A scratch-resistant and high-strength steel rail and its preparation method

Abstract

A scratch-resistant and highly tough steel rail has the following chemical composition and proportions: by mass percentage, C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 0.30-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30%, and at least one of V, Nb, and Ti, including V: 0.02-0.15%, Ti: 0.001-0.030%, and Nb: 0.01-0.08%, with the remainder being Fe and unavoidable impurities. Furthermore, the present invention also relates to a method for preparing a scratch-resistant and highly tough steel rail using the above chemical composition and proportions. The present invention resolves the contradiction between the mechanical properties and scratch resistance of the steel rail, achieving a good match between the rail's strength, toughness, and scratch resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of rail manufacturing, and in particular to a high-strength and tough rail with excellent abrasion resistance and a preparation method thereof. Background Art

[0002] Rails are one of the most core components of rail transit wheel-rail systems. With the construction of new rail transit projects and the ultimate pursuit of safety, comfort, efficiency, and longevity in rail transit, the performance and quality of existing rails face new challenges. As rails strive for longer life, they must possess not only excellent wear and fatigue resistance but also excellent abrasion resistance.

[0003] Rail abrasion is one of the main forms of rail damage on high-speed and heavy-load railways at home and abroad, and is found on almost all major lines. Rail abrasion seriously affects the smoothness of the track and may cause the rail surface to peel off, be dented, or develop fatigue cracks in the cross section. If not handled in a timely manner, it will increase the cost of rail maintenance and repair, and there is also a risk of rail breakage. Rail abrasion usually occurs when the locomotive starts or brakes. Due to abnormal sliding between the wheel and rail, a large amount of frictional heat is generated, and a deep white layer of structure usually forms on the surface of the rail. The abrasion process involves rapid heat exchange. The pearlite structure is first heated to transform into austenite, and then rapidly cooled to transform into white martensite. The formation process of the abrasion white layer structure is essentially the process of quenching the rail base material to form martensite structure. Therefore, the abrasion resistance of the rail can generally be evaluated based on the martensite forming ability of the rail steel and the ability to resist contact fatigue damage after the abrasion white layer is formed on the rail surface. The higher the critical cooling rate of rail steel, the better the rail's anti-scratch performance; the higher the austenitizing temperature of rail steel, the less likely it is to form a white layer of scratches during the wheel-rail friction process, and the thinner the thickness of the white layer of scratches, the better the rail's anti-scratch performance; for rail steels of the same composition, the higher the hardness of the rail base material, the smaller the hardness difference and gradient between the martensitic white layer and the base material, the higher the white layer's ability to resist peeling, and the stronger the rail's resistance to fatigue fracture.

[0004] Patent document CN 112226697 A discloses a scratch-resistant rail and its production method. This patent further reduces the carbon content of the rail surface by reducing the carbon content of the rail steel and using a long-term heating method to make the depth of the rail decarburization layer greater than 0.5mm, thereby obtaining a high resistance to martensite formation. At the same time, the interior of the rail maintains high strength. Although the method described in this patent improves the scratch resistance of the rail surface, due to its severe decarburization, the strength and hardness of the rail are reduced, and its wear resistance and contact fatigue performance will be greatly reduced, which will quickly lead to surface peeling and block damage, reducing the service life of the rail. At the same time, this method only improves the scratch resistance of the very shallow surface layer of the rail. After the surface layer is worn, the scratch resistance of the rail will decrease.

[0005] Therefore, in order to solve the above problems, it is desirable to provide a steel rail that is resistant to scratches and has high strength and toughness, and a method for manufacturing the same. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention aims to solve the technical problem that the existing rail composition design and production process cannot simultaneously improve strength and scratch resistance. Therefore, the present invention provides a scratch-resistant and high-strength rail and a method for preparing the same.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] According to one aspect of the present invention, a scratch-resistant and high-strength steel rail is provided, wherein the chemical composition and proportion of the steel rail are as follows: by mass percentage, C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 0.30-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30% and at least one of V, Nb and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, and the remainder is Fe and unavoidable impurities.

