EA041988B1 - METHOD OF MANUFACTURING RAILWAY WHEEL AND RAILWAY WHEEL - Google Patents

Description

Technical field

The present invention relates to a railway wheel manufacturing method and a railway wheel.

Prerequisites for the creation of the invention

A railway vehicle travels on rails that form a railroad track. The railway vehicle includes a plurality of railway wheels. The railway wheel provides support for this vehicle by contacting the rail and travels along the rail by rolling on it. Due to contact with the rail, the railway wheel wears out. In order to improve the efficiency of railway transportation, efforts are being made to increase the weight of the cargo carried by the railway vehicle and to increase the speed of the vehicle. Therefore, there is a need to improve the wear resistance of railway wheels used in a railway vehicle.

Technologies for improving the wear resistance of a railway wheel are proposed in Japanese Patent Publication No. 09-202937 (Patent Document 1), Japanese Patent Publication Application No. 2012-107295 (Patent Document 2), Japanese Patent Publication Application No. 2013-231212 ( Patent Document 3) and Japanese Patent Publication No. 2004-315928 (Patent Document 4).

The railway wheel described in Patent Document 1 is composed of the following (wt %): C, 0.4-0.75; Si - 0.4-0.95; Mn - 0.6-1.2; Cr - 0-0.2 or less; P - 0.03 or less; S - 0.03 or less; Fe and inevitable impurities - the rest. In this railway wheel, the region from the tread surface to a depth of at least 50 mm is composed of pearlite in structure. The method for manufacturing a railway wheel in Patent Document 1 includes a quenching step in which the tread surface of the wheel is cooled so that the cooling curve for this surface passes through the pearlite formation zone in the continuous cooling transformation curve and is on the longer time side of the martensitic transformation curve. .

The railway wheel described in Patent Document 2 has the following chemical composition (wt %): 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; S - 0.04 or less; Fe and impurities - the rest, and the content of P<0.05%, Cu<0.20% and Ni<0.20%. In addition, the following relationships are observed for the chemical composition:

< 2.7+29.5хС+2.9χSi+6.9*Mn+10.8хСг+30.3χΜο+44.3xV ,38χΜη)xexp(0.77хСг)хххр (3,ΟχΜο)хххр(4.6xV) < 25

Patent Document 2 claims that, by maintaining the above chemical composition and ratios, the railroad wheel steel is excellent in wear resistance, rolling contact fatigue resistance, and chipping resistance. The railway wheel described in Patent Document 3 is composed of the following (wt %): 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 - 0.02-0.12; Fe and impurities are the rest, and Fn1 calculated by formula (1) is from 32 to 43, and Fn2 calculated by formula (2) does not exceed 25. Formula (1) is as follows:

Fnl=2.7+29.5C+2.9Si+6.9Mn+10.8Cr+30.3Mo+44.3V and formula (2) is as follows:

Patent Document 3 states that a railway wheel steel can be excellent in wear resistance, rolling contact fatigue resistance, and spalling resistance if it has the above chemical composition, and Fn1 and Fn2 satisfy the above ratios. The railway wheel described in Patent Document 4 is an integral railway vehicle wheel composed of steel having the following chemical composition (wt %): C, 0.85-1.20; Si - 0.05-2.0; Mn - 0.05-2.0; and, if necessary, a predetermined amount of one or more of the following chemical elements: Cr, Mo, V, Nb, B, Co, Cu, Ni, Ti, Mg, Ca, Al, Zr and N, Fe and unavoidable impurities - the rest , wherein at least a portion of the tread surface and/or the surface of the wheel flange is composed of pearlite in structure. Patent Document 4 states that the service life of a railway vehicle wheel depends on the degree of wear of the tread surface and the ridge surface (paragraph [0002] of Patent Document 4), and further depends on the presence of cracks on these surfaces, the occurrence of which is due to an increase in heat generation. when braking in the case of a high-speed rail line. It also states that in the case where the wheel of a railway vehicle has the above structure, wear can be reduced and thermal cracks can be prevented from occurring on the tread surface and the crown surface.

- 1 041988

Bibliography

Patent Literature.

Patent Document 1: Japanese Patent Publication No. 09-202937.

Patent Document 2: Japanese Patent Publication No. 2012-107295.

Patent Document 3: Japanese Patent Publication No. 2013-231212.

Patent Document 4: Japanese Patent Publication No. 2004-315928.

non-patent literature.

Non-Patent Document 1: F. Wever et al., Zur Frage der Warmebehandlung der Stahle auf Grund ihrer Zeit-Temperatur-Umwandlungs-Schaubilder, Stahl u Eisen, 74 (1954), p. 749-761.

The essence of the invention

Technical problem.

In the railway wheels described in the above Patent Documents 1, 2 and 3, the wear resistance is improved by the active content in the V composition. , it is not always possible to provide sufficient wear resistance. At the same time, the railway wheel described in Patent Document 4 is made of a hypereutectoid steel that has an increased C content compared to Patent Documents 1, 2, 3. increase in speed, it is potentially possible to provide sufficient wear resistance. Meanwhile, this railway wheel is manufactured in the following manner. Billet (round billet) is subjected to hot processing to obtain a semi-finished product in the form of a railway wheel. The resulting semi-finished product is subjected to heat treatment (hardening of the rolling surface). When hardening the tread surface, after heating the semi-finished product, cooling water is sprayed onto its tread surface and the crest to cool them quickly. Note that with rapid cooling of the tread surface and the ridge, part of the hub and part of the disk are also cooled. As a result, fine-grained perlite with high wear resistance is formed in the matrix structure of the outer layer located directly under the tread surface and in the near-surface part of the ridge. However, in the outer layer immediately below the tread surface and in the near-surface part of the ridge, after hardening of the tread surface, a layer of martensite and/or bainite is also formed above the fine-grained pearlite layer. Further, a layer consisting of martensite and/or bainite, which occurs in the outer layer at the tread surface and the outer layer of the ridge when these surfaces and the ridge are rapidly cooled after heat treatment, is called a hardened layer. When using a railway wheel having a hardened layer in the outer layer at the tread and the outer layer of the crown, this hardened layer will be subject to wear during operation of the wheel. For this reason, in the conventional manufacture of a railway wheel, the hardened layer generated in the outer layer at the tread and the outer layer of the ridge is removed by cutting, so that fine pearlite is exposed to the tread surface and the crown surface of the semi-finished railway wheel after the tread surface is hardened. As a result of the described manufacturing process, a conventional railway wheel is obtained. However, as a result of the study carried out by the present inventors, it has been found that in the case where a railway wheel is composed of hypereutectoid steel as in Patent Document 4, the toughness of the hub part and the disc part may be degraded by using the conventional method to manufacture the wheel. For a conventional railway wheel, while the structure of the tread surface and the ridge constituting the rim part have been studied in order to prolong the service life of the railway wheel, studies have not been conducted on the structure of the hub part and the rim part of the railway wheel. It is an object of the present invention to provide a method for manufacturing a railway wheel that can securely obtain a hypereutectoid steel railway wheel having excellent toughness, and to provide such a railway wheel.

Troubleshooting.

A method for manufacturing a railway wheel according to one embodiment of the present invention includes a heating step and a cooling step. At the heating stage, a semi-finished product of a railway wheel, having the following chemical composition, consisting of, in wt.%: 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; V - 0-0.12; Fe and impurities - the rest, and including a hub part, a rim part having a tread surface and a ridge, and a disc part located between the hub part and the rim part, are heated to a transformation temperature not lower than A _cm (°C). At the cooling stage, the semi-finished product is cooled in such a way that the cooling rate in the range of 800-500°C on its surfaces, which differ from the tread surface and the ridge surface, was not more than Fn1°C/c, determined by expression (1);

the cooling rate in the range of 800-500°C in the area in which the cooling rate is minimal in the said semi-finished product is not less than Fn2°C/c, defined by expression (2); And

- 2 041988 cooling rate in the range of 800-500°C on the tread surface and the surface of the crest of the said semi-finished product is at least Fn2°C/s:

Fnl \u003d -5.0 + exp (5.651-1.427xC-1.280xSi-0.7723χΜη-1.815xCr1.519χΑ1-7.798xV) (1)

Fn2=0.515+exp(-24.816+24.121xC+1.210x31+0.529χΜη+2.458xCr15.116χΑ1-5.116xV) (2) moreover, each element symbol in expressions (1) and (2) shows the content of the corresponding element in wt.% . The railway wheel corresponding to this variant has the following chemical composition, consisting of, in wt.%: 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; V - 0-0.12; Fe and impurities are the rest, and include a hub part, a rim part having a tread and a ridge, and a disc part located between the hub part and the rim part. In the microstructure of the hub, the area ratio of pearlite is 95% or more, and the amount of secondary cementite (proeutectoid cementite from English proeutectoid cementite) determined by the following formula (A) does not exceed 1.0 particles/100 μm. In the microstructure of the disc part, the area ratio of pearlite is 95% or more, and the amount of secondary cementite determined by the following formula (A) does not exceed 1.0 particles/100 μm. In the microstructure of the rim part, the area ratio of pearlite is 95% or more, and the amount of secondary cementite, determined by the following formula (A), does not exceed 1.0 particles/100 µm, where the amount of secondary cementite (particles/100 µm) = total number of particles secondary cementite, through which two diagonals pass in a square field of view 200 µm χ 200 µm/(5, 6 6 χ 100 µm) (A).

advantages of the invention.

The method for manufacturing a railway wheel according to the present invention can securely obtain a hypereutectoid steel railway wheel that has excellent toughness.

Brief description of the drawings

In FIG. 1 shows a section in section with a plane passing parallel to the central axis of the railway wheel.

In FIG. 2 is a diagram illustrating the relationship between the Vickers hardness of a railway wheel and the wear rate of that wheel as determined by the Nishihara wear test.

In FIG. 3 schematically shows the Nishihara wear test.

In FIG. 4 is a graph illustrating the relationship between C content, cooling rate, and the presence of a hardened layer and secondary cementite, which is obtained based on the results of a heat treatment test simulating heat treatment in the manufacture of a railway wheel.

In FIG. 5 is a graph illustrating the relationship between Si content, cooling rate, and the presence of a hardened layer and secondary cementite, which is obtained based on the results of a heat treatment test simulating heat treatment in the manufacture of a railway wheel.

