Control method for stabilizing nitrogen increase of molten steel by using nitrogen in argon station

Abstract

The invention relates to a control method for stabilizing nitrogen increase of molten steel by using nitrogen in an argon station, and the production method comprises the following steps: accurately controlling the oxidability of converter tapping, combined blowing of gas, gas stirring control after tapping, alloying in the tapping process, use of nitrogen-containing alloy and the like, so that the nitrogen content is increased to 130-240 ppm, and the fluctuation of the nitrogen content of the same steel grade is controlled within 40 ppm; according to the method, a part of alloy is replaced by a relatively cheap nitrogen medium, so that the effects of saving energy and reducing consumption are achieved, and the problems of large nitrogen blowing and increasing fluctuation and easy generation of blow-by in the smelting process are well solved. According to the invention, the nitrogen content is integrally increased from the previous 86.4 ppm to 128.4 ppm, the steel strength is improved by about 30-50 Mpa, and the alloy cost is reduced by about 20 yuan / ton; the fluctuation of the nitrogen content is reduced and is reduced from 188 ppm to 40 ppm; and by means of automatic switching of the nitrogen and argon valve set, blow-by of nitrogen and argon is eradicated, and the influence on production of other steel types is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, and in particular to a control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station. Background Art

[0002] After the molten steel from the converter enters the ladle, the main gas medium used in the smelting process is argon. The composition and temperature are adjusted and inclusions are removed by stirring the molten steel with inert gas. Excessive nitrogen content will make the steel brittle and is generally considered a harmful element. However, nitrogen can refine the grains in steel and improve strength and toughness. For example, in rebar, the strength can be improved by increasing the nitrogen content in the steel. There are two ways to increase the nitrogen content: alloy nitrogen addition and nitrogen gas blowing. Nitrogen blowing in the ladle has become a smelting method.

[0003] A research institute studied the effect of vanadium-nitrogen microalloying on the yield strength of steel bars. Under the condition of maintaining the same or similar strength, steel with vanadium-nitrogen alloy can save more than 33.3% of vanadium. A steel plant conducted a comparative test of argon blowing and nitrogen blowing in 80tLF. LF was stirred with argon blowing, and the nitrogen content of LF molten steel was (28-36)×10 -6 , nitrogen absorption (8~15)×10 -6 LF is stirred with nitrogen blowing, and the nitrogen content of LF molten steel is (90~211)×10 -6 , nitrogen absorption (66~186)×10 -6 .

[0004] There are currently two main problems with nitrogen blowing and nitrogen addition: one is that the nitrogen content fluctuates greatly after nitrogen addition. The nitrogen content of a certain factory was between 65 and 243 ppm after nitrogen addition, so it was forced to change to alloy nitrogen addition; the other is that gas cross-talk is prone to occur when nitrogen and argon gases are used at the same time, as shown in the figure below. Once gas cross-talk occurs, the nitrogen content of other steel grades will increase, resulting in batch quality accidents. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a control method for using nitrogen to stabilize the nitrogen increase of molten steel in an argon station, which can accurately control the oxidizability of converter steel tapping, re-blowing gas, gas stirring control after steel tapping, alloying during steel tapping, use of nitrogen-containing alloys, etc., so as to achieve the effect of replacing part of the alloy with relatively cheap nitrogen medium, thereby achieving energy saving and consumption reduction.

[0006] The technical solution adopted by the present invention is: a control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station, characterized in that it comprises the following steps:

[0007] S1. The oxygen flow rate during converter blowing is controlled at 3.4~3.75m 3 / min.t, nitrogen is supplied by the combined blowing system during the whole blowing process, with a nitrogen flow rate of 100~200m 3 / h, tapping temperature 1650~1680℃, tapping carbon 0.05~0.10%;

[0008] S2. Deoxidation and alloying during steel tapping: Silicon alloy and / or manganese alloy are added to 1 / 3 of the steel tapping, followed by nitrogen-containing alloy. Nitrogen is blown for 3 to 5 minutes at the end of steel tapping, with a nitrogen flow rate of 180 to 250 m 3 / h;

[0009] S3. Arrive at the argon station for temperature measurement and sampling. According to the nitrogen content value tested, adjust the ladle blowing medium. Nitrogen blowing time (min) = (target nitrogen content - nitrogen content at the station) / (5-10), nitrogen flow rate 100-200m 3 / h; after the nitrogen blowing time reaches the calculated value, the ladle medium is switched to argon, and the temperature and composition are adjusted synchronously before pouring on the casting machine.

