RH refining decarburization and chromium protection method

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to an RH refining decarburization and chromium protection method which comprises the following steps: controlling the composition and flow of top lance blowing in the decarburization process, and cooperatively controlling the RH refining vacuum degree, the ascending pipe blowing flow and type, the content of dissolved oxygen in molten steel and the like by controlling the molten steel entering temperature and the RH dip pipe insertion depth. And efficient decarburization and chromium protection are realized. The advantages of RH vacuum refining are applied, the metallurgical effect of dispersed tiny hydrogen bubbles is exerted, control over oxygen in the molten steel is integrated, decarburization refining of the high-chromium molten steel is achieved, the production cost is reduced, and carbon emission in the high-chromium steel production process is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and particularly to a method for decarburization and chromium protection in RH refining. Background Art

[0002] In the smelting and refining of stainless steel and high-chromium steel, AOD and VOD are often used for decarburization and chromium protection smelting or refining, and the technology is relatively mature. However, due to the limitations of metallurgical thermodynamics and kinetics, it is difficult to achieve deep decarburization in AOD, and the decarburization efficiency of VOD is slow. Relatively speaking, RH has good thermodynamic and kinetic conditions for decarburization. However, there is little research on the decarburization and chromium protection smelting and refining of stainless steel and high-chromium steel by RH, and the related technology is very lacking. China has a large number of RH equipment. With the continuous increase in the demand for stainless steel and high-chromium steel, using RH for decarburization and chromium protection refining can make full use of the advantages of a large number of RH equipment in China, high RH decarburization efficiency, and the ability to achieve deep decarburization, forming a new productive force for producing stainless steel and high-chromium steel. However, when using RH for decarburization and chromium protection refining, the process technology is scarce, and it is difficult to achieve efficient decarburization and chromium protection. Summary of the Invention

[0003] To solve the problems existing in this technology, the main object of the present invention is to propose a method for decarburization and chromium protection in RH refining.

[0004] According to one aspect of the present invention, the following technical solutions are provided:

[0005] A method for decarburization and chromium protection in RH refining, comprising the following steps:

[0006] S1. After the RH enters the station, insert the RH immersion tube into the molten steel in the ladle;

[0007] S2. After the RH evacuates, conduct refining, blow hydrogen-rich gas through the riser pipe, generate dispersed tiny hydrogen bubbles in the molten steel in the vacuum tank, and promote the oxidation of carbon in the molten steel in the vacuum tank;

[0008] S3. When the opportunity to start blowing the oxygen-argon mixed gas for decarburization is met, spray the oxygen-argon mixed gas into the vacuum tank through the top lance arranged at the top of the vacuum tank to promote decarburization and chromium protection, and the oxygen-argon ratio in the oxygen-argon mixed gas gradually decreases as the carbon concentration in the molten steel decreases;

[0009] S4. After decarburization is completed, reduce the insertion depth of the RH immersion tube, switch the gas blown through the riser pipe to argon, and add a deoxidizer from the vacuum tank for refining.

[0010] The beneficial effects of the present invention are as follows:

[0011] The present invention provides a method for decarburization and chromium preservation in RH refining. During the decarburization process, the composition and flow rate of the top lance blowing are controlled, and by controlling the temperature of the molten steel entering the station, the insertion depth of the RH immersion tube, synergistically controlling the RH refining vacuum degree, the flow rate and type of the gas blown into the riser tube, the content of dissolved oxygen in the molten steel, etc., efficient decarburization and chromium preservation are achieved. By applying the advantages of RH vacuum refining, giving play to the metallurgical effect of dispersed tiny hydrogen bubbles, and comprehensively controlling the oxygen in the molten steel, decarburization refining of high-chromium molten steel is realized, the production cost is reduced, and the carbon emission during the production process of high-chromium steel is reduced. Detailed implementation mode

[0012] The technical solutions in the embodiments will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0013] A method for decarburization and chromium preservation in RH refining includes the following steps:

[0014] S1. After the RH enters the station, insert the RH immersion tube into the molten steel in the ladle;

[0015] S2. After the RH evacuates the vacuum, carry out refining. Blow hydrogen-rich gas into the riser tube to generate dispersed tiny hydrogen bubbles in the molten steel in the vacuum tank, and promote the oxidation of carbon in the molten steel in the vacuum tank;

[0016] S3. When the opportunity to start blowing the oxygen-argon mixed gas for decarburization is met, spray the oxygen-argon mixed gas into the vacuum tank through the top lance arranged on the top of the vacuum tank to promote decarburization and chromium preservation. The oxygen-argon ratio in the oxygen-argon mixed gas gradually decreases as the carbon concentration in the molten steel decreases;

[0017] S4. After the decarburization ends, reduce the insertion depth of the RH immersion tube, switch the gas blown into the riser tube to argon, and add a deoxidizer into the vacuum tank for refining.

