Manufacturing method for improving wear resistance of H340-grade heat treatment steel rail through rare earth elements

Abstract

The invention discloses a manufacturing method for improving wear resistance of a H340-grade heat-treated steel rail by using rare earth elements. The manufacturing method comprises the following steps: a smelting process: smelting in a vacuum induction furnace and heating a steel ingot in an electric induction heating furnace; the rolling process comprises the following steps: heating a cylindrical steel ingot, rolling by a pilot-scale small rolling mill, air-cooling and performing heat treatment; the steel rail comprises the following chemical components in percentage by mass: 0.75-0.0.80% of C; the content of Si is 0.55 to 0.0.70 percent; 0.80% to 1.00% of Mn; 0.04% to 0.08% of V; less than or equal to 0.015% of P; less than or equal to 0.015% of S; 0.001% to 0.010% of RE (rare earth); the total mass percent of the Fe and the impurities is 100%. According to the manufacturing method for improving the wear resistance of the H340-grade heat treatment steel rail through the rare earth elements, the low-cost and high-quality H340-grade U75VH steel rail meeting the standard strength and hardness and good toughness is smelted, and the manufacturing method is applied to railways.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a method for manufacturing a H340 grade heat-treated rail with improved wear resistance by using rare earth elements. Background Art

[0002] Railways have become an important means of economic development and transportation in countries around the world with their advantages of high speed, large operating volume, high punctuality rate and safe driving. At present, most of the rails used for railway freight in China are H340 grade U75VH heat-treated rails in the TB / T2344 standard. The chemical composition of this rail is mainly C, Si, Mn and V, and the online residual heat quenching method is used to improve the comprehensive performance of the rail. With the development of the economy, the number of transportation lines is increasing. The service of rails in small curves, low temperatures, different operating speeds and other environments causes problems such as surface fish scale cracks, peeling blocks, rapid wear, and even brittle fracture, which directly affects the safety of railway transportation. Combined with the service requirements of special sections, on the premise of meeting the standard requirements, the composition and production process of U75VH rails are optimized to further improve the strength, hardness, abrasion resistance, wear resistance and good welding performance of the rails within the standard range, improve the service safety of the section rails, and reduce the maintenance cost of the line rails.

[0003] The Chinese patent with announcement number CN1304618C discloses a highly wear-resistant pearlite steel with a carbon content of up to 1.4%, and further adds microalloy elements such as Nb, V, Mo, and B to control the carbide morphology, which has complex costs and production processes; the patent with announcement number CN101818312B discloses a method of low-temperature reheating of rolled rails combined with accelerated cooling to control the pearlite phase transformation to obtain fine pearlite to improve toughness, which increases energy consumption and production costs; CN 114855082 A adds different rare earth contents to hot-rolled U75V rails, and the low-temperature performance is improved by comparison; therefore, adding an appropriate amount of rare earth to steel can play a role in refining grains, purifying steel quality, and uniformly transforming the organization. The finer the grains, the more grain boundaries, the more obvious the effect of hindering dislocation movement, and comprehensively improves the service life of the rails. Focusing on the U75VH rail problems such as heavy-load line freight curves, the invention of adding different contents of rare earth Ce elements to the U75VH rail is made. While ensuring the various mechanical properties of the rail, the wear resistance of the rail is improved, which is of great significance to the development of railways and the improvement of the performance of material accessories. Summary of the invention

[0004] The purpose of the present invention is to provide a method for manufacturing H340 grade heat-treated rails with rare earth elements to improve the wear resistance, smelt low-cost high-quality H340 grade U75VH rails with standard strength, hardness and good toughness, and apply them to railways.

