JP4736621B2 - Perlite steel rail with excellent wear resistance and fatigue damage resistance - Google Patents

Description

  The present invention relates to a pearlite steel rail excellent in wear resistance and fatigue damage resistance, which is used under severe conditions such as a freight car with a large load weight and a sharp curve like an overseas mining railway.

  The loading weight of freight cars mainly for transporting ore like overseas mining railways is much larger than that of passenger cars. For this reason, the use environment of rails used in such fields is severe. Conventionally, hypoeutectoid or eutectoid pearlite steel rails have been mainly used for such heavy-duty railways, so-called high-axle railways, from the viewpoint of emphasizing wear resistance. It was. In recent years, however, the freight load of freight cars has tended to increase in order to increase the efficiency of railway transportation, and higher wear resistance has been demanded for rails for high-axle railways. ing.

  In order to meet such demands, for example, Patent Documents 1 and 2 disclose a technique for increasing wear resistance by increasing the amount of C to 0.85 to 1.20 mass% and increasing the cementite fraction. Is disclosed. Patent Documents 3 and 4 disclose a technique for improving the wear resistance by increasing the cementite fraction by setting the C amount to be more than 0.85 to 1.20 mass% and performing heat treatment on the rail head.

  On the other hand, rails used in the curved section of a high-axle heavy railway are subjected to sliding force due to rolling stress and centrifugal force due to wheels, so that wear becomes severe and fatigue damage due to slippage is likely to occur. However, as in the techniques of Patent Documents 1 to 4, simply increasing the amount of C to more than 0.85 to 1.20 mass%, a pearlite that produces a large amount of proeutectoid cementite structure or a layered structure depending on the heat treatment conditions. There is a problem that the fatigue damage resistance cannot be improved because the amount of the brittle cementite phase increases.

Therefore, Patent Document 5 proposes a technique for suppressing the formation of pro-eutectoid cementite and improving fatigue damage resistance by adding Al in excess of 0.07 to 3.00% and / or Si in excess of 1.00 to 3.00%.
JP-A-8-109439 JP-A-8-144016 JP-A-8-246100 JP-A-8-246101 JP 2002-69585 A

  However, if a large amount of Al or Si is added, a large amount of oxide that becomes the starting point of fatigue damage is generated and dispersed in the matrix, which becomes the starting point of fatigue damage, so that the fatigue damage property of the rail is reduced. There's a problem. Therefore, in the technique of the cited document 5, it is difficult to satisfy both the wear resistance and the fatigue damage resistance simultaneously in a steel rail having a pearlite structure.

  Accordingly, an object of the present invention is to improve the above-mentioned problems of conventional hypo-eutectoid, eutectoid and hyper-eutectoid pearlite steel rails, and pearlite steel excellent in both wear resistance and fatigue damage resistance To provide rails.

  In order to solve the above-mentioned problems of the prior art, the inventors focused on the influence of carbides on wear resistance and fatigue damage resistance, and manufactured and studied various rails. As a result, the present inventors have found that the wear resistance and fatigue damage resistance of the rail can be improved by finely dispersing the W carbide in the steel, thereby completing the present invention.

  That is, the present invention includes C: 0.6 to 1.1 mass%, Si: 0.1 to 1.2 mass%, Mn: 0.4 to 1.5 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, W: 0.01 to 1.0 mass. Is a pearlite steel rail excellent in wear resistance and fatigue damage resistance, characterized in that the balance is made of Fe and inevitable impurities.

  In addition to the above component composition, the rail of the present invention further includes one or two selected from V: 0.001 to 0.50 mass% and Nb: 0.001 to 0.05 mass%.

  In addition to the above component composition, the rail of the present invention is further selected from Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Cr: 1.5 mass% or less, and Mo: 0.5 mass% or less. Or it contains 2 or more types, It is characterized by the above-mentioned.

  According to the present invention, it is possible to stably manufacture a rail excellent in both wear resistance and fatigue damage resistance as compared with a conventional pearlite steel rail. As a result, it contributes to extending the life of rails used in high-axle railways and preventing railway accidents.

As described above, the present invention improves both wear resistance and fatigue damage resistance by finely dispersing W carbide in steel in pearlite steel rails used in high-axle railways and the like. There is a feature in the place where it was made In order to achieve the above characteristics, the present invention defines the composition of the rail components in the following ranges.
C: 0.6-1.1mass%
C is an element essential for forming cementite having a pearlite structure and ensuring wear resistance. Abrasion resistance improves with an increase in the amount of C. By containing 0.6 mass% or more, it is possible to obtain wear resistance superior to that of a conventional heat-treated pearlite steel rail. However, if added over 1.1 mass%, during the Acm transformation after hot rolling, initial cementite is formed at the austenite grain boundaries, and fatigue damage resistance decreases. Accordingly, the C amount is in the range of 0.6 to 1.1 mass%. Preferably, it is 0.7-0.95 mass%.

