JP3267124B2 - High-strength rail excellent in delayed fracture resistance, wear resistance and toughness, and a method for manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to not only the abrasion resistance required for high-speed trains or rails for mining railways under conditions of high axle load, but also the toughness required in cold regions. The present invention relates to a high-strength rail excellent in delayed fracture resistance and a method for manufacturing the same.

[0002]

2. Description of the Related Art Heretofore, railroad rails have been focused only on increasing strength from the viewpoint of placing importance on wear resistance, rolling contact fatigue resistance and the like. However, in recent years, with the speeding up of railway transportation and the increase in the axle load, rail use conditions have become increasingly severe. Particularly in cold regions such as Russia and Canada, high-strength rails with excellent toughness have been required.
However, the toughness of the current ordinary rail is as low as 2 mm U notch Charpy absorbed energy of less than 10 J at 20 ° C.
It is also difficult to increase J.

[0003] As means for improving the strength and toughness of the rail, the following two heat treatment methods have been disclosed. After the rails have been cooled once after the end of rail rolling, A
c An off-line heat treatment method of reheating to _three or more points to perform accelerated cooling (JP-A-63-128123). After the end of rail rolling, an on-line heat treatment method in which accelerated cooling is performed as it is at a temperature of at least _three points of Ar (Japanese Patent Publication No. Sho 6
No. 3-23244).

Further, the conventional rail has a fine pearlite structure from the viewpoint of enhancing strength and abrasion resistance. However, it is impossible to greatly improve the toughness of the pearlite structure. The following rail having the bainite structure of the following is also disclosed.

[0005] A rail having a bainite structure in which the C content is somewhat lower than that of the conventional component, a difference in hardness is provided between the top and the corner of the rail, and the resistance to rolling fatigue damage is improved (Japanese Patent Laid-Open No. Hei 2- 282448). A rail having a bainite structure effective for lowering the C content as compared with the conventional component and improving the rolling fatigue resistance of the rail head surface (Japanese Patent Laid-Open No. 5-271871).

[0006]

However, the above-described heat treatment methods and rails have the following problems, respectively. In the above method, the steel is transformed at a low temperature by accelerated cooling, and the structure can be refined, and the structure can be refined by repeating the transformation. Therefore, a rail having high strength and high toughness can be obtained. However, reheating is performed after cooling, which is not preferable from the viewpoint of thermal efficiency.

In the above method, accelerated cooling is performed as it is after rolling is completed, so that thermal efficiency is good. However, although conventional steel rails can improve strength by accelerated cooling, it is difficult to significantly improve toughness.

FIG. 1 shows the relationship between the hardness and wear of a rail having a pearlite structure, a bainite structure and a tempered martensitic structure. It can be seen that the bainite structure has a larger wear amount than the pearlite structure, even with the same hardness. The rails described above have been conceived in order to make up for the defect of the wear resistance of the bainite structure.

However, a rail having such a bainite structure has a drawback that when used under heavy-axial load conditions such as a mine railway, the rail life is significantly shortened. In addition, it is necessary to consider the occurrence of delayed fracture due to the increase in strength under the condition of a heavy axial load.

Accordingly, the present invention is directed to a high-strength steel having excellent delayed fracture resistance and toughness which does not cause the above-mentioned problem in characteristics even under severe conditions such as a cold region and a heavy axial load condition. It is an object to provide a strength rail and an inexpensive manufacturing method thereof.

Specifically, the rail has a tensile strength of 1300
MPa or more, Charpy absorbed energy of 2mmU notch at 20 ° C. or higher 30 J, delayed fracture resistance (K _1SCC) is an object of the rail is 100 Kgf · mm ^-3/2 or more. If the tensile strength is 1300 MPa or more,
This is because abrasion resistance equal to or higher than that of a conventional pearlite-type high-strength rail can be obtained, and if the toughness is 30 J or more, characteristics superior to Russia's standard 18 J by 1.5 times or more can be obtained.

[0012] The delayed fracture properties are evaluated by _K lscc obtained by using a cantilever-type delayed fracture testing machine, the stress from the rail, in the case of a severe 130kg class bolt steel notch condition,
If _K lscc is 100kgf ^{· m -3/2} or more,
Since it is known that there is no problem in using the rail, this value was used as a criterion.

