Heat treatment method for improving structure and property uniformity of railway wheels

Abstract

Disclosed in the present invention is a heat treatment method for improving the structure and property uniformity of railway wheels, belonging to the technical field of railway wheel manufacturing. The heat treatment method comprises the following steps: heating an entire wheel until same is completely austenitized; using flow-incremental cooling water to perform spray quenching on the tread of the wheel, wherein the flow rate L of cooling water of each spray gun gradually increases with the increase of the spray quenching time t, said two parameters are controlled to satisfy a specific linear functional relationship, after a peak water flow rate is reached, same is maintained for at least 90 s, and during the spray quenching process, the wheel is in a self-rotating state; and putting the entire wheel into a tempering furnace for heat preservation, and then taking same out for air cooling. The present invention performs precise control on linear increases of the flow rate of cooling water for wheels having different rim thicknesses, achieving a balanced change of cooling in the radial direction of rim portions, and ensuring the uniformity of the total cross-section structure and properties of rims.

Description

A heat treatment method to improve the uniformity of the microstructure and performance of railway wheels Technical Field

[0001] This invention belongs to the field of railway wheel manufacturing technology, specifically relating to a heat treatment method for improving the uniformity of the structure and performance of railway wheels. Background Technology

[0002] For the structure and performance of railway wheels, countries and regions around the world generally require that the microstructure in the wear area of ​​the rim be fine pearlite plus a small amount of ferrite. Railway wheels with a fine pearlite + small amount of ferrite structure have been widely used by countries and regions around the world due to their excellent wear resistance, machinability and thermal stability.

[0003] Regarding heat treatment processes for railway wheels, although they vary from country to country, according to publicly available literature, railway wheels currently mostly use "overall heating + continuous tread quenching + overall tempering" for heat treatment. Among these processes, tread quenching is the key step that determines the structure and performance of the wheel rim. Continuous quenching of the tread surface, which uses a constant water flow to cool the rim, has several problems: First, the radial cooling rate of the rim varies greatly. The constant water flow results in an extremely high cooling rate near the surface of the wheel tread, far exceeding the critical cooling rate for the complete pearlitic transformation of the wheel steel. This easily leads to the formation of a thick non-pearlitic structure near the surface, posing a risk of product rejection due to structural quality issues. Alternatively, this can be mitigated by increasing design margins, sacrificing metal utilization and increasing processing costs. Second, due to the large thickness of the rim cross-section, the cooling rate inside the rim decreases significantly with increasing depth. The slow cooling rate inside the rim results in insufficient strength and hardness, and the large cooling rate gradient within the rim leads to uneven cooling at different depths along the radial direction. This results in the formation of an undesirable mixed martensite and bainite structure near the surface of the wheel tread, which is detrimental to wheel performance (such as "early peeling"). It also leads to a large hardness gradient in the rim area, resulting in poor wear resistance in the later stages of wheel service, compromising service stability throughout the wheel's lifespan and shortening its service life.

[0004] Controlling or eliminating non-pearlitic microstructure in wheel components to improve performance uniformity and achieve balanced cooling has long been a pressing technical challenge and a research hotspot in the industry. Years of research and practice have proven that controlling the cooling process during wheel heat treatment and developing new cooling methods are the most direct and effective approaches.

[0005] Chinese Patent CN110055394A discloses a heat treatment cooling process for railway wheels, specifically a multi-stage aerosol cooling process for wheels. The steps include: first heating the whole wheel to complete austenitization; then transferring it to a quenching table, making the wheel in a rotating state, and using a pressure step-increasing aerosol two-phase flow to spray the tread of the wheel; then putting the whole wheel into a tempering furnace for heat preservation, and finally taking it out for air cooling. The pressure step-increasing aerosol two-phase flow spraying of the wheel tread includes three stages in sequence. The rotational speeds of the wheel in the three stages are controlled as v1>v2>v3, the water pressures are P1<P2<P3, and the quenching cooling times are T1<T2<T3. The number of nozzles distributed at equal intervals along the circumferential direction of the wheel started in the three stages is M, 2M, and 3M respectively. This method can increase the cooling capacity of the inner part of the rim, make the cooling speed from the wheel tread to the deep part of the rim obtain a balanced and consistent state, optimize the organizational structure of the entire cross-section of the rim, and then significantly reduce the radial hardness gradient of the rim, greatly improving the mechanical properties and service performance of the wheel. However, this patent needs to rely on special cooling nozzles, uses two cooling media of water and gas, and the process implementation is difficult.

