JP2000144327A - Bainitic steel rail excellent in fitness with wheel and rolling fatigue damage resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the fitness with a wheel and rolling fatigue damage resistance required for a rail for a rapid-transit railway. SOLUTION: This bainitic steel rail excellent in fitness with a wheel and rolling fatigue damage resistance is the one in which the structure of the part to a depth of 0.2 to 1 mm from the corner part of the head of the rail and the surface of the top part is formed of the bainitic one having hardness of 180 to <240 Hv, and, moreover, the structure of the part on the side inner than the rail compared to this part and also at least to a depth of 15 mm from the corner part of the head of the rail and the surface part of the top part is formed of the bainitic one having hardness of 240 to 300 Hv.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rail which is required particularly in a high-speed operation section of a passenger railway and which has both familiarity with wheels and anti-rolling fatigue damage.

[0002]

2. Description of the Related Art In recent years, the speed of trains has been increased in passenger railways in order to improve transportation efficiency. Along with this, rails in straight sections where high-speed operation is mainly performed, due to repeated contact between the rails and wheels, such as crack damage on the rail head surface called dark spot damage,
Rolling fatigue damage is likely to occur. The dark spot damage is likely to occur on a rail in a high-altitude operation section of a passenger railway in which a rail having a conventional pearlite structure is used.

The present inventors have studied the relationship between the formation of a fatigue layer (fatigue damage layer, texture) generated by repeated contact between a rail and a wheel and the metallographic structure. As a result, in the pearlite structure having a layered structure of ferrite phase and cementite phase, the fatigue damage layer easily accumulates, and further, the texture is easily developed, whereas the granular hard carbide is formed on the soft ferrite structure ground. It has been found that the bainite structure in which is dispersed has a difficulty in accumulating a fatigue damage layer, and furthermore, a texture that triggers surface fatigue damage does not easily develop, and as a result, dark spot damage does not easily occur. Therefore, the following products and manufacturing methods have been developed as rails having a bainite structure. A high-strength rail exhibiting a bainite structure as-rolled by adding a large amount of alloying elements such as Mn, Cr, and Mo with a low carbon component (Japanese Patent Application Laid-Open No. 5-271871). Addition of alloying elements such as Mn, Cr, and Mo as low-carbon components, accelerated cooling of rails that retain high-temperature heat after hot rolling, or the heads of rails heated to high temperatures, and further controlled cooling A method for producing a high-strength bainite rail (JP-A-6-248347). A method of manufacturing a bainite rail in which alloy elements such as Mn, Cr, and Mo are added as a low-carbon component, and a rail holding high-temperature heat after hot rolling or a rail head heated to a high temperature is accelerated and cooled. (JP-A-6-316727).

[0004] The features of these rails are that, in order to stably generate a bainite structure excellent in rolling fatigue damage resistance, the amount of carbon is reduced as compared with conventional ordinary carbon steel rails, and at the same time, Mn, Cr, and Mo are reduced. In addition, a large amount of alloying elements such as are added, and an appropriate heat treatment is performed to secure the strength.

[0005]

In recent years, passenger railways have been introducing new types of vehicles having lighter weights and various wheel shapes for the purpose of improving transportation efficiency.
Along with this, in a section where many new vehicles having wheel shapes poorly matched with high-speed railways or rails in which a lightweight passenger railway with a small wheel travels, the bainite-structure rail of the present invention has a pearlite structure. Compared to the rails, the wheel is less familiar with the wheels, and the continuous action of excessive surface pressure due to the phenomenon of contact area causes creaking and cracks due to plastic deformation.

The following rails have been developed to improve the familiarity with such wheels. A high-strength rail with a surface damage at the head having a maximum hardness of 2 to 8 mm from the surface of the rail head (Japanese Patent Laid-Open No. 62-233301). A rail in which the surface layer (0.3 to 1.0 mm) of the rail head has a bainite structure, and the other metal structure has a pearlite structure, and a method of manufacturing the same (Japanese Patent Laid-Open No. 8-926).
No. 45). The feature of these rails is to soften only the surface layer of the rail head compared to conventional high-strength rails, in order to improve the familiarity with wheels in heavy-duty freight railways that mainly carry iron ore, or In addition, an easily wearable material is disposed on the surface layer to prevent the occurrence of initial surface damage due to lack of conformity, and at the same time, to maintain wear resistance for a long time.

However, these invented rails are used in high-speed railways in which passenger vehicles having a small wheel load travel, and in the early stages required for rails in sections where many passenger vehicles having wheel shapes with poor matching with rails travel. It does not improve the familiarity with the wheel, nor does it prevent rolling fatigue damage on the rail head surface called dark spot damage due to repeated contact between the rail and the wheel for a long time.

