Medium-carbon vanadium railway wheel steel with optimized ferrite content and distribution, railway wheel and production method thereof

Abstract

The application provides a medium-carbon vanadium-containing railway wheel steel with optimized ferrite content and distribution, a wheel and a wheel production method. Through the adjustment and combination of chemical elements in the wheel steel and the optimization of a heat treatment system, the application realizes the accurate control of the cooling speed in a specific depth range inside the wheel rim, strengthens the cooling effect inside the wheel rim, effectively inhibits the precipitation of ferrite, makes the ferrite volume fraction at a position 25-40 mm away from the tread surface less than 10%, and improves the morphology and distribution of ferrite, so that the ferrite is discontinuously distributed along the grain boundaries. The ferrite volume fraction increasing gradient at the position 25-40 mm inside the wheel rim is 0.13%-0.16% / mm, the average value of the ferrite width is 1.5-2.5 microns, and the maximum value of the ferrite width is 3-4 microns. The application obtains a smaller pearlite interlamellar spacing, optimizes the microstructure state of the wheel at room temperature, and ensures the strength-toughness matching and wear resistance of the wheel.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of railway wheel production, and more particularly relates to a medium-carbon vanadium-containing railway wheel steel with optimized ferrite content and distribution, a railway wheel and a railway wheel production method. BACKGROUND

[0002] After the 1990s, the materials and processes for railway wheels were basically standardized. On the one hand, the fine pearlite and a small amount of ferrite type railway wheel has been widely used in various countries and regions in the world due to its excellent wear resistance, easy machinability and thermal stability. On the other hand, the current railway wheels are generally heat treated by "overall heating + continuous quenching of the tread + overall tempering"; among them, the continuous quenching of the tread surface by spraying a large amount of water is a key process that determines the structure and performance of the wheel rim.

[0003] ER7 wheel is a widely used wheel in European countries and regions, which is widely used in quasi-high speed, urban rail and freight vehicles, and executes the standard DIN EN 13262-2020 "Railway applications - Wheels and bogies - Wheels - Product requirements". The performance characteristics are medium strength + high toughness.

[0004] According to the search, on August 7, 2020, a Chinese invention patent, a medium-carbon wheel steel with good wear resistance and strength matching, a heat treatment method and a preparation method of a wheel, with the publication number CN 111500925 A, discloses the technical scheme as follows: chemical composition: C 0.49-0.52%, Si 0.20-0.40%, Mn 0.50-0.80%, P≤0.020%, S≤0.015%, V 0.08-0.12%, Als 0.008-0.030, N 0.0050-0.0010%, Cr 0.15-0.28%, and the rest is Fe and inevitable impurity elements. By controlling the content of V, Al and N elements, and adopting the composite heat treatment process of weak spraying + strong spraying, the wear resistance of the wheel and the strength matching of the rim are improved. However, the invention adopts V micro-alloying design, which belongs to micro-alloyed low-alloy steel, and the heat treatment process is complex.

[0005] For example, on September 27, 2019, a Chinese invention patent, a medium-carbon wheel steel and its heat treatment method and a wheel preparation method, with publication number CN 110284069 A, disclosed a steel composition of: C 0.48-0.52%, Si 0.20-0.40%, Mn 0.60-0.80%, P≤0.020%, S≤0.015%, Mo 0.09-0.12%, Cr 0.15-0.30%, and the rest is Fe and unavoidable impurity elements. It can significantly improve the strength of the wheel rim under the premise of basically equivalent rim toughness level. However, this invention uses high Mo content design, unless the feed weight is significantly increased, there is a risk of non-pearlite layer. SUMMARY

[0006] The purpose of the present application is to provide a medium-carbon vanadium-containing railway wheel steel, a wheel and a wheel production method for optimizing ferrite content and distribution. By strictly limiting the chemical composition of the wheel steel and optimizing the heat treatment system, the cooling speed in a specific depth range inside the rim is accurately controlled, the precipitation of ferrite is effectively inhibited, the morphology and distribution are improved, the pearlite interlamellar spacing is refined, and the mechanical properties and wear resistance are superior to conventional ER7 wheels, improving the wear resistance of the wheel in the middle and later stages of service, and meeting the user's usage requirements.

[0007] The specific technical solutions of the present application are as follows:

[0008] The present application discloses a medium-carbon vanadium-containing railway wheel steel for optimizing ferrite content and distribution, which comprises the following components by mass percentage:

[0009] C 0.49-0.52%, Si 0.20-0.50%, Mn 0.60-0.80%, Cr 0.22-0.30%, Ni 0.10-0.40%, Mo 0.03-0.08%, Al 0.020-0.030%, V 0.02-0.08%, P≤0.020%, S≤0.015%, and the rest is Fe and unavoidable impurity elements.

[0010] In the composition of the medium-carbon vanadium-containing railway wheel steel for optimizing ferrite content and distribution,

[0011] 0.28%≤Cr+Mo≤0.35%.

[0012] In the composition of the medium-carbon vanadium-containing railway wheel steel for optimizing ferrite content and distribution, Ti≤0.003%, Al 0.012-0.018%, N(70-100)×10 -4 %.

[0013] Cr, Mo are important elements for improving hardenability of steel, appropriate addition can improve the stability of supercooled austenite, reduce the transformation temperature, increase the supercooling degree, thereby effectively inhibit the precipitation of ferrite, also has the effect of refining pearlite interlamellar spacing. If the content of Cr+Mo is too high, the volume fraction of ferrite is significantly reduced, which leads to the significant increase of strength level, and has adverse effects on impact toughness and fracture toughness; if the content of Cr+Mo is too low, the effect of inhibiting ferrite precipitation is not obvious. Therefore, the upper and lower limits of Cr and Mo content are limited in the application.

