A 2Cr 12 Ni4Mo3VNbN stainless steel materials, their heat treatment methods, and turbine blades

Abstract

The application provides a 2Cr 12 Ni4Mo3VNbN stainless steel material, a heat treatment method thereof and a steam turbine blade, and belongs to the technical field of high alloy steel materials. The heat treatment method comprises the following steps: (1) the 2Cr 12 Ni4Mo3VNbN stainless steel material is heated to above 930 DEG C in an annealing furnace and is kept for at least 6 hours, and then is cooled to room temperature; (2) the steel sample obtained in the step (1) is continuously heated to 680-700 DEG C in the furnace and is kept for 4-12 hours, and then is cooled to room temperature; (3) the steel sample obtained in the step (2) is continuously heated to 680-700 DEG C in the furnace and is kept for4-12 hours, and then is cooled to room temperature. The heat treatment method can effectively reduce the hardness of the 2Cr 12 Ni4Mo3VNbN stainless steel material, so that the hardness of the delivery state can meet the requirements of the user, the supply conditions are met, and technical support is provided for steel enterprises to realize large-scale production and stable supply.

Description

Technical Field

[0001] This invention belongs to the technical field of high alloy steel materials, specifically relating to a 2Cr... 12 Ni4Mo3VNbN stainless steel materials, their heat treatment methods, and turbine blades. Background Technology

[0002] Steam turbine blades are one of the core components of a steam turbine, converting the kinetic energy of steam into mechanical energy. The last-stage blades are the longest and bear the heaviest centrifugal loads, thus requiring extremely high material properties. This is especially true for the 1200mm-class last-stage blades used in full-speed steam turbines in megawatt-class nuclear power plants, where the centrifugal load reaches approximately 500 tons, requiring the stainless steel material to have a yield strength of at least 1050 MPa.

[0003] However, the last-stage blades of current subcritical and supercritical steam turbine units use 1Cr... 12 Ni2W1Mo1V stainless steel material or 1Cr 12 The yield strength of Ni3Mo2VN stainless steel is insufficient to meet the design requirements of the 1200mm-class last-stage blades for a full-speed steam turbine in a megawatt-class nuclear power plant. Therefore, researchers specifically developed a 12%Cr series, graded 2Cr. 12 Martensitic stainless steel material of Ni4Mo3VNbN. For example, patent application CN 101117690A discloses a steel material and its heat treatment process for long blades of the last stage of high-power steam turbine units. It uses 12% Cr-Ni-Mo-V-Nb-N steel alloy material to manufacture 1200mm-grade last stage steel blades for high-power steam turbine units, which meets the needs of manufacturing 1200mm-grade last stage steel blades for high-power steam turbine units. Summary of the Invention

[0004] This invention is based on the inventor's discovery and understanding of the following facts and problems: To facilitate subsequent processing into finished products, users currently generally require 2Cr... 12 The delivered hardness of Ni4Mo3VNbN stainless steel cannot exceed 280 HBW. However, the actual hardness of 2Cr stainless steel produced by major steel mills... 12The hardness of Ni4Mo3VNbN stainless steel is generally too high. For example, the hardness of 12% Cr-Ni-Mo-V-Nb-N steel alloy material, hot-rolled or hot-forged as described in patent application CN 101117690A, is 42-47 HRC (equivalent to 400-450 HBW), which does not meet user requirements. Furthermore, the heat treatment method in patent application CN101117690A is a final heat treatment, aimed at modulating the comprehensive properties of the finished steel through quenching and tempering to meet application requirements, rather than a pre-treatment method, and therefore cannot reduce the hardness of hot-rolled or hot-forged semi-finished steel. Therefore, there is an urgent need to design a method to reduce the hardness of 2Cr... 12 The heat treatment method for Ni4Mo3VNbN hardness can perform pre-heat treatment on forged or rolled semi-finished steel to reduce the hardness of the steel in the supply state to below 280HBW, so as to meet the supply conditions and facilitate the user's subsequent processing into finished steel, and prepare for the final heat treatment (quenching and tempering).

