Bainite turnout steel rail suitable for heavy haul railway and preparation method of bainite turnout steel rail

Abstract

The invention discloses a bainite turnout steel rail suitable for a heavy haul railway and a preparation method, a metallographic structure of the steel rail takes a bainite structure as a main structure, and the steel rail comprises the following raw material components in percentage by mass: 0.16-0.30% of C, 1.40-2.00% of Si, 1.50-2.30% of Mn, less than or equal to 0.025% of P, less than or equal to 0.025% of S, 0.40-1.50% of Cr and 0.04-0.15% of V. And the balance of Fe. According to the turnout steel rail, specific component design is adopted, a specific heat treatment process is carried out, the tensile strength of the obtained bainite turnout rail is larger than or equal to 1350 MPa, the ductility is larger than or equal to 12%, the surface hardness is larger than or equal to 400 HB, the hardness of the steel rail is improved while the strength and toughness of the steel rail are guaranteed, and the bainite turnout steel rail is particularly suitable for turnout rails for heavy haul railways.

Description

Technical Field

[0001] The invention relates to the technical field of bainite turnout rails, in particular to a bainite turnout rail suitable for heavy-load railways and a preparation method thereof. Background Art

[0002] High-speed passenger transport and heavy-duty freight transport are the development direction of my country's railways. my country's rails have developed from the initial 50kg / m to 60kg / m, and the rail strength level has also increased from the initial 780MPa to 880MPa. In terms of heavy-duty railways, due to the continuous increase in train axle weight, transportation volume, and transportation density, the service environment of rails has become increasingly harsh, and the urgency and importance of developing high-wear resistance, fatigue resistance, good fatigue resistance, and easy-to-weld rails have become increasingly prominent. my country is actively developing bainite rails, and the developed products mainly cover 1180MPa, 1280MPa, and 1380MPa grades. Among them, 1280MPa grade and below are mainly produced by hot rolling air cooling + tempering process, which is divided into two types: carbide-free bainite and bainite / martensite duplex structure. It has the characteristics of moderate strength, good toughness and plasticity, good fatigue resistance, and excellent weldability. It has been applied on some lines, and its service performance is generally stable and reliable. At the same time, it has also been promoted and applied in the field of railway turnouts, improving the safety of turnout service and significantly extending its service life. 1380MPa grade bainitic rails are mainly produced through specific composition design and supplemented by online heat treatment technology. Compared with 1280MPa grade products, 1380MPa bainitic rails have higher strength and toughness and higher wear resistance requirements. At present, it has been proved through practice that bainitic rails 1380MPa will have damage within a certain depth below the surface of the rail head at the beginning of service, which affects the stability of product quality and safe use.

[0003] Therefore, how to improve the wear resistance and fatigue resistance of bainitic turnout rails, and improve their toughness and hardness while ensuring their strength, is a hot topic and trend in current research and development.

[0004] Chinese patent application CN107312976A discloses a bainite rail and a production method. By using elements such as Si, Mn and trace boron, the precipitation of carbides during the bainite phase transformation can be effectively prevented, the high-temperature transformation of supercooled austenite can be delayed, and the hardenability of steel can be improved, thereby achieving the separation of pearlite and bainite transformation curves. The bainite rail produced by this method has uniform structure, no decarburized structure on the surface, low residual austenite content, no martensite that affects performance, and low precious metal content, which greatly reduces production costs. However, although the bainite rail produced by this method improves the strength and toughness of the rail, its hardness is poor, and its use as a heavy-duty turnout rail is limited. Summary of the invention

