CN110541112B - Manufacturing method for improving toughness of large nuclear power SA508-3 connecting pipe forging - Google Patents

Manufacturing method for improving toughness of large nuclear power SA508-3 connecting pipe forging Download PDF

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CN110541112B
CN110541112B CN201910848468.9A CN201910848468A CN110541112B CN 110541112 B CN110541112 B CN 110541112B CN 201910848468 A CN201910848468 A CN 201910848468A CN 110541112 B CN110541112 B CN 110541112B
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汪洪宇
万东海
洪大军
赵晓光
石建平
张帅
冷廷梅
梁启超
贺开华
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Guizhou Aerospace Xinli Technology Co.,Ltd.
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Guizhou Aerospace Xinli Casting and Forging Co Ltd
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    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
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    • C21DMODIFYING 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
    • C21D1/00General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26Methods of annealing
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    • C21D1/00General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60Aqueous agents
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    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
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    • C22CALLOYS
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    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
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    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
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    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • CCHEMISTRY; METALLURGY
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    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
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    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/002Bainite

Abstract

The invention belongs to the technical field of steel for nuclear power steam generators, and particularly relates to a manufacturing method for improving the strength and toughness of a large forging of an SA508-3 connecting pipe for nuclear power. The chemical components of the SA508-3 raw material are accurately controlled, the combined forging and grain refinement are carried out on the steel billet by adopting 4000T and 800T forging presses, the requirements of high strength (the tensile strength is more than or equal to 620Mpa) and high toughness (the ductile-brittle transition temperature is less than or equal to-29 ℃) of the SA508-3 connecting pipe large forging are met through the optimized heat treatment process, and the method can be used for manufacturing large forgings such as main water supply connecting pipes, auxiliary water supply connecting pipes and the like with the wall thickness of 130-200 mm for nuclear power steam generators.

Description

Manufacturing method for improving toughness of large nuclear power SA508-3 connecting pipe forging
Technical Field
The invention belongs to the technical field of steel for nuclear power steam generators, and particularly relates to a manufacturing method for improving the strength and toughness of a large forging of an SA508-3 connecting pipe for nuclear power.
Background
The nuclear power is one of clean and environment-friendly energy sources, and has an important slowing effect on global warming. The SA508-3 material has excellent comprehensive performance and high neutron radiation resistance, is mainly used for nuclear power pressure vessels, steam generators and other core equipment, has extremely bad service conditions and needs to bear high temperature, high pressure, fluid scouring, corrosion and the like.
Along with the development of nuclear power construction in recent years, the power of a nuclear reactor is continuously increased, the service life of a power station is continuously prolonged, in order to further improve the efficiency and the safety of a single machine, reactor equipment tends to be integrated and integrated, the size and the wall thickness of a connecting pipe forging for a steam generator of the core equipment are obviously increased compared with the conventional method, the strength requirement is improved (the tensile strength is more than or equal to 620Mpa), and the ductile-brittle transition temperature requirement is also nearly strict (RT (reverse temperature resistance) and (reverse temperatureNDTThe temperature is less than or equal to-29 ℃), and the manufacturing difficulty of the material connecting pipe forging is undoubtedly increased. Therefore, the manufacturing problem of high strength and high toughness of the SA508-3 connecting pipe large forging is to be solved urgently. At present, the study on improving the performance of the SA508-3 heavy forging is mainly carried out by heat treatment, but due to the defects (such as poor components and uneven crystal grains) caused by the previous process of the forging, the performance requirement of the large connecting pipe forging for the nuclear steam generator cannot be met after the heat treatment.
The patent with the application number of CN201210470085.0 discloses a performance heat treatment method for improving the toughness of a large forging for a nuclear capacitor, which is used for treating a large forging with the material of SA508-3, the outer diameter of 3.5-6.5 m, the height of not more than 5m,Performing performance heat treatment on a nuclear power container forge piece with the wall thickness of 100-250 mm by using an electric heating annular furnace; the temperature control precision of the electric heating annular furnace is +/-10 ℃; the method comprises the following steps: firstly, performing sub-temperature quenching; secondly, quenching; and thirdly, tempering. The tensile strength Rm of the large forging for the nuclear capacitor obtained by the invention is increased to 640-650 MPa, and RT is increased toNDT-25 ℃ under vacuum; can not reach the large forged piece RT of the connecting pipe for the nuclear power steam generatorNDTThe performance requirement of less than or equal to-29 ℃.
