JP2021063258A - Railway wheel - Google Patents

Abstract

To provide a railway wheel excellent in abrasion resistance and in machinability when a production step is performed.SOLUTION: A chemical component of a railway wheel according to this embodiment comprises, by mass: 0.85 to 1.15% of C; 0.80% or less of Si; 1.50% or less of Mn; P:0.050% or less of P; S:0.050% or less of S; and the balance comprising Fe and impurities. In the railway wheel, Fn1 defined by formula (1): Fn1=30.52+6.96×C+4.96×Si+1.85×Mn+4.85×Cr+34.77×V is 42.0 or less; Fn2 defined by formula (2): Fn2=18.18+21.82×C+2.39×Si+1.01×Mn+6.97×Cr+24.79×V is 39.0 or more; a gross area ratio of perlite in a cross section perpendicular to a tread of a rim part is 95.0% or more; and an area ratio of a spheroidized cementite-containing minute region is 40.0% or less.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to railroad wheels.

Railroad vehicles run on the rails that make up the railroad tracks. Railroad vehicles include a plurality of railroad wheels. Railroad wheels support the vehicle, come into contact with the rails, and move while rotating on the rails. Railroad wheels wear due to contact with rails. Recently, for the purpose of improving the efficiency of railway transportation, the load weight on railway vehicles has been increased and the speed of railway vehicles has been increased. As a result, improvement in wear resistance of railway wheels is required.

Techniques for improving the wear resistance of railway wheels are described in JP-A-9-202937 (Patent Document 1), JP-A-2012-107295 (Patent Document 2), JP-A-2013-231212 (Patent Document 3). It is proposed in Japanese Patent Application Laid-Open No. 2004-315928 (Patent Document 4).

The wheels for railway vehicles disclosed in Patent Document 1 have a mass% of C: 0.4 to 0.75%, Si: 0.4 to 0.95%, Mn: 0.6 to 1.2%, and so on. It contains Cr: 0 to less than 0.2%, P: less than 0.03%, S: 0.03% or less, and the balance consists of Fe and other unavoidable impurities. In this railway wheel, a region from the surface of the wheel tread to a depth of at least 50 mm is composed of a pearlite structure. In the method for manufacturing a railway wheel of Patent Document 1, the wheel tread portion is formed under the condition that the cooling curve of the wheel tread portion passes through the pearlite generation region in the continuous cooling transformation curve diagram and is on the martensitic transformation curve side for a long time. Includes a quenching step to cool.

The steel for wheels disclosed in Patent Document 2 has a mass% of C: 0.65 to 0.84%, Si: 0.02 to 1.00%, Mn: 0.50 to 1.90%, and Cr. : 0.02 to 0.50%, V: 0.02 to 0.20%, S ≤ 0.04%, the balance is composed of Fe and impurities, P ≤ 0.05%, Cu ≤ 0.20 It has a chemical composition of% and Ni ≦ 0.20%. This chemical composition further satisfies the following relational expression. [34 ≦ 2.7 + 29.5 × C + 2.9 × Si + 6.9 × Mn + 10.8 × Cr + 30.3 × Mo + 44.3 × V ≦ 43] and [0.76 × exp (0.05 × C) × exp ( 1.35 × Si) × exp (0.38 × Mn) × exp (0.77 × Cr) × exp (3.0 × Mo) × exp (4.6 × V) ≦ 25]. Patent Document 2 describes that this vehicle steel is excellent in wear resistance, rolling fatigue resistance, and spoke resistance by satisfying the above chemical composition and the above formula.

The steel for wheels disclosed in Patent Document 3 is, in mass%, C: 0.65 to 0.84%, Si: 0.4 to 1.0%, Mn: 0.50 to 1.40%, Cr. : 0.02 to 0.13%, S: 0.04% or less, V: 0.02 to 0.12%, Fn1 defined in the formula (1) is 32 to 43, and the formula Fn2 represented by (2) is 25 or less, and the balance is composed of Fe and impurities. Here, the formula (1) is Fn1 = 2.7 + 29.5C + 2.9Si + 6.9Mn + 10.8Cr + 30.3Mo + 44.3V, and the formula (2) is Fn2 = exp (0.76) × exp (0.05C). × exp (1.35Si) × exp (0.38Mn) × exp (0.77Cr) × exp (3.0Mo) × exp (4.6V). Patent Document 3 describes that this wheel steel has the above chemical composition and is excellent in wear resistance, rolling fatigue resistance, and spalling resistance when Fn1 and Fn2 satisfy the above ranges. There is.

The wheels for railway vehicles disclosed in Patent Document 4 have a mass% of C: 0.85 to 1.20%, Si: 0.10 to 2.00%, Mn: 0.05 to 2.00%, and so on. If necessary, it further contains one or more of Cr, Mo, V, Nb, B, Co, Cu, Ni, Ti, Mg, Ca, Al, Zr, and N in a predetermined amount, and the balance is Fe and An integrated railroad vehicle wheel made of steel containing a chemical component consisting of other unavoidable impurities, and at least a part of the tread and / or flange surface of the wheel has a pearlite structure. In Patent Document 4, the life of wheels for railway vehicles depends on the amount of wear on the tread and flange surfaces (paragraph [0002] of Patent Document 4), and further, the amount of heat generated when braking is applied in a high-speed railway is increased. It is stated that it depends on the cracks on the tread and flange surfaces that occur with it. It is described that the wheels for railway vehicles have the above configuration, so that the wear resistance and thermal cracks of the tread surface and the flange surface can be suppressed.

Japanese Unexamined Patent Publication No. 9-202937 Japanese Unexamined Patent Publication No. 2012-107295 Japanese Unexamined Patent Publication No. 2013-231212 Japanese Unexamined Patent Publication No. 2004-315928

The wheel for a railway vehicle proposed in Patent Document 1 has a low Cr content and contains an appropriate amount of Si in order to have a property of obtaining a pearlite structure at the same time as an appropriate hardenability. However, the C content of the railroad vehicle wheel described in Patent Document 1 is 0.4 to 0.75%, and the wheel is made of so-called subeutectoid steel. Therefore, there is a limit to the improvement of wear resistance. Similarly, the wheel steels proposed in Patent Documents 2 and 3 are also made of subeutectoid steel. In Patent Documents 2 and 3, the pearlite structure is strengthened and the wear resistance is enhanced by containing V in the subeutectoid steel. However, there is a limit to the improvement of wear resistance only by containing V.

On the other hand, in the wheels for railway vehicles proposed in Patent Document 4, wear resistance is improved by using hypereutectoid steel having a high C content. However, it has been found that when manufacturing a railway wheel made of hypereutectoid steel, a new problem different from that of subeutectoid steel arises.

Railroad wheels are usually manufactured in the following steps. Manufacture intermediate products by hot forging and hot rolling. Tread quenching is performed on intermediate products. Then, the martensite layer formed on the tread surface of the rim portion of the intermediate product after the tread surface quenching is cut and removed, and the microstructure of the tread surface is made into a pearlite structure.

