Efficient continuous heat treatment process for carbon steel axle for railway train

Abstract

The invention discloses an efficient continuous heat treatment process for a carbon steel axle for a railway train, which comprises the following steps: S1, machining a hoisting hole in the axle which is uniformly cooled after forging for suspension heat treatment, drilling a hole in one end part of the axle to the axis part, and pre-embedding a thermocouple; s2, estimating the carbon steel axle Ac3 according to the chemical components of the steel and a formula (1), suspending the axle obtained in the step S1 into a heating furnace, heating to (Ac3 + 50-100 DEG C) at the furnace temperature of 2-5 DEG C / min, carrying out heat preservation until a thermocouple displays that the core part reaches the same target temperature, and immediately discharging and cooling for 50-90 minutes; ac3 (DEG C) = 910 <-20 > sqr (C) + 44.7 Si <-15 >. 2 Ni + 31.5 Mo + 104 V formula (1); s3, the axle cooled in the S2 is fed into the furnace with the temperature, heated to 530-560 DEG C again to be tempered, subjected to heat preservation for a period of time and then discharged out of the furnace to be cooled; and S4, the end of the axle obtained in the S3 is sawed, and the hole defect of the end is removed. The axle center reaches the normalizing temperature through heating furnace gas, axle austenitizing structure transformation and discharging can be completed, the carbon steel axle heat treatment time is greatly shortened, the production efficiency is improved, and energy consumption is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of rail transit axle manufacturing, and particularly to an efficient continuous heat treatment process for carbon steel axles used in railway trains. Background Art

[0002] As a key component of the running part of railway vehicles, the axle bears almost all the loads generated and obtained by the vehicle, and its quality is directly related to railway operation safety. To obtain reliable axle performance, it is necessary to achieve it through the regulation of axle steel composition and heat treatment.

[0003] As a common type of axle material, carbon steel axles have the advantages of low material cost and high cost performance, and are widely used at home and abroad. Common grades of carbon steel axles include EA1N, RSA1, LZ50, and AAR M-101F, etc. Carbon steel axles are delivered after normalizing (once or twice) + tempering or normalizing treatment, and are used in the largest quantity on railway locomotives, passenger cars, and freight cars. The normalizing equipment for axles is all high-power walking beam heat treatment furnaces or suspension type heat treatment furnaces, and the normalizing time is relatively long and the equipment energy consumption is relatively large under the traditional process design.

[0004] For example, Patent CN104404224A discloses a heat treatment process method for EA1N material urban rail axles, including two normalizing and one tempering processes. This process method takes a long time (the overall time reaches 15 hours), the process steps are complex, and the energy consumption is relatively large; another example is that Patent CN107937676A discloses a heat treatment process for EA1N axle steel, which adjusts the process path, including steps such as blank loading into the furnace, overall heating, normalizing and holding for 4 - 7 hours, and cooling, etc. This process omits the tempering step (tempering can eliminate the stress during normalizing), and the influence of heat treatment residual stress is not clear. Moreover, this process prolongs the normalizing and holding time for one time, and the energy consumption during the normalizing process is relatively high. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides an efficient continuous heat treatment process for carbon steel axles used in railway trains, which can greatly shorten the heat treatment time of carbon steel axles, improve production efficiency, and reduce energy consumption.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] An efficient continuous heat treatment process for carbon steel axles used in railway trains, comprising the following steps:

[0008] S1: Process and install a lifting hole on the axles cooled evenly after forging for hanging heat treatment, drill a hole at one end of the axle to the axial center part, and embed a thermocouple;

[0009] S2: According to the chemical composition of the steel, estimate carbon steel axle A according to formula (1)c3 , suspend the axle obtained in S1 and put it into a heating furnace. Heat the furnace temperature at a rate of 2 - 5 °C / min to (A c3 + 50 - 100 °C) and keep it warm until the thermocouple shows that the core reaches the same target temperature, then take it out of the furnace and cool for 50 - 90 min;

[0010] A c3 (°C) = 910 - 203sqr(C) + 44.7Si - 15.2Ni + 31.5Mo + 104V Formula (1)

[0011] S3: Put the axle cooled in S2 into the furnace while still warm, heat it again to 530 - 560 °C for tempering, keep it warm for a period of time, and then take it out of the furnace and cool;

[0012] S4: For the axle obtained in S3, saw off the ends and remove the hole defects at the ends.