[0010] Preferably, the steel is silicon deoxidized killed steel, the nitrogen content is controlled at 130-240 ppm, and the nitrogen content fluctuation in standard steel of the same composition is ≤40 ppm.

[0011] Preferably, in step S1, the scrap steel ratio of the converter is between 150 and 200 kg / t, argon is not turned on during the whole process of the converter re-blowing, and the oxygen content of the converter steel is between 300 and 800 ppm.

[0012] Preferably, in step S2, the nitrogen blowing pipeline and the argon blowing pipeline are in the same pipeline network, are arranged in parallel, and have a safety switching function.

[0013] Preferably, pressure regulating valves, pneumatic valves and check valves are installed in sequence on both nitrogen and argon branches. The pneumatic valves are remotely controlled, a group of bypass control valves are connected in parallel to the pneumatic valves, and a check valve is connected in series behind the pneumatic valves. The ends of the nitrogen and argon branches are merged and connected to the ladle.

[0014] Preferably, in step S2, the nitrogen-containing alloy includes vanadium nitrogen, silicon nitride and silicon manganese nitride alloy; when the vanadium content in the steel is lower than 0.01%, 0.5-1.0 kg / t of silicon manganese nitride is added; when the vanadium content in the steel is between 0.01% and 0.10%, all vanadium nitrogen alloy is used; when the vanadium content in the steel is greater than 0.10%, the amount of vanadium nitrogen alloy added is ≤1.2 kg / t, and the insufficient part is increased by vanadium iron alloy.

[0015] Preferably, in step S3, the cumulative nitrogen blowing time for the entire furnace of steel is 6 to 14 minutes.

[0016] Preferably, in step S3, when the nitrogen at the station is lower than 80 ppm, the bypass valve is opened and the nitrogen flow rate is increased to 200-300 m 3 / h, strong nitrogen blowing for 2 to 3 minutes.

[0017] The beneficial effects achieved by the present invention are as follows: the present invention precisely controls the oxidizability of steel tapping from the converter, the combined gas blowing, the gas stirring control after steel tapping, the alloying during the steel tapping process, the use of nitrogen-containing alloys, etc., so that the nitrogen content is increased to 130-240ppm, and the nitrogen content fluctuation of the same steel grade is controlled within 40ppm, so that part of the alloy is replaced by a relatively cheap nitrogen medium, which has the effect of energy saving and consumption reduction, and well solves the problem of large fluctuations in nitrogen blowing and nitrogen addition during the smelting process and easy occurrence of cross-gas. The nitrogen content of the present invention is increased overall from 86.4ppm to 128.4ppm, which increases the strength of the steel by about 30-50Mpa and reduces the alloy cost by about 20 yuan / ton; the fluctuation of nitrogen content becomes smaller, from 188ppm to 40ppm; safe gas use is achieved, and the nitrogen and argon cross-gas is eliminated through automatic switching of the nitrogen and argon valve group, which affects the production of other steel grades; the present invention has the following advantages:

[0018] 1. By controlling the oxygen supply flow rate, re-blowing gas and flow rate of the converter, the nitrogen content of the steel tapping from the converter can be stably increased. According to field experience, when the nitrogen content of the steel tapping is less than 20ppm, the nitrogen-enhancing effect of the subsequent process is poor;

[0019] 2. By controlling the steel-tapping temperature of the converter, the actual blowing and stirring time after steel-tapping can be prevented from being greatly affected by the temperature, which may cause the nitrogen blowing to be stopped due to low temperature;

[0020] 3. Require scrap steel ratio and tapping carbon, stabilize tapping nitrogen content. The higher the oxygen in molten steel, the less likely it is to absorb nitrogen. However, operations that lead to high oxygen may increase the nitrogen content in molten steel. Stabilizing tapping nitrogen content is an important factor to ensure accurate control of nitrogen content.

[0021] 4. Control the valve group of nitrogen and argon gas to solve the problem of nitrogen and argon cross-flow. By adjusting the pressure, the nitrogen pressure is less than the argon pressure. Add a set of check valves to prevent the possibility of nitrogen cross-flowing into argon. Through the solenoid valve, the precise control of the blowing flow can be achieved;

[0022] 5. Adding silicon manganese first and then nitrogen-containing alloy is mainly to reduce the oxygen content of steel first and increase the nitrogen yield;

[0023] 6. Control the argon blowing flow rate of the ladle at different stages. The main purpose is to promote nitrogen increase with a large flow rate in the early stage, and to adjust it appropriately in the middle and late stages to stabilize the nitrogen increase rate. When the nitrogen content in the steel is low, use the bypass valve to further increase the flow rate.

