Medium-carbon steel wheel steel with good toughness matching, wheel produced from medium-carbon steel wheel steel, and wheel heat treatment method

Abstract

A medium-carbon steel wheel steel with good toughness matching, wheel produced from the medium-carbon steel wheel steel, and a wheel heat treatment method. The medium-carbon steel wheel steel comprises the following components: C: 0.49-0.55%, Si: 0.30-0.60%, Mn: 0.70-1.20%, Cr: 0.26-0.35%, Al: 0.020-0.040%, Ni: 0.15-0.25%, P≤0.015%, S≤0.010%, and the balance being Fe and inevitable impurity elements, wherein 0.75≤C+Si / 4+Cr / 5+Mn / 6+Ni / 10≤1.00. The matched heat treatment method is designed, so that the contradiction relation of toughness matching is effectively overcome, and the wheels have good comprehensive mechanical properties and good economic efficiency; and the method does not affect the normal production rhythm, and is convenient to implement.

Description

Medium carbon steel wheel steel with good strength-toughness matching, wheel produced therefrom, and wheel heat treatment method

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on January 26, 2024, with application number 202410113300.4 and invention name “A medium carbon steel wheel steel with good strength-toughness matching and the wheels produced and wheel heat treatment method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention belongs to the technical field of railway wheel preparation, and more specifically relates to a medium carbon steel wheel steel with good strength-toughness matching, a wheel produced therefrom, and a wheel heat treatment method. The wheel is used for an EMU designed for a speed of 320 kilometers per hour. Background Art

[0003] Since the 1990s, railway wheel materials and processes have been largely finalized. Fine pearlite-minor ferrite railway wheels, due to their excellent wear resistance, machinability, and thermal stability, have been widely used worldwide. Furthermore, current railway wheels are generally heat treated using a process known as "overall heating + continuous tread quenching + overall tempering." The continuous tread quenching process, involving the direct application of large volumes of water to the wheel tread surface, is a critical step in determining the microstructure and performance of the wheel rim.

[0004] ER7 wheels are a common wheel designation used in European countries and regions, extensively used on pre-high-speed trains. They comply with BS EN 13262, "Railway Applications — Wheelsets and Bogies — Wheels — Product Requirements." Made of medium-low carbon steel, they feature medium strength and high toughness. Good wheel performance depends primarily on good wear resistance, which is closely related to wheel hardness. Higher hardness effectively reduces wheel wear rate and improves wear stability throughout its lifecycle. Therefore, to extend wheel service life and reduce operating costs, a growing number of industry customers are demanding wheels with higher hardness. At the same time, pre-high-speed wheels also require high fracture toughness to achieve superior resistance to fatigue crack growth during service. Due to the competitive relationship between toughness and strength, significantly increasing wheel hardness while maintaining sufficient fracture toughness is challenging. Therefore, overcoming the limitations of the strength-toughness balance of existing carbon steel wheels and fully realizing their ultimate performance are key challenges in developing the next generation of pre-high-speed wheels.

[0005] After searching, the patent with publication number CN 111500925 A published on August 7, 2020, discloses the Chinese invention patent "A medium-carbon wheel steel with good wear resistance and strength and toughness matching, its heat treatment method and wheel preparation method", including the following chemical components in weight percentage: 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 are Fe and unavoidable impurity elements; it improves the wear resistance of the wheel and the strength and toughness matching of the rim by controlling the content of V, Al, and N elements and adopting a composite heat treatment process of weak spraying + strong spraying. However, the invention adopts a V microalloying design, belongs to microalloyed low alloy steel, and has a complicated heat treatment process.

[0006] Patent publication number CN 110284069 A, published on September 27, 2019, discloses a medium-carbon wheel steel, a heat treatment method therefor, and a wheel manufacturing method. The medium-carbon wheel steel comprises the following chemical composition by weight: 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%, with the remainder being Fe and unavoidable impurities. This steel significantly improves wheel rim strength while maintaining a similar rim toughness level. However, this invention utilizes a high Mo content, which carries the risk of a non-pearlite layer unless the production feed weight is significantly increased.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to provide a medium-carbon steel wheel steel with good strength-toughness matching. In terms of composition design, the present invention abandons the simple addition of alloying elements to increase the hardness of the wheel. Instead, it adopts the addition of small amounts of alloying elements, the combination and coordination of the elements, and the optimization of the heat treatment system, which effectively overcomes the contradictory relationship between strength and toughness matching, so that the wheel has good comprehensive mechanical properties, good economy, does not affect the normal production rhythm, and is easy to implement.

[0009] Another object of the present invention is to provide a wheel produced by using the above-mentioned medium carbon steel wheel steel with good strength and toughness matching, and the produced wheel is used for an EMU with a design speed of 320 kilometers per hour.

