A rapid nitriding and micro-distortion process for large thin-walled inner gear rings

Abstract

The present invention relates to a rapid nitriding micro-distortion process method for a large thin-walled internal gear ring, comprising the following steps: (1) selecting a chromium-based alloy blank with a Brinell hardness range of 170-320HB, performing a forging upsetting treatment with a forging ratio of ≥8, punching and then rolling the ring, and then performing a normalizing treatment to obtain a ring blank; (2) sequentially performing rough turning, solution treatment, semi-finishing turning, rough toothing, quenching treatment, tempering treatment, finish turning, finish tooth milling, rough drilling and screw drilling, first aging treatment, finish drilling and screw drilling, finish turning, rough tooth grinding, second aging treatment, and finish tooth grinding on the ring blank to obtain a semi-finished product; and (3) finally performing a nitriding treatment on the semi-finished product to obtain a large thin-walled internal gear ring. The method of the present invention can effectively control the problem of severe distortion of large thin-walled internal gear rings after heat treatment. The distortion end runout can be controlled to ≤0.01mm / φ1000, the radial runout (Fr) can be controlled to ≤0.02mm / φ1000, the nitriding layer depth can be greater than 0.3mm, and the surface hardness can reach 600-800HV.

Description

Technical Field

[0001] The invention relates to the field of heat treatment technology, and in particular to a method for rapid nitriding and micro-distortion of a large thin-walled inner gear ring. Background Art

[0002] As wind turbine speed increasers grow in size, the size of the internal gear ring, a key component of the transmission, continues to increase. Current designs feature larger outer diameters, wider tooth widths, and smaller wall thicknesses. The internal gear ring is a key component in mechanical transmission structures, ensuring the stability and safety of the transmission components and even the entire system. This demands higher standards for surface hardness, wear resistance, fatigue strength, and corrosion resistance.

[0003] When processing the inner gear ring, surface strengthening is adopted to reduce problems such as wear, oxidation and corrosion on the surface of the inner gear ring. The usual method to form a strengthening layer on the surface of the inner gear ring is to nitride the workpiece. The so-called nitriding treatment refers to the penetration of nitrogen into the interior of the inner gear ring and the formation of a nitrogen-rich hardened layer on the surface of the inner gear ring. This process is a chemical heat treatment process. The principle of the process is: by heating ammonia until the penetrated nitrogen is decomposed and an iron-nitrogen alloy is formed on the surface of the inner gear ring, the purpose of improving the mechanical properties, physical properties and chemical properties of the inner gear ring is ultimately achieved. Generally, the nitriding treatment can be divided into three stages, namely: ammonia decomposes the required nitrogen; the surface of the inner gear ring absorbs nitrogen atoms; after the nitrogen on the surface of the inner gear ring reaches saturation, the nitrogen continues to diffuse into the interior of the inner gear ring, thereby increasing the thickness of the nitriding layer.

[0004] The conventional hardening process for internal gear rings is gas nitriding, typically at temperatures between 490-530°C. The greater the MW rating, the deeper the required nitriding layer depth. The difficulty in manufacturing internal gear rings lies in the fact that due to the thin wall and large workpiece, prolonged nitriding inevitably produces proportional distortion. Furthermore, long nitriding times increase manufacturing costs, while minor distortions require repairs and severe distortions can even lead to workpiece rejection. A process is urgently needed to quickly achieve the required effective hardening layer depth for large, thin-walled internal gear rings while simultaneously controlling distortion. Summary of the Invention

[0005] In order to solve the technical problem of severe distortion caused by nitriding of large thin-walled internal gear rings, a method for rapid nitriding and micro-distortion of large thin-walled internal gear rings is provided. The method of the present invention can effectively control the severe distortion of large thin-walled internal gear rings after heat treatment. The depth of the nitriding layer is greater than 0.3mm, and the surface hardness can reach 600-800HV.

