WO2021057094A1 - 一种降低热处理钢轨残余应力的生产方法及其所得钢轨 - Google Patents

一种降低热处理钢轨残余应力的生产方法及其所得钢轨 Download PDF

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WO2021057094A1
WO2021057094A1 PCT/CN2020/095377 CN2020095377W WO2021057094A1 WO 2021057094 A1 WO2021057094 A1 WO 2021057094A1 CN 2020095377 W CN2020095377 W CN 2020095377W WO 2021057094 A1 WO2021057094 A1 WO 2021057094A1
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Prior art keywords
rail
temperature
cooling
head
rail head
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PCT/CN2020/095377
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English (en)
French (fr)
Inventor
费俊杰
周剑华
董茂松
叶佳林
朱敏
王俊
郑建国
王瑞敏
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武汉钢铁有限公司
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Priority to BR112021022882A priority Critical patent/BR112021022882A2/pt
Publication of WO2021057094A1 publication Critical patent/WO2021057094A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rails
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the invention relates to a steel rail and a production method thereof, in particular to a production method for reducing the residual stress of a heat-treated steel rail and the obtained steel rail, belonging to the field of steel rail production and application.
  • Heat-treated steel rails can effectively improve the wear resistance and fatigue resistance of steel rails, and meet the requirements of heavy-duty railways and small-radius curve railways under severe conditions.
  • rail manufacturers at home and abroad have basically adopted online heat treatment processes to produce heat-treated rails.
  • the hot-rolled rail passes through the cooling unit at a certain speed, and the cooling unit sprays a cooling medium (water or mist or air) to accelerate the cooling of the rail to achieve the purpose of strengthening.
  • a cooling medium water or mist or air
  • accelerated cooling has a faster temperature drop, which is more likely to produce temperature stress and increase the residual stress of heat-treated steel rails.
  • the cross-sectional shape of the rail is not uniform, and the amount of metal at the bottom of the rail is far less than that of the rail head. If the cooling intensity of the rail head and the rail bottom is unreasonably distributed, after the heat treatment is completed, the rail will naturally cool down to room temperature. Large bends are produced, and after straightening, the residual stress at the bottom of the heat-treated rail is too large or exceeds the standard. The residual stress of the rail will directly affect the service life of the rail and the safe operation of the train.
  • the patent "100-meter heavy rail residual stress control method" (CN102284503A) provides a 100-meter hot-rolled rail residual stress control method, which uses universal rolling, post-rolling cooling, and composite straightening methods. Large arc pre-bending is adopted for the 100-meter rail during the cooling process after rolling, so that the chord height when the rail is cooled to room temperature is controlled within the range of 30-40mm.
  • the present invention effectively controls the residual stress of the rail bottom after straightening the 100-meter rail, and the residual stress value of the rail bottom is reduced on average 70MPa, all residual stress values are less than or equal to 250MPa.
  • this patent optimizes the residual stress of hot-rolled steel rails and cannot be applied to heat-treated steel rails.
  • the patent "A Method for Reducing Residual Stress of Steel Rails, and the Obtained Rails and Their Applications” provides a method of reducing residual stresses of steel rails by combining the center of the rail head tread, both sides of the rail head and the rail head after rolling.
  • the central part of the rail bottom is subjected to accelerated cooling, slow cooling and air cooling in sequence.
  • the opening cooling temperature of the accelerated cooling is 650-950°C
  • the cooling rate is 2-8°C/s
  • the final cooling temperature is 400-600°C.
  • the cooling rate of cooling is 0.1-1.5°C/s
  • the final cooling temperature is 180-300°C, which can effectively reduce the residual stress of the rail while ensuring the tensile performance of the rail.
  • the principle of the patent is to change the metallographic structure of the rail head to a certain extent, thereby reducing the residual stress of the rail.
  • the patent only controls the cooling rate of the rail head and the rail corners, and does not process the rail bottom.
  • the purpose of the present invention is to overcome the problem of excessive residual stress at the bottom of the current heat-treated steel rail, and to provide a production method that can effectively reduce the residual stress of the heat-treated steel rail and the rail obtained therefrom.
  • the method reasonably controls the cooling strength of the rail head and the rail bottom. And the temperature difference, so that the bending of the rail after heat treatment is controlled in a more ideal range, and the residual stress at the bottom of the rail is effectively reduced.
  • the present invention is specifically implemented as follows:
  • a production method for reducing the residual stress of heat-treated steel rails mainly includes performing on-line accelerated cooling of the hot-rolled rails, wherein the starting cooling temperature is controlled to 700-880°C, and the cooling rate of the rail head is 5-8°C /s, the cooling rate of the rail bottom is 1.5-3°C/s, until the temperature of the rail head drops to 460-550°C; then the rail head and the rail bottom are slowly cooled, and the slow cooling rate is 0.5-1°C/s, Slowly cool until the rail head temperature drops to 350-450°C; then keep the rail head cooling rate 0.5-1°C/s, control the rail bottom cooling rate to 0.5-2°C/s, when the temperature difference between the rail head and the rail bottom reaches When within a certain range, stop accelerated cooling and cool to room temperature naturally.
  • the said start cooling temperature is controlled to 720-850°C
  • the cooling rate of the rail head is 6-7°C/s
  • the cooling rate of the rail bottom is 1.8-2.8°C/s
  • the temperature of the rail head is cooled to 480-530°C.
  • the rail head and rail bottom are slowly cooled, at a slow cooling rate of 0.5-0.8°C/s, until the temperature of the rail head drops to 360-420°C; then keep the rail head cooling rate at 0.5-0.8°C/s
  • the cooling rate of the rail bottom is controlled to be 0.5-1.5°C/s.
