Micro-alloyed medium-carbon high-speed wheel with good comprehensive mechanical performance and heat treatment method and preparation method of micro-alloyed medium-carbon high-speed wheel

Abstract

The invention discloses a microalloyed medium-carbon high-speed wheel with good comprehensive mechanical performance and a heat treatment method and a preparation method of the microalloyed medium-carbon high-speed wheel. The microalloyed medium-carbon high-speed wheel comprises, by mass, 0.50%-0.55% of C, 0.30%-0.40% of Si, 0.70%-0.80% of Mn, 0.25%-0.35% of Cr, 0.03%-0.04% of Mo, 0.04%-0.12% of V, smaller than or equal to 0.002% of Ti, smaller than or equal to 0.020% of Al, 0.004%-0.010% of N and the balance Fe and inevitable impurity elements. On the basis that the content of C is not increased, the wheel obtains good toughness matching performance by regulating and controlling the content of Cr, Mo and V elements, and the wheel has high strength, high hardness, high impact toughness and high fracture toughness and has good use safety performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of wheel steel, and particularly relates to a microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties, a heat treatment method thereof, and a preparation method thereof. Background Art

[0002] As one of the key components of train operation, high-speed train wheels directly bear huge pressure and friction during high-speed operation. If there are quality problems or damages to the wheels, it will affect the speed, stability, safety, etc. of the train, and may even lead to accidents. Therefore, there are extremely high requirements for the wheel material, structure, performance, etc.

[0003] With the continuous speed increase of trains and the continuous expansion of the line layout, the service environment of wheels is more complex and changeable. Therefore, the requirements for wheel performance are getting higher and higher, especially for the safety and reliability of passenger car wheels. Traditional wheel materials can no longer meet the requirements. Therefore, various countries are actively exploring and researching alloy steel or microalloyed steel wheels to meet the needs of the development of the transportation industry.

[0004] The wheels of the in-service high-speed EMUs in China mainly adopt ER8 material wheels, which are medium-carbon non-alloyed steel wheels. Their tensile strength is 920 - 960 MPa, and the yield strength is about 570 - 630 MPa. Although they meet the requirements of the European standard EN13262 - 2020, problems such as wheel out-of-roundness, rapid wear, and low life have emerged during long-term service, affecting the safety and stability of train operation.

[0005] In addition, the European standard does not have clear requirements for the fracture toughness of ER8 wheels. However, the level of fracture toughness determines whether the wheels have good impact resistance and crack propagation resistance. Good fracture toughness can ensure that the wheels can maintain integrity when subjected to external force impact or stress concentration, delaying the occurrence of fracture. Therefore, fracture toughness is also an important index for evaluating the mechanical properties of high-speed wheels. Therefore, it is extremely necessary to design a preparation method for a microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties.

[0006] The patent with the publication number CN 111961963 A and the publication date of November 20, 2020 discloses a medium-carbon niobium-vanadium microalloyed high-speed wheel steel and a wheel preparation method. The composition is C: 0.52 - 0.56%, Si: 0.15 - 0.40%, Mn: 0.50 - 0.80%, P≤0.015%, S≤0.015%, Nb: 0.01 - 0.03%, V: 0.10 - 0.20%, and the rest are Fe and inevitable impurity elements. Although the strength and hardness levels of the wheels prepared by this method are more than 5% higher than those of ER8 wheels, and the contact fatigue resistance and wear resistance are also improved, the addition amounts of V and Nb alloys are relatively high, greatly increasing the smelting cost.

[0007] The patent with the publication number CN 116623098 A and the publication date of August 22, 2023 discloses a steel for passenger locomotive wheels applicable to alpine regions, its production method, the wheels and their production methods. The composition is C: 0.44 - 0.54%, Si: 0.40 - 0.65%, Mn: 0.80 - 1.2%, Cr: 0.15 - 0.30%, V: 0.08 - 0.15%, Al: 0.008 - 0.015%, P: 0.005 - 0.010%, S: 0.006 - 0.015%; T.O: ≤10 ppm, [H]: ≤1.5 ppm, [N]: 50 - 80 ppm, and the rest is Fe and inevitable impurity elements. Although the higher quenching temperature improves the strength, it increases the heat energy consumption and causes energy waste. At the same time, the higher quenching heating temperature results in lower impact toughness.

