Preparation method of high-strength heat treatment steel rail for niobium and rare earth microalloying heavy haul railway

Abstract

The invention discloses a preparation method of a high-strength heat treatment steel rail for a niobium and rare earth microalloyed heavy haul railway. The production process comprises the steps of molten iron preparation, converter smelting, LF refining, VD and continuous casting. A steel rail rolling process; the online waste heat quenching cooling medium is air or aerial fog or a mixture of aerial fog and air; the steel rail comprises the following chemical components in percentage by mass: 0.83-1.08% of C; 0.50 to 0.85 percent of Si; 0.75 to 1.25% of Mn; less than or equal to 0.025% of P; s is less than or equal to 0.025%; the alloy comprises the following components in percentage by weight: 0.15 to 0.50 percent of Cr, 0.03 to 0.08 percent of V and 0.02 to 0.06 percent of Nb; the adding amount of RE is 0.0010-0.010%, and the balance is Fe, and the total mass fraction is 100%. The invention aims to smelt a steel rail with good strength and toughness ratio and excellent wear resistance, so that the steel rail can be applied to a heavy-load line service environment.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a method for preparing a niobium and rare earth micro-alloyed high-strength heat-treated steel rail for heavy-duty railways. Background Art

[0002] Heavy-haul railway transportation has attracted extensive attention from railway departments around the world due to its large transportation capacity, high efficiency and low cost. In countries and regions with dense heavy-haul railways, such as China, Australia, Brazil and the United States, the continuous increase in the axle weight, speed and annual transportation volume of heavy-haul trucks has brought serious challenges to the selection of rail materials and their transportation safety. Heavy-haul line rails face problems such as large wear and peeling during service. In particular, the annual transportation volume of freight lines such as the Daqin Railway in my country has increased rapidly, which has significantly increased the performance requirements of rails working under heavy-haul line conditions, including higher requirements for tread hardness, toughness and corrosion resistance. At present, the rail materials used in my country's railway transportation are basically various types of rails in the TB / T2344-2012 standard, with the highest strength grade of 1280MPa, which are basically eutectoid pearlite rails. The comparative application of rail products in the world industry shows that hypereutectoid rails have high strength, hardness and other properties, and have good comprehensive serviceability in large axle weight lines and small radius curves, which is significantly improved compared to the highest performance H370 rails in the existing standards. Therefore, it is necessary to develop high-performance rails outside the standard to meet the needs of heavy-haul lines. In addition, rails are irreplaceable industrial products that are related to life safety. They are an important component and consumable part of railway transportation. According to statistics on the demand of China Railway Materials Company, the annual domestic demand for rails is about 1.5 million tons. According to statistics, the international market grows steadily every year, and the market demand continues to grow. Therefore, the development of high-strength and wear-resistant rails has very important production and economic significance. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a niobium and rare earth micro-alloyed high-strength heat-treated rail for heavy-duty railway, so as to smelt a rail with good strength and toughness ratio and excellent wear resistance, so that it can be used in the service environment of heavy-duty lines.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The invention discloses a method for preparing a niobium and rare earth microalloyed high-strength heat-treated steel rail for heavy-duty railways, wherein the production process is as follows: molten iron→converter smelting→LF refining→VD→continuous casting; the converter smelting adopts aluminum-free deoxidation alloying, and the whole process is argon-blown as normal refining; the vacuum degree is ≤0.10KPa, the deep vacuum time is ≥18min, the superheat ΔT is ≤30°C, and the rare earth alloy is added at the VD station;

[0006] The rail rolling process is: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal rolling mill continuous rolling → online residual heat quenching → sawing → cooling → cutting head and tail → straightening → inspection → packaging → weighing → storage; the billet heating and preheating section temperature is not more than 900℃; the heating time is not less than 3 hours and 15 minutes; the furnace temperature is not less than 1150℃, the starting rolling temperature is ≥1100℃, and the final rolling temperature is 910~940℃;

[0007] The cooling medium for online residual heat quenching is wind or mist or a mixture of mist and wind; the heat treatment temperature is determined based on the phase change temperature parameters in the steel and the actual capacity of the industrial equipment; the residual heat treatment temperature after the final rolling of the rail is 750℃~810℃, and the rail will leave the heat treatment production line after 120~160s of online heat treatment. In the first stage of the online process, mist cooling is used for the top surface, both sides, and the lower jaw of the gauge angle and the bottom of the rail; the cooling rate of the actual cooling section is 3℃ / s-5℃ / s, and the cooling time is 50s-80s, to ensure that the final structure of the rail is pearlite; in the second stage, weak cooling is used, and the top surface, both sides of the rail head, the lower jaw of the gauge angle and the bottom of the rail are cooled by mist, and the cooling rate is ≤2℃ / s. After cooling, the temperature of the rail head at the outlet is 480℃~530℃, and then naturally air-cooled to room temperature;

[0008] The chemical composition of the rail by mass percentage includes: C 0.83-1.08%; Si 0.50-0.85%; Mn 0.75-1.25%; P≤0.025%; S≤0.025%; Cr 0.15-0.50%, V 0.03-0.08%, Nb 0.02-0.06%; RE addition amount is 0.0010-0.010%, and the rest is Fe, with a total mass fraction of 100%.