[0014] Al is the most important deoxidizer in steel, Al exists in steel in the form of acid-soluble aluminum Als and insoluble aluminum; Als corresponds to alloying elements in steel, and insoluble aluminum forms alumina inclusions, the application limits Al and Als, and the whole and part purposes are to control the cleanliness of steel and ensure the degree of alloying. Als dissolved in the matrix can combine with N to form AlN second phase, due to its good thermal stability, it pins the grain boundary during hot working and has good effect of refining grains. However, when the content of Al is lower than 0.020%, the driving force for AlN precipitation is insufficient, and when it is higher than 0.030%, Al2O3 brittle inclusions are easily formed, therefore, the range of Al is determined as 0.020-0.030%, and the range of Als is determined as 0.012-0.018%.

[0015] N effectively combines with Als in wheel steel to form AlN particles with good thermal stability, which are segregated on the grain boundary and play a role in pinning the grain boundary during hot working. In theory, the higher the content of N, the greater the driving force for AlN particle precipitation, the more the number of AlN particles, the smaller the size of AlN particles, and the more uniform the distribution, but considering the stability of N control process during steelmaking, the content of nitrogen in the application is determined as (70-100) × 10 -4 %.

[0016] Because Ti and Al are both nitride forming elements, for carbon steel composition system, strict control of the content of Ti can avoid the competition with Al, thereby ensuring the effective combination of Als and N, promoting the formation of AlN particles, so as to achieve the effect of refining grains. The refinement of grains is beneficial to improve the uniformity of ferrite distribution, and can also coordinate the strength and toughness matching of the wheel. Therefore, the upper limit of Ti is limited in the application according to the current steelmaking process level.

[0017] Ni is an austenite forming element, which can promote the austenitizing process, and its main function is to refine the grain, improve the toughness of the matrix structure, obtain fine pearlite interlamellar spacing, and also has a good strengthening effect on ferrite. The use of Ni and Cr can further improve the strength and toughness of the internal structure of the wheel rim. However, when the content of Ni is more than 0.40%, the iron oxide scale of the steel billet is not easy to be removed during hot working of the wheel steel, and the risk of foreign matter folding is generated. Therefore, the range of Ni is determined as 0.10-0.40%.

[0018] V is a strong carbonitride forming element, which can form second phase particles such as interstitial VC, V4C3 and nitrogen-rich V(C, N) in the steel, has the effects of grain refinement and precipitation strengthening, and a small amount of solid-soluted V can also refine the pearlite interlamellar spacing. V is a very superior micro-alloying element for regulating the structure and improving the performance. However, V is also a ferrite forming element, which is beneficial to improve the formation driving force of ferrite. A large amount of V will lead to ferrite precipitation. Based on the purpose of the present application, the range of V is determined as 0.02-0.08%.

[0019] The medium-carbon vanadium-containing railway wheel steel for optimizing the ferrite content and distribution described above is produced through the following processes: electric furnace melting, LF furnace refining, RH vacuum treatment, round billet continuous casting and slow cooling treatment.

[0020] The present application provides a kind of wheel, which is produced by the medium-carbon vanadium-containing railway wheel steel for optimizing the ferrite content and distribution described above.

[0021] The microstructure of the wheel in room temperature state is pearlite + a small amount of ferrite, and the volume fraction of ferrite at a distance of 25-40 mm from the tread is <10%; the ferrite morphology is discontinuously network distributed along the grain boundary; the volume fraction of ferrite increases with the increase of the depth from the tread, and the specific change relationship is that the incremental gradient of the volume fraction of ferrite at a distance of 25-40 mm from the tread with the increase of the depth from the tread is 0.13%-0.16% / mm, i.e. the volume fraction of ferrite increases by 0.13%-0.16% with the increase of 1 mm of the depth from the tread. The incremental gradient of the volume fraction of ferrite at the corresponding depth of the wheel rim produced by the traditional process of similar composition is 0.35%-0.48% / mm. The average value of the ferrite width of the wheel is 1.5-2.5 μm, and the maximum value is 3-4 μm. Compared with the wheel produced by the traditional process of similar composition, the average value and the maximum value of the ferrite width in the structure of the wheel are reduced by ≥55% and ≥50%, respectively. In the microstructure of the wheel in room temperature state, the pearlite interlamellar spacing is 160-190 nm, and the average grain size is ≥7.5 grade.

[0022] The rim part of the wheel has a yield strength of 550-590 MPa, a tensile strength of 880-930 MPa, an elongation after fracture of greater than or equal to 17.0%, a room temperature impact energy KU5 single value of greater than or equal to 28.0 J, a -20 DEG C impact energy KV2 single value of greater than or equal to 16.0 J, and a -40 DEG C impact energy KV2 single value of greater than or equal to 12.0 J; the hardness at a distance of 25 mm from the tread is greater than or equal to 280 HB, and the hardness at a distance of 40 mm from the tread is greater than or equal to 265 HB; the spoke part of the wheel has a tensile strength of 730-770 MPa, and an elongation after fracture of greater than or equal to 20.0%.

[0023] The application provides a wheel production method, which uses the medium-carbon vanadium railway wheel steel with the optimized ferrite content and distribution to produce the wheel.

[0024] The application provides a wheel production method, which comprises the following steps:

[0025] S1: a rough wheel formed by rolling is loaded into a heating furnace, heated and kept, and fully austenitized;

[0026] S2: the rough wheel obtained in step S1 is cooled in a horizontal quenching table by using a tread large-flow spray quenching method, and the rough wheel rotates during the spray quenching process;

[0027] S3: the rough wheel obtained in step S2 is tempered;

[0028] S4: the rough wheel obtained in step S3 is processed to obtain a finished wheel.

[0029] In step S1, the heating and keeping refer to heating to Ac3+(70-110) DEG C, which is 20-30 DEG C higher than the conventional soaking temperature; the higher soaking temperature can improve the uniformity of the original austenite grains, delay the transformation of the supercooled austenite, thereby obtaining higher stability during the cooling phase change, and being beneficial to obtaining larger supercooling degree, and providing an initial condition for inhibiting the precipitation of ferrite. However, the soaking temperature cannot be too high, otherwise the grains will grow and coarsen, which is not conducive to the performance of the wheel.

[0030] In step S1, the total heating time is 2.5-3 h, and the specific time is determined according to the loading amount, the material distribution method, the actual condition of the heating furnace and other factors, but the keeping time in the uniform temperature section is not less than 1 h.