[0006] Chinese Patent CN110777241A discloses a railway wheel cooling device, cooling method and preparation method. Specifically, it discloses that the device includes a quenching table and a plurality of spray guns uniformly arranged along its circumferential direction. The spray gun includes a water outlet panel and an inlet branch pipe. The water outlet panel is provided with large spray holes and small spray holes with different diameters. Among them, the small spray holes are independently controlled for water outlet by one branch pipe, and the large spray holes are divided into upper and lower parts, and the water outlet is controlled by different branch pipes respectively. It can conveniently adjust the intensity of the cooling water sprayed onto the wheel, improving the cooling uniformity of the wheel rim in the radial and axial directions. This cooling method uses the above cooling device to perform heat treatment cooling on the wheel during the preparation of the wheel, effectively strengthening the hardness uniformity of the wheel rim and improving the service performance of the wheel. This preparation method uses the above cooling method to perform heat treatment cooling on the wheel during the preparation, and can prepare wheels with high hardness uniformity of the rim. However, this patent also needs to rely on special cooling nozzles and requires professional modification and upgrade of the quenching table, and the implementation cost is relatively high. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a heat treatment method for improving the uniformity of the organization and performance of railway wheels. For wheels with different rim thicknesses, precise linear increase control of the cooling water flow is carried out, realizing a balanced change in the radial cooling of the rim part, and ensuring the uniformity of the organization and performance of the entire cross-section of the rim.

[0008] The technical solution adopted in this invention is as follows: A heat treatment method for improving the uniformity of the microstructure and performance of railway wheels, the heat treatment method comprising the following steps: S1, heating: heating the entire wheel to complete austenitization; S2, quenching: quenching the wheel tread surface using incremental flow cooling water spray, wherein the flow rate L of the cooling water for each spray gun gradually increases with the extension of the quenching time t, and the linear functional relationship between the two is controlled as follows: In the formula, L is in L / min; t is in s; B is in mm; after reaching the peak water flow rate, maintain it for at least 90s; the wheel is in a self-rotating state during the spray quenching process; S3, tempering: put the wheel into the tempering furnace for heat preservation, and then take it out and air cool.

[0009] In step S1, the heating temperature is Ac3 + (70~120)℃, where Ac3 is the austenitizing critical temperature; the total heating time is 2.5~4h.

[0010] In step S1, the wheel is kept in the uniform temperature zone for no less than 1.25 hours.

[0011] In step S2, after reaching the peak flow rate, when the rim thickness B < 75 mm, the peak water flow rate is maintained for 90–120 s; when the rim thickness B < 75 mm, the peak water flow rate is maintained for 130–180 s; and when the rim thickness B ≥ 95 mm, the peak water flow rate is maintained for 190–260 s.

[0012] In step S2, during the water flow rate increase stage, the wheel rotation linear velocity v is 500≤v≤550mm / s; using a higher wheel speed during the water flow rate increase stage can achieve a better heat exchange effect, improve cooling capacity and cooling uniformity.

[0013] In step S2, during the peak water flow maintenance stage, the wheel's rotational linear velocity v is 450≤v≤500mm / s. Using a lower wheel speed during the peak water flow maintenance stage helps maintain the smoothness of wheel rotation, avoids the impact of high water pressure on the wheel, which would affect the quenching quality, and also helps save energy.

[0014] In step S2, box-type spray guns are evenly distributed around the quenching table at equal intervals. The distance between the spray guns and the wheel tread is consistent to ensure complete coverage of the wheel tread, and the water output of each spray gun is consistent.

[0015] The number of box-type spray guns is 6.

[0016] In step S3, the tempering temperature is 470–520℃, and the total heating time is 4–6 hours.

[0017] The wheel comprises the following chemical composition by weight percentage: C 0.50–0.80%, Si 0.30–1.20%, Mn 0.70–1.00%, P ≤0.015%, S ≤0.015%, Cr 0.10–0.30%, Ni 0.10–0.30%, Mo 0.01–0.10%, and V 0.01–0.20%. Wheels with other chemical compositions can also be heat-treated using the heat treatment method provided in this application to improve the uniformity of wheel structure and performance.

[0018] In the heat treatment method provided by this invention, during quenching, the wheel tread is quenched by spraying cooling water with an increasing flow rate. The flow rate L of the cooling water for each spray gun is controlled to have a linear functional relationship with the quenching time t. The intercept of the Lt slope represents the initial flow rate at the moment the quenching begins, and its value is set according to the rim thickness. This avoids the formation of undesirable non-pearlitic mixed structures near the surface of the tread due to excessive instantaneous cooling intensity. The slope of the Lt slope represents the increase in the flow rate of the quenching cooling water per unit time for a wheel with this rim thickness.