[0008] The patent with the publication number CN 114107823 A and the publication date of March 1, 2022 discloses a steel for high-speed wheels, its heat treatment method and the method for preparing high-speed wheels using the same. The composition is C 0.52 - 0.56%, Si 0.20 - 0.40%, Mn 0.60 - 0.90%, Cr 0.15 - 0.25, V 0.06 - 0.15, Nb 0.02 - 0.04%, P ≤ 0.015%, S ≤ 0.015%, Al 0.01 - 0.02%, W 0.3 - 0.6%, Mo 0.03 - 0.05%, N 60 - 80 ppm, and the balance is Fe and inevitable impurities. Although the impact toughness is relatively high, the tensile strength and yield strength need to be improved. Summary of the Invention

[0009] To solve the above technical problems, the present invention provides a microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties, which combines high strength, high hardness, high impact toughness and fracture toughness, and has good use safety performance.

[0010] The present invention also provides a heat treatment method and a preparation method for the microalloyed medium-carbon high-speed wheel. A stepwise cooling is carried out using an alkaline solution containing water glass with different concentrations to refine the pearlite lamellar spacing and improve the strength of the wheel.

[0011] The technical solutions adopted by the present invention are as follows:

[0012] A microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties, comprising the following components by mass percentage: C 0.50 - 0.55%, Si 0.30 - 0.40%, Mn 0.70 - 0.80%, Cr 0.25 - 0.35%, Mo 0.03 - 0.04%, V 0.04 - 0.12%, Ti ≤ 0.002%, Al ≤ 0.020%, N 0.004 - 0.010%, and the balance being Fe and unavoidable impurity elements.

[0013] The metallographic structure of the microalloyed medium-carbon high-speed wheel is fine pearlite + a small amount of ferrite; the grain size in the microstructure of the wear area is greater than or equal to grade 8.0, the volume fraction of ferrite is 7.0 - 8.0%, and the pearlite lamellar spacing is 120 - 145 nm.

[0014] The tensile strength of the rim of the microalloyed medium-carbon high-speed wheel is 975 - 1000 MPa, the yield strength is 660 - 685 MPa, and the elongation after fracture is ≥ 22.5%; the hardness at 5 mm from the tread of the rim is ≥ 290 HB, and the hardness at 35 mm from the tread is ≥ 270 HB; the impact energy at 20 °C is ≥ 25 J; the impact energy at -20 °C is ≥ 17 J; the fracture toughness is ≥ 60 MPa·m 1 / 2 。

[0015] The present invention also provides a heat treatment method for the microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties, and the heat treatment method comprises the following steps:

[0016] S1: Loading the rolled blank wheel into a heating furnace and heating and holding for a certain time;

[0017] S2: Taking out the wheel obtained in step S1 and transporting it to a quenching table, and performing spray quenching cooling on the tread in a step quenching manner. First, perform tread spray quenching with quenching liquid A for 120 - 150 s; then perform tread spray quenching with quenching liquid B for 150 - 180 s, ensuring that the surface temperature of the wheel tread is lower than 150 °C after the second-stage spray quenching, and the internal part of the rim is cooled to below 500 °C, and the pearlite structure transformation is completed;

[0018] S3: Flushing the tread of the wheel obtained in step S2 with water;

[0019] S4: Performing tempering treatment on the wheel obtained in step S3;

[0020] In step S2, both quenching liquid A and quenching liquid B are alkaline solutions containing water glass, and the concentration of water glass in quenching liquid A is greater than that in quenching liquid B.

[0021] In step S1, the heating and heat preservation are carried out at 860 - 880°C for 1.5 - 2 h. If the heating temperature is too high, the ferrite content will decrease and the grain size will be relatively large, resulting in a reduction in toughness. If the temperature is too low, the strength will be insufficient.

[0022] In step S2, the quenching liquid A is composed of the following substances by weight percentage: 10 - 13% NaCl, 10 - 13% Na2CO3, 18 - 21% water glass, 6 - 7% NaOH, and the balance is water.

[0023] In step S2, the quenching liquid B is composed of the following substances by weight percentage: 10 - 13% NaCl, 10 - 13% Na2CO3, 8 - 11% water glass, 6 - 7% NaOH, and the balance is water.

[0024] The use temperature of both the quenching liquid A and the quenching liquid B is 40 - 60°C.

