A method for smelting titanium-containing steel using a molten iron three-removal process combined with a vacuum refining process

Abstract

A method for smelting titanium-containing steel by combining a molten iron triple-removal process with a vacuum refining process. The production process is as follows: molten iron pretreatment → converter smelting → vacuum treatment → continuous casting. The method is characterized in that the molten steel is not subjected to LF refining outside the furnace during the production process. In the vacuum treatment process, Al-Mg cored wire is added after the molten steel is vacuum treated. The present invention increases the proportion of TiN composite inclusions in titanium-containing gear steel ingots from 3.1% to over 18%, and the number density of TiN inclusions with a size greater than 2μm increases from 30 / mm 2 Reduced to 15 / mm 2 Below; the size of TiN inclusions in rolled products is all below 4μm, and Ds type inclusions are ≤ level 0.5.

Description

Technical Field

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

[0002] In the actual production of titanium-containing gear steel, TiN inclusions will form in the steel due to the complex smelting process and solidification segregation. The premature precipitation of TiN inclusions has a tendency to aggregate and grow, forming large, angular, and non-deformable TiN inclusions in the molten steel. This will reduce the cleanliness of the steel and have an adverse effect on the fatigue performance and toughness of the steel. Therefore, the size of TiN inclusions in the steel should be reduced as much as possible while making their distribution more uniform.

[0003] The conventional production process of titanium-containing gear steel is converter / electric furnace, LF refining outside the furnace, RH / VD vacuum refining, and continuous casting. This process involves heating, slag making, and soft blowing in the LF refining furnace. The arc ionized air increases nitrogen levels significantly, and small oxide inclusions are easily removed. During the solidification process, heterogeneous nucleation with a larger number of TiN inclusions is impossible, resulting in a low proportion of TiN composite inclusions, which leads to larger TiN size.

[0004] CN107619983A, "Smelting Process for Reducing TiN Inclusions in 20CrMnTi Gear Steel," provides a smelting process for reducing TiN inclusions. The production process is converter → LF refining → RH vacuum refining → continuous casting. The nitrogen content in the ingot is >0.004%, and the TiN inclusion is level 1.5. This patented invention, produced through the LF refining furnace, has a high nitrogen content in the ingot, and the level of TiN inclusion control is not high.

[0005] CN114075617A, "A method for reducing the harmfulness of TiN inclusions in steel," provides a method for modifying TiN inclusions by adding V to steel. The maximum size of the TiN inclusions in this patent is 5 μm, resulting in poor dispersion. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for smelting titanium-containing steel by combining a hot metal triple-refining process with a vacuum refining process. This method avoids the increase of nitrogen from air ionized by the arc during the LF heating process, and disperses TiN inclusions, thereby reducing the size of TiN inclusions.

[0007] To solve the above technical problems, the technical solution of the present invention is: a method for smelting titanium-containing steel by combining a molten iron three-removal process with a vacuum refining process. The production process flow is molten iron pretreatment → converter smelting → vacuum treatment → continuous casting. The molten steel is not subjected to LF refining during the production process. In the vacuum treatment step, Al-Mg cored wire is added after the molten steel is vacuum treated.

[0008] Furthermore, the vacuum treatment step includes performing vacuum treatment to reduce the mass percentage of nitrogen in the molten steel to ≤0.004%.

[0009] Furthermore, in the vacuum treatment process, titanium content in the steel is adjusted using titanium-iron wire.

[0010] Furthermore, in the vacuum treatment process, a VD furnace is used to perform vacuum treatment on the molten steel, and the vacuum degree of the vacuum treatment process is below 1 mbar, wherein the deep vacuum of 0.6 mbar is maintained for ≥20 minutes.

[0011] Furthermore, the feed rate of the Al-Mg cored wire is 0.11-0.15 m / t.

[0012] Furthermore, a more detailed smelting method is provided.

