Forging piece for safety end of reactor pressure vessel and forging method of forging piece

Abstract

The invention relates to the technical field of nuclear reactors, and discloses a forge piece for a safety end of a reactor pressure vessel and a forging method of the forge piece, the forge piece comprises, by mass, 0.15%-0.20% of C, 0.15%-0.35% of Si, 1.20%-1.50% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.90%-1.20% of Cr, 0.90%-1.20% of Ni, 0.20%-0.30% of Mo, less than or equal to 0.20% of Cu, 0.02%-0.05% of V, 0.01%-0.03% of Nb, 0.01%-0.03% of Ti and the balance Fe and inevitable impurities, the yield strength of the forge piece is larger than or equal to 400 MPa, the tensile strength is larger than or equal to 550 MPa, by optimizing chemical components and adopting a specific forging process, the strength and toughness of the forge piece are improved, so that the forge piece has excellent mechanical properties, radiation resistance and corrosion resistance, is not easy to deform and crack when bearing high pressure and impact force, refines a grain structure, improves the internal quality of the forge piece, reduces the generation of defects, and improves the production efficiency. And the requirement of long-term stable operation of the nuclear reactor in a severe environment can be met.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear reactors, in particular to a forging for a safety end of a reactor pressure vessel and a forging method thereof. Background Art

[0002] In a nuclear reactor, the safety end of the reactor pressure vessel is one of the key components to ensure the safe operation of the reactor. It mainly connects the reactor pressure vessel with the main pipeline. Its performance and quality are directly related to the reliability and safety of the nuclear reactor. It ensures the sealing and integrity of the reactor coolant system and prevents the leakage of radioactive materials. It is crucial to the safe operation of the nuclear reactor.

[0003] At present, the existing forgings for the safety end of the reactor pressure vessel have complex processes, high costs and a need to improve the yield rate during the forging process, and the strength, toughness and corrosion resistance cannot fully meet the high-demand use environment. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a forging for a safety end of a reactor pressure vessel and a forging method thereof, which solves the problems of long-term stable operation and poor corrosion resistance in harsh environments.

[0005] To achieve the above objectives, the present invention is implemented through the following technical scheme: A forging for a safety end of a reactor pressure vessel, comprising the following components in mass percentage: C: 0.15% to 0.20%, Si: 0.15% to 0.35%, Mn: 1.20% to 1.50%, P≤0.015%, S≤0.010%, Cr: 0.90% to 1.20%, Ni: 0.90% to 1.20%, Mo: 0.20% to 0.30%, Cu≤0.20%, V: 0.02% to 0.05%, Nb: 0.01% to 0.03%, Ti: 0.01% to 0.03%, and the remainder is Fe and unavoidable impurities.

[0006] Preferably, the yield strength of the forging is ≥400 MPa, the tensile strength is ≥550 MPa, the elongation is ≥18%, the cross-sectional shrinkage is ≥45%, and the room temperature impact toughness is ≥60 J / cm².

[0007] Preferably, a forging method for a reactor pressure vessel safety end forging comprises: Step 1: Raw material preparation: Select high-quality steel ingots to ensure that their chemical composition meets the above requirements; Step 2: Heating: Put the steel ingot into a heating furnace, heat it to 1200-1250°C at a heating rate of 10-15°C / min, and keep it warm for 3-5 hours to make the steel ingot evenly heated; Step 3: Forging: The multi-directional forging process is adopted, the initial forging temperature is 1150-1200℃, the final forging temperature is not less than 850℃, firstly upsetting is performed, the upsetting ratio is 2-3, then drawing is performed, the drawing ratio is 3-5, the upsetting and drawing operations are repeated, and the total forging ratio is 6-8; Step 4: Cooling: After forging, the forging is quickly placed in a heat preservation pit at a temperature of 600-700°C for slow cooling for 5-8 hours, and then air-cooled to room temperature; Step 5: Heat treatment: The cooled forgings are normalized and tempered. The normalizing temperature is 900-950°C, kept warm for 2-3 hours, and then air-cooled. The tempering temperature is 650-700°C, kept warm for 3-5 hours, and then air-cooled.

[0008] Preferably, during the forging process in step three, the deformation amount of each pass is controlled within a range of 15% to 25%.

[0009] Preferably, during the normalizing and tempering treatments, the heating rate is controlled at 80-100° C. / h.

[0010] Preferably, during the heating process in step 2, after the steel ingot is heated to a predetermined temperature, it is ensured that the difference between the core temperature and the surface temperature of the steel ingot does not exceed 50° C., and the atmosphere in the heating furnace should be kept neutral or slightly oxidizing.

