Large alloy steel ring forge piece and preparation method thereof

Abstract

The invention relates to a large alloy steel ring forge piece and a preparation method thereof, and belongs to the technical field of forging. The preparation method of the large alloy steel ring forge piece comprises the following steps: (1) forging; (2) cooling after forging; (3) normalizing treatment; (4) primary tempering treatment; (5) quenching treatment; (6) secondary tempering; and (7) stress relief annealing. By controlling heat treatment parameters, the toughness, strength, hardness and uniformity of the large alloy steel ring forge piece are improved, and it is guaranteed that the service life of the large alloy steel ring forge piece meets the expectation.

Description

Technical Field

[0001] The invention relates to the technical field of forging, and in particular to a large alloy steel ring forging and a preparation method thereof. Background Art

[0002] Large alloy steel ring forgings are widely used in many fields due to their superior performance. For example, they can be used to manufacture shield machine main bearing rings and various high-performance slewing bearings to improve the overall performance and reliability of the equipment. In the manufacture of slewing bearings, large alloy steel ring forgings can be used to manufacture various connectors and supports. The use environment of large alloy steel ring forgings is relatively harsh. Not only do they bear the pressure and friction from the equipment, but they also need to maintain stability and uniformity during force and movement. Therefore, the processing accuracy, toughness, strength, hardness and uniformity of large alloy steel ring forgings are relatively high.

[0003] In order to obtain high-quality and high-performance large alloy steel ring forgings, the blank size of the ring must be accurately designed, and the roller feed speed and rotation speed during the ring rolling process must be strictly controlled to accurately control the performance of the ring. How to use heat treatment methods to improve the toughness, strength, hardness and uniformity of large alloy steel ring forgings is a technical gap in the existing preparation of large alloy steel ring forgings. Summary of the invention

[0004] In view of the problem that the prior art lacks a heat treatment method to improve the toughness, strength, hardness and uniformity of a large alloy steel ring forging, the present invention provides a large alloy steel ring forging and a preparation method thereof to solve the above problems. The present invention improves the toughness, strength, hardness and uniformity of the large alloy steel ring forging by controlling the heat treatment parameters, ensuring that its service life meets expectations.

[0005] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a large alloy steel ring forging, comprising the following steps: (1) forging; (2) cooling after forging; (3) normalizing; (4) primary tempering; (5) quenching; (6) secondary tempering; (7) stress relief annealing; wherein the specific steps are as follows: (1) Forging: Large ring forgings are forged by rolling, removing water risers, primary upsetting, drawing, secondary upsetting, secondary drawing, tertiary upsetting, punching, hole expansion and ring rolling to the size of the forging. The total forging ratio is not less than 10:1, and the total upsetting ratio is not less than 6.0:1. The temperature is heated to 1210~1250℃ before rolling, and the heating temperature of subsequent upsetting, drawing, punching, hole expansion and ring rolling is reduced in sequence. (2) Cooling after forging: (2.1) The large alloy steel ring forgings that have completed ring rolling are placed in the material area for air cooling; (2.2) The large alloy steel ring forging is cooled to a surface temperature of 630~680℃ and placed in a heat treatment furnace with a furnace temperature of 650℃±10℃ for isothermal treatment. The holding time is based on the minimum wall thickness and height of the large alloy steel ring forging, and is carried out in accordance with 1.8min / mm+120min; (2.3) After the insulation is completed, the large alloy steel ring forgings are slowly cooled in the heat treatment furnace to ≤300℃ and then taken out of the furnace for air cooling.

[0006] (3) Normalizing treatment: (3.1) Place the large alloy steel ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, heat it to 350℃±10℃, and keep it warm. The holding time is based on the minimum wall thickness and height of the large alloy steel ring forging, which is 0.6min / mm. (3.2) After the insulation is completed, the temperature is raised to 650℃±10℃ at a rate of ≤80℃ / h and the insulation is maintained. The insulation time is based on the minimum wall thickness and height of the large alloy steel ring forgings and is implemented at 0.6min / mm; (3.3) After the insulation is completed, the temperature is raised to 880~900℃ at a rate of ≤150℃ / h and the insulation is maintained. The insulation time is based on the minimum wall thickness and height of the large alloy steel ring forgings and is implemented at 1.2min / mm; (3.4) After the insulation is completed, take the product out of the furnace and air cool it.

[0007] (4) Primary tempering treatment: (4.1) Place the large alloy ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, heat it to 660~700℃ at a rate of ≤80℃ / h, and keep it warm. The holding time is based on the minimum wall thickness and height of the large alloy ring forging, which is 1.8min / mm. (4.2) After the insulation is completed, air cooling is implemented.

