Technical field
[0001]The present invention relates to a manufacturing method and a rail wheel of a railway wheel.
BACKGROUND
[0002]Railway vehicle travels on rails which constitute the line. Railway vehicle includes a plurality of rail wheel. Railway wheel supports the vehicle, in contact with the rail, moves while rotating on the rail. Railway wheel is worn due to contact with the rail. For the purpose of high efficiency of railway transportation, an increase of the loaded weight of the rail vehicle, and, speed of railway vehicles has been developed. As a result, improvement of the wear resistance of the train wheel used in railway vehicles has been demanded.
[0003]
　Technique for increasing the wear resistance of the rail wheel is, JP-A-9-202937 (Patent Document 1), JP 2012-107295 (Patent Document 2), JP 2013-231212 (Patent Document 3), and it has been proposed in JP 2004-315928 (Patent Document 4).
[0004]
　Railway wheel disclosed in Patent Document 1, by mass%, C: 0.4 ~ 0.75%, Si: 0.4 ~ 0.95%, Mn: 0.6 ~ 1.2%, Cr: less than 0 ~ 0.2%, P: 0.03% or less, S: 0.03% or less, the balance being Fe and unavoidable impurities. In this railway wheel, region up to at least a depth of 50mm from the surface of the wheel tread portion is composed of pearlite. Method of manufacturing a rail wheel in Patent Document 1, the cooling curve of the wheel tread portion, through the pearlite generation region in the continuous cooling transformation curves, and the conditions in the long side of the martensitic transformation curve, the wheel tread portion including the cooling quench process.
[0005]
　Steel disclosed in Patent Document 2 wheels, by mass%, C: 0.65 ~ 0.84%, Si: 0.02 ~ 1.00%, Mn: 0.50 ~ 1.90%, Cr : 0.02 ~ 0.50%, V: 0.02 ~ 0.20%, include S ≦ 0.04%, the balance being Fe and impurities, P ≦ 0.05%, Cu ≦ 0.20 %, a Ni ≦ 0.20% of the chemical composition. The chemical composition further satisfies the following relation. [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]. Steel for this vehicle, by satisfying the chemical composition and the formula, abrasion resistance, 耐転 dynamic fatigue properties, excellent resistance to spoke ring resistance, and are described in the patent document 2.
[0006]
　Steel disclosed in Patent Document 3 wheels, by mass%, C: 0.65 ~ 0.84%, Si: 0.4 ~ 1.0%, Mn: 0.50 ~ 1.40%, Cr : 0.02 ~ 0.13%, S: 0.04% or less, V: contains 0.02 ~ 0.12%, Fn1 of 32 to 43 as defined in formula (1), and the formula Fn2 represented by (2) is 25 or less, the balance being Fe and impurities. Here, equation (1) is a Fn1 = 2.7 + 29.5C + 2.9Si + 6.9Mn + 10.8Cr + 30.3Mo + 44.3V, equation (2) is, Fn2 = exp (0.76) × exp (0.05C) × is exp (1.35Si) × exp (0.38Mn) × exp (0.77Cr) × exp (3.0Mo) × exp (4.6V). Steel for this vehicle has the chemical composition, by Fn1 and Fn2 satisfies the above range, wear resistance, 耐転 dynamic fatigue properties, excellent resistance to spoke ring resistance, and is described in Patent Document 3 there.
[0007]
　Wheels for railway vehicle disclosed in Patent Document 4, by mass%, C: 0.85 ~ 1.20%, Si: 0.05 ~ 2.00%, Mn: 0.05 ~ 2.00%, required further Cr, Mo, V, Nb, B, Co, Cu, Ni, Ti, Mg, Ca, Al, Zr, and N 1, two or more of containing a predetermined amount in accordance with the balance being Fe and other a rail vehicle wheel integral comprised of steel containing chemical components consisting of unavoidable impurities, at least a portion of the tread and / or flange surface of the wheel is pearlite structure. In Patent Document 4, the wheel of life for rail vehicles is dependent on the amount of wear of the tread and the flange surface (Patent Document 4, paragraph [0002]), and further, the increase in the amount of heat generated when braking in high-speed rail and has been described to depend on the cracks in the tread and flange surfaces occurs no. By wheels for railway vehicles having the above configuration, the wear resistance and thermal cracking of tread and flange face can be suppressed, it has been described as.
CITATION
Patent Document
[0008]
Patent Document 1: JP-A-9-202937
Patent Document 2: JP 2012-107295 Patent Publication
Patent Document 3: JP 2013-231212 Patent Publication
Patent Document 4: JP 2004-315928 JP
Non-patent literature
[0009]
非 特許 文献 1: F.Wever et al, the question of the heat treatment of steels, due to their time-temperature conversion diagrams, steel and iron, 74 (1954), P749 ~ 761st
Summary of the Invention
Problems that the Invention is to Solve
[0010]
　Railway wheel disclosed in Patent Documents 1, 2 and 3 described above, by actively containing V, to enhance the abrasion resistance of the rail wheel. However, the rail wheel of these documents, if an increase and faster loading weight applied to the freight railways sought, sufficient wear resistance can not be obtained.
[0011]
　On the other hand, the railway wheel disclosed in Patent Document 4, as compared with Patent documents 1 to 3, from the over eutectoid steel with an increased C content. The railway wheels, if an increase and faster loading weight is applied to the cargo train sought, there is a possibility that sufficient abrasion resistance is obtained.
[0012]
　By the way, the train wheel is prepared in the following manner. The steel slab for forming the intermediate product of the rail wheel shape by hot working. Respect molded intermediate product, implementing a heat treatment (tread quenching). The tread quenching after heating the intermediate product is quenched by injecting cooling water into the intermediate product tread and the flange. Incidentally, while quenching the tread and flange, to cool the boss portion and the plate portion. Thus, the matrix tissue of the surface layer and the surface layer portion of the flange just below the tread surface, the wear resistance is high fine pearlite is generated.
[0013]
　However, the surface layer and the surface layer portion of the flange just below the tread after the tread surface hardening layer comprising the martensite and / or bainite further generates an upper layer of fine pearlite. Hereinafter, the rapid cooling of the tread after the heat treatment and a flange layer comprising a martensite and / or bainite is formed in the surface layer of the surface layer and the flanges of the tread is referred to herein as "hardened layers". When using a rail wheel having a hardened layer surface and the surface layer of the flange of the tread surface, during use of the rail wheel hardened layer is subject to wear. Therefore, in the conventional manufacturing process of the railway wheel, the intermediate products of the rail wheel after tread quenching, the surface layer and the hardened layer formed on the surface layer of the flange of the tread surface is removed by cutting, tread fine pearlite and it is exposed on the surface of the flange. With the above-described manufacturing steps, conventional railroad wheels are manufactured.
[0014]
　However, if the rail wheel is over-eutectoid steel as in Patent Document 4, in the conventional method of manufacturing a rail wheel, the toughness of the boss portion and the plate portion may be decreased is studies by the present inventors in became apparent. In conventional railway wheels, for the purpose of improving cycle life of railroad wheels, but has been studied for tread and a flange of the tissue of the rim, has not been a study focusing on the boss portion and the plate portion of the tissue of the rail wheel .
[0015]
　An object of the present invention, the railway wheels over eutectoid steel having excellent toughness can be manufactured stably, and to provide a manufacturing method and a rail wheel of a railway wheel.
Means for Solving the Problems
[0016]
　Method of manufacturing a rail wheel according to an embodiment of the present invention includes a heating step and a cooling step. In the heating step, in mass%, C: 0.80 ~ 1.15% , Si: 1.00% or less, Mn: 0.10 ~ 1.25%, P: 0.050% or less, S: 0. 030% or less, Al: 0.025 ~ 0.650%, N: 0.0030 ~ 0.0200%, Cr: 0 ~ 0.60%, and, V: 0 ~ 0.12%, and containing, the balance has a chemical composition consisting of Fe and impurities, and the boss portion, a rim portion including a tread and a flange, the intermediate product of the railway wheel and a plate portion disposed between the boss portion and the rim portion, a cm heated to transformation point (℃) or higher. In the cooling step is Fn1 ° C. / sec or less defined by the cooling rate equation in 800 ~ 500 ° C. tread and flange surfaces other than the surface in the intermediate product (1), in the region where the cooling rate is slowest in the intermediate products the cooling rate in 800 ~ 500 ° C. is at Fn2 ° C. / sec or more, which is defined by equation (2), such that the cooling rate in the 800 ~ 500 ° C. in tread and the flange surface is Fn2 ° C. / sec or more, the intermediate article is cooled.
　Fn1 = -5.0 + exp (5.651-1.427 × C-1.280 × Si-0.7723 × Mn-1.815 × Cr-1.519 × Al-7.798 × V) ··· (1)
　Fn2 = 0.515 + exp (-24.816 + 24.121 × C + 1.210 × Si + 0.529 × Mn + 2.458 × Cr-15.116 × Al-5.116 × V) · · · (2)
　where , each element symbol in the above formulas (1) and (2), the content of the corresponding element (mass%) is substituted.
[0017]
　Railway wheel according to the present embodiment, by mass%, C: 0.80 ~ 1.15% , Si: 1.00% or less, Mn: 0.10 ~ 1.25%, P: 0.050% or less, S: 0.030% or less, Al: 0.025 ~ 0.650%, N: 0.0030 ~ 0.0200%, Cr: 0 ~ 0.60%, and, V: 0 ~ 0.12%, contains, has a chemical composition the balance being Fe and impurities, it comprises a boss portion, a rim portion including a tread and a flange, and a plate portion disposed between the boss portion and the rim portion. In the microstructure of the boss portion, rate pearlite area is 95% or more, pro-eutectoid cementite amount defined by formula (A) is 1.0 present / 100 [mu] m or less. In the microstructure of the plate portion, rate pearlite area is 95% or more, pro-eutectoid cementite amount defined by formula (A) is 1.0 present / 100 [mu] m or less. In the microstructure of the rim portion, the area ratio of pearlite is less than 95%, pro-eutectoid cementite amount defined by formula (A) is 1.0 present / 100 [mu] m or less.
