JP6801747B2 - Manufacturing method for austenitic rails - Google Patents

Description

The present invention relates to a method for manufacturing an austenitic rail, and more particularly to a method for manufacturing an austenitic rail having excellent wear resistance and fatigue damage resistance.

In high-axle heavy railways used for transporting ore, the load applied to the axles of freight cars is much higher than that of passenger cars, and the rail usage environment is harsh. As a material for rails used in such an environment, steel having a pearlite structure has been mainly used from the viewpoint of emphasizing wear resistance.

However, in recent years, the weight loaded on freight cars has been further increased in order to improve the efficiency of transportation by rail, and further improvement in wear resistance and fatigue damage resistance is required. Therefore, in recent years, various studies have been conducted with the aim of further improving wear resistance. The high-axle heavy railway is a railway having a large load weight per train or freight car (for example, a load weight of about 150 tons or more).

For example, Patent Documents 1 and 2 propose to increase the amount of C in the rail material to more than 0.85% by mass and 1.20% by mass or less. Further, Patent Documents 3 and 4 propose that the amount of C is more than 0.85% by mass and 1.20% by mass or less, and that the rail head is heat-treated. In this way, a device is devised to improve the wear resistance by increasing the amount of C and increasing the cementite fraction.

On the other hand, the rails in the curved section of the high-axis heavy railway are subject to rolling stress due to the wheels and sliding force due to centrifugal force, so that the rail wear becomes more severe and fatigue damage due to slippage occurs. If the amount of C is simply increased as in the techniques proposed in Patent Documents 1 to 4, proeutectoid cementite is produced depending on the heat treatment conditions, and the amount of cementite in the brittle pearlite layered structure is increased. Therefore, the above technique cannot be expected to improve fatigue damage resistance.

Therefore, Patent Document 5 proposes a technique of suppressing the formation of proeutectoid cementite by adding Al and Si to improve fatigue damage resistance.

Further, as described in Non-Patent Document 1, as the crossing which is a component of the turnout, a crossing made of high Mn steel whose main structure is austenite is used from the viewpoint of improving wear resistance.

Japanese Patent No. 4666114 Japanese Unexamined Patent Publication No. 8-109439 Japanese Unexamined Patent Publication No. 8-144016 Japanese Unexamined Patent Publication No. 8-246100 Japanese Unexamined Patent Publication No. 8-246101 JP-A-2002-69585 Japanese Unexamined Patent Publication No. 10-195601

Matsuno, Ueda: Casting Optics, Vol. 70, No. 9 (1998), p. 659.

However, the technique proposed in Patent Document 5 has a problem that the addition of Al produces an oxide that is a starting point of fatigue damage. Therefore, it has been found that it is difficult to achieve both wear resistance and fatigue damage resistance in a steel rail having a pearlite structure (hereinafter referred to as "pearlite rail").

On the other hand, the crossing described in Non-Patent Document 1 has excellent characteristics as compared with the pearlite rail. Specifically, the austenitic high Mn crossing has excellent impact resistance in addition to excellent wear resistance due to high work hardening ability.

However, since the crossing is manufactured by casting, it is difficult to completely remove casting defects. Therefore, it has been difficult to obtain good fatigue damage resistance by the crossing.

An object of the present invention is to solve the above-mentioned various problems, and an object of the present invention is to provide a rail having excellent wear resistance and fatigue damage resistance as compared with conventional pearlite rails.

In order to solve the above problems, the inventors have manufactured rails having different contents of C, Mn, P, S, Al, N and O, and earnestly focused on the structure, wear resistance and fatigue damage resistance. investigated. As a result, it is possible to obtain a desired austenite area ratio and void ratio by controlling the composition of the steel constituents of the rail, the heating temperature, the cross-sectional reduction rate, and the cooling rate after hot rolling. , It has been found that a rail having both excellent wear resistance and fatigue damage resistance can be manufactured by hot rolling.

