CN111621631B - Efficient heat treatment production method for steel rail and steel rail prepared by same - Google Patents
Efficient heat treatment production method for steel rail and steel rail prepared by same Download PDFInfo
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- CN111621631B CN111621631B CN202010478646.6A CN202010478646A CN111621631B CN 111621631 B CN111621631 B CN 111621631B CN 202010478646 A CN202010478646 A CN 202010478646A CN 111621631 B CN111621631 B CN 111621631B
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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
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- 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
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- 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
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- 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
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- 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
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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Abstract
The invention discloses a high-efficiency heat treatment production method for a steel rail and the steel rail prepared by the method, and belongs to the technical field of steel making. The production method comprises the steps of carrying out on-line accelerated cooling treatment on a hot-rolled steel rail, controlling the running speed of the steel rail through a heat treatment cooling unit to be 1.5-2.0 m/s, controlling the initial cooling temperature to be 720-800 ℃, and carrying out staged cooling on the steel rail, wherein in the first stage, the accelerated cooling speed of a rail head is 9-11 ℃/s, and the cooling time is 10-14 s; in the second stage, the rail head accelerated cooling speed is 2-5 ℃/s, and the cooling time is 40-50 s; and in the third stage, the rail head is not cooled in an accelerated manner, the accelerated cooling speed of the rail bottom is 1-2 ℃/s, the cooling time is 20-26 s, then, the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature. The method reasonably controls the cooling intensity and the cooling time of the steel rail by improving the running speed of the steel rail heat treatment unit, so that the production rhythm of the heat-treated steel rail is matched with the rolling rhythm, the production efficiency is effectively improved, and the stability of the performance of the head and the tail of the steel rail is improved.
Description
Technical Field
The invention relates to a steel rail production process, belongs to the technical field of steel making, and particularly relates to a high-efficiency heat treatment production method for a steel rail and the steel rail prepared by the method.
Background
With the rapid development of railways in China, the running speed, the load capacity and the running density of trains are remarkably increased, and the problems of rail abrasion, fatigue damage and the like are remarkably increased, so that the service life of the rails and the running safety are seriously influenced. Research and application practice shows that the wear resistance and fatigue resistance of the steel rail can be effectively improved by heat treatment of the steel rail, and steel rail manufacturers at home and abroad commonly adopt an online heat treatment process to produce the heat-treated steel rail, namely, the hot-rolled steel rail is subjected to online accelerated cooling treatment, so that the strength and hardness of the steel rail are improved. The on-line steel rail treating process includes the following steps: the rail does not need to be reheated.
At present, the on-line heat treatment process of the steel rail mainly adopts a walking type, a plurality of groups of cooling units are arranged behind a rolling mill, the hot-rolled steel rail passes through the cooling units at a certain speed, and the cooling units spray cooling media to carry out accelerated cooling on the steel rail, so that the strengthening purpose is achieved. In order to ensure that the steel rail obtains a stable and uniform cooling effect as far as possible, the speed of the steel rail passing through a heat treatment cooling unit in the industry is generally controlled to be 1.0-1.2 m/s at present, but the running speed in the rolling production of the steel rail is 1.6-1.8 m/s, so that the on-line heat treatment rhythm is not matched with the rolling production rhythm, and the production efficiency of the heat treatment steel rail is low; meanwhile, the production length of the steel rail is 100 meters, the heat treatment running speed is low, after the head of the steel rail enters the heat treatment unit, the tail of the steel rail still needs to enter the heat treatment unit after about 100 seconds, the temperature difference between the head and the tail of the steel rail is increased, and the performance stability of the head and the tail of the steel rail is directly influenced.
In the on-line heat treatment method of steel rail, the patent "heat treatment method and device for producing high-strength steel rail by using rolling waste heat" (patent application publication No. CN1178250A, published: 1998-4-8) provides a heat treatment method for producing high-strength steel rail by using rolling waste heat, the high-temperature state of hot-rolled steel rail kept in austenite region is continuously sent into a machine set equipped with a heat treatment device, cooling medium is sprayed to the steel rail by a nozzle, so that the steel rail is uniformly accelerated and cooled, fine pearlite structure with gradually reduced hardness is obtained, and the produced heat-treated steel rail can meet the development requirements of railway transportation to high speed, heavy load and large transportation volume. However, the speed of the steel rail passing through the heat treatment cooling unit in the patent is 0.2-1.2 m/s, so that the speed is slow, the speed cannot be completely matched with the rolling speed, and meanwhile, the control of the temperature difference of the head and the tail of the steel rail is not mentioned.