[0006] In order to achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A method for rapid nitriding and micro-distortion of a large thin-walled internal gear ring comprises the following steps:

[0008] (1) A chromium-based alloy blank with a Brinell hardness range of 170-320 HB is selected for forging and upsetting treatment with a forging ratio of ≥8, and then punched and rolled, and then normalized to obtain a ring blank;

[0009] (2) performing rough turning, solution treatment, semi-finishing turning, rough toothing, quenching, tempering, finishing turning, finishing tooth milling, rough drilling and screw drilling, first aging treatment, finishing drilling and screw drilling, finishing turning, rough tooth grinding, second aging treatment, and finishing tooth grinding on the ring blank in sequence to obtain a semi-finished product;

[0010] (3) Finally, the semi-finished product is subjected to nitriding treatment to obtain a large thin-walled inner gear ring.

[0011] Furthermore, the chromium-based alloy blank is one of 42CrMo, 34CrNiMo6, and 31CrMoV9.

[0012] Furthermore, the temperature of the normalizing treatment is 850-950°C, the holding time is 4-6h, the heating rate is 200°C / h, and after the normalizing treatment is completed, the furnace is cooled to 200°C.

[0013] Furthermore, the temperature of the solution treatment is 900-950°C, the holding time is 4-6h, the heating rate is 200°C / h, and after the solution treatment is completed, the furnace is cooled to 200°C.

[0014] Furthermore, the quenching treatment is to first heat the temperature to 800-880°C and keep it warm for 1-2 hours, then quench and cool in PAG quenching liquid until the tooth root temperature reaches 200-250°C, remove the liquid, and then perform salt bath quenching; the temperature of the PAG quenching liquid is controlled at 30-40°C, and the cooling rate is ≥160°C / h; the salt bath quenching is to remove the workpiece when it is cooled to 140°C.

[0015] Furthermore, the tempering treatment temperature is at least 590°C, the temperature is maintained for 5-7 hours, the heating rate is at least 100°C / h, and after the tempering treatment is completed, the steel is air-cooled to below 200°C.

[0016] Furthermore, the temperature of the first aging treatment is 550-600°C, the holding time is 5-8h, the heating rate is 100-150°C / h, and after the first aging treatment is completed, the temperature is cooled to 150°C at a cooling rate of 50-100°C / h; the temperature of the second aging treatment is 200-250°C, the holding time is 4-6h, the heating rate does not exceed 100°C / h, and after the second aging treatment is completed, the temperature is cooled to below 100°C at a cooling rate of 50-100°C / h.

[0017] Furthermore, the nitriding treatment is to first heat the temperature to 550≤T1≤560℃ at a heating rate of 30-40℃ / h and keep it warm for 6-10h, then cool it to 540≤T2<550℃ at a cooling rate of 40-50℃ / h and keep it warm for 6-14h, cool it to 530≤T3<540℃ at a cooling rate of 40-50℃ / h and keep it warm for 10-20h, then cool it to 480≤T4<530℃ at a cooling rate of 40-50℃ / h and keep it warm for 16-26h, introduce ammonia into the T1, T2, T3 and T4 stages and control the ammonia decomposition rate to 50%, 55%, 60% and 65-68% respectively, and finally cool it to 80℃ at a cooling rate of 40-50℃ / h.

[0018] Beneficial technical effects:

[0019] The present invention adopts a forging ratio of ≥8 and then rolls the ring to improve the density of the alloy, refine the coarse grains to obtain a more uniform wall thickness, and promptly perform normalizing treatment after upsetting, which can promote further grain refinement, eliminate forging stress, and improve cutting ability; then, after rough turning, solid solution and quenching are performed to temper the alloy to improve the uniformity of the alloy composition, reduce dendrite segregation, and reduce nitriding distortion, thereby obtaining higher strength, excellent toughness, plasticity and cutting ability; quenching adopts salt water quenching and PAG cold quenching, which can maximize the hardening without generating cracks. The better the hardening depth, the better the hardness of the alloy matrix after nitriding, which is conducive to increasing the nitriding temperature to obtain a better Good nitriding strengthening effect increases the rigidity of the alloy matrix while making it less likely to produce high-temperature creep, thereby obtaining a slightly distorted workpiece; subsequent fine turning, fine milling, rough machining and other series of machining will produce obvious machining internal stress, so secondary aging treatment is required. First, high-temperature aging is used to remove the initial stress, and the heating and cooling rates are controlled to avoid secondary stress. At the same time, the internal stress of the workpiece is eliminated and the mechanical properties are improved. Then, fine machining, rough grinding and other operations are performed. During the grinding process, the metal bonds are broken and energy is released. The fluctuation of energy will inevitably lead to internal stress. Therefore, low-temperature aging treatment is required to further eliminate the internal stress, thereby stabilizing the structure and size.