[0010] The last object of the present invention is to provide a heat treatment method for wheels, in which the wheels are produced using the above-mentioned medium carbon steel wheel steel with good strength-toughness matching, and the heat treatment process is designed and matched according to the composition. The heat treatment process is simple, and at the same time, it ensures that the wheels have good comprehensive mechanical properties, good strength-toughness matching, and good economy.

[0011] The specific technical solutions of the present invention are as follows:

[0012] A medium carbon steel wheel steel with good strength and toughness matching, comprising the following components in percentage by mass:

[0013] C 0.49~0.55%, Si 0.30~0.60%, Mn 0.70~1.20%, Cr 0.26~0.35%, Al 0.020~0.040%, Ni 0.15~0.25%, P≤0.015%, S≤0.010%, and the rest are Fe and unavoidable impurity elements.

[0014] The composition of the medium carbon steel wheel steel with good strength and toughness matching meets the following requirements: Ti≤0.003%, Als0.017~0.035%, N(100~150)×10 -4 %.

[0015] The composition of the medium-carbon wheel steel with excellent strength-toughness matching also satisfies the following: 0.75 ≤ C + Si / 4 + Cr / 5 + Mn / 6 + Ni / 10 ≤ 1.00, where the index value of each element = the element's content in the steel × 100. These elements are key factors affecting strength and hardness. The purpose of limiting these values ​​is to consistently achieve the strength and hardness achievable by the wheel of the present invention while also taking into account fracture toughness and ensuring an excellent strength-toughness match. If the value is less than 0.75, the strength and hardness will not meet the design requirements, while if it is greater than 1.00, the strength and hardness will be too high, sacrificing fracture toughness.

[0016] The design ideas of the present invention are as follows:

[0017] Carbon (C) is one of the elements that contributes most to wheel hardness. Increasing the carbon content in wheel steel significantly increases wheel hardness, thereby improving wear resistance. However, excessive carbon content can reduce the wheel's plasticity and toughness. A high-hardness medium-carbon steel wheel designed for a 320 km / h speed must balance wear resistance and plasticity and toughness. Therefore, a medium carbon content is recommended. Therefore, the carbon content range is set at 0.49-0.55%.

[0018] Si element: Adding Si element can improve the strength and hardness of the wheel through solid solution strengthening, and at the same time increase the phase transformation point Ac3 of the wheel steel, which helps to improve the wheel's resistance to thermal damage. However, too high Si will increase the hot working sensitivity and brittleness of the wheel steel. Therefore, the range of Si is determined to be 0.30~0.60%.

[0019] Mn element: Mn can be dissolved in the matrix structure, improving the stability of the austenite structure, thereby increasing the strength and hardness of ferrite and austenite. However, excessive Mn will reduce the plasticity of the steel and destroy the thermoplasticity of the steel during hot rolling. Therefore, the range of Mn is determined to be 0.70~1.20%.

[0020] Cr element: Cr is a relatively cheap and beneficial element in steel. Adding an appropriate amount can improve the stability of supercooled austenite, reduce the transformation temperature, increase the supercooling degree, and significantly refine the spacing between pearlite lamellae. However, if the Cr content is too high, it will significantly reduce the volume fraction of ferrite, which is not conducive to plasticity and toughness. Therefore, the range of Cr is determined to be 0.26~0.35%.

[0021] Ni: Ni primarily increases the toughness of the matrix structure, refines the pearlite interlamellar spacing, and also strengthens ferrite. The combination of Ni and Cr further enhances the toughness of the internal structure of the wheel rim. However, if the Ni content exceeds 0.25%, the oxide scale on the steel billet will be difficult to remove during rolling and heating. Therefore, the Ni content is limited to 0.15-0.25%.

[0022] Al element: Al, as the main deoxidizer in steel, exists in steel in the form of acid-soluble aluminum (Als) and insoluble aluminum. Als is equivalent to an alloying element in steel, while insoluble aluminum forms aluminum oxide inclusions. The present invention limits both Al and Als, and the purpose of limiting both the whole and the part is to control the cleanliness of the steel while ensuring the degree of alloying. Als dissolved in the matrix can combine with nitrogen to form an AlN second phase. Due to its good thermal stability, it has a significant effect of pinning grain boundaries and can effectively hinder the growth and coarsening of austenite grains during hot working. When the Al content is less than 0.020%, the driving force for AlN precipitation is insufficient. When it is higher than 0.040%, there is a risk of forming Al2O3 brittle inclusions, which deteriorates the performance of the steel. Therefore, the range of Al is determined to be 0.020-0.040%, and the range of Als is determined to be 0.017-0.035%.