The patent with the application number of CN201210468761.0 discloses a performance heat treatment method for a SA508-3 large forging for a nuclear power container, which is used for performing performance heat treatment on a forging for the nuclear power container, wherein the forging is made of SA508-3, the outer diameter of the forging is 3.5-6.5 m, the height of the forging is not more than 5m, and the wall thickness of the forging is 100-250 mm, and the method comprises the following steps: the first step, quenching for the first time; heating the forge piece in a furnace to 600-700 ℃, and then preserving heat for 4-5 hours; then heating to 880-920 ℃ at a heating rate of less than or equal to 100 ℃/hour, and preserving heat for 4-5 hours; then discharging and cooling to room temperature; secondly, quenching for the second time; thirdly, tempering; heating the forging piece to 635-660 ℃ at a heating rate of less than or equal to 100 ℃/hour, preserving heat for 4-5 hours, discharging and air cooling. The processed forge piece has the temperature of-20 ℃ AKV/J of 150-200 and the tensile strength of 695-700 MPa.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a manufacturing method for improving the toughness of a large forging piece of an SA508-3 connecting pipe for nuclear power, which can meet the performance requirements that the tensile strength of the large forging piece such as a main water supply connecting pipe and an auxiliary water supply connecting pipe for a nuclear power steam generator with the wall thickness of 130-200 mm is more than or equal to 620Mpa, and the ductile-brittle transition temperature is less than or equal to-29 ℃, and is realized by the following technical scheme:
a manufacturing method for improving the toughness of a large nuclear power SA508-3 connecting tube forging comprises the steps of precise raw material control, fine grain forging and optimized heat treatment.
Preferably, the raw material precise control is to control the chemical components in the SA508-3 raw material to be as follows according to weight percentage: c: 0.19 to 0.22%, Si: 0.20 to 0.40%, Mn: 1.40-1.50%, P is less than or equal to 0.005%, S is less than or equal to 0.005%, Cr: 0.10 to 0.25%, Ni: 0.70 to 1.00%, Mo: 0.45-0.55%, Al: 0.018 to 0.025 percent, less than or equal to 0.06 percent of Cu, less than or equal to 0.007 percent of V, less than or equal to 0.05 percent of Co, less than or equal to 0.0005 percent of B, less than or equal to 0.015 percent of Ca, less than or equal to 0.015 percent of Ti, less than or equal to 0.8ppm of H, less than or equal to 20ppm of O, less than or equal to 200ppm of N, less than or equal to 0.010 percent of Sn, less than or equal to 0.010 percent of As, less.
Preferably, the SA508-3 material has a welding reheating crack sensitivity coefficient (delta G) of less than or equal to-0.10 percent after chemical composition control.
The functions and the content control purposes of the chemical components in the SA508-3 steel are as follows:
carbon: in the standard steel, C is a main element for realizing the strength index, the low content of C can not meet the requirement of strength, the high content of C reduces the toughness index of the steel, and the ductile-brittle transition temperature is increased. Therefore, the C content is controlled to be 0.19 to 0.22%.
Manganese: mn is used as a main alloy element, so that the martensitic transformation temperature of the steel and the phase transformation speed in the steel are reduced, and the hardenability of the steel is improved. Therefore, the Mn content is controlled to be 1.40 to 1.50%.
Nickel: the critical transformation temperature of Ni is reduced, the diffusion rate of each element in steel is reduced, the hardenability is improved, the cold-state toughness of the steel is changed, but the material has high Ni ratio and low Ni irradiation embrittlement, the requirements on product strength and drop weight are considered to be high, and the Ni content is controlled to be 0.70-1.00% of the upper limit.
Molybdenum: mo is used as a main alloy element, so that the heat resistance and the temper brittleness resistance can be improved, and the content of Mo is controlled to be 0.45-0.55%.
Aluminum: al can increase the coarsening temperature of steel crystal grains and play a role in refining the crystal grains, and the ductile-brittle transition temperature is in direct proportion to the square root of the crystal grain diameter. Therefore, the Al content is controlled to be 0.018-0.025%.
Chromium: cr improves the hardenability of steel and is beneficial to improving the strength. Therefore, the Cr content is controlled to be 0.10 to 0.25%.
Silicon: si improves hardenability of steel, but high Si increases irradiation brittleness. Therefore, the Si content is controlled to 0.20 to 0.40%.