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a 2Cr... 12 The heat treatment method for Ni4Mo3VNbN stainless steel can transform 2Cr 12 The supply hardness of Ni4Mo3VNbN stainless steel is reduced to below 280HBW.

[0006] 2Cr of the present invention 12 The heat treatment method for Ni4Mo3VNbN stainless steel includes the following steps:

[0007] (1) Forging or rolling 2Cr 12 Ni4Mo3VNbN stainless steel material is heated to above 930°C in an annealing furnace and held at that temperature for at least 6 hours, and then cooled to room temperature.

[0008] (2) The steel sample obtained in step (1) is heated to 680-700℃ in the furnace and held for 4-12 hours, and then cooled to room temperature;

[0009] (3) The steel sample obtained in step (2) is heated to 680-700℃ in the furnace and held for 4-12 hours, and then cooled to room temperature.

[0010] 2Cr of the present invention 12 The advantages and technical effects of the heat treatment method for Ni4Mo3VNbN stainless steel are as follows: 2Cr stainless steel obtained by the heat treatment method of this invention... 12The Ni4Mo3VNbN stainless steel material has a hardness below 280HBW, which solves the defect that the hardness of the martensitic blade steel on site is too high and does not meet the user's requirements, and provides technical support for steel companies to achieve large-scale production and stable supply.

[0011] In some embodiments, in step (1), 2Cr is forged or rolled into shape. 12 The Ni4Mo3VNbN stainless steel material is replaced with 2Cr steel that has been forged or rolled and then annealed. 12 Ni4Mo3VNbN stainless steel material.

[0012] In some embodiments, in step (1), the heat preservation temperature is 930-950℃; and / or the heat preservation time is 6-8h.

[0013] In some embodiments, in step (1), the cooling method is furnace cooling.

[0014] In some embodiments, in steps (2) and (3), the heat preservation temperature is 680-690℃; and / or the heat preservation time is 4-8h.

[0015] In some embodiments, in steps (2) and (3), the cooling method is air cooling.

[0016] This invention also provides a 2Cr 12 The Ni4Mo3VNbN stainless steel material is prepared by the heat treatment method of the present invention.

[0017] 2Cr of the present invention 12 The advantages and technical effects of Ni4Mo3VNbN stainless steel material are as follows: 2Cr in the embodiment of this invention 12 The hardness of Ni4Mo3VNbN stainless steel is below 280HBW, which meets user requirements and provides technical support for steel companies to achieve large-scale production and stable supply.

[0018] In some embodiments, the 2Cr 12 The hardness of Ni4Mo3VNbN stainless steel is below 280HBW.

[0019] This invention also provides a turbine blade, which is made of 2Cr according to this invention. 12 Ni4Mo3VNbN stainless steel material was prepared.

[0020] The advantages and technical effects of the turbine blades in this invention are as follows: the turbine blades in this invention have high yield strength, tensile strength and toughness, and excellent comprehensive performance.

[0021] In some embodiments, the turbine blades are 1200mm-class last-stage blades of a full-speed turbine in a megawatt nuclear power plant. Attached Figure Description

[0022] Figure 1 2Cr is an embodiment of the present invention. 12 A graph showing the heat treatment methods for Ni4Mo3VNbN stainless steel.

[0023] Figure 2 2Cr is an embodiment of the present invention. 12 Hardness test photos of the heat-treated object in the heat treatment method of Ni4Mo3VNbN stainless steel.

[0024] Figure 3 2Cr as described in Example 2 of this invention 12 Hardness test photos of Ni4Mo3VNbN stainless steel samples obtained after heat treatment.

[0025] Figure 4 2Cr as described in Example 10 of the present invention 12 Hardness test photos of Ni4Mo3VNbN stainless steel samples obtained after heat treatment. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] This invention provides a 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel includes the following steps:

[0028] (1) Forging or rolling 2Cr 12 Ni4Mo3VNbN stainless steel material is heated to above 930°C in an annealing furnace and held at that temperature for at least 6 hours, and then cooled to room temperature.

