AU2015204356B2 - High-strength bainitic steel rail and producing method thereof - Google Patents

Abstract

The present invention belongs to the steel making field, in particular relates to a high-strength bainitic steel rail and a producing method thereof The microscopic structure in the round corner part and in the tread center of the rail head is a multi-phase structure 5 composing of bainitic ferrite strips in 0.2-1.0[ m width, filmy residual austenite in 0.01~0.1Im thickness distributed alternatively between the bainitic ferrite strips, and 1~5% martensite. The producing method of the steel rail comprises: utilizing the residual heat in the steel rail, accelerated cooling the rail head part of the steel rail at a 3.0~6.0C/s cooling rate when the tread of the rail head is cooled naturally to 450-500'C, and stopping the accelerated 10 cooling when the temperature of the tread center of the rail head drops to 220-300'C and then air-cooling to room temperature. A multi-phase steel rail consisting of carbide-free bainite + a small amount of martensite + a small amount of residual austenite is obtained in the present invention, and the steel rail has an outstanding wear resistance property and is suitable for heavy-duty railroad. 6704019_1 (GHMatters) P100429.AU Fig. 1

Description

HIGH-STRENGTH BAINITIC STEEL RAIL AND PRODUCING 2015204356 25 Nov 2016

METHOD THEREOF

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Application No. 201410359547.0, filed on 5 July 25, 2014, entitled “High-Strength Bainitic Steel Rail and Producing Method Thereof’, which is specifically and entirely incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a steel rail material, in particular to a high-strength bainitic steel rail and a producing method thereof.

10 BACKGROUND OF THE INVENTION

The rapid development of railroad technology brings higher requirements for the service performance of steel rails. At present, most steel rails for railroads in China are pearlite carbon steel rails with 0.60%~0.85% carbon content, micro-alloyed steel rails, and high-strength heat-treated steel rails; in addition, some bainitic steel rails are also applied. 15 Pearlitic steel rails feature with simple manufacturing process, low production cost, and stable structure and performance, etc.. However, pearlitic steel rails have some drawbacks, for example, the contact fatigue strength is lower when compared with other steel rails of the same strength grade, the rail head part may have injuries such as peeling-off, cracks, and transyerse fissures, etc., under the reciprocal stress of the wheels, and these drawbacks are 20 adverse to long life of railroads. Especially, as the railroad traffic intensity and the axle loads of trains increase in recent years, the service environment of steel rails has become harsh increasingly. For example, in some railroad sections, especially in curve sections, the steel rails have to be replaced early within one year or even several months owing to severe damage or wear. Consequently, the operation efficiency is compromised, and safety risks of 25 railroad transportation arise. The progressive development of material technology brings new choices for steel rail material. Researchers are actively exploring an alternative choice for steel rail material in the future - bainitic steel rail, while optimizing the properties of existing pearlitic steel rails constantly. 1

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In China, since the 1990s, research and development efforts have been made on bainitic steel rails in different compositions. Most of the bainitic steel rails are designed in low carbon content, complemented with other elements in appropriate amounts, such as Si, Mn, Cr, Mo, Ni, V, and Nb, etc.. Multi-phase steel products that mainly consist of bainite structure and contain a small amount of proeutectoid ferrite, residual austenite and martensite are directly obtained under a continuous air-cooling condition. The steel rails are rolled, air-cooled to room temperature, and then are tempered in a heater for stabilization, to promote the transformation of semi-stable structures in the steel, such as residual austenite and martensite, so as to obtain steel rails that have stable structures at room temperature. Steel rails manufactured with that method have well strength and toughness matching, the tensile strength of the rail head is not lower than l,200MPa, the specific elongation is not lower than 12%, and the U-shape impact toughness at normal temperature is not lower than 50J. Thus, such steel rails essentially meet the requirements of application on railroad lines where the fatigue problem is prominent but the requirement for wear resistance is not high, and can achieve a good application effect. However, difficulties are encountered in industrialization and wide application: on one hand, since the bainite structure is obtained by direct air-cooling, it implies that a large amount of elements that can effectively inhibit pearlite-ferrite transformation but don't inhibit bainite transformation substantially have to be added into the steel, wherein, an element that can achieve the best effect is Mo element, but Mo is a noble alloying element, and the addition of Mo will cause severely increased cost of bainitic steel rails, and consequently it is unable to attain higher cost performance; furthermore, Ni element is added in some bainitic steel rails as required, and, similar to Mo, Ni is also a noble alloying element and will result in increased production cost. On the other hand, to reduce welded joints on railroads and improve the smoothness of railroad lines, long length steel rails are being vigorously promoted in all countries in the world. For example, in China, presently, the percentage of 100m long length steel rails has exceeded the percentage of 25m steel rails that were used previously. For bainitic steel rails, tempering treatment is required, but the conditions for tempering of 100m steel rails are unavailable yet. Consequently, the large-scale application of bainitic steel rails is further confined. Therefore, it is an urgent task to develop a high-strength bainitic steel rail that has low alloy content (especially noble alloy content) and can be applied directly on railroad lines without tempering treatment, to meet the demand for development of railroads, especially heavy-duty railroads. 2

