Low-cost RE and B microalloyed steel rail steel and preparation method thereof

Abstract

The invention discloses low-cost RE and B microalloyed steel rail steel and a preparation method thereof. The low-cost RE and B micro-alloyed rail steel provided by the invention comprises the following chemical components in percentage by mass: 0.68-0.76% of C, 0.18-0.26% of B, 0.18-0.18% of C, 0.18- 0.35% to 0.60% of Si; 0.90 to 1.10% of Mn; p is less than or equal to 0.02%; s is less than or equal to 0.02%; 0.05 to 0.1 percent of V; b: 0.001 to 0.005% of the total weight of the raw materials; 0.002 to 0.01 percent of RE (rare earth); and the balance is Fe and impurities. The low-temperature impact performance can be improved by adding RE, and the B microalloy is added to replace Mo and Ni alloy contents, so that the hardenability of the steel is improved. The steel rail steel has good obdurability, the alloy manufacturing cost is reduced, and the market competitiveness is improved.

Description

Technical Field

[0001] The invention belongs to the field of rail production and application, and specifically relates to a low-cost RE, B microalloyed rail steel and a preparation method thereof. Background Art

[0002] At present, some precious metals such as Ni and Mo are added to the rail composition system to ensure the excellent mechanical properties of the rail. Considering the reduction of production costs, there is a large room for optimization of the rail composition. Through different heat treatment processes and adjustment of internal control components, microalloying elements are used to ensure the hardenability of steel, refine grains and refine microstructures to ensure the mechanical properties of the rail, while improving contact fatigue performance and low-temperature impact toughness, improving service performance, and reducing alloy manufacturing costs. While meeting the requirements of line use, it increases rail sales profits and market competitiveness. Summary of the invention

[0003] The object of the present invention is to provide a low-cost RE, B microalloyed rail steel and a preparation method thereof, by adding RE, B alloy to replace the Mo and Ni alloy content, while also enabling the rail material to have good strength and toughness and low-temperature impact performance, thereby reducing the alloy manufacturing cost while ensuring that the rail steel has good strength and toughness, and improving market competitiveness.

[0004] The specific technical solutions of the present invention are as follows:

[0005] One aspect of the present invention provides a low-cost RE, B microalloyed rail steel, whose chemical composition by mass percentage is: C: 0.68-0.76%; Si: 0.35-0.60%; Mn: 0.90-1.10; P≤0.02%; S≤0.02%; V: 0.05-0.1%; B: 0.001-0.005%; RE: 0.002-0.01%; the rest is Fe and impurities.

[0006] In some embodiments, the mechanical properties of the low-cost RE, B microalloyed rail steel meet the following requirements: yield strength ≥850MPa, tensile strength ≥1200MPa, elongation ≥12%, tread hardness ≥350HBW, and impact energy at -60°C ≥28J.

[0007] In some embodiments, the chemical composition of the low-cost RE, B microalloyed rail steel is calculated by mass percentage as follows: C: 0.73%; Si: 0.47%; Mn: 1.02%; P: 0.008%; S: 0.011%; V: 0.05%; B: 0.002%; RE: 0.006%; the rest is Fe and impurities.

[0008] In some embodiments, the chemical composition of the low-cost RE, B microalloyed rail steel is calculated by mass percentage as follows: C: 0.74%; Si: 0.57%; Mn: 0.97%; P: 0.008%; S: 0.013%; V: 0.08%; B: 0.003%; RE: 0.008%; the rest is Fe and impurities.

[0009] In some embodiments, the chemical composition of the low-cost RE, B microalloyed rail steel is calculated by mass percentage as follows: C: 0.70%; Si: 0.51%; Mn: 0.95%; P: 0.009%; S: 0.009%; V: 0.06%; B: 0.004%; RE: 0.006%; the rest is Fe and impurities.

