JP5453624B2 - Perlite steel rail with excellent crack resistance - Google Patents

Description

  The present invention is a pearlite steel excellent in crack cracking resistance, in which cracks generated in a corner portion of a rail head (gauge corner portion; hereinafter also referred to as “GC portion”) due to contact between a rail and a wheel are reduced. It relates to rails.

  Rail transport is more efficient and environmentally friendly than other transport modes. In recent years, the transportation capacity has been increased by increasing the operation speed, increasing the freight load of freight cars, and congesting diamonds. It is being actively promoted. As a result, the load on the rail has become severe, and it is important to have excellent characteristics such as rail wear resistance, rolling damage resistance, dark spot damage characteristics (hereinafter collectively referred to as “wear resistance”). Yes.

  On the other hand, in recent years, before the rail replacement due to wear of the GC section, the frequency of the rail replacement due to scratch cracks gradually increases, which is a problem. This scramble is a continuous crack in the GC section such as an outer rail in a curved track section. When the crack grows, the portion between the cracks may peel off. . Therefore, high-strength rails have been used for rails used in curved track sections from the viewpoint of improving wear resistance. However, after making the wear resistance of the GC part equal to or higher than that of conventional rails, Furthermore, there is a demand for rails with improved crack resistance.

  Focusing on the wear resistance of the rail, many proposals have been made so far regarding techniques for improving this. For example, Patent Document 1 discloses damage resistance against rolling fatigue damage (referred to as “heavy shring damage”) that occurs inside the rail head by controlling the amount and composition of oxide inclusions within an appropriate range. A rail with an increased height is disclosed. Patent Document 2 discloses a technique for reducing damage (head chuck) generated at the center of the rail head by relaxing the contact stress state between the rail and the wheel by imparting an appropriate hardness distribution to the rail head. Is disclosed. Patent Document 3 discloses a martensite structure (white phase) that occurs in the top and corners of the wheels due to running and slipping of the wheels by controlling the hardness of the rail heads and the corners. A technique for preventing formation and improving rolling fatigue damage resistance is disclosed. Patent Document 4 discloses a technique for preventing the generation of martensite generated on the surface of a steel material during electric arc welding and improving the breakage resistance by controlling the component composition of the rail within an appropriate range. Yes. Furthermore, in Patent Document 5, in the steel rail having a pearlite structure, the initial hardness is set within a predetermined range and the impact value is further improved by performing an appropriate heat treatment at the same time as controlling the steel components to an appropriate range. Thus, a technique for improving the surface damage resistance and toughness of a rail used in a straight section or a gentle curve section is disclosed.

Japanese Patent Laid-Open No. 2001-220651 Japanese Patent No. 3317146 Japanese Patent No. 2620369 JP 2005-350723 A Japanese Patent No. 3631712

However, in recent years, where the speed of railways, the freight load of freight cars, and the congestion of diamonds are increasing, the load on rails has become more severe than before, especially outside the curved track section. In the rail, the wear resistance and the rolling damage resistance of the rail head surface are gradually becoming insufficient.
This is because, for example, the technique disclosed in Patent Document 1 is intended to prevent fatigue failure starting from inclusions present in the rail, but sufficient investigation is required for cracking in the GC portion. Not done. Moreover, although the technique of patent document 2 is effective in suppression of the head check which generate | occur | produces in the rail head center, it is inadequate for prevention of the crack of GC part. Moreover, although the technique of patent document 3 provides a hardness difference in a rail top part and a corner part, and suppresses rolling damage, sufficient examination is not made about the crack crack of GC part. Moreover, the technique of patent document 4 is a technique which suppresses the production | generation of a martensitic structure from a viewpoint of preventing the crack and breakage which generate | occur | produce when a martensitic structure is formed on the rail surface for a certain reason. Sufficient studies have not been made on suppressing cracking of the GC portion where no abnormal tissue is formed. Furthermore, the technique of Patent Document 5 is a technique for regulating the hardness and hardness difference between the rail top and a depth of 20 mm, and sufficient studies have not been made to improve the crack resistance.

  The present invention has been made in view of the above-described problems of the prior art, and its purpose is to reduce the wear resistance of a high-strength rail and to reduce the gauge corner by contact between the rail and the wheel. An object of the present invention is to provide a pearlite steel rail with reduced cracks generated in the part.