A pearlite heat-treated steel rail and a production method thereof (patent application publication No. CN1793403A, publication date: 2006-06-28) provide a pearlite heat-treated steel rail and a production method thereof, the production method comprises smelting, rolling and heat treatment, the steel rail is cooled to 400-500 ℃ from 650-880 ℃ at a cooling rate of 1-10 ℃/s, and then naturally cooled to room temperature, the produced steel rail has good wear resistance, a high-carbon high-strength heat-treated steel rail with excellent wear resistance and plasticity and a manufacturing method thereof (patent application publication No. CN102220545A, publication date: 2011-10-19) provide a high-carbon high-strength heat-treated steel rail with excellent wear resistance and plasticity and a production method, the residual temperature of the hot steel rail after rolling is 680-900 ℃, the steel rail is cooled to 400-500 ℃ at a cooling rate of 1.5-10 ℃/s, and then naturally cooled to room temperature, the tensile strength of the steel rail is more than or equal to 1330MPa, the elongation is more than or equal to 9 percent, the hardness of the rail head is more than or equal to 380HB, the depth of a hardened layer is more than 25mm, the structure is fine pearlite, the steel rail has excellent wear resistance and plasticity, and can meet the use requirements of heavy haul railways.
The Chinese invention patent application (application publication No. CN109182715A, application publication date: 2019-01-11) discloses a steel rail online heat treatment flatness control method, which specifically comprises the following steps: 1) bending treatment: after rolling the steel rail, controlling the hot steel rail to have the bending degree of 0.4-1.0 mm/1.5m to the rail bottom by a bending machine; 2) and (3) heat treatment: the accelerated cooling in the steel rail heat treatment process is divided into two stages, the accelerated cooling time in the first stage is 60-100 seconds, and the flow ratio of cooling media applied to the rail head and the rail bottom of the steel rail is 4-7: 1; the accelerated cooling time of the second stage is 25-50 seconds, and the flow ratio of the cooling medium applied to the rail head and the rail bottom of the steel rail is 1: 3-6; and after the heat treatment is finished, the temperature of the rail head of the steel rail is 60-120 ℃ lower than that of the rail bottom. The straightness of the steel rail obtained by the online heat treatment straightness control method of the steel rail is 0.9-1.2 mm/1.5 m.
The Chinese invention patent application (application publication No. CN110527816A, application publication date: 2019-12-03) discloses a heat treatment method for reducing the fatigue crack propagation rate of a steel rail, which comprises the following steps of carrying out sectional accelerated cooling heat treatment on a rail head of the steel rail after hot rolling: the starting cooling temperature is controlled to be 720-860 ℃, the first stage railhead cooling speed is 5-8 ℃/s, and the cooling time is 20-35 s; and then, carrying out second-stage cooling, namely, carrying out accelerated cooling on the railhead in a circulating periodic manner, namely, carrying out accelerated cooling on the railhead at a cooling speed of 3-6 ℃/s for 6-10 s, stopping accelerated cooling, naturally placing the steel rail for 2-5 s, namely a cooling period, stopping accelerated cooling when the temperature of the railhead is reduced to 300-450 ℃ through continuously circulating the cooling period, then carrying out heat preservation on the railhead for 10-20 min, and finally, naturally cooling to room temperature. The steel rail obtained by the method has a full-section room-temperature metallographic structure comprising fine lamellar pearlite and a small amount of ferrite, the fatigue crack propagation rate can be controlled to be 5-8 m/Gc (delta K is 10 MPa.m.0.5) and 14-18m/Gc (delta K is 13.5 MPa.m.0.5), and the steel rail can be applied to various lines such as passenger transport, mixed transport of passengers and goods, and the service life of the steel rail is prolonged, and the driving safety is improved.
The Chinese invention patent application (application publication number: CN110592355A, application publication date: 2019-12-20) discloses a production method for reducing residual stress of a heat-treated steel rail and the steel rail obtained by the method, and the method comprises the steps of carrying out on-line 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 the cooling is carried out until the temperature of the rail head is reduced to 460-550 ℃; carrying out slow cooling treatment at the slow cooling speed of 0.5-1 ℃/s until the temperature of the rail head is reduced to 350-450 ℃; 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.
However, the above patents do not mention the control of the running speed of the steel rail through the heat treatment unit and the temperature difference and performance between the head and the tail.
Aiming at the problems of unmatched heat treatment rhythm and rolling production rhythm, low production efficiency and head and tail performance fluctuation commonly existing in the current heat treatment steel rail production, a heat treatment production method capable of improving the steel rail production efficiency is urgently needed.
Disclosure of Invention
In order to solve the technical problems, the invention discloses a high-efficiency heat treatment production method for a steel rail and the steel rail prepared by the method. The method reasonably controls the cooling intensity and the cooling time of the steel rail by improving the running speed of the steel rail heat treatment unit, so that the production rhythm of the heat-treated steel rail is matched with the rolling rhythm, the production efficiency is effectively improved, and the stability of the performance of the head and the tail of the steel rail is improved.
