A method for smelting sulfur-containing steel by combining a two-step process of dephosphorization and decarburization with RH vacuum treatment

Abstract

A method for smelting sulfur-containing steel by combining a two-stage process of dephosphorization and decarburization with RH vacuum treatment. The production process flow is: hot metal pretreatment → dephosphorization converter smelting → decarburization converter smelting → RH vacuum refining → continuous casting. During the production process, the molten steel does not undergo LF secondary refining. In the RH vacuum refining process, the vacuum degree of RH vacuum treatment is ≥ 67 Pa; the vacuum treatment time is ≥ 20 min; aluminum pellets are added to the molten steel within 5 min after the vacuum degree reaches 67 Pa. After breaking the vacuum, a calcium wire is fed first, then soft blowing is carried out for 8 - 12 min, then a corresponding sulfur wire is fed according to the sulfur content of the molten steel, then soft blowing is carried out for ≥ 20 min, and then the molten steel is allowed to stand, and the standing time is 8 - 12 min. The proportion of sulfides with an aspect ratio ≥ 3 is reduced from 60% to below 35%.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgy, and further belongs to the field of steelmaking. Background Art

[0002] Sulphur-containing free-cutting structural steel has good comprehensive mechanical properties and cutting performance, and is an important type of steel material in the field of mechanical manufacturing, and is widely used in the production of automotive parts. However, the sulphide inclusions in sulphur-containing steel have good plasticity, generally distributed in clusters and unevenly, and are prone to deformation along the rolling direction during the rolling process, affecting the mechanical properties of the steel. Sulphide also becomes one of the important reasons for excessive inclusions and non-compliance in ultrasonic flaw detection. Therefore, the generation of long and thin strip-shaped sulphides should be reduced or avoided, and the sulphides should be spherical or spindle-shaped.

[0003] The traditional process for producing sulphur-containing steel is converter / electric furnace, LF ladle furnace refining, RH / VD vacuum refining, and continuous casting. After slag making and soft blowing treatment in the LF furnace, small particle Al2O3 inclusions can be easily removed, and during the solidification process, not many nucleation cores can be provided for sulphides, resulting in a low proportion of sulphide composite inclusions and limited control level of type A inclusions.

[0004] CN 104212942B "A Process Method for Improving the Morphology of Sulphides in Sulphur-containing Steel" provides a method for improving the distribution of sulphides. The production process is converter / electric furnace smelting → LF ladle furnace refining → VD vacuum refining → LF ladle furnace refining → continuous casting. The proportion of sulphides with an aspect ratio ≤ 6 reaches more than 60%, and the level of type A inclusions ≤ 3 grades. This invention patent requires two LF refining furnaces, with a long production process, low efficiency, high cost, and a low level of sulphide control.

[0005] CN110387452A "A Method for Controlling Sulphide Inclusions in Sulphur-containing Steel", the production process is converter smelting → LF ladle furnace refining - VD vacuum refining → continuous casting. The high magnification of the rolled material, the fine series and coarse series levels of type A inclusions are respectively ≤ 2.0 grades. This invention patent has a long LF furnace smelting time, low production efficiency, and poor sulphide dispersion effect.

[0006] CN113278764A "Smelting Method for Improving Sulphur Dispersion in Medium Carbon Sulphur-containing Steel", converter smelting → LF ladle furnace refining - VD vacuum refining → continuous casting. This method can improve the distribution morphology of sulphides in medium carbon sulphur-containing steel, reduce the proportion of long strip-shaped sulphides, and the fine series of type A inclusions ≤ 2.0 grades, the coarse series ≤ 1.5 grades. This invention patent is only applicable to medium carbon sulphur-containing steel, and the sulphide dispersion effect is not good. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for smelting sulfur-containing steel by combining a dephosphorization and decarburization double process with RH vacuum treatment. The method of the present invention retains small particle oxide inclusions, increases the proportion of sulfide composite inclusions, improves the morphology of sulfides, and reduces the proportion of sulfides with an aspect ratio ≥ 3.