  • the temperature difference between the rail head and the rail bottom ranges from -20°C to 60°C, where the temperature difference between the rail head and the rail bottom refers to the temperature of the rail head minus the temperature of the rail bottom.
  • the end of the rail After being naturally cooled to room temperature, the end of the rail remains straight or warped to a certain extent toward the rail head, and the height of the end of the rail with a length of 100m is in the range of 0-30mm.
  • the rail head temperature refers to the surface temperature at the center of the tread
  • the rail bottom temperature refers to the surface temperature at the center of the rail bottom.
  • Accelerated cooling treatment is performed on the rolled steel rail.
  • the principle of accelerated cooling is to use the residual temperature of the steel rail after rolling to accelerate the cooling, increase the degree of subcooling from the transformation of austenite to pearlite, reduce the transformation temperature of pearlite, and reduce the migration distance of carbon atoms in austenite, thereby obtaining a sheet
  • the pearlite with finer layer spacing improves the strength and hardness of the rail, and improves the wear resistance. This is the basic principle of the current rail heat treatment process.
  • the starting cooling temperature is controlled to 700-880°C.
  • the rail is heat treated by the residual temperature after rolling, so it must match the rolling rhythm.
  • the starting cooling temperature is too high, which means that the rail austenitization temperature and the final rolling temperature will increase, which directly causes the austenite grains to become coarse and coarse. Surface defects increase and other problems.
  • the cooling temperature is too high, and a greater cooling speed is needed to remove the heat from the rail head in time, increasing the energy consumption of the equipment; and the cooling temperature is too low, and the distance to the pearlite phase transition point is too low. Greater coldness will bring about the risk of abnormal tissue.
  • the temperature range selected in this application can perfectly match the utilization of the residual temperature after rolling, and also avoid the above-mentioned problems caused by excessively high or low temperatures.
  • the cooling rate of the rail head is 5-8°C/s, and the cooling rate of the rail bottom is 1.5-3°C/s.
  • the cooling rate of the rail head at this stage directly determines the mechanical properties of the heat-treated steel rail.
  • the cooling rate is less than 5°C/s, it is difficult to obtain pearlite with fine lamella spacing, and the strength and hardness of the rail are insufficient; when the cooling rate is greater than 8°C /s, the diffusion rate of carbides is reduced, and abnormal structures such as bainite and martensite are prone to appear, resulting in scrapped rails.
  • the amount of metal at the bottom of the rail is smaller than that of the rail head.
  • cooling should also be applied to the rail bottom, but the cooling rate is generally controlled at 1/2 or the rail head cooling rate.
  • the temperature of the rail head drops to 460-550°C.
  • the inventor found through a large number of experimental studies that when the temperature of the rail head drops to 550°C, the tissues within the depth of 20 mm below the surface of the rail head have completed the pearlite transformation, but the temperature of the core of the rail head is still high. If the cooling is terminated, The temperature of the core will diffuse outwards and affect the performance of the pearlite tissue; when the temperature of the rail head drops to 460°C, the pearlite transformation of the entire rail head has been completed, and the temperature of the core will also drop accordingly, so there is no need to continue accelerated cooling.
  • the slow cooling speed is 0.5-1°C/s.
  • the accelerated cooling in the previous stage has a faster cooling rate, and a certain temperature stress is generated inside the rail.
  • Slow cooling can uniform the temperature distribution of the entire cross section of the rail head, reduce the temperature stress, and thereby reduce the residual stress.
  • (6) Keep the cooling rate of the rail head at 0.5-1°C/s, and control the cooling rate of the rail bottom at 0.5-2°C/s. This is mainly to make the rail head and rail bottom reach a certain temperature difference range through a small cooling rate.
  • the temperature difference range between the rail head and the rail bottom (rail head temperature minus rail bottom temperature) is -20°C to 60°C.
  • the rail ends After natural cooling to room temperature, the rail ends remain straight or to a certain extent toward the rail head Warping, the height of the upturn of the rail end is in the range of 0-30mm. Setting a suitable temperature difference range between the rail head and the rail bottom is to keep the rails at an ideal degree of curvature during the natural cooling process after running out of the heat treatment unit. Because the amount of metal at the bottom of the rail is smaller than that of the rail head, the temperature drop at the bottom of the rail is slightly higher than that of the rail head during natural cooling.
  • the rail will have a degree of curvature towards the rail head, which is manifested as a slight upward warpage at the end. It is about 30mm.
  • the advantage of this is that in the subsequent straightening process, under the pressure of the straightening roll, the upward warping of the rail toward the rail head becomes straight. At this time, a certain compressive stress will be generated at the bottom of the rail, which will offset a part of the rolling The tensile stress generated in the process reduces the residual stress at the bottom of the rail.
  • the chemical composition of the steel rail includes 0.71-0.82% by weight of C, 0.45-0.85% by weight of Si, 0.85-1.20% by weight of Mn, and 0.08-0.15% by weight of V, 0.08-0.20% by weight of Cr, ⁇ 0.025% by weight of P, ⁇ 0.025% by weight of S, and the rest are Fe and unavoidable impurities.
  • the cooling medium for accelerated cooling and slow cooling is a commonly used cooling medium in the field, including but not limited to water, polymer solution, oil, compressed air, water mist or oil mist mixture.
  • the production method also includes: converter smelting, LF refining, vacuum treatment, continuous casting, billet heating, rolling, straightening and other steps.
  • the above steps are not particularly limited, and can be carried out according to the conventional steel rail production process method.
  • the casting process should be carried out under full protection to prevent contact with air; the cast billet should be slowly cooled; the walking beam heating furnace should be used for the casting billet heating and heat preservation treatment; the universal rolling production line should be used for rolling; It adopts the flat and vertical composite straightening process.