As described above, the manufacture of railway wheels includes a step of cutting and removing the martensite layer formed on the tread surface of the rim portion. In the case of subeutectoid steel railroad wheels, the cutting of the martensite layer could be carried out relatively easily. However, in the case of hypereutectoid steel, the hardness of the martensite layer is very high, which makes cutting difficult.

Therefore, an object of the present disclosure is to provide a railway wheel having excellent wear resistance and excellent machinability during a manufacturing process.

Railway wheels according to this disclosure
With the rim
With the boss
A plate portion arranged between the rim portion and the boss portion is provided.
The chemical composition of the railway wheel is mass%.
C: 0.85 to 1.15%,
Si: 0.80% or less,
Mn: 1.50% or less,
P: 0.050% or less,
S: 0.050% or less,
Cr: 0 to 0.50%,
V: 0 to 0.10%,
Mo: 0-0.20%,
Cu: 0-0.50%,
Ni: 0 to 0.50%,
Al: 0 to 0.500% and
The rest consists of Fe and impurities
Fn1 defined by the equation (1) is 42.0 or less, and
Fn2 defined by the equation (2) is 39.0 or more, and
The total area ratio of pearlite in the cross section perpendicular to the tread of the rim portion is 95.0% or more.
Of the pearlite having a cross section perpendicular to the tread of the rim portion, in a rectangular observation field of view of 20 μm in length × 20 μm in width, it is divided into 40 equal parts at a pitch of 0.5 μm in the vertical direction and 40 at a pitch of 0.5 μm in the horizontal direction. 40 × 40 microregions were divided into equal parts, and the microregion containing at least one cementite that fits within the microregion was defined as a spheroidized cementite-containing microregion. When
The spheroidized cementite-containing microregion area ratio, which is the ratio of the total number of the spheroidized cementite-containing microregions to the total number of the microregions, is 40.0% or less.
Fn1 = 30.52 + 6.96 × C + 4.96 × Si + 1.85 × Mn + 4.85 × Cr + 34.77 × V ... (1)
Fn2 = 18.18 + 21.82 × C + 2.39 × Si + 1.01 × Mn + 6.97 × Cr + 24.79 × V ... (2)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (1) and the formula (2).

The railway wheel according to the present disclosure has excellent wear resistance and excellent machinability during the manufacturing process.

FIG. 1 is a cross-sectional view including a central axis of a railway wheel. FIG. 2 is a schematic view of an observation field of view for explaining a method of measuring the spheroidized cementite-containing minute region area ratio. FIG. 3 is a schematic view showing an example in which 3 × 3 = 9 minute regions of the observation field of view shown in FIG. 2 are enlarged. FIG. 4 is a diagram for explaining the definition of the nine minute regions in FIG. FIG. 5 is a diagram of a photographic image (SEM image) showing an example of a microstructure of a part of the observation field of view. FIG. 6 is a diagram showing an example of a cooling device for cooling an intermediate product.

[Railway wheel configuration]
FIG. 1 is a cross-sectional view including a central axis of a railway wheel according to the present embodiment. With reference to FIG. 1, the railroad wheel 1 has a disk shape and includes a boss portion 2, a plate portion 3, and a rim portion 4. The boss portion 2 has a cylindrical shape and is arranged at the center portion in the radial direction (direction perpendicular to the central axis) of the railway wheel 1. The boss portion 2 has a through hole 21. The central axis of the through hole 21 coincides with the central axis of the railway wheel 1. A railway axle (not shown) is inserted into the through hole 21. The thickness T2 of the boss portion 2 is thicker than the thickness T3 of the plate portion 3. The rim portion 4 is formed on the outer peripheral edge portion of the railway wheel 1. The rim portion 4 includes a tread surface 41 and a flange 42. The tread 41 is connected to the flange 42. When the railroad wheel 1 is used, the tread 41 and the flange 42 come into contact with the rail surface. The thickness T4 of the rim portion 4 is thicker than the thickness T3 of the plate portion 3. The plate portion 3 is arranged between the boss portion 2 and the rim portion 4, and is connected to the boss portion 2 and the rim portion 4. Specifically, the inner peripheral edge portion of the plate portion 3 is connected to the boss portion 2, and the outer peripheral edge portion of the plate portion 3 is connected to the rim portion 4. The thickness T3 of the plate portion 3 is thinner than the thickness T2 of the boss portion 2 and the thickness T4 of the rim portion 4. The diameter of the railroad wheel 1 is not particularly limited, but is, for example, 700 mm to 1000 mm.

The present inventors have studied a railway wheel that can achieve both wear resistance and machinability. First, the present inventors, in terms of mass%, C: 0.85 to 1.15%, Si: 0.80% or less, Mn: 1.50% or less, P: 0.050% or less, S: 0.050% or less, Cr: 0 to 0.50%, V: 0 to 0.10%, Mo: 0 to 0.20%, Cu: 0 to 0.50%, Ni: 0 to 0.50% , Al: 0 to 0.500%, and if the balance is a chemical composition composed of Fe and impurities, it is considered that there is a possibility that both wear resistance and machinability can be achieved at the same time.

By the way, in order to improve the machinability of railway wheels, it is preferable that the hardness of martensite formed by tread quenching is suppressed. Further, in order to increase the wear resistance of the railway wheel, it is preferable to increase the hardness of pearlite. Therefore, a method for increasing the hardness of pearlite while suppressing the hardness of the martensite layer was investigated from the viewpoint of chemical composition. As a result, if Fn1 defined by the following formula (1) is 42.0 or less and Fn2 defined by the formula (2) is 39.0 or more, the martensite layer formed by tread quenching It has been found that the hardness of pearlite can be increased while suppressing the hardness from becoming excessively high.
Fn1 = 30.52 + 6.96 × C + 4.96 × Si + 1.85 × Mn + 4.85 × Cr + 34.77 × V ... (1)
Fn2 = 18.18 + 21.82 × C + 2.39 × Si + 1.01 × Mn + 6.97 × Cr + 24.79 × V ... (2)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (1) and the formula (2).

However, even if the chemical composition is within the above range, Fn1 is 42.0 or less, and Fn2 is 39.0 or more, the wear resistance may be low. Therefore, the present inventors further investigated. As a result, the present inventors obtained the following findings.

Tempering after tread quenching is an indispensable process in the manufacturing process of railway wheels made of hypereutectoid steel. In tempering, the higher the tempering temperature, the lower the hardness of martensite (tempering martensite) and the higher the machinability. Therefore, in the case of railway wheels made of hypereutectoid steel, it seems preferable to raise the tempering temperature in order to lower the hardness of martensite and improve the machinability.

However, in railway wheels made of hypereutectoid steel, if the tempering temperature is too high, the pearlite lamellae will collapse and the cementite in the pearlite will spheroidize. If cementite is excessively spheroidized, the wear resistance of the railway wheel becomes high even if the chemical composition is within the above range, Fn1 is 42.0 or less, and Fn2 is 39.0 or more. It gets lower.

