Smelting method of ultra-low phosphorus steel

Abstract

The invention belongs to the technical field of converter steelmaking in the ferrous metallurgy industry, and particularly provides a smelting method of ultra-low phosphorus steel. According to the method, refining slag slagging, slagging optimization, oxygen supply, temperature and end point control systems, bottom blowing process system optimization and the like are utilized, a duplex process is not needed, the purpose of stable production of the ultra-low-phosphorus steel can be achieved, and the phosphorus content in the ultra-low-phosphorus steel produced through the method is stably controlled to be 0.003% or below.

Description

Technical Field

[0001] The invention belongs to the technical field of converter steelmaking in the iron and steel metallurgical industry, and specifically relates to a method for smelting ultra-low phosphorus steel. Background Art

[0002] When the phosphorus content in steel is too high, it will significantly reduce the low-temperature impact toughness and deteriorate the welding performance. In recent years, with the strategic transformation of steel enterprises in terms of product quality and efficiency, the types of steel produced have gradually shifted to high-end steel varieties, and high-end steel varieties have very strict requirements on the phosphorus content in steel, especially for low-temperature steel, marine steel, container steel, hydrogen-induced cracking-resistant steel, etc., which require extremely low phosphorus content. Based on the impact of phosphorus on the performance of steel products, in order to meet the requirements of product applications in transportation, marine engineering, energy and other fields, the phosphorus content in steel products must be strictly controlled. Therefore, how to better reduce the phosphorus content in steel has become one of the key issues to be urgently solved in converter smelting production.

[0003] Chinese patent CN115369212A discloses a method for smelting ultra-low phosphorus steel, which improves the double slag smelting process by retaining the final slag of the previous furnace, increasing the slag basicity and dephosphorization efficiency; in the dephosphorization stage, optimizing the gun position and oxygen supply intensity, improving the slag removal efficiency, and then increasing the dephosphorization rate of one slag pouring; combined with subsequent decarburization blowing, the phosphorus content in the steel can be reduced to obtain ultra-low phosphorus steel. However, the phosphorus content of the final molten steel is still too high to meet the phosphorus content requirements in special fields. Summary of the invention

[0004] The object of the present invention is to provide a smelting method for ultra-low phosphorus steel, wherein the smelting method is to improve the slag making system and the like on the basis of the converter double slag smelting process, thereby obtaining ultra-low phosphorus steel.

[0005] The present invention provides a method for smelting ultra-low phosphorus steel, comprising the following steps:

[0006] 1) Steel material preparation process: pouring refined slag into molten iron to be put into the furnace to obtain molten iron for pre-furnace entry;

[0007] 2) Loading process: after slag splashing, pour out all the slag in the furnace, add lime, and then add scrap steel and molten iron pre-charged into the furnace;

[0008] 3) Blowing before slag pouring;

[0009] 4) dumping slag;

[0010] 5) Blowing after pouring slag;

[0011] 6) End point control: The end point carbon content is 0.04-0.06%, and the end point temperature is 1600-1610°C.

[0012] In step 1), the refined slag is aluminum killed steel refined slag,

[0013] Preferably, the production process of the aluminum killed steel is LF→RH→continuous casting or LF→continuous casting.

[0014] The composition of the refined slag is shown in the following table:

[0015] <![CDATA[SiO2 / %]]> CaO / % MgO / % <![CDATA[Al2O3 / %]]> Alkalinity 8～13 50～60 ≤6 20～30 4.0～7.0

[0016] Preferably, the amount of the refined slag added is 12-17 kg / t.

[0017] The Al2O3 in the refined slag acts as a slagging agent, and can achieve rapid slagging and dephosphorization.

[0018] The requirements for the composition of molten iron are: 0.45%≤silicon content≤0.65%. If the silicon content of molten iron is too low, it is not conducive to slag formation and the heat is not sufficient; if the silicon content of molten iron is too high, to achieve a certain alkalinity, too much lime needs to be added, which is not conducive to slag formation.

[0019] In step 2), the amount of lime added is 8-13 kg / t.

[0020] The temperature of the molten iron pre-charged into the furnace is controlled at 1290-1350° C., and the scrap steel ratio is controlled between 6.0% and 10.0%.