[0008] (5) Quenching treatment: (5.1) Place the large alloy steel ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, heat it to 350℃±10℃, and keep it warm. The holding time is based on the minimum wall thickness and height of the large alloy steel ring forging, and is implemented at 0.6min / mm; (5.2) After the insulation is completed, the temperature is raised to 760℃±10℃ at a rate of ≤80℃ / h and the insulation is maintained. The insulation time is based on the minimum wall thickness and height of the large alloy steel ring forgings and is implemented at 1.0min / mm; (5.3) After the insulation is completed, the temperature is rapidly raised to 850~870℃ at a rate of ≤150℃ / h, and insulation is carried out according to the minimum wall thickness and height of large alloy steel ring forgings at 1.2min / mm; (5.4) After the heat preservation is completed, the forging is taken out of the furnace and quenched. According to the effective thickness of the large alloy steel ring forging, the first quenching cooling time is 0.8~1.2s / mm, and the total quenching cooling time is 4~6s / mm. The quenching cooling is carried out in a water-air alternating manner, that is, after taking out of the heat treatment furnace, it is pre-cooled in the air, and then immersed in water for cooling. In order to release the structural transformation stress, it is lifted out of the water after a period of water cooling and air cooling is repeated. The first water cooling time refers to the first time it is cooled in water, and the total water cooling time is the total time of cooling in water.

[0009] (6) Secondary tempering: (6.1) Place the large alloy steel ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, heat it to 300~350℃ at a rate of ≤80℃ / h, and keep it warm. The holding time is based on the minimum wall thickness and height of the large alloy steel ring forging, which is 0.9min / mm. (6.2) After the insulation is completed, the temperature is raised to 560~620℃ at a rate of ≤60℃ / h and the temperature is maintained. The insulation time is based on the minimum wall thickness and height of the large alloy steel ring forgings, and secondary tempering and insulation is carried out at 1.8min / mm; (6.3) After the secondary tempering and heat preservation is completed, take the steel out of the furnace and air cool it to room temperature.

[0010] (7) Stress relief annealing: (7.1) Place the large ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, raise the temperature to 350℃±10℃, and keep it at this temperature for 4~6h; (7.2) After the insulation is completed, the temperature is raised to 500~580℃ at a rate of ≤60℃ / h and maintained for 6~8h; (7.3) After the insulation is completed, the furnace is cooled to ≤350℃ at ≤20℃ / h; (7.4) After the furnace cooling is completed, take the product out of the furnace and air cool it to room temperature.

[0011] Further, the chemical composition of the large alloy steel ring forging includes, by weight percentage, C 0.41%~0.45%, Si 0.25%~0.35%, Mn 0.70%~0.80%, Cr 1.05%~1.20%, Mo 0.25%~0.30%, Ni 0.45%~0.55%, Cu≤0.12%, P≤0.013%, S≤0.010%, [N]≤70ppm, [O]≤15ppm, [H]≤1.5ppm, and the rest is Fe and unavoidable impurities.

[0012] Furthermore, the step (1) includes the following steps: (1.1) Load the steel ingot for large alloy steel ring forgings into a forging heating furnace with a furnace temperature of ≤650℃, heat it to 640~680℃, and keep it warm. The holding time is based on the diameter of the steel ingot riser and is 0.6~0.8min / mm. (1.2) Rapidly heat to 1210~1250℃ at full power, and the holding time is based on the diameter of the ingot riser, which is 1.0~1.2min / mm; (1.3) After leaving the forging heating furnace, the steel is rolled and hot-cut on a ton press to form a water riser; (1.4) Return to the forging heating furnace and continue heating to 1200~1240℃. The holding time is based on the billet diameter and is 0.3~0.4min / mm. (1.5) After leaving the forging heating furnace, two upsetting and two stretching deformations are carried out on a ton press. Each upsetting forging is shorter than K. H ≥2.2; (1.6) Heat the forging heating furnace to 1180~1220℃, and the holding time is based on the billet diameter, which is 0.3~0.4min / mm; (1.7) After leaving the forging heating furnace, upsetting, punching and hole expansion are carried out on a ton press; (1.8) Heat the forging heating furnace to 1150~1180℃, and the holding time is based on the minimum value of the wall thickness and height of the ring blank, which is 0.3~0.4min / mm; (1.9) After leaving the forging heating furnace, the rings are rolled on a ring rolling machine.