In order to solve the above-mentioned problems, the inventors changed the content of C, Si, Mn, and Cr, and manufactured various pearlite steel rails with a 0.2% proof stress, and improved the strength and wear resistance. And crack resistance were investigated. As a result, the content of C, Si, Mn, Cr and their total content is controlled to an appropriate range, and the 0.2% proof stress is controlled to an appropriate range, so that the wear resistance is not lowered. It has been newly found that the cracking property can be improved. Furthermore, it has also been found that by controlling the tensile strength and the ratio between the 0.2% proof stress and the tensile strength (yield ratio: YR) within an appropriate range, the crack resistance can be improved more stably.
The present invention was developed by further studying the above knowledge.

That is, the present invention includes C: more than 0.75 mass% and less than 0.85 mass%, Si: 0.1 to 0.3 mass%, Mn: 0.7 to 1.1 mass%, P: 0.035 mass% or less, S : 0.0005 to 0.010 mass%, Cr: 0.05 to 0.25 mass%, the total of C, Si, Mn and Cr content is more than 1.9 mass% and less than 2.3 mass%, the balance is It has a component composition consisting of Fe and inevitable impurities, and has the following formula (1):
ρ [μΩ · cm] = 0.95 × A + 12.4 (1)
However, A = (13.8 * Si + 6.01 * Mn + 5.38 * Cr + 0.01) * ((1-0.15 * C) / (1-0.3 * C))
Here, the element symbol in the above formula is the content (mass%) of the element.
Is a pearlite steel rail having an electrical resistivity ρ of 21.1 to 23.7 μΩ · cm and a 0.2% proof stress of more than 500 MPa and less than 800 MPa.

  In addition to the above component composition, the pearlitic steel rail of the present invention is further provided with V: 0.001 to 0.03 mass%, Cu: 0.5 mass% or less, Ni: 0.5 mass% or less, and Mo: 0.1 mass% or less. 1 type or 2 types or more chosen from among are contained.

  The pearlite steel rail of the present invention is characterized in that the tensile strength is more than 900 MPa and less than 1080 MPa, and the ratio of 0.2% proof stress to tensile strength is more than 55%.

  According to the present invention, it is possible to stably provide a rail with improved cracking resistance without reducing wear resistance compared to conventional pearlite steel rails, so that the life of the rail can be extended. In addition, it can greatly contribute to the prevention of railway accidents.

It is a graph which shows the relationship between cooling stop temperature and 0.2% yield strength. It is a graph which shows the relationship between the cooling rate after hot rolling, and 0.2% yield strength. It is sectional drawing of the rail head which shows the sampling position of the test item used for a tension test. It is a figure explaining the test piece of the Nishihara type abrasion test used for evaluation of wear resistance. It is sectional drawing of the rail head which shows the sampling position of the test piece used for a Nishihara type abrasion test. It is a figure explaining the test piece used for evaluation of a crack crack resistance.

First, the reason for limiting the component composition of the pearlite steel rail of the present invention will be described.
C: More than 0.75 mass% and less than 0.85 mass% C is an essential element for forming cementite having a pearlite structure and ensuring strength. However, at 0.75 mass% or less, since the effect of increasing the 0.2% proof stress and tensile strength is small, the effect of suppressing the occurrence of cracks is not sufficient, and cracks are likely to occur. On the other hand, when it becomes 0.85 mass% or more, the 0.2% proof stress and tensile strength are increased and the wear resistance and the crack resistance are improved. On the other hand, once a crack is generated, this crack is removed by wear. Because it is difficult to be done, it will remain. By adding new cracks there, the number of cracks increases and the crack resistance is reduced. Therefore, the C content is in the range of more than 0.75 mass% and less than 0.85 mass%.

Si: 0.1-0.3 mass%
Si is an element added as a deoxidizer and for the purpose of strengthening steel by forming a pearlite structure, and needs to be added in an amount of 0.1 mass% or more. However, if added over 0.3 mass%, the electrical conductivity of the rail is lowered. Therefore, the Si content is in the range of 0.1 to 0.3 mass%.