[0021] In step 2), all the slag in the furnace is poured out after slag splashing to avoid the influence of phosphorus pentoxide in the slag in the furnace on the phosphorus distribution ratio, so as to improve the dephosphorization rate.

[0022] In step 3), the blowing process before slag pouring includes:

[0023] The blowing gun position is controlled at 1600-1650mm (the gun position refers to the distance between the oxygen gun nozzle and the molten pool liquid surface), and the blowing oxygen pressure is controlled at 0.80-0.82Mpa; blowing to 350-400Nm 3 Add 16-25kg / t of lime and 16-21kg / t of sintered ore at the same time, and blow to 800-900Nm 3 Add 16-25kg / t of lime and 16-21kg / t of sintered ore at the same time, and blow to 1500-1600Nm 3 When the oxygen lance is raised to 1700-1750mm, the oxygen pressure remains unchanged; blowing 2500-3000Nm 3 Turn off the oxygen and lift the gun.

[0024] In this step, low oxygen pressure blowing is used to extend the oxygen supply time and fully dephosphorize.

[0025] In step 4), the slag pouring process includes: after turning off the oxygen and lifting the gun, bottom blowing and strong stirring for 1 to 1.5 minutes, the bottom blowing intensity during strong stirring is 0.090 to 0.100 Nm 3 / min·t, after which the slag is poured out;

[0026] In this step, after turning off the oxygen and lifting the gun, bottom blowing and strong stirring are performed for 1 to 1.5 minutes to further dephosphorize.

[0027] In step 5), the post-slag pouring blowing process includes: the gun position after slag pouring is operated at a constant gun position of 1600-1650mm, and the oxygen pressure is controlled at 0.82-0.85Mpa; lime is added at one time after 20-40s of blowing, and the total amount added is controlled between 25-34kg / t, and dolomite is added at one time of 8-10kg / t, and sintered ore is added evenly in batches, 3-4kg / t is added in each batch, and the addition is completed 3 minutes before the end point; 1 minute before the end point, the gun position is lowered to 1200-1250mm, and the oxygen pressure is controlled at 0.85-0.88Mpa until the gun is lifted at the end point;

[0028] Preferably, in step 5), the sintered ore is added in batches of 3 to 7 times.

[0029] In step 6), if the final temperature is higher than 1610°C, the dephosphorization rate will be affected, and the phosphorus content of the molten steel will increase in the later stage; if the final temperature is lower than 1600°C, the subsequent production will be affected, and the temperature of the molten steel entering the refining station will be too low, and normal production cannot be achieved.

[0030] According to the above-mentioned ultra-low phosphorus steel, the phosphorus content is lower than 0.003%.

[0031] The kg / t in the present invention refers to the weight of raw materials required per ton of steel.

[0032] The technology of the present invention has the following advantages and effects compared with the prior art:

[0033] 1. The present invention adds refined slag to the molten iron pre-charged into the furnace, pours out all the slag in the furnace after slag splashing, and simultaneously adds part of the lime in the furnace for preheating, thereby improving the rapid slag reduction in the early stage. Under the premise of not affecting the basicity, the invention can also avoid the influence of phosphorus pentoxide in the slag in the furnace on the phosphorus distribution ratio by using the slag retention process;

[0034] 2. The present invention optimizes the slag making, oxygen supply, temperature and endpoint control systems, and optimizes the bottom blowing process system, etc., without adopting a duplex process, and can achieve the purpose of stable production of ultra-low phosphorus steel. The phosphorus content in the ultra-low phosphorus steel produced by the present invention is stably controlled to be below 0.003%. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the examples, but is not limited thereto. The following examples are produced using a 120t converter.

[0036] Embodiment 1~3:

[0037] The embodiment of the present invention discloses a method for smelting ultra-low phosphorus steel, comprising the following steps:

[0038] 1. Pour 12-17 kg / t of aluminum-killed steel refined slag in the ladle after the LF→RH→continuous casting process into the molten iron ready to be put into the furnace. Examples 1-3 The composition and weight of the aluminum-killed steel refined slag in the ladle after the LF→RH→continuous casting process are shown in Table 1.

