Carbide-free bainite / martensite complex-phase steel rail and preparation method thereof

Abstract

The invention discloses a carbide-free bainite / martensite complex-phase steel rail and a preparation method thereof.The preparation method comprises the steps that a steel billet obtained through smelting and casting according to component design is subjected to austenite homogenization treatment at the temperature of 1200-1280 DEG C and then rolled, and a steel rail intermediate is obtained; carrying out primary cooling treatment on the steel rail intermediate, and cooling the steel rail intermediate to 250-300 DEG C; carrying out first heating treatment, heating to 300-400 DEG C, and carrying out heat preservation for a first preset time; carrying out secondary cooling treatment, cooling to 250-300 DEG C, and carrying out heat preservation for a second preset time; and carrying out third cooling treatment, and cooling to room temperature. Based on the obdurability characteristic of the carbide-free bainite and the bainite / martensite complex phase structure, the novel carbide-free bainite / martensite complex phase structure with more excellent obdurability and the steel rail steel thereof are obtained through proper alloy elements in the carbon content range of 0.20-0.30% under the assistance of proper thermal deformation and heat treatment processes; good market application prospects are realized.

Description

Technical Field

[0001] The invention relates to the technical field of rail production, and in particular to a carbide-free bainite / martensite complex phase rail and a preparation method thereof. Background Art

[0002] With the rapid development of my country's economy, railway transportation has become the main mode of transportation in today's society with its high efficiency and safety, which is of great significance to my country's energy transportation and rapid economic development. The sustainable development advantages of freight heavy-haul railways in terms of environment and resources have been recognized internationally and have achieved remarkable development. With the development of the world economy and the rapid development of heavy-haul railways, the axle weight, running speed and traffic density of trains are constantly increasing, and the service conditions of rails are becoming increasingly severe, which puts forward higher requirements on the strength, toughness and fatigue performance of rails.

[0003] The existing railway rails are mainly made of high-carbon pearlite rail steel, whose strength and toughness have been optimized to the theoretical limit, and there is no room for further improvement, which makes it difficult to meet the transportation requirements of my country's high-speed and heavy-duty railways. Therefore, it is urgent to develop a new type of rail steel with better strength and toughness. Carbide-free bainite / martensite complex phase rail steel has attracted extensive attention from scholars at home and abroad due to its high strength, toughness and plasticity.

[0004] In the 1960s, people found that the bainite / martensite complex structure has better mechanical properties than the pure bainite or martensite structure, especially the strength and toughness combination is better. Therefore, steel with bainite / martensite complex structure has received widespread attention. Domestic and foreign researchers have found that the bainite / martensite complex structure obtained by isothermal treatment at different temperatures after different heat treatment times can further optimize the strength and toughness of steel. However, the preparation process of bainite / martensite complex structure steel obtained by isothermal treatment is relatively complicated and is only suitable for small and medium-sized structural parts, which technically limits its large-scale application and promotion as a structural material. By using microalloying, a certain amount of Si and Cr elements are added to the Mn-B series low-carbon bainite steel to replace the B element, and a low-carbon Mn-Si-Cr series bainite / martensite complex steel is invented. This series of experimental steels can obtain bainite / martensite complex structure in a wide range of cooling rates.

[0005] In recent years, domestic and foreign scholars have obtained carbide-free bainite steel by adding a certain amount of Si or Al and other elements to bainite steel, performing low-temperature isothermal quenching in the bainite transformation zone, and then air cooling to room temperature. The microstructure of this steel consists of bainite ferrite laths + residual austenite (blocky + film-like). The carbide-free bainite test steel has improved strength while still maintaining high toughness and plasticity, showing comprehensive mechanical properties that are significantly better than traditional high-strength steels.

[0006] Therefore, how to obtain rail steel with better strength and toughness by using appropriate alloy elements and appropriate processing technology has become a technical problem that needs to be urgently solved by technical personnel in this field.

[0007] Based on this, the existing technology still needs to be improved. Summary of the invention

[0008] In order to solve the above technical problems, the embodiments of the present invention provide a carbide-free bainite / martensite multiphase rail and a preparation method thereof, so as to solve the technical problem that the strength and toughness of the rail steel in the prior art cannot meet the requirements.