The present invention is based on the above findings, and its gist structure is as follows.

1. 1. By mass%
C: 0.10 to 2.50%,
Mn: 8.0-45.0%,
P: 0.300% or less,
S: 0.1000% or less,
Al: 0.001-5.000%,
N: 0.5000% or less, and O: 0.1000% or less,
Steel having a component composition with the balance consisting of Fe and unavoidable impurities is heated to a heating temperature of 950 to 1350 ° C.
The heated steel is hot-rolled under the conditions that the total cross-section reduction rate is 0.90 or more and the cross-section reduction rate at 1000 ° C. or higher is 0.60 or more to obtain a rail having a porosity of less than 1%.
A method for producing an austenitic rail, wherein the rail is cooled at an average cooling rate of 1 ° C./sec or more in a temperature range between 900 and 500 ° C. to make the area ratio of austenite 90% or more.

2. 2. The component composition is further increased by mass%.
Ti: 0.10 to 5.00%,
Si: 0.01-5.00%,
Cu: 0.1 to 10.0%,
Ni: 0.1 to 25.0%,
Cr: 0.1 to 30.0%,
Mo: 0.1 to 10.0%,
Nb: 0.005-2.000%,
V: 0.01 to 2.00%,
W: 0.01 to 2.00%,
B: 0.0003 to 0.1000%,
Ca: 0.0003 to 0.1000%,
The method for producing an austenitic rail according to 1 above, which contains 1 or 2 or more selected from the group consisting of Mg: 0.0001 to 0.1000% and REM: 0.0005 to 0.1000%.

The austenitic rail produced by the method of the present invention has far superior wear resistance and fatigue damage resistance as compared with the conventional pearlite rail. Therefore, the austenitic rail of the present invention can be extremely suitably used as a rail for high-axis heavy railways, and contributes to extending the life of the rail and preventing railway accidents.

It is a schematic diagram which shows the test method of the wear resistance by the Nishihara type wear tester. It is a schematic diagram which shows the sampling position of a rail test piece 1. It is a schematic diagram which shows the test method of the fatigue damage resistance by a Nishihara type wear tester.

Hereinafter, embodiments of the present invention will be described. The following description shows a preferred embodiment of the present invention, and the present invention is not limited to the following description.

[Ingredient composition]
The austenitic rail in one embodiment of the present invention has the above-mentioned component composition. In other words, the austenitic rail of the present invention is made of steel having the above-mentioned composition. Hereinafter, the reason for limiting the composition of steel to the above range will be described. Unless otherwise specified, "%" representing the content of each component means "mass%".

C: 0.10-2.50%
C is an element that stabilizes austenite and is an important element for obtaining an austenite structure at room temperature. If the C content is less than 0.10%, the stability of austenite is insufficient and a sufficient austenite structure cannot be obtained. Therefore, the C content is set to 0.10% or more, preferably 0.12% or more. On the other hand, when the C content exceeds 2.50%, the fatigue damage resistance is lowered due to the excessive formation of carbides. Therefore, the C content is 2.50% or less, preferably 2.00% or less.

Mn: 8.0-45.0%
Mn is an element that stabilizes austenite and is an important element for obtaining an austenite structure at room temperature. If the Mn content is less than 8.0%, the stability of austenite is insufficient and a sufficient austenite structure cannot be obtained. Therefore, the Mn content is set to 8.0% or more, preferably 10.0% or more. On the other hand, if the Mn content exceeds 45.0%, the effect of stabilizing austenite is saturated, which is disadvantageous in terms of cost. Therefore, the Mn content is 45.0% or less, preferably 40.0% or less.

P: 0.300% or less P is a grain boundary embrittlement element, and the toughness of steel is lowered by segregation of P at the grain boundaries. Therefore, the P content is set to 0.300% or less. The P content is preferably 0.250% or less. On the other hand, since the smaller the amount of P, the more preferable it is, the lower limit of the P content is not particularly limited and may be 0%. However, since P is usually an element unavoidably contained in steel as an impurity, it is industrial. May be greater than 0%. In addition, since excessively low P causes an increase in refining time and an increase in cost, the P content is preferably 0.001% or more.