[0013] Furthermore, in step (5.4), water cooling and air cooling are used alternately for quenching cooling, the first quenching cooling time is 0.8-1.2 s / mm, and the total quenching cooling time is 4-6 s / mm.

[0014] Furthermore, the cooling medium of the water cooling is water at 15-25°C. The cooling medium is first kept in a stable forced convection state, and the convection intensity is gradually weakened according to the number of times it enters the water.

[0015] Furthermore, after the secondary tempering, the hardness test of the surface of the large alloy steel ring forging is also included, including the following steps: (A) Roughly grind the surface of the selected position of the large ring forging, the rough grinding depth is controlled at 2~4mm, the rough grinding area is greater than 50mm×50mm, and the grinding area is flat without depression; (B) Finely grind and polish the coarsely ground parts, with a polishing depth of ≤1mm, a smooth polished area without depressions, and a surface roughness of Ra≤7μm; (C) Perform hardness test on the finely ground and polished parts, and take the average value of the test three times for each part.

[0016] Further, the surface hardness of the large alloy steel ring forging is tested after stress relief annealing, including the following steps: (A) Roughly grind the surface of the selected position of the large alloy steel ring forging, the rough grinding depth is controlled at 2~4mm, the rough grinding area is larger than 50mm×50mm, and ensure that the grinding area is flat and has no depression; (B) Finely grind and polish the coarsely ground parts, with a polishing depth of ≤1mm, and ensure that the polished part is flat and has no depressions, and the surface roughness Ra ≤7μm; (C) Perform hardness test on the finely ground and polished parts, and take the average value of the test three times for each part.

[0017] In the second aspect, the present invention provides a high-quality, high-uniformity, ultra-fine-grained large alloy steel ring forging prepared by the above-mentioned preparation method, wherein the hardness of the large alloy steel ring forging is ≥260HB, the hardness difference of a single piece is ≤20HB; the tensile strength is ≥850MPa, the yield strength is ≥700Mpa, and the elongation after fracture is ≥15%; the impact energy Akv at -40°C is ≥27J; and the grain size N is ≥7.

[0018] Furthermore, the outer diameter of the large alloy steel ring forging is 7600~13830mm, the inner diameter is 6500~12960mm, and the height is 100~456mm.

[0019] The beneficial effects of the present invention are: The present invention reasonably designs forging, quenching and tempering parameters, and controls the surface hardness difference of large alloy steel ring forgings after quenching and tempering within the range of 20HB. The alloy steel material used is more conducive to the realization of high toughness, high strength, hardness, uniform performance and ultra-fine grains of large ring forgings after heat treatment. Through actual production verification, a good match between strength, plasticity and toughness is achieved, thereby ensuring that the service life of large alloy steel ring forgings reaches a high level. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0021] Example 1 A large alloy steel ring forging with an outer diameter of 13830 mm, an inner diameter of 12960 mm, and a height of 385 mm is prepared according to the following preparation method: (1) Forging: (1.1) Select 126 tons of die-cast steel ingot raw materials, whose chemical composition meets the following requirements: C 0.41wt%, Si 0.30wt%, Mn 0.75wt%, Cr 1.11wt%, Mo 0.26wt%, Ni 0.45wt%, Cu 0.03wt%, P 0.006wt%, S 0.001wt%, [N] 51ppm, [O] 10ppm, [H] 0.8ppm, and the rest are Fe and unavoidable impurities. Control the total upsetting ratio to be 12:1. Load the steel ingot for large alloy steel ring forgings into a forging heating furnace with a furnace temperature of ≤650℃, heat it to 850℃, keep it warm for 8h, and even it out; continue to heat it to 1250℃ and keep it warm for 24h; (1.2) Rapidly heat to 1250℃ at full power, and the holding time is based on the riser diameter of the ingot, which is 1.2min / mm; (1.3) After leaving the forging heating furnace, the steel is rolled and hot-cut on a ton press to form a water riser; (1.4) Return to the forging heating furnace and continue heating to 1240℃. The holding time is based on the billet diameter and is 0.4min / mm. (1.5) After leaving the forging heating furnace, two upsetting and two stretching deformations are carried out on a ton press. Each upsetting forging is shorter than K. H ≥2.2; control the total forging ratio to 12:1 and the upsetting ratio to 6.6:1; (1.6) Return the forging heating furnace to 1220°C, and the holding time is based on the billet diameter and is executed at 0.4min / mm; (1.7) After leaving the forging heating furnace, upsetting, punching and hole expansion are carried out on a ton press; (1.8) Return the forging heating furnace to 1180°C, and the holding time is based on the minimum value of the wall thickness and height of the ring blank, which is 0.4min / mm; (1.9) After leaving the forging heating furnace, the rings are rolled on a ring rolling machine.

