CN117070727A - Repairing heat treatment method and application of 30Cr2Ni4MoV steel - Google Patents
Repairing heat treatment method and application of 30Cr2Ni4MoV steel Download PDFInfo
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- CN117070727A CN117070727A CN202311037451.8A CN202311037451A CN117070727A CN 117070727 A CN117070727 A CN 117070727A CN 202311037451 A CN202311037451 A CN 202311037451A CN 117070727 A CN117070727 A CN 117070727A
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 157
- 238000000034 method Methods 0.000 title claims abstract description 49
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 47
- 239000010959 steel Substances 0.000 title claims abstract description 47
- 238000005242 forging Methods 0.000 claims abstract description 123
- 238000001514 detection method Methods 0.000 claims abstract description 34
- 238000001816 cooling Methods 0.000 claims abstract description 31
- 230000035945 sensitivity Effects 0.000 claims abstract description 19
- 238000005496 tempering Methods 0.000 claims description 33
- 238000004321 preservation Methods 0.000 claims description 26
- 238000003723 Smelting Methods 0.000 claims description 13
- 238000010791 quenching Methods 0.000 claims description 10
- 230000000171 quenching effect Effects 0.000 claims description 10
- 230000008439 repair process Effects 0.000 claims description 8
- 230000000630 rising effect Effects 0.000 claims description 7
- 239000000956 alloy Substances 0.000 claims description 4
- 229910045601 alloy Inorganic materials 0.000 claims description 4
- 238000002360 preparation method Methods 0.000 claims description 4
- 239000002994 raw material Substances 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 3
- 238000012958 reprocessing Methods 0.000 claims 5
- 238000004519 manufacturing process Methods 0.000 claims 1
- 239000000203 mixture Substances 0.000 claims 1
- 230000007547 defect Effects 0.000 description 7
- 239000000523 sample Substances 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 239000013078 crystal Substances 0.000 description 5
- 238000005266 casting Methods 0.000 description 4
- 239000000306 component Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 238000005336 cracking Methods 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000010304 firing Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000007788 roughening Methods 0.000 description 2
- 238000010079 rubber tapping Methods 0.000 description 2
- 238000002791 soaking Methods 0.000 description 2
- 238000011895 specific detection Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000008358 core component Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000005489 elastic deformation Effects 0.000 description 1
- 238000011534 incubation Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
- 238000009489 vacuum treatment Methods 0.000 description 1
Classifications
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
-
- 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Forging (AREA)
Abstract
The application relates to a repairing heat treatment method and application of 30Cr2Ni4MoV steel, belongs to the field of heat treatment, and aims to solve the problem of extremely high flaw detection sensitivity caused by extremely fine grain size of the surface of a rotor forging. The reworking heat treatment method comprises the steps of heating the pretreated 30Cr2Ni4MoV steel, and heating to 650-700 ℃ at a heating rate of 10-25 ℃/h from 220 ℃; then adopting the heating speed of 25-60 ℃/h to heat to 970-990 ℃; preserving heat for 10-30h at 970-990 ℃; then adopting the cooling speed of 8-15 ℃/h to cool to 850-940 ℃, preserving the heat for 2-5h, and adopting air cooling to the room temperature after preserving the heat. The grain size of the surface of the obtained rotor forging is coarsened, the grain sizes of the surface and the core are kept at the same level, and reach 3.0-4.5 levels, so that the requirements of flaw detection standards are met, and the performance of the rotor forging is ensured to meet the requirements.
Description
Technical Field
The application relates to the technical field of heat treatment, in particular to a repairing heat treatment method and application of 30Cr2Ni4MoV steel.
Background
The high-voltage rotor and the low-voltage rotor of the general island of the integral forging nuclear power are one of core components for power generation of the nuclear power station, and an irreplaceable position exists in the nuclear power station. Therefore, the performance of the high-voltage rotor and the low-voltage rotor of the conventional island of the integral forging nuclear power directly influences the service life of the nuclear power plant.