[0013] The carbon steel axle for railway trains includes the following mass percentage components:

[0014] C: 0.28 - 0.59%, Si: 0.17 - 0.40%, Mn: 0.60 - 1.10%, P ≤ 0.030%, S ≤ 0.030%, Cr ≤ 0.30%, Ni ≤ 0.30%, Cu ≤ 0.30%, V: ≤ 0.05%, and the rest is Fe and other inevitable impurities.

[0015] In S1, use a suspension lifting arm to suspend the upper end of the axle.

[0016] In S1, the lifting hole penetrates the axle body radially and is lifted axially, and the thermocouple embedding hole is drilled radially.

[0017] In S1, the depth d of the hole for embedding the thermocouple varies with the diameter D of the axle. The size of the hole depth d is 1 / 2 × D, and the drilling position is at the extended part of the axle without affecting the finished axle.

[0018] In S1, for carbon steel axles with a diameter in the range of 190 - 220 mm, for the heat-treated axles of the same batch, only one thermocouple needs to be embedded.

[0019] In S2, for axles that need secondary normalizing, after the first normalizing and cooling out of the furnace, they can be put into the furnace while still warm and heated to Ac3 + 10 - 50 °C, and then cooled again after keeping warm.

[0020] In step S2, during normalizing, after the furnace temperature on the surface of the axle reaches the target temperature, heat preservation starts, and the heat preservation time t0 is determined according to the detection prompt of the temperature measurement system; to protect the finished axle, the position where the thermocouple is implanted is not at the maximum diameter of the axle. After the temperature measurement system shows that the target temperature is reached, the additional heat preservation time t1 can be obtained from the diameter difference ΔD between the extension body and the wheel seat, as shown in formula (2).

[0021] t = t0 + t1 = t0 + 1 / 6 × α × ΔD Formula (2)

[0022] Wherein, t — Normalizing heat preservation time;

[0023] ΔD — Diameter difference between the extension body and the wheel seat, mm;

[0024] α — Coefficient value is 1, min / mm;

[0025] For carbon steel axles of EA1N, RSA1, LZ50, and AAR M-101F within the axle diameter range of 190 - 220 mm, the heat treatment normalizing heat preservation treatment time is 2 - 4 h.

[0026] In step S3, the tempering heat preservation treatment time is controlled within 1.2 - 1.5 times of its normalizing heat preservation time, and after being taken out of the furnace, it is air-cooled or air-blown.

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

[0028] The high-efficiency continuous heat treatment process for carbon steel axles used in railway trains is reasonably designed. By using the furnace gas to make the core of the axle reach the normalizing temperature, the austenitization structure transformation of the axle can be completed and taken out of the furnace; and by measuring the temperature curve during the heat treatment process with a heat-resistant temperature recorder and analyzing and determining the temperature-reaching process of the core of the axle, the heat treatment time of the carbon steel axle is greatly shortened, the production efficiency is improved, and the energy consumption is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The following briefly describes the content expressed by each drawing in this specification and the marks in the drawings:

[0030] Figure 1 It is a schematic diagram of measuring the temperature of the core of the axle heat treatment of the present invention.

[0031] Figure 2 It is the temperature-time curve of the axle heat treatment in Embodiment 1 of the present invention.

[0032] Figure 3 It is the temperature-time curve of the axle heat treatment in Comparative Example 1 of the present invention.

[0033] Figure 4 It is the microstructural diagram of the core of the axle after heat treatment in Embodiment 1 of the present invention.

[0034] Figure 5Microstructure diagram of the axle center part of the car after heat treatment, which is Comparative Example 1 of the present invention. Specific embodiments

[0035] The following is a further detailed description of the specific embodiments of the present invention by describing the embodiments with reference to the accompanying drawings.

