METHOD FOR PRODUCING HYPEREUTECTOID STEEL RAIL RESISTANT TO CONTACT FATIGUE
20240279784 ยท 2024-08-22
Assignee
Inventors
Cpc classification
C21C7/0075
CHEMISTRY; METALLURGY
International classification
C21C7/00
CHEMISTRY; METALLURGY
Abstract
The present invention discloses a method for producing a hypereutectoid steel rail resistant to contact fatigue. The method includes performing molten iron desulphurization, converter smelting, LF refining, RH refining, continuous casting and billet heating, rolling and heat treatment after rolling to obtain a steel rail; the heat treatment after rolling includes performing accelerated cooling and air cooling on the center of a tread of a rail head, both sides of the rail head and the center of a rail bottom of the steel rail obtained after rolling, wherein the starting cooling temperature of the accelerated cooling is 650-900? C., the cooling rate is 1.0-5.0? C./s, and the final cooling temperature is 400-550? C.; and after reaching the final cooling temperature, the accelerated cooling is stopped and it is air-cooled to room temperature. The hypereutectoid steel rail has higher purity, better contact fatigue resistance and good wear resistance.
Claims
1. A method for producing a hypereutectoid steel rail resistant to contact fatigue, characterized in that the method comprises performing molten iron desulphurization, converter smelting, LF refining, RH refining, continuous casting and billet heating, rolling and heat treatment after rolling to obtain a steel rail; the heat treatment after rolling comprises performing accelerated cooling and air cooling on the center of a tread of a rail head, both sides of the rail head and the center of a rail bottom of the steel rail obtained after rolling, wherein the starting cooling temperature of the accelerated cooling is 650-900? C., the cooling rate is 1.0-5.0? C./s, and the final cooling temperature is 400-550? C.; and after reaching the final cooling temperature, the accelerated cooling is stopped and it is air-cooled to room temperature; wherein the chemical composition of the steel rail comprises 0.9 mass %-1.2 mass % of C, based on the total mass of the steel rail.
2. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 1, characterized in that the chemical composition of the rail further comprises, based on the total mass of the steel rail, 0.5 mass %?Si+Mn+P+S+Cr?3.5 mass %, 0.01 mass %-0.12 mass % of V, and the balance being Fe and inevitable impurities.
3. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 1, characterized in that the steel rail has a P content of ?0.015 mass %.
4. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 1, characterized in that the gas content of the steel rail comprises a hydrogen content of ?0.00012 mass %, an oxygen content of ?0.0008 mass %, and a nitrogen content of ?0.0035 mass %.
5. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 1, characterized in that a cooling medium for the accelerated cooling is compressed air and/or a water mist mixture, preferably a water mist mixture sprayed at an air pressure of 0.1-0.2 MPa cooperating with water having a volume of 200-350 L/h.
6. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 1, characterized in that the LF refining comprises slag top deoxidation with a slag charge including 10 mass %-30 mass % of silicon carbide, 5 mass %-20 mass % of fluorite, and 30 mass %-40 mass % of quartz sand.
7. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 6, characterized in that a thickness of the slag charge of the molten steel is controlled to be 30-100 mm.
8. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 7, characterized in that 5 mass % of slag charge is added for every 10 min.
9. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 1, characterized in that 10-30% of activated limestone, 5-25% of calcium carbide and 300-1500 m of calcium wire are added before the vacuum degassing treatment in the RH refining, and not added after vacuum degassing.
10. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 1, characterized in that the steel rail compression ratio during the rolling is ?12.
11. The method for producing the hypereutectoid steel rail resistant to contact fatigue according to claim 2, characterized in that a cooling medium for the accelerated cooling is compressed air and/or a water mist mixture, preferably a water mist mixture sprayed at an air pressure of 0.1-0.2 MPa cooperating with water having a volume of 200-350 L/h.
Description
DETAILED DESCRIPTION OF THE INVENTION
[0035] In order that the objects, technical solutions, and advantages of the present invention will become more apparent, a more particular description of the invention will be rendered by reference to the appended drawings and embodiments.
[0036] The main process flow of external refining includes LF refining and RH refining.
[0037] LF refining (Steel ladle refining furnace method): it is heated with an electric arc and stirred with bottom blowing argon for the ladle.