[0024] 7. Control the nitrogen blowing time to 6 to 14 minutes, mainly to prevent inaccurate nitrogen content in process testing. The nitrogen blowing time control range is obtained based on a large amount of data. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the pipeline connection of nitrogen and argon;

[0026] Among them: 1. Pressure regulating valve; 2. Pneumatic valve; 3. Check valve; 4. Bypass valve. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. 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.

[0028] A control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station of the present invention comprises the following steps:

[0029] S1. The oxygen flow rate during converter blowing is controlled at 3.4~3.75m 3 / min.t, nitrogen is supplied by the combined blowing system during the whole blowing process, with a nitrogen flow rate of 100~200m 3 / h, tapping temperature 1650~1680℃, tapping carbon 0.05~0.10%;

[0030] S2. Deoxidation and alloying during steel tapping: Silicon alloy and / or manganese alloy are added to 1 / 3 of the steel tapping, followed by nitrogen-containing alloy. Nitrogen is blown for 3 to 5 minutes at the end of steel tapping, with a nitrogen flow rate of 180 to 250 m 3 / h;

[0031] S3. Arrive at the argon station for temperature measurement and sampling. According to the nitrogen content value tested, adjust the ladle blowing medium. Nitrogen blowing time (min) = (target nitrogen content - nitrogen content at the station) / (5-10), nitrogen flow rate 100-200m 3 / h; after the nitrogen blowing time reaches the calculated value, the ladle medium is switched to argon, and the temperature and composition are adjusted synchronously before pouring on the casting machine.

[0032] In this embodiment, the steel is silicon deoxidized killed steel, the nitrogen content is controlled at 130-240 ppm, and the nitrogen content fluctuation in standard steel with the same composition is ≤40 ppm.

[0033] In this embodiment, in step S1, the scrap steel ratio of the converter is between 150 and 200 kg / t, argon is not turned on during the whole process of the converter re-blowing, and the oxygen content of the converter steel is between 300 and 800 ppm.

[0034] Combination Figure 1 As shown, in this embodiment, in step S2, the nitrogen blowing pipeline and the argon blowing pipeline are in the same pipe network, arranged in parallel, and have a safety switching function. A pressure regulating valve 1, a pneumatic valve 2 and a check valve 3 are installed in sequence on the two branches of nitrogen and argon. The pneumatic valve 2 is remotely controlled, and a group of bypass control valves 4 are connected in parallel to the pneumatic valve 2. The check valve 3 is connected in series behind the pneumatic valve 2; the ends of the two branches of nitrogen and argon are merged and connected to the ladle.

[0035] In this embodiment, in step S2, the nitrogen-containing alloy includes vanadium nitrogen, silicon nitride and silicon manganese nitride alloy; when the vanadium content in the steel is less than 0.01%, 0.5-1.0 kg / t of silicon manganese nitride is added; when the vanadium content in the steel is 0.01-0.10%, all vanadium nitrogen alloy is used; when the vanadium content in the steel is greater than 0.10%, the amount of vanadium nitrogen alloy added is ≤1.2 kg / t, and the insufficient part is increased by vanadium iron alloy.

[0036] In this embodiment, in step S3, the cumulative time of nitrogen blowing for the entire furnace of steel is 6 to 14 minutes.

[0037] In this embodiment, in step S3, when the nitrogen at the station is lower than 80 ppm, the bypass valve is opened and the nitrogen flow rate is increased to 200-300 m 3 / h, strong nitrogen blowing for 2 to 3 minutes.

[0038] Example 1

[0039] Melting number A325487, steel grade HRB400, finished product nitrogen 135ppm. The process is as follows:

[0040] 1) The scrap steel ratio is 155kg / t, and the oxygen flow rate during the converter blowing process is controlled at 3.42m 3 / min.t, nitrogen gas is blown throughout the whole process, nitrogen flow rate is 125m 3 / h, tapping temperature 1672℃, tapping carbon 0.07%, tapping oxygen 511ppm;

[0041] 2) During the steel-making process, 20.5 kg / t of silicon-manganese alloy is first added, followed by 0.3 kg / t of vanadium-nitrogen alloy. After steel-making, nitrogen blowing is performed for 3.5 minutes, with a nitrogen flow rate of 212 m 3 / h;

[0042] 3) The temperature at the argon station is 1594℃, the nitrogen content is 73ppm, the bypass valve is opened to blow nitrogen for 3 minutes, and the nitrogen flow rate is 273m 3 / h, measured temperature at 1569, switched to argon gas and continued to cool down to 1559℃ before leaving the station and going to the casting machine for pouring.