Mn: 0.7 to 1.1 mass%
Mn is an element that increases the 0.2% yield strength and tensile strength by lowering the pearlite transformation temperature and reducing the lamellar spacing. However, if the addition is less than 0.7 mass%, the effect of increasing the 0.2% proof stress and the tensile strength is not sufficient, and therefore the cracking suppression force is small and cracking is likely to occur. On the other hand, when it exceeds 1.1 mass%, 0.2% yield strength and tensile strength increase, and wear resistance and crack resistance can be improved. However, once a crack is generated, the crack remains without being removed by wear. By adding new cracks there, the number of cracks increases and the crack resistance is reduced. Therefore, Mn is added in the range of 0.7 to 1.1 mass%.

P: 0.035 mass% or less P is an element harmful to the ductility of steel, and in particular, inclusion exceeding 0.035% greatly reduces the ductility. Therefore, the content of P is set to 0.035 mass% or less.

S: 0.0005 to 0.010 mass%
S is present in steel materials mainly in the form of A-based inclusions. However, when it is contained in an amount exceeding 0.010 mass%, the amount of these inclusions is remarkably increased to form coarse inclusions. Remarkably deteriorates sex. Therefore, S is set to 0.010 mass% or less. However, excessive reduction of S causes an increase in steelmaking cost, so the lower limit is about 0.0005 mass%.

Cr: 0.05-0.25 mass%
Cr is an element that raises the pearlite equilibrium transformation temperature, contributes to increasing the strength by refining the lamellar spacing, and further increases the strength by solid solution strengthening. However, if the addition is less than 0.05 mass%, the effect of increasing the 0.2% proof stress and the tensile strength is poor, and thus the suppression of occurrence of cracking is small. On the other hand, if added over 0.25 mass%, the 0.2% proof stress and tensile strength are increased, and the wear resistance and crack resistance are improved. On the other hand, once a crack is generated, this crack is worn out. It remains without being removed by. By adding new cracks there, the number of cracks increases and the crack resistance is reduced. Therefore, the Cr content is in the range of 0.05 to 0.25 mass%.

In addition to satisfying the above component composition, the pearlite steel rail of the present invention is required to have the total content of C, Si, Mn and Cr satisfy the following range.
C + Si + Mn + Cr: more than 1.9 mass% and less than 2.3 mass% C, Si, Mn and Cr are elements added to increase the hardness of the pearlite steel rail, but the balance of the content of these elements is not appropriate. , Scratch cracking resistance decreases. In particular, when the total content of C, Si, Mn and Cr is 1.9 mass% or less, the 0.2% proof stress and tensile strength are lowered, and the crack resistance is lowered. On the other hand, if the total content of C, Si, Mn and Cr is 2.3 mass% or more, the 0.2% proof stress and tensile strength are increased, and the wear resistance and crack resistance are improved. Once a crack is generated, the crack remains without being removed by wear. By adding new cracks, the number of cracks increases and the crack crack resistance decreases. Therefore, the total content of C, Si, Mn, and Cr is in the range of more than 1.9 mass% and less than 2.3 mass%.

Furthermore, the pearlite steel rail of the present invention can further contain one or more selected from V, Cu, Ni and Mo in the following range in addition to the above components.
V: 0.001 to 0.03 mass%
V forms a carbonitride, disperses and precipitates in the matrix, and improves 0.2% proof stress and tensile strength. However, the effect is small if it is less than 0.001 mass%. On the other hand, if it exceeds 0.03 mass%, the 0.2% proof stress and tensile strength are increased, and the wear resistance and crack resistance are improved. However, once cracks occur, they remain because they are not removed by wear, and new cracks are added to the cracks, increasing the number of cracks and reducing crack resistance. become. Moreover, the addition exceeding 0.03 mass% increases raw material cost and causes an increase in manufacturing cost. Therefore, when adding V, it is preferable to set it as the range of 0.001-0.03 mass%.

Cu: 0.5 mass% or less Cu, like Cr, is an element added for the purpose of increasing the strength by solid solution strengthening. In order to obtain the effect, addition of 0.005 mass% or more is preferable. However, addition exceeding 0.5 mass% tends to cause cracks during hot rolling with Cu. Therefore, when adding Cu, it is preferable to set it as 0.5 mass% or less.

