Manufacturing method of high-strength heat treatment steel rail containing V, Nb and La-Ce mixed rare earth elements

Abstract

The invention discloses a manufacturing method of a high-strength heat treatment steel rail containing V, Nb and La-Ce mixed rare earth elements, and belongs to the technical field of ferrous metallurgy materials. The production process route comprises the steps of molten iron pretreatment, converter smelting, LF refining, VD vacuum treatment, continuous casting, slow cooling in a slow cooling pit, heating, rolling, online heat treatment, straightening, flaw detection, checking, machining and warehousing. The steel rail comprises the following elements in percentage by mass: 0.80 to 0.85 percent of C, 0.65 to 0.75 percent of S i, 0.90 to 1.05 percent of Mn, 0.30 to 0.45 percent of Cr, 0.06 to 0.10 percent of V, 0.02 to 0.06 percent of Nb, 0.0050 to 0.010 percent of La-Ce, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S and the balance of Fe and impurities. The invention aims to develop a steel rail with higher strength, hardness and toughness so as to meet the requirements of heavy-load lines.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel metallurgical materials, and in particular relates to a method for manufacturing a high-strength heat-treated steel rail containing V, Nb and La-Ce mixed rare earth elements. Background Art

[0002] Modern heavy-haul railway transportation is developing towards high axle loads and large transport volumes. Domestic railways such as the Daqin Line can handle a total annual throughput of 550 million tons, and trains on the Wanji Railway already have an axle load of 30 tons. However, existing standard U75V heat-treated rails, due to their low strength, poor wear resistance, and short service life, are no longer suitable for the development of heavy-haul railways. The Daqin Railway currently primarily utilizes HB370 U78CrVH heat-treated rails with a hardness of 75kg / m, produced by Panzhihua Iron and Steel. These rails can meet service requirements exceeding 1.5 billion tons on straight sections and over 500 million tons on curves with a radius of 800m. As the axle weight of trains gradually increases, the load capacity increases, the traffic density of lines increases, and the transportation volume of heavy-duty railways increases year by year, the existing rails cannot meet the current needs of super-large loads, high traffic density and small radius lines. It is necessary to further improve the comprehensive mechanical properties of rails, improve the strength, hardness and wear resistance of rails, and ensure that the rails have good toughness, peeling resistance and fatigue resistance, increase the service life of rails on the line, reduce the occurrence of damage such as peeling and falling blocks, and ensure the safety of railway transportation.

[0003] At present, the rail materials used in my country's railway transportation are basically various types of rails in railway standards, with the highest strength grade being 1280MPa. They are mainly composed of elements such as C, Si, Mn, and Cr. The strength, hardness, and toughness of the rails no longer meet the needs of the rapid development of heavy-load lines. Therefore, it is necessary to develop rails with higher strength, hardness, and toughness to meet the needs of heavy-load lines. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for manufacturing a high-strength heat-treated rail containing V, Nb and La-Ce mixed rare earth elements, and to develop a rail with higher strength, hardness and toughness to meet the requirements of heavy-load lines.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention discloses a method for manufacturing a high-strength heat-treated steel rail containing V, Nb and La-Ce mixed rare earth elements. The mass percentage content of each element in the steel rail is as follows: C: 0.80-0.85%, Si: 0.65-0.75%, Mn: 0.90-1.05%, Cr: 0.30-0.45%, V: 0.06-0.10%, Nb: 0.02-0.06%, La-Ce: 0.0050-0.010%, P≤0.015%, S≤0.010%, and the remainder is Fe and unavoidable impurities. The production process route is: molten iron pretreatment - converter smelting - LF refining - VD vacuum treatment - continuous casting - slow cooling in a slow cooling pit - heating - rolling - online heat treatment - straightening - flaw detection - inspection - processing - warehousing; wherein:

[0007] Ingot smelting: The molten iron needs to be pre-treated with desulfurization, and deoxidation and alloying are carried out in the tank using silicon manganese, ferromanganese and low-aluminum silicon iron alloy. The smelting process adopts aluminum-free deoxidation process, and the final deoxidizer is low-aluminum silicon calcium barium. The final slag basicity is ≥3.0. Slag blocking is required for steel tapping, and the slag basicity is controlled to be ≥2.0. The deep vacuum time is ≥18 minutes, the vacuum degree is less than ≤0.10KPa, and the soft blowing time is ≥18 minutes. The continuous casting adopts constant casting speed operation at 0.62-0.65m / min, the superheat is ≤30℃, and the ingot is placed in the slow cooling pit for ≥24 hours. La-Ce mixed rare earth alloy is added after refining. The grade of mixed rare earth alloy is ≥20%, of which La accounts for 28-32% and Ce accounts for about 68-72% in the mixed rare earth alloy.

