METHOD FOR SMELTING LOW NITROGEN STEEL USING ELECTRIC FURNACE

Abstract

Disclosed is a method for smelting low nitrogen steel by using an electric furnace. The smelting is performed using a dual-shell electric furnace, The dual-shell electric furnace has two furnace shells. An arc power system of the dual-shell electric furnace is used for alternatively electric heating on the two furnace shells, wherein when one of the two furnace shells is subjected to electric heating, feeding, sealing of a molten pool and blowing of a combustion medium and oxygen are sequentially carried out in the other furnace shell to start smelting. When the temperature of molten steel in the furnace shell subjected to electric heating reaches a target temperature, electric heating starts to be carried out on the other furnace shell. The method for efficiently smelting the low nitrogen steel by using the electric furnace of the disclosure, not only can shorten the smelting period and improve the throughput of a production line of an electric furnace, but also smelt low nitrogen steel to satisfy the requirements of the market on high-end steel. in addition, the method for efficiently smelting the low nitrogen steel by using the electric furnace of the disclosure can reduce the discharge of dust and smoke, thereby protecting the environment.

Claims

1. A method for smelting low nitrogen steel by using an electric furnace, wherein a dual-shell electric furnace is adopted to carry out smelting, and the dual-shell electric furnace is provided with two furnace shells and an arc power system; and the method comprises carrying out steps of feeding, sealing of a molten pool, blowing of a combustion medium and oxygen and electric heating respectively and sequentially in the two furnace shells, specifically, carrying out electric heating on the two furnace shells alternately by the arc power system, when electric heating is carried out on one of the two furnace shells, sequentially carrying out the steps of feeding, sealing of the molten pool and blowing of the combustion medium and oxygen in the other furnace shell, and when the temperature of molten steel in the furnace shell subjected to electric heating reaches a target temperature of 1,600-1,660□, starting to carry out electric heating on the other furnace shell.

2. The method for smelting the low nitrogen steel by using the electric furnace of claim 1, wherein the arc power system is a DC arc power system.

3. The method for smelting the low nitrogen steel by using the electric furnace of claim 2, wherein the DC arc power system has a rated power of 0.7 to 1 MW per ton of molten steel.

4. The method for smelting the low nitrogen steel by using the electric furnace of claim 2, wherein the DC arc power system is provided with a hollow argon blowing electrode, and a bottom electrode of the hollow argon blowing electrode is a flake electrode.

5. The method for smelting the low nitrogen steel by using the electric furnace of claim 4, wherein argon blowing of the hollow argon blowing electrode is throughout the entire electric heating process.

6. The method for smelting the low nitrogen steel by using the electric furnace of claim 5, wherein an argon blowing flow of the hollow argon blowing electrode is controlled to be 50-100 standard liters per minute.

7. The method for smelting the low nitrogen steel by using the electric furnace of claim 1, wherein each of the furnace shells is provided with 4 to 6 blowing guns for blowing the combustion medium and oxygen, and an oxygen blowing flow of each blowing gun is 2,500-4,000 standard cubic meters per hour.

8. The method for smelting the low nitrogen steel by using the electric furnace of claim 1, wherein the step of blowing the combustion medium and oxygen further comprises simultaneously blowing the combustion medium and oxygen for 5-10 min, and then only blowing oxygen to carry out decarburization smelting.

9. The method for smelting the low nitrogen steel by using the electric furnace of claim 1, wherein when electric heating is carried out on the furnace shell, a slagging material is added into the furnace shell to form foam slag; and after the foam slag is formed, the oxygen blowing flow, according to the carbon content of steel, is adjusted as follows: when the carbon content is smaller than 0.5%, the oxygen blowing flow is reduced to 40% to 60% of the oxygen blowing flow when the carbon content is greater than 0.5%, until smelting is finally finished.

10. The method for smelting the low nitrogen steel by using the electric furnace of claim 1, wherein in the step of feeding, a total carbon content of the molten steel is 1.5-2.5 wt % of a final quantity of the molten steel after tapping, and the nitrogen content of the molten steel after tapping is smaller than 25 ppm.

11. The method for smelting the low nitrogen steel by using the electric furnace of claim 1, wherein the step of feeding comprises firstly, adding at least one of light and thin scrap steel and direct reduced iron, cokes and lime, then adding molten iron, and finally, adding common scrap steel.

Description

DETAILED DESCRIPTION

[0032] A method for efficiently smelting low nitrogen steel by using an electric furnace, which is disclosed by the present disclosure, will be further explained and illustrated below in combination with the specific embodiments, but the explanation and illustration do not constitute improper limitation to the technical solution of the present disclosure.

Embodiments 1-6

[0033] The smelting process of a method for efficiently smelting low nitrogen steel by using an electric furnace according to Embodiments l -6 is as follows.

