JPH1192866A - Bainitic steel rail excellent in joinability in weld zone, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a bainitic steel rail having excellent rolling fatigue damage resistance as well as having joinability, at the time of rail welding, e.g. by flash butt welding or gas pressure welding, equal to that of the conventional pearlitic rail steel, and its production. SOLUTION: The rail steel has a composition consisting of, by weight, 0.15-0.4% C, 0.1-0.2% Si, 0.15-1.1% Mn, <=0.035% P, <=0.035% S, 0.05-0.45% Cr, 0.005-0.15% Nb, 0.05-0.85% Mo, and the balance essentially Fe with inevitable impurities and satisfying Mn%/Si%<=5.5. In this case, a railhead has a bainitic structure, and both a railhead and railhead corners can be provided with uniform hardness distribution, and Vickers hardness is regulated to HV230 to 320.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flash butt welding, gas The present invention relates to a bainite steel rail having excellent weldability at a welded portion and a method for manufacturing the same.

[0002]

2. Description of the Related Art Heretofore, pearlite steel has been used for rails mainly from the viewpoint of emphasizing wear resistance at the top and corners of the head. However, in recent years, the use conditions of rails have become more and more severe as the amount of transportation by rail has increased.
Especially in Japan, considering the convenience of users, the speed of both conventional lines and Shinkansen has been increased, and the schedules have become denser.
Rolling fatigue damage has also increased due to an increase in annual cumulative ton. For this reason, railway companies have come to demand rail steel having excellent rolling contact fatigue damage resistance from the viewpoint of reducing rail maintenance costs. In the section where rolling fatigue damage is a problem at present, JI
Although a pearlite-type ordinary rail having a strength standardized to S of 800 MPa is used, replacement of the ordinary rail due to wear of the head rarely occurs. Therefore, in the section where the present rolling fatigue damage becomes a problem from the viewpoint of wear resistance, the pearlite steel rail is given excessive wear resistance. On the other hand, although bainite steel is superior in rolling contact fatigue damage resistance to pearlite steel, it is said that the weldability is poor due to the addition of a large amount of alloying elements.

[0003]

In a bainite-structured rail, as disclosed in Japanese Patent Application Laid-Open No. 2-282448, the fatigue strength is increased, the wear is promoted, and the fatigue layer is removed. Despite the improvement in rolling contact fatigue damage resistance, the amount of alloying elements added is greater than that of pearlite steel rails, which may cause problems in flash butt welding and gas pressure welding joints. Has not been done.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to make the weldability of rail welding such as flash butt welding and gas pressure welding equal to that of a conventional pearlite type rail steel and to provide excellent rolling fatigue resistance. It is an object of the present invention to provide a bainite steel rail having a damage property and a method for manufacturing the same.

[0005]

In order to solve the above problems and achieve the object, the present invention uses the following means. (1) The rail of the present invention has a weight percentage of C: 0.15 to 0.15%.
0.4%, Si: 0.1 to 0.2%, Mn: 0.1
5 to 1.1%, P: 0.035% or less, S: 0.0
35% or less, Cr: 0.05 to 0.45%, and Nb:
0.005 to 0.15%, Mo: 0.05 to 0.85
%, Mn% / Si% ≦ 5.5, the balance being substantially composed of Fe and unavoidable impurities, the rail head having a bainite structure, the rail head and head. A bainite steel rail with excellent jointability of a welded part, characterized by having a uniform hardness distribution at any position of a corner portion and a Vickers hardness of HV230 to 320.

(2) The rail according to the present invention comprises,
The bainite steel rail according to (1) above, further comprising 0.1 to 1% by weight of Ni in terms of weight%.

(3) The rail according to the present invention comprises, as a steel component,
The bainite steel rail according to the above (1) or (2), further comprising V: 0.01 to 0.2% by weight in terms of% by weight.

(4) The method of the present invention comprises the steps of hot rolling a steel having the composition described in any one of the above (1) to (3) so that the rolling finish temperature is 800 to 1000 ° C. Cooling the hot-rolled steel material from a temperature not lower than the bainite transformation start point to 300 ° C. or lower at a cooling rate of air cooling to 5 ° C./sec. This is a method for manufacturing a bainite steel rail excellent in quality.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies on the relationship between the chemical composition, hardness, and weldability of bainite steel in order to solve the above problems, and have obtained the following findings. Reached.