[0008] Rail rolling: billet preheating section temperature ≤ 800℃, soaking end temperature ≤ 1260℃, heating time ≥ 210min, BD1 starting rolling temperature 1100-1140℃, finishing rolling temperature ≤ 930℃;

[0009] Online heat treatment: High-pressure air is used for online heat treatment of rails, with the air pressure at the rail head being 8-14 kPa and the air pressure at the rail bottom being 10-16 kPa. After final rolling, the heat treatment temperature of the rails is 750-800°C, the final cooling temperature is 490-510°C, and the cooling rate is 2-3°C / s. After controlled cooling, the rails are air-cooled to room temperature.

[0010] Furthermore, the mass percentage content of each element in the rail is: C: 0.80%, Si: 0.72%, Mn: 1.01%, Cr: 0.36%, V: 0.08%, Nb: 0.031%, La-Ce: 0.0055%, P: 0.013%, S: 0.008%, and the rest is Fe and unavoidable impurities.

[0011] Furthermore, the mass percentage content of each element in the rail is: C: 0.82%, Si: 0.70%, Mn: 0.98%, Cr: 0.37%, V: 0.08%, Nb: 0.029%, La-Ce: 0.0068%, P: 0.012%, S: 0.003%, and the rest is Fe and unavoidable impurities.

[0012] Furthermore, the mass percentage content of each element in the rail is: C: 0.85%, Si: 0.63%, Mn: 0.96%, Cr: 0.31%, V: 0.07%, Nb: 0.020%, La-Ce: 0.0051%, P: 0.014%, S: 0.003%, and the rest is Fe and unavoidable impurities.

[0013] Furthermore, the mass percentage content of each element in the rail is: C: 0.84%, Si: 0.68%, Mn: 0.97%, Cr: 0.33%, V: 0.07%, Nb: 0.026%, La-Ce: 0.0071%, P: 0.013%, S: 0.008%, and the rest is Fe and unavoidable impurities.

[0014] Furthermore, the manufactured high-strength heat-treated rails containing V, Nb and La-Ce mixed rare earth elements meet the following requirements: tensile strength ≥ 1370MPa, elongation ≥ 11%, tread hardness ≥ 390HB, and weight loss rate ≤ 0.10g / 100,000 times.

[0015] Furthermore, the manufactured rail has the characteristics of high strength, high hardness, high wear resistance and excellent toughness, meeting the service requirements of heavy-load lines.

[0016] The main functions of adding V, Nb and La-Ce mixed rare earth elements to high-strength heat-treated rails are:

[0017] V: Improved strength: Vanadium can form compounds such as vanadium carbide with carbon in steel. These compounds can be dispersed in the steel matrix, hindering dislocation movement, thereby significantly improving the strength of the rails and helping them withstand the huge pressure and impact forces during train operation. Grain refinement: Vanadium can inhibit the grain growth of steel during the heating and cooling process, making the grains of the rails finer and more uniform. The fine grain structure not only increases the strength of the rails, but also improves their toughness and plasticity, thereby enhancing the comprehensive mechanical properties of the rails. Improved wear resistance: Because vanadium increases the strength and hardness of the rails, the rail surface is more wear-resistant, reducing wear between the train wheels and the rails, extending the service life of the rails, and reducing railway maintenance costs. Improved fatigue resistance: The addition of vanadium can improve the fatigue resistance of the rail material, enabling it to withstand repeated loads from trains, reducing the generation and expansion of fatigue cracks, and improving the reliability and safety of the rails.

[0018] Nb: Grain Refinement: Niobium strongly inhibits austenite grain growth. During rail production, by controlling the niobium addition and process parameters, the rail can achieve a fine and uniform grain structure, thereby improving the rail's strength, toughness, and fatigue resistance. Precipitation Strengthening: Niobium reacts with carbon, nitrogen, and other elements in the steel to form fine niobium carbonitride precipitates. These precipitates are dispersed throughout the steel matrix, hindering dislocation motion and improving the rail's strength.

