A smelting method for a low-carbon, low-sulfur high-alloy steel

Abstract

A smelting method for a low-carbon, low-sulfur, high-alloy steel, belonging to the field of metallurgical technology, includes EAF electric furnace smelting, LF refining, RH vacuum refining, and continuous casting processes. In the EAF electric furnace smelting process, after completing the dephosphorization task, the molten steel temperature is adjusted. High-carbon ferrochrome is added in batches, oxygen is blown, and the C content at the end point is 0.1 - 0.15%. After the molten steel temperature ≥ 1600 °C, tapping is carried out. In the LF refining process, high-power heating is carried out in the early stage. After diffusion deoxidation, strong desulfurization is carried out until the end point S ≤ 0.003%. Silicon and manganese are not adjusted during the refining process, while the contents of chromium, nickel, and copper are adjusted. After maintaining a white slag, slag is removed. In the RH vacuum refining process, oxygen is blown under a vacuum degree of 2 - 10 kPa until the C content drops to the target value, and then deoxidation is carried out. The vacuum degree is adjusted to ≤ 67 Pa, the contents of silicon and manganese are adjusted, and after maintaining the vacuum, the vacuum is broken. The H content is determined, samples are taken, calcium-silicon wires are fed, and then tapping is carried out. The smelting cycle of the present invention is short, the production efficiency is high, the purity of the molten steel is high after RH vacuum treatment, and the number of non-metallic inclusions in the continuous casting billet is small.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a smelting method for low-carbon, low-sulfur, and high-alloy steel. Background Art

[0002] Currently, special steel manufacturers smelting low-carbon, low-sulfur, and high-alloy steel generally are equipped with VOD and AOD equipment. When smelting this kind of steel, due to the large amount of alloy added, the amount of alloy added during the tapping process in front of the furnace is insufficient, and alloy materials need to be added in batches in LF. After vacuum oxygen decarburization in the VOD / AOD process, the oxygen content in the molten steel increases, and the easily oxidized alloying elements are basically oxidized, and the sulfur content in the steel rises. It is necessary to re-enter LF for re-deoxidation, desulfurization, and addition of easily oxidized alloys. Finally, it is necessary to enter VOD / AOD for vacuum degassing. This method has a long smelting time, high consumption, and generally high inclusion levels in the steel. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a smelting method for low-carbon, low-sulfur, and high-alloy steel, which can greatly shorten the production cycle, reduce consumption, and solve the problem of high inclusions in the molten steel. To achieve the object of the invention, the technical solution adopted by the present invention is:

[0004] A smelting method for low-carbon, low-sulfur, and high-alloy steel, including EAF electric furnace smelting, LF refining, RH vacuum refining, and continuous casting processes;

[0005] In the EAF electric furnace smelting process, after completing the dephosphorization task in the later stage of smelting, the molten steel temperature is raised to 1600 - 1630 °C, high-carbon ferrochrome is added in batches, and power is continuously supplied during the addition of high-carbon ferrochrome to keep the molten steel temperature ≥ 1580 °C. Oxygen is blown in the electric furnace for decarburization to protect chromium, and the C content at the end of the electric furnace is 0.1 - 0.15%, and the molten steel is tapped after the molten steel temperature ≥ 1600 °C;

[0006] In the LF refining process, high-power heating is carried out in the early stage of refining. After diffusion deoxidation, strong desulfurization is carried out until the S content in the molten steel at the end of refining is ≤ 0.003%. Si and Mn are not adjusted during the refining process, and Cr, Ni, and Cu are adjusted to the target values. After maintaining a white slag for ≥ 25 minutes, the slag is removed;

[0007] In the RH vacuum refining process, oxygen is blown for decarburization under a vacuum degree of 2 - 10 kPa until the C content in the molten steel drops to the target value, and then aluminum pellets are added for deoxidation; the vacuum degree is adjusted to ≤ 67 Pa, and under this vacuum condition, ferrosilicon and metallic manganese are added to adjust Si and Mn to the target values. After maintaining the vacuum, the vacuum is broken, the H content is determined, samples are taken, calcium-silicon wire is fed, and the molten steel is tapped.

[0008] In the EAF steelmaking process, the molten steel is tapped after the temperature reaches 1600 - 1630°C. During tapping, 1.5 - 2.0 kg / t of steel-cored aluminum is added for pre-deoxidation, nickel beans and copper plates are added, and quicklime and refining slag are added along with the steel flow to form slag. After soft blowing for 2 - 5 minutes at the ladle furnace, Al wire is fed to ensure that the Al content in the LF ladle is 0.015 - 0.035%.

