JP2000328138A - Production of bainite type rail excellent in wear resistance and flaking resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a bainite type rail having characteristics of being excellent in wear resistance and flaking damage resistance. SOLUTION: As to the method for producing a bainite type rail having characteristics of being excellent in wear resistance and flaking damage resistance, steel contg., by weight, 0.35 to 0.5% C, <=41% Si, 0.4 to 2.5% Mn, <=0.035% P, <=0.035% S and 0.05 to 0.5% Nb is heated at 1100 to 1350 deg.C and is subjected to hot rolling in such a manner that the rolling finishing temp. is controlled to >=850 deg.C to form a rail stock, and next, the head of the rail is subjected to controlled cooling to <=500 deg.C at a cooling rate of <=5 deg.C/S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bainite which has many sharply curved sections, such as an overseas mining railway, and has excellent abrasion resistance and flaking damage resistance used under high axial load conditions. The present invention relates to a method for manufacturing a mold rail.

[0002]

2. Description of the Related Art The load applied to the wheel axle of a vehicle that mainly transports ore, such as an overseas mining railway, is much larger than that of a passenger car, and is used for such a high axle heavy railway. Conventionally, pearlite steel is used as the rail steel from the viewpoint of emphasizing wear resistance. In recent years, with the aim of further improving wear resistance, Japanese Patent Application Laid-Open Nos. 8-109439 and 8-144 have been disclosed.
No. 016, the C content is increased from 0.85% to 1.20%.
In Japanese Patent Publication No. 101, the C content is increased to 0.85% to 1.20% and the amount of C is increased by performing heat treatment on the rail head.
Some measures have been taken to improve the wear resistance by increasing the cementite fraction.

[0003] On the other hand, a rail in a curved section of a high axle heavy railway is subjected to a rolling force due to wheels and a sliding force due to centrifugal force, so that the rail is more worn and flaking damage due to the sliding occurs. The flaking damage has a problem that, in a curved section, the rail top surface and the rolling surface of the wheel slide in directions other than the rolling direction, so that plastic deformation occurs immediately below the rail top surface, and a crack is generated based on the plastic deformation. Proceedings of the Iron and Steel Institute of Japan, “Materials and Processes” vol. 10 (199
7) In p1365, it is proposed to increase the yield point or proof stress as a material of the rail steel and to reduce carbides such as brittle cementite.

[0004] However, the yield strength of the pearlite structure is almost determined by the layer spacing of the layered structure of cementite and pearlite, so that an increase in the yield point due to an increase in the amount of C cannot be expected. It was difficult to satisfy both the properties of the wear resistance and the resistance to flaking damage in a rail steel having a pearlite structure, for example, it was difficult to improve the resistance to flaking damage due to the increased amount.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been developed in consideration of wear resistance and flaking resistance as compared with conventional hypoeutectoid, eutectoid and hypereutectoid pearlite rail steels. An object of the present invention is to provide a method for producing a rail having a bainite structure excellent in both properties.

[0006]

In order to solve the above problems, the present invention provides: (1) C: 0.35 to 0.5% by weight, Si: 1% or less, Mn: 0.4 to 2.5%, P: 0.035% or less,
Steel containing S: 0.035% or less and Nb: 0.05 to 0.5% is heated to 1100 to 1350 ° C, and hot-rolled so that the rolling finish temperature becomes 850 ° C or more, to obtain a rail material. And then controlling the rail head at a cooling rate of 5 ° C./s or less to a temperature of 500 ° C. or less to produce a bainite-type rail excellent in abrasion resistance and flaking damage resistance. I will provide a.

(2) C: 0.35 to 0.5% by weight%
Si: 1% or less, Mn: 0.4 to 2.5%, P: 0.0
35% or less, S: 0.035% or less, Nb: 0.05 to
A steel containing 0.2% is heated to 1100 to 1350 ° C, and hot-rolled so that a rolling finish temperature is 850 ° C or higher to form a rail material, and then the rail head is heated at 5 ° C / s.
Provided is a method for manufacturing a bainite type rail excellent in wear resistance and flaking damage resistance, characterized in that controlled cooling to a temperature of 500 ° C. or less is performed at a cooling rate of below.