  • the present invention also provides the steel rail obtained by the production method.
  • the room temperature metallographic structure of the full section of the rail is fine flaky pearlite and a small amount of ferrite, and the residual stress at the bottom of the rail can be controlled at 50-90MPa, which can be applied to passenger transportation. And a variety of lines such as passenger and cargo mixed transportation to improve the service life of rails and driving safety.
  • the invention provides a production method that can effectively reduce the residual stress of heat-treated steel rails and the obtained steel rails.
  • the cooling intensity and temperature difference between the rail head and the rail bottom By reasonably controlling the cooling intensity and temperature difference between the rail head and the rail bottom, the bending of the steel rail after the heat treatment is controlled in an ideal range.
  • the residual stress at the bottom of the rail can be effectively reduced, and the service life and driving safety of the rail can be improved.
  • the production method is simple, has strong operability, and is easy to popularize and apply.
  • Figure 1 is a schematic diagram of the Rockwell hardness measurement of the cross section of the rail head
  • Figure 2 is a schematic diagram of the bending of the rail toward the rail head.
  • the present invention provides a production method for reducing the residual stress of heat-treated steel rails.
  • the method mainly includes performing online accelerated cooling treatment on the hot-rolled rails, wherein the starting cooling temperature is controlled to 700-880°C, and the cooling rate of the rail head is 5 -8°C/s, the cooling rate of the rail bottom is 1.5-3°C/s, wait until the rail head temperature drops to 460-550°C; then the rail head and rail bottom are slowly cooled, and the slow cooling rate is 0.5-1°C/ s, wait until the rail head temperature drops to 350-450°C; then keep the rail head cooling rate 0.5-1°C/s, control the rail bottom cooling rate to 0.5-2°C/s, when the temperature difference between the rail head and the rail bottom reaches When within a certain range, stop accelerated cooling and cool to room temperature naturally.
  • the starting cooling temperature is controlled to be 720-850°C
  • the cooling rate of the rail head is 6-7°C/s
  • the cooling rate of the rail bottom is 1.8-2.8°C/s.
  • the temperature of the rail head drops to 480- 530°C
  • slowly cool the rail head and rail bottom at a slow cooling rate of 0.5-0.8°C/s wait until the rail head temperature drops to 360-420°C; then keep the rail head cooling rate at 0.5-0.8°C/s
  • the cooling rate of the rail bottom is controlled to be 0.5-1.5°C/s.
  • the accelerated cooling is stopped and the cooling is naturally cooled to room temperature.
  • the temperature difference range between the rail head and the rail bottom is -20°C to 60°C
  • the rail head temperature refers to the temperature of the central part of the tread
  • the rail bottom temperature is Refers to the temperature of the surface at the center of the rail bottom.
  • the rail end after natural cooling to room temperature, the rail end remains straight or warped to a certain degree toward the rail head. As shown in Figure 2, after natural cooling to room temperature, the rail end remains straight or toward the rail head. There is a certain degree of warpage, and the height of the upturn of the 100m length of the rail end is in the range of 0-30mm.
  • the production method of the present invention can be used for on-line heat treatment of steel rails of any conventional composition to reduce the residual stress at the bottom of the rail.
  • steel rails with a specific chemical composition can have lower residual stress than steel rails with other chemical compositions, and Can be more suitable for this production method.
  • the steel rail of this specific chemical composition is based on the total weight of the steel rail.
  • the chemical composition of the steel rail includes 0.71-0.82% by weight of C, 0.45-0.85% by weight of Si, 0.85-1.20% by weight of Mn, and 0.08-0.15. Weight% of V, 0.08-0.20% by weight of Cr, ⁇ 0.025% by weight of P, ⁇ 0.025% by weight of S, and the rest are Fe and unavoidable impurities.
  • the cooling medium for accelerated cooling and slow cooling is a cooling medium commonly used in the field, including but not limited to water, polymer solution, oil, compressed air, water mist or oil mist mixture, which can provide a uniform cooling flow field Any substance can be used.
  • the production method also includes: converter smelting, LF refining, vacuum treatment, continuous casting, billet heating, rolling, straightening and other steps.
  • the above steps are not particularly limited, and follow the conventional rail production process. Go ahead.
  • the casting process should be carried out under full protection to prevent contact with air; the cast billet should be slowly cooled; the walking beam heating furnace should be used for the casting billet heating and heat preservation treatment; the universal rolling production line should be used for rolling; It adopts the flat and vertical composite straightening process.
  • the present invention also provides the steel rail obtained by the production method.
  • the room temperature metallographic structure of the full section of the steel rail is fine flake pearlite and a small amount of ferrite, no abnormal structures such as bainite and martensite, and the mechanical properties of the rail are uniform.
  • the residual stress at the bottom of the rail after straightening can be controlled at 50-90MPa, which can be applied to various lines such as passenger transportation and mixed passenger and cargo transportation to improve the service life of rails and driving safety.
  • Example 1-5 of the present invention The smelting chemical compositions of Examples 1-5 of the present invention are shown in 1-5# in Table 1, and Comparative Examples 1-2 are carried out in accordance with the composition range of Example 1-2.
  • the procedures include converter smelting, LF refining, vacuum treatment, and continuous casting.
  • the basicity of the converter slag is controlled at 2.5-4.5; when the molten steel is about 1/4, alloys and recarburizers such as silicon, manganese, and vanadium are added with the steel flow.
  • the alloys and recarburizers are all Add;
  • LF furnace treatment time should be greater than 40min;
  • RH vacuum degree ⁇ 100Pa pure vacuum treatment time should not be less than 15min
  • the casting process should be carried out under full protection to prevent contact with air, and the cast billet should be slowly cooled.