Therefore, the present inventors have improved the familiarity with the initial wheels required for the rails of a high-speed railway, and at the same time, reduced rolling fatigue damage (dark spot damage) due to repeated contact between the rails and the wheels. A method to prevent the occurrence for a long time was studied.

First, in order to examine the initial conformability, the strength characteristics of a rail having a bainite structure were examined by experiments. FIG. 1 shows an example of the relationship between the nominal stress and the elongation of the current pearlite-structured rail steel and bainite-structured rail steel. It was confirmed that the steel having the same strength level had a very high proof stress (0.2% proof stress) in the bainite-structured rail compared to the current pearlite-structured rail. As a result, plastic deformation is less likely to occur in the bainite-structured rail than in the pearlite-structured rail.
We found that the familiarity with the initial wheels became worse.

[0010] Based on the experimental results, the present inventors have conducted experiments to examine a method for reducing the proof stress of the bainite structure. As a result, it was confirmed that the proof stress of the bainite structure had a good correlation with the hardness (strength) of the bainite structure, and that the hardness of the bainite structure had only to be reduced to reduce the proof stress of the bainite structure. However, in general, when the hardness of the bainite structure is reduced, there arises a problem that damage due to plastic deformation such as creaking or flaking tends to occur. Therefore, the present inventors have improved the familiarity with the initial wheel, and prevented damage due to plastic deformation such as creaking and flaking, and at the same time, anti-rolling fatigue damage (dark spot damage resistance) for a long period of time. The hardness distribution of the rail head that secures the characteristics) was examined by experiments. As a result, by arranging a bainite structure having a low hardness in a certain range of the rail head surface and arranging a bainite structure having a higher hardness than the head surface inside the rail, the proof stress (hardness) of the head surface is low. The plastic deformation of the bainite structure ensures the initial conformity with the wheel, and before the metal is damaged by excessive metal flow (plastic deformation), the top of the wheel is worn by rolling contact with the wheel and the internal hardness is reduced. It was confirmed that the high bainite structure prevented the progress of plastic deformation and prevented the occurrence of rolling fatigue damage (dark spot damage) for a long period of time.

However, in order to stably generate a bainite structure, it is necessary to reduce the amount of carbon as compared with the conventional ordinary carbon steel rail and to add a large amount of alloying elements such as Mn, Cr, and Mo. As a result, the electric resistance value of the rail increases depending on the component system of the rail. Therefore, the present inventors have studied a method for securing electrical conductivity similar to that of a current pearlite structure rail in the bainite structure rail of the above invention. As a result, the amount of Mn added to the steel, which is effective for stably forming a bainite structure with a low carbon component, is increased, and further, the amount of Cr and Mo alloys is optimized to improve the compatibility with wheels, It was confirmed that rolling fatigue resistance was ensured, and at the same time, electrical resistance could be reduced.

That is, the present invention provides a rail exhibiting a bainite structure, which is required for a high-speed operation section of a passenger railway, and has a conformability with wheels, a rolling fatigue resistance, and an electric conductivity. Aim.

[0013]