[0008] To solve the above technical problems, the technical solution of the present invention is: a method for smelting sulfur-containing steel by combining a dephosphorization and decarburization double process with RH vacuum treatment. The production process flow is hot metal pretreatment → dephosphorization converter smelting → decarburization converter smelting → RH vacuum refining → continuous casting. During the production process, the molten steel does not undergo LF secondary refining. In the RH vacuum refining process, the vacuum degree of RH vacuum treatment is ≥ 67 Pa; the vacuum treatment time is ≥ 20 min; aluminum pellets are added to the molten steel within 5 min after the vacuum degree reaches 67 Pa. After breaking the vacuum, a calcium wire of 0.6 - 1.0 m / ton of steel is fed first, then soft blowing is carried out for 8 - 12 min, then a sulfur wire is fed according to the sulfur content of the molten steel, then soft blowing is carried out for ≥ 20 min, and then the molten steel is allowed to stand, and the standing time is 8 - 12 min.

[0009] The purpose of feeding the calcium wire into the molten steel is to modify part of Al2O3 to prevent the over-standard of type B inclusions. After feeding the calcium wire, most of the Ca forms semi-solid CaOAl2O3, which will also act as a nucleation core to form composite inclusions with sulfides;

[0010] Soft blowing and standing after feeding the sulfur wire into the molten steel both promote the floating of inclusions. One is to promote the floating of CaS inclusions formed after feeding the sulfur wire to prevent the blockage of the nozzle by CaS inclusions during the continuous casting process; the other is to promote the floating of large-size Al2O3 inclusions or large-size calcium aluminate inclusions formed after feeding the calcium wire.

[0011] The feeding of the corresponding sulfur wire according to the sulfur content of the molten steel means that the sulfur content in the molten steel is adjusted by feeding the sulfur wire to make the sulfur content in the finished molten steel meet the target requirements.

[0012] Further, in the hot metal pretreatment process, the mass fraction of silicon in the pretreated hot metal is ≤ 0.15%, the mass fraction of phosphorus is ≤ 0.04%, and the hot metal temperature is 1200 - 1350 °C.

[0013] Further, in the hot metal pretreatment process, KR hot metal pretreatment is carried out. During the hot metal pretreatment process, 11 - 15 kg / t of lime and 40 - 50 kg / t of sinter ore powder are added, and the treatment cycle is 25 - 35 min.

[0014] Further, in the dephosphorization converter smelting process, the tapping temperature is 1380 - 1480 °C, the mass percentage of carbon in the tapped steel is ≥ 1.5%, and the mass percentage of phosphorus at the end of smelting is ≤ 0.010%.

[0015] Furthermore, in the decarbonization converter smelting process, the tapping temperature ≥ 1670 °C; during the tapping process of the converter, deoxidation alloying is carried out, and 2.6 - 3.0 m / t of molten steel of aluminum wire is fed at the end of tapping.

[0016] Furthermore, for the deoxidation alloying, aluminum cored wire is added during the tapping process of the converter for deoxidation, and corresponding alloys are added according to the composition requirements. The purpose of using aluminum cored wire in this application is to deoxidize the molten steel, prevent the inclusions formed after adding a large amount of alloys to the molten steel from contaminating the molten steel, and the alloy recovery rate can be improved and the alloy cost can be saved after the molten steel is deoxidized and then alloys are added; in order to achieve this purpose, aluminum blocks can also be used for deoxidation.

[0017] Furthermore, the composition of the sulfur-containing steel and its mass percentage are: C 0.17 - 0.60%, Si 0.15 - 0.65%, Mn 0.60 - 1.50%, S 0.01 - 0.10%, P ≤ 0.020%, Cr 0.10 - 1.35%, Al 0.010 - 0.040, Ca 0.0005 - 0.002%, Ti ≤ 0.08%, and the balance is Fe and inevitable impurities.

[0018] The beneficial effects of adopting the above technical solutions are as follows:

[0019] 1. This method does not pass through LF secondary refining, and stabilizes the alloy recovery rate and the components of S, P, and C through the triple removal treatment of hot metal.

[0020] 2. Utilizing the vacuum treatment of RH vacuum refining, large particles of Al2O3 inclusions with a size > 3 μm are removed, and small particles of Al2O3 inclusions with a size of 1 - 3 μm are retained. During the solidification process, they form composite inclusions with sulfides, increasing the proportion of composite inclusions from 4.2% to over 14%, and reducing the proportion of sulfides with an aspect ratio ≥ 3 from 60% to below 35%. This improves the purity of the molten steel, and the fine series of type A inclusions in the rolled material ≤ 1.5 grades, and the coarse series ≤ 0.5 grades. At the same time, it will not block the continuous casting nozzle and will not cause production interruption, facilitating the popularization and application of sulfur-containing steel, and having significant social and economic benefits. Description of the Drawings

[0021] Figure 1 、 Figure 2 、 Figure 3 It is the morphology of typical Al2O3 - MnS composite sulfides in the sulfur-containing steel obtained according to the method of the present invention.

