阅读说明：本技术 钢轨的制造方法和钢轨 (Method for manufacturing steel rail and steel rail ) 是由 饭塚直辉 松冈谅 本庄稔 冈本成夫 于 2020-02-13 设计创作，主要内容包括：本发明提出了一种始终稳定地形成焊缝部的焊接条件,该焊缝部是闪光对焊焊缝部与钢轨母材的硬度差和弯曲试验时的挠曲量在更好的范围内。在通过由闪光对焊形成的接缝部接合多个钢轨母材时,以1.50×10～(5)kA～(2)×秒～4.50×10～(5)kA～(2)×秒的焊接热输入进行上述闪光对焊,上述钢轨母材具有如下成分组成：含有C：0.60～1.20质量％、Si：0.10～1.50质量％、Mn：0.10～1.50质量％和Cr：0.10～1.50质量％,剩余部分为Fe和不可避免的杂质。(The present invention provides a welding condition for forming a weld portion in a stable manner at all times, wherein the weld portion is formed such that the difference in hardness between the flash butt weld portion and a rail base metal and the amount of deflection in a bending test are in a better range. When a plurality of rail base materials are jointed by a joint part formed by flash butt welding, the joint part is 1.50 multiplied by 10 5 kA 2 X sec-4.50X 10 5 kA 2 The flash butt welding was performed with welding heat input of x seconds, and the rail base metal had the following composition: contains C: 0.60 to 1.20 mass%, Si: 0.10 to 1.50 mass%, Mn: 0.10 to 1.50 mass% and Cr: 0.10 to 1.50 mass%, and the balance of Fe and inevitable impurities.)

1. A method for manufacturing a rail, wherein when a plurality of rail base materials are joined by a joint portion formed by flash butt welding, the steel rail base materials are welded at a ratio of 1.50 x 10⁵kA²X sec-4.50X 10⁵kA²X seconds of weld heat input the flash butt weld was performed,

the steel rail base material comprises the following components: contains C: 0.60 to 1.20 mass%, Si: 0.10 to 1.50 mass%, Mn: 0.10 to 1.50 mass% and Cr: 0.10 to 1.50 mass%, and the balance of Fe and inevitable impurities.

2. The method for manufacturing a rail according to claim 1, wherein an absolute value of a difference in hardness between the rail base material and the joint portion at the surface layer portion of the rail head portion to a depth of 2.5mm after the welding is 20 or less in terms of Vickers hardness, and a deflection amount of the joint portion is 20mm or more.

3. The method for producing a steel rail according to claim 1 or 2, wherein the composition further contains a component selected from the group consisting of V: 0.30 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Nb: 0.2 mass% or less, Mo: 0.5 mass% or less, Al: 0.07 mass% or less, W: 1.0 mass% or less, B: 0.005 mass% or less and Ti: 0.05 mass% or less of 1 or more.

4. A rail is formed by joining a plurality of rail base materials through joints, wherein the rail base materials have the following composition: contains C: 0.60 to 1.20 mass%, Si: 0.10 to 1.50 mass%, Mn: 0.10 to 1.50 mass% and Cr: 0.10 to 1.50 mass%, the balance being Fe and inevitable impurities,

the absolute value of the difference in hardness between the rail base material and the joint portion at the surface layer portion from the surface of the rail head to a depth of 2.5mm is 20 or less in terms of Vickers hardness, and the amount of deflection of the joint portion is 20mm or more.

5. A rail according to claim 4, wherein said composition further comprises a component selected from V: 0.30 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Nb: 0.2 mass% or less, Mo: 0.5 mass% or less, Al: 0.07 mass% or less, W: 1.0 mass% or less, B: 0.005 mass% or less and Ti: 0.05 mass% or less of 1 or more.

Technical Field

The present invention relates to a method for manufacturing a rail, and more particularly, to a method for manufacturing a continuous long rail by welding a plurality of rail base materials by a flash butt welding. The present invention particularly relates to a method for producing a long-life rail and a rail that can suppress breakage from a joint formed by flash butt welding. The rail and the method for manufacturing the same according to the present invention are suitable for rails used under severe high-axle load conditions such as an overseas mine railway in which trucks are heavy and have a large number of sharp curves.