[0023] N element: N dissolved in steel effectively combines with Als to form AlN particles with good thermal stability. They are concentrated on the grain boundaries and play a role in pinning the grain boundaries during hot working, hindering the growth of grains. In theory, the higher the N content, the greater the driving force for the precipitation of AlN particles, the more AlN particles there are, the smaller the size, and the more uniform the distribution. A reasonable Al×N value has a significant effect on grain refinement, while an excessively high N content will form continuous casting defects such as subcutaneous "pinholes". Taking into account the stability of the N control process during steelmaking, the nitrogen content in the present invention is set to (100-150)×10 -4 %.

[0024] Ti: Because both Ti and Al are nitride-forming elements, strictly controlling the Ti content in carbon steel compositions prevents competition with Al, ensures effective bonding between AlS and N, and promotes the formation of AlN particles, resulting in grain refinement. This significantly improves wheel hardness while maintaining high fracture toughness. Therefore, the present invention sets an upper limit for Ti based on current steelmaking processes.

[0025] The present invention provides a wheel produced by using the above-mentioned medium carbon steel wheel steel with good strength-toughness matching.

[0026] The invention provides a wheel heat treatment method, which includes heating, tread spray quenching, and tempering.

[0027] The heating is to heat the entire blank wheel to an even temperature of 870-920° C., a total heating time of 2.5-3.5 hours, and a holding time of the even temperature section of 1.25-1.75 hours.

[0028] The heating is specifically as follows: the rolled blank wheel is loaded into a ring-shaped heating furnace, the temperature is gradually raised to 870-920°C and kept warm for a certain period of time to fully austenitize; the present invention is 30-50°C higher than the conventional soaking temperature. A higher soaking temperature can improve the uniformity of the original austenite grains and delay the transformation of supercooled austenite, thereby obtaining higher stability and greater supercooling during the cooling phase transformation, which is conducive to obtaining finer pearlite plate spacing. However, the soaking temperature cannot be too high, otherwise it will cause the grains to grow and coarsen, which is detrimental to the performance of the wheel. During heating, the total heating time is controlled at 2.5-3.5h. The specific time depends on factors such as the furnace load, the material distribution method, the actual condition of the heating furnace, etc. The soaking section is maintained for 1.25-1.75h.

[0029] Before tread quenching, cooling water is not turned on. The wheel is first spun in air for 60 to 90 seconds at an angular velocity of 70 to 80° / s before tread quenching. This is done to achieve a "high-temperature heating, low-temperature quenching" effect. This involves dissipating heat through air flow, reducing the overall heat storage of the wheel rim and allowing the temperature to drop slightly within the supercooled austenite region (ensuring the minimum temperature remains above the phase transition critical temperature Ar3). This reduces the heat flux density transferred from the tread subsurface and rim interior to the inner layers, creating a "pre-cooling effect." After the wheel spun ends, tread quenching is resumed.

[0030] The tread spray quenching is carried out on a horizontal quenching table.

[0031] The tread spray quenching is performed by continuous spray quenching of the tread, and the wheel rotates during the spray quenching process;

[0032] The tread is spray quenched for 350 to 500 seconds. A longer spray quenching time can reduce the overall heat storage of the wheel and reduce the temperature recovery of the rim after heat treatment. The surface temperature of the wheel tread is controlled to be lower than 70° C. after the spray quenching is completed, ensuring that the entire rim area is worn to a limited area and the pearlite structure transformation is completed.

[0033] The tread spray quenching uses a continuous large flow of circulating water to spray the wheel tread. The total water flow of the quenching table is 120 to 140 tons per hour. Compared with the total water flow of the previous quenching table, the total water flow is increased to more than 120 tons per hour. Although the water flow has reached the peak value and cannot enhance cooling to achieve the purpose of increasing hardness, it can reduce the temperature recovery after the spray quenching is completed and reduce the hardness loss caused by the "self-tempering" effect.

[0034] The tread spray quenching is carried out on a quenching table with 6 box-type spray guns evenly distributed along the circumference, and the water flow rate of each spray gun is equal, and the water output speed is 5-7m / s.

[0035] During the spray quenching process, the wheel rotates at an angular velocity of 55 to 65° / s.

[0036] After the tread is spray-quenched, the wheel is transferred to the annular tempering furnace via a chain plate bed for tempering treatment.

[0037] The transmission time of the chain bed is 8 to 10 minutes. At the same time, the overall temperature of the rim is controlled not to exceed 400°C through forced air blowing during the transmission process, reducing the "self-tempering" effect and ensuring that the lamellar pearlite does not deform or break.

[0038] The tempering treatment has a tempering temperature of 460-500° C. and a tempering time of 4-6 hours.

[0039] The wheel production method includes the above heat treatment method, specifically including the following process flow:

[0040] Electric furnace smelting → LF furnace refining → RH vacuum treatment → round billet continuous casting → slow cooling treatment → ingot cutting → heating before rolling → billet forging and rolling → stacking and slow cooling → heat treatment → subsequent machining.

