JP4994928B2 - Rail manufacturing method with excellent breakage resistance - Google Patents

Description

  The present invention relates to a rail manufacturing method for preventing breakage such as breakage from a rail foot portion, which is required for rails of passenger railways and freight railways.

  In passenger and freight railways, as a means of improving transportation efficiency, the train speed is increased and the train load is increased. Such an increase in the efficiency of rail transportation means that the rail use environment becomes severe, and further improvements in rail materials have been required. Specifically, in the rail laid in the curved section, the wear of the GC (gauge corner) part and the head side part increases rapidly, and it has become a problem in terms of the service life of the rail. It was.

Therefore, a high-strength (high hardness) rail as shown below and a manufacturing method thereof having a pearlite structure using high-carbon steel have been invented, and the rail life of a curved section of a passenger railway has been dramatically improved (for example, Patent Documents 1 and 2).
In the disclosed technology of Patent Document 1, a steel rail that has been rolled is cooled from an austenite region temperature to 800 to 450 ° C. at a cooling rate of 1 to 4 ° C./sec, thereby providing a rail with a high hardness pearlite structure. Can do.
In the disclosed technique of Patent Document 2, a steel rail that has been rolled is applied to a rail having a high hardness pearlite structure by applying a gas cooling medium to the rail head from a nozzle surrounding the rail head from the austenite temperature. Can be manufactured.

  However, in the rail manufactured by the disclosed technology of Patent Documents 1 and 2, it is possible to ensure the wear resistance of the head corner portion and the head side portion mainly contacting the wheel flange, but the rail bottom portion (rail foot) (Including the tip portion), the material control is not sufficient, and depending on the manufacturing method, there is a problem that fatigue damage occurs from the bottom of the rail and eventually breaks.

Therefore, in order to control the material of the rail bottom and prevent breakage starting from the rail bottom, a heat treatment method limited to the rail bottom has been invented, and the service life of the rail has been dramatically improved (for example, Patent Document 3). 4).
In the disclosed technology of Patent Document 3, the abdomen and bottom of the steel rail after rolling and heat treatment are reheated to the austenite region, then rapidly cooled to martensite transformation, reheated again, and rapidly cooled, thereby causing impact fracture. A rail having excellent resistance can be provided.
In the disclosed technique of Patent Document 4, a rail having excellent drop weight resistance can be provided by rapidly cooling the bottom of the steel rail after rolling and heat treatment to 600 to 750 ° C. and then rapidly cooling it.

  However, with the disclosed technique of Patent Document 3, it is difficult to uniformly heat the entire rail abdomen and bottom having a large cross-sectional area, and it is difficult to improve stable characteristics of the rail abdomen and bottom. In addition, the entire rail abdomen and bottom must be reheated, and a large-scale quenching device is required to produce a martensite structure thereafter, resulting in poor economic efficiency.

  Moreover, in the rail of the disclosed technology of Patent Document 4, although the drop weight resistance is improved by improving the toughness of the bottom of the rail by reheating, the fatigue strength decreases due to softening, resulting in the occurrence of fatigue damage and fatigue damage. It was difficult to prevent rail breakage.

Japanese Patent Laid-Open No. 62-56524 JP-A 61-149436 JP-A-62-227042 JP-A-4-202626

From the background described above, it has become desirable to provide a method for manufacturing a rail that can stably suppress the occurrence of breakage from the bottom, which is required for rails of passenger railways and freight railways.
Therefore, the present invention has been devised in view of the above-mentioned problems, and the object of the present invention is due to the occurrence of fatigue damage and fatigue damage at the bottom required for rails of passenger and freight railways. It is to suppress the occurrence of breakage and improve the service life of the rail.

  The rail manufacturing method with excellent breakage resistance according to the present invention optimizes the reheating temperature of the rail toe, the accelerated cooling rate, and the subsequent reheating temperature, and further optimizes the hardness. It was created for the purpose of suppressing the occurrence of fatigue damage at the toe portion and the occurrence of breakage due to fatigue damage, and improving the break resistance of the rail bottom portion.