[0009] Furthermore, the rare earth is a high-purity FeCe alloy or a lanthanum-cerium mixed rare earth.

[0010] Furthermore, the chemical composition of the rail by mass percentage includes: C 0.92%, Si 0.58%, Mn 1.00%, P 0.013%, S 0.007%, Cr 0.34%, V 0.042%, Nb 0.021%, RE 0.0024%, and the rest is Fe, with a total mass fraction of 100%.

[0011] Furthermore, the chemical composition of the rail by mass percentage includes: C 0.94%, Si 0.62%, Mn 0.98%, P 0.011%, S 0.003%, Cr 0.29%, V 0.045%, Nb 0.029%, RE 0.0028%, and the rest is Fe, with a total mass fraction of 100%.

[0012] Furthermore, the chemical composition of the rail by mass percentage includes: C 0.95%, Si 0.60%, Mn 1.01%, P 0.019%, S 0.003%, Cr 0.33%, V 0.048%, Nb 0.032%, RE 0.0035%, and the rest is Fe, with a total mass fraction of 100%.

[0013] Furthermore, the chemical composition of the rail by mass percentage includes: C 0.94%, Si 0.64%, Mn 0.99%, P 0.017%, S 0.005%, Cr 0.30%, V 0.051%, Nb 0.027%, RE 0.0021%, and the rest is Fe, with a total mass fraction of 100%.

[0014] Furthermore, the chemical composition of the rail by mass percentage includes: C 0.93%, Si 0.59%, Mn 1.02%, P 0.009%, S 0.004%, Cr 0.31%, V 0.047%, Nb 0.041%, RE 0.0033%, and the rest is Fe, with a total mass fraction of 100%.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are:

[0016] The present invention utilizes the online waste heat heat treatment process to improve the strength and hardness of the rails, and at the same time rationally designs the composition and adds the optimal Si, Mn, V, Nb, RE alloy elements into the rails, which can improve the tensile strength, elongation, tread hardness, wear resistance and other properties of the rails under this rolling process. The heat-treated rails produced by the present invention have good tensile strength and tread hardness. The heat-treated rails containing niobium and rare earth of the present invention have a unique production process, high production efficiency, energy saving and environmental protection, good economic benefits, are suitable for large-scale production, and have good promotion value. DETAILED DESCRIPTION

[0017] A method for preparing a niobium and rare earth micro-alloyed high-strength heat-treated rail for heavy-duty railways:

[0018] The smelting production process of steel is: molten iron → converter smelting → LF refining → VD → continuous casting. The converter smelting adopts aluminum-free deoxidation alloying, and the whole process is argon blowing as normal refining; vacuum degree ≤ 0.10KPa, deep vacuum time ≥ 18min, superheat ΔT ≤ 30℃. The chemical composition of each example is shown in Table 1.

[0019] Table 1 Composition of each example (mass percentage / %)

[0020]

[0021] The rolling process is: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal rolling mill continuous rolling → online residual heat quenching → sawing → cooling → cutting head and tail → straightening → inspection → packaging → weighing → storage. The temperature of the billet heating and preheating section is not more than 900℃; the heating time is not less than 3 hours and 15 minutes. The furnace temperature is not less than 1150℃, the rolling start temperature is ≥1100℃, and the final rolling temperature is 910~940℃.

[0022] The cooling medium for online residual heat quenching is a mixture of mist and wind. The heat treatment temperature is determined based on the phase change temperature parameters in the steel and the actual capacity of the industrial equipment. The residual heat treatment temperature of the rail after final rolling is 750℃~810℃. After 120~160s of online heat treatment, it leaves the heat treatment production line. In the first stage of the online process, mist cooling is used for the top surface, both sides, and the lower jaw of the gauge angle and the bottom of the rail. The actual cooling section has a cooling rate of 3℃ / s~5℃ / s, and the cooling time is 50s~80s. Ensure that the final structure of the rail is pearlite. In the second stage, weak cooling is used, and mist cooling is performed on the top surface, both sides of the rail head, the lower jaw of the gauge angle, and the bottom of the rail. The cooling rate is ≤2℃ / s. The temperature of the rail head at the outlet after cooling is 480℃~530℃, and then it is naturally air-cooled to room temperature.

[0023] Table 2 Examples of rolling process for rail materials

[0024]

[0025] The properties of steel samples after rolling: The specifications of the tensile specimens are as follows: diameter d0 = 10 mm, gauge length Lo = 5do. The tread hardness is randomly sampled on the rail, the specimen length is 250 mm, the top surface of the rail head is ground off 0.5 mm, and there are 5 test points. The Brinell hardness test is carried out and the average value is calculated. The test temperature is 20°C ± 5°C. The above sample sampling method, location and size are in accordance with the TB / T2344-2012 standard. The experimental results are shown in Table 3.