[0010] Another aspect of the present invention provides a method for preparing low-cost RE, B microalloyed rail steel, which comprises using deoxidized iron scaled discarded old rails as furnace charge and preparing the steel according to the following processes: rail steel smelting and degassing process, rail steel rolling process, and rail steel heat treatment process; wherein:

[0011] The rail steel smelting and degassing process comprises: smelting adopts aluminum-free deoxidation alloying, vacuum degree ≤0.10Kpa, molten steel temperature reaches 1535-1570℃, vacuum time ≥25min, standing for 3-5min before pouring out of the furnace;

[0012] The rail steel rolling process includes: ingot heating temperature is 1280±20℃, heat preservation for 40-50min; furnace temperature is not less than 1150℃, starting rolling temperature is 1100-1150℃, and final rolling temperature is 900-950℃;

[0013] The rail steel heat treatment process includes: the heat treatment quenching medium is high-pressure wind, the initial residual heat quenching temperature is 780-850°C, then cooled to 500-550°C at a cooling rate of 1-2.0°C / s, and then air-cooled to room temperature.

[0014] The main alloying elements Si and Mn added to the rail steel of the present invention are intended to improve the strength of the rail and the phase transformation temperature suitable for heat treatment. The C component in the steel is designed to have a large solid solubility with Fe, has a solid solution strengthening effect, and improves the strength and hardness of the steel. However, the increase in C content will reduce the toughness of the rail, so the C content of the present invention takes both strength and toughness into consideration. Mn expands the austenite phase region, increases the stability of the supercooled austenite of the steel, and significantly improves the hardenability of the steel. Si reduces the transformation rate from austenite to ferrite, improves the strength, elasticity and tempering resistance of the steel, and considering the weldability of the rail, the Si content should not be too high, because Si has poor heat conductivity, which is not conducive to rail welding: The B element can improve the hardness and wear resistance of the alloy material, and can also improve the melting point and oxidation resistance of the alloy. Enhance the mechanical strength and corrosion resistance of the alloy material, so that the alloy material has better high temperature strength and heat resistance. The added RE element is a rare earth alloy. The basic theoretical research on rare earth has proved that rare earth in steel can control the morphology of sulfides in the smelting process, so that the grains in the steel are refined. At the same time, rare earth can improve the oxidation resistance and low temperature resistance of steel. The presence of an appropriate amount of rare earth in steel materials can reduce the ductile-brittle transition temperature, which has important technical significance for the service of rails in low temperature areas.

[0015] The beneficial effects of the present invention are as follows: the present invention provides a low-cost RE, B microalloyed rail steel and a preparation method thereof, utilizing RE, B alloy elements and a suitable heat treatment process to improve the strength and hardness of the rail steel, while reasonably reducing the C content to ensure that the toughness of the material meets the technical requirements. The composition design and heat treatment of the present invention have a unique production process, are suitable for large-scale production, and have good promotion value. DETAILED DESCRIPTION

[0016] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0017] Example

[0018] The method for preparing low-cost RE, B microalloyed rail steel provided by the present invention uses deoxidized iron scale discarded old rails as furnace charge, and is prepared according to the following process: rail steel smelting and degassing process, rail steel rolling process, and rail steel heat treatment process, specifically comprising: waste rail furnace charge → deoxidized iron scale → alloy batching → 25kg small furnace vacuum induction heating smelting → adding rare earth → vacuuming → demoulding and cooling → rolling into 20mm thick plate → processing component treatment plate → heat treatment; wherein:

[0019] The rail steel smelting and degassing process includes: smelting using aluminum-free deoxidation alloying, vacuum degree ≤0.10Kpa, molten steel temperature reaching 1535-1570°C (e.g. 1560°C), vacuum time ≥25min (e.g. 26min), standing for 3-5min (e.g. 4min) before pouring out of the furnace; before adding rare earth, ensure that the molten steel is in a molten flow state, fully stir and achieve overall uniform composition, so that the molten steel composition of each embodiment is shown in Table 1 below by mass percentage;

[0020] Table 1: Chemical composition and content of molten steel in various examples

[0021]

[0022] The rail steel rolling process includes: ingot heating temperature is 1280±20°C (e.g. 1295°C), heat preservation time is 40-50min (e.g. 45min); furnace discharge temperature is not less than 1150°C (e.g. 1160°C), start rolling temperature is 1100-1150°C (e.g. 1110°C), and final rolling temperature is 900-950°C (e.g. 930°C);

[0023] The rail steel heat treatment process includes: the heat treatment quenching medium is high-pressure wind, the initial residual heat quenching temperature is 780-850°C (for example, 800°C), then cooled to 500-550°C (for example, 530°C) at a cooling rate of 1-2.0°C / s (for example, 1.2°C / s), and then air-cooled to room temperature.