[0013]

[Means for Solving the Problems]

(1) The first invention is a high-strength rail having the following characteristics (the component composition is wt%) and excellent in delayed fracture resistance, wear resistance and toughness. (A) C: 0.2 to 0.5%, Si: 0.1 to 2% Mn: 1 to 4%, P: 0.035% or less, S: 0.03
5% or less, Cr: 0.3 to 3% Nb: 0.05 to 0.1% A rail having a component composition substantially composed of iron, and (b) a bainite structure of the rail. (C) The hardness of the head and the corner of the head of the rail is between 400 and 500 in HV at any position.

(2) In the second invention, in addition to the component composition of the rail of the first invention, Ni: 0.1 to 1%, Mo: 0.1
A high-strength rail excellent in delayed fracture resistance, abrasion resistance and toughness, characterized in that it contains at least one kind of V, 0.01 to 0.1%.

(3) In the third invention, in the first and second inventions, the rail has a tensile strength of 1300 MPa or more,
Charpy absorbed energy of 2 mm U notch at 0 ° C is 30 J or more, and delayed fracture resistance (K _1SCC ) is 100 kg.
It is a high-strength rail excellent in delayed fracture resistance, abrasion resistance and toughness of not less than f · mm ^−3/2 .

(4) The fourth invention comprises the following steps.
Characterized in that (the component composition is Wt%)
This is a method for manufacturing a high-strength rail excellent in fragility, wear resistance and toughness. (A) C: 0.2 to 0.5%, Si: 0.1 to 2% Mn: 1 to 4%, P: 0.035% or less, S: 0.035% or less, Cr: 0.3 Nb: 0.05 to 0.1% A steel having a component composition substantially consisting of iron is prepared. (B) The steel is hot-rolled on a rail at a finishing temperature of 800 to 1000 ° C. (C) cooling the rail online from a temperature above the bainite transformation start point to 400 ° C. or less, at a cooling rate of 5 ° C./sec.
Cool below.

(5) In a fifth aspect based on the fourth aspect, the steel composition further comprises Ni: 0.1-1%, M
O: 0.1 to 1%, V: 0.01 to 0.1%, one or more of which are excellent in delayed fracture resistance, wear resistance and toughness. This is a method for manufacturing a high-strength rail.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The component composition (wt.
%), Microstructure, hardness and manufacturing conditions are described below.

C: 0.2-0.5%. C is an essential element for ensuring the strength and abrasion resistance of the steel, and if it is less than 0.2%, it is difficult to secure the hardness as rail steel at low cost. On the other hand, if it exceeds 0.5%, a uniform bainite structure cannot be obtained on the rail head, and the toughness is deteriorated. Therefore, the above range is set.

Si: 0.1 to 2%. Si is not only effective as a deoxidizing agent, but also is an element that forms a solid solution with ferrite in a bainite structure to increase the strength and improve the wear resistance. %, The steel becomes brittle. Therefore, the above range is set.

Mn: 1-4%. Mn is an element that contributes to increasing the strength of the rail by lowering the bainite transformation temperature and increasing the hardenability. However, if it is less than 1%, the effect is small, and if it exceeds 4%, a martensitic structure is liable to occur due to micro-segregation of steel, and hardening or embrittlement occurs during heat treatment and welding, resulting in deterioration of material. Therefore, the above range is set.

P: 0.035% or less. This is because if P exceeds 0.035%, the toughness deteriorates.

S: 0.035% or less. S is present in steel mainly in the form of inclusions, but 0.035
%, The amount of the inclusions is significantly increased to cause deterioration of the material.

Cr: 0.3 to 3%. Cr is an element that increases the hardenability of bainite, and is a very important element in the steel of the present invention in order to increase the strength by using the metal structure as a bainite structure. If it is less than 0.3%, the bainite hardenability is low, and the metal structure does not become a uniform bainite structure. On the other hand, when the content exceeds 3.5%, martensite is easily generated, which is not preferable. Therefore, the above range is set.

Nb: 0.05 to 0.1%. Nb is combined with C in bainite and precipitates after rolling, so it is effective to increase the hardness by precipitation strengthening to the inside of the head, improve wear resistance and extend the life of the rail. Also, Nb prevents crystal grains from being refined and carbides from being precipitated at grain boundaries, and improves delayed fracture resistance. However, the effect is not effective if less than 0.05%, and 0.1%.
%, The effect saturates. Therefore, the above range is set.