Ni: 0.5 mass% or less Ni is an element that can increase the strength without reducing the ductility of the steel. Further, since Ni has an effect of suppressing cracking due to Cu, when adding Cu, it is desirable to add Ni in combination. In order to obtain these effects, Ni is preferably added in an amount of 0.005 mass% or more. However, addition exceeding 0.5 mass% increases the hardenability and facilitates the formation of martensite, thus reducing the life of the rail. Therefore, when adding Ni, it is preferable to set it as 0.5 mass% or less.

Mo: 0.1 mass% or less Mo is an element added to increase the strength of steel by solid solution strengthening. In order to obtain the effect, addition of 0.005 mass% or more is preferable. However, addition exceeding 0.1 mass% increases the 0.2% proof stress and tensile strength to improve wear resistance and crack resistance, but once cracks occur, Cracks remain without being removed due to wear. If the number of cracks increases due to the addition of new cracks, the crack cracking resistance decreases. Therefore, when adding Mo, it is preferable to set it as 0.1 mass% or less.

  In the pearlite steel rail of the present invention, the balance other than the above components is composed of Fe and inevitable impurities. However, it does not refuse to contain other components as long as it does not adversely affect the effects of the present invention. For example, N mixed as an inevitable impurity can be allowed to be mixed if it is 0.006 mass% or less and O is 0.004 mass% or less. Further, Ti mixed as an impurity is an element that forms an oxide and causes a reduction in fatigue damage resistance, which is a basic characteristic of the rail. However, if it is 0.0010% or less, mixing can be permitted.

Furthermore, since the pearlite steel rail of the present invention requires an electrical signal to flow through the rail for safe operation, the electrical resistivity (specific resistance) ρ is controlled in the range of 21.1 to 23.7 μΩ · cm. For that purpose, C, Si, Mn and Cr are represented by the following formula (1):
ρ [μΩ · cm] = 0.95 × A + 12.4 (1)
However, A = (13.8 * Si + 6.01 * Mn + 5.38 * Cr + 0.01) * ((1-0.15 * C) / (1-0.3 * C))
Here, the element symbol in the above formula means the content (mass%) of the element.
It is necessary to contain and satisfy. This is because if the electrical resistivity falls outside the range of 21.1 to 23.7 μΩ · cm, a track short circuit is likely to occur, which hinders railway operation management.

Next, the mechanical characteristics of the pearlite steel rail of the present invention will be described.
0.2% proof stress: more than 500 MPa and less than 800 MPa Scratch cracking is a phenomenon that progresses into the rail along the plastic flow and decreases the service life of the rail. In order to increase the resistance against the cracks, the pearlite steel rail of the present invention needs to control the 0.2% proof stress within the range of more than 500 MPa and less than 800 MPa.
In the following, basic experiments that support this will be described.

(Basic experiment 1)
A steel material having the component composition shown in Table 1 was hot-rolled into a rail shape, and then acceleratedly cooled with various cooling stop temperatures as shown in Table 2. Next, the above-mentioned rail was subjected to a tensile test and a crack crack test using a Nishihara-type abrasion tester under the same conditions as in the examples described later, and the tensile properties and crack crack resistance were evaluated. The results are also shown in Table 2. Showed. In addition, the evaluation of the crack resistance was determined by cutting the test piece after the abrasion test in half in the thickness direction as shown in FIG. 6 described later, embedding in a carbon resin, polishing, and cracking generated in the sample. When the number of cracks is 10% or more smaller than the standard steel material (steel symbol B in Table 2), ◎, when the number of cracks is equal to the standard material, and when cracking is 5% or more than the standard material The case where the number was large was evaluated as Δ.

FIG. 1 shows the relationship between the cooling stop temperature and the 0.2% yield strength, and it can be seen that the 0.2% yield strength can be increased by lowering the cooling stop temperature.
Moreover, it can be seen from Table 2 that good crack resistance is obtained by setting the 0.2% proof stress to more than 500 MPa and less than 800 MPa.