Background

In a high axle load railway mainly used for transporting ores and the like, the load applied to the axle of a truck is much higher than that of a passenger car, and the service environment of a rail is also severe. In recent years, the load of trucks is further increasing in order to improve railway transportation efficiency. The high axle load railway refers to a railway in which the load of a train or a truck is large (for example, the load per 1 truck is 150 tons or more).

In addition, when laying the rails, a gap is provided between the end faces of the rails in consideration of the amount of expansion of the rails when exposed to high temperatures in summer. When a train or a truck passes through the gap, the end of the rail is easily worn by the impact from the wheel. On the other hand, if a continuous long rail (so-called long rail) is used, the gap when the rail is laid is reduced, so that the wear of the end portion of the rail is suppressed, and as a result, the durability of the rail can be improved.

Therefore, it is being discussed that the high axle load railway also uses long rails. Here, the long rail is a long rail formed by joining end faces of a plurality of rail base materials to each other by flash butt welding and having a total length of 200m or more. In the case where the characteristics of the weld portion are significantly inferior to those of the rail base material, if bending deformation is applied to the rail, the weld portion is broken. That is, when the characteristics of the weld portion are significantly inferior to those of the rail base metal, the weld portion is broken by the passage of a train or a truck, which is a problem.

Therefore, various studies have been made to improve the weldability of the rail. For example, patent document 1 discloses a flash butt welding method in which optimization of C, Si, and Mn and a flash length of a second flash in a second flash step in a second flash butt welding are defined.

Patent document 2 discloses a method of cooling a welded portion of a rail, and specifies a method of cooling the welded portion after welding the rail.

Patent document 3 discloses a flash butt welding method in which electrodes cooled by contact with a conductor provided with a water-cooled pipe via an insulator are disposed on the top and bottom surfaces of a rail steel, and the electrodes are disposed such that the distance between the end surfaces on the side close to the rail longitudinal direction surface is 100mm or less, and then flash butt welding is performed, and the range between the rail head immediately after welding and the rail longitudinal electrode is cooled by the electrodes, thereby defining the thermal influence width and the softening width of the weld portion.

The methods described in the above patent documents 1 to 3 are all methods of controlling the components alone, the amount of upset at the time of flash butt welding, or cooling, and there is no description of improving the characteristics of the flash butt weld itself.

In view of this, patent document 4 proposes a rail in which the hardness and deflection of the flash butt weld portion are specified. That is, patent document 4 discloses appropriate ranges for the difference in hardness between the flash butt weld portion and the rail base material and the amount of deflection in the bending test.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5659965

Patent document 2: japanese laid-open patent application No. 2010-188382

Patent document 3: japanese patent laid-open publication No. 2011-

Patent document 4: japanese patent No. 5532789

Disclosure of Invention

By limiting the difference in hardness between the flash butt weld joint portion and the rail base metal and the amount of deflection in the bending test disclosed in patent document 4, the fracture of the weld joint portion can be suppressed. As for a method for obtaining such a welded portion, patent document 4 discloses control of a component composition, an amount of upset at the time of flash butt welding, and cooling, as in the methods described in patent documents 1 to 3.

However, in the above conventional method, it is difficult to stably manufacture a rail having the flash butt weld portion having the above-described difference in hardness and deflection amount without causing performance deviation. In recent years, the use environment of rails is becoming more severe, and in order to improve the service life of rails, there is a problem that not only the mechanical properties of rails themselves such as wear resistance and fatigue damage resistance are improved, but also the degradation of the properties of a weld portion formed by flash butt welding is suppressed. Therefore, the welding conditions themselves need to be strictly limited.

Therefore, an object of the present invention is to provide a welding condition under which a weld portion is formed stably at all times, and the difference in hardness between the flash butt weld portion and the rail base metal and the amount of deflection during a bending test are in a range better than the range disclosed in patent document 4. Further, the present invention can stably provide a rail having more excellent characteristics of a flash butt weld portion than those of a conventional rail.

In order to solve the above problems, the inventors produced a flash butt weld portion of a rail by changing the welding heat input, and conducted extensive investigations on the hardness distribution of the rail and the difference between the hardness of the rail base material and the hardness of the weld portion. As a result, the inventors found that the welding heat input was set to 1.50X 10⁵kA²X sec-4.50X 10⁵kA²X second, not only the characteristics of the flash butt weld portion are improved, but also the characteristics of each portion are suppressedDeviation in the characteristics of the weld.