For decades, the heat treatment process of the whole forging nuclear power conventional island rotor forging still adopts the traditional heat treatment process mode: post-forging heat treatment of "multiple positive tempering" and tempering heat treatment of "quenching+high temperature tempering". However, due to the fact that the section of the rotor forging is large, when traditional heat treatment is adopted, the surface and the core of the rotor forging are seriously inconsistent in temperature rising and reducing speed, the grain sizes of the near surface and the core of the rotor forging are different, and finally the difference of the flaw detection limit sensitivity of the shaft body surface and the core of the rotor forging is large, so that the nuclear power standard of ultrasonic flaw detection defect display without lower limit requirement acceptance cannot be met.
Therefore, there is a need for a heat treatment method for repairing a rotor forging which is disqualified due to the display of micro defects caused by flaw detection after the conventional heat treatment, so that the grain sizes of the surface and the core of the rotor forging are kept at the same level, the excessive flaw detection sensitivity of the surface of the forging is reduced, and the nuclear power standard that the display of ultrasonic flaw detection defects has no lower limit requirement for acceptance is satisfied.
Disclosure of Invention
In view of the above analysis, the application aims to provide a repairing heat treatment method and application of 30Cr2Ni4MoV steel, which are used for solving the problem that the surface grain size of a rotor forging adopting traditional heat treatment is too fine, so that the surface flaw detection sensitivity is extremely high, and the grain sizes of the surface and the core of the rotor forging are kept at the same level.
On one hand, the application provides a repairing heat treatment method of 30Cr2Ni4MoV steel, which comprises the following steps,
s1: heating the pretreated 30Cr2Ni4MoV steel, and slowly heating to 650-700 ℃ at a heating rate of 10-25 ℃/h from 220 ℃; then adopting the heating speed of 25-60 ℃/h to quickly heat to 970-990 ℃;
s2: preserving heat at 970-990 ℃ for 10-30h;
s3: then adopting the cooling speed of 8-15 ℃/h to cool to 850-940 ℃, preserving the heat for 2-5h, and adopting air cooling to the room temperature after preserving the heat.
Further, in the slow temperature rise stage, the temperature rise speed is 10-15 ℃/h.
Further, in the rapid temperature rise stage, the temperature rise speed is 25-50 ℃/h.
Preferably, in the rapid temperature rise stage, the temperature rise speed is 40-50 ℃/h.
Further, the heat preservation is carried out within the range of 970-990 ℃ for 10-20h.
Preferably, the heat preservation is carried out within the range of 970-990 ℃ for 15-20h.
Further, the chemical components of the 30Cr2Ni4MoV steel comprise C in percentage by weight: less than or equal to 0.37 percent, si: less than or equal to 0.12 percent, mn:0.17-0.43%, cr:1.45-2.05%, mo:0.22-0.62%, ni:3.18-3.82%, V:0.06-0.16%, al: less than or equal to 0.012 percent, S: less than or equal to 0.015 percent, P: less than or equal to 0.015 percent.
On the other hand, the application provides application of a repairing heat treatment method of 30Cr2Ni4MoV steel, wherein the repairing heat treatment method is used for preparing a rotor forging, and the diameter of the rotor forging is phi 1300-phi 2000mm.
Further, the preparation of the rotor forging comprises the following steps:
s1: smelting: smelting alloy raw materials to prepare cast ingots;
s2: forging: forging the cast ingot to obtain a forging;
s3: and (3) heat treatment: carrying out post-forging heat treatment and tempering heat treatment on the forge piece;
s4: and (3) repairing heat treatment: the rotor forging is manufactured by adopting the repairing heat treatment method of the 30Cr2Ni4MoV steel.
Further, the post-forging heat treatment includes multiple normalizing and post-forging tempering.
Further, the quenching and tempering heat treatment comprises quenching and tempering.
Furthermore, the grain sizes of the near-surface part and the core part of the rotor forging are 3.0-4.5 grades, and the core part can meet the flaw detection sensitivity required by the standard.