[0031] In step S2, the tread large-flow spray quenching method refers to spraying the tread of the wheel with continuous large-flow circulating water, the total water flow of the quenching table is 110-140 tons per hour, there are six box-type spray guns uniformly distributed along the circumferential direction, the water flow of each spray gun is equal, and the total time of the spray quenching process is 200-350 s.

[0032] Further, the distance of 20-50mm deep from the tread surface is the inside of the rim, and the cooling speed at 25mm deep from the tread surface in the rim inside is controlled to be 1.5-1.8℃ / s, and the cooling speed at 40mm deep is controlled to be 0.8-1.0℃ / s in step S2.

[0033] The specific control cooling speed of the rim inside is executed according to the following formula:

[0034] v=[88.9xC 1 / 2 +53.5xMn+52.7x(Cr+1.2xMo)+10.4xAl+23.6xV] / h 1.33 ;

[0035] In the formula, v is the control cooling speed at the depth h of the rim inside, unit ℃ / s, the absolute value of the deviation of the actual control v from the calculated value is ≤0.1℃ / s; h is the depth from the tread surface, unit mm, 20mm≤h≤50mm; the index value of each element = the content of the element in the steel x 100.

[0036] To realize the cooling rate effect at the depth (20-50mm) from the tread surface (the inside of the rim), on the one hand, the spray quenching process in step S2 is divided into two stages, the duration of the first stage accounts for 3 / 5-2 / 3 of the total time of the spray quenching process, the total water flow is 110≤total water flow≤120 tons per hour, the water outlet speed is 4-6m / s, and the water flow and the tread surface maintain an inclination angle of 30-35°, which ensures that the water flow completely covers the wheel tread without splashing, and the angular speed of the wheel rotation is 55-65° / s; the total water flow in the second stage is controlled to be 120<total water flow≤140 tons per hour, the water outlet speed is 6-8m / s, the water flow and the tread surface maintain an inclination angle of 40-45°, and the angular speed of the wheel rotation is 70-80° / s. On the other hand, since the quenching pool is generally located outside the workshop, it is an open circulation system, and the water temperature sprayed to the wheel tread through various pipelines is generally high, such as in summer, the water temperature will be higher, and the refrigeration system is started to control the water temperature of the water used for spray quenching to be ≤10℃. Through the incremental cooling capacity of the two-stage cooling and the lower water temperature, the decrease of the cooling speed caused by the large thickness of the rim is offset, so as to enhance the cooling speed in the inside of the rim, inhibit the precipitation of ferrite, and improve the morphology and distribution thereof.

[0037] In step S3, the tempering treatment temperature is 470-500℃, and the tempering time is 4-6h.

[0038] Under laboratory conditions, compared with the wheels produced by the traditional process with similar composition, the wear resistance of the wheel rim material of the wheel of the present application is increased by ≥20%.

[0039] The wheel tread surface is sprayed, and due to the large rim section thickness, a large radial cooling gradient is caused. Correspondingly, the microstructure characteristics of the rim also present a gradient change from the surface to the inside, that is, the ferrite volume fraction and the pearlite interlamellar spacing gradually increase with the increase of the rim depth. However, ferrite is a plastic soft phase, and more ferrite and coarser pearlite interlamellar spacing significantly reduce the hardness of the wheel, damage the wear resistance of the wheel in the middle and later stages of service, and are not conducive to the service stability of the wheel in the whole life cycle, and affect the performance of the wheel in the middle and later stages of service. Therefore, precise microstructure control and strict strength and toughness matching pose higher challenges to the prior art, and the organization-performance relationship of the ER7 wheel must be re-coordinated from the aspects of material and process.

[0040] Compared with the prior art, the present application realizes the precise control of the cooling speed in the specific depth range inside the rim and strengthens the cooling effect inside the rim only by adjusting and combining the chemical elements of the wheel steel and optimizing the heat treatment system, effectively inhibits the precipitation of ferrite, so that the ferrite volume fraction at a position 25-40 mm away from the tread surface is less than 10%, and also improves the morphology and distribution of ferrite, so that the ferrite is discontinuously distributed along the grain boundaries, the ferrite volume fraction increasing gradient at a position 25-40 mm away from the tread surface inside the rim is 0.13%-0.16% / mm, the average value of the ferrite width is 1.5-2.5 mu m, and the maximum value is 3-4 mu m. The synergistic optimization of the composition and the process improves the stability of the supercooled austenite, reduces the transformation temperature of the pearlite-ferrite, increases the supercooling degree, obtains finer pearlite interlamellar spacing, optimizes the microstructure state of the wheel at room temperature, and ensures the strength and toughness matching of the wheel. Due to the reduction of the plastic soft phase ferrite, the wheel with the optimized ferrite content and morphological distribution is beneficial to improving the wear resistance in the middle and later stages of service and improving the service stability of the wheel in the whole life cycle. Moreover, the method is economical, does not affect the normal production rhythm, and is easy to implement. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The temperature drop curves of the wheels of Example 1 and Comparative Example 1 during the spray quenching cooling process at positions 25 and 40 mm away from the tread surface;

[0042] Figure 2 The ferrite volume fraction distribution of the wheel rims of Example 1 and Comparative Example 1 in the depth range of 25-40 mm away from the tread surface;

[0043] Figure 3 The microstructure of the wheel rim of Example 1 at a position 40 mm away from the tread surface;

[0044] Figure 4 The microstructure of the wheel rim of Comparative Example 1 at a position 40 mm away from the tread surface;

[0045] Figure 5Sample location and sample size for rolling contact wear test of the wheel rim of Example 1 and Comparative Example 1 under laboratory conditions;

[0046] Figure 6 Comparison of the weight loss after 10 million revolutions of the wheel rim samples of Example 1 and Comparative Example 1 under laboratory conditions;

[0047] Figure 7 Ferrite volume fraction distribution of the wheel rim of Example 2 and Comparative Example 2 at the depth range of 25-40 mm from the tread surface;

[0048] Figure 8 Microstructure of the wheel rim of Example 2 at the depth of 40 mm from the tread surface;

[0049] Figure 9 Microstructure of the wheel rim of Comparative Example 2 at the depth of 40 mm from the tread surface;