[0022] Figure 4 It is the surface scanning result of typical Al2O3 - MnS composite sulfides in the sulfur-containing steel obtained according to the method of the present invention.

[0023] Figure 5 It is the overall morphology of typical sulfide inclusions in the sulfur-containing steel obtained according to the method of the present invention.

[0024] Figure 6 Proportion of sulfide complex inclusions in the sulfur-containing steel obtained in Examples 1-5.

[0025] Figure 7 Proportion of sulfides with an aspect ratio ≥ 3 in the sulfur-containing steel obtained in Examples 1-5.

[0026] Figure 8 Detection results of fine and coarse A-type inclusions in the sulfur-containing steel obtained in Examples 1-5. Embodiment

[0027] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] The component content of the molten steel finished product in Examples 1-5 is shown in Table 1.

[0029] Table 1 (%)

[0030]

[0031] The following are the specific process parameters of Examples 1-5. Example 1

[0032] (1) Hot metal pretreatment process: 11 kg / t of lime and 40 kg / t of sinter ore powder are added during the hot metal pretreatment process. The treatment cycle is 25 min. Before entering the dephosphorization converter, the hot metal has Si: 0.15%, P: 0.04%, and the hot metal temperature is 1350 °C.

[0033] (2) Dephosphorization converter process: When tapping from the converter, C: 1.5%, P: 0.01%, and the tapping temperature is 1480 °C.

[0034] (3) Decarburization converter process: The tapping temperature of the converter is 1690 °C. Slag leakage is strictly prohibited during tapping. After tapping, 3 m / t of aluminum wire is fed into the steel.

[0035] (4) RH vacuum refining process: The RH vacuum holding time is 30 min, the vacuum degree is 67 Pa. 0.06 kg / t of aluminum pellets are added at 5 min of vacuum. After the RH breaks the vacuum, 0.6 m / t of calcium wire is fed into the steel. After soft blowing for 8 min, the sulfur wire is fed; after feeding the sulfur wire, S is 0.10%. After feeding the wire, soft blowing is carried out for 20 min, the soft blowing flow rate is 25 L / min, and it is static for 12 min.

[0036] (5) Continuous casting process: The continuous casting casting speed is 0.6 m / min, the specific water volume is 0.25 L / kg, the electromagnetic stirring current is 80 A, the electromagnetic stirring frequency is 2.0 HZ, and the continuous casting billet is taken off the line and stacked for cooling; the sulfur-containing steel rolled material is obtained after rolling the continuous casting billet. Example 2

[0037] (1) Hot metal pretreatment process: During the hot metal pretreatment, 12 kg / t of lime and 42 kg / t of sinter ore powder are added. The treatment cycle is 27 min. Before entering the dephosphorization converter, the hot metal has Si: 0.14%, P: 0.038%, and the hot metal temperature is 1310 °C.

[0038] (2) Dephosphorization converter process: When tapping from the converter, C: 1.7%, P: 0.009%, and the tapping temperature is 1460 °C.

[0039] (3) Decarburization converter process: The tapping temperature of the converter is 1685 °C. During tapping, slagging is strictly prohibited. After tapping, 2.9 m / t of aluminum wire is fed.

[0040] (4) RH vacuum refining process: The RH vacuum holding time is 28 min, the vacuum degree is 67 Pa. At 4 min of vacuum, 0.07 kg / t of aluminum pellets are added. After the RH breaks the vacuum, 0.7 m / ton of steel of calcium wire is fed. After soft blowing for 9 min, sulfur wire is fed; after feeding the sulfur wire, S is 0.08%. After feeding the wire, soft blowing is carried out for 21 min, the soft blowing flow rate is 24 L / min, and it is static for 11 min.