[0009] In the LF refining process, 2 - 5 kg / t of silicon carbide is added for diffusion deoxidation, and 1.5 - 2.5 kg / t of quicklime is added to enhance desulfurization; white slag means that MnO + FeO in the slag sample is ≤ 0.5%.

[0010] In the RH vacuum refining process, the vacuum is broken after the vacuum time is ≥ 10 minutes.

[0011] The above smelting method is applicable to low-carbon, low-sulfur, high-alloy steel with C content ≤ 0.08%, S content ≤ 0.005%, Si content ≤ 0.30%, and Cr + Mn + Ni + Cu content ≥ 13%.

[0012] The beneficial effects of adopting the above technical solutions are as follows:

[0013] (1) The present invention achieves the purpose of smelting low-carbon, low-sulfur, high-alloy steel using an RH vacuum furnace.

[0014] (2) In the later stage of EAF smelting, high-carbon ferrochrome is added, and oxygen blowing is carried out to decarbonize and protect chromium. That is, when the molten steel temperature ≥ 1600°C, EAF oxygen blowing can first oxidize C in the molten steel, while Cr is not oxidized. As the carbon content in the molten steel decreases, the molten steel temperature can be gradually increased to ensure that Cr in the molten steel is not oxidized. The EAF end-point C can be controlled at ≤ 0.15%, greatly reducing the alloy cost of smelting low-carbon, low-sulfur, high-alloy steel, reducing the pressure of adding a large amount of alloy in the LF furnace, shortening the smelting cycle, and improving production efficiency.

[0015] (3) RH vacuum feeding can greatly improve the absorption rate of alloy materials. Using RH vacuum treatment can greatly reduce the number of non-metallic inclusions in the steel and improve the purity of the molten steel.

[0016] For the non-metallic inclusion grades in the continuous casting billets obtained by the present invention: A coarse / A fine: ≤ 1.5 / 2.0 grades, B coarse / B fine: ≤ 1.5 / 2.0 grades, C coarse / C fine: ≤ 1.0 / 1.0 grades, D coarse / D fine: ≤ 1.0 / 1.5 grades, Ds: ≤ 1.0 grade. Specific embodiments Example 1

[0017] The low-carbon, low-sulfur, high-alloy steel smelted in this embodiment is sucker rod steel 00Cr12, with heat number 2213336, where the C content is 0.05 - 0.07%, the S content is ≤0.005%, the Si content is ≤0.30%, and the Cr + Mn + Ni + Cu content is ≥13.45%. The smelting method includes EAF electric furnace smelting, LF refining, RH vacuum refining, and continuous casting processes. The steps of each process are as follows:

[0018] (1)EAF electric furnace smelting process: Charge 31.1 tons of crushed materials, 71.8 tons of light scrap steel, 15.7 tons of medium scrap steel, and 24.9 tons of heavy scrap steel, with a total charge of 143.5 tons. After completing the dephosphorization task in the later stage of smelting, the P content in the molten steel composition is 0.006% and the S content is 0.026%. When the molten steel temperature rises to 1600°C, 30 tons of high-carbon ferrochrome are added in batches. While the electric furnace is powered on and heated, oxygen is blown to decarburize, keeping the molten steel temperature ≥1580°C. The oxygen lance on the furnace wall is used to blow oxygen for 5 minutes. The C content at the end of the electric furnace is 0.15%, and the molten steel is tapped after the temperature reaches 1625°C. During the tapping process, 200 kg of steel core aluminum is added for pre-deoxidation, and at the same time, 1 ton of nickel beans, 300 kg of copper plates, and 1.5 tons of ferromolybdenum are added. 600 kg of white lime and 500 kg of refining slag are added along with the steel flow to form slag. After soft blowing for 2 minutes, 110 meters of aluminum wire is fed to ensure that the Al content in the LF ladle is 0.015 - 0.035%.

[0019] (2)LF refining process: Lift the ladle to a 130-ton refining furnace for smelting, with a molten steel volume of 131.5 tons. In the early stage of refining, a voltage of 330V at gear 6 and a current of 23000A are used to melt the slag and raise the temperature. In the first 15 minutes of melting the slag, 40 kg of silicon carbide is added every 3 minutes for diffusion deoxidation. After taking the first sample, 200 kg of white lime is added for strong desulfurization. During the refining process, strong argon stirring is carried out, controlling the argon flow rate at 350 NL / min. After the first sample composition comes out, the Al content in the steel is 0.0156%. Adjust the chromium, nickel, and copper to the target values, without adjusting Si and Mn. Control the argon flow rate at 500 NL / min and carry out strong stirring for 10 minutes. Use a voltage of 280V at gear 5 and a current of 20000A to raise the temperature. 10 kg of silicon carbide is added every 3 minutes for diffusion deoxidation to ensure the formation of white slag, with MnO + FeO in the slag sample ≤0.5% and the white slag holding time ≥25 minutes. A total of 270 kg of silicon carbide is added to this furnace. Then take the second composition sample, with a carbon content of 0.18% and a sulfur content of 0.0023%. When the molten steel temperature rises to T, lift the molten steel to the slag skimmer for slag skimming, with a slag skimming amount of 800 kg. Then lift the molten steel to the RH vacuum furnace. The T = T 液相线 +△T, where T 液相线 is the liquidus temperature of the molten steel, and △T is 180°C.

