A method for preparing a RE, Nb, Ti alloy high-strength and high-toughness rail steel

Abstract

This invention discloses a method for preparing RE, Nb, and Ti alloy high-strength and high-toughness rail steel. The method involves using discarded old rails as furnace charge, heating and smelting them, and adding a certain amount of RE, Nb, and Ti alloys. The process then includes vacuum degassing, ingot casting, ingot heating, rolling, and heat treatment. The purpose of this invention is to provide a method for preparing RE, Nb, and Ti alloy high-strength and high-toughness rail steel, which, by adding RE, Nb, and Ti alloys, endows the rail material with good strength, toughness, and excellent wear resistance.

Description

TECHNICAL FIELD

[0001] The application relates to the field of rail production and application, in particular to a preparation method of RE, Nb and Ti alloy high-strength and high-toughness rail steel. BACKGROUND

[0002] With the development of railway construction in China, the railway along the line has covered all the provinces in China, and the corresponding railway construction lines have been established in remote areas. However, for the areas with high altitude and low-temperature severe cold environment, the performance of the steel rail needs to be further improved. In addition to meeting the requirements of strength, hardness and wear resistance, the steel rail also needs to have the ability to resist low-temperature brittle fracture. At present, there are few relevant literatures published at home and abroad about the low-temperature performance of the steel rail, and the research and development of high-tensile-strength and high-rail-surface-hardness steel rails and the application of line laying are focused on. The U71Mn steel rail laid in the low-temperature environment of the Qinghai-Tibet Railway has an average hardness of 275 HB and a tensile strength of 930 MPa at normal temperature, and the U-shaped impact value of the rail head at-40 DEG C is 7J. SUMMARY

[0003] The application aims to provide a preparation method of RE, Nb and Ti alloy high-strength and high-toughness rail steel, so that the rail material has good strength and toughness and excellent wear resistance by adding RE, Nb and Ti alloy.

[0004] To solve the above technical problems, the application adopts the following technical scheme:

[0005] The application provides a preparation method of RE, Nb and Ti alloy high-strength and high-toughness rail steel, wherein discarded old rails are selected as furnace charges, and a certain amount of RE, Nb and Ti alloy is added after heating and smelting, and then vacuum degassing, mold casting, ingot heating, rolling and heat treatment are carried out.

[0006] The rail steel smelting and degassing process is that the vacuum degree of the rail electric furnace smelting is controlled to be 30-35 Pa, the temperature of the molten steel reaches 1520-1580 DEG C, and the molten steel is poured out after being placed for 5-8 min, and the diameter of the poured ingot is 250-320 m.

[0007] The rail steel rolling process is that the heating temperature of the ingot is 1280 DEG C ± 20 DEG C, the heating time is greater than or equal to 180 min, the heating speed is less than 380 DEG C / h, the soaking temperature is 1160-1200 DEG C, and the soaking time is greater than 40 min; the out-of-furnace temperature should be higher than or equal to 1060 DEG C, the opening rolling temperature of the rail is greater than or equal to 1050 DEG C, the final rolling temperature is 900-950 DEG C, the rolling pass is greater than 9, and the rolling compression ratio is greater than 11:1.

[0008] The heat treatment process of the steel rail steel: the quenching medium of the heat treatment is high pressure air, the starting temperature of the quenching is 780-850℃, the heat treatment cooling time is 100-135s, the actual cooling speed is 1.8℃ / s-3.2℃ / s, and then the natural air cooling is performed to room temperature;

[0009] The chemical composition of the steel rail steel is as follows: C: 0.65-0.8%; Si: 0.25-0.58%; Mn: 0.85-1.05; P≤0.02%; S≤0.02%; V: 0.05-0.1%; Nb: 0.01-0.04%; Ti: 0.015%-0.025%, RE: 0.002-0.01%; and the rest is Fe and impurities.

[0010] Further, the chemical composition of the steel rail steel is as follows: C: 0.71%; Si: 0.47%; Mn: 1.00%; P: 0.008%; S: 0.011%; V: 0.05%; Nb: 0.03%; Ti: 0.018%, RE: 0.006%; and the rest is Fe and impurities, and the total mass fraction is 100%.