[0018] Preferably, in the step S1, the temperature of the molten steel when the RH enters the station is greater than 1550 °C to ensure the thermodynamic conditions for decarburization and chromium preservation.

[0019] Preferably, in the step S1, the RH immersion tube is preferably inserted with a large depth as much as possible to facilitate more molten steel to enter the vacuum tank and inhibit the overoxidation and splashing of the molten steel in the vacuum tank. Further preferably, the insertion depth of the RH immersion tube is 500 - 1000 mm. Specifically, the insertion depth of the RH immersion tube can be, for example, any one of 500 mm, 550 mm, 600 mm, 650 mm, 700 mm, 750 mm, 800 mm, 850 mm, 900 mm, 950 mm, 1000 mm or the range between any two of them.

[0020] Preferably, in the step S1, the chromium content of the molten steel entering the RH is 8-35 wt%, and the carbon content is 0.05-1.0 wt%.

[0021] Preferably, in the step S2, blowing hydrogen-rich gas through the riser tube can generate dispersed tiny hydrogen bubbles in the molten steel in the vacuum tank, promoting the oxidation of carbon in the molten steel in the vacuum tank; the hydrogen-rich gas is a mixed gas of hydrogen-containing gas and nitrogen-containing gas; more preferably, the hydrogen-containing gas can be hydrogen, natural gas, ammonia, etc., and the nitrogen-containing gas can be nitrogen, ammonia, etc.; even more preferably, the mass percentage of hydrogen in the hydrogen-rich gas is 15-100 wt%. Specifically, the mass percentage of hydrogen in the hydrogen-rich gas can be, for example, any one of 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 100 wt% or the range between any two of them.

[0022] Preferably, in the step S2, the flow rate of the hydrogen-rich gas is 1000-4000 NL / min. Specifically, the flow rate of the hydrogen-rich gas can be, for example, any one of 1000 NL / min, 1500 NL / min, 2000 NL / min, 2500 NL / min, 3000 NL / min, 3500 NL / min, 4000 NL / min or the range between any two of them.

[0023] Preferably, in the step S3, the timing of starting to blow the oxygen-argon mixed gas for decarburization includes:

[0024] (1) Increasing the RH vacuum degree to the ultimate vacuum degree;

[0025] (2) The RH vacuum pressure reaches below 5 kPa;

[0026] (3) The oxygen content of the molten steel in the vacuum tank is lower than 150×10 -6 ;

[0027] (4) The decarburization reaction is slow;

[0028] When at least one of the conditions (1)-(4) is met, the oxygen-argon mixed gas can be blown to start decarburization.

[0029] Preferably, in the step S3, the decarburization reaction situation is judged according to the tumbling and boiling state of the molten steel in the vacuum tank or the CO content of the RH tail gas; more preferably, when it is determined according to the camera information of the molten steel surface in the vacuum tank that the tumbling and boiling of the molten steel in the vacuum tank is weak or the CO concentration in the RH tail gas (the CO concentration in the tail gas is 10-30 vol%) is low, the decarburization reaction is considered slow.

[0030] Preferably, in the step S3, the oxygen-argon mixed gas is blown in a small flow rate to prevent the molten steel from being over-oxidized; more preferably, the flow rate of the oxygen-argon mixed gas is 300-2000 NL / min; specifically, the flow rate of the oxygen-argon mixed gas is any one of 300 NL / min, 400 NL / min, 500 NL / min, 600 NL / min, 700 NL / min, 800 NL / min, 900 NL / min, 1000 NL / min, 1100 NL / min, 1200 NL / min, 1300 NL / min, 1400 NL / min, 1500 NL / min, 1600 NL / min, 1700 NL / min, 1800 NL / min, 1900 NL / min, 2000 NL / min or the range between any two of them.