The welding heat input is obtained by the following formula (1).

Welding heat input (kA)²X seconds) heat input (kA) in the initial flash process²X sec) + Heat input in preheating Process (kA)²X sec) + Heat input in the later flashing step (kA)²X second. 1

Here, the first and second liquid crystal display panels are,

the heat input in the initial flashing process was defined as the average current (kA) in the initial flashing process x the time (seconds) in the initial flashing process

Heat input in the preheating step ∑ (average current (kA) in the ith preheating step × time (sec) in the ith preheating step)

Wherein i is an arbitrary integer, and the preheating step is carried out plural times

Heat input in the latter flash step (average current in the latter flash step (kA) × time in the latter flash step (sec))

The present invention has been completed based on the above findings, and the gist thereof is as follows.

1. A method for manufacturing a rail, wherein when a plurality of rail base materials are joined by a joint portion formed by flash butt welding,

at 1.50X 10⁵kA²X sec-4.50X 10⁵kA²The flash butt welding was performed with welding heat input of x seconds, and the rail base metal had the following composition: contains C: 0.60 to 1.20 mass%, Si: 0.10 to 1.50 mass%, Mn: 0.10 to 1.50 mass% and Cr: 0.10 to 1.50 mass%, and the balance of Fe and inevitable impurities.

2. The method of manufacturing a rail according to claim 1, wherein an absolute value of a difference in hardness between the rail base material and the joint portion at the surface layer portion of the rail head portion to a depth of 2.5mm after the welding is 20 or less in terms of vickers hardness, and a deflection amount of the joint portion is 20mm or more.

3. The method for producing a steel rail according to 1 or 2, wherein the composition further contains a component selected from the group consisting of: v: 0.30 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Nb: 0.2 mass% or less, Mo: 0.5 mass% or less, Al: 0.07 mass% or less, W: 1.0 mass% or less, B: 0.005 mass% or less and Ti: 0.05 mass% or less of 1 or more.

4. A rail comprising a plurality of rail base materials joined together at joint portions, the rail base materials having the following composition: contains C: 0.60 to 1.20 mass%, Si: 0.10 to 1.50 mass%, Mn: 0.10 to 1.50 mass% and Cr: 0.10 to 1.50 mass%, the balance being Fe and inevitable impurities,

the absolute value of the difference in hardness between the rail base material and the joint portion at the surface layer portion from the surface of the head portion of the rail to a depth of 2.5mm is 20 or less in terms of Vickers hardness, and the deflection amount of the joint portion is 20mm or more.

5. The rail according to claim 4, wherein the composition further comprises a component selected from the group consisting of V: 0.30 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Nb: 0.2 mass% or less, Mo: 0.5 mass% or less, Al: 0.07 mass% or less, W: 1.0 mass% or less, B: 0.005 mass% or less and Ti: 0.05 mass% or less of 1 or more.

According to the present invention, a rail joined by a flash butt weld which is far superior to a conventional rail weld can be stably manufactured, and the rail can be lengthened without reducing the characteristics of the weld formed by flash butt welding. As a result, the present invention contributes to prolonging the service life of rails laid on high-axle-weight railways and preventing railway accidents, and provides industrially advantageous effects.

Drawings

FIG. 1 is a schematic view illustrating the measurement positions of the hardness of the rail base metal and the weld portion.

FIG. 2 is a schematic representation of a bending test.

Fig. 3 is a graph showing a relationship between heat input at the time of flash butt welding and a hardness difference between a rail base material and a flash butt weld portion.

Fig. 4 is a graph showing a relationship between heat input at the time of flash butt welding and a deflection amount at the time of a bending test.

Detailed Description

The method for producing a rail according to the present invention will be described in order from the reasons for limiting the composition of the rail base material.

[ composition of Rail base Material ]

C: 0.60 to 1.20% by mass

C is an essential element for forming cementite in the pearlite structure and ensuring the strength of the flash butt weld joint portion of the rail steel. However, if the C amount is less than 0.60 mass%, it is difficult to ensure the strength of the flash butt weld portion of the rail steel, and the characteristics of the flash butt weld portion are degraded. On the other hand, if the C amount exceeds 1.20 mass%, proeutectoid cementite is generated at austenite grain boundaries in the flash butt weld portion, and therefore the characteristics of the flash butt weld portion are significantly reduced. Therefore, the amount of C is 0.60 to 1.20 mass%. The amount of C is preferably 0.70% by mass or more, preferably 1.10% by mass or less, and more preferably 0.70 to 1.10% by mass.

