WO2023173803A1 - Rolling contact fatigue resistant steel rail for mixed passenger and freight railway, and production method therefor - Google Patents

Abstract

The present invention discloses a rolling contact fatigue resistant steel rail for a mixed passenger and freight railway, characterized by comprising the following chemical components by weight percentage: 0.75-0.88% C, 0.10-0.60% Si, 0.75-1.30% Mn, 0.20-0.55% Ni, 0.10-0.20% V, 0.03-0.06% Nb, less than or equal to 0.025% P, less than or equal to 0.025% S, and the remainder being Fe and inevitable impurities. The production process comprises the following steps: molten iron desulfurization, converter smelting, LF refining, vacuum treatment, continuous casting, casting blank heating, rolling, accelerated cooling, and straightening. The present invention, by means of reasonably configuring chemical components and smelting and rolling processes, as well as performing accelerated cooling of a rolled steel rail head, rail web and rail bottom at different cooling rates, achieves good matching of yield ratio of the steel rail head and impact toughness of the rail web, thereby improving the overall service performance and service life of the steel rail, and meeting the requirements of railway development; the method is simple, has strong operability, and is easy to popularize and apply.

Description

A kind of rolling contact fatigue resistant rail for mixed passenger and freight railways and its production method Technical field

The invention belongs to the field of metallurgical technology, and specifically relates to a rolling contact fatigue resistant steel rail for a mixed passenger and freight railway and a production method thereof.

Background technique

With the rapid development of my country's railways in the direction of "high-speed passenger transportation and heavy-duty freight transportation", the running speed, load capacity and operating density of trains have increased, and the rolling contact fatigue damage of rails has increased significantly, especially in the small radius of mixed transportation of passengers and freight. On curved lines, under the repeated action of wheel-rail contact stress, the rails are prone to rolling contact fatigue damage such as fish scale damage, peeling off pieces and even nuclear damage, which seriously affects the service life of the rails and driving safety.

During the wheel-rail contact process, the rail is subjected to huge contact stress, and the maximum shear stress distribution will appear inside the rail head material. Especially in the small curve radius area, the maximum shear stress far exceeds the yield strength limit of the rail material, and the rail material will Due to the ratchet-shaped hysteresis effect of the stress-strain cycle, the material undergoes trace plastic deformation and forms work hardening. As the plastic deformation continues to accumulate, the material hardens to a certain extent, plastic exhaustion occurs, and irreversible plastic flow occurs. When the material The plastic flow exceeds the deformation limit, causing micro-cracks in the rail, and eventually develops into rolling contact fatigue damage.

In order to slow down the occurrence and development of rolling contact fatigue damage, online heat treatment processes are commonly used in the industry to produce heat-treated rails to improve the strength and hardness of the rails. Patent CN 100471974C provides a bainitic steel rail with excellent fatigue resistance and a production method thereof. Its chemical composition (wt%), C: 0.10~0.35%, Si: 0.80~2.00%, Mn: 0.80～3.30%, Cr: <2.00%, Mo: 0.05～0.80%, N: 10～100ppm, add Nb and Ti in composite, Nb: 0.005～0.10%, Ti: 0.005～0.13%, and Nb+Ti≤0.16 %, the rest is Fe and unavoidable impurities. After hot rolling, the rail is naturally cooled in the air, so that the rail has excellent fatigue resistance. In the rail fatigue test, it has been intact for more than 2 million times.

Patent CN 102534403A discloses a bainitic heat-treated rail that can improve the toughness and plasticity of the rail and its heat treatment method. The chemical composition is as follows in weight percentage: C: 0.10%-0.40%, Si: 0.80%-2.00%, Mn: 0.80%-2.60%, Cr: 0.1-2.00%, Nb: 0.005%-0.100%, V: 0.01% -0.26%, Ti: 0.001%-0.070%, W: 0.01-0.70%, the balance is Fe and inevitable impurities. The heat treatment method adopts online heat treatment. After the rail is rolled and formed, when the rail head temperature is cooled to the temperature range of 700-890°C, the rail head is accelerated to cool at a cooling rate of 0.4-8°C/s, and stops when the temperature reaches 200°C. Accelerate cooling, and then air cool to room temperature; or use offline heat treatment to perform full-section austenitization or rail head austenitization. The austenitization temperature is between 880-930°C, and when cooled to the temperature range of 700-890°C , implement accelerated cooling of the rail, the cooling rate is 0.4-8℃/s, stop accelerated cooling when cooling to 200℃, and then air-cool to room temperature.

