阅读说明：本技术 一种降低热处理钢轨残余应力的生产方法及其所得钢轨 (Production method for reducing residual stress of heat-treated steel rail and steel rail obtained by production method ) 是由 费俊杰 周剑华 董茂松 叶佳林 朱敏 王俊 郑建国 王瑞敏 于 2019-09-27 设计创作，主要内容包括：本发明公开了一种降低热处理钢轨残余应力的生产方法,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。本发明还提供了通过本生产方法得到的钢轨。本发明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。(The invention discloses a production method for reducing residual stress of a heat-treated steel rail, which comprises the steps of carrying out online accelerated cooling treatment on the hot-rolled steel rail, wherein the starting cooling temperature is 700-880 ℃, the cooling speed of a rail head is 5-8 ℃/s, the cooling speed of a rail bottom is 1.5-3 ℃/s, and cooling is carried out until the temperature of the rail head is reduced to 460-550 ℃; carrying out slow cooling treatment at a slow cooling speed of 0.5-1 ℃/s until the temperature of the rail head is reduced to 350-; keeping the cooling speed of the rail head at 0.5-1 ℃/s, controlling the cooling speed of the rail bottom at 0.5-2 ℃/s, stopping accelerated cooling when the temperature difference between the rail head and the rail bottom reaches a certain range, and naturally cooling to room temperature. The invention also provides the steel rail obtained by the production method. The invention can effectively reduce the residual stress of the rail bottom of the steel rail, prolong the service life of the steel rail and improve the driving safety.)

1. A production method for reducing residual stress of heat-treated steel rails is characterized by comprising the following steps: carrying out online accelerated cooling treatment on the hot-rolled steel rail, wherein the starting cooling temperature is controlled to be 700-880 ℃, the cooling speed of the rail head is 5-8 ℃/s, the cooling speed of the rail bottom is 1.5-3 ℃/s, and the rail head is cooled to be 460-550 ℃; then, slowly cooling the rail head and the rail bottom at the slow cooling speed of 0.5-1 ℃/s until the temperature of the rail head is reduced to 350-450 ℃; and then keeping the cooling speed of the rail head at 0.5-1 ℃/s, controlling the cooling speed of the rail bottom at 0.5-2 ℃/s, stopping accelerated cooling when the temperature difference between the rail head and the rail bottom reaches a certain range, and naturally cooling to room temperature.

2. The production method for reducing the residual stress of the heat-treated steel rail according to claim 1, wherein the production method comprises the following steps:

the starting cooling temperature is controlled to be 850 ℃ plus 720 ℃, the cooling speed of the rail head is 6-7 ℃/s, the cooling speed of the rail bottom is 1.8-2.8 ℃/s, the rail head is cooled to be 480 ℃ plus 530 ℃, then the rail head and the rail bottom are subjected to slow cooling treatment, the slow cooling speed is 0.5-0.8 ℃/s, and the slow cooling is carried out until the temperature of the rail head is reduced to be 360 ℃ plus 420 ℃; and then keeping the cooling speed of the rail head at 0.5-0.8 ℃/s, controlling the cooling speed of the rail bottom at 0.5-1.5 ℃/s, stopping accelerated cooling when the temperature difference between the rail head and the rail bottom reaches a certain range, and naturally cooling to room temperature.

3. The production method for reducing the residual stress of the heat-treated steel rail according to claim 1 or 2, wherein:

the rail head temperature refers to the surface temperature of the central part of the tread, and the rail bottom temperature refers to the surface temperature of the central part of the rail bottom.

4. The production method for reducing the residual stress of the heat-treated steel rail according to claim 1 or 2, wherein:

the temperature difference between the rail head and the rail bottom ranges from minus 20 ℃ to 60 ℃, wherein the temperature difference between the rail head and the rail bottom is the temperature of the rail head minus the temperature of the rail bottom.

5. The production method for reducing the residual stress of the heat-treated steel rail according to claim 1 or 2, wherein:

after naturally cooling to room temperature, the end of the steel rail is kept straight or warped to a certain degree towards the rail head, and the upwarping height of the end of the steel rail with the length of 100m is within the range of 0-30 mm.

6. The production method for reducing the residual stress of the heat-treated steel rail according to claim 1 or 2, wherein:

the chemical components of the steel rail comprise 0.71-0.82 wt% of C, 0.45-0.85 wt% of Si, 0.85-1.20 wt% of Mn, 0.08-0.15 wt% of V, 0.08-0.20 wt% of Cr, less than or equal to 0.025 wt% of P, less than or equal to 0.025 wt% of S and the balance of Fe and inevitable impurities based on the total weight of the steel rail.