S: 0.1000% or less S has an S content of 0.1000% or less in order to reduce the fatigue damage resistance and toughness of the rail material. The S content is preferably 0.080% or less. On the other hand, since the smaller the amount of S, the more preferable it is, the lower limit of the S content is not particularly limited and may be 0%, but industrially, it may be more than 0%. In addition, since excessively low S causes an increase in refining time and an increase in cost, the S content is preferably 0.001% or more.

Al: 0.001-5.000%
Al is an element that acts as an antacid. In order to obtain the above effect, the Al content is 0.001% or more, preferably 0.003% or more. On the other hand, when the Al content exceeds 5.000%, the cleanliness of the steel is lowered and the fatigue damage resistance is lowered. Therefore, the Al content is 5.000% or less, preferably 4.500% or less.

N: 0.5000% or less N is an element that deteriorates the fatigue damage resistance and toughness of the rail material through the formation of carbonitride. Therefore, the N content is set to 0.5000% or less. On the other hand, since the smaller the amount of N, the more preferable it is, the lower limit of the N content is not particularly limited and may be 0%. However, since N is usually an element unavoidably contained in steel as an impurity, it is industrial. May be greater than 0%. In addition, since excessively low N causes an increase in refining time and an increase in cost, the N content is preferably 0.0005% or more.

O: 0.1000% or less O is an element that deteriorates the fatigue damage resistance and toughness of the rail material. Therefore, the O content is set to 0.1000% or less. On the other hand, since the smaller the amount of O, the more preferable it is, the lower limit of the O content is not particularly limited and may be 0%. However, since O is usually an element unavoidably contained in steel as an impurity, it is industrial. May be greater than 0%. It should be noted that the O content is preferably 0.0005% or more because excessive reduction of O causes an increase in refining time and an increase in cost.

The austenitic rail in one embodiment of the present invention may have a component composition consisting of the above elements, the balance Fe and unavoidable impurities.

Further, in another embodiment of the present invention, the component composition may further optionally contain 1 or 2 or more selected from the elements listed below.

Ti: 0.10 to 5.00%
Ti is an element that forms hard carbides and has the effect of improving the wear resistance of the austenite structure. When Ti is added, the Ti content is set to 0.10% or more, preferably 0.12% or more in order to obtain the above effect. On the other hand, when the Ti content exceeds 5.00%, the fatigue damage resistance is lowered. Therefore, the Ti content is 5.00% or less, preferably 4.50% or less.

Si: 0.01-5.00%
Si is an element effective for deoxidation. Further, Si is an element that contributes to increasing the hardness of steel by solid solution strengthening. If the Si content is less than 0.01%, a sufficient effect cannot be obtained. Therefore, when Si is added, the Si content is 0.01% or more, preferably 0.05% or more. On the other hand, when the Si content exceeds 5.00%, the amount of inclusions increases and the fatigue damage resistance decreases. Therefore, the Si content is 5.00% or less, preferably 4.50% or less.

Cu: 0.1 to 10.0%
Cu is an element that can improve the strength of steel. In order to obtain the above effect, the Cu content needs to be 0.1% or more. Therefore, when Cu is added, the Cu content is 0.1% or more, preferably 0.5% or more. On the other hand, if the Cu content exceeds 10.0%, the effect is saturated and it is disadvantageous in terms of cost. Therefore, the Cu content is 10.0% or less, preferably 8.0% or less.

Ni: 0.1 to 25.0%
Ni is an element that has the effect of improving toughness. In order to obtain the above effect, the Ni content needs to be 0.1% or more. Therefore, when Ni is added, the Ni content is 0.1% or more, preferably 0.5% or more. On the other hand, if the Ni content exceeds 25.0%, the effect is saturated and it is disadvantageous in terms of cost. Therefore, the Ni content is 25.0% or less, preferably 20.0% or less.