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SUMMARY OF THE INVENTION

The high-strength bainitic steel rail according to the present invention has the advantange of having lower content of noble alloy and can be directly applied on railroad lines without tempering treatment and a producing method of the high-strength bainitic steel rail.

The present invention provides a high-strength bainitic steel rail, wherein the microscopic structure in the round corner part and in the tread center of the rail head is a multi-phase structure composing of bainitic ferrite strips in 0.2-1.0pm width, fdmy residual austenite in 0.01-0. lpm thickness distributed alternatively between the bainitic ferrite strips, and 1~5 vol.% martensite. The chemical composition of the high-strength bainitic steel rail is: C: 0.15-0.30%, Si: 1.00-1.80%, Mn: 1.50-2.50%, Cr: 0.20-0.60%, Mo: 0.05-0.10%, and 3.0% %S i+Μ n+Cr, and the remaining content is Fe and inevitable impurities, based on weight percentage. A producing method of the high-strength bainitic steel rail comprises smelting in a rotary furnace or an electric furnace —> LF refining —> RH or VD vacuum treatment —► continuous casting —> heating —> rolling —> heat treatment —> combined horizontal and vertical straightening, flaw inspection, and machining. All of the steps employ existing methods, except the step of heat treatment. Specifically, in accordance with the present invention, the method of producing the high-strength bainitic steel rail as described above comprises: utilizing the residual heat in a steel rail after final rolling, applying a cooling medium to the rail head part of the steel rail to carry out accelerated cooling at a 3.0~6.0°C/s cooling rate when the tread of the rail head is cooled naturally to 450~500°C, and stopping the accelerated cooling when the temperature of the tread center of the rail head drops to 220~300°C and then air-cooling to room temperature.

Mechanical property tests demonstrate: the tensile strength of the rail head part is >l,400MPa, the specific elongation is >12%, the hardness of the tread of the rail head is >420HB, the whole section hardness of the rail head is >40HRC, the U-shape impact strength of the rail head at room temperature is >60J, the fracture toughness Kic at -20°C is >80MPa m1/2, and all other performance indexes meet the current requirements in the railway industry, and the steel rails are suitable for use on heavy-duty railroads, especially in railroad 3 8450674J (GHMatters) P100429.AU sections which require higher properties of contact fatigue and wear resistance. 2015204356 25 Nov 2016

The present invention has the following beneficial effects: (1) The high-strength bainitic steel rail provided in the present invention has low content of alloy and low cost; 5 (2) The high-strength bainitic steel rail provided in the present invention has a finer microscopic structure, in which the average width of bainitic ferrite strips doesn't exceed l.Opm and the percentage of martensite is lower; the bainitic steel rail has higher strength and toughness matching when compared with that has the same carbon content; (3) The high-strength bainitic steel rail provided in the present invention has 10 outstanding mechanical properties, meets the provisions in current standards of the railway industry, and is suitable for use on heavy-duty railroads, especially in railroad sections which require higher properties of contact fatigue and wear resistance; (4) The high-strength bainitic steel rails provided in the present invention can be directly applied on railroad lines without tempering treatment. 15 Other characteristics and advantages of the present invention will be further detailed in the embodiments hereunder.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are provided here to facilitate further understanding on the present invention, and constitute a part of this description. They are used in conjunction 20 with the following embodiments to explain the present invention, but shall not be comprehended as constituting any limitation to the present invention. Among the drawings:

Fig.l is an optical metallographic image of the steel rail obtained according to embodiments of the present invention;

Fig.2 shows optical metallographic images of the steel rails obtained according to 25 comparative examples 1-6. 4

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DETAILED DESCRIPTION

Hereunder some embodiments of the present invention will be detailed, with reference to the accompanying drawings. It should be appreciated that the embodiments described here are only provided to describe and explain the present invention, but shall not be deemed as constituting any limitation to the present invention.