[0011] Further, the chemical composition of the steel rail steel is as follows: C: 0.74%; Si: 0.57%; Mn: 0.97%; P: 0.008%; S: 0.013%; V: 0.08%; Nb: 0.03%; Ti: 0.02%, RE: 0.008%; and the rest is Fe and impurities, and the total mass fraction is 100%.

[0012] Further, the chemical composition of the steel rail steel is as follows: C: 0.73%; Si: 0.51%; Mn: 0.95%; P: 0.009%; S: 0.009%; V: 0.06%; Nb: 0.02%; Ti: 0.017%, RE: 0.006%; and the rest is Fe and impurities, and the total mass fraction is 100%.

[0013] Further, the mechanical properties meet the following requirements: yield strength > 870 MPa, tensile strength > 1200 MPa, and elongation ≥ 12%.

[0014] The main alloying elements Si and Mn added in the material aims to improve the strength capacity of the rail and the phase transition temperature suitable for heat treatment line. The C component design in the steel has a large solid solubility with Fe, has a solid solution strengthening effect, improves the strength and hardness of the steel, but the increase of C content will reduce the toughness of the rail, therefore, the C content of the present application considers the strength and toughness. Mn expands the austenite phase region, increases the stability of the supercooled austenite of the steel, and significantly improves the hardenability of the steel. The austenite to ferrite transition speed is reduced, the strength, elasticity and tempering stability of the steel are improved, and the Si content is not too high considering the weldability of the rail, because Si has poor heat transfer property, which is not conducive to the welding of the rail. The added RE element is a rare earth alloy, and the basic theory research of rare earth has proved that the steel containing rare earth has the effect of controlling the morphology of sulfides in the smelting process, so that the grain size of the steel is refined. At the same time, the rare earth can improve the oxidation resistance and low temperature resistance of the steel, and the steel containing appropriate amount of rare earth can reduce the ductile-brittle transition temperature, which has important technical significance for the service of the rail in low temperature area.

[0015] Compared with the prior art, the present application has the beneficial technical effects:

[0016] The present application provides a preparation method of RE, Nb and Ti alloy high strength and toughness rail steel, which utilizes RE, Nb and Ti alloy elements and suitable heat treatment process to improve the strength and hardness of the rail steel, and reasonably reduces the C content to ensure that the toughness of the material meets the technical requirements. The component design and heat treatment of the present application have a unique production process, are suitable for large-scale production, and have good popularization value. DETAILED DESCRIPTION

[0017] A preparation method of RE, Nb and Ti alloy high strength and toughness rail steel, comprising:

[0018] The production process of the steel material is: furnace charge (waste rail) → 25 kg vacuum induction smelting furnace → adding RE, Nb, Ti and other alloy elements → tapping → rolling into 20 mm thick plate → processing into component treatment plate → laboratory heat treatment; wherein:

[0019] The rail steel smelting degassing process is: the vacuum degree of the rail electric furnace smelting is controlled at 33 Pa, the temperature of the molten steel reaches 1560℃, and the molten steel is poured after standing for 6 min, and the pouring ingot diameter is 300 mm.

[0020] The rail steel rolling process is: the heating temperature of the ingot is 1295℃, the heating time is 180 min, the heating speed is 350℃ / h, the soaking temperature is 1180℃, and the soaking time is 45 min; the out-of-furnace temperature is 1100℃, the rail opening rolling temperature is 1080, the final rolling temperature is 930℃, the rolling pass is > 9, and the rolling compression ratio is > 11:1.

[0021] The chemical components of the following table embodiments are as follows:

[0022] Chemical composition of each furnace in Table 1

[0023]

[0024] The heat treatment process of the steel rail: the quenching medium of the heat treatment is high-pressure air, the starting temperature of the quenching is 780-850℃, the heat treatment cooling time is 100-135s, the actual cooling speed of the cooling section is 1.8℃ / s-3.2℃ / s, and then the natural air cooling is performed until the room temperature.

[0025] The performance of the steel sample after the heat treatment: the specification of the tensile sample is that the diameter d0 is 10mm and the gauge length L0 is 5d0, the sample length is 230mm, the top surface of the rail head is ground by 0.5mm, 5 test points are arranged, the Brinell hardness test is performed, the average value is calculated, and the test temperature is 20℃-5℃. The impact sample position is the center of the tread, the direction is longitudinal, the size is 10mmx10mmx50mm, and the notch is AKU2 type. The experimental results are shown in Table 2.