Si: 0.10 to 1.50% by mass

Si is added as a deoxidizer, but if it is less than 0.10 mass%, the effect is small. On the other hand, if it exceeds 1.50 mass%, oxides are generated in the steel of the rail due to the high bonding force with oxygen possessed by Si, and the oxides remain in the welded portion after flash butt welding, and the characteristics of the flash butt welded portion deteriorate. Further, scale formed in the weld bead portion heated to a high temperature during flash butt welding is not easily peeled off, and scale formed by upsetting during welding is not easily discharged, so that scale is likely to remain in the weld bead portion, and good performance of the weld bead portion cannot be obtained. Therefore, the amount of Si is 0.10 to 1.50 mass%. The amount of Si is preferably 0.15 mass% or more, preferably 1.45 mass% or less, and more preferably 0.15 to 1.45 mass%.

Mn: 0.10 to 1.50% by mass

Mn is added in an amount of 0.10 mass% or more because it contributes to strengthening of the flash butt weld portion by lowering the pearlite transformation temperature and making the lamellar spacing fine. On the other hand, if the Mn content exceeds 1.50 mass%, the weld portion is hardened and embrittled after flash butt welding, and the properties of the weld portion are degraded. Therefore, the Mn content is set to 0.10 to 1.50 mass%. The Mn content is preferably 0.15 mass% or more, preferably 1.45 mass% or less, and more preferably 0.15 to 1.45 mass%.

Cr: 0.10 to 1.50% by mass

Cr is an element for improving the strength of the flash butt weld portion of the rail, and is added in an amount of 0.10 mass% or more. On the other hand, if Cr is added in an amount exceeding 1.50 mass%, scale formed in the weld bead portion heated to a high temperature during flash butt welding is less likely to peel off, and scale formed by upsetting during welding is less likely to be discharged, so that scale is more likely to remain in the weld bead portion, and good performance of the weld bead portion cannot be obtained. Therefore, the amount of Cr is 0.10 to 1.50 mass%. The amount of Cr is preferably 0.15 mass% or more, preferably 1.45 mass% or less, and more preferably 0.15 to 1.45 mass%.

The balance other than the above components is Fe and inevitable impurities.

In addition to the above basic components, the rail base metal of the present invention may further contain the following elements for the purpose of further increasing the hardness of the weld portion.

That is, it may further contain a compound selected from:

v: 0.30% by mass or less,

Cu: 1.0 mass% or less,

Ni: 1.0 mass% or less,

Nb: 0.2 mass% or less,

Mo: 0.5 mass% or less,

Al: 0.07% by mass or less,

W: 1.0 mass% or less,

B: 0.005% by mass or less of and

ti: 0.05 mass% or less

1 or more of them.

V: 0.30% by mass or less

V is an element for forming carbonitrides, dispersing and precipitating into the matrix, and increasing the strength of the flash butt weld portion of the rail. Therefore, it is preferable to add V in an amount of 0.005% by mass or more. On the other hand, if the V amount exceeds 0.30 mass%, the above effects are saturated and the alloy cost increases. Therefore, when V is added, the amount of V is preferably 0.30% by mass or less.

Cu: 1.0 mass% or less

Cu is an element for achieving further high strength of the flash butt weld portion of the rail by solid solution strengthening. Therefore, it is preferable to add Cu in an amount of 0.005 mass% or more. On the other hand, if the Cu amount exceeds 1.0 mass%, Cu cracks are likely to occur at the time of flash butt welding. Therefore, when Cu is added, the amount of Cu is preferably 1.0 mass% or less.

Ni: 1.0 mass% or less

Ni is an element for increasing the strength of a flash butt weld portion of a rail without deteriorating ductility. Further, since Cu cracks during flash butt welding are suppressed by adding Ni in combination with Cu, it is preferable to add Ni also in the case of adding Cu. Therefore, it is preferable to add Ni in an amount of 0.005 mass% or more. On the other hand, if the Ni amount exceeds 1.0 mass%, the above effects are saturated, and an increase in alloy cost is caused. Therefore, when Ni is added, the amount of Ni is preferably 1.0 mass% or less.