[0025] In step S2, the wheel rotates self - by the roller of the quenching table, and the rotational speed of the roller is 40 - 60 revolutions per minute.

[0026] In step S3, the rinsing time is 20 - 30 s.

[0027] In step S4, the tempering temperature is 500 - 520°C and the tempering time is 4.0 - 4.5 h. If the tempering temperature is too high, it is easy to cause the pearlite to deform and fracture, resulting in the deterioration of the wheel performance.

[0028] The present invention also provides a preparation method of the micro - alloyed medium - carbon high - speed wheel with good comprehensive mechanical properties. The preparation method includes the following steps: steelmaking → round billet continuous casting → ingot cutting and blanking → pre - rolling heating → forging and rolling → stacking and slow cooling → heat treatment; the heat treatment is carried out by using the heat treatment method described in any one of claims 4 - 9.

[0029] In the micro - alloyed medium - carbon high - speed wheel provided by the present invention, the functions and controls of each component are as follows:

[0030] C: C is an austenite-forming element that can dissolve in the matrix or exist in the form of carbides, making a major contribution to the strength and hardness of the material. It is the most important component of wheel steel. On the one hand, we hope to increase the C content as much as possible within the possible range to reduce the wear of the wheel tread and extend the service life of the wheel. However, on the other hand, an increase in the C content will cause a sharp decline in the toughness and thermal fatigue resistance of the wheel steel, and network cementite is a structure that the wheel steel must absolutely avoid forming. Therefore, the C content of high-speed wheels needs to be controlled within the range of 0.4 - 0.7%. Comprehensive evaluation of the influence of the C content on the overall performance of the wheel steel within this composition range shows that the best performance matching can be obtained when the C content is between 0.50 - 0.60%. In this invention, the C content is designed according to 0.50 - 0.55%.

[0031] Si: From the relationship between the chemical composition and the A C1 , A C3 point, increasing the Si content helps to make it difficult for the wheel to undergo austenite phase transformation and martensite transformation during heating and cooling, improving the thermal damage resistance of the wheel material. However, too high Si will increase the thermal sensitivity and brittleness of the material. As long as the Si content in the wheel steel does not exceed 1%, the impact toughness of the steel will not be greatly damaged. In this invention, the Si content is designed according to 0.30 - 0.40%.

[0032] Mn: The main function of adding Mn to the wheel steel is to improve the strength and hardness of the wheel and enhance its wear resistance. Research shows that when the Mn content is higher than 1%, the impact toughness and processing performance of the wheel will deteriorate. In this invention, the Mn content is controlled within 0.70% - 0.80%.

[0033] Cr: Cr is a secondary contributing element to the solid solution strengthening of the wheel steel. Adding Cr makes the pearlite structure more stable, delays the rate of transformation from the original structure to austenitization to a certain extent, and fundamentally reduces the possibility of martensite phase transformation during the subsequent cooling process, thereby improving the anti-peeling performance of the wheel. In this invention, the Cr content is designed according to 0.25 - 0.35%.

[0034] Mo: The Mo element has the effect of refining grains, can improve the hardenability and thermal strength performance of the steel, and can ensure that the steel maintains sufficient strength and creep resistance at high temperatures; the Mo element can also stably improve the tempering stability, and can slow down the precipitation of carbide at the grain boundaries of the martensite plate matrix during the phase transformation process, thereby improving the impact toughness of the steel and enhancing the comprehensive performance. In this invention, the Mo content is designed according to 0.03 - 0.04%.

[0035] V: The V element can combine with N to form precipitates, playing a role in grain refinement. At the same time, it can combine with C, reduce the content of cementite in pearlite, and promote the precipitation of ferrite, thereby improving the strength and toughness matching performance of the steel. In this invention, the V content is designed according to 0.04 - 0.12%.

[0036] Element Al: As a deoxidizer in steel, Al can combine with N to form AlN, which can not only reduce the free nitrogen content in steel, but also refine austenite grains to a certain extent and improve toughness. However, too high Al content is likely to form alumina inclusions. In the steel of the present invention, the Al content is controlled within 0.020%. To ensure the effect of grain refinement, the N content in the steel of the present invention is controlled within 0.004 - 0.010%.

[0037] Ti: Ti is a strong carbide - forming element, which is likely to affect the precipitation of M(CN) in wheel steel. Moreover, Ti will also compete with Al in the steel for N to generate TiN, weakening the fine - grain strengthening effect of AlN and affecting the final properties of the steel. In the steel of the present invention, the Ti content is controlled within 0.002%.