[0031] Preferably, in the step S3, the proportion of oxygen in the oxygen-argon mixed gas ≥ 5 vol%. More preferably, when the carbon content in the molten steel ≥ 0.1 wt%, the proportion of oxygen in the oxygen-argon mixed gas ≥ 20 vol%.

[0032] Preferably, in the step S3, when blowing the oxygen-argon mixed gas into the vacuum tank through the top lance arranged at the top of the vacuum tank, the flow rate of the hydrogen-rich gas in the riser is 300-2000 NL / min. Specifically, the flow rate of the hydrogen-rich gas in the riser is any one of 300 NL / min, 400 NL / min, 500 NL / min, 600 NL / min, 700 NL / min, 800 NL / min, 900 NL / min, 1000 NL / min, 1100 NL / min, 1200 NL / min, 1300 NL / min, 1400 NL / min, 1500 NL / min, 1600 NL / min, 1700 NL / min, 1800 NL / min, 1900 NL / min, 2000 NL / min or the range between any two of them.

[0033] Preferably, in the step S3, in the RH decarburization and chromium protection stage, the dissolved oxygen in the ladle molten steel is controlled at (40-250)×10 -6 , inhibiting the oxidation of chromium in the molten steel and at the same time ensuring the rapid progress of the carbon-oxygen reaction in the vacuum tank. Specifically, the dissolved oxygen in the ladle molten steel can be, for example, 40×10 -6 , 50×10 -6 , 60×10 -6 , 70×10 -6 , 80×10 -6 , 90×10 -6 , 100×10 -6 , 110×10 -6 , 120×10-6 、 130×10 -6 、 140×10 -6 、 150×10 -6 、 160×10 -6 、 170×10 -6 、 180×10 -6 、 190×10 -6 、 200×10 -6 、 210×10 -6 、 220×10 -6 、 230×10 -6 、 240×10 -6 、 250×10 -6 The range between any one or any two of them.

[0034] Preferably, in the step S3, the blowing process of the oxygen-argon mixed gas is stage blowing, that is, after blowing a certain amount of oxygen-argon mixed gas by the top lance, the oxygen content of the molten steel in the ladle is detected and evaluated. When the oxygen content of the molten steel in the ladle is (180 - 250)×10 -6 , stop blowing the oxygen-argon mixed gas. At this time, there can be a relatively high dissolved oxygen in the molten steel in the vacuum tank for the decarburization and chromium protection reaction, but it will not cause the peroxidation of chromium in the molten steel when the molten steel enters the ladle; and when the oxygen content of the molten steel in the ladle is less than 100×10 -6 , blow a certain amount of oxygen-argon mixed gas with a reduced oxygen content again by the top lance to promote the decarburization reaction in the molten steel in the vacuum tank, and so on.

[0035] Preferably, in the step S3, when the dissolved oxygen in the molten steel in the ladle is greater than 250×10 -6 , the top lance does not blow air, increase the flow rate of the hydrogen-rich gas in the riser to 1000 - 4000 NL / min, and add an oxygen adjusting agent to the molten steel through the vacuum tank to lower the oxygen in the molten steel and avoid the peroxidation of chromium. Specifically, the flow rate of the hydrogen-rich gas in the riser can be any one or the range between any two of, for example, 1000 NL / min, 1500 NL / min, 2000 NL / min, 2500 NL / min, 3000 NL / min, 3500 NL / min, 4000 NL / min.

[0036] Preferably, in the step S3, the oxygen adjusting agent is an aluminum-based oxygen adjusting agent or a silicon-based oxygen adjusting agent, and the addition amount of the oxygen adjusting agent is 0.01 - 0.1 kg / t 钢 . Specifically, the addition amount of the oxygen adjusting agent can be, for example, 0.01 kg / t 钢 、 0.02 kg / t 钢 、 0.03 kg / t 钢 、 0.04 kg / t 钢 、 0.05 kg / t 钢, 0.06 kg / t 钢 , 0.07 kg / t 钢 , 0.08 kg / t 钢 , 0.09 kg / t 钢 , 0.1 kg / t 钢 or the range between any two of them.

