CN117025902A - Heat treatment method for reducing near-surface flaw detection sensitivity of rotor forging and rotor forging - Google Patents

Heat treatment method for reducing near-surface flaw detection sensitivity of rotor forging and rotor forging Download PDF

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CN117025902A
CN117025902A CN202311037447.1A CN202311037447A CN117025902A CN 117025902 A CN117025902 A CN 117025902A CN 202311037447 A CN202311037447 A CN 202311037447A CN 117025902 A CN117025902 A CN 117025902A
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forging
heat treatment
heat
rotor
temperature
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彭亚敏
张国利
王新
赵希泉
赵丽
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TIANJIN HEAVY EQUIPMENT ENGINEERING RESEARCH CO LTD
China First Heavy Industries Co Ltd
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TIANJIN HEAVY EQUIPMENT ENGINEERING RESEARCH CO LTD
China First Heavy Industries Co Ltd
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Publication of CN117025902A publication Critical patent/CN117025902A/en
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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
    • C21D1/26—Methods of annealing
    • C21D1/28—Normalising
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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 heat treatment method for reducing near-surface flaw detection sensitivity of a rotor forging and the rotor forging, and belongs to the technical field of heat treatment. The heat treatment method comprises post-forging heat treatment and tempering heat treatment, wherein the secondary normalizing in the post-forging heat treatment comprises the following steps: carrying out low-temperature heat preservation on the rotor forging subjected to primary normalizing at 150-250 ℃ for 10-25h; heating to 650-700 ℃ at a heating rate of 6-15 ℃/h; then heating to 970-1000 ℃ at a heating rate of 15-40 ℃/h; preserving heat for 6-15h at 970-1000 ℃; after heat preservation, the temperature is reduced to 940-970 ℃ at a speed of 6-15 ℃/h, heat preservation is carried out for 5-15h, and then air cooling is carried out. By adopting the method provided by the application, the grain size of the rotor forging near-surface is coarsened, the flaw detection sensitivity is reduced, and the performance of the rotor forging is ensured.

Description

Heat treatment method for reducing near-surface flaw detection sensitivity of rotor forging and rotor forging
Technical Field
The application relates to the technical field of heat treatment, in particular to a heat treatment method for effectively reducing the near-surface flaw detection sensitivity of a rotor forging.
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+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, a heat treatment method is needed to coarsen the near-surface and near-surface grains of the rotor forging, keep the grain sizes of the surface and the core consistent, solve the problem that the defect display is unqualified after the traditional heat treatment, reduce the defect detection sensitivity of the surface of the forging, and meet the nuclear power standard that the ultrasonic defect detection display has no lower limit requirement for acceptance.
Disclosure of Invention
In view of the analysis, the application aims to provide a heat treatment method for effectively reducing the near-surface flaw detection sensitivity of a rotor forging, which is used for solving the problem of extremely high surface flaw detection sensitivity caused by extremely fine grain size of the surface of the rotor forging adopting traditional heat treatment.
In one aspect, the application provides a heat treatment method for effectively reducing the near-surface flaw detection sensitivity of a rotor forging, which comprises post-forging heat treatment and tempering heat treatment, wherein the post-forging heat treatment comprises primary normalizing and secondary normalizing;
the secondary normalizing comprises the following steps:
s1: carrying out low-temperature heat preservation on the rotor forging subjected to primary normalizing at 150-250 ℃ for 10-25h;
s2: slowly heating to 650-700 ℃ at a heating rate of 6-15 ℃/h; then adopting the heating speed of 15-40 ℃/h to quickly heat to 970-1000 ℃;
s3: preserving heat at 970-1000 ℃ for 6-15h;
s4: after heat preservation, adopting the cooling speed of 6-15 ℃/h to cool to 940-970 ℃;
s5: preserving heat at 940-970 deg.c for 5-15 hr, and air cooling.
Further, in step S1, the incubation time is 15-20 hours.
Further, in the slow temperature rising stage, the temperature rising speed is 8-12 ℃/h.
Further, in the rapid temperature rise stage, the temperature rise speed is 25-35 ℃/h.