[0029] (2) The steel sample obtained in step (1) is heated to 680-700℃ in the furnace and held for 4-12 hours, and then cooled to room temperature;

[0030] (3) The steel sample obtained in step (2) is heated to 680-700℃ in the furnace and held for 4-12 hours, and then cooled to room temperature.

[0031] Working principle: The heat treatment method of this invention adopts a "three-step method" for 2Cr 12The semi-finished Ni4Mo3VNbN martensitic steel is heat-treated to reduce its delivery hardness. First, in step (1), austenitization is performed above Ac3 to obtain a matrix structure with certain strength and hardness. Then, in steps (2) and (3), two-step annealing treatment is carried out, and the steel is held at a certain temperature in the two-phase region for a certain time to reduce the hardness of the stainless steel. The hardness of the steel sample obtained by the heat treatment method of this embodiment is below 280HBW, which solves the defect that the hardness of the martensitic blade steel on site is too high and does not meet the user's requirements. This facilitates the user's subsequent processing of the steel and prepares it for the final heat treatment (quenching and tempering). This provides technical support for steel companies to achieve large-scale production and stable supply.

[0032] The heat treatment method of this invention can be applied to forged or rolled 2Cr12Ni4Mo3VNbN semi-finished products, or to substandard products that have undergone other annealing treatments but still have a hardness higher than 280HBW (e.g., the product of the comparative example of this invention). Since the heat treatment process in step (1) has already removed the 2Cr... 12 The original microstructure of Ni4Mo3VNbN semi-finished product is re-austenitized, so the original microstructure will no longer affect the subsequent two annealing treatments. Therefore, whether the state of the processed object in step (1) is forged, rolled, or heat-treated is not important and will not affect the application and implementation of the technical solution of the present invention.

[0033] In the heat treatment method of this embodiment of the invention, when the holding temperature in step (1) is lower than 930°C or the holding time is lower than 6 hours, the 2Cr obtained by heat treatment... 12 The hardness of Ni4Mo3VNbN stainless steel is higher than the target value of 280HBW. Considering the current status of the steel plant equipment, the maximum temperature that the annealing furnace can withstand is no higher than 950℃. Preferably, in step (1), the holding temperature is 930-950℃. In order to reduce costs and increase efficiency, preferably, in step (1), the holding time is 6-8h.

[0034] The heat treatment method of this invention does not have any particular limitation on the cooling method in step (1). For example, furnace cooling, air cooling, oil cooling, water cooling, air cooling, cooling bed cooling, etc. can be used. Steel plant site uses furnace cooling and air cooling for control. Therefore, considering the current status of steel plant equipment, it is preferable to select furnace cooling as the cooling method in step (1).

[0035] In the heat treatment method of this embodiment of the invention, when the holding temperature in steps (2) and (3) is lower than 680°C or higher than 700°C, the 2Cr obtained by heat treatment... 12 The hardness of Ni4Mo3VNbN stainless steel is higher than the target value of 280HBW. Considering cost reduction and efficiency improvement, preferably, the heat preservation temperature in steps (2) and (3) is 680-690℃.

[0036] In the heat treatment method of this embodiment of the invention, when the holding time in steps (2) and (3) is less than 4 hours or more than 12 hours, the 2Cr obtained by heat treatment... 12 The hardness of Ni4Mo3VNbN stainless steel is higher than the target value of 280HBW. Considering cost reduction and efficiency improvement, preferably, the heat preservation time in steps (2) and (3) is 4-8 hours.

[0037] The heat treatment method of this invention does not have any particular limitation on the cooling method in steps (2) and (3). For example, furnace cooling, air cooling, oil cooling, water cooling, air cooling, cooling bed cooling, etc. can be used. Steel plant site is controlled by furnace cooling and air cooling. Therefore, considering the current status of steel plant equipment, preferably, air cooling is selected as the cooling method in steps (2) and (3).

[0038] It should be noted that the parameters such as heat preservation temperature, heat preservation time, and cooling method in step (3) can be the same as or different from the parameters in step (2).

[0039] This invention also provides a 2Cr 12 The Ni4Mo3VNbN stainless steel material is prepared by the heat treatment method of the present invention.