Cr: 0.1 to 30.0%
Cr is an element that can improve the strength of steel. In order to obtain the above effect, the Cr content needs to be 0.1% or more. Therefore, when Cr is added, the Cr content is 0.1% or more, preferably 0.5% or more. On the other hand, if the Cr content exceeds 30.0%, the effect is saturated and it is disadvantageous in terms of cost. Therefore, the Cr content is set to 30.0% or less, preferably 28.0% or less.

Mo: 0.1 to 10.0%
Mo is an element that can improve the strength of steel. In order to obtain the above effect, the Mo content needs to be 0.1% or more. Therefore, when Mo is added, the Mo content is 0.1% or more, preferably 0.5% or more. On the other hand, if the Mo content exceeds 10.0%, the effect is saturated and it becomes disadvantageous in terms of cost. Therefore, the Mo content is 10.0% or less, preferably 8.0% or less.

Nb: 0.005-2.000%
Nb is an element that has the effect of improving the wear resistance of the austenite structure by precipitating as a carbonitride. In order to obtain the above effect, the Nb content needs to be 0.005% or more. Therefore, when Nb is added, the Nb content is 0.005% or more, preferably 0.007% or more. On the other hand, if the Nb content exceeds 2.000%, the fatigue damage resistance deteriorates. Therefore, the Nb content is 2.000% or less, preferably 1.700% or less.

V: 0.01 to 2.00%
V is an element having an effect of improving the wear resistance of the austenite structure by precipitating as a carbonitride. In order to obtain the above effect, the V content needs to be 0.01% or more. Therefore, when V is added, the V content is 0.01% or more, preferably 0.02% or more. On the other hand, if the V content exceeds 2.00%, the fatigue damage resistance deteriorates. Therefore, the V content is 2.00% or less, preferably 1.80% or less.

W: 0.01 to 2.00%
W is an element that can improve the strength of steel. In order to obtain the above effect, the W content needs to be 0.01% or more. Therefore, when W is added, the W content is 0.01% or more, preferably 0.02% or more. On the other hand, if the W content exceeds 2.00%, the toughness deteriorates. Therefore, the W content is 2.00% or less, preferably 1.80% or less.

B: 0.0003 to 0.1000%
B is an element having an effect of improving the grain boundary strength by segregation at the grain boundary. In order to obtain the above effect, the B content needs to be 0.0003% or more. Therefore, when B is added, the B content is 0.0003% or more, preferably 0.0005% or more. On the other hand, when the B content exceeds 0.1000%, the fatigue damage resistance is lowered due to the grain boundary precipitation of the carbonitride. Therefore, the B content is 0.1000% or less, preferably 0.0800% or less.

Ca: 0.0003 to 0.1000%
Ca is an element that improves the strength and toughness of joints by forming acid sulfides with high stability at high temperatures to make the crystal grain size of welds finer by the pinning effect. In order to obtain the above effect, the Ca content needs to be 0.0003% or more. Therefore, when Ca is added, the Ca content is 0.0003% or more, preferably 0.0005% or more. On the other hand, if the Ca content exceeds 0.1000%, the cleanliness is lowered and the toughness of the steel is impaired. Therefore, the Ca content is 0.1000% or less, preferably 0.0800% or less.

Mg: 0.0001 to 0.1000%
Mg is an element that improves the strength and toughness of joints by forming acid sulfides with high stability at high temperatures to make the crystal grain size of welds finer by the pinning effect. In order to obtain the above effect, the Mg content needs to be 0.0005% or more. Therefore, when Mg is added, the Mg content is 0.0001% or more, preferably 0.0005% or more. On the other hand, if the Mg content exceeds 0.1000%, the cleanliness is lowered and the toughness of the steel is impaired. Therefore, the Mg content is 0.1000% or less, preferably 0.0800% or less.