  That is, the gist of the present invention is to optimize the reheating temperature of the rail foot, the accelerated cooling rate, and the subsequent reheating temperature in order to improve the break resistance of the rail bottom in the steel rail. In addition, the breakage resistance of the rail bottom is improved by optimizing the hardness.

The configuration of the present invention is as follows.
(1) By mass%, C: 0.65-1.20%, Si: 0.05-2.00%, Mn: 0.05-2.00%, the balance being Fe and inevitable impurities Manufacturing a rail consisting of
The foot part of the rail is reheated to the first stage, reheated to a temperature range of Ar3 transformation point or Arcm transformation point to 950 ° C., and then accelerated cooling at a cooling rate of 0.5 to 20 ° C./sec. Then, the accelerated cooling is stopped at 400 ° C. or higher, and then cooled to room temperature or accelerated cooled in the range of 0.2 to 6 ° C./sec .
Furthermore, as the second stage of reheating the foot portion of the rail, it is reheated to a temperature range of 500 to 650 ° C., and then cooled to room temperature or accelerated and cooled in the range of 1 to 20 ° C./sec .
And the hardness of the toe part of the said rail after heat processing is Hv320 or more, The manufacturing method of the rail excellent in breakage resistance characterized by the above-mentioned.
(2) The accelerated cooling stop temperature after reheating in the first stage is 500 to 650 ° C. The method for manufacturing a rail as described in (1) above,
(3) The rail manufacturing method according to (1), wherein an accelerated cooling stop temperature after the first stage reheating is 400 to 500 ° C.

  According to the present invention, by optimizing the reheating temperature of the rail toe, the accelerated cooling rate, and the subsequent reheating temperature, and further by optimizing the hardness, The breakage resistance required for the bottom of the rail can be improved.

  The present invention is described in detail below. The present inventors investigated the cause of breakage from the bottom of the rail in current passenger and freight railways. As a result, it was confirmed that the breakage from the bottom of the rail occurred mainly from the rail toe, and the generation of fatigue cracks was observed at the starting point.

  Furthermore, the present inventors investigated the material characteristic of the rail foot part. As a result, the toe part has a lower temperature during rail rolling and lower hardenability, and further, the transformation starts before heat treatment and the heat treatment start temperature of the rail cannot be secured. It was confirmed that the hardness was low and the fatigue strength was low.

  In view of this, the present inventors examined a heat treatment method for increasing the strength of the foot tip portion in order to prevent occurrence of fatigue damage at the rail foot tip portion. As a result, it has been found that a heat treatment in which the rail toe part is partially reheated and then accelerated cooling at a cooling rate within a certain range is effective.

  In order to verify this effect, the present inventors conducted a fatigue test using the real rails subjected to the heat treatment. As a result, in the rail subjected to the heat treatment, the occurrence of fatigue cracks can be suppressed, but after the fatigue cracks have been generated and propagated, there has been a problem that breakage (brittle fracture) occurs in a short time.

  The present inventors have elucidated a factor that causes a fracture (brittle fracture) in a short time after a fatigue crack is generated and propagated. As a result, it became clear that the toe portion was strengthened by heat treatment, so that the toughness was reduced and breakage (brittle fracture) was promoted.

  Therefore, the present inventors examined a heat treatment method that improves toughness without impairing the strength of the rail foot. As a result, first, in the heat treatment for increasing the strength of the foot portion, the reheating temperature is controlled to refine the crystal grains, and further, the toughness of the structure after accelerated cooling is improved. By optimizing the heating temperature, it was found that it was possible to avoid breakage in a short time, that is, brittle fracture, while suppressing the occurrence of fatigue cracks.

  From the above, the present inventors, in the steel rail with high carbon content, reheat the rail toe portion at a certain range of temperature, subjected to accelerated cooling, and then reheated at a certain range of temperature, In addition to this, it has been found that resistance to breakage of the rail bottom can be improved by controlling the hardness of the rail toe after heat treatment.

  Next, the reason for limitation of the present invention will be described in detail.

(1) Reasons for limiting the first stage reheating heat treatment conditions First, the reason for limiting the first stage reheating temperature of the rail toe portion to the Ar3 transformation point or Acm transformation point to 950 ° C will be described.

