Smelting method for reducing inclusions in export steel rail

Abstract

The invention discloses a smelting method for reducing inclusions in an export steel rail, which comprises the following steps: (1) smelting molten iron P is less than or equal to 130 ppm, iron is added in a converter, the smelting time is 38-45 minutes, and the tapping C% is more than or equal to 0.08%; (2) smelting deoxidation process: smelting LF refining is carried out for 80-85 minutes, the converter adopts an aluminum-free deoxidation process, the tapping temperature is 1580-1630 DEG C, and SiCaBa is used as a deoxidizing agent; (3) strictly controlling the basicity R of the slag in the LF furnace to be 2.0-2.5; (4) VD deep vacuum time is longer than or equal to 20 min, the vacuum degree is smaller than or equal to 6 kpa, and soft blowing time is longer than or equal to 18 min; (5) when the liquid level height of the tundish is larger than or equal to 650 mm, the molten steel stands for 4-5 minutes; and (6) protective casting is adopted for continuous casting, and the pulling speed ranges from 0.6 m / min to 0.66 m / min. According to the smelting method provided by the invention, steel inclusions can be effectively reduced, and a K method is adopted for inspection, so that the heat rate reaches 100% when K3 is less than or equal to 10.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a smelting method for reducing inclusions in export rails. Background Art

[0002] With the high-speed, safe and stable development of high-speed railways, higher and more stringent requirements are put forward for the internal quality and performance of rail steel. At present, the main development trend of rails is high strength, high toughness and high purity. High purity puts forward more stringent requirements on the internal quality of products. The internal quality of rails mainly relies on ultrasonic flaw detection. The presence of inclusions in steel is the main reason for the failure of rail ultrasonic flaw detection.

[0003] While occupying the domestic market share, my country's rail production enterprises also seize market opportunities and continuously expand overseas markets. They mass-produce export rails according to the different needs of foreign users, and implement different standards for export to different countries, such as European standards, American standards, Russian standards, etc. Among them: rails exported to EU countries usually comply with the European standard EN13674.1 "46kg / m and above T-type rails". The detection of inclusion cleanliness in the European standard EN13674.1 adopts the DIN50602 standard K method inspection, and the K method detection is a quantitative analysis test, which is different from the semi-quantitative detection of the A method in GB / T10561 "Determination of non-metallic inclusions in steel" adopted by my country's iron standard TB / T2344.1 "High-speed railway rails".

[0004] The national standard A method selects the most serious situation of each type of inclusions in the inspection field, including sulfides, alumina, silicates and spherical oxides, for inspection and evaluation. It mainly considers the size (length and diameter) of each type of inclusion, but does not consider the number (except for spherical oxide type D inclusions). The European standard considers that the factors affecting rail failure are mainly oxide inclusions. The standard mainly makes clear requirements for oxide cleanliness (including alumina, silicates and spherical oxides) inclusions, but does not make clear requirements for sulfides. At the same time, the K method test multiplies the number of each type of inclusion field observed by its related "harmful factor", adds the products and normalizes them. Therefore, the method not only considers the size of the inclusions, but also the number of inclusions. Summary of the invention

[0005] In order to solve the above technical problems, the object of the present invention is to provide a smelting method for reducing inclusions in export rails.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a smelting method for reducing inclusions in export rails, comprising:

[0008] 1) Hot metal pretreatment: smelting hot metal P≤130ppm, adding iron to converter, smelting time 38-45 minutes; strictly control the carbon content of converter steel, C%≥0.08%;

[0009] 2) Converter smelting and deoxidation process: the tapping temperature is 1580-1630℃, the smelting and LF refining are 80-85 minutes, the converter adopts aluminum-free deoxidation process, and the deoxidizer uses SiCaBa;

[0010] 3) Strictly control the LF furnace slag basicity to 2.0-2.5;

[0011] 4) Strictly control the VD deep vacuum time, vacuum degree ≤ 6kpa, and the soft blowing time after VD to promote the floating removal of inclusions, deep vacuum time ≥ 20min, soft blowing time ≥ 18min;

[0012] 5) In order to extend the steel industry retention time, promote the floating of inclusions, ensure that the tundish liquid level is ≥650mm, and the molten steel is stationary for 4-5 minutes, a U-shaped retaining wall plus a turbulence controller is used;

[0013] 6) Continuous casting adopts protective casting, the overheat of continuous casting start is ≤25℃, low aluminum protective slag is used, weak cooling water distribution is used in the second cooling section, and the whole process is operated at a constant casting speed of 0.6-0.66m / min.

[0014] Furthermore, the inclusion evaluation method adopts K method detection, and the heat ratio of K3≤10 reaches 100%.

[0015] Furthermore, the LF furnace slag basicity is strictly controlled, R=2.3.

[0016] Furthermore, VD vacuum degassing: deep vacuum degassing time 21min, soft blowing after vacuum degassing for 20min, soft blowing retention 50NL / min, vacuum degree 5.6kpa, argon flow rate during soft blowing process is stable, molten steel creeps without exposure.

[0017] Furthermore, an alkaline middle coating agent is used, with R=2.1.

[0018] Furthermore, the liquid level height of the middle package is 660mm.