REM: 0.0005 to 0.1000%
REM (rare earth metal) is an element that improves the strength and toughness of joints by forming acid sulfides with high stability at high temperatures to make the grain size of welds finer by the pinning effect. In order to obtain the above effect, the REM content needs to be 0.0005% or more. Therefore, when REM is added, the REM content is 0.0005% or more, preferably 0.0010% or more. On the other hand, if the REM content exceeds 0.1000%, the cleanliness is lowered and the toughness of the steel is impaired. Therefore, the REM content is 0.1000% or less, preferably 0.0800% or less.

[Micro tissue]
Austenite: 90% or more The austenitic rail of the present invention has a microstructure in which the area ratio of austenite in the region from the surface layer to a depth of 25 mm, which is a guideline for rail replacement, is 90% or more. If the area ratio of austenite in the region is less than 90%, in addition to reduced wear resistance and fatigue damage resistance, ductility, toughness, and workability are also reduced. Therefore, the area ratio of austenite is set to 90% or more. The area ratio of the austenite is preferably 95% or more, and more preferably 97% or more. On the other hand, the upper limit of the area ratio is not particularly limited. That is, the area ratio of austenite may be 100% or less.

Here, the "area ratio of austenite" refers to the area ratio of austenite in the base structure (matrix) of steel. "Base structure" refers to the structure of steel excluding inclusions and deposits. Further, the area ratio of the austenite shall indicate a measured value at a depth of 5 mm from the surface of the rail head. The area ratio of the austenite can be measured by the method described in Examples.

In the microstructure of the austenitic rail of the present invention, the structure other than austenite is not particularly limited. If the total area ratio is 10% or less, it is permissible that tissues other than austenite exist. Examples of the structure other than austenite include 1 or 2 or more selected from the group consisting of ferrite, pearlite, bainite, and martensite.

[Porosity]
The austenitic rail of the present invention has a porosity of less than 1%. If the porosity is 1% or more, the fatigue damage resistance deteriorates. The lower the porosity, the more preferable it is, so the lower limit is not particularly limited. That is, the porosity may be 0% or more. The product manufactured by casting has defects such as shrinkage cavities (casting defects) for manufacturing reasons, and therefore does not satisfy the above porosity condition.

[Production method]
Next, a method for manufacturing an austenitic rail according to an embodiment of the present invention will be described. The austenitic rail of the present invention can be produced by sequentially applying the following treatments (1) to (3) to a steel having the above-mentioned composition (also referred to as "steel material").
(1) Heating (2) Hot rolling (3) Cooling

The steel (steel material) used as a material can be produced by any method, but in general, it is preferable to produce the steel by casting, particularly continuous casting. The steel may be a piece of steel.

(1) Heating Heating temperature: 950 to 1350 ° C
First, the steel having the above-mentioned composition is heated so that the center temperature of the steel is in the range of 950 to 1350 ° C. If the heating temperature is lower than 950 ° C., the amount of solid solution C is insufficient because the carbides precipitated during production (casting) do not dissolve in solid solution. As a result, the degree of austenite stabilization is insufficient, and the austenite area ratio cannot be 90% or more after cooling. Therefore, the heating temperature is set to 950 ° C. or higher. On the other hand, if the heating temperature exceeds 1350 ° C., the cost for heating increases. Therefore, the heating temperature is set to 1350 ° C. or lower.