  If the reheating temperature exceeds 950 ° C, the austenite grains during reheating become coarse, the crystal grains after accelerated cooling become coarse, the toughness of the rail foot after the final heat treatment decreases, and fatigue cracks occur It is not possible to promote the brittle fracture of the rail and improve the break resistance of the rail bottom. When the reheating temperature is lower than the Ar3 transformation point or the Acm transformation point, the carbide remains undissolved even after reheating, and coarse carbides are generated in the austenite structure. For this reason, the toughness of the rail foot portion after the final heat treatment is lowered, the brittle fracture after the occurrence of the fatigue crack is promoted, and the break resistance of the rail bottom portion cannot be improved. From the above, the reheating temperature of the first stage of the rail foot portion was limited to the temperature range of Ar3 transformation point or Arcm transformation point to 950 ° C.

  The Ar3 transformation point and the Arcm transformation point differ depending on the carbon content and alloy composition of the steel. Experimental verification is necessary to accurately determine the transformation point. In order to obtain these values easily, read from the equilibrium diagram of the Fe-Fe3C system published in metallurgical textbooks (for example, steel materials, edited by the Japan Institute of Metals) based on the carbon content alone. Is desirable. The Ar3 transformation point and Arcm transformation point in actual rail rolling are values lower by 20 to 30 ° C. than the lines in the parallel state diagram.

  Moreover, it does not specifically limit about the holding time at the time of the 1st step reheating temperature of a rail foot part. However, if the heating time is longer than necessary, the rail bottom is deformed and the straightness of the rail is lost, and the austenite grains are also coarsened, so that the break resistance of the rail bottom after the final heat treatment is not improved. On the other hand, if the heating time is too short, austenitization is not completed, coarse carbides remain in the austenite structure, and the break resistance of the rail bottom after the final heat treatment is not improved. For this reason, about holding time, it is necessary to control according to reheating temperature, a component, rail shape, etc. In order to improve the fatigue strength and ductility of the rail foot after the final heat treatment and improve the break resistance of the rail bottom at least in the above temperature range, a holding time of about 5 to 10 minutes is desirable.

  Further, the first stage reheating method of the rail foot portion is not particularly limited, but the reheating is applied by gas flame heating or high frequency heating capable of selectively reheating only the rail foot portion. Is desirable.

  About the temperature at the time of reheating, it is possible to achieve the effect mentioned above by controlling the temperature of the surface layer of a rail foot part.

  Next, in the method of accelerating and cooling the rail foot after the first stage reheating to 400 ° C. or higher at a cooling rate of 0.5 to 20 ° C./sec, the accelerated cooling stop temperature and the accelerated cooling rate are The reason for the limitation will be described.

  First, the reason for limiting the accelerated cooling stop temperature will be described. When accelerated cooling is stopped at a temperature lower than 400 ° C, transformation from the austenite structure is not completed during accelerated cooling, and the remaining austenite structure is transformed into a martensite structure, and the shape of the foot part of the rail is secured by large transformation expansion. It becomes difficult. For this reason, the accelerated cooling stop temperature range was limited to 400 ° C. or higher.

  Although the upper limit value is not set for the accelerated cooling stop temperature, it is desirable to control the accelerated cooling stop temperature so as to obtain the target metal structure. For example, it is desirable to stop accelerated cooling in a temperature range of 400 to 500 ° C. to obtain a bainite structure and 500 to 650 ° C. to obtain a pearlite structure.

  Next, the reason why the acceleration cooling rate is limited will be described. When the accelerated cooling rate is less than 0.5 ° C./sec, transformation starts in a high temperature region during accelerated cooling. As a result, the hardness of the rail foot portion after the final heat treatment is lowered, and the fatigue strength cannot be improved. Specifically, the hardness of the rail foot portion is less than Hv320, and it is difficult to prevent the occurrence of fatigue damage. Further, depending on the component system, a pro-eutectoid cementite structure is formed, the toughness after the final heat treatment is lowered, and the break resistance of the rail bottom is not improved. If the accelerated cooling rate exceeds 20 ° C / sec, transformation from the austenite structure is not completed during accelerated cooling, and the remaining austenite structure is transformed into a martensite structure, and the shape of the foot part of the rail is secured by large transformation expansion. It becomes difficult. For this reason, the accelerated cooling rate was limited to the range of 0.5 to 20 ° C./sec.

