CN111172358B - Heat treatment method for controlling dimensional change of high-temperature bearing steel - Google Patents
Heat treatment method for controlling dimensional change of high-temperature bearing steel Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/773—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material under reduced pressure or vacuum
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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Abstract
The invention relates to a heat treatment method for controlling dimensional change of high-temperature bearing steel, which comprises the following steps: step one, 8Cr4Mo4V steel is forged, spheroidized and annealed and machined; step two, quenching and tempering the machined 8Cr4Mo4V steel; thirdly, carrying out primary cold-hot circulation stabilization treatment and coarse grinding on the quenched and tempered 8Cr4Mo4V steel; step four, carrying out secondary cold-hot circulation stabilization treatment on the coarsely ground 8Cr4Mo4V steel; and step five, carrying out cold and hot circulation stabilizing treatment and low-temperature stabilizing heat treatment for the 3 rd time on the 8Cr4Mo4V steel subjected to cold and hot circulation stabilizing treatment twice, and then carrying out fine grinding and grinding on the bearing raceway to obtain a finished product. The invention is based on the dimension stable heat treatment, the heat treatment is carried out on the bearing parts, thereby controlling the dimension change of the bearing to the maximum extent and improving the dimension precision of the bearing.
Description
Technical Field
The invention belongs to the technical field of heat treatment processes, and relates to a heat treatment method for controlling dimensional change of high-temperature bearing steel, in particular to 8Cr4Mo4V bearing steel.
Background
The dimensional stability is an important index influencing the manufacturing precision and the service life of the bearing, 8Cr4Mo4V steel is the most commonly used steel for high-temperature bearings of aero-engines at present, and the steel is widely used for the high-temperature bearings of aero-engines with the working temperature below 316 ℃ and the DN value of 2.4 multiplied by 106The service environment of the following main shaft bearing of the aircraft engine is complex. Dimensional stability is therefore an important indicator for evaluating bearing grade and service life. The steel 8Cr4Mo4V for aeroengine bearings causes a reduction in the machining accuracy of bearings due to dimensional changes during manufacture and use, or dimensional changes during storage, thereby reducing the grade and service life of bearings. Earlier researches show that the size change of the bearing steel can be effectively reduced by adopting the stabilizing heat treatment, and the bearing steel meets the requirements of relevant standards on the size change, but the treated bearing still has certain change, the size still has small-range fluctuation, the bearing steel still has problems for manufacturing higher-grade high-precision bearings, and the size change needs to be further controlled. The size change of the current 8Cr4Mo4V steel after heat treatment and size stabilization treatment is less than or equal to 5/100000, but the size change of the bearing exceeds the standard requirements of high-precision and high-end bearing grades due to the change in the application process, the manufacturing grade and the service life of the bearing are reduced, and the requirements of grade control and size control precision of the bearing in long-term use cannot be met.
Disclosure of Invention
The purpose of the invention is as follows:
aiming at the problem of size control in the prior art, the invention provides a heat treatment process which can make the size change of a bearing smaller and the size more stable after 8Cr4Mo4V steel is subjected to heat treatment and size stabilization treatment.
The technical scheme is as follows:
a heat treatment method for controlling dimensional change of high-temperature bearing steel comprises the following steps:
step one, 8Cr4Mo4V steel is forged, spheroidized and annealed and machined;
step two, quenching and tempering the machined 8Cr4Mo4V steel;
thirdly, carrying out primary cold-hot circulation stabilization treatment and coarse grinding on the quenched and tempered 8Cr4Mo4V steel;
step four, carrying out secondary cold-hot circulation stabilization treatment on the coarsely ground 8Cr4Mo4V steel;
and step five, carrying out cold and hot circulation stabilizing treatment and low-temperature stabilizing treatment for the 3 rd time on the 8Cr4Mo4V steel subjected to cold and hot circulation stabilizing treatment twice, and then carrying out fine grinding and grinding on the bearing raceway to obtain a finished product.
In the second step, the quenching is performed under vacuum condition, and the vacuum quenching temperature is 1060-1110 ℃. The machined 8Cr4Mo4V steel is put into a quenching furnace, the quenching furnace is vacuumized and then heated until the vacuum degree reaches 5 multiplied by 10-1-5×10-2And Pa, starting to heat up, namely heating up to 1045-1058 ℃ from room temperature at the heating rate of 6-9 ℃/min, then heating up to 25-52 ℃ for 10-20min, keeping the temperature for 0.5-2h when the temperature reaches 1060-1110 ℃, then cooling by adopting high-purity nitrogen, wherein the cooling capacity of the nitrogen meets the requirement that 8Cr4Mo4V steel is cooled to 200 ℃ or less within 10min, then cooling to 40 ℃ or less within 30-60min, and then carrying out three times of tempering, wherein the tempering heating up is to heat up to 520-560 ℃ from room temperature at the heating rate of 7-9 ℃/min, the keeping time is 2-3h, and the cooling air pressure is 1.5-2 bar.