[0020] The method of the present invention realizes rapid nitriding and achieves micro-distortion effect through process improvement, can control the nitriding layer depth to be greater than 0.3mm, and can reduce the process time by 25-60%. The surface hardness can reach 600-800HV, the depth of the white bright layer is less than 15μm, and the brittleness level of the nitriding layer reaches level 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of a large thin-walled internal gear ring. The internal teeth are not shown in the figure, but they exist in the actual manufacturing process.

[0022] Figure 2 This is the nitriding process diagram of Example 1. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention and the accompanying drawings to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] Unless otherwise specifically stated, the numerical value set forth in these embodiments does not limit the scope of the present invention. Technology and methods known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology and methods should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments can have different values.

[0025] In addition, it should be noted that the use of terms such as "first" and "second" to limit the aging treatment is only for the convenience of distinguishing the aging treatment in each step. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0026] In the following examples, experimental methods without specific conditions are generally measured according to national standards. If there are no corresponding national standards, they are measured according to the general international standards or the standards proposed by relevant companies. Unless otherwise stated, all parts are by weight and all percentages are by weight.

[0027] Example 1

[0028] A method for rapid nitriding micro-distortion of large thin-walled internal gear rings. The schematic diagram of the large thin-walled internal gear ring workpiece is as follows: Figure 1 As shown, Figure 1 The internal teeth are not shown in the figure, but they are present in the actual manufacturing process. The large thin-walled internal gear ring prepared in this embodiment has an outer diameter of 2500 mm, an inner diameter of 2300 mm, and a wall thickness of 100 mm, and includes the following steps:

[0029] (1) 42CrMo alloy billets were subjected to forging and upsetting treatment with 4 forgings and 3 drawing, followed by punching, hole expansion with a 10-ton electric hammer frame, and ring rolling. The billets were then heated to 900°C at a heating rate of 200°C / h and normalized for 5 hours, then cooled to 200°C in the furnace to obtain ring billets.

[0030] (2) rough turning the ring blank, then heating it to 920°C at a heating rate of 200°C / h for solution treatment, holding the temperature for 5 hours, and then cooling it to 200°C in the furnace;

[0031] Then, semi-finish turning and rough tooth opening are carried out, and the workpiece is heated to 820℃ for heat treatment and kept at this temperature for 2 hours. Subsequently, it is quenched and cooled in PAG quenching liquid, and the temperature of the PAG quenching liquid is kept at 30℃ and the cooling rate is 160℃ / h. When the temperature of the tooth root reaches 220℃, the liquid is removed and the workpiece is cooled to 140℃ in a salt bath and then taken out. The workpiece is then heated to 600℃ at a heating rate of 120℃ / h for tempering treatment and kept at this temperature for 6 hours, and then air-cooled to below 200℃.

[0032] Then carry out fine turning, fine milling, rough drilling and screw drilling;

[0033] The first aging treatment was carried out by heating the temperature to 570°C at a heating rate of 120°C / h and holding the temperature for 6 hours, and then cooling the temperature to 150°C at a cooling rate of 80°C / h;

[0034] Then carry out finishing drilling and screw drilling, precision turning and rough grinding of teeth;

[0035] The second aging treatment was carried out by heating the temperature to 230°C at a heating rate of 80°C / h and holding the temperature for 5 hours, and then cooling the temperature to below 100°C at a cooling rate of 50°C / h;

[0036] After fine grinding, the semi-finished product is obtained;

[0037] (3) Finally, the semi-finished product is subjected to nitriding treatment, specifically: first heating to T1 = 560 ° C at a heating rate of 35 ° C / h and keeping warm for 6 hours, then cooling to T2 = 545 ° C at a cooling rate of 45 ° C / h and keeping warm for 6 hours, then cooling to T3 = 535 ° C at a cooling rate of 45 ° C / h and keeping warm for 10 hours, then cooling to T4 = 520 ° C at a cooling rate of 45 ° C / h and keeping warm for 18 hours, ammonia is introduced in the above T1, T2, T3, and T4 stages and the ammonia decomposition rate is controlled to be 50%, 55%, 60%, and 68% respectively, finally cooling to 80 ° C at a cooling rate of 40-50 ° C / h to obtain a large thin-walled inner gear ring.

