is 20-100% of the total blowing flow rate of the riser.

9. The method for RH refining and efficient nitrogen addition and inclusion removal according to claim 1, characterized in that: The blowing flow rate of the downcomer is 1-18% of the blowing flow rate of the upcomer.

10. The RH refining high-efficiency nitrogen addition and inclusion removal method according to claim 1, characterized in that: The RH vacuum refining process controls the ultimate vacuum pressure of the vacuum chamber and the deep vacuum treatment time. The ultimate vacuum pressure of the vacuum chamber is greater than 50Pa, and the deep vacuum treatment time is ≤5min when the vacuum pressure of the vacuum chamber is ≤100Pa in the late stage of nitrogen addition.

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