Si: 0.1-1.2mass%
Si is an element to be added as a deoxidizer, and is also an element that improves strength (hardness) by dissolving in the ferrite phase in pearlite, so it is necessary to add 0.1 mass% or more. However, when the Si content exceeds 1.2 mass%, the weldability deteriorates due to the bonding force with high oxygen that Si has. Therefore, the Si content is set to 0.2 to 1.2 mass%. Preferably, it is 0.2 to 0.8 mass%.

Mn: 0.4-1.5mass%
Mn is reduced steel in the A ₁ transformation temperature (pearlite transformation temperature), by reducing the lamellar spacing of the pearlite structure, high strength of the rail, an element contributing to the high ductility. In order to acquire the said effect, content of Mn needs to be 0.4 mass% or more. However, if the Mn content exceeds 1.5 mass%, a martensitic structure is likely to occur due to microsegregation of Mn, and the material is deteriorated due to hardening and embrittlement of the steel during heat treatment and welding. Therefore, the Mn content is in the range of 0.4 to 1.5 mass%. Preferably, it is 0.7-1.4 mass%.

P: 0.035 mass% or less P is an element that deteriorates the ductility of steel. If it exceeds 0.035 mass%, its influence cannot be ignored. Therefore, the content of P is set to 0.035 mass% or less. Preferably, it is 0.020 mass% or less.

S: 0.035 mass% or less S is an element which exists in steel mainly in the form of inclusions and causes embrittlement of steel. In particular, when the S content exceeds 0.035 mass%, the adverse effect on brittleness cannot be ignored. Therefore, the content of S is set to 0.035 mass% or less. Preferably, it is 0.015 mass% or less.

W: 0.01-1.0mass%
W is an element that forms carbides, finely disperses and precipitates in the base of the steel, contributes to improvement of wear resistance, and also has a unique effect of improving fatigue damage resistance. Is an essential element. In order to acquire those effects, it is necessary to contain 0.01 mass% or more of W. However, even if added over 1.0 mass%, the effect of improving the wear resistance and fatigue damage resistance is saturated, and an effect commensurate with the amount added cannot be obtained. Therefore, the W content is set to 0.01 to 1.0 mass%. Preferably, it is 0.1 to 1.0 mass%.

The rail of the present invention can contain V and / or Nb in the following range in addition to the above components.
V: 0.001 ~ 0.50mass%
V, like W, is an element that forms carbides, finely disperses and precipitates in the steel matrix, and has the effect of improving wear resistance. In order to acquire the said effect, it is preferable to add V 0.001 mass% or more. However, if added over 0.50 mass%, not only the raw material cost increases, but also the workability deteriorates. Therefore, when adding V, it is preferable to set it as the range of 0.001-0.50 mass%.

Nb: 0.001 ~ 0.05mass%
Nb combines with C in steel, precipitates as carbide during and after rolling, refines pearlite colony size, and greatly improves wear resistance, fatigue damage resistance and ductility. Contribute. In order to obtain such an effect, it is preferable to add 0.001 mass% or more of Nb. However, even if added over 0.05 mass%, the effect of improving wear resistance and fatigue damage resistance is saturated, and an effect commensurate with the amount added cannot be obtained. Therefore, when adding Nb, it is preferable to set it as the range of 0.001-0.05 mass%.

In addition to the above components, the rail of the present invention may contain one or more selected from Cr, Cu, Ni and Mo in the following range in order to increase the strength.
Cr: 1.5 mass% or less
Cr is an element that has a large solid solution strengthening ability and is effective for increasing the strength. In order to acquire the effect, adding 0.05 mass% or more is more preferable. However, if it exceeds 1.5 mass%, the hardenability becomes high, martensite is generated, and the wear resistance and fatigue damage resistance are lowered. Therefore, the Cr amount when added is preferably 1.5 mass% or less.

Cu: 1.0 mass% or less
Cu, like Cr, is an element effective for increasing the strength by solid solution strengthening. In order to acquire the effect, it is more preferable to add 0.01 mass% or more. However, since the crack resulting from Cu will arise if it adds exceeding 1.0 mass%, when adding, it is preferable that content of Cu shall be 1.0 mass% or less.

Ni: 1.0 mass% or less
Ni is an element that can increase the strength without degrading the ductility of the steel. Further, since Ni has an effect of preventing cracking due to Cu, when adding Cu, it is preferable to add Ni in combination. In order to acquire these effects, it is more preferable to add 0.01 mass% or more. However, the addition of Cu exceeding 1.0 mass% increases the hardenability and produces martensite, which decreases the wear resistance and fatigue damage resistance. Therefore, when adding Ni, it is preferable to set it as 1.0 mass% or less.

Mo: 0.5mass% or less
Mo is an effective element for increasing the strength by solid solution strengthening. In order to acquire this effect, it is more preferable to add 0.01 mass% or more. However, if it exceeds 0.5 mass%, a bainite structure is likely to occur, and the wear resistance decreases. Therefore, the amount of Mo when added is preferably 0.5 mass% or less.