In FIG. 6 is a graph illustrating the relationship between Mn content, cooling rate, and the presence of a hardened layer and secondary cementite, which is obtained based on the results of a heat treatment test simulating heat treatment in the manufacture of a railway wheel.

In FIG. 7 is a graph illustrating the relationship between Cr content, cooling rate, and the presence of a hardened layer and secondary cementite, which is obtained based on the results of a heat treatment test simulating heat treatment in the manufacture of a railway wheel.

In FIG. 8 is a graph illustrating the relationship between Al content, cooling rate, and the presence of a hardened layer and secondary cementite, which is obtained based on the results of a heat treatment test simulating heat treatment in the manufacture of a railway wheel.

In FIG. 9 is a graph illustrating the relationship between V content, cooling rate, and the presence of a hardened layer and secondary cementite, which is obtained based on the results of a heat treatment test simulating heat treatment in the manufacture of a railway wheel.

In FIG. 10 schematically shows an exemplary cooling device used in the railway wheel manufacturing method of the present embodiment.

In FIG. 11 schematically shows a method for measuring the amount of secondary cementite.

- 3 041988

In FIG. 12 is a plot of Rockwell C hardness (HRC) versus distance from the water-cooled end of a Jominy test piece (Jominy curves) as obtained in the Jominy end-hardening example.

Detailed description of implementation options

Railway wheel design.

In FIG. 1 shows a section in section by a plane passing through the central axis of the railway wheel. As shown in FIG. 1, the railway wheel 1 is disc-shaped and includes a hub portion 2, a disc portion 3, and a rim portion 4. Hub part 2 has a cylindrical shape and is located in the middle part of the railway wheel 1. Hub part 2 has a through hole 21. The central axis of the through hole 21 coincides with the central axis of the railway wheel 1. An axial shaft, which is not shown, is inserted into the through hole 21. Thickness T2 of hub part 2 is greater than thickness T3 of disk part 3. The rim portion 4 is formed on the outer periphery of the railway wheel 1. The rim portion 4 includes a tread 41 and a ridge 42. The tread 41 is mated with the ridge 42. When using the railway wheel 1, the treads 41 and the ridge 42 are in contact with the rail surface. The thickness T4 of the rim part 4 is greater than the thickness T3 of the disk part 3. Part 3 of the disk is located between part 2 of the hub and part 4 of the rim. Part 3 of the disc along its inner edge is connected to part 2 of the hub and along the outer edge is connected to part 4 of the rim. The thickness T3 of the disc portion 3 is less than the thickness T2 of the hub portion 2 and the thickness T4 of the rim portion 4. The inventors of the present invention have studied ways to improve the wear resistance of a railway wheel. As a result, they found the following.

Improve wear resistance by increasing the C content.

In FIG. 2 is a diagram illustrating the relationship between the Vickers hardness of a railway wheel and the wear rate of that wheel as determined by the Nishihara wear test. Fig. 2 was obtained as a result of the experiment, which is discussed below. From each of the ingots having the chemical composition specified in table. 1, a round rod with a diameter of 40 mm was made.

Table 1

Steel No. Chemical composition (wt.%, rest - Its and impurities) WITH Si MP S A1 N R SG V 1 0.84 0.30 0.81 0.002 0.032 0.0038 0.001 - - 2 0.93 0.29 0.80 0.002 0.032 0.0042 0.001 - - 3 1.00 0.30 0.80 0.002 0.034 0.0040 0.001 - - 4 1.09 0.30 0.79 0.002 0.036 0.0040 0.001 - - 21 0.79 0.29 0.81 0.002 0.035 0.0030 0.001 0.10 - 22 0.76 0.29 0.79 0.001 0.034 0.0026 0.001 0.08 0.028 23 0.75 0.29 0.80 0.002 0.034 0.0033 0.001 0.10 0.058 24 0.75 0.29 0.80 0.002 0.034 0.0032 0.001 0.10 0.097 25 0.78 0.75 0.82 0.002 0.036 0.0038 0.001 0.10 - 26 0.75 0.77 0.79 0.001 0.038 0.0034 0.001 0.09 0.028 27 0.77 0.77 0.81 0.001 0.033 0.0032 0.001 0.10 0.058 28 0.76 0.76 0.82 0.001 0.036 0.0027 0.001 0.10 0.096

From a round rod, a raw test specimen (corresponding to a semi-finished railway wheel) was made in the form of a ring with a diameter of 32 mm and a width of 10 mm. The raw test specimen was subjected to a hardening process that simulated the hardening of the tread of a railway wheel. Specifically, an untreated test specimen of each steel listed under the corresponding number was held at a heat treatment temperature of 950°C for 20 minutes. To create a fine-grained pearlite structure after exposure, the untreated test piece was removed from the furnace and immersed in a salt bath having a temperature of 550°C. The residence time in the salt bath was 7 minutes. After these 7 minutes, the untreated test piece was removed from the salt bath and cooled to room temperature (25°C). To simulate tempering during the manufacture of a railway wheel, each untreated test piece after cooling was held at a heat treatment temperature of 450°C for 3 hours. After holding at a heat treatment temperature of 450°C for 3 hours, the untreated test piece was cooled to room temperature (25 °C).

After cooling, cutting was performed on the outer circumference of the raw test piece to obtain a wheel pattern (corresponding to a railway wheel) 100, which had the cylindrical shape shown in FIG. 3. The wheel sample 100 had a diameter D100 of 29.39 mm and a width W100 of 8 mm.

In addition, steel No. 29 was obtained, indicated in table. 2, which was used as the rail material.

- 4 041988

table 2

SteelNo. Chemical composition (wt.%, the rest - Her and impurities) WITH Si MP R S SG V 29 0.99 0.51 0.71 0.011 0.008 0.22 -

From steel No. 29 as the material of the rail, a rail specimen 200 having the shape of a ring and shown in FIG. 3. The rail sample 200 had a diameter D200 of 30.0 mm and a width W200 of 5 mm. Using an optical microscope at 500x magnification, the metal structure of the wheel sample 100 was studied at a position at a depth of 2-3 mm from the outer circumferential surface to the central axis. Similarly, using an optical microscope at 500x magnification, the metal structure of the rail sample 200 was studied at a position at a depth of 2-3 mm from the outer circumferential surface to the central axis. As a result of the study of the structure, it was found that the structure of the wheel samples 100 of steels No. 1-4 and 21-28 consisted of a single pearlite phase and the rail sample 200 also consisted of a single pearlite phase in structure. In addition, for the sample 100, the wheels are in the same position as in the study of the structure, i.e. at a position at a depth of 2-3 mm from the outer circumferential surface to the central axis, the Vickers hardness was measured by testing according to JIS Z 2244 (2009). In all cases, the test force was 2.9421 N. Similarly, for the sample 200 rail in the same position as in the study of the structure, i. at a position at a depth of 2-3 mm from the outer circumferential surface, the Vickers hardness was measured by testing according to JIS Z 2244 (2009). When tested, the force was 2.9421 N. As a result, the Vickers hardness of the rail sample 200 was 430 HV. The width center of the outer circumferential surface of the wheel specimen 100 and the width center of the outer circumferential surface of the rail specimen 200 were brought into contact with each other, and a mutual rotation wear test was performed on the wheel specimen 100 and the rail specimen 200 while pressed against each other with a force of 900 MPa. The rotation speed of the wheel sample 100 was 800 rpm, and the rotation speed of the rail sample 200 was 775 rpm. Thus, the relative slip of the wheel sample 100 and the rail sample 200 was 1.1%. At the end of the test, namely after the wheel sample 100 made 500,000 revolutions, its mass (g) was measured. Then, the difference between the mass (g) of the wheel sample 100 before the test and its mass (g) after the test was determined, and the result of dividing this mass difference by 50 (g/10000 rpm) was taken as the degree of wear of the wheel. Note that 4 wheel samples 100 were made from each steel, and for each steel, using such samples, the same test was carried out 4 times. The wear rate of the railway wheel of each steel was taken as the average of the wear rates of the wheel samples 100, which was obtained in these four tests. The Vickers hardness and wear rate of the wheel specimen 100 obtained for each steel were used to create FIGS. 2.

The symbol ◊ in FIG. 2 shows the test result using V-free steels in which the Si content is approximately constant at about 0.3% and the C content varies from 0.8 to 1.1% (hereinafter referred to as V-free hypereutectoid steels). The o symbol indicates test results using steels in which the C content ranges from 0.75 to 0.79%, the Si content is approximately constant at approximately 0.3%, and the V content varies from 0% to approximately 0.1 % (hereinafter referred to as hypereutectoid steels with different V content and low Si content). The symbol Δ indicates the results of tests using steels in which the content of C is in the range from 0.75 to 0.79%, the content of Si is approximately constant at approximately 0.8% and the content of V varies from 0% to approximately 0.1 % (hereinafter referred to as hypereutectoid steels with different V content and high Si content). The number next to each symbol in FIG. 2 is the number of steel in the table. 1. Referring to FIG. 2, as the V content increased, the Vickers hardness of the wheel made of hypereutectoid steels with different V content and low Si content (symbol o) increased. Specifically, Vickers hardness increased with increasing V content from vanadium-free steel (steel 21) to 0.028% (steel 22), 0.058% (steel 23) and 0.097% (steel 24). At the same time, the Vickers hardness remained at about 350 HV and the wear rate decreased to only about 0.015 g/10,000 rpm. At the same time, in hypereutectoid steels with different V content and high Si content (symbol Δ), as the V content increases from vanadium-free steel (steel 25) to 0.028% (steel 26), 0.058% (steel 27) and 0.096% (steel 27) and 0.096% (steel 28) the Vickers hardness increased to approximately 380 HV. However, even with the increase in Vickers hardness, the wear rate of the wheel remained constant at approximately 0.015 g/10,000 rpm and did not decrease further. At the same time, in hypereutectoid steels that do not contain V (symbol ◊), the Vickers hardness increased with increasing C content from 0.84% (steel 1) to 0.93% (steel 2), 1.00% (steel 3 ) and 1.09% (steel 4). In addition, as the Vickers hardness increased, the wear rate decreased to approximately 0.010 g/10,000 rpm.