[0026] Table 2 Mechanical properties

[0027]

[0028]

[0029] As shown in Table 2, the embodiments of the present application all have good strength, low-temperature impact toughness and mechanical properties, and the steel rails produced by the embodiments meet the technical requirements.

[0030] The above-described embodiments are only used to describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by the ordinary skilled in the art should fall into the protection scope determined by the claims of the present application.

Claims

1. A method for producing a RE, Nb, Ti alloy high strength and toughness rail steel, characterized in that, The abandoned old steel rail is selected as the furnace charge, is heated and smelted, a certain amount of RE, Nb and Ti alloy is added, and then vacuum degassing-mold casting-ingot casting heating-rolling-heat treatment are carried out. The rail steel smelting degassing process is that the vacuum degree of the rail electric furnace smelting is controlled at 30-35 Pa, the molten steel temperature reaches 1520-1580 DEG C, and the molten steel is poured after being placed for 5-8 min, and the poured ingot diameter is 250-320 mm. The rail steel rolling process is that the heating temperature of the ingot is 1280±20 DEG C, the heating time is greater than or equal to 180 min, the heating speed is less than 380 DEG C / h, the soaking temperature is 1160-1200 DEG C, the soaking time is greater than 40 min, the out-furnace temperature is not less than 1060 DEG C, the rail opening rolling temperature is greater than or equal to 1050 DEG C, the final rolling temperature is 900-950 DEG C, the rolling pass is greater than 9, and the rolling compression ratio is greater than 11:

1. The rail steel heat treatment process is that the heat treatment quenching medium is high-pressure air, the starting temperature of the afterheat quenching is 780-850 DEG C, the heat treatment cooling time is 100-135 s, the actual cooling speed is 1.8 DEG C / s-3.2 DEG C / s, and then the natural air cooling is carried out to room temperature. The chemical composition of the rail steel is that the weight percentage of C is 0.65-0.8%, the weight percentage of Si is 0.25-0.58%, the weight percentage of Mn is 0.85-1.05%, the weight percentage of P is less than or equal to 0.02%, the weight percentage of S is less than or equal to 0.02%, the weight percentage of V is 0.05-0.1%, the weight percentage of Nb is 0.01-0.04%, the weight percentage of Ti is 0.015%-0.025%, the weight percentage of RE is 0.002-0.01%, and the rest is Fe and impurities.

2. The method of producing a RE, Nb, Ti alloy high strength and toughness rail steel according to claim 1, characterized by, The chemical composition of the rail steel is that the weight percentage of C is 0.71%, the weight percentage of Si is 0.47%, the weight percentage of Mn is 1.00%, the weight percentage of P is 0.008%, the weight percentage of S is 0.011%, the weight percentage of V is 0.05%, the weight percentage of Nb is 0.03%, the weight percentage of Ti is 0.018%, the weight percentage of RE is 0.006%, and the rest is Fe and impurities, and the total mass fraction is 100%. The chemical composition of the rail steel is that the weight percentage of C is 0.74%, the weight percentage of Si is 0.57%, the weight percentage of Mn is 0.97%, the weight percentage of P is 0.008%, the weight percentage of S is 0.013%, the weight percentage of V is 0.08%, the weight percentage of Nb is 0.03%, the weight percentage of Ti is 0.02%, the weight percentage of RE is 0.008%, and the rest is Fe and impurities, and the total mass fraction is 100%.

3. The method of producing a RE, Nb, Ti alloy high strength and toughness rail steel according to claim 1, characterized by, The chemical composition of the rail steel is that the weight percentage of C is 0.73%, the weight percentage of Si is 0.51%, the weight percentage of Mn is 0.95%, the weight percentage of P is 0.009%, the weight percentage of S is 0.009%, the weight percentage of V is 0.06%, the weight percentage of Nb is 0.02%, the weight percentage of Ti is 0.017%, the weight percentage of RE is 0.006%, and the rest is Fe and impurities, and the total mass fraction is 100%.

4. The method of producing a RE, Nb, Ti alloy high strength and toughness rail steel according to claim 1, characterized by, The mechanical properties meet the requirements that the yield strength is greater than 870 MPa, the tensile strength is greater than 1200 MPa, and the elongation is greater than or equal to 12%.

5. The method of producing a RE, Nb, Ti alloy high strength and toughness rail steel according to claim 1, characterized by, ​

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