Compared with the prior art, the application has at least one of the following beneficial effects:
1. the application provides a repairing heat treatment method of 30Cr2Ni4MoV steel, which comprises the steps of firstly slowly heating to 650-700 ℃ from 220 ℃ at a heating rate of 10-25 ℃/h, then rapidly heating to 970-990 ℃ at a heating rate of 25-60 ℃/h, preserving heat for a period of time, cooling to 850-940 ℃ at a cooling rate of 8-15 ℃/h, preserving heat, cooling to room temperature, and finally performing tempering treatment. The repairing heat treatment method provided by the application is used after the pretreatment combining the post-forging heat treatment and the tempering heat treatment, so that the grain sizes of the surface and the core of the rotor forging reach 3.0-4.5 levels, the requirements of flaw detection standards are met, and the mechanical properties of the rotor forging are ensured to meet the standard requirements.
2. The repairing heat treatment method provided by the application is suitable for the rotor forging with the diameter of more than 1300mm, and after the repairing treatment, the grain size of the surface of the rotor forging is roughened, so that the grain sizes of the core and the surface are kept at the same level, and the integral mechanical property of the rotor forging is not influenced.
3. After the repairing heat treatment, the application can effectively shield the micro defect with the surface equivalent less than or equal to phi 0.4, and the central limit sensitivity less than or equal to phi 1.6, thereby meeting the standard requirement.
In the application, the technical schemes can be mutually combined to realize more preferable combination schemes. Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application. The objectives and other advantages of the application may be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the application, like reference numerals being used to refer to like parts throughout the several views.
FIG. 1 is a plot of a test block heat treatment process;
FIG. 2 is a metallographic photograph of the surface of a rotor forging obtained in example 3;
FIG. 3 is a metallographic photograph of the rotor forging core obtained in example 3;
FIG. 4 is a metallographic photograph of a surface of a conventional rotor forging;
fig. 5 is a metallographic photograph of a core of a conventional rotor forging.
Detailed Description
The following detailed description of preferred embodiments of the application is made in connection with the accompanying drawings, which form a part hereof, and together with the description of the embodiments of the application, are used to explain the principles of the application and are not intended to limit the scope of the application.
At present, for a rotor forging with a material of 30Cr2Ni4MoV, the grain size is adjusted by adopting traditional heat treatment, wherein the traditional heat treatment comprises post-forging heat treatment and tempering heat treatment. However, after the traditional heat treatment is adopted, the crystal grains on the surface of the rotor forging piece are thinner, the crystal grains on the core part are thicker, and the nuclear power standard of ultrasonic flaw detection defect display without lower limit requirement acceptance cannot be met.
Therefore, the application provides a repairing heat treatment method of 30Cr2Ni4MoV steel, which comprises the following steps,
s1: heating the pretreated 30Cr2Ni4MoV steel, and slowly heating to 650-700 ℃ at a heating rate of 10-25 ℃/h from 220 ℃; then adopting the heating speed of 25-60 ℃/h to quickly heat to 970-990 ℃;
s2: preserving heat at 970-990 ℃ for 10-30h;
s3: then adopting the cooling speed of 8-15 ℃/h to cool to 850-940 ℃, preserving the heat for 2-5h, and adopting air cooling to the room temperature after preserving the heat.
Compared with the prior art, the pre-treated 30Cr2Ni4MoV steel is reworked, and is subjected to temperature rise, heat preservation and temperature reduction stages, and finally is subjected to primary quenching and tempering treatment, so that the near-surface grain size of the 30Cr2Ni4MoV steel is coarsened, the sensitivity of surface ultrasonic flaw detection is reduced, the near-surface grains and the internal grains of the 30Cr2Ni4MoV steel are kept at the same level, and the nuclear power standard that ultrasonic flaw detection defects show no lower limit requirement acceptance is met.