[0041] The wheel produced by the present invention has a microstructure of pearlite + a small amount of ferrite at room temperature. The volume fraction of ferrite in the microstructure of the entire wear working area (i.e., from the tread surface of the finished wheel to the area 35 mm away from the tread) is 7% to 12%, the pearlite plate spacing is 150 to 180 nm, the pearlite pellet size is 10.0 to 13.5 μm, and the grain size is ≥ 7.5.

[0042] The wheel rim produced by the present invention has a hardness of ≥300HB at a distance of 5mm from the tread and a hardness of ≥275HB at a distance of 35mm from the tread; the rim has a tensile strength of 950-980MPa, a yield strength of 560-600MPa, and an elongation after fracture of 15.0-18.0%; the rim has a room temperature impact energy Ku5 value of ≥25J, a -20°C impact energy Kv2 value of ≥12J; and a rim fracture toughness value of ≥80MPa·m 1 / 2 , average value ≥85MPa·m 1 / 2 ; The tensile strength of the web is 730~780MPa, and the elongation after fracture is ≥20.0%.

[0043] For carbon steel wheels, significantly increasing wheel hardness through heat treatment alone is far from sufficient. Furthermore, the current wheel cooling water flow rate has reached its peak, limiting pearlite transformation strengthening. This goal can only be achieved through alloying. However, wheels designed for 320 km / h EMUs also require high fracture toughness to ensure high resistance to fatigue crack growth during service. Due to the competitive relationship between toughness and strength, significantly increasing wheel hardness while maintaining adequate fracture toughness is challenging.

[0044] To achieve a high strength-toughness match for wheel steel, the present invention, based on the composition of traditional ER7 wheels, optimizes elements such as C, Si, and Mn, while increasing the content of elements such as Cr and Ni, thereby improving the stability of supercooled austenite, increasing the supercooling degree during the cooling phase transformation stage, and obtaining a relatively fine pearlite interlamellar spacing. With the goal of pinning grain boundaries with AlN particles, the contents of Ti, Als, and N are strictly controlled to promote the effective combination of Als and N to form the AlN second phase. Due to its good thermal stability, it has a significant effect of pinning grain boundaries, and can effectively hinder the growth and coarsening of austenite grains during hot working, thereby achieving high hardness while also having good fracture toughness.

[0045] At the same time, corresponding improvements have also been made to the heat treatment process, such as appropriately increasing the quenching heating temperature, increasing the cooling water flow rate, and reducing the "self-tempering" effect. These measures aim to achieve a relatively fine pearlite plate spacing and minimize the hardness loss caused by the "self-tempering" effect. The present invention uses a higher soaking temperature to achieve higher undercooled austenite stability. For general wheel steel, austenite grains will grow and coarsen at such a high temperature. However, the present invention simultaneously uses high Al and N additions and controls the Ti content as low as possible to effectively promote the formation of AlN particles, pinning the grain boundaries and thereby increasing the critical temperature for austenite grain coarsening, achieving the effect of the present invention that the grain structure will not coarsen under high-temperature heating conditions. If Al, N, and Ti are not properly controlled, it cannot be guaranteed that the grains will not grow and coarsen at high temperatures.

[0046] In addition, air pre-cooling is added before spray quenching to achieve low supercooling in the austenite zone (i.e., to ensure that the lowest temperature is still above the critical temperature of phase transformation Ar3), producing a "pre-cooling effect", which is then superimposed on long-term spray quenching cooling to increase the average effective cooling rate in the range of 700-500°C, further increasing the potential for achieving higher hardness levels and significantly improving the strength-toughness matching of the wheel rim.

[0047] The present invention is based on the theory of supercooled austenite stability control and second phase grain boundary pinning, combined with the adjustment of heat treatment process, to overcome the limitations of the strength-toughness matching of traditional ER7 wheels and achieve a significant improvement in the comprehensive mechanical properties of the wheels. Compared with traditional ER7 wheels, the wheels produced by the present invention can increase the hardness of the wheels by more than 10%, while not reducing the fracture toughness, which is beneficial to improving the wear stability and fatigue crack propagation resistance of the wheels throughout the life cycle. The scheme of the present invention abandons the simple addition of alloying elements to increase the hardness of the wheels, and adopts a small amount of alloying elements, and the combination of elements, coupled with the optimization of the heat treatment system, to effectively overcome the contradictory relationship between strength and toughness matching, so that the wheels have good comprehensive mechanical properties, good economy, do not affect the normal production rhythm, and are easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG1 is the original austenite grain morphology of the wheel of Example 1;

[0049] FIG2 is the original austenite grain morphology of the wheel of Comparative Example 1;

