Martensitic stainless steel forge piece for pressurized water reactor turbine regulating valve and manufacturing method thereof

Abstract

The martensitic stainless steel forge piece for the pressurized water reactor turbine regulating valve is composed of, by weight, 0.12%-0.15% of C, 0.7%-1.0% of Mn, smaller than or equal to 0.04% of P, smaller than or equal to 0.030% of S, smaller than or equal to 1.00% of Si, 11.5%-12.5% of Cr, 0.45%-0.75% of Ni, 0.02%-0.03% of Tm and the balance iron. The invention further provides a manufacturing method of the martensitic stainless steel forge piece for the regulating valve of the pressurized water reactor steam turbine. The martensitic stainless steel forge piece for the regulating valve of the pressurized water reactor steam turbine, provided by the invention, has relatively high mechanical property and corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of alloy forging, specifically relating to a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve and its manufacturing method. Background Technology

[0002] my country's nuclear power construction is progressing rapidly, with 56 units currently generating electricity and 46 under construction, and approximately 10 units approved for construction each year. The control valve of a pressurized water reactor (PWR) turbine is a crucial component of the PWR unit. Its operating environment is extremely harsh, typically requiring it to withstand high pressure (above 15.5 MPa), high temperature (above 300℃), and strong radiation. This necessitates that the control valve material possess strong mechanical properties and corrosion resistance. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve, which has strong mechanical properties and corrosion resistance.

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

[0005] A martensitic stainless steel forging for a pressurized water reactor turbine regulating valve, comprising the following components by weight percentage: C 0.12-0.15%, Mn 0.7-1.0%, P≤0.04%, S≤0.030%, Si≤1.00%, Cr 11.5-12.5%, Ni 0.45-0.75%, Tm 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 martensitic stainless steel forgings for the control valves of pressurized water reactor turbines.

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

[0008] A method for manufacturing a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve includes the following steps:

[0009] S1. Electric furnace smelting: Prepare raw materials according to weight percentage, place the raw materials in an electric furnace, smelt to a temperature of 1590℃ and then blow oxygen to decarburize, then continue smelting to a temperature of 1620-1640℃ and tap out the steel to obtain molten steel, and then cast the molten steel into steel ingots.

[0010] S2. Forging: The steel ingot obtained in step S1 is forged into forgings by upsetting and drawing using an air hammer and a press;

[0011] S3. Heat treatment: The forgings obtained in step S2 are placed in an industrial resistance furnace for two heat treatments to obtain martensitic stainless steel forgings for pressurized water reactor turbine regulating valves.

[0012] S4. Inspection: Perform physical and chemical tests and non-destructive tests on the martensitic stainless steel forgings for pressurized water reactor turbine control valves obtained in step S3.

[0013] Furthermore, in step S2 of the present invention, the cutting ratio of the ingot head is 10%, and the cutting ratio of the ingot tail of the ingot billet is 5%.

[0014] Furthermore, in step S2 of the present invention, the initial forging temperature is 1110-1130℃, the final forging temperature is 850-880℃, and the total forging ratio is ≥5.5.

[0015] Furthermore, in step S3 of the present invention, the first heat treatment process is as follows: quenching at 1010-1030℃, holding at that temperature for 5-6 hours and then water cooling; tempering at 605-615℃, holding at that temperature for 3-4 hours and then water cooling.

[0016] Furthermore, in step S3 of the present invention, the second heat treatment process is as follows: quenching at 970-980℃, holding at that temperature for 5-6 hours and then water cooling; tempering at 315-325℃ for the first time, holding at that temperature for 3-4 hours and then water cooling; tempering at 315-325℃ for the second time, holding at that temperature for 3-4 hours and then water cooling.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) Based on ASTM A473 410, this invention adjusts the content of nickel and chromium elements, so that the martensitic stainless steel forgings for pressurized water reactor turbine control valves prepared by this invention have both strong mechanical properties and corrosion resistance.

[0019] 2) The present invention also adds a small amount of Tm thulium, which can effectively improve the resistance of forgings to sulfide stress corrosion and reduce the ferrite content of forgings.