[0019] La-Ce mixed rare earth elements: Purify molten steel: Rare earth elements are chemically active and have a strong affinity for impurities such as oxygen and sulfur in steel, forming high-melting-point rare earth oxides and sulfides. These compounds have a low density and easily float to the surface of the molten steel for removal, thereby reducing the impurity content in the steel, purifying the molten steel, and improving the purity of the rail. Modify inclusions: Rare earth elements can change the morphology and distribution of inclusions in steel, transforming them from long strips or flakes to spheres or short rods, with a more uniform distribution. This reduces the disruption of the rail matrix's continuity and improves the rail's toughness and fatigue resistance. Refine grains: Rare earth elements act as crystal nuclei in steel, promoting grain formation while inhibiting grain growth, resulting in grain refinement and improving the rail's overall properties, including strength, toughness, and wear resistance. Furthermore, in some specialty steels, they can improve the steel's high- and low-temperature properties, enhancing its strength, stability, and creep resistance at both high and low temperatures.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The present invention provides a high-strength heat-treated steel rail containing V, Nb and La-Ce mixed rare earth elements and a manufacturing method thereof. On the basis of strengthening the existing heavy rail steel with C, Si, Mn and Cr elements, V, Nb and La-Ce mixed rare earth elements are added, and smelting technology, rolling technology and online heat treatment technology are combined to improve the strength, hardness, wear resistance and fatigue performance of the steel rail, and achieve the purposes of grain refinement, microstructure refinement and purification of molten steel.

[0022] The resulting high-strength heat-treated rails have a tensile strength of ≥1370 MPa, an elongation of ≥11%, a tread hardness of ≥390 HB, and a weight loss rate of ≤0.10 g / 100,000 cycles. The rails feature high strength, high hardness, high wear resistance, and excellent toughness, meeting the demands of heavy-load line service. DETAILED DESCRIPTION

[0023] During the implementation of the present invention, the chemical compositions of different embodiments and comparative examples are shown in Table 1.

[0024] Table 1 Composition of rails in different embodiments and comparative examples (%)

[0025]

[0026] Table 2 Rail smelting processes in different embodiments and comparative examples

[0027]

[0028] Table 3 Rail rolling processes of different embodiments and comparative examples

[0029]

[0030] The production process of the V, Nb and La-Ce mixed rare earth element high-strength heat-treated rail of the present invention is: molten iron pretreatment - converter smelting - LF refining - VD vacuum treatment - continuous casting - slow cooling in a slow cooling pit - heating - rolling - online heat treatment - straightening - flaw detection - inspection - processing - warehousing.

[0031] According to the components and production processes in Tables 1 to 3, the rails of Examples 1 to 4 and Comparative Example 1 were produced. The finished rails were tested for tensile strength, elongation, tread hardness, and wear resistance in accordance with the TB / T2344 standard. The mechanical properties of the rails of different Examples and Comparative Examples are shown in Table 4.

[0032] Table 4 Mechanical properties of rails in different embodiments and comparative examples

[0033]

[0034] Table 4 shows that the rails of Examples 1-4 exhibit excellent strength, ductility, hardness, and wear resistance. The high-strength heat-treated rails containing V, Nb, and La-Ce mixed rare earth elements obtained in accordance with the present invention exhibit a tensile strength ≥1370 MPa, an elongation ≥11%, a tread hardness ≥390 HB, and a weight loss rate ≤0.10 g / 100,000 cycles. The rails of the present invention possess high strength, high hardness, high wear resistance, and excellent toughness, meeting the requirements of heavy-load line service.

