A high-speed wheel with high strength and toughness matching suitable for low-temperature environment and a heat treatment method and a preparation method thereof

Abstract

The application discloses a high-strength and high-toughness matching high-speed wheel suitable for a low-temperature environment and a heat treatment method and a preparation method thereof. The heat treatment method comprises the following steps: heating a wheel formed by rolling to 850-870 DEG C, slowly cooling to 810-830 DEG C in a furnace, and then naturally cooling in air; heating the wheel to 810-830 DEG C again and keeping the temperature; taking out the wheel and transferring to a quenching platform, spraying hot water on the tread of the wheel to make the metal within 5 mm below the tread to be cooled to below 500 DEG C at a cooling speed of <= 4 DEG C / s, and then spraying cold water on the tread of the wheel to make the metal in the inner rim of the wheel to be quickly cooled to below 500 DEG C at a cooling speed of 3-6 DEG C / s; and tempering the wheel at 500-520 DEG C for 4.0-4.5 h. The high-speed wheel has high strength, high hardness and high low-temperature impact toughness, thereby ensuring that the high-speed wheel has good use safety performance under a low-temperature service condition.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wheel steel, and particularly relates to a high-strength and high-toughness matching high-speed wheel suitable for a low-temperature environment and a heat treatment method and a preparation method thereof. BACKGROUND

[0002] Currently, the high-speed wheels in service in China are mainly ER8 material wheels in the European standard. The wheels of this grade can maintain good service performance under short-range, single-line, and stable climate. However, China has a vast territory and a large geographical span, including high-temperature and hot regions and low-temperature and cold regions, and the application service environment and conditions of high-speed rails are various. In recent years, the operation of high-speed trains in cold regions has gradually become popular, and therefore, the reliability problem of wheel service at low temperatures must be addressed.

[0003] The influence of a low-temperature environment on high-speed railways mainly manifests in the following aspects:

[0004] 1. At low temperatures, the strength of the material will decrease significantly, and deformation and brittle fracture are more likely to occur, which will seriously affect the stability of train travel.

[0005] 2. At low temperatures, the toughness of the material will also decrease, and cracking is more likely to occur, which will seriously affect the service life of the wheel and the safety of train travel.

[0006] Therefore, it is extremely necessary to design and manufacture high-speed wheels with high strength and toughness matching suitable for low-temperature service environments.

[0007] A Chinese patent with the publication number CN 116623098 A and the publication date of August 22, 2023 discloses a steel suitable for high-cold-region passenger locomotive wheels and a production method, a wheel and a production method, the composition 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: ≤10ppm, [H]: ≤1.5ppm, [N]: 50-80ppm, and the rest is Fe and inevitable impurity elements. The heat treatment method adopted is: first heating and holding: the heating section temperature is 880-910℃, the soaking section temperature is 840-880℃, and the total heating time is 2.5-3.0h, wherein the soaking section time is 0.5-1.0h; then weak cooling, the near-surface layer metal of the rim tread is cooled at a cooling speed of 0.2℃ / s-0.4℃ / s, then strong cooling, the cooling rate of the rim is 6-10℃ / s, and finally tempering. Although the higher quenching temperature improves the strength, it increases the heat energy consumption and causes energy waste, and the higher quenching heating temperature leads to lower impact toughness. Moreover, the use of micro-alloy element V increases the smelting cost.

[0008] A kind of high-speed wheel steel and its heat treatment method and the method for preparing high-speed wheel using it are disclosed in Chinese patent with publication number CN 114107823 A and publication date of March 1, 2022, composition 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 60-80ppm, the balance is Fe and inevitable impurities.Although the impact toughness is higher, but the tensile strength and yield strength need to be improved, in addition, a small amount of micro-alloying elements V, Nb increases certain strength and toughness, but increases the smelting cost.

[0009] A kind of medium-carbon wheel steel suitable for high-cold region freight car and the method for producing wheel using it are disclosed in Chinese patent with publication number CN 111270154 A and publication date of June 12, 2020, composition C 0.55-0.63%, Si 0.25-0.45%, Mn 0.65-0.90%, Cr≤0.30%, V≤0.10%, Nb 0.02-0.04%, P≤0.030%, S≤0.025%, Ni≤0.30%, N 0.0050-0.0100%, the balance is Fe and inevitable impurities.The production method includes cyclic quenching and tempering process, although cyclic quenching makes tensile strength and yield strength improve to a certain extent, but it is mainly due to high carbon and carbide precipitation strengthening effect of vanadium, and the addition of V increases the smelting cost to a certain extent, secondly, this patent does not test-20℃, -40℃ impact performance, which cannot ensure that the low temperature toughness is qualified.

