Method for manufacturing rail with low residual stress and corrosion resistance

Abstract

The application discloses a preparation method of a rail with low residual stress and corrosion resistance, and comprises the following steps: S1, cooling the steel rail after rolling; S2, adopting light pressing down to straighten the steel rail after the cooling for the first time; S3, heating the rail bottom of the steel rail after the first time of straightening; and S4, using multiple pairs of straightening rollers to straighten the steel rail after the heating for the second time, wherein each pair of straightening rollers symmetrically straightens the rail head and the rail bottom. The application can reduce the residual stress of the rail bottom and improve the corrosion resistance of the rail.

Description

Technical Field

[0001] This invention relates to the field of rail manufacturing technology, specifically to a method for manufacturing a corrosion-resistant rail with low residual stress at the rail base. Background Technology

[0002] As a key track component that directly supports train operation, rails are repeatedly subjected to train loading and impact during service. Under dynamic bending, the rail base experiences significant tensile stress along the longitudinal direction of the rail. Simultaneously, the straightening process during rail production introduces residual longitudinal tensile stress into the rail base. TB / T 2344.1-2020 stipulates that this value must not exceed 250 MPa; in practice, this value ranges from approximately 180 to 250 MPa for various rail grades.

[0003] Under the combined action of the tensile stress at the rail base caused by the bending action of train operation and the residual tensile stress introduced by the straightening process, fatigue cracks are easily initiated at the rail base. This is especially true when there is damage such as rust at the rail base, which makes the rail more prone to rail base damage and even breakage. Due to the special nature of track laying, it is difficult to inspect and maintain the rail base after the rails are laid. In some tunnels and high-humidity railway lines, the existing rail bases of various types of rails are severely corroded, and rail base breakage is frequent, which has seriously threatened the safety of train operation. Therefore, it is necessary to study a method for preparing corrosion-resistant rails with low residual stress at the rail base. Summary of the Invention

[0004] The main objective of this invention is to provide a method for preparing a corrosion-resistant rail with low residual stress at the rail base, in order to solve the problem that existing rail bases are prone to fracture and severe corrosion under residual stress.

[0005] According to one aspect of the present invention, a method for preparing a low residual stress corrosion-resistant rail at the rail base is provided, comprising the following steps:

[0006] S1, cooling the rolled rail;

[0007] S2, The cooled rail is straightened for the first time by lightly pressing down;

[0008] S3, heating the bottom of the rail after the first straightening;

[0009] S4, using multiple pairs of straightening rollers to perform a second straightening of the heated rail, wherein each pair of straightening rollers symmetrically straightens the rail head and rail bottom.

[0010] According to an embodiment of the present invention, in step S2, a horizontal-vertical composite straightening machine is used for straightening. The horizontal-vertical composite straightening machine includes four straightening rollers arranged along the length of the rail with straightening forces as follows: 1400-1600kN, 1200-1400kN, 800-1000kN, and 100-200kN.

[0011] According to one embodiment of the present invention, in step S3, induction heating is performed at a temperature of 300-350°C for a duration of 60-120 seconds.

[0012] According to one embodiment of the present invention, in step S4, the second straightening is performed using three pairs of straightening rollers, wherein the straightening forces of the three pairs of straightening rollers are 500-600kN, 300-400kN, and 100-200kN respectively along the length of the rail.

[0013] According to an embodiment of the present invention, step S1 includes:

[0014] Step S11: Accelerate cooling of the rail head and rail base after rolling; wherein the cooling rate of the rail head is 5-8℃ / s and the temperature is cooled to 420-450℃, the cooling rate of the rail base is 2-5℃ / s and the temperature is cooled to 450-480℃, and the temperature difference between the rail head and rail base after accelerated cooling is less than 20℃.

[0015] Step S12: Allow the accelerated-cooled rails to cool naturally to room temperature in the air.

[0016] According to one embodiment of the present invention, in step S11, the rail head is cooled by spraying water mist and the rail bottom is cooled by spraying air.

[0017] According to one embodiment of the present invention, before step S1, the method further includes: using the residual heat from rolling and a reheating device to control the temperature of the rail head and rail base at 790-830°C.