[0011] Preferably, during the cooling process in step 4, the placement of the forging in the insulation pit should ensure that all parts thereof are cooled evenly, and the temperature in the insulation pit should remain stable with a fluctuation range of no more than ±20°C.

[0012] Preferably, during the heat treatment process in step 5, the forging after normalizing should be air-cooled within 1 hour.

[0013] Preferably, the hardness of the forging after tempering should be controlled within the range of HB180 to HB220.

[0014] Preferably, the internal defect area of ​​the forgings manufactured by the forging method should be less than 0.5%, and the maximum size of the defect should not exceed 5% of the thickness of the forging.

[0015] The present invention provides a forging for a reactor pressure vessel safety end and a forging method thereof, which has the following beneficial effects: 1. The present invention improves the strength and toughness of forgings by optimizing chemical composition and adopting specific forging processes, so that the forgings have excellent mechanical properties, radiation resistance and corrosion resistance, are not easy to deform and crack when subjected to high pressure and impact force, refine the grain structure, improve the internal quality of forgings, reduce the generation of defects, and can meet the long-term stable operation requirements of nuclear reactors in harsh environments.

[0016] 2. The present invention forms a dense chromium oxide protective film on the metal surface by adding Cr, Ni and Mo to the raw materials, while enhancing the stability of the metal, improving the material's resistance to pitting and crevice corrosion, and through a multi-directional forging process, refines the grains, eliminates defects in the cast structure, makes the metal streamline distribution more reasonable, further improves the comprehensive performance of the forging, enhances its corrosion resistance, and prolongs its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of a forging for a safety end of a reactor pressure vessel of the present invention; Figure 2 The present invention is a schematic flow chart of a forging method for a reactor pressure vessel safety end forging. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0019] Please refer to the attached Figure 1 -Attached Figure 2 An embodiment of the present invention provides a forging for a safety end of a reactor pressure vessel, comprising the following components in percentage by mass: C: 0.15% to 0.20%, Si: 0.15% to 0.35%, Mn: 1.20% to 1.50%, P≤0.015%, S≤0.010%, Cr: 0.90% to 1.20%, Ni: 0.90% to 1.20%, Mo: 0.20% to 0.30%, Cu≤0.20%, V: 0.02% to 0.05%, Nb: 0.01% to 0.03%, Ti: 0.01% to 0.03%, and the remainder is Fe and unavoidable impurities.

[0020] The yield strength of the forging is ≥400MPa, the tensile strength is ≥550MPa, the elongation is ≥18%, the section shrinkage is ≥45%, and the room temperature impact toughness is ≥60J / cm².

[0021] A forging method for a reactor pressure vessel safety end forging, the method comprising: Step 1: Raw material preparation: Select high-quality steel ingots to ensure that their chemical composition meets the above requirements; Step 2: Heating: Put the steel ingot into the heating furnace, heat it to 1200-1250℃ at a heating rate of 10-15℃ / min, and keep it warm for 3-5 hours to make the steel ingot evenly heated. Reasonable heating rate and holding time can ensure that the steel ingot is evenly heated and avoid internal stress and defects caused by uneven temperature. Step 3: Forging: The multi-directional forging process is adopted, the initial forging temperature is 1150-1200℃, the final forging temperature is not less than 850℃, firstly, upsetting is performed, the upsetting ratio is 2-3, then stretching is performed, the stretching ratio is 3-5, the upsetting and stretching operations are repeated, and the total forging ratio is 6-8. During the forging process, the deformation of each pass is controlled at 15%-25%. The multi-directional forging process can effectively improve the organization and performance of the metal. Reasonable forging parameters and deformation control are helpful to refine the grains, eliminate defects, and improve the quality of forgings. Step 4: Cooling: After forging, the forgings are quickly placed in a holding pit at 600-700°C for slow cooling for 5-8 hours, and then air-cooled to room temperature. During the cooling process, the placement of the forgings in the holding pit should ensure that all parts are cooled evenly, and the temperature in the holding pit should remain stable with a fluctuation range of no more than ±20°C. Scientific cooling technology can reduce residual stress inside the forgings and avoid defects such as cracks.

[0022] Step 5: Heat treatment: The cooled forgings are normalized and tempered. The normalizing temperature is 900-950°C, kept warm for 2-3 hours, and then air-cooled. The tempering temperature is 650-700°C, kept warm for 3-5 hours, and then air-cooled.

[0023] During the forging process of step 3, the deformation of each pass is controlled at 15% to 25%.

[0024] During the normalizing and tempering processes, the heating rate is controlled at 80-100°C / h.