SUMMARY OF THE INVENTION The present invention achieves the above object, and the gist of the invention is as follows: (1) The rail has a depth of 0.2 to 0.2 mm from the surface of the head corner and the top of the rail. The hardness up to 1mm is Hv180-24
A bainite structure having a hardness of Hv 240 to 300, wherein the bainite structure has a hardness Hv of 240 to 300, and the bainite structure includes a bainite structure having a hardness of Hv 240 to 300, which is on the inner side of the rail and at least 15 mm deep from the surface of the head corner and the crown. A bainite steel rail excellent in conformability to wheels and rolling fatigue resistance, characterized by comprising: (2) In weight%, C: 0.15 to 0.45%, Si: 0.10 to 0.50%, Mn: more than 0.50 to 1.80%, Cr: 0.20 to 1.80 %, Mo: 0.01 to 0.60%, P: ≦ 0.025%, S: ≦ 0.025%, the balance being iron and unavoidable impurities, the head of which is a steel rail. Hardness Hv180 is a part from the surface of the corner and the crown to a depth of 0.2 to 1 mm.
A bainite structure having a hardness Hv of 240 to 300, which is composed of a bainite structure having a hardness of Hv 240 to 300 from the surface of the head corner and the top of the rail to a depth of at least 15 mm. A bainite-based steel rail having excellent conformability to wheels and excellent rolling fatigue resistance, characterized by comprising a structure. (3) In weight%, C: 0.15 to 0.45%, Si: 0.10 to 0.50%, Mn: more than 0.50 to 1.80%, Cr: 0.20 to 1.80 %, Mo: 0.01 to 0.60%, P: ≦ 0.025%, S: ≦ 0.025%, Cu: 0.05 to 0.50%, Ni: 0.05 To 1.00%, Ti: 0.01 to 0.05%, V: 0.01 to 0.30%, Nb: more than 0.01 to 0.05%, B: 0.0005 to 0.0050% A steel rail comprising one or more of the following, with the balance being iron and unavoidable impurities, the hardness of which is 0.2 to 1 mm in depth from the surface of the head corner and top of the rail. It is composed of a bainite structure having a Hv of less than 180 to 240, and is further inside the rail than this part,
In addition, at least a portion having a depth of at least 15 mm from the surface of the head corner and top of the rail has a hardness of Hv240 to Hv3.
A bainite-based steel rail comprising a bainite structure of No. 00 and having excellent conformability to wheels and resistance to rolling fatigue damage. (4) The electric resistance value according to the following equation 1 is 26.5 μΩ · c.
m. The bainite steel rail according to (1), (2) or (3), which is excellent in conformability and resistance to rolling fatigue damage according to (1), (2) or (3). * Electrical resistance calculation formula (μΩ · cm) Calculation formula = 10.1 + 6.1 [C] +13.8 [Si] +6.3 [Mn] +5.2 [Cr] +17.2 [P] +11.2 [S] +2.9 [Ti] + 2.5 [Ni] + 6.O [Cu] +5.5 [V] +3.3 [Mo] Formula 1 where [element] is% by weight.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. (1) Hardness of bainite structure and its range From the surface of the corner of the head and the top of the rail to the depth of 0.2 to 1 mm, hardness Hv 180 to 2
The reason why the bainite structure is less than 40 will be described.

First, the reason why the hardness of the bainite structure in this portion is limited to the range of Hv 180 to less than 240 will be described. If the hardness is less than Hv180, a large metal flow (plastic deformation) is generated on the rail head surface, and before this metal flow is worn by rolling contact with the wheel,
Crack damage occurs from the metal flow, causing damage such as creaking and flaking. The hardness is Hv240
Above, plastic deformation is less likely to occur due to an increase in proof stress, and as a result, it becomes impossible to secure the initial conformability to the wheel.
The range was limited to less than 40.

Next, the reason why the bainite structure having a hardness Hv of less than 180 to 240 is a portion having a depth of 0.2 to 1 mm from the surface of the rail head corner and the top of the rail will be described. When the depth is less than 0.2 mm, the area for securing the familiarity with the initial wheel is small, and before the familiarity with the wheel is generated, the bainite structure of the head surface having a hardness of less than Hv 180 to 240 is worn due to wear. It disappears, and a bainite structure with high internal hardness appears on the rolling surface, so that it cannot be sufficiently adapted to the wheel. Also, when the depth is 1.
If it exceeds 0 mm, the bainite structure having a hardness Hv of less than 180 to 240 is plastically deformed, and even after sufficient conformity with the wheel is generated, a plastically deformed region remains, and the rolling surface is squeezed by repeated rolling contact with the wheel. Since damage such as cracking and flaking occurs, the part consisting of bainite structure with a hardness of less than Hv 180 to 240 is limited to a part from the surface of the head corner and top of the rail to a depth of 0.2 to 1 mm. did.

As described above, the rail head surface is hardened by Hv1.
A bainite structure of less than 80 to less than 240, and a portion inside the rail from the surface of the rail head described above and at least a depth of 15 mm from the surface of the head corner and the top of the rail, having a hardness of Hv240 The reason for using a bainite structure of ~ 300 will be described.

First, the reason why the hardness of the bainite structure in this portion is limited to the range of Hv 240 to 300 will be described. If the hardness is less than Hv240, it is difficult to secure the basic strength and wear resistance required for the rail. Furthermore, when used in a gentle curve section, sufficient familiarity with the wheel is generated, and the hardness Hv180 to 2
After less than 40 bainite structures have disappeared due to wear,
G. FIG. C. A metal flow is generated in the part due to strong contact between the rail and the wheel, and as a result, surface damage such as creaking cracks and flaking is likely to occur. The hardness is Hv
If it exceeds 300, the difference in hardness between the head surface and the inside becomes large, and the strain generated from the external force acting on the rolling surface of the rail concentrates on the interface between the head surface and the inside, resulting in crack damage from the interface Occurs, the hardness of the bainite structure is increased by Hv
It was limited to the range of 240 to 300.