7. The production method for reducing the residual stress of the heat-treated steel rail according to claim 1 or 2, wherein:

the cooling medium for cooling and slow cooling is water, polymer solution, oil, compressed air, water mist or oil mist mixed gas.

8. A steel rail, characterized in that: the production method for reducing the residual stress of the heat-treated steel rail is produced according to any one of claims 1 to 7.

9. A rail according to claim 8, wherein: the room-temperature metallographic structure of the whole section of the steel rail is fine lamellar pearlite and a small amount of ferrite, and the residual stress of the rail bottom after correction is controlled to be 50-90 MPa.

Technical Field

The invention relates to a steel rail and a production method thereof, in particular to a production method for reducing residual stress of a heat-treated steel rail and the obtained steel rail, belonging to the field of steel rail production and application.

Background

The on-line heat treatment process is the most effective and economic technical means for improving the strength and the hardness of the steel rail at present, the heat treatment of the steel rail can effectively improve the wear resistance and the fatigue resistance of the steel rail, meet the use requirements of heavy haul railways, small radius curve railways and other severe conditions, prolong the service life, and the steel rail manufacturers at home and abroad basically adopt the on-line heat treatment process to produce the heat treatment steel rail at present.

In the heat treatment process, the hot-rolled steel rail passes through a cooling unit at a certain speed, and the cooling unit sprays cooling medium (water or fog or air) to accelerate cooling of the steel rail, so that the aim of strengthening is fulfilled. Compared with natural cooling, the cooling speed is accelerated, the temperature stress is easier to generate, and the residual stress of the heat-treated steel rail is increased. More importantly, the shapes of the sections of the steel rails are uneven, the quantity of metal at the rail bottoms is far less than that of the rail heads, if the cooling strength distribution of the rail heads and the rail bottoms is unreasonable, the steel rails can be bent greatly in the vertical direction in the process of naturally cooling to room temperature after the heat treatment is finished, the residual stress at the rail bottoms of the heat-treated steel rails is large or exceeds the standard after the heat treatment is carried out, and the service lives of the steel rails and the running safety of trains can be directly influenced by the residual stress of the steel rails.

In the method for controlling the residual stress of the steel rail, a patent of a hectometer heavy rail residual stress control method (CN102284503A) provides a hectometer hot rolled steel rail residual stress control method, a universal rolling, cooling after rolling and composite straightening method are adopted, large radian pre-bending is adopted for the hectometer steel rail in the cooling process after rolling, and the chord height of the steel rail when the steel rail is cooled to the room temperature is controlled within the range of 30-40 mm. By combining the optimized straightening deformation rule of the 8+1 multi-roll straightener and the control of the bending degree before straightening, the method effectively controls the rail bottom residual stress of the straightened hectometer steel rail, the average value of the rail bottom residual stress is reduced by 70MPa, and the residual stress values are all less than or equal to 250 MPa. However, the patent is about residual stress optimization of hot rolled rails and cannot be applied to heat treated rails.

The patent CN 106086370A provides a method for reducing the residual stress of a steel rail, and the steel rail and the application thereof, which is characterized in that the center of a rail head tread, two sides of the rail head and the center of a rail bottom of the rolled steel rail are sequentially subjected to accelerated cooling, slow cooling and air cooling, wherein the start cooling temperature of the accelerated cooling is 650 plus-950 ℃, the cooling speed is 2-8 ℃/s, the final cooling temperature is 400 plus-600 ℃, the cooling speed of the slow cooling is 0.1-1.5 ℃/s, and the final cooling temperature is 180 plus-300 ℃, so that the residual stress of the steel rail can be effectively reduced on the premise of ensuring the tensile property of the steel rail. However, the principle of the patent is to change the metallographic structure of the railhead to a certain extent, so as to reduce the residual stress of the steel rail, and the patent only controls the cooling speed of the railhead and the rail angle part and does not process the rail bottom.

Aiming at the problem of overlarge residual stress at the rail bottom commonly existing in the prior heat-treated steel rail and the potential safety hazard brought by the problem, a production method capable of effectively reducing the residual stress of the heat-treated steel rail is urgently needed.

Disclosure of Invention

The invention aims to overcome the problem of overlarge residual stress of the rail bottom of the conventional heat-treated steel rail, and provides a production method capable of effectively reducing the residual stress of the heat-treated steel rail and the obtained steel rail.