[0038] P, S: P and S are impurity elements. In the steel of the present invention, the P and S contents are controlled within 0.015%.

[0039] To achieve good strength - toughness matching, in the present invention, by increasing the content of Cr element to 0.25 - 0.35% and adding 0.03 - 0.04% of Mo element, the rate of transformation from the original structure to austenitization is delayed, the supercooling degree in the cooling phase transformation stage is increased, a relatively fine pearlite lamellar spacing is obtained, and the strength of the wheel is improved. The Mo element can also stably improve the tempering stability and slow down the precipitation of carbide at the grain boundaries of the martensite plate - like matrix during the phase transformation process, thereby improving the impact toughness of the steel. In the present invention, 0.04 - 0.12% of V element is added to the steel, which can not only refine grains by forming V(C, N), but also increase the content of grain - boundary ferrite. At the same time, in the present invention, the contents of Ti and Al in the steel are strictly controlled to promote the effective combination of Al and N to form the second - phase AlN, pin the grain boundaries, and effectively prevent the growth and coarsening of austenite grains, so as to have good toughness while obtaining high strength.

[0040] In the heat treatment method of the microalloyed medium-carbon high-speed wheel provided by the present invention, step quenching and cooling are carried out using an alkaline solution containing water glass with different concentrations. For the high-temperature region above 650°C, spray quenching is carried out using an alkaline solution containing 20% water glass, and the spray quenching time is 120 - 150 s. After the coolant is sprayed onto the hot wheel tread surface, a steam film composed of ductile water glass bubbles will be generated on the tread surface first. Therefore, the cooling rate of the wheel in this stage is relatively slow, and the tissue transformation is delayed, effectively avoiding the upper bainite region and reducing the generation of abnormal tissues. For the medium and low-temperature region below 650°C, spray quenching is carried out using an alkaline solution containing 10% water glass, and the spray quenching time is 150 - 180 s. In the temperature range of 650 - 550°C, due to the explosive action of NaOH, the steam film is quickly destroyed, accelerating the contact between the wheel and the coolant. At the same time, with the decrease in the water glass content, the cooling rate increases, which can significantly refine the pearlite lamellar spacing and thus improve the strength. As the spray quenching continues and the temperature enters the convection stage, since a water glass thin film covers the wheel tread surface and the water glass has a high viscosity, slow cooling is formed again, so that the solution has a relatively slow cooling rate at low temperatures, reducing the risk of deformation and cracking. In addition, the cooling capacity of the water glass solution is less affected by the ambient temperature than pure water, has higher stability, and is easier to control.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] By regulating the contents of Cr, Mo, and V elements and adopting the method of step spray quenching with alkaline solutions containing water glass with different concentrations during heat treatment, the wheel obtains good strength and toughness matching performance: the tensile strength of the rim is 975 - 1000 MPa, and the yield strength is 660 - 685 MPa; the hardness at 5 mm from the tread surface of the rim is ≥290 HB, and the hardness at 35 mm from the tread surface is ≥270 HB; the elongation after fracture is ≥22.5%; the single value and average value of the impact energy at 20°C are ≥25 J; the single value and average value of the impact energy at -20°C are ≥17 J; the single value and average value of the fracture toughness are ≥60 MPa·m1 / 2. The wheel made by the present invention can maintain the ferrite-pearlite tissue state of the original wheel without increasing the difficulty of wheel preparation. Description of the Drawings

[0043] Figure 1 is the original austenite grain of the wheel in Example 1;

[0044] Figure 2 is the original austenite grain of the wheel in Comparative Example 1;

[0045] Figure 3 is the original austenite grain of the wheel in Example 3;

[0046] Figure 4 is the original austenite grain of the wheel in Comparative Example 3;

[0047] Figure 5 Metallographic structure of the wheel in Example 1;

[0048] Figure 6 Metallographic structure of the wheel in Comparative Example 1;

[0049] Figure 7 Metallographic structure of the wheel in Example 3;

[0050] Figure 8 Metallographic structure of the wheel in Comparative Example 3;

[0051] Figure 9 Abnormal bainite structure of the wheel in Comparative Example 3;

[0052] Figure 10 Pearlite lamellar spacing of the wheel in Example 1;

[0053] Figure 11 Pearlite lamellar spacing of the wheel in Comparative Example 1;

[0054] Figure 12 Pearlite lamellar spacing of the wheel in Example 3;

[0055] Figure 13 Pearlite lamellar spacing of the wheel in Comparative Example 3. Detailed implementation manners

[0056] The present invention will be described in detail below in conjunction with the embodiments.