In the high-strength bainitic steel rail provided in the present invention, the microscopic structure in the round comer part and in the tread center of the rail head is a multi-phase structure composing of bainitic ferrite strips in 0.2-1 0pm width, filmy residual austenite in 0.01-0. lpm thickness distributed alternatively between the bainitic ferrite strips, and 1~5% (volume fraction) martensite.

According to a preferred embodiment of the present invention, to obtain the steel rail of the present invention, the contents of major chemical elements in the steel should meet the following requirement: C: 0.15%~0.30%, Si: 1.00%-1.80%, Mn: 1.50%~2.50%, Cr: 0.20%~0.60%, Mo: 0.05%~0.10%, and 3.0%<Si+Mn+Cr, and the remaining content is Fe and inevitable impurities. Hereunder the reasons for confining the major chemical elements in the steel rail of the present invention within above ranges will be explained:

Carbon (C) is the most important element for bainitic steel to obtain outstanding strength-toughness matching and overall mechanical properties. When the carbon content is lower than 0.15%, it is unable to give full play to the strengthening effect, and the strength and toughness of the steel rail will be too low, and consequently the wear resistance property of the steel rail can't be ensured; when the carbon content is higher than 0.30%, after the accelerated cooling process, the strength of the steel rail is too high, while the toughness and plasticity are too low, which are adverse to the service safety of the steel rail. Therefore, the carbon content is preferably confined within the range of 0.15%-0.30%.

As a major additional element in steel, silicon (Si) usually exists in ferrite in the form of solid solution, and can improve the strength of the structure. When the silicon content is lower than 1.00%, it is unable to effectively inhibit the precipitation of large carbides distributed discontinuously, and carbide-free bainitic steel can't be obtained; when the silicon content is higher than 1.80%, the structure and performance of the steel rail are not improved significantly, but the probability of occurrence of surface defects is increased. Therefore, the 5 8450674J (GHMatters) P100429.AU silicon content is preferably confined within the range of 1.00%-1.80%.

Manganese (Mn) can significantly decrease the initial transition temperature of bainitic structure, improve the hardness of carbides, and is an important additional element in bainitic steel. When the manganese content is lower than 1.50%, it will be difficult to attain the active effects on bainitic steel; when the manganese content is higher than 2.50%, the fatigue property of the steel rail will be severely degraded. Therefore, the manganese content is preferably confined within the range of 1.50%-2.50%.

Chromium (Cr) can promote the C-curve to right shift and enhance the hardenability of the steel rail, and is also an important additional element in bainitic steel. When the chromium content is lower than 0.20%, it is difficult for the role of chromium to take place in steel; when the chromium content is higher than 0.60%, chromium tends to react with the carbon in steel to form complex carbides, which, though beneficial for the improvement of wear resistance, will result in degradation of the toughness and plasticity of the steel rail. Therefore, the chromium content is preferably confined within the range of 0.20%-0.60%.

Molybdenum (Mo) has a remarkable effect for decreasing the initial transition temperature of bainitic structure, and is advantageous for stabilizing and strengthening bainitic structure. In hot-rolled and air-cooled steel for bainitic steel rails, to decrease the phase transition temperature, the molybdenum content is usually 0.20%-0.50%. However, the inventor has found: for steel rails that are treated by air cooling after rolling, an accelerated cooling process has a higher effect for decreasing the Bs point of bainite and promoting the formation of finer lower bainite structure than Mo. Thus, the content of Mo, which is a noble alloying element, can be significantly decreased; in addition, in consideration of other factors, including steel rail welding, the Mo content is preferably confined within the range of 0.05%-0.10%.