[0025] During the heating process of step 2, after the steel ingot is heated to the predetermined temperature, ensure that the difference between the core temperature and the surface temperature of the steel ingot does not exceed 50°C, and the atmosphere in the heating furnace should be kept neutral or slightly oxidizing.

[0026] Step 4 During the cooling process, the forgings should be placed in the insulation pit to ensure uniform cooling of all parts, and the temperature in the insulation pit should remain stable with a fluctuation range of no more than ±20°C.

[0027] Step 5 During the heat treatment process, the forgings after normalizing should be air-cooled within 1 hour.

[0028] The hardness of forgings after tempering should be controlled between HB180 and HB220.

[0029] For forgings manufactured by forging method, the internal defect area should be less than 0.5%, and the maximum size of the defect should not exceed 5% of the thickness of the forging.

[0030] C (Carbon): Carbon is an important element to improve the strength of steel, but too high a carbon content will reduce the toughness and welding performance of steel. An appropriate amount of carbon can ensure that the forging has a certain strength; Si (Silicon): Silicon can improve the strength and hardness of steel, and also increase the oxidation resistance of steel; Mn (manganese): Manganese can increase the strength and toughness of steel, and also improve the hardenability of steel; P (Phosphorus): Phosphorus is a harmful impurity that will reduce the toughness and plasticity of steel, and its content should be strictly controlled; S (sulfur): Sulfur is also a harmful impurity that can cause hot brittleness of steel and reduce its performance. Its content needs to be limited. Cr (chromium): Chromium can improve the strength, hardness and wear resistance of steel, while enhancing the corrosion resistance of steel; Ni (nickel): Nickel can increase the strength of steel while maintaining good toughness, and can also improve the toughness and corrosion resistance of steel at low temperatures; Mo (molybdenum): Molybdenum can improve the hardenability and heat resistance of steel and enhance the steel's resistance to temper softening; Cu (copper): Copper can improve the corrosion resistance of steel, but excessive amount will have an adverse effect on the hot working properties of steel; V (vanadium): Vanadium can refine the grains of steel and improve the strength and toughness of steel; Nb (niobium): Niobium can increase the strength and toughness of steel and improve the welding performance of steel; Ti (titanium): Titanium can refine grains, improve the strength and toughness of steel, and enhance the creep resistance of steel.

[0031] The following is an introduction in conjunction with specific embodiments: Example

[0032] C0.12%, Si0.20%, Mn1.2%, Cr1.0%, Ni0.8%, Mo0.30%, V0.08%, Ti0.02%, P0.012%, S0.010%, the balance is Fe and unavoidable impurities; The heating rate was 12°C / min, heated to 1230°C, and kept warm for 4 hours; The initial forging temperature is 1180℃, the final forging temperature is 880℃, the upsetting ratio is 2.5, the drawing ratio is 4, and the total forging ratio is 8; When cooling, slowly cool in a 650℃ holding pit for 6 hours; Then air-cooling, normalizing temperature during heat treatment is 920℃, keeping temperature for 2.5 hours, air-cooling; tempering temperature is 680℃, keeping temperature for 4 hours, air-cooling; The forging and heat treatment were carried out according to the forging method, and the test results of the forging performance were as follows: tensile strength was 750MPa, yield strength was 600MPa, elongation was 20%, impact toughness was 150J / cm², and the corrosion rate in the simulated reactor working environment was 0.05mm / year Example

[0033] C: 0.18%, Si: 0.25%, Mn: 1.35%, P: 0.010%, S: 0.008%, Cr: 1.05%, Ni: 1.05%, Mo: 0.25%, Cu: 0.15%, V: 0.03%, Nb: 0.02%, Ti: 0.02%, and the balance is Fe and inevitable impurities.

[0034] The heating rate was 10°C / min, heated to 1200°C, and kept at this temperature for 3 hours; The initial forging temperature is 1150℃, the final forging temperature is 850℃, the upsetting ratio is 2, the drawing ratio is 3, and the total forging ratio is 6; When cooling, slowly cool in a 600℃ holding pit for 5 hours, then air cool; During heat treatment, the normalizing temperature is 900℃, kept at this temperature for 2 hours, and air-cooled; the tempering temperature is 650℃, kept at this temperature for 3 hours, and air-cooled.