[0050] Figure 10 Temperature drop curve of the wheel of Example 3 and Comparative Example 3 during spray quenching at the depth of 25 and 40 mm from the tread surface;

[0051] Figure 11 Ferrite volume fraction distribution of the wheel rim of Example 3 and Comparative Example 3 at the depth range of 25-40 mm from the tread surface;

[0052] Figure 12 Microstructure of the wheel rim of Example 3 at the depth of 40 mm from the tread surface;

[0053] Figure 13 Microstructure of the wheel rim of Comparative Example 3 at the depth of 40 mm from the tread surface;

[0054] Figure 14 Original austenite grain level of the wheel of Example 3 (average 9.0 level);

[0055] Figure 15 Original austenite grain level of the wheel of Comparative Example 3 (average 8.0 level). DETAILED DESCRIPTION

[0056] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0057] Example 1-Example 3

[0058] A kind of composition of medium-carbon vanadium-containing railway wheel steel for optimizing ferrite content and distribution, see table 1, the balance not shown in table 1 is Fe and inevitable impurities.

[0059] Comparative example 1-comparative example 5

[0060] A kind of wheel steel, see table 1, the balance not shown in table 1 is Fe and inevitable impurities.

[0061] Table 1 main chemical components (wt%) of wheel of example and comparative example

[0062] Element C Si Mn P S Cr Mo Cr+Mo Example 1 0.49 0.21 0.63 0.011 0.008 0.23 0.05 0.28 Comparative Example 1 0.50 0.22 0.65 0.011 0.009 0.17 0.05 0.22 Example 2 0.50 0.34 0.75 0.010 0.009 0.25 0.03 0.28 Comparative Example 2 0.50 0.32 0.73 0.012 0.011 0.18 0.04 0.22 Example 3 0.52 0.38 0.80 0.010 0.007 0.28 0.07 0.35 Comparative Example 3 0.51 0.40 0.79 0.008 0.008 0.21 0.03 0.24 Comparative Example 4 0.49 0.20 0.64 0.010 0.008 0.23 0.05 0.28 Comparative Example 5 0.52 0.36 0.79 0.012 0.006 0.27 0.07 0.34

[0063] (Continued table 1)

[0064]

[0065] The wheel steel in example 1-example 3 and comparative example 1-comparative example 5 is prepared by the processes of electric furnace melting→LF furnace refining→RH vacuum treatment→round billet continuous casting→slow cooling treatment.

[0066] The wheel steel of example 1 is used to produce wheel, specifically including the following steps:

[0067] S1: blanking and rolling to obtain a blank wheel with an outer diameter of 940 mm, the blank wheel is loaded into a ring heating furnace, and is gradually heated to 890±10℃ (the soaking target temperature is 890℃), and is kept for 1h, to fully austenitize;

[0068] S2: the blank wheel is transferred to a horizontal quenching table by mechanical hand after furnace discharge, and is cooled by tread high-flow spray quenching, the total water flow of quenching table is 110-140 tons per hour, there are 6 box-type spray guns uniformly distributed along the circumference, the water flow of each spray gun is equal, the spray quenching is carried out in two stages, and the wheel rotates at a certain speed during the spray quenching. The specific cooling system is as follows: the total time of spray quenching is 200s, the first stage is controlled to last for 150s, the total water flow is 110≤total water flow≤120 tons per hour, the water flow speed is 4m / s, and the water flow and tread surface maintain an inclination angle of 30°, to ensure that the water flow completely covers the tread of the wheel without splashing, and the angular velocity of wheel rotation is 55° / s; the total water flow of the second stage is controlled to be 120<total water flow≤140 tons per hour, the water flow speed is 6m / s, the water flow and tread surface maintain an inclination angle of 40°, and the angular velocity of wheel rotation is 70° / s. In addition, if in summer, the refrigeration system needs to be started, and the water temperature is controlled to be ≤10℃. The temperature during the spray quenching and cooling of the wheel is recorded by embedding thermocouples. In engineering, the average temperature drop speed in the range of 800-500℃ is taken as the effective cooling speed, if the cooling time is short and does not drop to 500℃, the temperature data at the end of cooling is taken for calculation. For example Figure 1As shown, the actual cooling speed at the depth of 25 mm in the wheel rim can reach 1.58 ℃ / s, and the cooling speed at the depth of 40 mm can reach 0.91 ℃ / s, and the absolute deviation of the cooling speed v at the depths of 25 mm and 45 mm from the theoretical calculation value of 1.55 ℃ / s and 0.83 ℃ / s is less than 0.1 ℃ / s, and compared with the comparative example 1, the wheel rim of the wheel of the example 1 still has a higher cooling speed at a deep position.

[0069] S3: After the end of the spray quenching, the wheel is transferred to the annular tempering furnace by the chain plate bed for tempering treatment, and the tempering soaking temperature is 500 ℃, and the time length is 4 h.

[0070] S4: After the end of the tempering, the wheel is machined and treaded to obtain a finished wheel with an outer diameter of 920 mm.

[0071] The wheel is produced by using the wheel steel of the comparative example 1, and specifically includes the following steps:

[0072] S1: The blank wheel with an outer diameter of 940 mm is loaded into the annular heating furnace, and is gradually heated to 860±10 ℃ (the soaking target temperature is 860 ℃), which is 30 ℃ lower than that of the example 1, and is kept for 1 h to fully austenitize.

[0073] S2: The blank wheel is transferred to the horizontal quenching table by the mechanical hand after being discharged from the furnace, and is cooled by using the tread continuous spray quenching mode, which is not divided into two stages, the total time of the spray quenching process is 200 s, the wheel rotates at an angular speed of 55° / s during the spray quenching process, the total water flow of the quenching table is 110-120 tons per hour, there are six box-type spray guns uniformly distributed along the circumferential direction, the water flow of each spray gun is equal, the water speed is 5 m / s, but no control measures are taken for the quenching water temperature, and the actually measured water temperature is 22 ℃.

[0074] S3: After the end of the spray quenching, the wheel is tempered, and the tempering system is the same as that of the example 1.