Based on the above, it can be said that the wear resistance of a railway wheel made of the steel intended for its manufacture is improved more if the hardness is increased by increasing

- 5 041988 by changing the content of C, and not by increasing the content of V, even while maintaining the same hardness. Although the reason for this is not obvious, the following explanation is assumed. During the use of a railway wheel, an external force (load) from the side of the rail acts on the tread surface. Under the action of this force, the cementite, which is part of the perlite contained in the outer layer located directly under the tread surface, is destroyed, and the hardness is further increased as a result of precipitation strengthening. In addition, the carbon contained in the fine-grained destroyed cementite dissolves in the ferrite, which is part of the pearlite, with the appearance of a supersaturated solution, which leads to an increase in the hardness of the outer layer located directly under the tread surface, as a result of solid solution strengthening. An increase in the content of C in steel will lead to an increase in the volume fraction of cementite in perlite. In addition, the likelihood of smaller perlite plates will increase. In this case, under the action of the mechanism described above, the wear resistance of the railway wheel will increase. At the same time, if V is contained in steel, its hardness increases as a result of precipitation strengthening when V carbonitride occurs. In this case, since V carbonitride occurs in ferrite, it mainly increases the hardness of ferrite. Those. the V content does not significantly affect the grinding of perlite. For this reason, although the wear resistance can be improved to a certain extent by the V content, it cannot be improved as much as in the case of precipitation strengthening by cementite failure and hardening due to C solution. Therefore, even if the railway wheel steel has the same hardness, wear resistance can be improved more by increasing the C content than by adding V to the composition.

Based on the results of the study described above, the inventors of the present invention came to the conclusion that, in terms of improving wear resistance for a railway wheel, it is preferable to use a hypereutectoid steel with the following chemical composition (in wt.%): 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; V - 0-0.12; Fe and impurities - the rest.

Prevention of occurrence of secondary cementite.

As described above, a railroad wheel is manufactured by subjecting the semi-finished product to a heat treatment (hardening of the tread surface). In a railway wheel, wear resistance is required for the tread and flange that are brought into contact with the rail. Therefore, in the heat treatment of a semi-finished product in a conventional railroad wheel manufacturing process, a cooling medium (water or a fluid in the form of a mixture of water and air) is sprayed onto the tread and ridge, which are part of the rim of this semi-finished product, to quickly cool them to form a structure of fine-grained pearlite in the outer layer directly under the tread surface and in the outer layer of the ridge. At the same time, in conventional heat treatment, other railway wheel surfaces other than the tread surface and the flange surface, namely the hub surface, the disk surface and the rim side surface, are cooled without spraying the coolant. This is because, as described above, the wear resistance of the tread surface and the ridge surface constituting the rim is required, and the wear resistance of other surfaces (hub and disk surfaces and rim side surface) is not required.

In hypoeutectoid steel and eutectoid steel, in which the C content is low, as in a conventional railway wheel, secondary cementite will not occur. But in the case of hypereutectoid steel in which the content of C is 0.80% or more, as in the case of the above chemical composition, the study performed by the present inventors found for the first time that when a railway wheel is manufactured using a conventional method, this wheel may secondary cementite occurs and, in particular, it is likely to occur in the hub part and the disc part, which are subjected to conventional cooling during hardening of the tread surface. Secondary cementite degrades toughness. Therefore, in a railway wheel composed of a hypereutectoid steel in which the C content is 0.80% or more, it is preferable to prevent secondary cementite from occurring not only in the rim part but also in the hub part and the disc part. In addition, the toughness of the railway wheel is also degraded by the hardened layer that occurs in the outer layer of the semi-finished product during heat treatment if it remains in this wheel and is not removed by cutting. For this reason, on other surfaces other than the tread surface and the ridge surface on which the hardened layer is removed by cutting, namely the surfaces of the hub part and the disc part and the side surface of the rim part, it is preferable to prevent the occurrence of secondary cementite, and also to prevent the occurrence of on top of it is a hardened layer. Accordingly, the present inventors have studied ways to prevent the occurrence of secondary cementite in the manufacture of a railway wheel, not only in the tread and ridge part of the rim, but also in the disc part and the hub part. As a result, the inventors of the present invention have found the following. In FIG. 4-9 are diagrams illustrating the relationship between the content of each of the chemical elements in the steel (Fig. 4 content of C, Fig. 5 - content of Si, Fig. 6 - content of Mn, Fig. 7 - content of Cr, Fig. 8 - content of Al and Fig. 9 - the content of V), the average cooling rate (°C/s) in the range of 800-500°C and the presence

- 6 041988 hardened layer and secondary cementite, these bonds were obtained as a result of a heat treatment test simulating heat treatment during the manufacture of a railway wheel. Fig. 4 is based on the results obtained from the Jominy end hardening test, which will be described below, using a plurality of specimens (steel nos. 1, 2, 3, 4 in Table 3 below) that differed in C content. FIG. 5 is based on the results obtained from the Jominy end hardening test using a variety of specimens (steel nos. 5, 3, 6 in Table 3) that varied in Si content. Fig. 6 is based on the results obtained from the Jominy end-hardening test using a variety of specimens (steel nos. 7, 3, 8 in Table 3) that varied in Mn content. Fig. 7 is based on the results obtained from the Jominy end-hardening test using a variety of specimens (steel nos. 3, 9, 10, 11 in Table 3) that varied in Cr content. Fig. 8 is based on the results obtained from the Jominy end hardening test using a variety of specimens (steel nos. 3, 12, 13, 14, 15, 16 in Table 3) that varied in Al content. Fig. 9 is based on the results obtained from the Jominy end-hardening test using a plurality of specimens (steel nos. 3, 17, 18 in Table 3) that differed in V content. Symbol • in FIG. 4-9 indicates the occurrence of a hardened layer (martensite and/or bainite). The symbol o indicates that no hardened layer occurs, the microstructure consists essentially of pearlite, and the amount of secondary cementite in the microstructure is no more than 1.0 particles per 100 µm, i.e. secondary cementite is essentially absent. The symbol x indicates that no hardened layer occurs in the microstructure, the microstructure consists essentially of pearlite, and the amount of secondary cementite in the microstructure is more than 1.0 particles/100 µm, i.e. secondary cementite appears in the microstructure. Here, the wording microstructure consists essentially of pearlite means that the area ratio of pearlite in the microstructure is 95% or more. In addition, a method for determining the amount of secondary cementite (particles/100 μm) will be discussed later.

Fig. 4 is a confirmation that if the cooling rate is too high, a hardened layer occurs. In this description, the maximum cooling rate at which pearlite occurs in the structure and no hardened layer will occur (the cooling rate at the boundary between the symbols · and o in Fig. 4) is set as the limiting cooling rate when pearlite occurs. In FIG. 4-9, the limiting cooling rate when perlite occurs is shown by a dotted line. As shown in FIG. 4, as the C content increases, the limiting cooling rate when pearlite occurs decreases. As shown in FIG. 5, as the Si content increases, the limiting cooling rate at the occurrence of pearlite decreases. As shown in FIG. 6, as the Mn content increases, the limiting cooling rate at the occurrence of pearlite decreases. As shown in FIG. 7, as the Cr content increases, the limiting cooling rate at the occurrence of pearlite decreases. As shown in FIG. 8, as the Al content increases, the limiting cooling rate when pearlite occurs decreases. As shown in FIG. 9, as the V content increases, the limiting cooling rate when pearlite occurs decreases. Those. as shown in FIG. 4-9, C, Si, Mn, Cr, Al and V provide a reduction in the limiting cooling rate when perlite occurs.

On the other hand, if the cooling rate is too low, secondary cementite may occur in the structure. As shown in FIG. 4, as the C content increases, secondary cementite occurs even if the cooling rate is high.

Here, the maximum cooling rate at which secondary cementite occurs in an amount of more than 1.0 particles/100 μm (in the drawing, the cooling rate at the boundary between the symbols o and x) is set as the cooling rate critical for the occurrence of secondary cementite. In FIG. 4-9, the cooling rate critical for the occurrence of secondary cementite is shown as a solid line.

As shown in FIG. 4, with an increase in the content of C, the cooling rate, which is critical for the occurrence of secondary cementite, increases. Similarly, as shown in FIG. 5, although not as noticeable as in the case of C, but with an increase in the Si content, the cooling rate, which is critical for the formation of secondary cementite, increases. As shown in FIG. 7, although also not as noticeable as in the case of C, but with an increase in the Cr content, the cooling rate, which is critical for the formation of secondary cementite, increases. In addition, as shown in FIG. 6 and 9, with an increase in the content of Mn and V, the cooling rate, which is critical for the formation of secondary cementite, does not change so much. At the same time, as shown in FIG. 8, if the Al content increases, the cooling rate, which is critical for the occurrence of secondary cementite, decreases markedly.

Thus, C provides an increase in the cooling rate, which is critical for the formation of secondary cementite, and Al provides a decrease in the cooling rate, which is critical for the formation of secondary cementite.

Based on the above results, the inventors of the present invention further studied the relationship between the limiting cooling rate in the occurrence of pearlite/the cooling rate critical for the occurrence of secondary cementite and the content of C, Si, Mn, Cr, Al, and V. As a result,

- 7 041988 they found that if the railway wheel is made of hypereutectoid steel having the above chemical composition, in the manufacturing process, when the semi-finished product of this wheel is cooled after heat treatment at a temperature not lower than the transformation temperature Acm, it is possible to prevent the occurrence of a hardened layer if the cooling rate (°C/s) in the range of 800-500°C does not exceed the value of Fn1, which is the limiting cooling rate when pearlite occurs and is determined by expression (1). They also found that it is possible to prevent the occurrence of secondary cementite if this cooling rate is not less than the value of Fn2, which is the cooling rate critical for the occurrence of secondary cementite and is given by expression (2).

Fnl \u003d -5.0 + exp (5.651-1.427xC-1.280χ3ί-0.7723χΜη-1.815xCr1.519χΑ1-7.798xV) (1)

Fn2=0.515+exp(-24.816+24.121xC+l.210xSi+0.529xMn+2.458xCr15.116χΑ1-5.116xV) (2)

In formulas (1) and (2), instead of the designations of chemical elements, their content (in wt.%) is substituted. Note that 800-500°C is the temperature range in which perlite and secondary cementite occur.