Patent CN 106086622A provides a heat treatment production method for rails for mixed passenger and freight railways. The production method includes sequentially accelerated cooling, slow cooling and Air cooled. The opening cooling temperature of accelerated cooling is 650-950℃, the cooling rate is 2.5-7.0℃/s, the final cooling temperature is 400-600℃, the cooling rate of slow cooling is 0.1-1.5℃/s, and the final cooling temperature is 180- 300℃. This method can control the hardness within the appropriate range of 350-380HB suitable for mixed passenger and freight railways while ensuring the tensile properties of the rails.

Patent CN101646795A provides a high-hardness pearlite rail and a manufacturing method thereof. The chemical composition of the rail includes 0.73-0.85 mass% C, 0.50-0.75 mass% Si, 0.30-1.0 mass% Mn, 0.035 mass% % or less P, 0.0005-0.012 mass% S, 0.2-1.3 mass% Cr, and the remainder is Fe and inevitable impurities. The final rolling temperature of the rail is 850-950°C, and then the temperature above the pearlite phase transformation starting temperature is rapidly cooled to 400-650°C at a cooling rate of 1.2-5°C/s to obtain the rail head surface to a depth range of at least 25mm. The Vickers hardness is HV380-HV480.

Patent CN 1793403A provides a pearlite heat-treated rail and its production method. Its chemical composition includes by weight: C: 0.70% ~ 0.95%, Si: 0.20% ~ 1.10%, Mn: 0.50% ~ 1.50%, V : 0.01%～0.20%, Cr: 0.15%～1.20%, P: ≤0.035%, S: ≤0.035% and Al: ≤0.005%. The method includes the following steps: 1) smelting, 2) casting and rolling, 3) cooling the rail steel from 650 to 880°C to 400 to 500°C at a cooling rate of 1 to 10°C/s or cooling it to room temperature. After heating to 850~1100℃, then naturally cool to 650~880℃, cool to 400~500℃ at a cooling rate of 1~10℃/s, stop cooling, and 4) place it naturally. The produced rails have good durability. Abrasive.

Patent CN 102220545A provides a high-carbon, high-strength heat-treated rail with excellent wear resistance and plasticity and a production method. The chemical composition of the high-carbon, high-strength heat-treated rail includes by weight percentage: C: 0.80% ~ 1.20%, Si: 0.20% ~ 1.20% , Mn: 0.20% ~ 1.60%, Cr: 0.15% ~ 1.20%, V: 0.01% ~ 0.20%, Ti: 0.002% ~ 0.050%, P ≤ 0.030%, S ≤ 0.030%, Al ≤ 0.010%, N ≤ 0.0100%, the rest is iron and unavoidable impurities. After rolling, the residual temperature of the hot rail is 680-900℃. The rail is cooled to 400-500℃ at a cooling rate of 1.5-10℃/s, and then naturally cooled to room temperature. The rail tensile strength is ≥1330MPa, and the elongation is ≥9 %, the rail head hardness is ≥380HB, the depth of the hardened layer is more than 25mm, the structure is fine pearlite, has excellent wear resistance and plasticity, and can meet the requirements of heavy-haul railways.

The existing technology focuses on improving the tensile strength and hardness of rails through online heat treatment processes, and does not involve improving the yield strength of rails. Yield strength is an important factor affecting the initiation of rolling contact fatigue micro-cracks in rails. A high yield-strength ratio is important for improving the rail's yield strength. In terms of service performance, it is of great significance to reduce rolling contact fatigue damage; at the same time, as the strength of the rail increases, its toughness and plasticity will decrease, especially the impact performance of the rail waist part is poor, and the risk of fracture during use increases. Therefore, there is an urgent need to develop a rail with high rail head yield-to-strength ratio and good rail waist impact toughness that is resistant to rolling contact fatigue.