　Pro-eutectoid cementite amount (present / 100μm) = 200μm × 200μm /(5.66×100μm sum of the number of pro-eutectoid cementite which intersects the two diagonal lines of the square field of view) (A)
The invention's effect
[0018]
　Method of manufacturing a rail wheel according to the present embodiment, the railway wheels over eutectoid steel having excellent toughness can be stably manufactured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]
[1] Figure 1 is a cross-sectional view parallel to the central axis of the rail wheel.
FIG. 2 is based on the results of the Nishihara-type wear test is a diagram showing a relationship between Vickers hardness and wear amount of the railway wheels of a rail wheel.
FIG. 3 is a schematic diagram of Nishihara-type wear test.
FIG. 4 is based on the results of heat treatment test assuming a heat treatment in the manufacturing process of the railway wheel is a view showing the C content, and the cooling rate, the relationship between hardened layers and pro-eutectoid cementite.
FIG. 5 is based on the results of heat treatment test assuming a heat treatment in the manufacturing process of the railway wheel, and the Si content, and the cooling rate is a diagram showing a relationship between hardened layers and pro-eutectoid cementite.
FIG. 6 is based on the results of heat treatment test assuming a heat treatment in the manufacturing process of the railway wheel is a diagram showing the Mn content, and the cooling rate, the relationship between hardened layers and pro-eutectoid cementite.
[7] FIG. 7 is a diagram showing based on the results of heat treatment test assuming a heat treatment in the manufacturing process of the railway wheel, and Cr content, and the cooling rate, the relationship between hardened layers and pro-eutectoid cementite.
[8] FIG. 8 is based on the results of heat treatment test assuming a heat treatment in the manufacturing process of the railway wheel is a diagram showing the Al content, and the cooling rate, the relationship between hardened layers and pro-eutectoid cementite.
[9] FIG. 9 is a diagram showing based on the results of heat treatment test assuming a heat treatment in the manufacturing process of the railway wheel, the V content, and the cooling rate, the relationship between hardened layers and pro-eutectoid cementite.
[10] FIG 10 is a schematic diagram showing an example of a cooling apparatus used in the method of manufacturing a rail wheel according to the present embodiment.
[11] FIG 11 is a schematic view for explaining a method of measuring pro-eutectoid cementite amount.
FIG. 12 is obtained by Jomini formula end quenching test in Example illustrates the distribution of Rockwell hardness HRC to the distance from the water-cooled end of Jomini specimen (Jomini curve).
DESCRIPTION OF THE INVENTION
[0020]
　[Configuration rail wheel]
　FIG 1 is a cross-sectional view including the central axis of the rail wheel. Referring to FIG. 1, the railway wheel 1 is disc-shaped, provided with a boss portion 2, and a plate portion 3 and the rim portion 4. Boss 2 has a cylindrical shape, is disposed in the center of the rail wheel 1. Boss 2 has a through-hole 21. The central axis of the through-hole 21 is coincident with the central axis of the railway wheel 1. The through hole 21, an axle (not shown) is inserted. The thickness T2 of the boss portion 2 is thicker than the thickness T3 of the plate portion 3. Rim portion 4 is formed on the edge of the outer periphery of the rail wheel 1. Rim portion 4 includes a tread surface 41 and a flange 42. Tread 41 is connected to the flange 42. In use of the rail wheel 1, the surface of the tread 41 and flange 42 is in contact with the rail surface. The thickness T4 of the rim portion 4 is greater than the thickness T3 of the plate portion 3. The plate portion 3 is disposed between the boss portion 2 and the rim portion 4. Inner peripheral edge portion of the plate portion 3 is connected to the boss portion 2, the outer peripheral edge portion of the plate portion 3 is connected to the rim portion 4. The thickness of the plate portion 3 T3 is less than the thickness T4 of the thickness T2 and the rim portion 4 of the boss portion 2.
[0021]
　The present inventors have examined a method of enhancing the wear resistance of the rail wheel. As a result, the present inventors have obtained the following findings.
[0022]
　[C content increased improvement of the wear resistance due]
　Figure 2 is based on the results of the Nishihara-type wear test is a diagram showing a relationship between Vickers hardness and wear amount of the railway wheels of a rail wheel. Figure 2 was obtained by the following experiment. From an ingot having the chemical composition shown in Table 1, were prepared round bar having a diameter of 40 mm.
[0023]
[Table 1]

[0024]
　From round bar, to produce diameter 32 mm, an annular coarse width of the specimen of 10mm (corresponding to an intermediate product of the rail wheel).
[0025]
　The crude specimens was performed hardened simulating the tread quenching in the railway wheel. Specifically, the crude specimens of each steel numbers, soaking for 20 minutes at the heat treatment temperature of 950 ° C.. After soaking, in order to form a fine pearlite structure, a crude test specimen removed from the furnace and immersed in a salt bath of 550 ° C.. The immersion time in the salt bath was 7 minutes. When the crude specimen elapsed 7 minutes of immersion in a salt bath, removed and the crude specimen from soft bath and allowed to cool crude test specimen to ambient temperature (25 ° C.). To simulate tempering during wheel manufacture, and each crude test piece was allowed to cool and held for 3 hours at the heat treatment temperature of 450 ° C.. After the crude specimen was held for 3 hours at the heat treatment temperature of 450 ° C., allowed to cool and the crude specimen to ambient temperature (25 ° C.).
[0026]
　The outer peripheral surface of the cooling after the rough test pieces were machined to prepare a cylindrical wheel test piece 100 shown in FIG. 3 (corresponding to the train wheel). Diameter D100 of the wheel test piece 100 is 29.39Mm, width W100 was 8 mm.
[0027]
　Furthermore, it was prepared steel number 29 shown in Table 2 as a rail member.
[0028]
[Table 2]

[0029]
　An annular rail test piece 200 shown in FIG. 3 from the rail material of steel No. 29 was prepared. Diameter D200 of the rail test specimen 200 is 30.0 mm, the width W200 was 5 mm.
[0030]
　The metal structure at the position of depth 2 ~ 3 mm toward the central axis from the outer peripheral surface of the wheel test piece 100 was observed at 500 times using an optical microscope. Similarly, the metal structure of the position in the depth 2 ~ 3 mm toward the central axis from the outer peripheral surface of the rail test specimen 200 was observed at 500 times by an optical microscope. Structure observation results, any tissue of the wheel test piece 100 of the steel Nos. 1 to 4 and 21 to 28 are pearlite single phase structure of the rail test specimen 200 was also pearlite single phase.
[0031]
　Also, in the wheel test piece 100, the tissue observed at the same position, namely at the position of depth 2 ~ 3 mm toward the central axis from the outer peripheral surface was performed Vickers hardness test according to JIS Z2244 (2009). Both test force was 2.9421N. Similarly, in the rail test pieces 200, tissue observed at the same position, namely at the position of depth 2 ~ 3 mm toward the central axis from the outer peripheral surface was performed Vickers hardness test according to JIS Z2244 (2009). Test force was 2.9421N. As a result, the Vickers hardness of the rail test specimen 200 (HV) was 430.
[0032]
　Contacting a width center of the outer peripheral surface of the width center and the rail test pieces 200 of the outer peripheral surface of the wheel test piece 100, while pressing each other with a force of 900 MPa, by rotating the wheel test piece 100 and the rail test pieces 200 from each other wear the test was carried out. Rotational speed of the wheel test piece 100 was set to 800 rpm, the rotational speed of the rail test specimen 200 was 775Rpm. Accordingly, the slip ratio of the wheel test piece 100 and the rail test specimen 200 was 1.1%. After the wheel test piece 100 was 500,000 rotated, calculated mass of the wheel test piece 100 after test (g). The previously obtained and survey pre previously been tested in the mass of the wheel test piece 100 (g) prior to testing, the difference between the mass of the wheel test piece 100 (g) after the test, divided by the mass difference of 50 the value was defined as the amount of wear of the wheel (g / 10,000rev.). Incidentally, the wheel test piece 100 is prepared four in each steel numbers, and the same test using these carried four times per steel number. The average value of the wear amount of the wheel test piece 100 obtained by four tests was calculated as the amount of wear of railway wheels of the steel numbers. Using Vickers hardness and wear amount of the wheel test piece 100 obtained in each of the steel numbers, were prepared to FIG.
[0033]
　"◇" mark in FIG. 2, the Si content was nearly constant at about 0.3%, C content of 0.8 to 1.1% for V-free steels group was changed (hereinafter, " a test result using the V of free over-eutectoid steel group "). "○" mark, the C content is set to within a range of 0.75 to 0.79%, the Si content was nearly constant at about 0.3%, and a V content of about 0 to 0.1% steel group was changed to (hereinafter, referred to as "V content changes low Si eutectoid steel group") is a test result using the. "△" mark, the C content is set to within a range of 0.75 to 0.79%, the Si content was nearly constant at about 0.8%, change the V content to about 0 to 0.1 percent it is allowed steel group (hereinafter, referred to as "V content changes high Si eutectoid steel group") is a test result using the. Each mark next to the numerals in Figure 2 shows the steel numbers in Table 1.