[0043] Example 2

[0044] Melting number A312482, steel grade HRB400, finished product nitrogen 163ppm. The process is as follows:

[0045] 1) The scrap steel ratio is 188kg / t, and the oxygen flow rate during the converter blowing process is controlled at 3.64m 3 / min.t, nitrogen gas was blown throughout the whole process, nitrogen flow rate was 131m 3 / h, tapping temperature 1651℃, tapping carbon 0.08%, tapping oxygen 700ppm;

[0046] 2) During the steel-making process, 20.9 kg / t of silicon-manganese alloy was first added, followed by 0.38 kg / t of vanadium-nitrogen alloy. After steel-making, nitrogen blowing was performed for 3.9 minutes, with a nitrogen flow rate of 182 m 3 / h;

[0047] 3) The temperature at the argon station was 1588°C, the nitrogen content was 123ppm, the nitrogen blowing time was 5min, and the nitrogen flow rate was 154m 3 / h, measure the temperature at 1571, switch to argon gas and continue to cool down to 1557℃, then leave the station and go to the casting machine for pouring.

[0048] Example 3

[0049] Melting number A325480, steel grade HRB400, finished product nitrogen 131ppm. The process is as follows:

[0050] 1) The scrap steel ratio is 192kg / t, and the oxygen flow rate during the converter blowing process is controlled at 3.42m 3 / min.t, nitrogen gas was blown throughout the whole process, and the nitrogen flow rate was 139m 3 / h, tapping temperature 1665℃, tapping carbon 0.059%, tapping oxygen 505ppm;

[0051] 2) During the steel tapping process, 21.5 kg / t of silicon manganese alloy was first added, followed by 0.8 kg / t of silicon manganese nitride alloy. After the steel tapping was completed, nitrogen was blown for 4.2 minutes, with a nitrogen flow rate of 189 m 3 / h;

[0052] 3) The temperature at the argon station was 1594°C, the nitrogen content was 93ppm, the nitrogen blowing time was 3min, and the nitrogen flow rate was 178m 3 / h, measured temperature at 1577, switched to argon gas and continued to cool down to 1565℃ before leaving the station and going to the casting machine for pouring.

[0053] Example 4

[0054] Melting number A325495, steel grade HRB500, finished product nitrogen 167ppm. The process is as follows:

[0055] 1) The scrap steel ratio is 189kg / t, and the oxygen flow rate during the converter blowing process is controlled at 3.47m 3 / min.t, nitrogen gas is blown throughout the whole process, nitrogen flow rate is 169m 3 / h, tapping temperature 1671℃, tapping carbon 0.055%, tapping oxygen 614ppm;

[0056] 2) During the steel-making process, 23.5 kg / t of silicon-manganese alloy was first added, followed by 0.8 kg / t of vanadium-nitrogen alloy. After steel-making, nitrogen blowing was performed for 3.9 minutes, with a nitrogen flow rate of 197 m 3 / h;

[0057] 3) The temperature at the argon station was 1586°C, the nitrogen content was 123ppm, the nitrogen blowing time was 4.5min, and the nitrogen flow rate was 165m 3 / h, measured temperature at 1567, switched to argon gas and continued to cool down to 1558℃ before leaving the station and going to the casting machine for pouring.

[0058] Example 5

[0059] Melting number A325496, steel grade HRB500, finished product nitrogen 188ppm. The process is as follows:

[0060] 1) The scrap steel ratio is 192kg / t, and the oxygen flow rate during the converter blowing process is controlled at 3.68m 3 / min.t, nitrogen gas is blown throughout the whole process, nitrogen flow rate is 186m 3 / h, tapping temperature 1677℃, tapping carbon 0.08%, tapping oxygen 405ppm;

[0061] 2) During the steel-making process, 23.8 kg / t of silicon-manganese alloy is first added, followed by 0.68 kg / t of vanadium-nitrogen alloy. After steel-making, nitrogen blowing is performed for 4.5 minutes, with a nitrogen flow rate of 238 m 3 / h;

[0062] 3) The temperature at the argon station is 1612°C, the nitrogen content is 142ppm, the nitrogen blowing is 5min, and the nitrogen flow rate is 165m 3 / h, measured temperature at 1584, switched to argon gas and continued to cool down to 1564℃ before leaving the station and going to the casting machine for pouring.