In the third step and the fourth step, the cooling rate of the cold treatment is 2-4 ℃/min, the cold treatment is carried out in a controllable constant temperature and humidity test box, the temperature in the controllable constant temperature and humidity test box is-65 to-95 ℃, the heat preservation time is 2-3h, and after the heat preservation is finished, the temperature in the controllable constant temperature and humidity test box is raised to 50-70 ℃ within 10-15 min. Taking out the sample after the cold treatment is finished, then putting the sample into a vacuum furnace for heat treatment, vacuumizing the vacuum furnace firstly until the vacuum degree reaches 5 multiplied by 10-1-5×10- 2Heating at Pa, heating to 400 deg.C at a rate of 4-6 deg.C/min at room temperature, heating to 10-55 deg.C for 15-20min, and heating to 410-465 deg.CKeeping the temperature for 2-3h, cooling with nitrogen gas at 0.5-1.5bar after the heat preservation is finished, discharging at 40-60 deg.C for 30-40min, and performing 3 cycles of primary cold treatment and primary heat treatment.
The temperature of the low-temperature stabilizing treatment in the step five is 120-220 ℃, the low-temperature stabilizing treatment is carried out on 8Cr4Mo4V steel in a low-temperature stabilizing treatment furnace, and the heat preservation time is 7-9 h.
The lower part of the furnace body of low temperature stable processing stove is equipped with the furnace body landing leg, and the below of furnace body is equipped with the motor, and the motor shaft of motor passes the bottom of furnace body and the upper portion screw sleeve of motor shaft, and screw sleeve is connected with puts thing dish support, and the motor shaft passes furnace body department and is equipped with the bearing, puts thing dish leg joint and puts the thing dish, and one side of furnace body is equipped with fan and venthole, still is equipped with the hot plate in the furnace body, and the one side of keeping away from the fan in the furnace body is equipped with the arc. The rotating speed of the object placing disc rotating along with the motor is 2-10 r/min.
The object placing disc is in a structure with a plurality of cross-arranged air holes.
The advantages and effects are as follows:
the invention is based on the dimension stable heat treatment, the heat treatment is carried out on the bearing parts, thereby controlling the dimension change of the bearing to the maximum extent and improving the dimension precision of the bearing.
Drawings
FIG. 1 shows the dimensional change characteristics of a bearing at a working temperature of 120 ℃ after a low-temperature stabilizing heat treatment process;
FIG. 2 shows the dimensional change characteristics of a bearing at a working temperature of 150 ℃ after a low-temperature stabilizing heat treatment process;
FIG. 3 shows the dimensional change characteristics of a bearing at a working temperature of 220 ℃ after a low-temperature stabilization heat treatment process;
FIG. 4 is a schematic view of the overall structure of a low-temperature stabilization treatment furnace;
fig. 5 is a schematic top view of the tray, tray holder and threaded sleeve.
Description of reference numerals: 1. the furnace comprises an air outlet hole, 2 heating plates, 3 arc-shaped plates, 4 object placing discs, 5 object placing disc supports, 6 threaded sleeves, 7 motor supports, 8 bearings, 9 motor shafts, 10 furnace body supporting legs, 11 nuts, 12 motors, 13 furnace bodies, 14.8Cr4Mo4V steel and 15 fans.
The specific implementation mode is as follows:
the invention is described in detail below with reference to the accompanying drawings:
a heat treatment method for controlling dimensional change of high-temperature bearing steel comprises the following steps:
step one, 8Cr4Mo4V steel is forged, spheroidized and annealed and machined;
forging treatment: the 8Cr4Mo4V steel is forged into a blank, the height-diameter ratio of raw materials for the forged blank is less than 2, the processing temperature of the forged blank is 950-1150 ℃, the blank is returned to a furnace and kept warm for 5-8min after being forged, then the final preparation of the annular blank is finished by adopting rolling and expanding molding, the rolling and expanding molding requires that the single-side rolling and expanding time is 5-8 seconds, the rolling and expanding ratio is 1.0-1.6, and the preheating temperature of a die during forging is more than or equal to 300 ℃; after rolling and expanding, placing the qualified ring blank with the size meeting the requirements into an ash tank for ash cooling, and controlling the cooling speed to prevent cracks; when the ash cooling temperature reaches 400-500 ℃, the spheroidizing annealing operation is carried out.
Spheroidizing annealing operation: after the ring blank is forged, the ring blank is placed into ash cooling, and when the ash cooling temperature reaches 400-500 ℃, spheroidizing annealing operation is carried out. The time from forging to spheroidizing annealing is required to be 16 hours or less. The forging stock is boxed before annealing, the box is placed in an effective temperature zone in an annealing furnace, the preheating temperature is 700-750 ℃, the preheating time is 3h, then the box is heated to 830-860 ℃, the heat preservation time is 6-7h, then the box is cooled to 720-750 ℃ along with the furnace, the heat preservation time is 11-12h, then the box is cooled to 680 ℃ at the speed of 20 ℃/h, then the box is cooled to 500-550 ℃, and then the box is taken out of the furnace for air cooling, and after cooling, the next machining operation can be carried out.
And (3) machining treatment: and (3) adopting numerical control or common lathe processing, finishing by feeding more than two times when the size cutting depth of the final stage is required to be less than 2mm in rough processing, and finishing by feeding 3 times when the final allowance is less than 1mm and each cutting depth is less than 0.5 mm.
Step two, quenching and tempering the machined 8Cr4Mo4V steel; quenching is carried out on a vacuum stripThe vacuum quenching temperature is 1060-1110 ℃ when the quenching is carried out under the condition. The machined 8Cr4Mo4V steel is put into a quenching furnace, the quenching furnace is vacuumized and then heated until the vacuum degree reaches 5 multiplied by 10-1-5×10-2And Pa, starting to heat up, namely heating up to 1045-1058 ℃ from room temperature at the heating rate of 6-9 ℃/min, then heating up to 25-52 ℃ for 10-20min, keeping the temperature for 0.5-2h when the temperature reaches 1060-1110 ℃, then cooling by adopting high-purity nitrogen, wherein the cooling capacity of the nitrogen meets the requirement that 8Cr4Mo4V steel is cooled to 200 ℃ or less within 10min, then cooling to 40 ℃ or less within 30-60min, and then carrying out three times of tempering, wherein the tempering heating up is to heat up to 520-560 ℃ from room temperature at the heating rate of 7-9 ℃/min, the keeping time is 2-3h, and the cooling air pressure is 1.5-2 bar.