[0034]
　Referring to FIG. 2, the V content changes low Si eutectoid steel group ( "○" mark), in accordance with the V content is increased, the Vickers hardness of the wheels is increased. According Specifically, V-free (steel 21), V content of 0.028% (Steel 22), 0.058% (Steel 23), increases with 0.097% (Steel 24), Vickers hardness is increased. However, Vickers hardness remains about 350 HV, wear loss 0.015g / 10000rev. Only to the extent it was not reduced. On the other hand, the V content changes high Si eutectoid steel group ( "△" mark), V-free (steel 25), the V content is 0.028% (Steel 26), 0.058% (Steel 27) , according to increase 0.096% (steel 28), Vickers hardness of the wheels was increased to about 380 Hv. However, even if increased Vickers hardness, wheel wear amount 0.015g / 10000rev. It becomes constant in degree, more of the reduction was not observed.
[0035]
　In contrast, V in free over eutectoid steel group ( "◇" mark), C content of 0.84% ​​(Steel 1), 0.93% (Steel 2), 1.00% (Steel 3 ), in accordance with an increase 1.09% (steel 4), Vickers hardness increases. Furthermore, with the increase of Vickers hardness, the wear amount 0.010g / 10000rev. It was reduced to a degree.
[0036]
　These results, in the steel for railway wheels, even when achieving the same hardness, than increasing the hardness by increasing the V content is better to increase the hardness by increasing the C content, the railway wheels wear resistance when used as increases. The reason for this is not clear, it is believed the following matters. Tread rail wheel in use, receives an external force (load) from the rail. The external force cementite in pearlite of the surface layer immediately below the tread surface by is crushed, the hardness is increased by dispersion strengthening. Further, the carbon of the crushed fine in cementite is dissolved in supersaturation in the ferrite in the pearlite, enhancing the hardness of the surface layer immediately below the tread surface by solid solution strengthening.
[0037]
　If Takamere the C content of the steel, the volume fraction of cementite in the pearlite is increased. The perlite is easy to form a finer lamellae. In this case, the wear resistance of the rail wheel is increased by the above mechanisms. In contrast, when the content of the V, increasing the hardness of the steel by precipitation strengthening of V carbonitride. At this time, V carbonitrides to produce in ferrite mainly increase the hardness of ferrite. In other words, the content of V does not affect so much the miniaturization of the pearlite. Therefore, although it is possible to increase a degree abrasion resistance V content, the more enhanced dispersion strengthening and C solid solution by crushing cementite can not be enhanced abrasion resistance.
[0038]
　Accordingly, the steel for railway wheels, even when achieving the same hardness, better to increase the C content, than containing V, it is possible to enhance the abrasion resistance.
[0039]
　Based on the above study results, the present inventors have found that in order to increase the abrasion resistance, the chemical composition of the rail wheel, in mass%, C: 0.80 ~ 1.15%, Si: 1.00 % or less, Mn: 0.10 ~ 1.25%, P: 0.050% or less, S: 0.030% or less, Al: 0.025 ~ 0.650%, N: 0.0030 ~ 0.0200 %, Cr: 0 ~ 0.60%, and, V: 0 ~ 0.12%, and contains the balance is considered preferable to be over-eutectoid steel consisting of Fe and impurities.
[0040]
　[Pro-eutectoid cementite generation suppression]
　As described above, the railway wheels are manufactured performed heat treatment (tread quenching) to the intermediate product of the rail wheel. Abrasion resistance may contact the rail at rail wheel is required to tread and the flange. Accordingly, in the heat treatment for a conventional intermediate product in the manufacturing process of the railway wheel, in order to form a fine pearlite structure in the surface layer of the surface layer and the flange immediately below the tread surface, the tread and the flange of the rim portion of the intermediate product of the railway wheel and sprayed cooling medium (water, or water and air mixture fluid) against, it was quenched tread and flange. On the other hand, in the conventional heat treatment, for the surfaces other than the tread and the flange surface of the rail wheel (surface of the boss portion, a side surface and the rim portion of the plate portion), not sprayed cooling medium, it has implemented cool It was. As described above, a tread and flange surface of the rim portion of the wear resistance is required, the tread and the surface other than the flange surface of the rail wheel (boss surface, the plate portion and side surfaces of the rim portion) This is because abrasion resistance is not required.
[0041]
　If C content is less hypoeutectoid steel and eutectoid steel as in the conventional rail wheel, pro-eutectoid cementite is hard to generate. However, as in the above chemical composition, if C content is excessive eutectoid steel than 0.80% by the conventional manufacturing method be manufactured railway wheel, if the pro-eutectoid cementite inside rail wheel produces There, in particular, has been allowed to cool conventional in the tread surface hardening, the boss portion and the plate portion, pro-eutectoid cementite be easily generated was found for the first time in the survey of the present inventors. Pro-eutectoid cementite decreases the toughness. Therefore, in the railway wheel C content is 0.80% or more of the over-eutectoid steel, not only the rim portion, also in the boss portion and the plate portion, it is preferable to suppress the generation of pro-eutectoid cementite.
[0042]
　Furthermore, hardened layer to produce a surface layer of the intermediate product of the railway wheel during the heat treatment, if left intact rail wheel without removing by cutting, to reduce the toughness of the rail wheel. Therefore, in the other surface except for the tread and flange surfaces hardened layer is removed by cutting (boss surface, the plate portion surface and the rim portion side), while suppressing the generation of pro-eutectoid cementite, the hardened layers If you produce also can be suppressed is preferable.
[0043]
　Accordingly, the present inventors have found that in the manufacturing process of the railway wheel, not only the rim portion including a tread and a flange, in the plate portion and the boss portion, were investigated and studied a method of suppressing the pro-eutectoid cementite. As a result, the present inventors have obtained the following findings.
[0044]
　FIGS. 4-9, based on the results of heat treatment test assuming a heat treatment in the manufacturing process of the railway wheel, the content of each element in the steel (FIG. 4: C content, Figure 5: Si content, FIG. 6 : Mn content, Figure 7: Cr content, Figure 8: Al content, Figure 9: a V content), and the average cooling rate in the 800 ~ 500 ℃ (℃ / sec), hardened layers and pro-eutectoid cementite is a diagram showing the relationship between.
[0045]
　4, using a plurality of samples of varying the C content (Steel No. 1, 2, 3, 4 in Table 3 to be described later), based on the results obtained in Jomini formula end quenching test described below it was developed. 5, using a plurality of samples of varying the Si content (Steel No. 5,3,6 of Table 3 to be described later), it was developed based on the results obtained in Jomini formula end quenching test is there. 6, using a plurality of samples of varying the Mn content (Steel No. 7,3,8 of Table 3 to be described later), it was developed based on the results obtained in Jomini formula end quenching test is there. Figure 7 uses a plurality of samples with varying Cr content (Steel No. 3,9,10,11 in Table 3 to be described later), was created based on the results obtained in Jomini formula end quenching test it is intended. 8, using a plurality of samples of varying the Al content (Steel No. 3,12,13,14,15,16 in Table 3 to be described later), the results obtained with Jomini formula end quenching test which was developed on the basis of. 9, by using a plurality of samples of varying the V content (Steel No. 3,17,18 in Table 3 to be described later), was developed based on the results obtained in Jomini formula end quenching test is there.
[0046]
　"●" mark in FIGS. 4-9, it means that the hardened layer (martensite and / or bainite) is produced. "○" mark is not generated by hardened layer consists microstructure substantially pearlite, eutectoid cementite amount in the microstructure is 1.0 present / 100 [mu] m or less, pro-eutectoid cementite substantially means that did not exist in. "×" mark is not generated by the hardened layer in the microstructure, but microstructure consists essentially pearlite, pro-eutectoid cementite amount exceeds 1.0 this / 100 [mu] m, pro-eutectoid in the microstructure means that the cementite was produced. Here, "microstructure consists essentially of perlite" refers to the area ratio of pearlite in the microstructure means that 95% or more. Further, the later method of measuring the pro-eutectoid cementite amount (present / 100 [mu] m).
[0047]
　Referring to FIG. 4, when the cooling rate is too fast, it was confirmed that the hardened layer is formed. In this specification, pearlite is produced during tissue, and the maximum cooling rate quenching layer does not generate (cooling rate "●" mark and "○" mark of the boundary in FIG. 4), perlite It is defined as the critical cooling rate. In FIGS. 4-9, showing a pearlite critical cooling rate by a broken line. Referring to FIG. 4, with the increase of C content, perlite critical cooling rate has decreased. Referring to FIG. 5, with an increase in the Si content, perlite critical cooling rate has decreased. Referring to FIG. 6, with the increase of Mn content, perlite critical cooling rate has decreased. Referring to FIG. 7, with increasing Cr content, perlite critical cooling rate has decreased. Referring to FIG. 8, with the increase of the Al content, perlite critical cooling rate has decreased. Referring to FIG. 9, with the increase of V content, perlite critical cooling rate has decreased. That is, with reference to FIGS. 4 to 9, C, Si, Mn, Cr, Al, and V are all have the effect of lowering the pearlite critical cooling rate.
[0048]
　On the other hand, when the cooling rate is too low, there are cases where the pro-eutectoid cementite is produced in the tissue. Referring to FIG. 4, if increasing C content, even higher cooling rate, pro-eutectoid cementite is produced.
[0049]
　Here, the maximum cooling rate (boundary cooling rate of the "○" mark and "×" mark in the figure) of pro-eutectoid cementite amount to produce more than 1.0 present / 100 [mu] m, pro-eutectoid cementite critical cooling It is defined as speed. The pro-eutectoid cementite critical cooling rate, indicated by the solid line in FIGS. 4-9.
