Processing method of anti-cold brittle CrNiMo material turbine impeller forging

Abstract

The application discloses a processing method of a cold brittle resistant CrNiMo material steam turbine impeller forge piece, obtains a cold brittle resistant CrNiMo material, and obtains the steam turbine impeller forge piece through forging treatment of the material, so that the cold brittle resistant requirement of the forge piece is FATT50 <=-70 DEG C, and the steam turbine impeller with better performance is manufactured. It comprises the following steps: S1; obtaining the steel ingot corresponding to the cold brittle resistant 27Cr2Ni3MoV material through refining; S2, forming the cold brittle resistant CrNiMo material steam turbine impeller forge piece from the steel ingot; the processing steps of step S2 are as follows: S21, heating the steel ingot; S22, opening the round billet; S23, annealing; S24, sawing and cutting; S25, heating the block; S26, forging; S27, normalizing and tempering; S28, rough turning, which is used for removing surface defects; S29, UT, verifying internal defects in advance, and the internal defects must not be overproof; S210, quenching and tempering; S211, performance detection; and S212, machining.

Description

Technical Field

[0001] This invention relates to the technical field of heat treatment of alloy structural steel, specifically to a processing method for turbine impeller forgings made of CrNiMo material resistant to cold brittleness. Background Technology

[0002] In my country's JB / T 1266-2014 standard "Technical Conditions for Forgings of Steam Turbine Discs and Impellers for 25MW~200MW", the material grade used for impeller forgings is 30Cr2Ni4MoV. The cold brittleness resistance of impeller forgings is characterized by the ductile-brittle transition temperature FATT50, which corresponds to FATT50≤-30℃. FATT50 is an indicator of impact resistance. If a series of impact tests are conducted on a metallic material at various temperatures (for example, every 20℃) within a normally preset temperature range, the proportion of crystalline fracture surfaces on the fracture surface of the impact specimen will increase as the temperature decreases, meaning the toughness of the material will continuously decrease. FATT50 refers to the temperature at which crystalline fracture surfaces occupy 50% of the area on the fracture surface of the impact specimen, and is called the ductile-brittle transition temperature. As an example of the definition of FATT50, the test result FATT50=-56℃ is shown in Table 1.

[0003]

[0004] Table 1 Examples of FATT50 Definitions

[0005] With the continuous changes in the working environment of steam turbines, the cold brittleness resistance requirement for steam turbine impeller forgings is FATT50≤-70℃, which is far higher than the FATT50≤-30℃ of the JB / T 1266-2014 standard. Therefore, it is urgent to develop a cold brittleness resistant CrNiMo material steam turbine impeller forging. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for processing turbine impeller forgings made of CrNiMo material resistant to cold brittleness. The method yields a CrNiMo material resistant to cold brittleness, and then forges this material to obtain turbine impeller forgings. The forgings meet the cold brittleness resistance requirement of FATT50 ≤ -70℃, making them suitable for manufacturing turbine impellers with better performance.

[0007] A method for machining turbine impeller forgings made of CrNiMo material resistant to cold brittleness, characterized in that it includes:

[0008] S1; Obtain the steel ingot corresponding to the cold-brittle resistant 27Cr2Ni3MoV material through refining;

[0009] S2. The steel ingot is used to form a steam turbine impeller forging made of CrNiMo material resistant to cold brittleness;

[0010] The processing steps in step S2 are as follows:

[0011] S21. Steel ingot heating;

[0012] S22, Rounded blank

[0013] S23, Annealing

[0014] S24. Sawing and cutting

[0015] S25, Block heating

[0016] S26, Forging

[0017] S27, Normalizing and Tempering

[0018] S28, rough turning, used to remove surface defects;

[0019] S29, UT: Verify internal defects in advance; they must not exceed the standard.

[0020] S210, tempering

[0021] S211, Performance Testing

[0022] S212, Machining.