[0037] Preferably, in step S4, the insertion depth of the RH dipping tube is 400 - 700 mm. Specifically, the insertion depth of the RH dipping tube can be, for example, any value within the range of 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, 650 mm, 700 mm or the range between any two of them.

[0038] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0039] Example 1

[0040] In a 100t RH refining device of a domestic steel mill, the carbon content in the molten steel entering the RH is 0.3 wt%, the chromium content is 17.2 wt%, and the target decarburization is to 0.05 wt%.

[0041] Before RH refining, the temperature of the molten steel is raised by the LF furnace, and the temperature of the molten steel entering the RH is controlled at 1600°C; after the ladle trolley is driven to the molten steel receiving position, the ladle of the RH refining device is lifted so that the RH dipping tube is inserted into the molten steel in the ladle of the RH refining device, and the insertion depth of the RH dipping tube is 900 mm; the vacuum system is started to evacuate, and the liquid level of the molten steel is raised; after 0.5 minutes, the pressure in the vacuum tank is 9800 Pa, and immediately a hydrogen-argon mixed gas is blown into the molten steel through the RH riser tube. There are 16 blowing pipes in the RH riser tube, and the flow rate of the blown hydrogen-argon mixed gas is 2500 NL / min. The proportion of hydrogen in the hydrogen-argon mixed gas is 80 vol%; after 2 minutes of refining, the pressure in the vacuum tank drops to 2000 Pa, and after another 0.5 minutes, the oxygen content in the molten steel drops to 95×10 -6 , the oxygen-argon mixed gas of 90 vol% oxygen + 10 vol% argon is blown from the top lance of the RH refining vacuum tank, and the oxygen-argon mixed gas is blown for 200 m 3 , the blowing flow rate is 2000 NL / min, and at the same time, the blowing flow rate of the riser tube is adjusted to 1200 NL / min; after the oxygen-argon mixed gas is blown out, the oxygen content in the molten steel is measured to be 198×10 -6 , continue the vacuum treatment, raise the pressure in the vacuum tank to 100 Pa, and at the same time adjust the blowing flow rate of the riser tube to 2500 NL / min; after 2 minutes of refining, the oxygen content in the steel drops to 78×10 -6 , lower the pressure in the vacuum tank to 80 Pa, and blow the oxygen-argon mixed gas from the top lance of the RH refining vacuum tank, and the oxygen-argon mixed gas is blown for 200 m 3, the blowing gas flow rate is 2000 NL / min, the oxygen-argon mixed gas composition is 70 vol% oxygen + 30 vol% argon. At the same time, adjust the blowing gas flow rate of the riser pipe to 1200 NL / min. After blowing the oxygen-argon mixed gas, the oxygen content in the molten steel is 195×10 -6 , continue the vacuum treatment, and at the same time adjust the blowing gas flow rate of the riser pipe to 2500 NL / min; after 3 minutes of refining, the oxygen in the steel is reduced to 80×10 -6 , use the top lance of the RH refining vacuum tank to blow the oxygen-argon mixed gas, and blow the oxygen-argon mixed gas for 200 m 3 , the blowing gas flow rate is 2000 NL / min, the oxygen-argon mixed gas composition is 50 vol% oxygen + 50 vol% argon. At the same time, adjust the blowing gas flow rate of the riser pipe to 1200 NL / min; after blowing the oxygen-argon mixed gas, measure the oxygen content in the ladle steel to be 193×10 -6 , continue the vacuum treatment, the pressure drop of the vacuum tank is 50 Pa, and at the same time adjust the blowing gas flow rate of the riser pipe to 2500 NL / min; after 3 minutes of refining, the oxygen content in the steel is reduced to 85×10 -6 , use the top lance of the RH refining vacuum tank to start blowing the oxygen-argon mixed gas, and blow the oxygen-argon mixed gas for 200 m 3 , the blowing gas flow rate is 2000 NL / min, the mixed gas composition is 30 vol% oxygen + 70 vol% argon. At the same time, adjust the blowing gas flow rate of the riser pipe to 1200 NL / min; after blowing the oxygen-argon mixed gas, measure the oxygen content in the ladle steel to be 195×10 -6 , continue the vacuum treatment, the pressure drop of the vacuum tank is 45 Pa; measure the carbon content in the molten steel to be 0.048 wt%, and the chromium content to be 17.0 wt%, meeting the requirements of molten steel refining and achieving decarburization and chromium protection. The riser pipe is switched to argon blowing refining, and the argon blowing flow rate of the riser pipe is increased to 2800 NL / min; and the immersion tube insertion depth is reduced to 500 mm. After 3 minutes, add a deoxidizer for deoxidation, and continue refining for 8 minutes to end the refining.