[0050]
　4, as the C content increases, pro-eutectoid cementite critical cooling rate is increased. Similarly, in FIG. 5, but Si not be as pronounced as C, as Si content increases, pro-eutectoid cementite critical cooling rate is increased. 7, but Cr is not even noticeable as C, as the Cr content increases, pro-eutectoid cementite critical cooling rate is increased. Further, with reference to FIGS. 6 and 9, even if the Mn content or the V content is increased, pro-eutectoid cementite critical cooling rate does not change much. On the other hand, referring to FIG. 8, if the increase of Al content, pro-eutectoid cementite critical cooling rate decreases significantly.
[0051]
　Therefore, the pro-eutectoid cementite critical cooling rate, C has an effect of enhancing the pro-eutectoid cementite critical cooling rate, has the effect of Al is decreased pro-eutectoid cementite critical cooling rate.
[0052]
　Based on the above results, the present inventors have found that perlite critical cooling rate, and pro-eutectoid cementite critical cooling rate, C content, Si content, Mn content, Cr content, Al content, and, V containing It was further examined the relationship between the amount. As a result, when manufacturing a rail wheel consisting of over-eutectoid steel having the chemical composition described above, A in the manufacturing process cm in the intermediate product cooling rail wheel after heat treatment at transformation point or higher, at 800 ~ 500 ° C. the rate of cooling (° C. / sec), if Fn1 less defined by the equation be indicative of perlite critical cooling rate (1), it was found to be able to suppress the formation of hardened layer. Also, if Fn2 or defined by there formula (2) a measure of pro-eutectoid cementite critical cooling rate has been found to be able to suppress the formation of pro-eutectoid cementite.
　Fn1 = -5.0 + exp (5.651-1.427 × C-1.280 × Si-0.7723 × Mn-1.815 × Cr-1.519 × Al-7.798 × V) ··· (1)
　Fn2 = 0.515 + exp (-24.816 + 24.121 × C + 1.210 × Si + 0.529 × Mn + 2.458 × Cr-15.116 × Al-5.116 × V) · · · (2)
　where , each element symbol in the formula (1) and (2), the content of the corresponding element (mass%) is substituted. Incidentally, 800 ~ 500 ° C. is a temperature range in which pearlite and pro-eutectoid cementite is produced.
[0053]
　Method of manufacturing a rail wheel according to the present embodiment has been completed based on the above findings includes a heating step and a cooling step. In the heating step, in mass%, C: 0.80 ~ 1.15% , Si: 1.00% or less, Mn: 0.10 ~ 1.25%, P: 0.050% or less, S: 0. 030% or less, Al: 0.025 ~ 0.650%, N: 0.0030 ~ 0.0200%, Cr: 0 ~ 0.60%, and, V: 0 ~ 0.12%, and containing, the balance has a chemical composition consisting of Fe and impurities, and the boss portion, a rim portion including a tread and a flange, the intermediate product of the railway wheel and a plate portion disposed between the boss portion and the rim portion, A Cm is heated to a transformation point or higher. In the cooling step, cooling the intermediate product. In the cooling step is Fn1 ° C. / sec or less defined by the cooling rate equation in 800 ~ 500 ° C. of the intermediate products of the tread and the surface other than the flange surface of the railway wheel (1), the cooling rate in an intermediate product of the rail wheel in There is a Fn2 ° C. / sec or more, which is defined at a cooling rate of 800 ~ 500 ° C. at most slower regions formula (2), of the railway wheel of an intermediate product, 800 ~ 500 ° C. in tread and the flange surface as the cooling rate is Fn2 ° C. / sec or more to cool the intermediate product.
　Fn1 = -5.0 + exp (5.651-1.427 × C-1.280 × Si-0.7723 × Mn-1.815 × Cr-1.519 × Al-7.798 × V) ··· (1)
　Fn2 = 0.515 + exp (-24.816 + 24.121 × C + 1.210 × Si + 0.529 × Mn + 2.458 × Cr-15.116 × Al-5.116 × V) · · · (2)
　where , each element symbol in the above formulas (1) and (2), the content of the corresponding element (mass%) is substituted.
[0054]
　The cooling step in further cooling rate in 800 ~ 500 ° C. in the tread and the flange surface is at Fn2 ° C. / sec or more and 5 ° C. / sec or more, so that 200 ° C. / sec or less, cooling said intermediate product it may be.
[0055]
　Chemical composition of the intermediate products of the railway wheel, Cr: 0.02 ~ 0.60%, and, V: 0.02 ~ 0.12%, also contain one or more selected from the group consisting of good.
[0056]
　Railway wheel according to the present embodiment, by mass%, C: 0.80 ~ 1.15% , Si: 1.00% or less, Mn: 0.10 ~ 1.25%, P: 0.050% or less, S: 0.030% or less, Al: 0.025 ~ 0.650%, N: 0.0030 ~ 0.0200%, Cr: 0 ~ 0.60%, and, V: 0 ~ 0.12%, contains, has a chemical composition the balance being Fe and impurities, it comprises a boss portion, a rim portion including a tread and a flange, and a plate portion disposed between the boss portion and the rim portion. In the microstructure of the boss portion, the area ratio of pearlite is less than 95%, pro-eutectoid cementite amount defined by formula (A) is 1.0 present / 100 [mu] m or less. In the microstructure of the plate portion, the area ratio of pearlite is less than 95%, pro-eutectoid cementite amount defined by formula (A) is 1.0 present / 100 [mu] m or less. In the microstructure of the rim portion, the area ratio of pearlite is less than 95%, pro-eutectoid cementite write amount defined by formula (A) is 1.0 present / 100 [mu] m or less.
　Pro-eutectoid cementite amount (present / 100μm) = 200μm × 200μm /(5.66×100μm sum of the number of pro-eutectoid cementite which intersects the two diagonal lines of the square field of view) (A)
[0057]
　Chemical composition of the intermediate products of the railway wheel, Cr: 0.02 ~ 0.60%, and, V: 0.02 ~ 0.12%, also contain one or more selected from the group consisting of good.
[0058]
　It will be described in detail a method for manufacturing and railroad wheels of a rail wheel of the present embodiment. "%" Related elements, unless otherwise specified, means mass%.
[0059]
　[Chemical composition of the railway wheel]
　Railway wheels of this embodiment, for example, as shown in FIG. 1, has a boss portion 2, a plate portion 3, a shape having a rim portion 4 comprising a tread 41 and flange 42. The chemical composition of the rail wheel of the present embodiment contains the following elements.
[0060]
　C: 0.80 ~ 1.15%
　carbon (C) increases the hardness of the steel, improve the wear resistance. If the C content is too low, these effects can not be obtained. On the other hand, if the C content is too high, pro-eutectoid cementite is precipitated in the austenite grain boundaries, ductility of the steel, toughness and fatigue life decreases. Therefore, C content is from 0.80 to 1.15%. The preferable lower limit of C content is 0.85%, more preferably 0.86%, more preferably 0.87%, more preferably 0.90%. The preferable upper limit of C content is 1.05%, more preferably 1.00%.
[0061]
　Si: 1.00% or less
　silicon (Si) is contained inevitably. That, Si content is over 0%. Si is a ferrite solid solution strengthening to increase the hardness of steel. However, if Si content is too high, it becomes easy to produce the pro-eutectoid cementite. Further if the Si content is too high, too high hardenability of the steel, martensite is easily generated. Moreover, during use as a rail wheel, it contains the baked by frictional heat generated between the brake and may withstand crack resistance of the steel is lowered. Therefore, Si content is 1.00% or less. The preferable upper limit of the Si content is 0.80%, more preferably 0.65%, more preferably from 0.45%, more preferably 0.35%. A preferable lower limit of Si content is 0.01%, more preferably from 0.05%, more preferably 0.20%.
[0062]
　Mn: 0.10 ~ 1.25%
　manganese (Mn) of increasing the hardness of steel by solid solution strengthening of the ferrite. Mn is further configured to form MnS, it enhances the machinability of the steel. If the Mn content is too low, these effects can not be obtained. On the other hand, if the Mn content is too high, too high hardenability of steel, easily martensite is produced. Moreover, during use as a rail wheel, it contains the baked by frictional heat generated between the brake and may withstand crack resistance of the steel is lowered. Therefore, Mn content is 0.10 to 1.25%. The preferable lower limit of the Mn content is 0.50%, more preferably 0.60%, more preferably 0.70%. The preferable upper limit of the Mn content is 1.00%, more preferably 0.82%.
[0063]
　P: 0.050% or less
　phosphorus (P) is an impurity contained in the unavoidable. That, P content is over 0%. P lowers the toughness of the steel is segregated at the grain boundaries. Accordingly, P content is 0.050% or less. The preferable upper limit of the P content is 0.030%, more preferably 0.020%. P content is preferably as small as possible. However, if an attempt excessively reduced P content, refining cost becomes excessively high. Therefore, when considering the usual industrial production, preferable lower limit of the P content is 0.0001%, more preferably from 0.0005%.
[0064]
　S: 0.030% or less
　Sulfur (S) is inevitably contained. That, S content is over 0%. If positively to contain S, S enhances the machinability of the steel by forming a MnS. However, S is reduced the toughness of the steel. Thus, S content is 0.030% or less. The preferable upper limit of the S content is 0.020%. The preferable lower limit of the S content in the case of obtaining the effect of improving machinability is 0.001%, still more preferably 0.005%.