Ni: 0.1 to 1%. Mo: 0.1 to 1%. V: 0.01 to 0.1%. Both Ni and Mo are effective elements for forming a solid solution in bainite, improving the hardenability of bainite, and increasing the strength. However, the effect is not recognized below the above range,
If the addition exceeds the above range, the effect is saturated, so that the range is set to the above range. In addition, since V precipitates in bainite in combination with C after rolling, it is effective for increasing the hardness by precipitation strengthening to the inside of the head, improving wear resistance, and extending the life of the rail. However, the effect is not recognized below the above range, and the effect is saturated when added beyond the above range. Therefore, it is effective to add one or more of these elements within the above range.

Metal structure (microstructure): In addition to the above component composition, the metal structure of steel is a bainite structure. By using a bainite structure, it is possible to increase the strength and the toughness as compared with the pearlite structure of the conventional rail.

Hardness: For any of the following reasons, HV is 4 at both the top and the corner of the rail.
It is between 00 and 500.

Generally, there is a certain relationship between hardness and abrasion. It is most desirable to evaluate the amount of abrasion based on the amount of abrasion when actually laid. However, it is also effective to use a Nishihara-type abrasion tester to evaluate the abrasion by a comparative test that simulates the contact conditions of an actually laid rail. Using this test method, the abrasion resistance (relationship between hardness and abrasion loss ratio) of the test piece shown below
Was evaluated.

Table 1 shows the composition of the test steel.
6, 8, 10, 12, and 14, C, Si, M
n, Cr, Nb, Ni, Mo and V are variously changed steels, which are heated to 1250 ° C., and after rolling at 920 ° C. so as to satisfy the rolling and cooling conditions described in the claims. An air-cooled steel plate having a thickness of 12 mm was used.

From these steel plates, an outer diameter of 30 mm and a width of 8 mm
A Nishihara type abrasion test specimen was taken and subjected to a wear test under the conditions of a contact load of 50 kg, a slip ratio of -10%, and no lubricant.
The abrasion loss after 10,000 rotations was measured. The evaluation was performed by measuring the weight loss of the ordinary rail and measuring the wear loss ratio of the test steel to the ordinary rail.

FIG. 2 shows the results of an investigation on the effect of hardness on the wear loss ratio. The hardness of a normal rail having a pearlite structure is about HV250. In the bainite structure, the wear loss ratio decreases with increasing hardness,
At the same hardness, the bainite structure has a larger wear loss ratio than the pearlite structure.

However, in the bainite structure, Mn
When the amount is 1% or more, the Mn amount is less than 1%,
There is a tendency that the wear loss ratio at the same hardness is small, and when the hardness becomes HV400 or more, the wear loss ratio becomes equal to or less than that of the ordinary rail.

Therefore, if the hardness at any of the top and the corner of the rail having a bainite structure containing 1% or more of Mn is HV400 or more,
Abrasion resistance equal to or higher than that of ordinary rails currently used is obtained.

FIG. 3 shows the relationship between hardness and fatigue strength. When compared at the same hardness, bainite steel has higher fatigue strength than pearlite steel. For this reason, in the bainite steel, if the hardness is HV350 or more, the same fatigue strength as that of the conventional pearlite rail or more can be secured, and the damage resistance does not decrease. Therefore, the hardness is set to HV400 or more in consideration of abrasion resistance and damage resistance.

If the HV exceeds 500 at any of the top and the corner of the rail, FIG.
As shown, the delayed fracture resistance deteriorates. Therefore, the hardness is set to HV500 or less.

Further, since the rail of the present invention has high strength,
Considering the fastening of rails to sleepers, there is a possibility of delayed fracture. Delayed fracture was tested in 3% NaCl using a cantilevered delayed fracture tester and evaluated by _K1SCC .
The conventional pearlitic structure rail does not show the problem of delayed fracture, but _K1SCC is 100kg even in 130kg class bolt steel where the stress and notch condition are more severe than the rail.
It is known that there is no practical problem if f · m ^−3/2 or more.