[0020] (3)RH vacuum refining process: First, blow oxygen to decarburize at a vacuum degree of 10 kPa, with an oxygen blowing amount of 200m 3, the oxygen blowing time is 8 minutes. Then, control the RH pumping capacity to gradually reduce the vacuum degree. After the vacuum degree ≤ 67 Pa, the molten steel is continuously circulated for 3 minutes and then sampled. 60 kg of aluminum pellets are added from the high bin for deoxidation, and then 300 kg of ferrosilicon and 800 kg of ferromanganese are added from the high bin to adjust Si and Mn to the target values. After maintaining the vacuum for 12 minutes, the vacuum is broken. The determined H is 1.2 ppm, sampling is carried out, 50 m of silicon-calcium wire is fed, and soft blowing is carried out for 15 minutes. The chemical composition of the molten steel is C: 0.052 wt%, S: 0.0025 wt%, and other components meet the process requirements. When the molten steel temperature reaches T1, tapping is carried out, where T1 = T 液相线 + △T1, where T 液相线 is the liquidus temperature of the molten steel, and △T1 is 80 °C.

[0021] (4) Continuous casting process: The tapping temperature of RH meets the process requirements, and the molten steel is lifted to the continuous caster for pouring.

[0022] The non-metallic inclusion grade in the continuous casting billet of the sucker rod steel 00Cr12 obtained in this example is shown in Table 1. Example 2

[0023] The low-carbon, low-sulfur, and high-alloy steel smelted in this example is sucker rod steel 00Cr12, furnace number 2213158, with a C content of 0.05 - 0.07%, an S content ≤ 0.005%, an Si content ≤ 0.30%, and a Cr + Mn + Ni + Cu content ≥ 13.45%. This smelting method includes EAF electric furnace smelting, LF refining, RH vacuum refining, and continuous casting processes. The steps of each process are as follows:

[0024] (1) EAF electric furnace smelting process: Charge 31.8 tons of crushed materials, 71.2 tons of light scrap steel, 14.7 tons of medium scrap steel, and 23.9 tons of heavy scrap steel, with a total charge of 141.6 tons. After completing the dephosphorization task in the later stage of smelting, the P content in the molten steel composition is 0.008% and S: 0.022%. When the molten steel temperature rises to 1630 °C, 29.6 tons of high-carbon ferrochrome are added in batches. While the electric furnace is being powered on and heated up, oxygen is blown to decarburize, maintaining the molten steel temperature ≥ 1580 °C. The oxygen lance on the furnace wall is used to blow oxygen for 5 minutes. The C content at the end of the electric furnace is 0.10%, and after the molten steel temperature reaches 1623 °C, tapping is carried out; during tapping, 265 kg of steel core aluminum is added for preliminary deoxidation, and at the same time, 1 ton of nickel beans, 300 kg of copper plates, and 1.5 tons of ferromolybdenum are added. 600 kg of quicklime and 500 kg of refining slag are added along with the steel flow to form slag. After soft blowing for 5 minutes, 100 m of aluminum wire is fed to ensure that the Al content in the LF ladle is 0.015 - 0.035%.