[0075] S4: After the end of the tempering, the wheel is machined and treaded to obtain a finished wheel with an outer diameter of 920 mm.

[0076] The ferrite volume fraction distribution of the wheel rim of the example 1 and the comparative example 1 at the depth range of 25-40 mm from the tread is shown in Figure 2 As can be seen, the ferrite volume fraction of the wheel rim of the example 1 at the same depth is obviously lower than that of the wheel of the comparative example 1, and the ferrite volume fraction of the wheel rim of the example 1 increases gently with the depth, and the growth rate is also obviously lower than that of the wheel of the comparative example 1. Taking the increase amount of the unit wheel rim depth as the ferrite volume fraction change gradient, the ferrite volume fraction increase gradient of the wheel rim of the example 1 at the depth of 25-40 mm is 0.14% / mm, and the ferrite volume fraction increase gradient of the wheel rim of the comparative example 1 at the corresponding depth is 0.43% / mm.

[0077] The saturation picric acid deep etching was used to corrode the metallographic sample, and then the ferrite volume fraction in the structure was extracted by the "gray + binary" method under the optical microscope, and the ferrite width was measured by professional software. As shown in the table, the ferrite volume fraction of the wheel of Example 1 and Comparative Example 1 at 40 mm from the tread is 9.7±0.2%, which meets the design requirement of less than 10%, and the ferrite morphology is discontinuous network distribution along the grain boundary, while the ferrite volume fraction of the wheel of Comparative Example 1 is 16.1±0.3%, and the ferrite morphology is discontinuous network distribution or strip block distribution along the grain boundary. The maximum value, average value and minimum value of the ferrite width of the wheel of Example 1 are 3.42, 1.9 and 0.84 μm (sample size 50), respectively, and the maximum value, average value and minimum value of the ferrite width of the wheel of Comparative Example 1 are 7.64, 4.65 and 2.26 μm (sample size 50), respectively, compared with Comparative Example 1, the maximum value and average value of the ferrite width in the structure of the wheel of Example 1 are reduced by ≥55% and ≥59%, respectively. Figures 3-4

[0078] The average actual grain size of the wheel rims of Example 1 and Comparative Example 1 is equivalent, both of which are 7.5 grade. In the depth range of 25-40 mm from the tread, the pearlite interlamellar spacing of the wheel of Example 1 is 178-189 nm, and the average pearlite interlamellar spacing is 184 nm; while the pearlite interlamellar spacing of the wheel of Comparative Example 1 is 194-216 nm, and the average pearlite interlamellar spacing is 209 nm.

[0079] According to DIN EN 13262-2020 "Railway applications-Wheelsets and bogies-Wheels-Product requirements", tensile test samples were taken at the corresponding positions of the finished wheel rim and web, and tensile test was carried out according to GB / T 228.1 "Metallic materials-tensile test-Part 1:room temperature test methods". According to DIN EN 13262-2020 "Railway applications-Wheelsets and bogies-Wheels-Product requirements", Charpy impact samples were taken at three specified positions of the finished wheel rim, and Charpy pendulum impact test was carried out at room temperature, -20℃ and -40℃ according to GB / T 229 "Metallic materials-Charpy pendulum impact test method". The tensile mechanical properties of the wheel rims and webs of Example 1 and Comparative Example 1, the hardness of the wheel rim cross section, and the series temperature impact performance of the wheel rim are shown in Tables 2-4. It can be seen that, compared with the wheel of Comparative Example 1, the wheel of Example 1 has higher strength and toughness matching, which is related to the optimization of the structure parameters such as the refinement of the pearlite interlamellar spacing and the reduction of the ferrite volume fraction.

[0080] Table 2 Tensile mechanical properties of the wheels of the examples and comparative examples

[0081]

[0082] ​Table 3 Rim cross-section hardness of the wheels of the embodiment and the comparative example

[0083]

[0084]

[0085] Table 4 Series temperature shock performance of wheel rims of the embodiment and the comparative example

[0086]

[0087] like Figure 5 As shown, main specimens were taken from 10, 25, and 40 mm below the wheel tread in Example 1 and Comparative Example 1, and accompanying specimens were taken from a U71MnG rail. Rolling contact wear tests were conducted on a wheel-rail simulator. The tests were set at an initial contact compressive stress of 1100 MPa, a specimen rotation speed of 1500 rpm, a slip ratio of 0.75%, and air cooling. The total number of revolutions was 500,000. Three replicates were run for each test, and the average value was used to evaluate wear resistance.

[0088] The change of specimen wear loss weight with rim depth is as follows Figure 6 As shown, the wear loss increases with increasing rim depth. At the same rim depth, the wear loss of the wheel material of Example 1 is significantly lower than that of the wheel material of Comparative Example 1, with the lowest reduction exceeding 22%. The wear loss of the material at 25 mm decreases by over 30%. Furthermore, it can be seen that the wear performance of the wheel material of Example 1 is more uniform across the entire wear range, with the wear loss varying almost linearly with rim depth. This is beneficial for improving the lifecycle of the wheel, especially its service stability during the mid-to-late stages of service.

[0089] The method for producing wheels using the medium-carbon vanadium-containing railway wheel steel with optimized ferrite content and distribution described in Example 2 is similar to that in Example 1. The differences are:

[0090] S1: The target temperature for soaking is 870℃ and the temperature is kept at this temperature for 1.25h.

[0091] S2: The total time of the spray quenching process is 270s. The duration of the first stage is controlled to be 180s, the water outlet speed is 5m / s, the spray angle is 35°, and the wheel rotation angular velocity is 60° / s. The water outlet speed of the second stage is controlled to be 7m / s, the spray angle is 45°, and the wheel rotation angular velocity is 75° / s.

[0092] S3: Tempering temperature is 480℃, duration is 5h.

[0093] S4: Refer to Example 1.

[0094] The method for producing the wheel using the wheel steel of Comparative Example 2 was carried out according to the specific steps of Comparative Example 1. The difference is that:

[0095] S1: The target temperature of soaking was 850℃, which was 20℃ lower than that of Example 2, and the holding time was 1.25h.