FIG. 4 shows the results of an investigation on the effect of hardness on _K1SCC . The results of the evaluation by _K1SCC according to the above-described test method using 21 steel types whose components are shown in Tables 1 and 8 are shown as test steels. The K _1SCC decreases as the hardness increases, and at the same hardness, the _K1SCC is smaller in the bainite structure than in the pearlite structure.

However, in the bainite structure, Nb
Those having an amount of 0.05% or more show higher values of _{K1SCC at} the same hardness than those having an amount of less than 0.05%. This is presumably because, as described above, the addition of Nb reduced the size of the crystal grains and suppressed the precipitation of carbides at the grain boundaries, thereby preventing grain boundary destruction. If the Nb content is 0.05% or more, 100 kgf · m under the condition of HV 500 or less
^-3/2 or more of K _1SCC is obtained.

[0040]

[Table 1]

Rolling conditions: In order to obtain a steel having the above-mentioned composition and having a bainite structure and to obtain the material characteristics of the rail, the hot-rolling finishing temperature of the rail is set to 800 to 1000 ° C. Then, the temperature from the temperature above the bainite transformation start point to 400 ° C. or less is cooled at a cooling rate (including air cooling) of 5 ° C./sec or less. Here, the online cooling is a method of performing cooling in the rolling line immediately after the end of rail rolling. The on-line cooling has better thermal efficiency than a method of once cooling to room temperature after hot rolling and then reheating and heat treatment.

When the rolling finishing temperature is lower than 800 ° C., bainite transformation starts during rolling, and the strength is significantly reduced. On the other hand, when the rolling finish temperature exceeds 1000 ° C., austenite grains become coarse, and it becomes difficult to secure toughness after hot rolling. Therefore, the rolling temperature is set to 800 to 1000 ° C.

Regarding the cooling rate, a bainite structure can be obtained even by air cooling, and desired strength and toughness can be secured. However, when the temperature exceeds 5 ° C./sec, martensite is formed and the toughness is remarkably reduced. Therefore, the cooling rate is set to 5 ° C. or less.

[0044]

EXAMPLES Specific examples of the present invention will be described below. In the text, figures and tables, TS is the tensile strength and UE ₂₀ is 20 ° C.
Represents the absorbed energy in a 2 mm U notch Charpy test.

Example 1 A test steel having the components shown in Table 2 was heated to 1250 ° C.
After rolling at 920 ° C., a 12 mm-thick steel sheet air-cooled was used for a tensile test, a Charpy impact test and a wear test. For the abrasion test, the outer diameter is 30 mm and the width is 8 mm
From a rolled steel plate, and tire test pieces of the same dimensions from a railway wheel material, and using a Nishihara-type abrasion tester, a slip rate of -10%, a contact load of 50 kg, and no lubricant. The test was performed under the conditions, and the abrasion loss after 500,000 rotations was measured. The wear loss ratio is determined by taking the ratio with the wear loss of the ordinary rail material performed as a comparison.

Table 3 shows the measurement results of the mechanical properties and the wear loss ratio. For B-1 having a lower C content than the present invention,
The hardness is also HV333, which is less than the lower limit of the present invention, and therefore the wear loss ratio is as high as 2.64, which is not practical.

In the case of B-6 having a higher C content than the present invention and exhibiting a pearlite structure, the hardness is also HV35.
2, which is less than the lower limit of the present invention, and the wear loss ratio is also 1.30.
And high. Further, toughness _U E ₂₀ is less than 20.5J and the present invention the lower limit value. On the other hand, B-2, 3, 4, and 5 whose components satisfy the scope of the present invention show values within the target ranges for all of the strength, toughness, and wear reduction ratio.

[0048]

[Table 2]

[0049]

[Table 3]

Example 2 A test steel having the components and hardness shown in Table 4 was used in Example 1.
The resulting steel sheet was subjected to a tensile test, a Charpy impact test, and a wear test. The mechanical properties and the wear loss ratio are shown in Table 5. All the test steels have a bainite structure. C-1 and C-2 in which the content of Mn is lower than the claimed range have a low hardness and high wear loss ratios of 2.98 and 1.55, respectively.

On the other hand, C-3, 4, 5, 6, 7, 8, and 10 in which the content of Mn satisfies the claims of the present invention show the target values of the present invention in all of the strength, toughness and wear loss ratio. I have.
However, in the case of C-10 in which the Mn content is higher than the claimed range, the hardness exceeds HV500 specified in the claims, and the effect of improving the wear resistance of Mn is saturated.

