A heat treatment method for improving railway wheel structure and performance uniformity

Abstract

The invention discloses a heat treatment method for improving the uniformity of railway wheel structure and performance, belonging to the technical field of railway wheel manufacturing. The heat treatment method comprises the following steps: heating the entire wheel to complete austenitization; spraying the wheel tread with cooling water of increasing flow rate, and the flow rate of cooling water of each spray gun is set to L With quenching time t The water flow rate is gradually increased with the extension of the rim, and the two are controlled to meet a specific linear function relationship, and the peak water flow rate is maintained for at least 90 seconds; the wheel is in a self-rotating state during the spray quenching process; the wheel is placed in a tempering furnace for heat preservation, and then taken out for air cooling. The present invention performs precise linear increase control of the cooling water flow rate for wheels with different rim thicknesses, realizes a balanced change in the radial cooling of the rim part, and ensures the uniformity of the structure and performance of the entire cross-section of the rim.

Description

Technical Field

[0001] The invention belongs to the technical field of railway wheel manufacturing, and in particular relates to a heat treatment method for improving the uniformity of railway wheel structure and performance. Background Art

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

[0003] In terms of wheel heat treatment technology, although each country is different, according to publicly reported literature, currently, railway wheels are mostly heat treated by "overall heating + tread continuous quenching + overall tempering", among which tread quenching is the key process that determines the wheel rim structure and performance. The continuous tread quenching, that is, the rim is cooled with a constant amount of water, has the following problems: first, the radial cooling speed of the rim varies greatly. The constant water flow leads to a very large cooling speed near the surface of the wheel tread, which is far higher than the critical cooling speed of the complete pearlite transformation of the wheel steel material. A thicker non-pearlite structure is easily formed near the surface of the tread, which has the risk of product rejection due to tissue quality problems, or it must be eliminated by increasing the design margin, at the cost of sacrificing metal utilization and increasing processing costs; second, due to the large thickness of the rim section, the cooling speed inside the rim decreases significantly with the increase of depth. The slow cooling speed inside the rim makes the strength and hardness inside the rim insufficient, and the cooling speed gradient inside the rim is large, resulting in uneven cooling at different depths of the rim along the radial direction, thereby generating an undesirable martensite and bainite mixed structure near the surface of the wheel tread that is unfavorable to the service performance of the wheel (such as "early peeling"), and also resulting in a large hardness gradient in the rim, resulting in poor wear resistance in the middle and late stages of the wheel service, destroying the service stability of the wheel throughout its life cycle and shortening its service life.

[0004] Controlling or eliminating the non-pearlite structure of the wheel, improving the uniformity of performance, and obtaining balanced and consistent cooling have long been technical problems that the industry needs to solve, and are also one of the research hotspots. Years of research and practice have proved that controlling the cooling of wheel heat treatment and developing new cooling methods are the most direct and effective ways.

[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, keeping 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 the tread of the wheel includes three stages in sequence. Control the wheel rotation speeds in the three stages as v1>v2>v3, water pressures as P1<P2<P3, and quenching cooling times as T1<T2<T3; the number of nozzles evenly distributed 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 inside of the rim, make the cooling speed from the tread of the wheel to the deep inside of the rim balanced and consistent, optimize the organizational structure of the entire cross-section of the rim, and thus significantly reduce the radial hardness gradient of the rim, greatly improving the mechanical properties and service performance of the wheel. However, this patent requires the use of 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 evenly 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 individually controlled by a branch pipe for water outlet, 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, and improve 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 a wheel with high hardness uniformity of the rim. However, this patent also requires the use of special cooling nozzles and professional transformation and upgrading 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 organizational and performance uniformity of railway wheels. For wheels with different rim thicknesses, precise linear increase control of the cooling water flow rate is carried out, realizing the balanced change of 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 by the present invention is as follows:

[0009] A heat treatment method for improving the organizational and performance uniformity of railway wheels, the heat treatment method includes the following steps:

[0010] S1. Heating: heating the entire wheel to complete austenitization;

[0011] S2. Quenching: The wheel tread is quenched with cooling water of increasing flow rate. The flow rate L of cooling water of each spray gun gradually increases with the extension of spray quenching time t, and the linear function relationship between the two is controlled as follows:

[0012]

[0013] In the formula, the unit of L is L / min; the unit of t is s; the unit of B is mm;

[0014] After reaching the peak water flow rate, keep it for at least 90 seconds; during the quenching process, the wheel is in a self-rotating state;

[0015] S3. Tempering: Put the entire wheel into the tempering furnace for heat preservation, and then take it out for air cooling.