To ensure that the high-strength bainitic steel rail of the present invention achieves better service performance, the total content of Si+Mn+Cr should meet 3.0%<Si+Mn+Cr, because the total content of Si, Mn, and Cr in the steel must still be controlled within a specific range even though a post-rolling accelerated cooling process is utilized, in order to obtain fine bainite structures as much as possible in the continuous cooling process. When the total content of Si+Mn+Cr is lower than 3.0%, it is unable to completely inhibit the 6

8450674 1 (GHMatters) P100429.AU precipitation of proeutectoid ferrite in the steel and attain the object of the present invention, even though accelerated cooling is utilized. Therefore, the total content of Si+Mn+Cr preferably meets 3.0%<Si+Mn+Cr.

It is known to those skilled in the art that the inevitable impurities include phosphorus (P) and sulfur (S), etc.

In the producing method of the present invention, there is no special requirement for other processes involved in the production of the steel rail, except the heat treatment procedure. For example, steel containing the above-mentioned chemical composition can be smelted in a rotary furnace or electric furnace, LF refined, treated by RH or VD vacuum treatment, and then cast into continuous casting billets with a certain cross section, and fed into a walking beam furnace, heated to 1200-1300°C and kept at the temperature for 2h or longer, and finally rolled into steel rails with required cross section; here, the final rolling temperature of the steel rails is 850-950°C. Next, the steel rails are placed vertically on a roller bed, and standing cooled by air cooling in the air. The above-mentioned steps are known to those skilled in the art, and will not be detailed further here.

When the temperature in the surface layer of the rail head drops to 450-500°C, an accelerated cooling medium is applied on the top surface and two sides of the rail head. Here, the accelerated cooling medium may be compressed air or water vapor mixture (water mist mixture). Hereunder the reason for setting the initial temperature of accelerated cooling at 450-500°C will be explained. As indicated in the research, under the air-cooling condition post-rolling, the phase transition temperature of bainitic steel rails is within a range of 350-400°C. If the accelerated cooling is initiated from austenitic phase region, longer cooling time will be required and more cooling energy will be consumed, since the initial temperature of accelerated cooling is far away from the phase transition temperature; more severely, during the accelerated cooling process, the heat from the core part of rail head and the rail web part will diffuse towards the surface layer of rail head by heat transfer, while the surface layer of rail head is subjected to accelerated cooling by the external cooling medium; consequently, the rail head part can't accomplish phase transition at a higher super-cooling degree, ultimately the rigidity of the cross section of rail head will decrease gradually from the surface layer to the core part, and it can't be hardened entirely. By setting the initial 7 8450674_1 (GHMatters) P100429.AU cooling temperature at 450-500°C, the following benefit can be obtained: initiating the accelerated cooling in the temperature range from the austenitic phase region to 500°C has little contribution to the improvement of the overall performance of the steel rail. When the steel rail is cooled to 450-500°C, both the temperature of the rail web and the temperature of the rail base are lower than 450°C, and if the accelerated cooling is initiated at that temperature, the temperature of the surface layer of rail head will be decreased significantly, while the heat from the core part of rail head is not enough to replenish the heat loss in the surface layer; in addition, since the initial cooling temperature is close to the phase transition point, the entire cross section of rail head (in particular to core part of rail head) can accomplish phase transition at a higher super-cooling degree. In that process, the cooling rate is set at 3.0-6.0°C/s because: if the cooling rate is lower than 3.0°C/s, the temperature of the surface layer of rail head can't drop quickly and can't be transferred to the core part effectively; in addition, the heat from the core part will compensate for the surface layer, which is adverse to improving the overall performance of the steel rail, and it is difficult to give full play to the strong fine crystal strengthening effect of accelerated cooling; if the cooling rate is higher than 6.0°C/s, since the surface layer is cooled very quickly, a large quantity of martensite will be produced, and the strength and rigidity of the steel rail will be too high, which is adverse to safe application of the steel rail; in addition, it is unable to obtain a multi-phase structure composing of carbide-free bainite + a small amount of martensite + a small amount of residual austenite, as disclosed in the present invention.

