Low-cost method for purifying and modifying steel rail inclusions and improving comprehensive mechanical properties of steel rail inclusions

Abstract

The invention discloses a low-cost method for purifying and modifying steel rail inclusions and improving comprehensive mechanical properties of the steel rail inclusions, and the method comprises the following steps: adding a rare earth iron alloy containing 30% of rare earth into molten steel in VD (vacuum degassing), and determining O in the steel before adding, the O is required to be less than or equal to 10ppm, so that the prepared molten steel for continuous casting comprises the following chemical components in percentage by mass: 0.78-0.85% of C; 0.50% to 0.60% of Si; 1.10% to 1.30% of Mn; less than or equal to 0.020% of P; s < = 0.008%; 0.20% to 0.30% of Cr, 0.003% to 0.008% of RE iron alloy or 0.0010% to 0.0024% of RE; and the balance of Fe and inevitable impurities. According to the method, A-D type inclusions in the steel can be obviously reduced, the purification effect and the modification effect of rare earth on the steel inclusions are fully achieved, and the service life of the steel rail is prolonged.

Description

Technical Field

[0001] The invention belongs to the field of metallurgical materials, and in particular relates to a low-cost method for purifying and modifying rail inclusions and improving the comprehensive mechanical properties thereof. Background Art

[0002] With the economic development of overseas countries, the number of transportation routes has continued to increase, which has led to an increasing demand for the quality and performance of rails in railway lines. Rails used for railway transportation must have good mechanical properties such as strength, toughness, cross-sectional hardness, wear resistance and corrosion resistance. In addition, they also need excellent service performance. Therefore, based on the chemical composition and production process required by the material standards, designing a reasonable chemical composition and giving full play to the characteristics of the rolling process, while maximizing the strength and toughness of the rails and improving the internal metallurgical quality, has very important production and economic significance for increasing the service life of the rails. Summary of the invention

[0003] The present invention aims to provide a low-cost method for purifying and modifying rail inclusions and improving their comprehensive mechanical properties. To achieve this purpose, the present invention utilizes Baosteel's own ores and rare earth alloys, reasonably designs the composition and adds the optimal Si and Mn alloy elements to the rails, and optimizes the production process parameters. On this basis, the strength, elongation, tread hardness and other properties of the rails produced meet the standards, and the rails produced by utilizing the rare earth effect in the production process have good cleanliness and toughness, high production efficiency, energy saving and environmental protection, low cost, good economic benefits, are suitable for large-scale production, and have good promotion value.

[0004] The purpose of the present invention is to achieve through the following measures:

[0005] On one hand, the present invention provides a low-cost method for purifying and modifying rail inclusions and improving the comprehensive mechanical properties thereof, the method comprising: a smelting production process of the rail and a rolling production process of the rail, wherein the smelting production process of the rail is: molten iron → converter smelting → LF refining → VD → continuous casting, and the rolling production process of the rail is: billet → sawing → heating → BD1 rolling → BD2 rolling → CCS universal rolling mill continuous rolling → online residual heat quenching → sawing → cooling → head and tail cutting → straightening; wherein:

[0006] A rare earth iron alloy containing 30% rare earth is added to the molten steel in the VD, the added amount is 0.003-0.008%, and the O content in the steel is measured before adding, and O is required to be ≤10ppm. The chemical composition of the prepared molten steel for continuous casting is as follows according to mass percentage: C 0.78-0.85%; Si 0.50-0.60%; Mn 1.10-1.30%; P≤0.020%; S≤0.008%; Cr 0.20-0.30%, RE ferroalloy 0.003-0.008% or RE 0.0010-0.0024%; the rest is Fe and unavoidable impurities.

[0007] In some embodiments, the chemical composition of the prepared molten steel for continuous casting is calculated by mass percentage as follows: C 0.80-0.82%; Si 0.55-0.57%; Mn 1.17-1.22%; P≤0.015%; S≤0.005%; Cr 0.23-0.25%, RE 0.0010-0.0013%; the rest is Fe and unavoidable impurities.

[0008] In some embodiments, in the smelting production process of the rail, the converter smelting adopts aluminum-free deoxidation and alloying, and the whole process is argon-blown as normal refining; the vacuum degree is ≤0.10KPa, the deep vacuum time is ≥20min, and the superheat ΔT is ≤28°C.