[0038] Process advantages [0039] 1) Arc heating has high thermal efficiency, large heating range and temperature control accuracy of ?5? C.; [0040] 2) It has the functions of stirring and alloying, and it is easy to control the alloy composition in a narrow range and improve the stability of the product by the argon stirring; [0041] 3) It is suitable to produce ultra-low sulfur steel and ultra-low oxygen steel with less equipment investment and low refining cost.
[0042] Key points of LF refining production process [0043] 1) The heating and temperature control LF adopts arc heating, which has high thermal efficiency. The power consumption is 0.5-0.8 kW.Math.h when the temperature of molten steel is increased by 1? C. The heating rate of LF depends on the specific power of power supply (kVA/t), which in turn depends on the melting loss index of ladle refractory. Due to the use of submerged arc foam slag technology, the heat radiation loss of the arc can be reduced, the thermal efficiency can be improved by 10%-15%, and the accuracy of the end temperature is ??5? C. [0044] 2) White slag refining process. The slag removal amount is controlled at ?5 kg/t, and the slag package basicity R?3 is generally used to avoid the re-oxidation of slags. It should avoid exposing molten steel while argon stirring. [0045] 3) Alloy fine-tuning and narrow compositional range control. It has been reported experimentally that the use of alloy core wire technology can improve metal recovery.
[0046] RH refining (vacuum circulation degassing method) has the basic principle to continuously lift the molten steel into a vacuum chamber using bubbles to degas, decarburize and then back flow to the ladle.
Advantages of RH Refining
[0047] 1) Fast reaction. Vacuum degassing cycle is short, degassing operation can be completed in 10 minutes, and alloying and temperature homogenization can be completed in 5 minutes, which can be used in combination with converter. [0048] 2) High reaction efficiency. The molten steel is directly reacted in the vacuum chamber, and an ultra-pure steel of [H]?1.0?10.sup.?6, [N]?25?10.sup.?6, and [C]?10?10.sup.?6 can be obtained from the steel. [0049] 3) Oxygen decarburization and secondary combustion heat compensation can be performed to reduce the temperature drop in the refining process.
[0050] Embodiments of the present invention provide a method for producing a hypereutectoid steel rail resistant to contact fatigue. The method includes performing molten iron desulphurization, converter smelting, LF refining, RH refining, continuous casting and billet heating, rolling and heat treatment after rolling to obtain a steel rail.
[0051] In the embodiment of the present invention, the smelting process of the rolled steel of the steel rail is not particularly limited and may be performed according to a conventional smelting method. For example, in the smelting process of the rolled steel of the steel rail, the content of S in the molten iron entering the furnace is relatively low and may be ?0.015 wt %. The basicity of the refining slag is preferably 3-5, such as a mixture of aluminium trioxide, barium oxide and calcium fluoride. Preferably, the content of Al.sub.2O.sub.3 is from 20-25 wt %, the content of BaO is 8-12 wt %, and the content of CaF.sub.2 is 3-8 wt %. A carburizer is used. The carburizer used is anthracite and a low-N alloy. A blowing agent is used during heating of the LF furnace.
[0052] The continuous casting process of the steel rail after smelting to obtain molten steel is not particularly limited. For example, the continuous casting process of the steel rail may include that the molten steel obtained by smelting is cast into a billet, and the billet is slowly cooled to room temperature, then sent into a heating furnace for heating and heat preservation, and rolled.
[0053] The heat treatment after rolling includes performing accelerated cooling and air cooling on the center of a tread of a rail head, both sides of the rail head and the center of a rail bottom of the steel rail obtained after rolling, wherein the starting cooling temperature of the accelerated cooling is 650-900? C., the cooling rate is 1.0-5.0? C./s, and the final cooling temperature is 400-550? C.; and after reaching the final cooling temperature, the accelerated cooling is stopped and it is air-cooled to room temperature.
[0054] The chemical composition of the rail includes, based on the total mass of the steel rail, 0.9 mass %-1.2 mass % of C, 0.5 mass %?Si+Mn+P+S+Cr?3.5 mass %, 0.01 mass %-0.12 mass % of V, and the balance being Fe and inevitable impurities.
[0055] The P content in the steel rail is ?0.015 mass %. Preferably, the P content in the steel rail is ?0.008 mass %.
[0056] The steel rail also contains a gas with the gas content including a hydrogen content of ?0.00012 mass %, an oxygen content of ?0.0008 mass %, and a nitrogen content of ?0.0035 mass %.