The accelerated cooling is stopped when the surface layer of the steel rail is cooled down to 220-300°C. The final temperature of accelerated cooling is set at 220-300°C because: if the final cooling temperature is higher than 300°C, though fine bainitic structures have been obtained in the surface layer of rail head, coarse bainitic structures will be formed in the core part of rail head owing to the high temperature there, which will have an adverse effect to the performance of the steel rail at the room temperature and will be adverse to the uniformity of performance of the entire cross section; if the cooling temperature is lower than 220°C, a large quantity of martensite will be formed, causing severely degraded toughness and plasticity of the steel rail. After the accelerated cooling, the steel rail is air-cooled to room temperature (5-40°C), and then treated through subsequent procedures, to obtain a finished steel rail.

Hereunder the present invention will be further detailed in some examples. Unless 8 8450674J (GHMatlers) P100429.AU otherwise stated, all the experimental methods used in the following examples are conventional methods. Unless otherwise stated, all materials and reagents used in the following examples are commercially available. 2015204356 25 Nov 2016

Examples 1-6 and comparative examples 1-6 5 In the examples and comparative examples, six groups of chemical compositions of bainitic steel rail shown in Table 1 and Table 2 are used respectively, wherein, in the comparative examples, the chemical compositions of bainitic steel rail are chemical compositions in the prior art.

Table 1. Chemical Compositions of Steel Rails in Examples 1-6

No. Chemical Composition (%) C Si Mn P S Cr Mo Si+Mn+Cr A1 0.15 1.37 1.68 0.012 0.004 0.29 0.08 3.34 A2 0.20 1.00 2.50 0.010 0.008 0.48 0.09 3.98 A3 0.18 1.64 1.72 0.015 0.010 0.20 0.05 3.56 A4 0.24 1.72 1.50 0.014 0.012 0.55 0.10 3.77 A5 0.30 1.80 1.88 0.009 0.006 0.60 0.06 4.28 A6 0.22 1.38 1.69 0.007 0.007 0.39 0.07 3.46

Table 2. Chemical Compositions of Steel Rails in Comparative Examples 1-6

No. Chemical Composition (%) C Si Mn P S Cr Mo Si+Mn+Cr D1 0.15 0.88 2.33 0.012 0.006 0.57 0.41 3.78 D2 0.20 1.25 2.16 0.011 0.004 0.59 0.39 4.00 D3 0.18 1.69 1.91 0.009 0.004 0.72 0.37 4.32 D4 0.24 1.84 2.21 0.016 0.008 0.69 0.42 4.74 D5 0.30 1.77 2.42 0.007 0.007 0.78 0.35 4.97 D6 0.22 1.61 2.31 0.018 0.004 0.67 0.37 4.59

Steel billets containing the compositions shown in the examples and comparative examples are rolled into 60kg/m steel rails, and the steel rails with the same serial number are 9

8450674_1 (GHMatters) P100429.AU 2015204356 25 Nov 2016 cooled by accelerated cooling from the same initial cooling temperature to the same final cooling temperature within the error range as shown in Table 3. 10

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Table 3. Process Control Parameters in the Examples and Comparative Examples Example No. Initial temperature of accelerated cooling Final temperature of accelerated cooling Average cooling rate A1 472°C 300°C 4.2°C/s A2 450°C 284°C 5.1°C/s A3 466°C 267°C 3.0°C/s A4 500°C 242°C 6.0°C/s A5 453°C 220°C 5.6°C/s A6 489°C 235°C 4.7°C/s Comparative Example No. Initial temperature of accelerated cooling final temperature of accelerated cooling Average cooling rate D1 472°C 300°C 2.1 TVs D2 450°C 285°C 2.0°C/s D3 467°C 266°C 2.6°C/s D4 500°C 243°C 2.8°C/s D5 454°C 220°C 2.7°C/s D6 491°C 236°C 1.9°C/s

The steel rails are cooled down by air-cooling to room temperature (25°C) after the above-mentioned treatment. The mechanical properties of the steel rails ascertained in tests 5 are shown in Table 4.

Wherein, wearing tests are carried out on a MM200 wear testing machine to test the average weight loss resulted for wearing. The samples are taken from the rail heads of the steel rails A1-A6 and D1-D6. In all of the wearing tests, the abradant samples are made of the same material. The testing parameters are as follows: 10 Sample size: round sample in 10mm thickness and 36mm diameter

Test load: 150kg

Slippage: 10%

Material of abradant sample: U75V hot rolled steel rail with 280-310HB hardness, the hardness is equivalent to the hardness of train wheels. 15 Rotation speed: 200rpm 11

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Total wearing cycles: 100,000 cycles.