  In the rail of the present invention, the balance other than the above components is composed of Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the addition of other components than the above does not affect the scope of rights of the present invention.

Next, the manufacturing method of the pearlite steel rail of this invention is demonstrated.
The rail of the present invention can be produced by a generally known method except that the component composition of steel is specified as described above, and is preferably produced under the following conditions.
For example, steel is melted in a converter or electric furnace, and if necessary, after secondary refining such as degassing, the steel composition is adjusted to be within the above preferred range, continuously cast, and bloom. To do. Next, this bloom is heated to 1200-1350 ° C. in a heating furnace and hot-rolled to form a rail. At this time, the rolling end temperature is preferably 900 to 1000 ° C., and the cooling rate after rolling is preferably 1 to 5 ° C./s.

  As shown in Table 1, a test steel having a composition in which the W content was changed was heated to 1250 ° C., hot-rolled and finished at 900 ° C., and then a cooling rate of 2 ° C. / The rail was manufactured by cooling with s. This rail was evaluated for wear resistance and fatigue damage resistance in the following manner.

(Abrasion test)
Although it is desirable to evaluate the wear resistance by actually laying rails, there is a drawback that it takes a long time. Therefore, an accelerated test simulating the actual rail-wheel contact conditions was performed using the Nishihara-type wear tester, and the wear resistance was evaluated. In the wear test, a disk-shaped test piece having a diameter of 30 mm and a thickness of 8 mm taken from a position 2 mm below the top of the rail was used as a test piece, and the wheel material (diameter: 30 mm, thickness: 8 mm, As shown in FIG. 1, contact pressure: 1.4 GPa, rotation speed: 800 rpm, slip rate: -10%, rotating contact under dry conditions using Hv: 390, tempered martensitic steel disc-shaped test piece) The amount of wear after 100,000 revolutions was measured.

(Fatigue damage test)
It is desirable to evaluate the fatigue damage resistance by actually laying rails. However, as with the wear resistance evaluation, there is a problem that requires a long time. Therefore, the fatigue damage resistance of the rail was evaluated by conducting a rolling fatigue test using a Nishihara type wear tester. In the rolling fatigue test, a disk-shaped test piece having a diameter of 30 mm and a thickness of 8 mm having a curved surface with a radius of curvature of 15 mm is used as shown in FIG. 2. Thus, the wheel material diameter 30 mm, thickness: 8 mm, Hv: 390, tempered martensitic steel disk-like specimen), contact pressure: 2.2 GPa, rotation speed: 800 rpm, slip rate: −20 %, In a method of rotating contact under oil lubrication conditions. Then, the contact surface of the test piece was observed every 25000 revolutions, and the fatigue damage life was determined when a crack or delamination of 0.5 mm or more occurred on the contact surface.

  The results of the above test are shown together in Table 1. Further, FIG. 3 shows the influence of the amount of wear after 100,000 revolutions and the W content on the rolling fatigue life. From FIG. 3, it can be seen that the wear resistance and fatigue damage resistance of the rail of the present invention are improved by adding W. However, the above improvement effect of W tends to saturate when it exceeds 1.0 mass%, and even if it is added more than that, significant improvement in wear resistance and fatigue damage resistance cannot be obtained.

  A test steel having the composition shown in Table 2 was heated to 1250 ° C., hot-rolled, finished at 900 ° C., and then cooled at a cooling rate of 2 ° C./s to produce a rail. About this rail, it carried out similarly to Example 1, the test piece was extract | collected from the head, and abrasion resistance and fatigue damage resistance were evaluated.

  The results of the above test are shown together in Table 2. From these results, the composition of C, Si, Mn, and W is controlled within an appropriate range, and further, one or two selected from V and Nb, or one or two selected from Cr, Cu, Ni, and Mo. It can be seen that the wear resistance and fatigue damage resistance of the rail can be further improved by adding more than one component within an appropriate range.

It is a schematic diagram which shows the method of an abrasion test. It is a schematic diagram which shows the method of a fatigue damage test. It is a graph which shows the influence of the amount of W addition on the abrasion resistance and fatigue damage resistance of a rail.

Claims (3)

C: 0.6 to 1.1 mass%, Si: 0.1 to 1.2 mass%, Mn: 0.4 to 1.5 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, W: 0.01 to 1.0 mass%, the balance A pearlitic steel rail with excellent wear resistance and fatigue damage resistance, characterized by comprising Fe and inevitable impurities. The pearlite steel rail according to claim 1, further comprising one or two selected from V: 0.001 to 0.50 mass% and Nb: 0.001 to 0.05 mass% in addition to the component composition. . In addition to the above component composition, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Cr: 1.5 mass% or less, and Mo: 0.5 mass% or less The pearlite steel rail according to claim 1, wherein:

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