Forging piece for control rod driving mechanism of nuclear power station and manufacturing method of forging piece

Abstract

The invention provides a forge piece for a control rod driving mechanism of a nuclear power station, which is prepared from the following components in percentage by weight: 0.015 to 0.030 percent of C, 0.95 to 1.00 percent of Si, 1.70 to 2.00 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.005 percent of S, 19.00 to 20.00 percent of Cr, 9.30 to 10.00 percent of Ni, 0.96 to 1.00 percent of Cu, 0.050 to 0.075 percent of N, less than or equal to 0.0013 percent of B, less than or equal to 0.050 percent of Al, less than or equal to 0.050 percent of Co, 0.02 to 0.03 percent of Gd and the balance of iron. The invention further provides a manufacturing method of the forge piece for the control rod driving mechanism of the nuclear power station. The forge piece for the control rod driving mechanism of the nuclear power station, provided by the invention, has relatively good mechanical property and intergranular corrosion resistance, and can be applied to a CAP1000 nuclear power station.

Description

Technical Field

[0001] This invention belongs to the field of alloy forging, specifically relating to a forging for a control rod drive mechanism for nuclear power plants and its manufacturing method. Background Technology

[0002] As my country's independently developed third-generation pressurized water reactor nuclear power technology, the CAP1000's control rod drive mechanism forgings are one of the core components ensuring the safe operation of nuclear power plants. However, my country faces problems in manufacturing these forgings, including reliance on imports, insufficient process precision, and unstable material properties. These issues not only hinder the localization of nuclear power equipment but also pose supply chain security risks. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a forging for a control rod drive mechanism for nuclear power plants, which has good mechanical properties and resistance to intergranular corrosion and can be applied to CAP1000 nuclear power plants.

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0005] A forging for a control rod drive mechanism for a nuclear power plant, comprising the following components by weight percentage: C 0.015-0.030%, Si 0.95-1.00%, Mn 1.70-2.00%, P≤0.025%, S≤0.005%, Cr 19.00-20.00%, Ni 9.30-10.00%, Cu 0.96-1.00%, N 0.050-0.075%, B≤0.0013%, Al≤0.050%, Co≤0.050%, Gd 0.02-0.03%, with the remainder being iron.

[0006] Another technical problem to be solved by the present invention is to provide a method for manufacturing the forgings for the control rod drive mechanism of the above-mentioned nuclear power plant.

[0007] To solve the above technical problems, the technical solution is as follows:

[0008] A method for manufacturing a forging for a control rod drive mechanism in a nuclear power plant includes the following steps:

[0009] S1. Electric furnace smelting: Raw materials are prepared according to weight percentage, placed in an electric furnace, and smelted until the temperature reaches 1620-1640℃ to obtain molten steel.

[0010] S2. Ladle refining: The molten steel obtained in step S1 is placed in an LF furnace for refining for 60-80 minutes, vacuum degassing, soft blowing with argon, and then cast into steel ingot billets using a die casting process.

[0011] S3. Forging: The steel ingot billet obtained in step S3 is heated to 1160-1200℃, held for 2-3 hours, and then forged using an air hammer and press to obtain forgings;

[0012] S4. Heat treatment: The forgings obtained in step S3 are subjected to solution treatment, and then placed in a cooling water tank to cool to room temperature to obtain forgings for nuclear power plant control rod drive mechanism;

[0013] S5. Inspection: Perform physical and chemical testing and non-destructive testing on the forgings for the nuclear power plant control rod drive mechanism obtained in step S4.

[0014] Furthermore, in step S2 of the present invention, the entire process of furnace refining is protected by argon gas, the vacuum degree of vacuum degassing is 25-35 Pa, and the vacuum degassing time is 30-40 min.

[0015] Furthermore, in step S2 of the present invention, the time for soft argon blowing is 20-30 minutes.

[0016] Furthermore, in step S3 of the present invention, the cutting ratio of the ingot head of the steel ingot billet is 10%, and the cutting ratio of the ingot tail of the steel ingot billet is 3%.

[0017] Furthermore, in step S3 of the present invention, the initial forging temperature is 1110-1150℃, the main deformation temperature is 960-1000℃, the final forging temperature is 800-850℃, and the total forging ratio is ≥5.

[0018] Furthermore, in step S4 of the present invention, the solution treatment is carried out in an industrial resistance furnace, the heating temperature of the solution treatment is 1070-1090℃, and the holding time is calculated as 1.5-1.8min / mm.