And (3) three tempering requirements: and cooling to be less than or equal to 40 ℃ after quenching, so as to carry out tempering treatment, wherein the time interval for carrying out first tempering cannot exceed 5h after quenching is finished. The temperature rise rate of tempering is 7-9 ℃/min is raised to 520-560 ℃, the heat preservation time is 2-3h, the cooling air pressure is 1.5-2bar, the temperature is cooled to be less than or equal to 40 ℃, and then the next tempering treatment is carried out. There is no strict time requirement between the second and third tempering treatments and the first tempering treatment.
And step three, carrying out primary cold-hot circulation stable treatment and coarse grinding on the quenched and tempered 8Cr4Mo4V steel, preferably grinding by using a cylindrical grinding machine, wherein the single grinding feed amount is less than 2 microns.
Step four, carrying out secondary cold-hot circulation stabilization treatment on the coarsely ground 8Cr4Mo4V steel;
in the third step and the fourth step, the cooling rate of the cold treatment is 2-4 ℃/min, the cold treatment is carried out in a controllable constant temperature and humidity test box, the temperature in the controllable constant temperature and humidity test box is-65 to-95 ℃, the heat preservation time is 2-3h, and after the heat preservation is finished, the temperature of the controllable constant temperature and humidity test box is raised to 50-70 ℃ within 10-15 min. Taking out the sample after the cold treatment is finished, then putting the sample into a vacuum furnace for heat treatment, vacuumizing the vacuum furnace firstly until the vacuum degree reaches 5 multiplied by 10-1-5×10-2Heating at Pa and at room temperature at 4-6 deg.C/minHeating up to 400 ℃ at the heating rate, heating up to 10-55 ℃ again for the next 15-20min, preserving heat for 2-3h when the temperature reaches 410-.
And step five, carrying out 3 rd cold-hot circulation stabilizing treatment and low-temperature stabilizing treatment on the 8Cr4Mo4V steel subjected to the two times of cold-hot circulation stabilizing treatment, wherein the temperature of the low-temperature stabilizing treatment is 120-220 ℃, the low-temperature stabilizing treatment is carried out on the 8Cr4Mo4V steel in a low-temperature stabilizing treatment furnace, the heat preservation time is 7-9h, then carrying out fine grinding and grinding on the bearing raceway to obtain a finished product, and the surface roughness reaches the Ra0.08 level after grinding.
As shown in fig. 4 and 5, a furnace body support leg 10 is arranged at the lower part of a furnace body 13 of the low-temperature stable treatment furnace, a motor 12 is arranged below the furnace body 13, the motor 12 is supported by a motor support 7, a motor shaft 9 of the motor 12 penetrates through the bottom of the furnace body 13, a threaded sleeve 6 of a nut 11 is arranged at the upper part of the motor shaft 9, the threaded sleeve 6 is connected with a storage tray support 5 in a welding manner, a bearing 8 is arranged at the position where the motor shaft 9 penetrates through the furnace body 13, the storage tray support 5 is connected with a storage tray 4, the storage tray 4 is of a cross arrangement multi-vent structure, 8Cr4Mo4V steel 14 subjected to low-temperature stable treatment is arranged at the upper end of the storage tray 4, a fan 15 and an air outlet 1 are arranged at one side of the furnace body 13, a heating plate 2 is further arranged in the furnace body 13, a heat-resistant steel arc plate 3 is arranged at one side of the furnace body 13 far away from the fan 15, so that the direction of hot air circulation is more, and the placed 8Cr4Mo4V steel can be heated uniformly. When the motor 12 rotates, the rotation speed of the object placing disc 4 rotating along with the motor 12 is 2-10 r/min.
Example 1
A heat treatment method for controlling dimensional change of high-temperature bearing steel comprises the following steps:
step one, 8Cr4Mo4V steel is forged, spheroidized and annealed and machined;
forging treatment: the 8Cr4Mo4V steel is forged into a blank by adopting a method of forging, wherein the height-diameter ratio of raw materials for the forging blank is less than 2, the processing temperature of the forging blank is 950 ℃, the blank is re-melted and kept warm for 8min after being forged, then the preparation of the final annular blank is finished by adopting rolling and expanding molding, the rolling and expanding molding requirements are that the single-side rolling and expanding time is 5 seconds, the rolling and expanding ratio is 1.6, and the preheating temperature of a die is 300 ℃ during forging; after rolling and expanding, placing the qualified ring blank with the size meeting the requirements into an ash tank for ash cooling, and controlling the cooling speed to prevent cracks; when the ash cooling temperature reaches 400 ℃, spheroidizing annealing operation is carried out.