[0039] Table 1 Statistical table of composition and weight of aluminum killed steel refined slag in ladle after LF→RH→continuous casting process

[0040]

[0041] 2. Loading process: After slag splashing, pour out all the slag in the furnace and add 8-13 kg / t of lime into the furnace, then load scrap steel and molten iron. The specific amount of molten iron and scrap steel added into the furnace, as well as the molten iron composition and molten iron temperature of Examples 1-3 are shown in Table 2, and the amount of lime added into the furnace after slag splashing in Examples 1-3 is shown in Table 3.

[0042] Table 2 Statistics of molten iron composition, molten iron temperature, molten iron and scrap steel addition

[0043]

[0044] Table 3 Statistics of lime addition after slag splashing

[0045] Serial number Amount of lime added after slag splashing / t Example 1 1.2 Example 2 1.5 Example 3 1.3

[0046] 3. Blowing process before slag pouring:

[0047] Blowing gun position: 1600-1650mm (gun position refers to the distance between the oxygen gun nozzle and the molten pool liquid surface), blowing oxygen pressure is controlled at 0.80-0.82Mpa;

[0048] A batch of materials is added: blowing 350~400Nm 3 Add 16-25kg / t of lime and 16-21kg / t of sintered ore at the same time;

[0049] Second batch of materials added: blowing to 800-900Nm 3 Add 16-25kg / t of lime and 16-21kg / t of sintered ore at the same time;

[0050] Lifting gun: blowing to 1500~1600Nm 3 When the oxygen lance is lowered, the position of the oxygen lance is raised to 1700-1750mm, and the oxygen pressure remains unchanged;

[0051] Oxygen-free gun: blowing 2500~3000Nm 3 Turn off the oxygen and lift the gun.

[0052] 4. Slag dumping process: After turning off the oxygen and lifting the gun, bottom blowing and strong stirring are performed for 1 to 1.5 minutes. The bottom blowing intensity during strong stirring is 0.092Nm 3 / min·t, and then pour out the slag.

[0053] The specific oxygen supply process parameters of Examples 1 to 3 before slag pouring and the bottom blowing and strong stirring time after oxygen is turned off and the gun is lifted are shown in Table 4, and the bulk material addition conditions are shown in Table 5.

[0054] Table 4 Statistical table of specific oxygen supply process parameters of Examples 1 to 3 before slag pouring

[0055]

[0056]

[0057] Table 5 Statistical table of bulk material addition in Examples 1 to 3

[0058]

[0059] 5. Blowing process after slag pouring: After slag pouring, the initial gun position is operated at a constant gun position of 1600-1650mm, and the oxygen pressure is controlled at 0.82-0.85Mpa; lime is added at one time 30s after blowing starts, and the total amount added is controlled between 25-34kg / t. At the same time, dolomite is added at one time of 8-10kg / t. Sintered ore is added evenly in multiple batches according to the temperature conditions, and 3-4kg / t is added in each batch. The addition is completed 3 minutes before the end point; 1 minute before the end point, the gun position is lowered to 1200-1250mm, and the oxygen pressure is controlled at 0.85-0.88Mpa until the gun is lifted at the end point.

[0060] The specific oxygen supply process parameters of Examples 1 to 3 after slag pouring are shown in Table 6, and the bulk amount added is shown in Table 7.

[0061] Table 6 Specific oxygen supply process parameters after slag pouring

[0062] Serial number Early gun position / mm Initial oxygen pressure / Mpa End gun position / mm End point oxygen pressure / Mpa Example 1 1600 0.83 1200 0.86 Example 2 1620 0.85 1230 0.87 Example 3 1630 0.84 1220 0.88

[0063] Table 7 Statistics of bulk addition after slag pouring

[0064] Serial number Lime addition amount / t Dolomite addition amount / t Sintered ore addition amount / t Ore Adding Batch Example 1 3.5 1.2 2.3 5 Example 2 3.6 1.3 2.6 6 Example 3 3.3 1.1 2.8 6

[0065] 6. End point control:

[0066] End point carbon: 0.04~0.06%, end point temperature: 1600~1610℃.