[0016] In step S1, the heating temperature is Ac3+(70-120)°C, wherein Ac3 is the critical temperature of austenitization; and the total heating time is 2.5-4h.

[0017] In step S1, the wheel is kept in the uniform temperature section for no less than 1.25 hours.

[0018] In step S2, after reaching the peak flow rate, when the rim thickness B is less than 75 mm, the time for maintaining the peak water flow rate is 90 to 120 s; when the rim thickness B is less than 75 mm and less than 95 mm, the time for maintaining the peak water flow rate is 130 to 180 s; when the rim thickness B is greater than or equal to 95 mm, the time for maintaining the peak water flow rate is 190 to 260 s.

[0019] In step S2, during the water flow increasing stage, the wheel rotation linear speed v is 500≤v≤550mm / s; using a higher wheel speed during the water flow increasing stage can obtain a better heat exchange effect, improve the cooling capacity and cooling uniformity.

[0020] In step S2, during the peak water flow holding stage, the wheel's self-rotation linear speed v is 450≤v≤500mm / s; using a lower wheel speed during the peak water flow holding stage is beneficial to maintaining the stability of the wheel rotation, avoiding the impact of high water pressure on the wheel and affecting the quenching quality, and is also beneficial to energy saving.

[0021] In step S2, box-type spray guns are evenly distributed around the quenching table at equal distances, and the distances between the spray guns and the wheel tread are consistent to ensure that the wheel tread is fully covered and the water output of each spray gun is consistent.

[0022] The number of the box-type spray guns is 6.

[0023] In step S3, the tempering average temperature is 470-520° C., and the total heating time is 4-6 hours.

[0024] The wheel comprises the following chemical components in 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%, Mo0.01-0.10%, V 0.01-0.20%. Wheels with any other chemical composition can also be heat treated by the heat treatment method provided in the present application to achieve the purpose of improving the uniformity of wheel organization and performance.

[0025] In the heat treatment method provided by the present invention, during quenching, the wheel tread is sprayed with cooling water of increasing flow rate, and the flow rate L of the cooling water of each spray gun is controlled to be in a linear function relationship with the spraying time t, the intercept of the Lt oblique line represents the initial flow rate at the moment of quenching, and its value is set according to the rim thickness, thereby avoiding the formation of undesirable non-pearlite mixed structure near the surface of the tread due to the instantaneous excessive cooling intensity; the slope of the Lt oblique line represents the increase in the flow rate per unit time of the quenching cooling water taken for the wheel of the rim thickness.

[0026] Based on the coupling relationship between the supercooled austenite phase transformation characteristics of wheel steel and the cooling boundary, the present invention proposes an accurate control cooling strategy for wheels with different rim thicknesses. The cooling water flow rate is controlled to increase linearly with time to a flow peak 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 cooperatively controlled during the spray quenching process, so that a more evenly changing cooling rate is obtained at different radial depths of the rim part, which overcomes the unevenness of conventional constant flow cooling and is beneficial to improving the organizational consistency and performance uniformity of the entire cross-section of the rim.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) The cooling water flow rate is controlled to increase linearly with time, and a balanced cooling rate is obtained, which greatly improves the cooling uniformity of the rim area along the radial direction.

[0029] 2) The rim part obtains uniform fine pearlite and a small amount of ferrite structure, avoiding the formation of martensite, bainite and their mixtures caused by traditional constant water quenching, ensuring the consistency of the structure and helping to improve metal utilization.

[0030] 3) The improvement of quenching cooling uniformity can also significantly improve the uniformity of hardness and impact toughness of the wheel rim, achieving hardness fluctuation within 10HB at the same depth of the rim section, while obtaining smaller fluctuation of impact toughness.