The method for manufacturing a railway wheel according to this embodiment, which was created based on the above detected information, includes a heating step and a cooling step. At the heating stage, a semi-finished product of a railway wheel, which has the following chemical composition (in wt.%): 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; V - 0-0.12; Fe and impurities - the rest, and includes a hub, a rim having a tread surface and a ridge, and a disk located between the hub and the rim, are heated to a temperature not lower than the Acm temperature. At the stage of cooling, this semi-finished product is cooled. At the stage of cooling, the semi-finished product of the railway wheel is cooled so that the cooling rate in the range of 800-500°C on its surfaces, which differ from the tread surface and the ridge surface, is not more than Fn11°C/c, determined by expression (1), in that zone semi-finished product, where the cooling rate in the range of 800-500°C is minimal, it was not less than Fn2°C/c, determined by expression (2), and the cooling rate in the range of 800-500°C on the tread surface and the surface of the crest of this semi-finished product was not less than Fn2 °C/s.

Fnl = -5, 0 + exp(5, 651-1, 427xC-1.280x31-0, 7723χΜη-1.815xCr1.519χΑ1-7.798xV) (1)

Fn2 = 0.515+exp(-24.816+24.121xC+1.21 ΟχSi + 0.529χΜη+2.458xCr15.116χΑ1-5.116χV) (2)

In formulas (1) and (2), instead of the designations of chemical elements, their content (in wt.%) is substituted. In addition, in the above cooling step, the semi-finished product can be cooled so that the cooling rate in the range of 800-500°C on the tread surface and the ridge surface is not less than Fn2°C/s, not less than 5°C/s and not more than 200 °C/s.

The semi-finished product of the railway wheel described above may contain the following chemical elements, %: Cr - 0.02-0.60; and/or V - 0.02-0.12. The railway wheel corresponding to this option has the following chemical composition (in wt.%): 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; V - 0-0.12; Fe and impurities - the rest, and includes a hub, a rim having a tread surface and a ridge, and a disk located between the hub and the rim. In the microstructure of the hub, the area ratio of pearlite is 95% or more, and the amount of secondary cementite determined by the formula (A) does not exceed 1.0 particles/100 μm. In the microstructure of the disk, the area ratio of pearlite is 95% or more, and the amount of secondary cementite determined by the formula (A) does not exceed 1.0 particles/100 μm. In the microstructure of the rim, the area ratio of pearlite is 95% or more, and the amount of secondary cementite determined by the formula (A) does not exceed 1.0 particles/100 μm.

Amount of secondary cementite (particles/100 µm) = total amount of secondary cementite particles through which two diagonals pass in a square field of view 200 µm χ 200 µm/(5.6 6 χ 100 µm) (A)

The semi-finished product may contain the following chemical elements, %: Cr - 0.02-0.60; and/or V - 0.02-0.12.

Next, the railway wheel manufacturing method and the railway wheel according to this embodiment will be discussed in detail. When specifying the content of chemical elements, % is wt.%, unless otherwise indicated. The chemical composition of the railway wheel

The railway wheel in this embodiment includes a hub 2, a disc 3 and a rim 4 including a tread 41 and a ridge 42 as shown in FIG. 1. Chemical composition of the railway wheel

- 8 041988 in this embodiment is given below.

C: 0.80-1.15%.

Carbon (C) increases the steel's hardness and wear resistance. If the C content is too low, these effects cannot be achieved. On the other hand, if the C content is too high, secondary cementite precipitates at the grain boundaries of the precursor austenite, and the ductility, toughness, and fatigue life of the steel deteriorate. Therefore, the C content is 0.80-1.15%. The lower limit value of the C content is preferably 0.85%, more preferably 0.86%, even more preferably 0.87%, and even more preferably 0.90%. The upper limit value of the C content is preferably 1.05%, more preferably 1.00%.

Si: 1.00% or less.

Silicon (Si) is inevitably included. Those. the Si content is greater than 0%. Si provides hardening of the ferrite as a result of the occurrence of a solid solution, which leads to an increase in the hardness of the steel. However, if the Si content is too high, secondary cementite is likely to occur. In addition, if the Si content is too high, the hardenability of the steel becomes too high, and martensite is likely to occur. In addition, in the material used in the railway wheel, due to the heat generated by the friction of the wheel and the brake shoe, hardening may occur, which deteriorates the crack resistance of the steel. Therefore, the Si content does not exceed 1.00%. The upper limit value of the Si content is preferably 0.80%, more preferably 0.65%, even more preferably 0.45%, and even more preferably 0.35%. The lower limit value of the Si content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.20%.

Mn: 0.10-1.25%.

Manganese (Mn) provides hardening of ferrite as a result of the occurrence of a solid solution, which leads to an increase in the hardness of the steel. In addition, Mn forms MnS, which facilitates the machining of steel. If the Mn content is too low, these effects cannot be achieved. On the other hand, if the Mn content is too high, the hardenability of the steel is too high, and martensite is likely to occur. In addition, in a material used in a railway wheel, due to the frictional heat of the wheel and the brake shoe, hardening may occur and the crack resistance of the steel may deteriorate. Therefore, the Mn content is 0.10-1.25%. The lower limit value of the Mn content is preferably 0.50%, more preferably 0.60%, and even more preferably 0.70%. The upper limit value of the Mn content is preferably 1.00% and more preferably 0.82%.

P: 0.050% or less.

Phosphorus (P) is an inevitable impurity. Those. the content of P exceeds 0%. P precipitates at the grain boundaries, deteriorating the toughness of the steel. Therefore, the P content is 0.050% or less. The upper limit value of the P content is preferably 0.030% and more preferably 0.020%. Preferably, the P content is as low as possible. However, an excessive reduction in the content of P will lead to an excessive increase in the cost of purification. Therefore, considering the general conditions of industrial production, the lower limit value of P is preferably 0.0001%, and more preferably 0.0005%.

S: 0.030% or less.

Sulfur (S) inevitably enters the composition. Those. the S content is greater than 0%. When S is introduced into the composition, it forms MnS, which facilitates the machining of steel. However, S degrades the toughness of the steel. Therefore, the S content is 0.030% or less. The upper limit value of the S content is preferably 0.020%. Considering the ease of machining, the lower limit value of the S content is preferably 0.001% and more preferably 0.005%.

Al: 0.025-0.650%.

Aluminum (Al) prevents secondary cementite from occurring when the railway wheel of this embodiment contains C at 0.80% or more, which improves the toughness of the steel. In addition, Al combines with N to form AlN and provides crystal grain refinement. As a result of grinding the crystalline grain, the impact strength of the steel increases. These effects cannot be achieved if the Al content is too low. On the other hand, if the Al content is too high, large non-metallic inclusions increase, which deteriorates the toughness of the steel. Therefore, the Al content is 0.025-0.650%. The lower limit value of the Al content is preferably 0.030%, more preferably 0.040%, and even more preferably 0.050%. The upper limit value of the Al content is preferably 0.450%, more preferably 0.350%, even more preferably 0.250%, and even more preferably 0.115%. The Al content here refers to the content of Al soluble in acid (sol. Al).

N: 0.0030-0.0200%.

Nitrogen (N) combines with A1 to form A1N and provides refinement of the crystalline

- 9 041988 grains. As a result of grinding the crystalline grain, the impact strength of the steel increases. If the N content is too low, this effect cannot be achieved. On the other hand, if the N content is too high, such an effect saturates. Therefore, the N content is 0.0030-0.0200%. The lower limit value of the N content is preferably 0.0035%, and more preferably 0.0040%. The upper limit value of the N content is preferably 0.0100%, and more preferably 0.0080%.

The rest in the chemical composition of the railway wheel according to this option are Fe and impurities. Here, the impurity is a chemical element that comes from ore and scrap as raw materials or from the production environment, etc. in the manufacture of the above-described railway wheel in an industrial environment and the content of which is allowed in a range that does not adversely affect this wheel. According to the chemical composition, the railway wheel corresponding to this option, instead of a part of Fe, may also contain Cr and V.

Cr: 0-0.60%.

Chromium (Cr) is an optional chemical element and may not be included. Those. the Cr content may be 0%. If Cr is included in the composition, it reduces the distance between the pearlite plates, which greatly increases the hardness of the pearlite. However, if the Cr content is too high, secondary cementite is more likely to occur. In addition, if the Cr content is too high, hardenability increases and martensite is more likely to occur. Therefore, the Cr content is 0-0.60%. The upper limit value of the Cr content is preferably 0.30%, more preferably 0.25%, and even more preferably 0.10%. The preferred lower limit value of the Cr content to obtain the effect of reducing the distance between the pearlite lamellae is 0.02%.

V: 0-0.12%.

Vanadium (V) is an optional chemical element and may not be included. Those. the V content may be 0%. If V is included in the composition, it forms a carbide, nitride or carbonitride, which leads to precipitation strengthening of the steel. As a result, the hardness of the railway wheel is greatly increased, resulting in further improvement in wear resistance. However, if the V content is too high, the hardenability becomes high, and after hardening of the tread surface, the thickness of the hardened layer is excessively increased. Therefore, the V content is 0-0.12%. The upper limit value of the V content is preferably 0.09%. The lower limit value of the V content is preferably 0.02% and more preferably 0.03%.

A method of manufacturing a railway wheel.

Next, one exemplary method for manufacturing the above-described railway wheel will be described. The method for manufacturing a railway wheel according to this embodiment includes a heat treatment process. The heat treatment process includes a heating step and a cooling step.

heating stage.