  • the billet is sent to the walking beam heating furnace for heating and insulation, the heating temperature is 1200-1300°C, the holding time is 150-260min, and the rail is rolled by a universal rolling mill, and the rolling temperature is 1080-1150 °C, the final rolling temperature is 840-920°C.
  • Carry out on-line heat treatment on the steel rail The starting cooling temperature is controlled to 820°C, the cooling rate of the rail head is 5.2°C/s, and the cooling rate of the rail bottom is 1.6°C/s.
  • the rail head After the temperature of the rail head drops to 530°C; The bottom of the rail is slowly cooled, and the slow cooling rate is 0.6°C/s, and the temperature of the rail head is reduced to 380°C; then the rail head cooling rate is maintained at 0.6°C/s, and the cooling rate of the rail bottom is controlled to 1.2°C/s, and the rail head is controlled
  • the temperature difference with the rail bottom (rail head temperature minus rail bottom temperature) is 35°C, stop accelerated cooling, cool down naturally to room temperature, and finally straighten the rail using a flat composite straightening process.
  • the difference is that the rail is subjected to online heat treatment, the starting cooling temperature is controlled to 780°C, the cooling rate of the rail head is 6.5°C/s, and the cooling rate of the rail bottom is 2.1°C/s.
  • the rail head temperature is reduced to 460°C; then the rail head and rail bottom are slowly cooled at a slow cooling rate of 0.8°C/s, and the rail head temperature is reduced to 400°C; then the rail head cooling rate is maintained at 0.8°C/s, control
  • the cooling rate of the rail bottom is 0.5°C/s, and the temperature difference between the rail head and the rail bottom (rail head temperature minus rail bottom temperature) is controlled to -18°C.
  • the difference is that the rail is subjected to online heat treatment, the starting cooling temperature is controlled to 800°C, the cooling rate of the rail head is 5.8°C/s, and the cooling rate of the rail bottom is 2.0°C/s.
  • the rail head temperature is reduced to 490°C; then the rail head and rail bottom are slowly cooled at a slow cooling rate of 0.9°C/s, and the rail head temperature is reduced to 410°C; then the rail head cooling rate is maintained at 0.9°C/s, control
  • the cooling rate of the rail bottom is 0.7°C/s, and the temperature difference between the rail head and the rail bottom (rail head temperature minus rail bottom temperature) is controlled to -5°C.
  • the difference is that the rail is subjected to on-line heat treatment, the starting cooling temperature is controlled to 720°C, the cooling rate of the rail head is 7.8°C/s, and the cooling rate of the rail bottom is 2.8°C/s.
  • the rail head temperature is reduced to 520°C; then the rail head and rail bottom are slowly cooled at a slow cooling rate of 0.6°C/s, and the rail head temperature is reduced to 430°C; then the rail head cooling rate is maintained at 0.6°C/s, control
  • the cooling rate of the rail bottom is 1.4°C/s, and the temperature difference between the rail head and the rail bottom (rail head temperature minus rail bottom temperature) is controlled to 55°C.
  • the difference is that the rail is subjected to online heat treatment, the starting cooling temperature is controlled to 850°C, the cooling rate of the rail head is 6.9°C/s, and the cooling rate of the rail bottom is 2.3°C/s.
  • the rail head temperature is reduced to 500°C; then the rail head and rail bottom are slowly cooled, the slow cooling speed is 0.7°C/s, and the rail head temperature is reduced to 360°C; then the rail head cooling rate is maintained at 0.7°C/s, control
  • the cooling rate of the rail bottom is 1.3°C/s, and the temperature difference between the rail head and the rail bottom (rail head temperature minus rail bottom temperature) is controlled to 20°C.
  • Example 1 the difference is that according to the current conventional rail heat treatment process, the starting cooling temperature is controlled to 820°C, the cooling rate of the rail head is 5.2°C/s, and the cooling rate of the rail bottom is 1.6°C/s , When the temperature of the rail head drops to 530°C, stop the accelerated cooling, and cool to room temperature naturally.
  • Example 1 It is carried out according to the method of Example 1, the difference is that according to the hot-rolled rail production process, the rolled rail does not undergo an online heat treatment process, and is directly cooled to room temperature naturally.
  • the data in Table 3 is obtained from the measurement position shown in FIG. 1.
  • the first point closest to the surface of each line is 5mm away from the surface, and the distance between the remaining points is 5mm; the distance between the D and E lines and the lower jaw is 5mm; the B and C lines are the angular bisectors of the A, D and A, E lines .
  • the various properties and metallographic structure of the rail obtained in Examples 1-5 are good, and the residual stress at the bottom of the rail can be stably controlled within the range of 50-90MPa.
  • the present invention The method can effectively reduce the residual stress at the bottom of the rail under the premise of ensuring the structure and mechanical properties of the heat-treated steel rail.