[0031] 4) It has a wide range of applications, covering wheels with different rim thicknesses. It is simple and easy to operate, and is convenient for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The cooling rates at different depths of the wheel rims of Example 1 and Comparative Example 1;

[0033] Figure 2 The microstructure of the wheel tread near the surface (2.5 mm from the surface) of Example 1;

[0034] Figure 3 The microstructure of the subsurface layer (12.5 mm from the surface) of the wheel tread of Example 1;

[0035] Figure 4 The microstructure of the inner part (45 mm from the surface) of the wheel rim of Example 1;

[0036] Figure 5 The microstructure of the wheel tread near the surface (2.5 mm from the surface) of Comparative Example 1;

[0037] Figure 6 The microstructure of the subsurface layer (12.5 mm from the surface) of the wheel tread of Comparative Example 1;

[0038] Figure 7 The microstructure of the inner part (45 mm from the surface) of the wheel rim of Comparative Example 1;

[0039] Figure 8 It is a schematic diagram of the grid hardness test of the rim section of the blank wheel after heat treatment;

[0040] Fig. 9 The cross-sectional hardness at the same depth of the wheel rim of Example 1 and Comparative Example 1 is extremely different (hardness uniformity);

[0041] Fig.10 This is a schematic diagram of the location of the test specimens for the temperature shock test of the finished wheel rim series;

[0042] Fig.11 The cooling rates at different depths of the wheel rims of Example 2 and Comparative Example 2;

[0043] Fig.12 The cross-sectional hardness at the same depth of the wheel rim of Example 2 and Comparative Example 2 is extremely different (hardness uniformity);

[0044] Fig.13 The cooling rates at different depths of the wheel rims of Example 3 and Comparative Example 3;

[0045] Fig.14 The microstructure of the wheel tread near the surface (2.5 mm from the surface) of Example 3;

[0046] Fig.15 The microstructure of the subsurface layer (12.5 mm from the surface) of the wheel tread of Example 3;

[0047] Fig.16 The microstructure of the inner part (45 mm from the surface) of the wheel rim of Example 3;

[0048] Fig.17 The microstructure of the wheel tread near the surface (2.5 mm from the surface) of Comparative Example 3;

[0049] Fig.18 The microstructure of the subsurface layer (12.5 mm from the surface) of the wheel tread of Comparative Example 3;

[0050] Fig.19 The microstructure of the inner part of the wheel rim (45 mm from the surface) of Comparative Example 3;

[0051] Fig. 20 The cross-sectional hardness at the same depth of the wheel rim of Example 3 and Comparative Example 3 is extremely different (hardness uniformity);

[0052] Fig.21 Microstructure of the wheel at 1.5 mm from the tread surface of Comparative Example 6;

[0053] Fig. 22 The microstructure of the wheel at 6.5 mm from the tread surface of Comparative Example 6;

[0054] Fig.23 Microstructure of the wheel of comparative example 6 at 15 mm from the tread surface. DETAILED DESCRIPTION

[0055] The present invention is described in detail below with reference to the embodiments.

[0056] Example 1

[0057] The main chemical components of the wheel of Example 1 are shown in Table 1, and the rim thickness B is 68 mm.

[0058] The heat treatment method of the wheel is as follows: the rolled wheel is loaded into a ring heating furnace, gradually heated to 890±10℃ (target temperature is 890℃) after 2.5h, and then taken out of the furnace after keeping warm for 1.25h, and quenched on a quenching table. When quenching is started, the initial water flow rate of each spray gun is 5L / min, and the flow rate L of cooling water of each spray gun and the spraying time t are controlled to meet L=1.477t+5. After 155s, the flow rate increases linearly to 234L / min, and the rotation line speed of the wheel at this stage is 530mm / s; then maintain the flow rate of 234L / min for another 100s, and the water flow rate of the entire quenching table (6 spray guns) is 84 tons per hour at this stage, and the rotation line speed of the wheel is 475mm / s. After quenching, the wheel is put into the furnace for tempering treatment, and the tempering average temperature is 520℃, and the total heating time is 4h.