Nb: 0.2 mass% or less

Nb can be bonded to C, N in steel and precipitated as carbide, nitride, or carbonitride during and after rolling, thereby increasing the hardness of the flash butt weld portion of the rail. Therefore, Nb is preferably added at 0.005 mass% or more. On the other hand, if the Nb amount exceeds 0.2 mass%, the above effects are saturated, and an increase in alloy cost is caused. Therefore, when Nb is added, the Nb content is preferably 0.2 mass% or less.

Mo: 0.5% by mass or less

Mo is an element for achieving further high strength of the flash butt weld portion of the rail by solid solution strengthening. Therefore, it is preferable to add Mo in an amount of 0.005 mass% or more. On the other hand, if the Mo amount exceeds 0.5 mass%, the above effects are saturated, and an increase in alloy cost is caused. Therefore, when Mo is added, the Mo amount is preferably 0.5 mass% or less.

Al: 0.07% by mass or less

Al is an element added as a deoxidizer. Therefore, it is preferable to add Al in an amount of 0.001 mass% or more. On the other hand, if the Al content exceeds 0.07 mass%, the above effects are saturated, and an increase in alloy cost is caused. Therefore, when Al is added, the Al content is preferably 0.07 mass% or less.

W: 1.0 mass% or less

W is an element for precipitation as carbide and further strengthening the flash butt weld joint portion of the rail by precipitation strengthening. Therefore, it is preferable to add W in an amount of 0.001 mass% or more. On the other hand, if the W content exceeds 1.0 mass%, the above effects are saturated, and an increase in alloy cost is caused. Therefore, when W is added, the W content is preferably 1.0 mass% or less.

B: 0.005% by mass or less

B is an element for precipitating as a nitride and achieving further high strength of the flash butt weld portion of the rail by precipitation strengthening. Therefore, it is preferable to add B in an amount of 0.0001% by mass or more. However, if the B content exceeds 0.005 mass%, the above effect is saturated and leads to an increase in alloy cost. Therefore, when B is added, the B content is preferably 0.005 mass% or less.

Ti: 0.05 mass% or less

Ti is an element that precipitates as carbide, nitride, or carbonitride, and achieves further high strength of the flash butt weld joint portion of the rail by precipitation strengthening. Therefore, Ti is preferably added in an amount of 0.001 mass% or more. On the other hand, if the Ti content exceeds 0.05 mass%, the above effects are saturated, and an increase in alloy cost is caused. Therefore, when Ti is added, the Ti content is preferably 0.05 mass% or less.

The rail base metal having the above composition is formed into a plurality of long rails by joining a plurality of rail base metal members by a weld portion formed by flash butt welding. The welding conditions are described in detail below. The rail base metal may have the above-described composition, and a rail produced through a usual process may be used as the rail base metal. That is, as the rail base metal, a rail manufactured by melting steel having a predetermined composition, casting the steel to manufacture a bloom, and subjecting the bloom to hot rolling using a hole roll as a material can be used. The hot rolled rail may be forcibly cooled as necessary. In addition, the rails may be straightened as necessary.

[ welding conditions ]

Welding heat input: 1.50X 10⁵kA²X sec-4.50X 10⁵kA²X second

When a railway vehicle travels on a rail, a vertically downward load is applied to the rail, and as a result, the rail is bent. Here, the heat input at welding is less than 1.50X 10⁵kA²In the case of x seconds, the welding heat input is small, the hardness of the weld portion becomes hard, and the difference in hardness between the rail base material and the weld portion becomes large. Therefore, when a large load is applied to the weld portion of the rail by the wheel passing through the weld portion while the railway vehicle is running on the rail, the load cannot be absorbed by the deflection amount of the weld portion, and the rail weld portion is broken. Therefore, in order to suppress the fracture of the weld portion of the rail, the welding heat input is ensured to be 1.50 × 10⁵kA²X seconds or more. On the other hand, if the welding heat input exceeds 4.50X 10⁵kA²When the heat input is too large for x seconds, the hardness of the weld portion decreases, and the difference in hardness between the rail base material and the weld portion still increases. Then, local wear occurs at the weld portion, and when a large load is applied to the weld portion of the rail by the wheel passing through the weld portion while the railway vehicle is running on the rail, the rail weld portion is broken. Therefore, in order to suppress the fracture of the rail joint portion, it is necessary to set the welding heat input to 1.50 × 10⁵kA²X sec-4.50X 10⁵kA²X seconds. The welding heat input is preferably 1.55X 10⁵kA²X second or more, preferably 4.45X 10⁵kA²X second or less, more preferably 1.55X 10⁵kA²X second-4.45×10⁵kA²X seconds.