[0010] As measures against vibration and noise when passing through a train, rails are very frequently used as a measure to reduce seams with gaps, and from this point, jointability at the time of welding is required. Rail welding methods include flash butt welding, gas pressure welding, enclosed arc welding, and thermite welding. Of these, flash butt welding,
Regarding gas pressure welding, since the rail base material is directly bonded without using a weld metal, the bondability of the base material itself becomes a problem.
The bondability at the time of such flash butt welding and gas pressure welding is affected by the ability to generate an oxide of the added element, the melting temperature of the generated oxide, the ability to remove the oxide by a new surface at the time of bonding, and the like. The hardness having the components shown in Table 1 is HV3
Sample steel No. 20 or less 1a-1 to 9; 1b-1 to 9;
1c-1 to 9 and 1d-1 to 9
FIG. 3 shows the effect of the amounts of Cr, Mo, and Mn / Si added.
To # 6.

[0011]

[Table 1]

The vertical axis in FIGS. 3 to 6 is obtained by preparing a welded joint by flash butt welding and gas pressure welding using a 40φ round bar, and making the joint surface of the joint be the center of the parallel portion of the tensile test piece. It shows the average value of the aperture value of the fractured part when a tensile test was performed using a test piece, and the larger this value (RA), the higher the bondability. As can be understood from FIGS. 3 to 6, Si is 0.2% and Cr is 0.45%.
%, Mo exceeds 0.85%, and Mn / Si exceeds 5.5, the aperture value becomes 5% or less, and the bondability is significantly reduced. The reason will be described below.

Since Si and Cr are elements that are easily oxidized, a dense oxide film is formed on the joint surface by heating with a flash current or a gas flame, and this forms a joint surface even in the final upset during flash butt welding and gas pressure welding. Not removed from Mo does not sufficiently join the new surface in order to increase the deformation resistance during upsetting. Mn / Si is
In a region where the melting point of the composite oxide of Mn, Si, and Fe exceeds 5.5 in Mn / Si, the temperature becomes extremely high, and the viscosity of the composite oxide remaining on the joint surface becomes relatively high, so that it is removed in the upset. Hard to do. Therefore, from the viewpoint of bonding properties, it is necessary that Si is 0.2% or less, Cr is 0.45% or less, Mo is 0.85% or less, and Mn / Si is 5.5 or less.

FIG. 7 shows the hardness (H
The result of having investigated the influence of V) is shown. Table 2 shows the chemical composition and hardness of the test steel. As can be understood from FIG.
Even when each of r, Mo, Mn / Si satisfies the claims of the present invention, the bondability decreases with an increase in hardness, and particularly when the hardness exceeds HV320, the aperture value becomes 5% or less. This causes a practical problem.

If any of Si, Cr, Mo, and Mn / Si does not satisfy the claims of the present invention, HV23
Even between 0 and 320, there is a problem in bondability. Therefore, in order to ensure sufficient bondability, the content of Si should be 0.2% or less,
Is 0.45% or less, Mo is 0.85% or less, and Mn /
Si needs to be 5.5 or less and HV320 or less.

[0016]

[Table 2]

Based on the above findings, the present inventor has proposed that S
By controlling the amounts of i, Cr, Mo, and Mn / Si, the rolling finish temperature in hot rolling, and the cooling rate after rolling within a certain range, the metal structure of the rail head is made bainite, and the rail top and head are controlled. A bainite steel rail which controls the Vickers hardness of the corner portion within a certain range to ensure sufficient jointability at the time of welding and has excellent rolling contact fatigue damage resistance and a method for producing the same, and the present invention Was completed.

That is, the present invention restricts the steel composition, metal structure (microstructure), hardness and manufacturing conditions to the following ranges to thereby improve the jointability at the time of rail welding such as flash butt welding and gas pressure welding with a conventional pearlite type. It is possible to provide a bainite steel rail which is equivalent to rail steel and has excellent rolling contact fatigue damage resistance.

The reasons for adding the components, the reasons for limiting the components, the reasons for limiting the metallographic structure, the reasons for limiting the hardness, and the reasons for limiting the manufacturing conditions of the present invention are described below. (1) Component composition range C: 0.15 to 0.4% C is an essential element for securing strength, and is 0.15%
If it is less than 30, it is difficult to secure the hardness as rail steel at low cost. On the other hand, if it exceeds 0.4%, brittle martensite tends to be formed on the rail head. Therefore, its content is 0.15 to 0.4%.