[0019] Furthermore, in step S4 of the present invention, the temperature of the cooling water pool is 35°C.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) This invention optimizes the content of each component, the temperature of each forging stage, the solution treatment temperature, etc., and the resulting forging for the nuclear power plant control rod drive mechanism has better mechanical properties.

[0022] 2) The control rod drive mechanism of nuclear power plants requires forgings with low magnetic permeability (less than 1.1) and ferrite content needs to be controlled. To address this, the present invention appropriately increases the nickel equivalent and decreases the chromium equivalent, while also appropriately controlling the forging heating temperature to prevent ferrite formation and reduce magnetic permeability.

[0023] 3) The heating temperature of the solution treatment has a significant impact on the ferrite content. If the temperature is too high, high-temperature ferrite will be generated. To address this, the present invention controls the heating temperature of the solution treatment to 1070-1090℃, which can achieve the effect of sufficient solution treatment while avoiding the generation of high-temperature ferrite.

[0024] 4) The present invention also adds a small amount of gadolinium, which can refine the grains and improve the grain size and resistance to intergranular corrosion of the forgings. Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0026] Example 1

[0027] The forgings for the control rod drive mechanism of nuclear power plants are composed of the following components by weight percentage: C 0.020%, Si 0.98%, Mn 1.90%, P 0.024%, S 0.003%, Cr 19.70%, Ni 9.80%, Cu 0.98%, N 0.070%, B 0.0012%, Al 0.048%, Co 0.049%, Gd 0.03%, with the remainder being iron.

[0028] The manufacturing method of Example 1 includes the following steps:

[0029] S1. Electric furnace smelting: Raw materials are prepared according to weight percentage, placed in an electric furnace, and smelted until the temperature reaches 1630℃ to obtain molten steel.

[0030] S2. Ladle refining: Argon protection throughout the process. The molten steel obtained in step S1 is placed in an LF furnace for refining for 70 minutes, vacuum degassing at 30 Pa for 35 minutes, followed by soft argon blowing for 25 minutes, and then cast into steel ingot billets using the die casting process.

[0031] S3. Forging: The steel ingot billet obtained in step S3 is heated to 1180℃ and held for 2.5h. Then, it is forged using an air hammer and a press to obtain forgings. The cutting ratio of the ingot head is 10%, the cutting ratio of the ingot tail is 3%, the initial forging temperature is 1130℃, the main deformation temperature is 980℃, the final forging temperature is 830℃, and the total forging ratio is 5.2.

[0032] S4. Heat treatment: The forgings obtained in step S3 are subjected to solution treatment in an industrial resistance furnace. The heating temperature of the solution treatment is 1080℃ and the holding time is calculated at 1.6min / mm. Then, they are placed in a cooling water pool at 35℃ to cool to room temperature to obtain the forgings for the control rod drive mechanism of the nuclear power plant.

[0033] S5. Inspection: Perform physical and chemical testing and non-destructive testing on the forgings for the nuclear power plant control rod drive mechanism obtained in step S4.

[0034] Example 2

[0035] The forgings for the control rod drive mechanism of nuclear power plants are composed of the following components by weight percentage: C 0.030%, Si 0.95%, Mn 1.80%, P 0.025%, S 0.004%, Cr 19.50%, Ni 10.00%, Cu 0.96%, N 0.075%, B 0.0013%, Al 0.049%, Co 0.048%, Gd 0.02%, with the remainder being iron.

[0036] The manufacturing method of Example 2 includes the following steps:

[0037] S1. Electric furnace smelting: Raw materials are prepared according to weight percentage, placed in an electric furnace, and smelted until the temperature reaches 1620℃ to obtain molten steel.

[0038] S2. Ladle refining: Argon protection throughout the process. The molten steel obtained in step S1 is placed in an LF furnace for refining for 80 minutes, vacuum degassing at 35 Pa for 40 minutes, followed by soft argon blowing for 30 minutes, and then cast into steel ingot billets using the die casting process.

[0039] S3. Forging: The steel ingot billet obtained in step S3 is heated to 1160℃ and held for 3 hours. Then, it is forged using an air hammer and a press to obtain forgings. The cutting ratio of the ingot head of the steel ingot billet is 10%, the cutting ratio of the ingot tail of the steel ingot billet is 3%, the initial forging temperature is 1110℃, the main deformation temperature is 960℃, the final forging temperature is 850℃, and the total forging ratio is 5.