[0019] Based on the coupling relationship between the supercooled austenitic phase transformation characteristics of wheel steel and the cooling boundary, this invention proposes a precise controlled cooling strategy for wheels with different rim thicknesses. The cooling water flow rate is controlled to increase linearly with time to the peak flow rate and then maintained for a period of time until the quenching cooling is completed. At the same time, the rotation speed of the wheel is controlled in conjunction with the spray quenching process, so that the cooling rate of the rim part at different depths along the radial direction is obtained in a more balanced way. This overcomes the non-uniformity of conventional constant flow cooling and is conducive to improving the microstructure consistency and performance uniformity of the entire cross section of the rim.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1) By controlling the cooling water flow rate to increase linearly with time, a balanced cooling rate is obtained, which greatly improves the uniformity of cooling in the radial direction of the rim.

[0021] 2) It produces a uniform fine pearlite and a small amount of ferrite structure in the rim area, avoiding the formation of martensite, bainite and their mixtures caused by traditional constant water quenching, ensuring the consistency of the structure and improving the metal utilization rate.

[0022] 3) Improved uniformity of quenching and cooling can also significantly improve the uniformity of hardness and impact toughness of wheel rims, achieving hardness fluctuation within 10HB at the same depth of the rim cross section, while obtaining impact toughness with smaller fluctuations.

[0023] 4) It has a wide range of applications, covering wheels with different rim thicknesses, and is simple and easy to implement, facilitating industrial production. Attached Figure Description

[0024] Figure 1 shows the cooling rate at different depths of the wheel rims of Example 1 and Comparative Example 1; Figure 2 shows the microstructure of the near-surface layer (2.5 mm from the surface) of the wheel tread of Example 1; Figure 3 shows the microstructure of the subsurface layer (12.5 mm from the surface) of the wheel tread of Example 1; Figure 4 shows the microstructure of the interior of the wheel rim of Example 1 (45 mm from the surface); Figure 5 shows the microstructure of the near-surface layer (2.5 mm from the surface) of the wheel tread of Comparative Example 1; Figure 6 shows the microstructure of the subsurface layer (12.5 mm from the surface) of the wheel tread of Comparative Example 1; Figure 7 shows the microstructure of the interior of the wheel rim of Comparative Example 1 (45 mm from the surface); Figure 8 is a schematic diagram of the cross-sectional grid hardness test of the heat-treated blank wheel rim; Figure 9 shows the hardness difference (hardness uniformity) of the cross-section at the same depth of the wheel rims of Example 1 and Comparative Example 1; Figure 10 is a schematic diagram of the sample positions for a series of temperature shock tests on finished wheel rims; Figure 11 shows the cooling rate at different depths of the wheel rims of Example 2 and Comparative Example 2. Figure 12 shows the extreme difference in cross-sectional hardness (hardness uniformity) at the same depth in the wheel rims of Example 2 and Comparative Example 2; Figure 13 shows the cooling rate at different depths in the wheel rims of Example 3 and Comparative Example 3; Figure 14 shows the microstructure of the near-surface layer (2.5 mm from the surface) of the wheel tread of Example 3; Figure 15 shows the microstructure of the subsurface layer (12.5 mm from the surface) of the wheel tread of Example 3; Figure 16 shows the microstructure of the interior of the wheel rim of Example 3 (45 mm from the surface); Figure 17 shows the microstructure of the near-surface layer (2.5 mm from the surface) of the wheel tread of Comparative Example 3; Figure 18 shows the microstructure of the subsurface layer (12.5 mm from the surface) of the wheel tread of Comparative Example 3; Figure 19 shows the microstructure of the interior of the wheel rim of Comparative Example 3 (45 mm from the surface); Figure 20 shows the extreme difference in cross-sectional hardness (hardness uniformity) at the same depth in the wheel rims of Example 3 and Comparative Example 3; Figure 21 shows the microstructure of the wheel of Comparative Example 6 at 1.5 mm from the tread surface. Figure 22 shows the microstructure of the wheel of Comparative Example 6 at a distance of 6.5 mm from the tread surface; Figure 23 shows the microstructure of the wheel of Comparative Example 6 at a distance of 15 mm from the tread surface. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the embodiments. Embodiment 1

[0026] The main chemical composition of the wheel in Example 1 is shown in Table 1, and the rim thickness B is 68 mm.