Contents of the invention

In view of the current problem that rails on mixed passenger and freight transport lines are prone to rolling contact fatigue damage, the present invention provides a rolling contact fatigue-resistant high-strength and toughness rail and its production method. By reasonably setting the chemical composition and smelting, rolling and heat treatment processes, the invention realizes the rail The rail head yield ratio and the rail waist impact toughness are well matched to improve the comprehensive performance and service life of the rail and meet the needs of railway development.

In order to achieve the above purpose, the following technical solutions are adopted:

A kind of rolling contact fatigue resistant steel rail for mixed passenger and freight railways. Its chemical composition is 0.75-0.88% C, 0.10-0.60% Si, 0.75-1.30% Mn, 0.20-0.55% Ni, 0.10 in weight percentage. -0.20% V, 0.03-0.06% Nb, ≤0.025% P, ≤0.025% S, the rest is Fe and inevitable impurities.

In the optimized solution, its chemical composition is 0.76-0.86% C, 0.20-0.60% Si, 0.90-1.10% Mn, 0.35-0.55% Ni, 0.12-0.20% V, 0.04-0.06 by weight. % Nb, ≤0.025% P, ≤0.025% S, and the rest is Fe and inevitable impurities.

The invention also provides the production method of the above-mentioned rolling contact fatigue resistant rail, which includes the following processes: hot metal desulfurization, converter smelting, LF refining, vacuum treatment, continuous casting, slab heating, rolling, accelerated cooling, and straightening;

Among them, the desulfurization of molten iron adopts the magnesium powder desulfurization process;

Converter smelting adopts top-bottom double blowing process, and the tapping temperature is controlled at 1660~1680℃;

The alkalinity of the slag refined outside the LF furnace is controlled at 1.8-2.5;

RH adopts deep vacuum treatment, bottom blowing argon pressure is 0.40~0.55MPa, and soft blowing time is 8~12min;

During the continuous casting process, the long nozzle of the large tank and the immersed nozzle of the crystallizer are used to protect the casting. The immersion depth is 60~70mm, and the casting speed is controlled at 0.4~0.6m/min;

A walking beam heating furnace is used to heat the slab, with a heating temperature of 1200-1250°C and a holding time of 170-210 minutes;

The opening rolling temperature is 1080-1130℃, the compression ratio in the rough rolling stage is ≥5.8, the final rolling temperature is 830-860℃, and the compression ratio in the finishing rolling stage is ≥2.2;

Carry out online accelerated cooling of the rolled rail head. The starting cooling temperature is 700-720℃, the cooling speed of the rail head is 2-5℃/s, and the cooling speed of the rail waist and rail bottom is 1-2℃/s. When the head surface temperature drops below 450°C, the accelerated cooling is stopped and then air-cooled to room temperature.

According to the above plan, the off-site temperature of LF refining outside the furnace is controlled at 1585~1600℃.

According to the above plan, the processing time for RH vacuum pressure ≤ 50Pa is not less than 15 minutes, the temperature of RH molten steel leaving the station is controlled to 1540 ~ 1565°C, the hydrogen content of molten steel is ≤ 1.2ppm, and the total oxygen content of molten steel is ≤ 12ppm.

According to the above plan, the continuous casting billet is slowly cooled, and the cooling rate is controlled at 0.05°C/s~0.1°C/s.

According to the above plan, the opening rolling temperature is 1100-1130℃, the compression ratio in the rough rolling stage is ≥6.0, the final rolling temperature is 830-850℃, and the compression ratio in the finishing rolling stage is ≥2.3.

According to the above plan, the starting cooling temperature during accelerated cooling is controlled to 705-720°C, the rail head cooling rate is 2.5-4°C/s, the rail waist and rail bottom cooling rate is 1.5-2°C/s, and the rail head surface temperature is When the temperature drops below 430°C, the accelerated cooling is stopped and then air-cooled to room temperature.

According to the above solution, when the rail head stops accelerated cooling, the rail waist and rail bottom also stop cooling accordingly; the cooling medium for accelerated cooling includes but is not limited to water, polymer solution, oil, compressed air, water mist or oil mist mixture. gas.