Si: 0.1-0.2% Si is not only effective as a deoxidizing agent, but also an element which increases the strength by forming a solid solution, but if less than 0.1%, the effect is not recognized. . On the other hand, if the addition amount exceeds 0.2% due to the bonding force with high oxygen that Si has, a dense oxide is formed on the bonding surface during flash butt welding and gas pressure welding, thereby inhibiting the bonding of the new surface. Deteriorates the bondability.
Therefore, its content is 0.1-0.2%.

Mn: 0.15 to 1.1% 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 less than 0.15%, the effect is small, and 1.1%
%, The steel tends to have a martensitic structure due to micro-segregation of the steel, and hardening and embrittlement occur during heat treatment and welding, resulting in deterioration of the material. Therefore, the content is 0.15 to 1.1%. P: 0.035% or less P is 0.035% or less because P deteriorates toughness.

S: 0.035% or less S is present in steel mainly in the form of inclusions, but 0.035% or less.
%, The amount of these inclusions increases remarkably, causing deterioration of the material due to embrittlement.
035%.

Cr: 0.05 to 0.45% Cr is an element that promotes bainite transformation, and is an important element for changing the microstructure to a bainite structure as in the steel of the present invention. If it is less than 0.05%, the effect of promoting transformation is small, and the microstructure does not become a uniform bainite structure. On the other hand, when the content exceeds 0.45%, not only is martensite generated easily, but also a factor that inhibits bonding by the new surface by forming a dense oxide film on the bonding surface due to the high bonding force of Cr with high oxygen. Become. Therefore, its content is 0.0
5 to 0.45%. Mo: 0.05 to 0.85% Mo is an element that promotes bainite transformation, and is an important element for changing the microstructure to a bainite structure like the steel of the present invention. If it is less than 0.05%, the transformation promoting effect is low, and the microstructure does not become a uniform bainite structure. On the other hand, when the content exceeds 0.85%, not only martensite is easily formed, but also deformation resistance at high temperatures is increased, which is a factor to hinder the formation of a new surface at the bonding surface during upset. Therefore, its content is 0.05-0.85%.

Nb: 0.005 to 0.15% Nb not only promotes bainite transformation, but also C in steel.
This is effective in increasing the hardness and improving wear resistance by extending precipitation hardening to the inside of the rail head and extending the life of the rail. However,
This effect is not effective when the content of Nb is less than 0.005%, and the effect is saturated when the content exceeds 0.15%. Therefore, the content is 0.005 to 0.5.
15%.

Mn / Si ≦ 5.5 Mn and Si form a composite oxide together with Fe on the bonding surface during flash butt welding and gas pressure welding to lower the bondability. In particular, Mn / Si exceeds 5.5. In addition, the viscosity and melting point of the composite oxide increase, making it difficult to remove the composite oxide from the bonding surface, and lowering the bonding property. Therefore, from the viewpoint of bonding properties, Mn / Si
≤ 5.5.

In the present invention, in addition to the above-mentioned additional elements, Ni and V may be contained in order to enhance the strength and wear resistance of the steel material. The reasons for limiting the components will be described below. Ni: 0.1 to 1% Ni is an element effective for promoting bainite transformation and increasing the strength. However, if the content is less than 0.1%, the effect is not recognized, while the content exceeds 1%. The addition saturates the effect. Therefore, its content is 0.1-1%.

V: 0.01% to 0.2% V, like Nb, is combined with C in steel and precipitates after rolling, so that the hardness is increased by precipitation strengthening up to the inside of the rail head and wear resistance is improved. Is effective to improve the life of the rail. However, this effect is not effective when added less than 0.01%, and the effect is saturated even when added over 0.2%. Therefore, its content is 0.01-0.2%.

(2) Metal structure The rail head has a bainite structure. Compared with the pearlite structure of the conventional rail, the bainite structure has a higher fatigue strength and is effective in extending the rolling fatigue life when compared at the same tensile strength level. Since it is effective in removing the fatigue layer, the metal structure was a bainite structure.

(3) Hardness (wear resistance) The Vickers hardness is HV230 to HV3 at both the top 1 and the corner 2 of the rail head shown in FIG.
20.

Although it is most desirable to evaluate the amount of abrasion by the amount of abrasion in actual laying, it is also effective to use a Nishihara type abrasion tester to evaluate the abrasion by a comparative test simulating actual contact conditions. With this test method, the wear resistance (the relationship between the hardness and the wear loss ratio) can be evaluated in a short time.