[0009] In one embodiment of the present invention, the ratio of Si to Cr satisfies the following relationship: 1.20%≤Si+Cr≤1.65% by mass.

[0010] In one embodiment of the present invention, the proportion of Mn is 0.40-0.70% by mass.

[0011] In one embodiment of the present invention, the ratio of Cu to Ni satisfies the following relationship: 0.30%≤Cu+Ni≤0.50% by mass.

[0012] According to another aspect of the present invention, a method for preparing a scratch-resistant and high-strength rail is provided, comprising the following steps:

[0013] 1) Controlling the chemical composition and proportion of the molten steel as follows: by weight percentage, C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 0.30-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30% and at least one of V, Nb and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, and the remainder being Fe and unavoidable impurities;

[0014] 2) The molten steel is continuously cast in a tundish, and a multi-stage electromagnetic stirring, low superheat and high casting speed process is used to obtain a low-segregation steel billet;

[0015] 3) The steel billet is placed in a walking beam furnace for heating and then universally rolled into a rail;

[0016] 4) Accelerated cooling is performed from the austenite zone of the rail using compressed air at an accelerated cooling rate of 5.0-6.5°C / s. After cooling to 540-570°C, the rail is naturally cooled.

[0017] In one embodiment of the present invention, in step 2), a low-segregation steel billet is prepared from blast furnace molten iron through converter smelting, LF refining, electric heating and continuous casting; the C segregation in the narrow surface 50-150 mm region of the low-segregation billet is 0.96-1.04, the Mn segregation is 0.97-1.03 and the Cr segregation is 0.97-1.03.

[0018] In one embodiment of the present invention, the continuous casting process of low segregation steel billets adopts multi-stage composite electromagnetic stirring of crystallizer electromagnetic stirring, secondary cooling electromagnetic stirring and solidification end electromagnetic stirring, the casting superheat is 12-20°C, and the billet pulling speed is 0.82-0.95m / min.

[0019] In one embodiment of the present invention, in step 3), the heating process of the steel billet is divided into three stages: in the first stage, the furnace temperature of the heating furnace is 750-950°C, and the heating time is 50-70 minutes; in the second stage, the furnace temperature of the heating furnace is 1100-1280°C, and the heating time is 70-100 minutes; in the third stage, the furnace temperature of the heating furnace is 1200-1230°C, and the heating time is 50-90 minutes; and the time when the furnace temperature during the heating process of the steel billet is controlled to be greater than 1200°C is not less than 90 minutes.

[0020] In one embodiment of the present invention, in step 3), the universal rolling includes universal rough rolling, intermediate rolling and finish rolling.

[0021] In one embodiment of the present invention, in step 4), the accelerated cooling rate is 4.5-6.0° C. / s, and the mixture is cooled to 430-470° C. and then naturally cooled.

[0022] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0023] The present invention increases the austenitization temperature of the pearlite structure during the heating process of the rail abrasion through specific composition design, increases the threshold for the occurrence of abrasion, and reduces the thickness of the abrasion white layer; the present invention adopts a combination of multi-stage composite electromagnetic stirring, low superheat casting and high pulling speed technology to obtain low-segregation ingots, broadens the rail heat treatment process window, and thus can implement high cooling rate online heat treatment, fully giving play to the role of alloy elements and heat treatment technology in synergistically improving rail performance, obtaining strong and tough mechanical properties, and improving abrasion resistance, thus resolving the contradiction between mechanical properties and abrasion resistance and achieving a good match between rail strength, toughness and abrasion resistance. DETAILED DESCRIPTION

[0024] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in the present invention, it is readily apparent to those skilled in the art that various modifications are feasible without departing substantially from the teachings of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other replacements, modifications, variations, and deletions may be made to the design, operating conditions, and parameters of the following exemplary embodiments.