Before performing the heating step, first, a semi-finished product is produced that has the above chemical composition and a shape close to that of a railway wheel, and includes a hub part, a disc part, and a rim part. The semi-finished product is produced, for example, in the following way. Using an electric furnace or a converter, molten steels having the above chemical composition are obtained. Raw materials are obtained using these molten steels. For example, a cast part is made, for example, using a continuous casting process. Alternatively, an ingot is made using an ingot casting process. The cast part or ingot is subjected to bloom rolling or hot forging to produce a billet as a raw material. The starting material may be a cast part made using a continuous casting process. In the preferred case, the starting material has a cylindrical shape. Using the obtained source material, create the semi-finished product described above. The starting material is cut in a plane perpendicular to the longitudinal direction. The cut raw material is hot-worked in a direction perpendicular to the cut surface to obtain a disc shape. The subsequent hot working is carried out in such a way as to obtain a semi-finished product, the shape of which is close to that of a railway wheel. During hot working, for example, hot forging is performed, followed by hot rolling (wheel rolling) if necessary. As a result of the above processes, a semi-finished product is obtained. The semi-finished product is heated. Specifically, the semi-finished product is heated to a temperature not lower than the Acm temperature (°C). For example, the semi-finished product is placed in a heating furnace, which must be heated to a temperature (quenching temperature) not lower than the temperature A _cm . The heating rate and holding time at the quench temperature may be selected from those well known. Although the temperature Acm varies depending on the chemical composition of the steel, the quenching temperature is, for example, 850-1000°C.

cooling stage.

For the heated semi-finished product, a cooling step is performed. At this stage of cooling the microstructure

- 10 041988 rounds in the outer layer, located directly under the tread surface, and the outer layer of the crest of the semi-finished railway wheel, are converted into fine-grained perlite, which has high wear resistance. In the outer layer just below the tread and the outer layer of the ridge above the fine-grained pearlite, a hardened layer of a certain thickness (a layer consisting of martensite and/or bainite) can occur. In this case, the hardened layer is removed in a subsequent step by cutting. At the same time, the formation of a hardened layer on surfaces that differ from the tread surface and the surface of the crest of the semi-finished product is not allowed in the microstructure. As a result, the microstructure will consist essentially of pearlite (the area ratio of pearlite is 95% or more). Here, the surfaces different from the tread surface and the ridge surface of the semi-finished product are the surface of the disc part, the surface of the hub part and the surface of the rim part, except for the tread surface and the ridge surface. The reason why a hardened layer is not allowed to occur on surfaces other than the tread surface and the ridge surface of the semi-finished product is that it is difficult to remove the generated hardened layer from these different surfaces by machining. In addition, in any zone of the semi-finished product, the occurrence of secondary cementite is not allowed. Namely, in a railroad wheel semi-finished product having the above chemical composition corresponding to hypereutectoid steel, the occurrence of secondary cementite is not allowed not only in the rim part, but also in the disk part and the hub part. By avoiding the occurrence of a hardened layer and preventing the occurrence of secondary cementite in any area of the rim part other than the tread surface and the ridge, as well as in the disc part and the hub part, it is possible to prevent the deterioration of toughness even if the railway wheel has the above chemical composition corresponding to the hypereutectoid become. Specifically, the semi-finished product is cooled from the above quenching temperature so that the following conditions (A) to (C) are met.

(A) The semi-finished product is cooled so that the cooling rate is in the range of 800-500°C on its surfaces other than the tread surface and the ridge surface, i.e. on the surface of the hub part, the surface of the disc part and the side surface of the rim part (the surface of the rim, which is different from the tread surface and the surface of the ridge) was not more than Fn1°C/s.

(B) The semi-finished product is cooled in such a way that in that zone of the semi-finished product where the cooling rate in the range of 800-500°C is minimal, i.e. in the area inside the hub part, disc part and rim part where the cooling rate is minimal (hereinafter referred to as the zone with the minimum cooling rate), it was not less than Fn2°C/s.

(C) The semi-finished product is cooled so that the cooling rate in the range of 800-500°C on the tread surface and the ridge surface is not less than Fn2°C/s.

If the cooling rate on the tread and ridge surfaces is less than Fn2°C/s, secondary cementite will precipitate in the regions of the rim part near these surfaces. Therefore, the cooling rate is set in such a way that it is not less than Fn2°C/s on the tread surface and the ridge surface.

Note that the upper limit value of the cooling rate on the tread surface and the ridge surface is not specifically limited. However, if the cooling rate at the tread surface and the ridge surface is too high, the thickness of the resulting hardened layer increases and the removal depth increases in the cutting step. Therefore, the upper limit value of the cooling rate on the tread surface and the ridge surface is preferably 200°C/s. In addition, it is preferable that the cooling rate on the tread surface and the ridge surface is not less than Fn2°C/s and not less than 5°C/s. In this case, the perlite in the outer layer immediately below the tread and the outer layer of the ridge is more severely crushed, and even higher wear resistance can be obtained. Here, the reason for setting the cooling rate in the range of 800-500°C is that this is the temperature range in which pearlite transformation occurs, as well as the temperature range in which secondary cementite occurs. The cooling rate in the range of 800-500°C is taken as the average cooling rate (°C/s) in this range in each zone of the semi-finished railway wheel. Cooling rates on the surface and inside the semi-finished product will differ depending on its shape (ie the shape of a railway wheel) and the method of cooling. The temperature change at the surface (ie, the rate of cooling in each part) of the semi-finished product during cooling can be determined using a device that measures the distribution of heat, namely a thermographic device. Thus, the cooling rate in the zone with the minimum cooling rate can also be determined using such a device that measures the heat distribution.

For example, the change in temperature in each area (zone) of the semi-finished product is determined using the following method. In FIG. 10 is a side view of the cooling device 10 used in the cooling step. As shown in FIG. 10, the cooling device 10 includes a rotary device 11 having a rotating shaft and a plurality of cooling nozzles 12-14. Said plurality of cooling nozzles 12-14 include one or more nozzles 14 for cooling the tread surface, one or more nozzles 13 for cooling part of the disc, and one or more nozzles.

- 11 041988 nos 12 for cooling part of the hub. Said one or more nozzles 14 for cooling the tread are mounted in a conventional manner around the rotating shaft. The outlet of the nozzle 14 for cooling the tread surface is located opposite the tread surface 41 of the semi-finished product. The outlet of the nozzle 14 for cooling the tread surface can be located opposite the surface of the comb 42 of the semi-finished product. Said one or more nozzles 13 for cooling the disc part are arranged so that the outlet of each of them is located opposite the surface of the disc part 3. Said one or more nozzles 12 for cooling the hub part are installed so that the outlet of each of them is located opposite the surface of the hub part 2. The tread surface cooling nozzle 14 atomizes the cooling medium from the outlet to cool mainly the tread surface 41 and the ridge surface 42 of the rim part 4. The disc cooling nozzle 13 atomizes the cooling medium from the outlet to cool mainly the disc portion 3. The hub cooling nozzle 12 atomizes the cooling medium from the outlet to cool mainly the hub portion 2. The tread surface cooling nozzle 14 can not only cool the tread surface 41 and the ridge surface 42 of the rim part 4, but also cool at least part 3 of the disc. The disk part cooling jet 13 can cool not only the disk part 3 but also the cooling of at least the rim part 4 and/or at least the hub part 2. The hub cooling nozzle 12 can cool not only the hub part 2 but also cool at least part 3 of the disc. The location and number of nozzles 14 for cooling the tread surface, nozzles 13 for cooling part of the disk and nozzles 12 for cooling part of the hub, shown in Fig. 10 are exemplary and not limiting. The design of the cooling nozzles of the plurality of cooling nozzles included in the cooling device is not particularly limited as long as they can perform cooling under the above conditions (A) to (C) in the cooling step. The above-mentioned cooling medium is not particularly limited as long as the cooling rate suitable to obtain the desired structure can be provided. Examples of the cooling medium are water, air, mist, steam (mist), and the like. In addition, the cooling device 10 includes one or more thermographic devices (infrared devices for measuring heat distribution) 20. The thermographic devices 20 are installed so that in the semi-finished railway wheel installed in the cooling device 10, the temperature of the upper surface, lower surface, side surface of this semi-finished product and the temperature inside it. The arrangement and number of thermographic devices 20 shown in FIG. 10 are exemplary and not limiting. In FIG. 10, said plurality of thermographic devices 20 are installed so that the temperature distribution can be measured on the tread surface 41, the flange surface 42, the surfaces of the rim part 4 other than the tread surface 41 and the flange surface 42 (for example, on the side surface of the rim 4), and also the surface of part 3 of the disk and the surface of part 2 of the hub.

For example, a semi-finished sample (a sample that is designed to measure temperature and has the same shape and chemical composition as the semi-finished railway wheel from which the real product is obtained) is installed in the cooling device 10, heated to a temperature not lower than the transformation temperature Acm. The cooling medium is sprayed from the cooling nozzles 12-14 when the semi-finished sample is rotated by the rotary device 11, whereby cooling starts. During cooling, the changes in the temperature distribution in the semi-finished sample are measured using said plurality of thermographic devices 20. Said plurality of thermographic devices 20 are connected to a temperature distribution analysis means, which is not shown. The temperature distribution analysis tool, for example, includes a computer and a temperature distribution analysis program stored in the computer's memory. When the CPU executes the temperature distribution analysis program, the temperature distribution analysis means analyzes in three dimensions the change in temperature per unit time in each zone of the semi-finished sample (including the zone inside it). The temperature distribution analysis tool can perform analysis in a well-known manner using a well-known thermal conductivity analysis program that uses a three-dimensional finite element method (FEM). The semi-finished sample is cooled (quickly cooled) to room temperature in order to determine the temperature change in each of its zones. Then, on the basis of the determined temperature change, an area of the semi-finished sample is determined in which the cooling rate in the range of 800-500° C. is the minimum (zone with the minimum cooling rate). The cooling rate of the semi-finished sample is controlled using the cooling device 10 in such a way that the cooling rate in the range of 800-500°C, measured by the thermographic device 20 on the surfaces of this semi-finished sample, different from the surface 41 of the tread and the surface of the ridge 42, i.e. e. on the surface of the hub part 2, the surface of the disk part 3 and the surfaces of the rim part 4, different from the tread surface 41 and the ridge surface 42, was no more than Fn1°C/s, the cooling rate was in the range of 800-500°C in the area with the minimum cooling rate defined in this semi-finished sample

