A vacuum smelting method for precise nitrogen control in smelting nitrogen-containing steel

Abstract

This invention discloses a vacuum smelting method for precise nitrogen control in the smelting of nitrogen-containing steel. The method comprises: 1) loading the furnace and drawing a vacuum, then heating with electricity until the molten steel is completely melted; 2) maintaining the vacuum for refining, and stopping the vacuum process after refining; 3) rapidly introducing nitrogen gas to a nitrogen atmosphere of 0.06 MPa to 0.075 MPa, and adding a nitride alloy under this atmosphere; the amount of nitride alloy added is calculated according to the target nitrogen content using a formula; 4) after adding the nitride alloy, tapping the steel while continuously charging with nitrogen gas. This method, starting from the dissolution kinetics and thermodynamic behavior of nitrogen, precisely controls the nitrogen content in the steel by fixing the nitriding time and pressure and using relevant formulas to calculate the yield of the nitride alloy. The deviation of the smelted nitrogen-containing steel from the target value can be controlled within 0.015%, achieving precise nitrogen control in the smelting of nitrogen-containing steel. This method has advantages such as fast smelting speed, precise nitrogen control, low cost, strong controllability, pure molten steel, and dense ingots.

Description

Technical Field

[0001] This invention relates to the field of steelmaking and smelting technology, and in particular to a vacuum smelting method for precisely controlling nitrogen content in nitrogen-containing steel. Background Technology

[0002] Nitrogen, a common gaseous element, is a strong austenite-forming element. In duplex stainless steel, it has the ability to expand and stabilize the austenite structure, contributing 30 times more to austenite formation than nickel. The addition of nitrogen significantly improves the corrosion resistance of stainless steel. Furthermore, nitrogen can enhance austenite stability and reduce the formation rate of harmful intermetallic phases. The solid solution strengthening and grain refinement properties of nitrogen can improve the strength, wear resistance, and corrosion resistance of steel. Therefore, nitrogen is often added to some stainless steels, grain-oriented silicon steels, high-manganese steels, microalloyed steels, and some quenched and tempered steels.

[0003] Currently, there are several methods for nitrogen addition: one is using a pressurized induction furnace, which employs high nitrogen pressure for nitriding or alloy nitriding. For example, patent application CN102888550A provides a method for smelting high-purity, high-nitrogen duplex stainless steel. This process is only applicable to specific steel grades and the pressure is 3 to 7 times atmospheric pressure, requiring high-quality equipment and posing a significant risk. Another method involves using a vacuum induction furnace filled with nitrogen for vapor-phase nitriding. This method produces pure, uniformly structured nitrogen-containing molten steel, but the nitrogen content is difficult to control. A third method involves adding alloy nitriding under nitrogen or argon conditions. The disadvantage of this method is that the yield of the alloy nitriding is difficult to control. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a vacuum smelting method for precisely controlling nitrogen content in nitrogen-containing steel.

[0005] To solve the above-mentioned technical problems, the method steps adopted by the present invention are as follows:

[0006] 1) Load the furnace, evacuate it, and then power it on to heat it until it is completely melted;

[0007] 2) Maintain vacuum during refining, and stop vacuuming after refining;

[0008] 3) Rapidly purge nitrogen to a nitrogen atmosphere of 0.06 MPa to 0.075 MPa, and add the nitride alloy under the nitrogen atmosphere; the amount of nitride alloy added is calculated according to formula (Ⅰ) based on the target nitrogen content:

[0009]

[0010] In formula (Ⅰ): b is the correlation coefficient, which is 20 when manganese nitride is added and 12.5 when chromium nitride is added; P LP is the pressure of a nitrogen atmosphere. K At normal pressure; N s The nitrogen atmosphere pressure and the saturated solubility of N at 1873 K, in %; N r The target nitrogen content is %, M is the mass of nitride alloy added, kg.

[0011] 4) After adding the nitride alloy, the steel is tapped while nitrogen is being introduced.

[0012] Furthermore, in step 3), the total time for adding the nitride alloy is controlled between 29 min and 31 min.

[0013] Furthermore, in step 3), the nitride alloy is manganese nitride or chromium nitride.

[0014] Furthermore, in step 4), nitrogen gas at 0.005–0.008 MPa is continuously introduced during the tapping process.

[0015] Furthermore, maintain a vacuum of 5 Pa or below for refining for 5 to 10 minutes.

[0016] The beneficial effects of adopting the above technical solution are as follows: This invention starts from the dissolution kinetics and thermodynamic behavior of nitrogen element, and precisely controls the nitrogen content in steel by fixing the nitriding time and nitriding pressure and using relevant formulas to calculate the yield of nitrided alloys. The deviation of the nitrogen-containing steel smelted from the target value can be controlled within 0.015%, thus achieving precise nitrogen control in the smelting of nitrogen-containing steel. This invention has the advantages of fast smelting speed, precise nitrogen control, low cost, strong controllability, pure molten steel, and dense ingots, and has wide applicability. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments.