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

[0006] The present invention provides a method for manufacturing a H340 grade heat-treated rail with improved wear resistance by using rare earth elements, comprising:

[0007] Smelting process: vacuum induction furnace smelting → electric induction heating furnace heating steel ingot; including:

[0008] Vacuum smelting uses aluminum-free deoxidation alloying, and the whole smelting process is protected by vacuum;

[0009] The smelting raw materials are mainly industrially produced U75VH rail materials, and other auxiliary materials are pure iron, ferroalloy, and rare earth Ce ferroalloy as raw materials for smelting;

[0010] Add appropriate amount of U75VH scrap steel and pure iron into the electric furnace for smelting, evacuate the vacuum furnace, and add inert protective gas after the vacuum degree is ≤30pa. Turn on the power for induction heating to melt the charge;

[0011] The charge is melted by heating in an electric furnace for 18-20 minutes. According to the raw material composition and the loss of steel in electric furnace smelting, 70-80% ferrosilicon, 90-98% manganese, 50-60% ferrochrome, 75-85% ferrovanadium and other materials are appropriately added to the vacuum smelting furnace. The amount of various alloys added is to achieve the target composition. After heating for 2-5 minutes, 30% ferrocerium alloy is added for electromagnetic stirring for 3-5 minutes. During the smelting process, the melt is stirred by a bottom blowing device, or the forward and backward tilting operation of the tilting device is performed to tilt the crucible forward or backward, so that the melt can be stirred.

[0012] After stirring and melting the rare earth, continue heating for 10 minutes until the temperature of the molten steel reaches 1550-1570℃. After standing for 2-5 minutes, it is poured out of the furnace. The poured steel ingot needs to be slowly cooled in the ingot mold to room temperature before being taken out of the mold.

[0013] Rolling process: cylindrical steel ingot → heating → pilot small-scale rolling mill → air cooling → heat treatment: Among them:

[0014] The steel ingot is heated in an electric induction heating furnace at a heating rate of 15°C / s to 1230°C and kept at this temperature for 60min to 90min;

[0015] After uniform heating and heat preservation, the steel ingot is taken out of the furnace for rolling. The rolling is carried out by a two-roller large-scale rolling mill, with the initial rolling temperature of 1100℃~1050℃, 9 rolling passes, and the steel billet rolling reduction ratio ≥9:1; the final rolling temperature is 870℃~910℃.

[0016] The rolled plate was sawed and processed into 230 cm long and 150 mm wide samples for heat treatment; it was heated to 930°C at 10°C / s in a small heating furnace, kept at this temperature for 30 to 50 minutes, and then air-cooled to 750 to 820°C for heat treatment.

[0017] The heat treatment medium is wind, and the compressed air cools the entire heat treatment test through the cooling nozzle. The distance between the nozzle and the heat treatment sample is 25 to 30 cm; after cooling to 420 to 500 ° C, it is naturally cooled at room temperature;

[0018] The chemical composition of the rail by mass percentage is: C 0.75-0.0.80%; Si 0.55-0.0.70%; Mn 0.80-1.00%; V 0.04-0.08%; P≤0.015%; S≤0.015%; RE 0.001-0.010%; the rest is Fe and impurities, and the mass fraction is 100% in total.

[0019] Furthermore, the chemical composition of the rail by mass percentage is: C 0.776%; Si 0.646%; Mn 0.965%; V 0.045%; P 0.010%; S 0.006%; RE 0.0018%; the rest is Fe and impurities, with a total mass fraction of 100%.

[0020] Furthermore, the chemical composition of the rail by mass percentage is: C 0.780%; Si 0.660%; Mn 0.978%; V 0.043%; P 0.012%; S 0.007%; RE 0.0032%; the rest is Fe and impurities, with a total mass fraction of 100%.

[0021] Furthermore, the chemical composition of the rail by mass percentage is: C 0.779%; Si 0.649%; Mn 0.964%; V 0.044%; P 0.009%; S 0.007%; RE 0.0052%; the rest is Fe and impurities, with a total mass fraction of 100%.

[0022] Furthermore, the chemical composition of the rail by mass percentage is: C 0.782%; Si 0.653%; Mn 0.972%; V 0.048%; P 0.013%; S 0.002%; RE 0.0067%; the rest is Fe and impurities, with a total mass fraction of 100%.

[0023] Furthermore, the mechanical properties of the rails meet the following requirements: tensile strength ≥ 1180 MPa, elongation after fracture ≥ 10%, and tread hardness between 350-361 HBW.