[0041] (5) Continuous casting process: The continuous casting casting speed is 0.82 m / min, the specific water volume is 0.29 L / kg, the electric stirring current is 130 A, the electric stirring frequency is 2.0 HZ. The continuous casting billet is taken off the line and stacked for cooling; After rolling the continuous casting billet, sulfur-containing steel rolled products are obtained. Example 3

[0042] (1) Hot metal pretreatment process: During the hot metal pretreatment, 13 kg / t of lime and 45 kg / t of sinter ore powder are added. The treatment cycle is 30 min. Before entering the dephosphorization converter, the hot metal has S: 0.003%, Si: 0.13%, P: 0.036%, and the hot metal temperature is 1270 °C.

[0043] (2) Dephosphorization converter process: When tapping from the converter, C: 1.9%, P: 0.008%, and the tapping temperature is 1430 °C.

[0044] (3) Decarburization converter process: The tapping temperature of the converter is 1680 °C. During tapping, slagging is strictly prohibited. After tapping, 2.8 m / t of aluminum wire is fed.

[0045] (4) RH vacuum refining process: The RH vacuum holding time is 25 min, the vacuum degree is 67 Pa. At 3 min of vacuum, 0.08 kg / t of aluminum pellets are added. After the RH breaks the vacuum, 0.8 m / ton of steel of calcium wire is fed. After soft blowing for 10 min, sulfur wire is fed; after feeding the sulfur wire, S is 0.05%. After feeding the wire, soft blowing is carried out for 22 min, the soft blowing flow rate is 24 L / min, and it is static for 10 min.

[0046] (5) Continuous casting process: The continuous casting drawing speed is 0.90 m / min, the specific water volume is 0.35 L / kg, the electric stirring current is 190 A, the electric stirring frequency is 3.5 HZ, and the continuous casting billet is stacked and cooled offline; the sulfur-containing steel rolled material is obtained after rolling the continuous casting billet. Example 4

[0047] (1) Hot metal pretreatment process: 14 kg / t of lime and 48 kg / t of sinter ore powder are added during the hot metal pretreatment process. The treatment cycle is 32 min. Before entering the dephosphorization converter, the hot metal S: 0.004%, Si: 0.12%, P: 0.034%, and the hot metal temperature: 1230 °C.

[0048] (2) Dephosphorization converter process: The converter taps, C: 2.1%, P: 0.007%, and the tapping temperature is 1400 °C.

[0049] (3) Decarburization converter process: The converter tapping temperature is 1675 °C. Slag dropping is strictly prohibited during the tapping process. After tapping, 2.7 m / t of aluminum wire is fed to ensure the aluminum content in the molten steel.

[0050] (4) RH vacuum refining process: The RH vacuum holding time is 27 min, the vacuum degree is 67 Pa, 0.09 kg / t of aluminum pellets are added at 2 min of vacuum, 0.9 m / t of calcium wire is added after the RH breaks the vacuum, and soft blowing is carried out for 11 min and then sulfur wire is fed; after feeding the sulfur wire, S is 0.03%, soft blowing is carried out for 23 min after feeding the wire, the soft blowing flow rate is 25 L / min, and it is static for 9 min.

[0051] (5) Continuous casting process: The continuous casting drawing speed is 1.15 m / min, the specific water volume is 0.44 L / kg, the electric stirring current is 230 A, the electric stirring frequency is 4.5 HZ, and the continuous casting billet is stacked and cooled offline; the sulfur-containing steel rolled material is obtained after rolling the continuous casting billet. Example 5

[0052] (1) Hot metal pretreatment process: 15 kg / t of lime and 50 kg / t of sinter ore powder are added during the hot metal pretreatment process. The treatment cycle is 35 min. Before entering the dephosphorization converter, the hot metal S: 0.003%, Si: 0.11%, P: 0.032%, and the hot metal temperature: 1200 °C.

[0053] (2) Dephosphorization converter process: The converter taps, C: 2.3%, P: 0.006%, and the tapping temperature is 1380 °C.

[0054] (3) Decarburization converter process: The converter tapping temperature is 1670 °C. Slag dropping is strictly prohibited during the tapping process. After tapping, 2.6 m / t of aluminum wire is fed to ensure the aluminum content in the molten steel.

[0055] (4)RH vacuum refining process: The RH vacuum holding time is 20 min, the vacuum degree is 67 Pa. 0.10 kg / t of aluminum pellets are added at 1 min of vacuum. After the RH breaks the vacuum, 1.0 m of calcium wire is fed per ton of steel. The sulfur wire is fed after soft blowing for 12 min. The S content is 0.01% after feeding the sulfur wire. After feeding the wire, soft blowing is carried out for 24 min, the soft blowing flow rate is 25 L / min, and it is left standing for 8 min.