Next, the reason why the portion composed of the bainite structure having a hardness of Hv 240 to 300 is at least 15 mm deep from the surface of the head corner and top of the rail will be described. As for the rail head, the wear life of the rail used in the straight section of the high-speed railway is 15 mm, and therefore, when the range having a bainite structure having a hardness of Hv 240 to 300 is less than 15 mm, the rail head is required. Small area to prevent rolling fatigue damage,
Rolling fatigue damage such as dark spot damage occurs before the wear life is reached, and a sufficient life improvement effect cannot be expected. Therefore, the portion made of bainite structure is limited to at least 15 mm in depth.

Here, FIG. 2 shows the designation of the surface position and the hardness of the bainite structure in the cross section of the head of a bainite-based steel rail which is excellent in conformity with the wheel of the present invention and resistance to rolling fatigue damage. In the rail head, reference numeral 1 denotes the top of the head, reference numeral 2 denotes a corner of the head, reference numeral 3 (grid line portion:
The head portion) is a bainite structure having excellent compatibility with wheels having a hardness of less than Hv 180 to 240, and reference numeral 4 (hatched portion: inside the head) is a bainite structure having a hardness of Hv 240 to 300 and excellent in rolling fatigue resistance. It is. One of the head corner portions 2 is a gauge corner (GC) portion that mainly contacts the wheel.

As shown in FIG. 2, the hardness Hv 180 to 24
If the bainite structure of less than 0 exists in the grid line portion (reference numeral 3) of the rail head surface, the initial adaptation to the wheel is sufficiently secured by the plastic deformation of the bainite structure. Also,
The bainite structure having a hardness of Hv 240 to 300 can prevent rolling fatigue damage (dark spot damage) over a long period of time if it is present at least in a hatched portion (reference numeral 4) therein.

FIG. 3 is a schematic diagram showing the hardness distribution of the head surface section of the rail steel according to the present invention. As the hardness distribution of the rail steel of the present invention, as shown by reference numerals a and b, 0.2 to below the head surface.
It is desirable that the hardness changes gently within the range of 1 mm and falls within the respective hardness ranges shown in the above-mentioned limited range. Depending on the manufacturing method of the rail rolling material, a hardness distribution in which the hardness changes abruptly in the range of 0.2 to 1 mm below the head surface may be obtained as shown by a symbol c. Also in the distribution, if the hardness range of the grid line portion (reference numeral 3) of the rail head surface portion and the hatched portion (reference numeral 4) inside the above range is within the above-mentioned limited range, initial familiarity with the wheel, durability for a long time. Since sufficient rolling fatigue damage can be obtained, a rail having such a hardness distribution is also included as part of the rail steel of the present invention. The hardness distribution of the hatched portion (reference numeral 4) from 0.2 to 1 mm below the head surface to 15 mm below the head surface is not particularly limited. Is secured and there is no problem in use.

(2) Chemical Components First, the reasons for determining the chemical components of the rail as described above will be described. C is an essential element for ensuring the strength and wear resistance of the bainite structure, but if less than 0.15%, a ferrite structure is formed in the bainite structure, and the strength and wear resistance required for the bainite rail. Is difficult to secure. On the other hand, if the content exceeds 0.45%, a large amount of pearlite structure harmful to the occurrence of rolling fatigue in the bainite structure is likely to be formed, and the bainite transformation rate is significantly reduced, and a martensite structure harmful to rail toughness. Is easily generated, so the C amount is 0.15 to
Limited to 0.45%.

[0024] Si is an element that improves the strength by forming a solid solution in the base ferrite in the bainite structure. However, if it is less than 0.10%, the strength cannot be expected to be improved. Further, if added in excess of 0.50%, the weldability is reduced due to the formation of oxides, and the electrical resistance of the rail is excessively increased, so the amount of Si is limited to 0.10 to 0.50%. did.

Mn is an element indispensable for enhancing the hardenability of steel and for stably forming a bainite structure similarly to C. If the Mn content is 0.50% or less, the effect is weak, and depending on the combination of the added elements, a ferrite structure harmful to wear resistance and a pearlite structure harmful to surface damage resistance are likely to be formed in the bainite structure. . If the content exceeds 1.80%, a martensite structure harmful to the toughness of the rail is likely to be formed in the bainite structure, and the electric resistance of the rail is excessively increased.
The amount of n was limited to more than 0.50 to 1.80%.

Cr is an important element for finely dispersing carbides in the bainite structure and for securing strength.
If it is less than 0.20%, the effect is weak, and it is difficult to stably obtain a bainite structure depending on the combination of the additional elements. On the other hand, if the content exceeds 1.80%, a martensitic structure is likely to be formed on the surface of the rail head, reducing the toughness and wear resistance of the rail and excessively increasing the electrical resistance of the rail. .20-1.80
%.

