Smelting method for improving hardness of standard strength steel rail

Abstract

The invention discloses a smelting method for improving the hardness of a standard-strength steel rail, and belongs to the technical field of metallurgical materials. Comprising the following steps: 1) molten iron pretreatment; 2) smelting in a converter, wherein the tapping temperature is 1610-1625 DEG C; point blowing is performed once; 3) LF furnace refining; (4) VD vacuum degassing is conducted, the deep vacuum degassing time is longer than or equal to 18 min, and the soft blowing time after vacuum degassing is longer than or equal to 15 min; (5) continuous casting is conducted, specifically, the size of a casting blank is 280 mm * 380 mm, protective casting is adopted in the continuous casting process, and low-aluminum covering slag is adopted; the invention further discloses chemical components of the rail steel mass percentage meter. The center porosity of the casting blank is 0.5 grade, the rest is 0 or 0.5 grade, and the quality of the casting blank is good; the segregation indexes of the C element and the Mn element of the steel rail are basically between 0.95 and 1.08, segregation of the C element and segregation of the Mn element are relatively synchronous, and content fluctuation of all positions is small.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and in particular relates to a smelting method for improving the hardness of standard strength steel rails. Background Technology

[0002] To meet the requirements of American railway transportation, it is necessary to quickly develop a new version of the American standard carbon large-section 136RE steel rail with a rail head tread hardness of 310HB or higher, Rm ≥ 1000MPa, Rp0.2 ≥ 550MPa, and elongation of not less than 9%, to satisfy the needs of rail exports to the Americas. In the development of new steel grades, the focus should be on rails with higher strength levels, while emphasizing the balance between strength and toughness. Improving both strength and toughness / plasticity is crucial for enhancing the overall performance of the rails. Therefore, it is necessary to analyze the influence of chemical elements and process parameters on the microstructure and properties of rails in the new American standard, and to conduct a systematic study of the entire process from metallurgy, continuous casting, and controlled rolling and cooling to achieve stable quality control of American standard 310HB hardness 136RE steel rails. This lays a solid foundation for expanding the American standard rail market. The development of the new American standard 310HB hardness 136RE steel rails highlights the crucial role of railway transportation in national economic construction, which is rapidly developing towards higher capacity and efficiency. Summary of the Invention

[0003] To address the aforementioned technical problems, the purpose of this invention is to provide a smelting method for improving the hardness of standard strength steel rails, applicable to the North American market.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a smelting method for improving the hardness of standard strength steel rails, comprising:

[0006] 1) Hot metal pretreatment

[0007] Molten iron undergoes desulfurization pretreatment, requiring P≤0.120% and S≤0.030%; wheat kiln quicklime is used to control the phosphorus and sulfur content of scrap steel and pig iron blocks entering the furnace; low-aluminum ferrosilicon is used, and other raw materials and alloys meet their respective standard requirements;

[0008] 2) Converter smelting

[0009] Converter smelting: Steel with C content > 0.10% is tapped. Argon blowing is ensured during tapping. There is no slag agglomeration when the molten steel is refined and placed in place. The tapping temperature is 1610-1625℃. One stoking is performed.

[0010] 3) LF furnace refining

[0011] LF furnace refining: The main task of the LF furnace is to add alloys to make the chemical composition meet the design composition range. Silicon, calcium and barium are used for deoxidation. Ferrosilicon and medium carbon ferrochrome are added in the LF refining process. The heating time is 20-30 minutes and the in-situ temperature is 1587℃. The in-situ composition of the LF furnace meets the design composition requirements.

[0012] 4) VD vacuum degassing

[0013] VD vacuum degassing: VD vacuum degassing reduces the gas content in molten steel. The deep vacuum degassing time is ≥18min, and the soft blowing time after vacuum degassing is ≥15min. The argon flow rate is stable during the soft blowing process, and the molten steel creeps without being exposed.

[0014] 5) Continuous casting

[0015] Continuous casting: The billet size is 280mm×380mm. The continuous casting process adopts protective casting with low-alumina protective slag. The liquidus temperature is 1461℃ and the superheat ΔT is 25~29℃. The secondary cooling section adopts ultra-weak cooling water distribution. The entire process is operated at a constant casting speed of 0.63m / min. The electromagnetic stirring of the casting machine is turned on and the pressure is light. The billet quality is good.

