Preparation process for improving abrasion and rolling contact fatigue of high-strength heat-treated rare earth steel rail

Abstract

The invention discloses a preparation technology for improving abrasion and rolling contact fatigue of a high-strength heat treatment rare earth steel rail, and belongs to the technical field of steel rail preparation technologies. The preparation process comprises the steps of molten iron pre-desulfurization, converter treatment, LF refining, vacuum degassing, continuous casting, heating, rolling, heat treatment and cooling processing. The alloy comprises the following chemical components in percentage by mass: 0.85-1.10% of C; 0.60 to 0.85 percent of Si; 0.70 to 0.90 percent of Mn; less than or equal to 0.025% of P; s is less than or equal to 0.025%; 0.20%-0.50% of Cr, 0.04%-0.10% of V and 0.05%-0.20% of Ni are included; 0.02 to 0.08 percent of Nb; 0.0010-0.030% of RE, and the balance of Fe and impurity elements. 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 a heavy-load line service environment.

Description

Technical Field

[0001] The invention belongs to the technical field of rail preparation, and in particular relates to a preparation process for improving the wear and rolling contact fatigue of high-strength heat-treated rare earth rails. Background Art

[0002] The rails used on heavy-haul railways with annual freight volumes exceeding 200 million tons worldwide are typically high-strength, heat-treated rails with a hardness of 370 HB or higher. With the continued increase in axle loads, speeds, and annual freight volumes of heavy-haul trucks, heavy-haul rails are experiencing increasing wear and rolling contact fatigue damage, impacting rail use and routine maintenance. Therefore, there is an urgent need to improve the comprehensive service performance of rails operating under heavy-haul conditions.

[0003] At present, in order to solve the problem of service damage of heavy-load line rails, the railway industry has developed new high-strength and toughness bainite rails and hypereutectoid rails with increased carbon content. Patent CN 114672730 A provides a rolling contact fatigue-resistant rail for mixed passenger and freight railways and its production method. The main elements of the material composition are C, Si, Mn, V, Nb, Ni, and the rest are iron and inevitable impurities. The tensile strength of the rail after rolling heat treatment is ≥1231MPa and the elongation is ≥12%. However, the patented alloy adds expensive metal Ni, and the production process simultaneously accelerates cooling of the rail head, rail waist and rail bottom at different cooling rates. The process production control is unstable and complex, and the cooling rate control of the rail waist is based on the temperature change of the head and bottom. CN 113930667 A discloses a rail with good coupling of wear and rolling contact fatigue and its production method. The chemical composition of the rail is C-Si-Mn, and Cr, V and B elements are added to it. However, element B is a brittle element, and its addition reduces rail toughness. The resulting elongation is reduced by 11%, and the resulting rail hardness is around 360 HB, failing to meet the performance requirements for service procurement on narrow curves and high-volume, heavy-load lines. CN 118422055 A discloses a pearlitic rail steel with rolling contact fatigue resistance and high wear resistance, and its preparation method. However, this method only provides conventional tensile and hardness properties, with no disclosure of specific service fracture toughness or other properties.

[0004] Based on industry technological development and comparative application of rail products worldwide, heavy-haul railway rails require high strength, hardness, and other properties, as well as good toughness and ductility. Therefore, to address the wear and rolling contact fatigue damage problems of heavy-haul railway rails, it is of great significance to fully utilize the advantages of industrial equipment and develop a high-strength and toughness heat-treated rail through low-temperature tempering to improve the rolling contact fatigue resistance and wear resistance of pearlite rail steel. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation process for improving the wear and rolling contact fatigue of high-strength heat-treated rare earth rails, and to prepare rails with good strength and toughness ratio and excellent wear resistance, so that they can be used in heavy-load line service environments.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a preparation process for improving the wear and rolling contact fatigue of high-strength heat-treated rare earth rails, comprising molten iron pre-desulfurization → converter → LF refining → vacuum degassing → continuous casting → heating → rolling → heat treatment → cooling processing; and is characterized in that:

[0008] The molten iron desulfurization adopts the magnesium powder spraying desulfurization process;

[0009] The converter smelting adopts the top and bottom combined blowing process, and the tapping temperature is controlled at 1650-1680℃, and the tapping C is ≥0.12%;

[0010] The slag basicity of LF refining is controlled at 2.0-2.8;

[0011] Degassing adopts VD deep vacuum treatment, bottom blowing argon pressure is 0.40~0.55MPa, deep vacuum is below 0.1Kpa; soft blowing time is 13~18min, rare earth alloy is added; let it stand for 3-5min and put it on the big bag;

[0012] The continuous casting process uses a large tank long nozzle and a crystallizer immersion nozzle to protect the pouring, the immersion depth is 60-70mm, and the casting speed is controlled at 0.6-0.65m / min;

[0013] After sawing, the continuous casting billet is placed in a slow cooling pit at a temperature of 450-600°C and naturally cooled for 48 hours;

[0014] The specific rolling and heat treatment processes are as follows:

[0015] A walking beam / regenerative heating furnace is used for three-stage heating of the ingot, with a preheating section temperature of ≤800°C, a heating section temperature of 1200-1280°C, and a soaking section temperature of 1220-1260°C. The total heating time is 3h20min-3h45min.