[0038] Example 2

[0039] A method for rapid nitriding and micro-distortion of a large thin-walled internal gear ring, wherein the size of the large thin-walled internal gear ring is the same as that of Example 1, and the depth of the nitriding layer is controlled to be 0.6 mm, comprises the following steps:

[0040] (1) 34CrNiMo6 alloy billets were subjected to a forging and upsetting process of 4 forgings and 3 drawing, followed by punching, hole expansion using a 10-ton electric hammer frame, and ring rolling. The billets were then heated to 920°C at a heating rate of 200°C / h and normalized for 4 hours, then cooled to 200°C in the furnace to obtain ring billets.

[0041] (2) rough turning the ring blank, then heating it to 950°C at a heating rate of 200°C / h for solution treatment, holding the temperature for 6 hours, and then cooling it to 200°C in the furnace;

[0042] Then, semi-finish turning and rough toothing are carried out, and the workpiece is heated to 830℃ for heat treatment and kept at this temperature for 2 hours. Subsequently, it is quenched and cooled in PAG quenching liquid, and the temperature of the PAG quenching liquid is kept at 30℃ and the cooling rate is 160℃ / h. When the temperature of the tooth root reaches 200℃, the liquid is removed. The workpiece is then cooled to 140℃ in a salt bath and taken out. The temperature is then raised to 650℃ at a heating rate of 130℃ / h for tempering treatment and kept at this temperature for 6 hours. It is then air-cooled to below 200℃.

[0043] Then carry out fine turning, fine milling, rough drilling and screw drilling;

[0044] The first aging treatment was carried out by heating the sample to 600°C at a heating rate of 130°C / h and holding the temperature for 5h, and then cooling the sample to 150°C at a cooling rate of 90°C / h;

[0045] Then carry out finishing drilling and screw drilling, precision turning and rough grinding of teeth;

[0046] The temperature was raised to 250°C at a heating rate of 60°C / h for the second aging treatment and kept at that temperature for 4 hours, and then the temperature was lowered to below 100°C at a cooling rate of 50°C / h;

[0047] After fine grinding, the semi-finished product is obtained;

[0048] (3) Finally, the semi-finished product is subjected to nitriding treatment, specifically: first heating to T1 = 550 ° C at a heating rate of 30 ° C / h and keeping warm for 10 hours, then cooling to T2 = 540 ° C at a cooling rate of 40 ° C / h and keeping warm for 14 hours, then cooling to T3 = 530 ° C at a cooling rate of 40 ° C / h and keeping warm for 16 hours, then cooling to T4 = 500 ° C at a cooling rate of 40 ° C / h and keeping warm for 24 hours, ammonia is introduced in the above T1, T2, T3, and T4 stages and the ammonia decomposition rate is controlled to be 50%, 55%, 60%, and 65% respectively, finally cooling to 80 ° C at a cooling rate of 40-50 ° C / h to obtain a large thin-walled inner gear ring.

[0049] Example 3

[0050] A method for rapid nitriding and micro-distortion of a large thin-walled internal gear ring, wherein the size of the large thin-walled internal gear ring is the same as that of Example 1, comprises the following steps:

[0051] (1) 31CrMoV9 alloy billets were subjected to a forging and upsetting process of 4 forgings and 3 drawing, followed by punching, hole expansion using a 10-ton electric hammer frame, and ring rolling. The billets were then heated to 900°C at a heating rate of 200°C / h and normalized for 6 hours, then cooled to 200°C in the furnace to obtain ring billets.

[0052] (2) rough turning the ring blank, then heating it to 950°C at a heating rate of 200°C / h for solution treatment, holding the temperature for 5 hours, and then cooling it to 200°C in the furnace;

[0053] Then, semi-finish turning and rough tooth opening are carried out, and the workpiece is heated to 840℃ for heat treatment and kept at this temperature for 2 hours. Subsequently, it is quenched and cooled in PAG quenching liquid, and the temperature of the PAG quenching liquid is kept at 30℃ and the cooling rate is 160℃ / h. When the temperature of the tooth root reaches 250℃, the liquid is removed. The workpiece is then cooled to 140℃ in a salt bath and taken out. The temperature is then raised to 700℃ at a heating rate of 140℃ / h for tempering treatment and kept at this temperature for 6 hours. The workpiece is then air-cooled to below 200℃.