[0020] 3) This invention utilizes a combination of upsetting and drawing processes to fully forge the forgings, with a forging ratio greater than 5.5. Appropriately increasing the forging ratio can improve the forging effect. The material recrystallization effect during the forging process is used to refine the grains of the forgings and improve the overall performance of the forgings.

[0021] 4) This invention fully utilizes the phase transformation during the heat treatment process to further refine the grains, controls the heat treatment temperature and holding time to prevent grain growth, and the two heat treatments improve the overall performance of the forgings. Moreover, the two tempering processes used in the second heat treatment can effectively reduce the internal stress of the forgings. Detailed Implementation

[0022] 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.

[0023] Example 1

[0024] The martensitic stainless steel forgings for the regulating valves of pressurized water reactor turbines are composed of the following components by weight percentage: C 0.14%, Mn 0.9%, P 0.03%, S 0.028%, Si 0.99%, Cr 12.0%, Ni 0.60%, Tm 0.03%, with the remainder being iron.

[0025] The manufacturing method of the martensitic stainless steel forging for the regulating valve of the pressurized water reactor turbine described in Example 1 includes the following steps:

[0026] S1. Electric furnace smelting: Prepare raw materials according to weight percentage, place the raw materials in an electric furnace, smelt to a temperature of 1590℃ and then blow oxygen to decarburize, then continue smelting to a temperature of 1630℃ and tap out the steel to obtain molten steel, and then cast the molten steel into steel ingots.

[0027] S2. Forging: The steel ingot obtained in step S1 is forged by upsetting and drawing 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 5%, the initial forging temperature is 1120℃, the final forging temperature is 865℃, and the total forging ratio is 5.7.

[0028] S3. Heat treatment: The forgings obtained in step S2 are placed in an industrial resistance furnace for two heat treatments to obtain martensitic stainless steel forgings for the regulating valve of a pressurized water reactor turbine. The first heat treatment process is as follows: quenching at 1020℃, holding for 5.5 hours and then water cooling, tempering at 610℃, holding for 3.5 hours and then water cooling; the second heat treatment process is as follows: quenching at 975℃, holding for 5.5 hours and then water cooling, tempering at 320℃ for the first time, holding for 3.5 hours and then water cooling, tempering at 320℃ for the second time, holding for 3.5 hours and then water cooling.

[0029] S4. Inspection: Perform physical and chemical tests and non-destructive tests on the martensitic stainless steel forgings for pressurized water reactor turbine control valves obtained in step S3.

[0030] Example 2

[0031] The martensitic stainless steel forgings for the regulating valves of pressurized water reactor turbines are composed of the following components by weight percentage: C 0.12%, Mn 1.0%, P 0.04%, S 0.029%, Si 0.98%, Cr 11.8%, Ni 0.70%, Tm 0.02%, with the remainder being iron.

[0032] The manufacturing method of the martensitic stainless steel forging for the regulating valve of the pressurized water reactor turbine described in Example 2 includes the following steps:

[0033] S1. Electric furnace smelting: Prepare raw materials according to weight percentage, place the raw materials in the electric furnace, smelt to a temperature of 1590℃ and then blow oxygen to decarburize, then continue smelting to a temperature of 1620℃ and tap out the steel to obtain molten steel, and then cast the molten steel into steel ingots.

[0034] S2. Forging: The steel ingot obtained in step S1 is forged by upsetting and drawing 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 5%, the initial forging temperature is 1110℃, the final forging temperature is 850℃, and the total forging ratio is 5.5.

[0035] S3. Heat treatment: The forgings obtained in step S2 are placed in an industrial resistance furnace for two heat treatments to obtain martensitic stainless steel forgings for pressurized water reactor turbine regulating valves. The first heat treatment process is as follows: quenching at 1010℃, holding for 6 hours and then water cooling, tempering at 605℃, holding for 4 hours and then water cooling. The second heat treatment process is as follows: quenching at 970℃, holding for 6 hours and then water cooling, tempering at 315℃ for the first time, holding for 4 hours and then water cooling, tempering at 315℃ for the second time, holding for 4 hours and then water cooling.