[0057] The chemical compositions of the wheels in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1.

[0058] Table 1 Main chemical components of the wheels in the examples and comparative examples (wt%)

[0059]

[0060]

[0061] The preparation processes of the wheels in Examples 1 to 3 and Comparative Examples 1 to 3 are all: electric furnace smelting → LF furnace refining → vacuum degassing (RH / VD) → round billet continuous casting → slow cooling treatment → ingot cutting and blanking → pre-rolling heating → forging and rolling → stacking and slow cooling → heat treatment.

[0062] In Examples 1 to 3 and Comparative Example 2, the composition of quenching liquid A used in the heat treatment quenching process is: 12% NaCl, 12% Na2CO3, 20% water glass, 7% NaOH, and the balance is water; the composition of quenching liquid B used is: 12% NaCl, 12% Na2CO3, 9% water glass, 6% NaOH, and the balance is water.

[0063] The heat treatment processes of the wheels in each example and comparative example are as follows:

[0064] Example 1

[0065] The heat treatment process of Example 1 includes "pre - heating before overall quenching → stepped surface spray quenching → overall tempering", and the specific operation steps are as follows:

[0066] S1: Cut and roll to obtain a blank wheel with an outer diameter of 915 mm, transfer the blank wheel into a heating furnace, heat it to 880 °C and hold for 2 h.

[0067] S2: Take out the wheel obtained in step S1 from the heating furnace and transfer it to the quenching table, and cool it by stepped surface spray quenching. First, use quenching liquid A for surface spray quenching of the tread, and the spray quenching time is 130 s. After the spraying ends, switch to quenching liquid B for surface spray quenching of the tread, and the time is 170 s. The spray quenching water pressure throughout the process is 0.08 Mpa. Ensure that the surface temperature of the wheel tread is lower than 150 °C and the inside of the rim is cooled to below 500 °C after the second - stage spray quenching, and the pearlite structure transformation is completed. During the cooling process, the wheel rotates with the roller of the quenching table, and the roller speed is 50 revolutions per minute;

[0068] S3: Spray - quench and rinse the tread of the wheel obtained in step S2 with normal - temperature water at 15 - 20 °C for 30 s;

[0069] S4: Transfer the wheel obtained in step S3 to a tempering furnace, set the tempering temperature to 520 °C, and the tempering duration to 4.5 h.

[0070] Comparative Example 1

[0071] The heat treatment process steps of Comparative Example 1 refer to Example 1. The compositions of the two are different, and Comparative Example 1 does not have the stepped quenching treatment in the S2 stage of Example 1. The specific operation steps are as follows:

[0072] S1: Load the blank wheel obtained by rolling into a heating furnace, heat it to 880 °C, and hold for 2 h.

[0073] S2: Take out the wheel obtained in step S1 from the heating furnace and transfer it to the quenching table by a manipulator, and cool it by continuous surface spray quenching. The quenching liquid is pure water at 15 - 20 °C, and the spray quenching time is 300 s. The spray quenching water pressure throughout the process is 0.08 Mpa.

[0074] S3: After the spray quenching ends, perform a tempering treatment, and the tempering regime is the same as that of Example 1.

[0075] The original austenite grain morphology of the wheels in Example 1 and Comparative Example 1 is as shown in Figure 1 、 2As shown, it can be seen that compared with the wheel of Comparative Example 1, the grains of the wheel of Example 1 are significantly finer and have better distribution uniformity, and the grain size is maintained at grade 8.0. This is mainly due to the fine grain strengthening effect of V(C, N). And these fine and uniform grain structures are the key to obtaining good strength-ductility matching.

[0076] The metallographic microstructures of the wheels of Example 1 and Comparative Example 1 are as Figure 5 , 6 shown, both are fine pearlite + a small amount of ferrite. The volume fraction of ferrite in the wheel of Example 1 is about 7.5%, and the volume fraction of ferrite in the wheel of Comparative Example 1 is about 5.1%. More ferrite is the key to obtaining high toughness. The size of a single ferrite block in the wheel of Example 1 is significantly larger than that of Comparative Example 1. The main way of increase is the extension along the long axis direction of the ferrite. The extension of the ferrite reduces the direct contact area between pearlite clusters, which can also improve toughness.