[0040] 2Cr of the present invention 12 The hardness of Ni4Mo3VNbN stainless steel is below 280HBW, which meets user requirements and provides technical support for steel companies to achieve large-scale production and stable supply.

[0041] This invention also provides a turbine blade, which is made of 2Cr according to this invention. 12 Ni4Mo3VNbN stainless steel material was prepared.

[0042] 2Cr of the present invention 12 Ni4Mo3VNbN stainless steel can be used as turbine blade steel, especially for manufacturing the 1200mm-class last-stage blades of full-speed turbines in megawatt nuclear power plants. Turbine blades have high yield strength, tensile strength and toughness, and excellent comprehensive performance.

[0043] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0044] The heat treatment methods in the following embodiments and comparative examples are used for forging 2Cr steel. 12The semi-finished Ni4Mo3VNbN martensitic blade steel is prepared by the following method: after the ingot is refined by smelting equipment, it is first cast and solidified into a billet, and then cooled to room temperature. Then it is precision forged in one heat, with the initial forging temperature above 950℃, the final forging temperature above 850℃, and the final forging target temperature above 900℃. After forging, it is cooled to below 280℃ on a cooling bed, and then air-cooled to below 60℃ to forge martensitic blade steel into bars of the size specified by the user.

[0045] Example 1

[0046] A 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel includes the following steps:

[0047] (1) Forging 2Cr 12 Ni4Mo3VNbN stainless steel material was heated to 950℃ in an annealing furnace and held for 6 hours. After holding, the furnace was cooled to room temperature.

[0048] (2) The steel sample obtained in step (1) is heated to 680°C in the furnace and held for 4 hours. After the holding period, it is air-cooled to room temperature.

[0049] (3) The steel sample obtained in step (2) is heated to 680°C in the furnace and kept at that temperature for 4 hours. After the holding time is over, it is air-cooled to room temperature.

[0050] Example 2

[0051] The 2Cr in this embodiment and in Embodiment 1 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that in steps (2) and (3), the holding temperature is 700℃ and the holding time is 12h.

[0052] Example 3

[0053] The 2Cr in this embodiment and in Embodiment 1 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the heat treatment time in step (1) is 8 hours.

[0054] Example 4

[0055] The 2Cr in this embodiment and in Embodiment 1 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding temperature in step (1) is 930℃.

[0056] Example 5

[0057] The 2Cr in this embodiment and Embodiment 2 12The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding temperature in step (1) is 930℃.

[0058] Example 6

[0059] The 2Cr in this embodiment and in Embodiment 1 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding time in steps (2) and (3) is 12h.

[0060] Example 7

[0061] The 2Cr in this embodiment and in Embodiment 1 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that in steps (2) and (3), the holding temperature is 700℃ and the holding time is 4h.

[0062] Comparative Example 1

[0063] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding temperature in step (1) is 890℃.

[0064] Comparative Example 2

[0065] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the heat treatment time in step (1) is 4 hours.

[0066] Comparative Example 3

[0067] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding temperature is 660℃ in steps (2) and (3).

[0068] Comparative Example 4

[0069] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding temperature is 750℃ in steps (2) and (3).

[0070] Comparative Example 5

[0071] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding time in steps (2) and (3) is 2 hours.

[0072] Comparative Example 6

[0073] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding time in steps (2) and (3) is 24h.

[0074] Comparative Example 7

[0075] The comparative example and Example 3 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding temperature in step (1) is 910℃.

[0076] Comparative Example 8

[0077] The comparative example and Example 2 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the holding temperature in step (1) is 890℃.

[0078] Comparative Example 9

[0079] The comparative example of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel includes the following steps:

[0080] (1) Forging 2Cr 12 Ni4Mo3VNbN stainless steel material was heated to 950℃ in the furnace and held for 4 hours. After holding, the furnace was cooled to room temperature.

[0081] (2) The steel sample obtained in step (1) is heated to 680°C in the furnace and held for 4 hours. After the holding period, it is air-cooled to room temperature.