Further, the heat preservation is carried out within the range of 970-1000 ℃ for 6-10h.
Further, the primary normalizing includes the steps of:
s1: carrying out low-temperature heat preservation on the forge piece at 170-270 ℃ for 10-25h;
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 ℃.
Further, the rotor forging is made of 30Cr2Ni4MoV steel, and the chemical components comprise 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.
Still further, the rotor forging has a diameter of Φ1300-2000mm.
In another aspect, the application provides a rotor forging prepared by the heat treatment method.
Further, the grain size of the surface is 3.5-4.5 grade.
Compared with the prior art, the application has at least one of the following beneficial effects:
1. the method comprises the steps of carrying out post-forging heat treatment and tempering heat treatment on a rotor forging, wherein the post-forging heat treatment comprises primary normalizing and secondary normalizing; and the secondary normalizing adopts low temperature heat preservation at 150-250 ℃, then adopts a mode of combining slow temperature elevation and rapid temperature elevation to heat to 970-1000 ℃, carries out heat preservation at 970-1000 ℃, and firstly cools to 940-970 ℃ after heat preservation, and then carries out air cooling to room temperature after heat preservation for a period of time. By adopting the heat treatment mode to treat the rotor forging, the grain size of the rotor forging near-surface is coarsened, the flaw detection sensitivity is reduced, the grain size of the rotor forging near-surface is more similar to the internal grain size, and the mechanical property of the rotor forging is ensured to meet the standard requirement.
2. The post-forging heat treatment and tempering heat treatment provided by the application can coarsen the crystal grain size of the rotor forging near surface by controlling the secondary normalizing in the post-forging heat treatment, and are suitable for the rotor forging with the diameter of more than 1300mm, so that the crystal grain size of the core part and the surface is kept consistent, the crystal grain size reaches 3.5-4.5 levels, the requirements of flaw detection standards are met, and the integral mechanical performance of the rotor forging is not influenced.
3. By adopting the heat treatment process disclosed by the application, ultrasonic flaw detection is carried out on the rotor forging, the tiny defects with the surface equivalent less than or equal to phi 0.4 are effectively shielded, the central limit sensitivity is less than or equal to phi 1.6, and the standard requirement is met.
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 schematic diagram of a secondary normalizing process;
FIG. 2 is a photograph of the surface of example 1;
FIG. 3 is an internal metallographic photograph of example 1;
FIG. 4 is a surface metallographic photograph of comparative example 1;
FIG. 5 is an internal metallographic photograph of comparative example 1.
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 size and the performance of grain size are adjusted by adopting traditional heat treatment. The conventional heat treatment includes a post-forging heat treatment including twice normalizing and one tempering, wherein the processes of the twice normalizing are the same, and a tempering heat treatment. However, after the traditional heat treatment is adopted, the grains of the near-surface area of the rotor forging are thinner, the grains of 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 heat treatment method for effectively reducing the near-surface flaw detection sensitivity of a rotor forging, which comprises post-forging heat treatment and tempering heat treatment; the post-forging heat treatment comprises primary normalizing and secondary normalizing, and the secondary normalizing is controlled to coarsen crystal grains of the near-surface area of the rotor forging, so that the flaw detection standard is met, and the mechanical performance of the rotor forging is not affected.
The secondary normalizing comprises the following steps:
s1: carrying out heat preservation on the rotor forging subjected to primary normalizing at 150-250 ℃ for 10-25h;
s2: slowly heating to 650-700 ℃ at a heating rate of 6-15 ℃/h; then adopting the heating speed of 15-40 ℃/h to quickly heat to 970-1000 ℃;
s3: preserving heat at 970-1000 ℃ for 6-15h;
s4: after heat preservation, adopting the cooling speed of 6-15 ℃/h to cool to 940-970 ℃;
s5: preserving heat at 940-970 deg.c for 5-15 hr, and air cooling.