[0036] S4. Inspection: Perform physical and chemical tests and non-destructive tests on the martensitic stainless steel forgings for pressurized water reactor turbine control valves obtained in step S3.

[0037] Example 3

[0038] The martensitic stainless steel forgings for the regulating valves of pressurized water reactor turbines are composed of the following components by weight percentage: C 0.15%, Mn 0.7%, P 0.02%, S 0.030%, Si 0.99%, Cr 11.5%, Ni 0.75%, Tm 0.02%, with the remainder being iron.

[0039] The manufacturing method of the martensitic stainless steel forging for the pressurized water reactor turbine regulating valve described in Example 3 includes the following steps:

[0040] S1. Electric furnace smelting: Prepare raw materials according to weight percentage, place the raw materials in the electric furnace, smelt to a temperature of 1590℃ and then blow oxygen to decarburize, then continue smelting to a temperature of 1640℃ and tap out the steel to obtain molten steel, and then cast the molten steel into steel ingots.

[0041] S2. Forging: The steel ingot obtained in step S1 is forged by upsetting and drawing 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 5%, the initial forging temperature is 1130℃, the final forging temperature is 880℃, and the total forging ratio is 5.6.

[0042] S3. Heat treatment: The forgings obtained in step S2 are placed in an industrial resistance furnace for two heat treatments to obtain martensitic stainless steel forgings for the regulating valve of a pressurized water reactor turbine. The first heat treatment process is as follows: quenching at 1030℃, holding for 5 hours and then water cooling, tempering at 615℃, holding for 3 hours and then water cooling. The second heat treatment process is as follows: quenching at 980℃, holding for 5 hours and then water cooling, tempering at 325℃ for the first time, holding for 3 hours and then water cooling, tempering at 325℃ for the second time, holding for 3 hours and then water cooling.

[0043] S4. Inspection: Perform physical and chemical tests and non-destructive tests on the martensitic stainless steel forgings for pressurized water reactor turbine control valves obtained in step S3.

[0044] Example 4

[0045] The martensitic stainless steel forgings for the regulating valves of pressurized water reactor turbines are composed of the following components by weight percentage: C 0.13%, Mn 0.8%, P 0.03%, S 0.029%, Si 1.00%, Cr 12.5%, Ni 0.45%, Tm 0.03%, with the remainder being iron.

[0046] The manufacturing method of the martensitic stainless steel forging for the pressurized water reactor turbine regulating valve described in Example 4 includes the following steps:

[0047] S1. Electric furnace smelting: Prepare raw materials according to weight percentage, place the raw materials in an electric furnace, smelt to a temperature of 1590℃ and then perform oxygen blowing decarburization, then continue smelting to a temperature of 1625℃ and tap out the steel to obtain molten steel, and then cast the molten steel into steel ingots.

[0048] S2. Forging: The steel ingot obtained in step S1 is forged by upsetting and drawing 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 5%, the initial forging temperature is 1115℃, the final forging temperature is 855℃, and the total forging ratio is 5.6.

[0049] S3. Heat treatment: The forgings obtained in step S2 are placed in an industrial resistance furnace for two heat treatments to obtain martensitic stainless steel forgings for pressurized water reactor turbine regulating valves. The first heat treatment process is as follows: quenching at 1015℃, holding for 5.5 hours and then water cooling, tempering at 610℃, holding for 4 hours and then water cooling. The second heat treatment process is as follows: quenching at 975℃, holding for 5 hours and then water cooling, tempering at 320℃ for the first time, holding for 3 hours and then water cooling, tempering at 320℃ for the second time, holding for 3 hours and then water cooling.

[0050] S4. Inspection: Perform physical and chemical tests and non-destructive tests on the martensitic stainless steel forgings for pressurized water reactor turbine control valves obtained in step S3.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that the composition of the forging does not include Tm.