(3) C: 0.35 to 0.5% by weight,
Si: 1% or less, Mn: 0.4 to 2.5%, P: 0.0
35% or less, S: 0.035% or less, Nb: 0.05 to
0.5%, Cr: 1.5% or less, Cu: 1
%, Ni: 1% or less, Mo: 2% or less, V: 0.2
% Or less of one or more kinds of steel,
~ 1350 ° C, hot-rolled so that the rolling finish temperature is 850 ° C or higher to form a rail material, and then control the rail head at a cooling rate of 5 ° C / s or less to a temperature of 500 ° C or less. Provided is a method for manufacturing a bainite type rail which is excellent in wear resistance and flaking damage resistance characterized by cooling.

(4) C: 0.35 to 0.5% by weight,
Si: 1% or less, Mn: 0.4 to 2.5%, P: 0.0
35% or less, S: 0.035% or less, Nb: 0.05 to
0.2%, Cr: 1.5% or less, Cu: 1
%, Ni: 1% or less, Mo: 2% or less, V: 0.2
% Or less of one or more kinds of steel,
~ 1350 ° C, hot-rolled to a rolling finish temperature of 850 ° C or higher to form a rail material, and then control the rail head to a temperature of 500 ° C or less at a cooling rate of 5 ° C / s or less. Provided is a method for manufacturing a bainite type rail which is excellent in wear resistance and flaking damage resistance characterized by cooling.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the component composition, microstructure and manufacturing method of a rail according to the present invention will be described.

According to the method for producing rail steel of the present invention, the C content is set to 0.1.
35-0.5%, significantly reduced C content compared to conventional pearlitic rail steel, 0.05% -0.5% Nb added to improve microstructure to bainite to improve flaking damage resistance In order to improve wear resistance by finely dispersing special carbides such as Nb carbide with high hardness compared to cementite in steel, the hot rolling conditions and cooling method after hot rolling are specified. It was done.

(Component composition) C: 0.35 to 0.5%. C is an essential element for ensuring strength and wear resistance. However, if it is less than 0.35%, it is difficult to secure a sufficient amount of special carbide necessary for maintaining wear resistance, and if it exceeds 0.5%, a uniform bainite structure cannot be obtained, and pearlite or martensite cannot be obtained. And the flaking damage resistance is significantly reduced. Therefore, the amount of C is 0.35% to 0.5%
Range.

Si: 1% or less. Although Si is effective as a deoxidizing material, if it exceeds 1%, the welding characteristics deteriorate due to the high bonding force of Si with oxygen. Therefore, the amount of Si is 1%
The above range is set.

Mn: 0.4% to 2.5%. Mn is an element that lowers the pearlite transformation temperature and enhances hardenability, thereby promoting the formation of bainite in the structure, and contributing to higher rail strength and higher ductility. However, if the content is less than 0.4%, a sufficient effect cannot be obtained. If the content is more than 2.5%, a martensitic structure is liable to be generated due to micro-segregation of steel, and hardening or embrittlement occurs during heat treatment and welding to deteriorate the material. It is not preferred. Therefore, the Mn content is set in the range of 0.4% to 2.5%.

P: 0.035% or less. Since P is an element that deteriorates toughness, it is set to 0.035% or less.

S: 0.035% or less. S is mainly present in the form of inclusions in the steel, but if it exceeds 0.035%, the amount of these inclusions will increase significantly and cause deterioration of the material.

