DE102018125047A1 - Rail of a railway line with mixed passenger and freight traffic and method for its production - Google Patents

Abstract

The invention relates to the technical field of rail production, and more particularly to a rail of a railway line with mixed passenger and freight traffic and the method for their production. In view of the low overall strength and overall toughness of the pearlitic rail made with an existing process, the invention provides a railway rail production method for a mixed passenger and freight railway comprising the following steps: a. Hot rolling a steel billet into a rail, with a final rolling temperature of 900-1000 ° C; b. Blowing a cooling medium onto the upper surface of the rail head, the two sides of the rail head, and the lower lands on both sides of the rail head when the center of the upper surface of the rail is air cooled to 800-850 ° C and then air cooling the rail to room temperature, after the middle of the upper surface of the rail has cooled to 520-550 ° C. By regulating the composition of the steel and applying two-stage accelerated cooling, the invention is capable of producing a better performing rail suitable for a railway line with mixed passenger and freight traffic.

Description

Field of the invention

The invention relates to a rail, in particular a rail of a railway line with mixed passenger and freight traffic and the method for their production.

Background of the invention

The rapid development of the railways puts higher demands on the efficiency of the rail. With the continuous improvement of China's high-speed rail network, a gradual transformation of heavy goods traffic will be carried out on the existing main railway lines with mixed passenger and freight traffic. Heavy rail traffic will develop towards a large volume, a high axle load and a high density. As a key component of the railways, rail quality and performance are closely linked to rail transport efficiency and road safety. As the transport capacity of the railways has improved, the rail milieu has become increasingly harsh and complex, causing all kinds of damage and breakdowns. Some rails in low-radius turns present damage and failures such as rapid abrasive wear and concomitant detachment, making their service life incompatible with the service life of mainline rails, thereby limiting the further development of rail transport.

Currently, the on-line or off-line heat treatment method is mainly applied to pearlitic rails to improve the performance of the rail in curves of a mixed passenger and freight railroad. By blowing compressed air or a water-air spray mixture onto the rail head of the austenitic rail, the rail head is rapidly cooled, and is capable of forming a refined and lamellar pearlitic structure from the surface of the rail head to a certain depth. The strength and toughness of the rail can be improved synchronously by grain refinement, so that the wear resistance and contact fatigue resistance can be simultaneously improved. With regard to an accelerated cooling process, few research reports are available on the influence of cooling nozzle design on the performance of the rail at home and abroad.

patent CN101646795B , Internal High-Hardness Pearlitic Rail with Excellent Wear Resistance and Fatigue Damage Resistance and Manufacturing Method Thereof, describes a production process for a perlitic rail with a high internal hardness, characterized in that the steel at a final rolling temperature of 850-950 ° C in a Hot rolled rail shape, and the surface of the rail head from the temperature above the temperature of the pearlitic transformation to 400-650 ° C at a rate of 1.2-5 ° C / s is rapidly cooled. The patent discloses only the temperature of the initial and final cooling as well as the corresponding range of the cooling rate in different stages of the heat treatment of the rail, but does not indicate a cooling process.

patent CN105483347A discloses a heat treatment process for curing a pearlitic rail, characterized in that a rail is heated to 880-920 ° C and insulated for 10-15 minutes and thereafter cooled to a specific temperature range in a specific range of cooling speed corresponding to different types of steel and insulated for 30 seconds The process for curing a U75V pearlitic rail is: insulating the rail at 880-920 ° C for 10-15 minutes, and cooling the rail to 570-600 ° C with a cooling rate of 8-15 ° C / s, and then air cooling the rail to 20-25 ° C with a cooling rate of 0.2-0.5 ° C / s; the method of hardening a U76CrRE pearlitic rail is: isolating the rail at 850-900 ° C for 10-15 minutes, and cooling the rail to 590-610 ° C with a cooling rate of 6-10 ° C / s, and thereafter Air cooling the rail to 20-25 ° C with a cooling rate of 0.2-0.5 ° C / s. The heat treatment process disclosed by the patent for the two types of material, ie U75V and U76CrRE, also does not relate to a particular cooling process.

patent CN103898303A discloses a heat treatment method for a switch rail and a switch rail, characterized in that accelerated cooling is performed on a switch rail to be treated at a temperature of the upper surface of the rail head of 650-900 ° C, to the switch rail with completely pearlitic structures obtained, wherein the speed of the accelerated cooling of the running surface of the rail head of the switch rail is higher than that of the non-running surface of the rail head of the switch rail, with a difference of 0.1-1.0 ° C / s. The patent describes the advantages of different cooling rates on the two sides of the rail head for the rail, in particular for improving the performance and regulating the flatness of the rail with asymmetrical cross section, but does not explain the influence of the nozzle design and the cooling rate in the different stages the performance of the rail after the heat treatment.