Spheroidizing annealing operation: and after the ring blank is forged, cooling in ash, and when the temperature of the ash cooling reaches 400 ℃, carrying out spheroidizing annealing operation. The time from forging to spheroidizing annealing is required to be equal to 16 h. The forging stock is boxed before annealing, the box is placed in an effective temperature zone in an annealing furnace, the preheating temperature is 700 ℃, the preheating time is 3 hours, then the box is heated to 830 ℃, the heat preservation time is 7 hours, then the box is cooled to 720 ℃ along with the furnace, the heat preservation time is 12 hours, then the box is cooled to 680 ℃ at the speed of 20 ℃/h, then the box is cooled to 500 ℃ along with the furnace, taken out of the furnace for air cooling, and after cooling, the next machining operation can be carried out.
And (3) machining treatment: and (3) adopting numerical control or common lathe processing, finishing by feeding more than two times when the size cutting depth of the final stage is required to be less than 2mm in rough processing, and finishing by feeding 3 times when the final allowance is less than 1mm and each cutting depth is less than 0.5 mm.
Step two, quenching and tempering the machined 8Cr4Mo4V steel; quenching was carried out under vacuum conditions at a vacuum quenching temperature of 1060 ℃. The machined 8Cr4Mo4V steel is put into a quenching furnace, the quenching furnace is vacuumized and then heated until the vacuum degree reaches 5 multiplied by 10-1Pa, starting to heat up, namely heating up the room temperature to 1045 ℃ at the heating rate of 6 ℃/min, then heating up the room temperature for 25 min, keeping the temperature for 2h when the temperature reaches 1060 ℃, then cooling by adopting high-purity nitrogen, wherein the cooling capacity of the nitrogen meets the requirement that 8Cr4Mo4V steel is cooled to 200 ℃ within 8min, then cooling to 40 ℃ within 60min, and then carrying out three times of tempering, wherein the tempering heating up is to heat up the room temperature to 520 ℃ at the heating rate of 7 ℃/min, the keeping time is 2h, and the air pressure is 2 bar. Taking a small amount of samples after three times of tempering, placing the samples at a working temperature for simulation, wherein the simulation method is to keep the temperature for 2 hours, then taking the samples out, cooling the samples to the normal temperature, then performing simulation at the working temperature, and circulating the steps till the samples are accumulatedThe heat preservation time is accumulated for 20h, the size is measured once, the size change characteristics are as quenching and tempering in figure 1, and the size change is large.
And (3) three tempering requirements: after quenching, the steel is cooled to 40 ℃, so that tempering treatment can be carried out, and after quenching, the time interval of primary tempering is 5 hours. The temperature is raised to 520 ℃ at the temperature raising rate of 7 ℃/min for tempering, the heat preservation time is 2h, the cooling air pressure is 2bar, the temperature is cooled to 40 ℃, and then the next tempering treatment is carried out. There is no strict time requirement between the second and third tempering treatments and the first tempering treatment.
And step three, carrying out primary cold-hot circulation stable treatment and coarse grinding on the quenched and tempered 8Cr4Mo4V steel, preferably grinding by using a cylindrical grinding machine, wherein the single grinding feed amount is less than 2 microns.
Step four, carrying out secondary cold-hot circulation stabilization treatment on the coarsely ground 8Cr4Mo4V steel; and (3) after secondary cold-hot circulation stabilization treatment, taking a small amount of samples, placing the samples at a working temperature for simulation, wherein the simulation method is to keep the temperature for 2 hours, then taking the samples out, cooling the samples to the normal temperature, then performing simulation at the working temperature, circulating the operation until the accumulated heat preservation time is 20 hours, measuring the primary size, and performing size change characteristics such as quenching, tempering and stabilization treatment in the figure 1, so that the size fluctuation is obviously reduced.
And in the third step and the fourth step, the cooling rate of the cold treatment is 2 ℃/min, the cold treatment is carried out in a controllable constant temperature and humidity test box, the temperature in the controllable constant temperature and humidity test box is-65 ℃, the heat preservation time is 3h, and after the heat preservation is finished, the temperature in the controllable constant temperature and humidity test box is raised to 50 ℃ within 10 min. Taking out the sample after the cold treatment is finished, then putting the sample into a vacuum furnace for heat treatment, vacuumizing the vacuum furnace firstly until the vacuum degree reaches 5 multiplied by 10-1Heating at Pa, heating to 400 deg.C at a rate of 4 deg.C/min at room temperature, heating to 10 deg.C for 15min, maintaining at 410 deg.C for 3h, cooling with nitrogen gas (0.5 bar) at 40min, discharging at a temperature below 60 deg.C, and circulating for 3 circulations
And step five, carrying out cold and hot circulation stabilizing treatment and low-temperature stabilizing treatment for the 3 rd time on the 8Cr4Mo4V steel subjected to cold and hot circulation stabilizing treatment twice, and then carrying out fine grinding and grinding on the bearing raceway to obtain a finished product, wherein the surface roughness reaches the Ra0.08 level after grinding. The temperature of the low-temperature stabilizing treatment is 120 ℃, the low-temperature stabilizing treatment is carried out on 8Cr4Mo4V steel in a low-temperature stabilizing treatment furnace, and the heat preservation time is 9 hours. After low-temperature heat treatment, a small amount of samples are taken and placed at the working temperature for simulation, the simulation method is that heat preservation is carried out for 2 hours, then the samples are taken out and cooled to the normal temperature, then simulation is carried out at the working temperature, the operation is circulated in the way until the accumulated heat preservation time is 10 hours, the size is measured once, the size change characteristics are as quenching, tempering, stabilizing treatment and re-stabilizing treatment in the figure 1, the size fluctuation is found to be smaller, and the size stability is greatly improved.