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Abstract

一种降低热处理钢轨残余应力的生产方法及其所得钢轨，将热轧后的钢轨进行在线的加速冷却处理，其中，开始冷却温度为700-880℃，轨头的冷却速度为5-8℃/s，轨底的冷却速度为1.5-3℃/s，冷却至轨头温度降至460-550℃；进行缓冷处理，缓冷速度为0.5-1℃/s，至轨头温度降至350-450℃；保持轨头冷却速度为0.5-1℃/s，控制轨底冷却速度为0.5-2℃/s，当轨头与轨底的温度差达到一定范围时，停止加速冷却，自然冷却至室温。所述生产方法能有效降低钢轨轨底残余应力，提高钢轨使用寿命和行车安全。

Description

一种降低热处理钢轨残余应力的生产方法及其所得钢轨 技术领域
本发明涉及一种钢轨及其生产方法，具体涉及一种降低热处理钢轨残余应力的生产方法及所得钢轨，属于钢轨生产及应用领域。
背景技术
在线热处理工艺是目前提高钢轨强度和硬度最有效最经济的技术手段，热处理钢轨能有效提高钢轨的耐磨性能和抗疲劳性能，满足重载铁路和小半径曲线铁路等恶劣条件下的使用要求，提高使用寿命，目前国内外钢轨厂家基本都采用了在线热处理工艺来生产热处理钢轨。
在热处理过程中，热轧后的钢轨以一定的速度通过冷却机组，冷却机组喷射冷却介质(水或雾或空气)对钢轨进行加速冷却，达到强化目的。与自然冷却相比，加速冷却温降速度快，更容易产生温度应力，增加热处理钢轨的残余应力。更为重要的是，钢轨断面形状不均匀，轨底金属量远少于轨头，如果轨头和轨底的冷却强度分配不合理，热处理结束后自然冷却到室温过程，钢轨在垂直方向上会产生较大的弯曲，矫直后导致热处理钢轨轨底残余应力偏大或者超标，钢轨残余应力的大小会直接影响到钢轨使用寿命和列车的运行安全。
在钢轨残余应力控制方法中，专利《百米重轨残余应力控制方法》(CN102284503A)提供了一种百米热轧钢轨残余应力控制方法，采用万能轧制、轧后冷却，复合矫直方法，对轧后冷却过程中的百米钢轨采用大弧度预弯，使钢轨冷却至室温时的弦高控制在30～40mm范围内。结合优化的8+1多辊矫直机矫直变形规程，结合矫前弯曲度的控制，本发明有效地控制了百米钢轨矫直后的轨底残余应力，轨底残余应力值平均降低了70MPa，残余应力值全部≤250MPa。但是该专利是对热轧钢轨进行的残余应力优化，无法应用到热处理钢轨中。
专利《一种降低钢轨残余应力的方法以及所得钢轨及其应用》(CN 106086370 A)提供了一种降低钢轨残余应力的方法，将轧制后所得钢轨的轨头踏面中心、轨头两侧和轨底中心部位依次进行加速冷却、缓慢冷却和空冷，所述加速冷却的开冷温度为650-950℃，冷却速度为2-8℃/s，终冷温度为400-600℃，所述缓慢冷却的冷却速度为0.1-1.5℃/s，终冷温度为180-300℃，能够在保证钢轨的拉伸性能的前提下有效降低钢轨的残余应力。但是该专利的原理是使轨头金相组织发生一定程度的变化，从而降低钢轨的残余应力，而且该专利只是对轨头和轨角部位进行了冷却速度的控制，对轨底未进行处理，而研究和试验表明，轨底和轨头的冷却速度控制以及热处理后的温度差异，是导致钢轨垂直方向弯曲的关键因素，也是影响残余应力的关键因素。
针对目前热处理钢轨普遍存在的轨底残余应力过大的问题，以及随之带来的行车安全隐患，亟需一种能有效降低热处理钢轨残余应力的生产方法。
发明内容
本发明的目的在于克服目前热处理钢轨轨底残余应力过大的问题，提供一种能有效降低热处理钢轨残余应力的生产方法及其所得钢轨，该方法通过合理控制钢轨轨头和轨底的冷却强度和温度差，使得热处理后钢轨的弯曲控制在较理想的范围，有效降低钢轨轨底残余应力。
本发明具体是这样实现的：
一种降低热处理钢轨残余应力的生产方法，该方法主要包括将热轧后的钢轨进行在线的加速冷却处理，其中，开始冷却温度控制为700-880℃，轨头的冷却速度为5-8℃/s，轨底的冷却速度为1.5-3℃/s，冷却至轨头温度降至460-550℃；随后对轨头和轨底进行缓冷处理，缓冷速度为0.5-1℃/s，缓冷至轨头温度降至350-450℃；随后保持轨头冷却速度为0.5-1℃/s，控制轨底冷却速度为0.5-2℃/s，当轨头与轨底的温度差达到一定范围时，停止加速冷却，自然冷却至室温。
更进一步的方案是：
所述的开始冷却温度控制为720-850℃，轨头的冷却速度为6-7℃/s，轨底的冷却速度为1.8-2.8℃/s，冷却至轨头温度降至480-530℃，随后对轨头和轨底进行缓冷处理，缓冷速度为0.5-0.8℃/s，缓冷至轨头温度降至360-420℃；随后保持轨头冷却速度为0.5-0.8℃/s，控制轨底冷却速度为0.5-1.5℃/s，当轨头与轨底的温度差达到一定范围时，停止加速冷却，自然冷却至室温。
更进一步的方案是：
轨头与轨底的温度差范围为-20℃至60℃，其中轨头与轨底的温度差是指轨头温度减去轨底温度。
更进一步的方案是：
自然冷却至室温后，钢轨端部保持平直或者向轨头有一定程度的翘曲，100m长度的钢轨端部上翘的高度在0-30mm范围内。
更进一步的方案是：
轨头温度是指踏面中心部位表面的温度，轨底温度是指轨底中心部位表面的温度。