[0024] The main alloying elements V and Fe added in the material have a large solid solubility, have a solid solution strengthening effect, and improve the strength and hardness of the steel. 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, and improves the strength, elasticity and anti-tempering stability of the steel. In order to give full play to the heat treatment ability, the Mn and V elements of the rail alloy are controlled according to the standard lower limit, meet the standard composition, and combine the cooling transformation characteristics of the material composition to improve the online heat treatment cooling capacity and ensure the mechanical performance of the material. The present invention also gives full play to the RE element advantage of Baosteel, adds an iron alloy containing high-purity rare earth Ce, has the function of controlling the morphology of sulfides in the smelting process, forms rare earth sulfur oxides and reduces the formation of other metal sulfur compounds. This new sulfur compound does not deform or is very small during the rolling process, so that the grains in the steel are refined. In addition, rare earth can improve the oxidation resistance and corrosion resistance of the steel.

[0025] Compared with the prior art, the beneficial technical effects of the present invention are:

[0026] The steel rail of the present invention meets the following requirements: tensile strength ≥ 1180MPa, elongation after fracture ≥ 10%, tread hardness between 350-361HBW, and meets the performance requirements for U75VH steel rails in the standard "TB / T 2344.12020 Steel Rails Part 1 43kgm-75kgm Steel Rails". It also has excellent wear resistance. DETAILED DESCRIPTION

[0027] The chemical compositions of each example are shown in Table 1.

[0028] Table 1 Composition of each embodiment (mass percentage / %)

[0029]

[0030]

[0031] As shown in Table 1, Examples 1 to 5 are all U75VH rail smelting compositions within the standard composition range, wherein the contents of C, Si, Mn, Cr, V, P, and S are substantially the same. No rare earth Ce element is added to Example 1, 18 ppm rare earth Ce element is added to Example 2, 32 ppm rare earth Ce element is added to Example 3, 52 ppm rare earth Ce element is added to Example 4, and 67 ppm rare earth Ce element is added to Example 5.

[0032] The mechanical test results of each embodiment are shown in Table 2.

[0033] Table 2 Mechanical properties of each embodiment

[0034]

[0035] As can be seen from Table 2, each embodiment has good strength, hardness and mechanical properties, and the rails produced by them meet the technical requirements of the U75VH standard. As can be seen from Table 2, the tensile strength of embodiments 1 to 5 is ≥1180MPa, the elongation after fracture is ≥10%, and the tread hardness is between 350-361HBW, which meets the performance requirements for U75VH rails in the standard "TB / T2344.12020 Rails Part 1 43kgm~75kgm Rails". Compared with embodiment 1, the elongation after fracture of embodiments 2 to 5 is increased, and the maximum can reach 12.7%; the tensile strength is increased, and the maximum tensile strength of embodiment 4 is 1268MPa, and the tread hardness is ≥350HBW. While the strength and hardness of embodiments 2 to 5 are increased relative to embodiment 1, the toughness is also improved accordingly.

[0036] Table 3 Wear test parameters during the embodiment; Wear tests were performed on Examples 1 to 5.

[0037] Table 3 Material wear test parameters

[0038]

[0039] Table 4 shows the wear values ​​during the embodiment process. It can be seen that the average values ​​of embodiments 2-5 are lower than those of embodiment 1 without rare earth addition, and the lowest wear average value is 11.98 μg / m. The addition of rare earth relatively improves the wear resistance of H340 grade U75VH. The wear amount of embodiment 2 is 97.14% relative to embodiment 1 without rare earth addition, and the wear resistance is improved by 2.96%. The wear amount of embodiment 5 is 92.58% relative to embodiment 1, and the relative wear resistance is improved by 8%.