In the prior art, the heat treatment of the rail is mainly directed to the control of different cooling rates in different temperature ranges to control the heat treatment processes, it does not specify the refined control such as various nozzle design and blowing method, therefore, no perlitic rail excellent in strength and Toughness.

Brief description of the invention

The technical problem to be solved by the invention is this: In the prior art, the method using different cooling rates in different temperature ranges is used for the heat treatment of a rail, therefore, the obtained pearlitic rail has a poor performance.

The technical scheme of the invention for solving the technical problem is to provide a railway rail production method for a mixed passenger and freight railway, comprising the following steps:

Rolling a rail

Hot rolling a steel billet into a rail, with a final rolling temperature range of 900-1000 ° C;

Cooling the rail

Blowing a cooling medium onto the upper surface of the rail head, the two sides of the rail head and the lower lands on both sides of the rail head when the center of the upper surface of the rail is air cooled to 800-850 ° C, and then air cooling the rail to room temperature after the middle of the upper surface of the rail has cooled to 520-550 ° C.

In the railway rail production method for mixed passenger and freight transport, the composition of the rail in step a, in weight percent: C: 0.70% to 0.85%, Si: 0.15% to 0.60%, Mn: 0.70% to 1.05%, Cr: 0.15% to 0.50%, at least one of V, Nb and Ti, wherein V: 0.02% to 0.10%, if present, Ti : 0.001% to 0.030%, if any, and Nb: 0.005% to 0.08%, if any, and the balance: Fe and unavoidable impurities.

In the production process for the rail of a railway line with mixed passenger and freight traffic, the cooling medium in steps b and c is at least one of compressed air or water-air spray mixture.

In the production process for the rail of a railway line with mixed passenger and freight traffic, the cooling rate in step b is 3.0-7.0 ° C / s.

The invention also provides a Rail of a railway line with mixed passenger and freight traffic, with the composition, in weight percent: C: 0.70% -0.85%, Si: 0.15% to 0.60%, Mn: 0.70% to 1 , 0.05%, Cr: 0.15% to 0.50%, at least one of V, Nb and Ti, wherein V: 0.02% to 0.10%, if present, Ti: 0.001% to 0.030%, if present, and Nb: 0.005% to 0.08%, if any, and the remainder: Fe and unavoidable impurities.

Compared with the prior art, the advantageous effects of the invention are that: the invention uses a rail with a special composition and a method of two-stage accelerated cooling, therefore, compared to the existing single method for the heat treatment, the rail produced in this process more excellent strength, hardness, toughness and ductility, in particular a much better strength and toughness, has. The method of the invention can be easily performed and has a low equipment requirement, and the manufactured rail of a mixed passenger and freight railway can improve the overall strength and toughness of a rail head and extend the life under the same conditions.

Detailed Description of the Preferred Embodiments

The invention provides a railway rail production method for a mixed passenger and freight railway, comprising the following steps:

Rolling a rail

Hot rolling a steel billet into a rail, with a final rolling temperature range of 900-1000 ° C;

Cooling the rail

Blowing a cooling medium onto the upper surface of the rail head, the two sides of the rail head and the lower lands on both sides of the rail head when the center of the upper surface of the rail is air cooled to 800-850 ° C, and then air cooling the rail to room temperature after the middle of the upper surface of the rail has cooled to 520-550 ° C.

The rail of a mixed passenger and freight railway line according to the invention has the following composition, by weight: C: 0.70% to 0.85%, Si: 0.15% to 0.60%, Mn: 0.70 % to 1.05%, Cr: 0.15% to 0.50%, at least one of V, Nb and Ti, wherein V: 0.02% to 0.10%, if present, Ti: 0.001% to 0.030 %, if any, and Nb: 0.005% to 0.08%, if present, and balance: Fe and unavoidable impurities.