In the present application, the pretreatment includes smelting, forging, and heat treatment, wherein the heat treatment includes post-forging heat treatment and tempering heat treatment. However, during the pretreatment, the surface of the 30Cr2Ni4MoV steel rotor forging heats up and cools down faster than the core, so that the grain size of the surface is finer than that of the core, even much finer than that required by the standard. Therefore, the pre-treated 30Cr2Ni4MoV steel has uneven inner and outer grain size distribution, and the sensitivity difference of ultrasonic flaw detection of the surface and the core is larger.
According to the application, the pretreated 30Cr2Ni4MoV steel is reworked, and the surface grain size of the pretreated 30Cr2Ni4MoV steel forging is coarsened as much as possible on the premise of meeting the standard requirement by adjusting the heating, heat preservation and cooling processes, and the mechanical properties of the 30Cr2Ni4MoV steel are not affected.
In the heating stage, a combination of slow heating and rapid heating is adopted for heating. In the slow temperature rising stage, the temperature rising is selected at a slow speed in order to avoid cracking caused by increasing thermal stress due to the fact that the temperature rising speed is high in the elastic deformation stage of the forging piece. Ac of 30Cr2Ni4MoV steel 1 At a temperature of 705℃ Ac 3 After the temperature is 800 ℃ and the rotor forging is slowly heated to 650-700 ℃, the forging is in a plastic deformation stage, the rapid heating does not have cracking risk, and the core with slower heating speed can be effectively prevented from being in a subsequent heat preservation stage when the two-phase region is rapidly heatedThe segment coarsening is severe.
Illustratively, during the slow warm-up phase, the warm-up rate may be: 25 ℃/h, 22 ℃/h, 21 ℃/h, 20 ℃/h, 18 ℃/h, 15 ℃/h, 14 ℃/h, 13 ℃/h, 12 ℃/h, 11 ℃/h or 10 ℃/h.
Preferably, in the slow temperature rise stage, the temperature rise speed is 10-15 ℃/h.
In the rapid heating stage, in order to ensure that the temperature difference between the inside and outside of the same section of the forging occurs in the high-temperature stage, the surface is heated to the roughening temperature as soon as possible, and the temperature is kept, and the core part cannot reach the higher roughening temperature, so that the effects that the grain size of the surface is obviously roughened and the core part is not obviously roughened are realized.
Illustratively, the ramp rate during the rapid ramp up phase may be: 25 ℃/h, 28 ℃/h, 30 ℃/h, 33 ℃/h, 35 ℃/h, 38 ℃/h, 40 ℃/h, 42 ℃/h, 45 ℃/h, 48 ℃/h, 50 ℃/h, 52 ℃/h, 55 ℃/h, 57 ℃/h, 59 ℃/h or 60 ℃/h.
Preferably, in the rapid temperature rise stage, the temperature rise speed is 25-50 ℃/h.
Preferably, in the rapid temperature rise stage, the temperature rise speed is 40-50 ℃/h.
And in the heat preservation stage, heat preservation is carried out within the range of 970-990 ℃, the heat preservation time is 10-30h according to the actual cross section size of the forging, and the larger the cross section is, the longer the heat preservation time is, so that the temperature of the forging in the near-surface range reaches over 960 ℃ for 10h, and the coarsening of grains of the forging in the near-surface range is realized.
Illustratively, the incubation is performed at a temperature in the range of 970-990 ℃ for a time of: 10h, 12h, 15h, 17h, 18h, 20h, 22h, 24h, 26h, 28h or 30h.
Preferably, the heat preservation is carried out within the range of 970-990 ℃ for 10-20h.
Preferably, the heat preservation is carried out within the range of 970-990 ℃ for 15-20h.
In the cooling stage, cooling to 850-940 ℃ at a cooling speed of 8-15 ℃/h, and preserving heat for a period of time. The cooling and heat preservation process is to ensure that the forging is close to the surface to avoid excessive coarsening caused by long-time high-temperature heat preservation, and simultaneously ensure that the temperature of the core of the forging can be raised to 930-950 ℃ which is not obviously coarsened.