Mo, like Mn or Cr, stably forms a bainite structure.
r is a promising element that can improve the strength without extremely increasing the electric resistance,
If it is less than 1%, the contribution to strength is small, and if it is added more than 0.60%, a martensite structure harmful to the toughness of the rail is generated in the segregated portion and the electric resistance of the rail is excessively increased. The amount of Mo was limited to 0.01 to 0.60%.

P and S are not elements to be added intentionally, but if each contains more than 0.025%, a segregation zone is easily formed and a martensitic structure or the like which lowers toughness is easily formed. In order to excessively increase the electric resistance of the rails, each is limited to 0.025% or less.

In the rail manufactured with the above composition, one or more of the following elements are added as necessary for the purpose of preventing strength, ductility, toughness and deterioration of the material during welding. . Cu: 0.05-0.50%, Ni: 0.05-1.
00%, Ti: 0.01 to 0.05%, V: 0.0
1 to 0.30%, Nb: more than 0.01 to 0.05%, B
: 0.0005 to 0.0040%

Cu is an element which improves the strength without deteriorating the toughness of the steel, and its effect is greatest in the range of 0.05 to 0.50%. Cu content is 0.05 to 0.5
Limited to 0%.

Ni is an element that stabilizes austenite and has the effect of lowering the bainite transformation temperature, refining the bainite structure, and improving the toughness.
If it is less than 5%, the effect is remarkably small.
%, The amount of Ni is limited to 0.05 to 1.00% in order to greatly reduce the bainite transformation rate and to easily generate a martensite structure harmful to the toughness of the rail.

Titanium is used to reduce the size of austenite crystal grains during rail rolling heating by utilizing the fact that Ti carbide and Ti nitride precipitated during melting and solidification do not dissolve even at the high temperature of rail rolling heating. It also contributes to improving the toughness of the joint. However, if it is less than 0.0005%, the effect is small, and if it exceeds 0.050%, coarse Ti carbon / nitride is generated, which becomes a starting point of fatigue damage during use of the rail,
In order to generate cracks, the amount of Ti is set to 0.005 to 0.05.
Limited to 0%.

V increases the strength of the bainite structure by precipitation hardening due to V carbide and V nitride generated in the cooling process during hot rolling, and at the same time, in the heat-affected zone reheated to a temperature range near the Ac1 point, V is an effective component for generating carbon / nitride in a relatively high temperature range and preventing softening of the bainite structure in the heat-affected zone of the welded joint. However, if it is less than 0.01%, the effect is sufficiently expected. No further effect can be expected even if added over 0.30%, and the electrical resistance is unnecessarily increased.
Limited to.

Like V, Nb increased the strength of the bainite structure by precipitation hardening by Nb carbon / nitride generated in the cooling process during hot rolling, and was reheated to a temperature range near the Ac1 point. In the heat-affected zone, Nb is a component effective for stably generating Nb carbon / nitride from a low temperature range to a high temperature range and preventing softening of a bainite structure in a heat-affected zone of a welded joint. The effect cannot be expected at 0.01% or less, and when excessive addition exceeding 0.05% is performed, Nb
The amount of Nb was limited to more than 0.01 to 0.05% since the intermetallic compounds and coarse precipitates of (1) generated to lower the toughness.

B is an element that suppresses the formation of a pro-eutectoid ferrite structure formed from the prior austenite grain boundary and a pearlite structure that is transformed with the structure, and stably forms a bainite structure by increasing hardenability. But,
If less than 0.0005%, the effect is weak, and 0.0050%
%, A large amount of nitrides and carbides of B are formed at the austenite grain boundaries, conversely reducing the hardenability,
The amount of B was limited to 0.0005 to 0.0050% in order to easily generate a proeutectoid ferrite structure or a pearlite structure.

The rail steel having the above-mentioned composition is melted in a commonly used melting furnace such as a converter or an electric furnace, and the molten steel is subjected to an ingot-bulking method or a continuous casting method. After producing blooms or slabs by any method,
Manufactured on rails by hot forming and rolling. Further, if necessary, a heat treatment is performed to control the material of the head portion of the rail.

(3) Electric resistance value The reason for limiting the electric resistance value (μΩ · cm) to a calculated value of 26.5 μΩ · cm or less in claim 4 will be described. Table 1 shows the chemical composition of a typical passenger railway rail,
6 shows an example of an electric resistance calculation value and an actual measurement value according to Expression 1.

[0038]

[Table 1]

* Electric resistance calculation formula (μΩ · cm) Calculation formula = 10.1 + 6.1 [C] +13.8 [Si] +6.3 [Mn] +5.2 [Cr] +17.2 [P] +11.2 [S] +2.9 [ Ti] +2.5 [Ni] + 6.O [Cu] +5.5 [V] +3.3 [Mo] (1) where [element] is% by weight. In the above electric resistance calculation formula, when the corresponding steel component is not contained, the term of the component is set to zero, and even if a component other than that shown in the calculation formula is contained, it is not included in the calculation.