Therefore, the present inventors further investigated the form of a microstructure capable of achieving both machinability and wear resistance in a railway wheel made of hypereutectoid steel. As a result, the following matters were found.

Note the pearlite region in the cross section perpendicular to the tread of the rim of the hypereutectoid steel railroad wheel. In this pearlite region, in a rectangular observation field of 20 μm in length × 20 μm in width, 40 equal parts are divided into 40 equal parts at a pitch of 0.5 μm in the vertical direction and 40 equal parts at a pitch of 0.5 μm in the horizontal direction. Partition a small area. Then, among these microregions, a microregion containing at least one cementite (spheroidized cementite) that can be entirely contained within the microregion is defined as a “spheroidized cementite-containing microregion”. Here, "containing at least one cementite that can be entirely contained in the minute region" means that at least one cementite among the plurality of cementites is completely contained in the minute region. That is, cementite that partially protrudes from the minute region does not fall under "cementite that fits entirely within the minute region".

Further, the spheroidized cementite-containing minute region area ratio (%) is defined by the following equation.
Spheroidized cementite-containing microregion area ratio (%) = total number of spheroidized cementite-containing microregions / total number of microregions x 100

The present inventors have found that when the spheroidized cementite-containing minute region area ratio defined by the above formula is 40.0% or less, both high machinability and high wear resistance can be achieved at the same time. The railway wheel of the present embodiment completed based on the above findings has the following configuration.

[1]
Railroad wheels
With the rim
With the boss
A plate portion arranged between the rim portion and the boss portion is provided.
The chemical composition of the railway wheel is mass%.
C: 0.85 to 1.15%,
Si: 0.80% or less,
Mn: 1.50% or less,
P: 0.050% or less,
S: 0.050% or less,
Cr: 0 to 0.50%,
V: 0 to 0.10%,
Mo: 0-0.20%,
Cu: 0-0.50%,
Ni: 0 to 0.50%,
Al: 0 to 0.500% and
The rest consists of Fe and impurities
Fn1 defined by the equation (1) is 42.0 or less, and
Fn2 defined by the equation (2) is 39.0 or more, and
The total area ratio of pearlite in the cross section perpendicular to the tread of the rim portion is 95.0% or more.
Of the pearlite having a cross section perpendicular to the tread of the rim portion, in a rectangular observation field of view of 20 μm in length × 20 μm in width, it is divided into 40 equal parts at a pitch of 0.5 μm in the vertical direction and 40 at a pitch of 0.5 μm in the horizontal direction. 40 × 40 microregions were divided into equal parts, and the microregion containing at least one cementite that fits within the microregion was defined as a spheroidized cementite-containing microregion. When
The spheroidized cementite-containing microregion area ratio, which is the ratio of the total number of the spheroidized cementite-containing microregions to the total number of the microregions, is 40.0% or less.
Railroad wheels.
Fn1 = 30.52 + 6.96 × C + 4.96 × Si + 1.85 × Mn + 4.85 × Cr + 34.77 × V ... (1)
Fn2 = 18.18 + 21.82 × C + 2.39 × Si + 1.01 × Mn + 6.97 × Cr + 24.79 × V ... (2)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (1) and the formula (2).

[2]
The railway wheel according to [1].
The chemical composition of the railway wheel is
Al: Containing 0.010 to 0.500%,
Railroad wheels.

[3]
The railway wheel according to [1] or [2].
The chemical composition of the railway wheel is
Cr: 0.01-0.50%,
V: 0.01 to 0.10%,
Mo: 0.01 to 0.20%,
Cu: 0.01 to 0.50%, and
Ni: Contains one element or two or more elements selected from the group consisting of 0.01 to 0.50%.
Railroad wheels.

Hereinafter, the railway wheels of the present embodiment will be described in detail. In the present specification, "%" for an element means mass% unless otherwise specified.

[Chemical composition of railway wheels]
As shown in FIG. 1, the railway wheel 1 of the present embodiment includes a boss portion 2, a plate portion 3, and a rim portion 4. The plate portion 3 is arranged between the rim portion 4 and the boss portion 2. The chemical composition of the railway wheel 1 of the present embodiment contains the following elements.

C: 0.85 to 1.15%
Carbon (C) increases the hardness of steel and enhances the wear resistance of the railway wheel 1. If the C content is less than 0.85%, this effect cannot be obtained even if the content of other elements is within the range of this embodiment. On the other hand, if the C content exceeds 1.15%, even if the content of other elements is within the range of the present embodiment, pro-eutectoid cementite is excessively generated, and the toughness of the railway wheel 1 is lowered. Therefore, the C content is 0.85 to 1.15%. The lower limit of the C content is preferably 0.86%, more preferably 0.87%. The preferable upper limit of the C content is 1.10%, more preferably 1.05%, still more preferably 1.00%, still more preferably 0.95%.

Si: 0.80% or less Silicon (Si) is inevitably contained. That is, the Si content is more than 0%. Si enhances the hardness of steel by solid solution strengthening ferrite. However, if the Si content exceeds 0.80%, the hardenability of the steel becomes too high and martensite is likely to be generated even if the content of other elements is within the range of the present embodiment. In this case, the thickness of the quenching layer formed on the tread 41 at the time of tread quenching increases. As a result, the cutting amount increases and the yield decreases. If the Si content exceeds 0.80%, the rim portion 4 is further burned by the frictional heat generated between the railroad wheels 1 and the brakes during use. In this case, the crack resistance of the steel may decrease. Therefore, the Si content is 0.80% or less. The preferred upper limit of the Si content is 0.78%, more preferably 0.75%, still more preferably 0.70%, still more preferably 0.50%. The lower limit of the Si content is not particularly limited. However, excessive reduction of Si content increases manufacturing costs. Therefore, the preferred lower limit of the Si content is 0.01%, more preferably 0.05%. From the viewpoint of increasing the hardness of the steel, the lower limit of the Si content is more preferably 0.10%, still more preferably 0.15%.

Mn: 1.50% or less Manganese (Mn) is inevitably contained. That is, the Mn content is more than 0%. Mn strengthens ferrite by solid solution to increase the hardness of steel. Mn further forms MnS and enhances the machinability of steel. However, if the Mn content exceeds 1.50%, the hardenability of the steel becomes too high even if the content of other elements is within the range of the present embodiment. In this case, the thickness of the martensite layer increases. As a result, the cutting amount increases and the yield decreases. Further, when the railroad wheel 1 is used, the rim portion 4 is burnt due to the frictional heat generated between the railroad wheel 1 and the brake. In this case, the crack resistance of the steel may decrease. Therefore, the Mn content is 1.50% or less. The preferred upper limit of the Mn content is 1.40%, more preferably 1.30%, still more preferably 1.20%, still more preferably 1.10%, still more preferably 1.00%. %. From the viewpoint of increasing the hardness of the steel, the preferable lower limit of the Mn content is 0.10%, more preferably 0.30%, further preferably 0.50%, still more preferably 0.60%. It is more preferably 0.70%.