[0082] (3) The steel sample obtained in step (2) is heated to 680°C in the furnace and held for 4 hours. After the holding period, it is air-cooled to room temperature.

[0083] (4) The steel sample obtained in step (3) is heated to 950°C in the furnace and held for 4 hours. After the holding period, the furnace is cooled to room temperature. Then the steel sample is heated to 680°C in the furnace and held for 4 hours. After the holding period, the steel sample is cooled to room temperature in the air. Then the steel sample is heated to 680°C in the furnace and held for 4 hours. After the holding period, the steel sample is cooled to room temperature in the air.

[0084] Comparative Example 10

[0085] The comparative example and Example 2 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that the heat treatment time in step (1) is 4 hours.

[0086] Comparative Example 11

[0087] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that steps (2) and (3) are omitted.

[0088] Comparative Example 12

[0089] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that step (3) is omitted.

[0090] Comparative Example 13

[0091] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that in step (2), the steel sample obtained in step (1) is heated to 680°C in the furnace and held for 16 hours. After the holding is completed, it is air-cooled to room temperature. Step (3) is omitted.

[0092] Comparative Example 14

[0093] The comparative example and Example 1 of 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel is the same, except that step (4) is performed after step (3): the steel sample obtained in step (3) is heated to 680°C in the furnace and held for 4 hours. After the holding period, it is air-cooled to room temperature.

[0094] Hardness test

[0095] The holding temperatures and holding times for the heat treatment methods in each embodiment and comparative example are shown in Table 1. The heat treatment object is the forged 2Cr... 12 Ni4Mo3VNbN stainless steel material, and 2Cr obtained after heat treatment in each embodiment and comparative example. 12 The Brinell hardness of Ni4Mo3VNbN stainless steel materials was measured. The specific method for measuring Brinell hardness was as follows: an HB3000C electronic Brinell hardness tester was used, with a 5mm diameter indenter and a load of 750kg. Five measurement points were used for each sample, and the average value was taken. The Brinell hardness measurement results are shown in Table 2. The acceptance criterion was a Brinell hardness ≤ 280HBW.

[0096] Table 1. Holding temperature and holding time for the heat treatment methods of each embodiment and comparative example.

[0097]

[0098] Table 2. Heat treatment objects and heat treatment methods for 2Cr obtained in each embodiment and comparative example. 12 The hardness of Ni4Mo3VNbN stainless steel material

[0099] Heat-treated objects 523.2 - Example 1 273.8 qualified Example 2 271.9 qualified Example 3 273.8 qualified Example 4 277.8 qualified Example 5 275.5 qualified Example 6 277.4 qualified Example 7 276.9 qualified Comparative Example 1 298.9 Unqualified Comparative Example 2 310.4 Unqualified Comparative Example 3 287.4 Unqualified Comparative Example 4 303.2 Unqualified Comparative Example 5 298 Unqualified Comparative Example 6 285.8 Unqualified Comparative Example 7 287.6 Unqualified Comparative Example 8 301.3 Unqualified Comparative Example 9 314.2 Unqualified Comparative Example 10 283 Unqualified Comparative Example 11 445.2 Unqualified Comparative Example 12 308.4 Unqualified Comparative Example 13 312.4 Unqualified Comparative Example 14 284.5 Unqualified

[0100] As shown in Examples 1-7, the heat treatment object of this invention is the forged 2Cr 12 The hardness of the Ni4Mo3VNbN semi-finished product is 523.2 HBW. After undergoing the heat treatment method of this embodiment, the obtained 2Cr... 12 The hardness of Ni4Mo3VNbN stainless steel materials is all below 280HBW, which meets the pass rate judgment standard.