[0009] In some embodiments, in the rolling production process of the rail, the temperature of the square billet heating preheating section is controlled to be no more than 890°C; the heating time is no less than 2 hours and 45 minutes; the furnace temperature is no less than 1160°C, the starting rolling temperature is ≥1120°C, and the final rolling temperature is 820-850°C; after the final rolling, the rail spacing is ≥250mm during the cooling process of the rails on the cooling bed, and they are naturally cooled to below 80°C for straightening.

[0010] In some embodiments, the steel rail produced by the method has a Class A inclusion of ≤1.0, a Class B inclusion of ≤1.0, a Class C inclusion of ≤1.0, and a Class D inclusion of ≤1.0.

[0011] In some embodiments, the mechanical properties of the steel rail produced by the method meet the following requirements: yield strength ≥580 MPa, tensile strength ≥1080 MPa, elongation ≥10%, and Brinell hardness ≥315 HB.

[0012] Another aspect of the present invention provides a steel rail produced by the above method. DETAILED DESCRIPTION

[0013] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0014] The present invention utilizes Baosteel's own ore and rare earth alloy, adds the optimal Si and Mn alloy elements to the rails through reasonable design of the composition and optimization of the production process parameters, and the rails produced on this basis have performances such as strength, elongation, and tread hardness that meet the standards, and the rails produced by the rare earth effect in the production process have good cleanliness and toughness, high production efficiency, energy saving and environmental protection, low cost, good economic benefits, and are suitable for large-scale production. The main alloying elements Si, Mn, and Cr added to the rail material provided by the present invention are intended to improve the strength capacity of the rails and the phase change transformation temperature suitable for the heat treatment line. The C component design in the steel has a large solid solubility with Fe, has a solid solution strengthening effect, and improves the strength and hardness of the steel. However, the increase in the C content will reduce the toughness of the rails, so the C content of the present invention also considers the elongation. Mn expands the austenite phase region, increases the stability of the supercooled austenite of the steel, and significantly improves the hardenability of the steel. Si reduces the transformation rate from austenite to ferrite, improves the strength, elasticity and tempering resistance of steel, and considering the weldability of rails, the Si content should not be too high, because Si has poor heat conductivity, which is not conducive to rail welding; in addition, the added RE element is a rare earth alloy, and the basic theoretical research of 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. In the present invention, the rare earth alloy is added at the VD station, and the O in the steel is measured before adding, requiring O≤10ppm, which allows the rare earth to fully play the role of grain refinement in the steel, further greatly reducing the AD inclusions in the steel, fully playing the role of rare earth in purifying and modifying steel inclusions, and improving the service life of the rails.

[0015] Example

[0016] The method provided by the present invention comprises the following process:

[0017] The smelting production process of the rail 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 ≥ 20min, superheat ΔT ≤ 28°C, the amount of rare earth alloy added is in the VD vacuum degassing process, and the O in the steel is measured before adding, requiring O ≤ 10ppm (other process parameters can be carried out according to conventional steelmaking methods (for example, see: Wang Guoxin et al., Application Research on Dynamic Soft Reduction Technology for Continuous Casting of 350km / h High-speed Rail Steel at Baotou Steel, Continuous Casting, 2011.09: 434-440; Zhao Aijun et al., Production Process and Quality Control of Baotou Steel Rail, Baotou Steel Science and Technology, 2000.09, Vol. 26, No. 3: 6-12, etc.)). The chemical composition of the molten steel for continuous casting in each example is shown in Table 1.

[0018] Table 1: Composition of each example (mass percentage / %)

[0019]

[0020] The rolling process of rails 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 → warehousing. The temperature of the billet heating preheating section is not more than 890°C; the heating time is not less than 2 hours and 45 minutes; the furnace discharge temperature is not less than 1160°C, the rolling start temperature is ≥1120°C, and the final rolling temperature is 820-850°C; the rail spacing of the rails after final rolling is ≥250mm during the cooling process of the rails on the cooling bed, and they are naturally cooled to below 80°C for straightening (other operation processes can be carried out according to conventional rolling methods (for example, see: Wang Guoxin et al., Application Research on Dynamic Soft Reduction Technology of Continuous Casting of 350km / h High-speed Rail Steel for Baotou Steel, Continuous Casting, 2011.09: 434-440; Zhao Aijun et al., Production Process and Quality Control of Baotou Steel Rails, Baotou Steel Science and Technology, 2000.09, Vol. 26, No. 3: 6-12, etc.)); compared with the rolling process in the prior art, the final rolling temperature is lowered, and rare earth is used to refine the steel grains; the cooling interval after rolling is increased, the temperature drop rate of the rails after rolling is enhanced, and the internal microstructure is refined.