[0024] The performance of steel samples after heat treatment: The tensile specimen specifications are: diameter d0 = 10mm, gauge length L0 = 5d0. The specimen length is 230mm, the top surface of the rail head is ground off 0.5mm, and there are 5 test points. The Brinell hardness test is carried out and the average value is calculated. The test temperature is 20℃ ± 5℃. The impact sampling position is at the center of the tread, the direction is longitudinal, the size is 10mmx10mmx50mm, and it is AKU 2 The experimental results are shown in Table 2.

[0025] Table 2: Mechanical properties of rail steel in various examples

[0026]

[0027] It can be seen from Table 2 that each embodiment of the present invention has good strength, low-temperature impact toughness and mechanical properties, and meets the following requirements: yield strength ≥850MPa (preferably ≥900MPa), tensile strength ≥1200MPa (preferably ≥1220MPa), elongation ≥12%, tread hardness ≥350HBW, -60℃ impact energy ≥28J (preferably ≥30J), and the produced rails meet the technical requirements for use.

[0028] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-cost RE, B microalloyed rail steel, characterized in that: The chemical composition of the low-cost RE, B microalloyed rail steel is as follows by mass percentage: C: 0.68-0.76%; Si: 0.35-0.60%; Mn: 0.90-1.10; P≤0.02%; S≤0.02％； V：0.05-0.1％； B：0.001-0.005％； RE: 0.002-0.01%; the rest is Fe and impurities.

2. The low-cost RE, B microalloyed rail steel according to claim 1, characterized in that: The mechanical properties of the low-cost RE and B microalloyed rail steels meet the following requirements: yield strength ≥850MPa, tensile strength ≥1200MPa, elongation ≥12%, tread hardness ≥350HBW, and -60°C impact energy ≥28J.

3. The low-cost RE, B microalloyed rail steel according to claim 1 or 2, characterized in that: The chemical composition of the low-cost RE, B microalloyed rail steel is as follows by mass percentage: C: 0.73%; Si: 0.47%; Mn: 1.02%; P: 0.008%; S: 0.011%; V: 0.05%; B: 0.002%; RE: 0.006%; others are Fe and impurities.

4. The low-cost RE, B microalloyed rail steel according to claim 1 or 2, characterized in that: The chemical composition of the low-cost RE, B microalloyed rail steel is as follows by mass percentage: C: 0.74%; Si: 0.57%; Mn: 0.97%; P: 0.008%; S: 0.013%; V: 0.08%; B: 0.003%; RE: 0.008%; others are Fe and impurities.

5. The low-cost RE, B microalloyed rail steel according to claim 1 or 2, characterized in that: The chemical composition of the low-cost RE, B microalloyed rail steel is as follows by mass percentage: C: 0.70%; Si: 0.51%; Mn: 0.95%; P：0.009％； S：0.009％； V：0.06％； B：0.004％； RE: 0.006%; the rest is Fe and impurities.

6. The method for preparing low-cost RE, B microalloyed rail steel according to any one of claims 1 to 5, characterized in that: The preparation method comprises using the deoxidized iron scaled discarded old rails as furnace materials and preparing the rail steel according to the following processes: rail steel smelting and degassing process, rail steel rolling process, and rail steel heat treatment process; wherein: The rail steel smelting and degassing process comprises: smelting adopts aluminum-free deoxidation alloying, vacuum degree ≤0.10Kpa, molten steel temperature reaches 1535-1570℃, vacuum time ≥25min, standing for 3-5min before pouring out of the furnace; The rail steel rolling process includes: ingot heating temperature is 1280±20℃, heat preservation for 40-50min; furnace temperature is not less than 1150℃, starting rolling temperature is 1100-1150℃, and final rolling temperature is 900-950℃; The rail steel heat treatment process includes: the heat treatment quenching medium is high-pressure wind, the initial residual heat quenching temperature is 780-850°C, then cooled to 500-550°C at a cooling rate of 1-2.0°C / s, and then air-cooled to room temperature.

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