[0059] Comparative Example 1

[0060] The main chemical components of the wheel of comparative example 1 are shown in Table 1, the rim thickness B is 70 mm, and the chemical components and rim thickness are equivalent to those of the wheel of embodiment 1. In terms of heat treatment system, the quenching heating and tempering process are the same as those of embodiment 1, except 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, the water flow rate of the entire quenching station (6 spray guns) is 130 tons per hour, the duration is 270 seconds, and the rotational linear speed of the wheel during the spray quenching process is 475 mm / s.

[0061] By embedding thermocouples, the temperature at different depths of the wheel rim during the spray quenching cooling process is recorded. In engineering, the average temperature drop rate in the range of 800-500°C is usually taken as the effective cooling rate. The cooling rates at different depths of the wheel rim of Example 1 and Comparative Example 1 are as follows: Figure 1 As shown in the figure, the cooling rate of the wheel rim of Example 1 at different depths along the radial direction is relatively balanced and consistent, with a small change gradient, almost linearly decreasing, and the cooling rate of the tread near the surface (i.e. Figure 1 The cooling rate of the tread surface (2.5 mm from the surface), subsurface (12.5 mm from the surface) and inside the rim (45 mm from the surface) is not more than 6°C / s, which is lower than the critical cooling rate of complete pearlite transformation of the wheel steel material, and the cooling rate is still relatively high in the deep part of the rim. The microstructures of the tread surface (2.5 mm from the surface), subsurface (12.5 mm from the surface) and inside the rim (45 mm from the surface) are shown as follows: Figures 2 to 4 As shown in the figure, it can be seen that the different depths of the rim are all fine pearlite + a small amount of ferrite, and the organization is consistent and uniform.

[0062] In contrast, the cooling rate of the wheel tread near the surface of the comparative example 1 is above 16°C / s, and the cooling rate of the subsurface is also above 7°C / s, which exceeds the critical speed of complete pearlite transformation. Undesirable non-pearlite structures of martensite, bainite and their mixtures are inevitably generated near the surface and subsurface of the tread, such as Figures 5-6As shown in the figure. The cooling rate inside the rim (45 mm from the surface) is lower than 1°C / s, and the microstructure there is as follows: Figure 7 The cooling rate gradient along the radial direction of the rim is extremely large, which leads to the deterioration of the uniformity of the structure and performance.

[0063] like Figure 8 As shown in the figure, according to GB / T 231.1 "Metallic Materials Brinell Hardness Test Part 1: Test Method", the cross-section hardness specimen is directly taken from the wheel rim after heat treatment for grid hardness test. The hardness extreme difference (i.e. the difference between the maximum and minimum hardness) at the same depth under the tread is defined as the hardness uniformity, such as Fig. 9 As shown, the cross-sectional hardness difference at the same depth of the wheel rim of Example 1 is controlled within 10HB, while the cross-sectional hardness difference at the same depth of the wheel rim of Comparative Example 1 can reach up to 20HB or more. Compared with the traditional process, the present invention can significantly optimize the cross-sectional hardness uniformity of the wheel rim.

[0064] like Fig.10 As shown, considering the cutting allowance of 10 mm, Charpy impact specimens were taken at three positions on the rim of the finished wheel, and a series of temperature pendulum impact tests were carried out according to GB / T 229 "Metallic Material 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.

[0065] Table 1 Main chemical components of wheels of the embodiment and comparative example (wt%)

[0066] element C Si Mn P S Cr Ni Mo V Example 1 0.53 0.33 0.74 0.009 0.007 0.17 0.12 0.02 0.13 Comparative Example 1 0.54 0.30 0.72 0.010 0.008 0.16 0.14 0.03 0.11 Example 2 0.65 0.52 0.82 0.011 0.009 0.25 0.14 0.05 0.08 Comparative Example 2 0.64 0.55 0.80 0.012 0.009 0.22 0.16 0.07 0.04 Example 3 0.74 0.89 0.85 0.010 0.010 0.15 0.20 0.06 0.05 Comparative Example 3 0.73 0.92 0.85 0.010 0.008 0.17 0.24 0.07 0.03 Comparative Example 4 0.54 0.31 0.75 0.009 0.006 0.17 0.10 0.02 0.12 Comparative Example 5 0.55 0.30 0.78 0.007 0.007 0.18 0.11 0.01 0.11 Comparative Example 6 0.55 0.30 0.77 0.008 0.007 0.16 0.10 0.03 0.12 Comparative Example 7 0.54 0.33 0.79 0.011 0.008 0.17 0.11 0.02 0.13