C is the most important and cost-effective element to improve the strength and hardness of a pearlitic rail and to promote perlitic transformation. Under the conditions of the present invention, when the C content is <0.70%, the strength and hardness values are too low and the hardness and wear resistance required for the rail can not be ensured; When the C content is> 0.85%, traces of secondary cementite are precipitated at the grain boundaries even if accelerated cooling is applied after the finish rolling, thereby deteriorating the toughness and deformability of the rail. Therefore, the C content is limited within the range of 0.70% to 0.85%.

As a solid solution strengthening element of steel, Si is present in ferrite and austenite to improve the strength of the structure, while suppressing the precipitation of pre-eutectic cementite, thereby improving the toughness and ductility of the rail. Under the conditions of the present invention, when the Si content is <0.10%, the solubility in the solid state is relatively low, resulting in low solidification effects; If the Si content is> 0.60%, the toughness and deformability of the rail deteriorate and the bending ability of the rail deteriorates. Therefore, the Si content is limited within the range of 0.10% to 0.60%.

Mn can form a mixed crystal with Fe, with solidification of ferrite and austenite. Meanwhile, Mn is a carbide former and, after entering the cementite, can partially replace the Fe atom, thereby improving the hardness of carbide and ultimately improving the hardness of the rail. Under the conditions of the present invention, when the Mn content is <0.70%, the solidification effect is not remarkable, and the performance of the steel can be improved only slightly by solid solution strengthening; if the Mn content is> 1.05%, the hardness of the carbide in the steel is too high and the toughness and ductility deteriorate considerably; however, Mn has a marked diffusion effect on carbon when present in the steel, and the precipitation zone of Mn can still form B-structure, M-structure, and other abnormal structures even under air-cooling conditions. Therefore, the Mn content is limited within the range of 0.70% to 1.05%.

As a middle carbide former, Cr can form several carbides with carbon in the steel; however, Cr can even cause a distribution of the carbides in the steel, reduce the size of the carbides, and improve the wear resistance of the rail. Under the conditions of the present invention, when the Cr content is <0.15%, the carbide formed has a low hardness and a small proportion, and aggregates in a plate form, in this way, the wear resistance of the rail can not be effectively improved; When the Cr content is> 0.50%, there is a susceptibility to the formation of coarse carbide, which causes the Toughness and deformability of the rail deteriorate. Therefore, the Cr content is limited within the range of 0.15% to 0.50%.

V has a low solubility in steel at room temperature, and when V is in austenite grain boundaries and other zones during hot rolling, it is precipitated through fine grained V carbonitride [V (C, N)] or together with Ti in the steel, causing the Growth of austenite grains is suppressed, thus refining the grain and improving performance. Under the conditions of the present invention, when the V content is <0.02%, the precipitation of V carbonitride is limited and the rail can not be effectively solidified; if the V content is> 0.10%, there is a susceptibility to the formation of coarse carbonitride, which deteriorates the toughness and ductility of the rail. Therefore, the V content is limited within the range of 0.02% to 0.10%.

The primary function of Ti in the steel is to refine the austenite grains during heating, rolling and cooling, and ultimately to improve the ductility and rigidity of the rail. When the Ti content is <0.001%, the amount of carbides formed in the rail is extremely limited. On the one hand, under the conditions of the present invention, when the Ti content is> 0.030%, too much TiC is formed because Ti is a strong carbonitride former, thereby making the hardness of the rail too high, and on the other hand, excess TiN and TiC may be added to enrich the TiC Lead precipitates and form coarse carbonitride, which deteriorates the toughness and ductility and makes the contact surface of the rail under impact load susceptible to cracking and leads to breakage. Therefore, the Ti content is limited within the range of 0.001% to 0.030%.

The main function of Nb in the steel is similar to that of V, that is, to refine the austenite grains with the precipitated Nb carbonitride and to cause precipitation strengthening with the carbonitride formed during the cooling process after rolling. Nb can improve the hardness of the rail, improve the toughness and ductility of the rail and help prevent the softening of welded joints. Under the conditions of the present invention, when the Nb content is <0.005%, the precipitation of Nb-carbonitride is limited and the rail can not be effectively solidified; if the Nb content is> 0.08%, there is a susceptibility to the formation of coarse carbonitride, which deteriorates the toughness and deformability of the rail. Therefore, the Nb content is limited within the range of 0.005% to 0.08%.