[0010] A kind of high-carbon wheel steel and its heat treatment method and the method for preparing wheel using it are disclosed in Chinese patent with publication number CN 110616374 A and publication date of December 27, 2019, composition C 0.60-0.70%, Si≤0.60%, Mn 0.70-0.90%, P≤0.015%, S≤0.015%, Als≤0.035%, N 50-150ppm, the balance is Fe and inevitable impurities.Its heat treatment method includes the following steps: normalizing + quenching + tempering process, although the obvious strength and hardness are improved by adopting pre-normalizing, but continuous high temperature normalizing for a long time not only increases the heat consumption, but also may cause grain coarsening and thus deteriorate the performance, and the performance data also show that the impact toughness needs to be improved, and this patent does not test-40℃ impact performance, which cannot ensure that the impact toughness of wheel in-40℃ extremely cold area is still qualified. SUMMARY

[0011] To solve the above technical problems, the application provides a high-speed wheel with high strength and toughness matching suitable for low-temperature environment, and a heat treatment method and a preparation method thereof.

[0012] The technical scheme adopted by the application is as follows:

[0013] The heat treatment method of the high-speed wheel with high strength and toughness matching suitable for low-temperature environment comprises the following steps:

[0014] S1: heating the wheel formed by rolling to 850-870 DEG C, then slowly cooling to 810-830 DEG C in the furnace and keeping warm, and then naturally cooling in air; the heating at 850 DEG C-870 DEG C is to ensure full transformation of austenite, and the low-temperature soaking at 810-830 DEG C can avoid the deterioration of the performance of the wheel caused by the growth and coarsening of the grains at high temperature for a long time;

[0015] S2: heating the wheel obtained in step S1 to 810-830 DEG C again and keeping warm; too high temperature will lead to a decrease in the content of ferrite and a large grain size, thereby causing a decrease in toughness, and too low temperature will lead to insufficient strength and difficulty in stable control on site;

[0016] S3: taking out the wheel obtained in step S2 to a quenching platform, first spraying the tread of the wheel with hot water to make the tread below 5 mm at a cooling rate of ≤4 DEG C / s to below 500 DEG C, and then spraying the tread of the wheel with cold water to make the metal inside the rim rapidly cool to below 500 DEG C at a cooling rate of 3-6 DEG C / s, so that the transformation of the pearlite structure is completed;

[0017] S4: tempering the wheel obtained in step S3 at 500-520 DEG C for 4.0-4.5 h; too high tempering temperature is easy to cause deformation and fracture of the pearlite, thereby leading to deterioration of the strength performance of the wheel.

[0018] In step S1, the total heating time of the wheel is 2.0-3.0 h, and the keeping warm time at 810-830 DEG C is 1.0-1.5 h.

[0019] In step S2, the total heating time of the wheel is 2.0-3.0 h, and the keeping warm time at 810-830 DEG C is 1.0-1.5 h.

[0020] In step S2, the surface temperature of the tread of the wheel is lower than 150 DEG C after the second-stage spray quenching is completed.

[0021] In step S3, the temperature of the hot water is 55-60 DEG C, and the spraying time is 60-80s; the temperature of the cold water is 5-10 DEG C, and the spraying time is 190-210s.

[0022] In step S3, the wheel rotates with the quenching trolley roller, and the roller rotating speed is 40-60r / min.

[0023] The application further provides a high-speed wheel with high strength and toughness matching suitable for a low-temperature environment, which is obtained by adopting the heat treatment method.

[0024] The steel composition of the high-speed wheel is as follows in terms of weight percentage: C 0.50-0.56%, Si 0.30-1.10%, Mn 0.70-0.80%, Cr 0.20-0.30%, Al≤0.020%, P≤0.015%, S≤0.015%, Ti≤0.002%, and the rest is Fe and inevitable impurity elements.

[0025] The metallographic structure of the high-speed wheel is ferrite and pearlite; the grain size in the microstructure of the area from the wheel tread surface to 35mm below the tread surface is greater than or equal to 8.0 grade, the ferrite volume fraction is 8.5%-10.5%, and the pearlite interlamellar spacing is 115-127nm.

[0026] The rim Rm of the high-speed wheel is 1100-1120MPa, the R P0.2 is 720-735MPa, and the A is 19.0-21%; the hardness of the wheel rim at a position 5mm away from the tread surface is greater than or equal to 310HB, the hardness at a position 35mm away from the tread surface is greater than or equal to 280HB; the K Q is greater than or equal to 90MPa.m 1 / 2 , the average value is greater than or equal to 94MPa.m 1 / 2 ; the KV at-20 DEG C is greater than or equal to 19J, the average value is greater than or equal to 21.0J; the KV at-40 DEG C is greater than or equal to 12J, the average value is greater than or equal to 13.5J; the KU at-60 DEG C is greater than or equal to 90MPa.m 1 / 2 , the average value is greater than or equal to 100MPa.m 1 / 2 .