[0050] FIG3 shows the temperature drop during the spray quenching cooling stage of the wheels of Example 1 and Comparative Example 1 and the temperature rise during the chain plate bed transmission process;

[0051] FIG4 is the microstructure of the wheel of Example 1;

[0052] FIG5 is the microstructure of the wheel of Comparative Example 1;

[0053] FIG6 shows the cross-sectional hardness and fracture toughness of the wheel rims of Examples 1-3 and Comparative Examples 1-3;

[0054] FIG7 is the microstructure of the wheel of Example 2;

[0055] FIG8 is the microstructure of the wheel of Comparative Example 2;

[0056] FIG9 is the original austenite grain morphology of the wheel of Example 3;

[0057] FIG10 shows the original austenite grain morphology of the wheel of Comparative Example 3;

[0058] FIG11 is the microstructure of the wheel of Example 3;

[0059] FIG12 is the microstructure of the wheel of Comparative Example 3;

[0060] FIG13 is an EBSD analysis of the pearlite pellet size of the wheel of Example 3;

[0061] FIG14 is an EBSD analysis of the pearlite pellet size of the wheel of Comparative Example 3. DETAILED DESCRIPTION

[0062] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings and embodiments.

[0063] Example 1-Example 3

[0064] A medium carbon steel wheel steel with good strength-toughness matching includes the components and contents shown in Table 1.

[0065] Comparative Example 1-Comparative Example 3

[0066] Conventional ER7 wheel steel includes the components and contents shown in Table 1.

[0067] The production of wheels using the steel of each embodiment and comparative example includes the following process flow: electric furnace smelting → LF furnace refining → RH vacuum treatment → round billet continuous casting → slow cooling treatment → ingot cutting → pre-rolling heating → billet forging and rolling → stacking and slow cooling → heat treatment → subsequent machining.

[0068] The heat treatment method for producing wheels using the steel of Example 1 includes overall heating → tread spray quenching → chain plate bed transmission → overall tempering. The specific operation steps include:

[0069] S1, blank wheel with outer diameter of 940mm is obtained by blanking and rolling. The blank wheel is loaded into a ring heating furnace, and the temperature is gradually increased to 870±10℃ (the target temperature of the uniform heating is 870℃). It is kept warm for 1.75h, with a total heating time of 3.5h. After sufficient austenitization, it is taken out of the furnace and transferred to the horizontal quenching table by a robot.

[0070] S2: Before quenching, the wheel is idling in air for 60 seconds without cooling water, at an angular velocity of 70° / s. The tread is then continuously quenched, with the wheel rotating at a constant speed. The specific cooling regime is as follows: tread quenching for 350 seconds. A longer quenching time reduces the overall heat storage of the wheel and the reheating of the rim after heat treatment. The surface temperature of the wheel tread is controlled below 70°C after quenching to ensure that the entire rim area is worn within the restricted area and completes the pearlite transformation. The total water flow rate of the quenching station is set at 120 tons per hour. Although a higher total water flow rate does not enhance cooling and thus increase hardness, it can reduce the reheating after quenching and minimize hardness loss caused by the "self-tempering" effect. The quenching station is equipped with six box-type spray guns distributed circumferentially, each with an equal water flow rate and a water velocity of 5.5 m / s. During this process, the wheel rotates at an angular velocity of 55° / s.

[0071] S3. After the spray quenching is completed, the wheel is transferred to the annular tempering furnace via a chain plate bed for 10 minutes. At the same time, during the transmission process, the overall temperature of the rim is controlled to not exceed 400℃ by forced blowing to reduce the "self-tempering" effect and ensure that the lamellar pearlite does not deform or break. Then, the wheel is put into the tempering furnace and the tempering temperature is set to 500±10℃ (the target temperature for uniform heating is 500℃) and the tempering time is 4h.

[0072] The heat treatment method for producing wheels using the steel in Comparative Example 1 includes the following specific steps:

[0073] S1, the blank wheel obtained by rolling is placed in an annular heating furnace, and the temperature is gradually increased to 840±10°C (the target temperature for the soaking is 840°C), which is 30°C lower than that in Example 1, and kept warm for 1.5 hours.

[0074] S2, after being fully austenitized, the wheel is taken out of the furnace and transferred to a horizontal quenching table by a robot, and directly cooled by continuous tread spray quenching. During the spray quenching process, the wheel rotates at an angular velocity of 55° / s, the tread spray quenching time is 240s, and the total water flow rate of the quenching table is set to 114 tons per hour. Other control measures are the same as in Example 1.

[0075] S3, after the quenching is completed, tempering treatment is performed, and the tempering system is the same as that in Example 1.