  In order to increase the hardness of the rail foot and obtain a uniform structure in the cross section, the accelerated cooling rate is most preferably in the range of 2 to 10 ° C./sec. Moreover, although the acceleration cooling method of the first step of the rail foot part is not particularly limited, it is desirable to use air, water, or brackish water that can selectively cool only the rail foot part.

  Regarding the cooling stop temperature and the cooling rate of the rail foot portion, the above-described effects can be achieved by controlling the temperature of the surface layer of the rail foot portion.

  Moreover, about the cooling method after accelerated cooling, it is preferable to cool to normal temperature or accelerated cooling. In particular, when the cooling stop temperature is high, softening is promoted, the fatigue strength of the rail foot portion is lowered, and the break resistance of the rail bottom portion is lowered. For this reason, it is desirable to perform accelerated cooling again after cooling is stopped. There is no particular limitation on the accelerated cooling rate to the room temperature after the accelerated cooling stop and the cooling method, but the cooling rate is 0.2 ° C / sec in order to suppress the softening of the tissue and reduce the thermal effect of the surrounding part as much as possible. The above cooling is desirable. In order to control the cooling rate, it is desirable to apply a refrigerant that can be slowly cooled, such as air.

(2) Reason for limitation of the second stage reheating heat treatment conditions Next, after the first stage reheating heat treatment of the rail foot, reheating to a temperature range of 500 to 650 ° C., and then allowing to cool or accelerated cooling. The reason why the second stage reheating temperature is limited as described above in the method will be described.

  When the reheating temperature exceeds 650 ° C., the tempering effect becomes excessive, the hardness decreases rapidly, the fatigue strength of the rail foot portion decreases, and the break resistance of the rail bottom cannot be improved. If the reheating temperature is less than 500 ° C., the toughness cannot be improved, the transition from fatigue failure to brittle failure cannot be delayed, and the break resistance at the bottom of the rail does not improve. For this reason, the reheating temperature of the 2nd step | paragraph of a rail foot part was limited to the range of 500-650 degreeC.

  In addition, although the holding time at the time of the 2nd stage reheating temperature of a rail foot part is not specifically limited, When heating time is long, a rail bottom part will deform | transform and the straightness of a rail will be lost. When the heating time is short, the toughness is not improved, and the breakage resistance of the rail foot portion is not improved. For this reason, about holding time, it is necessary to control according to reheating temperature, a component, rail shape, etc. At least in the above temperature range, a holding time of about 5 to 10 minutes is desirable in order to improve the fatigue strength and ductility of the foot portion and improve the break resistance of the rail bottom.

  Although there is no particular limitation on the second stage reheating method, heating rate, and subsequent accelerated cooling method of the rail foot portion, reheating can selectively reheat only the rail foot portion. Application of gas flame heating or high frequency heating is desirable. In particular, in order to mitigate the thermal effects of the surrounding parts as much as possible, rapid heating at a heating rate of 1 ° C./sec or more, further heating by a high-frequency heating coil capable of heat treatment only at the toe, and use of a gas torch such as acetylene are required. desirable.

  About the temperature at the time of reheating, it is possible to achieve the effect mentioned above by controlling the temperature of the surface layer of a rail foot part.

  As for cooling after reheating, it is preferable to cool to room temperature or accelerate cooling. In particular, when the temperature after reheating is high, softening is promoted, the fatigue strength of the rail foot portion is lowered, and the break resistance of the rail bottom portion is lowered. For this reason, it is desirable to perform accelerated cooling after reheating. Further, in order to further suppress the occurrence of fatigue cracks at the rail toe portion and improve the breakage resistance, it is desirable to perform accelerated cooling for the purpose of imparting compressive residual stress.