下面对本发明的技术效果进行具体说明：(1)对轧后钢轨进行加速冷却处理。加速冷却的原理，是利用轧后钢轨的余温加速冷却，增加奥氏体向珠光体转变的过冷度，降低珠光体转变温度，减小奥氏体中碳原子的迁移距离，从而获得片层间距更加细小的珠光体，提高钢轨的强度和硬度，提高耐磨性，这是目前钢轨热处理工艺的基本原理。(2)开始冷却温度控制为700-880℃。钢轨是利用轧后余温进行热处理，所以必须与轧制节奏相匹配，开始冷却温度过高，意味着钢轨奥氏体化温度和终轧温度就要提高，直接造成奥氏体晶粒粗大以及表面缺陷增多等问题，同时开始冷却温度过高，需要更大的冷却速度才能及时带走轨头热量， 增加设备能耗；而开始冷却温度过低，与珠光体相变点距离较近，过冷度较大，会带来产生异常组织的风险。本申请选择的温度范围，能够完美的配合轧后余温的利用，也避免了温度过高或过低而带来的上述问题。(3)轨头的冷却速度为5-8℃/s，轨底的冷却速度为1.5-3℃/s。这一阶段的轨头的冷却速度直接决定了热处理钢轨的力学性能，当冷却速度小于5℃/s时，难以获得片层间距细小的珠光体，钢轨强度和硬度不足；当冷却速度大于8℃/s时，碳化物扩散速率降低，容易出现贝氏体和马氏体等异常组织，导致钢轨报废。而轨底金属量小于轨头，为了防止钢轨热处理过程中轨头轨底温度差过大造成钢轨弯曲，对轨底也要施加冷却，但是冷速一般控制在轨头冷速的1/2或者1/3左右，尽量保持轨头轨底的温度一致性。(4)轨头温度降至460-550℃。本发明人通过大量试验研究发现，轨头温度降至550℃时，轨头表面及以下20mm深度范围内的组织已完成了珠光体转变，但是轨头心部温度仍较高，如终止冷却，心部温度会向外扩散，影响珠光体组织性能；轨头温度降至460℃时，整个轨头的珠光体转变均已完成，心部温度也相应下降，无需继续进行加速冷却。(5)对轨头和轨底进行缓冷处理，缓冷速度为0.5-1℃/s。前一阶段的加速冷却冷速较快，钢轨内部会产生一定的温度应力，缓冷可以均匀轨头整个横断面的温度分布，降低温度应力，从而减少残余应力。(6)保持轨头冷却速度为0.5-1℃/s，控制轨底冷却速度为0.5-2℃/s。这主要是为了通过较小的冷却速率，使轨头与轨底达到一定的温度差范围。(7)轨头与轨底的温度差范围(轨头温度减去轨底温度)为-20℃至60℃，自然冷却至室温后，钢轨端部保持平直或者向轨头有一定程度的翘曲，钢轨端部上翘的高度在0-30mm范围内。设置一个合适的轨头与轨底温度差范围，是为了使钢轨在运行出热处理机组后的自然冷却过程中，能保持较理想的弯曲度。因为钢轨轨底金属量小于轨头，自然冷却时，轨底温降稍高于轨头。本发明人通过大量试验研究发现，当轨头比轨底低20℃，在自然冷却至室温过程中，轨头和轨底温度会逐渐趋于一致，最终钢轨基本保持平直，大大减少矫直过程中钢轨变形带来的残余应力；而轨头比轨底高60℃，在自然冷却至室温过程中，钢轨会产生一个弯向轨头的弯曲度，表现为端部略微上翘，其高度为30mm左右，这样的好处是在随后矫直过程中，在矫直辊压力下，钢轨向轨头的上翘变得平直，此时轨底会产生一定的压应力，抵消一部分在轧制过程中产生的拉应力，从而降低轨底残余应力。
更进一步的方案是：
本生产方法中，以钢轨的总重量为基准，所述钢轨的化学成分包括0.71-0.82重量％的C、0.45-0.85重量％的Si、0.85-1.20重量％的Mn、0.08-0.15重量％的V、0.08-0.20重量％的Cr，≤0.025重量％的P、≤0.025重量％的S，其余为Fe和不可避免的杂质。
更进一步的方案是：
所述加速冷却和缓冷的冷却介质为本领域常用的冷却介质，包括但是不限于水、聚合物溶液、油、压缩空气、水雾或者油雾混合气。
更进一步的方案是：
所述生产方法还包括：转炉冶炼、LF精炼、真空处理、连铸、铸坯加热、轧制、矫直等工序，对上述工序没有特别的限定，按照常规的钢轨生产工艺方法进行即可。例如，浇铸过程应在全程保护下进行，防止与空气接触；浇铸成的钢坯应进行缓冷处理；采用步进梁加热炉进行铸坯加热，并进行保温处理；采用万能轧制生产线进行轧制；采用平立复合矫直工艺。
本发明还提供了通过本生产方法得到的钢轨，钢轨全断面的室温金相组织为细片状珠光体和少量铁素体，矫后轨底残余应力可以控制在50-90MPa，可应用于客运及客、货混运等多种线路，提高钢轨使用寿命和行车安全。
本发明提供的一种能有效降低热处理钢轨残余应力的生产方法及其所得钢轨，通过合理控制钢轨轨头和轨底的冷却强度和温度差，使得热处理后钢轨的弯曲控制在较理想的范围，在保证热处理钢轨组织和力学性能的前提下，能有效降低钢轨轨底残余应力，提高钢轨使用寿命和行车安全，该生产方法简单，可操作性强，易于推广应用。
附图说明
图1为钢轨轨头横断面洛氏硬度测量示意图；
图2为钢轨向轨头弯曲示意图。
具体实施方式
本发明提供一种降低热处理钢轨残余应力的生产方法，该方法主要包括将热轧后的钢轨进行在线的加速冷却处理，其中，开始冷却温度控制为700-880℃，轨头的冷却速度为5-8℃/s，轨底的冷却速度为1.5-3℃/s，待轨头温度降至460-550℃；随后对轨头和轨底进行缓冷处理，缓冷速度为0.5-1℃/s，待轨头温度降至350-450℃；随后保持轨头冷却速度为0.5-1℃/s，控制轨底冷却速度为0.5-2℃/s，当轨头与轨底的温度差达到一定范围时，停止加速冷却，自然冷却至室温。