[0054] Then carry out fine turning, fine milling, rough drilling and screw drilling;

[0055] The first aging treatment was carried out by heating the temperature to 550°C at a heating rate of 130°C / h and holding the temperature for 8 hours, and then cooling the temperature to 150°C at a cooling rate of 60°C / h;

[0056] Then carry out finishing drilling and screw drilling, precision turning and rough grinding of teeth;

[0057] The second aging treatment was carried out by heating the temperature to 200°C at a heating rate of 80°C / h and holding the temperature for 6 hours, and then cooling the temperature to below 100°C at a cooling rate of 60°C / h;

[0058] After fine grinding, the semi-finished product is obtained;

[0059] (3) Finally, the semi-finished product is subjected to nitriding treatment, specifically: first heating to T1 = 555 ° C at a heating rate of 40 ° C / h and keeping warm for 8 hours, then cooling to T2 = 540 ° C at a cooling rate of 50 ° C / h and keeping warm for 12 hours, then cooling to T3 = 530 ° C at a cooling rate of 50 ° C / h and keeping warm for 18 hours, then cooling to T4 = 500 ° C at a cooling rate of 50 ° C / h and keeping warm for 16 hours, introducing ammonia in the above T1, T2, T3, and T4 stages and controlling the ammonia decomposition rate to be 50%, 55%, 60%, and 65% respectively, finally cooling to 80 ° C at a cooling rate of 40-50 ° C / h to obtain a large thin-walled inner gear ring.

[0060] Example 4

[0061] A method for rapid nitriding and micro-distortion of a large thin-walled internal gear ring. The large thin-walled internal gear ring has the same size as that of Example 1, the depth of the nitrided layer is controlled to be 0.6 mm, and the preparation method is the same as that of Example 1, except that: in step 3, the semi-finished product is finally subjected to a nitriding treatment. The specific treatment is: first heating to T1 = 555° C. at a heating rate of 40° C. / h and holding the temperature for 10 hours, then cooling to T2 = 540° C. at a cooling rate of 50° C. / h and holding the temperature for 14 hours, then cooling to T3 = 530° C. at a cooling rate of 50° C. / h and holding the temperature for 20 hours, then cooling to T4 = 500° C. at a cooling rate of 50° C. / h and holding the temperature for 26 hours, introducing ammonia in the above stages T1, T2, T3, and T4, and controlling the ammonia decomposition rates to be 50%, 55%, 60%, and 65%, respectively, and finally cooling to 80° C. at a cooling rate of 40-50° C. / h to obtain a large thin-walled internal gear ring.

[0062] Comparative Example 1

[0063] This comparative example uses 42CrMo alloy to manufacture a large thin-walled inner gear ring. The inner gear ring has the same dimensions as Example 1, except that:

[0064] Forging billet (3 forgings and 3 drawing) → normalizing → rough turning → flaw detection → quenching and tempering (850℃ heating and holding for 1.5h → oil quenching → 600℃ tempering and holding for 1.5h → furnace cooling → air cooling) → semi-finishing turning → rough milling → rough drilling and screw drilling → low temperature aging treatment (500℃ annealing and holding for 6h, cooling to 150℃ and taking out of the furnace, heating rate ≤50℃ / h, cooling rate ≤20℃ / h) → finishing drilling and screw drilling → finishing turning → finishing milling → finishing grinding → nitriding (heating to 350±5℃ and holding for 2h for preheating → then heating to 450±5℃ and holding for 2h for nitrogen exhaust → then heating to 515±5℃ and holding for 2h, in this During the process, ammonia gas was ignited, and the ammonia decomposition rate was controlled at 6±2% at this time → then strong nitriding was carried out at 515±5°C for 19h, and the ammonia decomposition rate was controlled at 40±5% → the first diffusion was carried out at 515±5°C for 26h, and the ammonia decomposition rate at this stage was controlled to 55±5% → the second diffusion was carried out at 515±5°C for 26h, and the ammonia decomposition rate at this stage was controlled to 60±5% → the third diffusion was carried out at 515±5°C for 25h, and the ammonia decomposition rate at this stage was controlled to 68±5% → finally cooled to 80°C at a cooling rate of 40-50°C / h; the above nitriding treatment heating rate and cooling rate were consistent with Example 1) → a large thin-walled inner gear ring was obtained.