Compared with the prior art, the beneficial effects of the present invention are as follows:

This invention achieves a good match between the rail head yield ratio and the rail waist impact toughness by reasonably setting the chemical composition and the smelting and rolling processes, while simultaneously performing accelerated cooling at different cooling rates on the rolled rail head, rail waist and rail bottom. , thereby improving the comprehensive performance and service life of the rail and meeting the needs of railway development; the method is simple, highly operable, and easy to promote and apply.

The rolling contact fatigue-resistant high-strength and toughness rail obtained by the method of the present invention has a rail head metallographic structure of fine pearlite and a small amount of ferrite, a rail tensile strength ≥ 1200 MPa, an elongation ≥ 12%, and a rail head yield ratio ≥ 0.72, rail waist room temperature impact energy Aku≥10J.

Detailed ways

The specific embodiment provides a rolling contact fatigue resistant steel rail for mixed passenger and freight railways, the chemical composition of which is: 0.75-0.88% C, 0.10-0.60% Si, 0.75-1.30% Mn, 0.20% by weight. -0.55% Ni, 0.15-0.30% Cr, 0.03-0.06% Nb, ≤0.025% P, ≤0.025% S, the rest is Fe and inevitable impurities.

Preferably, its chemical composition is: 0.76-0.86% C, 0.20-0.60% Si, 0.90-1.10% Mn, 0.35-0.55% Ni, 0.15-0.20% Cr, 0.04-0.06 % Nb, ≤0.025% P, ≤0.025% S, and the rest is Fe and inevitable impurities.

The functions and mechanisms of each alloying element:

C is the main element that forms pearlite and carbide, and is also the main element that determines the strength of steel. If the C content is too low, the density of the lamellar cementite in the pearlite structure cannot be guaranteed, and the basic strength and hardness of the rail are insufficient, which affects Usage effect; if the C content is too high, on the one hand, the hardness of the rail will be too high, which will accelerate the expansion of fatigue cracks and also reduce the welding performance. Therefore, the present invention controls the C content in the range of 0.75-0.88% by weight.

As the main additive element of steel, Si usually exists in ferrite and austenite in the form of solid solution to improve the strength of the matrix structure, inhibit the formation of cementite in steel, and promote the transformation of ferrite. When the Si content in steel gradually increases When it is high, local segregation is prone to occur, and the Si content is controlled within the range of 0.10-0.60% by weight.

Mn is a solid solution strengthening element in steel. It can improve the strength of ferrite and is also a carbide-forming element. After entering cementite, it can partially replace Fe atoms and improve the strength and hardness of steel. Increased Mn content will significantly reduce the weldability of the steel, coarsen the grain size, and increase the susceptibility to the formation of white spots and slab segregation. Therefore, the Mn content is controlled within the range of 0.75-1.30% by weight.

V is a precipitation strengthening element that improves the strength and hardness of the rail. However, as the V content is increased, the strength and hardness of the rail will further increase while the toughness will decrease. The V content is controlled within the range of 0.08-0.15% by weight.

Nb is an important micro-alloying element in steel. Its mechanism for improving strength is grain refinement strengthening and precipitation strengthening. Through the pinning effect of precipitates, it prevents the austenite grains from growing during the rolling process and refines the grains. Grain, improves strength but does not reduce the impact toughness of steel. However, niobium reduces the high-temperature thermoplasticity of steel, thereby increasing the tendency of hot cracking of niobium-containing steel billets. The content should not be too high, so the Nb content is controlled within the range of 0.03-0.06% by weight.

Ni can improve the hardenability of steel and improve the strength of rails after heat treatment while maintaining good plasticity and toughness. By solid solution in steel, it increases stacking fault energy, promotes dislocation slip, increases the work consumed by crack propagation, and improves toughness. The Nb content is controlled within the range of 0.20-0.55% by weight.

P and S are generally considered to be harmful residual elements in steel, which will greatly increase the crack sensitivity of steel, increase the low-temperature brittle transition temperature of steel, and reduce the impact performance of steel. Therefore, without affecting the performance of the rail, it is required The lower the content of P and S, the better. According to the current relevant standards for rails, it should be controlled at a level of ≦0.025% by weight.