In order to realize the aim, the invention discloses a high-efficiency heat treatment production method of a steel rail, which comprises the following processes: converter smelting, refining, vacuum treatment, continuous casting, casting blank heating and rolling, and further comprises the steps of carrying out online accelerated cooling treatment on the steel rail after hot rolling, controlling the running speed of the steel rail at 1.5-2.0 m/s through a heat treatment cooling unit, controlling the initial cooling temperature at 720-800 ℃, and carrying out staged cooling on the steel rail, wherein in the first stage, the rail head accelerated cooling speed is 9-11 ℃/s, and the cooling time is 10-14 s; in the second stage, the rail head accelerated cooling speed is 2-5 ℃/s, and the cooling time is 40-50 s; and in the third stage, the rail head is not cooled in an accelerated manner, the accelerated cooling speed of the rail bottom is 1-2 ℃/s, the cooling time is 20-26 s, then, the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature.
Further, when the rail head is accelerated and cooled in the first stage and the second stage, the rail bottom is also accelerated and cooled.
Further, the first stage rail head cooling medium is a water mist mixed gas which is formed by mixing 65-75 KPa of compressed air and 180-220L/h of water, and the second stage rail head cooling medium is a water mist mixed gas which is formed by mixing 30-45 KPa of compressed air and 40-60L/h of water.
Furthermore, the strength of the cooling medium of the rail bases in the first stage and the second stage is controlled to be 50-70% of the cooling strength of the corresponding rail heads, and the cooling time of the rail bases in the first stage and the second stage is kept equal to the cooling time of the corresponding rail heads.
Further, the third-stage rail bottom cooling medium is compressed air of 12-18 KPa.
Further, the running speed of the steel rail passing through the heat treatment cooling unit is controlled to be 1.6-1.8 m/s, and the starting cooling temperature is 740-780 ℃.
Further, in the first stage, the rail head accelerated cooling speed is 10-11 ℃/s, and the cooling time is 11-13 s; in the second stage, the rail head accelerated cooling speed is 2.5-4 ℃/s, and the cooling time is 42-48 s; and in the third stage, the rail head is not cooled in an accelerated manner, the accelerated cooling speed of the rail bottom is 1.2-1.6 ℃/s, and the cooling time is 23-25 s.
Further, the steel rail comprises the following chemical components in percentage by mass:
0.72-0.80% of C, 0.60-0.80% of Si, 0.85-1.2% of Mn, 0.04-0.08% of V, 0.08-0.15% of Cr, 0.002-0.006% of B, less than or equal to 0.025% of P, less than or equal to 0.025% of S, and the balance of Fe and inevitable impurities.
In order to better achieve the technical purpose of the invention, the invention also discloses a steel rail which is prepared by adopting the preparation method, wherein the room-temperature metallographic structure of the whole section of the steel rail is fine lamellar pearlite and a small amount of ferrite.
Furthermore, the tensile strength of the steel rail is 1260-1350 MPa, the elongation is 10-13%, and the brinell hardness of a rail head tread is 362-388 HB. Therefore, the steel rail prepared by the invention can be applied to various lines such as passenger transport, passenger and goods mixed transport and the like.
Has the advantages that:
1. the steel rail production method designed by the invention reasonably controls the cooling intensity and the cooling time of the steel rail by stages by increasing the running speed of the steel rail heat treatment unit, and the steel rail structure and the performance are consistent with those of the conventionally produced on-line heat treatment steel rail, thereby meeting the requirements of the standard TB/T2344-.
2. The production method of the steel rail designed by the invention can improve the production efficiency of the heat-treated steel rail by more than 30% by completely matching the production rhythm of the heat-treated steel rail with the rolling rhythm.
3. The production method of the steel rail designed by the invention can improve the running speed of the steel rail heat treatment unit, reduce the temperature difference between the head and the tail of the steel rail and improve the stability of the head and the tail of the steel rail. On the other hand, the production method is simple, strong in operability and easy to popularize and apply.
4. The tensile strength of the steel rail prepared by the design method is 1260-1350 MPa, the elongation is 10-13%, the brinell hardness of a rail head tread is 362-388 HB, and the steel rail can be applied to various lines such as passenger transport, mixed transport of passengers and goods, and the like.
Drawings
FIG. 1 is a metallographic photograph of a room temperature structure of a steel rail according to an example of the present invention.
Detailed Description
The invention discloses a high-efficiency heat treatment production method for steel rails, which mainly aims at solving the problems that the heat treatment rhythm is not matched with the rolling production rhythm, the production efficiency is low and the head and tail performance fluctuates in the conventional heat treatment steel rail production.