[0025] The present invention provides a scratch-resistant and high-strength steel rail, wherein the chemical composition and proportion of the steel rail are as follows: by mass percentage, C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 0.30-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30% and at least one of V, Nb and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, and the remainder is Fe and unavoidable impurities.

[0026] The invention increases the austenitization temperature of the pearlite structure during the rail abrasion process by means of a specific component design, thereby increasing the threshold for abrasion occurrence and reducing the thickness of the abrasion white layer.

[0027] In the above rail, the ratio of Si to Cr satisfies, by mass percentage, 1.20%≤Si+Cr≤1.65%; the ratio of Mn is 0.40-0.70%; and the ratio of Cu to Ni satisfies, 0.30%≤Cu+Ni≤0.50%.

[0028] In addition, the present invention also provides a method for preparing a scratch-resistant and high-toughness steel rail, comprising the following steps:

[0029] 1) Controlling the chemical composition and proportion of the molten steel as follows: by weight percentage, C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 0.30-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30% and at least one of V, Nb and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, and the remainder being Fe and unavoidable impurities;

[0030] 2) The molten steel is continuously cast in a tundish, and a multi-stage electromagnetic stirring, low superheat and high casting speed process is used to obtain a low-segregation steel billet;

[0031] 3) The steel billet is placed in a walking beam furnace for heating and then universally rolled into a rail;

[0032] 4) Accelerated cooling is performed from the austenite zone of the rail using compressed air at an accelerated cooling rate of 5.0-6.5°C / s. After cooling to 540-570°C, the rail is naturally cooled.

[0033] The method of the present invention increases the austenitization temperature of the pearlite structure during the heating process of the rail abrasion through specific component design, increases the threshold for the occurrence of abrasion, and reduces the thickness of the abrasion white layer; the method of the present invention adopts multi-stage composite electromagnetic stirring, low superheat casting and high pulling speed technology to obtain low-segregation casting billets, broadens the rail heat treatment process window, and thus can implement high cooling rate online heat treatment, give full play to the role of alloy elements and heat treatment technology in synergistically improving rail performance, obtain strong and tough mechanical properties, and improve abrasion resistance, thereby resolving the contradiction between mechanical properties and abrasion resistance and achieving a good match between rail strength, toughness and abrasion resistance.

[0034] In the above preparation method, in step 2), the low-segregation steel billet is prepared from blast furnace molten iron through converter smelting, LF refining, electric heating and continuous casting; the C segregation degree in the narrow surface 50-150 mm region of the low-segregation billet is 0.96-1.04, the Mn segregation degree is 0.97-1.03 and the Cr segregation degree is 0.97-1.03.

[0035] In the above preparation method, the continuous casting process of low segregation steel billets adopts multi-stage composite electromagnetic stirring of crystallizer electromagnetic stirring, secondary cooling electromagnetic stirring and solidification end electromagnetic stirring, the casting superheat is 12-20°C, and the billet pulling speed is 0.82-0.95m / min.

[0036] In the above preparation method, in step 3), the heating process of the steel billet is divided into three stages: in the first stage, the furnace temperature of the heating furnace is 750-950°C, and the heating time is 50-70 minutes; in the second stage, the furnace temperature of the heating furnace is 1100-1280°C, and the heating time is 70-100 minutes; in the third stage, the furnace temperature of the heating furnace is 1200-1230°C, and the heating time is 50-90 minutes; and the furnace temperature during the heating process of the steel billet is controlled to be greater than 1200°C for no less than 90 minutes.

[0037] In the above preparation method, in step 3), the universal rolling includes universal rough rolling, intermediate rolling and finish rolling.

[0038] In the above preparation method, in step 4), preferably, the accelerated cooling rate is 4.5-6.0° C. / s, and the mixture is cooled to 430-470° C. and then naturally cooled.

[0039] The above technical solutions of the present invention are described in detail below through specific embodiments.