[0096] S2: The total time of spray quenching was 250s, the water outlet speed was 6m / s, the wheel rotation angular velocity was 60° / s, and the measured water temperature was 26℃.

[0097] S3: The tempering soaking temperature was 480℃, and the time was 5h.

[0098] S4: Refer to Comparative Example 1.

[0099] The ferrite volume fraction distribution of the wheel rim of Example 2 and Comparative Example 2 in the depth range of 25-40mm from the tread surface is shown in Figure 7 It can be seen that the ferrite volume fraction of the wheel rim of Example 2 at the same depth is significantly lower than that of Comparative Example 2, and the ferrite volume fraction of the wheel rim of Example 2 increases gently with the depth, and the growth rate is also significantly lower than that of Comparative Example 2. Taking the increase of unit rim depth as the ferrite volume fraction change gradient, the ferrite volume fraction increase gradient of the wheel rim of Example 2 in the depth range of 25-40mm is 0.14% / mm, while the ferrite volume fraction increase gradient of the wheel rim of Comparative Example 2 in the corresponding depth is 0.45% / mm.

[0100] The ferrite volume fraction of the wheel rim of Example 2 and Comparative Example 2 at the depth of 40mm from the tread surface is shown in Figures 8-9 The ferrite volume fraction of Example 2 wheel is 9.6±0.2%, which meets the design requirement of less than 10%, and the ferrite morphology is discontinuous network distribution along the grain boundary, while the ferrite volume fraction of Comparative Example 2 wheel is 15.8±0.4%, and the ferrite morphology is discontinuous network distribution or block distribution along the grain boundary. The maximum value, average value and minimum value of ferrite width of Example 2 wheel are 3.52, 1.83 and 0.83μm respectively (sample size 50), and the maximum value, average value and minimum value of ferrite width of Comparative Example 2 wheel are 8.04, 4.76 and 2.34μm respectively (sample size 50), compared with Comparative Example 2, the maximum value and average value of ferrite width in the microstructure of Example 2 wheel are reduced by ≥56% and ≥61% respectively.

[0101] The average actual grain size of the wheel rim of Example 2 is 8.0, and that of Comparative Example 2 is 7.5. In the depth range of 25-40mm from the tread surface, the pearlite interlamellar spacing of Example 2 wheel is 171-182nm, and the average pearlite interlamellar spacing is 177nm; while the pearlite interlamellar spacing of Comparative Example 2 wheel is 186-202nm, and the average pearlite interlamellar spacing is 194nm.

[0102] The rim and web tensile mechanical properties, the rim section hardness, and the rim series temperature impact performance of the wheel of Example 1 and Comparative Example 1 were tested, and the results are shown in Tables 2-4. It can be seen that the wheel of Example 2 has higher strength and toughness than the wheel of Comparative Example 2.

[0103] The rolling contact wear test of the wheel of Example 1 and Comparative Example 1 was performed on a wheel-rail simulation tester. The results show that the wear loss weight of the sample at a depth of 10, 25, and 40 mm from the tread surface of the wheel of Example 2 is 0.38±0.02, 0.44±0.03, and 0.53±0.02 g, respectively, while the wear loss weight of the sample at the corresponding depths of the wheel of Comparative Example 2 is 0.50±0.02, 0.71±0.03, and 0.82±0.03 g, respectively. At the same depth of the rim, the wear loss weight of the material of the wheel of Example 2 is significantly lower than that of the wheel of Comparative Example 2, with a minimum reduction of more than 24%.

[0104] The method for producing a wheel using the medium-carbon vanadium-containing railway wheel steel with an optimized ferrite content and distribution described in Example 3 was used, and the specific steps refer to Example 1. The difference is that:

[0105] S1: The target temperature of soaking is 860℃, and the holding time is 1.5h.

[0106] S2: The total time of the spray quenching process is 350s, the first stage is controlled to have a duration of 220s, a water outlet speed of 6m / s, and a wheel rotation angular velocity of 65° / s, and the second stage is controlled to have a water outlet speed of 8m / s and a wheel rotation angular velocity of 80° / s. During the spray quenching process, the temperature is recorded by embedding a thermocouple. As shown in Figure 10 The actual cooling speed at a depth of 25mm in the rim can reach 1.75℃ / s, and the cooling speed at a depth of 40mm can reach 0.98℃ / s, and the absolute value of the deviation from the theoretical calculation value of the cooling speed v at depths of 25mm and 45mm, i.e., 1.77℃ / s and 0.95℃ / s, is less than 0.1℃ / s. Compared with Comparative Example 3, the wheel of Example 3 still has a higher cooling speed at a deep depth of the rim.

[0107] S3: The tempering soaking temperature is 470℃, and the time is 6h.

[0108] S4: Refer to Example 1.

[0109] The method for producing a wheel using the wheel steel described in Comparative Example 3 was used, and the specific steps refer to Comparative Example 1. The difference is that:

[0110] S1: The target temperature of soaking is 840℃, which is 20℃ lower than that of Example 3, and the holding time is 1.5h.

[0111] S2: The total time of the spray quenching process was 300 s, the water outlet speed was 7 m / s, the wheel rotation angular velocity was 65° / s, and the measured water temperature was 17℃.

[0112] S3: The tempering soaking temperature was 470℃, and the time length was 6 h.

[0113] S4: Refer to Comparative Example 1.

[0114] The ferrite volume fraction distribution of the wheel rim of the Example 3 wheel in the depth range of 25-40 mm from the tread surface is shown in Figure 11 It can be seen that the ferrite volume fraction of the wheel rim of the Example 3 wheel at the same depth is significantly lower than that of the Comparative Example 3 wheel, and the ferrite volume fraction of the wheel rim of the Example 3 wheel increases gently with the depth, and the growth rate is also significantly lower than that of the Comparative Example 3 wheel. Taking the increase of the unit rim depth as the ferrite volume fraction change gradient, the ferrite volume fraction increase gradient of the Example 3 wheel rim at 25-40 mm is 0.14% / mm, and the ferrite volume fraction increase gradient of the Comparative Example 3 wheel rim at the corresponding depth is 0.38% / mm.