Compared with the prior art, the secondary normalizing is carried out at a lower temperature on the basis of traditional heat treatment, and then the secondary normalizing is heated in a mode of combining slow heating and rapid heating; and then carrying out cooling operation after preserving heat for a period of time, firstly adopting a furnace cooling mode to cool to a certain temperature, and then adopting an air cooling mode to cool to room temperature after preserving heat for a period of time. By controlling the treatment process of secondary normalizing, the crystal grains close to the surface of the rotor forging can be gradually coarsened, the grain size reaches 3.5-4.5 level after tempering heat treatment, the flaw detection sensitivity is reduced, the nuclear power standard that ultrasonic flaw detection defect shows no lower limit requirement acceptance is met, and the mechanical properties of the rotor forging all meet the use requirement.
In the application, the integral preparation of the rotor forging comprises smelting, forging, post-forging heat treatment and tempering heat treatment. The heat treatment after forging comprises primary normalizing and secondary normalizing, and the secondary normalizing is roughly divided into a low-temperature heat preservation stage, a heating stage, a high-temperature heat preservation stage and a cooling stage.
In the low-temperature heat preservation stage, heat preservation is carried out at 150-250 ℃, and the main function is to ensure that the tissue after the first normalizing is fully transformed into a bainitic tissue in the low-temperature heat preservation stage, so that the content of residual austenite is reduced as much as possible, the fully transformed tissue has obvious effects on cutting off tissue inheritance and refining grains, and the tissue of the core part of the forging piece is fully transformed as much as possible.
Illustratively, the low temperature incubation temperature may be 150 ℃, 170 ℃, 190 ℃, 200 ℃, 210 ℃, 230 ℃, or 250 ℃.
For example, the time of incubation at low temperature may be 10h, 12h, 13h, 15h, 18h, 20h, 22h, 23h or 25h.
Preferably, in step S1, the incubation time at low temperature is 15-20 hours.
In the heating stage, a combination of slow heating and rapid heating is adopted for heating. In the slow temperature rising stage, in order to avoid the existence of black skin and rough large cross section on the surface after forging, the temperature is slowly raised to avoid increasing thermal stress when the temperature is below 700 ℃ in the elastic deformation stage of the forging, so that the risk of cracking of the rotor forging is reduced.
After the forging is slowly heated to 650-700 ℃, the forging is in a plastic deformation stage, and the cracking risk is avoided when the forging is heated more quickly. The rapid temperature rise can ensure that the temperature difference between the inside and the outside of the same section of the forging occurs in the high temperature stage, the surface is heated to a higher temperature as soon as possible, the heat is preserved, and the core part reaches Ac 3 Above and below coarsening temperature, thereby realizing that the surface grain size is not refined on the basis of primary normalizing, ensuring the coarser level of the grains, and the core part only reaches Ac 3 The lower temperature recrystallization realizes the refining effect on the basis of primary normalizing. And further, the phenomenon of grain size deviation of inner thickness and outer thickness of the rotor forging is avoided after primary normalizing and secondary normalizing, and the defect that the gradient of the grain size inside and outside the forging is smaller is achieved after subsequent quenching and tempering heat treatment, so that the flaw detection sensitivity of the surface of the forging is effectively controlled.
Illustratively, during the slow warm-up phase, the warm-up rate may be: 15 ℃/h, 14 ℃/h, 13 ℃/h, 12 ℃/h, 11 ℃/h, 10 ℃/h, 9 ℃/h, 8 ℃/h or 6 ℃/h.
Preferably, in the slow temperature rise stage, the temperature rise speed is 8-12 ℃/h.
Illustratively, during the rapid warming phase, the warming rate may be 16 ℃/h, 18 ℃/h, 20 ℃/h, 22 ℃/h, 25 ℃/h, 28 ℃/h, 30 ℃/h, 33 ℃/h, 35 ℃/h, 38 ℃/h, or 40 ℃/h.
Preferably, in the rapid temperature rise stage, the temperature rise speed is 25-35 ℃/h.