[0034] A dual-shell electric furnace is adopted to carry out smelting, wherein the dual-shell electric furnace is provided with two furnace shells, and the molten steel smelting capacity of each furnace shell is 100 to 250 t. When the capacity exceeds 250 t, casting may he influenced, i.e., the casting time is excessively long, so that the temperature of molten steel may be excessively low in the later period of casting to influence casting; and when the capacity is smaller than 100 t, the throughput may he influenced, resulting in failure of efficient production required by the present disclosure, The two furnace shells are alternately subjected to electric heating by a DC arc power system of the dual-shell electric furnace, the DC arc power system is provided with a hollow argon blowing electrode, a bottom electrode is a flake electrode, and a rated power is 0,7 to 1 MW per ton of molten steel. When electric heating is carried out on one of the two furnace shells, feeding, sealing of a molten pool and blowing of a combustion medium and oxygen are sequentially carried out in the other furnace shell to start smelting, and when the temperature of molten steel in the furnace shell subjected to electric heating reaches a target temperature of 1,600-1,660□, electric heating starts to be carried out on the other furnace shell. Argon blowing of the hollow argon blowing electrode is throughout the entire electric heating process, and an argon blowing flow of the hollow argon blowing electrode is controlled to be 50-100 In addition, both a furnace door of the dual-shell electric furnace and an electrode port of the DC arc power system are provided with automatic sealing furnace covers. 4 to 6 blowing guns for blowing the combustion medium and oxygen are arranged in each furnace shell. The combustion medium may be fuel gas or fuel oil, or may be a mixture of the fuel gas and the fuel oil.

[0035] In addition, in the step of feeding, at least one of a small amount (e.g., 10-20 t) of light and thin scrap steel and direct reduced iron, cokes and lime are added, then molten iron is added, and finally, common scrap steel is added according to the volume of the molten pool. The total carbon content of the molten steel is 1.5 to 2.5 wt % of a final quantity of molten steel after tapping, and the nitrogen content of the molten steel after tapping is smaller than 25 ppm.

[0036] In the step of sealing of the molten pool, the furnace cover of the dual-shell electric furnace, a furnace door cover and an electrode port ver are closed, and a feeding opening is isolated from the molten pool by a separator so as to reduce release of dust and smoke, thereby protecting the environment.

[0037] In the step of blowing of the combustion medium and oxygen to start smelting, before starting smelting, a dust removal device integrated with the dual-shell electric furnace is switched on so as to reduce the discharge of dust and smoke, thereby protecting the environment. Then, the combustion medium and oxygen are simultaneously blown as follows: the blowing guns simultaneously run, a total flow of the combustion medium blown by the blowing gun is 300-400 NL/h, and an oxygen blowing flow of one single blowing gun is 1,000 to 1,200 Nm.sup.3/h, wherein in the first 2 min, the total flow of the combustion medium is controlled to be 180 to 240 NL/h. Timing is carried out from the moment when the combustion medium and oxygen are blown, after blowing is carried out for 5-10 min, blowing of the combustion medium is stopped, then only oxygen is blown to carry out decarburization smelting, and the oxygen blowing flow of one single blowing gun is 3,000 Nn.sup.3/.sub.11.

[0038] When electric heating is carried out on the furnace shell, the tasks of slagging dephosphorization, oxygen blowing decarburization and warming are required to be completed. Specifically, a slagging material including lime and dolomite is added into the furnace shell in batches to form foam slag so as to carry out dephosphorization. After the foam slag is formed, the oxygen blowing flow is adjusted according to the carbon content of steel, i.e., when the carbon content is smaller than 0.5%, the oxygen blowing flow is reduced to 40% to 60% of the oxygen blowing flow when the carbon content is greater than 0.5%, until smelting is finally finished, so as to carry out decarburization. In addition, when all the scrap steel in the molten pool is molten, the furnace door cover is opened to enable dephosphorized slag to automatically flow out; then after electric heating is continued for I min, carbon powder is blown to maintain the foam slag; then electric heating is continued until the temperature of the molten steel reaches a target temperature of 1,600-1,660, and then a tapping state is present; and after tapping, there are 30 to 40 t of residual molten steel and residual slag.

[0039] Table 1-1 to Table 1-5 list specific process parameters used in the method for efficiently smelting the low nitrogen steel by using the electric furnace according to Embodiments 1-6.

TABLE-US-00001 TABLE 1-1 Molten Steel Rated Power (MW Step of Feeding Smelting Capacity per ton of molten Number (piece) of Light and Thin (t) of Each Furnace steel) of DC Arc Blowing Guns in Scrap Steel Coke Lime Serial Number Shell Power System Each Furnace (t) (t) (t) Embodiment 1 150 1 5 15 1 2 Embodiment 2 200 0.9 5 20 1.2 2 Embodiment 3 250 0.72 6 20 2 2.5 Embodiment 4 100 1 4 10 1 1.8 Embodiment 5 180 1 5 18 1.1 2 Embodiment 6 220 0.82 6 20 1.8 2.3

TABLE-US-00002 TABLE 1-2 Step of Feeding Percentage of Total Carbon Direct Common Content of Molten Steel to Step of Blowing Reduced Molten Scrap Final Quantity of Molten of Combustion Iron Iron Steel Steel after Tapping Medium and Oxygen Serial Number (t) (t) (t) (wt %) Combustion Medium Embodiment 1 0 60 90 2.1 heavy oil Embodiment 2 0 80 120 2.0 heavy oil Embodiment 3 20 90 140 2.4 heavy oil Embodiment 4 0 40 60 2.4 liquid gas Embodiment 5 0 72 108 2.0 liquid gas Embodiment 6 0 95 130 2.3 liquid gas

[0040] Wherein the combustion medium mainly adopts heavy oil or liquid gas, so that cost can be saved, hut other natural gas can also he adopted in the technical solution of the present application.