[0019] Furthermore, the continuous casting adopts protective casting, the superheat of the opening casting is ≤25℃, low-aluminum protective slag is used, weak cooling water distribution is adopted in the second cooling section, the whole process is operated at a constant pulling speed of 0.64m / min, and the electromagnetic stirring and light pressure of the casting machine are turned on.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are:

[0021] According to the smelting method provided by the present invention, the K method inspection is carried out using the export rail procurement inspection standard requirements, and the rail inclusions can meet the requirements of European standard EN13674.1 "46kg / m and above T-rails", and the furnace ratio of K3≤10 reaches 100%. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below in conjunction with specific implementation examples. The percentages in the following implementation examples are all by weight.

[0023] A smelting method for reducing inclusions in export rails, specifically comprising:

[0024] 1. Hot metal pretreatment: P≤0.120%, S≤0.030%; wheat kiln lime is used to control the phosphorus and sulfur content of scrap steel and pig iron entering the furnace;

[0025] 2. Converter smelting: strictly control the C content of steel ≥ 0.08%, and the steel tapping temperature is 1615℃. Adopt aluminum-free deoxidation process, high-drawing and blowing at the end point, the steel tapping end point composition w[C] ≥ 0.06%, w[P] ≤ 0.120%, SiCaBa is used as deoxidizer, and the argon blowing effect is guaranteed during the steel tapping process. There is no lumping phenomenon on the top slag when the molten steel is refined in place;

[0026] 3. LF furnace refining: The main task of the LF furnace is to add alloys to make the chemical composition meet the design composition range. The refining temperature is required to be ≥1530℃; the LF furnace slag basicity is strictly controlled, R=2.3.

[0027] 4. VD vacuum degassing: VD vacuum degassing reduces the gas content in molten steel. The deep vacuum degassing time is 21 minutes. After vacuum degassing, soft blowing is performed for 20 minutes. The soft blowing retention is 50NL / min, and the vacuum degree is 5.6kpa. During the soft blowing process, the argon flow rate is stable, and the molten steel creeps without exposure.

[0028] 5. Protective pouring: In order to promote the floating and removal of inclusions, an alkaline middle ladle covering agent is used, R=2.1; the middle ladle is filled with water to extend the retention time of the molten steel. The liquid level height of the middle ladle is 660mm, and a U-shaped retaining wall plus a turbulence controller is used.

[0029] 6. Continuous casting of large square billets: Protective pouring is adopted in the continuous casting process, the superheat of pouring is ≤25℃, low-aluminum protective slag is used, weak cooling water distribution is adopted in the second cooling section, constant casting speed operation is carried out throughout the process, the casting speed is 0.64m / min, and the electromagnetic stirring and light pressure of the casting machine are turned on.

[0030] According to the export rail procurement inspection standard EN13674.1 "46kg / m and above T-rail" specified position sampling, wake up the inclusions K method inspection, the K method inspection results of each example are shown in Table 1:

[0031] Table 1 K-method test results for each example

[0032]

[0033] It can be seen from Table 1 above that according to the smelting method provided by the present invention, the rail inclusions can meet the requirements of European standard EN13674.1 "46kg / m and above T-rails", and the heat ratio of K3≤10 reaches 100%.

[0034] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A smelting method for reducing inclusions in export rails, characterized in that: include: 1) Hot metal pretreatment: smelting hot metal P≤130ppm, adding iron to converter, smelting time 38-45 minutes; Strictly control the carbon content of converter steel, C% ≥ 0.08%; 2) Converter smelting and deoxidation process: the tapping temperature is 1580-1630℃, the smelting and LF refining are 80-85 minutes, the converter adopts aluminum-free deoxidation process, and the deoxidizer uses SiCaBa; 3) Strictly control the LF furnace slag basicity to 2.0-2.5; 4) Strictly control the VD deep vacuum time, vacuum degree ≤ 6kpa, and the soft blowing time after VD to promote the floating and removal of inclusions, deep vacuum time ≥ 20min, soft blowing time ≥ 18min; 5) In order to extend the steel industry retention time, promote the floating of inclusions, ensure that the tundish liquid level is ≥650mm, and the molten steel is stationary for 4-5 minutes, a U-shaped retaining wall plus a turbulence controller is used; 6) Continuous casting adopts protective casting, the overheat of continuous casting start is ≤25℃, low aluminum protective slag is used, weak cooling water distribution is used in the second cooling section, and the whole process is operated at a constant pulling speed of 0.6-0.66m / min.

2. The smelting method for reducing inclusions in export rails according to claim 1, characterized in that: The inclusion evaluation method adopts K method detection, and the heat ratio of K3≤10 reaches 100%.

3. The smelting method for reducing inclusions in export rails according to claim 1, characterized in that: Strictly control the LF furnace slag basicity, R=2.

3.

4. The smelting method for reducing inclusions in export rails according to claim 1, characterized in that: VD vacuum degassing: deep vacuum degassing time is 21min, soft blowing is performed for 20min after vacuum degassing, the soft blowing retention is 50NL / min, the vacuum degree is 5.6kpa, the argon flow rate is stable during the soft blowing process, the molten steel creeps and there is no exposure.

5. The smelting method for reducing inclusions in export rails according to claim 1, characterized in that: An alkaline middle coating agent is used, R=2.

1.

6. The smelting method for reducing inclusions in export rails according to claim 1, characterized in that: The liquid level height of the middle package is 660mm.

7. The smelting method for reducing inclusions in export rails according to claim 1, characterized in that: The continuous casting adopts protective casting, the superheat of pouring is ≤25℃, low-aluminum protective slag is used, weak cooling water distribution is used in the secondary cooling section, the whole process is operated at a constant casting speed of 0.64m / min, and the electromagnetic stirring and light pressure of the casting machine are turned on.

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