A calcium treatment process for rh furnaces

Abstract

The application discloses a RH furnace calcium treatment process and relates to the technical field of molten steel calcium treatment. The process comprises the following steps: S1, molten steel is kept circulating in vacuum; S2, silicon calcium barium alloy is added after first-stage wire feeding and second-stage wire feeding; S3, nitrogen is introduced again; S4, normal pressure is restored, and molten steel after calcium treatment is obtained, the silicon calcium barium alloy is added in an amount of 40-47 kg per ton of molten steel, the first-stage wire feeding time is 3-5 min, the vacuum degree of the first-stage wire feeding is 55-67 Pa, the mass ratio of the silicon calcium barium alloy to the molten steel added in the first-stage wire feeding is 22-26 kg / t, the second-stage wire feeding time is 2-4 min, and the vacuum degree of the second-stage wire feeding is 50-55 Pa. The two-stage wire feeding mode is matched with multiple wire feeding ports, the wire feeding time and the vacuum degree are adjusted, the silicon calcium barium alloy is uniformly distributed in the molten steel, segregation is avoided, the calcium treatment effect is good, and the steel performance is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of steelmaking calcium treatment technology, specifically a calcium treatment process for an RH furnace. Background Technology

[0002] Calcium treatment is widely used in the production of clean steel. The traditional RH furnace calcium treatment method involves adding pure calcium wire to the molten steel via a wire feeding process. Utilizing the strong binding affinity between calcium and sulfur, sulfides are transformed from MnS to high-melting-point CaS. This avoids the selective crystallization of MnS, which could lead to its enrichment in the core of the billet and negatively impact billet quality. Furthermore, the high-melting-point CaS improves the crack resistance of the steel. After adding calcium wire, calcium can convert brittle Al₂O₃ inclusions into low-melting-point calcium aluminate, thereby improving the casting properties of the molten steel.

[0003] Currently, CN102899448A discloses a method for calcium treatment of molten steel, which involves adding a silicon-calcium-barium alloy to intermediate molten steel under vacuum conditions. However, this method has some problems, such as a high content and large size of Class A inclusions, which may lead to poor corrosion resistance and toughness of the steel, as well as the occurrence of billet cracks during smelting and rolling processes.

[0004] Among them, Type A (sulfide type) has high ductility, with a wide range of morphology ratios (length / width) of individual gray inclusions, generally with rounded ends; Type B (alumina type) consists mostly of undeformed, angular, small morphology ratios (generally <3), black or bluish particles, arranged in a row along the rolling direction (at least 3 particles); Type C (silicate type) has high ductility, with a wide range of morphology ratios (generally ≥3) of individual black or dark gray inclusions, generally with acute angles at the ends; Type D (spherical oxide type) consists of undeformed, angular or rounded, small morphology ratios (generally <3), black or bluish particles, irregularly distributed; Type DS (single-particle spherical type) consists of round or nearly round single-particle inclusions with a diameter >13 μm.

[0005] Therefore, in order to obtain steel with low inclusion content and small size, thereby improving the mechanical properties of the steel, an improved wire feeding process is necessary; in view of this, we propose an RH furnace calcium treatment process. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an RH furnace calcium treatment process that solves the problems mentioned in the background section.

[0007] To achieve the above objectives, the present invention provides the following technical solution: an RH furnace calcium treatment process, the process comprising the following steps: S1. Molten steel is kept circulating in a vacuum; S2. Add silicon-calcium-barium alloy after the first and second stages of wire feeding; S3. Introduce nitrogen gas again; S4. Once the pressure is restored to normal, the calcium-treated molten steel can be obtained.

[0008] Optionally, the amount of silicon-calcium-barium alloy added is 40-47 kg per ton of molten steel.

[0009] Optionally, the feeding time in the first stage is 3 to 5 minutes; the vacuum degree in the first stage is 55 to 67 Pa; and the mass ratio of silicon-calcium-barium alloy added to molten steel in the first stage is 22 to 26 kg / t.

[0010] Optionally, the second stage of wire feeding time is 2 to 4 minutes; the vacuum degree of the second stage of wire feeding is 50 to 55 Pa.

[0011] Optionally, the mass ratio of silicon-calcium-barium alloy added to molten steel in the second stage of wire feeding is 17-22 kg / t; after the second stage of wire feeding is completed, the circulation continues for 2-3 minutes.

[0012] Optionally, nitrogen gas is introduced to a pressure of 80 kPa.

[0013] Optionally, the silicon-calcium-barium alloy comprises Si≥52%, Ba>13.5%, Ca>12.5%, Ba+Ca≥28%, P≤0.1%, and S≤0.15%.

[0014] Optionally, the calcium content in the molten steel after calcium treatment is 33~38 ppm.

[0015] Optionally, the oxygen content of the calcium-treated molten steel is 9.8~12.8 ppm, and the nitrogen content is 38~47 ppm.

[0016] This invention provides a calcium treatment process for RH furnaces. It has the following beneficial effects: 1. The RH furnace calcium treatment process uses a two-stage wire feeding method with multiple wire feeding ports. By adjusting the wire feeding time and vacuum degree, the silicon-calcium-barium alloy is ensured to be evenly distributed in the molten steel, avoiding segregation and resulting in good calcium treatment effect; the steel performance is greatly improved.