The chemical components of the 30Cr2Ni4MoV steel in the application comprise the following components in percentage by weight: less than or equal to 0.37 percent, si: less than or equal to 0.12 percent, mn:0.17-0.43%, cr:1.45-2.05%, mo:0.22-0.62%, ni:3.18-3.82%, V:0.06-0.16%, al: less than or equal to 0.012 percent, S: less than or equal to 0.015 percent, P: less than or equal to 0.015 percent.
The application provides an application of a repairing heat treatment method of 30Cr2Ni4MoV steel in preparing a rotor forging, wherein the diameter of the rotor forging is phi 1300-phi 2000mm.
The preparation of the rotor forging comprises the following steps:
s1: smelting: smelting alloy raw materials to prepare cast ingots;
s2: forging: forging the cast ingot to obtain a forging;
s3: and (3) heat treatment: carrying out post-forging heat treatment and tempering heat treatment on the forge piece;
s4: and (3) repairing heat treatment: and (3) adopting the repairing heat treatment method of the 30Cr2Ni4MoV steel to prepare the rotor forging.
Compared with the prior art, the preparation of the rotor forging comprises the steps of smelting, forging, heat treatment, repairing heat treatment and the like, and specifically, the integral heat treatment of the rotor forging comprises the heat treatment after forging, tempering heat treatment, repairing heat treatment and secondary tempering heat treatment. After the repairing heat treatment is added, the crystal grains close to the surface of the rotor forging piece are coarsened, so that the crystal grains close to the surface are more close to the crystal grains at the center; and the flaw detection sensitivity of the rotor forging near surface is reduced, and the nuclear power standard that ultrasonic flaw detection defect display has no lower limit requirement acceptance is met. After the repairing heat treatment, the mechanical property and the flaw detection are qualified, and the forge piece reaches the qualified and usable level.
Preferably, during the smelting process, the molten steel is roughed by an alkaline electric furnace, and is refined by a proper slag making system and a ladle, and is subjected to vacuum carbon deoxidation (LVCD+VCD). Vacuum treatment is carried out before casting and in the process of casting steel ingot, the vacuum degree is less than or equal to 266Pa, the tapping temperature is 1620-1640 ℃, and the casting temperature is 1575-1595 ℃, so as to prepare the steel ingot.
Preferably, in the forging process, the steel ingot is forged into a forging piece in a process mode of 'pressing jaw + first upsetting + second upsetting + drawing out of a finished product', wherein the forging temperature is 1250 ℃, the final forging temperature is 750 ℃, the process fire is four fires, and the total deformation is more than or equal to 3.5%.
Further, the post-forging heat treatment includes twice normalizing and once post-forging tempering.
Preferably, the normalizing process is as follows:
s1: heating the forging, and preserving heat at a low temperature within the range of 170-270 ℃ for 10-20 hours;
s2: slowly heating to 650-700 ℃ at a heating rate of 6-15 ℃/h; then heating to 860-910 ℃ at a heating rate of 5-10 ℃/h;
s3: preserving heat at 860-910 deg.c for 30-50 hr;
s4: and (5) after heat preservation, discharging from the furnace and air cooling to 170-270 ℃.
Preferably, the post-forging tempering process is as follows:
s1: heating the forging piece cooled to the temperature, and preserving heat at the low temperature within the range of 170-210 ℃ for 10-20 hours;
s2: slowly heating to 640-660 ℃ at a heating speed of 10-25 ℃/h;
s3: preserving heat at 640-660 ℃ for 40-70h;
s4: after heat preservation, adopting the cooling speed less than or equal to 10 ℃/h to slowly cool to 250 ℃, and then air-cooling to room temperature.
Further, the quenching and tempering heat treatment comprises quenching and tempering.
Preferably, the quenching heat treatment process is as follows:
s1: heating the forged piece subjected to the heat treatment after forging, and slowly heating to 650-700 ℃ at a heating rate of 10-25 ℃/h; then adopting the heating speed of 25-50 ℃/h to quickly heat to 830-850 ℃;
s2: preserving heat at 830-850 ℃ for 30-50h;
s4: after heat preservation, spraying water or soaking water for cooling to be less than or equal to 50 ℃.