[0005] The object of the present invention is to provide a bainitic turnout rail steel and a preparation method. The bainitic turnout rail of the present invention adopts a specific bainite composition design; adopts a specific preparation process, that is, after smelting and casting, the steel billet is heated and rolled into a turnout rail, and the final rolling temperature is 900-950°C; using the residual heat of rolling, an online heat treatment device is used to open the cooling temperature at 650-850°C, and a Laval nozzle device is used on the top surface and both sides of the turnout rail to finally cool to 200-350°C within the range of 100-600s. Finally, it is air-cooled to room temperature, straightened, and processed to form a high-strength bainitic turnout rail product. The high-strength bainitic turnout rail produced by this method has a tensile strength of ≥1350MPa, an elongation of ≥12%, and a surface hardness of ≥400HB. While ensuring the strength and toughness of the rail, its hardness is improved, and it is particularly suitable for turnout rails for heavy-duty railways.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a bainite turnout rail suitable for heavy-duty railways, wherein the metallographic structure of the rail is mainly bainite structure; and the rail comprises the following raw material components in terms of mass percentage: C 0.16-0.30%, Si 1.40-2.00%, Mn 1.50-2.30%, P≤0.025%, S≤0.025%, Cr 0.40-1.50%, V 0.04-0.15%; the balance is Fe.

[0007] According to the bainite turnout rail suitable for heavy-load railways described in the present invention, preferably, the rail has a Cr content of 1.20-1.50% and a V content of 0.12-0.15% in terms of mass percentage.

[0008] According to the bainite turnout rail suitable for heavy-haul railways of the present invention, preferably, the mass percentages of Si, Mn, Cr and V in the rail satisfy the following formula: Si+Mn+Cr+0.01V=3.3-6.0%.

[0009] According to the bainite turnout rail suitable for heavy-load railways described in the present invention, preferably, the head working side of the rail is a multi-phase bainite structure, and the multi-phase bainite structure includes a martensite structure, a bainite structure and a residual austenite structure.

[0010] According to the bainite turnout rail suitable for heavy-load railways described in the present invention, preferably, the mass percentage of bainite structure in the multi-phase bainite structure is 30-60%, the mass percentage of martensite structure is 20-40%, and the mass percentage of residual austenite structure is 5-20%.

[0011] According to the bainite turnout rail suitable for heavy-load railways described in the present invention, preferably, the tensile strength of the rail is ≥1350 MPa, the elongation is ≥12%, and the cross-sectional surface hardness of the rail head is ≥400 HB.

[0012] According to the bainite rail suitable for heavy-load railways described in the present invention, preferably, the residual stress of the rail is below 350 MPa.

[0013] In addition, the present invention also provides a method for preparing a bainite turnout rail suitable for heavy-duty railways as described above, comprising the following steps: online heat treatment: controlling the temperature of the working side of the rail head after final rolling to 650-850°C, and final cooling to 200-350°C within the range of 100-600s; heat-averaging and heat-insulating: the rail is heat-averaged and heat-insulated after heat treatment, the heat-insulating temperature is 1150-1250°C, and the heat-insulating time is 30-300s; tempering and heat-insulating: tempering and heat-insulating at 200-450°C for 4-40h.

[0014] According to the preparation method as described above, preferably, during the online heat treatment process, a Laval nozzle device is used to cool the rail.

[0015] According to the preparation method as described above, preferably, an induction coil is added to the rail during the equalization process to achieve the purpose of equalizing the temperature of the bainite turnout rail, and the voltage of the induction coil is controlled at 650-700V and the power is 30-80kW.

[0016] The beneficial effects of the present invention are: The present invention provides a bainitic turnout rail steel and a preparation method. The bainitic structure of the rail is set to a specific composition and has undergone a specific heating process, which effectively reduces the occurrence of abnormal structures in the rail, thereby improving the fatigue resistance and wear resistance of the bainitic turnout rail. The tensile strength is ≥1350MPa, the elongation is ≥12%, and the surface hardness is ≥400HB. The strength and toughness of the rail are ensured while the hardness is improved. The rail is particularly suitable for turnout rails for heavy-duty railways. DETAILED DESCRIPTION In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with specific embodiments.

[0017] The present invention mainly studies the design of trace chemical composition of bainite turnout rails, cooperates with heat treatment process regulation, effectively reduces the occurrence of abnormal tissues in the rails, thereby improving the fatigue and wear resistance of bainite turnout rails. The product is suitable for the field of heavy-load railways.