[0025] (2)LF Refining Process: Lift the ladle to a 130-ton refining furnace for smelting. The amount of molten steel in this heat is 132.5 tons. In the early stage of refining, use a voltage of 330V at gear 6 and a current of 23000A to melt the slag and raise the temperature. Add 60 kg of silicon carbide every 3 minutes for diffusion deoxidation in the first 15 minutes of slag melting. After taking the first sample, add 330 kg of quicklime for strong desulfurization; during the refining process, stir with large argon gas, control the argon gas flow rate at 360 NL / min. After the composition of the first sample comes out, the Al content of the molten steel is 0.035%. Adjust chromium, nickel, and copper to the target values, without adjusting Si and Mn. Control the argon gas flow rate at 600 NL / min and stir strongly for 10 minutes. Use a voltage of 280V at gear 5 and a current of 20000A to raise the temperature. Add 20 kg of silicon carbide every 3 minutes for diffusion deoxidation to ensure the formation of white slag, with MnO + FeO ≤ 0.5% in the slag sample and the white slag retention time ≥ 25 minutes. A total of 660 kg of silicon carbide is added in this heat. Then take the second composition sample, with a carbon content of 0.15% and a sulfur content of 0.0015%. When the temperature of the molten steel rises to T, lift the molten steel to the slag skimmer for slag skimming, and the slag skimming amount is 800 kg. Then lift the molten steel to the RH vacuum furnace. The T = T 液相线 + △T, where T 液相线 is the liquidus temperature of the molten steel, and △T is 182°C.

[0026] (3)RH Vacuum Refining Process: First, blow oxygen for decarburization at a vacuum of 2 kPa, with an oxygen blowing amount of 180 m 3 , and the oxygen blowing time is 7.2 minutes. Then control the pumping capacity of RH to gradually reduce the vacuum. After the vacuum ≤ 67 Pa, the molten steel is continuously circulated for 3 minutes and then sampled. Add 60 kg of aluminum pellets for deoxidation in the upper bin, and then add 310 kg of ferrosilicon and 800 kg of metallic manganese in the upper bin to adjust Si and Mn to the target values. After maintaining the vacuum for 10 minutes, break the vacuum, determine the H content to be 1.36 ppm, sample, feed 50 m of silicon-calcium wire, and soft blow for 15 minutes. The composition of the molten steel is C: 0.056 wt%, S: 0.0021 wt%, and other components meet the process requirements. When the temperature of the molten steel reaches T1, tap the steel. T1 = T 液相线 + △T1, where T 液相线 is the liquidus temperature of the molten steel, and △T1 is 83°C.

[0027] (4)Continuous Casting Process: The tapping temperature of RH meets the process requirements. Lift the molten steel to the continuous caster for pouring.

[0028] The non-metallic inclusion grade in the continuous casting billet of the sucker rod steel 00Cr12 obtained in this example is shown in Table 1. Example 3

[0029] The low-carbon, low-sulfur, high-alloy steel smelted in this embodiment is sucker rod steel 00Cr12, with heat number 2213159, where the C content is 0.05 - 0.07%, the S content is ≤0.005%, the Si content is ≤0.30%, and the Cr + Mn + Ni + Cu content is ≥13.45%. This smelting method includes EAF electric furnace smelting, LF refining, RH vacuum refining, and continuous casting processes. The steps of each process are as follows:

[0030] (1) EAF electric furnace smelting process: Charge 32.5 tons of crushed materials, 70.8 tons of light scrap, 16.5 tons of medium scrap, and 23.6 tons of heavy scrap, with a total charge of 143.4 tons. After completing the dephosphorization task in the later stage of smelting, the P content in the molten steel composition is 0.009% and the S content is 0.033%. When the molten steel temperature rises to 1611°C, add 31 tons of high-carbon ferrochrome in batches. While the electric furnace is powering up and heating, blow oxygen to decarbonize, keeping the molten steel temperature ≥1580°C. Use the furnace wall lance to blow oxygen for 4 minutes. The C content at the end of the electric furnace is 0.11%, and the molten steel is tapped after the temperature reaches 1619°C. During tapping, add 230 kg of steel core aluminum for pre-deoxidation, and at the same time add 1 ton of nickel beans, 300 kg of copper plates, and 1.5 tons of ferromolybdenum. Add 600 kg of quicklime and 500 kg of refining slag to make slag along with the steel flow. After soft blowing for 4 minutes, feed 90 meters of aluminum wire to ensure that the Al content in the LF ladle is 0.015 - 0.035%.

[0031] (2) LF refining process: Lift the ladle to a 130-ton refining furnace for smelting, with a molten steel volume of 131.6 tons. In the early stage of refining, use a 6th gear voltage of 330V and a current of 23000A to melt the slag and raise the temperature. Add 40 kg of silicon carbide for diffusion deoxidation every 3 minutes in the first 15 minutes of melting the slag. After taking the first sample, add 280 kg of quicklime for strong desulfurization. Stir with large argon gas during the refining process, controlling the argon gas flow rate at 350 NL / min. After the first sample composition comes out, the Al content in the steel is 0.020%. Adjust Cr, Ni, and Cu to the target values, without adjusting Si and Mn. Control the argon gas flow rate at 500 NL / min and stir strongly for 10 minutes. Use a 5th gear voltage of 280V and a current of 20000A to raise the temperature. Add 10 kg of silicon carbide for diffusion deoxidation every 3 minutes to ensure the production of white slag, with MnO + FeO ≤0.5% in the slag sample and the white slag holding time ≥25 minutes. The amount of silicon carbide added in this furnace is 395 kg. Then take the second component sample, with a carbon content of 0.136% and a sulfur content of 0.0018%. When the molten steel temperature rises to T, lift the molten steel to the slag skimmer for slag skimming, with a slag skimming amount of 600 kg. Then lift the molten steel to the RH vacuum furnace. The T = T 液相线 +△T, where T 液相线 is the liquidus temperature of the molten steel, and △T is 185°C.