[0115] The ferrite volume fraction of the Example 3 wheel and the Comparative Example 3 wheel in the rim at a depth of 40 mm from the tread surface is shown in Figures 12-13 The ferrite volume fraction of the Example 3 wheel is 8.9±0.2%, which meets the design requirement of less than 10%, and the ferrite morphology is discontinuous network distribution along the grain boundary, while the ferrite volume fraction of the Comparative Example 3 wheel is 14.3±0.4%, and the ferrite morphology is discontinuous network distribution or strip block distribution along the grain boundary. The maximum value, average value and minimum value of the ferrite width of the Example 3 wheel are 3.48, 1.82 and 0.92 μm (sample size 50), respectively, and the maximum value, average value and minimum value of the ferrite width of the Comparative Example 3 wheel are 8.14, 4.56 and 2.29 μm (sample size 50), respectively. Compared with the Comparative Example 3, the maximum value and average value of the ferrite width in the structure of the Example 3 wheel are reduced by ≥57% and ≥60%, respectively.

[0116] The average actual grain size of the rim of the Example 3 wheel is 9.0, and the rim of the Comparative Example 3 wheel is 8.0. In the depth range of 25-40 mm from the tread surface, the pearlite interlamellar spacing of the Example 3 wheel is 162-173 nm, and the average pearlite interlamellar spacing is 168 nm; while the pearlite interlamellar spacing of the Comparative Example 3 wheel is 177-193 nm, and the average pearlite interlamellar spacing is 186 nm.

[0117] The rim and web tensile mechanical properties, rim hardness, and rim series temperature impact performance tests were carried out on the rim and web of the Comparative Example 1 and the Comparative Example 3, and the results are shown in Tables 2-4. It can be seen that compared with the Comparative Example 3 wheel, the Example 3 wheel has higher strength and toughness matching.

[0118] The rolling contact wear tests were carried out on the wheel-rail simulation tester for the reference example 1 and the comparative example 1. The results show that the wear loss weight of the samples of the reference example 3 wheel at 10, 25, 40 mm from the tread surface are 0.37±0.03, 0.40±0.03, 0.47±0.02 g respectively, while the wear loss weight of the samples of the comparative example 3 wheel at the corresponding depths are 0.50±0.02, 0.72±0.02, 0.79±0.03 g respectively. At the same rim depth, the wear loss weight of the reference example 3 wheel material is significantly lower than that of the comparative example 3 wheel material, with the lowest reduction rate being more than 26%.

[0119] The wheel steel of the comparative example 4 was used to produce the wheel, and the specific steps and parameters were performed according to the comparative example 1. The chemical composition of the comparative example 4 wheel is very close to that of the reference example 1.

[0120] The ferrite volume fraction gradient of the comparative example 4 wheel increases by 0.35% per mm at 25-40 mm from the inside of the rim. At 40 mm from the tread surface, the ferrite volume fraction of the comparative example 4 wheel is 14.6±0.3%, which is much higher than 10%. The maximum, average and minimum ferrite width are 6.52, 4.08, 1.78 μm (sample size 50) respectively. The tensile mechanical properties of the rim and web of the comparative example 4 wheel, the rim hardness and the series temperature impact performance of the rim are shown in Tables 2-4. Compared with the reference example 1 wheel, the strength and toughness of the comparative example 4 wheel are both lower. The wear loss weight of the samples of the comparative example 4 wheel at 10, 25, 40 mm from the tread surface are 0.49±0.04, 0.71±0.02, 0.78±0.03 g respectively, and the wear loss weight of the comparative example 4 wheel material at the same rim depth is significantly higher than that of the reference example 1 wheel material.

[0121] The wheel steel of the comparative example 5 was used to produce the wheel, and the specific steps and parameters were performed according to the comparative example 3. The chemical composition of the comparative example 5 wheel is very close to that of the reference example 3.

[0122] The ferrite volume fraction gradient of the wheel rim of the comparative example 5 at 25-40 mm is 0.30% / mm. The ferrite volume fraction of the wheel rim of the comparative example 5 at 40 mm from the tread surface is 12.9±0.2%. The maximum value, the average value and the minimum value of the ferrite width are 5.82, 3.07, 1.44 μm (the sample amount is 50). The tensile mechanical properties of the wheel rim and the spoke of the comparative example 5, the rim hardness and the series temperature impact performance of the wheel rim are shown in Tables 2-4. Compared with the wheel of the example 3, the strength and the toughness of the wheel of the comparative example 5 are both lower. The wear loss weight of the samples of the comparative example 5 at 10, 25, 40 mm from the tread surface is 0.42±0.03, 0.63±0.02, 0.71±0.04 g respectively, and the wear loss weight of the material of the comparative example 5 at the same depth of the wheel rim is obviously higher than that of the example 3.

[0123] According to the material properties of the medium-carbon vanadium-containing steel and the larger thickness (generally 70-120 mm) of the wheel rim, under the working condition of the tread spray quenching, the cooling speed gradually decreases from the surface to the inside, and correspondingly, the microstructure features of the wheel rim also gradually change from the surface to the inside. With the increase of the depth from the surface of the wheel rim, the ferrite volume fraction and the pearlite interlamellar spacing gradually increase. Especially, when the cooling speed inside the wheel rim is below 0.5 ℃ / s, the slow cooling speed promotes the more complete precipitation of ferrite, and the ferrite volume fraction is higher. The present application realizes the accurate control of the cooling speed in the specific depth range inside the wheel rim by strictly limiting the chemical composition of the wheel steel and optimizing the heat treatment system, improves the stability of the supercooled austenite, reduces the transformation temperature of the pearlite-ferrite, increases the supercooling degree, thereby effectively inhibits the precipitation of ferrite, realizes the accurate control of the ferrite volume fraction inside the wheel rim, and improves the morphology and distribution of ferrite. At the same time, it is also beneficial to obtain finer pearlite interlamellar spacing, and beneficial to obtain good mechanical properties and wear resistance.