[0013] In the molten iron pretreatment step, the mass fraction of Si in the molten iron after pretreatment is ≤0.20%, the mass fraction of P is ≤0.01%, the mass fraction of S is ≤0.01%, and the molten iron temperature is 1250-1350°C;

[0014] In the converter smelting process, the converter tapping temperature is ≥1660°C; 3-5kg / t of silicon-aluminum-barium alloy is added for deoxidation in the early stage of the converter tapping process, and then alloys are added according to the target composition requirements of the molten steel;

[0015] The purpose of adding silicon-aluminum-barium alloy is to deoxidize the molten steel and prevent inclusions formed after a large amount of alloy is added to the molten steel from contaminating the molten steel. Adding alloy after the molten steel is deoxidized can increase the alloy yield and save alloy costs. Composite silicon-aluminum-iron or aluminum ingots can also be used to deoxidize the molten steel, but the degree of deoxidation of the molten steel and the price of the alloy itself are different.

[0016] The vacuum treatment process involves adding 1.0-2.5 kg / t of aluminum pellets during the vacuum process. After the vacuum is broken, 80-120 m of calcium wire is first fed. After soft-blowing the molten steel, titanium-iron wire is fed according to the titanium content of the molten steel. The molten steel is then soft-blown again. After soft-blowing, the Al-Mg cored wire is fed, and the molten steel is then allowed to rest for 8-12 minutes. This vacuum treatment process is most suitable for a VD furnace, but an RH furnace can also be used in production.

[0017] If an RH furnace is used instead of a VD furnace for vacuum treatment, the vacuum degree of the RH vacuum treatment shall be ≥67 Pa; the vacuum treatment time shall be ≥20 min; aluminum particles shall be added to the molten steel within 5 min after the vacuum degree reaches 67 Pa, and 80-120 m calcium wire shall be fed first after breaking the air. After soft blowing for 8-12 min, the corresponding titanium-iron wire shall be fed according to the titanium content of the molten steel, and then the molten steel shall be soft blown for another 8-12 min. After soft blowing, the Al-Mg cored wire shall be fed, and then the molten steel shall be allowed to stand for 8-12 min.

[0018] The titanium content in the molten steel is adjusted by feeding the corresponding titanium-ferro-wire according to the titanium content in the molten steel, so that the titanium content in the finished molten steel meets the target requirement.

[0019] The purpose of feeding 80-120m calcium wire is to modify part of Al2O3, transforming Al2O3 into semi-solid CaOAl2O3, and preventing Class B inclusions from exceeding the standard. CaOAl2O3 will also serve as a nucleation core to form composite inclusions with TiN. As long as this purpose can be achieved, the amount of calcium wire fed can be adjusted according to the diameter of the calcium wire and the amount of molten steel.

[0020] Furthermore, in the converter smelting process, argon is blown throughout the steel tapping process, and argon is blown for 2-6 minutes at the argon station after steel tapping.

[0021] Furthermore, the soft blowing time for each soft blowing is 8-12 minutes.

[0022] Furthermore, in the molten iron pretreatment process, 50-60 kg / t of rolled steel scale, 15-18 kg / t of lime, and 4-6 kg / t of fluorite are added, and the treatment cycle is 35-45 minutes.

[0023] Furthermore, the titanium-containing steel composition and its mass percentage are: C 0.17-0.45%, Si 0.17-1.60%, Mn 0.85-1.25%, S ≤0.030%, P ≤0.030%, Cr 1.00-1.95%, Al 0.015-0.050%, Ti0.01-0.10%, and the balance is Fe and unavoidable impurities.

[0024] The beneficial effects of adopting the above technical solution are:

[0025] 1. This method does not involve refining outside the LF furnace, which avoids the increase of nitrogen in the air due to arc ionization during the heating process.

[0026] 2. Use VD deep vacuum treatment to remove large oxide inclusions larger than 3μm, retaining small oxide inclusions of 1-3μm, and feed Al-Mg cored wire in the later stage of VD refining to form TiN composite inclusions with Al2O3-MgO as the heterogeneous nucleation core.

[0027] 3. Adjust the titanium content through titanium-iron wire to avoid large-sized TiN inclusions in titanium-iron alloy.

