Smelting method of IS steel rail for export

Abstract

The invention discloses a smelting method of an IS steel rail for export, which comprises the following steps: 1) molten iron pretreatment: the molten iron pretreatment adopts the following processes: blast furnace molten iron, blowing a magnesium lime composite deoxidizer in a tank, feeding into a metal mixer, and feeding into a converter; 2) converter smelting; 3) LF furnace refining; (4) VD (vacuum degassing); 5) continuous casting; the steel rail comprises the following chemical components in percentage by mass: 0.76-0.85% of C; si: 0.47 to 0.57%; 0.9 to 1.1% 8 of Mn; less than or equal to 0.020% of P; less than or equal to 0.020% of S; 0.20 to 0.3% of Cr; and the balance of Fe and inevitable impurities. According to the steel rail casting blank smelted through the method, the segregation indexes of the C element and the Mn element are basically within 0.95-1.05, segregation of the C element and segregation of the Mn element are relatively synchronous, and content fluctuation of all the positions is small.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgical materials, and particularly relates to a smelting method for IS steel rails for export. Background Art

[0002] With the innovation of rail transit technology and the progress of metallurgical processes, modern rail standards have put forward higher requirements in terms of material properties. Its core development direction has focused on two major technical dimensions: the coordinated improvement of material strength and toughness and the control of metallurgical purity. In view of the wear resistance requirements of track components for the unique heavy-haul transportation conditions of the American railway network, the industry urgently needs to develop carbon medium-strength rail products that meet the new version of ASTM standards. The research and development of such products not only need to break through the traditional strength limit, but also need to pay attention to the coordinated optimization of material strength, toughness and plasticity. By establishing the corresponding relationship between microstructure and macroscopic properties, the comprehensive service performance can be comprehensively improved.

[0003] In terms of the technical implementation path, the following systematic research needs to be carried out: 1) Establish a quantitative relationship model between the new rail alloy composition system and heat treatment process parameters; 2) Analyze the influence mechanism of the metallurgical process (including steelmaking refining and continuous casting solidification) on steel purity; 3) Develop an optimization technology for the controlled rolling and controlled cooling process window to achieve precise control of phase transformation microstructure. Through the integrated innovation of the above full-process manufacturing technology, the stability and batch consistency of the performance of American standard rail products can be effectively guaranteed, providing technical support for expanding the rail markets in North America and South America. The successful development of this product will significantly improve the economy and reliability of the heavy-haul railway transportation system, and strongly support the strategic needs of the development of modern railway transportation towards large capacity and high density. Summary of the Invention

[0004] The purpose of the present invention is to provide a smelting method for IS steel rails for export, so as to provide a smelting method for medium-strength heat-treated rail steel that meets the AREMA-2020 standard.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A smelting method for IS steel rails for export of the present invention includes:

[0007] 1) Hot metal pretreatment

[0008] For hot metal pretreatment, the adopted process is: blast furnace hot metal - injecting magnesium lime composite deoxidizer in the ladle - entering the mixing iron furnace - entering the converter; where:

[0009] The hot metal temperature is 1314 ± 10 °C, the mass percentage of P ≤ 0.12%, S ≤ 0.02%, the special hot metal addition amount is 1282 - 1382 t, and the scrap addition amount is 25 - 30 t;

[0010] 2) Converter smelting

[0011] During the tapping process, ensure the argon blowing effect, and there is no caking phenomenon of the top slag when the molten steel is in place for refining. The refining temperature after converter smelting is 1490 - 1530 °C;

[0012] 3) LF furnace refining

[0013] LF furnace refining: The main task of the LF furnace is to add alloys to make the chemical composition meet the designed composition range. Silicon-calcium-barium is used for deoxidation. Ferrosilicon, low-aluminum silicon-calcium-barium, and high-carbon ferrochrome are added during LF refining. The heating time is 22 min, and the off-position temperature is 1515 - 1523 °C. The off-position composition of LF meets the requirements of the designed composition;

[0014] 4) VD vacuum degassing: VD vacuum degassing reduces the gas content in the molten steel. The deep vacuum degassing time is 14 - 18 min, and the soft blowing time after vacuum degassing is 17 - 20 min. The argon flow rate is stable during the soft blowing process, and the molten steel peristalsis is normal without exposure;