[0027] The application further provides a preparation method of the high-speed wheel with high strength and toughness matching suitable for a low-temperature environment, which comprises the following steps: electric furnace smelting, LF furnace refining, vacuum degassing, round billet continuous casting, slow cooling treatment, cutting ingot blanking, pre-rolling heating, forging and rolling, drop and slow cooling, heat treatment, processing, and finished product detection.

[0028] The heat treatment method for the high-strength and high-toughness matching high-speed wheel in a low-temperature environment provided by the application increases a pretreatment before quenching, and the essence is complete austenitization and pro-eutectoid transformation, and the phenomenon of coarse grains in the wheel rim in a rolled state, fine grains at the edge, and extremely uneven size distribution is improved through one recrystallization, and 840-860 DEG C heating is adopted to ensure that the complete austenite transformation zone is reached, and the transformation is not insufficient due to the difference between the furnace temperature and the steel temperature and the difference between the furnace temperature and the instrument temperature during heating, and then slow cooling to 810-830 DEG C is adopted for soaking, and fine and uniformly distributed austenite grains can be obtained, which lays a foundation for obtaining fine pearlite interlamellar spacing after quenching and cooling, and it is necessary to note that the soaking temperature cannot be lower than 800 DEG C, the temperature is close to Ac3, and it is not conducive to the composition homogenization and the on-site production regulation stability, the heating temperature for quenching is appropriately reduced to increase the ferrite content, and thus high plasticity and toughness are realized, and different water temperatures are adopted for staged quenching, hot water is sprayed on the tread in the high-temperature zone for slow cooling, and the bainite structure in the near surface layer of the wheel tread is inhibited or eliminated, cold water is sprayed on the tread in the medium and low temperature zone for rapid cooling, the faster the cooling speed is, the greater the supercooling degree is, more energy can be provided to increase the interface formed by ferrite and cementite, the pearlite interlamellar spacing is finer, and the strength is higher.

[0029] In the high-strength and high-toughness matching high-speed wheel in a low-temperature environment provided by the application, the functions and controls of the components are as follows.

[0030] C: C is an austenite forming element, can be dissolved in the matrix or exist in the form of carbide, plays a major role in the strength and hardness of the material, and is the most important component of the wheel steel. On the one hand, we want to increase the C content as much as possible within the possible range to reduce the wear of the wheel tread and prolong the service life of the wheel; but on the other hand, the increase of the C content will cause the toughness and the thermal fatigue resistance of the wheel steel to decrease sharply, and the network cementite is an organization that the wheel steel absolutely avoids forming, therefore the C content of the high-speed wheel needs to be controlled in the range of 0.4-0.7, and the comprehensive evaluation of the influence of the C content on the overall performance of the wheel steel in the component range shows that the best performance matching can be obtained when the C content is between 0.50-0.56%, and the C content is designed to be 0.50-0.56% in the application.

[0031] Si: From the relationship between the chemical composition and the Ac1 and Ac3 points, the increase of the Si content is helpful to make the wheel not easy to have austenite transformation and martensite transformation when heated and cooled, and improve the thermal damage resistance of the wheel material, but too high Si will increase the thermal sensitivity and brittleness of the material; and the decrease of the Si content can improve the toughness of the steel, because Si can promote the generation of Laves phase in the steel, and as long as the Si content in the wheel steel is not more than 1%, the impact toughness of the steel will not be greatly lost.

[0032] Mn: Mn is added in the wheel steel mainly to improve the strength and hardness of the wheel and the wear resistance of the wheel. Research shows that when the content of Mn is higher than 1%, the impact toughness and the processing performance of the wheel will be deteriorated, so the content of Mn is controlled to be 0.70% to 0.80%.

[0033] Cr: Cr is a secondary contribution element of solid solution strengthening of the wheel steel, the addition of Cr makes the pearlite structure more stable, delays the rate of the original structure to austenite transformation to a certain extent, fundamentally reduces the possibility of martensite phase transition in the subsequent cooling process, thereby improving the anti-peeling performance of the wheel. The content of Cr is designed to be 0.20 to 0.30% in the application.

[0034] Al element: Al is a deoxidizer in steel, can combine with N to form AlN, not only can reduce the free nitrogen content in steel, but also can refine austenite grains to a certain extent, improve toughness, but too high Al content is easy to form aluminum oxide inclusions, so the content of Al in the steel is controlled to be less than 0.020%.