[0009] In order to solve the above technical problems, on the one hand, some embodiments of the present invention disclose a method for producing a carbide-free bainite / martensite dual-phase rail, comprising: Step 1: subjecting the steel billet obtained by smelting and casting according to the designed composition to austenite homogenization treatment at 1200-1280° C. and then rolling to obtain a rail intermediate; Step 2: subjecting the rail intermediate to a first cooling treatment, cooling the rail intermediate to 250-300° C.; Step 3: performing a first heating treatment, heating to 300-400° C. and then keeping the temperature for a first predetermined time; Step 4: performing a second cooling process, cooling to 250-300°C and then keeping the temperature for a second predetermined time; Step 5: performing a third cooling process to cool to room temperature. In some embodiments, in step 1, the temperature is kept at 1200-1280° C. for 60-180 min.

[0010] In some embodiments, in step 1, the final cooling temperature of rolling is 850-950°C.

[0011] In some embodiments, in step 2, the first cooling treatment has a starting temperature of 650-800° C. and a cooling rate of 1.5-3.0° C. / s.

[0012] In some embodiments, in step three, the heating rate of the first heating treatment is 5-10° C. / s, and the first predetermined time is 120-240.

[0013] In some embodiments, in step 4, the cooling rate of the second cooling treatment is 1.5-3.0° C. / s, and the second predetermined time is 240-600 min.

[0014] In some embodiments, in step five, the cooling rate of the third cooling treatment is 1.0-1.5° C. / s.

[0015] In some embodiments, the composition is designed to have a carbon content of 0.20-0.30%.

[0016] On the other hand, some embodiments of the present invention further disclose a carbide-free bainite / martensite duplex steel rail, which is manufactured by the aforementioned production method of the carbide-free bainite / martensite duplex steel rail.

[0017] In some embodiments, the tensile strength is ≥1280 MPa, the elongation is ≥12%, and the cross-sectional shrinkage is ≥45%; Or, shock at room temperature ≥80J, shock at -40℃ ≥40J; Alternatively, the structure contains 40-55% bainitic ferrite, 35-50% martensite and 5-15% retained austenite.

[0018] By adopting the above technical solution, the present invention has at least the following beneficial effects: The present invention provides a carbide-free bainite / martensite complex phase rail and preparation method. Based on the strength and toughness characteristics of carbide-free bainite and bainite / martensite complex phase structures, a new carbide-free bainite / martensite complex phase structure and rail steel with better toughness are obtained by appropriate alloying elements, supplemented by appropriate thermal deformation and heat treatment processes within the carbon content range of 0.20-0.30%. While ensuring the strength and toughness of the existing online heat-treated carbide-free bainite / martensite complex phase rail, the rail operation safety is improved to meet the requirements of heavy-duty railway rails or turnout railway rails. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 The present invention is a flowchart of a method for preparing a carbide-free bainite / martensite complex phase rail disclosed in some embodiments of the present invention. DETAILED DESCRIPTION

[0021] The following is a further detailed description of the embodiments of the present disclosure in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present disclosure, but cannot be used to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

[0022] The present disclosure provides these embodiments to make the present disclosure thorough and complete, and to fully express the scope of the present disclosure to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of the parts and steps, the composition of the materials, the numerical expressions and the numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary, and not as limiting.

[0023] It should be noted that, in the description of the present disclosure, unless otherwise specified, the meaning of "multiple" is greater than or equal to two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating the orientation or positional relationship, are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present disclosure. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0024] In addition, the words "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different parts. "Vertical" does not mean vertical in the strict sense, but is within the tolerance range. "Parallel" does not mean parallel in the strict sense, but is within the tolerance range. "Include" or "comprising" and similar words mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of including other elements.

[0025] It should also be noted that in the description of the present disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to the specific circumstances. When a specific device is described as being located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0026] All terms used in the present disclosure have the same meanings as those understood by those of ordinary skill in the art to which the present disclosure belongs, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries, for example, should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an idealized or extremely formal sense, unless explicitly defined as such herein.