[0065]
　Al: 0.025 ~ 0.650%
　of aluminum (Al), in the chemical composition of the rail wheel of this embodiment is more 0.80% C content, suppresses the formation of pro-eutectoid cementite, the toughness of the steel increase. Al further, AlN was formed by combining the N, refining the crystal grains. By crystal grains finer, it increases the toughness of the steel. If the Al content is too low not these effects can not be obtained. On the other hand, if the Al content is too high, coarse nonmetallic inclusions is increased, toughness of the steel is lowered. Therefore, Al content is 0.025 to 0.650 percent. A preferable lower limit of Al content is 0.030%, more preferably 0.040%, still more preferably 0.050%. The preferable upper limit of Al content is 0.450%, more preferably 0.350%, still more preferably 0.250%, still more preferably 0.115%. Al content referred herein means the content of acid-soluble Al (sol. Al).
[0066]
　N: 0.0030 ~ 0.0200%
　nitrogen (N) combines with Al to form AlN, refining the crystal grains. By crystal grains finer, increasing the toughness of the steel. This effect can not be obtained if the N content is too low. On the other hand, if the N content is too high, its effect is saturated. Therefore, N content is 0.0030 to 0.0200%. The preferable lower limit of the N content is 0.0035%, more preferably 0.0040%. The preferable upper limit of the N content is 0.0100%, more preferably 0.0080%.
[0067]
　The remainder of the chemical composition of the rail wheel according to the present embodiment is composed of Fe and impurities. Here, the impurity, when the industrial production of the rail wheel, the ore as a raw material, there is to be mixed etc. Scrap or manufacturing environment, does not adversely affect the railway wheels of the embodiment means what is allowed in the range.
[0068]
　The chemical composition of the rail wheel according to the present embodiment further includes, in place of part of Fe, may contain one or more selected from the group consisting of Cr and V.
[0069]
　Cr: 0 ~ 0.60%
　chromium (Cr) is an optional element and may not be contained. That, Cr content may be 0%. If contained, Cr, by reducing the lamellar spacing of pearlite, significantly increase the hardness of the pearlite. However, if the Cr content is too high, it becomes easy to produce the pro-eutectoid cementite. Further if the Cr content is too high, the hardenability is increased, tends to martensite is produced. Therefore, Cr content is from 0 to 0.60 percent. The preferable upper limit of the Cr content is 0.30%, preferably 0.25%, more preferably from 0.10%. A preferable lower limit of the Cr content in the case of obtaining the effect of the lamellar spacing reduction of pearlite is 0.02%.
[0070]
　V: 0 ~ 0.12%
　vanadium (V) are optional elements may not be contained. That, V content may be 0%. If contained, V is a carbide, to form one of the nitrides, and carbonitrides, to precipitation strengthening steel. As a result, the hardness of the rail wheel is significantly increased, further increase the abrasion resistance. However, if the V content is too high, the hardenability is increased, the thickness of the hardened layer after tread quenching increases excessively. Therefore, V content is from 0 to 0.12%. The preferable upper limit of the V content is 0.09%. The preferable lower limit of V content is 0.02%, more preferably from 0.03%.
[0071]
　[Method rail wheel]
　explaining the manufacturing method described above rail wheel. Method of manufacturing a rail wheel according to the present embodiment includes a heat treatment step. Heat treatment step comprises a heating step and a cooling step.
[0072]
　[Heating Step]
　In the heating step, initially having a chemical composition described above, the boss portion, to prepare the intermediate product having a rough shape of a railroad wheel comprising a plate portion and a rim portion. Intermediate product, for example, be prepared in the following manner.
[0073]
　Using an electric furnace or a converter or the like, to produce a molten steel having the chemical composition described above. To produce the material by using a molten steel. For example, by continuous casting to produce a cast slab. Or by ingot casting method to produce an ingot. Against the billet or ingot, to implement the slabbing or hot forging to produce a billet as a material. Material may be a slab produced by continuous casting. The shape of the material is cylindrical is preferred.
[0074]
　Using the prepared material, molding the aforementioned intermediate product. Materials to the longitudinal cut in the direction perpendicular. And hot working in the direction perpendicular to the cutting plane, is formed into a disc shape. Moreover, in hot working, molding the intermediate article of railway wheels so that the wheels of the coarse shape. For example, in the hot working, it carried out hot forging, then carried hot rolling (wheel rolling) as needed. Through the above steps, the production of intermediate products.
[0075]
　Heating the manufactured intermediate product. Specifically, the intermediate product A cm heating transformation point to (℃) or higher. For example, charged with intermediate product in a heating furnace, A cm is heated at transformation point or higher temperature (quenching temperature). Retention time at the heating rate and the quenching temperature is sufficient at conditions well known. A cm transformation point will vary depending the chemical composition of the steel, the quenching temperature is, for example, 850 ~ 1000 ° C..
[0076]
　[Cooling Step]
　relative to the heated intermediate product, to implement the cooling process. By this cooling step, the surface layer and the flange surface of the microstructure just under the tread surface of the intermediate product of railroad wheels, and the abrasion resistance is high fine pearlite structure. In the surface layer and the surface layer of the flange just below the tread surface, may be overlayed to produce hardened layer (layer composed of martensite and / or bainite) is some fine pearlite. In this case, to remove the hardened layer performs cutting in a subsequent step. On the other hand, in the tread and the surface other than the flange surface of the intermediate product, restrain the hardened layer is produced in the microstructure. Then, substantially pearlite microstructures (perlite 95% or more by area ratio). Among the intermediate product, the tread and the flange surface than the surface, the surface of the plate portion, the surface of the boss portion, and means a surface other than the tread and the flange surface of the rim portion. In tread and a surface other than the flange surface of the intermediate product, to suppress the generation of hardened layer, of the intermediate product, in the surface other than the tread and the flange surface to be machined and the resulting hardened layer it is due to the difficulty.
[0077]
　Further, in any of the regions of the intermediate product, inhibiting the formation of pro-eutectoid cementite. That is, in the intermediate product of the railway wheel having a chemical composition which is over-eutectoid steel described above, not only the rim portion, also in the plate portion and the boss portion, to suppress the generation of pro-eutectoid cementite. Rim portion other than the tread and the flange, and prevent the hardening layer is generated in all of the microstructure of the plate portion and the boss portion, and by suppressing the generation of pro-eutectoid cementite, is over-eutectoid steel above even rail wheel having a chemical composition, it is possible to suppress a decrease in toughness.
[0078]
　Specifically, the intermediate product of the aforementioned quenching temperature, so as to satisfy all of the following (A) ~ (C), carrying out the cooling.
　(A) tread and a surface other than the flange surface of the intermediate product, i.e. boss surface, the cooling rate in the 800 ~ 500 ° C. of the plate portion surface and the rim portion side (tread and the rim portion surfaces other than the flange surface) Fn1 ° C. / It s to be equal to or less than to cool the intermediate product.
　(B) of the intermediate product, the slowest becomes region cooling rate at 800 ~ 500 ° C., i.e., inside the boss portion, most slower region cooling rate at the inner plate portion inside and the rim portion (hereinafter, referred slowest area) the cooling rate in the so that Fn2 ° C. / sec or more to cool the intermediate product.
　(C) such that the cooling rate in the 800 ~ 500 ° C. tread and flange surface of the intermediate product is Fn2 ° C. / sec or more to cool the intermediate product.
[0079]
　In tread and the flange surface, is less than the cooling rate is Fn2 ° C. / sec, of the rim portion, the tread and the flange surface portion near, pro-eutectoid cementite is precipitated. Accordingly, the tread and the flange surface, the cooling rate and Fn2 ° C. / sec or more.
[0080]
　The upper limit of the cooling rate of the tread and the flange surface is not particularly limited. However, if the cooling rate at the tread and the flange surface is too fast, thickness increases of the resulting hardened layer, in the cutting process step, the range must be removed increases. Accordingly, the preferred upper limit of the cooling rate of the tread and the flange surface is 200 ° C. / sec. The cooling rate of the tread and the flange surface is preferably not Fn2 ° C. / sec or more, and is 5 ° C. / sec or more. In this case, the surface layer of the pearlite structure of the surface layer and the flange just below the tread surface is further made fine, the wear resistance can be obtained more excellent.
[0081]
　Here, what is defined as "cooling rate in the 800 ~ 500 ° C." is the temperature range, a temperature range pearlite transformation occurs, and, because a temperature range in which pro-eutectoid cementite is produced. The "cooling rate in 800 ~ 500 ° C." refers to the average cooling rate in the 800 ~ 500 ° C. in the region of the intermediate product of the railway wheel (° C. / sec).
[0082]
　Cooling rate at the surface and inside of the intermediate product is different, the shape of the intermediate product (i.e., rail wheel), and, by cooling method. The temperature change of the surface of the intermediate product during the cooling (i.e., cooling rate in each part), by using a heat distribution analyzer represented by thermography, can be identified. Therefore, the cooling rate of the slowest region, the heat distribution measuring instrument, it is possible to specify.
[0083]
　For example, the temperature change of each part of the intermediate product (area) identified in the following manner. Figure 10 is a side view of the cooling device 10 used in the cooling step. Referring to FIG. 10, the cooling device 10 includes a rotary device 11 having a rotary shaft, and a plurality of cooling nozzles 12-14. A plurality of cooling nozzles 12 to 14, including one or more tread cooling nozzle 14, and one or more of the plate portion cooling nozzle 13, one or more of the boss portion cooling nozzle 12. 1 or more tread cooling nozzle 14, as in the prior art, is disposed about the rotation axis. Nozzle opening tread cooling nozzle 14 is disposed opposite to the tread 41 of the intermediate product. Nozzle opening tread cooling nozzle 14 may be disposed so as to face the surface of the intermediate products flange 42. 1 or more of the plate portion cooling nozzle 13, the nozzle opening is arranged to face the surface of the plate portion 3. 1 or more bosses cooling nozzle 12, the nozzle opening is arranged to face the surface of the boss portion 2.