[0027] The heat treatment method for the wheel is as follows: The rolled wheel is placed in a ring-shaped heating furnace and gradually heated to 890±10℃ (target temperature is 890℃) over 2.5 hours, and held at that temperature for 1.25 hours before being removed from the furnace and quenched on a quenching table. At the start of quenching, the initial water flow rate of each spray gun is 5 L / min. The flow rate L of the cooling water for each spray gun is controlled to satisfy L = 1.477t + 5 with the quenching time t. After 155 seconds, the flow rate linearly increases to 234 L / min, during which the wheel's rotational linear velocity is 530 mm / s. This flow rate is then maintained at 234 L / min for another 100 seconds. During this stage, the water flow rate of the entire quenching table (6 spray guns) is 84 tons per hour, and the wheel's rotational linear velocity is 475 mm / s. After quenching, the wheel is tempered in a furnace with a uniform tempering temperature of 520℃ and a total heating time of 4 hours. (Comparative Example 1)

[0028] The main chemical composition of the wheel in Comparative Example 1 is shown in Table 1. The rim thickness B is 70 mm. The chemical composition and rim thickness are similar to those of the wheel in Example 1. Regarding the heat treatment process, the quenching heating and tempering processes are the same as in Example 1. The difference is that a constant water flow rate is used for cooling during the spray quenching stage. The flow rate of each spray gun is 361 L / min, and the total water flow rate of the entire quenching table (6 spray guns) is 130 tons per hour for 270 seconds. The linear velocity of the wheel's rotation during the spray quenching process is 475 mm / s.

[0029] The temperature at different depths of the wheel rim during the spray cooling process was recorded using embedded thermocouples. In engineering, the average temperature drop rate within the range of 800–500℃ is often taken as the effective cooling rate. Figure 1 shows the cooling rates at different depths of the wheel rims in Example 1 and Comparative Example 1. It can be seen that the cooling rate at different depths along the radial direction of the wheel rim in Example 1 is relatively uniform, with a small gradient, decreasing almost linearly. The cooling rate near the surface of the tread (i.e., 5 mm in Figure 1) does not exceed 6℃ / s, which is lower than the critical cooling rate for the complete pearlitic transformation of the wheel steel material, and the deeper parts of the rim still exhibit a relatively high cooling rate. Figures 2–4 show the microstructures of the near-surface layer (2.5 mm from the surface), subsurface layer (12.5 mm from the surface), and interior of the rim (45 mm from the surface), respectively. It can be seen that the different depths of the rim all exhibit a fine pearlitic structure with a small amount of ferrite, and the microstructure is consistent and uniform.

[0030] In contrast, the cooling rate of the near-surface layer of the wheel tread in Comparative Example 1 exceeded 16℃ / s, and the cooling rate of the subsurface layer also exceeded 7℃ / s, exceeding the critical rate for complete pearlite transformation. This inevitably resulted in the formation of undesirable non-pearlitic structures of martensite, bainite, and their mixtures in the near-surface and subsurface layers of the tread, as shown in Figures 5 and 6. Meanwhile, the cooling rate inside the rim (45mm from the surface) was less than 1℃ / s, and the microstructure at this location is shown in Figure 7. The radial cooling rate gradient in the rim area was extremely large, leading to poor uniformity in microstructure and properties.

[0031] As shown in Figure 8, according to GB / T 231.1 "Metallic Materials - Brinell Hardness Test - Part 1: Test Method", cross-sectional hardness samples were directly taken from the heat-treated wheel rim for grid hardness testing. The hardness range at the same depth under the tread (i.e., the difference between the maximum and minimum hardness) is defined as the uniformity of hardness. As shown in Figure 9, in Example 1, the cross-sectional hardness range at the same depth of the wheel rim is controlled within 10 HB, while in Comparative Example 1, the cross-sectional hardness range at the same depth of the wheel rim can reach over 20 HB. Compared to traditional processes, this invention can significantly optimize the uniformity of cross-sectional hardness of the wheel rim.

[0032] As shown in Figure 10, considering a 10mm machining allowance, Charpy impact specimens were taken at three locations on the finished wheel rim, and a series of temperature pendulum impact tests were conducted according to GB / T 229 "Metallic Materials - Charpy Pendulum Impact Test Method". The series of temperature impact properties of the wheel rims of Example 1 and Comparative Example 1 are shown in Table 2. It can be seen that, compared with the wheel of Comparative Example 1, the wheel of Example 1 can obtain more uniform impact toughness.

