Preparation method of RE, Cu and V microalloy high-toughness steel rail

Abstract

The invention discloses a preparation method of an RE, Cu and V microalloy high-toughness steel rail. The preparation method comprises the following steps: a steel rail material steelmaking production process; a steel rail rolling process; a pre-bending cooling process; the steel rail material comprises the following chemical components in percentage by mass: 0.67-0.75% of C; 0.30 to 0.55 percent of Si; 0.55 to 1.00% of Mn; less than or equal to 0.025% of P; s is less than or equal to 0.025%; 0.005 to 0.015 percent of Cu; the content of V is 0.25 to 0.55 percent, and the content of RE is 0.0005 to The total mass percent of the Fe and the impurities is 100%. The low-carbon component design and the pre-bending cooling process are adopted, the obdurability of the material can be improved at the same time, meanwhile, elements such as Cu and V are added, and the service performance of the material is further stabilized and improved.

Description

Technical Field

[0001] This invention belongs to the field of rail preparation technology, and particularly relates to a method for preparing RE, Cu, V microalloyed high-strength and high-toughness rails. Background Technology

[0002] Winters are long and cold in most parts of my country, with temperatures in some areas sometimes dropping below -40°C. Prolonged service in low-temperature environments can lead to brittle fracture of rails, directly impacting railway transport safety. With the expansion of railway construction and the increasing demands of line operation, it is necessary to research and find ways to improve the wear resistance of rails while simultaneously enhancing their toughness and mechanical properties. Currently, rail standards in various countries only specify elongation and fracture toughness for rail steel. The Russian standard GOSTPR 51685-2013 includes requirements for the impact performance of rails resistant to low temperatures.

[0003] With the increase in railway freight volume, new requirements have been placed on the low-temperature toughness of rails used in low-temperature environments such as the Qinghai-Tibet Plateau and some northern regions of my country. The increased freight volume requires rails to have high wear resistance as well as the ability to resist brittle fracture at -40℃. As an important component of railway transportation, research shows that low sulfur, phosphorus, and gas inclusions in rails, i.e., the purity of the steel, are of great significance to the material's toughness, fracture strength, fatigue, and other service indicators. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing RE, Cu, V microalloyed high-strength and tough steel rails. By adopting a low-carbon composition design and a pre-bending and cooling process, the strength and toughness of the material can be improved simultaneously. At the same time, the addition of elements such as Cu and V further stabilizes and improves the service performance of the material.

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

[0006] This invention discloses a method for preparing RE, Cu, V microalloyed high-strength and high-toughness steel rails, comprising:

[0007] Steelmaking process for rail materials: molten iron → converter smelting → LF refining → VD → continuous casting; converter smelting adopts aluminum-free deoxidation alloying, and the whole process is carried out by normal argon blowing according to refining; vacuum degree ≤0.12KPa, deep vacuum time ≥20min, superheat ΔT≤25℃, rare earth alloy is added at the crystallizer position.

[0008] Rail rolling process: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal mill continuous rolling → online residual heat quenching → sawing → cooling → head and tail trimming → straightening → inspection → packaging → weighing → warehousing; the billet heating and preheating section temperature shall not exceed 920℃; the heating time shall not be less than 3 hours and 20 minutes; the furnace exit temperature shall not be lower than 1060℃, the initial rolling temperature shall be ≥1080℃, and the final rolling temperature shall be 890~930℃; the pre-bending cooling start temperature shall be 820℃~880℃, and the cooling bed step distance shall not be less than 500mm during the cooling process;

[0009] Pre-bending cooling process: The pre-bending cooling medium is mainly natural air and compressed air from the fans in the cooling bed section; the initial pre-bending cooling temperature of the rail is 820℃~880℃. In the first stage, the actual cooling rate of the rail head is 2.3℃ / s~3.9℃ / s, cooling to a rail head temperature of 520℃~610℃; in the second stage, the actual cooling rate of the rail head is 1.3℃ / s~2.0℃ / s, cooling to a rail head temperature of 360℃~420℃; in the third stage, the actual cooling rate of the rail head is 0.1℃ / s~0.5℃ / s, cooling to a rail head temperature of 90℃~150℃.

[0010] The chemical composition of the rail material by mass percentage is as follows: C 0.67–0.75%; Si 0.30–0.55%; Mn 0.55–1.00%; P ≤0.025%; S ≤0.025%; Cu 0.005–0.015%; V 0.25–0.55%; RE 0.0005–0.0015%; the remainder is Fe and impurities, totaling 100% by mass.

[0011] Furthermore, the chemical composition of the rail material by mass percentage is as follows: C 0.68%; Si 0.43%; Mn 0.90%; P 0.012%; S 0.007%; Cu 0.006%; V 0.32%; RE 0.0008%; the remainder being Fe and impurities, totaling 100% by mass.