[0023] Its further features are:

[0024] The turbine impeller forgings made of CrNiMo material, which is resistant to cold brittleness, are forged from 27Cr2Ni3MoV material. The final mass percentages of each element are as follows: Carbon (C): 0.25%–0.29%, Silicon (Si): ≤0.30%, Manganese (Mn): 0.50%–0.75%, Chromium (Cr): 1.50%–1.80%, Nickel (Ni): 2.50%–3.50%, Molybdenum (Mo): 0.30%–0.60%. Vanadium (V): 0.08%–0.15%, Copper (Cu): ≤0.15%, Phosphorus (P): ≤0.010%, Sulfur (S): ≤0.005%, Arsenic (As): ≤0.012%, Tin (Sn): ≤0.012%, Antimony (Sb): ≤0.003%, Lead (Pb): ≤0.010%, Bismuth (Bi): ≤0.010%, Calcium (Ca): ≤0.010%, H ≤2ppm, O ≤35ppm, N ≤90ppm, with the remainder being Iron (Fe).

[0025] The mechanical properties of the obtained cold-brittle resistant 27Cr2Ni3MoV material turbine impeller forgings are as follows: tensile strength Rm ranges from 900 to 1050 MPa, yield strength Rel ranges from ≥760 MPa, elongation after fracture A ranges from ≥13%, reduction of area Ψ ranges from ≥40%, Charpy impact test KV2 absorbed energy at 20℃ is ≥60 J, and FATT50 is ≤-70℃.

[0026] Its further characteristic is:

[0027] In step S21, when heating the steel ingot, its furnace loading temperature is ≤600℃, the heating rate is ≤120℃ / hour, and it is heated to 1230℃ and held at that temperature. The holding time is calculated based on the average thickness of the steel ingot. The holding time = (120 minutes + 30 minutes / 100mm thickness) ±30 minutes. That is, based on 120 minutes, for every 100mm increase in thickness, the total time increases by 30 minutes, and the fluctuation of the holding time is ±30 minutes.

[0028] During annealing in step S23, the holding time at 620-680℃ is (120 min + 40 min / 100 mm thickness) ± 30 min. After furnace cooling to ≤ 400℃, the furnace is removed and air-cooled. The holding time is based on 120 min, with the total time increasing by 40 min for every 100 mm increase in thickness, and the fluctuation of the holding time is ± 30 min.

[0029] When heating the block material in step S25, the furnace temperature should be ≤600℃, the heating rate should be ≤120℃ / hour, and the temperature should be held at 1230℃. The holding time is calculated based on the average thickness. The holding time = (120 minutes + 30 minutes / 100mm thickness) ±30 minutes. That is, the holding time is based on 120 minutes. For every 100mm increase in thickness, the total time increases by 30 minutes, and the fluctuation of the holding time is ±30 minutes.

[0030] The specific process of forging in step S26 is as follows: upsetting → drawing → upsetting → rotary pressing → rounding → forming. The total upsetting forging ratio is ≥4:1, the total drawing forging ratio is ≥5:1, the forging ratio of the last forging pass is ≥2.5 times the critical deformation degree, the forging ratio is set to 2.5~3.5, the final forging temperature is ≥800℃, and after forging, it is air-cooled to 500-250℃ and then normalized in the furnace.

[0031] In step S27, during normalizing and tempering, the normalizing temperature is maintained at 860-960℃ for a time of (120 minutes + 40 minutes / 100mm thickness) ± 30 minutes. That is, the holding time is based on 120 minutes, and for every 100mm increase in thickness, the total time increases by 40 minutes, with a fluctuation of ± 30 minutes. After that, the furnace is removed and air-cooled to 350-200℃, then put back into the furnace for tempering. The tempering temperature is maintained at 600-680℃ for a time of (120 minutes + 100 minutes / 100mm thickness) ± 30 minutes. That is, the holding time is based on 120 minutes, and for every 100mm increase in thickness, the total time increases by 100 minutes, with a fluctuation of ± 30 minutes. After that, the furnace is removed and air-cooled to room temperature.