[0040] S4. Heat treatment: The forgings obtained in step S3 are subjected to solution treatment in an industrial resistance furnace. The heating temperature of the solution treatment is 1070℃, and the holding time is calculated at 1.8min / mm. Then, they are placed in a cooling water pool at 35℃ to cool to room temperature to obtain the forgings for the control rod drive mechanism of the nuclear power plant.

[0041] S5. Inspection: Perform physical and chemical testing and non-destructive testing on the forgings for the nuclear power plant control rod drive mechanism obtained in step S4.

[0042] Example 3

[0043] The forgings for the control rod drive mechanism of nuclear power plants are composed of the following components by weight percentage: C 0.015%, Si 1.00%, Mn 1.70%, P 0.025%, S 0.004%, Cr 20.00%, Ni 9.30%, Cu 0.99%, N 0.065%, B 0.0012%, Al 0.050%, Co 0.049%, Gd 0.02%, with the remainder being iron.

[0044] The manufacturing method of Example 3 includes the following steps:

[0045] S1. Electric furnace smelting: Raw materials are prepared according to weight percentage, placed in an electric furnace, and smelted until the temperature reaches 1640℃ to obtain molten steel.

[0046] S2. Ladle refining: Argon protection throughout the process. The molten steel obtained in step S1 is placed in an LF furnace for refining for 60 minutes, vacuum degassing at 25 Pa for 30 minutes, followed by soft argon blowing for 20 minutes, and then cast into steel ingot billets using the die casting process.

[0047] S3. Forging: The steel ingot billet obtained in step S3 is heated to 1200℃ and held for 2 hours. Then, it is forged using an air hammer and a press to obtain forgings. The cutting ratio of the ingot head is 10%, the cutting ratio of the ingot tail is 3%, the initial forging temperature is 1150℃, the main deformation temperature is 1000℃, the final forging temperature is 800℃, and the total forging ratio is 5.1.

[0048] S4. Heat treatment: The forgings obtained in step S3 are subjected to solution treatment in an industrial resistance furnace. The heating temperature of the solution treatment is 1090℃, and the holding time is calculated at 1.5min / mm. Then, they are placed in a cooling water pool at 35℃ to cool to room temperature to obtain the forgings for the control rod drive mechanism of the nuclear power plant.

[0049] S5. Inspection: Perform physical and chemical testing and non-destructive testing on the forgings for the nuclear power plant control rod drive mechanism obtained in step S4.

[0050] Example 4

[0051] The forgings for the control rod drive mechanism of nuclear power plants are composed of the following components by weight percentage: C 0.025%, Si 0.96%, Mn 2.00%, P 0.024%, S 0.005%, Cr 19.00%, Ni 9.50%, Cu 1.00%, N 0.050%, B 0.0013%, Al 0.048%, Co 0.050%, Gd 0.03%, with the remainder being iron.

[0052] The manufacturing method of Example 4 includes the following steps:

[0053] S1. Electric furnace smelting: Raw materials are prepared according to weight percentage, placed in an electric furnace, and smelted until the temperature reaches 1630℃ to obtain molten steel.

[0054] S2. Ladle refining: Argon protection throughout the process. The molten steel obtained in step S1 is placed in an LF furnace for refining for 75 minutes, vacuum degassing at 30 Pa for 30 minutes, followed by soft argon blowing for 20 minutes, and then cast into steel ingot billets using the die casting process.

[0055] S3. Forging: The steel ingot billet obtained in step S3 is heated to 1190℃ and held for 3 hours. Then, it is forged using an air hammer and a press to obtain forgings. The cutting ratio of the ingot head is 10%, the cutting ratio of the ingot tail is 3%, the initial forging temperature is 1140℃, the main deformation temperature is 990℃, the final forging temperature is 840℃, and the total forging ratio is 5.1.

[0056] S4. Heat treatment: The forgings obtained in step S3 are subjected to solution treatment in an industrial resistance furnace. The heating temperature of the solution treatment is 1085℃, and the holding time is calculated at 1.8min / mm. Then, they are placed in a cooling water pool at 35℃ to cool to room temperature to obtain the forgings for the control rod drive mechanism of the nuclear power plant.

[0057] S5. Inspection: Perform physical and chemical testing and non-destructive testing on the forgings for the nuclear power plant control rod drive mechanism obtained in step S4.

[0058] Comparative Example 1

[0059] The composition of the forging is: C 0.020%, Si 0.98%, Mn 1.90%, P 0.024%, S 0.003%, Cr 19.70%, Ni 9.20%, Cu 0.98%, N 0.070%, B 0.0012%, Al 0.048%, Co 0.049%, Gd 0.03%, with the remainder being iron; its manufacturing method is the same as in Example 1. The difference from Example 1 is that the Ni content in Comparative Example 1 is lower than the range defined in this invention.