[0076] Figures 1 and 2 show the prior austenite grain morphology of the wheels from Example 1 and Comparative Example 1. As can be seen, compared to the wheels from Comparative Example 1, at the higher heating temperature of 870°C, the grain size of the wheels from Example 1 did not significantly grow, remaining at 8.5. Small, uniform grains are essential for achieving a good balance of strength and toughness.

[0077] Figure 3 shows the temperature drop during the spray quenching cooling phase and the temperature rise during the chain-plate transport process for the wheels of Example 1 and Comparative Example 1. As can be seen, the overall temperature recovery of the wheels of Example 1 is approximately 300°C, over 100°C lower than that of the wheels of Comparative Example 1. This lower temperature recovery reduces the "auto-tempering" effect and prevents deformation and breakage of the lamellar pearlite.

[0078] The microstructures of the wheels of Example 1 and Comparative Example 1 are shown in Figures 4 and 5. As can be seen, the microstructures of both wheels are composed of fine pearlite with a small amount of ferrite. Within the rim, 35 mm from the tread, the ferrite volume fraction of the wheel of Example 1 is 11.7 ± 0.2%, while that of the wheel of Comparative Example 1 is 13.1 ± 0.3%, a similar difference between the two. However, inside the rim at 35 mm from the tread, the pearlite lamellae spacing of the wheel of Example 1 is 171-179 nm, the average pearlite lamellae spacing is 176 nm, the pearlite globule size is 10.0-10.5 μm, and the average pearlite globule size is 10.3 μm, while the pearlite lamellae spacing of the wheel of Comparative Example 1 is 193-204 nm, the average pearlite lamellae spacing is 199 nm, the pearlite globule size is 12.6-14.3 μm, and the average pearlite globule size is 13.4 μm. There is a big difference between the two. The smaller pearlite lamellae spacing and pearlite globule size are the main reasons for obtaining high hardness and high fracture toughness.

[0079] In accordance with BS EN 13262, "Railway Applications — Wheelsets and Bogies — Wheels — Product Requirements," tensile test specimens and Charpy impact specimens were taken from corresponding locations on the rim and web of the finished wheels. Room-temperature tensile testing and a series of temperature pendulum impact tests were conducted in accordance with GB / T 228.1, "Metallic Materials — Tensile Tests — Part 1: Room-Temperature Test Methods," and GB / T 229, "Metallic Materials — Charpy Pendulum Impact Test Methods," respectively. The tensile mechanical properties of the rims and webs, as well as the series of temperature impact properties of the rims, of the wheels of Example 1 and Comparative Example 1 are shown in Tables 2 and 3. As can be seen, compared to the wheels of Comparative Example 1, the wheels of Example 1 achieve higher strength properties while maintaining the same plasticity and impact energy performance.

[0080] In accordance with BS EN 13262 "Railway applications - Wheelsets and bogies - Wheels - Product requirements", rim cross-section hardness test specimens and fracture toughness compact tensile test specimens (6 pieces evenly distributed along the circumference) were taken from the corresponding positions of the rim and web of the finished wheel. The hardness test specimens were tested 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 K IC Test Methods》 Hardness test and fracture toughness test were conducted. The hardness and fracture toughness of the rim section of the wheels of Example 1 and Comparative Example 1 are shown in Figure 6. The hardness of the wheel of Example 1 at 5mm and 35mm were (304±3)HB and (277±2)HB respectively, and the fracture toughness was (94±4)MPa·m 1 / 2 , while the hardness of the wheel at 5mm and 35mm of the comparative example 1 is (279±5)HB and (244±3)HB respectively, and the fracture toughness is (96±3)MPa·m 1 / 2It can be seen that compared with the traditional ER7 wheel, the solution of the present invention can achieve higher rim cross-section hardness while also having higher fracture toughness, and the strength and toughness are well matched.

[0081] The heat treatment method for producing wheels using the steel of Example 2 is similar to that of Example 1. The differences are:

[0082] The target temperature of step S1 is 890℃, and the holding time is 1.5h, with a total heating time of 3.0h.

[0083] The idling time in air of step S2 is 75s, the wheel rotation angular velocity is 75° / s, while the quenching time is 420s, the wheel rotation angular velocity is 60° / s;

[0084] The target soaking temperature of step S3 is 480°C, and the tempering time is 5 hours.

[0085] The heat treatment process steps of the steel in Comparative Example 2 are referred to Comparative Example 1, except that:

[0086] The target soaking temperature in step S1 is 860°C and the soaking temperature is maintained for 1.25h.

[0087] The quenching time of step S2 is 270s, and the wheel rotation angular velocity is 60° / s.

[0088] Step S3 is the same as in Example 2.