- 12 041988 using three-dimensional analysis, was not less than Fn2°C/s, and the cooling rate in the range of 800-500°C, measured using a thermographic device 20 on the surface 41 of the tread and the surface of the ridge 42 of this semi-finished sample, was not less than Fn2°C/s. Specifically, the cooling rates are controlled by adjusting the flow rate of the cooling medium supplied to the nozzle 14 for cooling the tread surface, the nozzle 13 for cooling part of the disk and the nozzle 12 for cooling part of the hub, and by selecting the cooling nozzles used from the plurality of nozzles 14 for cooling the surface. 13 for cooling part of the disc and nozzles 12 for cooling part of the hub, which are installed in the cooling device 10. temperature A _cm . In the preferred case, the cooling rate of the semi-finished sample is controlled by the cooling device 10 so that the cooling rate in the range of 800-500°C on surfaces other than the tread surface 41 and the surface of the ridge 42 is not more than Fn1°C/s, the speed cooling in the range of 800-500°C in the area with the minimum cooling rate determined in this semi-finished sample by three-dimensional analysis was not less than Fn2°C/s, and the cooling rate in the range of 800-500°C, measured by thermographic device 20 on the tread surface 41 and the surface of the ridge 42 of this semi-finished sample, was not less than Fn2°C/s, not less than 5°C/s and not more than 200°C/s. If the cooling rate of the tread surface 41 and the surface of the ridge 42 of the semi-finished product is set at a level of at least 5°C/s at the cooling stage, fine-grained pearlite occurs in the near-surface part immediately below the tread surface 41 and the near-surface part of the ridge 42. The content of C in the railway wheel according to this option is high and amounts to 0.80-1.15%. This improves the wear resistance of fine-grained perlite. In addition, cooling the semi-finished product in such a way that the cooling rates of the tread surface 41 and the ridge surface 42 are not less than Fn2°C/s also makes it possible to prevent the occurrence of secondary cementite on these surfaces. In addition, the semi-finished product is cooled so that the cooling rate on surfaces other than the tread surface 41 and the surface of the ridge 42 (i.e., on the surface of the hub part 2, the surface of the disc part 3 and the surfaces of the rim part 4 other than the tread surface 41 and ridge surface 42) was no more than Fn1°C/s. As a result, the formation of a hardened layer on surfaces other than the tread surface 41 and the surface of the ridge 42 is not allowed. rim, was not less than Fn2°C/s. As a result, the occurrence of secondary cementite is not allowed. Those. in the above-described cooling step, in addition to the tread 41 and the ridge 42, cooling is increased in areas different from them (on the hub part 2, the disc part 3, and on the side surface of the rim part 4). Thus, the cooling step is performed by performing the operations described above. After the end of the cooling phase, the temperature of the semi-finished product, for example, will be equal to room temperature (25°C). However, the temperature of the semi-finished product after the end of the cooling step is not specifically limited, and it can be any, but not higher than 500°C.

Vacation stage.

After the cooling step, the semi-finished product is tempered if necessary. Tempering may be performed using a well-known temperature and time period. The tempering temperature does not exceed the temperature A _c1 . The tempering temperature is, for example, 400-600°C, and the holding time at the tempering temperature, for example, is 60-180 minutes. But the tempering temperature and holding time are not limited to those indicated. Leave may not be taken.

Cutting step.

While fine pearlite occurs in the outer layer immediately below the tread 41 and in the outer layer of the ridge 42 of the semi-finished product after the heat treatment process (heating step and cooling step), a hardened layer may occur above it. When using a railway wheel, the hardened layer has poor wear resistance. Therefore, at this stage, the hardened layers in the outer layer immediately below the tread 41 and in the outer layer of the ridge 42 are removed by cutting. The cutting may be performed using a well-known method. Note that in the manufacturing method of this embodiment, the hardened layer will not occur on surfaces other than the tread surface 41 and the surface of the ridge 42 (i.e., the surface of the hub part 2, the surface of the disc part 3, and the surfaces of the rim part 4 other than the surface 41 riding and ridge surface 42). For this reason, in the railway wheel manufacturing method of this embodiment, even though not only the semi-finished railway wheel rim portion 4 but also the disc portion 3 and the hub portion 2 are cooled, there is no need to machine surfaces other than the tread surface 41 and surfaces of the ridge 42 (i.e., the surface of the hub portion 2, the surface of the disc portion 3, and the side surface of the rim portion 4). As a result of the steps described above, a railway wheel corresponding to this embodiment is obtained. When the train

- 13 041988 An horn wheel is made by the method of this embodiment, even though hypereutectoid steel is used in this wheel, secondary cementite is not allowed to occur in disc part 3 and hub part 2, which deteriorates toughness. In addition, even though hypereutectoid steel is used in this wheel, it is possible to prevent the occurrence of a hardened layer in the disc part 3 and the hub part 2, which degrades the toughness. Note that the occurrence of secondary cementite is also not allowed in part 4 of the rim.

The structure of the railway wheel.

The following is a microstructure of a railway wheel made using the method described above. According to the structure, the outer layer, located directly under the tread surface, and the near-surface part of the ridge are perlite. The amount of secondary cementite does not exceed 1.0 particles/100 µm. The hub part, the disc part, and the rim part, other than the tread and the ridge, are composed essentially of pearlite in structure. Those. the area ratio of perlite is 95% or more. In addition, the amount of secondary cementite does not exceed 1.0 particles/100 µm.

More specifically, in the hypereutectoid railway wheel having the above chemical composition, in the microstructure of the hub portion, the area ratio of pearlite is 95% or more, and the amount of secondary cementite does not exceed 1.0 particles/100 µm. And in the microstructure of the disc portion, the area ratio of pearlite is 95% or more, and the amount of secondary cementite does not exceed 1.0 particles/100 μm. In addition, in the microstructure of the rim portion, the area ratio of pearlite is 95% or more, and the amount of secondary cementite does not exceed 1.0 particles/100 μm. Here, the amount of secondary cementite is determined by the formula (A)

Amount of secondary cementite (particles/100 µm) = total amount of secondary cementite particles through which two diagonals pass in a square field of view 200 µm χ 200 µm/(5.6 6 χ 100 µm) (A)

In this case, the microstructure can be visually examined using the following method. A sample for visual examination of the microstructure is taken from each part (hub, disc and rim) of a railway wheel at a position more than 5 mm below the surface. The studied surface of each sample is polished to a mirror finish mechanically. After that, the surface to be studied is etched in a solution containing a mixture of picric acid and sodium hydroxide. After etching, a photograph of an arbitrary field of view (200x200 μm) is obtained on the surface under study using an optical microscope at 500x magnification. The presence of secondary cementite is determined based on the fact that this cementite, which occurs at the grain boundary of the previous austenite, has a black color. As shown in FIG. 11, in a square field of view 100 of 200x200 µm, two diagonals 101 are drawn. Next, the total amount of secondary cementite particles through which these two diagonals 101 pass is determined. As given by expression (A), the amount of secondary cementite per 100 µm (particles/100 µm) is determined by dividing the total number of secondary cementite particles obtained by the total length of the two diagonals 101 (5.66x100 µm). If the amount of secondary cementite does not exceed 1.0 particles per 100 µm, it is considered that its occurrence is not sufficiently tolerated.

Next, the same surface under study is again polished to a mirror finish mechanically and then etched in nital (a solution containing a mixture of nitric acid and ethanol). After etching, a photograph of an arbitrary field of view (200x200 μm) is obtained on the surface under study using an optical microscope at 500x magnification. Ferrite, bainite, martensite and pearlite vary in tone. Thus, based on the tone, it is possible to determine the presence of a hardened layer and perlite on the surface under study. The relative area of perlite is determined from the total area of perlite thus determined and the area of the surface under study. In the railway wheel produced by the method described above, the part of the rim, including the tread and the ridge, in which the area ratio of pearlite is 95% or more, is essentially composed of pearlite. And the amount of secondary cementite does not exceed 1.0 particles/100 µm. Therefore, this railway wheel has excellent wear resistance. In addition, in the railway wheel, the hub part, the disc part, and the rim part other than the tread and the ridge are essentially composed of perlite. In addition, in the hub part, the disc part, and the rim part different from the tread surface and the ridge, the amount of secondary cementite does not exceed 1.0 particles/100 µm. Thus, the railway wheel according to this embodiment has excellent toughness even though it has a chemical composition corresponding to hypereutectoid steel. Note that immediately after the cooling step as described above, the railway wheel may have a hardened layer in the outer layer just below the tread surface and the outer layer of the rim part ridge. However, before using the railway wheel, this hardened layer is removed by cutting as described above. As a result, the microstructure on the tread surface and the ridge surface essentially consists of perlite.

- 14 041988

Example 1

Were obtained molten steel No. 1-18 having the chemical composition shown in table. 3.

Table 3

SteelNo. Chemical composition (wt.%, the rest - Her and impurities) Temperature А _st , °C fnl Fn2 Notes WITH Si MP R S A1 N SG V 1 0.84 0.30 0.81 0.001 0.002 0.032 0.0038 0.00 0.00 768 24.8 0.5 Invention 2 0.93 0.29 0.80 0.001 0.002 0.032 0.0042 0.00 0.00 802 21.7 0.6 Invention 3 1.00 0.30 0.80 0.001 0.002 0.034 0.0040 0.00 0.00 828 18.8 1.2 Invention 4 1.09 0.30 0.79 0.001 0.002 0.036 0.0040 0.00 0.00 860 16.0 6, 1 Invention 5 1.02 0.05 0.81 0.002 0.001 0.031 0.0042 0.00 0.00 829 26, 8 1.3 Invention 6 1.03 0.89 0.80 0.001 0.002 0.036 0.0040 0.00 0.00 854 5.7 3.2 Invention 7 1.04 0.29 0.40 0.002 0.001 0.030 0.0056 0.00 0.00 842 26.2 2.0 Invention 8 1.02 0.31 1.23 0.002 0.001 0.030 0.0058 0.00 0.00 836 11.5 1.9 Invention 9 1.05 0.29 0.79 0.001 0.001 0.033 0.0030 0.11 0.00 853 13.6 3.4 Invention 10 1.03 0.29 0.78 0.001 0.001 0.034 0.0034 0.21 0.00 852 11.0 2.7 Invention eleven 1.02 0.28 0.79 0.001 0.001 0.033 0.0036 0.51 0.00 868 4.5 4.2 Invention 12 1.03 0.29 0.79 0.001 0.001 0.063 0.0041 0.00 0.00 838 17.3 1.4 Invention 13 1.03 0.29 0.80 0.001 0.001 0.100 0.0044 0.00 0.00 836 15.9 1.0 Invention 14 1.03 0.29 0.80 0.001 0.001 0.200 0.0046 0.00 0.00 832 13.0 0.6 Invention 15 1.00 0.29 0.81 0.001 0.002 0.300 0.0034 0.00 0.00 817 11.0 0.5 Invention 16 1.00 0.30 0.80 0.001 0.002 0.610 0.0034 0.00 0.00 804 4.9 0.5 Invention 17 1.03 0.29 0.80 0.002 0.001 0.029 0.0048 0.00 0.03 843 13.4 1.7 Invention 18 1.03 0.29 0.80 0.002 0.001 0.026 0.0047 0.00 0.09 842 6, 6 1.5 Invention

By means of an ingot casting process using the above molten steel, a round ingot (truncated cone shaped with a top surface diameter of 107 mm, a bottom surface diameter of 97 mm, and a height of 230 mm) was produced. After heating to 1250°C, the ingot was hot forged in a temperature range of 850-1100°C to obtain a round bar for a railway wheel, which has a diameter of 40 mm.