[0028] 4. Based on the above operation, the proportion of TiN composite inclusions in the ingot increased from 3.1% to more than 18%, and the number density of TiN inclusions with a size of >2μm increased from 30 / mm 2 Reduced to 15 / mm 2Below; the size of TiN inclusions in rolled products is all below 4μm, and Ds type inclusions are ≤ level 0.5. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 、 Figure 2 、 Figure 3 This is the typical Al2O3-MgO-TiN composite inclusion morphology in titanium-containing gear steel obtained according to the method of the present invention.

[0030] Figure 4 This is the surface scanning result of typical Al2O3-MgO-TiN composite inclusions in titanium-containing gear steel obtained according to the method of the present invention.

[0031] Figure 5 The ratio of TiN composite inclusions in the titanium-containing gear steel obtained in Examples 1-5.

[0032] Figure 6 The number density ratio of TiN inclusions with a size greater than 2 μm in the titanium-containing gear steel obtained in Examples 1-5.

[0033] Figure 7 This is the level of type D inclusions in the titanium-containing gear steel obtained in Examples 1-5. Implementation Method

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] The components and mass percentages of the finished molten steel of Examples 1-5 are shown in Table 1.

[0036] Table 1

[0037]

[0038] The following are the specific process parameters of Examples 1-5. Example 1

[0039] (1) Hot metal pretreatment process: add 60kg / t of rolled steel scale, 18kg / t of lime, and 6.0kg / t of fluorite. The treatment cycle is 45min. After pretreatment, the Si content of the hot metal is 0.10%, P is 0.006%, and S is 0.006%. The hot metal temperature is 1250℃.

[0040] (2) Converter process: 5.0 kg / t of silicon, aluminum and barium is added to the converter steel, the steel tapping temperature is 1660 °C, and argon is blown at the argon station for 6 minutes.

[0041] (3) VD vacuum refining process: 0.6 mbar deep vacuum time 20 min, molten steel N content 0.0040%; 1.5 kg / t aluminum particles are added during the vacuum process, and 120 m calcium wire is fed first after breaking the air. After soft blowing for 12 min, the corresponding titanium-iron wire is fed according to the sampled titanium content. The titanium content of the molten steel is ≥0.02%. After soft blowing for 12 min, 0.11 m / t Al-Mg cored wire is fed and the standing time is 8 min.

[0042] (4) Continuous casting process: The superheat of the continuous casting tundish is controlled at 15-30°C, the casting speed is controlled at 1.30m / min, the crystallizer is electromagnetically stirred, dynamic soft reduction technology is used, and the continuous casting billet is cooled off the line; the continuous casting billet is rolled to obtain titanium-containing gear steel rolled products. Example 2

[0043] (1) Hot metal pretreatment process: 57 kg / t of rolled steel scale, 17 kg / t of lime, and 5.5 kg / t of fluorite were added. The treatment cycle was 42 min. After pretreatment, the Si content in the hot metal was 0.12%, P was 0.007%, and S was 0.007%. The hot metal temperature was 1280 °C.

[0044] (2) Converter process: 4.5 kg / t of silicon, aluminum and barium is added to the converter steel, the steel tapping temperature is 1665 °C, and argon is blown at the argon station for 5 minutes.

[0045] (3) VD vacuum refining process: 0.6 mbar deep vacuum time 22 min, molten steel N content 0.0038%; 1.8 kg / t aluminum particles were added during the vacuum process, and 110 m calcium wire was fed first after breaking the air. After soft blowing for 11 min, the corresponding titanium-iron wire was fed according to the sampled titanium content. The titanium content of the molten steel was ≥0.02%. After soft blowing for 11 min, 0.12 m / t Al-Mg cored wire was fed and the standing time was 9 min.

[0046] (4) Continuous casting process: The superheat of the continuous casting tundish is controlled at 15-30°C, the casting speed is controlled at 1.15m / min, the crystallizer is electromagnetically stirred, dynamic soft reduction technology is used, and the continuous casting billet is cooled off the line; the continuous casting billet is rolled to obtain titanium-containing gear steel rolled products. Example 3

[0047] (1) Hot metal pretreatment process: add 55kg / t of rolled steel scale, 16.5kg / t of lime, and 5.0kg / t of fluorite. The treatment cycle is 40min. After pretreatment, the Si content of the hot metal is 0.15%, P is 0.008%, and S is 0.008%. The hot metal temperature is 1300℃.