[0032] (3) RH vacuum refining process: First, blow oxygen to decarbonize under a vacuum of 5 kPa, with an oxygen blowing amount of 160m 3, the oxygen blowing time is 6.4 min. Then, control the RH pumping capacity to gradually reduce the vacuum degree. After the vacuum degree ≤ 67 Pa, the molten steel is continuously circulated for 3 min and then sampled. 60 kg of aluminum pellets are added to the high bin for deoxidation, and then 250 kg of ferrosilicon and 850 kg of ferromanganese are added to the high bin to adjust Si and Mn to the target values. After maintaining the vacuum for 14 min, the vacuum is broken. The determined H is 1.05 ppm, samples are taken, 60 m of silicon-calcium wire is fed, and soft blowing is carried out for 18 min. The chemical composition of the molten steel is C: 0.045 wt%, S: 0.003 wt%, and other components meet the process requirements. When the temperature of the molten steel reaches T1, tapping is carried out, and T1 = T 液相线 + ΔT1, where T 液相线 is the liquidus temperature of the molten steel, and ΔT1 is 82 °C.

[0033] (4) Continuous casting process: The tapping temperature of RH meets the process requirements, and the molten steel is lifted to the continuous casting machine for pouring.

[0034] The non-metallic inclusion grade in the continuous casting billet of the sucker rod steel 00Cr12 obtained in this example is shown in Table 1. Example 4

[0035] The low-carbon, low-sulfur and high-alloy steel smelted in this example is 0Cr18Ni9, furnace number 2213650, where the C content < 0.08%, the S content ≤ 0.003%, the Si content ≤ 0.30%, and the Cr + Mn + Ni + Cu content ≥ 25%. This smelting method includes EAF electric furnace smelting, LF refining, RH vacuum refining, and continuous casting process. The steps of each process are as follows:

[0036] (1) EAF electric furnace smelting process: Charge 32.6 tons of crushed materials, 69.8 tons of light scrap, 17.5 tons of medium scrap, and 23.5 tons of heavy scrap, with a total charge of 143.4 tons. After completing the dephosphorization task in the later stage of smelting, the P content in the molten steel composition is 0.008%, S: 0.030%. When the temperature of the molten steel rises to 1623 °C, 40 tons of high-carbon ferrochrome are added in batches. The electric furnace is powered on and heated while blowing oxygen for decarburization, maintaining the molten steel temperature ≥ 1580 °C. The oxygen lance on the furnace wall is used to blow oxygen for 5 min, and the C content at the end of the electric furnace is controlled to be 0.12%. After the molten steel temperature reaches 1620 °C, tapping is carried out; during tapping, 240 kg of steel-cored aluminum is added for pre-deoxidation, and at the same time, 10 tons of nickel beans are added. 700 kg of quicklime and 500 kg of refining slag are added along with the steel flow for slag making. Soft blowing is carried out for 3 min after tapping, and 120 m of aluminum wire is fed to ensure that the Al content in the LF ladle is 0.015 - 0.035%.

[0037] (2) LF refining process: Lift the ladle to a 130-ton refining furnace for smelting, with a molten steel amount of 132.5 tons. In the early stage of refining, use a voltage of 280V at gear 5 and a current of 20000A to melt the slag and raise the temperature. Add 50 kg of silicon carbide every 3 minutes for diffusion deoxidation in the first 20 minutes of slag melting. After taking the first sample, add 300 kg of quicklime for strong desulfurization until the sulfur content in the molten steel at the end of refining is S≤0.003%. Stir with large argon gas during the refining process, and control the argon gas flow rate at 400 NL / min. After the composition of the first sample comes out, the Al content in the steel is 0.030%. Adjust chromium, nickel, and copper to the target values, without adjusting Si and Mn. Control the argon gas flow rate at 550 NL / min and stir strongly for 10 minutes. Use a voltage of 280V at gear 5 and a current of 2000A to raise the temperature. Add 10 kg of silicon carbide for diffusion deoxidation every 3 minutes to ensure the formation of white slag, with MnO+FeO≤0.5 wt% in the slag sample and the white slag preservation time ≥25 minutes. A total of 530 kg of silicon carbide is added in this furnace. Then take the second composition sample, with a C content of 0.145% and an S content of 0.0025%. When the molten steel temperature rises to T, lift the molten steel to the slag skimmer for slag skimming, with a slag skimming amount of 650 kg. Then lift the molten steel to the RH vacuum furnace. The T = T 液相线 + △T, where T 液相线 is the liquidus temperature of the molten steel, and △T is 185°C.