Copper: cu belongs to the most harmful element for irradiation embrittlement, and the Cu content is controlled to be less than or equal to 0.06 percent in order to limit the harmful effect of Cu
Vanadium: v can refine grains and improve strength, but is easy to increase the welding reheating crack sensitivity coefficient, causes embrittlement of a welding heat affected zone and improves the sensitivity of reheating cracks, so that the content of V is controlled to be less than or equal to 0.007%.
Phosphorus, sulfur: p has cold brittleness and S has hot brittleness, and both of them tend to accelerate radiation embrittlement. Therefore, the P, S content is controlled to be less than or equal to 0.005 percent.
Hydrogen, oxygen, nitrogen: H. o, N is not good for steel performance, and the content is as low as possible, H is less than or equal to 0.8ppm, O is less than or equal to 20ppm, and N is less than or equal to 200 ppm.
Other residual elements: the residual impurity elements are not good for the performance, the content is As low As possible, Co is less than or equal to 0.05 percent, B is less than or equal to 0.0005 percent, Ca is less than or equal to 0.015 percent, Ti is less than or equal to 0.015 percent, Sn is less than or equal to 0.010 percent, As is less than or equal to 0.010 percent, and Sb is less than or equal to 0.005 percent.
Welding reheat crack susceptibility coefficient: through reasonable proportion of alloy elements, the welding reheating crack sensitivity coefficient (delta G) is controlled to be less than or equal to-0.10 percent.
The SA508-3 raw material is prepared into a billet through conventional smelting and casting.
Preferably, the fine grain forging: carrying out combined forging on the steel billet by adopting a 4000T forging press and an 800T forging press, and forming by three fire in total; the first two fire forming is to adopt a 4000T forging press to forge and form a steel billet, the initial forging temperature is 1180 +/-20 ℃, the final forging temperature is more than or equal to 850 ℃, the deformation is large, the penetrating power is strong, and crystal grains are refined; the third fire forming is to finish the appearance of the formed forge piece by adopting an 800T quick forging machine, the initial forging temperature is reduced to 1050 ℃, the final forging temperature is more than or equal to 850 ℃, and the crystal grains are prevented from growing; the forging ratio of the billet after the three-fire forming is more than 19.
Preferably, the optimized heat treatment process is as follows:
(1) performing pre-heat treatment after forging: normalizing: heating the forge piece to 680 +/-10 ℃ along with a furnace, preserving heat for 3-4 h, then heating to 930 +/-10 ℃ at a heating rate of less than or equal to 150 ℃/h, preserving heat for 5-7 h, then air cooling, and tempering: heating the forging piece to 650 +/-10 ℃ at the heating rate of less than or equal to 100 ℃/h, preserving the heat for 7-10 h, and then cooling in air;
(2) quenching and tempering heat treatment: quenching: heating the forge piece to 680 +/-10 ℃ along with a furnace, preserving heat for 3-4 h, then heating to 910 +/-10 ℃ at a heating rate of less than or equal to 150 ℃/h, preserving heat for 4-6 h, and then quickly cooling; tempering: heating the forging piece to 635 +/-10 ℃ at a heating rate of less than or equal to 100 ℃/h, preserving heat for 6-9 h, and then cooling in air;
(3) simulating postweld heat treatment: heating the forge piece to be less than or equal to 350 ℃ along with the furnace, then heating to 610 +/-10 ℃ at the heating rate of less than or equal to 55 ℃/h, preserving heat for 24-24.5 h, discharging the forge piece from the furnace after the furnace is cooled to be less than or equal to 350 ℃, and air-cooling.
Preferably, in the step (2), the rapid cooling is performed by using a mixture of ice and water as a cooling medium. The temperature of 910 +/-10 ℃ is the austenite temperature of the forging, and the mixture of ice and water is used as a cooling medium to improve the quenching cooling rate.
The invention has the beneficial effects that:
1. according to the invention, through the accurate control of the chemical components of the raw materials, the strength and the toughness are better matched, and the forging in industrial production obtains a more favorable lower bainite structure.
2. The invention solves the problems of uneven crystal grains and growing up crystal grains in the forging process of the large forgings by fine grain forging, and the obdurability of the forgings strengthened by fine grains is improved.
3. The invention optimizes the heat treatment process parameters, adopts the mixture of ice and water as the quenching cooling medium, improves the quenching cooling rate, increases the hardenability and enhances the toughness.