[0022] (2) Cooling after forging: (2.1) The large alloy steel ring forgings that have completed ring rolling are placed in the material area for air cooling; (2.2) The large alloy steel ring forging is cooled to a surface temperature of 640°C and placed in a heat treatment furnace at a temperature of 650°C ± 10°C for isothermal treatment for 17 hours; (2.3) After the insulation is completed, the large alloy steel ring forgings are slowly cooled in the heat treatment furnace to ≤300℃ and then taken out of the furnace for air cooling.

[0023] (3) Normalizing treatment: (3.1) Place the large alloy steel ring forging into a heat treatment furnace at 300°C, raise the temperature to 350°C, and keep it at that temperature for 5 hours; (3.2) After the insulation is completed, the temperature is raised to 650℃ at a rate of 35℃ / h and maintained for 5h; (3.3) After the heat preservation is completed, the temperature is raised to 880℃ at a rate of 50℃ / h, and the heat preservation is carried out three times for a total of 14h; (3.4) After three insulation cycles, remove from the furnace and allow air cooling.

[0024] (4) Primary tempering treatment: (4.1) Place the large alloy ring forging into a heat treatment furnace at 300°C, heat it to 680°C at a rate of 30°C / h, and keep it at that temperature for 21h; (4.2) After the insulation is completed, air cooling is implemented.

[0025] (5) Quenching treatment: (5.1) Before quenching treatment, the large alloy steel ring forgings after primary tempering are subjected to rough machining before quenching and tempering, and the machining allowances of various parts after quenching and tempering are kept close as much as possible, and then the whole quenching treatment is carried out. The process is as follows: the large alloy steel ring forgings are placed in a heat treatment furnace with a furnace temperature of 320℃, the temperature is raised to 350℃, and the temperature is kept for 5h; (5.2) After the insulation is completed, the temperature is raised to 760℃ at a rate of 30℃ / h and maintained for 7.5h; (5.3) After the heat preservation is completed, the temperature is rapidly raised to 860℃ at 50℃ / h, and the heat preservation is carried out three times for a total of 13.0h; (5.4) After the three insulation cycles, the steel is taken out of the furnace for alternating water-air cooling. First, it is cooled in the air to a temperature ≤ 350°C. Then, water at 21°C is selected as the cooling medium. The first water cooling is for 10 minutes to keep the cooling medium in a stable forced convection state. The second water cooling time is 9 minutes, and the cooling medium is in a stable forced convection state. The third water cooling time is 8 minutes, and the cooling medium is in a stable forced convection state. The fourth water cooling time is 7 minutes, and the cooling medium is in a natural convection state. The fifth water cooling time is 6 minutes, and the cooling medium is in a natural convection state. The sixth water cooling time is 5 minutes, and the cooling medium is in a natural convection state.

[0026] (6) Secondary tempering: (6.1) Place the large alloy steel ring forging into a heat treatment furnace at 300°C, heat it to 350°C at a rate of 30°C / h, and keep it at that temperature for 5.0h; (6.2) After the insulation is completed, the temperature is raised to 560℃ at a rate of 50℃ / h, and a second insulation is carried out for 18.5h; (6.3) After the second heat preservation, take the product out of the furnace and air cool it to room temperature.

[0027] (7) After secondary tempering, the surface hardness of the large alloy steel ring forging is tested. The test method is as follows: (7.1) Rough grinding is performed at 24 locations of the outer diameter surface, inner diameter surface, upper and lower end surfaces of large alloy steel ring forgings at intervals of 60°. The rough grinding depth is controlled at 2mm, the grinding area is larger than 50mm×50mm, and the grinding area is ensured to be flat and free of depressions; (7.2) Finely grind and polish the coarsely ground parts, with a polishing depth of ≤1mm, and ensure that the polished parts are flat and free of depressions, and the surface roughness Ra ≤7μm; (7.3) Hardness test was performed on the finely ground and polished parts. Each part was tested three times and the average value was taken. The surface hardness was measured to be 275~288HB.

[0028] (7.4) Sampling and testing were carried out on large alloy steel ring forgings that had completed hardness testing. A 30 mm × 30 mm test ring was cut with a cutter at a distance of 135 mm from the upper plane and 65 mm from the inner diameter surface. A 600 mm long test block was cut at the 0° and 180° positions of the test ring for tensile, impact, hardness and metallographic testing. The results are shown in Table 1 below.