The invention is realized in such a way that:

a production method for reducing residual stress of a heat-treated steel rail mainly comprises the steps of carrying out online accelerated cooling treatment on the hot-rolled steel rail, wherein the starting cooling temperature is controlled to be 700-880 ℃, the cooling speed of a rail head is 5-8 ℃/s, the cooling speed of a rail bottom is 1.5-3 ℃/s, and the steel rail is cooled until the temperature of the rail head is reduced to 460-550 ℃; then, slowly cooling the rail head and the rail bottom at the slow cooling speed of 0.5-1 ℃/s until the temperature of the rail head is reduced to 350-450 ℃; and then keeping the cooling speed of the rail head at 0.5-1 ℃/s, controlling the cooling speed of the rail bottom at 0.5-2 ℃/s, stopping accelerated cooling when the temperature difference between the rail head and the rail bottom reaches a certain range, and naturally cooling to room temperature.

The further scheme is as follows:

the starting cooling temperature is controlled to be 850 ℃ plus 720 ℃, the cooling speed of the rail head is 6-7 ℃/s, the cooling speed of the rail bottom is 1.8-2.8 ℃/s, the rail head is cooled to be 480 ℃ plus 530 ℃, then the rail head and the rail bottom are subjected to slow cooling treatment, the slow cooling speed is 0.5-0.8 ℃/s, and the slow cooling is carried out until the temperature of the rail head is reduced to be 360 ℃ plus 420 ℃; and then keeping the cooling speed of the rail head at 0.5-0.8 ℃/s, controlling the cooling speed of the rail bottom at 0.5-1.5 ℃/s, stopping accelerated cooling when the temperature difference between the rail head and the rail bottom reaches a certain range, and naturally cooling to room temperature.

The further scheme is as follows:

the temperature difference between the rail head and the rail bottom ranges from minus 20 ℃ to 60 ℃, wherein the temperature difference between the rail head and the rail bottom is the temperature of the rail head minus the temperature of the rail bottom.

The further scheme is as follows:

after naturally cooling to room temperature, the end of the steel rail is kept straight or warped to a certain degree towards the rail head, and the upwarping height of the end of the steel rail with the length of 100m is within the range of 0-30 mm.

The further scheme is as follows:

the rail head temperature refers to the surface temperature of the central part of the tread, and the rail bottom temperature refers to the surface temperature of the central part of the rail bottom.

The technical effects of the present invention are specifically explained below: (1) and carrying out accelerated cooling treatment on the rolled steel rail. The principle of accelerated cooling is that the residual temperature of the rolled steel rail is utilized to accelerate cooling, the supercooling degree of austenite to pearlite transformation is increased, the pearlite transformation temperature is reduced, and the migration distance of carbon atoms in austenite is reduced, so that pearlite with finer interlayer spacing is obtained, the strength and hardness of the steel rail are improved, and the wear resistance is improved, which is the basic principle of the existing steel rail heat treatment process. (2) The initial cooling temperature was controlled to 700-. The steel rail is subjected to heat treatment by using the residual heat after rolling, so the cooling starting temperature is too high and is matched with the rolling rhythm, the austenitizing temperature and the finishing temperature of the steel rail are increased, the problems of thick austenite grains, increased surface defects and the like are directly caused, and meanwhile, the cooling starting temperature is too high, so that the heat of a rail head can be timely taken away by a higher cooling speed, and the energy consumption of equipment is increased; the initial cooling temperature is too low, the distance between the initial cooling temperature and the pearlite phase transformation point is short, the supercooling degree is large, and the risk of generating abnormal structures is brought. The temperature range selected by the application can perfectly match the utilization of the residual temperature after rolling, and the problem caused by overhigh or overlow temperature is avoided. (3) The cooling speed of the rail head is 5-8 ℃/s, and the cooling speed of the rail bottom is 1.5-3 ℃/s. The cooling speed of the rail head at this stage directly determines the mechanical property of the heat-treated steel rail, when the cooling speed is less than 5 ℃/s, pearlite with fine lamellar spacing is difficult to obtain, and the strength and hardness of the steel rail are insufficient; when the cooling speed is more than 8 ℃/s, the diffusion rate of carbide is reduced, and abnormal structures such as bainite and martensite are easy to appear, so that the steel rail is scrapped. The amount of metal at the rail bottom is less than that of the rail head, and in order to prevent the rail bending caused by overlarge temperature difference of the rail head and the rail bottom in the heat treatment process of the rail, the rail bottom is also cooled, but the cooling speed is generally controlled to be about 1/2 or 1/3 of the cooling speed of the rail head, so that the temperature consistency of the rail bottom of the rail head is kept as much as possible. (4) The rail head temperature is reduced to 460-550 ℃. Through a great deal of experimental research, the inventor finds that when the temperature of the rail head is reduced to 550 ℃, the structure on the surface of the rail head and in the depth range of 20mm below the surface of the rail head completes pearlite transformation, but the core temperature of the rail head is still high, and if cooling is stopped, the core temperature can diffuse outwards to influence the pearlite structure performance; when the rail head temperature is reduced to 460 ℃, the pearlite transformation of the whole rail head is finished, the core temperature is correspondingly reduced, and the accelerated cooling is not needed to be carried out continuously. (5) And (4) carrying out slow cooling treatment on the rail head and the rail bottom at a slow cooling speed of 0.5-1 ℃/s. The accelerated cooling in the previous stage is fast, certain temperature stress can be generated inside the steel rail, the slow cooling can be used for homogenizing the temperature distribution of the whole cross section of the rail head, and the temperature stress is reduced, so that the residual stress is reduced. (6) Keeping the cooling speed of the rail head at 0.5-1 ℃/s, and controlling the cooling speed of the rail bottom at 0.5-2 ℃/s. This is mainly to achieve a certain temperature difference range between the rail head and the rail bottom through a smaller cooling rate. (7) The temperature difference range between the rail head and the rail bottom (the temperature of the rail head minus the temperature of the rail bottom) is-20 ℃ to 60 ℃, after the rail head and the rail bottom are naturally cooled to room temperature, the end part of the steel rail is kept straight or warped to a certain degree towards the rail head, and the upwarping height of the end part of the steel rail is within the range of 0-30 mm. The proper temperature difference range between the rail head and the rail bottom is set so that the steel rail can keep ideal bending degree in the natural cooling process after running out of the heat treatment unit. Because the metal content of the rail bottom of the steel rail is less than that of the rail head, the temperature of the rail bottom is slightly higher than that of the rail head when the steel rail is naturally cooled. The inventor discovers through a large amount of experimental researches that when the rail head is 20 ℃ lower than the rail bottom, the temperature of the rail head and the rail bottom gradually tends to be consistent in the process of naturally cooling to room temperature, and finally the steel rail is basically kept straight, so that the residual stress caused by the deformation of the steel rail in the straightening process is greatly reduced; and the railhead is 60 ℃ higher than the railbase, and in the process of naturally cooling to room temperature, the steel rail can generate a bending degree which bends to the railhead and shows that the end part slightly upwarps, and the height of the steel rail is about 30 mm.