[0077] The pearlite lamellar spacing of the wheels of Example 1 and Comparative Example 1 is as Figure 10 , 11 shown. Among them, the pearlite lamellar spacing of the wheel of Example 1 is 124 - 143 nm, and the pearlite lamellar spacing of the wheel of Comparative Example 1 is 175 - 184 nm, with an obvious difference. The increase in the contents of Cr, Mo, and V and the realization of the "weak cooling + strong cooling" cooling effect through step quenching with water glass solutions of different concentrations are the reasons for the fine pearlite lamellar spacing obtained in Example 1 and an important guarantee for obtaining high hardness. In addition, obvious abnormal feathery upper bainite structures are generated at 10 mm below the tread of the wheel of Comparative Example 1, which is also one of the important factors causing poor mechanical properties of the wheel of Comparative Example 1, as Figure 9 shown.

[0078] According to BS EN 13262 "Railway applications - Wheelsets and bogies - Wheels - Product requirements", tensile test specimens, Charpy impact specimens, rim section hardness specimens, and fracture toughness compact tension specimens (6 pieces evenly distributed circumferentially) are taken at the corresponding positions of the rim and web of the finished wheel. Room temperature tensile tests and series temperature pendulum impact tests are carried out respectively in accordance with GB / T 228.1 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature" and GB / T 229 "Metallic materials - Charpy pendulum impact test method". The performance results are shown in Tables 3 - 4. Hardness tests and fracture toughness tests are carried out in accordance with GB / T 231.1 "Metallic materials - Brinell hardness test - Part 1: Test method" and GB / T 4161 - 2007 "Metallic materials - Plane strain fracture toughness KIC test method", and the results are shown in Table 5. It can be seen that compared with the wheel of Comparative Example 1, the wheel adopting the solution of the present invention can maintain good elongation, impact energy, and fracture toughness indexes while maintaining a relatively high level of rim strength and section hardness, and has a good strength-ductility matching effect.

[0079] Example 2, Comparative Example 2

[0080] The heat treatment processes of Example 2 and Comparative Example 2 are the same, but the chemical composition ratios of Cr, Mo, and V are different. The specific operation steps of the heat treatment include:

[0081] S1: Cut and roll to obtain a blank wheel with an outer diameter of 915 mm. Load the blank wheel into a heating furnace and gradually heat it to 860 °C and hold for 1.5 h.

[0082] S2: Take out the wheel obtained in step S1 from the heating furnace and transfer it to a quenching table. Cool it by means of stepped surface spraying quenching. First, perform surface spraying quenching with quenching liquid A for 150 s. After the spraying is completed, switch to quenching liquid B for surface spraying quenching for 150 s. The spraying water pressure throughout the process is 0.10 Mpa. Ensure that the surface temperature of the wheel tread is lower than 150 °C after the second-stage spraying quenching, and the inside of the rim is cooled below 500 °C, and the pearlite structure transformation is completed. During the cooling process, the wheel rotates with the roller of the quenching test bench, and the roller speed is 40 revolutions per minute;

[0083] S3: Spray and rinse the wheel tread obtained in step S2 with normal temperature water at 15 - 20 °C for 20 s;

[0084] S4: Transfer the wheel obtained in step S3 to a tempering furnace, load it into the tempering furnace, set the tempering temperature to 500 °C, and the tempering duration to 4.5 h.

[0085] Referring to Example 1 and Comparative Example 1, tensile tests at room temperature, series temperature pendulum impact tests, hardness tests, and fracture toughness tests were carried out on the wheels of Example 2 and Comparative Example 2. The relevant results are shown in Tables 2 - 5. Although the wheels of Comparative Example 2 were treated with the same heat treatment process as Example 2, there was a certain improvement in the abnormal structure situation compared with Comparative Example 1 and a certain increase in hardness, but the lack of the refinement effect of Cr, Mo, and V elements on the original austenite grains and pearlite lamellae resulted in lower comprehensive mechanical properties. Compared with the wheels of Comparative Example 2, the wheels prepared by the scheme of the present invention can maintain a high fracture toughness while obtaining a high hardness of the rim cross-section, and the strength and toughness are well matched.