[0035] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for manufacturing a high-strength heat-treated rail containing V, Nb and La-Ce mixed rare earth elements, characterized in that: The mass percentage content of each element in the rail is: C: 0.80-0.85%, Si: 0.65-0.75%, Mn: 0.90-1.05%, Cr: 0.30-0.45%, V: 0.06-0.10%, Nb: 0.02-0.06%, La-Ce: 0.0050-0.010%, P≤0.015%, S≤0.010%, and the rest is Fe and unavoidable impurities; The production process is as follows: hot metal pretreatment - converter smelting - LF refining - VD vacuum treatment - continuous casting - slow cooling in a slow cooling pit - heating - rolling - online heat treatment - straightening - flaw detection - inspection - processing - warehousing; among which: Ingot smelting: The molten iron needs to be pre-treated with desulfurization, and deoxidation and alloying are carried out in the tank using silicon manganese, ferromanganese and low-aluminum silicon iron alloy. The smelting process adopts aluminum-free deoxidation process, and the final deoxidizer is low-aluminum silicon calcium barium. The final slag basicity is ≥3.

0. Slag blocking is required for steel tapping, and the slag basicity is controlled to be ≥2.

0. The deep vacuum time is ≥18 minutes, the vacuum degree is less than ≤0.10KPa, and the soft blowing time is ≥18 minutes. The continuous casting adopts constant casting speed operation at 0.62-0.65m / min, the superheat is ≤30℃, and the ingot is placed in the slow cooling pit for ≥24 hours. La-Ce mixed rare earth alloy is added after refining. The grade of mixed rare earth alloy is ≥20%, of which La accounts for 28-32% and Ce accounts for about 68-72% in the mixed rare earth alloy. Rail rolling: billet preheating section temperature ≤ 800℃, soaking end temperature ≤ 1260℃, heating time ≥ 210min, BD1 starting rolling temperature 1100-1140℃, finishing rolling temperature ≤ 930℃; Online heat treatment: High-pressure air is used for online heat treatment of rails, with the air pressure at the rail head being 8-14 kPa and the air pressure at the rail bottom being 10-16 kPa. After final rolling, the heat treatment temperature of the rails is 750-800°C, the final cooling temperature is 490-510°C, and the cooling rate is 2-3°C / s. After controlled cooling, the rails are air-cooled to room temperature.

2. The method for manufacturing a high-strength heat-treated steel rail containing V, Nb and La-Ce mixed rare earth elements according to claim 1, characterized in that: The mass percentage content of each element in the rail is: C: 0.80%, Si: 0.72%, Mn: 1.01%, Cr: 0.36%, V: 0.08%, Nb: 0.031%, La-Ce: 0.0055%, P: 0.013%, S: 0.008%, and the rest is Fe and unavoidable impurities.

3. The method for manufacturing a high-strength heat-treated rail containing V, Nb and La-Ce mixed rare earth elements according to claim 1, characterized in that: The mass percentage content of each element in the rail is: C: 0.82%, Si: 0.70%, Mn: 0.98%, Cr: 0.37%, V: 0.08%, Nb: 0.029%, La-Ce: 0.0068%, P: 0.012%, S: 0.003%, and the rest is Fe and unavoidable impurities.

4. The method for manufacturing a high-strength heat-treated rail containing V, Nb and La-Ce mixed rare earth elements according to claim 1, characterized in that: The mass percentage content of each element in the rail is: C: 0.85%, Si: 0.63%, Mn: 0.96%, Cr: 0.31%, V: 0.07%, Nb: 0.020%, La-Ce: 0.0051%, P: 0.014%, S: 0.003%, and the rest is Fe and unavoidable impurities.

5. The method for manufacturing a high-strength heat-treated steel rail containing V, Nb and La-Ce mixed rare earth elements according to claim 1, characterized in that: The mass percentage content of each element in the rail is: C: 0.84%, Si: 0.68%, Mn: 0.97%, Cr: 0.33%, V: 0.07%, Nb: 0.026%, La-Ce: 0.0071%, P: 0.013%, S: 0.008%, and the rest is Fe and unavoidable impurities.

6. The method for manufacturing a high-strength heat-treated steel rail containing V, Nb and La-Ce mixed rare earth elements according to any one of claims 1 to 5, characterized in that: The manufactured high-strength heat-treated rails containing V, Nb and La-Ce mixed rare earth elements meet the following requirements: tensile strength ≥1370MPa, elongation ≥11%, tread hardness ≥390HB, and weight loss rate ≤0.10g / 100,000 times.

7. The method for manufacturing a high-strength heat-treated rail containing V, Nb and La-Ce mixed rare earth elements according to claim 1, characterized in that: The manufactured rail has the characteristics of high strength, high hardness, high wear resistance and excellent toughness, and meets the service requirements of heavy-load lines.

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