FIG. 8 shows the results of an investigation on the effect of hardness (HV) on the wear loss ratio. As shown in Table 3, the test steel was heated to 1250 ° C with various amounts of alloying elements added, and after rolling at 920 ° C which satisfied the rolling and cooling conditions of the present invention. , 3 OD from air-cooled steel
A 0 mm, 8 mm wide Nishihara type abrasion test piece was sampled and subjected to an abrasion test under the conditions of a contact load of 130 kg, a slip rate of -10%, and no lubricant, and the abrasion loss after 500,000 revolutions was measured.
In the evaluation, the wear loss of the pearlite-type ordinary rail standardized by JIS was measured, and the wear loss ratio of the test steel to the pearlite-type ordinary rail was determined. The hardness of the pearlite type ordinary rail is about HV280.

[0032]

[Table 3]

As can be understood from FIG. 8, at the same hardness, the wear loss ratio of the bainite structure is larger than that of the pearlite structure, which is about twice as large. In consideration of the removal of the fatigue layer due to the wear of the head in actual installation, the wear reduction ratio needs to be 1.3 times or more. In the bainite steel, the wear loss ratio decreases as the hardness increases, but HV320
Up to this point, the wear loss ratio shows a value of 1.3 times or more,
The upper limit of hardness was limited to HV320. HV230
If it is less than 3, the abrasion loss ratio exceeds 3 times, and the replacement life due to abrasion is significantly shorter than the rail replacement life based on cumulative ton, which causes a practical problem. Therefore, the lower limit of hardness is H
Limited to V230.

Attempts have been made to control the contact state with the wheels by intentionally changing the hardness of the crown and the corner of the head, but on actual routes, the contact between the wheels and the rails depends on the situation. It is constantly changing, and it is practically difficult to change the hardness of the head to control the contact situation and extend the life of the rail. Therefore, the value was set to HV230 to 320 with a uniform hardness distribution at both the top and the corner of the head. In addition, this uniform hardness distribution can be obtained by performing heat treatment (cooling condition of the present invention) under the same conditions at both the top and the corner. By adjusting to the above composition range, metal structure and hardness, the jointability at the time of rail welding such as flash butt welding and gas pressure welding is equivalent to that of conventional pearlite type rail steel, and excellent rolling fatigue damage resistance Can be obtained.

A rail having such characteristics can be manufactured by the following manufacturing method. (4) Rail manufacturing process (Manufacturing method) Steel having the above-described composition is hot-rolled so that the rolling finish temperature is 800 to 1000 ° C, and then air-cooled to 5 ° C from the temperature equal to or higher than the bainite transformation start point.
At a cooling rate of 300 ° C./sec.

A. Rolling finishing temperature: 800 to 1000 ° C If the rolling finishing temperature is lower than 800 ° C, ferrite transformation starts and the strength is reduced. On the other hand, when the rolling finish temperature is higher than 1000 ° C., the bainite structure after hot rolling becomes extremely coarse, and it becomes difficult to secure toughness. Therefore, the rolling finishing temperature is 800 to 1000 ° C.

B. Cooling rate: air cooling to 5 ° C./sec. Even with air cooling, a bainite structure can be obtained, and desired strength and toughness can be secured. However, when the temperature exceeds 5 ° C./sec, martensite is formed, and the toughness is significantly reduced. Therefore, the cooling rate is from air cooling to 5 ° C./sec.

Hereinafter, the effects of the present invention will be proved by giving examples of the present invention. In the text, figures and tables, HV indicates Vickers hardness, and RA indicates the aperture value in the tensile test of the joint surface after flash butt welding and gas pressure welding as the bondability evaluation.

[0039]

【Example】

(Example 1) Twelve test steels (inventive steels: Nos. 2 to 4, comparative steels: Nos. 1, 5, and 6) having the components shown in Table 4
After heating to 50 ° C. and finishing rolling at 920 ° C., a 12 mm thick steel plate which had been allowed to cool was used for hardness measurement, abrasion test, and bondability evaluation test. For wear test, outer diameter 30m
m, a test piece having a width of 8 mm was taken from a rolled steel plate, a tire test piece having the same dimensions was taken from a railway wheel material, and these were subjected to a slip rate of -10% and a contact load of 130 kg using a Nishihara type abrasion tester. The test was performed under the condition without a lubricant, and the abrasion loss after 500,000 rotations was measured. In addition, H performed as a comparison
The wear loss ratio is determined by taking the ratio with the wear loss of the rail steel having the pearlite structure of V275. Table 5 shows the hardness, the wear loss ratio, and the bondability.