(2) Hot rolling Next, the heated steel is hot-rolled to form a rail shape. In the hot rolling, the cross-section reduction rate must satisfy the following two conditions in order to reduce the porosity of the rail to less than 1%.
-Total cross-section reduction rate: 0.90 or more-Cross-section reduction rate at 1000 ° C. or higher: 0.60 or more The total cross-section reduction rate is defined by the following equation.
Total cross-section reduction rate = (Ai-Af) / Ai
Further, the cross-sectional reduction rate at 1000 ° C. or higher is defined by the following formula.
Cross-sectional reduction rate at 1000 ° C or higher = (Ai-A ₁₀₀₀ ° C) / Ai
Here, Ai is the cross-sectional area of the steel before hot rolling (cm ² ), Af is the cross-sectional area of the rail after hot rolling (cm ² ), and A ₁₀₀₀ ° C is the rolled when the temperature reaches 1000 ° C. The cross-sectional area (cm ² ) of the material is shown respectively. Ai, Af, and A ₁₀₀₀ ° C. refer to the cross-sectional area in the cross section orthogonal to the stretching direction during hot rolling, respectively.

If one or both of the above two conditions are not satisfied, the porosity in the rail cross section becomes 1% or more, and the fatigue damage resistance deteriorates. Therefore, the total cross-section reduction rate is 0.90 or more, and the cross-section reduction rate in the temperature range of 1000 ° C. or higher is 0.60 or more. The total cross-sectional reduction rate is preferably 0.92 or more, and more preferably 0.93 or more. Further, the cross-sectional reduction rate at 1000 ° C. or higher is preferably 0.62 or higher, more preferably 0.64 or higher.

(3) Cooling Average cooling rate between 900 and 500 ° C.: 1 ° C./sec or more Next, the steel after hot rolling is cooled. In the cooling step, the average cooling rate in the temperature range between 900 and 500 ° C. is set to 1 ° C./sec or more. Here, the average cooling rate is
It was calculated by measuring the surface temperature of the side surface of the rail head with a radiation thermometer and measuring the temperature change from the start of cooling to the stop of cooling. By cooling under the above conditions, the area ratio of austenite in the finally obtained rail can be 90% or more. If the average cooling rate is less than 1 ° C./sec, carbides are precipitated and the amount of solid solution C is insufficient. As a result, the stability of austenite is insufficient, and the area ratio of austenite cannot be 90% or more. The average cooling rate is preferably 2 ° C./sec or higher, and more preferably 5 ° C./sec or higher. On the other hand, the upper limit of the average cooling rate is not particularly limited, but the equipment cost becomes very high in order to realize the average cooling rate of 100 ° C./sec or more. Therefore, the average cooling rate is preferably 100 ° C./sec or less, more preferably 50 ° C./sec or less, and even more preferably 30 ° C./sec or less.

Next, the present invention will be described in more detail based on Examples. However, the present invention is not limited by the following examples, and can be appropriately modified within a range that can be adapted to the gist of the present invention, all of which are included in the technical scope of the present invention. Is done.

The rail was manufactured by the following procedure and its characteristics were evaluated.

First, the steel material (steel piece) having the composition shown in Table 1 was heated to the heating temperature shown in Table 2. Next, the heated steel material was hot-rolled under the conditions shown in Table 2 to form a rail shape. After that, cooling was performed to obtain a rail. The cooling was performed only on the rail head. During cooling, the surface temperature of the side surface of the rail head was measured with a radiation thermometer, and the temperature change from the start of cooling to the stop of cooling was measured. From the measurement results, the average cooling rate (° C./sec) in the cooling was calculated.

A rail having a pearlite structure was prepared to be used as a reference in the evaluation of wear resistance and fatigue damage resistance described later (No. 1). Hereinafter, this pearlite rail is referred to as a "reference material".

Further, for comparison, a rail material was produced by casting instead of hot rolling (No. 33). The cast rail material was manufactured by the following procedure. First, 150 kg of steel ingot was melted by vacuum melting. Then, a rail material having the shape of a rail head was obtained by casting from the obtained steel ingot. The rail material was heat-treated at 1000 ° C. for 1 hour, and then water-cooled.

The microstructure, porosity, wear resistance, and fatigue damage resistance of each of the obtained rails were evaluated. The evaluation method will be described below.

(Micro tissue)
A sample for microstructure observation was taken from the obtained rail. The sample was taken from the vicinity of the surface layer of the rail head (depth 1 mm), at depths 5 mm, 10 mm, 15 mm, 20 mm and 25 mm so that the observation surface of the sample was parallel to the rolling direction.