4. The forging piece manufactured by the invention has the tensile strength of 629Mpa or above and RTNDTCan be reduced to-34 deg.C or below; the method can be used for manufacturing large forgings such as a main water supply connecting pipe, an auxiliary water supply connecting pipe and the like for the nuclear power steam generator with the tensile strength of more than or equal to 620Mpa, the drop weight performance of less than or equal to-29 ℃ and the wall thickness of 130-200 mm. Schematic diagrams of 3 models of large forgings such as a main water supply connecting pipe and an auxiliary water supply connecting pipe for the nuclear steam generator are shown in FIG. 5.
The manufacturing method provided by the invention is not limited to the manufacturing of 3 models of heavy forgings such as the main water supply connecting pipe and the auxiliary water supply connecting pipe for the nuclear power steam generator shown in fig. 5.
Drawings
FIG. 1 is a schematic temperature-time diagram of the thermal refining process (quenching and tempering heat treatment) in the present invention.
FIG. 2 is a schematic temperature-time diagram of a quenching and tempering process (quenching and tempering heat treatment) of an example of the present invention.
FIG. 3 is a metallographic structure diagram of a forging according to embodiment 1 of the invention.
FIG. 4 is a metallographic structure diagram of a forging according to embodiment 2 of the invention.
FIG. 5 is a schematic diagram of 3 models of a large forging such as a main water supply connecting pipe and an auxiliary water supply connecting pipe for a nuclear power steam generator.
In the figures 1 and 2, 1 indicates temperature rise along with the furnace, 2 indicates speed-controlled temperature rise (less than or equal to 150 ℃/h), 3 adopts ice-water mixture to rapidly cool, 4 indicates speed-controlled temperature rise (less than or equal to 100 ℃/h), and 5 indicates air cooling.
Detailed Description
The technical solution of the present invention is further defined below with reference to the specific embodiments, but the scope of the claims is not limited to the description.
The chemical compositions of the SA508-3 material and the 3t steel billet used in example 1 and example 2 are shown in Table 1.
Table 1: chemical composition (%)
Figure BDA0002196103610000061
Example 1
(1) Carrying out combined forging on the steel billet by adopting a 4000T and 800T forging press, and forming by three fire steps; the first two fire forming processes adopt a 4000T forging press for forging and forming, the initial forging temperature is 1180 +/-20 ℃, and the final forging temperature is more than or equal to 850 ℃; finishing the appearance of the formed forge piece by adopting an 800T quick forging machine in the third fire forming process, reducing the initial forging temperature to 1050 ℃, and cooling the finish forging temperature to be more than or equal to 850 ℃ after finishing the process;
(2) performing preliminary heat treatment after forging the connecting pipe forging, normalizing: heating the forge piece to 680 ℃ along with a furnace, preserving heat for 3h, then heating at a controlled speed (less than or equal to 150 ℃/h) to 930 ℃, preserving heat for 5.5h, then air cooling, and tempering: heating the forging piece to 650 ℃, keeping the temperature for 8 hours and then cooling the forging piece in air, wherein the heating rate is less than or equal to 100 ℃/h. And (3) carrying out rough machining flaw detection on the forged piece after the preliminary heat treatment is finished, and then carrying out quenching and tempering treatment, quenching: heating the forge piece to 680 ℃ along with a furnace, preserving heat for 3h, then heating at a controlled speed (less than or equal to 150 ℃/h) to 910 ℃, preserving heat for 5h, and then quickly cooling by adopting a mixture of ice and water; tempering: heating the forging piece to 635 +/-10 ℃, keeping the temperature for 8 hours and then cooling the forging piece in air, wherein the heating rate is less than or equal to 100 ℃/h;
(3) and (3) performing simulated post-weld heat treatment on a sample with a section T (T: the maximum distance from the high tensile stress region to the nearest heat treatment surface) cut on the forging: heating the forge piece along with the furnace to raise the temperature of the forge piece along with the furnace to be less than or equal to 350 ℃, then heating the forge piece to 610 +/-10 ℃ at a heating rate of less than or equal to 55 ℃/h, preserving the heat for 24-24.5 h, discharging the forge piece out of the furnace after the furnace is cooled to be less than or equal to 350 ℃, and air-cooling; the thickness of the finished product forging is 150mm, and T is 40 mm.
Example 2
The embodiment is the same as example 1.