[0038] (3) RH vacuum refining process: First, blow oxygen for decarburization at a vacuum degree of 8 kPa, with an oxygen blowing amount of 140 m 3 , an oxygen blowing time of 5.6 minutes. Then control the pumping capacity of RH to gradually reduce the vacuum degree. After the vacuum degree ≤67 Pa, the molten steel is continuously circulated for 3 minutes and then sampled. Add 50 kg of aluminum pellets for deoxidation in the high bin, and then add 250 kg of ferrosilicon and 300 kg of metallic manganese in the high bin to adjust Si and Mn to the target values. After maintaining the vacuum for 13 minutes, break the vacuum, determine the H content at 1.08 ppm, sample, feed 50 m of silicon-calcium wire, and soft blow for 30 minutes. The composition of the molten steel is C: 0.05%, S: 0.0025%, and other components meet the process requirements. When the molten steel temperature reaches T1, tap the steel, where T1 = T 液相线 + △T1, where T 液相线 is the liquidus temperature of the molten steel, and △T1 is 80°C.

[0039] (4) Continuous casting process: The tapping temperature of RH meets the process requirements, and the molten steel is lifted to the continuous caster for pouring.

[0040] The non-metallic inclusion grade in the 0Cr18Ni9 continuous casting billet obtained in this example is shown in Table 1. Example 5

[0041] The low-carbon, low-sulfur, high-alloy steel smelted in this embodiment is 0Cr18Ni9, with the furnace number 2213651, where the C content < 0.08%, the S content ≤ 0.003%, the Si content ≤ 0.30%, and the Cr + Mn + Ni + Cu content ≥ 25%. The smelting method includes EAF electric furnace smelting, LF refining, RH vacuum refining, and continuous casting processes. The steps of each process are as follows:

[0042] (1) EAF electric furnace smelting process: Charge 32.5 tons of crushed materials, 70.2 tons of light scrap, 17.3 tons of medium scrap, and 23.6 tons of heavy scrap, with a total charge of 143.6 tons. After completing the dephosphorization task in the later stage of smelting, the P content in the molten steel composition is 0.007% and the S content is 0.023%. When the molten steel temperature rises to 1604 °C, 40 tons of high-carbon ferrochrome are added in batches. While the electric furnace is powered on and heated, oxygen is blown to decarburize, maintaining the molten steel temperature ≥ 1580 °C. The wall lance is used to blow oxygen for 5 minutes, controlling the C content at the end of the electric furnace to be 0.13%. After the molten steel temperature reaches 1620 °C, tapping is carried out; during tapping, 220 kg of steel core aluminum is added for pre-deoxidation, and at the same time, 10 tons of nickel beans are added. 700 kg of quicklime and 500 kg of refining slag are added along with the steel flow to form slag. Soft blowing is carried out for 3 minutes after tapping, and 130 meters of aluminum wire is fed to ensure that the Al content in the LF ladle is 0.015 - 0.035%.

[0043] (2) LF refining process: Lift the ladle to a 130-ton refining furnace for smelting. The amount of molten steel in this furnace is 133.1 tons. In the early stage of refining, a voltage of 280 V at gear 5 and a current of 20000 A are used to melt the slag and raise the temperature. In the first 20 minutes of melting the slag, 40 kg of silicon carbide is added every 3 minutes for diffusion deoxidation. After taking the first sample, 240 kg of quicklime is added to strongly desulfurize until the S content in the molten steel at the end of refining is ≤ 0.003%. During the refining process, strong argon stirring is carried out, controlling the argon flow rate at 420 NL / min. After the first sample composition comes out, the Al content in the steel is 0.016%. Adjust Cr, Ni, and Cu to the target values, without adjusting Si and Mn, control the argon flow rate at 550 NL / min, and strongly stir for 10 minutes. A voltage of 280 V at gear 5 and a current of 2000 A are used to raise the temperature. 10 kg of silicon carbide is added every 3 minutes for diffusion deoxidation to ensure the formation of white slag, with MnO + FeO in the slag sample ≤ 0.5 wt%, and the white slag holding time ≥ 25 minutes. A total of 330 kg of silicon carbide is added to this furnace. Then take the second component sample, with the C content being 0.143% and the S content being 0.0021%. When the molten steel temperature rises to T, lift the molten steel to the slag skimmer for slag skimming, and the slag skimming amount is 630 kg. Then lift the molten steel to the RH vacuum furnace. The T = T 液相线 + △T, where T 液相线 is the liquidus temperature of the molten steel, and △T is 183 °C.