[0052]

[Table 4]

[0053]

[Table 5]

Example 3 Example 1 was applied to a test steel having the components and hardness shown in Table 6.
The resulting steel sheet was subjected to a tensile test, a Charpy impact test, and a wear test. Table 7 shows the mechanical properties and the wear loss ratio. All test steels have a bainite structure.

D-1 has a lower Cr content than the claimed range,
The wear loss ratio is as high as 2.52. On the other hand, D-2,3,4,5,6,7,8 having a Cr content in the claims satisfy the target values of the present invention in all of the strength, toughness, and wear reduction ratio. However, the effect of Cr is saturated in D-9 in which the Cr content exceeds the claimed range.

[0056]

[Table 6]

[0057]

[Table 7]

Example 4 A test steel having the components and hardness shown in Table 8 was used in Example 1.
The resulting steel sheet was subjected to a tensile test, a Charpy impact test, and a wear test. Table 9 shows the mechanical properties and the wear loss ratio. All test steels have a bainite structure. E-1, 2 in which the Nb content is lower than the claimed range, each of the strength, toughness, and wear loss ratio are values within the target range of the present invention, but the delayed fracture property is 10%.
It has not reached 0 kgf · m ^-3/2 . On the other hand, Nb
E-3,4 satisfying the claims satisfy the target values of the present invention in all of the strength, toughness, wear loss ratio, and delayed fracture resistance.

[0059]

[Table 8]

[0060]

[Table 9]

Example 5 A tensile test, a Charpy impact test and an abrasion test were performed on a test steel having the components and hardness shown in Table 10 in the same manner as in Example 1. Table 11 shows the mechanical properties and the wear loss ratio.
All the test steels have a bainite structure. F-1 is N
Although i and Mo were not added, it was within the scope of claims, and the strength,
Both the toughness and the wear loss ratio achieve the target values of the present invention.

F-2 and F6, in which the contents of Ni and Mo are lower than the claimed range, have almost no change in any of the strength, toughness and wear reduction ratio as compared with F-1 in which Ni and Mo are not added. And the effect of the addition of Mo does not appear. Ni, Mo
The amount of one or two of the above E satisfies the claims.
-3, 4, 7, 8, and 10 show the target values of the present invention in all of the strength, toughness, and wear reduction ratio, and show values superior to F-1. F-5, 9 in which the added amounts of Ni and Mo exceed the scope of the present invention, the strength, toughness and wear loss ratio are F-4,
8 and the effect of adding Ni and No is saturated.

[0063]

[Table 10]

[0064]

[Table 11]

Example 6 A tensile test, a Charpy impact test and an abrasion test were carried out in the same manner as in Example 1 on a test steel having the components and hardness shown in Table 12. Table 13 shows the mechanical properties and the wear loss ratio.
All the test steels have a bainite structure. G-1 is V
Is not added, but the composition is within the scope of the claims, and the strength, toughness, and wear reduction ratio all achieve the goals of the present invention.

The amount of added V satisfies the claims.
2, 3 show the target values of the present invention in all of the strength, toughness, and wear loss ratio, and show values superior to G-1. G-4 in which the added amount of V exceeds the claimed range has the same strength, toughness, and wear reduction ratio as G-3, and the effect of V is saturated.

G-5 satisfies Ni, Mo, and V all within the scope of the present invention, but has a higher strength, toughness, and abrasion than the addition of only one type or only two types (F-10, G-3). Both weight loss ratios show excellent values.

[0068]

[Table 12]

[0069]

[Table 13]

Example 7 Table 14 shows H-1, 2 steels satisfying the component conditions of the present invention. Table 15 shows that the rolling finish temperatures of these two steel types were 7
The temperature was changed from 60 to 1030 ° C. and actually rolled into a rail shape, and then the cooling temperature was changed from air-cooled to 6.5 ° C./s. Tensile properties of the manufactured rails, shock absorption energy at 20 ° C. in a 2 mm U notch Charpy test , Microstructure, hardness and wear loss ratio. The wear loss ratio was evaluated by the same test method as in Example 1 by taking a sample for the wear test shown in Example 1 from the head of the rolled material.