[0084]
　Tread cooling nozzle 14, by injecting coolant from the nozzle opening, mainly cool the surface of the tread 41 and flange 42 of the rim portion 4. Plate portion cooling nozzle 13 injects the coolant from the nozzle opening, mainly cooling the plate portion 3. Boss cooling nozzle 12, by injecting coolant from the nozzle opening, mainly cool the boss portion 2. Tread cooling nozzle 14 is not only to cool the surface of the tread 41 and flange 42 of the rim portion 4, it may be cooled at least a portion of the plate portion 3. Plate portion cooling nozzle 13 is not only to cool the plate portion 3, at least a portion of at least a portion of the rim portion 4 and / or the boss portion 2 may be cooled. Boss cooling nozzle 12 is not only to cool the boss portion 2, may be cooled at least a portion of the plate portion 3. Tread cooling nozzle 14 in FIG. 10, the arrangement and number of the plate portion cooling nozzle 13 and the boss portion cooling nozzle 12 is an example, not limited to this. A plurality of cooling nozzles of the cooling device, in the cooling step, cooling satisfying the above (A) ~ (C) is possible, the configuration is not particularly limited.
[0085]
　The cooling medium is not particularly limited as long as the cooling speed suitable for the desired structure is obtained, it is not particularly limited. Cooling medium, for example, water, air (air), a mist, brackish (spray) or the like.
[0086]
　Cooling apparatus 10 further includes one or more of thermography (infrared heat distribution measuring instrument) comprises a 20. Thermography 20 is in a state of mounting the intermediate product of the rail wheel in a cooling device 10, the upper surface temperature of the intermediate product, the lower surface temperature, so that it is possible measure the internal temperature of the side surface temperature and the intermediate products are placed. Arrangement and the number of thermography 20 in FIG. 10 is an example and is not limited to this. In Figure 10, a plurality of thermography 20, tread 41, the surface of the flange 42, the surface other than the surface of the tread 41 and flange 42 of the surface of the rim portion 4 (for example, the side surface of the rim portion 4), the surface of the plate portion 3 , and the temperature distribution of the surface of the boss portion 2 is arranged so as to be measured.
[0087]
　For example, A cm transformation point or more to the heated sample intermediate product (actually rail wheel comprising a product intermediate product with the same shape, have the same composition, sample products intended for temperature measurement) arranged in the cooling device 10 to. While rotating the sample intermediate product by rotating device 11, by spraying a cooling medium from the cooling nozzles 12-14, to start cooling. During cooling, a plurality of thermography 20, measuring the change in the temperature distribution of the sample intermediate product.
[0088]
　A plurality of thermography 20 is connected to the temperature distribution analyzer (not shown). Temperature distribution analyzer, for example, includes a computer and a temperature distribution analysis program stored in a memory of a computer. By the temperature distribution analysis program is executed by a CPU, a temperature distribution analyzer analyzes the temperature change per unit time in each area of ​​the sample intermediate product (the internal region of the sample intermediate product including) a three-dimensionally. Temperature distribution analyzer, for example, using known thermal conduction analysis program using 3D FEM (finite element method), can be analyzed in a known manner.
[0089]
　Samples intermediate product is cooled (quenched) to normal temperature, to identify the change in temperature of each region of the sample intermediate product. Then, based on the result of temperature change, of the sample intermediate product, to identify the latest area cooling rate at 800 ~ 500 ° C. (slowest area).
[0090]
　Of the region of the measured sample intermediate product by thermography 20, the surface other than the surface of the tread 41 and flange 42, i.e. the boss portion 2 surface, the surface of the plate portion 3, and, other than the tread 41 and flange 42 of the rim portion 4 cooling rate in 800 ~ 500 ° C. of the surface becomes less Fn1 ° C. / sec, a cooling rate in the 800 ~ 500 ° C. at a specified slowest area in the sample intermediate product by three-dimensional analysis becomes Fn2 ° C. / sec or more, thermography as the cooling rate is Fn2 ° C. / sec or more at 800 ~ 500 ° C. the measured tread 41 and flange 42 the surface of the sample intermediate product by 20, adjusting the cooling rate of the sample intermediate product in the refrigerator 10. Specifically, the tread surface cooling nozzle 14, the plate portion cooling nozzle 13, and the boss portion to adjust the flow rate of each of the cooling medium of the cooling nozzle 12, a plurality of tread arranged in the cooling unit 10 cooling nozzles 14, plate portion cooling nozzles 13 and, among the boss cooling nozzle 12, and to select the cooling nozzles used to adjust the cooling rate. After the adjustment, in place of the sample intermediate product, A cm for the intermediate products for products that are heated above the transformation point, carrying out cooling using a cooling device 10. Preferably, the cooling rate at 800 ~ 500 ° C. of the surface other than the surface of the tread 41 and flange 42 becomes less Fn1 ° C. / sec, 800 ~ 500 ° C. in the slowest areas identified in the sample intermediate product by three-dimensional analysis the cooling rate becomes Fn2 ° C. / sec or more, the cooling rate at 800 ~ 500 ° C. tread 41 and flange 42 the surface of the sample intermediate product measured by thermography 20 be Fn2 ° C. / sec or more and 5 ° C. / sec or more at , so that 200 ° C. / sec or less, to adjust the cooling rate of the sample intermediate product in the refrigerator 10.
[0091]
　In the cooling step, by the cooling rate of the intermediate product of the tread 41 and the surface of the flange 42 and 5 ° C. / sec or more, the surface layer portion and surface layer portion of the flange 42 immediately below the tread surface 41, a fine pearlite is formed . C content of the railway wheel of this embodiment from 0.80 to 1.15% and higher. Therefore, it increases the wear resistance of the fine pearlite. Further, by cooling the intermediate product to the cooling rate of the surface of the tread 41 and flange 42 becomes Fn2 ° C. / sec or more, the generation of eutectoid cementite is suppressed even in the surface of the tread 41 and flange 42.
[0092]
　Further, tread 41 and the surface other than the surface of the flange 42 (the surface of the boss portion 2, the surface of the plate portion 3, and the surface other than the tread 41 and flange 42 the surface of the rim portion 4), the cooling rate is Fn1 ° C. / seconds to cool the intermediate product to be equal to or less than. Thus, generation of the hardened layers at the surface other than the tread 41 and flange 42 are suppressed. Further, the boss portion 2, the plate 3, and, in the region of the rim portion 4, the cooling rate in the slowest area to cool the intermediate product so that Fn2 ° C. / sec or more. Thus, generation of pro-eutectoid cementite is suppressed. That is, in the above cooling step, in addition to the tread 41 and flange 42, tread 41 and flange 42 the other portion (the boss portion 2, the plate portions 3, and a side of the rim portion 4) cooling is promoted even. Through the above steps, the cooling step is performed. Temperature of the intermediate product after the cooling step is, for example, a normal temperature (25 ° C.). However, the temperature of the intermediate product after the cooling step, if 500 ° C. or less is not particularly limited.
[0093]
　[Tempering process]
　the intermediate product after the cooling step, carried tempering as necessary. Tempering suffices be performed at a known temperature and time. Tempering temperature A c1 is below the transformation point. Tempering temperature is, for example, a 400 ~ 600 ° C., holding time at the tempering temperature, for example, 60 to 180 minutes. However, no tempering temperature and holding time is not limited to this. Tempering may not be performed.
[0094]
　[Cutting Step]
　Although the heat treatment step (heating and cooling steps) after the surface layer and the surface layer in the fine pearlite flange 42 immediately below the tread 41 of the intermediate product of is formed, hardened layer in the upper layer of fine pearlite formation there is a case to be. In use of the rail wheel, the wear resistance of the hardened layer is low. Therefore, in this step, removing the surface layer of the hardened layer of the surface layer and the flange 42 immediately below the tread 41 by cutting. Cutting the reporting may be made in a known manner.
[0095]
　In the manufacturing method of this embodiment, other surfaces other than the surface of the tread 41 and flange 42 (the boss portion 2 surface, the surface of the plate portion 3, and, the tread 41 and flange 42 of the surface of the rim portion 4 on the surface) other than the surface it is hard hardened layer is formed. Therefore, in the manufacturing method of the railway wheel of the present embodiment, not only the rim portion 4 of the intermediate product of the railway wheel, despite the well plate portion 3 and the boss portion 2 is cooled, other than the surface of the tread 41 and flange 42 surface (a surface of the boss portion 2, the surface of the plate portion 3, and a side of the rim portion 4) may not be cut.
[0096]
　Through the above steps, the railway wheels of the present embodiment is manufactured. When produced the railway wheels in the production method of this embodiment, over-eutectoid steel despite the railway wheels using, in the region of the plate portion 3 and the boss portion 2, eutectoid cementite which is a cause of decrease in toughness generation of is suppressed. Furthermore, despite the railway wheels with peracetic eutectoid steel, in the region of the plate portion 3 and the boss portion 2, it can also be suppressed generation of hardened layers to be the cause of decrease in toughness. Also in the rim portion 4, the generation of pro-eutectoid cementite is suppressed.
[0097]
　[Railway wheels Organization
　microstructure rail wheel manufactured by the manufacturing method described above is as follows. Tissue surface layer and the surface layer portion of the flange just below the tread surface is pearlite structure. Pro-eutectoid cementite amount is 1.0 present / 100 [mu] m or less. Boss, the plate portion, microstructure of tread and the portion other than the flange of the rim portion consists essentially pearlite. In other words, more than 95% of the area ratio is pearlite. Furthermore, pro-eutectoid cementite amount is 1.0 present / 100 [mu] m or less.