[0018] This vacuum smelting method for precisely controlling nitrogen content in nitrogen-containing steel is applicable to the production of nitrogen-containing steel with a nitrogen content of 0.2% to 0.4% (wt), and the method steps are as follows:

[0019] 1) Grind and bake the required steel material at a temperature ≥200℃ for a time ≥1.5h;

[0020] 2) Load the non-oxidizable volatile alloy into the crucible of the vacuum induction furnace, and load the easily oxidizable volatile alloy into the feeding hopper. Evacuate the furnace to 5 Pa or below, and then power on the vacuum induction furnace to heat it up until the steel material is completely melted.

[0021] 3) Maintain a vacuum level of 5 Pa or below inside the vacuum induction furnace for 5 to 10 minutes for refining. After refining, turn off the vacuum system of the vacuum induction furnace.

[0022] 4) The vacuum induction furnace is rapidly filled with nitrogen until a nitrogen atmosphere of 0.06 MPa to 0.075 MPa is formed inside the furnace. Nitrogen alloys are then added in batches under this nitrogen atmosphere, with other easily oxidized and volatile alloy materials added along with the nitriding alloys. The purity of the nitrogen gas must be greater than 99.9%, and the total time for adding the nitriding alloy under nitrogen atmosphere must be controlled between 29 and 31 minutes. The nitriding alloy is manganese nitride or chromium nitride, and the amount of nitriding alloy added is calculated according to the target nitrogen content using formula (Ⅰ):

[0023]

[0024] In formula (Ⅰ): b is the correlation coefficient, which is 20 when manganese nitride is added and 12.5 when chromium nitride is added; P L The nitriding pressure is the pressure of the nitrogen atmosphere; 0.06 MPa ≤ P L ≤0.075MPa; P K At atmospheric pressure, 0.101 MPa; N s The nitrogen atmosphere pressure and the saturated solubility of N at 1873 K, in %; N r The target nitrogen content is %, M is the mass of nitride alloy added, kg.

[0025] 5) The nitrogen atmosphere pressure and the saturated solubility of molten steel N at 1873K. s The calculation formula is as follows:

[0026]

[0027] In the formula Nitrogen partial pressure, atm; The first-order interaction coefficient of an element with nitrogen in molten steel; [j]: the content of element j in molten steel, wt%.

[0028] 6) After the nitriding alloy is added, nitrogen gas is introduced while steel is being tapped, and the amount of nitrogen introduced is controlled between 0.005 and 0.008 MPa.

[0029] Example 1: The vacuum smelting method for precisely controlling nitrogen in the smelting of nitrogen-containing steel is described in detail below.

[0030] A 100kg vacuum induction furnace with a rated power of 180kW and an ultimate vacuum of 6.67×10⁻⁶ is used. -2 Pa; Calculate the ingredients according to the target composition, weigh 57.84 kg of pure iron rod, 13 kg of nickel plate, 1.5 kg of molybdenum bar and 20 kg of metallic chromium and put them into a crucible, 0.076 kg of carbon powder, 0.58 kg of metallic silicon, 3.55 kg of manganese nitride and 4.34 kg of electrolytic manganese; The steel material is baked at 200℃ for 2 hours before being added.

[0031] The added nitride alloy is manganese nitride. The saturated solubility N of the molten steel is calculated using formulas (II) and (I). s And the mass M of manganese nitride added:

[0032] Lg[N s ]=1 / 2lg P 0.6 -188 / 1873 - 1.245 - (3280 / 1873 - 0.75) × -0.92765

[0033] The saturated solubility of molten steel [N] was calculated. s ] = 0.296;

[0034]

[0035] The calculated mass of manganese nitride added is M = 3.55 kg.

[0036] 1) Add the required pure iron bars, nickel plates, metallic chromium, and molybdenum bars into the crucible, and place the remaining alloy materials into the feeding hopper. Place manganese nitride into the secondary feeding hopper. 2) When the vacuum is reduced to below 5 Pa, power is supplied to raise the temperature until all the steel materials are melted. 3) After refining for 10 minutes while maintaining the vacuum level below 5 Pa, the vacuum system is turned off. 4) Quickly charge 0.06 MPa of nitrogen and start adding manganese nitride in batches, which takes 30 minutes. 5) Start charging nitrogen while tapping the steel, with a charging amount of 6000 Pa. 6) After the steel ingot temperature drops to room temperature, start demolding and take samples for testing and analysis. The analysis results are shown in Tables 1 and 2.