[0035] Ti: Ti is a strong carbide forming element, which is easy to affect the precipitation of M(CN) in the wheel steel, and Ti also competes with Al in steel for N to form TiN, which weakens the fine-grain strengthening effect of AlN and affects the final performance of the steel, so the content of Ti in the steel is controlled to be less than 0.002%.

[0036] P and S: P and S are impurity elements, so the content of P and S in the steel is controlled to be less than 0.015%.

[0037] Compared with the prior art, the application has the following beneficial effects:

[0038] The wheel prepared by the application innovatively proposes a new product manufacturing scheme on the basis of the ER8 wheel material, without increasing the content of C, by adjusting the content of Si and Cr elements, pretreatment before quenching and different water temperature grading quenching, the wheel obtains good strength and toughness matching performance, especially excellent low temperature impact toughness at-40℃, wherein: the rim Rm is 1100 to 1120 MPa, R P0.2 720 to 735 MPa, A19.0 to 21%; the hardness of the wheel rim at 5mm from the tread is greater than or equal to 310HB, and the hardness at 35mm from the tread is greater than or equal to 280HB; K Q single value is greater than or equal to 90 MPa.m 1 / 2 , the average value is greater than or equal to 94 MPa.m 1 / 2 ; -20℃KV single value is greater than or equal to 19J, the average value is greater than or equal to 21.0J; -40℃KV single value is greater than or equal to 12J, the average value is greater than or equal to 13.5J; -60℃KU is greater than or equal to 90 MPa.m 1 / 2 , the average value is greater than or equal to 100 MPa.m 1 / 2, ensure that the wheel has good use safety performance under low temperature service condition. In addition, the wheel prepared by the application can keep the original ferrite-pearlite organization state of the wheel, reduce or eliminate the non-pearlite organization in the near surface layer of the wheel tread, reduce the cutting processing amount, and does not increase the difficulty of wheel preparation. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The original austenite grain of the wheel of Example 1.

[0040] Figure 2 The original austenite grain of the wheel of Comparative Example 1.

[0041] Figure 3 The original austenite grain of the wheel of Comparative Example 3. Figure 4 The metallographic structure of the wheel of Example 1.

[0042] Figure 5 The metallographic structure of the wheel of Comparative Example 1.

[0043] Figure 6 The metallographic structure of the wheel of Comparative Example 3.

[0044] Figure 7 The pearlite lamellar spacing of the wheel of Example 1.

[0045] Figure 8 The pearlite lamellar spacing of the wheel of Comparative Example 1.

[0046] Figure 9 The pearlite lamellar spacing of the wheel of Comparative Example 3.

[0047] Figure 10 The original austenite grain of the wheel of Example 2.

[0048] Figure 11 The original austenite grain of the wheel of Comparative Example 2.

[0049] Figure 12 The original austenite grain of the wheel of Comparative Example 4.

[0050] Figure 13 The metallographic structure of the wheel of Example 2.

[0051] Figure 14 The metallographic structure of the wheel of Comparative Example 2.

[0052] Figure 15 The metallographic structure of the wheel of Comparative Example 4.

[0053] Figure 16 The pearlite lamellar spacing of the wheel of Example 2.

[0054] Figure 17 The pearlite lamellar spacing of the wheel of Comparative Example 2.

[0055] Figure 18 Wheel Pearlite interlamellar spacing of Comparative Example 4. DETAILED DESCRIPTION

[0056] The application will be described in detail below with reference to the examples.

[0057] Example 1

[0058] A high-strength and high-toughness matching high-speed wheel suitable for low-temperature environment, the chemical composition of which is shown in Table 1.

[0059] The preparation process of the high-speed wheel is as follows: electric furnace smelting→LF furnace refining→RH or VD vacuum degassing→round billet continuous casting→slow cooling treatment→cutting and blanking→pre-rolling heating→forging and rolling→stacking slow cooling→heat treatment→processing→finished product testing.

[0060] The heat treatment process includes: overall pretreatment→overall quenching preheating→different water temperature grading spray quenching→overall tempering, and the specific operation steps are as follows:

[0061] S1: blanking and rolling to obtain a blank wheel with an outer diameter of 915 mm, the blank wheel is loaded into a ring heating furnace, heated to 850℃, and then slowly cooled to 810℃ in the furnace for 1.5h, and then taken out by a mechanical hand and naturally cooled to room temperature in air.

[0062] S2: the wheel obtained in step S1 is again placed into a ring heating furnace, heated to 810℃ and kept for 1.5h.