In the high-temperature heat preservation stage, heat preservation is carried out for 6-15h at 970-1000 ℃, and the temperature of the surface of the forging is gradually reduced to 940-970 ℃ after the temperature of the surface of the forging is rapidly increased to 940-960 ℃ due to the temperature difference between the furnace temperature and the temperature of the rotor forging, so that the temperature of the forging in the range of 150mm close to the surface reaches 940-960 ℃, and the temperature of the core part of the rotor forging is 830-880 ℃. Realizes that the grain size of the surface of the rotor forging is not refined on the basis of primary normalizing, ensures the coarser level of grains, and the core part only reaches Ac 3 The lower temperature recrystallization realizes the refining effect on the basis of primary normalizing.
Illustratively, the incubation is performed at a temperature in the range of 970-990 ℃ for a time of: 6h, 8h, 10h, 12h or 15h.
Preferably, the heat preservation is carried out within the range of 970-1000 ℃ for 6-10h.
The temperature is reduced after the short-time heat preservation within the range of 970-1000 ℃, and the temperature is mainly reduced slowly after the temperature of the surface of the forging is raised below the coarsening temperature, so that the surface of the forging is not obviously coarsened, and the core of the forging is always in the temperature raising stage during the slow temperature reduction process and the subsequent heat preservation at the lower temperature of 940-970 ℃. And after the central temperature is raised to be within the range of 830-880 ℃, discharging and air cooling so as to realize the effects of not refining the surface grain size and refining the central part.
Specifically, the primary normalizing includes the following steps:
s1: carrying out low-temperature heat preservation on the forge piece at 170-270 ℃ for 10-25h;
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 ℃.
The purpose of primary normalizing is to refine the coarse structure and grains after forging; the purpose of the secondary normalizing is to refine the core of the primary normalizing coarse grain size and the structure, and the surface is not further refined, so that the grain size gradient of the core and the surface of the forging is reduced.
Specifically, the rotor forging is made of 30Cr2Ni4MoV steel, and the chemical components comprise 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.
Specifically, the diameter of the rotor forging is phi 1300-2000mm.
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: heat treatment after forging: the method comprises primary normalizing, secondary normalizing and tempering after forging, wherein the secondary normalizing is provided by the application;
s4: tempering heat treatment: comprises primary quenching and tempering.
Specifically, in the smelting process, an alkaline electric furnace is adopted to roughen molten steel, and a proper slag making system and ladle refining are adopted and vacuum carbon deoxidation (LVCD+VCD) is adopted. 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.
Specifically, in the forging process, a process of forging the steel ingot to obtain a forging piece by adopting a process form of a pressing jaw, a first upsetting, a second upsetting and a finished product drawing, wherein the forging initial forging temperature is 1250 ℃, the final forging temperature is 750 ℃, the process fire time is four fires, and the total deformation is more than or equal to 3.5%.
Specifically, the primary normalizing comprises the following steps:
s1: heating a 30Cr2Ni4MoV steel rotor forging, and preserving heat at a low temperature within the range of 170-270 ℃ for 10-25 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 ℃.
Further, the post-forging tempering includes the steps of:
s1: heating the secondarily normalized rotor forging, and preserving heat at a low temperature within a 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 includes the steps of:
s1: heating the rotor forging 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 quenched rotor forging, and preserving heat at a 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.
In order to more clearly understand the present application, the following examples and comparative examples are provided.
The rotor forging is prepared from 30Cr2Ni4MoV steel through smelting and forging, and the diameter is phi 1500mm. And then carrying out post-forging heat treatment and tempering treatment on the rotor forging, wherein the post-forging heat treatment comprises primary normalizing, secondary normalizing and post-forging tempering, and the tempering treatment comprises quenching and tempering.
Referring to fig. 1, the examples and comparative examples differ in the secondary normalization, and the specific preparation process is as follows:
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%;
the primary 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.
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.
Example 1
The secondary normalizing comprises the following steps:
s1: carrying out low-temperature heat preservation on the rotor forging subjected to primary normalizing for 20 hours within the range of 200 ℃;
s2: slowly heating to 680 ℃ at a heating speed of 12 ℃/h; then adopting the heating speed of 25 ℃/h to quickly heat up to 980 ℃;
s3: preserving heat at 980 ℃ for 8 hours;
s4: then adopting a cooling speed of 10 ℃/h to cool to 950 ℃;
s5: and (3) heat preservation is carried out at 950 ℃ for 8 hours, and air cooling is adopted to 200 ℃ after heat preservation.