[0037] Table 1: Target composition and test values ​​(wt%) of the stainless steel described in Example 1

[0038] Target ingredient 0.07 0.65 7 13 20 1.5 0.28 Measured value 0.068 0.64 7.01 12.96 19.95 1.48 0.275

[0039] Table 2: Nitrogen content in steel at different parts of the ingot obtained in Example 1

[0040]

[0041] In Table 2, the difference is the difference between the nitrogen content in the obtained ingot and the target nitrogen content.

[0042] Example 2: The vacuum smelting method for precisely controlling nitrogen in the smelting of nitrogen-containing steel is described in detail below.

[0043] A 50kg vacuum induction furnace with a rated power of 100kW and an ultimate vacuum of 6.67×10⁻⁶ is used. -2Pa; Calculate the ingredients according to the target composition, weigh 20.24 kg of pure iron rod, 3.68 kg of nickel plate, 0.3808 kg of ferrotungsten and 6.72 kg of metallic chromium and put them into a crucible, add 0.0278 kg of carbon powder, 0.2457 kg of ferroniobium, 0.176 kg of metallic silicon, 1.98 kg of chromium nitride and 0.528 kg of electrolytic manganese; the steel material is baked at 250℃ for 1.5 h before being added.

[0044] The added nitride alloy is chromium nitride. The saturated solubility N of the molten steel is calculated using formulas (II) and (I). s And the mass of chromium nitride added: M:

[0045] Lg[N s ]=1 / 2lg P 0.7 -188 / 1873 - 1.245 - (3280 / 1873 - 0.75) × -0.96025

[0046] The saturated solubility of molten steel [N] was calculated. s ] = 0.345;

[0047]

[0048] The calculated mass of chromium nitride added is M = 1.98 kg.

[0049] 1) Add the required pure iron rods, nickel plates, metallic chromium, and ferrotungsten to the crucible. Place the remaining alloy materials into the feeding hopper, and chromium nitride into the secondary feeding hopper. 2) Evacuate to 5 Pa and then power on to heat until all the steel materials are melted. 3) Maintain the vacuum at 5 Pa or below and refine for 7 minutes, then turn off the vacuum system. 4) Quickly charge in 0.07 MPa of nitrogen and begin adding chromium nitride in batches, taking 29 minutes. 5) Begin charging the steel while charging nitrogen at a rate of 8000 Pa. 6) Once the ingot temperature has dropped to room temperature, begin demolding and take samples for testing and analysis. The analysis results are shown in Tables 3 and 4.

[0050] Table 3: Target composition and test values ​​(wt%) of the steel grade described in Example 2

[0051] Target value / % 0.08 0.55 5 0.9 0.5 11.5 21 0.32 end / % 0.083 0.54 4.98 0.92 0.49 11.56 21.1 0.309

[0052] Table 4: Nitrogen content in steel at different parts of the ingot obtained in Example 2

[0053]

[0054] In Table 4, the difference is the difference between the nitrogen content in the obtained ingot and the target nitrogen content.

[0055] Example 3: The vacuum smelting method for precisely controlling nitrogen in the smelting of nitrogen-containing steel is described in detail below.

[0056] It uses a 500kg vacuum induction furnace with a rated power of 360kW and an ultimate vacuum of 6.67×10⁻⁶. -2 Pa; Calculate the ingredients according to the target composition, weigh 208.77 kg of pure iron rod, 89.41 kg of nickel plate, 3.69 kg of molybdenum bar, and 119.58 kg of metallic chromium and put them into a crucible, add 0.2935 kg of carbon powder, 3.25 kg of niobium iron, 13.63 kg of copper plate, 1.35 kg of metallic silicon, 2.42 kg of metallic chromium, 6.75 kg of electrolytic manganese, and 1.49 kg of chromium nitride; the steel materials are baked at 220℃ for 1 hour and 40 minutes before being added.

[0057] The added nitride alloy is chromium nitride. The saturated solubility N of the molten steel is calculated using formulas (II) and (I). s And the mass of chromium nitride added: M:

[0058] Lg[N s ]=1 / 2lg P 0.75 -188 / 1873 - 1.245 - (3280 / 1873 - 0.75) × -1.10727

[0059] The saturated solubility of molten steel [N] was calculated. s ] = 0.485;

[0060]

[0061] The calculated mass of chromium nitride added is M = 1.49 kg.

[0062] 1) Add the required pure iron bars, nickel plates, metallic chromium, and molybdenum bars into the crucible, and place the remaining alloy materials into the feeding hopper. Place chromium nitride into the secondary feeding hopper. 2) Evacuate to 4 Pa ​​and then power on to heat until all the steel materials are melted. 3) Maintain the vacuum at 4 Pa ​​and refine for 5 minutes before turning off the vacuum system. 4) Quickly charge 0.075 MPa of nitrogen and start adding the alloy materials in batches, with the last addition of chromium nitride, which takes 31 minutes. 5) Start charging nitrogen while tapping the steel, with a charging rate of 8000 Pa. 6) Once the steel ingot temperature drops to room temperature, begin demolding and take samples for testing and analysis. The analysis results are shown in Tables 5 and 6.