[0016] After uniform heating and insulation, the billet is rolled out of the heating furnace, with the starting rolling temperature at 1100-1150℃, the billet rolling reduction ratio ≥9:1, and the final rolling temperature at 880-930℃;

[0017] The rail head is subjected to online accelerated cooling after rolling. The cooling medium is a mixture of air and air mist. The initial cooling temperature is 750-810°C. The rail head cooling rate in the first stage is 2.8-5.0°C / s, and the rail head surface temperature is reduced to 520-560°C. The rail head cooling rate in the second stage is 2.0-3.5°C / s, and the rail head surface temperature is reduced to 480-520°C. The rail head cooling rate in the third stage is 0.8-1.7°C / s, and the rail head surface temperature is reduced to 420-440°C. The rail head is then air-cooled to room temperature.

[0018] After heat treatment, the rails are tempered: heated to 220-350℃ and kept warm for 6-10 hours, then taken out of the furnace and air-cooled for shipment;

[0019] The chemical composition of the steel rail by mass percentage is: C 0.85-1.10%; Si 0.60-0.85%; Mn 0.70-0.90%; P≤0.025%; S≤0.025%; Cr 0.20-0.50%, V 0.04-0.10%, Ni 0.05-0.20%; Nb 0.02-0.08%; RE 0.0010-0.030%, and the rest are Fe and impurity elements, with a total mass fraction of 100%.

[0020] Furthermore, the chemical composition of the rail by mass percentage is: C 0.869%; Si 0.776%; Mn 0.869%; P 0.010%; S 0.006%; Cr 0.251%, V 0.045%, Ni 0.11%; Nb 0.045%; RE 0.0060%, and the rest are Fe and impurity elements, with a total mass fraction of 100%.

[0021] Furthermore, the chemical composition of the rail by mass percentage is: C 0.873%; Si 0.769%; Mn 0.858%; P 0.012%; S 0.007%; Cr 0.235%, V 0.043%, Ni 0.10%; Nb 0.048%; RE 0.0018%, and the rest are Fe and impurity elements, with a total mass fraction of 100%.

[0022] Furthermore, the chemical composition of the rail by mass percentage is: C 0.875%; Si 0.782%; Mn 0.870%; P 0.009%; S 0.007%; Cr 0.256%, V 0.044%, Ni 0.11%; Nb 0.047%; RE 0.0024%, and the rest are Fe and impurity elements, with a total mass fraction of 100%.

[0023] Furthermore, a walking beam / regenerative heating furnace was used for three-stage heating of the ingot, with a preheating temperature of 800°C, a heating temperature of 1240°C, and a soaking temperature of 1240°C, with a total heating time of 3h30min.

[0024] After uniform heating and insulation, the billet is taken out of the heating furnace for rolling. The starting rolling temperature is 1125℃, the billet rolling reduction ratio is ≥9:1, and the final rolling temperature is 900℃.

[0025] Furthermore, the rail head was subjected to online accelerated cooling after rolling. The cooling medium was a mixture of air and air mist. The initial cooling temperature was 780°C. In the first stage, the rail head was cooled at a rate of 40°C / s, and the surface temperature of the rail head dropped to 540°C. In the second stage, the rail head was cooled at a rate of 2.5°C / s, and the surface temperature dropped to 500°C. In the third cooling stage, the rail head was cooled at a rate of 1.2°C / s, and the surface temperature dropped to 430°C. The rail was then air-cooled to room temperature.

[0026] Furthermore, the steel is tempered and heated to 300° C. and then kept warm for 8 hours.

[0027] The main alloying elements added to this material are Si, Mn, Nb, Cr, V, Ni, and RE (rare earths are high-purity FeCe alloys or lanthanum-cerium mixed rare earths). Their purpose is to improve the rail's strength and toughness, and to achieve a well-designed phase transition temperature in conjunction with heat treatment. The carbon content in this steel is designed to have a high solid solubility with Fe, providing solid solution strengthening, thereby increasing the steel's strength and hardness and improving the rail's resistance to contact fatigue. Mn expands the austenite phase, increasing the stability of the steel's supercooled austenite and significantly improving its hardenability, but its content affects rail welding. Si increases the material's yield strength, resisting premature rail delamination and fish-scale cracking. However, considering rail weldability, the Si content should be kept to a minimum, as Si's poor thermal conductivity makes it less conducive to rail welding. V, Ni, and Nb alloying elements refine the material's microstructure and precipitate C and N compounds, enhancing its strength and toughness. Nb, in particular, plays a crucial role in initial grain refinement, allowing it to replace some of the more expensive V alloys. In addition, the added RE element controls the morphology of sulfides during the smelting process, forming rare earth oxysulfides 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. At the same time, rare earths can improve the oxidation resistance and low-temperature resistance of steel. The presence of an appropriate amount of rare earth in steel materials can reduce the ductile-brittle transition temperature, which has important technical significance for the service of rails.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] The steel rails prepared by the optimized preparation process of the present invention have excellent mechanical properties, meeting the requirements for application in heavy-load line service environments. DETAILED DESCRIPTION