(Basic experiment 2)
A steel material having the composition shown in Table 3 was hot-rolled into a rail shape, and then accelerated and cooled as shown in Table 4 with various cooling rates. Next, the above-mentioned rail was subjected to a tensile test and a crack crack test using a Nishihara-type abrasion tester under the same conditions as in the examples described later, and the tensile properties and crack crack resistance were evaluated. The results are also shown in Table 4. Showed. In addition, the evaluation of the crack resistance was determined by cutting the test piece after the abrasion test in half in the thickness direction as shown in FIG. 6 described later, embedding in a carbon resin, polishing, and cracking generated in the sample. When the number of cracks is 10% or more smaller than the standard steel material (steel symbol B in Table 4), ◎, when the number of cracks is the same as the standard material, and when cracking is 5% or more than the standard material The case where the number was large was evaluated as Δ.

FIG. 2 shows the relationship between the cooling rate and the 0.2% proof stress. When the cooling rate is 0.5 ° C./second or less, no difference is observed compared to the case of cooling. It can be seen that by increasing the cooling rate, the 0.2% proof stress can be increased, and if it exceeds 3 ° C./second, it becomes 800 MPa or more.
In addition, from Table 4, it can be seen that, as in Table 2 described above, by setting the 0.2% proof stress to more than 500 MPa and less than 800 MPa, good crack resistance is obtained.

From the above, it can be seen that by setting the 0.2% proof stress in the range of more than 500 MPa and less than 800 MPa, a rail with good crack resistance can be obtained. The influence of the 0.2% proof stress on the plastic flow depth, the crack crack depth and number, and the wear amount as described above can be explained as follows.
When the 0.2% proof stress is 500 MPa or less, the plastic flow depth and the crack crack depth increase and the crack crack resistance decreases, but the wear amount also increases at the same time, so the number of crack cracks does not increase. On the other hand, although the wear resistance and crack crack resistance are improved by increasing the 0.2% proof stress, once the crack exceeds 800 MPa, the crack remains without being removed by wear. It is considered that the crack crack resistance is lowered because a new crack crack is added and the number of cracks is increased.

Tensile strength: more than 900 MPa and less than 1080 MPa The pearlite steel rail of the present invention preferably has a tensile strength controlled in a range of more than 900 MPa and less than 1080 MPa. When the tensile strength is 900 MPa or less, the crack resistance is reduced and cracking is likely to occur. On the other hand, the tensile strength increases and the wear resistance and crack crack resistance are improved. However, once the tensile strength becomes 1080 MPa or more, once a crack crack occurs, the crack remains without being removed by wear. However, by adding new cracks here, the number of cracks increases, and the crack crack resistance decreases. Therefore, the pearlite steel rail of the present invention preferably has a tensile strength in the range of more than 900 MPa and less than 1080 MPa.

Ratio between 0.2% yield strength and tensile strength (yield ratio: YR): over 55% When the yield ratio YR, which is the ratio between 0.2% yield strength and tensile strength, is controlled to exceed 55%, 0.2% yield strength Further, it is possible to control the tensile strength within a preferable range, and it is possible to obtain a rail that is more stable and has excellent crack resistance. Therefore, the ratio between the 0.2% proof stress and the tensile strength is preferably more than 55%.

Next, the pearlite steel rail of the present invention can be manufactured by hot-rolling the steel material adjusted to the above-described component composition of the present invention, for example, under the following conditions, and allowing to cool or accelerate. .
Rolling finishing temperature: 850-950 ° C
The rolling finishing temperature in the hot rolling is preferably in the range of 850 to 950 ° C. When the rolling finishing temperature is lower than 850 ° C., rolling is performed in a low temperature range of austenite, so that not only processing strain is introduced into the austenite crystal grains, but also the degree of elongation of the crystal grains increases and the austenite grain boundary Increases area. As a result, the number of pearlite nucleation sites increases and the pearlite colony size becomes finer. However, the increase in the pearlite nucleation site increases the pearlite transformation start temperature and coarsens the lamellar spacing of the pearlite layer, thus reducing the 0.2% proof stress and tensile strength, and reducing the resistance to cracking. Resulting in. On the other hand, when the rolling finishing temperature exceeds 950 ° C., the austenite crystal grains become coarse and pearlite nucleation sites decrease, so that the pearlite transformation start temperature decreases and the lamellar spacing of the pearlite layer becomes fine. Therefore, 0.2% proof stress and tensile strength are increased, and wear resistance and crack resistance are improved. However, once a crack is generated, the crack remains without being removed by wear. This is because the number of cracks increases and the crack crack resistance decreases due to the addition of new cracks.