[0065] The performance of the product workpieces of the above embodiments and comparative examples was tested, and the results are shown in Table 1.

[0066] Table 1 Product workpiece performance of the embodiment and comparative example

[0067]

[0068] As can be seen from Table 1, the large thin-walled inner gear ring of the embodiment can be controlled after being processed by the process steps of the present invention. It has good flatness and small distortion. The method of the present invention can effectively control the problem of severe distortion of large thin-walled inner gear rings after heat treatment; and the nitriding layer depth is greater than 0.3mm (the nitriding layer depth can be adjusted according to different application fields), and the surface hardness can reach 600-800HV. Although the nitriding layer of Example 1 is shallower than that of Comparative Example 1, Example 1 can achieve the surface hardness that can be achieved by the longer nitriding treatment time (96h) of Comparative Example 1 through a shorter nitriding treatment time (40h), and the process distortion of Example 1 is smaller than that of Comparative Example 1.

[0069] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for rapid nitriding and micro-distortion of large thin-walled internal gear rings, characterized in that: The steps include: (1) A chromium-based alloy blank with a Brinell hardness range of 170-320 HB is selected for forging and upsetting treatment with a forging ratio of ≥8, and then punched and rolled, and then normalized to obtain a ring blank; (2) performing rough turning, solution treatment, semi-finishing turning, rough toothing, quenching, tempering, finishing turning, finishing tooth milling, rough drilling and screw drilling, first aging treatment, finishing drilling and screw drilling, finishing turning, rough tooth grinding, second aging treatment, and finishing tooth grinding on the ring blank in sequence to obtain a semi-finished product; The normalizing treatment temperature is 850-950°C, the holding time is 4-6h, the heating rate is 200°C / h, and the furnace is cooled to 200°C after the normalizing treatment is completed; The temperature of the solution treatment is 900-950°C, the holding time is 4-6h, the heating rate is 200°C / h, and the furnace is cooled to 200°C after the solution treatment is completed; The quenching treatment is to first heat the temperature to 800-880°C and keep it warm for 1-2 hours, then quench and cool it in PAG quenching liquid until the tooth root temperature reaches 200-250°C, then remove the liquid and perform salt bath quenching. The temperature of the PAG quenching liquid is controlled at 30-40°C and the cooling rate is ≥160°C / h. The salt bath quenching is to remove the workpiece when it cools to 140°C. The tempering treatment temperature is at least 590°C, the temperature is kept for 5-7 hours, the heating rate is at least 100°C / h, and after the tempering treatment is completed, the temperature is air-cooled to below 200°C; The temperature of the first aging treatment is 550-600°C, the holding time is 5-8h, the heating rate is 100-150°C / h, and after the first aging treatment is completed, the temperature is lowered to 150°C at a cooling rate of 50-100°C / h; the temperature of the second aging treatment is 200-250°C, the holding time is 4-6h, the heating rate does not exceed 100°C / h, and after the second aging treatment is completed, the temperature is lowered to below 100°C at a cooling rate of 50-100°C / h; (3) finally performing nitriding treatment on the semi-finished product to obtain a large thin-walled inner gear ring; The nitriding treatment comprises the following steps: first heating the temperature to 550≤T1≤560°C at a heating rate of 30-40°C / h and keeping the temperature for 6-10h; then cooling the temperature to 540≤T2<550°C at a cooling rate of 40-50°C / h and keeping the temperature for 6-14h; then cooling the temperature to 530≤T3<540°C at a cooling rate of 40-50°C / h and keeping the temperature for 10-20h; then cooling the temperature to 480≤T4<530°C at a cooling rate of 40-50°C / h and keeping the temperature for 16-26h; introducing ammonia in stages T1, T2, T3 and T4 and controlling the ammonia decomposition rates to be 50%, 55%, 60% and 65-68% respectively; and finally cooling the temperature to 80°C at a cooling rate of 40-50°C / h.

2. The method for rapid nitriding and micro-distortion of a large thin-walled internal gear ring according to claim 1, characterized in that: The chromium-based alloy blank is one of 42CrMo, 34CrNiMo6 and 31CrMoV9.

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