[0042] Example 2

[0043] For an 80t RH refining device in a domestic steel plant, the temperature of the molten steel entering the RH is 1590 °C, the chromium content of the molten steel entering the station is 15 wt%, the carbon content is 0.2 wt%, and the target carbon content is 0.03 wt%.

[0044] After the ladle car is moved to the molten steel receiving position, the ladle of the RH refining device is lifted so that the insertion depth of the RH immersion tube is 850 mm; the vacuum system is started to evacuate, and the liquid level of the molten steel is raised; after 0.5 minutes, the pressure in the vacuum tank is 8000 Pa, and a hydrogen-argon mixed gas is immediately blown into the molten steel through the RH riser tube. The flow rate of the blown mixed gas is 2300 NL / min, and the hydrogen content in the hydrogen-argon mixed gas is 85 vol%. After 2 minutes of refining, the pressure in the vacuum tank drops to 1000 Pa. The video camera of the molten steel surface in the vacuum tank shows that the carbon-oxygen reaction in the vacuum tank is intense and the splashing of the molten steel is relatively serious; after another 1.0 minute, the oxygen content in the molten steel drops to 80×10 -6 , the volume concentration of CO in the RH tail gas is 25 vol%. The oxygen-argon mixed gas of 80 vol% oxygen + 20 vol% argon is blown from the top by the oxygen lance in the RH refining vacuum tank, and the oxygen-argon mixed gas is blown for 200 m 3 , the blowing flow rate is 2000 NL / min, and at the same time, the blowing flow rate of the riser tube is adjusted to 1200 Nl / min; after blowing the oxygen-argon mixed gas, the oxygen content in the molten steel is measured to be 218×10 -6 , continue the vacuum treatment, increase the pressure in the vacuum tank to 80 Pa, and at the same time adjust the blowing flow rate of the riser tube to 2500 NL / min; after 2 minutes of refining, the oxygen content in the steel drops to 83×10 -6 , reduce the pressure in the vacuum tank to 60 Pa, and blow the oxygen-argon mixed gas from the top gun of the RH refining vacuum tank. The oxygen-argon mixed gas is blown for 200 m 3 , the blowing flow rate is 2000 NL / min, the composition of the oxygen-argon mixed gas is 50 vol% oxygen + 50 vol% argon, and at the same time, the blowing flow rate of the riser tube is adjusted to 1200 NL / min. After blowing the oxygen-argon mixed gas, the oxygen content in the molten steel is measured to be 215×10 -6 , continue the vacuum treatment, and at the same time adjust the blowing flow rate of the riser tube to 2500 NL / min; after 3 minutes of refining, the oxygen content in the steel drops to 40×10 -6 , blow the oxygen-argon mixed gas from the top gun of the RH refining vacuum tank. The oxygen-argon mixed gas is blown for 140 m 3 , the blowing flow rate is 2000 NL / min, the composition of the oxygen-argon mixed gas is 30 vol% oxygen + 70 vol% argon, and at the same time, the blowing flow rate of the riser tube is adjusted to 1200 NL / min; after blowing the oxygen-argon mixed gas, the oxygen content in the molten steel is measured to be 223×10 -6 , continue the vacuum treatment, the pressure in the vacuum tank drops to 40 Pa, the carbon content in the molten steel is measured to be 0.026 wt%, and the chromium content is 15.0 wt%, meeting the requirements of molten steel refining and achieving decarburization and chromium preservation. The riser tube is switched to argon blowing for refining, and the argon blowing flow rate of the riser tube is increased to 2600 NL / min; and the insertion depth of the immersion tube is reduced to 500 mm. After 3 minutes, deoxidizer is added for deoxidation, and refining continues for 6 minutes to end the refining.