[0098]
　More specifically, in railway wheels over eutectoid steel having the chemical composition described above, in the microstructure of the boss portion, the area ratio of pearlite is less than 95%, pro-eutectoid cementite amount 1.0 present / 100 [mu] m less. Then, the microstructure of the plate portion, the area ratio of pearlite is less than 95%, pro-eutectoid cementite amount is one / 100 [mu] m or less. Then, the microstructure of the rim portion, the area ratio of pearlite is less than 95%, pro-eutectoid cementite amount is 1.0 present / 100 [mu] m or less. Here, the pro-eutectoid cementite amount is defined by the formula (A).
　Pro-eutectoid cementite amount (present / 100μm) = 200μm × 200μm /(5.66×100μm sum of the number of pro-eutectoid cementite which intersects the two diagonal lines of the square field of view) (A)
[0099]
　Here, the microstructure can be observed in the following manner. Railway wheels of each unit (the boss portion, the plate portion, the rim portion) at a position deeper than 5mm from the surface of, taking samples for microstructure observation. After mirror-finished by mechanical polishing an observation surface of the sample, corrode observation surface with a mixture of picric acid with sodium hydroxide. For any one field of view in the observation plane after the corrosion (200μm × 200μm), to produce a photographic image using a 500 × optical microscope. In the observation plane, pro-eutectoid cementite generated in prior austenite grain boundaries for exhibiting a black color, generation presence of pro-eutectoid cementite is identified.
[0100]
　As shown in FIG. 11, the 200 [mu] m × 200 [mu] m square visual field 100 of, catching diagonal 101 of two. Then, a sum of the number of pro-eutectoid cementite which intersects the diagonal 101 of these two. As defined by equation (1), the total number of pro-eutectoid cementite obtained, by dividing by two the total length of the diagonal line 101 (5.66 × 100 [mu] m), eutectoid cementite per 100 [mu] m (the / seek 100μm).
[0101]
　If pro-eutectoid cementite amount of 1.0 present / 100 [mu] m or less, and can sufficiently suppress the generation of pro-eutectoid cementite.
[0102]
　Then, the same observation plane again, mirror finished by mechanical polishing, corroded with nital solution (mixed solution of nitric acid and ethanol). For any one field of view in the observation plane after the corrosion (200μm × 200μm), to produce a photographic image using a 500 × optical microscope. Ferrite, bainite, martensite, perlite, each contrast different. Therefore, based on the contrast, hardened layers in the observation plane, and, identifies the perlite. Area ratio of pearlite is determined based on the area of ​​the observation plane and the total area of ​​the identified perlite.
[0103]
　The railway wheels manufactured by the manufacturing method described above, in the rim portion of the microstructure including a tread and a flange, pearlite area ratio is 95% or more, consists essentially of perlite. The pro-eutectoid cementite amount is 1.0 present / 100 [mu] m or less. Therefore, the railway wheel is excellent in wear resistance. Further, a boss portion of the rail wheel, even microstructure tread and the portion other than the flange of the plate portion and the rim portion consists essentially of perlite. The boss, in the microstructure of the tread and the portion other than the flange of the plate portion and the rim portion, pro-eutectoid cementite amount is 1.0 present / 100 [mu] m or less, respectively. Therefore, the railway wheel according to the present embodiment, have a chemical composition as the over-eutectoid steel, excellent in toughness.
[0104]
　Incidentally, immediately after the cooling step, as described above, the railway wheels, the surface layer of the surface layer and the flange just below the tread of the rim may include a hardened layer. However, before the railway wheels are used, hardened layer is removed by cutting the above. As a result, the microstructure of the tread and the flange surface of the rim portion consists essentially of perlite.
Example 1
[0105]
　The molten steel of the steel Nos. 1 to 18 having chemical compositions shown in Table 3 were prepared.
[0106]
[table 3]

[0107]
　It was produced round ingots (top diameter 107mm, base diameter 97 mm, the truncated cone-shaped height 230 mm) by ingot using the above-molten steel. After heating the ingot to 1250 ° C., and hot forging within a temperature range of 850 ~ 1100 ° C., to produce a round bar for a railway wheel with a diameter of 40 mm.
[0108]
　[Jomini formula end quenching test]
　from round bar with a diameter of 40mm of steel Nos. 1 to steel No. 18 was prepared Jomini specimen diameter 25 mm, length 100 mm. Specifically, by turning, and a round bar with a diameter of 40mm and steel bars with a diameter of 25 mm. Then, by cutting the round bar at a length of 100 mm, were prepared Jomini specimen.
[0109]
　To simulate the heat treatment step in the manufacturing process of the railway wheel (heating and cooling steps), using Jomini specimens was performed Jomini Formula end quench test according to JIS G0561 (2011). Specifically, in the air atmosphere Jomini specimen, A cm and held for 30 minutes in an oven at 950 ° C. the temperature of the transformation point or higher, the tissue Jomini specimen was austenite single phase. After that, it was carried out one end quenching (water-cooled). Specifically, it was cooled by injecting water at one end of Jomini specimen. After water cooling, and mechanically polishing the side surface of Jomini test piece was carried out water-cooling, at regular intervals in the axial direction from one end (water cooling end), Rockwell hardness using the C scale conforming to JIS Z2245 (2011) (HRC ) test was performed to obtain a HRC distribution. Measurement interval of HRC is a 1.0mm pitch from the water-cooling end to 15mm position, the 15mm or more positions from the water-cooled end was 2.5mm pitch.
[0110]
　An example of the resulting HRC distribution shown in FIG. 12. In Figure 12, we show the results of the steel No. 1-4. Referring to FIG. 12, Jomini curve, based on the hardness of the water cooling end position of the test piece, and the region A where the distance increases along the hardness of the water cooled end suddenly decreases, water-cooled end than the area A a position away from, which is classified into a region B in which the distance hardness than the region a with respect to the water-cooled end decreases gradually. Tissue observation in region A corresponded to hardened layer consisting of martensite and / or bainite. Region B was tissue consisting essentially pearlite. Based on the HRC distribution as shown in FIG. 12 to obtain the hardened layer depth.
[0111]
　[Microstructure observation]
　microstructure observed at each distance from the water-cooling end was performed in the following manner. At each distance from the water-cooled end of Jomini test piece as an observation surface measurement surface of the sample side were HRC measurement, a mixed solution after the mirror-finished by mechanical polishing, the observation surface and picric acid and sodium hydroxide corroded. For any one field of view in the observation plane after the corrosion (200μm × 200μm), to produce a photographic image using a 500 × optical microscope. In the observation plane, pro-eutectoid cementite generated in prior austenite grain boundaries for exhibiting a black color, can be specified generation presence of pro-eutectoid cementite.
[0112]
　As shown in FIG. 11, the 200 [mu] m × 200 [mu] m square visual field 100 of, minus the diagonal 101 of the two. Then, the total sum of the number of pro-eutectoid cementite which intersects the diagonal 101 of these two. The total number of pro-eutectoid cementite obtained, by dividing by two the total length of the diagonal line 101 (5.66 × 100 [mu] m), was determined eutectoid cementite per 100 [mu] m (the present / 100 [mu] m). That is, based on equation (A), defining the pro-eutectoid cementite amount.
[0113]
　If pro-eutectoid cementite amount of 1.0 present / 100 [mu] m or less, it is determined that it is possible to suppress the generation of pro-eutectoid cementite. The numerical values ​​set forth in response to the distance from the water-cooling end of each steel numbers in Table 4 shows pro-eutectoid cementite amount (present / 100 [mu] m). For example, the cooling rate 13.1 ° C. / sec Test No. 4 the value of (Distance 13mm from water-cooled end) (0.5), in the test piece of test No. 4, at a length position of 13mm in the axial direction from the water cooled end the amount of pro-eutectoid cementite which means that was 0.5 present / 100 [mu] m.
[0114]
[Table 4]

[0115]
　Then, the same observation plane again, mirror finished by mechanical polishing, and corroded by nital solution (mixed solution of nitric acid and ethanol). For any one field of view in the observation plane after the corrosion (200μm × 200μm), to produce a photographic image using a 500 × optical microscope. Ferrite, bainite, martensite, perlite, each contrast different. Therefore, based on the contrast, hardened layers in the observation plane, identified perlite. Area ratio of pearlite was determined on the basis of the area of ​​the observation plane and the total area of ​​the identified perlite.
[0116]
　Incidentally, the relationship between the cooling time from the distance and 800 ° C. from water cooled end at Jomini formula end quench test to 500 ° C., the literature data (F.Wever et al shown experimentally., Zur Frage der Warmebehandlung der Stahle auf Grund ihrer Zeit-Temperatur-Umwandlungs-Schaubilder, Stahl u Eisen, 74 (1954), p749 ~ 761) is present. Based on this literature data, converts the distance from the water cooled end and the average cooling rate in the 800 ~ 500 ° C. at each position. The water cooling rate, as described in Table 4 corresponds to the distance from the water-cooled end.
[0117]
　[Formastor Test]
　Using the above Jomini specimen, can not be reproduced by Jomini formula end quenching test was carried out continuously cooled test at low cooling rate. The heat treatment was used Fuji radio Koki made of Four master testing machine. A round bar having a diameter of 40mm of steel Nos. 1 to steel No. 18, the diameter of 3 mm, a length of 10mm of the test piece were prepared one by one for each steel number. The test piece was soaked for 5 minutes at 950 ° C.. Then cooled at a constant cooling rate 1.0 ° C. / sec. On specimens after cooling, by the method described above, it was calculated pro-eutectoid cementite amount (present / 100 [mu] m).