As shown in Table 1, the measured value of the electric resistance of the rail has a very good correlation with the value calculated by the formula 1. Considering the manufacturing variation of rail chemical components,
When the calculated electrical resistance exceeds 26.5 μΩ · cm,
It is considered that there is a high possibility that the electric resistance value increases in actual measurement as compared with a typical railroad rail with a high carbon pearlite structure currently used. Therefore, when the calculated value of the electric resistance exceeds 26.5 μΩ · cm, the electric resistance of the rail increases more than that of the current rail, the track current, which is the power source of the train, decreases, and the train operates in a dense line section. Since it is expected that a problem in operation such as a decrease in train running speed due to a decrease in current will occur, the electric resistance of the rail is limited to a calculated value of 26.5 μΩ · cm or less.

The metal structure of the rail steel of the present invention is desirably a bainite structure. However, depending on the combination of the component systems, the cooling method of the rail, and the segregation state of the material, a trace amount of pearlite structure and martensite structure may be contained in the bainite structure. In some cases, a pro-eutectoid ferrite structure may be formed. However, even if these structures are formed in trace amounts in the bainite structure, they do not significantly affect the rolling fatigue resistance, wear resistance and strength of the rail. Includes mixed organizations.

As described above, the bainite-based rail of the present invention has the familiarity with wheels, anti-rolling fatigue damage, and electrical conductivity required for a high-speed operation section of a passenger railway.

[0043]

Next, an embodiment of the present invention will be described. Table 2 shows the chemical composition of the rail steel of the present invention, the structure and hardness of the material of the head and its region, and the structure and hardness of the material of the inner surface of the head and its region. Further, the results of a water lubrication rolling fatigue test by a rolling fatigue damage tester shown in FIG. 4, the calculated electrical resistance calculated by the following equation 1, and the measured results of the rail electrical resistance shown in FIG. 5 are also shown.

[0044]

[Table 2]

Table 3 shows the chemical composition of the comparative rail steel,
The texture / hardness of the material on the head surface and its area, and the texture / hardness of the material on the inner surface of the head and its area are shown. Further, FIG.
The results of water lubricated rolling fatigue test by the rolling fatigue damage tester shown in the table, the electrical resistance calculated by the following equation 1,
The measured results of the rail electric resistance shown in FIG. 5 are also shown.

[0046]

[Table 3]

FIG. 6 shows the rail steel of the present invention (reference numeral:
A, D, and I) show the hardness distribution of the head surface section. FIG.
Shows the head surface section hardness distribution of the comparative rail steel (symbol: L, M, N).

* Electric resistance calculation formula (μΩ · cm) Calculation formula = 10.1 + 6.1 [C] +13.8 [Si] +6.3 [Mn] +5.2 [Cr] +17.2 [P] +11.2 [S] +2.9 [ Ti] +2.5 [Ni] + 6.O [Cu] +5.5 [V] +3.3 [Mo] (1) where [element] is% by weight.

The configuration of the rail is as follows. Inventive rail steel 1 (8 pieces) code: A, B, D, F,
H, I, J, K Within the above component ranges, a structure having a hardness of Hv less than 180 to 240 and a bainite structure having a depth of 0.2 to 1 mm starting from the surface of the head corner and the top of the rail is defined as a structure. Yes,
15 mm deep from the bainite structure and starting from the surface of the head corner and top of the rail
The bainite steel rail for high-speed railways, which is excellent in conformability to wheels and rolling fatigue resistance, characterized in that the structure in the range of is a bainite structure having a hardness of Hv 240 to 300. Reference rail steel 2 of the present invention 2 (three) Code: C, E, G Within the above component range, the structure having a depth of 0.2 to 1 mm starting from the surface of the head corner and top of the rail is hardened. A bainite structure having a Hv of less than 180 to 240,
15 mm deep from the bainite structure and starting from the surface of the head corner and top of the rail
Is a bainite structure having a hardness of Hv 240 to 300, and an electric resistance value according to Formula 1 is 26.5 μΩ.
・ Familiarity with wheels, which is not more than cm
A bainite steel rail for high-speed railways with excellent rolling fatigue resistance and electrical conductivity. Reference rail steel (11 pieces) Code: L to V Code L to O: Within the above component range, hardness of the rail head and its range are out of the above range. Symbols P to V: comparative rail steels outside the above component range.