[0045] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made by using the content of the specification of the present invention under the inventive concept of the present invention, or any direct / indirect application in other related technical fields shall be included within the patent protection scope of the present invention.

Claims

1. A RH refining decarburization and chromium preservation method, characterized in that: The steps include: S1. After RH enters the station, insert the RH immersion tube into the molten steel in the ladle; S2 and RH are refined after vacuuming, and hydrogen-rich gas is blown into the riser to generate dispersed tiny hydrogen bubbles in the molten steel in the vacuum tank, which promotes the oxidation of carbon in the molten steel in the vacuum tank; S3. When the time for blowing oxygen-argon mixed gas for decarburization is met, the oxygen-argon mixed gas is sprayed into the vacuum tank through the top gun arranged on the top of the vacuum tank to promote decarburization and chromium preservation. The oxygen-argon ratio in the oxygen-argon mixed gas gradually decreases as the carbon concentration in the molten steel decreases. S4. After decarburization is completed, the insertion depth of the RH immersion tube is reduced, the gas blown into the riser is switched to argon, and a deoxidizer is added from the vacuum tank for refining.

2. The RH refining, decarburization and chromium preservation method according to claim 1, characterized in that: In step S1, the temperature of the RH inlet molten steel is greater than 1550°C.

3. The RH refining, decarburization and chromium preservation method according to claim 1, characterized in that: In the step S1, the insertion depth of the RH immersion tube is 500-1000 mm.

4. The RH refining, decarburization and chromium preservation method according to claim 1, characterized in that: In the step S1, the chromium content of the RH incoming steel liquid is 8-35wt%, and the carbon content is 0.05-1.0wt%.

5. The RH refining decarburization and chromium preservation method according to claim 1, characterized in that: In step S2, the mass percentage of hydrogen in the hydrogen-rich gas is 15-100wt%; and the flow rate of the hydrogen-rich gas is 1000-4000NL / min.

6. The RH refining decarburization and chromium preservation method according to claim 1, characterized in that: In step S3, the timing of starting to blow oxygen-argon mixed gas for decarburization includes: (1) Increase the RH vacuum to the ultimate vacuum; (2) RH vacuum pressure reaches below 5 kPa; (3) The oxygen content of liquid steel in the vacuum tank is less than 150×10 -6 ; (4) The decarburization reaction is slow; When at least one of the timings (1) to (4) is met, blowing of the oxygen-argon mixed gas for decarburization is started.

7. The RH refining, decarburization and chromium preservation method according to claim 1, characterized in that: In step S3, the flow rate of the oxygen-argon mixed gas is 300-2000 NL / min; the proportion of oxygen in the oxygen-argon mixed gas is ≥5 vol%.

8. The RH refining decarburization and chromium preservation method according to claim 1, characterized in that: In step S3, when the oxygen-argon mixed gas is sprayed into the vacuum tank through the top gun arranged on the top of the vacuum tank, the flow rate of the hydrogen-rich gas in the riser is 300-2000 NL / min; when the dissolved oxygen in the ladle steel liquid is greater than 250×10 -6 When the top gun is not blown, the flow rate of hydrogen-rich gas in the riser is increased to 1000-4000NL / min, and an oxygen regulator is added to the molten steel through a vacuum tank. The oxygen regulator is an aluminum oxygen regulator or a silicon oxygen regulator, and the amount of oxygen regulator added is 0.01-0.1kg / t 钢 .

9. The RH refining, decarburization and chromium preservation method according to claim 1, characterized in that: In step S3, during the RH decarburization and chromium preservation stage, the dissolved oxygen in the ladle steel liquid is controlled to be (40-250)×10 -6 The oxygen-argon mixed gas injection process is staged injection, that is, a certain amount of oxygen-argon mixed gas is injected by the top gun to detect or evaluate the oxygen content of the ladle steel liquid. The oxygen content of the ladle steel liquid is (180-250)×10 -6 Stop blowing oxygen-argon mixed gas; when the oxygen content of ladle steel liquid is less than 100×10 -6 When the oxygen content is reduced, a certain amount of oxygen-argon mixed gas with reduced oxygen content is sprayed by the top gun again; and so on.

10. The RH refining decarburization and chromium preservation method according to claim 1, characterized in that: In step S4, the RH immersion tube is inserted to a depth of 400-700 mm.