[0032] Step S210: Tempering. During the tempering heat treatment process, the impeller forging is vertically mounted and subjected to double-liquid quenching using water followed by quenching liquid. During quenching, the furnace temperature is ≤600℃, the heating rate is ≤80℃ / hour, and the temperature is raised to 820-900℃ and held. The holding time is calculated based on the average thickness: Holding time = (120 minutes + 30 minutes / 100mm thickness) ± 30 minutes. That is, the holding time is based on 120 minutes, with an increase of 30 minutes for every 100mm increase in thickness, and the fluctuation of the holding time is ±30 minutes. Afterwards, the forging is removed from the furnace and quenched within 100 seconds. For water quenching, after water cooling to a surface temperature ≤500℃, immediately transfer the forging into the quenching liquid for cooling until it reaches 250-150℃. Then, remove it from the quenching liquid and place it in a tempering furnace. During tempering, the heating rate should be ≤80℃ / hour. Heat to 620-660℃ and hold for 120 minutes. The holding time is calculated based on the average thickness. The holding time = (120 minutes + 100 minutes / 100mm thickness) ± 30 minutes. That is, the holding time is based on 120 minutes. For every 100mm increase in thickness, the total time increases by 100 minutes, and the fluctuation of the holding time is ±30 minutes. After that, remove it from the furnace and air cool to room temperature.

[0033] By adopting the above technical solution and formulating a reasonable matching of steel ingot base material composition, the martensitic toughening ability and resistance to temper brittleness of the material are improved, resulting in a cold-brittle-resistant 27Cr2Ni3MoV material. Then, the steel ingot corresponding to the cold-brittle-resistant 27Cr2Ni3MoV material is processed through the following steps: ingot heating → billet preparation → annealing → sawing → block heating → forging → normalizing and tempering → rough turning → UT → quenching and tempering → performance testing → machining to obtain a cold-brittle-resistant CrNiMo material turbine impeller forging. This improves the cold-brittle resistance of the forging, achieving a ductile-brittle transition temperature (FATT50) ≤ -70℃. A cold-brittle-resistant CrNiMo material is obtained, and this material is then forged to obtain a turbine impeller forging, achieving the cold-brittle resistance requirement of FATT50 ≤ -70℃, which is used to manufacture turbine impellers with better performance. Detailed Implementation

[0034] A machining method for turbine impeller forgings made of CrNiMo material resistant to cold brittleness includes the following steps:

[0035] S1; Obtain the steel ingot corresponding to the cold-brittle resistant 27Cr2Ni3MoV material through refining;

[0036] Electric Arc Furnace (EAF) Primary Refining → Ladle Refining → Vacuum Degassing Furnace (VD) Degassing → Ar Gas Protected Casting → Annealing → Surface Cleaning → Marking

[0037] S2. The steel ingot is used to form a steam turbine impeller forging made of CrNiMo material resistant to cold brittleness;

[0038] S21. Steel ingot heating: furnace loading temperature ≤ 600℃, heating rate ≤ 120℃ / hour, heating to 1230℃ and holding for a period of time. The holding time is calculated based on the average thickness of the steel ingot. Holding time = (120 minutes + 30 minutes / 100mm thickness) ± 30 minutes. That is, based on 120 minutes, for every 100mm increase in thickness, the total time increases by 30 minutes, and the fluctuation of the holding time is ± 30 minutes.

[0039] S22, round billet, forging ratio ≥3:1;

[0040] S23. Annealing: Hold at 620-680℃ for (120 min + 40 min / 100 mm thickness) ± 30 min, then cool in the furnace to ≤ 400℃, and air cool after removal from the furnace. The holding time is based on 120 min, with an increase of 40 min for every 100 mm increase in thickness, and the holding time fluctuates by ± 30 min.

[0041] S24. Sawing and cutting: According to the process weight, the round billet is sawn into several segments of block material;

[0042] S25. For block material heating, the furnace loading temperature is ≤600℃, the heating rate is ≤120℃ / hour, and the temperature is held at 1230℃. The holding time is calculated based on the average thickness. The holding time = (120 minutes + 30 minutes / 100mm thickness) ±30 minutes. That is, the holding time is based on 120 minutes. For every 100mm increase in thickness, the total time increases by 30 minutes, and the fluctuation of the holding time is ±30 minutes.