The production method comprises the following steps: the method comprises the following steps of smelting in a converter, refining, vacuum treatment, continuous casting, heating of casting blanks, rolling and the like, meanwhile, on-line accelerated cooling treatment is carried out on the hot-rolled steel rail, the running speed of the steel rail is controlled to be 1.5-2.0 m/s through a heat treatment cooling unit, the running speed is matched with that of the existing steel rail rolling production to be 1.6-1.8 m/s, the steel rail is subjected to heat treatment by using the residual temperature after rolling, and the production efficiency can be effectively improved only by being matched with the rolling rhythm, so that the running speed range consistent with that of steel rail rolling is set.
In addition, the initial cooling temperature of the steel rail is 720-800 ℃, because if the start cooling temperature is too high, the heating temperature and the finish rolling temperature of the steel rail are correspondingly increased, the problems of coarse grains, increased surface defects and the like are easily caused, and if the start cooling temperature is too low, the phase change driving force is insufficient under the effective cooling speed condition, and the rail head pearlite cannot be fully refined.
The rail is then cooled in stages.
Specifically, in the first stage, the rail head accelerated cooling speed is 9-11 ℃/s, and the cooling time is 10-14 s; in the second stage, the rail head accelerated cooling speed is 2-5 ℃/s, and the cooling time is 40-50 s; and in the third stage, the rail head is not cooled in an accelerated manner, the accelerated cooling speed of the rail bottom is 1-2 ℃/s, the cooling time is 20-26 s, then, the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature. In the first stage and the second stage of accelerated cooling, the rail head is accelerated and cooled, and simultaneously, the rail bottom is accelerated and cooled, the cooling speed of each rail bottom is 50-70% of the cooling speed of each rail head, and the cooling time of each rail bottom is equal to the cooling time of each rail head. The running speed of the steel rail is increased, compared with the conventional heat treatment steel rail production, the time for passing through a cooling unit is correspondingly shortened, namely the effective heat treatment time is shortened, and therefore, the cooling intensity is required to be enhanced. However, the on-line heat treatment of the steel rail is a process of dynamically balancing the heat of the rail head and an external cooling medium, and the cross section of the steel rail is irregular in shape, so that the cooling strength cannot be simply increased on the basis of the production of the conventional heat-treated steel rail. The inventor finds that the steel rail structure performance can be well controlled by adopting staged cooling through a large amount of experimental researches, the first stage adopts higher cooling speed to ensure the tread hardness on one hand, and forms a pearlite cap shape with lower temperature on a rail head on the other hand, so as to create conditions for the cooling of the second stage, the cooling time is relatively shorter and is set to be 10-14 s, so as to reduce the risk of abnormal structures; along with the end of the first stage, the area of the high-temperature region in the center of the steel rail is reduced, heat is dissipated to the pearlite hat-shaped region with lower temperature of the rail head through heat conduction, the cooling speed applied in the first stage can be controlled within the range of 2-5 ℃/s, the requirement of pearlite transformation on the cooling speed can be met, meanwhile, the residual stress of the rail head of the steel rail and the deformation degree in the heat treatment process can be reduced at a relatively low cooling speed, the cooling time is relatively long, the cooling time is set to be 40-50 s, and the purpose of ensuring that the hardened layer of the rail head of the steel rail has enough depth is achieved. Meanwhile, in the first stage and the second stage, because the temperature of the rail head of the steel rail is reduced quickly, in order to ensure that the temperature distribution of the whole section of the steel rail is as consistent as possible, the temperature stress is reduced, and meanwhile, the rail bottom is cooled in an accelerated manner, the metal content of the rail bottom is smaller than that of the rail head, and the strength of the cooling medium of the rail bottom is controlled to be 50-70% of the cooling strength of the rail head; and in the third stage, the rail head finishes the heat treatment process, the bending degree of the steel rail is mainly controlled in the stage, more favorable straightening conditions are created, the rail bottom is independently and rapidly cooled, the temperature of the rail bottom of the steel rail is lower than that of the rail head after the heat treatment is finished, in the natural cooling process, the steel rail can be bent towards the rail head to a certain degree due to expansion and contraction, the upward bending of the end part of the steel rail can be quantified, generally, the upward bending is 10-50 mm, the advantage is that in the subsequent straightening process, the upward bending of the steel rail towards the rail head is straightened under the pressure of a straightening roller, the rail bottom can generate certain compressive stress, and according to the measurement comparison of the residual stress of the rail bottom before and after the straightening of the steel rail, the generated compressive stress is 20-60 MPa, the tensile stress generated in the rolling process is counteracted, and the residual stress of the rail bottom is reduced. According to the measurement comparison of the residual stress of the rail bottom before and after the rail is straightened, the generated compressive stress is 20-60 MPa, the residual stress of the rail bottom is tensile stress, and the residual stress of the rail bottom can be reduced by 20-60 MPa.