[0063] S3: the wheel obtained in step S2 is taken out from the ring heating furnace and transported to a quenching platform, and the tread is cooled by a continuous spray quenching method in different stages and at different water temperatures, the first stage water temperature is 60℃, the spray quenching time is 60s, and the cooling speed of the tread surface is ≤4℃ / s to ensure that the tread surface is cooled to below 500℃ at a cooling speed of ≤4℃ / s and the rim core temperature remains in the austenite region, the second stage water temperature is 10℃, and the spray quenching time is 200s, and during the spray quenching process, the wheel rotates at a speed of 50 revolutions per minute with the supporting roller to ensure that the surface temperature of the tread is below 150℃ after the spray quenching, and the metal in the rim interior is rapidly cooled to below 500℃ at a cooling speed of 3-6℃ / s to ensure that the entire wear limit zone is within the pearlite structure transformation;

[0064] S4: the wheel obtained in step S3 is transported by a chain plate bed to a ring tempering furnace, and the wheel is put into the tempering furnace, and the tempering temperature is set to 520℃, and the tempering time is 4.0h.

[0065] Example 1 Based on the composition of the conventional ER8 wheel, the content of Cr element is increased to 0.29%, which delays the original organization to austenite conversion rate, increases the supercooling degree of the cooling phase, so as to obtain a relatively small pearlite interlamellar spacing. At the same time, the content of Ti and Al is strictly controlled, which promotes the effective combination of Al and N to form AlN second phase, pins the grain boundary, effectively hinders the growth and coarsening of austenite grains, and has good toughness while obtaining high strength. In addition, in the heat treatment process, by increasing a pretreatment, the original grain coarsening and uneven distribution phenomenon is obviously improved, and by means of step quenching cooling, the generation of abnormal organization in the tread surface layer of the wheel is reduced, and the pearlite structure is refined, so as to realize the synchronous improvement of strength and toughness.

[0066] Example 2

[0067] A high-strength and high-toughness high-speed wheel suitable for low-temperature environment, the chemical composition of which is shown in Table 1.

[0068] The preparation process of the high-speed wheel is: electric furnace smelting→LF furnace refining→RH or VD vacuum degassing→round billet continuous casting→slow cooling treatment→cutting blanking→pre-rolling heating→forging and rolling→stacking slow cooling→heat treatment→processing→finished product detection.

[0069] The heat treatment process includes: overall pretreatment→overall quenching preheating→different water temperature step quenching→overall tempering, and the specific operation steps are as follows:

[0070] S1: blanking and rolling to obtain a blank wheel with an outer diameter of 915mm, the blank wheel is loaded into a ring heating furnace, heated to 870℃, then slowly cooled to 830℃ and kept for 1.0h, and then taken out by a mechanical hand and naturally cooled to room temperature in air.

[0071] S2: the wheel obtained in step S1 is put into the ring heating furnace again, heated to 830℃ and kept for 1.0h.

[0072] S3: the wheel obtained in step S2 is taken out from the ring heating furnace and transported to the quenching platform, and the tread is cooled by continuous spraying quenching in different water temperatures in stages, the first stage water temperature is 60℃, the spraying quenching time is 55s, which ensures that the tread of the wheel is cooled to below 500℃ at a cooling rate of ≤4℃ / s within 5mm, and the rim core temperature still remains in the austenite zone, the second stage water temperature is 5℃, the spraying quenching time is 190s, and the wheel rotates at a speed of 50 revolutions per minute during the spraying quenching process, which ensures that the surface temperature of the tread of the wheel is below 150℃ after the spraying quenching, and the metal in the rim core is quickly cooled to below 500℃ at a cooling rate of 3-6℃ / s, which ensures that the pearlite organization in the whole wear limit zone is transformed;

[0073] S4: The wheel obtained in step S3 is transferred from the chain bed to the annular tempering furnace, and is set to a tempering temperature of 500℃ and a tempering time of 4.5h.

[0074] Example 2 is based on the composition of the conventional ER8 wheel, and the content of Si element is increased from 0.35% to 0.95%, which increases the solid solution strengthening effect of ferrite and the difficulty of rearrangement of alloy elements in the phase transition process, refines the pearlite interlamellar spacing, and thus improves the overall strength of the steel. In addition, in the heat treatment process, by adding a pretreatment, the original grain coarsening and uneven distribution are significantly improved, and by means of step quenching cooling, the generation of abnormal organization in the near surface layer of the wheel tread is reduced, and the pearlite structure is refined, so as to realize the synchronous improvement of strength and toughness.

[0075] Comparative Example 1

[0076] A high-speed wheel, which has the same chemical composition as Example 1.

[0077] The preparation process of the high-speed wheel is the same as Example 1, and the heat treatment process includes: overall preheating before quenching→different water temperature step quenching→overall tempering. Before the overall quenching preheating, no pretreatment is performed, and the specific process is as follows:

[0078] S1: The blank wheel with an outer diameter of 915mm is obtained by blanking and rolling, and the blank wheel is loaded into an annular heating furnace, heated to 810℃ and kept for 1.5h.