[0027] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0028] like Figure 1 As shown, some embodiments of the present invention disclose a carbide-free bainite / martensite complex phase rail and a preparation method thereof, which adopts a 0.2-0.30% carbon content composition design, and after smelting and casting, adopts 1200-1280℃ austenite homogenization, and after dephosphorization of the steel billet, it is universally rolled into a rail shape, and the final rolling temperature is between 850-950℃; after rolling, the rolling waste heat is used for an online heat treatment process, the start cooling temperature is 650-800℃, and the cooling rate is 1.5-3.0℃ / s. When the final cooling temperature is cooled to 250-300℃, it is heated to 300-400℃ at 5-10℃ / s, and after keeping it for 120-240min, it is reduced to 250-300℃ at 1.5-3.0℃ / s, and after keeping it for 240-600min, it is cooled to room temperature at 1.0-1.5℃ / s. The carbide-free bainite / martensite composite rail produced by this method has a tensile strength of ≥1280MPa, an elongation of ≥12%, a cross-sectional shrinkage of ≥45%, a room temperature impact of ≥80J, a -40℃ low temperature impact of ≥40J, and contains 40-55% bainite ferrite, 35-50% martensite and 5-15% residual austenite in the structure. It is particularly suitable for heavy-duty railway rails or turnout railway rails.

[0029] The carbide-free bainite / martensite composite rail with excellent toughness and the production method thereof in the present invention are described in detail below in conjunction with specific embodiments. In the following embodiments and comparative examples, the prepared rails are subjected to the same straightening process and then subjected to tensile properties, impact properties and metallographic structure tests in accordance with the requirements of TB / T 2344 "Technical Conditions for Ordering 43kg / m~75kg / m Rails".

[0030] Example 1 A carbide-free bainite / martensite composite rail and a preparation method thereof, which is designed with a carbon content of 0.2-0.30%, specifically, C 0.2%; Si 1.0%; Mn 1.5%; P 0.015%; S 0.06%; Cr 0.7%; No 0.30%; V0.01%; Ni 0.15%; Al 0.003%; gas content includes: H 0.8ppm; O 5ppm; N 40ppm. After smelting and casting, austenite homogenization is performed at 1200°C for 60 minutes, and after dephosphorization of the steel billet, the steel billet is universally rolled into a rail shape, and the final rolling temperature is between 850°C; after rolling, the rolling waste heat is used for an online heat treatment process, the cooling start temperature is 650°C, and the cooling rate is 1.5°C / s. When the final cooling temperature is cooled to 250℃, it is heated to 300℃ at 5℃ / s, kept warm for 120min, then cooled to 250℃ at 1.5℃ / s, kept warm for 240min, and finally cooled to room temperature at a rate of 1.0-1.5℃ / s. The carbide-free bainite / martensite composite rail produced by this method has a tensile strength of 1285MPa, an elongation of 12%, a cross-sectional shrinkage of 46%, a room temperature impact of 85J, a -40℃ low temperature impact of 40J, and a structure containing 50% bainitic ferrite, 35% martensite and 15% residual austenite. It is particularly suitable for heavy-duty railway rails or turnout railway rails.

[0031] Example 2 A carbide-free bainite / martensite composite rail and a preparation method thereof, which is designed with a carbon content of 0.2-0.30%, specifically, C 0.22%; Si 1.3%; Mn 1.7%; P 0.015%; S 0.06%; Cr 0.5%; No 0.35%; V0.03%; Ni 0.20%; Al 0.003%; gas content includes: H 0.9ppm; O 6ppm; N 45ppm. After smelting and casting, 1220℃ austenite homogenization is adopted for 80min, and after dephosphorization of the steel billet, it is universally rolled into a rail shape, and the final rolling temperature is between 870℃; after rolling, the rolling waste heat is used for an online heat treatment process, the cooling start temperature is 720℃, and the cooling rate is 2.0℃ / s. When the final cooling temperature is cooled to 260℃, it is heated to 320℃ at 6℃ / s, kept warm for 160min, then cooled to 260℃ at 1.7℃ / s, kept warm for 360min, and finally cooled to room temperature at 1.0-1.5℃ / s. The carbide-free bainite / martensite composite rail produced by this method has a tensile strength of 1304MPa, an elongation of 14%, a cross-sectional shrinkage of 51%, a room temperature impact of 95J, a -40℃ low temperature impact of 45J, and contains 53% bainitic ferrite, 37% martensite and 10% residual austenite in the structure. It is particularly suitable for heavy-duty railway rails or turnout railway rails.