优选地，所述的开始冷却温度控制为720-850℃，轨头的冷却速度为6-7℃/s，轨底的冷却速度为1.8-2.8℃/s，待轨头温度降至480-530℃，随后对轨头和轨底进行缓冷处理，缓冷速度为0.5-0.8℃/s，待轨头温度降至360-420℃；随后保持轨头冷却速度为0.5-0.8℃/s，控制轨底冷却速度为0.5-1.5℃/s，当轨头与轨底的温度差达到一定范围时，停止加速冷却，自然冷却至室温。
本发明中，优选地，轨头与轨底的温度差范围(轨头温度减去轨底温度)为-20℃至60℃，轨头温度是指踏面中心部位表面的温度，轨底温度是指轨底中心部位表面的温度。
本发明中，自然冷却至室温后，钢轨端部保持平直或者向轨头有一定程度的翘曲，如附图2所示，自然冷却至室温后，钢轨端部保持平直或者向轨头有一定程度的翘曲，100m长度 的钢轨端部上翘的高度在0-30mm范围内。
本发明的生产方法可以用于任何常规成分的在线热处理钢轨，降低其轨底残余应力，同时本发明人发现，特定化学成分的钢轨能够具有相对于其他化学成分的钢轨更低的残余应力，并且能够更适于本生产方法。这种特定化学成分的钢轨，以钢轨的总重量为基准，所述钢轨的化学成分包括0.71-0.82重量％的C、0.45-0.85重量％的Si、0.85-1.20重量％的Mn、0.08-0.15重量％的V、0.08-0.20重量％的Cr，≤0.025重量％的P、≤0.025重量％的S，其余为Fe和不可避免的杂质。
本发明中，所述加速冷却和缓冷的冷却介质为本领域常用的冷却介质，包括但是不限于水、聚合物溶液、油、压缩空气、水雾或者油雾混合气，能够提供均匀冷却流场的物质均可。
本发明中，所述生产方法还包括：转炉冶炼、LF精炼、真空处理、连铸、铸坯加热、轧制、矫直等工序，对上述工序没有特别的限定，按照常规的钢轨生产工艺方法进行即可。例如，浇铸过程应在全程保护下进行，防止与空气接触；浇铸成的钢坯应进行缓冷处理；采用步进梁加热炉进行铸坯加热，并进行保温处理；采用万能轧制生产线进行轧制；采用平立复合矫直工艺。
本发明还提供了通过本生产方法得到的钢轨，钢轨全断面的室温金相组织为细片状珠光体和少量铁素体，未出现贝氏体和马氏体等异常组织，钢轨力学性能均满足相关标准要求，矫后轨底残余应力可以控制在50-90MPa，可应用于客运及客、货混运等多种线路，提高钢轨使用寿命和行车安全。
为了更好地理解本发明，下面结合附图和实施例进一步阐明本发明的内容，但应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不限定本发明。
本发明实施例1-5的冶炼化学成分分别按照表1中的1-5#所示，对比例1-2分别按实施例1-2的成分范围进行。
表1实施例和对比例的化学成分
Figure PCTCN2020095377-appb-000001
实施例1：
按照常规的冶炼和浇铸方法进行，工序包括转炉冶炼、LF精炼、真空处理、连铸。其中，转炉炉渣碱度控制在2.5～4.5；出钢水1/4左右时，随钢流加入硅、锰、钒等合金和增碳剂， 钢水出至3/4时，合金、增碳剂全部加入；LF炉处理时间应大于40min；RH真空度≤100Pa，纯真空处理时间应不低于15min，浇铸过程应在全程保护下进行，防止与空气接触，同时浇铸成的钢坯应进行缓冷处理。随后按照常规的钢轨轧制方法进行，钢坯送入步进梁加热炉中加热并保温，加热温度1200-1300℃，保温时间150-260min，用万能轧机轧制成钢轨，开轧温度1080-1150℃，终轧温度840-920℃。对钢轨进行在线热处理，开始冷却温度控制为820℃，轨头的冷却速度为5.2℃/s，轨底的冷却速度为1.6℃/s，待轨头温度降至530℃；随后对轨头和轨底进行缓冷处理，缓冷速度为0.6℃/s，待轨头温度降至380℃；随后保持轨头冷却速度为0.6℃/s，控制轨底冷却速度为1.2℃/s，控制轨头与轨底的温度差(轨头温度减去轨底温度)为35℃，停止加速冷却，自然冷却至室温，最后采用平立复合矫直工艺对钢轨进行矫直。
实施例2：
按照实施例1的方法进行，所不同的是，对钢轨进行在线热处理，开始冷却温度控制为780℃，轨头的冷却速度为6.5℃/s，轨底的冷却速度为2.1℃/s，待轨头温度降至460℃；随后对轨头和轨底进行缓冷处理，缓冷速度为0.8℃/s，待轨头温度降至400℃；随后保持轨头冷却速度为0.8℃/s，控制轨底冷却速度为0.5℃/s，控制轨头与轨底的温度差(轨头温度减去轨底温度)为-18℃。
实施例3：
按照实施例1的方法进行，所不同的是，对钢轨进行在线热处理，开始冷却温度控制为800℃，轨头的冷却速度为5.8℃/s，轨底的冷却速度为2.0℃/s，待轨头温度降至490℃；随后对轨头和轨底进行缓冷处理，缓冷速度为0.9℃/s，待轨头温度降至410℃；随后保持轨头冷却速度为0.9℃/s，控制轨底冷却速度为0.7℃/s，控制轨头与轨底的温度差(轨头温度减去轨底温度)为-5℃。
实施例4：