[0067] Table 2 Series temperature impact energy (J) of wheels of the embodiment and the comparative example

[0068]

[0069]

[0070] Example 2

[0071] The main chemical components of the wheel of Example 2 are shown in Table 1, and the rim thickness B is 90 mm.

[0072] The heat treatment method of the wheel is as follows: the rolled wheel is loaded into a ring heating furnace, gradually heated to 870±10℃ (target temperature is 870℃) after 3h, and then taken out of the furnace after keeping warm for 1.5h, and quenched on a quenching table. When quenching is started, the initial water flow of each spray gun is 10L / min, and the flow rate L of cooling water of each spray gun and the spraying time t are controlled to meet L=1.60t+10. After 175s, the flow rate increases linearly to 290L / min, and the rotation line speed of the wheel at this stage is 530mm / s; then maintain the flow rate of 290L / min for another 150s, and the water flow rate of the entire quenching table (6 spray guns) is 104 tons per hour at this stage, and the rotation line speed of the wheel is 475mm / s. After quenching, the wheel is put into the furnace for tempering treatment, and the tempering average temperature is 490℃, and the total heating time is 5h.

[0073] Comparative Example 2

[0074] The main chemical components of the wheel of comparative example 2 are shown in Table 1, the rim thickness B is 89 mm, and the chemical components and rim thickness are equivalent to those of the wheel of example 2. In terms of heat treatment system, the quenching heating and tempering process are the same as those of example 2, except 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, the water flow rate of the entire quenching station (6 spray guns) is 130 tons per hour, the duration is 360 seconds, and the rotation linear speed of the wheel during the spray quenching process is 475 mm / s.

[0075] The cooling speeds at different depths of the wheel rims of Example 2 and Comparative Example 2 are as follows: Fig.11 As shown. It can be seen that the cooling rate of the wheel rim of Example 2 at different depths along the radial direction is relatively balanced and consistent, with a small change gradient, almost linearly decreasing, the cooling rate near the surface of the tread is lower than the critical cooling rate of the complete pearlite transformation of the wheel steel material, and the deep part of the rim still has a high cooling rate. In contrast, the cooling rate gradient of the wheel of Comparative Example 2 is significant, the cooling rate near the surface of the tread exceeds 16℃ / s, and the cooling rate inside the rim is less than 1℃ / s, and the cooling uniformity of the rim is poor.

[0076] Referring to Example 1 and Comparative Example 1, grid hardness tests were performed on the wheels of Example 2 and Comparative Example 2. Fig.12 As shown, the cross-sectional hardness extreme difference at the same depth of the wheel rim of Example 2 is controlled within 10 HB, while the cross-sectional hardness extreme difference at the same depth of the wheel rim of Comparative Example 2 is up to nearly 20 HB. Compared with the traditional process, the present invention can significantly optimize the cross-sectional hardness uniformity of the wheel rim.

[0077] Referring to Example 1 and Comparative Example 1, a series of temperature pendulum impact tests were performed on the wheels of Example 2 and Comparative Example 2. The series of temperature impact performances 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 can obtain more uniform impact toughness.

[0078] Example 3

[0079] The main chemical components of the wheel of Example 3 are shown in Table 1, and the rim thickness B is 110 mm.