[0040] The main methods for improving rail steel strength include alloying, heat treatment, and alloying combined with heat treatment. Alloying combined with heat treatment is the most common and effective method. For most alloying elements, their addition shifts the rail steel's cooling C curve to the right, reducing the critical cooling rate for martensitic transformation. This increases the ability to form a white layer at the expense of anti-scratch performance. Under the current composition and production process, further increasing rail strength will inevitably reduce anti-scratch performance.

[0041] Therefore, in the present invention, through specific composition design, combined with smelting and heating processes, segregation in the ingot and rail is reduced, the critical cooling rate for martensitic transformation is significantly increased, and the process window for rail heat treatment is widened. This allows for high-cooling-rate online heat treatment, fully leveraging the synergistic effect of alloying elements and heat treatment processes on improving rail performance. Furthermore, through specific alloy composition design, the A1 and A3 temperatures of the rail are increased, further enhancing the rail's anti-scratch performance. This invention improves rail performance while maintaining the same overall alloy content level, or reduces the overall alloy content while maintaining existing performance, thereby improving rail anti-scratch performance.

[0042] The present invention provides a scratch-resistant and high-strength steel rail. The chemical composition of the steel rail matrix consists of the following elements in weight percentage: C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 0.30-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30% and at least one of V, Nb and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, and the rest is Fe and unavoidable impurities.

[0043] Preferably, in the above rail, the mass percentage contents of Si and Cr satisfy the relationship: 1.20%≤Si+Cr≤1.65%, the mass percentage content of Mn is: 0.40-0.70%, and the mass percentage contents of Cu and Ni satisfy the relationship: 0.30%≤Cu+Ni≤0.50%.

[0044] The present invention provides a scratch-resistant and high-strength rail, whose eutectoid transformation temperature A1 is above 780°C, A3 is above 810°C, the critical cooling rate of martensitic transformation is greater than 6.0°C / s, and after the wheel-rail scratch test, the hardness ratio of the scratch white layer to the rail base material is less than 1.80.

[0045] The present invention also provides a method for preparing a scratch-resistant and high-toughness steel rail, the method comprising the following steps:

[0046] (1) Preparation of molten steel

[0047] Molten steel having the following composition is obtained by smelting blast furnace molten iron in a converter, refining by LF, and vacuum degassing: C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 0.30-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30% and at least one of V, Nb, and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, and the remainder is Fe and unavoidable impurities.

[0048] (2) Preparation of low segregation billets or ingots

[0049] The molten steel with the aforementioned composition was placed in a tundish for continuous casting. The continuous casting process employed multi-stage electromagnetic stirring, including mold electromagnetic stirring, secondary cooling electromagnetic stirring, and final solidification electromagnetic stirring. The casting superheat was 12-20°C, and the strand casting speed was 0.82-0.95 m / min. This continuous casting process produced low-segregation strands, with C segregation of 0.96-1.04, Mn segregation of 0.97-1.03, and Cr segregation of 0.97-1.03 in the narrow 50-150 mm region.

[0050] (3) Heating of the ingot

[0051] The ingot containing the aforementioned composition is placed in a walking beam heating furnace for heating. The heating process is divided into three stages: the first stage, the furnace temperature is 750-950°C for 50-70 minutes; the second stage, the furnace temperature is 1100-1280°C for 70-100 minutes; and the third stage, the furnace temperature is 1200-1230°C for 50-90 minutes. The furnace temperature is kept above 1200°C for at least 90 minutes during the heating process. The prolonged high-temperature heating process is intended to fully diffuse segregated elements in the ingot, improve the compositional uniformity of the ingot, and prevent the formation of dotted martensitic structures due to the high cooling rate during the subsequent accelerated cooling heat treatment.

[0052] In order to prevent the problem of serious decarburization on the surface of the billet caused by long-term high-temperature heating of the billet, the surface of the billet is sprayed with high-temperature protective coating before the billet is loaded into the furnace.