[0026] Table 3 Mechanical properties of each example

[0027]

[0028] It can be seen from 3 that each example has good strength, toughness and mechanical properties, and the rails produced therefrom have good wear resistance and contact fatigue resistance.

[0029] 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 method for preparing a niobium and rare earth microalloyed high-strength heat-treated rail for heavy-duty railway, characterized in that: Its production process is: molten iron → converter smelting → LF refining → VD → continuous casting; converter smelting adopts aluminum-free deoxidation alloying, and the whole process is argon blowing as normal refining; vacuum degree ≤ 0.10KPa, deep vacuum time ≥ 18min, superheat ΔT ≤ 30℃, and rare earth alloy is added at the VD station; The rail rolling process is: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal rolling mill continuous rolling → online residual heat quenching → sawing → cooling → cutting head and tail → straightening → inspection → packaging → weighing → storage; the billet heating and preheating section temperature is not more than 900℃; the heating time is not less than 3 hours and 15 minutes; the furnace temperature is not less than 1150℃, the starting rolling temperature is ≥1100℃, and the final rolling temperature is 910~940℃; The cooling medium for online residual heat quenching is wind or mist or a mixture of mist and wind; the heat treatment temperature is determined based on the phase change temperature parameters in the steel and the actual capacity of the industrial equipment; the residual heat treatment temperature after the final rolling of the rail is 750℃~810℃, and the rail will leave the heat treatment production line after 120~160s of online heat treatment. In the first stage of the online process, mist cooling is used for the top surface, both sides, and the lower jaw of the gauge angle and the bottom of the rail; the cooling rate of the actual cooling section is 3℃ / s-5℃ / s, and the cooling time is 50s-80s, to ensure that the final structure of the rail is pearlite; in the second stage, weak cooling is used, and the top surface, both sides of the rail head, the lower jaw of the gauge angle and the bottom of the rail are cooled by mist, and the cooling rate is ≤2℃ / s. After cooling, the temperature of the rail head at the outlet is 480℃~530℃, and then naturally air-cooled to room temperature; The chemical composition of the rail by mass percentage includes: C 0.83-1.08%; Si 0.50-0.85%; Mn 0.75-1.25%; P≤0.025%; S≤0.025%; Cr 0.15-0.50%, V 0.03-0.08%, Nb 0.02-0.06%; RE addition amount is 0.0010-0.010%, and the rest is Fe, with a total mass fraction of 100%.

2. The method for preparing niobium and rare earth microalloyed high-strength heat-treated rail for heavy-duty railway according to claim 1, characterized in that: The rare earth is a high-purity FeCe alloy or a lanthanum-cerium mixed rare earth.

3. The method for preparing niobium and rare earth microalloyed high-strength heat-treated rail for heavy-duty railway according to claim 1, characterized in that: The chemical composition of the rail by mass percentage includes: C 0.92%, Si 0.58%, Mn 1.00%, P 0.013%, S 0.007%, Cr 0.34%, V 0.042%, Nb 0.021%, RE 0.0024%, and the rest is Fe, with a total mass fraction of 100%.

4. The method for preparing niobium and rare earth microalloyed high-strength heat-treated rail for heavy-duty railway according to claim 1, characterized in that: The chemical composition of the rail by mass percentage includes: C 0.94%, Si 0.62%, Mn 0.98%, P 0.011%, S 0.003%, Cr 0.29%, V 0.045%, Nb 0.029%, RE 0.0028%, and the rest is Fe, with a total mass fraction of 100%.

5. The method for preparing niobium and rare earth microalloyed high-strength heat-treated rail for heavy-duty railway according to claim 1, characterized in that: The chemical composition of the rail by mass percentage includes: C 0.95%, Si 0.60%, Mn 1.01%, P 0.019%, S 0.003%, Cr 0.33%, V 0.048%, Nb 0.032%, RE 0.0035%, and the rest is Fe, with a total mass fraction of 100%.

6. The method for preparing niobium and rare earth microalloyed high-strength heat-treated rail for heavy-duty railway according to claim 1, characterized in that: The chemical composition of the rail by mass percentage includes: C 0.94%, Si 0.64%, Mn 0.99%, P 0.017%, S 0.005%, Cr 0.30%, V 0.051%, Nb 0.027%, RE 0.0021%, and the rest is Fe, with a total mass fraction of 100%.

7. The method for preparing niobium and rare earth microalloyed high-strength heat-treated rail for heavy-duty railway according to claim 1, characterized in that: The chemical composition of the rail by mass percentage includes: C 0.93%, Si 0.59%, Mn 1.02%, P 0.009%, S 0.004%, Cr 0.31%, V 0.047%, Nb 0.041%, RE 0.0033%, and the rest is Fe, with a total mass fraction of 100%.

Images