The rolling fatigue test was performed under the following conditions.
(See Fig. 4)-Test piece shape Rail: 60kg rail x 2.5m Wheel: Conventional wire shape wheel (diameter 920mm)-Test load Radial load: 49000N (5 tons) Thrust load: 0 to 2940N (intermittent load) -Lubrication Dry + water (intermittent water supply)-Number of repetitions Up to 10 mm in surface damage and maximum wear (If no damage occurs, stop the test after 10 million times)

The measurement of the rail electric resistance was carried out in the following manner. As a method for measuring the electric resistance of the rail shown in FIG. 5, a voltage drop method was used. As a measuring method, current terminals were attached to the pillars on both sides of the rail end, and the reference current was 25A.
And set the voltage terminal on the rail foot at a position about 1 m inside the current terminal. From the current value and the voltage value thus measured, the electric resistance was obtained by the following equation. ρ (μΩ · cm) = (ρ ₂₀ × A) × 10 ⁻¹ / LA A: cross-sectional area of measurement rail (mm ² ), L: distance between voltage terminals (mm) where ρ ₂₀ is at 20 ° C. The following formula was used for the resistance value (μΩ) of the measurement material converted to the value. ρ ₂₀ = ρ _t / {1 + α (t−20)} ρ _t ; electric resistance measured at temperature t, α was obtained from a change in resistance value actually measured by actually changing the rail temperature with a temperature correction coefficient.

[0052]

As shown in Tables 2 and 3, in the rail steel according to the present invention, the range of bainite structure at the rail head and its hardness, the appropriate selection of chemical components and the amount of addition thereof were adjusted. As shown in FIG. 6, by arranging a bainite structure having a lower hardness in a certain range of the front surface of the rail and arranging a bainite structure having a higher hardness than the front surface inside the rail, the proof stress (hardness) of the front surface is obtained. The plastic deformation of the low bainite structure ensures the initial conformity with the wheel, and before the damage occurs due to excessive metal flow (plastic deformation), the surface of the head wears due to rolling contact with the wheel and the internal hardness The high bainite structure prevents the plastic deformation from progressing, thereby making it possible to prevent the occurrence of rolling fatigue damage (dark spot damage) for a long period of time. Further, the electric resistance value of the invention rail steel according to the formula 1 is 26.5 μΩ.
By setting the diameter to not more than cm, the rail steel of the present invention can impart not only conformability to wheels and resistance to rolling contact fatigue damage but also electrical conductivity as shown by symbols C, E and G. According to the present invention, it has become possible to provide a rail, which is required particularly in a high-speed operation section of a passenger train, and which has both familiarity with wheels, anti-rolling fatigue damage, and electric conductivity.

[Brief description of the drawings]

FIG. 1 is a chart showing an example of the relationship between the nominal stress and the elongation value of a current rail steel having a pearlite structure and a rail steel having a bainite structure.

FIG. 2 is a diagram showing the designation of the surface position and the configuration of the hardness of the bainite structure in the cross section of the head of the rail steel of the present invention.

FIG. 3 is a schematic diagram of a head surface section hardness distribution of the rail steel of the present invention.

FIG. 4 is a schematic diagram of a rolling fatigue damage tester.

FIG. 5 is a schematic diagram showing a method for measuring electric resistance.

FIG. 6 is a diagram showing an example of a head surface section hardness distribution of the rail steel (symbols: A, D, I) of the present invention.

FIG. 7 is a view showing an example of a head surface section hardness distribution of comparative rail steel (symbols: L, M, N, O).

[Explanation of symbols]

1: Top of the crown 2: Corner of the head 3: Bainite structure excellent in conformability to wheels having a hardness of Hv less than 180 to 240 4: Bainite structure excellent in rolling fatigue resistance to a hardness of Hv 240 to 300 V5: Rail Slider for movement 6: Rail 7: Wheel 8: Motor 9: Load device

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[Procedure amendment]

[Submission date] November 13, 1998 (1998.11.
13)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

FIG. 3 is a schematic diagram showing the hardness distribution of the head surface section of the rail steel according to the present invention. As the hardness distribution of the rail steel of the present invention, the hardness changes gradually in the range of 0.2 to 1 mm below the head surface as shown in the rail steel of the symbol a and the rail steel of the symbol b , It is desirable that the hardness be within the range of hardness. In addition, depending on the manufacturing method of the rail rolled material, as shown in the rail steel of the reference symbol c , the lower part of the head surface has a thickness of 0.
The hardness changes rapidly within the range of 2 to 1 mm (black circles over white circles)
In some cases, a hardness distribution can be obtained, but even in such a hardness distribution, the hardness range of the grid line portion (reference numeral 3) of the rail head surface portion and the hatched portion (reference numeral 4) inside thereof is the above-described limited range. Within this range, the initial conformability with the wheel and the rolling fatigue resistance over a long period of time can be sufficiently obtained, so that a rail having such a hardness distribution is also included in a part of the rail steel of the present invention. The hardness distribution of the hatched portion (reference numeral 4) from 0.2 to 1 mm below the head surface to 15 mm below the head surface is not particularly limited. Is secured and there is no problem in use.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction contents]