[0124] In the present application, on the one hand, the contents of Cr and Mo are limited to improve the stability of the supercooled austenite, reduce the transformation temperature, increase the supercooling degree, thereby effectively inhibit the precipitation of ferrite, and also have the effect of refining the pearlite interlamellar spacing; on the other hand, by strictly controlling the contents of Ti, Als and N, the effective combination of Als and N is ensured, the formation of AlN particles is promoted, and the effect of refining the grains is achieved. Figures 14-15As shown, compared with the wheel of Comparative Example 3, the wheel of Example 3 still has finer austenite grains even at a higher heating temperature, and the refinement of the grains is beneficial to improve the uniformity of the distribution of ferrite. On the other hand, the higher austenite soaking temperature, the two-stage cooling with the increasing cooling capacity, and the lower water temperature can offset the decrease of the cooling rate caused by the large thickness of the rim, so as to enhance the cooling rate inside the rim, inhibit the precipitation of ferrite, and improve the morphology and distribution of the ferrite. Through the synergistic optimization of the composition and process, the precise control of the ferrite inside the wheel rim is realized, and it is also beneficial to obtain finer pearlite interlamellar spacing.

[0125] The above description of the embodiments is to enable those skilled in the art to understand and use the invention. Those skilled in the art can easily make various modifications to the embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the invention is not limited to the above-described embodiments, and improvements and modifications made by those skilled in the art within the scope of the invention without departing from the scope of the invention should be within the protection scope of the invention.

Claims

1. A medium carbon vanadium railway wheel steel with optimized ferrite content and distribution, characterized in that: The medium carbon vanadium-containing railway wheel steel with optimized ferrite content and distribution includes the following components in percentage by mass: C 0.49~0.52%, Si 0.20~0.50%, Mn 0.60~0.80%, Cr 0.22~0.30%, Ni 0.10~0.40%, Mo 0.03~0.08%, Al 0.020~0.030%, V 0.02~0.08%, P≤0.020%, S≤0.015%, 0.28%≤Cr+Mo≤0.35%, Ti≤0.003%, Als 0.012~0.018%, N (70~100)×10 -4 %, and the rest are Fe and inevitable impurity elements.

2. A wheel, characterized in that: The steel is produced by using the medium-carbon vanadium-containing railway wheel steel with optimized ferrite content and distribution as described in claim 1.

3. The wheel according to claim 2, characterized in that The microstructure of the wheel at room temperature is pearlite + a small amount of ferrite, the volume fraction of ferrite at 25 to 40 mm from the tread is less than 10%, the ferrite morphology is discontinuously networked along the grain boundaries, the ferrite volume fraction at 25 to 40 mm from the tread increases with the depth from the tread at a gradient of 0.13% to 0.16% / mm, the average ferrite width is 1.5 to 2.5 μm, and the maximum is 3 to 4 μm; in the microstructure of the wheel at room temperature, the pearlite plate spacing is 160 to 190 nm, and the average grain size is ≥ 7.

5.

4. The wheel according to claim 2 or 3, characterized in that The yield strength of the wheel rim is 550-590 MPa, the tensile strength is 880-930 MPa, and the elongation after fracture is ≥17.0%; the room temperature impact energy KU5 single value is ≥28.0 J, the -20°C impact energy KV2 single value is ≥16.0 J, and the -40°C impact energy KV2 single value is ≥12.0 J; the hardness at 25 mm from the tread is ≥280 HB, and the hardness at 40 mm from the tread is ≥265 HB; the tensile strength of the wheel spoke plate is 730-770 MPa; and the elongation after fracture is ≥20.0%.

5. A wheel production method according to any one of claims 2 to 4, characterized in that: The production method comprises the following steps: S1: The rolled blank wheel is placed into a heating furnace for heating and heat preservation to achieve full austenitization; S2: Cooling the wheel blank obtained in step S1 on a horizontal quenching table by using a high-flow spray quenching method on the tread, during which the wheel blank rotates; S3: Tempering the blank wheel obtained in step S2; S4: Processing the blank wheel obtained in step S3 to obtain a finished wheel.

6. The production method according to claim 5, characterized in that In step S1, the heating and heat preservation refers to heating to Ac3+(70-110)°C.

7. The production method according to claim 5, characterized in that In step S2, the tread high-flow spray quenching cooling method refers to the use of continuous high-flow circulating water to spray the wheel tread. The total water flow rate of the quenching table is 110 to 140 tons per hour. There are 6 box-type spray guns evenly distributed along the circumference. The water flow rate of each spray gun is equal. The total time of the spray quenching process is 200 to 350 seconds.

8. The production method according to claim 5, characterized in that In step S2, the cooling rate of the inner portion of the rim at a position 25 mm below the tread surface is controlled to be 1.5-1.8°C / s, and the cooling rate of the position 40 mm below the tread surface is controlled to be 0.8-1.0°C / s.

9. The production method according to claim 5, characterized in that The specific controlled cooling rate inside the rim is executed according to the following formula: v =[88.9×C 1 / 2 +53.5×Mn+52.7×(Cr+1.2×Mo)+10.4×Al+23.6×V] / h 1.33 ; Where, v is the inner depth of the rim h The controlled cooling rate at the position, unit is ℃ / s, the actual controlled v The absolute value of the deviation from the calculated value is ≤0.1℃ / s; h Depth below the tread surface, unit: mm, 20mm≤ h ≤50mm; the index value of each element = the content of the element in the steel × 100.

10. The production method according to claim 5, characterized in that The spray quenching process in step S2 is divided into two stages. The duration of the first stage is controlled to account for 3 / 5 to 2 / 3 of the total time of the spray quenching process, the total water flow rate is 110 ≤ total water flow rate ≤ 120 tons per hour, the water outlet speed is 4 to 6 m / s, and the water flow maintains an inclination angle of 30 to 35 degrees with the tread surface, and the wheel rotation angular velocity is 55 to 65 degrees / s; the total water flow rate of the second stage is controlled to be 120 < total water flow rate ≤ 140 tons per hour, the water outlet speed is 6 to 8 m / s, the water flow maintains an inclination angle of 40 to 45 degrees with the tread surface, and the wheel rotation angular velocity is 70 to 80 degrees / s; the water temperature of the water used for spray quenching is ≤ 10°C.

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