[0030] The chemical compositions of each example are shown in Table 1.

[0031] Table 1 Composition of each embodiment (mass percentage / %)

[0032]

[0033] As shown in Table 1, the contents of C, Si, Mn, Cr, V, Ni, Nb, P, and S in Examples 1-4 are essentially the same. Example 1 contains no rare earth element Ce, while Example 2 contains 6 ppm of rare earth element Ce, Example 3 contains 18 ppm of rare earth element Ce, and Example 4 contains 24 ppm of rare earth element Ce.

[0034] Performance testing: Tensile specimens were specified with a diameter of d0 = 10 mm and a gauge length of Lo = 5 do. Tread hardness was measured by randomly sampling heat-treated rolled steel, removing 0.5 mm of surface oxide scale. Brinell hardness testing was performed at five test points, and the average value was calculated. The test temperature was 20°C ± 5°C. Testing was performed on an MPG-60N rolling wear and contact fatigue testing machine.

[0035] The mechanical test results of each embodiment are shown in Table 2.

[0036] The heat treatment process of the comparative example and the embodiment is as follows: the rail head after rolling is subjected to online accelerated cooling, the cooling medium is a mixture of air and air mist, the initial cooling temperature is 780°C, the rail head cooling rate in the first stage is 40°C / s, and the rail head surface temperature is reduced to 540°C; the rail head cooling rate in the second stage is 2.5°C / s, and the rail head surface temperature is reduced to 500°C; the rail head cooling rate in the third cooling stage is 1.2°C / s, and the rail head surface temperature is reduced to 430°C; and then air cooling is performed to room temperature.

[0037] Table 2 Mechanical properties of each embodiment after heat treatment

[0038]

[0039] As can be seen from Table 2, each example exhibits excellent strength, hardness, and mechanical properties, and the rails produced using them possess high strength and toughness. As can be seen from Table 2, Examples 2-4 exhibit tensile strengths ≥1400 MPa, elongation ≥10%, and tread hardnesses ranging from 400 to 411 HBW. Compared to Comparative Example 11, Examples 2-4 exhibit increased elongation, reaching a maximum of 11.5%. The tensile strength is also increased, with Example 3 achieving a maximum tensile strength of 1423 MPa and a tread hardness ≥400 HBW. Compared to Comparative Example 1, Examples 2-4 exhibit increased strength and hardness, while also achieving corresponding improvements in toughness.

[0040] Table 3 Material properties after tempering in Example

[0041] The tempering process of the comparative example and the embodiment is as follows: tempering heating to 300° C. and then keeping the temperature for 8 hours.

[0042] Table 3 Mechanical properties of each embodiment after tempering

[0043]

[0044] As can be seen from Table 3, after tempering, the strength and hardness of each embodiment are basically unchanged, but the tensile elongation and fracture toughness are relatively increased.

[0045] Table 4 Wear test parameters; Wear tests were performed on Examples 1 to 4.

[0046] Table 4 Material wear test parameters

[0047]

[0048] Table 5 shows the wear values ​​during the process of the examples. It can be seen that the average values ​​of tempered Examples 2-4 are lower than those of Comparative Example 1, which does not add rare earth. The lowest average wear value is 7.72 μg / m. The addition of rare earth significantly improves the wear resistance of the material. Compared with untempered Examples 2-4, tempered Examples 2-4 show improved toughness and reduced wear. The tempered average value of 7.72 μg / m is 0.30 μg / m lower than the untempered average of 8.02 μg / m.

