Manufacturing method for improving yield strength of exit steel rail through rare earth

Abstract

The invention discloses a manufacturing method for improving the yield strength of an outlet steel rail by rare earth. The manufacturing method comprises the following steps: a smelting process: molten iron preparation, converter smelting, LF (ladle furnace) refining, VD (vacuum degassing) and continuous casting; the rolling process comprises the steps of square billet heating, BD1 rolling, BD2 rolling, continuous rolling through a CCS universal rolling mill, pre-bending cooling and straightening; the steel rail comprises the following chemical components in percentage by mass: 0.74-0.86% of C; 0.35% to 0.60% of Si; 1.10% to 1.25% of Mn; less than or equal to 0.015% of P; less than or equal to 0.015% of S; 0.20% to 0.30% of Cr; the content of RE is 0.0010 to 0.010 percent; the total mass percent of the components is 100%. After the steel rail is hot-rolled, the tensile strength is larger than or equal to 980 MPa, the yield strength is larger than or equal to 510 MPa, the elongation is larger than or equal to 10%, and the steel rail tread hardness is larger than or equal to 310 HB.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to a method for manufacturing a rare earth-enhanced export rail yield strength. Background Art

[0002] my country exports more than 300,000 tons of rails overseas each year. As the main material for railways, the performance indicators of rails in the standards purchased by various countries are mainly strength and wear resistance. AREMA, as one of the world's major rail standards, is the main standard for purchasing rails for the construction of railways in North America, South America and some Southeast Asian countries. The rail component system in the AREMA standard is C-Mn steel, and the carbon content of the material is above 0.70%. The high carbon content achieves the strength and hardness of the material to meet the wear resistance and serviceability of railways. The technical standards put forward higher requirements for the yield strength of the material.

[0003] During the service of the line, rails usually produce major failure forms such as wear and tear and peeling cracks. If the rail peeling cracks occur too early, serious damage such as peeling off will occur, affecting the safety of train operation. It is closely related to the yield strength of the material's mechanical properties. Improving the yield strength of the material can increase the material's ability to resist deformation. Therefore, based on the chemical composition and production process required by the material standard, designing a reasonable chemical composition and giving full play to the characteristics of the rolling process can maximize the strength and toughness of the rails. It has very important production and economic significance to reduce the occurrence of early peeling cracks in the service of rails. Summary of the invention

[0004] The purpose of the present invention is to provide a method for manufacturing export rails with rare earth to improve their yield strength. The performance of the rails after hot rolling meets the following requirements: tensile strength ≥ 980MPa, yield strength ≥ 510MPa, elongation ≥ 10%, and rail tread hardness ≥ 310HB.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for manufacturing a rare earth-based export rail with improved yield strength, comprising:

[0007] Smelting process: molten iron → converter smelting → LF refining → VD vacuum degassing → 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℃; continuous casting billet is slowly cooled for 48 hours after sawing;

[0008] Rolling process: billet → heating → BD1 rolling → BD2 rolling → CCS universal rolling mill continuous rolling → pre-bending cooling → straightening; the temperature of the billet heating and preheating section is not more than 900℃; the heating time is 3h~3h30min; the furnace temperature is 1150℃~1180℃, the rolling start temperature is 1100℃~1150℃, and the final rolling temperature is 870~920℃; the pre-bending cooling start temperature is 830℃~880℃, and the cooling bed step distance is 350~580mm during the cooling process;

[0009] The chemical composition of the rail by mass percentage is: C 0.74-0.86%; Si 0.35-0.60%; Mn 1.10-1.25%; P≤0.015%; S≤0.015%; Cr 0.20-0.30%; RE 0.0010-0.010%; the rest is Fe, and the mass fraction is 100% in total.

[0010] Furthermore, the rail tensile test specimen is placed for more than 24 hours.

[0011] Furthermore, the mechanical properties of the rail after hot rolling meet the following requirements: tensile strength ≥ 980 MPa, yield strength ≥ 510 MPa, elongation ≥ 10%, and rail tread hardness ≥ 310 HB.

[0012] Furthermore, the chemical composition of the rail by mass percentage is: C 0.808%; Si 0.593%; Mn 1.190%; P 0.012%; S 0.005%; Cr 0.234%; RE 0.0038%; and the rest is Fe, with a total mass fraction of 100%.

[0013] Furthermore, the chemical composition of the rail by mass percentage is: C 0.815%; Si 0.590%; Mn 1.192%; P 0.013%; S 0.004%; Cr 0.240%; RE 0.0047%; and the rest is Fe, with a total mass fraction of 100%.

