Preparation process of medium-carbon high-toughness steel rail

Abstract

The invention discloses a preparation technology of a medium-carbon high-toughness steel rail. The preparation technology comprises the steps of molten iron desulfurization pretreatment, 150t top-bottom combined blown converter smelting, LF refining, VD vacuum degassing refining, square billet continuous casting, heating, high-pressure water descaling, BD1 rough rolling, BD2 rough rolling, universal rolling mill rolling and online heat treatment. The bead steel rail steel is prepared from, by mass, 0.55%-0.65% of C, 0.45%-0.55% of Si, 0.75%-0.95% of Mn, 0.20%-0.25% of Cr, smaller than or equal to 0.020% of P, smaller than or equal to 0.025% of S, 0.06%-0.12% of V and the balance Fe. The alloy comprises, by weight, 0.015-0.025% of Cu, Ni, Nb and RE, 0.006-0.008% of N and the balance iron and impurities. The invention aims to prepare the steel rail with good strength and toughness ratio and excellent wear resistance, so that the steel rail can be applied to severe regional environments.

Description

Technical Field

[0001] This invention belongs to the field of steel materials, and particularly relates to a preparation process for medium carbon high toughness steel rails. Background Technology

[0002] With the extension of railway construction lines and the increase in rail exports, some high-altitude and frigid environments require rails that, in addition to meeting strength and wear resistance requirements, also possess the ability to resist low-temperature brittle fracture and exhibit excellent low-temperature toughness below -40°C. High-carbon pearlitic rails require a relatively high carbon content to meet wear resistance requirements; generally, the carbon content of the rail material is above 0.70% to achieve the necessary strength and hardness. However, this type of pearlitic rail has low impact energy, with an impact energy of less than 10J at -40°C.

[0003] Currently, most rails, both domestically and internationally, are high-carbon pearlitic rail steel. To improve the strength and toughness of the material and reduce the influence of carbon on toughness, different contents of v and nitrogen are added to C-Si-Mn-Cu-Cr-Ni pearlitic steel, followed by rolling and heat treatment. The aim is to obtain nano-sized v (c, n) precipitates in the pearlitic steel to improve the strength and hardness of the rail. VN alloys have been widely used in the strengthening and toughening of structural steel. Utilizing the bond between v and nitrogen, adding these alloys to steel can simultaneously achieve the refining effect of v and the strengthening effect of nitrogen, while reducing the amount of carbon added and improving the toughness of the steel. With the development of railway construction and the increase in rail exports, Russia has put forward a demand for low-temperature resistant rails in accordance with Russian standards. Therefore, developing a low-temperature resistant (-60℃) rail material can seize market opportunities and bring positive social benefits to enterprises. Summary of the Invention

[0004] The purpose of this invention is to provide a manufacturing process for medium-carbon high-toughness steel rails, which produces steel rails with a good strength-toughness ratio and excellent wear resistance, making them suitable for use in harsh environments.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a manufacturing process for medium-carbon, high-toughness steel rails, comprising: desulfurization pretreatment of molten iron—150t top-and-bottom blowing converter smelting—LF refining—VD vacuum degassing refining—square billet continuous casting—heating—high-pressure water descaling—BD1 rough rolling—BD2 rough rolling—universal rolling mill rolling—online heat treatment—straightening—flaw detection—machining—inspection and warehousing; characterized in that, specifically:

[0007] Steelmaking includes: magnesium-based powder injection desulfurization for hot metal pretreatment, with S ≤ 0.030% in the hot metal entering the furnace; C > 0.08% at the end of converter smelting, T > 1620℃ at the tapping temperature, P ≤ 0.120% at the tapping temperature, and the addition of ferrosilicon, ferromanganese and ferrosilicon alloys for in-ladle deoxidation and alloying.