[0048] (2) Converter process: 4.0 kg / t of silicon, aluminum and barium is added to the converter steel, the steel tapping temperature is 1670 °C, and argon is blown at the argon station for 4 minutes.

[0049] (3) VD vacuum refining process: 0.6 mbar deep vacuum time 25 min, molten steel N content 0.0034%; 2.0 kg / t aluminum particles were added during the vacuum process, and 100 m calcium wire was fed first after breaking the air. After soft blowing for 10 min, the corresponding titanium-iron wire was fed according to the sampled titanium content. The titanium content of the molten steel was ≥0.02%. After soft blowing for 10 min, 0.13 m / t Al-Mg cored wire was fed and allowed to stand for 10 min.

[0050] (4) Continuous casting process: The superheat of the continuous casting tundish is controlled at 15-30°C, the casting speed is controlled at 1.01m / min, the crystallizer is electromagnetically stirred, dynamic soft reduction technology is used, and the continuous casting billet is cooled off the line; the titanium-containing gear steel rolled product is obtained after the continuous casting billet is rolled. Example 4

[0051] (1) Hot metal pretreatment process: 52 kg / t of rolled steel scale, 16 kg / t of lime, and 4.5 kg / t of fluorite were added. The treatment cycle was 37 min. After pretreatment, the Si content in the hot metal was 0.18%, P was 0.009%, and S was 0.009%. The hot metal temperature was 1320 °C.

[0052] (2) Converter process: 3.5kg / t of silicon, aluminum and barium is added to the converter steel, the steel tapping temperature is 1675℃, and argon is blown at the argon station for 3 minutes.

[0053] (3) VD vacuum refining process: 0.6 mbar deep vacuum time 28 minutes, molten steel nitrogen content 0.0032%; 2.2 kg / t aluminum particles were added during the vacuum process, and 90 m calcium wire was fed first after breaking the air. After soft blowing for 9 minutes, the corresponding titanium-iron wire was fed according to the sampled titanium content. The titanium content of the molten steel was ≥0.02%. After the soft blowing time of 9 minutes, 0.14 m / t Al-Mg cored wire was fed and the standing time was 11 minutes.

[0054] (4) Continuous casting process: The superheat of the continuous casting tundish is controlled at 15-30°C, the casting speed is controlled at 0.92m / min, the crystallizer is electromagnetically stirred, dynamic soft reduction technology is used, and the continuous casting billet is cooled off the line; the titanium-containing gear steel rolled product is obtained after the continuous casting billet is rolled. Example 5

[0055] (1) Hot metal pretreatment process: add 50kg / t of rolled steel scale, 15kg / t of lime, and 4.0kg / t of fluorite. The treatment cycle is 35min. After pretreatment, the Si content of the hot metal is 0.20%, P is 0.010%, and S is 0.010%. The hot metal temperature is 1350℃.

[0056] (2) Converter process: 3.0 kg / t of silicon, aluminum and barium is added to the converter steel, the steel tapping temperature is 1680 °C, and argon is blown at the argon station for 2 minutes.

[0057] (3) RH vacuum refining process: After the RH vacuum degree reaches 67 Pa, the deep vacuum treatment time is 20 minutes. 2.5 kg / t aluminum particles are added to the molten steel in the 4th minute of deep vacuum treatment. After breaking the air, 80 m calcium wire is fed first. After soft blowing for 8 minutes, the corresponding titanium-iron wire is fed according to the titanium content measured by sampling. The titanium content of the molten steel is ≥0.02%. After soft blowing for 8 minutes, 0.15 m / t Al-Mg cored wire is fed. Then the molten steel is allowed to stand for 12 minutes.

[0058] (4) Continuous casting process: The superheat of the continuous casting tundish is controlled at 15-30°C, the casting speed is controlled at 0.80m / min, the crystallizer is electromagnetically stirred, dynamic soft reduction technology is used, and the continuous casting billet is cooled off the line; the titanium-containing gear steel rolled product is obtained after the continuous casting billet is rolled.