[0063] Example 6

[0064] Melting number A325497, steel grade HRB500, finished product nitrogen 184ppm. The process is as follows:

[0065] 1) The scrap steel ratio is 165kg / t, and the oxygen flow rate during the converter blowing process is controlled at 3.59m 3 / min.t, nitrogen gas was blown throughout the whole process, nitrogen flow rate was 172m 3 / h, tapping temperature 1654℃, tapping carbon 0.081%, tapping oxygen 325ppm;

[0066] 2) During the steel-making process, 22.9 kg / t of silicon-manganese alloy was first added, followed by 0.76 kg / t of vanadium-nitrogen alloy. After steel-making, nitrogen blowing was performed for 3.9 minutes, with a nitrogen flow rate of 242 m 3 / h;

[0067] 3) The temperature at the argon station was 1579°C, the nitrogen content was 153ppm, the nitrogen blowing time was 4min, and the nitrogen flow rate was 164m 3 / h, measured temperature at 1565, switched to argon gas and continued to cool down to 1556℃ before leaving the station and going to the casting machine for pouring.

[0068] It should be noted that the description of the above technical solutions is exemplary, and this specification can be embodied in different forms and should not be interpreted as being limited to the technical solutions set forth herein. On the contrary, providing these descriptions will make the disclosure of the present invention thorough and complete, and will fully convey the scope disclosed in this specification to those skilled in the art. In addition, the technical solutions of the present invention are limited only by the scope of the claims.

[0069] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention should be considered to belong to the protection scope of the present invention.

Claims

1. A control method for stabilizing nitrogen addition in molten steel using nitrogen in an argon station, characterized in that: The following steps are involved: S1. The oxygen flow rate during converter blowing is controlled at 3.4~3.75m 3 / min.t, nitrogen is supplied by the combined blowing system during the whole blowing process, with a nitrogen flow rate of 100~200m 3 / h, tapping temperature 1650~1680℃, tapping carbon 0.05~0.10%; S2. Deoxidation and alloying during steel tapping: Silicon alloy and / or manganese alloy are added to 1 / 3 of the steel tapping, followed by nitrogen-containing alloy. Nitrogen is blown for 3 to 5 minutes after steel tapping is completed, with a nitrogen flow rate of 180 to 250 m 3 / h; S3. Arrive at the argon station for temperature measurement and sampling. According to the nitrogen content value tested, adjust the ladle blowing medium. Nitrogen blowing time = (target nitrogen content - nitrogen content at the station) / (5-10), nitrogen flow rate 100-200m 3 / h; after the nitrogen blowing time reaches the calculated value, the ladle medium is switched to argon, and the temperature and composition are adjusted synchronously before pouring on the casting machine.

2. The control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station according to claim 1, characterized in that: The steel type is silicon deoxidized killed steel, and the nitrogen content is controlled at 130-240ppm. The nitrogen content fluctuation in standard steel with the same composition is ≤40ppm.

3. The control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station according to claim 1, characterized in that: In step S1, the scrap steel ratio of the converter is between 150 and 200 kg / t, argon is not turned on during the whole process of the converter re-blowing, and the oxygen content of the converter steel is between 300 and 800 ppm.

4. The control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station according to claim 1, characterized in that: In step S2, the nitrogen blowing pipeline and the argon blowing pipeline are in the same pipeline network, are arranged in parallel, and have a safe switching function.

5. The control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station according to claim 4, characterized in that: Pressure regulating valves, pneumatic valves and check valves are installed in sequence on the nitrogen and argon branches. The pneumatic valves are remotely controlled. A group of bypass control valves are connected in parallel to the pneumatic valves. A check valve is connected in series behind the pneumatic valves. The ends of the nitrogen and argon branches are merged and connected to the ladle.

6. The control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station according to claim 1, characterized in that: In step S2, the nitrogen-containing alloy includes vanadium nitrogen, silicon nitride and silicon nitride manganese alloy; when the vanadium content in the steel is less than 0.01%, 0.5-1.0 kg / t of silicon manganese nitride is added; when the vanadium content in the steel is 0.01-0.10%, all vanadium nitrogen alloy is used; when the vanadium content in the steel is greater than 0.10%, the amount of vanadium nitrogen alloy added is ≤1.2 kg / t, and the insufficient part is increased by vanadium iron alloy.

7. The control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station according to claim 1, characterized in that: In step S3, the cumulative nitrogen blowing time for the entire furnace of steel is 6 to 14 minutes.

8. The control method for stabilizing nitrogen addition in molten steel by using nitrogen in an argon station according to claim 5, characterized in that: In step S3, when the nitrogen at the station is lower than 80 ppm, the bypass valve is opened and the nitrogen flow rate is increased to 200-300 m 3 / h, strong nitrogen blowing for 2 to 3 minutes.

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