[0032] Example 3 A carbide-free bainite / martensite composite rail and a preparation method thereof, which is designed with a carbon content of 0.2-0.30%, specifically, C 0.24%; Si 1.5%; Mn 1.9%; P 0.015%; S 0.06%; Cr 0.7%; No 0.40%; V0.05%; Ni 0.30%; Al 0.003%; gas content includes: H 1.0ppm; O7ppm; N 40ppm. After smelting and casting, austenite homogenization is performed at 1240℃ for 120min, and after dephosphorization of the steel billet, it is universally rolled into a rail shape, and the final rolling temperature is between 890℃; after rolling, the rolling waste heat is used for an online heat treatment process, the cooling start temperature is 760℃, and the cooling rate is 2.5℃ / s. When the final cooling temperature is cooled to 270℃, it is heated to 340℃ at 7℃ / s, kept warm for 200min, then cooled to 270℃ at 2.0℃ / s, kept warm for 480min, and finally cooled to room temperature at a rate of 1.0-1.5℃ / s. The carbide-free bainite / martensite composite rail produced by this method has a tensile strength of 1361MPa, an elongation of 15%, a cross-sectional shrinkage of 53%, a room temperature impact of 98J, a -40℃ low temperature impact of 50J, and a structure containing 55% bainitic ferrite, 39% martensite and 6% residual austenite. It is particularly suitable for heavy-duty railway rails or turnout railway rails.

[0033] Example 4 A carbide-free bainite / martensite composite rail and a preparation method thereof, which is designed with a carbon content of 0.2-0.30%, specifically, C 0.28%; Si 1.8%; Mn 2.1%; P 0.015%; S 0.06%; Cr 0.9%; No 0.45%; V0.06%; Ni 0.50%; Al 0.003%; gas content includes: H 0.9ppm; O 8ppm; N 45ppm. After smelting and casting, austenite homogenization is performed at 1260°C for 150 minutes, and after dephosphorization of the steel billet, the steel billet is universally rolled into a rail shape, and the final rolling temperature is between 920°C; after rolling, the rolling waste heat is used for an online heat treatment process, the cooling start temperature is 780°C, and the cooling rate is 2.8°C / s. When the final cooling temperature is cooled to 280℃, heat to 360℃ at 9℃ / s, keep warm for 220min, then reduce to 280℃ at 2.5℃ / s, keep warm for 550min, and finally cool to room temperature at 1.0-1.5℃ / s.

[0034] The carbide-free bainite / martensite composite rail produced by this method has a tensile strength of 1461MPa, an elongation of 16%, a cross-sectional shrinkage of 55%, a room temperature impact of 102J, a -40℃ low temperature impact of 55J, and a structure containing 50% bainite ferrite, 40% martensite and 10% residual austenite. It is particularly suitable for heavy-duty railway rails or turnout railway rails.

[0035] Example 5 A carbide-free bainite / martensite composite rail and a preparation method thereof, which is designed with a carbon content of 0.2-0.30%, specifically, C 0.3%; Si 2.0%; Mn 2.5%; P 0.015%; S 0.06%; Cr 1.5%; No 0.60%; V0.08%; Ni 0.70%; Al 0.003%; gas content includes: H 0.8ppm; O 6ppm; N 40ppm. After smelting and casting, 1280℃ austenite homogenization is adopted for 180min, and after dephosphorization of the steel billet, it is universally rolled into a rail shape, and the final rolling temperature is between 950℃; after rolling, the rolling waste heat is used for an online heat treatment process, the cooling start temperature is 800℃, and the cooling rate is 3.0℃ / s. When the final cooling temperature is cooled to 300℃, it is heated to 400℃ at 10℃ / s, kept warm for 240min, then cooled to 300℃ at 3.0℃ / s, kept warm for 600min, and finally cooled to room temperature at 1.0-1.5℃ / s. The carbide-free bainite / martensite composite rail produced by this method has a tensile strength of 1520MPa, an elongation of 17%, a cross-sectional shrinkage of 62%, a room temperature impact of 120J, a low temperature impact of -40℃ of 60J, and the organization contains 50% bainite ferrite, 45% martensite and 5% residual austenite. It is particularly suitable for heavy-duty railway rails or turnout railway rails.