[0053] Comparative Example 2

[0054] The composition of the forging is the same as in Example 1. The difference from Example 1 is that step S3 is changed to:

[0055] The forgings obtained in step S2 are placed in an industrial resistance furnace for two heat treatments to obtain martensitic stainless steel forgings for pressurized water reactor turbine regulating valves. The first heat treatment process is as follows: quenching at 1020℃, holding for 5.5 hours and then water cooling, followed by tempering at 610℃, holding for 3.5 hours and then water cooling. The second heat treatment process is as follows: quenching at 975℃, holding for 5.5 hours and then water cooling, followed by tempering at 320℃, holding for 3.5 hours and then water cooling.

[0056] That is, the second heat treatment process in step S3 of Comparative Example 2 only involves one tempering.

[0057] Comparative Example 3

[0058] The composition of the forging is the same as in Example 1. The difference from Example 1 is that step S3 is changed to:

[0059] The forging obtained in step S2 is placed in an industrial resistance furnace for heat treatment to obtain a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve. The heat treatment process is as follows: quenching at 1020℃, holding for 5.5 hours and then water cooling, tempering at 610℃, holding for 3.5 hours and then water cooling.

[0060] That is, in step S3 of Comparative Example 3, there is only one heat treatment process.

[0061] Experiment Example 1: Mechanical Property Testing

[0062] The martensitic stainless steel forgings for pressurized water reactor turbine regulating valves prepared in Examples 1-4 were subjected to room temperature tensile tests according to ASTM A370. The test results are shown in Table 1.

[0063] Yield strength (0.2% residual deformation) (MPa) Tensile strength (MPa) Specified value ≥585 ≥760 Example 1 653 822 Example 2 645 814 Example 3 648 818 Example 4 657 825

[0064] Table 1

[0065] As can be seen from Table 1, the yield strength (0.2% residual deformation) and tensile strength of Examples 1-4 all meet the specified requirements, indicating that the martensitic stainless steel forgings for pressurized water reactor turbine regulating valves prepared by the present invention have good mechanical properties.

[0066] Experimental Example 2: Grain Size Test

[0067] The martensitic stainless steel forgings for pressurized water reactor turbine regulating valves prepared in Examples 1-4 and Comparative Example 3 were subjected to grain size testing according to GB / T 6394-2017. The test results are shown in Table 2.

[0068] Grain size level Example 1 6 Example 2 6.5 Example 3 7 Example 4 6.5 Comparative Example 3 4.5

[0069] Table 2

[0070] As shown in Table 2, the grain size levels of Examples 1-4 are all above level 5, indicating that the martensitic stainless steel forgings for pressurized water reactor turbine control valves prepared by this invention have good grain size. Compared with Example 1, the grain size level of Comparative Example 3 is reduced to 4.5, indicating that the two heat treatment processes in step S3 of this invention can effectively improve the grain size of the martensitic stainless steel forgings for pressurized water reactor turbine control valves.

[0071] Experiment Example 3: Sulfide Stress Corrosion Resistance Test

[0072] The martensitic stainless steel forgings for pressurized water reactor turbine control valves prepared in Examples 1-4 and Comparative Example 1 were subjected to slow-strain tensile stress corrosion tests according to ISO 7539-7-2005. The tests were conducted under the same experimental environment: a temperature of 25°C, a standard NACE A solution (5 wt% NaCl + 0.5 wt% HAc), a hydrogen sulfide partial pressure of 1 MPa, and a tensile rate of 3.5 × 10⁻⁶. -4 The test results are shown in Table 3, with a speed of mm / s.

[0073] Internal work (J) Example 1 60.56 Example 2 60.29 Example 3 60.58 Example 4 60.30 Comparative Example 1 29.83

[0074] Table 3

[0075] As shown in Table 3, the internal work product of Examples 1-4 is relatively high, indicating that the martensitic stainless steel forgings for pressurized water reactor turbine control valves prepared by this invention have good resistance to sulfide stress corrosion. Compared with Example 1, the internal work product of Comparative Example 1 is significantly reduced, indicating that the Tm added to the composition of this invention can effectively improve the resistance to sulfide stress corrosion of the martensitic stainless steel forgings for pressurized water reactor turbine control valves.

[0076] Experiment Example 4: Ferrite Test

[0077] The martensitic stainless steel forgings for pressurized water reactor turbine regulating valves prepared in Examples 1-4 and Comparative Example 1 were tested for ferrite content according to YB / T 4402-2014. The test results are shown in Table 4.