[0018] According to one embodiment of the present invention, the chemical composition of the steel billet used to form the rail, by mass percentage, is as follows: C: 0.55%–0.75%; Si: 0.40%–0.90%; Mn: 0.40%–0.80%; Cr: 0.25%–0.65%; Cu: 0.20%–0.50%; Ni: 0.15%–0.35%; Mn+Cr: 1.10%–1.50%; Cu+Ni: 0.40%–0.70%; at least one of V, Nb, and Ti; the remainder being Fe and unavoidable impurities; wherein, when V is included, the V content is 0.02%–0.15%; when Nb is included, the Nb content is 0.01%–0.08%; and when Ti is included, the Ti content is 0.001%–0.030%.

[0019] According to one embodiment of the present invention, the longitudinal residual stress at the center of the rail base of the low residual stress corrosion-resistant rail is less than or equal to 150 MPa, and the residual stress fluctuation range is less than or equal to 30 MPa.

[0020] In the method for preparing a low residual stress corrosion-resistant rail according to an embodiment of the present invention, the residual stress introduced by the first straightening is reduced by using a light pressing method; the residual stress on the surface of the rail base after the first straightening is eliminated to a certain extent by heating the rail base after the first straightening; and the second straightening (symmetrically straightening the rail head and rail base) introduces compressive stress on the rail surface to counteract the original residual tensile stress, thereby further reducing the residual stress of the rail. By reducing the residual stress, the corrosion resistance of the rail can be improved to a certain extent. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A flowchart illustrating a method for preparing a low residual stress corrosion-resistant rail according to an embodiment of the present invention is shown. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0024] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0025] Figure 1 A flowchart illustrating a method for preparing a low residual stress corrosion-resistant rail according to an embodiment of the present invention is shown, as follows: Figure 1 As shown, the method includes the following steps:

[0026] S1, cooling the rolled rail;

[0027] S2, The cooled rail is straightened for the first time by lightly pressing down;

[0028] S3, heating the bottom of the rail after the first straightening;

[0029] S4, using multiple pairs of straightening rollers to perform a second straightening of the heated rail, wherein each pair of straightening rollers symmetrically straightens the rail head and rail bottom.

[0030] In embodiments of the present invention, the residual stress introduced by the first straightening process using a light pressing method can be reduced. Heating the rail base after the first straightening can eliminate residual stress on the rail base surface to some extent. A second straightening process (symmetrically straightening the rail head and base) introduces compressive stress into the rail surface, offsetting the original residual tensile stress and further reducing residual stress. Reducing residual stress can improve the corrosion resistance of the rail to some extent.

[0031] In some embodiments, in step S2, straightening is performed using a horizontal-vertical composite straightening machine (e.g., vertical straightening). The horizontal-vertical composite straightening machine includes four straightening rollers arranged along the length of the rail with straightening forces of 1400–1600 kN, 1200–1400 kN, 800–1000 kN, and 100–200 kN, respectively. Thus, a gentle pressing method is achieved by reducing the straightening force. In the prior art, the straightening force can reach up to 2000 kN during straightening. This invention reduces the residual stress introduced by straightening by reducing the straightening force.

[0032] In some embodiments, in step S3, induction heating is performed at a temperature of 300–350°C for a duration of 60–120 seconds. Heating can, to some extent, eliminate residual stress on the surface of the rail base. If the heating temperature is below 300°C or the heating time is less than 60 seconds, the effect of eliminating residual stress is not significant; when the heating temperature is above 350°C or the heating time is greater than 120 seconds, it may cause coarsening of the rail structure and reduce rail performance.

[0033] In some embodiments, in step S4, the multiple pairs of straightening rollers can be arranged along the length of the rail. Two straightening rollers in each pair are symmetrically arranged on the outer sides of the rail head and rail bottom along the rail height direction, used to symmetrically straighten the rail head and rail bottom, introducing compressive stress into the rail surface to counteract the original residual tensile stress. In some embodiments, in step S4, the second straightening (e.g., vertical straightening) is performed using three pairs of straightening rollers. The straightening forces of the three pairs of straightening rollers along the rail length direction are successively 500–600 kN, 300–400 kN, and 100–200 kN. If the straightening force of each pair of straightening rollers is below the lower limit of the numerical range, the effect of reducing residual stress is not significant; if the straightening force of each pair of rollers is above the upper limit of the numerical range, it may cause defects in the rail surface structure, affecting the rail quality.