[0017] 2. The RH furnace calcium treatment process ensures that the molten steel does not contain Class A inclusions, Class B, C, and D inclusions are all below Grade 0.5, and Ds inclusions are below Grade 1, resulting in better quality finished products. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: As Figure 1 As shown, the present invention provides a technical solution: a calcium treatment process for an RH furnace, comprising the following steps: Before 1.45 tons of ED5P7J00 molten steel were put into the RH furnace for smelting, the normal furnace operation procedure was followed, namely, argon blowing, ladle lifting, temperature measurement and sampling, vacuuming, and vacuum maintenance after the ladle arrived at the station. The molten steel temperature is 1580~1585℃. In the first stage of wire feeding, under a vacuum of 58~62Pa, 34kg of silicon-calcium-barium alloy is added, with a length of 68m, and the feeding time is 4min. In the second stage of wire feeding, under a vacuum of 50~52Pa, 26kg of silicon-calcium-barium alloy is added, with a length of 52m, and the feeding time is 3min. After recirculation for 4min, nitrogen gas is introduced to 80kPa, and then atmospheric gas is introduced to restore the pressure to normal.

[0021] The calcium content in the steel is 33 ppm; the inclusion test results are rated as Class B inclusions, Class C inclusions, Class D inclusions less than 0.5, and Ds inclusions less than 1, and there are no Class A inclusions; the oxygen content is 9.8 ppm; and the nitrogen content is 39 ppm.

[0022] Example 2: As Figure 1 As shown, the present invention provides a technical solution: a calcium treatment process for an RH furnace, comprising the following steps: Before 1.45 tons of ED5P7J00 molten steel were put into the RH furnace for smelting, the normal furnace operation procedure was followed, namely, argon blowing, ladle lifting, temperature measurement and sampling, vacuuming, and vacuum maintenance after the ladle arrived at the station. The molten steel temperature is 1580~1585℃. In the first stage of wire feeding, under a vacuum of 55~60Pa, 35kg of silicon-calcium-barium alloy is added with a length of 70m and the feeding time is 5min. In the second stage of wire feeding, under a vacuum of 51~55Pa, 30kg of silicon-calcium-barium alloy is added with a length of 60m and the feeding time is 3min. After circulating for 3min, nitrogen gas is introduced to 80kPa, and then atmospheric gas is introduced to restore the pressure to normal. The ladle is then lowered.

[0023] The calcium content in the steel is 35 ppm; the inclusion test results are rated as Class B inclusions, Class C inclusions, Class D inclusions less than 0.5, and Ds inclusions less than 1, and it does not contain Class A inclusions; the oxygen content is 12.8 ppm; and the nitrogen content is 47 ppm.

[0024] Example 3: As Figure 1 As shown, before 1.45 tons of ED5P7J00 molten steel were put into the RH furnace for smelting, the normal furnace operation procedure was followed, namely, argon blowing, ladle lifting, temperature measurement and sampling, vacuuming, and vacuum maintenance after the ladle arrived at the station. The molten steel temperature is 1580~1585℃. In the first stage of wire feeding, under a vacuum of 55~60Pa, 37kg of silicon-calcium-barium alloy is added with a length of 74m and the feeding time is 5min. In the second stage of wire feeding, under a vacuum of 50~53Pa, 31kg of silicon-calcium-barium alloy is added with a length of 62m and the feeding time is 4min. After recirculation for 3min, nitrogen gas is introduced to 80kPa, and then atmospheric gas is introduced to restore the pressure to normal. The ladle is then lowered.

[0025] The calcium content in the steel is 36 ppm; the inclusion test results are rated as Class B inclusions, Class C inclusions, Class D inclusions less than 0.5, and Ds inclusions less than 1, and there are no Class A inclusions; the oxygen content is 10.0; the nitrogen content is 42 ppm.

[0026] This RH furnace calcium treatment process employs a two-stage wire feeding method with multiple feeding ports. By adjusting the feeding time and vacuum level, it ensures that the silicon-calcium-barium alloy is evenly distributed in the molten steel, avoiding segregation and resulting in excellent calcium treatment effect; the steel properties are significantly improved. Furthermore, the molten steel is free of Class A inclusions, Class B, C, and D inclusions are all below grade 0.5, and Ds inclusions are below grade 1, leading to better quality finished products.

[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A calcium treatment process for an RH furnace, characterized in that: The process includes the following steps: S1. Molten steel is kept circulating in a vacuum; S2. Add silicon-calcium-barium alloy after the first and second stages of wire feeding; S3. Introduce nitrogen gas again; S4. Returning to normal pressure will yield calcium-treated molten steel. The first stage of wire feeding time is 3-5 minutes; the vacuum degree of the first stage of wire feeding is 55-67 Pa; the mass ratio of silicon-calcium-barium alloy added to molten steel in the first stage of wire feeding is 22-26 kg / t. The second stage of wire feeding takes 2–4 minutes; the vacuum level during the second stage of wire feeding is 50–55 Pa. In the second stage of wire feeding, the mass ratio of silicon-calcium-barium alloy added to molten steel is 17-22 kg / t; after the second stage of wire feeding is completed, the circulation continues for 2-3 minutes. The silicon-calcium-barium alloy comprises Si≥52%, Ba>13.5%, Ca>12.5%, Ba+Ca≥28%, P≤0.1%, and S≤0.15%.

2. The RH furnace calcium treatment process according to claim 1, characterized in that: The silicon-calcium-barium alloy is added at a rate of 40-47 kg per ton of molten steel.

3. The RH furnace calcium treatment process according to claim 1, characterized in that: Nitrogen gas is introduced until the pressure reaches 80 kPa.

4. The RH furnace calcium treatment process according to claim 1, characterized in that: The calcium content in the molten steel after calcium treatment is 33~38 ppm.

5. The RH furnace calcium treatment process according to claim 1, characterized in that: The oxygen content of the calcium-treated molten steel is 9.8~12.8 ppm, and the nitrogen content is 38~47 ppm.

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