The conventional melting method in the art is used to melt steel for the above rail: to carry out the continuous casting of the molten steel in accordance with the above compositional requirements to produce a steel billet having the cross section of 250 mm x 250 mm to 450 mm x 450 mm Cooling the steel billet, placing the steel billet in a heating furnace for heating at 1200-1300 ° C, isolating the steel billet for a period of time and removing it from the furnace, removing phosphorus with high pressure water, and then rolling the billet into a rail having 50- 75 kg / m with the required cross-section through universal rollers or grooved rollers.

At present, the main method for carrying out the heat treatment of a rail is to perform accelerated cooling of the rail head of the austenitic rail, and the cooling nozzles are mainly arranged on the upper surface and both sides of the rail head. This is determined by the characteristics of the rail: the upper surface and one side of the rail head carry multiple complex loading of the wheel, and the rail has a symmetrical cross-section along the vertical direction. Both sides may be exposed to the load of the wheel as their location varies. Therefore, the power of the claimed upper surface and the claimed two sides of the rail head should be higher than that of the other parts of the rail.

In the process of accelerated cooling of the top surface and the two sides of the rail head, upon sudden drop in surface temperature, the core of the rail head transfers heat across the surface, the performance of the surface of the rail head must not deteriorate, but instead can interfere with the release of improve latent heat during the phase change of perlite. This means that the supercooling of the core of the rail head decreases during the phase change. Finally, at room temperature, not only is the hardness of the core of the rail head significantly lower than that of the surface, but also the toughness is relatively low. The invention applies the method of adding nozzles to the lower lands on both sides of the rail head for inflating cooling medium. During the heat treatment, since the difference in the cooling rate between the core of the rail head and the surface of the rail head decreases, the phase transformation of the surface of the rail head may begin at a much lower temperature, and the The strength and toughness of the rail can be further improved. Although the improvement is quite limited, it can still improve the overall strength and toughness of the steel rail, such as a heat treated pearlite rail, with strength and toughness already reaching the limit.

In the invention, when the rail is air-cooled to 800-850 ° C, the upper surface of the rail head, the both sides of the rail head and the lower lands on both sides of the rail head become at a cooling rate of 3.0-7.0 ° C / s cooled to 520-550 ° C.

During the cooling process, the surface temperature drops rapidly under the action of the cooling medium, and the heat from the core of the rail head and the rail land is continuously circulated and supplied to the surface of the rail head and a certain depth, resulting in a supercooling of the core of the rail head, which results in a reduction in the strength and toughness of the rail at room temperature; when the cooling of the lower webs of the rail head is applied simultaneously, new ways are provided for heat dissipation in the rail head, and the heat input to the core of the rail head is significantly reduced, thereby enhancing the supercooling of the part of the rail head, especially the core of the rail head , As the grains of the entire rail head are further refined, the rail has superior overall strength and toughness at room temperature. When the temperature of the upper surface of the rail head decreases to 520-550 ° C, air cooling is performed until the rail head reaches room temperature, and straightening, error checking and machining, etc. are performed in later stages to obtain the finished rail.

The preferred embodiments of the invention will be further explained as follows, but this does not mean that the scope of the invention is limited as described in the embodiments.

Embodiments 1-6: Production of a perlitic rail of a railway line with mixed passenger and freight traffic with the method according to the invention

The chemical composition of the steel billet for the pearlitic rail in Embodiments 1-6 is shown in Table 1: Table 1: List of the chemical composition of the steel billet for the pearlitic rail (%) C Si Mn P S Cr V / Ti / Nb Embodiment 1 0.82 0.37 0.70 0.011 0,007 0.44 0,03V Embodiment 2 0.85 0.19 0.88 0,012 0.005 0.15 0,04Nb Embodiment 3 0.70 0.60 1.05 0,013 0,006 0.27 0,019Ti Embodiment 4 0.77 0.52 0.94 0,010 0,006 0.38 0,07Nb Embodiment 5 0.80 0.15 0.77 0,015 0,008 0.50 0,10V Embodiment 6 0.74 0.44 0.98 0.011 0,007 0.22 0,009Nb

The steel billets shown in the above table are all rolled into rails of 60 kg / m and cooled by the following procedure:

Rolling a rail

Hot rolling a steel billet into a rail, with a final rolling temperature range of 900-1000 ° C;

Cooling the rail

Blowing a cooling medium onto the upper surface of the rail head, the two sides of the rail head and the lower lands on both sides of the rail head when the center of the upper surface of the rail is air cooled to 800-850 ° C, and then air cooling the rail to room temperature after the middle of the upper surface of the rail has cooled to 520-550 ° C.