[0057] A cooling medium for the accelerated cooling is compressed air and/or a water mist mixture, preferably a water mist mixture sprayed at an air pressure of 0.1-0.2 MPa cooperating with water having a volume of 200-350 L/h.
[0058] The LF refining comprises slag top deoxidation with a slag charge including 10 mass %-30 mass % of silicon carbide, 5 mass %-20 mass % of fluorite, and 30 mass %-40 mass % of quartz sand.
[0059] The slag thickness of the molten steel is controlled to be 30-100 mm. 5 mass % of slag charge is added for every 10 min.
[0060] A10-30% of activated limestone, 5-25% of calcium carbide and 300-1500 m of calcium wire are added before the vacuum degassing treatment in the RH refining, and not added after vacuum degassing.
[0061] In the embodiment of the present invention, the LF refining and the RH refining of the rolled steel of the steel rail are not particularly limited except for the above conditions, and may be performed according to a conventional LF refining and a RH refining method.
[0062] The steel rail compression ratio during the rolling is ?12.
[0063] A type inclusions in the steel rail are ?1.5; B type inclusions in the steel rail are ?1.0; C type inclusions in the steel rail are ?1.0; and D type inclusions in the steel rail are ?1.0.
[0064] The properties of the steel rail are as follows:
[0065] The present invention relates to a method for producing a hypereutectoid steel rail resistant to contact fatigue by using a low-S molten iron into the furnace and a high-basicity refining slag for a steel rail in a smelting process, and full-course protective casting. Anthracite and low-N alloys are used for the carburizer. The LF and RH processes reduce the content of C, P, S, O, H, N and other elements in the steel. LF molten steel slags in the process contain 10%-30% of silicon carbide, 5-20% of fluorite and 30-40% of quartz sand. 10-30% of activated limestone, 5-25% of calcium carbide and 300-1500 m of calcium wire are additionally added before the vacuum treatment, and not added after the vacuum treatment. The thickness of molten steel slag charge is controlled at 30-100 mm, and 5% of mixed slag charge is additionally added per 10 min. The LF and RH processes reduce the content of C, P, S, O, H, N and other elements in the steel. A certain cooling medium is applied at the central part of the rail bottom within the range of 900? C.-650? C. The cooling rate of the rail head tread, the rail head and the rail bottom center is 1.0-5.0? C./s. When the temperature of the rail head tread drops to 400-550? C., the accelerated cooling is stopped and it is air-cooled to room temperature. The hypereutectoid steel rail manufactured by this method has a tread hardness >420 HB, a laboratory steel rail wear of less than 0.2 g, and an increase in contact fatigue performance by 20%. The hypereutectoid steel rail has higher purity, better contact fatigue resistance and good wear resistance. As a result, the strength of hypereutectoid steel rail is greatly improved while the strength of hypereutectoid steel rail is increased. Finally, the steel rail produced has improved contact fatigue resistance.
[0066] Hereinafter, a method for producing a high-strength high-toughness hypereutectoid according to the present invention will be specifically described with reference to embodiments.
[0067] The following nine sets of steel rail chemistries are chosen for both the embodiments and the corresponding comparative examples in the invention. Table 1 shows different contents of C, P S, H, O, and N obtained by smelting process control.
TABLE-US-00001 TABLE 1 Chemical composition/mass % of Embodiments and Comparative examples Chemical elements/% Gas contents/ppm Items No. C P S H O N Embodi- 1# 0.90 0.004 0.002 0.6 4 31 ments 2# 0.94 0.005 0.002 0.6 5 32 3# 0.96 0.006 0.003 0.7 5 30 4# 0.98 0.007 0.003 0.6 6 30 5# 1.02 0.008 0.004 0.7 5 31 6# 1.06 0.009 0.004 0.8 5 32 7# 1.08 0.010 0.005 0.7 6 31 8# 1.12 0.012 0.005 0.7 7 30 Compar- 1# 0.96 0.015 0.006 1.0 10 49 ative 2# 0.98 0.016 0.007 1.1 11 51 examples 3# 0.96 0.019 0.008 1.2 12 52 4# 0.98 0.016 0.012 1.1 11 53
[0068] The comparative example in the present invention uses the same smelting, heating and heat treatment process as those in the embodiments.