Nb: 0.05 to 0.5%. Nb not only increases the hardenability to bainite the microstructure, but also combines with C in the steel and precipitates finely as carbide after hot rolling, so transformation strengthening and precipitation strengthening up to the inside of the rail head Thereby, the hardness can be increased. As a result, abrasion resistance and flaking damage resistance are improved, which greatly contributes to extending the life of the rail. However, if the content is less than 0.05%, the effect is not effectively exhibited. Conversely, if the content exceeds 0.5%, the weldability deteriorates. Therefore, the Nb content is set to 0.05%
０．５0.5%. In addition, from the viewpoints of abrasion resistance, the effect of improving the resistance to flaking damage, and economic efficiency, 0.05
% Is preferred.

Cr: 1.5% or less. Cr is an element that increases the hardenability and promotes the microstructure to be bainite. However, if the content exceeds 1.5%, the weldability is impaired due to the high bonding strength of Cr with oxygen, so the content is set to 1.5% or less.

Cu: 1% or less. Cu is an element that aims to increase the strength by solid solution strengthening, but if it exceeds 1%, Cu cracks occur, so it is set to 1% or less.

Ni: 1% or less. Ni is an element for increasing strength and toughness by solid solution strengthening. In addition, since Cu cracking is suppressed by adding Cu in combination, Ni is preferably added when Cu is added. However, if it exceeds 1%, the effect of improving strength and toughness saturates, so it is set to 1% or less.

Mo: 2% or less. Mo is an element that promotes the formation of bainite in the microstructure. However, if it exceeds 2%, the hardenability is further improved, a martensite structure is easily generated, and the flaking damage resistance is reduced. .

V: 0.2% or less. V is finely precipitated as carbide after hot rolling in combination with C in steel,
The hardness can be increased by precipitation strengthening up to the inside of the rail head, which is effective for extending the life of the rail. However, even if added over 0.2%, the effect is saturated. I do.

(Manufacturing method) In the present invention, the steel having the above-described composition, specifically, a steel slab is heated to 1100 ° C or higher and 1350 ° C or lower, and the steel slab is heated to a rolling finish temperature of 850 ° C or higher. Then, the head of the rail is controlled and cooled to 500 ° C. or less at a cooling rate of 5 ° C./s or less.

The heating temperature is from 1100 ° C. to 1350 ° C. In order to roll a complicated three-dimensional shape such as a rail with high dimensional accuracy, it is desirable to perform hot rolling in a high temperature region (recrystallization γ region) where the hot deformation resistance value of the steel is as low as possible. The lower limit of the heating temperature is 1100 ° C. or higher. On the other hand, if the heating temperature exceeds 1350 ° C., the steel slab is likely to be scratched, which causes a problem in the surface properties of the rail after finish rolling. Therefore, the upper limit of the heating temperature is 1350 ° C. or less.

Cooling rate: 5 ° C./s or less. If the cooling rate of the rail head after finish rolling is within the range of 5 ° C./s or less, a uniform bainite structure can be obtained and desired characteristics can be secured. However, if the cooling rate exceeds 5 ° C./s, a martensite structure is formed, and the resistance to flaking damage decreases, so the cooling rate is set to 5 ° C./s or less.

Cooling stop temperature: 500 ° C. or less. Since the bainite transformation start temperature at the above cooling rate of the steel of the composition of the present invention is 550 ° C. to 650 ° C., in order to obtain a homogeneous bainite structure at the above cooling rate, the cooling stop temperature is 50 ° C. or lower than the bainite transformation start temperature. Need to secure. Therefore, the cooling stop temperature is set to 500 ° C. or less.

(Abrasion Resistance Test) Regarding the abrasion resistance, it is most desirable to evaluate by actual laying of the rail. However, a method of evaluating by a comparative test simulating actual contact conditions using a Nishihara type abrasion tester is also effective. is there.

According to this test, the abrasion resistance can be evaluated in a short period of time. Therefore, the results of the examples of the present invention evaluated by a Nishihara type abrasion tester are shown. 30m shown in Fig. 3
A Nishihara type abrasion test piece having a width of 8 mm and a width of 8 mm was collected from the rail head, and the contact pressure: 1.5 GPa, the slip ratio: -10%, the test environment conditions: The amount of wear after 100,000 rotations in a dry state was measured.