The lower part of a furnace body 13 of the low-temperature stable treatment furnace is provided with furnace body supporting legs 10, a motor 12 is arranged below the furnace body 13, the motor 12 is supported by a motor support 7, a motor shaft 9 of the motor 12 penetrates through the bottom of the furnace body 13, a threaded sleeve 6 of a nut 11 is arranged on the upper part of the motor shaft 9, the threaded sleeve 6 is connected with a storage disc support 5 in a welding mode, a bearing 8 is arranged at the position, where the motor shaft 9 penetrates through the furnace body 13, of the storage disc support 5, the storage disc 4 is connected with a storage disc 4, the storage disc 4 is of a cross arrangement multi-vent structure, 8Cr4Mo4V steel 14 subjected to low-temperature stable treatment is arranged at the upper end of the storage disc 4, one side of the furnace body 13 is provided with a fan 15 and an air outlet 1, a heating plate 2 is further arranged in the furnace body 13, one side, far away from the fan 15, of the furnace body is provided with a heat-resistant steel arc plate 3, so that the direction of hot air circulation is more, and the placed 8Cr4Mo4V steel can be heated uniformly. When the motor 12 rotates, the rotation speed of the object placing disk 4 rotating along with the motor 12 is 2 r/min.
Example 2
A heat treatment method for controlling dimensional change of high-temperature bearing steel comprises the following steps:
step one, 8Cr4Mo4V steel is forged, spheroidized and annealed and machined;
forging treatment: the 8Cr4Mo4V steel is forged into a blank by adopting a method of forging, wherein the height-diameter ratio of raw materials for the forging blank is less than 2, the processing temperature of the forging blank is 1150 ℃, the blank is returned to a furnace and kept warm for 5min after being forged, then the preparation of the final annular blank is finished by adopting rolling and expanding molding, the rolling and expanding molding requirements are that the single-side rolling and expanding time is 8 seconds, the rolling and expanding ratio is 1.0, and the preheating temperature of a die during forging is 320 ℃; after rolling and expanding, placing the qualified ring blank with the size meeting the requirements into an ash tank for ash cooling, and controlling the cooling speed to prevent cracks; the ash cooling temperature reaches 500 ℃, and spheroidizing annealing operation is carried out.
Spheroidizing annealing operation: and after the ring blank is forged, cooling the ring blank in ash, and performing spheroidizing annealing when the ash cooling temperature reaches 500 ℃. The time from forging to spheroidizing annealing was required to be 15 hours. The forging stock is boxed before annealing, the box is placed in an effective temperature zone in an annealing furnace, the preheating temperature is 750 ℃, the preheating time is 3 hours, then the box is heated to 860 ℃, the heat preservation time is 6 hours, then the box is cooled to 750 ℃ along with the furnace, the heat preservation time is 11 hours, then the box is cooled to 680 ℃ at the speed of 20 ℃/h, then the box is cooled to 550 ℃ along with the furnace, taken out of the furnace for air cooling, and after cooling, the next machining operation can be carried out.
And (3) machining treatment: and (3) adopting numerical control or common lathe processing, finishing by feeding more than two times when the size cutting depth of the final stage is required to be less than 2mm in rough processing, and finishing by feeding 3 times when the final allowance is less than 1mm and each cutting depth is less than 0.5 mm.
Step two, quenching and tempering the machined 8Cr4Mo4V steel; quenching was performed under vacuum conditions, with a vacuum quenching temperature of 1110 ℃. The machined 8Cr4Mo4V steel is put into a quenching furnace, the quenching furnace is vacuumized and then heated until the vacuum degree reaches 5 multiplied by 10-2And Pa, starting to heat up, namely heating up to 1058 ℃ from room temperature at a heating rate of 9 ℃/min, heating up to 52 ℃ for 20min, keeping the temperature for 0.5h when the temperature reaches 1110 ℃, cooling by adopting high-purity nitrogen, wherein the cooling capacity of the nitrogen meets the requirement that 8Cr4Mo4V steel is cooled to 190 ℃ within 9min, then cooling to 38 ℃ within 30min, and then tempering for three times, wherein the tempering heating up is to heat up to 560 ℃ from room temperature at a heating rate of 9 ℃/min, the keeping time is 3h, and the air pressure is 1.5 bar. Taking a small amount of samples after three times of tempering, placing the samples at a working temperature for simulation, wherein the simulation method comprises the steps of preserving heat for 2 hours, taking out the samples, cooling the samples to the normal temperature, simulating the samples at the working temperature, circulating the simulation to the accumulated heat preservation time for 20 hours, measuring the size once and changing the sizeThe chemical characteristics are as quenching + tempering in fig. 2, and the dimensional change is large.
And (3) three tempering requirements: after quenching, the steel is cooled to 39 ℃, so that tempering treatment can be carried out, and after quenching, the time interval of first tempering is 4 hours. The temperature is raised to 560 ℃ at the temperature raising rate of 9 ℃/min for tempering, the heat preservation time is 3h, the cooling air pressure is 1.5bar, the temperature is cooled to 39 ℃, and then the next tempering treatment is carried out. There is no strict time requirement between the second and third tempering treatments and the first tempering treatment.
And step three, carrying out primary cold-hot circulation stable treatment and coarse grinding on the quenched and tempered 8Cr4Mo4V steel, preferably grinding by using a cylindrical grinding machine, wherein the single grinding feed amount is less than 2 microns.