[0016] Furthermore, the chemical composition of the rail steel by mass percentage includes: C: 0.81-0.86; Si: 0.52-0.59; Mn: 1.07-1.25; P≤0.020; S≤0.020; Cr: 0.23-0.28; Ni: 0.03-0.05, with the balance being Fe and unavoidable impurities.

[0017] Furthermore, VD vacuum degassing: deep vacuum degassing time 18 min, deep vacuum degree 22 Pa / mbar, soft blowing time after vacuum degassing 16 min, soft blowing flow rate 100 Nl / min.

[0018] Furthermore, VD vacuum degassing: deep vacuum degassing time 19 min, deep vacuum degree 24 Pa / mbar, soft blowing time after vacuum degassing 17 min, soft blowing flow rate 100 Nl / min.

[0019] Furthermore, VD vacuum degassing: deep vacuum degassing time 20 min, deep vacuum degree 23 Pa / mbar, soft blowing time after vacuum degassing 18 min, soft blowing flow rate 100 Nl / min.

[0020] Further, LF furnace refining: heating time 25 min.

[0021] Furthermore, the porosity at the center of the billet is grade 0.5, while the rest is grade 0 or 0.5, indicating good billet quality.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] The central porosity of the billet is grade 0.5, while the rest is grade 0 or 0.5, indicating good billet quality.

[0024] The segregation indices of C and Mn elements in steel rails are generally between 0.95 and 1.08, indicating that the segregation of C and Mn elements is relatively synchronous, with small fluctuations in content at different locations. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] Figure 1 Photographs of hot acid castings of steel rail billets;

[0027] Figure 2 This is due to the segregation of chemical composition in the cast billet. Detailed Implementation

[0028] A smelting method for improving the hardness of standard strength steel rails:

[0029] 1) Hot metal pretreatment

[0030] The molten iron undergoes desulfurization pretreatment, requiring P ≤ 0.120% and S ≤ 0.030%. Wheat kiln quicklime is used to control the phosphorus and sulfur content of scrap steel and pig iron blocks entering the furnace. Low-aluminum ferrosilicon is used, and other raw materials and alloys must meet their respective standard requirements. Specific details regarding the molten iron entering the converter are shown in Table 1.

[0031] Table 1. Iron smelting conditions in high-carbon standard steel rail converters

[0032]

[0033] 2) Converter smelting

[0034] Converter smelting: The carbon content of the tapped steel is >0.10%. Argon blowing effect is ensured during tapping. There is no slag agglomeration when the molten steel is refined and placed in place. The converter smelting process is shown in Table 2.

[0035] Table 2. High-carbon steel rail converter smelting process

[0036]

[0037] 3) LF furnace refining

[0038] LF furnace refining: The main task of the LF furnace is to add alloys to make the chemical composition meet the design composition range. Silicon-calcium-barium deoxidation is used. LF refining adds ferrosilicon, (low-silicon-calcium-barium) and medium-carbon ferrochrome. The heating time is 25 minutes and the in-situ temperature is 1587℃. The LF in-situ composition meets the design composition requirements.

[0039] 4) VD vacuum degassing

[0040] VD vacuum degassing: VD vacuum degassing reduces the gas content in molten steel. The deep vacuum degassing time is ≥18 min, and the soft blowing time after vacuum degassing is ≥15 min. The argon flow rate is stable during the soft blowing process, and there is no exposed molten steel during creep.

[0041]

[0042]

[0043] 5) Continuous casting

[0044] Continuous casting: The billet size is 280mm × 380mm. Protective casting is used during the continuous casting process, employing low-alumina protective slag. The liquidus temperature is 1461℃, and the superheat ΔT is 25~29℃. The secondary cooling section uses ultra-weak cooling water distribution, and the entire process is operated at a constant casting speed of 0.63m / min. Electromagnetic stirring and light pressure are used on the casting machine, resulting in good billet quality. The composition of the finished product is shown in Table 3.