P: 0.050% or less Phosphorus (P) is an impurity that is inevitably contained. That is, the P content is more than 0%. P segregates at the grain boundaries and reduces the toughness of the steel. Therefore, the P content is 0.050% or less. The preferred upper limit of the P content is 0.030%, more preferably 0.020%. The P content is preferably as low as possible. However, excessive reduction of P content increases manufacturing costs. Therefore, when considering normal industrial production, the preferable lower limit of the P content is 0.001%, and more preferably 0.002%.

S: 0.050% or less Sulfur (S) is inevitably contained. That is, the S content is more than 0%. S forms MnS and enhances the machinability of steel. On the other hand, if the S content is too high, the toughness of the steel will decrease. Therefore, the S content is 0.050% or less. The preferred upper limit of the S content is 0.035%, more preferably 0.020%. Excessive reduction of S content increases manufacturing costs. Therefore, the preferred lower limit of the S content is 0.001%, more preferably 0.002%, and even more preferably 0.005%.

The balance of the chemical composition of the railway wheel 1 according to the present embodiment is composed of Fe and impurities. Here, the impurities are those mixed from ore, scrap, manufacturing environment, etc. as a raw material when the railway wheel 1 is industrially manufactured, and adversely affect the railway wheel 1 of the present embodiment. It means what is allowed within the range not given. Impurities other than the above-mentioned impurities are, for example, N: 0.0150% or less, O: 0.0070% or less, and the like.

[About Optional Elements]
The chemical composition of the railway wheel 1 of the present embodiment may further contain one element or two or more elements selected from the group consisting of Cr, V, Mo, Cu, and Ni instead of a part of Fe. Good. Both of these elements increase the hardness of pearlite.

Cr: 0 to 0.50%
Chromium (Cr) is an optional element and may not be contained. That is, the Cr content may be 0%. When included, Cr narrows the lamella spacing of perlite. As a result, the hardness of the pearlite is increased, and the wear resistance of the railway wheel 1 is increased. If even a small amount of Cr is contained, the above effect can be obtained to some extent. However, if the Cr content exceeds 0.50%, the hardenability becomes excessively high even if the content of other elements is within the range of the present embodiment, and the thickness of the martensite layer after tread quenching becomes thick. Excessively increase. In this case, the amount of cutting increases and the yield decreases. Therefore, the Cr content is 0 to 0.50%. The lower limit of the Cr content is preferably more than 0%, more preferably 0.01%, still more preferably 0.03%. The preferred upper limit of the Cr content is 0.40%, more preferably 0.20%.

V: 0 to 0.10%
Vanadium (V) is an optional element and may not be contained. That is, the V content may be 0%. When contained, V forms any of carbides, nitrides, and carbonitrides to precipitate and reinforce steel (specifically, ferrite in pearlite). As a result, the hardness of the pearlite is increased, and the wear resistance of the railway wheel 1 is increased. If even a small amount of V is contained, the above effect can be obtained to some extent. However, if the V content exceeds 0.10%, the hardenability becomes excessively high, and the thickness of the martensite layer after tread quenching becomes excessively high. Therefore, the V content is 0 to 0.10%. The preferable lower limit of the V content is more than 0%, more preferably 0.01%, still more preferably 0.02%, still more preferably 0.03%. The preferred upper limit of the V content is 0.09%, more preferably 0.08%.

Mo: 0-0.20%
Molybdenum (Mo) is an optional element and may not be contained. That is, the Mo content may be 0%. When contained, Mo dissolves and strengthens ferrite in pearlite. As a result, the hardness of the pearlite is increased, and the wear resistance of the railway wheel 1 is increased. If even a small amount of Mo is contained, the above effect can be obtained to some extent. However, if the Mo content exceeds 0.20%, the hardenability becomes excessively high, and the thickness of the martensite layer after tread quenching becomes excessively high. Therefore, the Mo content is 0 to 0.20%. The lower limit of the Mo content is more than 0%, more preferably 0.01%, still more preferably 0.02%, still more preferably 0.03%. The preferred upper limit of the Mo content is 0.10%, more preferably 0.07%, still more preferably 0.05%.

Cu: 0 to 0.50%
Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. When contained, Cu dissolves and strengthens ferrite in pearlite. As a result, the hardness of the pearlite is increased, and the wear resistance of the railway wheel 1 is increased. If even a small amount of Cu is contained, the above effect can be obtained to some extent. However, if the Cu content exceeds 0.50%, surface cracks are likely to occur during casting or hot working. Therefore, the Cu content is 0 to 0.50%. The lower limit of the Cu content is more than 0%, more preferably 0.01%, still more preferably 0.02%, still more preferably 0.03%. The preferred upper limit of the Cu content is 0.40%, more preferably 0.25%, still more preferably 0.10%.

Ni: 0 to 0.50%
Nickel (Ni) is an optional element and may not be contained. That is, the Ni content may be 0%. When contained, Ni dissolves and strengthens ferrite in pearlite. As a result, the hardness of the pearlite is increased, and the wear resistance of the railway wheel 1 is increased. If even a small amount of Ni is contained, the above effect can be obtained to some extent. However, if the Ni content exceeds 0.50%, the hardenability becomes excessively high, and the thickness of the martensite layer after tread quenching becomes excessively high. Therefore, the Ni content is 0 to 0.50%. The lower limit of the Ni content is preferably more than 0%, more preferably 0.01%, still more preferably 0.02%, still more preferably 0.03%. The preferred upper limit of the Ni content is 0.40%, more preferably 0.25%, still more preferably 0.10%.

The chemical composition of the railway wheel 1 of the present embodiment may further contain Al instead of a part of Fe.

Al: 0 to 0.500%
Aluminum (Al) is an optional element and may not be contained. That is, the Al content may be 0%. When contained, Al suppresses the formation of proeutectoid cementite and enhances the toughness of the steel. Al further combines with N to form AlN, which refines the crystal grains. By refining the crystal grains, the toughness of the steel is further increased. If Al is contained even in a small amount, the above effect can be obtained to some extent. However, if the Al content exceeds 0.500%, coarse non-metal inclusions may be formed in the steelmaking process, and the toughness of the steel may decrease. Therefore, the Al content is 0 to 0.500%. The lower limit of the Al content is more than 0%, more preferably 0.010%, still more preferably 0.020%, still more preferably 0.030%. The upper limit of the Al content is preferably 0.400%, more preferably 0.300%, still more preferably 0.200%, still more preferably 0.100%. The Al content as used herein means the content of acid-soluble Al (sol.Al).

[About Fn1]
The chemical composition of the railway wheel 1 of the present embodiment further has Fn1 defined by the formula (1) of 42.0 or less.
Fn1 = 30.52 + 6.96 × C + 4.96 × Si + 1.85 × Mn + 4.85 × Cr + 34.77 × V ... (1)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (1).