[0053] (4) Rail rolling

[0054] After heating, the ingot is rolled into rails through ingot rolling and universal rolling. The starting rolling temperature is 1150℃-1220℃ and the finishing rolling temperature is 880℃-930℃.

[0055] (5) Online heat treatment after rolling

[0056] After rolling, the rails are treated with residual heat. The rail top surface temperature is accelerated from 790-820°C to 430-470°C at a rate of 4.5-6.0°C / s and then cooled naturally.

[0057] In the present invention, the steel billets in the following examples and comparative examples are prepared by methods well known to those skilled in the art from blast furnace molten iron through converter smelting, LF refining, electric heating, and continuous casting.

[0058] Example 1

[0059] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C: 0.53%, Si: 0.63%, Mn: 0.68%, Cr: 0.76%, Cu: 0.30%, Ni: 0.17%, V: 0.09%, and the balance is Fe and other inevitable impurities.

[0060] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0061] The molten steel containing the above-mentioned components, obtained from blast furnace iron through converter smelting, LF refining, and vacuum treatment, is continuously cast in a continuous casting tundish. Electromagnetic stirring is employed in the mold, during secondary cooling, and at the end of solidification. The casting superheat is 13-17°C, and the average casting speed is 0.86 m / min. After cooling and cleaning, the ingots are sprayed with an anti-decarburization coating before being loaded into a walking-beam heating furnace. In the first stage, the furnace temperature averages 836°C over a heating time of 67 minutes; in the second stage, the furnace temperature averages 1250°C over a heating time of 86 minutes; and in the third stage, the furnace temperature averages 1214°C over a heating time of 81 minutes. The ingots undergo blooming rolling, universal primary rolling, universal intermediate rolling, and universal finishing rolling to produce rails, reaching a post-rolling temperature of 904°C. The center temperature of the rail top surface is 826℃ when it enters the rail online heat treatment unit, where it is accelerated cooled to 447℃ at an average speed of 5.7℃ / s and then returns to the cooling bed to cool naturally to room temperature.

[0062] Example 2

[0063] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C: 0.59%, Si: 0.78%, Mn: 0.57%, Cr: 0.52%, Cu: 0.24%, Ni: 0.15%, V: 0.07%, and the balance is Fe and other inevitable impurities.

[0064] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0065] The molten steel containing the above-mentioned components, obtained from blast furnace iron through converter smelting, LF refining, and vacuum treatment, is continuously cast in a continuous casting tundish. Electromagnetic stirring is employed, including in-mold electromagnetic stirring, secondary cooling electromagnetic stirring, and final solidification electromagnetic stirring. The casting superheat is 14-17°C, and the average casting speed is 0.85 m / min. After cooling and cleaning, the ingots are sprayed with an anti-decarburization spray before being loaded into a walking-beam heating furnace. In the first stage, the furnace temperature averages 847°C over a heating time of 71 minutes; in the second stage, the furnace temperature averages 1243°C over a heating time of 91 minutes; and in the third stage, the furnace temperature averages 1207°C over a heating time of 66 minutes. The ingots undergo blooming rolling, universal primary rolling, universal intermediate rolling, and universal finishing rolling to produce rails, reaching a post-rolling temperature of 893°C. The center temperature of the rail top surface is 821℃ when it enters the rail online heat treatment unit, where it is accelerated cooled to 442℃ at an average speed of 5.3℃ / s and then returns to the cooling bed to cool naturally to room temperature.

[0066] Example 3

[0067] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C: 0.63%, Si: 0.76%, Mn: 0.41%, Cr: 0.61%, Cu: 0.22%, Ni: 0.16%, V: 0.05%, and the balance is Fe and other inevitable impurities.