In addition, although it does not specifically limit about an accelerated cooling rate, in order to suppress softening and to provide sufficient compression residual stress, it accelerates and cools at a cooling rate of 1 degreeC / sec or more to a normal temperature range after reheating. It is desirable. In order to impart a high compressive residual stress and dramatically improve the breakage resistance, it is desirable to perform accelerated cooling to a normal temperature range at a cooling rate of 10 ° C./sec to 20 ° C./sec.
Although the accelerated cooling method after reheating is not particularly limited, it is desirable to apply accelerated cooling to air, water, or brackish water that can selectively cool only the rail foot.

(3) Explanation of reheating part Next, the part which reheats a rail foot part is demonstrated. The reheating portion of the rail foot portion is not particularly limited, but it is necessary to perform the reheating process around the rail foot portion that is the starting point of breakage. Here, FIG. 1 shows the name of the pearlite rail at the bottom cross-sectional surface position and the reheat heat treatment region. 1 is a sole part, 2 is a foot part, 3 is a bottom part, W is the width | variety of the bottom part of a rail. The rail bottom portion is a region that comprehensively includes a rail foot sole portion and a foot tip portion. It is desirable that the reheating of the rail foot portion is performed at least on the portion from the left and right foot tip portions to 0.2 W.

(4) Reason for limiting the hardness of the rail foot portion Next, the reason for limiting the hardness of the rail foot portion to Hv320 or more will be described. When the hardness of the rail foot portion is less than Hv320, if the acting stress is large, a fatigue crack is generated from the rail foot portion, and breakage from the rail bottom portion is likely to occur. For this reason, the hardness of the pearlite structure was limited to Hv320 or more. In addition, what is necessary is just to make hardness of the range of 1-5 mm under the surface of a rail foot part into an above-described range.

  Note that the hardness of the rail foot portion can be adjusted mainly by controlling the accelerated cooling rate in the first-stage reheating heat treatment and the heating temperature in the second-stage reheating heat treatment. It is desirable to perform the above-mentioned control according to the use condition of the rail and adjust so as to obtain an optimum hardness characteristic.

  Thus, by applying the reheating heat treatment of the rail toe part to the part from the left and right toe part end portions to, for example, 0.2 W, the fatigue strength and toughness of the steel are improved, and further, the compressive residual stress is reduced. By providing, the break resistance of the rail bottom is greatly improved.

  Furthermore, if the hardness of the said area | region is Hv360 or more, the fatigue strength of a rail foot part will further improve, the breakage from a rail bottom part will be suppressed further, and breakage resistance will further improve. The upper limit of the hardness is not particularly limited. However, in a metal structure mainly composed of a pearlite structure and a bainite structure, about Hv460 is substantial in order to ensure both fatigue strength and toughness. It becomes the upper limit.

(5) Reason for limiting the chemical composition of the steel rail In claim 1, the reason why the chemical composition of the rail steel is limited to the above claims will be described in detail. Hereinafter, the mass% in the composition is simply described as%.

  C is an effective element that ensures the strength of the toe portion. When the C content is 0.65% or less, a pro-eutectoid ferrite structure is generated, the hardness of the rail foot portion cannot be secured, the fatigue strength is reduced, and the service life of the rail is reduced. On the other hand, when the C content exceeds 1.20%, a pro-eutectoid cementite structure is generated at the rail foot portion, the toughness is lowered, and the break resistance of the rail bottom portion is greatly lowered. Therefore, the C content is limited to 0.65 to 1.20%.

  Si is an element that increases the hardness (strength) of the rail foot by solid solution hardening in the ferrite phase, but its content is less than 0.05%, and the minimum required for the rail foot. It is difficult to ensure the strength of the. Moreover, when it exceeds 2.00%, the toughness of a rail foot part will fall and the breakage resistance of a rail bottom part will fall large. For this reason, the amount of Si was limited to 0.05 to 2.00%.

  Mn is an element that contributes to increasing the strength of the rail foot portion by lowering the transformation temperature and increasing the hardenability, but if the content is less than 0.05%, the effect is small, and as the rail foot portion, It becomes difficult to ensure the necessary minimum strength. On the other hand, if it exceeds 2.00%, the hardenability increases, a martensite structure is generated in the toe portion depending on the heat treatment conditions, and it becomes difficult to ensure the shape of the toe portion of the rail due to the large transformation expansion. For this reason, the amount of Mn was limited to 0.05 to 2.00%.