Fn1 is an index of the hardness of martensite on the premise that the content of each element in the chemical composition of the railway wheel 1 is within the range of the present embodiment. If Fn1 exceeds 42.0, the hardness of the martensite of the railway wheel 1 is too high. In this case, the machinability of the railway wheel 1 is reduced. When Fn1 is 42.0 or less, the hardness of martensite is sufficiently kept low. Therefore, the machinability can be improved in the railway wheel 1 in which the content of each element in the chemical composition is within the range of the present embodiment.

The preferred upper limit of Fn1 is 41.5, more preferably 41.0, even more preferably 40.5, still more preferably 40.0. Fn1 is a value obtained by rounding off the second decimal place of the value obtained by substituting the corresponding element content into the equation (1).

[About Fn2]
The chemical composition of the railway wheel 1 of the present embodiment further has Fn2 defined by the formula (2) of 39.0 or more.
Fn2 = 18.18 + 21.82 × C + 2.39 × Si + 1.01 × Mn + 6.97 × Cr + 24.79 × V ... (2)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (2).

Fn2 is an index of the hardness of pearlite on the premise that the content of each element in the chemical composition of the railway wheel 1 is within the range of the present embodiment. If Fn2 is less than 39.0, the hardness of the pearlite of the railway wheel 1 is too low. In this case, the wear resistance of the railway wheel 1 is lowered. When Fn2 is 39.0 or more, the hardness of pearlite is sufficiently high. Therefore, it is possible to improve the wear resistance of the railway wheel 1 in which the content of each element in the chemical composition is within the range of the present embodiment.

The preferred lower limit of Fn2 is 39.5, more preferably 40.0, even more preferably 40.5, still more preferably 41.0. Fn2 is a value obtained by rounding off the second decimal place of the value obtained by substituting the corresponding element content into the equation (2).

[Total area ratio of pearlite in the microstructure of railway wheel 1]
In the microstructure of the rim portion 4 of the railway wheel 1 of the present embodiment, the total area ratio of pearlite in the cross section perpendicular to the tread 41 is 95.0% or more. Here, the cross section perpendicular to the tread 41 is an arbitrary surface within a depth of 15 mm in the vertical direction from the tread 41 to the tread 41. In the microstructure of the rim portion 4, the phase other than pearlite is at least one of martensite, bainite, ferrite and proeutectoid cementite.

Preferably, in the microstructure of the boss portion 2 of the railway wheel 1 of the present embodiment, the total area ratio of pearlite is 95.0% or more. In the microstructure of the boss portion 2, the phase other than pearlite is at least one of martensite, bainite, ferrite and proeutectoid cementite.

Preferably, in the microstructure of the plate portion 3 of the railway wheel 1 of the present embodiment, the total area ratio of pearlite is 95.0% or more. In the microstructure of the plate portion 3, the phase other than pearlite is at least one of martensite, bainite, ferrite and proeutectoid cementite.

The total area ratio of pearlite in the microstructure of the rim portion 4 is determined by the following method. A sample having a cross section perpendicular to the tread 41 is collected from a depth of 15 mm in the direction perpendicular to the tread 41 of the rim portion 4. Of the samples, the cross section perpendicular to the tread 41 is defined as the observation surface. The observation surface is mirror-finished by mechanical polishing. Etching using a mixed solution of nitric acid and ethanol is performed on the mirror-finished observation surface. A photographic image is generated using a 500x optical microscope for any one field of view (200 μm × 200 μm) in the observation plane of the sample after etching. On the observation surface, pearlite and other phases (such as martensite) have different contrasts. Therefore, each phase of the microstructure can be discriminated based on the contrast. Therefore, the pearlite is specified based on the contrast. The total area ratio of pearlite is determined based on the total area of the specified pearlite and the area of the observation field of view (40,000 μm ² ).

The total area ratio of pearlite in the microstructure of the plate portion 3 (%) and the total area ratio of pearlite in the microstructure of the boss portion 2 (%) are the same as the total area ratio of pearlite in the microstructure of the rim portion 4. Can be measured by. Specifically, a sample is taken from the center position in the thickness direction of the plate portion 3 (the center position of the thickness T3 in FIG. 1) and the boss portion 2 (the center position of the thickness T2 in FIG. 1). The observation surface of each sample is mirror-finished by mechanical polishing. Then, the mirror-finished observation surface is etched with a mixed solution of nitric acid and ethanol. A photographic image is generated using a 500x optical microscope for any one field of view (200 μm × 200 μm) in the observation plane of the sample after etching. On the observation surface, identify pearlite based on contrast. The total area ratio of pearlite is determined based on the total area of the specified pearlite and the area of the observation field of view (40,000 μm ² ).

[Regarding the area ratio of spheroidized cementite-containing minute regions]
Attention is paid to the pearlite structure in the cross section perpendicular to the tread 41 in the rim portion 4 of the railway wheel 1 of the present embodiment. Here, the cross section perpendicular to the tread 41 is an arbitrary surface within a depth of 15 mm in the vertical direction from the tread 41 to the tread 41. The cross section perpendicular to the tread 41 is used as the observation surface.

Select any observation field in the pearlite tissue region of the observation surface described above. The observation field of view is a rectangle (square) having a length of 20 μm and a width of 20 μm. The observation field of view is observed with a 5000 times scanning electron microscope (SEM). As shown in FIG. 2, the observation field of view 410 is divided into 40 equal parts at a pitch of 0.5 μm in the vertical direction and 40 equal parts at a pitch of 0.5 μm in the horizontal direction. As a result, the observation field of view 410 is divided into 40 × 40 = 1600 minute regions SA.

Observe the aspects of cementite in each microregion SA. FIG. 3 is a schematic view showing an enlarged example of 3 × 3 = 9 minute region SAs in the observation field of view 410 shown in FIG. With reference to FIG. 3, the hatched region shows ferrite 200 in pearlite. The white region in FIG. 3 shows cementite 100. In order to facilitate the explanation described later, as shown in FIG. 4, the nine microregions SA in FIG. 3 are divided into the microregions SA11, SA12, SA13, SA21, SA22, based on the arrangement position of the microregion SA. It is defined as SA23, SA31, SA32, and SA33.

Of the 1600 micro-regions SA of the observation field of view 410 shown in FIG. 2, the number of micro-region SAs containing at least one cementite 100 that is entirely contained within the micro-region SA is counted. Here, "cementite 100 in which the whole is contained in the minute region SA" means cementite 100 in which the entire cementite 100 is contained in one minute region SA. When at least a part of cementite 100 protrudes from one micro region SA, it does not correspond to "cementite 100 in which the whole is contained in the micro region SA".

For example, note SA11 with reference to FIGS. 3 and 4. Cementite 100A-100F is present in SA11. Of these, the cementites 100A and 100B as a whole do not fit in the micro-region SA11, and a part of the cementites 100A and 100B protrudes from the micro-region SA11. On the other hand, the entire cementite 100C to 100F is contained in the minute region SA11.