[0080] The heat treatment method of the wheel is as follows: the rolled wheel is loaded into a ring heating furnace, gradually heated to 860±10℃ (target temperature is 860℃) after 4h, and then taken out of the furnace after keeping warm for 2h, and quenched on a quenching table. When quenching is started, the initial water flow of each spray gun is 20L / min, and the flow rate L of cooling water of each spray gun and the spraying time t are controlled to meet L=1.749t+20. After 195s, the flow rate increases linearly to 361L / min, and the rotation line speed of the wheel at this stage is 530mm / s; then maintain the flow rate of 361L / min for another 240s, and the water flow rate of the entire quenching table (6 spray guns) is 130 tons per hour at this stage, and the rotation line speed of the wheel is 475mm / s. After quenching, the wheel is put into the furnace for tempering treatment, and the tempering average temperature is 470℃, and the total heating time is 6h.

[0081] Comparative Example 3

[0082] The main chemical components of the wheel of comparative example 3 are shown in Table 1, the rim thickness B is 110 mm, and the chemical components and rim thickness are equivalent to those of the wheel of example 3. In terms of heat treatment system, the quenching heating and tempering process are the same as those of example 3, except 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, the water flow rate of the entire quenching station (6 spray guns) is 130 tons per hour, the duration is 480 s, and the rotational linear speed of the wheel during the spray quenching process is 475 mm / s.

[0083] The cooling speeds at different depths of the wheel rims of Example 3 and Comparative Example 3 are as follows: Fig.13 As shown. It can be seen that the cooling rate at different depths along the radial direction of the wheel rim of Example 3 is relatively balanced and consistent, with a small change gradient, and is almost linearly reduced. The cooling rate near the surface of the tread is lower than the critical cooling rate of the complete pearlite transformation of the wheel steel material, and the deep part of the rim still has a relatively high cooling rate. The microstructures of the near surface layer (2.5mm from the surface), the subsurface layer (12.5mm from the surface) and the inside of the rim (45mm from the surface) of the wheel tread of Example 3 are shown as follows: Figures 14 to 16 As shown. It can be seen that the rim has fine pearlite + a small amount of ferrite at different depths, and the organization is consistent and uniform. In contrast, the cooling rate gradient of the wheel in comparative example 3 is significant, the cooling rate near the surface of the tread is close to 15℃ / s, and the cooling rate inside the rim is less than 1℃ / s, and the cooling uniformity of the rim is poor. Undesirable non-pearlite organizations of martensite, bainite and their mixtures are generated near the surface and sub-surface of the tread, such as Figures 17-18 As shown; the cooling rate inside the rim (45mm from the surface) is lower than 1℃ / s, and the microstructure there is as follows Fig.19 shown.

[0084] Referring to Example 1 and Comparative Example 1, grid hardness tests were performed on the wheels of Example 3 and Comparative Example 3. Fig. 20 As shown, the cross-sectional hardness extreme difference of the wheel rim at the same depth of Example 3 is controlled within 10HB, while the cross-sectional hardness extreme difference of the wheel rim at the same depth of Comparative Example 3 is up to more than 15HB. Compared with the traditional process, the present invention can significantly optimize the cross-sectional hardness uniformity of the wheel rim.

[0085] Referring to Example 1 and Comparative Example 1, a series of temperature pendulum impact tests were performed on the wheels of Example 3 and Comparative Example 3. The series of temperature impact performances 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 can obtain more uniform impact toughness.

[0086] Comparative Example 4

[0087] The main chemical components of the wheel of comparative example 4 are shown in Table 1, and the rim thickness B is 69 mm. The heat treatment procedure is the same as that of Example 1, consisting of heating, quenching and tempering. Among them, the control parameters of the heating and tempering system are the same as those of Example 1, except that the water flow rate of the quenching system increases linearly at a faster rate, specifically: when quenching is started, the initial water flow rate of each spray gun is 5 L / min, and the flow rate L of the cooling water of each spray gun and the spraying time t are controlled to satisfy L=1.71t+5. After 155s, the flow rate increases linearly to 270L / min, and the rotational linear speed of the wheel at this stage is 530mm / s; then it is maintained at a flow rate of 270L / min for another 100s. At this stage, the water flow rate of the entire quenching station (6 spray guns) is 97 tons per hour, and the rotational linear speed of the wheel is 475mm / s.