The cooling rate in Embodiments 1-6 is shown in Table 2. Table 2: Cooling rate for different processes Temperature for starting the accelerated cooling / ° C Mean speed of accelerated cooling / ° C / s Temperature to terminate the accelerated cooling / ° C Embodiment 1 827 3.8 540 Embodiment 2 838 3.0 550 Embodiment 3 800 4.9 544. Embodiment 4 846 5.2 535 Embodiment 5 850 6.3 527 Embodiment 6 809 7.0 520

Reference Examples 1-6: Preparation of Perlitic Rail Using Existing Methods

The composition of the steel billet used in Reference Examples 1-6 is the same as that of Embodiments 1-6, the steel billet of Reference Example 1 being the same as that of Embodiment 1, and so on.

Referential Examples 1-6 apply an existing cooling method: A cooling medium is blown only on the top surface of the rail head and the two sides of the rail head, and the rail is air-cooled to room temperature after the surface of the rail head is cooled to 520-550 ° C ,

The cooling rate in Reference Examples 1-6 is shown in Table 3: Table 3: Cooling rate for different processes Temperature for starting the accelerated cooling / ° C Mean speed of accelerated cooling / ° C / s Temperature to terminate the accelerated cooling / ° C Reference Example 1 826 3.9 538 Reference Example 2 839 3.2 549 Reference Example 3 801 5.0 546 Reference Example 4 846 5.1 535 Reference Example 5 849 6.2 528 Reference Example 6 811 7.1 519

Air cooling the rail treated to room temperature according to the embodiments and the reference examples, taking a circular double shoulder tensile test with d ₀ = 10 mm, l ₀ = 5d ₀ at 10 mm and 30 mm below the surface of the rail head and determining R _p0.2 , R _m , A and Z according to GB / T 228.1; and taking out a Charpy notched specimen (U-shape) of 10 mm × 10 mm × 55 mm at the same position, and determining the notch impact work according to GB / T 229. Also, taking out each transverse test piece for hardness testing from the rail head of the rail 10 mm or 30 mm from the surface of the rail head and check Rockwell hardness at the top corner and center of the top surface according to GB / T 230.1. The test positions and methods in the embodiments and the reference examples are the same. The detailed results are shown in Tables 4 and 5. Table 4: Mechanical properties of rails made by different methods (10 mm below the surface of the rail head) tensile KU / J (room temperature) Hardness / HRC _Rp / MPa R _m / MPa A /% Z /% corner Upper surface Embodiment 1 795 1296 11.5 29 28 39.2 39.0 Embodiment 2 860 1389 10.5 18 26 41.3 41.0 Embodiment 3 761 1272 11.5 27 27 38.2 38.0 Embodiment 4 802 1312 11.0 26 23 39.3 39.4 Embodiment 5 809 1319 11.0 28 25 39.7 39.5 Embodiment 6 820 1341 11.0 24 25 39.8 39.9 Reference Example 1 816 1336 11.0 23 25 39.4 39.3 Reference Example 2 853 1384 9.5 18 21 41.0 40.8 Reference Example 3 761 1265 11.0 22 25 38.1 38.0 Reference Example 4 799 1306 11.0 24 23 39.0 39.2 Reference Example 5 805 1315 10.5 26 24 38.5 38.8 Reference Example 6 789 1290 10.5 24 28 38.6 38.7 Table 5: Mechanical properties of rails produced by different methods (30 mm below the surface of the rail head) tensile KU / J (room temperature) Hardness / HRC _Rp / MPa R _m / MPa A /% Z /% corner Upper surface Embodiment 1 740 1213 11.0 25 23 38.7 38.5 Embodiment 2 820 1300 10.5 20 21 38.9 38.8 Embodiment 3 714 1188 11.0 24 25 37.0 36.8 Embodiment 4 762 1240 11.0 21 24 38.2 38.0 Embodiment 5 746 1258 11.0 22 24 38.5 38.3 Embodiment 6 774 1262 11.5 24 21 39.0 38.8 Reference Example 1 749 1218 10.5 19 17 37.4 37.6 Reference Example 2 793 1264 9.5 16 18 38.0 38.3 Reference Example 3 700 1154 10.0 21 19 36.0 36.1 Reference Example 4 734 1201 9.5 16 17 37.4 37.3 Reference Example 5 720 1228 9.5 18 16 37.8 37.6 Reference Example 6 724 1182 10.0 20 18 37.5 37.4