The further scheme is as follows:

in the production method, the chemical components of the steel rail comprise 0.71-0.82 wt% of C, 0.45-0.85 wt% of Si, 0.85-1.20 wt% of Mn, 0.08-0.15 wt% of V, 0.08-0.20 wt% of Cr, less than or equal to 0.025 wt% of P, less than or equal to 0.025 wt% of S and the balance of Fe and inevitable impurities based on the total weight of the steel rail.

The further scheme is as follows:

the cooling medium for accelerated cooling and slow cooling is a cooling medium commonly used in the art, and includes, but is not limited to, water, polymer solution, oil, compressed air, water mist, or oil mist mixture.

The further scheme is as follows:

the production method further comprises: the method comprises the following working procedures of converter smelting, LF refining, vacuum treatment, continuous casting, casting blank heating, rolling, straightening and the like, and the working procedures are not particularly limited and can be carried out according to a conventional steel rail production process method. For example, the casting process should be carried out under full protection from air contact; slowly cooling the cast steel billet; heating a casting blank by adopting a walking beam heating furnace, and carrying out heat preservation treatment; rolling by adopting a universal rolling production line; adopts a horizontal and vertical composite straightening process.

The invention also provides the steel rail obtained by the production method, the room-temperature metallographic structure of the whole section of the steel rail is fine lamellar pearlite and a small amount of ferrite, the residual stress of the rail bottom after correction can be controlled to be 50-90MPa, and the steel rail can be applied to various lines such as passenger transport, mixed transport of passengers and goods, and the like, so that the service life of the steel rail is prolonged, and the driving safety is improved.

The production method capable of effectively reducing the residual stress of the heat-treated steel rail and the obtained steel rail provided by the invention have the advantages that the bending control of the steel rail after heat treatment is in a more ideal range by reasonably controlling the cooling strength and the temperature difference of the rail head and the rail bottom of the steel rail, the residual stress of the rail bottom of the steel rail can be effectively reduced on the premise of ensuring the tissue and the mechanical property of the heat-treated steel rail, the service life of the steel rail is prolonged, the driving safety is improved, the production method is simple, the operability is strong, and the popularization and the application are easy.

Drawings

FIG. 1 is a schematic representation of Rockwell hardness measurement of a rail head cross section of a steel rail;

fig. 2 is a schematic view of a rail bending towards the railhead.