按照实施例1的方法进行，所不同的是，对钢轨进行在线热处理，开始冷却温度控制为720℃，轨头的冷却速度为7.8℃/s，轨底的冷却速度为2.8℃/s，待轨头温度降至520℃；随后对轨头和轨底进行缓冷处理，缓冷速度为0.6℃/s，待轨头温度降至430℃；随后保持轨头冷却速度为0.6℃/s，控制轨底冷却速度为1.4℃/s，控制轨头与轨底的温度差(轨头温度减去轨底温度)为55℃。
实施例5：
按照实施例1的方法进行，所不同的是，对钢轨进行在线热处理，开始冷却温度控制为850℃，轨头的冷却速度为6.9℃/s，轨底的冷却速度为2.3℃/s，待轨头温度降至500℃；随后对轨头和轨底进行缓冷处理，缓冷速度为0.7℃/s，待轨头温度降至360℃；随后保持轨头冷却速度为0.7℃/s，控制轨底冷却速度为1.3℃/s，控制轨头与轨底的温度差(轨头温度 减去轨底温度)为20℃。
对比例1：
按照实施例1的方法进行，所不同的是，按目前常规的钢轨热处理工艺，开始冷却温度控制为820℃，轨头的冷却速度为5.2℃/s，轨底的冷却速度为1.6℃/s，待轨头温度降至530℃，停止加速冷却，自然冷却至室温。
对比例2：
按照实施例1的方法进行，所不同的是，按照热轧钢轨生产工艺，轧制后的钢轨不进行在线热处理过程，直接自然冷却至室温。
按照TB/T 2344-2012标准规定的方法测定实施例和对比例中所得钢轨的抗拉强度、踏面硬度、横断面洛式硬度、金相组织、轨底残余应力等性能指标，结果见表2-表3。
表2实施例和对比例的性能对比
Figure PCTCN2020095377-appb-000002
表3实施例和对比例的横断面洛氏硬度对比
Figure PCTCN2020095377-appb-000003
其中，表3的数据是如附图1所示的测量位置测量得到的。其中每条线的离表面最近的第1点距表面5mm，其余点间距均为5mm；D、E线与下颚距离为5mm；B、C线为A、D和A、E线的角平分线。
可以看出，实施例1-5所得到的钢轨各项性能和金相组织良好，轨底残余应力可稳定控 制在50-90MPa范围内，与对比例1-2钢轨性能对比来看，本发明方法在保证热处理钢轨组织和力学性能的前提下，能有效降低钢轨轨底残余应力。
尽管这里参照本发明的解释性实施例对本发明进行了描述，上述实施例仅为本发明较佳的实施方式，本发明的实施方式并不受上述实施例的限制，应该理解，本领域技术人员可以设计出很多其他的修改和实施方式，这些修改和实施方式将落在本申请公开的原则范围和精神之内。

Claims (9)

  1. 一种降低热处理钢轨残余应力的生产方法，其特征在于：将热轧后的钢轨进行在线的加速冷却处理，其中，开始冷却温度控制为700-880℃，轨头的冷却速度为5-8℃/s，轨底的冷却速度为1.5-3℃/s，冷却至轨头温度降至460-550℃；随后对轨头和轨底进行缓冷处理，缓冷速度为0.5-1℃/s，缓冷至轨头温度降至350-450℃；随后保持轨头冷却速度为0.5-1℃/s，控制轨底冷却速度为0.5-2℃/s，当轨头与轨底的温度差达到一定范围时，停止加速冷却，自然冷却至室温。
  2. 根据权利要求1所述降低热处理钢轨残余应力的生产方法，其特征在于：
    所述的开始冷却温度控制为720-850℃，轨头的冷却速度为6-7℃/s，轨底的冷却速度为1.8-2.8℃/s，冷却至轨头温度降至480-530℃，随后对轨头和轨底进行缓冷处理，缓冷速度为0.5-0.8℃/s，缓冷至轨头温度降至360-420℃；随后保持轨头冷却速度为0.5-0.8℃/s，控制轨底冷却速度为0.5-1.5℃/s，当轨头与轨底的温度差达到一定范围时，停止加速冷却，自然冷却至室温。
  3. 根据权利要求1或2所述降低热处理钢轨残余应力的生产方法，其特征在于：
    轨头温度是指踏面中心部位表面的温度，轨底温度是指轨底中心部位表面的温度。
  4. 根据权利要求1或2所述降低热处理钢轨残余应力的生产方法，其特征在于：
    轨头与轨底的温度差范围为-20℃至60℃，其中轨头与轨底的温度差是指轨头温度减去轨底温度。
  5. 根据权利要求1或2所述降低热处理钢轨残余应力的生产方法，其特征在于：
    自然冷却至室温后，钢轨端部保持平直或者向轨头有一定程度的翘曲，100m长度的钢轨端部上翘的高度在0-30mm范围内。
  6. 根据权利要求1或2所述降低热处理钢轨残余应力的生产方法，其特征在于：
    以钢轨的总重量为基准，所述钢轨的化学成分包括0.71-0.82重量％的C、0.45-0.85重量％的Si、0.85-1.20重量％的Mn、0.08-0.15重量％的V、0.08-0.20重量％的Cr，≤0.025重量％的P、≤0.025重量％的S，其余为Fe和不可避免的杂质。
  7. 根据权利要求1或2所述降低热处理钢轨残余应力的生产方法，其特征在于：
    所述冷却和缓冷的冷却介质为水、聚合物溶液、油、压缩空气、水雾或者油雾混合气。
  8. 一种钢轨，其特征在于：是根据权利要求1至7任一权利要求所述的降低热处理钢轨残余应力的生产方法生产得到的。
  9. 根据权利要求8所述的钢轨，其特征在于：钢轨全断面的室温金相组织为细片状珠光体和少量铁素体，矫后轨底残余应力控制在50-90MPa。
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