[0068] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0069] The molten steel containing the above-mentioned composition, obtained from blast furnace iron through converter smelting, LF refining, and vacuum treatment, is continuously cast in a continuous casting tundish. Electromagnetic stirring is employed in the mold, during secondary cooling, and at the end of solidification. The casting superheat is 15-18°C, and the average casting speed is 0.84 m / min. After cooling and cleaning, the ingots are sprayed with an anti-decarburization spray before being loaded into a walking-beam heating furnace. In the first stage, the furnace temperature averages 876°C over a heating time of 61 minutes; in the second stage, the furnace temperature averages 1262°C over a heating time of 85 minutes; and in the third stage, the furnace temperature averages 1224°C over a heating time of 92 minutes. The ingots undergo blooming rolling, universal primary rolling, universal intermediate rolling, and universal finishing rolling to produce rails, reaching a post-rolling temperature of 907°C. The center temperature of the rail top surface is 817℃ before entering the rail online heat treatment unit, where it is accelerated cooled to 453℃ at an average speed of 5.0℃ / s and then returned to the cooling bed to cool naturally to room temperature.

[0070] Example 4

[0071] The chemical composition of the rail matrix in this embodiment consists of the following elements in weight percentage: C: 0.58%, Si: 0.95%, Mn: 0.58%, Cr: 0.43%, Cu: 0.21%, Ni: 0.16%, V: 0.08%, and the balance is Fe and other inevitable impurities.

[0072] In this embodiment, the chemical composition of the steel billet is consistent with that of the rail substrate.

[0073] The molten steel containing the above-mentioned composition, obtained from blast furnace iron through converter smelting, LF refining, and vacuum treatment, is continuously cast in a continuous casting tundish. Electromagnetic stirring is employed in the mold, during secondary cooling, and at the end of solidification. The casting superheat is 12-15°C, and the average casting speed is 0.86 m / min. After cooling and cleaning, the ingots are sprayed with an anti-decarburization coating before being loaded into a walking-beam heating furnace. In the first stage, the furnace temperature averages 836°C over a heating time of 65 minutes; in the second stage, the furnace temperature averages 1256°C over a heating time of 89 minutes; and in the third stage, the furnace temperature averages 1215°C over a heating time of 85 minutes. The ingots undergo blooming rolling, universal primary rolling, universal intermediate rolling, and universal finishing rolling to produce rails, reaching a post-rolling temperature of 886°C. The center temperature of the rail top surface is 820℃ when it enters the rail online heat treatment unit, where it is accelerated cooled to 543℃ at a rate of 5.5℃ / s and then returns to the cooling bed to cool naturally to room temperature.

[0074] Comparative Example 1

[0075] The rail substrate in Comparative Example 1 has the following chemical composition by weight: C: 0.73%, Si: 0.35%, Mn: 1.13%, Cr: 0.12%, with the remainder being Fe and other unavoidable impurities. Comparative Example 1 was produced using existing methods. The continuous casting superheat was 26-35°C, and the casting speed was 0.71 m / min. Universal rolling was used, with a universal finishing temperature of 931°C. After rolling, the rail was subjected to in-line heat treatment utilizing residual rolling heat, with accelerated cooling at a rate of 2.1°C / s to 548°C, followed by natural cooling in air to room temperature.

[0076] Comparative Example 2

[0077] The rail substrate in Comparative Example 2 has the following chemical composition by weight: C: 0.77%, Si: 0.61%, Mn: 0.87%, Cr: 0.02%, V: 0.05%, with the remainder being Fe and other unavoidable impurities. Comparative Example 1 was produced using existing methods. The continuous casting superheat was 28-36°C, and the casting speed was 0.71 m / min. Rolling was performed using a universal rolling method, with a universal finishing temperature of 927°C. After rolling, the rail substrate was subjected to in-line heat treatment utilizing residual rolling heat, with accelerated cooling at a rate of 2.6°C / s to 523°C, followed by natural cooling in air to room temperature.