[0079] S2: The wheel obtained in step S1 is taken out of the annular heating furnace and transferred to the quenching table by the mechanical hand, and the tread is cooled by using the continuous spray quenching method in different stages and different water temperatures, and the control measures are the same as Example 1.

[0080] S3: After the spray quenching, tempering treatment is performed, and the tempering system is the same as Example 1.

[0081] Comparative Example 2

[0082] A high-speed wheel, which has the same chemical composition as Example 2.

[0083] The preparation process of the high-speed wheel is the same as Example 2, and the heat treatment process includes: overall pretreatment→overall preheating before quenching→different water temperature step quenching→overall tempering. Different from Example 2, in step S1, after heating to 870℃, no temperature reduction treatment is performed, and then the quenching and tempering are performed, and the specific process is as follows:

[0084] S1: The blank wheel with an outer diameter of 915mm is obtained by blanking and rolling, and the blank wheel is loaded into an annular heating furnace, heated to 870℃ and kept for 1h, and then taken out by the mechanical hand and cooled to room temperature in the air.

[0085] S2: Place the wheel obtained in step S1 back into the annular heating furnace, heat it to 830℃ and keep it at that temperature for 1.0h.

[0086] S3: Take the wheel obtained in step S2 out of the annular heating furnace and transfer it to the quenching table. Cool the tread surface by continuous spray quenching with different water temperatures in stages. The control measures are the same as in Example 2.

[0087] S4: After the spray quenching is completed, a tempering treatment is performed, and the tempering process is the same as in Example 2.

[0088] Comparative Example 3

[0089] A high-speed wheel, the chemical composition of which is shown in Table 1.

[0090] The manufacturing process of the high-speed wheel is as follows: electric furnace smelting → LF furnace refining → RH or VD vacuum degassing → round billet continuous casting → slow cooling treatment → ingot cutting → pre-rolling heating → forging and rolling → stacking and slow cooling → heat treatment → processing → finished product inspection.

[0091] The heat treatment process is the same as in Example 1, except that the cooling stage does not involve graded cooling at different water temperatures. Specifically, it includes: overall pretreatment → heating before overall quenching → continuous spray quenching at the same water temperature → overall tempering, as detailed below:

[0092] S1: The blank wheel with an outer diameter of 915mm is obtained by blanking and rolling. The blank wheel is put into the annular heating furnace, heated to 850℃, and then slowly cooled to 810℃ and held for 1.5h. Then it is taken out by the robot and naturally cooled to room temperature in the air.

[0093] S2: Place the wheel obtained in step S1 back into the annular heating furnace, heat it to 810℃ and keep it at that temperature for 1.5 hours.

[0094] S3: Take the wheel obtained in step S2 out of the annular heating furnace and transfer it to the quenching table. Use continuous water spray cooling to rapidly cool the metal inside the rim to below 500℃ at a cooling rate of 3-5℃ / s.

[0095] S4: After the spray quenching is completed, a tempering treatment is performed, and the tempering process is the same as in Example 1.

[0096] Comparative Example 4

[0097] A high-speed wheel, the chemical composition of which is shown in Table 1.

[0098] The manufacturing process of the high-speed wheel is as follows: electric furnace smelting → LF furnace refining → RH or VD vacuum degassing → round billet continuous casting → slow cooling treatment → ingot cutting → pre-rolling heating → forging and rolling → stacking and slow cooling → heat treatment → processing → finished product inspection.

[0099] The heat treatment process includes: overall pretreatment → preheating before overall quenching → staged spray quenching at different water temperatures → overall tempering, as detailed below:

[0100] S1: blank rolling to obtain a blank wheel with an outer diameter of 915 mm, loading the blank wheel into a ring heating furnace, heating to 870°C and holding for 1.0 h;

[0101] S2: loading the wheel obtained in step S1 into the ring heating furnace again, heating to 870°C and holding for 1.5 h;

[0102] S3: taking the wheel obtained in step S2 out of the ring heating furnace and transferring to a quenching platform, continuously quenching the tread by using different water temperatures in stages, and the control measures are the same as in Example 2;

[0103] S4: after quenching, carrying out tempering treatment, and the tempering system is the same as in Example 2.

[0104] Table 1: Main chemical components (wt%) of the wheels of the examples and comparative examples

[0105]

[0106] The original austenite grain morphology of the wheels of Example 1 and Comparative Examples 1 and 3 is shown in Figure 1 、 2 and 6. It can be seen that, compared with the wheel of Comparative Example 1, the grains of the wheel of Example 1 are obviously finer and the distribution is more uniform, and these fine and uniform grain structures are the key to obtaining good strength and toughness matching.