(Flaking damage resistance test) It is most desirable to evaluate the flaking damage resistance by actually laying a rail in a curved section and evaluating the occurrence of flaking. However, the evaluation of this characteristic is also the evaluation of abrasion resistance. In the same manner as in the above, it can be evaluated by a comparative test that simulates the contact conditions under which flaking actually occurs with a Nishihara-type abrasion tester. Specific conditions were as follows: contact pressure: 2.1 GPa, slip rate: -20%, test environment condition: the contact surface of the test piece was observed every 25,000 revolutions in an oil lubricated state, and the time when cracks or peeling occurred Was defined as the flaking occurrence life.

[0030]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 A test steel having the composition shown in Table 1 was heated to 1250 ° C., hot rolled at 920 ° C., and cooled at 0.5 to 3 ° C./s. An abrasion test piece, a flaking damage test piece, and a hardness test piece were sampled from the rail, and an evaluation test was performed under the test conditions described above.

[0032]

[Table 1]

The evaluation of wear resistance is based on the wear amount of steel type A-27 currently used as a rail, that is, a pearlite-type heat-treated rail having a C content of 0.68% (hereinafter referred to as reference material 1). The increase / decrease of the wear amount of each steel type with respect to the reference wear amount is shown in%. It was determined that the abrasion resistance was sufficiently improved if a value of 3% or more with respect to the reference wear amount was obtained.

In the evaluation of the flaking damage resistance, it was judged that the flaking damage resistance was sufficiently improved when the flaking generation life was 1.5 times or more as compared with the reference material 1 described above. Table 2 shows the evaluation test results.

[0035]

[Table 2]

No1-1,1-2,1-3,1-21,1-22,1-23,
No. 1-24 did not show a reduction in the amount of wear of 3% or more as compared with Reference Material 1 (No. 1-27), and the effect of improving the wear resistance was small.
Also, the amount of C higher than the present invention No1-8, 1-9, 1-10, 1-12, 1-1
4,1-18,1-19,1-26 have flaking resistance less than 1.5 times that of the reference material (No1-27) because microstructure shows coarse pearlite structure or mixed structure of martensite and bainite No improvement in damage was expected. No1-13 had low wear resistance due to low Mn content. On the other hand, No. 1-25 had a high Mo content and a structure with a mixed structure of martensite and bainite, so that the hardness was high but the flaking generation life was short. On the other hand, Nos. 1-4, 1-5, 1-6, 1-7, 1-11, 1-15, 1-16, 1-17 and 1-20 whose component compositions satisfy the range of the present invention are hard. Hv280 or more, and exhibited excellent properties in both abrasion resistance and flaking damage resistance.

FIG. 1 shows the effect of the amount of carbon on wear resistance and flaking damage resistance based on data on steel types A-1 to A-10. It can be seen that good wear resistance and anti-flaking damage can be obtained with a bainite structure having a C content of 0.35 to 0.5%, which is within the range of the present invention.

Example 2 A test steel having the composition shown in Table 3 was heated to 1280 ° C., hot rolled at 950 ° C., and cooled at 0.5 to 3 ° C./s. An abrasion resistance test piece, a flaking resistance damage test piece, and a hardness test piece were collected from the rail, and an evaluation test was performed under the same test conditions as in Example 1. Table 4 shows the evaluation test results.

[0039]

[Table 3]

[0040]

[Table 4]

Steel type B-12 is a pearlite-type heat-treated rail material (hereinafter referred to as reference material 2) of 0.68% C, which is a reference material for a wear resistance test and a flaking resistance test. Table 4 shows the results of the abrasion test, the anti-flaking damage test, and the hardness test.
2-12 shows the evaluation result of Reference Material 2.