[0033] Table 1. Main chemical components (wt%) of the wheels in the examples and comparative examples

[0034] Table 2. Series of temperature shock energy (J) for the wheels of the embodiments and comparative examples Example 2

[0035] The main chemical components of the wheel in Example 2 are shown in Table 1, and the rim thickness B is 90 mm.

[0036] The heat treatment method for the wheel is as follows: The rolled wheel is placed in a ring-shaped heating furnace and gradually heated to 870±10℃ (target temperature is 870℃) over 3 hours. After holding at this temperature for 1.5 hours, the wheel is removed from the furnace and quenched on a quenching table. At the start of quenching, the initial water flow rate of each spray gun is 10L / min. The flow rate L of the cooling water for each spray gun is controlled to satisfy L = 1.60t + 10 with the quenching time t. After 175 seconds, the flow rate linearly increases to 290L / min. During this stage, the wheel's rotational linear velocity is 530mm / s. Then, the flow rate is maintained at 290L / min for another 150 seconds. During this stage, the water flow rate of the entire quenching table (6 spray guns) is 104 tons per hour, and the wheel's rotational linear velocity is 475mm / s. After quenching, the wheel is tempered in a furnace. The tempering temperature is 490℃, and the total heating time is 5 hours. (Comparative Example 2)

[0037] The main chemical composition of the wheel in Comparative Example 2 is shown in Table 1. The rim thickness B is 89 mm. The chemical composition and rim thickness are comparable to those of the wheel in Example 2. Regarding the heat treatment process, the quenching heating and tempering processes are the same as in Example 2. The difference is that a constant water flow rate is used for cooling during the spray quenching stage. The flow rate of each spray gun is 361 L / min, and the total water flow rate of the entire quenching table (6 spray guns) is 130 tons per hour for 360 seconds. The linear velocity of the wheel's rotation during the spray quenching process is 475 mm / s.

[0038] Figure 11 shows the cooling rates at different depths of the wheel rims in Example 2 and Comparative Example 2. It can be seen that the cooling rate at different depths along the radial direction of the wheel rim in Example 2 is relatively uniform, with a small gradient and an almost linear decrease. The cooling rate near the surface of the tread is lower than the critical cooling rate for the complete pearlitic transformation of the wheel steel, and the deeper parts of the rim still exhibit a relatively high cooling rate. In contrast, the cooling rate gradient of the wheel in Comparative Example 2 is significant, with the cooling rate near the surface of the tread exceeding 16°C / s, while the cooling rate inside the rim is lower than 1°C / s, indicating poor cooling uniformity in the rim area.

[0039] Referring to Example 1 and Comparative Example 1, grid hardness tests were conducted on the wheels of Example 2 and Comparative Example 2. As shown in Figure 12, the hardness difference at the same depth in the rim of the wheel of Example 2 was controlled within 10 HB, while the hardness difference at the same depth in the rim of Comparative Example 2 was as high as nearly 20 HB. Compared with traditional processes, the present invention can significantly optimize the uniformity of hardness in the rim section of the wheel.

[0040] Referring to Example 1 and Comparative Example 1, a series of temperature pendulum impact tests were conducted on the wheels of Example 2 and Comparative Example 2. The series of temperature impact performance of the wheel rims of Example 2 and Comparative Example 2 are shown in Table 2. It can be seen that, compared with the wheel of Comparative Example 2, the wheel of Example 2 achieves more uniform impact toughness. Example 3

[0041] The main chemical composition of the wheel in Example 3 is shown in Table 1, and the rim thickness B is 110 mm.

[0042] The heat treatment method for the wheel is as follows: The rolled wheel is placed in a ring-shaped heating furnace and gradually heated to 860±10℃ (target temperature is 860℃) over 4 hours. After holding at this temperature for 2 hours, the wheel is removed from the furnace and quenched on a quenching table. At the start of quenching, the initial water flow rate of each spray gun is 20L / min. The flow rate L of the cooling water for each spray gun is controlled to satisfy L = 1.749t + 20 with the quenching time t. After 195 seconds, the flow rate linearly increases to 361L / min, during which the wheel's rotational linear velocity is 530mm / s. This flow rate is then maintained at 361L / min for another 240 seconds. During this stage, the water flow rate of the entire quenching table (6 spray guns) is 130 tons per hour, and the wheel's rotational linear velocity is 475mm / s. After quenching, the wheel is tempered in a furnace with a uniform tempering temperature of 470℃ and a total heating time of 6 hours. (Comparative Example 3)

[0043] The main chemical composition of the wheel in Comparative Example 3 is shown in Table 1. The rim thickness B is 110 mm. The chemical composition and rim thickness are similar to those of the wheel in Example 3. Regarding the heat treatment process, the quenching heating and tempering processes are the same as in Example 3. The difference is that a constant water flow rate is used for cooling during the spray quenching stage. The flow rate of each spray gun is 361 L / min, and the total water flow rate of the entire quenching table (6 spray guns) is 130 tons per hour for 480 seconds. The linear velocity of the wheel's rotation during the spray quenching process is 475 mm / s.