[0029] Table 1- Mechanical properties of large alloy steel ring forgings

[0030] (8) Stress relief annealing: (8.1) Place the large alloy steel ring forging into a heat treatment furnace at 200°C, raise the temperature to 350°C, and keep it at this temperature for 3 hours; (8.2) After the insulation is completed, the temperature is raised to 560℃ at a rate of 30℃ / h and maintained for 7h; (8.3) After the insulation is completed, cool the furnace to 350℃ at a rate of 10~15℃ / h; (8.4) After the furnace cooling is completed, take the product out of the furnace and air cool it to room temperature.

[0031] For large alloy steel ring forgings that have completed stress relief annealing, the surface hardness test is then carried out as follows: A. Roughly grind 24 locations of the outer diameter surface, inner diameter surface, upper and lower end surfaces of large alloy steel ring forgings at intervals of 60°. The rough grinding depth is controlled at 2mm. The grinding area is larger than 50mm×50mm and the grinding area is ensured to be flat and without depressions. B. Finely grind and polish the coarsely ground parts, with a polishing depth of ≤1mm, and ensure that the polished parts are flat and without depressions, and the surface roughness Ra≤7μm; C. Perform hardness test on fine grinding and polishing parts, test each part 3 times and take the average value, the surface hardness is 270~283HB.

[0032] Example 2 A large alloy steel ring forging with an outer diameter of 8268 mm, an inner diameter of 7306 mm, and a height of 456 mm is prepared according to the following preparation method: (1) Forging: (1.1) Select 126 tons of die-cast steel ingot raw materials, whose chemical composition meets C 0.42%, Si 0.29wt%, Mn0.72wt%, Cr 1.10wt%, Mo 0.27wt%, Ni 0.46wt%, Cu 0.03wt%, P 0.006wt%, S 0.001wt%, [N] 70ppm, [O] 12ppm, [H] 1.0 ppm, and the rest are Fe and unavoidable impurities. Control the total upsetting ratio to be 14:1. Load the steel ingot for large alloy steel ring forgings into a forging heating furnace with a furnace temperature of ≤650℃, heat it to 850℃, keep it warm for 10h, and even it out; continue to heat it to 1250℃ and keep it warm for 28h; (1.2) Rapidly heat to 1250℃ at full power, and the holding time is based on the riser diameter of the ingot, which is 1.2min / mm; (1.3) After leaving the forging heating furnace, the steel is rolled and hot-cut on a ton press to form a water riser; (1.4) Return to the forging heating furnace and continue heating to 1240℃. The holding time is based on the billet diameter and is 0.4min / mm. (1.5) After leaving the forging heating furnace, two upsetting and two stretching deformations are carried out on a ton press. Each upsetting forging is shorter than K. H ≥2.2; control the total forging ratio to 12:1 and the upsetting ratio to 6.6:1; (1.6) Return the forging heating furnace to 1220°C, and the holding time is based on the billet diameter and is executed at 0.4min / mm; (1.7) After leaving the forging heating furnace, upsetting, punching and hole expansion are carried out on a ton press; (1.8) Return the forging heating furnace to 1180°C, and the holding time is based on the minimum value of the wall thickness and height of the ring blank, which is 0.4min / mm; (1.9) After leaving the forging heating furnace, the rings are rolled on a ring rolling machine.

[0033] (2) Cooling after forging: (2.1) The large alloy steel ring forgings that have completed ring rolling are placed in the material area for air cooling; (2.2) The large alloy steel ring forging is cooled to a surface temperature of 640°C and placed in a heat treatment furnace at a temperature of 650°C ± 10°C for isothermal treatment for 15 hours; (2.3) After the insulation is completed, the large alloy steel ring forgings are slowly cooled in the heat treatment furnace to ≤300℃ and then taken out of the furnace for air cooling.

[0034] (3) Normalizing treatment: (3.1) Place the large alloy steel ring forging into a heat treatment furnace at 310°C, heat it to 350°C, and keep it at that temperature for 5.0h; (3.2) After the insulation is completed, the temperature is raised to 650℃ at a rate of 30℃ / h and maintained for 5.0h; (3.3) After the heat preservation is completed, the temperature is raised to 880℃ at a rate of 50℃ / h, and the heat preservation is carried out three times for a total of 13.0h; (3.4) After three insulation cycles, remove from the furnace and allow air cooling.