The mechanical property test and metallographic structure observation are carried out on the die-welded samples of the examples 1 and 2 of the invention, the processing of the samples meets the ASTM standard, the mechanical test results are shown in the table 2, and the metallographic structure is shown in the table 1. According to the figure 1, the microstructure of the large connecting pipe forging manufactured by the invention is the lower bainite structure. As can be seen from Table 2, the tensile strength of the large connecting pipe forging piece manufactured by the method is more than 620Mpa, and the tensile strength of the large connecting pipe forging piece manufactured by the method is RTNDT<29 ℃ below zero, higher strength and lower ductile-brittle transition temperature. And the finished product forged piece is qualified through ultrasonic, magnetic powder and liquid permeation detection.
Table 2: mechanical property detection value
Figure BDA0002196103610000071
It should be noted that the above examples and test examples are only for further illustration and understanding of the technical solutions of the present invention, and are not to be construed as further limitations of the technical solutions of the present invention, and the invention which does not highlight essential features and significant advances made by those skilled in the art still belongs to the protection scope of the present invention.

Claims (3)

1. A manufacturing method for improving the toughness of a large SA508-3 connecting pipe forging for nuclear power is characterized by being used for manufacturing a large connecting pipe forging for a nuclear power steam generator with the wall thickness of 130-200 mm, and comprising the steps of accurately controlling raw materials, forging fine grains and optimizing a heat treatment process;
the raw material precise control is that the chemical components in the SA508-3 raw material are controlled according to the weight percentage as follows: c: 0.19 to 0.22%, Si: 0.20 to 0.40%, Mn: 1.40-1.50%, P is less than or equal to 0.005%, S is less than or equal to 0.005%, Cr: 0.10 to 0.25%, Ni: 0.70 to 1.00%, Mo: 0.45-0.55%, Al: 0.018 to 0.025 percent, less than or equal to 0.06 percent of Cu, less than or equal to 0.007 percent of V, less than or equal to 0.05 percent of Co, less than or equal to 0.0005 percent of B, less than or equal to 0.015 percent of Ca, less than or equal to 0.015 percent of Ti, less than or equal to 0.8ppm of H, less than or equal to 20ppm of O, less than or equal to 200ppm of N, less than or equal to 0.010 percent of Sn, less than or equal to 0.010 percent of As, less than;
and (3) fine crystal forging: carrying out combined forging on the steel billets cast by the raw materials by adopting a 4000T forging press and an 800T forging press, forming by three fire altogether, and forging into a forged piece;
the three-fire molding is as follows: the first two-fire forming is to adopt a 4000T forging press to carry out forging forming on the billet, wherein the initial forging temperature is 1180 +/-20 ℃, and the final forging temperature is more than or equal to 850 ℃; the third fire forming is to finish the formed forge piece by adopting an 800T quick forging machine, wherein the initial forging temperature is reduced to 1050 ℃, and the final forging temperature is more than or equal to 850 ℃; the forging ratio of the billet after the three-fire forming is more than 19;
the optimized heat treatment process comprises the following steps:
(1) performing pre-heat treatment after forging: normalizing: heating the forge piece to 680 +/-10 ℃ along with a furnace, preserving heat for 3-4 h, then heating to 930 +/-10 ℃ at a heating rate of less than or equal to 150 ℃/h, preserving heat for 5-7 h, and then air cooling; tempering: heating the forging piece to 650 +/-10 ℃ at a heating rate of less than or equal to 100 ℃/h, preserving heat for 7-10 h, and then air cooling;
(2) quenching and tempering heat treatment: quenching: heating the forge piece to 680 +/-10 ℃ along with a furnace, preserving heat for 3-4 h, then heating to 910 +/-10 ℃ at a heating rate of less than or equal to 150 ℃/h, preserving heat for 4-6 h, and then quickly cooling; tempering: heating the forging piece to 635 +/-10 ℃ at a heating rate of less than or equal to 100 ℃/h, preserving heat for 6-9 h, and then cooling in air;
(3) simulating postweld heat treatment: heating the forge piece to be less than or equal to 350 ℃ along with the furnace, then heating to 610 +/-10 ℃ at a heating rate of less than or equal to 55 ℃/h, and preserving heat for 24-24.5 h; and discharging the furnace and air cooling after the furnace is cooled to be less than or equal to 350 ℃.
2. The manufacturing method for improving the toughness of the large forging of the SA508-3 connecting tube for nuclear power as claimed in claim 1, wherein the SA508-3 material is welded with a reheat crack sensitivity coefficient (delta G) of less than or equal to-0.10% after chemical composition control.
3. The manufacturing method for improving the toughness of the large forging of the SA508-3 connecting pipe for nuclear power as claimed in claim 1, wherein in the step (2), the mixture of ice and water is used as a cooling medium for quick cooling.
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