Cooling after hot rolling: Allowing to cool or accelerating cooling After the hot rolling, the rolled rail is cooled to room temperature. The cooling method at this time may be either cooling or acceleration cooling. However, when it is desired to increase the 0.2% proof stress and tensile strength, the rail head surface portion is from 0.5 ° C / second over 3 ° C / second from pearlite transformation start temperature to 550-700 ° C. Accelerated cooling is preferably performed at the following speed. Hereinafter, the accelerated cooling condition will be described. At this time, the bottom of the rail may be accelerated or cooled.

Accelerated cooling start temperature: pearlite transformation start temperature or higher When performing accelerated cooling, the cooling start temperature is preferably set to the pearlite transformation start temperature or higher. This is because when the cooling start temperature is lower than the pearlite transformation start temperature, it is difficult to increase the 0.2% yield strength and the tensile strength. The pearlite transformation start temperature varies depending on the component composition and the cooling rate, but in the present invention, it means the equilibrium transformation temperature. Therefore, in the component composition range of the rail of the present invention, accelerated cooling may be started from a temperature of 720 ° C. or higher.

Accelerated cooling rate: more than 0.5 ° C./second and not more than 3 ° C./second The cooling rate in accelerated cooling is preferably more than 0.5 ° C./second and not more than 3 ° C./second. As is clear from the relationship between the cooling rate shown in FIG. 4 and the 0.2% yield strength, when the cooling rate is 0.5 ° C./second or less, there is no difference from the 0.2% yield strength when allowed to cool, and acceleration The cooling effect cannot be obtained. On the other hand, when the cooling rate exceeds 3 ° C./second, the 0.2% proof stress is excessively increased and falls outside the range of the present invention (over 500 MPa and less than 800 MPa).

Accelerated cooling stop temperature: 550-700 ° C
The cooling stop temperature in the accelerated cooling is preferably in the range of 550 to 700 ° C. As is clear from the relationship between the cooling stop temperature and the 0.2% yield strength shown in FIG. 1, when the cooling stop temperature exceeds 700 ° C., there is no difference in the cooling conditions from the case of cooling, so 0.2% The yield strength is reduced to 500 MPa or less. On the other hand, when the cooling stop temperature is less than 550 ° C., cooling is performed until after completion of the pearlite transformation, so that the 0.2% proof stress is excessively increased to 800 MPa or more. Therefore, the cooling stop temperature is preferably 550 to 700 ° C. when accelerated cooling is performed.

  A steel material having the composition shown in Table 5 was hot-rolled under the conditions shown in Table 6 and allowed to cool or accelerated to produce a rail. In addition, accelerated cooling was performed only on the rail head, and was allowed to cool after cooling was stopped. The rolling finish temperature in Table 6 is a value obtained by measuring the temperature of the rail head side surface layer on the final rolling mill entry side with a radiation thermometer, and the cooling stop temperature is the rail head side surface on the cooling equipment exit side. The temperature of the surface layer is a value measured with a radiation thermometer, and the cooling rate is the average time change in temperature from the start to the stop of cooling, and standing to cool indicates that accelerated cooling is not performed .

The various rails obtained as described above were evaluated for tensile tests, wear resistance, and crack resistance in the following manner.
<Tensile test>
A No. 4 test piece specified in JIS Z2201 was taken from the sampling position of the tensile test piece specified in JIS E1101 (see FIG. 3), and a tensile test was conducted in accordance with JIS Z2241, and a 0.2% proof stress (0 .2% PS) and tensile strength (TS) were measured, and the yield ratio (YR), which is the ratio of 0.2% proof stress to tensile strength, was determined.