[0034] In some embodiments, step S1 includes: step S11, accelerating the cooling of the rail head and rail base of the rolled rail; wherein the cooling rate of the rail head is 5-8°C / s and the rail base is cooled to a temperature of 420-450°C, the cooling rate of the rail base is 2-5°C / s and the rail base is cooled to a temperature of 450-480°C, and the temperature difference between the rail head and rail base after accelerated cooling is less than 20°C; step S12, naturally cooling the accelerated-cooled rail to room temperature in air. In some embodiments, in step S11, the rail head is cooled by spraying water mist, and the rail base is cooled by spraying air.

[0035] The rail head area is larger than the rail base area, and the rail head has a larger heat capacity. During natural cooling, the different degrees of cooling deformation cause rail bending. By employing different accelerated cooling processes, after the accelerated cooling process ends, the rail base temperature (450–480℃) is slightly higher than the rail head temperature (420–450℃), with a temperature difference of less than 20℃. This helps reduce the difference in cooling deformation between the rail head and rail base during subsequent natural cooling, improving rail straightness. Accelerated cooling is discontinued because temperatures below 420℃ may produce abnormal martensitic structures.

[0036] In some embodiments, before step S1, the method further includes: using the residual heat from rolling and a reheating device to control the temperature of the rail head and rail base at 790-830°C, thereby preparing for the subsequent step-by-step cooling of the rail head and rail base. If the temperature is below 790°C, abnormal martensitic structure may be generated during the subsequent accelerated cooling process. If the temperature is too high, the strength of the rail will be reduced and it will not meet the usage requirements.

[0037] In some embodiments, the chemical composition of the steel billet used to form the rail, by mass percentage, is as follows: C: 0.55%–0.75%; Si: 0.40%–0.90%; Mn: 0.40%–0.80%; Cr: 0.25%–0.65%; Cu: 0.20%–0.50%; Ni: 0.15%–0.35%; Mn+Cr: 1.10%–1.50%; Cu+Ni: 0.40%–0.70%; at least one of V, Nb, and Ti; the remainder being Fe and unavoidable impurities; wherein, when V is included, the V content is 0.02%–0.15%; when Nb is included, the Nb content is 0.01%–0.08%; and when Ti is included, the Ti content is 0.001%–0.030%. By employing such a chemical composition, the corrosion resistance of the rail can be further improved.

[0038] Carbon (C) is the most important element for achieving a good balance of strength and toughness and comprehensive mechanical properties in steel. Under the rail preparation method described in this invention, when the carbon content is below 0.55% by weight, the strengthening effect cannot be fully realized, resulting in poor rail strength and fatigue resistance; when the carbon content is above 0.75% by weight, the rail's toughness and plasticity decrease, failing to achieve the goal of improving the rail's contact fatigue performance. Therefore, this invention limits the carbon content range to 0.55–0.75% by weight.

[0039] Silicon (Si) is typically dissolved in ferrite in steel, which can improve the material's strength and wear resistance. Under the rail manufacturing method described in this invention, when the silicon content is below 0.40% by weight, the rail's strength and wear resistance cannot meet the requirements of railway line service. Furthermore, silicon is a crack-sensitive element in rail steel; a content above 0.90% by weight will cause a deterioration in fatigue fracture performance. Therefore, this invention limits the silicon content to the range of 0.40–0.90% by weight.

[0040] Manganese (Mn) plays a role in improving hardenability in steel. Under the conditions of the rail preparation method described in this invention, when the manganese content is below 0.40% by weight, the hardenability of the rail is insufficient, and the strength and fatigue performance of the finished rail cannot meet the service requirements of the railway line; when the manganese content is above 0.80% by weight, the hardenability of the rail is too strong, and heat treatment will cause abnormal structures such as martensite. Therefore, this invention limits the silicon content to the range of 0.40–0.80% by weight.

[0041] Chromium (Cr) also plays a role in improving hardenability in steel, and also has a certain antioxidant effect. It can improve the strength and corrosion resistance of steel. Under the conditions of the rail preparation method described in this invention, when the chromium content is below 0.25%, the rail strength is insufficient and cannot meet the service requirements of the line; when the chromium content is above 0.65%, the hardenability is too strong, and abnormal structures are prone to appear in the rail. Therefore, this invention limits the chromium content range to 0.25–0.65% by weight.