Step four, carrying out secondary cold-hot circulation stabilization treatment on the coarsely ground 8Cr4Mo4V steel; and after secondary cooling and heating circulation stabilization treatment, taking a small amount of samples, placing the samples at a working temperature for simulation, wherein the simulation method is to keep the temperature for 2 hours, then taking the samples out, cooling the samples to the normal temperature, then performing simulation at the working temperature, circulating the operation until the accumulated heat preservation time is 20 hours, measuring the primary size, and performing size change characteristics such as quenching, tempering and stabilization treatment in the figure 2, so that the size fluctuation is obviously reduced.
And in the third step and the fourth step, the cooling rate of the cold treatment is 4 ℃/min, the cold treatment is carried out in a controllable constant temperature and humidity test box, the temperature in the controllable constant temperature and humidity test box is-95 ℃, the heat preservation time is 2h, and after the heat preservation is finished, the temperature in the controllable constant temperature and humidity test box is raised to 70 ℃ within 15 min. Taking out the sample after the cold treatment is finished, then putting the sample into a vacuum furnace for heat treatment, vacuumizing the vacuum furnace firstly until the vacuum degree reaches 5 multiplied by 10-2Heating at Pa, raising the temperature to 400 deg.C at 6 deg.C/min at room temperature, heating to 55 deg.C for 20min, maintaining the temperature at 465 deg.C for 2h, cooling with nitrogen gas at 1.5bar for 30min, discharging at a temperature below 40 deg.C, and circulating for 3 circulations
And step five, carrying out cold and hot circulation stabilizing treatment and low-temperature stabilizing heat treatment for the 3 rd time on the 8Cr4Mo4V steel subjected to cold and hot circulation stabilizing treatment twice, and then carrying out fine grinding and grinding on the bearing raceway to obtain a finished product, wherein the surface roughness reaches the Ra0.08 level after grinding. The temperature of the low-temperature stabilizing treatment is 220 ℃, the low-temperature stabilizing treatment is carried out on 8Cr4Mo4V steel in a low-temperature stabilizing treatment furnace, and the heat preservation time is 7 hours. After low-temperature heat treatment, a small amount of samples are taken and placed at the working temperature for simulation, the simulation method is that heat preservation is carried out for 2 hours, then the samples are taken out and cooled to the normal temperature, then simulation is carried out at the working temperature, the operation is circulated in the way until the accumulated heat preservation time is 10 hours, the size is measured once, the size change characteristics are as quenching, tempering, stabilizing treatment and re-stabilizing treatment in the graph 2, the size fluctuation is found to be smaller, and the size stability is greatly improved.
The lower part of a furnace body 13 of the low-temperature stable treatment furnace is provided with furnace body supporting legs 10, a motor 12 is arranged below the furnace body 13, the motor 12 is supported by a motor support 7, a motor shaft 9 of the motor 12 penetrates through the bottom of the furnace body 13, a threaded sleeve 6 of a nut 11 is arranged on the upper part of the motor shaft 9, the threaded sleeve 6 is connected with a storage disc support 5 in a welding mode, a bearing 8 is arranged at the position, where the motor shaft 9 penetrates through the furnace body 13, of the storage disc support 5, the storage disc 4 is connected with a storage disc 4, the storage disc 4 is of a cross arrangement multi-vent structure, 8Cr4Mo4V steel 14 subjected to low-temperature stable treatment is arranged at the upper end of the storage disc 4, one side of the furnace body 13 is provided with a fan 15 and an air outlet 1, a heating plate 2 is further arranged in the furnace body 13, one side, far away from the fan 15, of the furnace body is provided with a heat-resistant steel arc plate 3, so that the direction of hot air circulation is more, and the placed 8Cr4Mo4V steel can be heated uniformly. When the motor 12 rotates, the rotation speed of the object placing disk 4 rotating along with the motor 12 is 10 r/min.
Example 3
A heat treatment method for controlling dimensional change of high-temperature bearing steel comprises the following steps:
step one, 8Cr4Mo4V steel is forged, spheroidized and annealed and machined;
forging treatment: the 8Cr4Mo4V steel is forged into a blank by adopting a method of forging, wherein the height-diameter ratio of raw materials for the forging blank is less than 2, the processing temperature of the forging blank is 1050 ℃, the blank is re-melted and insulated for 6min after being forged, then the preparation of the final annular blank is finished by adopting rolling and expanding molding, the rolling and expanding molding requirements are that the single-side rolling and expanding time is 6 seconds, the rolling and expanding ratio is 1.3, and the preheating temperature of a die is 350 ℃ during forging; after rolling and expanding, placing the qualified ring blank with the size meeting the requirements into an ash tank for ash cooling, and controlling the cooling speed to prevent cracks; when the ash cooling temperature reaches 450 ℃, spheroidizing annealing operation is carried out.
Spheroidizing annealing operation: and after the ring blank is forged, cooling the ring blank in ash, and performing spheroidizing annealing when the ash cooling temperature reaches 450 ℃. The time from forging to spheroidizing annealing is required to be 16 hours or less. The forging stock is boxed before annealing, the box is placed in an effective temperature zone in an annealing furnace, the preheating temperature is 725 ℃, the preheating time is 3 hours, then the box is heated to 850 ℃, the heat preservation time is 6.5 hours, then the box is cooled to 730 ℃ along with the furnace, the heat preservation time is 11.5 hours, then the box is cooled to 680 ℃ at the speed of 20 ℃/h, then the box is cooled to 525 ℃ along with the furnace, taken out of the furnace and cooled in air, and after cooling, the next machining operation can be carried out.