After the surface of the collected sample was mirror-polished, it was analyzed by electron backscatter diffraction (EBSD) to obtain an Inverse Pole Figure map (reverse pole figure map). The analysis by EBSD was performed under the conditions of observation range: 1 mm × 1 mm, accelerating voltage 20 kV, and step size 1 μm. From the obtained Inverse Pole Figure map, the ratio (area ratio) of the area of austenite to the area of the steel matrix structure (ferrite, pearlite, austenite, bainite, martensite) excluding inclusions and precipitates is near the surface layer (depth). It was calculated at the positions of 1 mm), 5 mm, 10 mm, 15 mm, 20 mm and 25 mm in depth, and the average value was adopted.

(Porosity)
After cutting the rail head, the entire surface was mirror-polished, and a 50-fold cross-section was observed with an optical microscope in a no-etched state. The porosity was determined by image analysis from the obtained optical microscope structure of the entire cross section of the rail head. The voids referred to here are defects that can be recognized by a 50x optical microscope structure, and the main targets are zaku, porosity, and shrinkage cavities.

After the surface of the collected sample was mirror-polished, it was analyzed by electron backscatter diffraction (EBSD) to obtain an Inverse Pole Figure map (reverse pole figure map). The analysis by EBSD was performed under the conditions of observation range: 1 mm × 1 mm, accelerating voltage 20 kV, and step size 1 μm. From the obtained Inverse Pole Figure map, the ratio (area ratio) of the area of austenite to the area of the steel matrix structure (ferrite, pearlite, austenite, bainite, martensite) excluding inclusions and precipitates was calculated.

(Abrasion resistance)
It is desirable to evaluate the wear resistance by actually laying the rail, but it takes a long time for the test. Therefore, in this embodiment, the wear resistance is determined by a test simulating the actual contact conditions between the internal high-hardness rail and the wheel using a Nishihara-type wear tester that can evaluate the wear resistance in a short time. evaluated.

1A and 1B are schematic views showing a test method by a Nishihara type wear tester, where FIG. 1A is a side view and FIG. 1B is a front view. This test is carried out by rotating a rail test piece 1 (Nishihara type wear test piece) having an outer diameter of 30 mm in contact with the tire test piece 2 as shown in FIG.

The rail test piece 1 was taken from the position shown in FIG. 2 on the rail head. On the other hand, the tire test piece 2 was produced by the following procedure. First, a round bar having a diameter of 32 mm was collected from the head of an ordinary rail specified in JIS E1101. Next, the round bar was heat-treated so that the Vickers hardness (load 98N) was Hv390 and the structure was a tempered martensite structure. The round bar after the heat treatment was processed into the shape shown in FIG. 1 to obtain a tire test piece 2.

In the test, the rail test piece 1 and the tire test piece 2 were rotated in the directions indicated by arrows in FIG. 1, and the amount of wear (weight reduction) of the rail test piece 1 after 100,000 rotations was measured. The test was carried out in a dry state, and the test conditions were: contact pressure: 1.6 GPa, slip ratio: -10%, rotation speed of rail test piece 1: 675 times / min (rotation speed of tire test piece was 750 times / min). ). The measured wear amount (g) is shown in Table 2.

In addition, the amount of improvement in wear resistance (%) based on the amount of wear of the pearlite rail (No. 1) as the above-mentioned "reference material" is also shown in Table 2. The amount of improvement in the wear resistance of the rail test piece is {(wear amount of reference material (g) -wear amount of the rail test piece (g)) / (wear amount of reference material (g))} × 100. Calculated. The amount of improvement is preferably 10% or more.