As shown in Table 5, Comparative Steel No. having a lower C content than that of the present invention. With respect to No. 1, the hardness is HV221, which is less than the lower limit of the present invention, and the wear loss ratio is as high as 3.21, which is not suitable for practical use. Further, the comparative steel N having a higher C content than the present invention has
o. Microstructures of Nos. 5 and 6 have a pearlite microstructure. Although the wear characteristics are excellent, they are inferior in the resistance to flaking damage.

On the other hand, the steel No. of the present invention whose components satisfy the scope of the present invention. 2, 3, and 4 show both the hardness and the wear loss ratio within the range of the present invention (hardness: HV230 to 320, wear loss ratio: 1.3 to 3). Regarding the bondability, Mn / Si was less than 5.5 in all cases, and HV was 3
Since it is 20 or less, a sufficient value is shown.

[0042]

[Table 4]

[0043]

[Table 5]

(Example 2) Test steels having the components shown in Table 6 (inventive steels: Nos. 2 to 6, 9, 10, 13; comparative steels: Nos. 1, 7, 8, 11, 12, 12) For 14), a hardness measurement, a wear test, and a bondability evaluation test were performed in the same manner as in Example 1. Table 7 shows the hardness, the wear loss ratio, and the bondability.

As shown in Table 7, the test steels all have a bainite structure. Comparative steel No. with Mn, Cr and Mo contents lower than the range of the present invention. 1, 8, and 12 show high values of the bondability, but low hardness, and high wear loss ratios of 3.15, 3.45, and 3.22, respectively.

On the other hand, the steel No. of the present invention in which the contents of Mn, Cr and Mo satisfy the range of the present invention. 2-6,9,1
Nos. 0 and 13 show excellent values in all of the hardness, the wear loss ratio, and the bondability. However, Comparative Steel No. in which the contents of Mn, Cr, and Mo were higher than the range of the present invention. In 7, 11, and 14, the wear loss ratio is 1.3 or less. Also, the bondability is reduced to 5% or less.

[0047]

[Table 6]

[0048]

[Table 7]

(Example 3) Test steels having the components shown in Table 8 (Steel of the present invention: Nos. 1, 3, 4, 7, 10; Comparative steel:
No. 2, 5, 6, 8, 9, 11) were measured for hardness, abrasion test, and bondability evaluation test in the same manner as in Example 1.
Table 9 shows the hardness, the wear loss ratio, and the bondability.

As shown in Table 9, all the test steels have a bainite structure. The steel No. of the present invention. No. 1 does not contain Ni and V, but is a component within the range of the present invention, and all of the hardness, the wear loss ratio, and the bondability are values within the range of the present invention. Comparative steel No. in which the contents of Ni and V are lower than the range of the present invention. Steel Nos. 2, 6, and 8 of the present invention to which Ni and V were not added. Compared to No. 1, there was almost no change in any of the hardness, the wear loss ratio, and the bondability, and the effect of adding Ni and V did not appear. The steel No. of the present invention in which the addition amount of Ni satisfies the range of the present invention. Nos. 3, 4, and 7 show values within the range of the present invention in all of the hardness, the wear loss ratio, and the bondability, and the steel N of the present invention.
o. The value is superior to 1. Comparative steel No. in which the amount of Ni added exceeds the range of the present invention. Steel Nos. 5 and 9 of the present invention have hardness, wear reduction ratio and bondability. Equivalent to 4,7, Ni
The effect of addition is saturated. Inventive steel No. V in which the addition amount of V satisfies the scope of the present invention. 10 is hardness, wear loss ratio,
Each of the bonding properties shows a value within the range of the present invention, and the steel No. of the present invention. Comparative steel No. 1 having a value superior to that of the present invention, but having a value of V exceeding the range of the present invention. 11 is hardness,
The steel of the present invention has the abrasion loss ratio and the jointability. 10 and the effect of V addition is saturated.

[0051]

[Table 8]

[0052]

[Table 9]

(Example 4) Test steels having the components shown in Table 10 (Steel of the present invention: Nos. 2, 3, 5, 6; Comparative steel: N
o. 1, 4, 7, 8) were measured for hardness, abrasion test, and bondability evaluation test in the same manner as in Example 1. Table 11 shows the hardness, the wear loss ratio, and the bondability.

As shown in Table 11, the test steels all have a bainite structure. The steel No. of the present invention in which the addition amounts of Si, Cr and Mo each satisfy the range of the present invention and Mn / Si is 5.5 or less. 2, 3, 5, and 6 show excellent values in all of the hardness, the wear loss ratio, and the bondability.