[0049] Table 5 Wear rate values ​​of materials in different embodiments

[0050]

[0051]

[0052] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A preparation process for improving wear and rolling contact fatigue of high-strength heat-treated rare earth rails, comprising molten iron pre-desulfurization → converter → LF refining → vacuum degassing → continuous casting → heating → rolling → heat treatment → cooling; characterized in that: The molten iron desulfurization adopts the magnesium powder spraying desulfurization process; The converter smelting adopts the top and bottom combined blowing process, and the tapping temperature is controlled at 1650-1680℃, and the tapping C is ≥0.12%; The slag basicity of LF refining is controlled at 2.0-2.8; Degassing adopts VD deep vacuum treatment, bottom blowing argon pressure is 0.40~0.55MPa, deep vacuum is below 0.1Kpa; soft blowing time is 13~18min, rare earth alloy is added; let it stand for 3-5min and put it on the big bag; The continuous casting process uses a large tank long nozzle and a crystallizer immersion nozzle to protect the pouring, the immersion depth is 60-70mm, and the casting speed is controlled at 0.6-0.65m / min; After sawing, the continuous casting billet is placed in a slow cooling pit at a temperature of 450-600°C and naturally cooled for 48 hours; The specific rolling and heat treatment processes are as follows: A walking beam / regenerative heating furnace is used for three-stage heating of the ingot, with a preheating section temperature of ≤800°C, a heating section temperature of 1200-1280°C, and a soaking section temperature of 1220-1260°C. The total heating time is 3h20min-3h45min. After uniform heating and insulation, the billet is rolled out of the heating furnace, with the starting rolling temperature at 1100-1150℃, the billet rolling reduction ratio ≥9:1, and the final rolling temperature at 880-930℃; The rail head is subjected to online accelerated cooling after rolling. The cooling medium is a mixture of air and air mist. The initial cooling temperature is 750-810°C. The rail head cooling rate in the first stage is 2.8-5.0°C / s, and the rail head surface temperature is reduced to 520-560°C. The rail head cooling rate in the second stage is 2.0-3.5°C / s, and the rail head surface temperature is reduced to 480-520°C. The rail head cooling rate in the third stage is 0.8-1.7°C / s, and the rail head surface temperature is reduced to 420-440°C. The rail head is then air-cooled to room temperature. After heat treatment, the rails are tempered: heated to 220-350℃ and kept warm for 6-10 hours, then taken out of the furnace and air-cooled for shipment; The chemical composition of the steel rail by mass percentage is: C 0.85-1.10%; Si 0.60-0.85%; Mn 0.70-0.90%; P≤0.025%; S≤0.025%; Cr 0.20-0.50%, V 0.04-0.10%, Ni 0.05-0.20%; Nb 0.02-0.08%; RE 0.0010-0.030%, and the rest are Fe and impurity elements, with a total mass fraction of 100%.

2. The preparation process for improving wear and rolling contact fatigue of high-strength heat-treated rare earth rail according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.869%; Si 0.776%; Mn 0.869%; P 0.010%; S 0.006%; Cr 0.251%, V 0.045%, Ni 0.11%; Nb 0.045%; RE 0.0060%, and the rest are Fe and impurity elements, with a total mass fraction of 100%.

3. The preparation process for improving wear and rolling contact fatigue of high-strength heat-treated rare earth rail according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.873%; Si 0.769%; Mn 0.858%; P 0.012%; S 0.007%; Cr 0.235%, V 0.043%, Ni 0.10%; Nb 0.048%; RE 0.0018%, and the rest are Fe and impurity elements, with a total mass fraction of 100%.

4. The preparation process for improving wear and rolling contact fatigue of high-strength heat-treated rare earth rail according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.875%; Si 0.782%; Mn 0.870%; P 0.009%; S 0.007%; Cr 0.256%, V 0.044%, Ni 0.11%; Nb 0.047%; RE 0.0024%, and the rest are Fe and impurity elements, with a total mass fraction of 100%.

5. The preparation process for improving wear and rolling contact fatigue of high-strength heat-treated rare earth rail according to claim 1, characterized in that: A walking beam / regenerative heating furnace is used for three-stage heating of the ingot, with a preheating temperature of 800°C, a heating temperature of 1240°C, and a soaking temperature of 1240°C. The total heating time is 3 hours and 30 minutes. After uniform heating and insulation, the billet is taken out of the heating furnace for rolling. The starting rolling temperature is 1125℃, the billet rolling reduction ratio is ≥9:1, and the final rolling temperature is 900℃.

6. The preparation process for improving wear and rolling contact fatigue of high-strength heat-treated rare earth rail according to claim 1, characterized in that: The rail head was subjected to online accelerated cooling with a mixture of air and mist as the cooling medium. The initial cooling temperature was 780°C, and the surface temperature of the rail head was reduced to 540°C at a cooling rate of 40°C / s in the first stage. The surface temperature of the rail head was reduced to 500°C at a cooling rate of 2.5°C / s in the second stage. In the third stage, the surface temperature of the rail head was reduced to 430°C at a cooling rate of 1.2°C / s. The rail head was then air-cooled to room temperature.

7. The preparation process for improving wear and rolling contact fatigue of high-strength heat-treated rare earth rail according to claim 1, characterized in that: After tempering, the steel was heated to 300°C and kept at this temperature for 8 hours.

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