The production method of rolling contact fatigue resistant rails described in the specific embodiment includes the following processes: hot metal desulfurization, converter smelting, LF refining, vacuum treatment, continuous casting, billet heating, rolling, accelerated cooling, and straightening;

Among them, the desulfurization of molten iron adopts the magnesia powder desulfurization process; the converter smelting adopts the top-bottom double blowing process, and the tapping temperature is controlled at 1660-1680°C; the alkalinity of the slag refined outside the LF furnace is controlled at 1.8-2.5, which improves low melting point inclusions. The proportion of materials makes it easy to float and remove and has a certain deformation ability during the rolling process, thereby improving the fatigue resistance and service life of the rail. RH adopts deep vacuum treatment, bottom blowing argon pressure is 0.40~0.55MPa, and soft blowing time is 8~12 minutes. Through RH vacuum treatment, the content of hydrogen, oxygen and other harmful gases in the molten steel is reduced as much as possible, and the purity of the steel is improved. Thereby improving the impact toughness of the rail; during the continuous casting process, a large tank long nozzle and a crystallizer immersed nozzle are used to protect the casting to prevent the molten steel from being oxidized by the air. At the same time, in order to further reduce the hydrogen content and prevent hydrogen embrittlement defects such as white spots, the continuous casting billet should be Slow cooling treatment, the cooling rate is controlled at 0.05℃/s～0.1℃/s.

A walking beam heating furnace is used to heat the slab. The heating temperature is 1200-1250°C and the holding time is 170-210 minutes. This is to ensure that the alloy elements are fully dissolved in the austenite and to avoid excessive growth and refinement of the austenite grains. Pearlite group size; the opening rolling temperature is 1080-1130℃, the compression ratio in the rough rolling stage is ≥5.8, the final rolling temperature is 830-860℃, and the compression ratio in the finishing rolling stage is ≥2.2, mainly through lower rolling temperature and higher Large compression ratio obtains refined austenite grain size, thereby refining the final pearlite structure and improving mechanical properties.

After rolling, the rail head undergoes online accelerated cooling. The starting cooling temperature is 700-720℃, the cooling speed of the rail head is 2-5℃/s, and the cooling speed of the rail waist and rail bottom is 1-2℃/s. When the rail head is ready When the surface temperature drops below 450°C, the accelerated cooling is stopped and then air cooled to room temperature. The basic principle of the rail online heat treatment process is to accelerate the cooling of the rolled rail, use the residual temperature of the rolled rail to accelerate the cooling, increase the degree of supercooling for the transformation of austenite to pearlite, and obtain a thinner layer spacing than that of hot-rolled rails. Fine pearlite structure, thereby improving the strength and hardness of the rail. The cooling speed of the rail head is 2-5℃/s. The purpose is to quickly take away the heat from the surface of the rail head, quickly form a stable and refined pearlite layer, ensure the strength and hardness of the rail head, and improve the rolling contact fatigue resistance of the rail head; The rail waist and rail bottom are not directly affected by wheel-rail stress, but as a support and fixed structure, they have higher requirements for impact toughness than the rail head. The cooling rate of the rail waist and rail bottom is 1-2°C/s. On the one hand, In order to exert the effect of Nb element in refining grains and improving impact toughness through a relatively certain cooling rate, on the other hand, because the metal content of the rail waist and rail bottom is less than that of the rail head and the heat capacity is low, a certain cooling rate can be applied. Reduce the temperature difference between the rail head, rail waist and rail bottom, avoid excessive temperature difference causing large bending of the rail, and ensure the straightness of the rail during the heat treatment process.

The rolling contact fatigue-resistant rail obtained through the specific implementation method has a rail head metallographic structure of fine pearlite and a small amount of ferrite, a rail tensile strength ≥ 1200 MPa, an elongation ≥ 12%, and a rail head yield ratio ≥ 0.72. Rail waist room temperature impact energy A _ku ≥10J.

In order to better understand the present invention, the content of the present invention will be further explained below in conjunction with the examples. However, it should be understood that the specific embodiments described here are only used to explain the present invention and do not limit the present invention.