And for the cooling medium used for accelerating the cooling, the invention selects water mist mixed gas and compressed air. Preferably, the first stage rail head cooling medium is a water mist mixed gas which is formed by mixing and spraying 65-75 KPa of compressed air and 180-220L/h of water; the second stage rail head cooling medium is water mist mixed gas which is formed by mixing and spraying 30-45 KPa of compressed air and 40-60L/h of water; and the strength of the rail bottom cooling medium in the first stage and the second stage is controlled to be 50-70% of the corresponding rail head cooling strength. And the third stage rail bottom cooling medium is compressed air of 12-18 KPa. According to the invention, the strong water amount is set in the first stage, so that the impact force of water mist is increased, the iron oxide scales on the surface of the steel rail are removed, the accuracy of temperature measurement is improved, and the cooling effect is enhanced; the water quantity is reduced in the second stage, and the water is mainly cooled by compressed air, so that the uniformity of a cooling medium and the stability of a flow field are improved.
For the alloy element composition of the steel rail, the steel rail comprises the following chemical components in percentage by mass:
0.72-0.80% of C, 0.60-0.80% of Si, 0.85-1.2% of Mn, 0.04-0.08% of V, 0.08-0.15% of Cr, 0.002-0.006% of B, less than or equal to 0.025% of P, less than or equal to 0.025% of S, and the balance of Fe and inevitable impurities. The steel rail with the specific chemical composition has better structure performance and stability compared with steel rails with other chemical compositions, and can be more suitable for the production method.
In addition, for the working procedures of converter smelting, refining, vacuum treatment, continuous casting, casting blank heating, rolling and the like adopted in the steel rail heat treatment process, the molten iron desulphurization is selected to adopt a magnesium powder spraying desulphurization process, the converter smelting adopts a top-bottom combined blowing process, the slag alkalinity of LF external refining is controlled within the range of 1.9-2.3, the vacuum treatment time is not less than 20min, the tundish temperature in the continuous casting process is controlled within the range of 20-28 ℃ of a liquidus line, the drawing speed is 0.6-1.0 m/min, the continuous casting process is carried out under the protection of the whole process to prevent the continuous casting process from contacting with air, and the cast steel blank is subjected to slow cooling treatment. Heating a casting blank by using a walking beam heating furnace, and carrying out heat preservation treatment, wherein the heating temperature is 1250-1300 ℃, the heat preservation time is 180-230 min, the initial rolling temperature is controlled to be 1080-1120 ℃, and the final rolling temperature is controlled to be 860-920 ℃.
Preferably, the running speed of the steel rail through the heat treatment cooling unit is controlled to be 1.6-1.8 m/s, the starting cooling temperature is 740-780 ℃, and the steel rail is cooled in a staged mode. In the first stage, the rail head accelerated cooling speed is 10-11 ℃/s, and the cooling time is 11-13 s; in the second stage, the rail head accelerated cooling speed is 2.5-4 ℃/s, and the cooling time is 42-48 s; and in the third stage, the rail head is not cooled in an accelerated manner, the accelerated cooling speed of the rail bottom is 1.2-1.6 ℃/s, the cooling time is 23-25 s, then the accelerated cooling is stopped, and the steel rail is naturally cooled to the room temperature on a cooling bed.
The room-temperature metallographic structure of the full-section of the steel rail prepared by the production method is fine lamellar pearlite and a small amount of ferrite, and performance tests show that the tensile strength of the steel rail is 1260-1350 MPa, the elongation is 10-13%, and the brinell hardness of a rail head tread is 362-388 HB.
In order to better explain the present invention, the following detailed description is given in conjunction with specific examples.
The smelting chemical compositions of the examples 1 to 5 of the invention are shown in # 1 to # 5 in Table 1, and the compositions of the comparative examples 1 to 3 of the invention are in the ranges of the examples 1 to 5.