[0018] The invention provides a bainite turnout rail suitable for heavy-load railways, wherein the metallographic structure of the rail is mainly bainite structure; the bainite structure comprises the following raw material components according to mass percentage: C 0.16-0.30%, Si 1.40-2.00%, Mn 1.50-2.30%, P≤0.025%, S≤0.025%, Cr 0.40-1.50%, V 0.04-0.15%; the balance is Fe.

[0019] As a specific embodiment of the present invention, the steel rail has a Cr content of 1.20-1.50% and a V content of 0.12-0.15% in terms of mass percentage.

[0020] As another specific embodiment of the present invention, the mass percentages of Si, Mn, Cr and V in the rail satisfy the following formula: Si+Mn+Cr+0.01V=3.3-6.0%.

[0021] As the most basic element in rail composition design, carbon element's main function is to ensure the strength and hardness of rail. An appropriate amount of carbon element can improve the strength, wear resistance and toughness of rail, and improve the performance and life of rail.

[0022] It is found in the present invention that, by adopting the process preparation method of the present invention, when the carbon content in the turnout rail is lower than 0.16%, the appropriate hardness of the rail cannot be guaranteed, and the wear resistance and fatigue resistance of the rail cannot be guaranteed; when the carbon content is higher than 0.30%, the strength of the rail will be too high, and the safe use performance of the rail cannot be effectively guaranteed. Therefore, the mass percentage of the carbon content is limited to 0.16-0.30%.

[0023] On the one hand, a proper amount of silicon in the rail can increase the martensitic transformation start temperature of the new bainite / martensite duplex ductile iron, thereby enhancing the strength of the material; on the other hand, silicon can inhibit the precipitation of carbides during the bainite transformation process, thereby forming a stable austenite film between the bainitic ferrite laths, and this carbide-free bainite structure exhibits high strength and toughness under static load. Therefore, in the method described in the present invention, the content of silicon is limited to 1.40-2.00%.

[0024] Manganese can significantly reduce the temperature at which bainite structure begins to transform in rails, and is an important alloying element for obtaining refined bainite ferrite strips in bainite steel. When the manganese content is lower than 1.50% by weight, the positive effect on bainite steel is difficult to achieve; when the manganese content is higher than 2.30% by weight, the segregation of the rails and the disadvantages of the martensitic structure at room temperature will increase, and the fatigue performance and service safety performance of the rails will be significantly reduced. Therefore, the present invention limits the manganese content to 1.50-2.30% by weight.

[0025] Chromium in steel can form different types of carbides with carbides in steel. In addition, an appropriate amount of chromium can refine the size of carbides, thereby improving the wear resistance of rails. When the chromium content is lower than 0.40%, the proportion of carbides formed in the bainite structure is low, the wear resistance effect cannot be achieved, and the hardness is insufficient; when the chromium content is higher than 1.50%, the proportion of martensite in bainite will increase, reducing toughness and affecting the safe use of rails. Therefore, under the present invention, the chromium content is controlled at 0.40-1.50% by weight.

[0026] Vanadium is an important element for microstructure refinement. When added to steel, it can refine bainite ferrite lamellar strips, thereby improving the strength and toughness of the steel. When the vanadium content is less than 0.04% by weight, the grain refinement effect is not obvious, and when the vanadium content is higher than 0.15% by weight, the impact toughness index of the rail will deteriorate. Therefore, under the present invention, the vanadium content is controlled at 0.04-0.15% by weight.

[0027] During the research and development process, the inventors found that controlling the mass percentage of Si+Mn+Cr+0.01V in the steel billet of bainitic rails to 3.3-6.0% can achieve better mechanical properties. The inventors speculate that the reason is that Si, Mn, Cr, and V elements can play a synergistic role in bainitic steel, regulating the strength, size, and proportion of carbides in the steel, thereby ensuring that the bainite structure of the rails is refined after the "multi-pass rolling + heat treatment" process, thereby improving the wear resistance of the rails.

[0028] The present invention also provides a bainite turnout rail suitable for heavy-load railways, wherein the head working side of the rail is a multi-phase bainite structure, and the multi-phase bainite structure includes a martensite structure, a bainite structure and a residual austenite structure; wherein the bainite structure is the bainite structure as described above, which will not be repeated here.