[0035] (4) Primary tempering treatment: (4.1) Place the large alloy steel ring forging into a heat treatment furnace at 300°C, heat it to 680°C at a rate of 35°C / h, and keep it at that temperature for 18.5h; (4.2) After the insulation is completed, air cooling is implemented.

[0036] (5) Quenching treatment: (5.1) Before quenching treatment, the large alloy steel ring forgings after primary tempering are subjected to rough machining before quenching and tempering, and the machining allowances of various parts after quenching and tempering are kept close as much as possible, and then the whole quenching treatment is carried out. The process is as follows: the large alloy steel ring forgings are placed in a heat treatment furnace with a furnace temperature of 300°C, heated to 350°C, and kept at this temperature for 5.0h; (5.2) After the insulation is completed, the temperature is raised to 760℃ at a rate of 35℃ / h and maintained for 7.5h; (5.3) After the heat preservation is completed, the temperature is rapidly raised to 860℃ at 50℃ / h, and the heat preservation is carried out three times for a total of 13.5h; (5.4) After the three insulation cycles, the furnace is taken out for alternating water-air cooling. The cooling medium is water at 25°C. The first water cooling is for 8 minutes to keep the cooling medium in a stable forced convection state; the second water cooling time is 6 minutes, and the cooling medium is in a stable forced convection state; the third water cooling time is 5 minutes, and the cooling medium is in a stable forced convection state; the fourth water cooling time is 4 minutes, and the cooling medium is in a natural convection state; the fifth water cooling time is 4 minutes, and the cooling medium is in a natural convection state; the sixth water cooling time is 3 minutes, and the cooling medium is in a natural convection state.

[0037] (6) Secondary tempering: (6.1) Place the large alloy steel ring forging into a heat treatment furnace at 260°C, heat it to 350°C at a rate of 30°C / h, and keep it at that temperature for 5h; (6.2) After the insulation is completed, the temperature is raised to 600℃ at a rate of 50℃ / h, and a second insulation is carried out for 16.5h; (6.3) After the second heat preservation, take the product out of the furnace and air cool it to room temperature.

[0038] (7) After secondary tempering, the surface hardness of the large alloy steel ring forging is tested. The test method is as follows: (7.1) Rough grinding is performed at 24 locations of the outer diameter surface, inner diameter surface, upper and lower end surfaces of large alloy steel ring forgings at intervals of 60°. The rough grinding depth is controlled at 2mm, the grinding area is larger than 50mm×50mm, and the grinding area is ensured to be flat and free of depressions; (7.2) Finely grind and polish the coarsely ground parts, with a polishing depth of ≤1mm, and ensure that the polished parts are flat and free of depressions, and the surface roughness Ra ≤7μm; (7.3) Hardness test was carried out on the finely ground and polished parts. Each part was tested three times and the average value was taken. The surface hardness was measured to be 315~330HB.

[0039] (7.4) Sampling and testing were carried out on the large alloy steel ring forgings that had completed the hardness test. A 30mm×30mm test ring was cut with a cutter at a distance of 15mm from the upper plane and 15mm from the outer diameter surface. A 600mm long test block was cut at the 0° and 180° positions of the test ring for tensile, impact, hardness and metallographic testing. The results are shown in Table 2 below.

[0040] Table 2- Mechanical properties of large alloy steel ring forgings

[0041] (8) Stress relief annealing: (8.1) Place the large alloy steel ring forging into a heat treatment furnace at 210°C, raise the temperature to 350°C, and keep it at this temperature for 3 hours; (8.2) After the insulation is completed, the temperature is raised to 500℃ at a rate of 30℃ / h and maintained for 7h; (8.3) After the insulation is completed, cool the furnace to 350℃ at 10℃ / h~15℃ / h; (8.4) After the furnace cooling is completed, take the product out of the furnace and air cool it to room temperature.

[0042] For large alloy steel ring forgings that have completed stress relief annealing, the surface hardness test is then carried out as follows: A. Roughly grind 24 locations of the outer diameter surface, inner diameter surface, upper and lower end surfaces of large alloy steel ring forgings at intervals of 60°. The rough grinding depth is controlled at 2mm. The grinding area is larger than 50mm×50mm and the grinding area is ensured to be flat and without depressions. B. Finely grind and polish the coarsely ground parts, with a polishing depth of ≤1mm, and ensure that the polished parts are flat and without depressions, and the surface roughness Ra≤7μm; C. Perform hardness test on fine grinding and polishing parts, test each part 3 times and take the average value, the surface hardness is 310~330HB.