[0101] By comparing Example 1 and Comparative Example 1, Example 2 and Comparative Example 8, and Example 3 and Comparative Example 7, it can be seen that when the heat preservation temperature in step (1) is lower than 930℃, the obtained 2Cr 12 The hardness of Ni4Mo3VNbN stainless steel will exceed the target value of 280 HBW, resulting in a substandard product. A comparison between Example 1 and Comparative Example 2, and between Example 2 and Comparative Example 10, shows that when the holding time in step (1) is less than 6 hours, the obtained 2Cr... 12 The hardness of Ni4Mo3VNbN stainless steel will also be higher than the target value of 280HBW, and the product will be unqualified. Through the comparison of Example 1, Comparative Example 2 and Comparative Example 9, it can be seen that when the heat preservation time in step (1) is less than 6 hours, even if steps (1)-(3) are repeated, the hardness still cannot be reduced to the target value. Moreover, the process of Comparative Example 9 is too complicated, which seriously increases the cost of steel mills.

[0102] A comparison of Example 1 and Comparative Example 3 shows that when the heat preservation temperature in steps (2) and (3) is below 680℃, the obtained 2Cr 12 The hardness of the Ni4Mo3VNbN stainless steel material exceeds the target value of 280 HBW, making the product unqualified. A comparison of Example 1 and Comparative Example 4 shows that when the holding temperature in steps (2) and (3) exceeds 700℃, the obtained 2Cr... 12 The hardness of Ni4Mo3VNbN stainless steel will also exceed the target value of 280HBW, making the product unqualified.

[0103] A comparison between Example 1 and Comparative Example 5 shows that when the heat preservation time in steps (2) and (3) is less than 4 hours, the obtained 2Cr 12The hardness of Ni4Mo3VNbN stainless steel will also exceed the target value of 280HBW, resulting in a substandard product. A comparison between Example 1 and Comparative Example 6 shows that when the holding time in steps (2) and (3) exceeds 12 hours, the obtained 2Cr... 12 The hardness of Ni4Mo3VNbN stainless steel will also exceed the target value of 280HBW, making the product unqualified.

[0104] A comparison between Example 1 and Comparative Example 11 shows that performing only the heat treatment in step (1) effectively reduces the 2Cr content. 12 The hardness of Ni4Mo3VNbN stainless steel has little effect, resulting in substandard products.

[0105] A comparison between Example 1 and Comparative Example 12 shows that performing only the heat treatments in steps (1) and (2) effectively reduces the 2Cr content. 12 The hardness of Ni4Mo3VNbN stainless steel is insufficient, resulting in substandard products. The reasons are as follows: Omitting step (3) prevents the full precipitation of a large number of elements in the stainless steel, leaving a large amount of alloying elements in the stainless steel matrix, which increases the hardness of the matrix. On the other hand, in both steps (2) and (3), austenite reversal occurs, and the austenite stabilizing element Ni gradually distributes into the reversed austenite during the isothermal process. If only step (2) is performed, Ni cannot be fully distributed into the reversed austenite, causing these reversed austenites to stabilize at room temperature, thus undergoing martensitic transformation, which in turn increases the hardness, exceeding the target value of 280HBW.

[0106] A comparison between Example 1 and Comparative Example 13 shows that omitting step (3) but extending the holding time in step (2) reduces 2Cr. 12 The hardness of Ni4Mo3VNbN stainless steel is insufficient, resulting in substandard products. The reasons are as follows: Comparative Example 13 omitted step (3) but extended the holding time of step (2) to 16 hours. Although this enhances the stability of the reverse-transformed austenite, allowing it to stabilize at room temperature, it also leads to a further increase in the number of precipitates in the steel and a rapid coarsening. A large number of large-sized precipitates are formed and densely distributed in the steel matrix. As a result, the hardness of the steel is mainly controlled by these large-sized precipitates, which are hard phases. The large number of coarsened precipitates leads to an increase in hardness. Therefore, the hardness of the steel obtained by the heat treatment method of Comparative Example 13 is higher than that of Example 1.