[0008] LF refining uses silicon-calcium-barium deoxidation, adds ferrosilicon and ferrochrome alloys, desulfurizes and fine-tunes the chemical composition;

[0009] 15% FeV alloy (1-2 kg / t) was added to the LF furnace during initial placement, followed by composition fine-tuning and heating. Samples were taken after 10 minutes. When the V content reached 0.06%, the nitrogen content in the molten steel significantly increased to approximately 0.004%. 10% VN alloy (1-2 kg) was then added. During refining and removal from the furnace, the V content was controlled at a target of 0.09%, and the N content at a target of 0.008%. The initial LF furnace temperature was 1565℃, the heating time was 25 minutes, and the removal temperature was 1580℃. The VD vacuum degree was no greater than 0.10 kPa, the deep vacuum treatment time was ≥15 minutes, and the soft blowing time after vacuum treatment was guaranteed to be at least 15 minutes. No exposed steel surface was observed during the entire soft blowing process.

[0010] The tundish covering agent for the large billet continuous casting machine uses calcium-magnesium granules, and the crystallizer uses low-aluminum protective slag. It provides full protection during casting and simultaneously activates the electromagnetic stirring and light pressing mode at the end of solidification in the crystallizer. The casting speed is constant throughout the process, at 0.85m / min.

[0011] The rolling process includes: after the continuously cast billet is heated for 3.5 hours in a three-stage walking beam furnace, it is rolled in 13 passes on line #2 with a compression ratio of 13.1. The rolling pass distribution is as follows: 3 passes for BD1 billet opening + 7 passes for BD2 roughing + 3 passes for the universal mill. The BD1 opening rolling temperature is 1100℃~1160℃, and the final rolling temperature is 920℃~960℃.

[0012] Online heat treatment process: The online residual heat quenching cooling medium is pure air or a mixture of air and mist; the initial residual heat treatment temperature of the rail is 750℃~830℃. After online heat treatment, the rail exits the heat treatment production line. In the first stage online, strong cooling is performed on the top surface, sides, lower jaw of the gauge angle, and bottom of the rail head; the actual cooling rate is 2.2℃ / s~5.7℃ / s, and the surface temperature of the rail head after cooling is 620℃~660℃; the second stage is weak cooling, cooling the top surface, sides, lower jaw of the gauge angle, and bottom of the rail, with a cooling rate of 1.5℃ / s~2.0℃ / s; the third stage is weak cooling, with a cooling rate ≤1.0℃ / s, and the final exit rail head temperature is 450℃~520℃, followed by natural air cooling to room temperature;

[0013] The Zhuhai Steel rail steel comprises the following elemental components by mass percentage: C: 0.55-0.65%, Si: 0.45-0.55%, Mn: 0.75-0.95%, Cr: 0.20-0.25%, P≤0.020%, S≤0.025%, V: 0.06~0.12%; Cu+Ni+Nb+RE: 0.015-0.025%, N: 0.006~0.008%, with the remainder being Fe and impurities.

[0014] Furthermore, the dimensions of the cast billet are 280 mm × 380 mm.

[0015] Furthermore, the liquidus temperature of the rail is 1464℃, and the superheat ΔT is controlled at 29℃.

[0016] Furthermore, the Zhuhai Steel rail steel comprises the following elemental components by mass percentage: C: 0.58%, Si: 0.48%, Mn: 0.79%, Cr: 0.22%, P: 0.013%, S: 0.007%, V: 0.08%; Cu+Ni+Nb+RE: 0.019%, N: 0.0072%, with the remainder being Fe and impurities.

[0017] Furthermore, the Zhuhai Steel rail steel comprises the following elemental components by mass percentage: C: 0.60%, Si: 0.55%, Mn: 0.82%, Cr: 0.25%, P: 0.011%, S: 0.003%, V: 0.11%; Cu+Ni+Nb+RE: 0.016%, N: 0.0065%, with the remainder being Fe and impurities.

[0018] Furthermore, the Zhuhai Steel rail steel comprises the following elemental components by mass percentage: C: 0.62%, Si: 0.52%, Mn: 0.75%, Cr: 0.28%, P: 0.019%, S: 0.003%, V: 0.1%; Cu+Ni+Nb+RE: 0.022%, N: 0.0069%, with the remainder being Fe and impurities.