[0059] Example 1-5 produced titanium-containing gear steel with dispersed TiN inclusions. The results are shown in the attached figure. Figure 1-5 As shown in the figure, a large number of composite TiN inclusions are generated in the steel, the proportion of composite inclusions increases from 3.1% to more than 18%, and the number density of TiN inclusions with a size of more than 2 μm increases from 30 / mm to 1. 2 Reduced to 15 / mm 2 Below; the size of TiN inclusions in rolled products is all below 4μm, and Ds type inclusions are ≤ level 0.5.

[0060] The above embodiments 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 embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for smelting titanium-containing steel by combining a molten iron three-removal process with a vacuum refining process, wherein the production process is molten iron pretreatment → converter smelting → vacuum treatment → continuous casting, characterized in that: The molten steel in the production process does not undergo LF refining. In the vacuum treatment process, 1.0-2.5 kg / t of aluminum particles are added during the vacuum treatment. After the molten steel is vacuum treated, Al-Mg cored wire is added; the feeding amount of the Al-Mg cored wire is 0.11-0.15 m / t.

2. The method for smelting titanium-containing steel by combining a molten iron three-removal process with a vacuum refining process according to claim 1, characterized in that: The vacuum treatment step is to perform vacuum treatment so that the mass percentage of nitrogen in the molten steel is ≤0.004%.

3. The method for smelting titanium-containing steel by combining a molten iron three-removal process with a vacuum refining process according to claim 1, characterized in that: The vacuum treatment process uses titanium-iron wire to adjust the titanium content in the steel.

4. The method for smelting titanium-containing steel by combining a hot metal three-removal process with a vacuum refining process according to claim 1, characterized in that: The vacuum treatment process uses a VD furnace to vacuum treat the molten steel. The vacuum degree of the vacuum treatment process is below 1 mbar, and the deep vacuum of 0.6 mbar is maintained for ≥20 minutes.

5. The method for smelting titanium-containing steel by combining a hot metal three-removal process with a vacuum refining process according to claim 1, characterized in that: In the molten iron pretreatment step, the mass fraction of Si in the molten iron after pretreatment is ≤0.20%, the mass fraction of P is ≤0.01%, the mass fraction of S is ≤0.01%, and the molten iron temperature is 1250-1350°C; In the converter smelting process, the converter tapping temperature is ≥1660°C; 3-5kg / t of silicon-aluminum-barium alloy is added for deoxidation at the early stage of converter tapping, and then alloys are added according to the target composition requirements of the molten steel; In the vacuum treatment process, after breaking the air, 80-120m calcium wire is first fed, the molten steel is soft-blown, and then the corresponding titanium-iron wire is fed according to the titanium content of the molten steel. The molten steel is soft-blown again, and the Al-Mg cored wire is fed after soft blowing. The molten steel is then left to stand for 8-12 minutes.

6. The method for smelting titanium-containing steel by combining a hot metal triple desulfurization process with a vacuum refining process according to claim 1, characterized in that: In the converter smelting process, argon is blown throughout the steel tapping process, and argon is blown for 2-6 minutes at the argon station after steel tapping.

7. The method for smelting titanium-containing steel by combining a molten iron three-removal process with a vacuum refining process according to claim 5, characterized in that: The soft blowing process lasts for 8 to 12 minutes each time.

8. The method for smelting titanium-containing steel by combining a molten iron three-removal process with a vacuum refining process according to claim 5, characterized in that: In the molten iron pretreatment process, 50-60 kg / t of rolled steel scale, 15-18 kg / t of lime, and 4-6 kg / t of fluorite are added, and the treatment cycle is 35-45 minutes.

9. The method for smelting titanium-containing steel by combining a molten iron three-removal process with a vacuum refining process according to claim 1, characterized in that: The titanium-containing steel has the following components and their mass percentages: C 0.17-0.45%, Si 0.17-1.60%, Mn 0.85-1.25%, S ≤0.030%, P ≤0.030%, Cr 1.00-1.95%, Al 0.015-0.050%, Ti 0.01-0.10%, and the balance is Fe and unavoidable impurities.

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