(Fatigue damage resistance)
The evaluation of fatigue resistance and damage resistance was also carried out using the Nishihara type wear tester in the same manner as the evaluation of wear resistance. However, as the rail test piece 1, as shown in FIG. 3, a test piece having a diameter of 30 mm, in which the contact surface with the tire test piece 2 is a curved surface having a radius of curvature of 15 mm, was used. The test piece was taken from the rail head in the same manner as the rail test piece used for the evaluation of wear resistance.

In the test, the rail test piece 1 and the tire test piece 2 were rotated in the directions indicated by the arrows in FIG. 3, respectively. The test environment was an oil lubrication condition, and the test was conducted under the conditions of contact pressure: 2.4 GPa, slip ratio: -20%, and rotation speed of rail test piece: 600 rpm (rotation speed of tire test piece is 750 rpm).

The surface of the rail test piece 1 was observed every 25,000 times to confirm whether or not a crack of 0.5 mm or more was generated. Table 2 shows the number of rotations at the time when a crack of 0.5 mm or more occurred as the number of rotations until the occurrence of fatigue damage. The number of revolutions can be regarded as an index of fatigue damage resistance (fatigue damage life).

In addition, Table 2 also shows the amount of improvement in fatigue damage resistance (%) based on the number of revolutions until the occurrence of fatigue damage in the pearlite rail (No. 1) as the above-mentioned "reference material". The amount of improvement in the fatigue damage resistance of the rail test piece is {(rotation speed until fatigue damage occurs in the rail test piece-rotation speed until fatigue damage occurs in the reference material) / (until fatigue damage occurs in the reference material). Rotation speed)} × 100 was calculated. The amount of improvement is preferably 10% or more. When the improvement amount is a negative value, it means that the fatigue damage resistance is inferior to that of the reference material.

As can be seen from the evaluation results shown in Table 2, the austenitic rails satisfying the conditions of the present invention had both wear resistance and fatigue damage resistance improved by 10% or more as compared with the pearlite rail as the reference material. .. On the other hand, the rails of the comparative examples that do not satisfy the conditions of the present invention were inferior to the present invention in at least either wear resistance and fatigue damage resistance. Further, the austenitic rails satisfying the conditions of the present invention all had a void ratio of 0%, whereas the cross-sectional reduction rate during hot rolling did not satisfy the conditions of the present invention (No. 31, No. 31). In the rail (No. 33) produced by 32) or casting, the void ratio was as high as 1 to 3% due to the presence of defects, and as a result, the fatigue damage resistance was significantly inferior to that of the invention example.

1 Rail test piece 2 Tire test piece 3 Rail head

Claims (2)

By mass%
C: 0.10 to 2.50%,
Mn: 8.0-45.0%,
P: 0.300% or less,
S: 0.1000% or less,
Al: 0.001-5.000%,
N: 0.5000% or less, and O: 0.1000% or less,
Steel having a component composition with the balance consisting of Fe and unavoidable impurities is heated to a heating temperature of 950 to 1350 ° C.
The heated steel is hot-rolled under the conditions that the total cross-section reduction rate is 0.90 or more and the cross-section reduction rate at 1000 ° C. or higher is 0.60 or more to obtain a rail having a porosity of less than 1%.
A method for producing an austenitic rail, wherein the rail is cooled at an average cooling rate of 1 ° C./sec or more in a temperature range between 900 and 500 ° C. to make the area ratio of austenite 90% or more. The component composition is further increased by mass%.
Ti: 0.10 to 5.00%,
Si: 0.01-5.00%,
Cu: 0.1 to 10.0%,
Ni: 0.1 to 25.0%,
Cr: 0.1 to 30.0%,
Mo: 0.1 to 10.0%,
Nb: 0.005-2.000%,
V: 0.01 to 2.00%,
W: 0.01 to 2.00%,
B: 0.0003 to 0.1000%,
Ca: 0.0003 to 0.1000%,
The method for producing an austenitic rail according to claim 1, which contains 1 or 2 or more selected from the group consisting of Mg: 0.0001 to 0.1000% and REM: 0.0005 to 0.1000%.

Images