Jominy end hardening test.

From a round rod with a diameter of 40 mm from each steel No. 1-18, a Jominy test specimen with a diameter of 25 mm and a height of 100 mm was made. Specifically, a 40 mm round rod was turned into a 25 mm round rod by turning. After that, the round rod was cut to a length of 100 mm to obtain a specimen for the Jominy test. Using a Jominy test piece in accordance with JIS G0561 (2011), a Jomini end hardening test was conducted to simulate the heat treatment process (heating step and cooling step) of a railroad wheel manufacturing process. Specifically, the Jominy test specimen was held in a furnace atmosphere at a temperature of 950° C., which is not lower than the Acm temperature, for 30 minutes, resulting in the structure of this specimen being composed of a single austenite phase. After that, the hardening of the end face (water cooling) was performed. Specifically, water was sprayed to cool one end of the Jominy specimen. After water cooling, the side surface of the Jominy test specimen was mechanically polished, and in accordance with JIS Z 2245 (2011), the Rockwell C hardness (HRC) in the axial direction was measured starting from the mentioned end (water-cooled end) and with a constant spacing to get the hardness distribution. Rockwell C hardness was measured in 1.0 mm increments from the water-cooled end to a point 15 mm from that end and in 2.5 mm increments after that point.

In FIG. 12 shows, by way of example, one obtained Rockwell C hardness distribution. In FIG. 12 shows the results for steels No. 1-4. As can be seen in FIG. 12, starting from the hardness at the water-cooled end of the test piece, the Jominy curve is divided into two regions - region A, in which the hardness decreases rapidly with increasing distance from the water-cooled end, and region B, which is farther from this end compared to region A, and in which, with increasing distance from this end, the hardness decreases more gradually than in region A. As a result of a visual study of the structure, it was found that region A is a hardened layer consisting of martensite and/or bainite. Region B consisted essentially of perlite. Based on the Rockwell C hardness distribution shown in FIG. 12, the depth of the hardened layer was determined.

Visual study of the microstructure.

Visual study of the microstructure at all distances from the water-cooled end was carried out as follows. The area of the lateral surface of the sample for testing according to Jominy was chosen as the surface under study, at some points of which the hardness was measured on the Rockwell C scale, the surface under study was polished to a mirror finish mechanically, after which it was etched using a solution containing a mixture of picric acid and sodium hydroxide. After etching using an optical microscope at

- 15 041988

A photograph of an arbitrary field of view (200x200 µm) was obtained at 500x magnification on the surface under study. The presence of secondary cementite could be determined based on the fact that this cementite, which occurs at the grain boundary of the preceding austenite, has a black color on the surface under study. As shown in FIG. 11, two diagonals 101 were drawn in a 200x200 µm square field of view 100. After that, the number of secondary cementite particles through which these two diagonals 101 pass was determined. The amount of secondary cementite per 100 µm (particles/100 µm) was determined by the amount of secondary cementite particles obtained per total length of two diagonals 101 (5.66x100 µm). Those. the amount of secondary cementite was determined according to expression (A). If the amount of secondary cementite did not exceed 1.0 particles/100 µm, it was considered that its occurrence was not allowed. The numerical values given in table. 4 for the respective distances from the water-cooled end for each steel, this is the amount of secondary cementite (particles/100 µm). For example, a value of 0.5 at a cooling rate of 13.1°C/s (distance of 13 mm from the water-cooled end) for Test No. 4 means that in the test piece from Test No. 4, the amount of secondary cementite at a point located at a distance of 13 mm from the water-cooled end, measured in the axial direction, was 0.5 particles/100 μm.

Table 4

Jominy end hardening test Trial Formaster fnl Fn2 Notes Distance from water cooled end, mm 3 4 5 b 7 8 9 10 eleven 12 13 14 15 17.5 20 22.5 25 27.5 thirty 32.5 35 37.5 40 Cooling rate, °C, s 148 85.7 59.4 42.4 33.5 27.4 22.9 19.5 16.9 14.8 13.1 11.7 10.5 8.3 6.8 5.7 4.8 4.2 3.7 3.2 2.9 2.6 2.4 1.0 0.1 Steel No. 1 • • • • • ABOUT ABOUT ABOUT O ABOUT O O ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT O ABOUT ABOUT ABOUT ABOUT ABOUT O 24.8 0.5 Invention 2 • • • • • • • ABOUT 0 ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT 0.3 1.6 21.7 0.6 Invention 3 • • • • • • • • O ABOUT O O O O O ABOUT ABOUT ABOUT O O O ABOUT 0.3 2.4 4.8 18.8 1.2 Invention 4 • • • • • • • O ABOUT O 0.5 ABOUT 0.3 O 0.5 0.8 2.1 2.4 1.6 1.6 2.9 3.5 3.2 6.1 5.1 16.0 6.1 Invention 5 • • • • • • ABOUT ABOUT 0 ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT 2.1 3.5 26.8 1.3 Invention 6 • • • • • • • • • • • • • O ABOUT ABOUT ABOUT ABOUT O O 0.5 0.5 1.1 3.7 3.2 5.7 3.2 Invention 7 • • • • • • O O ABOUT O O ABOUT O O ABOUT ABOUT ABOUT ABOUT O O ABOUT ABOUT ABOUT 2.1 2.9 26.2 2.0 Invention 8 • • • • • • • • • • O O O O ABOUT ABOUT ABOUT ABOUT O O ABOUT ABOUT O 3.2 - 11.5 1.9 Invention 9 • • • • • • O O ABOUT O O ABOUT O O ABOUT ABOUT ABOUT ABOUT O O O O O 2.4 2.9 13.6 3.4 Invention 10 • • • • • • O O ABOUT O O ABOUT O O ABOUT ABOUT ABOUT O 0.3 0.5 0.5 0.8 1.3 4.0 4.0 11.0 2.7 Invention eleven • • • • • • • • • • • • • • • O ABOUT O 1.1 1.3 1.3 1.3 1.3 3.5 3.5 4.5 4.2 Invention 12 • • • • • • • O ABOUT O O ABOUT O O O O O O O O O O O 2.9 2.9 17.3 1.4 Invention 13 • • • • • • • • ABOUT O O ABOUT O O O O O O O O O O O 2.7 2.9 15.9 1.0 Invention 14 • • • • • • • O O O O O O O O O O O O O O O O 0.3 1.6 13.0 0.6 Invention 15 • • • • • • • • ABOUT O O ABOUT O O O O O O O O O O O ABOUT 0.3 11.0 0.5 Invention 16 • • • • • • • • • • • • • • O O O O O O O O O O 0.3 4.9 0.5 Invention 17 • • • • • • • • • O O ABOUT O O O O O O O O O O O 2.1 - 13.4 1.7 Invention 18 • • • • • • • • • • • • ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT ABOUT 2.4 - 6.6 1.5 Invention

Next, the same surface under study was again polished to a mirror finish by mechanical means, and then etching was performed in nital (a solution containing a mixture of nitric acid and ethanol). After etching, a photograph of an arbitrary field of view (200x200 μm) was obtained on the surface under study using an optical microscope at 500x magnification. Ferrite, bainite, martensite and pearlite vary in tone. As a result, based on the tone, the presence of a hardened layer and perlite on the surface under study was determined. The area fraction of perlite was determined from the total area of perlite thus determined and the area of the surface under study. Note that the relationship between the distance from the water-cooled end and the cooling time from 800 to 500°C during the Jominy end hardening test obtained by experiment is given in the literature source (F. Wever et al., Zur Frage der Warmebehandlung der Stahle auf Grund ihrer Zeit-Temperatur-Umwandlungs-Schaubilder, Stahl u Eisen, 74 (1954), pp. 749-761). Based on data from this source, the distance from the water-cooled end was converted to an average cooling rate ranging from 800 to 500°C at each point. The water cooling rate corresponding to the distance from the water-cooled end is given in Table. 4.

Formaster test.

Using the Jominy test specimen described above, a continuous cooling test was performed at a low rate that cannot be reproduced in the Jominy end-hardening test. For heat treatment, a Formaster tester manufactured by Fuji Electronic Industrial Co., Ltd. was used. From a round rod with a diameter of each steel No. 1-18, one test piece with a diameter of 3 mm and a length of 10 mm was obtained. The test piece was held at 950°C for 5 minutes. Thereafter, the test piece was cooled down at a constant cooling rate of 1.0°C/s. After cooling by the method described above, the amount of secondary cementite (particles/100 µm) in the test piece was calculated.

For steel in which secondary cementite was not confirmed at a cooling rate of 1.0°C/s, a heat treatment test was additionally performed with continuous cooling at a rate of 0.1°C/s, and by the same method described above, quantity

- 16 041988 secondary cementite.

Results.