[0029] As a specific embodiment of the present invention, the mass percentage of bainite structure in the multiphase bainite structure is 30-60%, the mass percentage of martensite structure is 20-40%, and more preferably, the mass percentage of retained austenite structure is 5-20%.

[0030] In the present invention, the tensile strength of the rail is ≥1350 MPa, the elongation is ≥12%, and the cross-sectional surface hardness of the rail head is ≥400 HB; more preferably, the residual stress of the rail is below 350 MPa.

[0031] In addition, the present invention also provides a method for preparing a bainite turnout rail suitable for heavy-duty railways as described above, the preparation method comprising the following steps: Smelting and heating rolling: After smelting and casting, the steel billet is heated and rolled into turnout rails, with the final rolling temperature at 900-950℃; Online heat treatment: the temperature of the working side of the rail head after final rolling is controlled at 650-850℃, and finally cooled to 200-350℃ within the range of 100-600s; Heat-averaging and heat-insulation: After heat treatment, the rails are subjected to heat-averaging and heat-insulation, with the heat-insulation temperature being 1150-1250°C and the heat-insulation time being 30-300s; Tempering and heat preservation: Tempering and heat preservation at 200-450℃ for 4-40h.

[0032] According to the preparation method of the present invention, during the online heat treatment process, a Laval nozzle device can be used to cool the rail. Preferably, an induction coil is added to the bainite turnout rail during the equalization process to achieve the purpose of equalization temperature of the bainite turnout rail. The voltage of the induction coil is controlled at 650-700V and the power is 30-80kW; more preferably, the working equalization time of the induction coil is controlled at 30-300s. The tempered rail is then straightened and processed to form a bainite turnout rail.

[0033] When a bainitic turnout rail is subjected to a heat treatment, an induction coil is added in the heat treatment process to provide a stable heat input to the rail during the heat treatment process. On the one hand, this method achieves the purpose of low-temperature tempering by reducing residual stress in a shorter heat preservation time; on the other hand, sufficient time is given to the bainite phase transformation process so that the austenite can be fully transformed; in addition, it also provides an early platform time for the subsequent tempering process. The heat of the induction coil comes from the waste heat recovery of the production line. The present invention improves product quality without increasing the heat energy cost of the production line, while achieving the purpose of energy saving and environmental protection.

[0034] This method can effectively enhance the cooling strength of the working side of the turnout rail, thereby effectively improving the surface hardness and strength of the turnout rail. In the method of the present invention, after smelting and casting the steel billet, the steel billet is heated and rolled into a turnout rail, and the final rolling temperature is 900-950°C. The heat treatment process of the present invention limits the final cooling to 200-350°C, taking into account the phase change characteristics and organizational changes of the entire section. Too low a final cooling temperature will cause the supercooled austenite to transform into a martensite structure. The heat treatment limits the cooling rate, mainly considering that the turnout rail is an asymmetric section, the cooling rate is too large, and the residual stress of the entire section is too large, which has an adverse effect on the line service.

[0035] The turnout rail steel prepared by the present invention adopts a specific composition design and undergoes a specific heat treatment process. The obtained bainite turnout rail has a tensile strength of ≥1350MPa, an elongation of ≥12%, and a surface hardness of ≥400HB. The strength and toughness of the rail are ensured while the hardness is improved. The turnout rail is particularly suitable for turnout rails for heavy-load railways.

[0036] Examples 1-3 The metallographic structure of the turnout rails prepared in Examples 1-3 is mainly bainite, and the working side of the rail head is multiphase bainite. The chemical composition of the rails is shown in Table 1, and the specific process parameters are shown in Table 2.

[0037] Comparative Example 1-2 The metallographic structure of the turnout rail prepared in Comparative Example 1-2 is mainly bainite structure, and the working side of the rail head is multi-phase bainite structure. The chemical composition of the rail is shown in Table 1, and the specific process parameters are shown in Table 2.