[0043] It can be seen from the test results of Example 1 and Example 2 that the various performance indicators and uniformity of the two large alloy steel ring forgings with different specifications and alloy compositions prepared by the present invention meet the use requirements.

[0044] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A method for preparing a large alloy steel ring forging, comprising the following steps: (1) forging; (2) cooling after forging; (3) normalizing; (4) primary tempering; (5) quenching; (6) secondary tempering; (7) stress relief annealing; characterized in that the specific steps are as follows: (1) Forging: Large ring forgings are forged by rolling, removing water risers, primary upsetting, drawing, secondary upsetting, secondary drawing, tertiary upsetting, punching, hole expansion and ring rolling to the size of the forging. The total forging ratio is not less than 10:1, and the total upsetting ratio is ≥6.0:

1. The temperature is heated to 1210~1250℃ before rolling, and the heating temperature of subsequent upsetting, drawing, punching, hole expansion and ring rolling is reduced in sequence. (2) Cooling after forging: (2.1) The large alloy steel ring forgings that have completed ring rolling are placed in the material area for air cooling; (2.2) The large alloy steel ring forging is cooled to a surface temperature of 630~680℃ and placed in a heat treatment furnace with a furnace temperature of 650℃±10℃ for isothermal treatment. The holding time is based on the minimum wall thickness and height of the large alloy steel ring forging, and is carried out in accordance with 1.8min / mm+120min; (2.3) After the insulation is completed, the large alloy steel ring forgings are slowly cooled in the heat treatment furnace to ≤300℃ and then taken out of the furnace for air cooling; (3) Normalizing treatment: (3.1) Place the large alloy steel ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, heat it to 350℃±10℃, and keep it warm. The holding time is based on the minimum wall thickness and height of the large alloy steel ring forging, which is 0.6min / mm. (3.2) After the insulation is completed, the temperature is raised to 650℃±10℃ at a rate of ≤80℃ / h and the insulation is maintained. The insulation time is based on the minimum wall thickness and height of the large alloy steel ring forgings and is implemented at 0.6min / mm; (3.3) After the insulation is completed, the temperature is raised to 880~900℃ at a rate of ≤150℃ / h and the insulation is maintained. The insulation time is based on the minimum wall thickness and height of the large alloy steel ring forgings and is implemented at 1.2min / mm; (3.4) After the heat preservation is completed, take the furnace out of the oven and implement air cooling; (4) Primary tempering treatment: (4.1) Place the large alloy ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, heat it to 660~700℃ at a rate of ≤80℃ / h, and keep it warm. The holding time is based on the minimum wall thickness and height of the large alloy ring forging, which is 1.8min / mm. (4.2) After the insulation is completed, air cooling is implemented; (5) Quenching treatment: (5.1) Place the large alloy steel ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, heat it to 350℃±10℃, and keep it warm. The holding time is based on the minimum wall thickness and height of the large alloy steel ring forging, and is implemented at 0.6min / mm; (5.2) After the insulation is completed, the temperature is raised to 760℃±10℃ at a rate of ≤80℃ / h and the insulation is maintained. The insulation time is based on the minimum wall thickness and height of the large alloy steel ring forgings and is implemented at 1.0min / mm; (5.3) After the insulation is completed, the temperature is rapidly raised to 850~870℃ at a rate of ≤150℃ / h, and insulation is carried out according to the minimum wall thickness and height of large alloy steel ring forgings at 1.2min / mm; (5.4) After the heat preservation is completed, take the furnace out and implement quenching cooling; (6) Secondary tempering: (6.1) Place the large alloy steel ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, heat it to 300~350℃ at a rate of ≤80℃ / h, and keep it warm. The holding time is based on the minimum wall thickness and height of the large alloy steel ring forging, which is 0.9min / mm. (6.2) After the insulation is completed, the temperature is raised to 560~620℃ at a rate of ≤60℃ / h and the temperature is maintained. The insulation time is based on the minimum wall thickness and height of the large alloy steel ring forgings, and secondary tempering and insulation is carried out at 1.8min / mm; (6.3) After the secondary tempering and heat preservation is completed, take the furnace out and air cool to room temperature; (7) Stress relief annealing: (7.1) Place the large ring forging into a heat treatment furnace with a furnace temperature of ≤350℃, raise the temperature to 350℃±10℃, and keep it at this temperature for 4~6h; (7.2) After the insulation is completed, the temperature is raised to 500~580℃ at a rate of ≤60℃ / h and maintained for 6~8h; (7.3) After the insulation is completed, the furnace is cooled to ≤350℃ at ≤20℃ / h; (7.4) After the furnace cooling is completed, take the product out of the furnace and air cool it to room temperature.