In condition 1, the cooling rate was satisfied, but the rolling finishing temperature was not satisfied, so that TS was 1168 MPa.
a, a low value of a wear loss ratio of 2.19 (hardness HV350). Conditions 2, 3, 4, 5, 6, 8, 9, 10,
12 both finishing rolling temperature, because it satisfies the cooling rate, TS ≧ 1300 MPa, and _U E ₂₀ ≧ 30 J, abrasion loss ratio of 1 or less (hardness HV400～500) show good values.

The conditions 7, 11, and 13 satisfy the condition of the rolling finish temperature but do not satisfy the cooling rate. Therefore, under the condition 7, _U E ₂₀ = 23.0 J, and under the condition 11, _U E ₂₀ = 23.0 J.
₂₀ = 28.5 J, and under the condition 13, _U E ₂₀ = 21.1 J, which is a low value. Conditions 14 and 15 satisfy the cooling rate but do not satisfy the rolling finishing temperature.
Under condition 14, _U E ₂₀ = 28.9J, and under condition 15, _U E ₂₀
= 22.0J, which is a low value.

[0073]

[Table 14]

[0074]

[Table 15]

[0075]

As described above, the rail according to the present invention has a delayed fracture resistance that does not cause a problem in characteristics even under severe conditions such as a cold region and a heavy axial load condition. High-strength rail with excellent wear resistance and toughness. Specifically, the tensile strength of the rail is 1300 MPa or more, and the Charpy absorbed energy of a 2 mm U notch at 20 ° C. is 3
0J or more, delayed fracture resistance (K _1SCC ) of 100 kgf · m
a rail is m ^-3/2 or more. Further, according to the method of the present invention, a rail having the above characteristics can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between hardness and wear of rail steel having various metal structures.

FIG. 2 is a diagram showing the relationship between the hardness of rail steel having different Mn amounts and the wear loss ratio.

FIG. 3 is a diagram showing a relationship between hardness of rail steel and fatigue strength.

FIG. 4 is a diagram showing a relationship between hardness of rail steel and delayed fracture characteristics (K _1SCC ).

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00 C21D 8/00 C22C 38/58

Claims (5)

(57) [Claims] 1. The following characteristics (component composition is wt%)
High strength rail with excellent delayed fracture resistance, abrasion resistance and toughness. (A) C: 0.2 to 0.5%, Si: 0.1 to 2% Mn: 1 to 4%, P: 0.035% or less, S: 0.035% or less, Cr: 0.3 Nb: more than 0.05% to 0.1 % Nb: a rail having a component composition substantially composed of iron, (b) the metal structure of the rail is a bainite structure, and (c) the rail. The hardness of the head and the corner of the head is between 400 and 500 in HV at any position. 2. In addition to the rail composition, Ni:
0.1-1%, Mo: 0.1-1%, V: 0.01-
2. The composition according to claim 1, wherein the composition contains at least one kind of 0.1%.
High-strength rail with excellent delayed fracture resistance, abrasion resistance and toughness described in. 3. The high-strength rail has a tensile strength of 1300.
MPa or more, Charpy absorbed energy of 2mmU notch at 20 ° C. or higher 30 J, delayed fracture resistance (K _ISCC) is delayed fracture resistance as set forth in claim 1 or 2 is 100 Kgf · mm ^-3/2 or more, resistance to High-strength rail with excellent wear and toughness. 4. A method for producing a high-strength rail having the following steps (component composition is wt.%) And excellent in delayed fracture resistance, abrasion resistance and toughness. (A) C: 0.2 to 0.5%, Si: 0.1 to 2% Mn: 1 to 4%, P: 0.035% or less, S: 0.035% or less, Cr: 0.3 ３3% Nb: more than 0.05〜0.1% A steel having a component composition substantially consisting of iron is prepared, and (b) the steel is hot-rolled on a rail in the range of 800 to 1000 ° C. (C) cooling the rail online at a cooling rate of 5 ° C./s from a temperature above the bainite transformation start point to 400 ° C. or less;
ec or less. 5. The steel according to claim 5, wherein the composition of the steel further comprises Ni: 0.1
-1%, Mo: 0.1-1%, V: 0.01-0.1%
The method for producing a high-strength rail excellent in delayed fracture resistance, abrasion resistance and toughness according to claim 4, comprising one or more kinds.