[0078] Ferrite content (%) Example 1 1.3 Example 2 1.5 Example 3 1.6 Example 4 1.4 Comparative Example 1 5.8

[0079] Table 4

[0080] As shown in Table 4, the ferrite content in Examples 1-4 is relatively low, indicating that the martensitic stainless steel forgings for pressurized water reactor turbine control valves prepared by this invention have a low ferrite content. Compared with Example 1, the ferrite content in Comparative Example 1 is significantly increased, indicating that the Tm added to the composition of this invention can effectively reduce the ferrite content of the martensitic stainless steel forgings for pressurized water reactor turbine control valves.

[0081] Experimental Example 5: Residual Stress Test

[0082] The martensitic stainless steel forgings for pressurized water reactor turbine regulating valves prepared in Examples 1-4 and Comparative Example 2 were subjected to residual stress tests according to GB / T 7704-2008. The test results are shown in Table 5.

[0083] Residual stress (MPa) at a distance of 0.25 mm from the surface of the forging. Example 1 39 Example 2 43 Example 3 40 Example 4 42 Comparative Example 2 95

[0084] Table 5

[0085] As shown in Table 5, the residual stress at a distance of 0.25 mm from the surface of the forgings in Examples 1-4 is relatively low, indicating that the martensitic stainless steel forgings for pressurized water reactor turbine control valves prepared by this invention have low residual stress. Compared with Example 1, the residual stress at a distance of 0.25 mm from the surface of the forging in Comparative Example 2 is significantly increased, indicating that the two tempering operations used in the second heat treatment process in step S3 of this invention can effectively reduce the residual stress of the martensitic stainless steel forgings for pressurized water reactor turbine control valves.

[0086] 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 martensitic stainless steel forging for a regulating valve of a pressurized water reactor turbine, characterized in that: By weight percentage, it consists of the following components: C 0.12-0.15%, Mn 0.7-1.0%, P≤0.04%, S≤0.030%, Si≤1.00%, Cr 11.5-12.5%, Ni 0.45-0.75%, Tm 0.02-0.03%, with the remainder being iron.

2. The manufacturing method of a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve according to claim 1, characterized in that: Includes the following steps: S1. Electric furnace smelting: Prepare raw materials according to weight percentage, place the raw materials in an electric furnace, smelt to a temperature of 1590℃ and then blow oxygen to decarburize, then continue smelting to a temperature of 1620-1640℃ and tap out the steel to obtain molten steel, and then cast the molten steel into steel ingots. S2. Forging: The steel ingot obtained in step S1 is forged into forgings by upsetting and drawing using an air hammer and a press; S3. Heat treatment: The forgings obtained in step S2 are placed in an industrial resistance furnace for two heat treatments to obtain martensitic stainless steel forgings for pressurized water reactor turbine regulating valves. S4. Inspection: Perform physical and chemical tests and non-destructive tests on the martensitic stainless steel forgings for pressurized water reactor turbine control valves obtained in step S3.

3. The method for manufacturing a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve according to claim 2, characterized in that: In step S2, the cutting ratio of the ingot head is 10%, and the cutting ratio of the ingot tail is 5%.

4. The manufacturing method of a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve according to claim 2, characterized in that: In step S2, the initial forging temperature is 1110-1130℃, the final forging temperature is 850-880℃, and the total forging ratio is ≥5.

5.

5. A method for manufacturing a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve according to claim 2, characterized in that: In step S3, the first heat treatment process is as follows: heat to 1010-1030℃ for quenching, hold for 5-6 hours and then water cool; heat to 605-615℃ for tempering, hold for 3-4 hours and then water cool.

6. A method for manufacturing a martensitic stainless steel forging for a pressurized water reactor turbine regulating valve according to claim 2, characterized in that: In step S3, the second heat treatment process is as follows: heat to 970-980℃ for quenching, hold for 5-6 hours and then water cool; heat to 315-325℃ for tempering, hold for 3-4 hours and then water cool; heat to 315-325℃ for tempering, hold for 3-4 hours and then water cool.