[0056] (5)Continuous casting process: The continuous casting casting speed is 1.3 m / min, the specific water volume is 0.55 L / kg, the electric stirring current is 270 A, the electric stirring frequency is 5.0 HZ. The continuous casting billet is taken off the production line and stacked for cooling. The sulfur-containing steel rolled products are obtained after rolling the continuous casting billet.

[0057] In Examples 1-5, the morphology control of sulfide inclusions in the sulfur-containing steel is ideal. The inclusion detection results are as shown in the appendix Figures 1-5 As shown. A large number of composite sulfides are generated in the steel, and there are fewer fine strip-shaped sulfides. The proportion of composite sulfide inclusions increases from 4.2% to more than 14%. The proportion of sulfides with an aspect ratio ≥ 3 decreases from 60% to less than 35%. The fine series of type A inclusions ≤ 1.5 grades, and the coarse series ≤ 0.5 grades.

[0058] The above examples are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above examples, those of ordinary skill in the art should understand that: The present invention can still be modified or equivalently replaced, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A method for smelting sulfur-containing steel by combining a two-step process of dephosphorization and decarburization with RH vacuum treatment, the production process flow being hot metal pretreatment → dephosphorization converter smelting → decarburization converter smelting → RH vacuum refining → continuous casting, characterized in that, During the production process, the molten steel is not subjected to LF secondary refining. In the RH vacuum refining process, the vacuum degree of RH vacuum treatment is ≥67 Pa; the time of vacuum treatment is ≥20 min; aluminum pellets are added to the molten steel within 5 min after the vacuum degree reaches 67 Pa. After breaking the vacuum, 0.6 - 1.0 m / t of calcium wire is fed first, then soft blowing is carried out for 8 - 12 min, then the corresponding sulfur wire is fed according to the sulfur content of the molten steel, then soft blowing is carried out for ≥20 min, and then the molten steel is left standing for 8 - 12 min; in the hot metal pretreatment process, the mass fraction of silicon in the pretreated hot metal is ≤0.15%, the mass fraction of phosphorus is ≤0.04%, and the hot metal temperature is 1200 - 1350 °C.

2. The method for smelting sulfur-containing steel by combining a dephosphorization and decarburization double process with RH vacuum treatment according to claim 1, wherein, In the hot metal pretreatment process, KR hot metal pretreatment is carried out. During the hot metal pretreatment process, 11 - 15 kg / t of lime and 40 - 50 kg / t of sinter ore powder are added, and the treatment cycle is 25 - 35 min.

3. A method for smelting sulfur-containing steel by combining a dephosphorization and decarburization double process with RH vacuum treatment according to claim 1, characterized in that, In the phosphorus removal converter smelting process, the tapping temperature is 1380 - 1480 °C, the mass percentage of carbon in the tapped steel is ≥1.5%, and the mass percentage of phosphorus at the end of smelting is ≤0.010%.

4. A method for smelting sulfur-containing steel by combining a dephosphorization and decarburization double process with RH vacuum treatment according to claim 1, characterized in that, In the decarbonization converter smelting process, the tapping temperature is ≥1670 °C; deoxidation alloying is carried out during the tapping process of the converter, and 2.6 - 3.0 m / t of aluminum wire is fed after the tapping is completed.

5. A method for smelting sulfur-containing steel by combining a dephosphorization and decarburization double process with RH vacuum treatment according to claim 4, characterized in that, For the deoxidation alloying, steel-cored aluminum is added during the tapping process of the converter for deoxidation, and the corresponding alloys are added according to the composition requirements.

6. A method for smelting sulfur-containing steel by combining a dephosphorization and decarburization double process with RH vacuum treatment according to claim 1, characterized in that, The composition and mass percentage of the sulfur-containing steel are as follows: C 0.17 - 0.60%, Si 0.15 - 0.65%, Mn 0.60 - 1.50%, S 0.01 - 0.10%, P ≤0.020%, Cr 0.10 - 1.35%, Al 0.010 - 0.040, Ca 0.0005 - 0.002%, Ti ≤0.08%, and the balance is Fe and unavoidable impurities.

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