[0044] Figure 13 shows the cooling rates at different depths of the wheel rims in Example 3 and Comparative Example 3. It can be seen that the cooling rate at different depths along the radial direction of the wheel rim in Example 3 is relatively uniform, with a small gradient and an almost linear decrease. The cooling rate near the surface of the tread is lower than the critical cooling rate for the complete pearlitic transformation of the wheel steel, while the deeper parts of the rim still exhibit a relatively high cooling rate. Figures 14-16 show the microstructures of the near-surface (2.5 mm from the surface), subsurface (12.5 mm from the surface), and interior (45 mm from the surface) of the wheel rim in Example 3. It can be seen that the rim at different depths exhibits a fine pearlitic structure with a small amount of ferrite, resulting in a consistent and uniform microstructure. In contrast, the cooling rate gradient of the wheel in Comparative Example 3 is significant, with the cooling rate near the surface of the tread approaching 15℃ / s, while the cooling rate inside the rim is below 1℃ / s, indicating poor cooling uniformity in the rim area. Undesirable non-pearlitic structures of martensite, bainite, and their mixtures were formed in the near-surface and subsurface layers of the tread surface, as shown in Figures 17-18; while the cooling rate inside the rim (45 mm from the surface) was less than 1 °C / s, and the microstructure there is shown in Figure 19.

[0045] Referring to Example 1 and Comparative Example 1, a grid hardness test was conducted on the wheels of Example 3 and Comparative Example 3. As shown in Figure 20, the hardness difference at the same depth in the rim of the wheel of Example 3 was controlled within 10 HB, while the hardness difference at the same depth in the rim of the wheel of Comparative Example 3 exceeded 15 HB. Compared with traditional processes, the present invention can significantly optimize the uniformity of the hardness of the wheel rim.

[0046] Referring to Example 1 and Comparative Example 1, a series of temperature pendulum impact tests were conducted on the wheels of Example 3 and Comparative Example 3. The series of temperature impact performance of the wheel rims of Example 3 and Comparative Example 3 are shown in Table 2. It can be seen that, compared with the wheel of Comparative Example 3, the wheel of Example 3 achieves more uniform impact toughness. Comparative Example 4

[0047] The main chemical composition of the wheel in Comparative Example 4 is shown in Table 1, and the rim thickness B is 69 mm. The heat treatment procedure is the same as in Example 1, consisting of heating, quenching, and tempering. The control parameters for the heating and tempering regimes are the same as in Example 1, except that the quenching regime has a faster rate of linear increase in water flow rate. Specifically, the initial water flow rate of each spray gun at the start of quenching is 5 L / min, and the flow rate L of the cooling water for each spray gun is controlled to satisfy L = 1.71t + 5 with the spraying and quenching time t. After 155 s, the flow rate linearly increases to 270 L / min, and the wheel's rotational linear velocity is 530 mm / s during this stage. Then, the flow rate is maintained at 270 L / min for another 100 s. During this stage, the water flow rate of the entire quenching table (6 spray guns) is 97 tons per hour, and the wheel's rotational linear velocity is 475 mm / s.

[0048] As shown in Figure 8, a grid hardness test was conducted on the wheel of Comparative Example 4. The results show that the hardness range of the cross-section at 5, 15, 25, 35, and 45 mm from the tread surface of Comparative Example 4 wheel is 6, 9, 14, 18, and 19 HB, respectively, while the hardness range of the cross-section at the same depth of the wheel of Example 1 is 2, 4, 5, 7, and 8 HB, respectively. It can be seen that the uniformity of cross-sectional hardness of Comparative Example 4 wheel is significantly lower than that of Example 1 wheel.