[0107] The metallographic structure of the wheels of Example 1 and Comparative Examples 1 and 3 at a position 5 mm below the tread is shown in Figure 4 、 5 and 6. It mainly consists of fine pearlite and a small amount of ferrite. The volume fraction of ferrite of the wheel of Example 1 is about 10.7%, the volume fraction of ferrite of the wheel of Comparative Example 1 is about 8.8%, and the volume fraction of ferrite of the wheel of Comparative Example 3 is about 8.4%, and the difference between them is not large. The wheel of Comparative Example 3 has obvious feather-like bainite structure, and the proportion of abnormal structure is close to 10%.

[0108] The pearlite interlamellar spacing of the wheels of Example 1 and Comparative Examples 1 and 3 is shown in Figure 7 、 8 and 9. The pearlite interlamellar spacing of the wheel of Example 1 is 116-130 nm, and the fine pearlite interlamellar spacing is the main reason for obtaining high strength and toughness. The pearlite interlamellar spacing of the wheel of Comparative Example 1 is 137-142 nm, and the pearlite interlamellar spacing of the wheel of Comparative Example 3 is 122-221 nm, which is obviously coarsened compared with Example 1. In addition, the wheel of Comparative Example 3 obviously has uneven structure due to the use of traditional continuous quenching cooling.

[0109] The original austenite grain morphology of the wheels of Example 2 and Comparative Examples 2 and 4 is shown in Figure 10 、 11, 12. It can be seen that compared with the wheel of example 2, the wheels of comparative examples 2 and 4 are subjected to high-temperature heating and holding for a long time, so that the grains are significantly coarsened and grown.

[0110] The microstructures of the wheels of example 2 and comparative examples 2 and 4 are shown in Figs. Figure 13 、 14 , 15. It can be seen that the microstructures are all fine pearlite + a small amount of ferrite, the volume fraction of ferrite of the wheel of example 2 is about 8.5%, the volume fraction of ferrite of the wheel of comparative example 2 is about 7.4%, and the volume fraction of ferrite of the wheel of comparative example 4 is about 5.9%, the difference is obvious, and more ferrite is the key to obtain high toughness. In addition, the size of single ferrite block of example 2 is obviously larger than that of comparative example 4, and the main way of increase is the extension along the long axis of ferrite. The extension of ferrite makes the area of direct contact between pearlite nodules smaller, which also improves the toughness.

[0111] The pearlite interlamellar spacing of the wheels of example 2 and comparative example 2 is shown in Figs. Figure 16 、 17 , 18. The pearlite interlamellar spacing of the wheel of example 2 is 115-124 nm, the pearlite interlamellar spacing of the wheel of comparative example 2 is 135-139 nm, and the pearlite interlamellar spacing of the wheel of comparative example 4 is 135-139 nm, the difference is large, and the smaller pearlite interlamellar spacing is the main reason for example 2 to obtain high strength and toughness.

[0112] The wheels of example 1 and comparative examples 1 and 3, and example 2 and comparative examples 2 and 4 are subjected to room temperature tensile test, series temperature pendulum impact test, hardness test and fracture toughness test. Specifically, according to BS EN 13262 “Railway applications-Wheelsets and bogies-Wheels-Product requirements”, tensile test samples, charpy impact samples, rim section hardness samples and fracture toughness compact tension samples (6 samples evenly distributed in the circumferential direction) are taken at the corresponding positions of the rim and web of the finished wheel, and the room temperature tensile test and series temperature pendulum impact test are carried out according to GB / T 228.1 “Metallic materials-Tensile test-Part 1: Method of test at room temperature”, GB / T 229 “Metallic materials-Charpy pendulum impact test method”, and the performance results are shown in Tables 2-3; the hardness test and fracture toughness test are carried out according to GB / T 231.1 “Metallic materials-Brinell hardness test-Part 1: Test method”, GB / T 4161-2007 “Metallic materials-Plane strain fracture toughness KIC test method”, and the related results are shown in Table 2-4. It can be seen that compared with the traditional ER8 wheel, the wheels obtained by the scheme of the present application have higher impact toughness and fracture toughness while having higher rim section hardness, and have good comprehensive performance.

[0113] Table 2 Tensile mechanical properties of the wheels of examples and comparative examples

[0114]

[0115] Table 3 Series temperature impact performance of the wheel rims of the examples and the comparative examples

[0116]

[0117]

[0118] Table 4 Section hardness and fracture toughness of the wheel rims of the examples and the comparative examples

[0119]

[0120] From the above data, it can be seen that the tensile properties, impact toughness, fracture toughness and section hardness of the steel in Examples 1-2 controlled according to the present application are all good. Compared with Example 1, Comparative Example 1 is not pretreated before quenching heating, resulting in a relatively coarse grain size and poor uniformity, a relatively large interlamellar spacing of pearlite, and thus deteriorated strength and impact toughness of the wheel; Comparative Example 3 has more abnormal bainite structure, which not only has an adverse effect on the strength and toughness, but also requires more machining allowance, and is poor in economy. Compared with Example 2, Comparative Example 4 has a low Si and Cr content, resulting in poor solid solution strengthening effect of the steel, and Comparative Examples 2 and 4 are in a high temperature environment for a long time, resulting in grain growth, and the quenching temperature of Comparative Example 4 is relatively high, which is not conducive to obtaining more proeutectoid ferrite, and thus the comprehensive performance is also poor.