[0063] Table 5: Target composition and test values ​​(wt%) of the steel grade described in Example 3

[0064] Target value / % 0.06 0.3 1.5 0.82 0.47 19.87 27.3 3.03 0.4 end / % 0.058 0.29 1.5 0.81 0.47 19.8 27.28 3.01 0.385

[0065] Table 6: Nitrogen content in steel at different parts of the ingot obtained in Example 3

[0066]

[0067] In Table 6, the difference is the difference between the nitrogen content in the obtained ingot and the target nitrogen content.

[0068] Example 4: The vacuum smelting method for precisely controlling nitrogen in the smelting of nitrogen-containing steel is described in detail below.

[0069] A 50kg vacuum induction furnace with a rated power of 100kW and an ultimate vacuum of 6.67×10⁻⁶ is used. -2 Pa; Calculate the ingredients according to the target composition, weigh 8 kg of nickel plate, 2.2 kg of molybdenum strip and 3.77 kg of metallic chromium and put them into the crucible, 0.026 kg of carbon powder, 0.192 kg of metallic silicon, 2.8 kg of electrolytic manganese and 1.89 kg of chromium nitride; The steel material is baked at 210℃ for 2 hours and 10 minutes before being added.

[0070] The added nitride alloy is chromium nitride. The saturated solubility N of the molten steel is calculated using formulas (II) and (I). s And the mass of chromium nitride added: M:

[0071] Lg[N s ]=1 / 2lg P 0.65 -188 / 1873 - 1.245 - (3280 / 1873 - 0.75) × -0.73544

[0072] The saturated solubility of molten steel [N] was calculated. s ] = 0.205;

[0073]

[0074] The calculated mass of chromium nitride added is M = 1.89 kg.

[0075] 1) Add the required pure iron bars, nickel plates, metallic chromium, and molybdenum bars into the crucible, and place the remaining alloy materials into the feeding hopper. Place chromium nitride into the secondary feeding hopper. 2) Evacuate to 4.5 Pa and then turn on the power to heat until all the steel materials are melted. 3) Maintain the vacuum at 4.5 Pa and refine for 8 minutes before turning off the vacuum system. 4) Quickly charge 0.065 MPa of nitrogen and start adding chromium nitride in batches, which takes 30 minutes. 5) Start charging nitrogen while tapping the steel with a charging amount of 5000 Pa. 6) After the steel ingot temperature drops to room temperature, start demolding and take samples for testing and analysis. The analysis results are shown in Tables 7 and 8.

[0076] Table 7: Target composition and test values ​​(wt%) of the stainless steel described in Example 4

[0077] Target ingredient / % 0.06 0.48 7 20 16.25 5.5 0.21 Measured value / % 0.06 0.48 6.98 20.01 16.3 5.48 0.201

[0078] Table 8: Nitrogen content in steel at different parts of the ingot obtained in Example 4

[0079]

[0080] In Table 8, the difference is the difference between the nitrogen content in the obtained ingot and the target nitrogen content.

[0081] As can be seen from the above examples, the vacuum smelting method for smelting nitrogen-containing steel has the advantages of precise nitrogen control and stable nitrogen content.

Claims

1. A vacuum smelting method for precise nitrogen control in smelting nitrogen-containing steel, characterized in that, The method and steps are as follows: 1) Load the furnace, evacuate it, and power on to heat it until it is completely melted; 2) Maintain a vacuum of 5 Pa or below for 5 to 10 minutes, then stop vacuuming after refining; 3) Rapidly purge with nitrogen to a nitrogen atmosphere of 0.06 MPa to 0.075 MPa, and add a nitride alloy under the nitrogen atmosphere; the nitride alloy is manganese nitride or chromium nitride, and the amount added is calculated according to the target nitrogen content based on formula (Ⅰ): （Ⅰ） In formula (I), b is a correlation coefficient, b is 20 when the nitrogenized alloy added is manganese nitride, and b is 12.5 when the nitrogenized alloy added is chromium nitride; P L P is the nitriding pressure, i.e. the nitrogen atmosphere pressure, 0.06 MPa ≤ P L ≤ 0.075 MPa; P K is normal pressure, 0.101 MPa; N s N is the saturated solubility of nitrogen at 1873 K, %; N r M is the mass of the nitrogenized alloy added, kg; 4) After adding the nitride alloy, steel is tapped while nitrogen is being introduced; In step 3), the total time for adding the nitride alloy is controlled between 29 min and 31 min. In step 4), nitrogen gas at 0.005–0.008 MPa is continuously introduced during the tapping process; The vacuum smelting method described above is suitable for producing nitrogen-containing steel with a nitrogen content of 0.2 to 0.4 wt%.

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