<Abrasion test>
Although it is most desirable to evaluate the wear resistance by actually laying the rail, this method requires a long time for the evaluation. Therefore, in the present invention, an acceleration test simulating actual contact conditions between the rail and the wheel was performed using a Nishihara type wear tester (manufactured by Shimadzu Corporation) that can evaluate the wear resistance in a short time. In this wear test, a wear test piece a having a curved surface with a radius of curvature of 15 mm on the outer peripheral surface (test surface) of a ring-shaped wear test piece having an outer diameter of 30 mmφ, an inner diameter of 16 mmφ, and a thickness of 8 mm is the same shape, The wear resistance is evaluated by bringing the tire test piece b having the dimensions into contact with each other as shown in FIG. 4 and rotating it with slipping. In addition, the arrow in a figure shows the rotation direction of the abrasion test piece a and the tire test piece b.
The abrasion test piece a to be evaluated was collected from the position shown in FIG. 5 of the rail head. The tire test piece b is a test after heat treating a 32 mmφ round bar taken from the head of a normal rail described in JIS E1101 to obtain a tempered martensite structure with a Vickers hardness Hv (load 98 N) of 390. It is processed into a single shape.
The abrasion test was performed at a contact pressure of 1.4 GPa, a rotation speed of the test piece a: 675 rpm, a rotation speed of the tire test piece b: 750 rpm (slip rate: −10%), and after 162,000 rotations. The amount of wear was determined from the difference between the mass and the mass before the test. In addition, evaluation of abrasion resistance evaluated that it was excellent in abrasion resistance, so that there was little abrasion amount from the steel materials used as a reference | standard (steel No. 1 of Table 5).

<Crack resistance>
The crack resistance is most preferably evaluated by actually laying rails, but this method requires a long time. Therefore, in the present invention, the specimen a after the abrasion test described above was cut in half in the thickness direction as shown in FIG. 6, embedded in carbon resin, polished, and then the number of cracks generated in the sample was measured. . In addition, the evaluation of the crack crack resistance is ◎ when the number of cracks is 10% or more less than the standard steel material (steel No. 1 in Table 6), ○ when the number of cracks is equal to the standard material, and better than the standard material A case where the number of cracks was 5% or more was evaluated as Δ.

  From the results in Table 6, the component composition of C, Si, Mn, P, S and Cr is controlled within the proper range of the present invention, and the 0.2% proof stress is more than 500 MPa and less than 800 MPa with the production conditions as the scope of the present invention. It can be seen that the rails (Nos. 2 to 10) of the inventive examples controlled to have improved cracking resistance without lowering the wear resistance as compared with the reference material (No. 1). On the other hand, the Si of the present invention is higher than the range of the present invention. The rail No. 11 has excellent tensile characteristics and crack resistance, but has high electrical resistivity. In addition, the component composition is out of the scope of the present invention. The 12-19 rails have 0.2% proof stress outside the scope of the present invention, and the crack resistance is reduced compared to the reference material. Even when the component composition is within the range of the present invention, the production conditions are not preferred. The 20 to 24 rails have 0.2% proof stress outside the scope of the present invention, and the crack resistance is reduced compared to the reference material.

a: Wear test piece b: Tire test piece

Claims (3)

C: more than 0.75 mass% and less than 0.85 mass%, Si: 0.1 to 0.3 mass%, Mn: 0.7 to 1.1 mass%, P: 0.035 mass% or less, S: 0.0005 to 0 0.010 mass%, Cr: 0.05 to 0.25 mass%, the total of C, Si, Mn and Cr content is more than 1.9 mass% and less than 2.3 mass%, the balance is Fe and inevitable impurities A pearlite steel rail having an electrical resistivity ρ expressed by the following formula (1) of 21.1 to 23.7 μΩ · cm and a 0.2% proof stress of more than 500 MPa and less than 800 MPa.
ρ [μΩ · cm] = 0.95 × A + 12.4 (1)
Here, A = (13.8 * Si + 6.01 * Mn + 5.38 * Cr + 0.01) * ((1-0.15 * C) / (1-0.3 * C))
Here, the element symbol in the above formula is the content (mass%) of the element. In addition to the above component composition, V: 0.001 to 0.03 mass%, Cu: 0.5 mass% or less, Ni: 0.5 mass% or less, and Mo: 0.1 mass% or less The pearlite steel rail according to claim 1, comprising two or more kinds. The pearlite steel rail according to claim 1 or 2, wherein the tensile strength is more than 900 MPa and less than 1080 MPa, and the ratio of 0.2% proof stress to tensile strength is more than 55%.

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