Preferably, the tempering process comprises the following steps:
s1: heating the forging piece cooled to the temperature, and preserving heat at the low temperature within the range of 170-210 ℃ for 10-20 hours;
s2: slowly heating to 640-660 ℃ at a heating speed of 10-25 ℃/h;
s3: preserving heat at 590-630 ℃ for 40-60h;
s4: after heat preservation, adopting the cooling speed less than or equal to 10 ℃/h to slowly cool to 250 ℃, and then air-cooling to room temperature.
After the heat treatment, the repair heat treatment provided by the application is added, so that the grain size of the rotor forging near-surface is coarsened, the flaw detection sensitivity is reduced, the grain sizes of the rotor forging near-surface and the core are close to the grain size of the core, the grain sizes of the near-surface and the core are 3.0-4.5 levels, and the core can meet the flaw detection sensitivity required by the standard.
In order to more clearly understand the present application, the following examples and comparative examples are provided.
The existing rotor forging is prepared from 30Cr2Ni4MoV steel and specifically comprises smelting, forging and heat treatment, wherein the heat treatment comprises post-forging heat treatment and tempering heat treatment, and the diameter of the obtained rotor forging is phi 1500mm.
Smelting: smelting alloy raw materials, wherein the vacuum degree is 266Pa, the tapping temperature is 1630 ℃, and the casting temperature is 1585 ℃ to prepare a steel ingot;
forging: forging the steel ingot, wherein the forging starting temperature is 1250 ℃, the final forging temperature is 750 ℃, the process firing time is four firing times, and the total deformation is 5%;
heat treatment after forging: twice normalizing and once forging and tempering,
the normalizing process is as follows:
s1: heating the forging, and preserving heat at 270 ℃ for 15 hours;
s2: slowly heating to 700 ℃ at a heating rate of 8 ℃/h; then heating to 900 ℃ by adopting the heating speed of 7 ℃/h;
s3: preserving heat at 900 ℃ for 35 hours;
s4: and (5) discharging the material from the furnace for air cooling to 200 ℃ after heat preservation.
The tempering process after forging is as follows:
s1: heating the forging piece cooled to the temperature, and preserving heat at the low temperature of 200 ℃ for 10 hours;
s2: heating to 650 ℃ at a heating rate of 15 ℃/h;
s3: preserving heat at 650 ℃ for 50 hours;
s4: after heat preservation, adopting the cooling speed of 10 ℃/h to slowly cool to 250 ℃, and then air-cooling to room temperature.
Tempering heat treatment: comprises quenching, tempering and tempering,
the quenching process comprises the following steps:
s1: heating the forged piece subjected to the heat treatment after forging, and slowly heating to 650 ℃ at a heating rate of 15 ℃/h; then adopting the heating speed of 35 ℃/h to quickly heat to 840 ℃;
s2: preserving heat at 840 ℃ for 40h;
s4: soaking in water to cool to less than or equal to 50 ℃ after heat preservation.
The tempering process comprises the following steps:
s1: heating the forging piece cooled to the temperature, and preserving heat at the low temperature of 190 ℃ for 15 hours;
s2: heating to 650 ℃ at a heating rate of 20 ℃/h;
s3: preserving heat at 600 ℃ for 40h;
s4: and (3) after heat preservation, slowly cooling to 250 ℃ by adopting a cooling speed of 10 ℃/h, and then air-cooling to room temperature to obtain the rotor forging.
The grain size and mechanical properties of the rotor forgings were measured, and the measurement results are shown in table 1.
Table 1 results of detection of existing rotor forgings
Example 1
The sample area of the existing rotor forging (the sample area with the radial depth of 150mm of the shaft body of the forging) is sampled, the size of the test block is 20mm multiplied by 20mm, and the relation between the grain size, the heating temperature and the heat preservation time is explored.