The results are shown in table. 4. In this table, the symbol · in the column for a specific distance from the water-cooled end indicates that the structure at that distance was a hardened layer (martensite and/or bainite). In addition, the symbol in the column of the specific distance from the water-cooled end indicates that at this distance the structure consisted essentially of pearlite (the area ratio of pearlite was 95% or more), the absence of martensite or bainite was confirmed, and the absence of secondary cementite was confirmed. The number in the specific distance column from the water-cooled end indicates that the structure was composed essentially of pearlite (perlite area ratio was 95% or more), and represents the number of secondary cementite particles per 100 µm at that distance. In addition, in Table. 4, for each steel, the range in which the cooling rate (°C/s) does not exceed Fn1 given by expression (1) and is not less than Fn2 given by expression (2) is grayed out. As can be seen from Table. 4, in the cooling rate range filled with gray, the hardened layer did not occur, and the amount of secondary cementite did not exceed 1.0 particles/100 μm.

As can be seen from Table. 3 and 4, when the cooling rate was not less than Fn2 in any steel, the amount of secondary cementite did not exceed 1.0 particles/100 µm, even if this steel was a hypereutectoid steel having a C content of 0.80-1.15% , i.e. the occurrence of secondary cementite was not allowed. Therefore, it would be expected to provide sufficient impact strength of the railway wheel. In addition, if the cooling rate did not exceed Fn1, the formation of a hardened layer was not allowed. Therefore, it would be expected to provide sufficient impact strength of the railway wheel. Thus, it has been found that if the semi-finished product is cooled in this way, the cooling rate in the range of 800-500° C. on its surfaces other than the tread surface and the ridge surface, i. e. on the surface of the hub, the surface of the disk and the side surface of the rim (the surface of the rim, which differs from the tread surface and the surface of the ridge), is no more than Fn1°C/s in that zone of the semi-finished product, where the cooling rate in the range of 800-500°C is minimal, t .e. in the zone inside the hub, disc and rim where the cooling rate is minimal (hereinafter referred to as the zone with the minimum cooling rate), it is not less than Fn2°C/s, and the cooling rate is in the range of 800-500°C on the tread surface and the surface flange of this semi-finished product is not less than Fn2°C/s, in the manufactured railway wheel, the pearlite area ratio will be 95% or more in the hub, disc and rim, and the amount of secondary cementite will not be more than 1.0 particles/100 µm, and can not allow the formation of a hardened layer on the surfaces of the hub and disk.

Example 2

Using a round rod with a diameter of 40 mm made of steel No. 9, shown in table. 3, the relationship between the amount of recycled cementite and Charpy impact strength (J/cm ² ) was studied. Four round rods of steel No. 9 were kept at 950°C for 30 min, after which they were cooled at the rate indicated in table. 5. The cooling rate was set by immersing the round rod in a salt bath having a different temperature.

Table 5

Steel No. Cooling rate, °С/s fnl Fn2 Amount of toric cementite, particles/100 µm Charpy impact strength, J / cm ² 9-1 3.86 13.6 3.4 0.53 23.3 9-2 0.88 13.6 3.4 2.67 19.0 9-3 0.50 13.6 3.4 2.40 17.8 9-4 0.35 13.6 3.4 3.20 15.0

Visual study of the microstructure.

After cooling, a sample was taken from the middle part of the round rod with each test number (from 9-1 to 9-4) for visual examination of the microstructure. The studied surface of the sample was a plane perpendicular to the axis of the round rod. The surface under study was mechanically polished to a mirror finish, after which it was etched in a solution containing a mixture of picric acid and sodium hydroxide. After etching, a photograph of an arbitrary field of view (200x200 μm) was obtained on the surface under study using an optical microscope at 500x magnification. The presence of secondary cementite could be determined based on the fact that this cementite, which occurs at the grain boundary of the preceding austenite, has a black color on the surface under study. In addition, using the same method as in Example 1, the area ratio of perlite was determined. As a result, the perlite area ratio was 95% or more in all tests. As shown in FIG. 11, in a 100 square field of view measuring 200x200 µm,

-

Claims (7)

two diagonals 101. The total amount of secondary cementite particles through which these two diagonals 101 pass was then determined. 101 (5.66x100 µm). Those. the amount of secondary cementite was determined according to expression (A). Charpy impact test. From the round bar from each test (9-1 to 9-4), a Charpy impact test specimen (10x10x55 mm) was obtained. The axis of the sample for testing impact strength according to Charpy coincided with the axis of the round rod. Using Charpy impact test specimens in accordance with JIS Z 2242 (2005) at room temperature (25°C), a Charpy impact test was conducted. Test results. The test results are given in table. 5. As can be seen from the table. 5, when the cooling rate was not less than Fn2 (3.4) (steel No. 9-1), the amount of secondary cementite did not exceed 1.0 particles/100 μm. For this reason, the Charpy impact strength was high and was not less than 20.0 J/cm ² , i.e. provided sufficient impact strength. On the other hand, when the cooling rate was less than Fn2 (steel numbers 9-2 to 9-4), the Charpy impact strength was low and was less than 20.0 J/cm ² . The embodiments of the present invention have been discussed above. However, the above options are just examples of the implementation of the present invention in practice. Thus, the present invention is not limited to the embodiments discussed above and can be practiced by appropriate modification of these variations within the spirit of this invention. List of reference designations. 1 - railway wheel; 2 - part of the hub; 3 - part of the disk; 4 - part of the rim; 10 - cooling device. CLAIM 1. A method for manufacturing a railway wheel, comprising a heating step, in which a semi-finished product of a railway wheel is heated to a temperature not lower than the transformation temperature A _cm , moreover, the semi-finished product has the following chemical composition, consisting of, in wt.%: 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; Fe and impurities are the rest, and has a hub part, a rim part including the tread and a ridge, and a disc part located between the hub part and the rim part; and a cooling step, in which the heated semi-finished product is cooled, and in the cooling step, the semi-finished product is cooled in such a way that the cooling rate in the range of 800-500°C on the surface of the semi-finished product, which is different from the tread surface and the ridge surface, is not more than Fn1°C/s, defined by expression (1); the cooling rate in the range of 800-500°C in the area in which the cooling rate is minimal in the said semi-finished product is not less than Fn2°C/c, defined by expression (2); and the cooling rate in the range of 800-500°C on the tread surface and the surface of the crest of the said semi-finished product is at least Fn2°C/s: Fnl \u003d -5.0 + exp (5.651-1.427 * C-1.280 * 31-0.7723 * Mp-1.519χΑ1) (1) Fn2=0.515+exp(-24.816+24.121xC+l.210xSi+0.529χΜη-15.116χΑ1) (2) moreover, each element symbol in expressions (1) and (2) indicates the content of the corresponding element in wt.%. 2. A method for manufacturing a railway wheel, comprising a heating step, in which a semi-finished product of a railway wheel is heated to a temperature not lower than the transformation temperature A _cm , moreover, the semi-finished product has the following chemical composition, consisting of, in wt.%: 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; one or more elements selected from the group consisting of Cr - more than 0-0.60; V - more than 0-0.12; Fe and impurities - the rest, and has - 18 041988 part of the hub, part of the rim, including the tread surface and the ridge, and part of the disc located between the part of the hub and part of the rim; and a cooling step, in which the heated semi-finished product is cooled, and in the cooling step, the semi-finished product is cooled in such a way that the cooling rate in the range of 800-500°C on the surface of the semi-finished product, which is different from the tread surface and the ridge surface, is not more than Fn1°C/s, defined by expression (1); the cooling rate in the range of 800-500°C in the area in which the cooling rate is minimal in the said semi-finished product is not less than Fn2°C/c, defined by expression (2); and the cooling rate in the range of 800-500°C on the tread surface and the surface of the crest of the said semi-finished product is at least Fn2°C/s: Fnl = -5.0 + exp (5.651-1.427><С-1.280><Si-0.7723χΜη-1, 815><Сг1.519χΑ1-7.798xV) (1) Fn2=0.515+exp(-24.816+24.121xC+l.210xSi+0.529χΜη+2.458xCr15.116xAl-5.116xV) (2) moreover, each element symbol in expressions (1) and (2) shows the content of the corresponding element in wt. %. 3. The method according to claim 2, in which the chemical composition contains one or more elements selected from the group consisting of, %: Cr - 0.02-0.60; and V - 0.02-0.12. 4. The method according to any one of claims 1 to 3, in which, additionally, at the cooling stage, the semi-finished product is cooled in such a way that the cooling rate in the range of 800-500°C on the tread and ridge surface is at least Fn2°C/s, and at least than 5°C/s, and not more than 200°C/s. 5. Railway wheel containing a chemical composition consisting of, in wt.%: 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; Fe and impurities - the rest, moreover, the railway wheel has a hub part, a rim part including a tread surface and a ridge, and a disk part located between the hub part and the rim part, and in the microstructure of the hub part, the pearlite area ratio is 95% or more and the amount of secondary cementite does not exceed 1.0 particles per 100 µm, in the microstructure of the disc part, the area ratio of pearlite is 95% or more, and the amount of secondary cementite does not exceed 1.0 particles per 100 µm, and in the microstructure of the rim part, the area ratio of pearlite is 95% or more and the amount of secondary cementite does not exceed 1.0 particles per 100 µm, and the amount of secondary cementite (particles/100 µm) is defined as the total amount of secondary cementite particles through which two diagonals pass in a square field of view of 200x200 µm/(5.66x100 µm) . 6. Railway wheel containing a chemical composition consisting of, in wt.%: 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; one or more elements selected from the group consisting of Cr - more than 0-0.60; V - more than 0-0.12; Fe and impurities - the rest, moreover, the railway wheel has a hub part, a rim part including a tread surface and a ridge, and a disk part located between the hub part and the rim part, and in the microstructure of the hub part, the pearlite area ratio is 95% or more and the amount of secondary cementite does not exceed 1.0 particles per 100 µm, in the microstructure of the disc part, the area ratio of pearlite is 95% or more, and the amount of secondary cementite does not exceed 1.0 particles per 100 µm, and in the microstructure of the rim part, the area ratio of pearlite is 95% or more and the amount of secondary cementite does not exceed 1.0 particles per 100 µm, and the amount of secondary cementite (particles/100 µm) is defined as the total amount of secondary cementite particles through which two diagonals pass in a square field of view of 200x200 µm/(5.66x100 µm) . 7. Railway wheel according to claim 6, in which the chemical composition contains one or more elements selected from the group consisting of, %: Cr - 0.02-0.60; and V - 0.02-0.12. -