[0069] The tensile properties of the steel rail of Embodiments and Comparative examples are tested according to the standard requirements on both sides of the rail head, and the tread hardness samples are tested on a tread position of the rail head. The test results are shown in Table 2. Table 2 illustrates the variation values of the tensile strength Rm and the elongation ratio Ain the tensile properties of the finished steel rail at the contents of C, P, S, H, O and N described in Table 1, and the corresponding formula values. The larger the number of HBW is, the more wear resistant it is. The larger the value of C*HBW/[(P+S+H+O+N)], the better the fatigue resistance. Larger value of Rm*A indicates better wear resistance and fatigue resistance of the rail.
TABLE-US-00002 TABLE 2 Tensile properties and tread hardness of Embodiments and Comparative examples in the invention Chemical Gas C*HBW/ elements/ contents/ Tensile [(P + % ppm properties S + H + Rm* Items No. C P S H O N HBW Rm A O + N)] A Embodi- 1# 0.90 0.004 0.002 0.6 4 31 405 1438 11.5 38127.6 16537.0 ments 2# 0.94 0.005 0.002 0.6 5 32 409 1445 11 35730.5 15895.0 3# 0.96 0.006 0.003 0.7 5 30 411 1469 10.5 31389.0 15424.5 4# 0.98 0.007 0.003 0.6 6 30 416 1481 10 29844.8 14810.0 5# 1.02 0.008 0.004 0.7 5 31 420 1510 9.5 27338.9 14345.0 6# 1.06 0.009 0.004 0.8 5 32 426 1532 9 26910.6 13788.0 7# 1.08 0.010 0.005 0.7 6 31 432 1539 8.5 24856.7 13081.5 8# 1.12 0.012 0.005 0.7 7 30 440 1551 8 23726.5 12408.0 Compar- 1# 0.96 0.015 0.006 1.0 10 49 415 1451 7.0 14755.6 10157.0 ative 2# 0.98 0.016 0.007 1.1 11 51 414 1452 7.5 13842.4 10890.0 examples 3# 0.96 0.019 0.008 1.2 12 52 416 1453 7.5 11914.1 10897.5 4# 0.98 0.016 0.012 1.1 11 53 416 1455 7.5 11813.4 10912.5
[0070] According to the requirements of TB/T 2344-2012 Ordering technical conditions for 43 kg/m-75 kg/i steel rails, it inspects the non-metallic inclusions at 10-15 mm under the rail head tread, and ranks them, as shown in Table 3. Table 3 illustrates the relationship between the sizes and classes of non-metallic inclusions present in the steel rail and the hardness HBW in a center line of the top surface of the finished steel rail at the contents of C, P, S, H, O and N described in Table 1.
TABLE-US-00003 TABLE 3 Nonmetallic inclusions of Embodiments and Comparative examples in the invention Chemical Gas Non-metallic HBW/ elements/ contents/ inclusion (A + % ppm Class Class Class Class B + Items No. C P S H O N HBW A B C D C + D) Embodi- 1# 0.90 0.004 0.002 0.6 4 31 405 0.5 0 0 0 810.0 ments 2# 0.94 0.005 0.002 0.6 5 32 409 0.5 0 0 0 818.0 3# 0.96 0.006 0.003 0.7 5 30 411 1.0 0 0 0 411.0 4# 0.98 0.007 0.003 0.6 6 30 416 0.5 0 0 0 832.0 5# 1.02 0.008 0.004 0.7 5 31 420 0.5 0 0.5 0 420.0 6# 1.06 0.009 0.004 0.8 5 32 426 1.0 0.5 0 0 284.0 7# 1.08 0.010 0.005 0.7 6 31 432 0.5 0 0.5 0.5 288.0 8# 1.12 0.012 0.005 0.7 7 30 440 0.5 0 0 0 880.0 Compar- 1# 0.96 0.015 0.006 1.0 10 49 415 1.0 0.5 0.5 0.5 166.0 ative 2# 0.98 0.016 0.007 1.1 11 51 414 1.5 0.5 1.0 0.5 118.3 examples 3# 0.96 0.019 0.008 1.2 12 52 416 2.5 1.5 2 1.5 55.5 4# 0.98 0.016 0.012 1.1 11 53 416 2.5 2 2.5 2 46.2
[0071] Wear samples are taken at the rail heads of the embodiments and the comparative examples, respectively, and the test results are shown in Table 4.
[0072] Table 4 shows the hardness of a center line of a top surface of the steel rail vs. the wear amount of the finished steel rail at the contents of C, P, S, H, O and N described in Table 1. The wear amount is closely related to the hardness of steel rail. By increasing the carbon content of the steel rail and assisted by the heat treatment process, the hardness of the center line of the rail top surface is increased, and then the rail wear is reduced.