[0038] The rails of Examples 1-3 and Comparative Examples 1-2 of the present invention are cast through full protection, and their chemical compositions are shown in Table 1. The heat treatment process parameters during their preparation are shown in Table 2. The turnout rails of Examples 1-3 and Comparative Examples 1-2 adopt the same soaking, tempering and insulation treatment, and straightening process parameters, wherein the soaking temperature is 1150-1250°C, and the insulation time is 30-300s; tempering and insulation: tempering and insulation at 200-450°C for 4-40h. At the same time, the metallographic structure and mechanical properties are tested in accordance with the requirements of TB / T 2344.2-2022 "Rail Part 2: Asymmetric Section Rails for Turnouts". The tensile and mechanical data statistics are shown in Table 3.

[0039] Table 1 Chemical composition of rails in examples and comparative examples (%)

[0040] Table 2 Heat treatment process parameters of examples and comparative examples

[0041] Table 3 Microstructure and mechanical properties of rails in the examples and comparative examples

[0042] From the above comparison, it can be seen that the turnout rail prepared by using the bainite and preparation method of the present invention not only improves the tensile strength and hardness performance of the working side of the turnout rail, but also improves the toughness and plasticity of the turnout rail, thereby ensuring the safe operation of the rail.

[0043] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A bainite turnout rail suitable for heavy-haul railways, characterized in that: The metallographic structure of the rail is mainly bainite; according to mass percentage, it includes the following raw material components: C 0.16-0.30%, Si 1.40-2.00%, Mn 1.50-2.30%, P≤0.025%, S≤0.025%, Cr 0.40-1.50%, V 0.04-0.15%; The balance is Fe.

2. The bainite turnout rail suitable for heavy-load railway according to claim 1, characterized in that: The steel rail has a Cr content of 1.20-1.50% and a V content of 0.12-0.15% in terms of mass percentage.

3. The bainite turnout rail suitable for heavy-load railway according to claim 1, characterized in that: The mass percentages of Si, Mn, Cr and V in the rail satisfy the following formula: Si+Mn+Cr+0.01V=3.3-6.0%.

4. A bainite turnout rail suitable for heavy-load railway according to any one of claims 1 to 3, characterized in that: The working side of the head of the rail is a multi-phase bainite structure, and the multi-phase bainite structure includes a martensite structure, a bainite structure and a residual austenite structure.

5. The bainite turnout rail suitable for heavy-load railway according to claim 4, characterized in that: The mass percentage of the bainite structure in the multiphase bainite structure is 30-60%, the mass percentage of the martensite structure is 20-40%, and the mass percentage of the retained austenite structure is 5-20%.

6. The bainite turnout rail suitable for heavy-load railway according to claim 1, characterized in that: The tensile strength of the rail is ≥1350MPa, the elongation is ≥12%, and the cross-sectional surface hardness of the rail head is ≥400HB.

7. The bainite turnout rail suitable for heavy-load railway according to claim 6, characterized in that: The residual stress of the rail is below 350 MPa.

8. A method for preparing a bainite turnout rail suitable for heavy-load railway according to any one of claims 1 to 7, characterized in that: The following steps are involved: Smelting and heating rolling: After smelting and casting, the steel billet is heated and rolled into turnout rails, with the final rolling temperature at 900-950℃; Online heat treatment: the temperature of the working side of the rail head after final rolling is controlled at 650-850℃, and finally cooled to 200-350℃ within the range of 100-600s; Heat-averaging and heat-insulation: After heat treatment, the rails are subjected to heat-averaging and heat-insulation, with the heat-insulation temperature being 1150-1250°C and the heat-insulation time being 30-300s; Tempering and heat preservation: Tempering and heat preservation at 200-450℃ for 4-40h.

9. The preparation method according to claim 8, characterized in that: During the online heat treatment process, the rail is cooled by using a Laval nozzle device.

10. The preparation method according to claim 8, characterized in that: During the heat-averaging process, an induction coil is added to the rail to achieve the purpose of heat-averaging the bainite turnout rail. The voltage of the induction coil is controlled at 650-700V and the power is 30-80kW.

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