TABLE 1 chemical compositions of examples and comparative examples
Example 1
The high-efficiency production method of the heat-treated steel rail is carried out according to the conventional steel rail production smelting, casting and rolling processes, wherein molten iron desulphurization adopts a magnesium powder spraying desulphurization process, converter smelting adopts a top-bottom combined blowing process, when molten steel is discharged about 1/4, alloys such as silicon, manganese, vanadium and the like and carburant are added along with steel flow, when the molten steel is discharged to 3/4, the alloys and the carburant are all added, the alkalinity of slag refined outside an LF furnace is controlled within the range of 1.9-2.3, the treatment time of the LF furnace is more than 40min, the RH vacuum degree is less than or equal to 100Pa, the vacuum treatment time is not less than 20min, the tundish temperature in the continuous casting process is controlled within the range of 20-28 ℃, the drawing speed is 0.6-1.0 m/min, the continuous casting process is carried out under the protection of the whole process, the contact with air is prevented, and the cast steel billet is subjected to slow cooling treatment. Heating a casting blank by using a walking beam heating furnace, carrying out heat preservation treatment, wherein the heating temperature is 1250-1300 ℃, the heat preservation time is 180-230 min, rolling the steel rail by using a universal rolling mill, and controlling the initial rolling temperature to be 1080-1120 ℃ and the final rolling temperature to be 860-920 ℃. After rolling, the steel rail is subjected to on-line heat treatment, the running speed of the steel rail passing through a heat treatment cooling unit is 1.6m/s, the starting cooling temperature is 740 ℃, and the steel rail is subjected to stage cooling. In the first stage, the rail head accelerated cooling speed is 9.5 ℃/s, the cooling medium is 66KPa compressed air matched with 190L/h water to mix sprayed water mist mixed gas, and the cooling time is 12 s; in the first stage, the rail bottom accelerated cooling speed is 5 ℃/s, the cooling time is 12s, and the cooling medium is water mist mixed gas which is sprayed by mixing compressed air with 35KPa and water with 110L/h.
In the second stage, the rail head accelerated cooling speed is 3 ℃/s, the cooling medium is 36KPa compressed air matched with 45L/h water quantity to mix the sprayed water mist mixed gas, and the cooling time is 42 s; the accelerated cooling speed of the rail bottom in the second stage is 1.5 ℃/s, the cooling time is 42s, and the cooling medium is 15KPa of compressed air. And in the third stage, the rail head is not subjected to accelerated cooling, the accelerated cooling speed of the rail bottom is 1.2 ℃/s, the cooling medium is compressed air of 13KPa, the cooling time is 25s, then the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature.
Example 2
The procedure is as in example 1, except that the rail is subjected to an in-line heat treatment, the running speed of the rail through the heat treatment cooling unit is 1.8m/s, the initial cooling temperature is 760 ℃, and the rail is cooled in stages. In the first stage, the rail head accelerated cooling speed is 10 ℃/s, the compressed air with the cooling medium of 68KPa is matched with the water quantity of 195L/h to mix the sprayed water mist mixed gas, and the cooling time is 10 s; in the first stage, the rail bottom accelerated cooling speed is 6 ℃/s, the cooling time is 10s, and the cooling medium is water mist mixed gas which is sprayed by mixing compressed air with 40KPa and water with the volume of 120L/h.
In the second stage, the rail head accelerated cooling speed is 2.2 ℃/s, the cooling medium is compressed air of 30KPa and water of 40L/h are mixed with the sprayed water mist mixed gas, and the cooling time is 46 s; the accelerated cooling speed of the rail bottom in the second stage is 1.2 ℃/s, the cooling time is 46s, and the cooling medium is compressed air of 13 KPa.
And in the third stage, the rail head is not subjected to accelerated cooling, the accelerated cooling speed of the rail bottom is 1.5 ℃/s, the cooling medium is 15KPa of compressed air, the cooling time is 22s, then the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature.
Example 3
The procedure is as in example 1, except that the rail is subjected to an in-line heat treatment, the running speed of the rail through the heat treatment cooling unit is 2.0m/s, the initial cooling temperature is 780 ℃, and the rail is cooled in stages. In the first stage, the rail head accelerated cooling speed is 9 ℃/s, the cooling medium is 65KPa compressed air matched with 180L/h water to mix sprayed water mist mixed gas, and the cooling time is 13 s; in the first stage, the rail bottom accelerated cooling speed is 5.5 ℃/s, the cooling time is 13s, and the cooling medium is a water mist mixed gas which is mixed and sprayed by compressed air with 37KPa and water with 116L/h.
In the second stage, the rail head accelerated cooling speed is 2.5 ℃/s, the cooling medium is 35KPa compressed air matched with 40L/h water, the sprayed water mist mixed gas is mixed, and the cooling time is 48 s; the accelerated cooling speed of the rail bottom in the second stage is 1.7 ℃/s, the cooling time is 48s, and the cooling medium is 18KPa of compressed air.
And in the third stage, the rail head is not subjected to accelerated cooling, the accelerated cooling speed of the rail bottom is 1.6 ℃/s, the cooling medium is compressed air of 16KPa, the cooling time is 20s, then the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature.