[0040] Table 4 Wear rate values ​​of materials in different embodiments

[0041]

[0042]

[0043] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for manufacturing H340 grade heat-treated rails with rare earth elements to improve wear resistance, characterized in that: include: Smelting process: vacuum induction furnace smelting → electric induction heating furnace heating steel ingot; including: Vacuum smelting uses aluminum-free deoxidation alloying, and the whole smelting process is protected by vacuum; The smelting raw materials are mainly industrially produced U75VH rail materials, and other auxiliary materials are pure iron, ferroalloy, and rare earth Ce ferroalloy as raw materials for smelting; Add appropriate amount of U75VH scrap steel and pure iron into the electric furnace for smelting, evacuate the vacuum furnace, and add inert protective gas after the vacuum degree is ≤30pa. Turn on the power for induction heating to melt the charge; The charge is melted by heating in an electric furnace for 18-20 minutes. According to the raw material composition and the loss of steel in electric furnace smelting, 70-80% ferrosilicon, 90-98% manganese, 50-60% ferrochrome and 75-85% ferrovanadium are appropriately added to the vacuum smelting furnace. The amount of various alloys added is to achieve the target composition. After heating for 2-5 minutes, 30% ferrocerium alloy is added for electromagnetic stirring for 3-5 minutes. During the smelting process, the melt is stirred by using a bottom blowing device, or the forward and backward tilting operation of the tilting device is performed to tilt the crucible forward or backward, so that the melt can be stirred. After stirring and melting the rare earth, continue heating for 10 minutes until the temperature of the molten steel reaches 1550-1570℃. After standing for 2-5 minutes, it is poured out of the furnace. The poured steel ingot needs to be slowly cooled in the ingot mold to room temperature before being taken out of the mold. Rolling process: cylindrical steel ingot → heating → pilot small-scale rolling mill → air cooling → heat treatment: Among them: The steel ingot is heated in an electric induction heating furnace at a heating rate of 15°C / s to 1230°C and kept at this temperature for 60min to 90min; After uniform heating and heat preservation, the steel ingot is taken out of the furnace for rolling. The rolling is carried out by a two-roller large-scale rolling mill, with the initial rolling temperature of 1100℃~1050℃, 9 rolling passes, and the steel billet rolling reduction ratio ≥9:1; the final rolling temperature is 870℃~910℃. The rolled plate was sawed and processed into 230 cm long and 150 mm wide samples for heat treatment; it was heated to 930°C at 10°C / s in a small heating furnace, kept at this temperature for 30 to 50 minutes, and then air-cooled to 750 to 820°C for heat treatment. The heat treatment medium is wind, and the compressed air cools the entire heat treatment test through the cooling nozzle. The distance between the nozzle and the heat treatment sample is 25 to 30 cm; after cooling to 420 to 500 ° C, it is naturally cooled at room temperature; The chemical composition of the rail by mass percentage is: C 0.75-0.0.80%; Si 0.55-0.0.70%; Mn 0.80-1.00%; V 0.04-0.08%; P≤0.015%; S≤0.015%; RE 0.001-0.010%; the rest is Fe and impurities, and the mass fraction is 100% in total.

2. The method for manufacturing H340 grade heat-treated rails with rare earth elements to improve wear resistance according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.776%, Si 0.646%, Mn 0.965%, V 0.045%, P 0.010%, S 0.006%, RE 0.0018%, and the rest is Fe and impurities, with a total mass fraction of 100%.

3. The method for manufacturing H340 grade heat-treated rails with rare earth elements to improve wear resistance according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.780%, Si 0.660%, Mn 0.978%, V 0.043%, P 0.012%, S 0.007%, RE 0.0032%, and the rest is Fe and impurities, with a total mass fraction of 100%.

4. The method for manufacturing H340 grade heat-treated rails with rare earth elements to improve wear resistance according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.779%; Si 0.649%; Mn 0.964%; V 0.044%; P 0.009%; S 0.007%; RE 0.0052%; the rest is Fe and impurities, and the total mass fraction is 100%.

5. The method for manufacturing H340 grade heat-treated rails with rare earth elements to improve wear resistance according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.782%, Si 0.653%, Mn 0.972%, V 0.048%, P 0.013%, S 0.002%, RE 0.0067%, and the rest is Fe and impurities, with a total mass fraction of 100%.

6. The method for manufacturing H340 grade heat-treated rails with rare earth elements to improve wear resistance according to claim 1, characterized in that: The mechanical properties of the rails meet the following requirements: tensile strength ≥ 1180 MPa, elongation after fracture ≥ 10%, and tread hardness between 350-361 HBW.

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