FIG. 2 shows N based on the test results of steel types B-1 to B-11.
The relationship between the amount of b and the wear characteristics is illustrated. As is clear from Table 4 and FIG. 2, No. 2-1, 2-2 having a small Nb content has a large amount of abrasion and a reduction in abrasion of 3% or more compared to the reference material 2 and a reduction in the life of flaking. It was difficult to achieve an extension of more than .5 times. On the other hand, when the Nb content was 0.05% or more, excellent abrasion resistance and flaking damage resistance were obtained. Therefore, it can be seen that excellent wear resistance and anti-flaking damage can be obtained by setting the Nb addition amount to 0.05% or more and 0.5% or less in consideration of weldability. On the other hand, the effect of improving the wear resistance and the resistance to flaking damage due to the addition of Nb tends to saturate at 0.2% or more. Therefore, considering the economics of the alloy addition, the Nb addition is 0.05% to 0.1%. 2
% Is more preferable.

(Example 3) Using test steels having the component compositions shown in Table 5, abrasion test pieces, flaking damage test pieces, and hardness tests were made from rails manufactured under the manufacturing conditions listed in Table 6. The pieces were sampled and subjected to an evaluation test under the same test conditions as in Example 1.

[0044]

[Table 5]

[0045]

[Table 6]

Steel type C-2 is a 0.68% C pearlite-type heat-treated rail material (hereinafter referred to as reference material 3) which is a reference material for a wear resistance test and a flaking resistance test. Table 7 shows the evaluation test results.

[0047]

[Table 7]

No. 3-12 are evaluation results of the reference material 3. No 3
In case of -1, the heating temperature of the slab was too low, and the dimensional accuracy of the rail after rolling was poor, so that it could not be a product. In addition, No. 3-2 could not be made into a product like No. 3-1 because the heating temperature of the slab was too high and the scratches generated in the slab remained on the rail even after rolling. In No. 3-3, the bainite structure with a uniform microstructure was not obtained due to the low rolling finish temperature, and a mixed structure of ferrite and bainite was exhibited, so that both the wear resistance and the flaking damage resistance were inferior to the reference material 3. Was the result. In No. 3-4, since the cooling rate exceeded 5 ° C./S, the microstructure exhibited a mixed structure of bainite and martensite, resulting in inferior flaking damage resistance. In No. 3-5, the cooling stop temperature was too high, and a homogeneous bainite structure with a fine lath interval could not be obtained. On the other hand, No 3-6, 3-7, 3
-8, 3-9, 3-10, and 3-11 all meet the requirements of the present invention, so wear resistance, flaking damage resistance, dimensional accuracy, surface texture, and texture Excellent rails were obtained.

[0049]

According to the present invention, there is provided a method of manufacturing a bainite type rail having excellent characteristics of abrasion resistance and flaking damage resistance used under high axial load conditions.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of wear, the life of flaking, and the amount of carbon.

FIG. 2 is a view showing a relationship between a wear loss and an Nb amount.

FIG. 3 is a view showing the shape of a test piece for evaluating abrasion resistance and flaking damage resistance.

Claims (3)

[Claims] 1. C: 0.35 to 0.5% by weight, S
i: 1% or less, Mn: 0.4 to 2.5%, P: 0.03
5% or less, S: 0.035% or less, Nb: 0.05 to
A steel containing 0.5% is heated to 1100 to 1350 ° C., and hot-rolled to a rolling finish temperature of 850 ° C. or higher to form a rail material, and then the rail head is heated to 5 ° C./s.
A method for producing a bainite-type rail excellent in wear resistance and flaking damage resistance, characterized by controlled cooling to a temperature of 500 ° C. or lower at the following cooling rate. 2. The method for producing a bainite type rail according to claim 1, which contains 0.05 to 0.2% by weight of Nb. 3. Cr: 1.5% or less, Cu:
1% or less, Ni: 1% or less, Mo: 2% or less, V: 0.
The method for producing a bainite type rail excellent in wear resistance and flaking damage resistance according to claim 1 or 2, which contains one or more kinds of 2% or less.