Example 4
The procedure is as in example 1, except that the rail is subjected to an in-line heat treatment, the running speed of the rail through the heat treatment cooling unit is 1.5m/s, the initial cooling temperature is 800 ℃, and the rail is cooled in stages. In the first stage, the rail head accelerated cooling speed is 11 ℃/s, the cooling medium is 74KPa compressed air matched with 215L/h water, the sprayed water mist mixed gas is mixed, and the cooling time is 14 s; in the first stage, the rail bottom accelerated cooling speed is 6.5 ℃/s, the cooling time is 14s, and the cooling medium is water mist mixed gas which is mixed and sprayed by 42KPa of compressed air and 135L/h of water.
In the second stage, the rail head accelerated cooling speed is 4 ℃/s, the cooling medium is 38KPa compressed air matched with 55L/h water quantity to mix the sprayed water mist mixed gas, and the cooling time is 40 s; the accelerated cooling speed of the rail bottom in the second stage is 2 ℃/s, the cooling time is 40s, and the cooling medium is water mist mixed gas which is mixed and sprayed by using compressed air with 26KPa and water with 30L/h.
And in the third stage, the rail head is not subjected to accelerated cooling, the accelerated cooling speed of the rail bottom is 1.7 ℃/s, the cooling medium is 20KPa of compressed air, the cooling time is 24s, then the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature.
Example 5
The procedure is as in example 1, except that the rail is subjected to an in-line heat treatment, the running speed of the rail through the heat treatment cooling unit is 1.7m/s, the initial cooling temperature is 720 ℃, and the rail is cooled in stages. In the first stage, the rail head accelerated cooling speed is 10.5 ℃/s, the cooling medium is 70KPa compressed air and is matched with water of 200L/h to mix sprayed water mist mixed gas, and the cooling time is 11 s; in the first stage, the rail bottom accelerated cooling speed is 7 ℃/s, the cooling time is 11s, and the cooling medium is water mist mixed gas which is sprayed by mixing compressed air with 48KPa and water with the volume of 140L/h.
In the second stage, the rail head accelerated cooling speed is 4.5 ℃/s, the compressed air with the cooling medium of 43KPa is matched with the water quantity of 50L/h to mix the sprayed water mist mixed gas, and the cooling time is 45 s; the accelerated cooling speed of the rail bottom in the second stage is 2.5 ℃/s, the cooling time is 45s, and the cooling medium is water mist mixed gas which is sprayed by mixing compressed air with 35KPa and water with the amount of 40L/h.
And in the third stage, the rail head is not subjected to accelerated cooling, the accelerated cooling speed of the rail bottom is 1.0 ℃/s, the cooling medium is compressed air of 12KPa, the cooling time is 23s, then the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature.
Comparative example 1
The procedure is as in example 1, except that, in accordance with the current conventional rail heat treatment process, the rail is run through the heat treatment cooling unit at a speed of 1.0 m/s.
Comparative example 2
The procedure is as in example 2, except that, in accordance with the current conventional rail heat treatment process, the rail is run through the heat treatment cooling unit at a speed of 1.2 m/s.
Comparative example 3
The procedure of example 1 was followed except that the rail was cooled in a manner different from that of the present application, that is, the rail head and rail foot were simultaneously cooled, the accelerated cooling rate was 2.5 ℃/s, compressed air with a cooling medium of 35KPa was mixed with water in an amount of 40L/h to mix the sprayed mist mixed gas, the cooling time was 80s, and then the accelerated cooling was stopped and the mixture was naturally cooled to room temperature.
The performance indexes of tensile strength, elongation, tread hardness, metallographic structure and the like of the steel rails obtained in the examples and the comparative examples are measured according to the method specified in TB/T2344-.
TABLE 2 comparison of the Properties of the examples and comparative examples
FIG. 1 is a metallographic photograph of a structure at room temperature of a steel rail product according to an example of the present invention, and it can be seen from FIG. 1 that an internal microstructure is pearlite and a small amount of ferrite, and abnormal structures such as martensite and bainite are not found. It can be seen that the steel rails obtained in the embodiments 1 to 5 have good performances and metallographic structures, are consistent with the on-line heat-treated steel rails produced by the conventional process in the comparative examples 1 to 3, meet the requirements of the railway industry standard TB/T2344-; meanwhile, the performance difference of the head and the tail of the steel rail in the embodiments 1-5 is obviously smaller than that in the comparative examples 1-3, which shows that the stability of the performance of the head and the tail of the steel rail can be effectively improved by the method.
The above-described embodiments are merely illustrative of specific embodiments of the present invention, and are not intended to limit the scope of the present invention, and various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention are intended to fall within the scope of the present invention defined by the claims.