[0036] As Figure 1 shown, the carbon steel axle for railway trains includes the following components by mass percentage:

[0037] C: 0.28 - 0.59%, Si: 0.17 - 0.40%, Mn: 0.60 - 1.10%, P ≤ 0.030%, S ≤ 0.030%, Cr ≤ 0.30%, Ni ≤ 0.30%, Cu ≤ 0.30%, V: ≤ 0.05%, and the rest are Fe and other inevitable impurities; the increase of carbon and alloy elements in the axle steel will reduce its thermal conductivity, which is not conducive to the microstructure transformation during normalizing heating.

[0038] The high-efficiency heat treatment process for the carbon steel axle of the present invention has the following detailed technical steps:

[0039] S1: Process a lifting hole for the forged and uniformly cooled axle for hanging heat treatment, drill a hole at one end of the axle to the axle center, and embed a thermocouple.

[0040] S2: According to the chemical composition of the steel, estimate the Ac1 of the carbon steel axle according to Formula 1 c3 , hang the axle obtained in S1 into the heating furnace, heat the furnace temperature to (Ac1 c3 +50 - 100 °C) at a rate of 2 - 5 °C / min and hold for heat until the thermocouple shows that the center reaches the same target temperature, and then take it out of the furnace and cool for 50 - 90 min.

[0041] Ac1 c3 (°C) = 910 - 203√C + 44.7Si - 15.2Ni + 31.5Mo + 104V Formula (1)

[0042] S3: Put the cooled axle in S2 into the furnace while it is still warm, heat it again to 530 - 560 °C for tempering, hold for a period of time, and then take it out of the furnace and cool.

[0043] S4: Saw the ends of the axle obtained in S3 to remove the hole defects at the ends.

[0044] Furthermore:

[0045] In step S1 of the present invention, the upper end of the axle is suspended by a hanging lifting arm; the lifting holes are along the axial direction, and the holes for embedding thermocouples are along the radial direction. The depth d of the hole for embedding the thermocouple varies with the diameter D of the axle. The size of the depth d is 1 / 2×D, and the drilling position is at the extended body of the axle without affecting the finished axle. For carbon steel axles with a diameter in the range of 190 - 220 mm, for the heat-treated axles of the same batch, only one thermocouple needs to be embedded.

[0046] In step S2 of the present invention, for axles that require secondary normalizing (TB / T 2945 - 1999 stipulates that LZ50 axles must undergo two normalizing and one tempering treatments), after the first normalizing and cooling out of the furnace, it can be reheated while still warm (TB / T2945 - 1999 stipulates that the furnace inlet temperature of LZ50 axles should be lower than 500°C) to (A c3 +10 - 50°C) and then cooled again after holding.

[0047] In step S2 of the present invention, the heat treatment time varies with the steel type, specification, and the number of axles charged into the furnace. During normalizing, after the surface of the axle (furnace temperature) reaches the target temperature, heat preservation starts, and the heat preservation time t0 is determined according to the detection prompt of the temperature measurement system. To protect the finished axle, the position where the thermocouple is implanted is not at the maximum diameter of the axle. After the temperature measurement system shows that the target temperature has been reached, the additional heat preservation time t1 can be obtained from the diameter difference ΔD between the extended body and the wheel seat, as shown in formula (2).

[0048] t = t0 + t1 = t0 + 1 / 6×α×ΔD Formula (2)

[0049] Where, t - normalizing heat preservation time;

[0050] ΔD - diameter difference between the extended body and the wheel seat, mm;

[0051] α - coefficient value is 1, min / mm.

[0052] For EA1N, RSA1, LZ50, and AAR M - 101F carbon steel axles with a diameter in the range of 190 - 220 mm, the heat treatment normalizing heat preservation treatment time is generally 2 - 4 h.

[0053] Furthermore, in step S3 of the present invention, the tempering heat preservation treatment time is controlled to be 1.2 - 1.5 times of its normalizing heat preservation time; after being taken out of the furnace, it is air - cooled or air - blast cooled.