Detailed Description

The invention provides a production method for reducing residual stress of a heat-treated steel rail, which mainly comprises the steps of carrying out online accelerated cooling treatment on the hot-rolled steel rail, wherein the starting cooling temperature is controlled to be 700-880 ℃, the cooling speed of a rail head is 5-8 ℃/s, the cooling speed of a rail bottom is 1.5-3 ℃/s, and the temperature of the rail head is reduced to be 460-550 ℃; then, slowly cooling the rail head and the rail bottom at the slow cooling speed of 0.5-1 ℃/s until the temperature of the rail head is reduced to 350-; and then keeping the cooling speed of the rail head at 0.5-1 ℃/s, controlling the cooling speed of the rail bottom at 0.5-2 ℃/s, stopping accelerated cooling when the temperature difference between the rail head and the rail bottom reaches a certain range, and naturally cooling to room temperature.

Preferably, the starting cooling temperature is controlled to be 720-850 ℃, the cooling speed of the rail head is 6-7 ℃/s, the cooling speed of the rail bottom is 1.8-2.8 ℃/s, the temperature of the rail head is reduced to 480-530 ℃, and then the rail head and the rail bottom are subjected to slow cooling treatment, the slow cooling speed is 0.5-0.8 ℃/s, and the temperature of the rail head is reduced to 360-420 ℃; and then keeping the cooling speed of the rail head at 0.5-0.8 ℃/s, controlling the cooling speed of the rail bottom at 0.5-1.5 ℃/s, stopping accelerated cooling when the temperature difference between the rail head and the rail bottom reaches a certain range, and naturally cooling to room temperature.

In the present invention, it is preferable that the difference between the rail head temperature and the rail foot temperature (the rail head temperature minus the rail foot temperature) is in the range of-20 ℃ to 60 ℃, the rail head temperature is the surface temperature of the central portion of the tread, and the rail foot temperature is the surface temperature of the central portion of the rail foot.

In the present invention, after naturally cooling to room temperature, the rail end remains straight or warps to some extent toward the rail head, as shown in fig. 2, after naturally cooling to room temperature, the rail end remains straight or warps to some extent toward the rail head, and the upturned height of the rail end with a length of 100m is in the range of 0-30 mm.

The production method of the invention can be used for on-line heat treatment of steel rails with any conventional composition to reduce the residual stress at the rail bottom, and the inventor finds that the steel rail with a specific chemical composition can have lower residual stress relative to the steel rail with other chemical compositions and can be more suitable for the production method. The steel rail with the specific chemical composition comprises 0.71-0.82 wt% of C, 0.45-0.85 wt% of Si, 0.85-1.20 wt% of Mn, 0.08-0.15 wt% of V, 0.08-0.20 wt% of Cr, less than or equal to 0.025 wt% of P, less than or equal to 0.025 wt% of S and the balance of Fe and inevitable impurities based on the total weight of the steel rail.

In the present invention, the cooling medium for accelerated cooling and slow cooling is a cooling medium commonly used in the art, and includes, but is not limited to, water, polymer solution, oil, compressed air, water mist or oil mist mixture, and any substance capable of providing a uniform cooling flow field.

In the present invention, the production method further comprises: the method comprises the following working procedures of converter smelting, LF refining, vacuum treatment, continuous casting, casting blank heating, rolling, straightening and the like, and the working procedures are not particularly limited and can be carried out according to a conventional steel rail production process method. For example, the casting process should be carried out under full protection from air contact; slowly cooling the cast steel billet; heating a casting blank by adopting a walking beam heating furnace, and carrying out heat preservation treatment; rolling by adopting a universal rolling production line; adopts a horizontal and vertical composite straightening process.

The invention also provides the steel rail obtained by the production method, the room-temperature metallographic structure of the whole section of the steel rail is fine lamellar pearlite and a small amount of ferrite, abnormal structures such as bainite and martensite are not generated, the mechanical properties of the steel rail meet the requirements of relevant standards, the residual stress of the rail bottom after correction can be controlled to be 50-90MPa, the steel rail can be applied to various lines such as passenger transport, mixed transport of passengers and goods, and the like, the service life of the steel rail is prolonged, and the driving safety is improved.

For a better understanding of the present invention, the following further illustrates the subject matter of the invention with reference to the drawings and examples, but it should be understood that the specific examples described herein are for purposes of illustration only and are not intended to limit the invention.

The metallurgical chemical compositions of examples 1 to 5 of the present invention were as shown in # 1 to # 5 in Table 1, respectively, and comparative examples 1 to 2 were as shown in the compositional ranges of examples 1 to 2, respectively.

TABLE 1 chemical compositions of examples and comparative examples