[0012] Furthermore, the chemical composition of the rail material by mass percentage is as follows: C 0.73%; Si 0.52%; Mn 0.85%; P 0.011%; S 0.003%; Cu 0.010%; V 0.26%; RE 0.0006%; the remainder being Fe and impurities, totaling 100% by mass.

[0013] Furthermore, the chemical composition of the rail material by mass percentage is as follows: C 0.70%; Si 0.45%; Mn 0.92%; P 0.019%; S 0.003%; Cu 0.012%; V 0.40%; RE 0.0010%; the remainder being Fe and impurities, totaling 100% by mass.

[0014] Furthermore, the initial rolling temperature is 1092℃, the final rolling temperature is 925℃, and the initial pre-bending cooling temperature is 864℃.

[0015] Furthermore, the initial rolling temperature is 1100℃, the final rolling temperature is 907℃, and the initial pre-bending cooling temperature is 880℃.

[0016] Furthermore, the initial rolling temperature is 1125℃, the final rolling temperature is 911℃, and the initial pre-bending cooling temperature is 875℃.

[0017] The main alloying elements Si, Mn, and V added to this material are intended to improve the strength of the rail and ensure a suitable heat treatment temperature for the phase transformation temperature. The carbon (C) content in this steel is designed to have a high solid solubility with Fe, resulting in solid solution strengthening and improving the strength and hardness of the steel. However, increasing the C content will reduce the toughness of the rail; therefore, the C content in this invention considers both strength and toughness. Mn expands the austenite phase region, increasing the stability of the supercooled austenite and significantly improving the hardenability of the steel. Si reduces the austenite-ferrite transformation rate, improving the strength, elasticity, and tempering resistance of the steel. However, considering the weldability of the rail, the Si content should not be too high because Si has poor thermal conductivity, which is detrimental to rail welding. V improves the hardenability of the steel, increasing the strength and hardness of the material. The solid solubility of Cu in ferrite decreases sharply with decreasing temperature. Through solid solution strengthening, dislocation movement can be effectively hindered, thereby significantly improving the strength of the steel. Furthermore, the added RE element is a rare earth alloy. Basic theoretical research on rare earths has proven that the presence of rare earth elements in steel controls the morphology of sulfides during smelting, resulting in refined grains in the steel. Simultaneously, rare earth elements improve the oxidation resistance and low-temperature resistance of steel. The presence of appropriate amounts of rare earth elements in steel materials can lower the ductile-brittle transition temperature, which is of significant technical importance for the service of rails in low-temperature regions.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] This invention provides a manufacturing process for high-toughness rail materials containing rare earth elements (RE), Cu, and V. Utilizing the residual heat after online rail rolling, and with a rationally designed composition and optimal addition of RE, Cu, and Vr alloying elements, the process increases the cooling step distance, improves and controls the cooling rate and temperature of each section, refines the internal microstructure of the rail, and enhances its strength and hardness while maintaining dimensional consistency throughout its length. Furthermore, by determining the natural aging time for tensile specimens, the toughness of the rail is further improved. This invention's rare earth-containing rail has a unique production process, high production efficiency, energy saving and environmental protection, and good economic benefits, making it suitable for large-scale production and possessing significant potential for widespread application. Detailed Implementation

[0020] The steel smelting process is as follows: molten iron → converter smelting → LF refining → VD → continuous casting. The converter smelting adopts aluminum-free deoxidation alloying, and the entire process is carried out with normal argon blowing as in refining; vacuum degree ≤0.12KPa, deep vacuum time ≥20min, superheat ΔT ≤25℃, and rare earth alloys are added at the crystallizer position.

[0021] The chemical composition of each example is shown in Table 1.

[0022] Table 1. Components of each example (mass percentage / %)

[0023]

[0024] The rolling process is as follows: billet → sawing → heating → BD1 rolling → BD2 rolling → continuous rolling on the CCS universal mill → online residual heat quenching → sawing → cooling → head and tail trimming → straightening → inspection → packaging → weighing → warehousing. The preheating temperature of the billet should not exceed 920℃; the heating time should not be less than 3 hours and 20 minutes. The furnace exit temperature should not be lower than 1060℃, the initial rolling temperature ≥1080℃, and the final rolling temperature 890~930℃. The pre-bending cooling start temperature is 820℃~880℃, and the cooling bed step distance during the cooling process should not be less than 500mm. Tensile testing of the rails is conducted after being placed for at least 24 hours.