FIG. 6 shows the rail steel of the present invention (reference numeral:
A, D, and I) show the hardness distribution of the head surface section. In the figure, steel I
The black circles and white circles indicate rapid changes in hardness.
You. FIG. 7 shows comparative rail steels (symbols: L, M, N).
2 shows the hardness distribution of the head surface section.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction contents]

[0052]

As shown in Tables 2 and 3, in the rail steel according to the present invention, the range of bainite structure at the rail head and its hardness, the appropriate selection of chemical components and the amount of addition thereof were adjusted. As shown in FIG. 2 , a bainite structure having a lower hardness is arranged in a certain range of the front surface of the rail, and a bainite structure having a higher hardness than the front surface is arranged inside the rail, so that the yield strength (hardness) of the front surface is improved. The plastic deformation of the low bainite structure ensures the initial conformity with the wheel, and before the damage occurs due to excessive metal flow (plastic deformation), the surface of the head wears due to rolling contact with the wheel and the internal hardness The high bainite structure prevents the plastic deformation from progressing, thereby making it possible to prevent the occurrence of rolling fatigue damage (dark spot damage) for a long period of time. Further, the electric resistance value of the invention rail steel according to the formula 1 is 26.5 μΩ.
By setting the diameter to not more than cm, the rail steel of the present invention can impart not only conformability to wheels and resistance to rolling contact fatigue damage but also electrical conductivity as shown by symbols C, E and G. According to the present invention, it has become possible to provide a rail, which is required particularly in a high-speed operation section of a passenger train, and which has both familiarity with wheels, anti-rolling fatigue damage, and electric conductivity.

Claims (4)

[Claims] 1. The hardness of the rail is from Hv180 to 0.2 mm in depth from the surface of the corner and top of the rail.
A bainite structure having a hardness Hv of 240 to 300, which is composed of a bainite structure having a hardness of Hv 240 to 300 from the surface of the head corner and the top of the rail to a depth of at least 15 mm. A bainite-based steel rail having excellent conformability to wheels and excellent rolling fatigue resistance, characterized by comprising a structure. 2. In% by weight, C: 0.15 to 0.45%, Si: 0.10 to 0.50%, Mn: more than 0.50 to 1.80%, Cr: 0.20 to 1 80%, Mo: 0.01 to 0.60%, P: ≦ 0.025%, S: ≦ 0.025%, the balance being iron and unavoidable impurities. The portion from the surface of the head corner and the crown to the depth of 0.2 to 1 mm has a hardness of Hv180.
A bainite structure having a hardness Hv of 240 to 300, which is composed of a bainite structure having a hardness of Hv 240 to 300 from the surface of the head corner and the top of the rail to a depth of at least 15 mm. A bainite-based steel rail having excellent conformability to wheels and excellent rolling fatigue resistance, characterized by comprising a structure. 3. In% by weight, C: 0.15 to 0.45%, Si: 0.10 to 0.50%, Mn: more than 0.50 to 1.80%, Cr: 0.20 to 1 .80%, Mo: 0.01 to 0.60%, P: ≤ 0.025%, S: ≤ 0.025%, Cu: 0.05 to 0.50%, Ni: 0 0.05-1.00%, Ti: 0.01-0.05%, V: 0.01-0.30%, Nb: more than 0.01-0.05%, B: 0.0005-0. A steel rail containing one or more of 0050%, the balance being iron and unavoidable impurities, wherein a part of the rail from the surface at the head corner and top to a depth of 0.2 to 1 mm is formed. It consists of a bainite structure having a hardness of less than Hv 180 to 240, and further inside the rail than this part,
In addition, at least a portion having a depth of at least 15 mm from the surface of the head corner and top of the rail has a hardness of Hv240 to Hv3.
A bainite-based steel rail comprising a bainite structure of No. 00 and having excellent conformability to wheels and resistance to rolling fatigue damage. 4. The electric resistance according to the following equation 1 is 26.5 μm.
The bainite steel rail according to claim 1, 2 or 3, wherein the bainite steel rail is excellent in conformability and rolling fatigue damage resistance. * Electrical resistance calculation formula (μΩ · cm) Calculation formula = 10.1 + 6.1 [C] +13.8 [Si] +6.3 [Mn] +5.2 [Cr] +17.2 [P] +11.2 [S] +2.9 [Ti] + 2.5 [Ni] + 6.O [Cu] +5.5 [V] +3.3 [Mo] Formula 1 where [element] is% by weight.