[0121] The above detailed description of the reference examples of the high-strength and high-toughness matching high-speed wheel suitable for low-temperature environment, the heat treatment method and the preparation method is illustrative rather than limiting, and several examples can be listed according to the defined range, and thus the changes and modifications without departing from the overall concept of the present application shall be within the protection scope of the present application.

Claims

1. A heat treatment method for high-speed wheels with high strength and toughness matching suitable for low-temperature environments, characterized in that, The heat treatment method includes the following steps: S1: The rolled wheels are heated to 850-870°C and then slowly cooled in the furnace to 810-830°C and held at that temperature. They are then allowed to cool naturally in the air. S2: Reheat the wheel obtained in step S1 to 810-830℃ and keep it warm; S3: Take out the wheel obtained in step S2 and transfer it to the quenching table. First, use hot water to spray the wheel tread to cool the bottom 5mm of the wheel tread to below 500℃ at a cooling rate of ≤4℃ / s. Then, use cold water to spray the wheel tread to rapidly cool the metal inside the rim to below 500℃ at a cooling rate of 3-6℃ / s. S4: Temper the wheels obtained in step S3 at 500-520℃ for 4.0-4.5 hours; The steel composition and weight percentage of the high-speed wheel are as follows: C 0.50-0.56%, Si 0.30-1.10%, Mn 0.70-0.80%, Cr 0.20-0.30%, Al≤0.020%, P≤0.015%, S≤0.015%, Ti≤0.002%, with the remainder being Fe and unavoidable impurity elements.

2. The heat treatment method according to claim 1, characterized in that, In step S1, the total heating time of the wheel is 2.0 to 3.0 hours, and the heat preservation time at 810 to 830°C is 1.0 to 1.5 hours.

3. The heat treatment method according to claim 1, characterized in that, In step S2, the total heating time of the wheel is 2.0 to 3.0 hours, and the heat preservation time at 810 to 830°C is 1.0 to 1.5 hours.

4. The heat treatment method according to claim 1, characterized in that, In step S3, the temperature of the hot water is 55-60℃ and the spraying time is 60-80s; the temperature of the cold water is 5-10℃ and the spraying time is 190-210s.

5. The heat treatment method according to claim 1, characterized in that, In step S3, the wheel rotates along with the quenching table roller, and the roller speed is 40-60 revolutions per minute.

6. A high-speed wheel with high strength and toughness suitable for low-temperature environments, characterized in that, The high-speed wheel is obtained by heat treatment using the heat treatment method described in any one of claims 1 to 5.

7. The high-speed wheel with high strength and toughness matching suitable for low-temperature environments according to claim 6, characterized in that, The metallographic structure of the high-speed wheel consists of ferrite and pearlite; the grain size in the microstructure of the region from the surface of the wheel tread to 35 mm below the tread is greater than or equal to grade 8.0, the volume fraction of ferrite is 8.5% to 10.5%, and the interlamellar spacing of pearlite is 115 to 127 nm.

8. The high-speed wheel with high strength and toughness matching suitable for low-temperature environments according to claim 6, characterized in that, The rim of the high-speed wheel has a strength of Rm1100~1120MPa and a bearing capacity of R. P0.2 720~735MPa, A19.0~21%; Hardness of wheel rim 5mm from tread ≥310HB, Hardness of wheel rim 35mm from tread ≥280HB; K Q Single value ≥90MPa.m 1 / 2 Mean ≥ 94 MPa.m 1 / 2 -20℃ KV single value ≥19J, average value ≥21.0J; -40℃ KV single value ≥12J, average value ≥13.5J; -60℃ KU single value ≥90MPa·m 1 / 2 Mean value ≥ 100 MPa·m 1 / 2 .

9. The method for preparing a high-speed wheel with high strength and toughness suitable for low-temperature environments as described in claim 6, characterized in that, The preparation method includes the following steps: electric furnace smelting → LF furnace refining → vacuum degassing → round billet continuous casting → slow cooling treatment → ingot cutting → pre-rolling heating → forging and rolling → slow cooling after falling into the slab → heat treatment → processing → finished product inspection.

Images