A micro-region SA in which at least one cementite is entirely contained within the micro-region SA, such as the micro-region SA11, is defined as a “spheroidized cementite-containing micro-region SAx”. Of the nine microregions SA in FIG. 3, the microregions SA11, SA21, SA22, SA31 and SA32 correspond to the spheroidized cementite-containing microregions SAx. Therefore, in FIG. 3, there are five spheroidized cementite-containing microregions SAx.

FIG. 5 is a diagram of a photographic image (SEM image) showing an example of a part of the microstructure of the observation field of view 410. In FIG. 5, the white region is cementite 100. The black region is ferrite 200. The region separated by the broken line is the minute region SA. The region delimited by the solid line in the thick frame corresponds to the spheroidized cementite-containing microregion SAx.

By the above determination method, in the 1600 micro-regions SA of the observation field of view 410 shown in FIG. 2, the number of micro-region SAs containing at least one cementite 100 that can be entirely contained in the micro-region SA is counted. That is, the total number of spheroidized cementite-containing microregions SAx in the microregions SA of the observation field of view 410 is counted. Using the total number of spheroidized cementite-containing microregions SAx obtained, the spheroidized cementite-containing microregion area ratio (%) is obtained by the following equation.
Spheroidized cementite-containing microregion area ratio (%) = total number of spheroidized cementite-containing microregions SAx / total number of microregions SA (1600) x 100

In the railway wheel 1, each element in the chemical composition is within the above range, Fn1 defined by the formula (1) is 42.0 or less, and Fn2 defined by the formula (2) is 39. Even if it is 0 or more, if the spheroidized cementite-containing minute region area ratio exceeds 40.0%, sufficient hardness cannot be obtained in the pearlite in the vicinity of the tread surface 41 of the rim portion 4. In this case, the wear resistance of the railway wheel 1 is lowered.

In the railway wheel 1 of the present embodiment, each element in the chemical composition is within the above range, Fn1 is 42.0 or less, Fn2 is 39.0 or more, and spheroidized cementite-containing minute amounts. The area area ratio is 40.0% or less. Therefore, it is possible to achieve both excellent machinability and excellent wear resistance.

The preferred upper limit of the spheroidized cementite-containing microregional area ratio is 38.0%, more preferably 35.0%, further preferably 30.0%, still more preferably 25.0%, and further. It is preferably 20.0%.

[Manufacturing method of railway wheel 1]
An example of the method for manufacturing the above-mentioned railway wheel 1 will be described. This manufacturing method includes a process of manufacturing steel materials for railway wheels (material manufacturing process), a process of forming a wheel-shaped intermediate product from steel materials for railway wheels by hot working (molding process), and a molded intermediate product. A process of performing heat treatment (quenching) (quenching process), a process of performing tempering after tread quenching (tempering process), and a martensite layer (quenching layer) from the tread surface of an intermediate product after the tempering process. It includes a process (cutting process) of removing by cutting to obtain a railroad wheel 1. Hereinafter, each step will be described.

[Material manufacturing process]
In the material manufacturing process, molten steel having the above-mentioned chemical composition is melted using an electric furnace, a converter, or the like. The molten steel is cast into a casting material. The cast material may be a slab obtained by continuous casting or an ingot cast by a mold.

The slabs or ingots are hot-worked to produce steel for railroad wheels of the desired size. Hot working is, for example, hot forging, hot rolling, and the like. When the steel material for railway wheels is manufactured by hot rolling, for example, the steel material for railway wheels is manufactured by the following method. In hot rolling, for example, a block matrix rolling mill is used. A block rolling machine is used to perform block rolling on the material to produce steel materials for railway wheels. When a continuous rolling mill is installed downstream of the block rolling mill, hot rolling is further performed on the steel material after block rolling using the continuous rolling mill to manufacture steel materials for railway wheels. May be good. In a continuous rolling mill, horizontal stands having a pair of horizontal rolls and vertical stands having a pair of vertical rolls are alternately arranged in a row. The heating temperature of the heating furnace in hot rolling is not particularly limited, but is, for example, 1100 to 1350 ° C. A steel material for railway wheels is manufactured by the above manufacturing process.

The steel material for railway wheels may be a cast material (slab or ingot). That is, the above-mentioned hot working step may be omitted. Through the above steps, a steel material for railway wheels, which is a material for railway wheels 1, is manufactured.

[Molding process]
In the forming process, the prepared steel material for railway wheels is used to form an intermediate wheel-shaped product by hot working. Since the intermediate product has a wheel shape, it includes a boss portion, a plate portion, and a rim portion including a tread and a flange. Hot working is, for example, hot forging, hot rolling, and the like. In the forming step, for example, first, rough ground forging is performed in which a rough intermediate product having a wheel shape is formed by hot forging. Hot rolling using a wheel rolling mill is carried out on the rough intermediate product after rough terrain forging. Rotational forging is performed on the rough intermediate product after hot rolling to form a through hole in the central portion corresponding to the boss portion. Through the above steps, a wheel-shaped intermediate product is formed.

The preferable heating temperature of the steel material for railway wheels during hot working in the forming process is 1220 ° C. or higher. In this case, the preferable lower limit of the heating temperature during hot working is 1230 ° C, more preferably 1250 ° C, still more preferably 1300 ° C. The preferred upper limit of the heating temperature during hot working is 1350 ° C.

The cooling method of the intermediate product after hot working is not particularly limited. It may be left to cool or water cooled.

[Quenching process]
In the quenching process, tread quenching is performed on the molded wheel-shaped intermediate product. Specifically, the intermediate product after hot working (hot forging or hot rolling) _{is reheated to the A cm} transformation point or higher (reheat treatment). After heating, quench (quench) the tread and flange of the intermediate product.

FIG. 6 is a diagram showing an example of a cooling device for cooling an intermediate product. With reference to FIG. 6, the cooling device 10 includes a rotating device 11 having a rotating shaft and one or more tread cooling nozzles 14. The tread cooling nozzle 14 is arranged around the rotation axis of the cooling device 10. The nozzle port of the tread cooling nozzle 14 is arranged so as to face the tread 41 of the intermediate product. The nozzle port of the tread cooling nozzle 14 may be arranged so as to face the surface of the flange 42 of the intermediate product. The tread cooling nozzle 14 injects a cooling liquid from the nozzle port to mainly cool the surfaces of the tread 41 and the flange 42 of the rim portion 4. The coolant is, for example, water, mist, spray or the like. The cooling device 10 may include a plurality of temperature gauges 20.

In the quenching step, _{an intermediate product heated to the A cm} transformation point or higher is placed in the cooling device 10. While rotating the intermediate product by the rotating device 11, the coolant is injected from the tread cooling nozzle 14 to perform tread quenching.