[0044] (3) RH vacuum refining process: First, blow oxygen to decarburize at a vacuum degree of 3.5 kPa, and the oxygen blowing amount is 140 m 3, the oxygen blowing time is 5.6 min. After that, the RH pumping capacity is controlled to gradually reduce the vacuum degree. After the vacuum degree ≤ 67 Pa, the molten steel is continuously circulated for 3 min and then sampled. 50 kg of aluminum pellets are added to the high bin for deoxidation, and then 250 kg of ferrosilicon and 300 kg of ferromanganese are added to the high bin to adjust Si and Mn to the target values. After maintaining the vacuum for 15 min, the vacuum is broken. The determined H is 0.95 ppm, sampled, and 50 m of silicon-calcium wire is fed. Soft blowing is carried out for 30 min. The molten steel composition is C: 0.045%, S: 0.0026%, and other components meet the process requirements. When the molten steel temperature reaches T1, tapping is carried out, where T1 = T 液相线 + ΔT1, where T 液相线 is the liquidus temperature of the molten steel, and ΔT1 is 81 °C.

[0045] (4) Continuous casting process: The tapping temperature of RH meets the process requirements, and the molten steel is lifted to the continuous caster for pouring.

[0046] The non-metallic inclusion grade in the 0Cr18Ni9 continuous casting billet obtained in this example is shown in Table 1. Example 6

[0047] The low-carbon, low-sulfur, and high-alloy steel smelted in this example is 0Cr18Ni9, furnace number 2213652, where the C content < 0.08%, S content ≤ 0.003%, Si content ≤ 0.30%, and Cr + Mn + Ni + Cu content ≥ 25%. The smelting method includes EAF electric furnace smelting, LF refining, RH vacuum refining, and continuous casting processes. The steps of each process are as follows:

[0048] (1) EAF electric furnace smelting process: 31.6 tons of crushed materials, 72.8 tons of light scrap, 18.5 tons of medium scrap, and 23.6 tons of heavy scrap are charged, with a total charge of 146.5 tons. After completing the dephosphorization task in the later stage of smelting, the P content in the molten steel composition is 0.008%, S: 0.032%. When the molten steel temperature rises to 1606 °C, 40 tons of high-carbon ferrochrome are added in batches. The electric furnace is powered on and heated while blowing oxygen for decarburization, maintaining the molten steel temperature ≥ 1580 °C. The oxygen lance on the furnace wall is used to blow oxygen for 5 min, and the end-point C content of the electric furnace is controlled to be 0.145%. After the molten steel temperature reaches 1620 °C, tapping is carried out; during tapping, 235 kg of steel-cored aluminum is added for pre-deoxidation, and at the same time, 10 tons of nickel beans are added. 700 kg of quicklime and 500 kg of refining slag are added with the steel flow to make slag. Soft blowing is carried out for 3.5 min after tapping, and 110 m of aluminum wire is fed to ensure that the Al content in the LF ladle is 0.015 - 0.035%.

[0049] (2) LF Refining Process: Lift the ladle to a 130-ton refining furnace for smelting. The amount of molten steel in this furnace is 131.1 tons. In the early stage of refining, use a voltage of 280V at gear 5 and a current of 20,000A to melt the slag and raise the temperature. Add 40 kg of silicon carbide every 3 minutes for diffusion deoxidation in the first 20 minutes of slag melting. After taking the first sample, add 260 kg of quicklime for strong desulfurization until the sulfur content in the molten steel at the end of refining is ≤0.003%. Stir with large argon gas during the refining process, control the argon gas flow rate at 400 NL / min. After the composition of the first sample comes out, adjust chromium, nickel, and copper to the target values, without adjusting Si and Mn. Control the argon gas flow rate at 550 NL / min and stir strongly for 10 minutes. Use a voltage of 280V at gear 5 and a current of 2,000A to raise the temperature. Add 10 kg of silicon carbide every 3 minutes for diffusion deoxidation to ensure the formation of white slag, with MnO + FeO in the slag sample ≤0.5 wt%, and the white slag holding time ≥25 minutes. A total of 390 kg of silicon carbide is added in this furnace. Then take the second composition sample with a C content of 0.15% and an S content of 0.0026%. When the molten steel temperature rises to T, lift the molten steel to the slag skimmer for slag skimming, and the slag skimming amount is 650 kg. Then lift the molten steel to the RH vacuum furnace. The T = T 液相线 + △T, where T 液相线 is the liquidus temperature of the molten steel, and △T is 183°C.