The chemical compositions of Examples 1-4 are shown in Table 1. Comparative Examples 1-2 select U75V rails, which are currently the most widely used in railways, and the chemical compositions are shown in Table 1.

Chemical composition of the examples in Table 1

Example 1:

The desulfurization of molten iron adopts the magnesia powder desulfurization process; the converter smelting adopts the top-bottom double blowing process, and the tapping temperature is controlled at 1660°C; the basicity of the slag refined outside the LF furnace is controlled at 2.3, and the leaving station temperature is controlled at 1590°C; the RH adopts deep Vacuum degree treatment, the processing time of vacuum pressure ≤ 50Pa is 18 minutes, the bottom blowing argon pressure is 0.45MPa, and the soft blowing time is 10 minutes; the continuous casting process uses a large tank long nozzle and a crystallizer immersed nozzle to protect the casting, and the immersion depth is 60mm. The billet drawing speed is controlled at 0.45m/min, and the billet is slowly cooled; a walking beam heating furnace is used to heat the billet, with a heating temperature of 1230°C and a holding time of 180min; the opening rolling temperature is 1110°C, and the compression ratio in the rough rolling stage is ≥5.8 , the final rolling temperature is 840°C, and the compression ratio in the finishing rolling stage is ≥ 2.2; the rolled rail head is subjected to online accelerated cooling, the starting cooling temperature is 700°C, the cooling speed of the rail head is 3°C/s, and the rail waist and rail bottom are cooled The speed is 1.5°C/s. When the surface temperature of the rail head drops below 450°C, the accelerated cooling is stopped and then air-cooled to room temperature.

Example 2: The desulfurization of molten iron adopts the magnesia powder desulfurization process; the converter smelting adopts the top-bottom double blowing process, and the tapping temperature is controlled at 1680°C; the alkalinity of the slag refined outside the LF furnace is controlled at 2.0, and the leaving station temperature is controlled at 1600°C. ; RH adopts deep vacuum treatment, the processing time of vacuum pressure ≤ 50Pa is 20 minutes, the bottom blowing argon pressure is 0.50MPa, and the soft blowing time is 8 minutes; the continuous casting process uses a large tank long nozzle and a crystallizer immersed nozzle to protect the casting, and the immersion depth At 65mm, the billet drawing speed is controlled at 0.50m/min, and the billet is slowly cooled; a walking beam heating furnace is used to heat the billet, the heating temperature is 1220°C, and the holding time is 200min; the opening rolling temperature is 1090°C, and the rough rolling stage The compression ratio is ≥5.8, the final rolling temperature is 850°C, and the compression ratio in the finishing rolling stage is ≥2.2; the rolled rail head is accelerated and cooled online, the starting cooling temperature is 720°C, the cooling speed of the rail head is 4°C/s, and the rail waist The cooling rate of the rail bottom is 1.2°C/s. When the surface temperature of the rail head drops below 450°C, the accelerated cooling is stopped and then air-cooled to room temperature.

Example 3: The desulfurization of molten iron adopts the magnesia powder desulfurization process; the converter smelting adopts the top-bottom double blowing process, and the tapping temperature is controlled at 1660°C; the alkalinity of the slag refined outside the LF furnace is controlled at 1.9, and the leaving station temperature is controlled at 1590°C. ; RH adopts deep vacuum treatment, the processing time of vacuum pressure ≤ 50Pa is 16 minutes, the bottom blowing argon pressure is 0.40MPa, and the soft blowing time is 11 minutes; the continuous casting process uses a large tank long nozzle and a crystallizer immersed nozzle to protect the casting, and the immersion depth At 65mm, the billet drawing speed is controlled at 0.55m/min, and the billet is slowly cooled; a walking beam heating furnace is used to heat the billet, the heating temperature is 1240°C, and the holding time is 210min; the opening rolling temperature is 1120°C, and the rough rolling stage The compression ratio is ≥5.8, the final rolling temperature is 855°C, and the compression ratio in the finishing rolling stage is ≥2.2; the rolled rail head is accelerated and cooled online, the starting cooling temperature is 710°C, the cooling speed of the rail head is 2°C/s, and the rail waist The cooling rate of the rail bottom is 1.8°C/s. When the surface temperature of the rail head drops below 450°C, accelerated cooling is stopped and then air-cooled to room temperature.