By quenching the tread surface, fine pearlite is generated on the tread surface 41. The C content of the railway wheel 1 of this embodiment is as high as 0.85 to 1.15%. Therefore, the wear resistance of the railway wheel 1 is increased. The martensite layer is formed on the tread 41 by quenching the tread.

In the above description, the intermediate product is reheated, but the intermediate product after hot working may be subjected to tread quenching directly (without reheating).

[Tempering process]
In the tempering process, the intermediate product after quenching on the tread is tempered. The tempering temperature is 400 to 550 ° C. If the tempering temperature exceeds 550 ° C., the lamellar structure of pearlite on the tread 41 of the rim portion 4 is broken, and cementite is spheroidized. As a result, the spheroidized cementite-containing minute region area ratio (%) exceeds 40.0%. In this case, the wear resistance of the railway wheel 1 is lowered.

When the tempering temperature is 400 to 550 ° C., the lamellar structure of pearlite on the tread 41 of the rim portion 4 is maintained, and the spheroidized cementite-containing minute region area ratio (%) is 40.0% or less. As a result, the railway wheel 1 has excellent wear resistance.

[Cutting process]
As described above, fine pearlite is formed on the surface layer of the tread surface of the intermediate product after the heat treatment, and a martensite layer (quenched layer) is formed on the upper layer. Since the wear resistance of the martensite layer is low in the use of the railway wheel 1, the martensite layer is removed by cutting. In the chemical composition of the intermediate product of the present embodiment, the content of each element is within the range of the present embodiment, Fn1 is 42.0 or less, and Fn2 is 39.0 or more. Therefore, in the present embodiment, the hardness of the martensite layer is suppressed. Therefore, in the manufacturing process of the railway wheel 1 of the present embodiment, sufficient machinability can be obtained. It is sufficient to perform the cutting process by a well-known method.

The railway wheel 1 of the present embodiment is manufactured by the above steps. In the railway wheel 1 of the present embodiment manufactured in the above manufacturing process, each element in the chemical composition is within the range of the present embodiment, Fn1 is 42.0 or less, and Fn2 is 39.0 or more. Is. Further, the spheroidized cementite-containing minute region area ratio is 40.0% or less. Therefore, in the railway wheel 1 of the present embodiment, both excellent wear resistance and excellent machinability can be achieved at the same time.

Molten steels of test numbers 1 to 25 having the chemical compositions shown in Table 1 were produced.

The blanks in Table 1 indicate that the corresponding element content was below the detection limit (ie, was not contained). A round slab was produced by a continuous casting method using the molten steel. Round slabs were hot-rolled (hot-worked) by a slabbing mill and a continuous rolling mill to produce round steel pieces (steel materials for railway wheels). The heating temperature during hot working was 1250 ° C. A forming process was carried out on steel materials for railway wheels. Specifically, hot forging (rough ground forging) was carried out on the steel material for railway wheels to form a rough intermediate product having a wheel shape. Hot rolling using a wheel rolling mill was carried out on the rough intermediate product after roughland forging. Rotational forging was performed on the rough intermediate product after hot rolling to form a through hole in the central portion corresponding to the boss portion. By the above molding process, a wheel-shaped intermediate product was molded. The heating temperature of the steel material during the molding step was 1250 ° C.

Tread quenching was performed on the manufactured intermediate products. In tread quenching, the tread and flange of the intermediate product were water-cooled using the cooling device shown in FIG. Tempering was carried out on the intermediate products after the tread quenching. The tempering temperature of the intermediate product of each test number was as shown in Table 1. “Appropriate” in the “Tempering temperature” column in Table 1 indicates that the tempering temperature was in the range of 400 to 550 ° C. “Inappropriate” indicates that the tempering temperature was in the range of more than 550 ° C to 650 ° C. Through the above manufacturing process, a railway wheel on which a martensite layer was formed was manufactured.

[Vickers hardness measurement test of martensite layer]
The Vickers hardness of the martensite layer of the railway wheel of each test number was measured by the following method. One test piece containing the martensite layer was collected from the portion near the tread of the rim portion of the railway wheel of each test number. A Vickers hardness test conforming to JIS Z 2241 (2009) was carried out at any three points of the martensite layer of the test piece. The test force was 2.9421N in each case. The arithmetic mean of the three Vickers hardnesses obtained was defined as the Vickers hardness (HV) of martensite. Vickers hardness of martensite correlates with machinability. Therefore, it was determined that sufficient machinability can be obtained if the Vickers hardness of martensite is 410 HV or less. The Vickers hardness of the obtained martensite is shown in the "Martensite hardness (HV)" column of Table 1.

[Microstructure observation test of rim part]
The martensite layer of the railway wheel of each test number was removed by cutting. The total area ratio of pearlite on the rim of the removed railway wheel was determined by the following method. A sample having a cross section perpendicular to the tread was taken from within a depth of 15 mm in the direction perpendicular to the tread from the tread of the rim portion. Of the samples, the cross section perpendicular to the tread was defined as the observation surface. The observation surface was mirror-finished by mechanical polishing. The mirror-finished observation surface was etched with a mixed solution of nitric acid and ethanol. A photographic image was generated using a 500x optical microscope for any one field of view (200 μm × 200 μm) in the observation plane of the sample after etching. On the observation surface, pearlite and other phases (such as martensite) have different contrasts. Therefore, each phase of the microstructure could be discriminated based on the contrast. Therefore, pearlite was identified based on the contrast. The total area ratio (%) of pearlite was determined based on the total area of the specified pearlite and the area of the observation field of view (40,000 μm ² ). The obtained total area ratio of pearlite is shown in the "total area ratio of pearlite (%)" column in Table 1. In all the test numbers, the total area ratio of pearlite in the cross section perpendicular to the tread of the rim portion was 95.0% or more.

As with the rim portion, the total area ratio of pearlite in the plate portion and the boss portion of the railway wheel of each test number was also determined. Specifically, from the center position in the thickness direction of the plate portion (corresponding to the center position of the thickness T3 in FIG. 1) and the center position in the thickness direction of the boss portion (corresponding to the center position of the thickness T2 in FIG. 1). A sample was taken. One of the surfaces of each sample was used as an observation surface. The observation surface of each sample was mirror-finished by mechanical polishing. Then, the mirror-finished observation surface was etched with a mixed solution of nitric acid and ethanol. A photographic image was generated using a 500x optical microscope for any one field of view (200 μm × 200 μm) in the observation plane of the sample after etching. On the observation surface, pearlite was identified based on the contrast. The total area ratio of pearlite was determined based on the total area of the specified pearlite and the area of the observation field of view (40,000 μm ² ). The total area ratio of pearlite was 95.0% or more in both the plate portion and the boss portion of each test number.