[0049] A series of temperature pendulum impact tests were conducted on the wheel of Comparative Example 4, and the results are shown in Table 2. It can be seen that compared to the wheel of Example 1, the wheel of Comparative Example 4 not only has lower series temperature impact energy values, but also a larger standard deviation, indicating that the impact performance level and uniformity of the wheel of Comparative Example 4 are significantly lower than those of the wheel of Example 1. Comparative Example 5

[0050] The main chemical composition of the wheel in Comparative Example 5 is shown in Table 1, and the rim thickness B is 70 mm. The heat treatment procedure is the same as in Example 1, consisting of heating, quenching, and tempering. The control parameters for the heating and tempering regimes are the same as in Example 1, except that the quenching regime has a slower rate of linear increase in water flow rate. Specifically, the initial water flow rate of each spray gun at the start of quenching is 5 L / min. The flow rate L of the cooling water for each spray gun is controlled to satisfy L = 1.355t + 5 with the spraying and quenching time t. After 155 s, the flow rate linearly increases to 215 L / min. During this stage, the wheel's rotational linear velocity is 530 mm / s. Then, the flow rate is maintained at 215 L / min for another 100 s. During this stage, the water flow rate of the entire quenching table (6 spray guns) is 77 tons per hour, and the wheel's rotational linear velocity is 475 mm / s.

[0051] As shown in Figure 8, a grid hardness test was conducted on the wheel of Comparative Example 5. The results showed that the average cross-sectional hardness of the wheel of Comparative Example 5 at distances of 5, 15, 25, 35, and 45 mm from the tread surface was 287, 278, 272, 263, and 258 HB, respectively, with ranges of 6, 9, 14, 18, and 18 HB, respectively. In contrast, the average cross-sectional hardness of the wheel of Example 1 at the same depth was 293, 285, 277, 270, and 266 HB, respectively, with ranges of 2, 4, 5, 7, and 8 HB, respectively. It is evident that the cross-sectional hardness level and uniformity of the wheel of Comparative Example 5 are significantly lower than those of the wheel of Example 1, which is related to the slower rate of increase in water flow leading to insufficient cooling intensity.

[0052] A series of temperature pendulum impact tests were conducted on the wheel of Comparative Example 5, and the results are shown in Table 2. It can be seen that compared to the wheel of Example 1, the wheel of Comparative Example 5 not only has lower series temperature impact energy values, but also a larger standard deviation, indicating that the impact performance level and uniformity of the wheel of Comparative Example 5 are significantly lower than those of the wheel of Example 1. Comparative Example 6

[0053] The main chemical composition of the wheel in Comparative Example 6 is shown in Table 1, and the rim thickness B is 69 mm. The heat treatment procedure is the same as in Example 1, consisting of heating, quenching, and tempering. The control parameters for the heating and tempering regimes are the same as in Example 1, except for the quenching regime. The initial water flow rate at the start of quenching is larger. Specifically, the initial water flow rate of each spray gun at the start of quenching is 8 L / min. The flow rate L of the cooling water for each spray gun is controlled to satisfy L = 1.458t + 8 with the spraying and quenching time t. After 155 s, the flow rate linearly increases to 234 L / min. During this stage, the rotational linear velocity of the wheel is 530 mm / s. Then, the flow rate is maintained at 234 L / min for another 100 s. During this stage, the water flow rate of the entire quenching table (6 spray guns) is 84 tons per hour, and the rotational linear velocity of the wheel is 475 mm / s.

[0054] The microstructures of the wheel at distances of 1.5, 6.5, and 15 mm from the tread surface in Comparative Example 6 are shown in Figures 21-23. It can be seen that due to the large initial water flow rate during quenching, and the direct contact between the tread surface and the cooling water, the cooling rate was high, exceeding the critical rate for complete pearlite transformation. This resulted in the formation of undesirable non-pearlitic structures of martensite, bainite, and their mixtures in the near-surface and subsurface layers of the tread surface. These non-pearlitic structures disappeared only at a distance of approximately 8 mm from the tread surface, while the interior of the wheel rim consisted of fine pearlite with a small amount of ferrite.

[0055] A series of temperature pendulum impact tests were conducted on the wheel of Comparative Example 6, and the results are shown in Table 2. It can be seen that compared to the wheel of Example 1, the wheel of Comparative Example 6 not only has a lower series of temperature impact energy values, but also a larger standard deviation, indicating that the impact performance level and uniformity of the wheel of Comparative Example 6 are significantly lower than those of the wheel of Example 1. Comparative Example 7

[0056] The main chemical composition of the wheel in Comparative Example 7 is shown in Table 1, and the rim thickness B is 68 mm. The heat treatment procedure is the same as in Example 1, consisting of heating, quenching, and tempering. The control parameters for the heating and tempering regimes are the same as in Example 1, except that the peak water flow rate maintenance period is shorter in the quenching regime. Specifically, the initial water flow rate of each spray gun at the start of quenching is 5 L / min, and the flow rate L of the cooling water for each spray gun is controlled to satisfy L = 1.477t + 5 with the spraying and quenching time t. After 155 s, the flow rate linearly increases to 234 L / min, and the wheel's rotational linear velocity is 530 mm / s during this stage. Then, the flow rate of 234 L / min is maintained for another 70 s. During this stage, the water flow rate of the entire quenching table (6 spray guns) is 84 tons per hour, and the wheel's rotational linear velocity is 475 mm / s.