[0019] Furthermore, the prepared rails meet the following requirements: tensile strength greater than 1000 MPa, yield strength greater than 300 MPa, impact energy at -40℃ greater than 15 J, and fracture toughness at -20℃ greater than 35 MPa·m. 0.5 .

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

[0021] This invention utilizes VN alloying elements and heat treatment processes to improve the strength and hardness of rails, while reasonably reducing the C content to ensure that the low-temperature impact toughness of the material meets technical requirements. The composition design and heat treatment of this invention feature a unique production process, making it suitable for large-scale production and possessing significant potential for widespread application. Detailed Implementation

[0022] The chemical composition of the rail materials prepared in each embodiment is shown in Table 1.

[0023] Table 1. Components of each embodiment (mass percentage / %)

[0024]

[0025] Table 2 Gas content ×10 -4 %

[0026]

[0027]

[0028] The specific implementation of the heat treatment process for steel rails is shown in Table 2.

[0029] Table 3 Examples of Heat Treatment Processes for Rail Materials

[0030]

[0031] Performance of rolled steel samples: Tensile test specimens were prepared with a diameter d0 = 10 mm and a gauge length Lo = 5 do. Tread surface hardness was measured by random sampling on the rail, with a specimen length of 250 mm. 0.5 mm of the rail head was ground off the top surface. Five test points were used for Brinell hardness testing, and the average value was calculated. The test temperature was 20℃ ± 5℃. The sampling method, location, and dimensions of the above samples conformed to TB / T2344-2012 standard. Impact sampling was performed according to GB / T229-2007. The sampling location was at the center of the tread surface, in the longitudinal direction, with dimensions of 10 mm × 10 mm × 50 mm, classified as A. KU2 Type notch. The experimental results are shown in Table 4.

[0032] Table 4 Mechanical properties of each embodiment

[0033]

[0034] As can be seen from Table 4, each embodiment has good strength, low-temperature impact toughness and mechanical properties, and the rails produced using them meet the technical requirements of low-temperature areas.

[0035] 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 manufacturing process for medium-carbon high-toughness steel rails, comprising the following steps: desulfurization pretreatment of molten iron—150t top-and-bottom blowing converter smelting—LF refining—VD vacuum degassing refining—square billet continuous casting—heating—high-pressure water descaling—BD1 rough rolling—BD2 rough rolling—universal rolling mill rolling—online heat treatment—straightening—flaw detection—machining—inspection and warehousing; characterized in that, Specifically: Steelmaking includes: magnesium-based powder injection desulfurization for hot metal pretreatment, with S ≤ 0.030% in the hot metal entering the furnace; C > 0.08% at the end of converter smelting, T > 1620℃ at the tapping temperature, P ≤ 0.120% at the tapping temperature, and the addition of ferrosilicon, ferromanganese and ferrosilicon alloys for in-ladle deoxidation and alloying. LF refining uses silicon-calcium-barium deoxidation, adds ferrosilicon and ferrochrome alloys, desulfurizes and fine-tunes the chemical composition; 15% FeV alloy (1-2 kg / t) was added to the LF furnace during initial placement, followed by composition fine-tuning and heating. Samples were taken after 10 minutes. When the V content reached 0.06%, the nitrogen content in the molten steel significantly increased to 0.004%. 10% VN alloy (1-2 kg) was then added. During refining and removal from the furnace, the V content was controlled at a target of 0.09%, and the N content at a target of 0.008%. The initial LF furnace temperature was 1565℃, the heating time was 25 minutes, and the removal temperature was 1580℃. The VD vacuum degree was no greater than 0.10 kPa, the deep vacuum treatment time was ≥15 minutes, and the soft blowing time after vacuum treatment was guaranteed to be at least 15 minutes. No exposed steel surface was observed during the entire soft blowing process. The tundish covering agent for the large billet continuous casting machine uses calcium-magnesium granules, and the crystallizer uses low-aluminum protective slag. It provides full protection during casting and simultaneously activates the electromagnetic stirring and light pressing mode at the end of solidification in the crystallizer. The casting speed is constant throughout the process, at 0.85m / min. The rolling process includes: after the continuously cast billet is heated for 3.5 hours in a three-stage walking beam furnace, it is rolled in 13 passes on line #2 with a compression ratio of 13.