  Moreover, the rail manufactured with said component composition is Cr, Mo, V, Nb, B for the purpose of improving the hardness (strengthening) of a toe part, the improvement of toughness, and prevention of the softening of a heat affected zone. , Co, Cu, Ni, Ti, Mg, Ca, Al, and N are added as necessary.

  Here, Cr and Mo raise the equilibrium transformation point and mainly ensure hardness. V and Nb suppress the growth of austenite grains by carbides and nitrides generated by hot rolling and the subsequent cooling process, and further improve toughness and hardness by precipitation hardening. In addition, carbides and nitrides are stably generated during reheating to prevent softening of the heat affected zone. B reduces the cooling rate dependency of the transformation temperature and improves the hardness. Co and Cu are dissolved in the ferrite phase to increase the hardness. Ni prevents embrittlement during hot rolling due to the addition of Cu, and at the same time, improves hardness and further prevents softening of the heat affected zone. Ti refines the structure of the heat-affected zone and prevents embrittlement. Mg and Ca reduce the austenite grain size, and at the same time promote transformation and improve toughness. Al moves the eutectoid transformation temperature to the high temperature side and improves the strength. Furthermore, the amount of eutectoid carbon is moved to the high carbon side, and the formation of proeutectoid cementite structure is suppressed. N is mainly added for the purpose of improving toughness by promoting transformation from the austenite grain boundary and making the structure fine.

(6) The structure of the rail foot portion The metal structure of the rail foot portion is not particularly limited, but in the steel of the above component range, in order to ensure fatigue strength and simultaneously ensure toughness, The final structure after the heat treatment is preferably a pearlite structure, a bainite structure, or a mixed structure thereof as a base structure.

  Rail steel composed of the above components is melted in a commonly used melting furnace such as a converter, electric furnace, etc., and this molten steel is ingot / bundled or continuously cast. It is manufactured as a rail through rolling and heat treatment. Next, by heat-treating the rail foot, it is possible to suppress breakage from the rail bottom and improve the service life of the rail.

Next, examples of the present invention will be described.
Table 1 shows the chemical composition of the test rail steel.

  Table 2 shows the heat treatment conditions of the toe portion in the rail manufactured by the rail manufacturing method of the present invention using the test rail steel shown in Table 1, the hardness after the heat treatment, the base metal structure, and the impact test result. The fatigue test results are shown.

  Table 3 shows the heat treatment conditions of the toe portion of the rail manufactured by the comparative rail manufacturing method using the test rail steel shown in Table 1, the hardness after heat treatment, the base metal structure, and the impact test results, fatigue The test results are shown.

The configuration of the rail is as follows.
● Heat treatment rail of the present invention (27) Code: 1-27
The rail which manufactured the rail steel in the said component range on the rail tip part heat processing conditions in the said limited range.
● Comparative heat treatment rails (13) Code: 28-40
The rail which manufactured the rail steel in the said component range on the rail foot part heat processing conditions outside the said limited range.

    FIG. 2 illustrates the sampling position of the impact test piece on the rail foot. Further, in FIG. 3, the fatigue test results of the rail steel of the present invention shown in Table 1 (reference numerals: 1 to 27) and the comparative rail steel shown in Table 2 (reference numerals: 28 to 36, 39, 40) A graph organized by the number of breaks is shown. In addition, about the name in the bottom cross-section surface position of a rail, and a reheating heat processing area | region, it follows FIG.

Various test conditions are as follows.
● Impact test Specimen: JIS3 2mm U-notch Charpy impact test specimen Specimen sampling position: Rail foot (see Fig. 2)
Test temperature: Normal temperature (+ 20 ° C)
● Fatigue Test Tester: Three-point bending fatigue tester Shape of test piece: 141 pound rail x 1500mm
Test form Span length: 1000 mm, 3-point bending (loading 1 point on the head, supporting 2 points on the bottom)
Test conditions Rail foot toe working stress: 450 MPa
(Loading load is controlled from the static stress of the strain gauge attached to the toe)
Test temperature: Normal temperature (+ 20 ° C)
Repeat count: Until breakage.