Example 2
Example 2 is substantially the same as example 1 except that the low temperature of example 2 is maintained for 15 hours;
in the step S2, the temperature rising speed of slowly rising temperature is 8 ℃/h; the temperature rising speed of the rapid temperature rising is 35 ℃/h;
in the step S4, the cooling speed is 8 ℃/h;
in step S5, the incubation time is 12h.
Example 3
Example 3 is substantially the same as example 1 except that the rotor forging diameter of example 3 is Φ1800mm and the heat retention time in S1 is 25h.
Example 4
Example 4 is substantially the same as the treatment of example 3, except that the soak temperature of S3 of example 4 is 990 ℃.
Comparative example 1
The secondary normalization in comparative example 1 was the same as the primary normalization.
Comparative example 2
Comparative example 2 is substantially the same as the heat treatment of example 1 except that slow and fast temperature increases to 870 ℃ are employed in the secondary normalizing step S2 of comparative example 2; in step S3, incubation is performed at 870 ℃.
Performance detection
The rotor forgings obtained after the heat treatment of examples 1 to 4 and comparative examples 1 to 2 were subjected to grain size and performance detection, the specific detection results are shown in table 1, and the metallographic structures are shown in fig. 2 to 5.
TABLE 1 detection results
As can be seen by combining examples 1-4 and comparative examples 1-2 and combining table 1, referring to fig. 2-5, the grain size of the rotor forging near-surface is coarsened from 6.5 level to about 3.5-4.5 level, so that UT flaw detection sensitivity can be effectively reduced, and the effect of effectively shielding UT micro defect display can be realized, and the performance of the rotor forging is still satisfied within the coarsening range of the grain size.
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. The heat treatment method is characterized in that the post-forging heat treatment comprises primary normalizing and secondary normalizing;
the secondary normalizing comprises the following steps:
s1: carrying out low-temperature heat preservation on the rotor forging subjected to primary normalizing at 150-250 ℃ for 10-25h;
s2: slowly heating to 650-700 ℃ at a heating rate of 6-15 ℃/h; then adopting the heating speed of 15-40 ℃/h to quickly heat to 970-1000 ℃;
s3: preserving heat at 970-1000 ℃ for 6-15h;
s4: after heat preservation, adopting the cooling speed of 6-15 ℃/h to cool to 940-970 ℃;
s5: preserving heat at 940-970 deg.c for 5-15 hr, and air cooling.
2. The heat treatment method according to claim 1, wherein in step S1, the holding time is 15 to 20 hours.
3. The heat treatment method according to claim 1, wherein in the slow temperature rise stage, the temperature rise rate is 8-12 ℃/h.
4. The heat treatment method according to claim 1, wherein in the rapid temperature rise stage, the temperature rise rate is 25 to 35 ℃/h.
5. The heat treatment method according to claim 1, wherein the heat preservation is performed at 970 to 1000 ℃ for 6 to 10 hours.
6. The heat treatment method according to claim 1, wherein the primary normalizing comprises the steps of:
s1: carrying out low-temperature heat preservation on the forge piece at 170-270 ℃ for 10-25h;
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 ℃.
7. The heat treatment method according to claim 1, wherein the rotor forgings are made of 30Cr2Ni4MoV steel, and the chemical components include 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.
8. The heat treatment method according to claim 1, wherein the rotor forgings have a diameter Φ1300-2000mm.
9. A rotor forging, characterized in that it is produced by the heat treatment method according to any one of claims 1 to 8.
10. The rotor forging as recited in claim 9, wherein a grain size of the surface is 3.5 to 4.5 grade.
CN202311037447.1A 2023-08-17 2023-08-17 Heat treatment method for reducing near-surface flaw detection sensitivity of rotor forging and rotor forging Pending CN117025902A (en)

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