Referring to fig. 1, the test block is heat-treated as follows:
(1) After the furnace is heated to the heat preservation temperature, 2 metallographic test blocks are put into the furnace, and are respectively kept for 2 hours and 10 hours and taken out for air cooling;
(2) The temperature T was set to 960 ℃, 970 ℃, 980 ℃, 990 ℃, 1000 ℃, 1010 ℃, 1020 ℃, 1030 ℃ and 1050 ℃, respectively.
The test pieces after heat treatment were subjected to grain size detection, and specific detection results are shown in table 2.
TABLE 2 test block detection results (grain size/grade)
Conclusion: the results according to Table 2 show that the grain size coarsens gradually (the larger the number, the finer the grains) with increasing holding temperature in the range of 960℃to 1050 ℃. At the same temperature, the grains coarsen with the extension of the heat preservation time.
Example 2
The test block was sampled from the sample area of the existing rotor forging (sample area 150mm deep in the radial direction of the forging shaft), and the size of the test block was 40mm×150mm×170mm. The influence relationship between the grain size and the sensitivity was observed, and the flaw detection test pieces were heated in the same manner as in example 1 at 970 ℃, 990 ℃, 1020 ℃ and 1050 ℃ for 10 hours.
The flaw detection method adopts a test block method required by nuclear power standards, a flaw detector adopts HS511/51208/51184, the probe type is 2.25MHz/1.0 (17E 01U 2P), the probe frequency is 2.25MHz, and the obtained grain size and flaw detection sensitivity are shown in Table 3.
TABLE 3 grain size and flaw detection sensitivity relationship
| Group of | Heating temperature/. Degree.C | Grain size/grade of flaw detection test block | Sensitivity/mm of flaw detection test block |
| 1 | 1050 | 00 | Φ0.45 |
| 2 | 1020 | 1.0 | Φ0.42 |
| 3 | 990 | 2.0 | Φ0.40 |
| 4 | 970 | 2.5 | Φ0.38 |
| 5 | In the as-modified state | 6.5 | Φ0.36 |
* The original quenched and tempered state refers to the existing rotor forging.
As can be seen from Table 3, as the heating temperature was increased, the grain size of the flaw detection pieces was also increased (the larger the number, the finer the grains). And as the grain size of the flaw detection block is gradually coarsened, the flaw detection sensitivity gradually decreases (the larger the numerical value is, the lower the sensitivity is).
Example 3
The existing rotor forging is prepared from 30Cr2Ni4MoV steel and specifically comprises smelting, forging and heat treatment, wherein the heat treatment comprises post-forging heat treatment and tempering heat treatment, and the diameter of the obtained rotor forging is phi 1500mm.
The method comprises the following steps of:
s1: heating the forging after heat treatment, and starting at 220 ℃, and slowly heating to 650 ℃ by adopting a heating speed of 15 ℃/h; then adopting the heating speed of 40 ℃/h to quickly heat up to 980 ℃;
s2: preserving heat at 980 ℃ for 15 hours;
s3: then adopting a cooling speed of 10 ℃/h to cool to 930 ℃, preserving heat for 3h, and adopting air cooling to room temperature after preserving heat.
And finally, carrying out tempering heat treatment again to obtain the rotor forging.
Example 4
Example 4 is substantially the same as the repair process of example 3, except that the forging diameter of example 4 is Φ1900mm and the holding time in S2 is 20h.
Example 5
Example 5 is substantially the same as the repair process of example 3 except that in S1, starting at 220 ℃, a slow temperature increase to 650 ℃ is performed with a temperature increase rate of 10 ℃/h; then the temperature is quickly increased to 980 ℃ by adopting the temperature increasing speed of 25 ℃/h.
Example 6
Example 6 is substantially the same as the repair process of example 3 except that in S1, starting at 220 ℃, a slow ramp up to 650 ℃ is performed with a ramp up rate of 25 ℃/h; then the temperature is quickly increased to 980 ℃ by adopting the temperature increasing speed of 60 ℃/h.