Example 4: The desulfurization of molten iron adopts the magnesia powder desulfurization process; the converter smelting adopts the top-bottom double blowing process, and the tapping temperature is controlled at 1670°C; the alkalinity of the slag refined outside the LF furnace is controlled at 2.2, and the leaving station temperature is controlled at 1590°C. ; RH adopts deep vacuum treatment, the processing time of vacuum pressure ≤ 50Pa is 17 minutes, the bottom blowing argon pressure is 0.45MPa, and the soft blowing time is 10 minutes; the continuous casting process uses a large tank long nozzle and a crystallizer immersed nozzle to protect the casting, and the immersion depth At 70mm, the billet drawing speed is controlled at 0.6m/min, and the billet is slowly cooled; a walking beam heating furnace is used to heat the billet, the heating temperature is 1240°C, and the holding time is 210min; the opening rolling temperature is 1120°C, and the rough rolling stage The compression ratio is ≥5.8, the final rolling temperature is 860°C, and the compression ratio in the finishing rolling stage is ≥2.2; the rolled rail head is accelerated and cooled online, the starting cooling temperature is 720°C, the cooling speed of the rail head is 3°C/s, and the rail waist The cooling rate of the rail bottom is 1.6°C/s. When the surface temperature of the rail head drops below 450°C, the accelerated cooling is stopped and then air-cooled to room temperature.

Comparative Examples 1-2 were carried out according to the production method of Example 1, and the tensile strength, yield strength, elongation and rail head of the rail heads of the Examples and Comparative Examples were measured according to the methods specified in the national railway industry standard TB/T 2344-2012. Performance indicators such as waist room temperature impact energy A _ku are shown in Table 2.

Table 2 Comparison of mechanical properties between Examples and Comparative Examples

In order to verify the rolling contact fatigue resistance of the rails obtained in the present invention, the M-2000 rolling contact wear testing machine was used to conduct contact fatigue tests on the rails of the Examples and Comparative Examples under the same test conditions. The test was carried out by relatively rolling the cylindrical samples. The samples were taken from the rail head area of the Example and Comparative Examples respectively, and the lower sample was taken from the wheel steel. The sample dimensions are thickness 8mm, inner diameter 10mm, outer diameter 20mm; test load: 500N; rotation speed: upper sample 180r/min, lower sample 200r/min; slip rate: 10%. The rolling contact fatigue test results are shown in Table 3.

Table 3 Rolling contact fatigue test results of Examples and Comparative Examples

​	Rolling times/times where fatigue cracks occur	Number of scrolls/times when peeled off blocks occur
Example 1	6.2×10 4	2.7×10 5
Example 2	6.4×10 4	3.3×10 5
Example 3	5.8×10 4	3.1×10 5
Example 4	6.1×10 4	2.8×10 5
Comparative example 1	4.5×10 4	1.7×10 5
Comparative example 2	4.2×10 4	1.5×10 5

It can be seen that the mechanical properties of the rails obtained in the examples are good. Compared with the comparative example, the tensile strength, yield strength and room temperature impact energy of the rail waist are significantly improved. The rail head yield ratio can be guaranteed to be above 0.72, and the rail waist can be guaranteed to be above 0.72. Room temperature impact energy A _ku ≥10J. In the rolling contact fatigue test, the rail obtained in the Example showed better rolling contact fatigue resistance, and the number of rolling times where fatigue cracks appeared and pieces peeled off was significantly later than that of the Comparative Example. Generally speaking, the method of the present invention achieves a good match between the rail head yield ratio and the rail waist impact toughness on the premise of ensuring various mechanical properties of the heat-treated rail, and improves the rolling contact fatigue life of the rail.

The above-described embodiments are only descriptions of specific implementations of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, those of ordinary skill in the art may make various modifications to the technical solutions of the present invention. All modifications and improvements shall fall within the protection scope determined by the claims of the present invention.