[0089] The microstructures of wheels produced from the steels of Example 2 and Comparative Example 2 are shown in Figures 7 and 8. As can be seen, the microstructures of both wheels are composed of fine pearlite with a small amount of ferrite. Within the rim, 35 mm from the tread, the ferrite volume fraction for the wheels of Example 2 is 10.3 ± 0.3%, while that for the wheels of Comparative Example 2 is 12.5 ± 0.3%, a similar difference between the two. However, inside the rim at 35 mm from the tread, the pearlite lamellae spacing of the wheel of Example 2 is 163-167 nm, the average pearlite lamellae spacing is 165 nm, the pearlite globule size is 11.1-12.0 μm, and the average pearlite globule size is 11.5 μm, while the pearlite lamellae spacing of the wheel of Comparative Example 2 is 185-192 nm, the average pearlite lamellae spacing is 188 nm, the pearlite globule size is 13.3-15.6 μm, and the average pearlite globule size is 14.6 μm. There is a big difference between the two. The smaller pearlite lamellae spacing and pearlite globule size are the main reasons for obtaining high hardness and high fracture toughness.

[0090] Referring to Example 1 and Comparative Example 1, the wheels of Example 2 and Comparative Example 2 were subjected to room temperature tensile testing, a series of temperature pendulum impact tests, hardness, and fracture toughness tests. The relevant results are shown in Tables 2-3 and Figure 6. The hardness of the wheels of Example 2 at 5mm and 35mm were (311±4) HB and (285±4) HB, respectively, and the fracture toughness was (89±5) MPa·m. 1 / 2 , while the hardness of the wheel in comparative example 2 at 5mm and 35mm is (283±6)HB and (252±6)HB respectively, and the fracture toughness is (87±4)MPa·m 1 / 2 It can be seen that compared with the traditional ER7 wheel, the solution of the present invention can achieve higher rim cross-section hardness while also having higher fracture toughness, and the strength and toughness are well matched.

[0091] The heat treatment method for producing wheels using the steel of Example 3 is similar to that of Example 1, except that:

[0092] The target soaking temperature in step S1 is 920°C, the soaking time is 1.25 hours, and the total heating time is 2.5 hours;

[0093] The idling time in air in step S2 is 90 s, the wheel rotation angular velocity is 80° / s, while the quenching time is 500 s, the wheel rotation angular velocity is 65° / s;

[0094] The target soaking temperature of step S3 is 460°C, and the tempering time is 6 hours.

[0095] The heat treatment method for producing wheels using the steel in Comparative Example 3 is similar to that in Comparative Example 1, except that:

[0096] The target soaking temperature in step S1 is 880°C and the soaking temperature is maintained for 1.0 h.

[0097] The quenching time of step S2 is 300s, and the wheel rotation angular velocity is 65° / s.

[0098] Step S3 is the same as in Example 3.

[0099] Figures 9 and 10 show the prior austenite grain morphology of the wheels from Example 3 and Comparative Example 3. It can be seen that at 880°C, the grains of the wheels from Comparative Example 3 exhibited localized growth and coarsening, with an average grain size of 6.0. However, at 920°C, the grains of the wheels from Example 3 showed no significant localized abnormal growth, with an average grain size of 7.5.

[0100] The microstructures of the wheels of Example 3 and Comparative Example 3 are shown in Figures 11-14. As can be seen, the microstructures of both wheels are composed of fine pearlite and a small amount of ferrite. Within the rim, 35 mm from the tread, the ferrite volume fraction for the wheel of Example 3 is 8.3 ± 0.4%, while that for the wheel of Comparative Example 3 is 9.9 ± 0.3%, a similar difference between the two. However, within the rim at 35 mm from the tread, the pearlite interlamellar spacing of the wheel in Example 3 is 155-163 nm, with an average interlamellar spacing of 159 nm, and the pearlite pellet size is 11.9-13.3 μm, with an average pellet size of 12.8 μm. In contrast, the pearlite interlamellar spacing of the wheel in Comparative Example 3 is 179-190 nm, with an average interlamellar spacing of 185 nm, and the pearlite pellet size is 14.5-16.4 μm, with an average pellet size of 15.7 μm, a significant difference. Figures 13 and 14 also show that the pearlite pellet size uniformity of the wheel in Example 3 is superior to that of the wheel in Comparative Example 3. The finer pearlite interlamellar spacing and pearlite pellet size are the primary factors contributing to the higher hardness and fracture toughness.

[0101] Referring to Example 1 and Comparative Example 1, the wheels of Example 3 and Comparative Example 3 were subjected to room temperature tensile testing, a series of temperature pendulum impact tests, hardness, and fracture toughness tests. The relevant results are shown in Tables 2-3 and Figure 6. The hardness of the wheels of Example 3 at 5mm and 35mm were (316±7) HB and (289±5) HB, respectively, and the fracture toughness was (85±3) MPa·m. 1 / 2 , while the hardness of the wheel in comparative example 3 at 5mm and 35mm is (287±5)HB and (256±3)HB respectively, and the fracture toughness is (80±4)MPa·m 1 / 2 It can be seen that compared with the traditional ER7 wheel, the solution of the present invention can achieve higher rim cross-section hardness while also having higher fracture toughness, and the strength and toughness are well matched.