[0107] A comparison of Example 1 and Comparative Example 14 shows that firstly, austenitizing is performed above Ac3, followed by three heat treatments and holding at a certain temperature in the two-phase region for a certain period of time, which leads to the formation of 2Cr... 12The hardness of Ni4Mo3VNbN stainless steel increases, making it impossible to control the hardness within the target range, resulting in a substandard product. The reasons are analyzed as follows: Adding step (4) to Comparative Example 14 will cause the formation of more precipitates in the steel, resulting in an extremely dense distribution of these precipitates. These densely packed precipitates are hard phases, and their large-scale presence will cause a further increase in hardness and the formation of more reverse-transformed austenite that can be stabilized at room temperature. However, these reverse-transformed austenite are soft phases, which will reduce the hardness to a certain extent. Therefore, the hardness of the steel obtained by the heat treatment method of Comparative Example 14 is higher than that of Example 1, but only slightly higher.

[0108] By comparing Comparative Examples 12 and 14, it was found that the hardness of the steel obtained by the heat treatment method of Comparative Example 14 was lower than that of Comparative Example 12. The reasons are as follows: In Comparative Example 12, step (3) was omitted and only step (2) was performed. This would result in the Ni element not being fully distributed into the reverse austenite, so that the reverse austenite would stabilize at room temperature and undergo martensitic transformation, thereby increasing the hardness to 308.4 HBW. In Comparative Example 14, step (4) was added after step (3), which further promoted the formation of reverse austenite. The Ni element would be further distributed into the reverse austenite, so that the Ni content in the reverse austenite was high enough to stabilize it at room temperature. The residual austenite, as a soft phase, would reduce the hardness of the steel to a certain extent. Therefore, the hardness of the steel obtained by the heat treatment method of Comparative Example 14 was lower than that of Comparative Example 12.

[0109] In summary, regarding the forging of 2Cr... 12 During the heat treatment of Ni4Mo3VNbN semi-finished products, a three-step heat treatment method is adopted. First, austenitization is performed above Ac3, followed by two more heat treatments, holding at a certain temperature in the two-phase region for a certain period of time. This method can control the hardness within the target range, effectively avoiding the phenomenon that the hardness is too high and cannot meet the delivery requirements, thus preventing the supply from being realized.

[0110] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0111] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A 2Cr 12 The heat treatment method for Ni4Mo3VNbN stainless steel material is characterized by... Includes the following steps: (1) Forging or rolling 2Cr 12 Ni4Mo3VNbN stainless steel material is heated to 930-950 ℃ in an annealing furnace and held for 6-8 h, then cooled to room temperature; (2) The steel sample obtained in step (1) is heated to 680-700 ℃ in the furnace and held for 4-12 h, and then cooled to room temperature; (3) The steel sample obtained in step (2) is further heated in the furnace to 680-700 ℃ and held for 4-12 h, then cooled to room temperature, and the resulting 2Cr steel is heat-treated. 12 The hardness of Ni4Mo3VNbN stainless steel is below 280HBW.

2. The 2Cr according to claim 1 12 The heat treatment method for Ni4Mo3VNbN stainless steel material is characterized by... In step (1), 2Cr is forged or rolled. 12 The Ni4Mo3VNbN stainless steel material is replaced with 2Cr steel that has been forged or rolled and then annealed. 12 Ni4Mo3VNbN stainless steel material.

3. The 2Cr according to claim 1 or 2 12 The heat treatment method for Ni4Mo3VNbN stainless steel material is characterized by... In step (1), the cooling method is furnace cooling.

4. The 2Cr according to claim 1 or 2 12 The heat treatment method for Ni4Mo3VNbN stainless steel material is characterized by... In steps (2) and (3), the heat preservation temperature is 680-690 ℃; and / or the heat preservation time is 4-8 h.

5. The 2Cr according to claim 1 or 2 12 The heat treatment method for Ni4Mo3VNbN stainless steel material is characterized by... In steps (2) and (3), the cooling method is air cooling.

6. A 2Cr 12 Ni4Mo3VNbN stainless steel material, characterized in that... It is prepared by the heat treatment method according to any one of claims 1-5.

7. A steam turbine blade, characterized in that, The 2Cr as described in claim 6 12 Ni4Mo3VNbN stainless steel material was prepared.

8. The turbine blade according to claim 7, characterized in that, The turbine blades are the 1200mm-class final stage blades of a full-speed turbine in a megawatt nuclear power plant.

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