[0054] To achieve the carbon axle steel described in the present invention, it is a low - alloy structural steel with a C content of 0.28 - 0.59%. Normalizing heat treatment is to refine the grains and obtain a uniform ferrite + pearlite microstructure, so as to obtain higher strength and toughness. The normalizing temperature of the carbon axle steel generally takes A c3Above 50 - 100°C, temperature has a decisive influence on the final properties of the material. To ensure the consistency of axle performance and eliminate the influence of diameter differences at different positions of the axle, it is necessary to ensure that the core of the axle can reach the target temperature. The heating austenitization process of the equilibrium structure of axle steel can be divided into three stages: austenite nucleation and growth, dissolution of residual cementite, and austenite homogenization. The increase in heating temperature significantly increases the nucleation rate and growth rate of austenite, greatly shortening the transformation incubation period and the transformation completion time. For carbon structural steel, during the heating process to the normalizing temperature, it is sufficient to complete the transformation of austenite and achieve short-time heat preservation. At this time, some carbides in the steel do not have time to dissolve, providing composition fluctuations for the transformation of supercooled austenite, which is beneficial to grain refinement. Therefore, the complete dissolution of carbides is not necessary. The size of austenite under short-time heat preservation is not completely uniform, with concentration fluctuations, which is beneficial to the refinement of the microstructure. When excessive pursuit of homogenization leads to an extension of the heat preservation time, it will result in coarse grains and consume a large amount of energy. Therefore, for carbon steel axles, there is a lag in the heat treatment heating process at the core compared to the surface. When the core reaches the temperature and is taken out of the furnace, the austenitization structure transformation of the axle can be completed, and then a uniform ferrite + pearlite structure can be obtained. Therefore, the process of taking the axle out of the furnace when the core reaches the temperature adopted in the present invention can greatly shorten the heat treatment time of carbon steel axles, improve production efficiency, and reduce energy consumption.

[0055] Example 1 of the present invention

[0056] The LZ50 axle steel described in this example, A c3 Estimated by the empirical formula according to the chemical composition, it is about 760°C, and the forging heating temperature is 1150 - 1250°C. After final forging, the axle enters the cooling bed for uniform cooling. As Figure 1 shown, before heat treatment, holes are drilled at the end of the forged blank axle. The hanging lifting hole is located at the extended part of the axle end and penetrates the axle body. The thermocouple implantation hole is located at the extended part of the other axle end, with a hole depth of about 90 mm (1 / 2 axle diameter), and is connected to the online temperature measurement system of the heating furnace. Among them, the temperature measurement system with data wireless transmission function is fixed at the upper end of the outside furnace lifting tool and enters the hanging heat treatment line together, thereby continuously recording the temperature change during the heat treatment process and realizing online feedback. According to the heat treatment process in Table 1, after the axle surface is heated to 850 ± 10°C, normalizing heat preservation is carried out. According to the signal of the temperature measurement system, the time taken for the measured value to reach the target temperature of about 850°C is t 11 . According to formula (2), the diameter difference between the implanted thermocouple axle diameter and the maximum diameter of the wheel seat is about 60 mm, and it can be obtained that the extended heat preservation time is about 10 min. The actual heat preservation time is (t 11 + 10 min). Then it is taken out of the furnace and air-cooled for about 70 min. After the axle temperature is less than 500°C, the axle is put into the furnace with temperature for secondary normalizing. After heating to 800 ± 10°C, the heat preservation time is t 12 . Then it is taken out of the furnace and air-cooled to below 250°C for tempering. The tempering temperature is 540°C, and the heat preservation is 1.5t11 After being taken out of the furnace, it is air-cooled. The temperature-time curve of the axle center part obtained by the temperature measurement system is shown in Figure 2 , and there are obvious inflection points in the heating process curve, that is, the endothermic reaction of the phase change process occurs. After the reaction ends, the curve continues to rise, and the phase change completion time can be inferred. It can be seen that the austenitization of the carbon steel axle is relatively rapid during the normalizing heating process, and it is easy to achieve short-time heat preservation. The temperature reaching process of the axle center part is sufficient to complete the tissue transformation.