[0042] Copper (Cu) primarily functions as an antioxidant and corrosion resistant agent in steel. Under the conditions of the rail preparation method described in this invention, when the copper content is below 0.20%, the improvement in corrosion resistance of the rail is not significant. When the copper content is above 0.50%, copper embrittlement easily occurs, leading to a deterioration in rail performance. Therefore, this invention limits the copper content to the range of 0.20–0.50% by weight.

[0043] Nickel (Ni) in steel can suppress copper embrittlement and improve corrosion resistance. Based on the copper content of the rails described in this invention, when the nickel content is below 0.15%, the effect of suppressing copper embrittlement is not significant. When the nickel content is above 0.35%, it is detrimental to rail welding.

[0044] Niobium (Nb), vanadium (V), and titanium (Ti) in steel mainly react with carbon and nitrogen to form carbonitrides, which inhibit grain growth and improve the strength and toughness of the rail. However, excessive content can affect weldability and reduce the plasticity of the rail.

[0045] In some embodiments, under room temperature and normal air conditions, the longitudinal residual stress at the center of the rail base of the low residual stress corrosion-resistant rail prepared by the above method is less than or equal to 150 MPa, and the residual stress fluctuation range is less than or equal to 30 MPa. This rail is suitable for various lines, especially railway lines in humid environments where rails are prone to corrosion.

[0046] In summary, the present invention significantly reduces the longitudinal residual stress at the bottom of the rail through specific production processes (especially steps S2 to S4), and improves the corrosion resistance of the rail by using specific chemical components.

[0047] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for preparing a corrosion-resistant steel rail with low residual stress at the rail base, characterized in that, Includes the following steps: S1, cooling the rolled rail; S2, The cooled rail is straightened for the first time by applying light pressure; S3, the bottom of the rail after the first straightening is heated; S4, using multiple pairs of straightening rollers to perform a second straightening of the heated rail, wherein each pair of straightening rollers symmetrically straightens the rail head and rail bottom; In step S2, a horizontal-vertical composite straightening machine is used for straightening. The horizontal-vertical composite straightening machine includes four straightening rollers arranged along the length of the rail with straightening forces as follows: 1400-1600kN, 1200-1400kN, 800-1000kN, and 100-200kN. In step S3, induction heating is performed at a temperature of 300–350°C for a duration of 60–120 seconds. In step S4, the second straightening is performed using three pairs of straightening rollers, with the straightening forces of the three pairs of straightening rollers being 500-600kN, 300-400kN, and 100-200kN respectively along the length of the rail.

2. The method according to claim 1, characterized in that, Step S1 includes: Step S11: Accelerate cooling of the rail head and rail base after rolling; wherein the cooling rate of the rail head is 5-8℃ / s and the temperature is cooled to 420-450℃, the cooling rate of the rail base is 2-5℃ / s and the temperature is cooled to 450-480℃, and the temperature difference between the rail head and rail base after accelerated cooling is less than 20℃. Step S12: Allow the accelerated-cooled rails to cool naturally to room temperature in the air.

3. The method according to claim 2, characterized in that, In step S11, the rail head is cooled by spraying water mist, and the rail base is cooled by spraying air.

4. The method according to claim 1, characterized in that, Before step S1, the method further includes: using the residual heat from rolling and a reheating device to control the temperature of the rail head and rail base at 790-830°C.

5. The method according to claim 1, characterized in that, The chemical composition of the steel billet used to form the rail, by mass percentage, is as follows: C: 0.55%–0.75%; Si: 0.40%–0.90%; Mn: 0.40%–0.80%; Cr: 0.25%–0.65%; Cu: 0.20%–0.50%; Ni: 0.15%–0.35%; Mn+Cr: 1.10%–1.50%; Cu+Ni: 0.40%–0.70%; at least one of V, Nb, and Ti; the remainder being Fe and unavoidable impurities; wherein, when V is included, the V content is 0.02%–0.15%; when Nb is included, the Nb content is 0.01%–0.08%; and when Ti is included, the Ti content is 0.001%–0.030%.

6. The method according to claim 1, characterized in that, The longitudinal residual stress at the center of the rail base of the low residual stress corrosion-resistant steel rail is less than or equal to 150 MPa, and the residual stress fluctuation range is less than or equal to 30 MPa.

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