[0057] As shown in Figure 8, a grid hardness test was conducted on the wheel of Comparative Example 7. The results showed that the average cross-sectional hardness of the wheel of Comparative Example 7 at distances of 5, 15, 25, 35, and 45 mm from the tread surface was 294, 283, 271, 265, and 260 HB, respectively, while the average cross-sectional hardness at the same depth on the wheel of Example 1 was 293, 285, 277, 270, and 266 HB, respectively. It is evident that the hardness level inside the rim of the wheel of Comparative Example 7 is significantly lower than that of the wheel of Example 1, which is related to insufficient cooling inside the rim due to the shorter duration of the peak water flow maintenance phase.

[0058] A series of temperature pendulum impact tests were conducted on the wheel of Comparative Example 7, and the results are shown in Table 2. It can be seen that compared with the wheel of Example 1, the wheel of Comparative Example 7 not only has a lower series of temperature impact energy values, but also a larger standard deviation, indicating that the impact performance level and uniformity of the wheel of Comparative Example 7 are significantly lower than those of the wheel of Example 1.

[0059] The above detailed description of a heat treatment method for improving the uniformity of the structure and performance of railway wheels, with reference to the embodiments, is illustrative rather than limiting. Several embodiments may be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method of heat treating railroad wheels to improve the uniformity of the microstructure and properties of the wheels, comprising the steps of: The heat treatment method includes the following steps: S1. Heating: Heating the entire wheel until it is fully austenitic; S2. Quenching: The wheel tread is quenched using a progressively increasing flow rate cooling water spray. The flow rate L of the cooling water for each spray gun gradually increases with the extension of the quenching time t, and the linear function relationship between the two is controlled as follows: In the formula, L is in L / min; t is in s; and B is in mm. Maintain the peak water flow rate for at least 90 seconds; the wheel is in a self-rotating state during the spray quenching process. S3. Tempering: Place the entire wheel into the tempering furnace for heat preservation, then remove it and air cool.

2. The heat treatment method according to claim 1, characterized by, In step S1, the heating temperature is Ac3 + (70~120)℃. Ac3 is the austenitizing critical temperature; the total heating time is 2.5 to 4 hours.

3. The heat treatment method according to claim 1 or 2, characterized by, In step S1, the wheel is kept in the uniform temperature zone for no less than 1.25 hours.

4. The heat treatment method according to claim 1, characterized by, In step S2, after reaching the peak flow rate, when the rim thickness B < 75 mm, the peak water flow rate is maintained for 90–120 s; when the rim thickness B < 75 mm, the peak water flow rate is maintained for 130–180 s; and when the rim thickness B ≥ 95 mm, the peak water flow rate is maintained for 190–260 s.

5. The heat treatment method according to claim 1 or 4, characterized by, In step S2, during the stage of increasing water flow, the linear velocity v of the wheel's rotation is 500 < v ≤ 550 mm / s.

6. The heat treatment method according to claim 1 or 4, characterized by, In step S2, during the peak water flow maintenance phase, the wheel's self-rotation linear velocity v is 450≤v≤500mm / s.

7. The heat treatment method according to claim 1 or 4, characterized by, In step S2, box-type spray guns are evenly distributed around the quenching table at equal intervals. The distance between the spray guns and the wheel tread is consistent to ensure complete coverage of the wheel tread, and the water output of each spray gun is consistent.

8. The heat treatment method according to claim 7, characterized by, The number of box-type spray guns is 6.

9. The heat treatment method according to claim 1 or 2, characterized by, In step S3, the tempering temperature is 470–520℃. Total heating time: 4-6 hours.

10. The heat treatment method according to claim 1 or 2, characterized by, The wheel comprises the following chemical composition by weight percentage: C 0.50–0.80%, Si 0.30–1.20%, Mn 0.70–1.00%, P ≤0.015%, S ≤0.015%, Cr 0.10–0.30%, Ni 0.10–0.30%, Mo 0.01–0.10%, and V 0.01–0.20%.

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