[0060] Comparative Example 2

[0061] The composition of the forging is: C 0.020%, Si 0.98%, Mn 1.90%, P 0.024%, S 0.003%, Cr 20.10%, Ni 9.80%, Cu 0.98%, N 0.070%, B 0.0012%, Al 0.048%, Co 0.049%, Gd 0.03%, with the remainder being iron; its manufacturing method is the same as in Example 1. The difference from Example 1 is that the Cr content in Comparative Example 2 is higher than the range defined in this invention.

[0062] Comparative Example 3

[0063] The composition of the forging is the same as that of Example 1. The difference from Example 1 is that the heating temperature for the solution treatment in step S4 is 1095°C, which is higher than the range defined in this invention.

[0064] Comparative Example 4

[0065] The composition of the forging is: C 0.020%, Si 0.98%, Mn 1.90%, P 0.024%, S 0.003%, Cr 19.70%, Ni 9.80%, Cu 0.98%, N 0.070%, B 0.0012%, Al 0.048%, Co 0.049%, with the remainder being iron; its manufacturing method is the same as in Example 1. The difference from Example 1 is that the composition of Comparative Example 4 does not include Gd.

[0066] Experiment Example 1: Mechanical Property Testing

[0067] The forgings for nuclear power plant control rod drive mechanisms prepared in Examples 1-4 were subjected to room temperature tensile tests according to GB / T 228.1. The sample size was φ12.5mm. The test results are shown in Table 1.

[0068] Rp0.2 (MPa) Rm (MPa) Specified value ≥205 ≥515 Example 1 247 589 Example 2 241 581 Example 3 252 595 Example 4 238 577

[0069] Table 1

[0070] As can be seen from Table 1, Rp0.2 and Rm in Examples 1-4 all meet the specified value requirements, indicating that the forgings for the nuclear power plant control rod drive mechanism prepared by the present invention have good mechanical properties.

[0071] Experimental Example 2: Ferrite Content Test

[0072] The forgings for nuclear power plant control rod drive mechanisms prepared in Examples 1-4 and Comparative Examples 1-3 were tested for ferrite content according to GB / T15749-2008. The test results are shown in Table 2.

[0073] Ferrite content (%) Example 1 0.8 Example 2 0.6 Example 3 0.8 Example 4 0.7 Comparative Example 1 1.3 Comparative Example 2 1.4 Comparative Example 3 1.3

[0074] Table 2

[0075] As shown in Table 2, the ferrite content in Examples 1-4 is relatively low, indicating that the forgings for the nuclear power plant control rod drive mechanism prepared by this invention have a low ferrite content. Compared with Example 1, the ferrite content in Comparative Examples 1-3 is increased, indicating that higher Ni content, lower Cr content, and higher solution treatment heating temperature than specified in this invention all lead to an increase in the ferrite content of the forgings for the nuclear power plant control rod drive mechanism.

[0076] Experiment Example 3: Magnetic Permeability Test

[0077] The forgings for nuclear power plant control rod drive mechanisms prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to magnetic permeability tests according to ASTM A342 Method 4. The test results are shown in Table 3.

[0078] Magnetic permeability (%) Example 1 1.06 Example 2 1.09 Example 3 1.07 Example 4 1.08 Comparative Example 1 1.12 Comparative Example 2 1.13

[0079] Table 3

[0080] As shown in Table 2, the magnetic permeability of Examples 1-4 is low and less than 1.1, indicating that the forgings for the nuclear power plant control rod drive mechanism prepared by this invention have low magnetic permeability. Compared with Example 1, the magnetic permeability of Comparative Examples 1-3 is increased, indicating that higher Ni content and lower Cr content than specified in this invention both lead to increased magnetic permeability of the forgings for the nuclear power plant control rod drive mechanism.

[0081] Experiment Example 4: Grain Size Test

[0082] The forgings for nuclear power plant control rod drive mechanisms prepared in Examples 1-4 and Comparative Example 4 were subjected to grain size testing according to GB / T 6394-2017. The test results are shown in Table 4.

[0083] Grain size level Example 1 6 Example 2 5.5 Example 3 5.5 Example 4 6 Comparative Example 4 4.5

[0084] Table 4

[0085] As shown in Table 4, the grain size levels of Examples 1-4 are all above level 5, indicating that the forgings for nuclear power plant control rod drive mechanisms prepared by this invention have good grain size. Compared with Example 1, the grain size level of Comparative Example 4 is reduced to 4.5, indicating that the Gd element added by this invention can effectively improve the grain size of the forgings for nuclear power plant control rod drive mechanisms.