[0015] 5) Continuous casting

[0016] During continuous casting, protective casting is adopted, and low-aluminum protective slag is used. The off-position temperature after refining is 1515 - 1523 °C, the liquidus temperature is 1464 °C, and the superheat ΔT is 27 - 31 °C. Ultra-weak cooling water distribution is adopted in the secondary cooling section, and constant casting speed operation is carried out throughout the process. The casting speed is 0.62 - 0.64 m / min. The electromagnetic stirring and soft reduction of the caster are turned on, and the quality of the cast slab is good;

[0017] The chemical composition of the said rail in mass percentage includes: C: 0.76 - 0.85%; Si: 0.47 - 0.57%; Mn: 0.9 - 1.1%; P ≤ 0.020%; S ≤ 0.020%; Cr: 0.20 - 0.3%; the balance is Fe and inevitable impurities.

[0018] Further, the deep vacuum degassing time is 15 - 17 min, and the soft blowing time after vacuum degassing is 18 - 19 min.

[0019] Further, the deep vacuum degassing time is 17 min, and the soft blowing time after vacuum degassing is 19 min.

[0020] Further, the deep vacuum degree is 15 - 30 KPa.

[0021] Further, the soft blowing flow rate is 100 - 190 Nl / min.

[0022] Further, the off-position temperature is 1515 - 1523 °C.

[0023] Further, the size of the cast slab is 280 mm × 380 mm.

[0024] Compared with the prior art, the beneficial technical effects of the present invention:

[0025] For the rail billets smelted by the present invention, the segregation indexes of C and Mn elements are basically between 0.95 and 1.05. The segregation of C and Mn elements is relatively synchronous, and the content fluctuations at each position are small. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below in conjunction with the drawings.

[0027] Figure 1 It is a schematic diagram for taking samples;

[0028] Figure 2 It is the segregation of C and Mn components of the IS rail billet. SPECIFIC EMBODIMENTS

[0029] A smelting method for IS rails for export, comprising:

[0030] 1) Hot metal pretreatment

[0031] The adopted process: blast furnace hot metal - injection of magnesium lime composite deoxidizer in the ladle - entering the mixing furnace - entering the converter. The purpose is to reduce the sulfur content of the hot metal entering the converter. The specific situation of the hot metal entering the converter is shown in Table 1.

[0032] Table 1 Hot metal situation in converter smelting of high-carbon steel rails

[0033]

[0034] 2) Converter smelting

[0035] During the tapping process, ensure the argon blowing effect, and there is no caking phenomenon in the top slag when the molten steel is refined in place. The refined composition and temperature after converter smelting are shown in Table 2.

[0036] Table 2 Converter smelting process table of high-carbon steel rails

[0037]

[0038] 3) LF furnace refining

[0039] LF furnace refining: The main task of the LF furnace is to add alloys to make the chemical composition meet the designed composition range. Calcium-silicon-barium deoxidation is adopted. Silicon iron, low-aluminum calcium-silicon-barium and high-carbon ferrochrome are added during LF refining. The heating time is 22 min, and the off-position temperature is 1515 - 1523 °C. The off-position composition of LF meets the designed composition requirements. The alloy addition amounts are shown in Table 3.

[0040] Table 3 LF alloy addition amounts for IS rails

[0041]

[0042]

[0043] 4) VD Vacuum Degassing: VD vacuum degassing reduces the gas content in the molten steel. The deep vacuum degassing time is 15 min, and the soft blowing time after vacuum degassing is 19 min. The argon flow rate is stable during the soft blowing process, and the molten steel peristalsis is normal without exposure. The VD process and off-position composition are shown in Table 4.

[0044] Table 4 VD Process and Off-position Composition of IS Rails

[0045]

[0046] 5) Continuous Casting

[0047] The size of the casting blank is 280 mm × 380 mm. During continuous casting, protective casting is adopted, and low-aluminum protective slag is used. The off-position temperature after refining is 1515 - 1523 °C, the liquidus temperature is 1464 °C, and the superheat ΔT is 27 - 31 °C. Ultra-weak cooling water distribution is adopted in the secondary cooling section, and constant casting speed operation is carried out throughout the process. The casting speed is 0.63 m / min. The electromagnetic stirring and soft reduction of the casting machine are turned on, and the quality of the casting blank is good. The finished product composition of IS is shown in Table 5.