In the present invention, it is important to limit the welding heat input during flash butt welding to the above range, and other welding conditions can be made in accordance with those for general rail production. That is, flash butt welding generally includes an initial flashing step, a preheating step, a post flashing step, and an upsetting step. The welding heat input is the sum of the heat inputs of the initial flashing step, the preheating step, and the post-flashing step. Incidentally, any welding machine such as a Chemetron welding machine, a scheletter welding machine, or the like may be used as the flash butt welding machine.

Here, a method of calculating the welding heat input of flash butt welding is described in detail. That is, the average current (kA) in the initial flashing step and the time (sec) in the initial flashing step, the average current (kA) in each preheating step and the time (sec) in each preheating step, and the average current (kA) in the later flashing step and the time (sec) in the later flashing step were obtained. Note that, as each preheating step, since the preheating step is performed by applying an arbitrary current i times 2 or more (heating a plurality of times), each preheating step is considered. As described above, the welding heat input can be obtained by the following equation (1).

[ welding Heat input (kA)²X second)]Heat input (kA) in the initial flashing process²X sec) + Heat input in preheating Process (kA)²X sec) + Heat input in the later flashing step (kA)²X second. 1

Here, the first and second liquid crystal display panels are,

the heat input in the initial flashing process was defined as the average current (kA) in the initial flashing process x the time (seconds) in the initial flashing process

Heat input in the preheating step ∑ (average current (kA) in the ith preheating step × time (sec) in the ith preheating step)

Wherein the preheating process is performed a plurality of times.

Heat input in the latter flash step (average current in the latter flash step (kA) × time in the latter flash step (sec))

In order to control the welding heat input determined in this way within the above range, it is necessary to control the current, time, and number of preheating steps in each welding step.

After the post flash process is completed with the expected weld heat input, the upsetting is preferably performed at a pressure of 45 to 75 tons in the upsetting process. Natural cooling or air cooling may also be performed after the flash butt welding. For example, the flash butt welding can be finished 10-70 seconds later when the air pressure: air cooling is performed for 15 to 60 seconds at 5 to 20 psi.

The weld joint obtained by welding based on the above welding heat input satisfies the following characteristics: the absolute value of the difference in hardness between the rail base material and the joint portion at the surface portion (hereinafter simply referred to as the surface portion) of the rail head portion to a depth of 2.5mm after welding is not more than 20 in terms of Vickers hardness and the deflection of the joint portion is not less than 20 mm.

Absolute value of difference Δ H between hardness of rail base material and hardness of weld portion: less than 20 ]

In this specification, the hardness of the rail base metal and the weld portion at the surface layer portion is measured as a vickers hardness at a depth of 2.5mm from the surface of the rail head after production in the manner described later. The difference Δ H in hardness is calculated from [ hardness of base material ] - [ hardness of weld portion ] based on the measured value. If Δ H exceeds +20, it indicates that the hardness of the weld portion is reduced, and as described above, local wear occurs in the weld portion to cause the weld portion to break. On the other hand, if the difference Δ H in hardness is less than-20, it means that the hardness of the weld portion is significantly increased as compared with the base material, and as described above, if the wheel passes through the weld portion, a large load is applied to the rail weld portion, and the rail weld portion is broken. Or, even if the weld portion is not broken, the rail base metal is worn and the weld portion protrudes from the surface, and therefore, the protruding portion needs to be ground by a grinding machine or the like. Therefore, the absolute value of the difference Δ H in hardness between the rail base metal and the weld portion is set to 20 or less in vickers hardness.