[0057] Comparative Example 1 of the present invention

[0058] The LZ50 axle used in this comparative example has the same furnace number, same specification, and is produced in the same batch as that in Example 1. The same heat treatment method as that in Example 1 is adopted, and the heat preservation time is selected according to traditional experience, that is, the heat preservation time is set according to the calculation formula of diameter (mm) × 1 min / mm, as shown in Table 1. The axle is heated to 850 ± 10 °C for the first normalizing and kept warm for 4 - 5 h. After being taken out of the furnace and cooled, it is heated to 800 ± 10 °C again and kept warm for 4 - 5 h, then taken out of the furnace and cooled to below 250 °C, and kept warm for 6 h at a temperature of 540 °C, and then taken out of the furnace and air-cooled. In order to record the temperature change during the heat treatment process of the axle in this example, the same temperature measurement method as that in Example 1 is adopted for the axle with an extension body in this example, and the temperature-time curve of the axle heat treatment is obtained, as shown in Figure 3 . Under the same heat treatment heating system, obvious mutations have occurred in the temperature-time curves of both Example 1 and Comparative Example 1, and austenitization phase change has occurred. Before reaching the target temperature, the tissue transformation has been fully completed. The heat preservation time in Comparative Example 1 is much longer than that in Example 1. For the carbon steel axle, there is a large surplus in the heat preservation time in Comparative Example 1.

[0059] According to GB 228, tensile tests are carried out on the axle. The specimens are taken from any position at half the distance from the surface to the center line of the axle and are parallel to the axle axis. The results are shown in Table 2, and Example 1 is equivalent to Comparative Example 1. Specimens are intercepted on the cross-section perpendicular to the axis at the large end of the tensile specimen where there is no deformation. According to YB / T 5148, the grain size of the axle is inspected. The results are shown in Table 3, and the metallographic structure of the axle is shown in Figure 4 、 Figure 5 , both of which are ferrite and pearlite, and the grain size inspection results are equivalent. Therefore, Example 1 can obtain tissues and properties equivalent to those of Comparative Example 1, and meet the requirements of TB / T 2945, while the time-consuming of the heat treatment heat preservation process is shortened by 41%, the heat treatment energy consumption is reduced, and the heat treatment efficiency is improved.

[0060] Table 1 Heat treatment process of carbon steel axle

[0061]

[0062] Table 2 Detection results of mechanical properties of LZ50 axle

[0063]

[0064] Table 3 Inspection Results of Grain Size of LZ50 Axle Structure

[0065]

[0066]

[0067] Example 2 of the Present Invention

[0068] For the EA1N axle steel described in this example, A c3 Estimated by an empirical formula according to the chemical composition, it is about 785°C, and the forging heating temperature is 1150 - 1250°C. After final forging, the axle enters the cooling bed for uniform cooling. As Figure 1 shown, holes are drilled at the end of the blank axle. The hanging lifting hole is located at the extended body of the axle end and penetrates the axle body. The thermocouple implantation hole is located at the other extended body of the axle end, with a hole depth of about 85 mm (1 / 2 axle diameter), and is connected to the on-line temperature measurement system of the heating furnace. Among them, the temperature measurement system with data wireless transmission function is fixed at the upper end of the outside furnace sling and enters the hanging heat treatment line together, thereby continuously recording the temperature change during the heat treatment process and realizing on-line feedback. After the axle surface is heated to 860°C according to the heat treatment process in Table 1, normalizing and holding heat. According to the signal of the temperature measurement system, the time t2 is used when the measured value reaches the target temperature of about 860°C. According to formula (2), the difference between the diameter of the implanted thermocouple axle and the diameter of the wheel seat with the largest diameter is about 55 mm, and it can be obtained that the holding time is extended by about 9 min. The actual holding time is (t2 + 9 min). Then it is taken out of the furnace and air-cooled to below 250°C for tempering. The tempering temperature is 540°C, and after holding heat for 1.5t2, it is taken out of the furnace and air-cooled. The temperature-time curve of the axle center part obtained by the temperature measurement system is similar to Figure 2 shown.

[0069] Comparative Example 2 of the Present Invention

[0070] The EA1N axle used in this comparative example is of the same furnace number, same specification, and same batch production as that in Example 2. The same heat treatment method as in Example 1 is adopted, and the holding time is selected according to traditional experience, that is, the holding time is set according to the calculation formula of diameter (mm) × 1 min / mm, as shown in Table 1. The axle is heated to 860 ± 10°C for the first normalizing and held for 4 - 5 h, then taken out of the furnace and cooled to below 250°C, held for 6.9 h at 540°C, and then taken out of the furnace and air-cooled. For the axle with an extended body in this example, the same temperature measurement method as in Example 2 is adopted, and the heat treatment temperature-time curve of the axle can be obtained. The curve is similar to Figure 3 shown.