[0045] Table 3. Composition of high-carbon steel rail billet (%)

[0046]

[0047] 6) Sulfur printing and hot acid

[0048] Two high-carbon steel rail billets, numbered 102# and 602#, underwent hot acid testing. The test results are shown below. Figure 1 Table 4.

[0049] Table 4. Hot acid test results (grade) of SS136RE cast billets

[0050]

[0051]

[0052] The central porosity is grade 0.5, while the rest are grade 0 or 0.5, indicating good billet quality.

[0053] 7) Segregation of chemical composition in the billet

[0054] Depend on Figure 2 It can be seen that the segregation indices of C and Mn elements in SS136RE rails are basically between 0.95 and 1.08, and the segregation of C and Mn elements is relatively synchronous with small fluctuations in content at different locations.

[0055] 7) Rail performance

[0056] A comparison of the rail performance before and after the implementation shows that the rail performance has been significantly improved, especially the rail hardness, as detailed in Table 5.

[0057] Table 5 Comparison of rail performance before and after implementation

[0058]

[0059] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A smelting method for improving the hardness of standard strength steel rails, characterized in that: include: 1) Hot metal pretreatment Molten iron undergoes desulfurization pretreatment, requiring P≤0.120% and S≤0.030%; wheat kiln quicklime is used to control the phosphorus and sulfur content of scrap steel and pig iron blocks entering the furnace; low-aluminum ferrosilicon is used, and other raw materials and alloys meet their respective standard requirements; 2) Converter smelting Converter smelting: Steel with C content > 0.10% is tapped. Argon blowing is ensured during tapping. There is no slag agglomeration when the molten steel is refined and placed in place. The tapping temperature is 1610-1625℃. One stoking is performed. 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 design composition range. Silicon, calcium and barium are used for deoxidation. Ferrosilicon and medium carbon ferrochrome are added in the LF refining process. The heating time is 20-30 minutes and the in-situ temperature is 1587℃. The in-situ composition of the LF furnace meets the design composition requirements. 4) VD vacuum degassing VD vacuum degassing: VD vacuum degassing reduces the gas content in molten steel. The deep vacuum degassing time is ≥18min, and the soft blowing time after vacuum degassing is ≥15min. The argon flow rate is stable during the soft blowing process, and the molten steel creeps without being exposed. 5) Continuous casting Continuous casting: The billet size is 280mm×380mm. The continuous casting process adopts protective casting with low-alumina protective slag. The liquidus temperature is 1461℃ and the superheat ΔT is 25~29℃. The secondary cooling section adopts ultra-weak cooling water distribution. The entire process is operated at a constant casting speed of 0.63m / min. The electromagnetic stirring of the casting machine is turned on and the pressure is light. The billet quality is good.

2. The smelting method for improving the hardness of standard strength steel rails according to claim 1, characterized in that: The chemical composition of the rail steel by mass percentage includes: C: 0.81~0.86; Si: 0.52~0.59; Mn: 1.07~1.25; P≤0.020; S≤0.020; Cr: 0.23~0.28; Ni: 0.03~0.

05.

3. The smelting method for improving the hardness of standard strength steel rails according to claim 1, characterized in that: VD vacuum degassing: deep vacuum degassing time 18 min, deep vacuum degree 22 Pa / mbar, soft blowing time after vacuum degassing 16 min, soft blowing flow rate 100 Nl / min.

4. The smelting method for improving the hardness of standard strength steel rails according to claim 1, characterized in that: VD vacuum degassing: deep vacuum degassing time 19 min, deep vacuum degree 24 Pa / mbar, soft blowing time after vacuum degassing 17 min, soft blowing flow rate 100 Nl / min.

5. The smelting method for improving the hardness of standard strength steel rails according to claim 1, characterized in that: VD vacuum degassing: deep vacuum degassing time 20 min, deep vacuum degree 23 Pa / mbar, soft blowing time after vacuum degassing 18 min, soft blowing flow rate 100 Nl / min.

6. The smelting method for improving the hardness of standard strength steel rails according to claim 1, characterized in that: LF furnace refining: heating time 25 min.

7. The smelting method for improving the hardness of standard strength steel rails according to claim 1, characterized in that: The central porosity of the billet is grade 0.5, while the rest is grade 0 or 0.5, indicating good billet quality.

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