[ deflection amount: over 20mm ]

The deflection of the rail of the present invention obtained by the bending test described later is 20mm or more. That is, if the deflection amount is less than 20mm, when the railway vehicle travels on the rail and the wheel passes through the weld portion, a large load is applied to the weld portion of the rail, and the deflection amount of the weld portion cannot be absorbed, and the rail weld portion breaks. Therefore, the deflection is set to 20mm or more.

[ hardness test ]

Here, as shown in fig. 1, the hardness test was conducted by measuring vickers hardness at a distance of 1mm and under a load of 98N over a range of 50mm from the center of the weld portion 2, i.e., the joint interface 3 between the rail base materials, to both sides in the rail longitudinal direction at a depth of 2.5mm from the surface of the rail head of the rail 1 after manufacture. The average measured value of the rail base material was taken as the hardness of the base material, and the hardness difference Δ H was calculated from [ hardness of base material ] - [ hardness of joint portion ] using the average measured value of the joint portion as the hardness of the joint portion.

[ bending test ]

Here, the bending test is in accordance with the American Railway Engineering and road Maintenance institute (American Rail Engineering and Maintenance-of-Way Association) standard: AREMA-sec.2.3.3.6. That is, as shown in fig. 2, the distance between the fulcrums 4 was set to 24 inches from the center of the bead portion 2 (i.e., the joint interface 3 between the rail base materials), and the amount of deflection until fracture was measured by applying a load. In the present invention, if the deflection amount is 20mm or more, it is determined that the characteristics of the weld portion are good.

Example 1

Using a rail base material (invention steel A-1) having a composition shown in Table 1, flash butt welding was performed according to the welding heat input shown in Table 2. Then, the difference Δ H in hardness between the rail base metal and the weld portion and the amount of deflection in the bending test were examined in accordance with the above-described procedure. For flash butt welding, DC Rail weld #923 manufactured by Chemetron corporation was used. In addition, 50 seconds after the end of welding, the air pressure: air cooling was performed at 10psi for 45 seconds.

The results of measurement of Δ H and the amount of deflection are shown in table 2. Fig. 3 shows a relationship between heat input during flash butt welding and a hardness difference Δ H between a rail base material and a flash butt weld portion, and fig. 4 shows a relationship between heat input during flash butt welding and a deflection amount during a bending test.

Further, the resistance of the weld portion of the obtained rail to fracture was examined as follows. That is, in the present invention, if the deflection amount is 20mm or more, it is determined that the characteristics of the bead portion are good, and therefore the deflection amount: the rail was not broken at 20 mm. On the other hand, in the present invention, in order to examine the original characteristics of the weld portion, the test was not interrupted even if the deflection was 20mm or more, the test was carried out until the rail was broken, and the deflection at the time of the breakage was examined.

[ Table 1]

[ TABLE 1] (Mass%)

	C	Si	Mn	Cr	Remarks for note
						A-1	0.84	0.55	0.61	0.71	Invention steel

[ Table 2]

[ Table 2]

As can be seen from Table 2 and FIGS. 3 and 4, if the welding heat input is 1.5X 10⁵kA²X sec-4.5X 10⁵kA²X second, a good flash butt weld portion can be formed, and the deflection is ensured to be 20mm or more, the deflection: no rail break occurred at 20 mm.

Example 2

A rail base material (inventive steels B-1 to 10 and B-19 to 26, comparative steels B-11 to 18) having the composition shown in Table 3 was subjected to flash butt welding, and the difference in hardness between the rail base material and a weld portion, Δ H, and the amount of deflection in a bending test were examined in the same manner as in example 1. The results are shown in Table 4.

[ Table 4]

[ Table 4]

As can be seen from table 4, the steel rail obtained by the manufacturing method of the present invention has the following flexural modulus: the rail does not break at 20mm, and the rail having excellent characteristics of the weld portion can be stably obtained by the manufacturing method of the present invention. In addition, the rails of the invention examples having the predetermined composition, the difference in hardness Δ H, and the deflection amount defined in the present invention were: no breakage occurred at 20 mm. On the other hand, in the rail of the comparative example which did not satisfy the conditions of the present invention, both the difference Δ H in hardness between the rail base material and the weld portion and the deflection amount in the bending test were not satisfactory, and in the deflection amount: fracture occurred below 20 mm.

Industrial applicability

The rail manufactured by the present invention is useful for extending the life of a rail laid on a high axle load railway and preventing railway accidents, and has industrially significant effects.