[0067] The specific endpoint control conditions of Examples 1 to 3 are shown in Table 8.

[0068] Table 8 Statistics of temperature measurement, carbon determination and sampling for phosphorus content of auxiliary gun TSO

[0069] Serial number End point carbon / % End point temperature / ℃ End point phosphorus content / % Example 1 0.042 1605 0.0023 Example 2 0.053 1607 0.0028 Example 3 0.055 1600 0.0029

Claims

1. A method for smelting ultra-low phosphorus steel, characterized in that: The steps include: 1) Steel material preparation process: pouring refined slag into molten iron to be put into the furnace to obtain molten iron for pre-furnace entry; 2) Loading process: after slag splashing, pour out all the slag in the furnace, add lime, and then add scrap steel and molten iron pre-charged into the furnace; 3) Blowing before slag pouring; 4) dumping slag; 5) Blowing after slag pouring; 6) End point control: The end point carbon content is 0.04-0.06%, and the end point temperature is 1600-1610°C.

2. The smelting method of ultra-low phosphorus steel according to claim 1, characterized in that: In step 1), the refined slag is aluminum killed steel refined slag, Preferably, the production process of the aluminum killed steel is LF→RH→continuous casting or LF→continuous casting; The refined slag composition includes: 8-13% SiO2, 50-60% CaO, ≤6% MgO, 20-30% Al2O3; The basicity of the refined slag is 4.0-7.

0.

3. The smelting method of ultra-low phosphorus steel according to claim 2, characterized in that: The added amount of the refined slag is 12-17 kg / t.

4. The smelting method of ultra-low phosphorus steel according to claim 1, characterized in that: In step 3), the blowing process before slag pouring includes: The opening gun position is controlled at 1600-1650mm, and the opening oxygen pressure is controlled at 0.80-0.82Mpa; Blowing to 350~400Nm 3 Add lime 16-25kg / t, add sinter 16-21kg / t, and blow to 800-900Nm 3 Add 16-25kg / t of lime and 16-21kg / t of sintered ore at the same time, and blow to 1500-1600Nm 3 When the oxygen lance is raised to 1700-1750mm, the oxygen pressure remains unchanged; blowing 2500-3000Nm 3 Turn off the oxygen and lift the gun.

5. The smelting method of ultra-low phosphorus steel according to claim 1, characterized in that: In step 4), the slag pouring process includes: after turning off the oxygen and lifting the gun, bottom blowing and strong stirring for 1 to 1.5 minutes, the bottom blowing intensity during strong stirring is 0.090 to 0.100 Nm 3 / min·t, and then pour out the slag.

6. The smelting method of ultra-low phosphorus steel according to claim 1, characterized in that: In step 5), the post-slag pouring blowing process includes: the gun position after slag pouring is operated at a constant gun position of 1600-1650mm, and the oxygen pressure is controlled at 0.82-0.85Mpa; lime is added at one time after 20-40s of blowing, and the total amount added is controlled between 25-34kg / t, and dolomite is added at one time of 8-10kg / t, and sintered ore is added evenly in batches, 3-4kg / t is added in each batch, and the addition is completed 3 minutes before the end point; 1 minute before the end point, the gun position is lowered to 1200-1250mm, and the oxygen pressure is controlled at 0.85-0.88Mpa until the gun is lifted at the end point; Preferably, the sintered ore is added in batches of 3 to 7 times.

7. The method for smelting ultra-low phosphorus steel according to claim 1, characterized in that: In step 1), the silicon content of the molten iron is 0.45%≤0.65%.

8. The method for smelting ultra-low phosphorus steel according to claim 1, characterized in that: In step 2), the amount of lime added is 8-13 kg / t.

9. The method for smelting ultra-low phosphorus steel according to claim 1, characterized in that: In step 2), the temperature of the molten iron pre-charged into the furnace is controlled at 1290-1350° C., and the scrap steel ratio is controlled between 6.0% and 10.0%.

10. The method for smelting ultra-low phosphorus steel according to any one of claims 1 to 9, characterized in that: The ultra-low phosphorus steel smelted according to the ultra-low phosphorus steel smelting method has a phosphorus content of less than 0.003%.

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