[0118]
　For eutectoid cementite at a cooling rate of 1.0 ° C. / sec is not confirmed steel numbers, further, the continuous cooling heat treatment test at 0.1 ° C. / sec separately performed, eutectoid cementite in a manner similar to that described above determine the amount.
[0119]
　[Test Results]
　The results are shown in Table 4. In Table 4, "●" mark in the column corresponding to the distance from the water-cooling end indicates tissue at that distance was hardened layer (martensite and / or bainite). Further, "○" mark in the column corresponding to the distance from the water-cooling end, the distance in tissue substantially consists of pearlite (an area ratio be 95% or higher pearlite), martensite or bainite is not verified , indicating that the pro-eutectoid cementite was also not confirmed. "Numeric" in the column corresponding to the distance from the water-cooling end, tissue (with 95% or more by area ratio pearlite) substantially of pearlite, indicating the number per 100μm of eutectoid cementite at that distance. In each steel numbers in Table 4, the cooling rate (° C. / sec) is less than or equal Fn1 defined by formula (1), colored range is Fn2 than defined in Equation (2) in gray did. Table 4 See, in a range of cooling rates that are colored in gray, without generation hardened layer, and pro-eutectoid cementite amount was 1.0 present / 100 [mu] m or less.
[0120]
　Table 3 and Table 4, in each of the steel numbers, if the cooling rate becomes Fn2 above, even over-eutectoid steel C content of 0.80 to 1.15%, the first amount analysis cementite becomes 1.0 present / 100 [mu] m or less, could suppress the formation of pro-eutectoid cementite. Therefore, in the railway wheel, sufficient toughness was expected that can be secured. Furthermore, the cooling rate is equal to or Fn1 less, generation of hardened layers is suppressed. Therefore, in the railway wheel, sufficient toughness was expected that can be secured. Accordingly, tread and flange surfaces other than the surface of the intermediate product, i.e. boss surface, the cooling rate in the 800 ~ 500 ° C. of the plate portion surface and the rim portion side (tread and the rim portion surfaces other than the flange surface) is Fn1 ° C. / sec as the following, among the intermediate product, 800 slowest a region cooling rate at ~ 500 ° C., i.e., inside the boss portion, the plate portion within and regions where the cooling rate is slowest in the interior rim portion (hereinafter, slowest cooling rate in) that area set to be Fn2 ° C. / sec or more, such that the cooling rate in the 800 ~ 500 ° C. tread and flange surface of the intermediate product is Fn2 ° C. / sec or more, by cooling the intermediate product if, in the railway wheel to be manufactured, the boss portion, the plate portion, pearlite area rate is 95% or more in both the rim portion, pro-eutectoid cementite amount 1.0 / 100 [mu] m or less and becomes, on the surface of the boss portion and the plate portion was found to be inhibiting the formation of hardened layer.
Example 2
[0121]
　Using round bar having a diameter of 40mm of steel No. 9 in Table 3, pro-eutectoid cementite amount and Charpy impact value (J / cm 2 was investigated the relationship between). Four round bar of steel No. 9 30 minutes soaked at 950 ° C., and then cooled at a cooling rate shown in Table 5. Cooling rate, by immersion in a salt bath of various temperatures were adjusted.
[0122]
[table 5]

[0123]
　[Microstructure observation]
　from the central portion of the round bar of each test number after cooling (9-1 to 9-4), samples were taken for microstructure observation. Viewing surface of the sample was a plane perpendicular to the central axis of the round bar. After mirror finishing the observation surface by mechanical polishing, and corrosion of the observation surface with a mixture of picric acid with sodium hydroxide. For any one field of view in the observation plane after the corrosion (200μm × 200μm), to produce a photographic image using a 500 × optical microscope. In the observation plane, pro-eutectoid cementite generated in prior austenite grain boundaries for exhibiting a black color, can be specified generation presence of pro-eutectoid cementite. Further, in the same manner as in Example 1 to obtain pearlite area ratio. As a result, in any of the test numbers, pearlite area ratio was 95% or more.
[0124]
　As shown in FIG. 11, the 200 [mu] m × 200 [mu] m square visual field 100 of, minus the diagonal 101 of the two. Then, the total sum of the number of pro-eutectoid cementite which intersects the diagonal 101 of these two. The total number of pro-eutectoid cementite obtained, by dividing by two the total length of the diagonal line 101 (5.66 × 100 [mu] m), was determined eutectoid cementite per 100 [mu] m (the present / 100 [mu] m). That is, based on equation (A), defining the pro-eutectoid cementite amount.
[0125]
　[Charpy impact test]
　from round bar of each test number (9-1 to 9-4) were prepared Charpy test piece (10mm × 10mm × 55mm). The central axis of the Charpy test pieces were aligned with the central axis of the round bar. Using Charpy test pieces, and the Charpy impact test according to JIS Z 2242 (2005) was performed at room temperature (25 ° C.).
[0126]
　[Test Results]
　Table 5 shows the test results. Table 5 See, cooling rate if the Fn2 above (3.4) (Steel No. 9-1), pro-eutectoid cementite amount was 1.0 present / 100 [mu] m or less. Therefore, the Charpy impact value 20.0 J / cm 2 as high as or higher, sufficient toughness is obtained. On the other hand, if the cooling rate is less than Fn2 (steels No. 9-2 ~ 9-4), Charpy impact value 20.0 J / cm 2 was as low as less than.
[0127]
　It has been described an embodiment of the present invention. However, the above-described embodiment is merely an example for implementing the present invention. Accordingly, the present invention is not limited to the embodiments described above, it can be implemented by changing the embodiment described above without departing from the scope and spirit thereof as appropriate.
DESCRIPTION OF SYMBOLS
[0128]
　1 Railway wheels
　2 boss
　3 plate portion
　4 the rim portion
　10 the cooling device

The scope of the claims

[Requested item 1]By
　mass%, C: 0.80
　~ 1.15%, Si: 1.00% or
　less, Mn: 0.10
　~ 1.25%, P: 0.050% or
　less, S: 0.030% or less,
　al:
　0.025 ~ 0.650%, N: 0.0030
　~ 0.0200%, Cr: 0 ~ 0.60%,
　and, V: 0 ~ 0.12%,
　containing the balance Fe and has a chemical composition consisting of impurities,
　the boss portion and,
　the rim portion including a tread and a flange,
　and a plate portion which is disposed between the boss portion and the rim portion, the intermediate product of the rail wheel a cm a heating step of heating above the transformation point,
　and a cooling step of cooling the heated said intermediate product,
　in the cooling step, the cooling rate at 800 ~ 500 ° C. of the tread and the surface other than the flange surface in the intermediate product There is a Fn1 ° C. / sec or less, which is defined by equation (1), the intermediate product Cooling rate in 800 ~ 500 ° C. in the region where the cooling rate is slowest is at Fn2 ° C. / sec or more, which is defined by equation (2), the cooling rate at 800 ~ 500 ° C. in the tread and the flange surface Fn2 ° C. / so that the above second, cooling the intermediate product,
　the production method of the rail wheel.
　Fn1 = -5.0 + exp (5.651-1.427 × C-1.280 × Si-0.7723 × Mn-1.815 × Cr-1.519 × Al-7.798 × V) ··· (1)
　Fn2 = 0.515 + exp (-24.816 + 24.121 × C + 1.210 × Si + 0.529 × Mn + 2.458 × Cr-15.116 × Al-5.116 × V) · · · (2)
　where , each element symbol in the above formulas (1) and (2), the content of the corresponding element (mass%) is substituted.
[Requested item 2]
　A method of manufacturing a rail wheel according to claim 1,
　wherein the further cooling step, the cooling rate in the 800 ~ 500 ° C. in the tread and the flange surface is at Fn2 ° C. / sec or more and 5 ° C. / sec or more, as it will be 200 ° C. / sec or less, cooling the intermediate product,
　the production method of the rail wheel.
[Requested item 3]
　A method of manufacturing a rail wheel according to claim 1 or claim 2,
　wherein the chemical
　composition, Cr: 0.02 ~ 0.60%,
　and, V: 0.02 ~ 0.12%,
　consisting of It contains one or more selected from the group,
　method for producing a rail wheel.
[Requested item 4]
　By
　mass%, C: 0.80
　~ 1.15%, Si: 1.00% or
　less, Mn: 0.10
　~ 1.25%, P: 0.050% or
　less, S: 0.030% or less,
　al:
　0.025 ~ 0.650%, N: 0.0030
　~ 0.0200%, Cr: 0 ~ 0.60%,
　and, V: 0 ~ 0.12%,
　containing the balance Fe and has a chemical composition consisting of impurities,
　and the boss portion,
　a rim portion including a tread and a flange,
　and a plate portion disposed between said boss portion and the rim portion,
　the microstructure of the boss portion, area ratio of pearlite is less than 95%, pro-eutectoid cementite amount defined by formula (a) is 1.0 present / 100 [mu] m or less,
　in the microstructure of the plate portion, the area ratio of pearlite over 95% , and the pro-eutectoid cementite amount defined by formula (A) is 1.0 present / 100 microns m or less,
　in the microstructure of the rim portion, the area ratio of pearlite is less than 95%, pro-eutectoid cementite amount defined by formula (A) is 1.0 present / 100 [mu] m or less,
　the railway wheels.
　Pro-eutectoid cementite amount (present / 100μm) = 200μm × 200μm /(5.66×100μm sum of the number of pro-eutectoid cementite which intersects the two diagonal lines of the square field of view) (A)
[Requested item 5]
　A rail wheel according to claim 4,
　wherein the chemical
　composition, Cr: 0.02 ~ 0.60%,
　and, V: 0.02 ~ 0.12%,
　1 kind selected from the group consisting of containing more than,
　railway wheels.