[0088] according to Figure 8 As shown, a grid hardness test was conducted on the wheel of comparative example 4. The results show that the extreme differences in cross-sectional hardness of the wheel of comparative example 4 at 5, 15, 25, 35, and 45 mm from the tread are 6, 9, 14, 18, and 19 HB, respectively, while the extreme differences in cross-sectional hardness of the wheel of embodiment 1 at the same depth are 2, 4, 5, 7, and 8 HB, respectively. It can be seen that the cross-sectional hardness uniformity of the wheel of comparative example 4 is significantly lower than that of the wheel of embodiment 1.

[0089] The wheel of Comparative Example 4 was subjected to a series of temperature pendulum impact tests, 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 4 not only has a lower series temperature impact energy value, but also has 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.

[0090] Comparative Example 5

[0091] The main chemical components of the wheel of comparative example 5 are shown in Table 1, and the rim thickness B is 70 mm. The heat treatment procedure is the same as that of Example 1, consisting of heating, quenching and tempering. Among them, the control parameters of the heating and tempering system are the same as those of Example 1, except that the water flow rate of the quenching system increases linearly at a slower rate, specifically: when quenching is started, the initial water flow rate of each spray gun is 5 L / min, and the flow rate L of the cooling water of each spray gun and the spraying time t are controlled to satisfy L=1.355t+5. After 155s, the flow rate increases linearly to 215L / min, and the rotational linear speed of the wheel at this stage is 530mm / s; then it is maintained at a flow rate of 215L / min for another 100s. At this stage, the water flow rate of the entire quenching station (6 spray guns) is 77 tons per hour, and the rotational linear speed of the wheel is 475mm / s.

[0092] according to Figure 8 As shown, a grid hardness test was conducted on the wheels of comparative example 5. The results show that the average cross-sectional hardness of the wheels of comparative example 5 at 5, 15, 25, 35, and 45 mm from the tread is 287, 278, 272, 263, and 258 HB, respectively, and the range is 6, 9, 14, 18, and 18 HB, respectively, while the average cross-sectional hardness of the wheels of embodiment 1 at the same depth is 293, 285, 277, 270, and 266 HB, respectively, and the range is 2, 4, 5, 7, and 8 HB, respectively. It can be seen that the cross-sectional hardness level and uniformity of the wheels of comparative example 5 are significantly lower than those of the wheels of embodiment 1, which is related to the insufficient cooling intensity caused by the slow rate of increase of water flow.

[0093] The wheel of Comparative Example 5 was subjected to a series of temperature pendulum impact tests, 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 5 not only has a lower series temperature impact energy value, but also has 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.

[0094] Comparative Example 6

[0095] The main chemical components of the wheel of comparative example 6 are shown in Table 1, and the rim thickness B is 69 mm. The heat treatment procedure is the same as that of Example 1, consisting of heating, quenching and tempering. Among them, the control parameters of the heating and tempering system are the same as those of Example 1, and the difference lies in the quenching system. The initial water flow rate at the start of quenching is relatively large, specifically: the initial water flow rate of each spray gun at the start of quenching is 8L / min, and the flow rate L of the cooling water of each spray gun and the spraying time t are controlled to satisfy L=1.458t+8. After 155s, the flow rate increases linearly to 234L / min, and the rotational linear speed of the wheel at this stage is 530mm / s; then it is maintained at a flow rate of 234L / min for another 100s. At this stage, the water flow rate of the entire quenching station (6 spray guns) is 84 tons per hour, and the rotational linear speed of the wheel is 475mm / s.

[0096] The microstructures of the wheel at 1.5, 6.5 and 15 mm from the tread surface of Comparative Example 6 are as follows: Figures 21 to 23 As shown. It can be seen that due to the large initial water flow rate at the start of quenching and the direct contact of the tread surface with cooling water, the cooling rate is large, exceeding the critical speed of complete pearlite transformation, and undesirable non-pearlite structures of martensite, bainite and their mixtures are generated near the surface and sub-surface of the tread. The non-pearlite structure disappears at about 8mm from the tread, and the inside of the rim is fine pearlite + a small amount of ferrite structure.