And (3) machining treatment: and (3) adopting numerical control or common lathe processing, finishing by feeding more than two times when the size cutting depth of the final stage is required to be less than 2mm in rough processing, and finishing by feeding 3 times when the final allowance is less than 1mm and each cutting depth is less than 0.5 mm.
Step two, quenching and tempering the machined 8Cr4Mo4V steel; quenching was performed under vacuum at 1090 ℃. The machined 8Cr4Mo4V steel is put into a quenching furnace, the quenching furnace is vacuumized and then heated until the vacuum degree reaches 1 x 10-1And Pa, starting to heat up, namely heating up the room temperature to 1050 ℃ at a heating rate of 7 ℃/min, heating up the room temperature for 15min, then heating up the room temperature to 40 ℃ again, keeping the temperature for 1.5h when the temperature reaches 1090 ℃, then cooling the 8Cr4Mo4V steel to 160 ℃ by adopting high-purity nitrogen, wherein the cooling capacity of the nitrogen meets the requirement that the 8Cr4Mo4V steel is cooled to 30 ℃ within 10min, then cooling the steel to 30 ℃ within 45min, and then carrying out tempering for three times, wherein the tempering heating up is realized by heating up the room temperature to 540 ℃ at a heating rate of 8 ℃/min, the keeping temperature for 2.5h, and the air pressure is 1.8 bar. Taking a small amount of samples after three times of tempering, placing the samples at a working temperature for simulation, wherein the simulation method comprises the steps of preserving heat for 2 hours, taking out the samples, cooling the samples to the normal temperature, then performing simulation at the working temperature, circulating the steps until the accumulated heat preservation time is 20 hours, measuring the size once, and measuring the size change characteristics as shown in the graph 3The size change is large by quenching and tempering.
And (3) three tempering requirements: after quenching, the steel is cooled to 30 ℃, so that tempering treatment can be carried out, and after quenching is finished, the time interval of first tempering is 3.5 h. The temperature is raised to 540 ℃ at the tempering temperature rise rate of 8 ℃/min, the heat preservation time is 2.5h, the cooling air pressure is 1.8bar, the temperature is cooled to 30 ℃, and then the next tempering treatment is carried out. There is no strict time requirement between the second and third tempering treatments and the first tempering treatment.
And step three, carrying out primary cold-hot circulation stable treatment and coarse grinding on the quenched and tempered 8Cr4Mo4V steel, preferably grinding by using a cylindrical grinding machine, wherein the single grinding feed amount is less than 2 microns.
Step four, carrying out secondary cold-hot circulation stabilization treatment on the coarsely ground 8Cr4Mo4V steel; and after secondary cooling and heating circulation stabilization treatment, taking a small amount of samples, placing the samples at a working temperature for simulation, wherein the simulation method is to keep the temperature for 2 hours, then taking the samples out, cooling the samples to the normal temperature, then performing simulation at the working temperature, circulating the operation until the accumulated heat preservation time is 20 hours, measuring the primary size, and performing size change characteristics such as quenching, tempering and stabilization treatment in the figure 3, so that the size fluctuation is obviously reduced.
And in the third step and the fourth step, the cooling rate of the cold treatment is 3 ℃/min, the cold treatment is carried out in a controllable constant temperature and humidity test box, the temperature in the controllable constant temperature and humidity test box is-80 ℃, the heat preservation time is 2.5h, and after the heat preservation is finished, the temperature in the controllable constant temperature and humidity test box is raised to 60 ℃ within 12 min. Taking out the sample after the cold treatment is finished, then putting the sample into a vacuum furnace for heat treatment, vacuumizing the vacuum furnace firstly until the vacuum degree reaches 1 multiplied by 10-1Heating at Pa, heating to 400 deg.C at room temperature at a rate of 5 deg.C/min, heating to 35 deg.C for 17min, maintaining at 435 deg.C for 2.5h, cooling with nitrogen gas at 1bar for 35min, discharging at a temperature below 50 deg.C, and circulating for 3 circulations
And step five, carrying out cold and hot circulation stabilizing treatment and low-temperature stabilizing heat treatment for the 3 rd time on the 8Cr4Mo4V steel subjected to cold and hot circulation stabilizing treatment twice, and then carrying out fine grinding and grinding on the bearing raceway to obtain a finished product, wherein the surface roughness reaches the Ra0.08 level after grinding. The temperature of the low-temperature stabilizing treatment is 160 ℃, the low-temperature stabilizing treatment is carried out on 8Cr4Mo4V steel in a low-temperature stabilizing treatment furnace, and the heat preservation time is 8 hours. After low-temperature heat treatment, a small amount of samples are taken and placed at the working temperature for simulation, the simulation method is that heat preservation is carried out for 2 hours, then the samples are taken out and cooled to the normal temperature, then simulation is carried out at the working temperature, the operation is circulated in the way until the accumulated heat preservation time is 10 hours, the size is measured once, the size change characteristics are as shown in quenching, tempering, stabilizing treatment and re-stabilizing treatment in the graph 3, the size fluctuation is found to be smaller, and the size stability is greatly improved.