Claims (7)
1. A high-efficiency heat treatment production method of a steel rail comprises the following processes: converter smelting, refining, vacuum treatment, continuous casting, casting blank heating and rolling, and the method is characterized by further comprising the step of carrying out online accelerated cooling treatment on the steel rail after hot rolling, controlling the running speed of the steel rail at 1.5-2.0 m/s through a heat treatment cooling unit, controlling the initial cooling temperature at 720-800 ℃, and carrying out stage cooling on the steel rail, wherein: in the first stage, the rail head accelerated cooling speed is 9-11 ℃/s, and the cooling time is 10-14 s; in the second stage, the rail head accelerated cooling speed is 2-5 ℃/s, and the cooling time is 40-50 s; when the rail heads are subjected to accelerated cooling in the first stage and the second stage, the rail bottoms are also subjected to accelerated cooling, the cooling speed of the rail bottoms is 50-70% of that of each rail head, and the cooling time of each rail bottom is equal to that of each rail head; in the third stage, the rail head is not cooled in an accelerated manner, the accelerated cooling speed of the rail bottom is 1-2 ℃/s, the cooling time is 20-26 s, then the accelerated cooling is stopped, and the rail is naturally cooled to the room temperature;
the steel rail comprises the following chemical components in percentage by mass:
0.72 to 0.80% of C, 0.60 to 0.80% of Si, 0.85 to 1.2% of Mn, 0.04 to 0.06% of V, 0.08 to 0.15% of Cr, 0.002 to 0.006% of B, less than or equal to 0.025% of P, less than or equal to 0.025% of S, and the balance of Fe and unavoidable impurities;
the rail head and the tail made by the production method have stable performance and small difference.
2. The method for producing a steel rail through efficient heat treatment according to claim 1, wherein the first-stage rail head cooling medium is a water mist mixed gas obtained by mixing 65-75 KPa of compressed air with a water amount of 180-220L/h and spraying, and the second-stage rail head cooling medium is a water mist mixed gas obtained by mixing 30-45 KPa of compressed air with a water amount of 40-60L/h and spraying.
3. The efficient steel rail heat treatment production method according to claim 1 or 2, wherein the third-stage rail bottom cooling medium is compressed air of 12-18 KPa.
4. The efficient steel rail heat treatment production method according to claim 1 or 2, wherein the running speed of the steel rail passing through the heat treatment cooling unit is controlled to be 1.6-1.8 m/s, and the initial cooling temperature is 740-780 ℃.
5. The efficient heat treatment production method for the steel rail according to the claim 1 or 2, characterized in that in the first stage, the rail head accelerated cooling speed is 10-11 ℃/s, and the cooling time is 11-13 s; in the second stage, the rail head accelerated cooling speed is 2.5-4 ℃/s, and the cooling time is 42-48 s; and in the third stage, the rail head is not cooled in an accelerated manner, the accelerated cooling speed of the rail bottom is 1.2-1.6 ℃/s, and the cooling time is 23-25 s.
6. A steel rail produced by the production method according to any one of claims 1 to 5, wherein the room-temperature metallographic structure of the whole cross section of the steel rail is fine lamellar pearlite and a small amount of ferrite.
7. A steel rail according to claim 6, wherein said steel rail has a tensile strength of 1260 to 1350MPa, an elongation of 10 to 13%, and a berkovich hardness of 362 to 388HB on the tread surface.
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| CN111961810B (en) * | 2020-09-23 | 2022-02-15 | 武汉科技大学 | Method for improving hardness uniformity of cross section of heat-treated steel rail head |
| CN112410659A (en) * | 2020-10-19 | 2021-02-26 | 攀钢集团攀枝花钢铁研究院有限公司 | Pearlite steel rail with rail head hardened layer having uniform hardness gradient and preparation method thereof |
| CN112708748A (en) * | 2020-11-12 | 2021-04-27 | 邯郸钢铁集团有限责任公司 | Method for improving temperature uniformity of head and tail of heat-treated steel rail |
| CN113403467B (en) * | 2021-05-26 | 2022-04-22 | 武汉钢铁有限公司 | Production method for improving wear resistance of heat-treated steel rail |
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| CN114058824B (en) * | 2021-11-26 | 2023-12-08 | 武汉钢铁有限公司 | Production method for improving hardness uniformity of heat-treated steel rail tread and steel rail obtained by production method |
| CN114250349A (en) * | 2021-12-09 | 2022-03-29 | 邯郸钢铁集团有限责任公司 | Method for improving hardness of heat-treated steel rail tread |
| CN114854963B (en) * | 2022-04-29 | 2023-09-05 | 武汉钢铁有限公司 | Groove-type steel rail with low residual stress and preparation method thereof |
| CN115927814A (en) * | 2022-12-15 | 2023-04-07 | 攀钢集团攀枝花钢铁研究院有限公司 | Production method of steel for low-torsion bainite frog |
| CN116590609A (en) * | 2023-04-12 | 2023-08-15 | 包头钢铁（集团）有限责任公司 | Low-cost heat-treated steel rail and production method thereof |
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