[0102] Table 1 Main chemical components (wt%) of wheels of the embodiment and comparative example

[0103] (Continued Table 1)

[0104] Table 2 Tensile mechanical properties of wheels of the embodiment and comparative example

[0105] Table 3 Series temperature shock performance of wheel rims of the embodiment and the comparative example

[0106] The underlined data do not meet the requirements of the present invention.

[0107] The above-mentioned reference examples 1 to 3, comparative examples 1 to 3 and Figures 1 to 14 provide a detailed description of a medium carbon steel wheel with good strength-toughness matching and a preparation method thereof. This is merely illustrative and not restrictive. Several embodiments may be listed within the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A medium carbon steel wheel steel with good strength and toughness matching, characterized in that, The medium-carbon steel wheel steel with good strength-ductility matching comprises the following components by mass percentage: C 0.49 - 0.55%, Si 0.30 - 0.60%, Mn 0.70 - 1.20%, Cr 0.26 - 0.35%, Al 0.020 - 0.040%, Ni 0.15 - 0.25%, P ≤ 0.015%, S ≤ 0.010%, and the balance is Fe and inevitable impurity elements.

2. The medium carbon steel wheel steel with good strength and toughness matching according to claim 1, characterized in that, The composition of the medium carbon steel wheel steel with good strength and toughness matching satisfies: Ti ≤ 0.003%, Als 0.017 - 0.035%, N (100 - 150) × 10 -4 %.

3. The medium-carbon steel wheel steel with good strength-ductility matching according to claim 1 or 2, characterized in that, The composition of the medium-carbon steel wheel steel with good strength-ductility matching further satisfies: 0.75 ≤ C + Si / 4 + Cr / 5 + Mn / 6 + Ni / 10 ≤ 1.00, where the numerical value of each element = the content of the element in the steel × 100.

4. A heat treatment method for a wheel, characterized in that, When using the medium-carbon steel wheel steel with good strength-ductility matching described in any one of claims 1 - 3 to produce a wheel, the heat treatment method includes heating, tread spray quenching, and tempering.

5. The heat treatment method according to claim 4, characterized in that, For the heating, the blank wheel is heated as a whole, the soaking temperature is 870 - 920 °C, and the holding time in the soaking section is 1.25 - 1.75 h.

6. The heat treatment method according to claim 4 or 5, characterized in that, Before tread spray quenching, the cooling water is not turned on. The wheel first idles in the air for 60 - 90 s, the rotational angular velocity of the wheel is 70 - 80 ° / s, and then tread spray quenching is carried out.

7. The heat treatment method according to any one of claims 4 to 6, characterized in that For the tread spray quenching, the spray quenching time is 350 - 500 s, the total water flow rate of the quenching table is 120 - 140 tons per hour, the wheel rotates by itself during the spray quenching process, the rotational angular velocity is 55 - 65 ° / s, and it is controlled that the surface temperature of the wheel tread is lower than 70 °C after the spray quenching ends.

8. The heat treatment method according to any one of claims 4-7, characterized in that, After tread spray quenching, the wheel is transported to a ring-type tempering furnace through a chain plate bed for tempering treatment; the transportation time of the chain plate bed is 8 - 10 min, and during the transportation process, it is controlled that the overall temperature rise of the wheel rim does not exceed 400 °C.

9. A wheel produced by the heat treatment method according to any one of claims 4-9, characterized in that, The microstructure of the wheel at room temperature is pearlite + a small amount of ferrite. The volume fraction of ferrite in the microstructure of the entire wear working area is 7% - 12%, the pearlite lamellar spacing is 150 - 180 nm, the pearlite spheroid size is 10.0 - 13.5 μm, and the grain size is ≥ 7.5 grades.

10. The wheel according to claim 9, wherein The hardness at a distance of 5 mm from the tread of the wheel rim is ≥ 300 HB, and the hardness at a distance of 35 mm from the tread is ≥ 275 HB; the tensile strength of the wheel rim is 950 - 980 MPa, the yield strength is 560 - 600 MPa, and the elongation after fracture is 15.0 - 18.0%; the single value of the impact energy Ku5 of the wheel rim at room temperature is ≥ 25 J, and the single value of the impact energy Kv2 at -20 °C is ≥ 12 J; the single value of the fracture toughness of the wheel rim is ≥ 80 MPa·m 1 / 2 , and the average value is ≥ 85 MPa·m 1 / 2 ; the tensile strength of the web is 730 - 780 MPa, and the elongation after fracture is ≥ 20.0 / %.

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