The lower part of a furnace body 13 of the low-temperature stable treatment furnace is provided with furnace body supporting legs 10, a motor 12 is arranged below the furnace body 13, the motor 12 is supported by a motor support 7, a motor shaft 9 of the motor 12 penetrates through the bottom of the furnace body 13, a threaded sleeve 6 of a nut 11 is arranged on the upper part of the motor shaft 9, the threaded sleeve 6 is connected with a storage disc support 5 in a welding mode, a bearing 8 is arranged at the position, where the motor shaft 9 penetrates through the furnace body 13, of the storage disc support 5, the storage disc 4 is connected with a storage disc 4, the storage disc 4 is of a cross arrangement multi-vent structure, 8Cr4Mo4V steel 14 subjected to low-temperature stable treatment is arranged at the upper end of the storage disc 4, one side of the furnace body 13 is provided with a fan 15 and an air outlet 1, a heating plate 2 is further arranged in the furnace body 13, one side, far away from the fan 15, of the furnace body is provided with a heat-resistant steel arc plate 3, so that the direction of hot air circulation is more, and the placed 8Cr4Mo4V steel can be heated uniformly. When the motor 12 rotates, the rotation speed of the object placing disk 4 rotating along with the motor 12 is 6 r/min.
Claims (4)
1. A heat treatment method for controlling dimensional change of high-temperature bearing steel is characterized by comprising the following steps: the method comprises the following steps:
step one, 8Cr4Mo4V steel is forged, spheroidized and annealed and machined;
step two, quenching and tempering the machined 8Cr4Mo4V steel;
thirdly, carrying out primary cold-hot circulation stabilization treatment and coarse grinding on the quenched and tempered 8Cr4Mo4V steel;
step four, carrying out secondary cold-hot circulation stabilization treatment on the coarsely ground 8Cr4Mo4V steel;
step five, carrying out cold and hot circulation stabilizing treatment and low-temperature stabilizing treatment for the 3 rd time on the 8Cr4Mo4V steel subjected to cold and hot circulation stabilizing treatment twice, and then carrying out fine grinding and grinding on the bearing raceway to obtain a finished product;
in the second step, the quenching is carried out under the vacuum condition, and the vacuum quenching temperature is 1060-1110 ℃;
the machined 8Cr4Mo4V steel is put into a quenching furnace, the quenching furnace is vacuumized and then heated until the vacuum degree reaches 5 multiplied by 10-1-5×10-2 Pa, starting heating, namely heating the room temperature to 1045-1058 ℃ at a heating rate of 6-9 ℃/min, then heating the room temperature to 25-52 ℃ within 10-20min, keeping the temperature for 0.5-2h when the temperature reaches 1060-1110 ℃, then cooling the room temperature to 520-560 ℃ within 30-60min by adopting high-purity nitrogen, wherein the cooling capacity of the nitrogen meets the requirement that the 8Cr4Mo4V steel is cooled to 200 ℃ or less within 10min, then cooling the room temperature to 40 ℃ or less within 30-60min, and then carrying out three times of tempering, wherein the tempering heating is realized by heating the room temperature to 520-560 ℃ at a heating rate of 7-9 ℃/min, the keeping time is 2-3h, and the cooling pressure is 1.5-2 bar;
in the third step and the fourth step, the cooling rate of the cold treatment is 2-4 ℃/min, the cold treatment is carried out in a controllable constant temperature and humidity test box, the temperature in the controllable constant temperature and humidity test box is-65 to-95 ℃, the heat preservation time is 2-3h, and after the heat preservation is finished, the temperature in the controllable constant temperature and humidity test box is raised to 50-70 ℃ within 10-15 min; taking out the sample after the cold treatment is finished, then putting the sample into a vacuum furnace for heat treatment, vacuumizing the vacuum furnace firstly until the vacuum degree reaches 5 multiplied by 10-1-5×10-2 Heating is started when Pa, the temperature is raised to 400 ℃ at the heating rate of 4-6 ℃/min at room temperature, the temperature is raised to 10-55 ℃ again in the next 15-20min, the temperature is kept for 2-3h when the temperature reaches 410-465 ℃, nitrogen is adopted for cooling after the heat preservation is finished, the nitrogen pressure is 0.5-1.5bar, the cooling process needs 30-40min, the temperature is discharged from the furnace at 40-60 ℃, one-time cold treatment and one-time heat treatment are a cycle, and 3 cycles are carried out;
the temperature of the low-temperature stabilizing treatment in the step five is 120-220 ℃, the low-temperature stabilizing treatment is carried out on 8Cr4Mo4V steel in a low-temperature stabilizing treatment furnace, and the heat preservation time is 7-9 h.
2. The heat treatment method for controlling dimensional change of high temperature bearing steel according to claim 1, wherein: the lower part of furnace body (13) of low temperature stable processing stove is equipped with furnace body landing leg (10), the below of furnace body (13) is equipped with motor (12), motor shaft (9) of motor (12) pass the bottom of furnace body (13) and the upper portion of motor shaft (9) is equipped with threaded sleeve (6), threaded sleeve (6) are connected with puts thing dish support (5), motor shaft (9) pass furnace body (13) department and are equipped with bearing (8), it is connected with puts thing dish (4) to put thing dish support (5), one side of furnace body (13) is equipped with fan (15) and venthole (1), still be equipped with hot plate (2) in furnace body (13), one side of keeping away from fan (15) in furnace body (13) is equipped with arc (3).
3. The heat treatment method for controlling dimensional change of high temperature bearing steel according to claim 2, wherein: the rotating speed of the object placing disc (4) rotating along with the motor (12) is 2-10 r/min.
4. The heat treatment method for controlling dimensional change of high temperature bearing steel according to claim 2 or 3, wherein: the object placing disc (4) is in a structure of multi-vent holes which are arranged in a cross way.
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