[0048] Table 5 Finished Product Composition and Gas Content of IS Rails

[0049]

[0050] 6) Sulfur Print and Hot Acid

[0051] The macrostructure of the rail casting blank is inspected, and the inspection results are shown in Table 6.

[0052] Table 6 Macrostructure Inspection Results of the Casting Blank

[0053]

[0054]

[0055] After the macrostructure inspection of the steel billet, C and Mn segregation inspections are carried out. Starting from the center 0 point of the cross-section of the steel billet, a point is taken every 15 mm for C and Mn element detection. The segregation degree of the casting blank = element content in the local area / average content of the steel billet (segregation degree > 1 is enrichment, segregation degree < 1 is depletion).

[0056] 7) Chemical Composition Segregation

[0057] Specimens are taken for composition segregation inspection, and a point is taken every 15 mm (E outer arc).

[0058] It can be seen from Figure 2 that the segregation indices of C and Mn elements in IS350 rails are basically between 0.95 and 1.05. The segregation of C and Mn elements is relatively synchronous, and the content fluctuations at each position are small.

[0059] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the spirit of the present invention's design, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A smelting method for IS steel rails used for export, characterized in that: Including: 1) Hot metal pretreatment The adopted process: Blast furnace hot metal - injecting magnesium lime composite deoxidizer in ladle - entering torpedo mixer - entering converter; where: The hot metal temperature is 1314 ± 10 °C, the mass percentage of P ≤ 0.12%, S ≤ 0.02%, the special water addition amount is 1282 - 1382 t, and the scrap addition amount is 25 - 30 t; 2) Converter smelting Ensure the argon blowing effect during tapping, and there is no caking phenomenon of the top slag when the molten steel is in place for refining. The refining temperature after converter smelting is 1490 - 1530 °C; 3) LF furnace refining LF furnace refining: The main task of the LF furnace is to add alloys to make the chemical composition meet the designed composition range. Silicon calcium barium is used for deoxidation. Silicon iron, low - aluminum silicon calcium barium, and high - carbon ferrochrome are added during LF refining. The heating time is 22 min, the off - position temperature is 1515 - 1523 °C, and the LF off - position composition meets the designed composition requirements; 4) VD vacuum degassing: VD vacuum degassing reduces the gas content in the molten steel. The deep vacuum degassing time is 14 - 18 min, and the soft blowing time after vacuum degassing is 17 - 20 min. The argon flow rate is stable during the soft blowing process, and the molten steel creeps without exposure; 5) Continuous casting Protective casting is adopted during continuous casting. Low - aluminum protective slag is used. The off - position temperature after refining is 1515 - 1523 °C, the liquidus temperature is 1464 °C, and the superheat ΔT: 27 - 31 °C. Ultra - weak cooling water distribution is adopted in the secondary cooling section, and constant casting speed operation is carried out throughout the process. The casting speed is 0.62 - 0.64 m / min. The electromagnetic stirring and soft reduction of the casting machine are turned on, and the quality of the cast slab is good; The chemical composition of the said rail in mass percentage includes: C: 0.76 - 0.85%; Si: 0.47 - 0.57%; Mn: 0.9 - 1.1%; P ≤ 0.020%; S ≤ 0.020%; Cr: 0.20 - 0.3%; the balance is Fe and unavoidable impurities.

2. The smelting method of the IS rail for export according to claim 1, characterized in that: The deep vacuum degassing time is 15 - 17 min, and the soft blowing time after vacuum degassing is 18 - 19 min.

3. The smelting method of the IS rail for export according to claim 2, characterized in that: The deep vacuum degassing time is 17 min, and the soft blowing time after vacuum degassing is 19 min.

4. The smelting method of the IS rail for export according to claim 1, characterized in that: The deep vacuum degree is 15 - 30 KPa.

5. The smelting method of the IS rail for export according to claim 1, characterized in that: The soft blowing flow rate is 100 - 190 Nl / min.

6. The smelting method of the IS rail for export according to claim 1, characterized in that: The off - position temperature is 1515 - 1523 °C.

7. The smelting method of the IS steel rail for export according to claim 1, characterized in that: The cast slab size is 280 mm × 380 mm.

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