2. The method for preparing a large alloy steel ring forging according to claim 1, characterized in that: In terms of weight percentage, the chemical composition of large alloy steel ring forgings includes C 0.41%~0.45%, Si 0.25%~0.35%, Mn 0.70%~0.80%, Cr1.05%~1.20%, Mo 0.25%~0.30%, Ni 0.45%~0.55%, Cu≤0.12%, P≤0.013%, S≤0.010%, [N]≤70ppm, [O]≤15ppm, [H]≤1.5ppm, and the rest is Fe and unavoidable impurities.

3. The method for preparing a large alloy steel ring forging according to claim 1, characterized in that: The step (1) comprises the following steps: (1.1) Load the steel ingot for large alloy steel ring forgings into a forging heating furnace with a furnace temperature of ≤650℃, heat it to 640~680℃, and keep it warm. The holding time is based on the diameter of the steel ingot riser and is 0.6~0.8min / mm. (1.2) Rapidly heat to 1210~1250℃ at full power, and the holding time is based on the diameter of the ingot riser, which is 1.0~1.2min / mm; (1.3) After leaving the forging heating furnace, the steel is rolled and hot-cut on a ton press to form a water riser; (1.4) Return to the forging heating furnace and continue heating to 1200~1240℃. The holding time is based on the billet diameter and is 0.3~0.4min / mm. (1.5) After leaving the forging heating furnace, two upsetting and two stretching deformations are carried out on a ton press. Each upsetting forging is shorter than K. H ≥2.2; (1.6) Heat the forging heating furnace to 1180~1220℃, and the holding time is based on the billet diameter, which is 0.3~0.4min / mm; (1.7) After leaving the forging heating furnace, upsetting, punching and hole expansion are carried out on a ton press; (1.8) Heat the forging heating furnace to 1150~1180℃, and the holding time is based on the minimum value of the wall thickness and height of the ring blank, which is 0.3~0.4min / mm; (1.9) After leaving the forging heating furnace, the rings are rolled on the ring rolling machine.

4. The method for preparing a large alloy steel ring forging according to claim 1, characterized in that: During the quenching cooling in step (5.4), water cooling and air cooling are alternately used for cooling. The first quenching cooling time is 0.8~1.2s / mm, and the total quenching cooling time is 4~6s / mm.

5. The method for preparing a large alloy steel ring forging according to claim 4, characterized in that: The cooling medium for water cooling is water at 15~25℃. First, keep the cooling medium in a stable forced convection state. The convection intensity decreases in turn according to the number of times it enters the water.

6. The method for preparing a large alloy steel ring forging according to claim 1, characterized in that: After secondary tempering, the hardness test of the surface of large alloy steel ring forgings is also included, including the following steps: (A) Roughly grind the surface of the selected position of the large ring forging, the rough grinding depth is controlled at 2~4mm, the rough grinding area is greater than 50mm×50mm, and the grinding area is flat without depression; (B) Finely grind and polish the coarsely ground parts, with a polishing depth of ≤1mm, a smooth polished area without depressions, and a surface roughness of Ra≤7μm; (C) Perform hardness test on the finely ground and polished parts, and take the average value of the test three times for each part.

7. The method for preparing a large alloy steel ring forging according to claim 1, characterized in that: The surface hardness of large alloy steel ring forgings is tested after stress relief annealing, including the following steps: (A) Roughly grind the surface of the selected position of the large alloy steel ring forging, the rough grinding depth is controlled at 2~4mm, the rough grinding area is larger than 50mm×50mm, and ensure that the grinding area is flat and has no depression; (B) Finely grind and polish the coarsely ground parts, with a polishing depth of ≤1mm, and ensure that the polished part is flat and has no depressions, and the surface roughness Ra ≤7μm; (C) Perform hardness test on the finely ground and polished parts, and take the average value of the test three times for each part.

8. A large alloy steel ring forging produced by the production method according to claim 1, characterized in that: The hardness of large alloy steel ring forgings is ≥260HB, the hardness difference of a single piece is ≤20HB; the tensile strength is ≥850MPa, the yield strength is ≥700Mpa, the elongation after fracture is ≥15%; the impact energy Akv at -40℃ is ≥27J; the grain size N is ≥7.

9. The large alloy steel ring forging according to claim 8, characterized in that: The outer diameter of large alloy steel ring forgings is 7600~13830mm, the inner diameter is 6500~12960mm, and the height is 100~456mm.

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