Claims (10)

1. A rolling contact fatigue resistant steel rail for mixed passenger and freight railways, which is characterized in that the chemical composition is 0.75-0.88% C, 0.10-0.60% Si, 0.75-1.30% Mn, and 0.20-0.55% Ni by weight. , 0.10-0.20% V, 0.03-0.06% Nb, ≤0.025% P, ≤0.025% S, and the rest is Fe and inevitable impurities.
2. The rolling contact fatigue resistant steel rail for mixed passenger and freight railways according to claim 1, characterized in that the chemical composition is 0.76-0.86% C, 0.20-0.60% Si, 0.90-1.10% Mn, 0.35- 0.55% Ni, 0.12-0.20% V, 0.04-0.06% Nb, ≤0.025% P, ≤0.025% S, the rest is Fe and inevitable impurities.
3. The production method of rolling contact fatigue resistant steel rails for mixed passenger and freight railways according to claim 1, which is characterized in that it includes the following processes: hot metal desulfurization, converter smelting, LF refining, vacuum treatment, continuous casting, billet heating, rolling, acceleration cooling, straightening;

   Among them, the desulfurization of molten iron adopts the magnesium powder desulfurization process;

   Converter smelting adopts top-bottom double blowing process, and the tapping temperature is controlled at 1660~1680℃;

   The alkalinity of the slag refined outside the LF furnace is controlled at 1.8-2.5;

   RH adopts deep vacuum treatment, bottom blowing argon pressure is 0.40~0.55MPa, and soft blowing time is 8~12min;

   During the continuous casting process, the long nozzle of the large tank and the immersed nozzle of the crystallizer are used to protect the casting. The immersion depth is 60~70mm, and the casting speed is controlled at 0.4~0.6m/min;

   A walking beam heating furnace is used to heat the slab, with a heating temperature of 1200-1250°C and a holding time of 170-210 minutes;

   The opening rolling temperature is 1080-1130℃, the compression ratio in the rough rolling stage is ≥5.8, the final rolling temperature is 830-860℃, and the compression ratio in the finishing rolling stage is ≥2.2;

   Carry out online accelerated cooling of the rolled rail head. The starting cooling temperature is 700-720℃, the cooling speed of the rail head is 2-5℃/s, and the cooling speed of the rail waist and rail bottom is 1-2℃/s. When the head surface temperature drops below 450°C, the accelerated cooling is stopped and then air-cooled to room temperature.
4. The production method of rolling contact fatigue resistant rails according to claim 3, characterized in that the off-site temperature of refining outside the LF furnace is controlled at 1585-1600°C.
5. The production method of rolling contact fatigue-resistant rails according to claim 3, characterized in that the processing time of RH vacuum pressure ≤ 50 Pa is not less than 15 minutes, the temperature of RH molten steel leaving the station is controlled to 1540~1565°C, the hydrogen content of the molten steel is ≤ 1.2ppm, and the molten steel Total oxygen content ≤12ppm.
6. The production method of rolling contact fatigue resistant rails according to claim 3, characterized in that the continuous casting billet is subjected to slow cooling treatment, and the cooling rate is controlled at 0.05°C/s～0.1°C/s.
7. The production method of rolling contact fatigue resistant rails according to claim 3, characterized in that the opening rolling temperature is 1100-1130°C, the compression ratio in the rough rolling stage is ≥ 6.0, the final rolling temperature is 830-850°C, and the compression ratio in the finishing rolling stage is ≥ 2.3.
8. The production method of rolling contact fatigue-resistant rails according to claim 3, characterized in that during accelerated cooling, the starting cooling temperature is controlled to 705-720°C, the cooling speed of the rail head is 2.5-4°C/s, and the cooling speed of the rail waist and rail bottom is 2.5-4°C/s. is 1.5-2℃/s. When the surface temperature of the rail head drops below 430℃, the accelerated cooling will be stopped and then air-cooled to room temperature.
9. The production method of rolling contact fatigue resistant rails according to claim 3, characterized in that when the rail head stops accelerating cooling, the rail waist and rail bottom also stop cooling accordingly.
10. The production method of rolling contact fatigue resistant rails according to claim 3, characterized in that the cooling medium for accelerated cooling is water, polymer solution, oil, compressed air, water mist or oil mist mixture.