However, even when the addition amounts of Si, Cr and Mo alone satisfy the range of the present invention, the comparative steel No. having Mn / Si exceeding 5.5 was used. 1 and 4 are inferior in bondability. On the other hand, M
Even when n / Si satisfies 5.5 or less, S
Comparative steel N in which the amount of i alone exceeds the range of the present invention
o. Nos. 7 and 8 also have poor bonding properties.

[0056]

[Table 10]

[0057]

[Table 11]

(Example 5) Table 12 shows that the steel No. of the present invention satisfying the component conditions of the present invention. 1 and 2 are shown. Table 13 shows this 2
For the steel type, the rolling finish temperature is changed from 760 to 1030 ° C., and the steel is actually rolled into a rail shape, and then the cooling rate is changed from air cooling to 6.5 ° C./sec, and the hardness of the manufactured rail is
It shows the wear loss ratio and the bondability (Examples of the present invention: Nos. 2 to 6,
Nos. 8 to 10, 12, Comparative Example: No. 1,7,11,1
3).

The abrasion loss ratio was determined by taking the abrasion test sample shown in Example 1 from the head of the rolled material and using the same test method as in Example 1. Comparative Example No. 1 shows that although the cooling rate satisfies the condition of the present invention, but does not satisfy the rolling finishing temperature, the bondability is good, but HV220,
The wear characteristics are inferior with a wear loss ratio of 3.11. Invention Example No. Since 2 to 6, 8 to 10 and 12 all satisfy the rolling finish temperature and the cooling rate, they exhibit good values of HV 230 to 320 and a wear loss ratio of 1.3 to 3, and also have excellent joining properties. .

Comparative Example No. In the cases of Nos. 7 and 11, the rolling finish temperature satisfies the conditions, but the cooling rate is too fast,
Exceeds 320, and the wear characteristics and the bondability are degraded. In Comparative Example No. No. 13 has a high rolling finish temperature and a coarse structure, so that hardenability is high, and HV exceeds 320.

[0061]

[Table 12]

[0062]

[Table 13]

[0063]

As described above, according to the present invention, by specifying the steel composition, the metal structure, the hardness, and the manufacturing conditions, it is possible to manufacture a bainite steel rail having excellent weldability. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing names of rail head surface positions according to an embodiment of the present invention.

FIG. 2 is a view showing a relationship between a tensile strength and a wear amount of the steel material according to the embodiment of the present invention.

FIG. 3 is a view showing the relationship between the amount of Si added to steel and the bondability according to the embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the amount of Cr added and the bondability of the steel according to the embodiment of the present invention.

FIG. 5 is a view showing the relationship between the amount of Mo added to a steel material and the bondability according to the embodiment of the present invention.

FIG. 6 is a view showing the relationship between the Mn / Si content and the bondability of the steel according to the embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between hardness and bondability of a steel material according to the embodiment of the present invention.

FIG. 8 is a view showing the relationship between the hardness of the steel material and the wear loss ratio according to the embodiment of the present invention.

[Explanation of symbols]

 1. Top of head, 2 ... Corner of head.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/26 C22C 38/26 38/48 38/48 E01B 5/02 E01B 5/02

Claims (4)

[Claims] (1) C: 0.15 to 0.4% by weight
Si: 0.1 to 0.2%, Mn: 0.15 to 1.1%
, P: 0.035% or less, S: 0.035% or less, Cr: 0.05 to 0.45%, and Nb: 0.005
0.15% and Mo: 0.05 to 0.85%, satisfying Mn% / Si% ≦ 5.5, with the balance being substantially Fe and unavoidable impurities. A rail head having a bainite structure, a uniform hardness distribution at any position of a rail head and a head corner, and a Vickers hardness of HV230-320, Bainite steel rail with excellent properties. 2. The steel composition further comprises Ni:
The bainite steel rail according to claim 1, wherein the bainite steel rail contains 0.1 to 1%. 3. The steel composition further comprises, in weight%, V:
The bainite steel rail according to claim 1 or 2, characterized in that it contains 0.01 to 0.2%. 4. A step of hot-rolling a steel having the composition according to any one of claims 1 to 3 so that the finishing temperature is 800 to 1000 ° C., and transforming the hot-rolled steel into bainite transformation. A method of cooling from a temperature equal to or higher than the starting point to 300 ° C. or lower at a cooling rate of air cooling to 5 ° C./sec.