[0078] Comparative Example 3

[0079] The rail substrate in Comparative Example 3 is chemically composed of the following elements by weight: C: 0.59%, Si: 0.78%, Mn: 0.64%, Cr: 0.53%, Cu: 0.24%, Ni: 0.15%, V: 0.06%, with the remainder being Fe and other unavoidable impurities. Comparative Example 3 was produced using existing methods. The continuous casting superheat was 27-35°C, and the casting speed was 0.71 m / min. Rolling was performed using a universal rolling method, with a universal finishing temperature of 926°C. After rolling, the rail substrate was subjected to in-line heat treatment utilizing residual rolling heat, with accelerated cooling at a rate of 2.6°C / s to 527°C, followed by natural cooling in air to room temperature.

[0080] Comparative Example 4

[0081] The chemical composition of the rail substrate in Comparative Example 4 consists of the following elements in weight percentage: C: 0.71%, Si: 0.36%, Mn: 1.04%, Cr: 0.09%, and the balance is Fe and other inevitable impurities.

[0082] In this comparative example, the chemical compositions of the steel billet and the rail substrate are consistent.

[0083] The molten steel containing the above-mentioned composition, obtained from blast furnace iron through converter smelting, LF refining, and vacuum treatment, is continuously cast in a continuous casting tundish. A multi-stage composite electromagnetic stirring system, including electromagnetic stirring in the mold, secondary cooling, and final solidification, is used. The casting superheat is 14-19°C, and the average casting speed is 0.84 m / min. After cooling and cleaning, the ingots are sprayed with an anti-decarburization spray before being loaded into a walking-beam heating furnace. In the first stage, the furnace temperature averages 877°C over a heating time of 65 minutes; in the second stage, the furnace temperature averages 1250°C over a heating time of 76 minutes; and in the third stage, the furnace temperature averages 1219°C over a heating time of 88 minutes. The ingots undergo bloom rolling, universal primary rolling, universal intermediate rolling, and universal finishing rolling to produce rails, reaching a final temperature of 902°C. The center temperature of the rail top surface is 811℃ when it enters the rail online heat treatment unit, where it is accelerated cooled to 463℃ at a rate of 3.2℃ / s and then returns to the cooling bed to cool naturally to room temperature.

[0084] The rails prepared in Examples 1-4 and Comparative Examples 1-4 were tested for yield strength, tensile strength, and elongation according to GB / T 228.1, and for Brinell hardness according to GB / T 231.1. Contact fatigue life testing was conducted on a TIME 8123 rolling contact fatigue testing machine, with a contact stress of 1200 MPa and a slip of 1.0%. Specific microstructure and general mechanical property data from the relevant tests are shown in Tables 1-2 below.

[0085] Table 1 Microstructure and general mechanical properties of Examples and Comparative Examples

[0086]

[0087]

[0088] As can be seen from Table 1 above, the rails produced using the composition and process of the present invention exhibit high strength and hardness while maintaining high elongation after fracture. The A1 temperature reaches above 775°C, the A3 temperature reaches above 819°C, and the critical cooling rate for martensitic transformation reaches above 6.0°C / s. Comparative Example 1 is a U71Mn heat-treated rail produced using conventional processes. Its strength, hardness, and elongation after fracture are all lower than those of the rails produced using the present invention. Its A1 temperature is 726°C, its A3 temperature is 743°C, and its critical cooling rate for martensitic transformation is 3.0°C / s. Comparative Example 2 is a U75V heat-treated rail produced using conventional processes. Although its strength and hardness are slightly higher than those of the rails produced using the present invention, its elongation after fracture is significantly lower than that of the rails produced using the present invention. Its A1 temperature is 726°C, its A3 temperature is 743°C, and its critical cooling rate for martensitic transformation is 3.5°C / s. Comparative Example 3 is a rail produced using the composition of the present invention but conventionally processed. While its strength and hardness are improved, its elongation after fracture is low, failing to achieve a balanced strength-toughness balance. Comparative Example 4 is a rail produced using the process of the present invention with an improved composition based on U71Mn. Its strength and ductility are slightly improved compared to U71Mn rails produced using conventional processes, but its A1 temperature is 726°C, its A3 temperature is 743°C, and its martensitic transformation critical cooling rate is 3.0°C / s. Therefore, rails produced using this process exhibit excellent strength and toughness properties, with significantly higher A1, A3, and martensitic transformation critical cooling rates compared to conventional compositions and processes.