TABLE-US-00003 TABLE 1-3 Step of Blowing of Combustion Medium and Oxygen Flow (Nm.sup.3/h) of Oxygen Total Flow (NL/h) Time (min) Flow (Single Blowing Gun, Blown by Single Blowing of Combustion Medium Total Flow (NL/h) of Blowing Nm.sup.3/h) of Oxygen Blown Gun in Process of Only Blown by All Blowing of Combustion Medium Combustion Simultaneously with Blowing Oxygen for Serial Number Guns in First 2 min Medium Combustion Medium Decarburization Smelting Embodiment 1 300 180 8 1000 3000 Embodiment 2 400 200 9 1200 3600 Embodiment 3 400 240 10 1200 4000 Embodiment 4 300 180 8 1000 3000 Embodiment 5 350 190 9 1100 3300 Embodiment 6 400 220 9 1200 3600

TABLE-US-00004 TABLE 1-4 Step of Electric Heating Percentage (%) of Oxygen Blowing Flow Batch to Previous Oxygen Adding Blowing Flow when Lime Dolomite Number Carbon Content is Serial Number (t) (t) (batch) Smaller Than 0.5% Embodiment 1 4 1 3 40 Embodiment 2 5 1.2 3 50 Embodiment 3 6 1.5 4 60 Embodiment 4 3 0.6 2 40 Embodiment 5 5 0.8 3 45 Embodiment 6 5.5 1.3 4 55

[0041] The “batch adding number” herein does not require the same feeding amount in different batches, depending on the specific smelting furnace slag condition. Generally, the lime and the dolomite are mixed and then the mixture is added in batches; or it can be that the lime is added first, and then the dolomite is added.

TABLE-US-00005 TABLE 1-5 Step of Electric Heating Nitrogen Content Argon Blowing Flow Residual Molten Steel Target (ppm) of Molten (NL/min) of Hollow and Residual Slag (t) Temperature(□) Steel after Argon Blowing Serial Number after Tapping of Molten Steel Tapping Electrode Embodiment 1 35 1620 20 60 Embodiment 2 40 1620 22 60 Embodiment 3 40 1640 24 100 Embodiment 4 30 1635 25 50 Embodiment 5 38 1620 21 60 Embodiment 6 40 1640 24 80

[0042] Table 2 lists the tapping quantity, consumed time, the smelting period and the annual output in the method for efficiently smelting the low nitrogen steel by using the electric furnace according to Embodiments 1-6.

TABLE-US-00006 TABLE 2 Tapping Time (min) of Each Smelt- Quanti- Furnace Shell from ing Annual Output ty Feeding to Tapping Period (ten thousand (t) finished (min) tons) Embodiment 1 150 60 30 200 Embodiment 2 200 66 33 240 Embodiment 3 250 72 36 270 Embodiment 4 100 50 25 160 Embodiment 5 180 64 32 220 Embodiment 6 220 68 34 260

[0043] By adopting the smelting method according to the technical solution of the present disclosure, the tapping quantity is 100 t-250 t, and the annual output can reach 1.6-2.7 million tons, while the maximum annual output of an existing furnace is 1.2 million tons, and the average annual output of the existing furnace is smaller than 900,000 tons. The smelting period in the technical solution of the present application is 25-36 min, while the average smelting period of a common dual-shell furnace is 56 min.

[0044] Thus, it can seen that the method for efficiently smelting the low nitrogen steel by using the electric furnace, which is disclosed by the present disclosure, not only can shorten the smelting period and improve the throughput of an electric furnace production line, but also can smelt the low nitrogen steel so as to meet the requirements of the market for high-end steel. Moreover, the method for efficiently smelting the low nitrogen steel by using the electric furnace, which is disclosed by the present disclosure, can reduce the discharge of dust and smoke, thereby protecting the environment.

[0045] It should be noted that in the scope of protection of the present disclosure, the prior art part is not limited to the embodiments provided by the present application, and all the prior arts without confliction with the solution of the present disclosure, including, but not limited to, the prior patent literatures, the prior publications, prior publication use and the like, all shall fall within the scope of protection of the present disclosure,

[0046] In addition, the combination mode of technical features in the present disclosure is not limited to the combination modes recorded in claims or the combination modes recorded in the specific embodiments, and all the technical features recorded in the present disclosure can be freely combined or integrated in any way, unless there is confliction between them.

[0047] It further should be noted that the foregoing embodiments merely are specific embodiments of the present disclosure. It is obvious that the present disclosure is not limited to the above embodiments, and similar variations or modifications, which can be directly obtained or easily conceived by those skilled in the art accordingly from the contents disclosed by the present disclosure, all shall fall within the scope of the present disclosure.