  As shown in Table 2, Table 3, and FIG. 3, the rail steel of the present invention (symbol: 1-27) is a comparative rail steel (symbol: 28) by controlling the heat treatment conditions of the rail toe part within a certain range. Compared with ˜36, 39, 40), compared with the same carbon amount, the number of repetitions until the fracture in the fatigue test is increased, and the break resistance of the rail bottom is improved.

  Examples will be described in detail. As shown in Table 2 and FIG. 3, in the rail steel of the present invention, the reheating temperature of the first stage heat treatment of the rail foot portion is reduced (symbol: 8, 9) and the accelerated cooling rate is increased (symbols: 10, 11). ), By applying accelerated cooling after the accelerated cooling rate (signs: 19, 20: suppression of softening), the hardness and toughness of the toe part are further improved, and the number of repetitions until breakage in the fatigue test increases, Fracture resistance at the bottom of the rail is improved.

  In addition, as shown in Table 2 and FIG. 3, in the rail steel of the present invention, the reheating temperature of the second stage heat treatment of the rail foot portion is reduced (symbol: 25, 26), and further after the second stage reheating. By applying accelerated cooling (signs: 21, 22: applying compressive residual stress), the hardness and toughness of the toe part are improved and the residual stress is further optimized, and the number of repetitions until fracture in the fatigue test is increased. In addition, the break resistance at the bottom of the rail is improved.

  Furthermore, as shown in Tables 2 and 3, in the rail steel of the present invention, compared with the comparative rail steel (untreated, code: 28 to 31), the fatigue test is performed by improving the hardness of the rail foot portion. The number of repetitions until rupture increases in the rail, and the break resistance of the rail bottom is improved.

  In addition, as shown in Tables 2 and 3, in the rail steel of the present invention, the first stage reheating temperature, the accelerated cooling rate, and the accelerated cooling of the rail foot portion are compared with the comparative rail (reference numerals: 32 to 40). By optimizing the stop temperature and the second stage reheating temperature and improving the hardness and toughness of the rail foot, the number of repetitions until fracture in the fatigue test increases and the resistance to breakage of the rail bottom improves. is doing.

  As described above, according to the present invention, it is possible to improve the breakage resistance required for the bottom of the rails of passenger railways and freight railways.

The figure which showed the name in the bottom cross-section surface position of a rail. The figure which showed the collection position of the impact test piece of a rail foot part. The figure which arranged the fatigue test result of this invention rail steel (code | symbol: 1-16) shown in Table 1 and the comparison rail steel (code | symbol: 17-28, 28, 29) shown in Table 2 by the carbon content and the frequency | count of fracture of steel. .

Explanation of symbols

1: foot sole,
2: Toe part,
3: Bottom W: Width of rail bottom

Claims (3)

A rail containing, by mass%, C: 0.65-1.20%, Si: 0.05-2.00%, Mn: 0.05-2.00%, the balance being Fe and inevitable impurities Manufacture and
The foot part of the rail is reheated to the first stage, reheated to a temperature range of Ar3 transformation point or Arcm transformation point to 950 ° C., and then accelerated cooling at a cooling rate of 0.5 to 20 ° C./sec. Then, the accelerated cooling is stopped at 400 ° C. or higher, and then cooled to room temperature or accelerated cooled in the range of 0.2 to 6 ° C./sec .
Furthermore, as the second stage of reheating the foot portion of the rail, it is reheated to a temperature range of 500 to 650 ° C., and then cooled to room temperature or accelerated and cooled in the range of 1 to 20 ° C./sec .
And the hardness of the toe part of the said rail after heat processing is Hv320 or more, The manufacturing method of the rail excellent in breakage resistance characterized by the above-mentioned.   The method for manufacturing a rail according to claim 1, wherein an accelerated cooling stop temperature after reheating in the first stage is 500 to 650 ° C.   The method for manufacturing a rail according to claim 1, wherein the accelerated cooling stop temperature after reheating in the first stage is 400 to 500 ° C.

Images