[0089] Table 2 Microstructure and general mechanical properties of the embodiments and comparative examples.

[0090]

[0091] As can be seen in Table 2, the rails produced using the composition and process of the present invention have high base metal hardness, but the white layer formed by scratches has a low hardness, resulting in a low white layer / base metal hardness ratio (below 1.80). This means that the hardness difference between the white layer and the base metal, or the hardness gradient, is small. Furthermore, the scratched white layer is also thin, resulting in a high number of rolling contact fatigue cycles. However, in Comparative Examples 1-4, whether the rails were produced using conventional compositions and processes, or using optimized compositions and conventional processes, or using existing compositions and improved processes, none of them achieved both strong and tough properties and scratch resistance.

[0092] It can be seen from Examples 1-4 and Comparative Examples 1-4 that the rails prepared by the present invention have good anti-scratch performance and good matching of strength and toughness.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of implementation of the present invention. If the present invention is modified or replaced with equivalents without departing from the spirit and scope of the present invention, it should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a scratch-resistant and high-toughness steel rail, characterized in that: The following steps are involved: 1) Control the chemical composition and proportion of the molten steel as follows: by weight percentage, C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 0.30-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30% and at least one of V, Nb, and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, calculated by mass percentage, the ratio of Si to Cr satisfies: 1.20%≤Si+Cr≤1.65%, the rest is Fe and unavoidable impurities; 2) placing the molten steel in a tundish for continuous casting, and adopting multi-stage electromagnetic stirring, low superheat and high casting speed processes to obtain low-segregation steel billets. The continuous casting process of the low-segregation steel billets adopts multi-stage composite electromagnetic stirring of crystallizer electromagnetic stirring, secondary cooling electromagnetic stirring and solidification end electromagnetic stirring. The casting superheat is 12-20° C. and the billet casting speed is 0.82-0.95 m / min. 3) placing the steel billet in a walking beam furnace for heating and then universally rolling the billet into a rail. The heating process of the steel billet is divided into three stages: in the first stage, the furnace temperature of the heating furnace is 750-950°C for 50-70 minutes; in the second stage, the furnace temperature of the heating furnace is 1100-1280°C for 70-100 minutes; and in the third stage, the furnace temperature of the heating furnace is 1200-1230°C for 50-90 minutes. During the heating process of the steel billet, the furnace temperature is controlled to be greater than 1200°C for at least 90 minutes. 4) Use compressed air to accelerate cooling from the austenite zone of the rail at an accelerated cooling rate of 5.0-6.5℃ / s. Cool to 540-570℃ and then cool naturally.

2. The preparation method according to claim 1, characterized in that In step 2), the low-segregation steel billet is prepared from blast furnace molten iron through converter smelting, LF refining, electric heating and continuous casting; the C segregation degree in the narrow surface 50-150 mm region of the low-segregation steel billet is 0.96-1.04, the Mn segregation degree is 0.97-1.03 and the Cr segregation degree is 0.97-1.

03.

3. The preparation method according to claim 1, characterized in that In the step 3), the universal rolling includes universal rough rolling, intermediate rolling and finishing rolling.

4. The preparation method according to claim 1, characterized in that In the step 4), the accelerated cooling rate is 4.5-6.0° C. / s, and the mixture is cooled to 430-470° C. and then cooled naturally.

5. The preparation method according to claim 1, characterized in that Calculated by mass percentage, the proportion of Mn is 0.40-0.70%.

6. The preparation method according to claim 1, characterized in that Calculated by mass percentage, the ratio of Cu to Ni satisfies: 0.30%≤Cu+Ni≤0.50%.

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