Comparative example 1
Comparative example 1 is substantially the same as the repair process of example 3 except that the S2 soak temperature in the repair process of comparative example 1 is 950 ℃.
And detecting the grain size and the performance of the rotor forging obtained after repair, wherein specific detection results are shown in table 4, and metallographic structure photos are shown in fig. 2-5 respectively.
TABLE 4 detection results
As can be seen by combining examples 3-6 and comparative examples 1-2 and combining table 4, referring to fig. 2-5, the grain size is coarsened from 6.5 level to about 3.0-4.5 level, so that the UT flaw detection sensitivity can be effectively reduced, and the effect of effectively shielding UT micro-defect display can be realized; in the coarsening range of the grain size, the performance requirement of the rotor forging can still be met.
The present application is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present application are intended to be included in the scope of the present application.
Claims (10)
1. A repairing heat treatment method of 30Cr2Ni4MoV steel is characterized by comprising the following steps,
s1: heating the pretreated 30Cr2Ni4MoV steel, and slowly heating to 650-700 ℃ at a heating rate of 10-25 ℃/h from 220 ℃; then adopting the heating speed of 25-60 ℃/h to quickly heat to 970-990 ℃;
s2: preserving heat at 970-990 ℃ for 10-30h;
s3: then adopting the cooling speed of 8-15 ℃/h to cool to 850-940 ℃, preserving the heat for 2-5h, and adopting air cooling to the room temperature after preserving the heat.
2. The method for reprocessing heat-treated 30Cr2Ni4MoV steel as claimed in claim 1, wherein the temperature rising rate is 10-15 ℃/h during the slow temperature rising stage.
3. The method for reprocessing heat-treated 30Cr2Ni4MoV steel as claimed in claim 1, wherein in the rapid temperature rise stage, the temperature rise rate is 25-50 ℃/h;
preferably, the temperature rising speed is 40-50 ℃/h.
4. The method for reprocessing heat treatment of 30Cr2Ni4MoV steel according to claim 1, wherein the heat preservation is performed at 970-990 ℃ for 10-20 hours;
preferably, the heat preservation time is 15-20h.
5. The method for reprocessing heat treatment of 30Cr2Ni4MoV steel as claimed in claim 1, wherein the chemical composition of the 30Cr2Ni4MoV steel comprises, in weight percent, C: less than or equal to 0.37 percent, si: less than or equal to 0.12 percent, mn:0.17-0.43%, cr:1.45-2.05%, mo:0.22-0.62%, ni:3.18-3.82%, V:0.06-0.16%, al: less than or equal to 0.012 percent, S: less than or equal to 0.015 percent, P: less than or equal to 0.015 percent.
6. Use of a method according to any one of claims 1 to 5 for the heat treatment of a 30Cr2Ni4MoV steel for the manufacture of a rotor forging having a diameter of 1300 to 2000mm.
7. The use of a method for the reprocessing of 30Cr2Ni4MoV steel according to claim 6, wherein the preparation of the rotor forgings comprises the steps of:
s1: smelting: smelting alloy raw materials to prepare cast ingots;
s2: forging: forging the cast ingot to obtain a forging;
s3: and (3) heat treatment: carrying out post-forging heat treatment and tempering heat treatment on the forge piece;
s4: and (3) repairing heat treatment: a rotor forging is produced by a reworking heat treatment method of 30Cr2Ni4MoV steel as claimed in any one of claims 1 to 5.
8. The use of a method for the heat treatment for the repair of 30Cr2Ni4MoV steel as defined in claim 7 wherein the post-forging heat treatment comprises a plurality of normalizing and post-forging tempering.
9. The use of a heat treatment method for repairing 30Cr2Ni4MoV steel as defined in claim 7 wherein the tempering heat treatment is quenching and tempering.
10. The application of the reworking heat treatment method of 30Cr2Ni4MoV steel according to claim 7, wherein the grain sizes of the rotor forging near surface and the core are 3.0-4.5 grade, and the core can meet the flaw detection sensitivity required by the standard.
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