[0086] Example 3

[0087] The specific operation steps of the heat treatment in Example 3 include:

[0088] S1: Cut and roll to obtain a blank wheel with an outer diameter of 915 mm. Load the blank wheel into a heating furnace and gradually heat it to 870 °C and hold for 1.5 h.

[0089] S2: Take out the wheel obtained in step S1 from the heating furnace and transfer it to the quenching table. Cool it by means of stepped spray quenching on the tread. First, perform tread spray quenching with quenching liquid A for 140 s. After the spraying is completed, switch to quenching liquid B for tread spray quenching for 170 s. The spray quenching water pressure throughout the process is 0.10 Mpa. Ensure that the surface temperature of the wheel tread is lower than 150 °C and the inside of the rim is cooled to below 500 °C after the second-stage spray quenching, and the pearlite structure transformation is completed. During the cooling process, the wheel rotates self-drivenly along with the roller of the quenching test bench, and the roller speed is 50 revolutions per minute;

[0090] S3: Spray quench and rinse the tread of the wheel obtained in step S2 with normal temperature water at 15 - 20 °C for 20 s;

[0091] S4: Transfer the wheel obtained in step S3 to the tempering furnace, put it into the tempering furnace, and set the tempering temperature to 520 °C and the tempering duration to 4.5 h.

[0092] Comparative Example 3

[0093] The difference between Comparative Example 3 and Example 3 is that Comparative Example 3 uses pure water spray quenching, and realizes the stepped quenching effect of "weak spray + strong spray" by adjusting the water pressure. The specific operation steps of heat treatment in Comparative Example 3 include:

[0094] S1: Obtain a blank wheel with an outer diameter of 915 mm by blanking and rolling. Load the blank wheel into the heating furnace and gradually heat it up to 870 °C and hold for 1.5 h.

[0095] S2: Take out the wheel obtained in step S1 from the heating furnace and transfer it to the quenching table. Cool it by means of stepped spray quenching on the tread. First, perform tread spray quenching with pure water at 15 - 20 °C, the spray quenching water pressure is 0.06 Mpa, and the spray quenching time is 100 s. After the spraying is completed, switch to continue tread spray quenching with a water pressure of 0.14 Mpa for 180 s. Ensure that the surface temperature of the wheel tread is lower than 150 °C and the inside of the rim is cooled to below 500 °C after the second-stage spray quenching, and the pearlite structure transformation is completed. During the cooling process, the wheel rotates self-drivenly along with the roller of the quenching test bench, and the roller speed is 50 revolutions per minute;

[0096] S3: Transfer the wheel obtained in step S2 to the tempering furnace, put it into the tempering furnace, and set the tempering temperature to 520 °C and the tempering duration to 4.5 h.

[0097] Referring to Example 1 and Comparative Example 1, tensile tests at room temperature, series temperature Charpy impact tests, hardness tests, and fracture toughness tests were carried out on the wheels of Example 3 and Comparative Example 3. The relevant results are shown in Tables 2 to 5. Although the wheels of Comparative Example 3 were subjected to stepped cooling with different water pressures, pure water is greatly affected by the ambient temperature, its cooling capacity is severely affected and difficult to control, so the comprehensive mechanical properties are not good. Compared with the wheels of Comparative Example 3, the wheels prepared by the scheme of the present invention can maintain a high fracture toughness while obtaining a higher hardness of the rim cross-section, and the strength and toughness are well matched.

[0098] Table 2 Heat treatment processes of wheels in examples and comparative examples

[0099]

[0100] Table 3 Tensile mechanical properties of wheels in examples and comparative examples

[0101]

[0102]

[0103] Table 4 Series temperature impact properties of rims of wheels in examples and comparative examples

[0104]

[0105] Table 5 Rim cross-section hardness and fracture toughness of wheels in examples and comparative examples

[0106]

[0107]

[0108] It can be seen from the above data that the tensile properties, impact toughness, fracture toughness, and cross-section hardness of the wheels in Examples 1 to 3 controlled according to the present invention are all good. Compared with Comparative Examples 1 and 3, in Examples 1 to 3, the tread surface was slowly cooled with a high-concentration water glass solution in the high-temperature zone, suppressing or eliminating the bainite structure near the surface layer of the wheel tread. In the medium- and low-temperature zones, the tread surface was spray quenched with a low-concentration water glass solution for rapid cooling. The faster the cooling rate, the greater the supercooling degree, which can provide more energy to increase the interface formed by ferrite and cementite. The finer the pearlite lamellar spacing, the higher the strength.