[0050] (3) RH Vacuum Refining Process: First, blow oxygen for decarburization at a vacuum of 8.5 kPa, with an oxygen blowing amount of 200 m 3 , and the oxygen blowing time is 8 minutes. Then control the pumping capacity of RH to gradually reduce the vacuum. After the vacuum ≤67 Pa, sample after the molten steel circulates continuously for 3 minutes. Add 50 kg of aluminum pellets for deoxidation from the high bin, and then add 250 kg of ferrosilicon and 300 kg of ferromanganese from the high bin to adjust Si and Mn to the target values. Break the vacuum after maintaining the vacuum for 13.5 minutes. Determine the H content at 1.08 ppm, sample, feed 50 m of silicon-calcium wire, and soft blow for 30 minutes. The composition of the molten steel is C: 0.05%, S: 0.0025%, and other components meet the process requirements. Tap the molten steel when the molten steel temperature reaches T1, T1 = T 液相线 + △T1, where T 液相线 is the liquidus temperature of the molten steel, and △T1 is 80°C.

[0051] (4) Continuous Casting Process: The tapping temperature of RH meets the process requirements. Lift the molten steel to the continuous caster for pouring.

[0052] The non-metallic inclusion grade in the 0Cr18Ni9 continuous casting billet obtained in this example is shown in Table 1.

[0053] Table 1. Non-metallic inclusion grades in continuous casting billets of each example

[0054] .

Claims

1. A smelting method for a low-carbon, low-sulfur, high-alloy steel, characterized in that, It includes the EAF steelmaking process, LF refining process, RH vacuum refining process, and continuous casting process; In the EAF steelmaking process, after the dephosphorization task is completed in the later stage of smelting, the molten steel temperature is raised to 1600 - 1630 °C. High-carbon ferrochrome is added in batches, and oxygen is blown in the electric furnace for decarburization to protect chromium. The C content at the end of the electric furnace is 0.1 - 0.15%; during the process of adding high-chromium in batches, the temperature of the molten steel is maintained ≥1580 °C, and the molten steel is tapped after the molten steel temperature reaches 1600 - 1630 °C; during the tapping process, 1.5 - 2.0 kg / t of steel core aluminum is added for pre-deoxidation, nickel beans and copper plates are added, and quicklime and refining slag are added with the steel flow for slag making; after soft blowing for 2 - 5 min at the furnace rear, Al wire is fed to make up the Al content in the LF ladle to 0.015 - 0.035%; In the LF refining process, in the early stage of refining, the temperature is raised with high power. After diffusion deoxidation, strong desulfurization is carried out until the S content in the molten steel at the end of refining is ≤0.003%. During the refining process, Si and Mn are not adjusted, and Cr, Ni, and Cu are adjusted to the target values. After maintaining white slag for ≥25 min, the slag is removed; In the RH vacuum refining process, oxygen is blown for decarburization under a vacuum of 2 - 10 kPa until the C content in the molten steel drops to the target value, and then aluminum pellets are added for deoxidation; the vacuum degree is adjusted to ≤67 Pa. Under this vacuum condition, ferrosilicon and ferromanganese are added to adjust Si and Mn to the target values. After maintaining the vacuum, the vacuum is broken, H is determined, samples are taken, silicon-calcium wire is fed, and the molten steel is tapped; The smelting method is applicable to low-carbon, low-sulfur, high-alloy steel with C content ≤0.08%, S content ≤0.005%, Si content ≤0.30%, and Cr + Mn + Ni + Cu content ≥13%.

2. The smelting method of the low-carbon, low-sulfur and high-alloy steel according to claim 1, characterized in that: In the LF refining process, 2 - 5 kg / t of silicon carbide is added for diffusion deoxidation, and 1.5 - 2.5 kg / t of quicklime is added to strengthen desulfurization.

3. The smelting method of the low-carbon, low-sulfur and high-alloy steel according to claim 2, characterized in that: In the LF refining process, white slag means that MnO + FeO in the slag sample is ≤0.5%.

4. The smelting method of the low-carbon, low-sulfur and high-alloy steel according to claim 3, characterized in that: In the RH vacuum refining process, the vacuum is broken after maintaining the vacuum for ≥10 min.