Table 4. Some Mechanical Properties of the Steel Rails Obtained in the Examples and Comparative Examples

Items No Tensile property Impact property at normal temperature (Aku/J) Average width of bainitic ferrite strips (pm) Averag e width of residual austenit e(pm) Weight loss by wearing (g) Percentag e of martensit e(%) Rm (MPa ) A (%) Examples A1 1420 14.5 105 0.9 0.06 0.5287 1.0 A2 1480 14.0 84 0.8 0.07 0.5129 2.2 A3 1450 14.0 93 1.0 0.10 0.5412 1.8 A4 1460 14.5 90 0.2 0.01 0.5084 3.9 A5 1520 13.0 78 0.3 0.04 0.4928 5.0 A6 1480 15.0 92 0.5 0.05 0.5130 2.9 Comparativ e Examples D1 1450 13.0 98 2.2 - 0.5176 6.7 D2 1500 13.5 78 2.0 - 0.5201 8.9 D3 1480 13.0 81 2.1 - 0.5398 5.6 D4 1470 14.0 79 1.4 - 0.5148 6.6 D5 1540 13.0 74 1.6 - 0.4966 5.2 D6 1500 13.5 80 1.7 - 0.5189 7.1 2015204356 25 Nov 2016 5 The steel rails obtained in the examples and comparative examples are observed under an optical metalloscope, and microscopic structure images are obtained, as shown in Fig. 1 and Fig.2, wherein, Figs. 1A-IF are optical metallographic images of the steel rails in the examples 1-6, and Figs. 2A-2F are optical metallographic images of the steel rails in the comparative examples 1-6. 10 The carbon content, initial temperature of accelerated cooling, and final temperature of accelerated cooling of steel rails with the same serial number in the examples and comparative examples are essentially the same. The contents of alloying elements in the examples are apparently lower than those in the comparative examples, but the accelerated cooling rates in the examples are apparently higher than those in the comparative examples; in 15 the examples, finer microscopic structures are obtained, and the average width of bainitic ferrite strips doesn't exceed l.Opm; in addition, the percentage of martensite in the steel is lower, and the steel rails have better strength-toughness matching under the same carbon 12

8450674_1 (GHMatters) P100429.AU content. Moreover, the steel rails in the examples have wear resistance equivalent to those in the comparative examples, which is beneficial for prolonging the service life of steel rails, especially steel rails for heavy-duty railroads. In other words, the bainitic steel rail disclosed in the present invention has performance that is close to the performance of existing bainitic 5 steel rails, but has lower contents of alloying elements. Therefore, the bainitic steel rail of the present invention has higher economic efficiency and is suitable for large-scale and wide application. 2015204356 25 Nov 2016

While a high-strength bainitic steel rail and a producing method of the high-strength bainitic steel rail provided in the present invention are described above, those skilled in the art 10 should appreciate that various modifications can be made without departing from the spirit and scope of the present invention.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive 15 sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 20 13

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Claims (3)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS;

   1. A high-strength bainitic steel rail, wherein the microscopic structure in the round comer part and in the tread center of the rail head is a multi-phase structure composing of bainitic ferrite strips in 0.2-1.Opm width, filmy residual austenite in 0.01-0.lpm thickness distributed alternatively between the bainitic ferrite strips, and 1~5 vol.% martensite and wherein the chemical composition of the high-strength bainitic steel rail is: C: 0.15-0.30%, Si: 1.00-1.80%, Mn: 1.50-2.50%, Cr: 0.20-0.60%, Mo: 0.05-0.10%, and 3.0%<Si+Mn+Cr, and the remaining content is Fe and inevitable impurities, based on weight percentage.
2. 2. A producing method of the high-strength bainitic steel rail as described in claim 1 or 2, comprising: utilizing the residual heat in a steel rail after final rolling, applying a cooling medium to the rail head part of the steel rail to carry out accelerated cooling at a 3.0~6.0°C/s cooling rate when the tread of the rail head is cooled naturally to 450-500°C, and stopping the accelerated cooling when the temperature of the tread center of the rail head drops to 220~300°C and then air-cooling to room temperature.
3. 3. The producing method according to claim 3, wherein the cooling medium is at least one of compressed air and water vapor mixture.