[0025] Table 2 Examples of cooling processes for steel rail materials

[0026]

[0027]

[0028] The pre-bending cooling process primarily uses natural air and compressed air from the cooling bed's fans as the cooling medium. The initial pre-bending cooling temperature of the rail is 810℃~870℃. In the first stage, the actual cooling rate of the rail head is 2.3℃ / s~3.9℃ / s, cooling to a rail head temperature of 520℃~610℃. In the second stage, the actual cooling rate of the rail head is 1.3℃ / s~2.0℃ / s, cooling to a rail head temperature of 360℃~420℃. In the third stage, the actual cooling rate of the rail head is 0.1℃ / s~0.5℃ / s, cooling to a rail head temperature of 90℃~150℃.

[0029] Table 3 Examples of Pre-bending 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 3.

[0032] Table 3 Mechanical properties of each example

[0033]

[0034] As can be seen from Table 3, each example has good strength, toughness and mechanical properties, and the rails produced from them have good wear resistance and low-temperature toughness.

[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 method for preparing RE, Cu, V microalloyed high-strength and high-toughness steel rails, characterized in that, include: Steelmaking process for rail materials: molten iron → converter smelting → LF refining → VD → continuous casting; converter smelting adopts aluminum-free deoxidation alloying, and the whole process is carried out with normal argon blowing according to the refining process; Vacuum degree ≤ 0.12KPa, deep vacuum time ≥ 20min, superheat ΔT ≤ 25℃, rare earth alloy is added at the crystallizer position; Rail rolling process: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal mill continuous rolling → online residual heat quenching → sawing → cooling → head and tail trimming → straightening → inspection → packaging → weighing → warehousing; the billet heating and preheating section temperature shall not exceed 920℃; the heating time shall not be less than 3 hours and 20 minutes; the furnace exit temperature shall not be lower than 1060℃, the initial rolling temperature shall be ≥1080℃, and the final rolling temperature shall be 890~930℃; the pre-bending cooling start temperature shall be 820℃~880℃, and the cooling bed step distance shall not be less than 500mm during the cooling process; Pre-bending cooling process: The pre-bending cooling medium is mainly natural air and compressed air from the fans in the cooling bed section; the initial pre-bending cooling temperature of the rail is 820℃~880℃. In the first stage, the actual cooling rate of the rail head is 2.3℃ / s~3.9℃ / s, cooling to a rail head temperature of 520℃~610℃; in the second stage, the actual cooling rate of the rail head is 1.3℃ / s~2.0℃ / s, cooling to a rail head temperature of 360℃~420℃; in the third stage, the actual cooling rate of the rail head is 0.1℃ / s~0.5℃ / s, cooling to a rail head temperature of 90℃~150℃. The chemical composition of the rail material by mass percentage is as follows: C 0.67–0.75%; Si 0.30–0.55%; Mn 0.55–1.00%; P ≤0.025%; S ≤0.025%; Cu 0.005–0.015%; V 0.25–0.55%; RE 0.0005–0.0015%; the remainder is Fe and impurities, totaling 100% by mass.

2. The method for preparing RE, Cu, V microalloyed high-strength and high-toughness steel rails according to claim 1, characterized in that, The chemical composition of the rail material by mass percentage is as follows: C 0.68%; Si 0.43%; Mn 0.90%; P 0.012%; S 0.007%; Cu 0.006%; V 0.32%; RE 0.0008%; the remainder is Fe and impurities, with a total mass fraction of 100%.

3. The method for preparing RE, Cu, V microalloyed high-strength and high-toughness steel rails according to claim 1, characterized in that, The chemical composition of the rail material by mass percentage is as follows: C 0.73%; Si 0.52%; Mn 0.85%; P 0.011%; S 0.003%; Cu 0.010%; V 0.26%; RE 0.0006%; the remainder is Fe and impurities, with a total mass fraction of 100%.

4. The method for preparing RE, Cu, V microalloyed high-strength and high-toughness steel rails according to claim 1, characterized in that, The chemical composition of the rail material by mass percentage is as follows: C 0.70%; Si 0.45%; Mn 0.92%; P 0.019%; S 0.003%; Cu 0.012%; V 0.40%; RE 0.0010%; the remainder is Fe and impurities, with a total mass fraction of 100%.

5. The method for preparing RE, Cu, V microalloyed high-strength and high-toughness steel rails according to claim 1, characterized in that, The initial rolling temperature is 1092℃, the final rolling temperature is 925℃, and the initial pre-bending cooling temperature is 864℃.

6. The method for preparing RE, Cu, V microalloyed high-strength and high-toughness steel rails according to claim 1, characterized in that, The initial rolling temperature is 1100℃, the final rolling temperature is 907℃, and the initial pre-bending cooling temperature is 880℃.

7. The method for preparing RE, Cu, V microalloyed high-strength and high-toughness steel rails according to claim 1, characterized in that, The initial rolling temperature is 1125℃, the final rolling temperature is 911℃, and the initial pre-bending cooling temperature is 875℃.

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