[0097] A series of temperature pendulum impact tests were performed on the wheels of Comparative Example 6, and the results are shown in Table 2. It can be seen that compared with the wheels of Example 1, the wheels of Comparative Example 6 not only have lower series temperature impact energy values, but also have larger standard deviations, indicating that the impact performance level and uniformity of the wheels of Comparative Example 6 are significantly lower than those of the wheels of Example 1.

[0098] Comparative Example 7

[0099] The main chemical components of the wheel of comparative example 7 are shown in Table 1, and the rim thickness B is 68mm. The heat treatment procedure is the same as that of Example 1, consisting of heating, quenching and tempering. Among them, the control parameters of the heating and tempering system are the same as those of Example 1, except that the quenching system has a shorter peak water flow holding stage, specifically: when quenching is started, the initial water flow of each spray gun is 5L / min, and the flow rate L of the cooling water of each spray gun and the spraying time t are controlled to satisfy L=1.477t+5. After 155s, the flow rate increases linearly to 234L / min, and the rotational linear speed of the wheel at this stage is 530mm / s; then it is maintained at a flow rate of 234L / min for another 70s. At this stage, the water flow of the entire quenching station (6 spray guns) is 84 tons per hour, and the rotational linear speed of the wheel is 475mm / s.

[0100] according to Figure 8 As shown, a grid hardness test was conducted on the wheel of comparative example 7. The results show that the average cross-sectional hardness of the wheel of comparative example 7 at 5, 15, 25, 35, and 45 mm from the tread is 294, 283, 271, 265, and 260 HB, respectively, while the average cross-sectional hardness of the wheel of embodiment 1 at the same depth is 293, 285, 277, 270, and 266 HB, respectively. It can be seen that the hardness level inside the rim of the wheel of comparative example 7 is significantly lower than that of the wheel of embodiment 1, which is related to the short time of the peak water flow retention stage resulting in insufficient cooling inside the rim.

[0101] A series of temperature pendulum impact tests were performed 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 value, but also has 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.

[0102] The above-mentioned 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 restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A heat treatment method for improving the uniformity of railway wheel structure and performance, characterized in that: The heat treatment method comprises the following steps: S1. Heating: heating the entire wheel to complete austenitization; S2. Quenching: The wheel tread is quenched with cooling water spraying with increasing flow rate. The flow rate L of cooling water of each spray gun gradually increases with the extension of spraying time t, and the linear function relationship between the two is controlled as follows: In the formula, the unit of L is L / min; the unit of t is s; the unit of B is mm; After reaching the peak water flow rate, when the rim thickness B is less than 75mm, the time of maintaining the peak water flow rate is 90 to 120s; when the rim thickness is 75mm≤B<95mm, the time of maintaining the peak water flow rate is 130 to 180s; when the rim thickness B≥95mm, the time of maintaining the peak water flow rate is 190 to 260s; during the quenching process, the wheel is in a self-rotating state; S3. Tempering: Put the entire wheel into the tempering furnace for heat preservation, and then take it out for air cooling.

2. The heat treatment method according to claim 1, characterized in that In step S1, the heating temperature is Ac3+(70-120)°C, wherein Ac3 is the critical temperature of austenitization; and the total heating time is 2.5-4h.

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

4. The heat treatment method according to claim 1, characterized in that: In step S2, during the water flow increasing stage, the wheel self-rotation linear velocity v is 500<v≤550mm / s.

5. The heat treatment method according to claim 1, characterized in that: In step S2, during the peak water flow maintenance stage, the self-rotation linear velocity v of the wheel is 450≤v≤500mm / s.

6. The heat treatment method according to claim 1, characterized in that: In step S2, box-type spray guns are evenly distributed around the quenching table at equal distances, and the distances between the spray guns and the wheel tread are consistent to ensure that the wheel tread is fully covered and the water output of each spray gun is consistent.

7. The heat treatment method according to claim 6, characterized in that: The number of the box-type spray guns is 6.

8. The heat treatment method according to claim 1 or 2, characterized in that: In step S3, the tempering average temperature is 470-520° C., and the total heating time is 4-6 hours.

9. The heat treatment method according to claim 1 or 2, characterized in that: The wheel comprises the following chemical components in 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%, V0.01-0.20%.

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