TABLE-US-00004 TABLE 4 Wear of the rail head of the steel rail in Embodiments and Comparative examples in the invention Chemical Gas Test parameters elements/ contents/ Revolutions Wear % ppm Load (10,000 amount Items No. C P S H O N HBW (N) times) (g) Embodi- 1# 0.90 0.004 0.002 0.6 4 31 405 980 10 0.22 ments 2# 0.94 0.005 0.002 0.6 5 32 409 980 10 0.21 3# 0.96 0.006 0.003 0.7 5 30 411 980 10 0.20 4# 0.98 0.007 0.003 0.6 6 30 416 980 10 0.19 5# 1.02 0.008 0.004 0.7 5 31 420 980 10 0.18 6# 1.06 0.009 0.004 0.8 5 32 426 980 10 0.17 7# 1.08 0.010 0.005 0.7 6 31 432 980 10 0.16 8# 1.12 0.012 0.005 0.7 7 30 440 980 10 0.15 Compar- 1# 0.96 0.015 0.006 1.0 10 49 415 980 10 0.20 ative 2# 0.98 0.016 0.007 1.1 11 51 414 980 10 0.21 examples 3# 0.96 0.019 0.008 1.2 12 52 416 980 10 0.20 4# 0.98 0.016 0.012 1.1 11 53 416 980 10 0.21
[0073] Contact fatigue samples are taken at the rail head of the embodiments and comparative Examples, respectively, and the test results are shown in Table 5.
[0074] Table 5 shows the relationship between rail contact fatigue performance, hardness and internal hardness at the contents of C, P, S, H, O and N as described in Table 1. The fatigue performance of the steel rail can be improved by reducing C, P, S, H, O and N.
TABLE-US-00005 TABLE 5 Rail contact fatigue in Embodiments and Comparative examples of the invention Chemical Gas Rota- Contact elements/ contents/ Contact tional fatigue/ % ppm Stress/ Slip/ speed 1,000 Items No. C P S H O N HBW MPa % rpm 0 times Embodi- 1# 0.90 0.004 0.002 0.6 4 31 405 1350 5 1000 40 ments 2# 0.94 0.005 0.002 0.6 5 32 409 1350 5 1000 39 3# 0.96 0.006 0.003 0.7 5 30 411 1350 5 1000 38 4# 0.98 0.007 0.003 0.6 6 30 416 1350 5 1000 37 5# 1.02 0.008 0.004 0.7 5 31 420 1350 5 1000 37 6# 1.06 0.009 0.004 0.8 5 32 426 1350 5 1000 36 7# 1.08 0.010 0.005 0.7 6 31 432 1350 5 1000 36 8# 1.12 0.012 0.005 0.7 7 30 440 1350 5 1000 35 Compar- 1# 0.96 0.015 0.006 1.0 10 49 415 1350 5 1000 21 ative 2# 0.98 0.016 0.007 1.1 11 51 414 1350 5 1000 19 examples 3# 0.96 0.019 0.008 1.2 12 52 416 1350 5 1000 18 4# 0.98 0.016 0.012 1.1 11 53 416 1350 5 1000 17
[0075] In view of the above, the method for producing a hypereutectoid steel rail according to the present invention provides an effective method for improving the contact fatigue resistance of the steel rail while improving the strength of the rail. The product is applicable to lines with heavy axle load, high density, and heavy load.
[0076] The foregoing is the exemplary embodiments of the present disclosure. It should be noted that various changes and modifications can be made herein without departing from the scope of the disclosed embodiments as defined by the appended claims. Although elements disclosed in the embodiments of the present invention can be described or required in individual forms, a plurality is contemplated unless explicitly limited to the singular.
[0077] Those of ordinary skill in the art will appreciate that the above discussion of any embodiments is intended to be exemplary only, and is not intended to suggest that the scope of the disclosed embodiments (including the claims) is limited to these examples. Combinations of features in the above embodiments or in different embodiments are also possible within the idea of embodiments of the invention, and many other variations of different aspects of the embodiments of the invention as described above are not provided in detail for the sake of clarity. Therefore, any omission, modification, equivalent substitution or improvement made within the spirit and principle of the embodiment of the invention shall be included in the scope of protection of the embodiment of the invention.