[0036] In order to prove the technical effect of the technical solution of the present invention, the present invention also discloses two comparative examples, whose process operations are the same as those of Examples 1-5, the chemical composition of the rails is shown in Table 1, the heating and rolling process parameters are shown in Table 2, the process parameters of the heat treatment process are shown in Table 3, and the tensile properties of the obtained rails are shown in Table 4.

[0037] Table 1 Chemical composition of rails

[0038] Table 2 Heating and rolling process parameter control

[0039] Table 3 Heat treatment process

[0040] Table 4

[0041] In summary, the carbide-free bainite / martensite complex phase rail and the preparation method thereof disclosed in the embodiments of the present invention control the normalizing + carbon partitioning + tempering heat treatment process to obtain a carbide-free bainite / martensite complex phase rail with excellent toughness. Based on the strength and toughness characteristics of carbide-free bainite and bainite / martensite complex phase structure, within the carbon content range of 0.20-0.30%, through appropriate alloying elements, assisted by appropriate hot deformation and heat treatment process, a new carbide-free bainite / martensite complex phase structure and rail steel with better toughness are obtained, which have good market application prospects.

[0042] So far, various embodiments of the present disclosure have been described in detail. In order to avoid obscuring the concept of the present disclosure, some details known in the art are not described. Based on the above description, those skilled in the art can fully understand how to implement the technical solution disclosed here.

[0043] Although some specific embodiments of the present disclosure have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present disclosure. It should be understood by those skilled in the art that the above embodiments may be modified or some technical features may be replaced by equivalents without departing from the scope and spirit of the present disclosure. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict.

Claims

1. A method for producing a carbide-free bainite / martensite composite rail, characterized in that: include: Step 1: subjecting the steel billet obtained by smelting and casting according to the designed composition to austenite homogenization treatment at 1200-1280° C. and then rolling to obtain a rail intermediate; Step 2: subjecting the rail intermediate to a first cooling treatment, cooling the rail intermediate to 250-300° C.; Step 3: performing a first heating treatment, heating to 300-400° C. and then keeping the temperature for a first predetermined time; Step 4: performing a second cooling process, cooling to 250-300°C and then keeping the temperature for a second predetermined time; Step 5: performing a third cooling process to cool to room temperature.

2. The method for producing a carbide-free bainite / martensite composite rail according to claim 1, characterized in that: In step 1, keep warm at 1200-1280°C for 60-180 minutes.

3. The method for producing a carbide-free bainite / martensite composite rail according to claim 1, characterized in that: In step 1, the final cooling temperature of rolling is 850-950°C.

4. The method for producing a carbide-free bainite / martensite dual-phase rail according to claim 1, characterized in that: In step 2, the first cooling treatment has a start temperature of 650-800°C and a cooling rate of 1.5-3.0°C / s.

5. The method for producing a carbide-free bainite / martensite dual-phase rail according to claim 1, characterized in that: In step three, the heating rate of the first heating treatment is 5-10°C / s, and the first predetermined time is 120-240.

6. The method for producing a carbide-free bainite / martensite dual-phase rail according to claim 1, characterized in that: In step 4, the cooling rate of the second cooling treatment is 1.5-3.0°C / s, and the second predetermined time is 240-600min.

7. The method for producing a carbide-free bainite / martensite dual-phase rail according to claim 1, characterized in that: In step 5, the cooling rate of the third cooling treatment is 1.0-1.5°C / s.

8. The method for producing a carbide-free bainite / martensite dual-phase rail according to claim 1, characterized in that: The composition is designed to use a carbon content of 0.20-0.30%.

9. A carbide-free bainite / martensite duplex rail, characterized in that: The rail is produced by the method for producing carbide-free bainite / martensite complex phase rail according to any one of claims 1 to 8.

10. The carbide-free bainite / martensite dual-phase rail according to claim 9, characterized in that: Tensile strength ≥1280MPa, elongation ≥12%, section shrinkage ≥45%; Or, shock at room temperature ≥80J, shock at -40℃ ≥40J; Alternatively, the structure contains 40-55% bainitic ferrite, 35-50% martensite and 5-15% retained austenite.

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