[0071] Temperature-time curve analysis, microstructure grain size, and tensile property inspection were carried out with reference to Example 1 and Comparative Example 1. The relevant results are shown in Table 4 and Table 5. It can be seen that the soaking time during normalizing heat treatment in Example 2 was shortened by 46%, ensuring the axle performance, reducing the heat treatment energy consumption, and improving the heat treatment efficiency.

[0072] Table 4 Detection Results of Mechanical Properties of EA1N Axles

[0073]

[0074] Table 5 Inspection Results of Microstructure Grain Size of EA1N Axles

[0075]

[0076] Example 3 of the present invention

[0077] For the RSA1 axle steel described in this example, A c3 Estimated by the empirical formula according to the chemical composition, it is about 776 °C, and the forging heating temperature is 1150 - 1250 °C. After final forging, the axle enters the cooling bed for uniform cooling. As Figure 1 shown, holes are drilled at the end of the blank axle. The hanging lifting hole is located at the end extension of the axle and penetrates the axle body. The thermocouple implantation hole is located at the other end extension of the axle, with a hole depth of about 95 mm (1 / 2 axle diameter), and is connected to the online temperature measurement system of the heating furnace. The temperature measurement system with data wireless transmission function is fixed at the upper end of the outside furnace sling and enters the hanging heat treatment line together, thereby continuously recording the temperature change during the heat treatment process and realizing online feedback. After the axle surface is heated to 860 °C according to the heat treatment process in Table 1, normalizing heat preservation is carried out. According to the signal of the temperature measurement system, the time t3 is used when the measured value reaches the target temperature of about 860 °C. According to formula (2), the difference between the diameter of the implanted thermocouple axle and the diameter of the wheel seat with the largest diameter is about 50 mm, and it can be obtained that the soaking time is extended by about 8 min. The actual soaking time is (t3 + 8 min). Then it is taken out of the furnace and air-cooled to below 250 °C for tempering. The tempering temperature is 540 °C, and after soaking for 1.5t2, it is taken out of the furnace and air-cooled. The temperature-time curve of the axle center obtained by the temperature measurement system is similar to Figure 2 shown.

[0078] Comparative Example 3 of the present invention

[0079] The RSA1 axle used in this comparative example was produced in the same furnace batch, with the same specifications and the same lot as that in Example 3. The same heat treatment method as in Example 1 was adopted, and the holding time was selected according to traditional experience, that is, the holding time was set according to the calculation formula of diameter (mm) × 1 min / mm, as shown in Table 1. The axle was heated to 860 ± 10 °C for normalizing for the first time and held for 4 - 5 h, then taken out of the furnace and cooled to below 250 °C, held at 540 °C for 7.5 h, and then taken out of the furnace and air-cooled. For the axle with an extension body in this example, the same temperature measurement method as in Example 2 was adopted, and the temperature-time curve of the axle heat treatment could be obtained. The curve was similar to Figure 3 that shown

[0080] Refer to Example 1 and Comparative Example 1 for temperature-time curve analysis, microstructure grain size and tensile property inspection. The relevant results are shown in Table 6 and Table 7. It can be seen that the holding time of the normalizing process in Example 3 was shortened by 40%, which ensured the axle performance, reduced the heat treatment energy consumption, and improved the heat treatment efficiency.

[0081] Table 6 Detection Results of Mechanical Properties of RSA1 Axle

[0082]

[0083] Table 7 Inspection Results of Microstructure Grain Size of RSA1 Axle

[0084]

[0085] The high-efficiency continuous heat treatment process for carbon steel axles used in railway trains of the present invention is reasonably designed. By using the furnace gas to make the core of the axle reach the normalizing temperature, the austenitization structure transformation of the axle can be completed and the axle can be taken out of the furnace; and by measuring the temperature curve during the heat treatment process with a heat-resistant temperature recorder and analyzing and determining the process of the core of the axle reaching the temperature, the heat treatment time of the carbon steel axle is greatly shortened, the production efficiency is improved, and the energy consumption is reduced.