[0086] Experiment Example 5: Test of resistance to intergranular corrosion

[0087] The forgings for nuclear power plant control rod drive mechanisms prepared in Examples 1-4 and Comparative Example 4 were subjected to intergranular corrosion tests according to Method E in GB / T 4334-2020. The intergranular corrosion resistance of each forging in the sensitized state (sensitization temperature 650℃, holding for 2h, air cooling) was determined. The test results are shown in Table 5.

[0088] Example 1 No intergranular corrosion cracks were observed on the bent surface. Example 2 No intergranular corrosion cracks were observed on the bent surface. Example 3 No intergranular corrosion cracks were observed on the bent surface. Example 4 No intergranular corrosion cracks were observed on the bent surface. Comparative Example 4 A small number of intergranular corrosion cracks appeared on the curved surface.

[0089] Table 5

[0090] As shown in Table 5, no intergranular corrosion cracks appeared on the bent surfaces of Examples 1-4, indicating that the forgings for the nuclear power plant control rod drive mechanism prepared by the present invention have good resistance to intergranular corrosion. Compared with Example 1, a small number of intergranular corrosion cracks appeared on the bent surface of Comparative Example 4, indicating that the Gd element added by the present invention can effectively improve the resistance to intergranular corrosion of the forgings for the nuclear power plant control rod drive mechanism.

[0091] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A forging for a control rod drive mechanism in a nuclear power plant, characterized in that: By weight percentage, it consists of the following components: C 0.015-0.030%, Si 0.95-1.00%, Mn 1.70-2.00%, P≤0.025%, S≤0.005%, Cr 19.00-20.00%, Ni 9.30-10.00%, Cu 0.96-1.00%, N 0.050-0.075%, B≤0.0013%, Al≤0.050%, Co≤0.050%, Gd 0.02-0.03%, with the remainder being iron.

2. The method for manufacturing a forging for a nuclear power plant control rod drive mechanism according to claim 1, characterized in that: Includes the following steps: S1. Electric furnace smelting: Raw materials are prepared according to weight percentage, placed in an electric furnace, and smelted until the temperature reaches 1620-1640℃ to obtain molten steel. S2. Ladle refining: The molten steel obtained in step S1 is placed in an LF furnace for refining for 60-80 minutes, vacuum degassing, soft blowing with argon, and then cast into steel ingot billets using a die casting process. S3. Forging: The steel ingot billet obtained in step S3 is heated to 1160-1200℃, held for 2-3 hours, and then forged using an air hammer and press to obtain forgings; S4. Heat treatment: The forgings obtained in step S3 are subjected to solution treatment, and then placed in a cooling water tank to cool to room temperature to obtain forgings for nuclear power plant control rod drive mechanism; S5. Inspection: Perform physical and chemical testing and non-destructive testing on the forgings for the nuclear power plant control rod drive mechanism obtained in step S4.

3. A method for manufacturing a forging for a nuclear power plant control rod drive mechanism according to claim 2, characterized in that: In step S2, the entire process of furnace refining is protected by argon gas, the vacuum degree of vacuum degassing is 25-35 Pa, and the vacuum degassing time is 30-40 min.

4. A method for manufacturing a forging for a nuclear power plant control rod drive mechanism according to claim 2, characterized in that: In step S2, the soft blowing time of argon is 20-30 minutes.

5. A method for manufacturing a forging for a nuclear power plant control rod drive mechanism according to claim 2, characterized in that: In step S3, the cutting ratio of the ingot head of the steel ingot billet is 10%, and the cutting ratio of the ingot tail of the steel ingot billet is 3%.

6. A method for manufacturing a forging for a nuclear power plant control rod drive mechanism according to claim 2, characterized in that: In step S3, the initial forging temperature is 1110-1150℃, the main deformation temperature is 960-1000℃, the final forging temperature is 800-850℃, and the total forging ratio is ≥5.

7. A method for manufacturing a forging for a nuclear power plant control rod drive mechanism according to claim 2, characterized in that: In step S4, the solution treatment is carried out in an industrial resistance furnace. The heating temperature for the solution treatment is 1070-1090℃, and the holding time is calculated as 1.5-1.8 min / mm.

8. A method for manufacturing a forging for a nuclear power plant control rod drive mechanism according to claim 2, characterized in that: In step S4, the temperature of the cooling water pool is 35°C.