[Spheroidized cementite-containing micro-region area ratio measurement test]
A sample having a cross section perpendicular to the tread was taken from within a depth of 15 mm in the vertical direction of the tread from the tread of the rim portion of the railway wheel of each test number from which the martensite layer was removed. Of the samples, the cross section perpendicular to the tread was defined as the observation surface. The observation surface was mirror-finished by mechanical polishing. The mirror-finished observation surface was etched with a mixed solution of nitric acid and ethanol. After etching, any observation field in the pearlite structure region of the observation surface described above was selected. The observation field of view was a square of 20 μm in length × 20 μm in width. The observation field of view was observed with a 5000 times scanning electron microscope (SEM). As shown in FIG. 2, the observation field of view 410 was divided into 40 equal parts at a pitch of 0.5 μm in the vertical direction and 40 equal parts at a pitch of 0.5 μm in the horizontal direction. As a result, the observation field of view 410 was divided into 40 × 40 = 1600 minute regions SA.

Of the 1600 microregions SA, the microregion SA in which the entire cementite is contained within the microregion SA is defined as "spheroidized cementite-containing microregion SAx". In the 1600 micro-regions SA of the observation field of view 410, the number of micro-region SAs containing at least one cementite that is entirely contained in the micro-region SA was counted. That is, the number of spheroidized cementite-containing microregions SAx in the microregions SA of the observation field of view 410 was counted. Using the number of spheroidized cementite-containing microregions SAx obtained, the spheroidized cementite-containing microregion area ratio (%) was determined by the following formula.
Spheroidized cementite-containing microregion area ratio (%) = total number of spheroidized cementite-containing microregions SAx / total number of microregions SA (1600) x 100
The obtained spheroidized cementite-containing micro-region area ratio (%) is shown in the “Spheroidized cementite-containing micro-region area ratio (%)” column in Table 1.

[Perlite Vickers hardness test]
The Vickers hardness of the pearlite on the rim of the railway wheel of each test number was measured by the following method. A sample was taken including a cross section within a depth of 15 mm in the vertical direction of the tread from the tread of the rim portion of the railway wheel of each test number. This cross section was used as the measurement surface. A Vickers hardness test conforming to JIS Z 2241 (2009) was carried out at any three points on the measurement surface. The test force was 2.9421N in each case. The arithmetic mean of the three Vickers hardnesses obtained was defined as the Vickers hardness (HV) of perlite. Vickers hardness of perlite correlates with wear resistance. Therefore, it was determined that if the Vickers hardness of pearlite is 380 HV or more, sufficient wear resistance can be obtained. The Vickers hardness of the obtained pearlite is shown in the "Pearlite hardness (HV)" column in Table 1.

[Test results]
With reference to Table 1, the railroad wheels of test numbers 4-6, 9, 11-13, 15-18, 20, 21, and 24 have a suitable chemical composition and Fn1 of 42.0 or less. , Fn2 was 39.0 or more. In addition, the tempering temperature was also appropriate. Therefore, the total area ratio of pearlite in the rim portion, the plate portion, and the boss portion of the railway wheel was 95.0% or more, and the area ratio of the spheroidized cementite-containing minute region was 40.0% or less. Therefore, it was expected that the Vickers hardness of martensite was 410 HV or less, and excellent machinability could be obtained. Further, the Vickers hardness of pearlite was 380 HV or more, and it was expected that excellent wear resistance could be obtained.

On the other hand, in Test Nos. 1 and 2, the C content was too low, and the material of the railway wheel was subeutectoid steel. Therefore, it was expected that the Vickers hardness of pearlite would be less than 380 HV, and sufficient wear resistance could not be obtained.

In Test Nos. 3, 8 and 14, the content of each element in the chemical composition was appropriate, but Fn2 was less than 39.0. Therefore, it was expected that the Vickers hardness of pearlite would be less than 380 HV, and sufficient wear resistance could not be obtained.

In test number 7, the C content was too high. Therefore, it was expected that the Vickers hardness of martensite would exceed 410 HV and sufficient machinability could not be obtained.

In test number 10, the Si content was too high. Therefore, it was expected that the Vickers hardness of martensite would exceed 410 HV and sufficient machinability could not be obtained.

In Test Nos. 19 and 25, although the content of each element in the chemical composition was appropriate, Fn1 exceeded 42.0. Therefore, it was expected that the Vickers hardness of martensite would exceed 410 HV and sufficient machinability could not be obtained.

In test numbers 22 and 23, the content of each element in the chemical composition was appropriate, Fn1 was 42.0 or less, and Fn2 was 39.0 or more. However, the tempering temperature exceeded 550 ° C. Therefore, the area ratio of the spheroidized cementite-containing minute region exceeded 40.0%. Therefore, it was expected that the Vickers hardness of pearlite would be less than 380 HV, and sufficient wear resistance could not be obtained.

The embodiments of the present invention have been described above. However, the embodiments described above are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

1 Railroad wheel 2 Boss part 3 Plate part 4 Rim part 41 Tread 42 Flange

Claims (3)

Railroad wheels
With the rim
With the boss
A plate portion arranged between the rim portion and the boss portion is provided.
The chemical composition of the railway wheel is mass%.
C: 0.85 to 1.15%,
Si: 0.80% or less,
Mn: 1.50% or less,
P: 0.050% or less,
S: 0.050% or less,
Cr: 0 to 0.50%,
V: 0 to 0.10%,
Mo: 0-0.20%,
Cu: 0-0.50%,
Ni: 0 to 0.50%,
Al: 0 to 0.500% and
The rest consists of Fe and impurities
Fn1 defined by the equation (1) is 42.0 or less, and
Fn2 defined by the equation (2) is 39.0 or more, and
The total area ratio of pearlite in the cross section perpendicular to the tread of the rim portion is 95.0% or more.
Of the pearlite having a cross section perpendicular to the tread of the rim portion, in a rectangular observation field of view of 20 μm in length × 20 μm in width, it is divided into 40 equal parts at a pitch of 0.5 μm in the vertical direction and 40 at a pitch of 0.5 μm in the horizontal direction. 40 × 40 microregions were divided into equal parts, and the microregion containing at least one cementite that fits within the microregion was defined as a spheroidized cementite-containing microregion. When
The spheroidized cementite-containing microregion area ratio, which is the ratio of the total number of the spheroidized cementite-containing microregions to the total number of the microregions, is 40.0% or less.
Railroad wheels.
Fn1 = 30.52 + 6.96 × C + 4.96 × Si + 1.85 × Mn + 4.85 × Cr + 34.77 × V ... (1)
Fn2 = 18.18 + 21.82 × C + 2.39 × Si + 1.01 × Mn + 6.97 × Cr + 24.79 × V ... (2)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (1) and the formula (2). The railway wheel according to claim 1.
The chemical composition of the railway wheel is
Al: Containing 0.010 to 0.500%,
Railroad wheels. The railway wheel according to claim 1 or 2.
The chemical composition of the railway wheel is
Cr: 0.01-0.50%,
V: 0.01 to 0.10%,
Mo: 0.01 to 0.20%,
Cu: 0.01 to 0.50%, and
Ni: Contains one element or two or more elements selected from the group consisting of 0.01 to 0.50%.
Railroad wheels.

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