[0086] The present invention has been described exemplarily above with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above methods. As long as various non-substantive improvements are made by adopting the concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A high-efficiency continuous heat treatment process for carbon steel axles for railway trains, characterized in that: The treatment process comprises the following steps: S1: Process a hoisting hole on the axle that is evenly cooled after forging for hanging heat treatment, and drill a hole at one end of the axle to the axis center and embed a thermocouple; S2: Estimate the carbon steel axle A according to the chemical composition of the steel using formula (1). c3 The axle obtained in S1 is hung into a heating furnace and heated at a temperature of 2 to 5°C / min to (A c3 +50~100℃) and keep warm until the thermocouple shows that the core reaches the same target temperature, then take it out of the furnace and cool for 50~90min; A c3 (℃)=910-203sqr(C)+44.7Si-15.2Ni+31.5Mo+104V Formula (1) S3: the axle cooled in S2 is put into the furnace with the temperature kept high, and is heated to 530-560°C for tempering again, and after being kept at the temperature for a period of time, it is taken out of the furnace and cooled; S4: For the axle obtained in S3, sawing the end to remove the hole defect at the end.

2. The high-efficiency continuous heat treatment process for carbon steel axles for railway trains as claimed in claim 1, characterized in that: The carbon steel axle for railway trains comprises the following components in percentage by mass: C: 0.28~0.59%, Si: 0.17~0.40%, Mn: 0.60~1.10%, P≤0.030%, S≤0.030%, Cr≤0.30%, Ni≤0.30%, Cu≤0.30%, V: ≤0.05%, and the rest are Fe and other inevitable impurities.

3. The high-efficiency continuous heat treatment process for carbon steel axles for railway trains as claimed in claim 1, characterized in that: In S1, a suspension hoisting arm is used to suspend the upper end of the axle.

4. The high-efficiency continuous heat treatment process for carbon steel axles for railway trains as claimed in claim 1, characterized in that: In S1, the hoisting hole penetrates the shaft body in the radial direction, the shaft body is hoisted in the axial direction, and the pre-embedded thermocouple is drilled in the radial direction.

5. The high-efficiency continuous heat treatment process for carbon steel axles for railway trains as claimed in claim 1, characterized in that: In S1, the hole depth d for embedding the thermocouple varies with the change of the axle diameter D. The hole depth d is 1 / 2×D, and the drilling position is located at the axle extension body without affecting the finished axle.

6. The high-efficiency continuous heat treatment process for carbon steel axles for railway trains as claimed in claim 5, characterized in that: In S1, for carbon steel axles with axle diameters ranging from 190 to 220 mm, a thermocouple may be pre-embedded for the same batch of heat-treated axles.

7. The high-efficiency continuous heat treatment process for carbon steel axles for railway trains as claimed in claim 1, characterized in that: In S2, for the axle that needs secondary normalizing, after being cooled after the primary normalizing, it can be brought back into the furnace and heated to Ac3+10~50°C, and then cooled again after being kept warm.

8. The high-efficiency continuous heat treatment process for carbon steel axles for railway trains as claimed in claim 1, characterized in that: In S2, when normalizing, the axle surface temperature is kept warm after reaching the target temperature, and the warm-keeping time t0 is determined according to the detection prompt of the temperature measurement system. In order to protect the finished axle, the thermocouple is not embedded at the position where the shaft diameter is the largest. After the temperature measurement system shows that the target temperature has been reached, the warm-keeping time t1 to be extended can be obtained by the diameter difference ΔD between the extension body and the wheel seat, as shown in formula (2). t=t0+t1=t0+1 / 6×α×ΔD Formula (2) Among them, t is the normalizing and holding time; ΔD—Difference between the extension body and the wheel seat diameter, mm; α—coefficient value is 1, min / mm; For EA1N, RSA1, LZ50 and AAR M-101F carbon steel axles with a diameter of 190 to 220 mm, the heat treatment normalizing and insulation treatment time is 2 to 4 hours.

9. The high-efficiency continuous heat treatment process for carbon steel axles for railway trains as claimed in claim 1, characterized in that: In S3, the tempering and heat-holding treatment time is controlled to be 1.2 to 1.5 times of the normalizing and heat-holding time, and the furnace is air-cooled or wind-cooled after being taken out of the furnace.

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