[0035] Forging and heat treatment were performed according to the forging method described above, and the test results of the forging performance were as follows: tensile strength was 780MPa, yield strength was 620MPa, elongation was 18%, impact toughness was 140J / cm², and the corrosion rate in the simulated reactor working environment was 0.04mm / year. Example

[0036] Steel ingot containing C: 0.18%, Si: 0.25%, Mn: 1.35%, P: 0.010%, S: 0.008%, Cr: 1.05%, Ni: 1.05%, Mo: 0.25%, Cu: 0.15%, V: 0.03%, Nb: 0.02%, Ti: 0.02%, and the balance being Fe and inevitable impurities.

[0037] Forging was performed according to the forging method, with a heating rate of 15°C / min, heating to 1250°C, and keeping the temperature for 5 hours; The initial forging temperature is 1200℃, the final forging temperature is 850℃, the upsetting ratio is 3, the drawing ratio is 4.5, and the total forging ratio is 8; When cooling, slowly cool in a 700℃ holding pit for 8 hours, then air cool; During heat treatment, the normalizing temperature is 950℃, kept warm for 3 hours, and air-cooled; the tempering temperature is 700℃, kept warm for 4.5 hours, and air-cooled.

[0038] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A forging for a safety end of a reactor pressure vessel, characterized in that: It includes the following components in mass percentage: C: 0.15%~0.20%, Si: 0.15%~0.35%, Mn: 1.20%~1.50%, P≤0.015%, S≤0.010%, Cr: 0.90%~1.20%, Ni: 0.90%~1.20%, Mo: 0.20%~0.30%, Cu≤0.20%, V: 0.02%~0.05%, Nb: 0.01%~0.03%, Ti: 0.01%~0.03%, and the balance is Fe and unavoidable impurities.

2. The reactor pressure vessel safety end forging according to claim 1, characterized in that: The yield strength of the forging is ≥400MPa, the tensile strength is ≥550MPa, the elongation is ≥18%, the cross-sectional shrinkage is ≥45%, and the room temperature impact toughness is ≥60J / cm².

3. A forging method for a reactor pressure vessel safety end forging, characterized in that: A forging for a safety end of a reactor pressure vessel according to any one of claims 1 to 2, the method comprising: Step 1: Raw material preparation: Select high-quality steel ingots to ensure that their chemical composition meets the above requirements; Step 2: Heating: Put the steel ingot into a heating furnace, heat it to 1200-1250°C at a heating rate of 10-15°C / min, and keep it warm for 3-5 hours to make the steel ingot evenly heated; Step 3: Forging: The multi-directional forging process is adopted, the initial forging temperature is 1150-1200℃, the final forging temperature is not less than 850℃, firstly upsetting is performed, the upsetting ratio is 2-3, then drawing is performed, the drawing ratio is 3-5, the upsetting and drawing operations are repeated, and the total forging ratio is 6-8; Step 4: Cooling: After forging, the forging is quickly placed in a heat preservation pit at a temperature of 600-700°C for slow cooling for 5-8 hours, and then air-cooled to room temperature; Step 5: Heat treatment: The cooled forgings are normalized and tempered. The normalizing temperature is 900-950°C, kept warm for 2-3 hours, and then air-cooled. The tempering temperature is 650-700°C, kept warm for 3-5 hours, and then air-cooled.

4. The reactor pressure vessel safety end forging according to claim 1, characterized in that: During the forging process of step three, the deformation amount of each pass is controlled within 15% to 25%.

5. The reactor pressure vessel safety end forging according to claim 1, characterized in that: During the normalizing and tempering treatments, the heating rate is controlled at 80-100° C. / h.

6. The reactor pressure vessel safety end forging according to claim 1, characterized in that: During the heating process of step 2, after the steel ingot is heated to a predetermined temperature, it is ensured that the difference between the core temperature and the surface temperature of the steel ingot does not exceed 50° C., and the atmosphere in the heating furnace should be kept neutral or slightly oxidizing.

7. The reactor pressure vessel safety end forging according to claim 1, characterized in that: During the cooling process in step 4, the forgings should be placed in the insulation pit to ensure that all parts thereof are cooled evenly, and the temperature in the insulation pit should remain stable with a fluctuation range of no more than ±20°C.

8. A forging for a safety end of a reactor pressure vessel and a forging method thereof according to claim 1, characterized in that: During the heat treatment process in step 5, the forgings after normalizing should be air-cooled within 1 hour.

9. A reactor pressure vessel safety end forging and a forging method thereof according to claim 1, characterized in that: The hardness of the forging after the tempering treatment should be controlled within the range of HB180 to HB220.

10. A forging for a safety end of a reactor pressure vessel and a forging method thereof according to claim 1, characterized in that: The internal defect area of ​​the forgings manufactured by the forging method should be less than 0.5%, and the maximum size of the defect should not exceed 5% of the thickness of the forging.

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