[0014] The main alloying elements Si and Mn added to the material are intended to improve the strength of the rail and the phase transformation temperature suitable for heat treatment. The C component in the steel is designed to have a large solid solubility with Fe, has a solid solution strengthening effect, and improves the strength and hardness of the steel. The present invention takes toughness into consideration, combines the rolling process, and adopts a medium-high C approach. Mn expands the austenite phase region, increases the stability of the supercooled austenite of the steel, and significantly improves the hardenability of the steel. The addition of Cr elements improves the hardenability of the rail and improves the strength and hardness. In addition, the added RE element is a rare earth alloy. The basic theoretical research on rare earths has proved that the rare earth contained in steel has the function of controlling the morphology of sulfides during the smelting process, forming rare earth sulfur oxides and reducing the formation of other metal sulfur compounds. This new sulfur compound does not deform or is very small during the rolling process, so that the grains in the steel are refined. Grain refinement has a significant effect on improving the yield strength of the material. At the same time, the steel material contains an appropriate amount of rare earths, which can reduce the tough-brittle transition temperature, which has important technical significance for the service of rails in low temperature areas.

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

[0016] The present invention designs a preparation and production process for increasing the yield strength of export American standard SS rails by adding rare earth, which involves a cooling process after hot rolling. By increasing the cooling step distance, the internal microstructure of the rail is refined, the strength and hardness of the rail are improved while ensuring the full-length dimensional properties of the rail; and the toughness of the rail is further improved by formulating the natural aging time of the tensile specimen.

[0017] The steel rail manufactured by the method of the present invention has a good strength and toughness ratio and excellent wear resistance, and can be used in high-cold area environments. DETAILED DESCRIPTION

[0018] The chemical compositions of the rail materials are shown in Table 1.

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

[0020]

[0021]

[0022] As shown in Table 1, Examples 1 to 3 are all SS rail metallurgical compositions within the AREMA standard composition range, wherein the contents of C, Si, Mn, Cr, V, P, and S are substantially the same. No rare earth Ce element is added to Example 1, 38 ppm rare earth Ce element is contained in Example 2, and 47 ppm rare earth Ce element is contained in Example 3.

[0023] Table 2 Example of cooling process for rail materials

[0024]

[0025] Steel sample performance: The tensile sample specifications are: diameter d0 = 12.5mm, gauge length Lo = 5do. The top surface of the rail head is ground off 0.5mm, and 5 test points are tested. The Brinell hardness test is carried out and the average value is calculated. The test temperature is 20℃ ± 5℃. The sampling method, location and size of the above sample performance are in accordance with the AREMA standard. The experimental results are shown in Table 3.

[0026] Table 3 Mechanical properties of each example

[0027]

[0028]

[0029] It can be seen from Figure 3 that each example has good strength, hardness and mechanical properties. The rails produced using them meet the technical requirements, and the yield strength is improved, which plays an important role in reducing and minimizing the formation of early peeling cracks.

[0030] 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 manufacturing a rare earth-based rail to improve the yield strength of export rails, characterized in that: include: Smelting process: molten iron → converter smelting → LF refining → VD vacuum degassing → 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, overheat ΔT ≤ 30℃; slow cooling for 48 hours after continuous casting billet sawing; Rolling process: billet → heating → BD1 rolling → BD2 rolling → CCS universal rolling mill continuous rolling → pre-bending cooling → straightening; the temperature of the billet heating and preheating section is not more than 900℃; the heating time is 3h~3h30min; the furnace temperature is 1150℃~1180℃, the rolling start temperature is 1100℃~1150℃, and the final rolling temperature is 870~920℃; the pre-bending cooling start temperature is 830℃~880℃, and the cooling bed step distance is 350~580mm during the cooling process; The chemical composition of the rail by mass percentage is: C 0.74-0.86%; Si 0.35-0.60%; Mn 1.10-1.25%; P≤0.015%; S≤0.015%; Cr 0.20-0.30%; RE 0.0010-0.010%; the rest is Fe, and the mass fraction is 100% in total.

2. The method for manufacturing export rails with rare earth to improve yield strength according to claim 1, characterized in that: The rail tensile test specimens are placed for more than 24 hours.

3. The method for manufacturing export rails with rare earth to improve yield strength according to claim 1, characterized in that: The mechanical properties of the rails after hot rolling meet the following requirements: tensile strength ≥980MPa, yield strength ≥510MPa, elongation ≥10%, and rail tread hardness ≥310HB.

4. The method for manufacturing export rails with rare earth to improve yield strength according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.808%, Si 0.593%, Mn 1.190%, P 0.012%, S 0.005%, Cr 0.234%, RE 0.0038%; the rest is Fe, and the total mass fraction is 100%.

5. The method for manufacturing export rails with rare earth to improve yield strength according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.815%, Si 0.590%, Mn 1.192%, P 0.013%, S 0.004%, Cr 0.240%, RE 0.0047%; the rest is Fe, and the total mass fraction is 100%.

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