[0021] Performance of rail samples after rolling: The tensile specimens were processed according to the American standard AREMA, with a diameter of d0 = 12.5 mm and a gauge length of Lo = 5do. Random sampling of tread hardness was performed on the rails, with a specimen length of 250 mm, 0.5 mm ground off the top surface of the rail head, and 5 test points. The Brinell hardness test was performed and the average value was calculated. The test temperature was 20°C ± 5°C. The experimental results are shown in Table 2. The test was performed according to the inclusion A method, and the results are shown in Table 3. In Tables 2 and 3, the average without rare earth addition refers to the average value of the values ​​obtained in Examples 1-3 without adding rare earth.

[0022] Table 2: Mechanical properties of each example

[0023]

[0024] Table 3: Inclusions in each example

[0025]

[0026] It can be seen from Tables 2 and 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. In addition, AD inclusions in the steel are significantly reduced, and the rare earth has a full role in purifying and modifying steel inclusions, thereby increasing the service life of the rails.

[0027] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-cost method for purifying and modifying rail inclusions and improving their comprehensive mechanical properties, the method comprising: The smelting production process of the rail and the rolling production process of the rail, wherein the smelting production process of the rail is: molten iron → converter smelting → LF refining → VD → continuous casting, and the rolling production process of the rail 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; characterized in that: A rare earth iron alloy containing 30% rare earth is added to the molten steel in the VD, the added amount is 0.003-0.008%, and the O in the steel is measured before adding, and O is required to be ≤10ppm. The chemical composition of the prepared molten steel for continuous casting is as follows according to mass percentage: C 0.78-0.85%; Si 0.50-0.60%; Mn 1.10-1.30%; P≤0.020%; S≤0.008%; Cr0.20-0.30%, RE ferroalloy 0.003-0.008% or RE 0.0010-0.0024%; the rest is Fe and unavoidable impurities.

2. The method according to claim 1, characterized in that The chemical composition of the prepared molten steel for continuous casting is as follows by mass percentage: C 0.80-0.82%, Si 0.55-0.57%, Mn 1.17-1.22%, P≤0.015%, S≤0.005%, Cr 0.23-0.25%, RE 0.0010-0.0013%, and the rest is Fe and unavoidable impurities.

3. The method according to claim 1 or 2, characterized in that: In the smelting production process of the rail, aluminum-free deoxidation and alloying are adopted in the converter smelting, and argon is blown in the whole process as normal refining; the vacuum degree is ≤0.10KPa, the deep vacuum time is ≥20min, and the superheat ΔT is ≤28°C.

4. The method according to any one of claims 1 to 3, characterized in that In the rolling production process of the rail, the temperature of the billet heating preheating section is controlled to be no more than 890°C; the heating time is no less than 2 hours and 45 minutes; the furnace temperature is no less than 1160°C, the start rolling temperature is ≥1120°C, and the final rolling temperature is 820-850°C; after the final rolling, the rail spacing is ≥250mm during the cooling process of the rails on the cooling bed, and the rails are naturally cooled to below 80°C for straightening.

5. The method according to any one of claims 1 to 4, characterized in that The steel rails produced thereby have Class A inclusions ≤1.0, Class B inclusions ≤1.0, Class C inclusions ≤1.0, and Class D inclusions ≤1.

0.

6. The method according to any one of claims 1 to 5, characterized in that The mechanical properties of the steel rails produced by the production thereof meet the following requirements: yield strength ≥580MPa, tensile strength ≥1080MPa, elongation ≥10%, and Brinell hardness ≥315HB.

7. A steel rail, characterized in that: The rail is produced by the method according to any one of claims 1-6.

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