1. The rolling pass distribution is as follows: 3 passes for BD1 billet opening + 7 passes for BD2 roughing + 3 passes for the universal mill. The BD1 opening rolling temperature is 1100℃~1160℃, and the final rolling temperature is 920℃~960℃. Online heat treatment process: The online residual heat quenching cooling medium is pure air or a mixture of air and mist; the initial residual heat treatment temperature of the rail is 750℃~830℃. After online heat treatment, the rail exits the heat treatment production line. In the first stage online, strong cooling is performed on the top surface, sides, lower jaw of the gauge angle, and bottom of the rail head; the actual cooling rate is 2.2℃ / s~5.7℃ / s, and the surface temperature of the rail head after cooling is 620℃~660℃; the second stage is weak cooling, cooling the top surface, sides, lower jaw of the gauge angle, and bottom of the rail, with a cooling rate of 1.5℃ / s~2.0℃ / s; the third stage is weak cooling, with a cooling rate ≤1.0℃ / s, and the final exit rail head temperature is 450℃~520℃, followed by natural air cooling to room temperature; The Zhuhai Steel rail steel comprises the following elemental components by mass percentage: C: 0.55-0.65%, Si: 0.45-0.55%, Mn: 0.75-0.95%, Cr: 0.20-0.25%, P≤0.020%, S≤0.025%, V: 0.06~0.12%; Cu+Ni+Nb+RE: 0.015-0.025%, N: 0.006~0.008%, with the remainder being Fe and impurities.

2. The manufacturing process of medium-carbon high-toughness steel rail according to claim 1, characterized in that, The dimensions of the cast billet are 280 mm × 380 mm.

3. The manufacturing process of medium-carbon high-toughness steel rail according to claim 1, characterized in that, The liquidus temperature of the rail is 1464℃, and the superheat ΔT is controlled at 29℃.

4. The manufacturing process of medium-carbon high-toughness steel rail according to claim 1, characterized in that, The Zhuhai Steel rail steel comprises the following elemental components by mass percentage: C: 0.58%, Si: 0.48%, Mn: 0.79%, Cr: 0.22%, P: 0.013%, S: 0.007%, V: 0.08%; Cu+Ni+Nb+RE: 0.019%, N: 0.0072%, with the remainder being Fe and impurities.

5. The manufacturing process of medium-carbon high-toughness steel rail according to claim 1, characterized in that, The Zhuhai Steel rail steel comprises the following elemental components by mass percentage: C: 0.60%, Si: 0.55%, Mn: 0.82%, Cr: 0.25%, P: 0.011%, S: 0.003%, V: 0.11%; Cu+Ni+Nb+RE: 0.016%, N: 0.0069%, with the remainder being Fe and impurities.

6. The manufacturing process of medium-carbon high-toughness steel rail according to claim 1, characterized in that, The Zhuhai Steel rail steel comprises the following elemental components by mass percentage: C: 0.62%, Si: 0.52%, Mn: 0.75%, Cr: 0.28%, P: 0.019%, S: 0.003%, V: 0.1%; Cu+Ni+Nb+RE: 0.022%, N: 0.0065%, with the remainder being Fe and impurities.

7. The manufacturing process of medium-carbon high-toughness steel rail according to claim 1, characterized in that, The prepared rails meet the following requirements: tensile strength greater than 1000 MPa, yield strength greater than 300 MPa, impact energy at -40℃ greater than 15 J, and fracture toughness at -20℃ greater than 35 MPa·m. 0.5 .

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