[0109] Compared with Comparative Example 2, the wheels in Examples 1 to 3 have higher Cr and Mo contents, which delay the rate of transformation of the original structure to austenitization and increase the supercooling degree in the cooling phase transformation. Therefore, the pearlite lamellar spacing is smaller, and thus the strength of the wheels is higher. At the same time, the microalloying element V added to the wheels in Examples 1 to 3 brings about the effects of fine grain strengthening and precipitation strengthening, so that the grain size is relatively small and the distribution uniformity is good, thereby improving the strength and toughness of the wheels.

[0110] The above detailed description of a microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties, its heat treatment method and preparation method with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be enumerated within the defined scope. Therefore, changes and modifications without departing from the general concept of the present invention shall fall within the protection scope of the present invention.

Claims

1. A microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties, characterized in that, It includes the following components by mass percentage: C 0.50 - 0.55%, Si 0.30 - 0.40%, Mn 0.70 - 0.80%, Cr 0.25 - 0.35%, Mo 0.03 - 0.04%, V 0.04 - 0.12%, Ti ≤ 0.002%, Al ≤ 0.020%, N 0.004 - 0.010%, and the balance is Fe and inevitable impurity elements.

2. The microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties according to claim 1, wherein, The metallographic structure of the microalloyed medium-carbon high-speed wheel is fine pearlite + a small amount of ferrite; the grain size in the microstructure of the wear area is greater than or equal to grade 8.0, the volume fraction of ferrite is 7.0 - 8.0%, and the pearlite lamellar spacing is 120 - 145 nm.

3. The microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties according to claim 1, characterized in that, The tensile strength of the rim of the microalloyed medium-carbon high-speed wheel is 975 - 1000 MPa, the yield strength is 660 - 685 MPa, and the elongation after fracture is ≥ 22.5%; the hardness at 5 mm from the tread of the rim is ≥ 290 HB, and the hardness at 35 mm from the tread is ≥ 270 HB; the impact energy at 20 °C is ≥ 25 J; the impact energy at -20 °C is ≥ 17 J; Fracture toughness ≥ 60 MPa·m 1 / 2 .

4. The heat treatment method of the microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties according to any one of claims 1-3, characterized in that, The heat treatment method includes the following steps: S1: Load the rolled blank wheel into a heating furnace and heat and hold for a certain time. S2: Take out the wheel obtained in step S1 and transfer it to a quenching table, and spray-quench and cool the tread in a stepped quenching manner. First, spray-quench the tread with quenching liquid A for 120 - 150 s; then spray-quench the tread with quenching liquid B for 150 - 180 s. S3: Rinse the tread of the wheel obtained in step S2 with water. S4: Temper the wheel obtained in step S3. In step S2, both quenching liquid A and quenching liquid B are alkaline solutions containing water glass, and the concentration of water glass in quenching liquid A is greater than that in quenching liquid B.

5. The heat treatment method according to claim 4, characterized in that, In step S1, the heating and holding is to heat and hold at 860 - 880 °C for 1.5 - 2 h.

6. The heat treatment method according to claim 4, wherein In step S2, quenching liquid A is composed of the following substances by weight percentage: NaCl 10 - 13%, Na2CO3 10 - 13%, water glass 20%, NaOH 5%, and the balance is water.

7. The heat treatment method according to claim 4, characterized in that, In step S2, quenching liquid B is composed of the following substances by weight percentage: NaCl 10 - 13%, Na2CO3 10 - 13%, water glass 10%, NaOH 5%, and the balance is water.

8. The heat treatment method according to claim 4, characterized in that, In step S2, the wheel rotates with the roller of the quenching table, and the rotational speed of the roller is 40 - 60 revolutions per minute.

9. The heat treatment method according to claim 4, wherein In step S4, the tempering temperature is 500 - 520 °C, and the tempering time is 4.0 - 4.5 h.

10. The preparation method of the microalloyed medium-carbon high-speed wheel with good comprehensive mechanical properties according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: steelmaking → round billet continuous casting → ingot cutting and blanking → pre-rolling heating → forging and rolling → stacking and slow cooling → heat treatment; the heat treatment is carried out by using the heat treatment method described in any one of claims 4 - 9.

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