It can be concluded from the above embodiments and reference examples that the embodiments using the heat treatment method of the present invention are comparable to the reference examples using the existing heat treatment method for the material having the same chemical composition. In the embodiments, the cooling medium is blown onto the upper surface of the rail head and both sides of the rail head and the lower lands on both sides of the rail head after the heat-treated rail is air-cooled to 800-850 ° C, and the rail is air-cooled again Room temperature after the center of the upper surface of the rail has cooled to 520-550 ° C at a cooling rate of 3.0-7.0 ° C / s. In contrast, the existing method uses the simple method for heat treatment of the top surface of the rail head and both sides of the rail head at a cooling rate of 3.0-7.0 ° C / s. The results of the comparison in Tables 4 and 5 show that the strength, hardness, toughness and deformability of the part 10 mm below the surface of the rail head in the method of the present invention are slightly higher than those of the Reference Examples; more importantly, the strength and toughness of the part at 30 mm below the surface of the rail head are significantly higher than those in the existing heat treatment process. Thus, it can be concluded that adding the accelerated cooling of the rail head lower lands can improve the overall strength and toughness of the rail head and prolong the life under the same conditions.

The invention provides a rail of a railway line with mixed passenger and freight traffic and the method for their production. With the same composition and manufacturing method, the method can improve the strength and toughness of a rail. The product is suitable for a railway line with mixed passenger and freight traffic.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• CN 101646795 B [0004]
• CN 105483347 A [0005]
• CN 103898303 A [0006]

Claims (5)

Manufacturing method for a railway of a mixed passenger and freight railway, characterized by the steps of: a. Rolling a rail; hot rolling a steel billet into a rail, with a final rolling temperature range of 900-1000 ° C; b. Cooling the rail Blowing a cooling medium onto the upper surface of the rail head, the two sides of the rail head and the lower lands on both sides of the rail head when the center of the upper surface of the rail is air cooled to 800-850 ° C, then air cooling the rail the room temperature after the center of the upper surface of the rail has cooled to 520-550 ° C. Manufacturing method for a rail of a railway line with mixed passenger and freight traffic Claim 1 characterized in that the composition (in weight percent) of the rail in step a is: C: 0.70% to 0.85%, Si: 0.15% to 0.60%, Mn: 0.70% to 1 , 0.05%, Cr: 0.15% to 0.50%, at least one of V, Nb and Ti, wherein V: 0.02% to 0.10%, if present, Ti: 0.001% to 0.030%, if present, and Nb: 0.005% to 0.08%, if any, and the remainder: Fe and unavoidable impurities. Manufacturing method for a rail of a railway line with mixed passenger and freight traffic Claim 1 , characterized in that the cooling medium in steps b and c is at least one of compressed air or water-air spray mixture. Manufacturing method for a rail of a railway line with mixed passenger and freight traffic Claim 1 , characterized in that the cooling rate in step b is 3.0-7.0 ° C / s. Rail of a railway line with mixed passenger and freight traffic, manufactured by the method of one of Claims 1 - 4 characterized in that the composition, in weight percent, of the rail is: C: 0.70% to 0.85%, Si: 0.15% to 0.60%, Mn: 0.70% to 1.05% , Cr: 0.15% to 0.50%, at least one of V, Nb and Ti, wherein V: 0.02% to 0.10%, if present, Ti: 0.001% to 0.030%, if present, and Nb: 0.005% to 0.08%, if any, and the remainder: Fe and unavoidable impurities.