[0043] S26. Forging, the specific process is upsetting → drawing → upsetting → rotary pressing → rounding → forming. The total upsetting forging ratio is ≥4:1, the total drawing forging ratio is ≥5:1, the forging ratio of the last forging pass is ≥2.5 times the critical deformation degree, the forging ratio is set to 2.5~3.5, the final forging temperature is ≥800℃, after forging, air cool to 500-250℃, and then normalize in the furnace.

[0044] S27. Normalizing and tempering: The normalizing temperature is maintained at 860-960℃ for a time of (120 minutes + 40 minutes / 100mm thickness) ± 30 minutes. That is, the holding time is based on 120 minutes, and the total time increases by 40 minutes for every 100mm increase in thickness, with a fluctuation of ± 30 minutes. After that, the furnace is removed and air-cooled to 350-200℃, then put into the furnace for tempering. The tempering temperature is maintained at 600-680℃ for a time of (120 minutes + 100 minutes / 100mm thickness) ± 30 minutes. That is, the holding time is based on 120 minutes, and the total time increases by 100 minutes for every 100mm increase in thickness, with a fluctuation of ± 30 minutes. After that, the furnace is removed and air-cooled to room temperature.

[0045] S28, rough turning, used to remove surface defects;

[0046] S29, UT: Verify internal defects in advance; they must not exceed the standard.

[0047] S210. Quenching and tempering: During the quenching and tempering heat treatment process, the impeller forging is installed vertically and subjected to double-liquid quenching using water followed by quenching liquid. During quenching, the furnace loading temperature is ≤600℃, the heating rate is ≤80℃ / hour, and the temperature is raised to 820-900℃ and held. The holding time is calculated based on the average thickness, and the holding time = (120 minutes + 30 minutes)

[0048] The holding time is calculated as follows: (120 minutes + 100 minutes / 100mm thickness) ± 30 minutes. This means that the holding time is increased by 30 minutes for every 100mm increase in thickness, based on a base of 120 minutes, with a fluctuation of ±30 minutes. Afterward, the forging is removed from the furnace and quenched. Within 100 seconds of removal from the furnace, the forging must be water-quenched until the surface temperature reaches ≤500℃. Immediately afterward, the forging is transferred to a quenching liquid for further cooling until it reaches 250-150℃. Then, it is removed from the quenching liquid and placed in a tempering furnace. During tempering, the heating rate is ≤80℃ / hour, and the temperature is raised to 620-660℃ and held. The holding time is calculated based on the average thickness: Holding Time = (120 minutes + 100 minutes / 100mm thickness) ± 30 minutes. This means that the holding time is increased by 100 minutes for every 100mm increase in thickness, based on a base of 120 minutes, with a fluctuation of ±30 minutes. Afterward, the forging is removed from the furnace and air-cooled to room temperature.

[0049] S211, Performance testing, including tensile testing, impact testing, and FATT50 testing;

[0050] S212. Machining, according to the delivery drawings.

[0051] The turbine impeller forgings made of CrNiMo material, which is resistant to cold brittleness, are forged from 27Cr2Ni3MoV material. The final mass percentages of each element are as follows: Carbon (C): 0.25%–0.29%, Silicon (Si): ≤0.30%, Manganese (Mn): 0.50%–0.75%, Chromium (Cr): 1.50%–1.80%, Nickel (Ni): 2.50%–3.50%, Molybdenum (Mo): 0.30%–0.60%. Vanadium (V): 0.08%–0.15%, Copper (Cu): ≤0.15%, Phosphorus (P): ≤0.010%, Sulfur (S): ≤0.005%, Arsenic (As): ≤0.012%, Tin (Sn): ≤0.012%, Antimony (Sb): ≤0.003%, Lead (Pb): ≤0.010%, Bismuth (Bi): ≤0.010%, Calcium (Ca): ≤0.010%, H ≤2ppm, O ≤35ppm, N ≤90ppm, with the remainder being Iron (Fe).

[0052] The mechanical properties of the obtained cold-brittle resistant 27Cr2Ni3MoV material turbine impeller forgings are as follows: tensile strength Rm ranges from 900 to 1050 MPa, yield strength Rel ranges from ≥760 MPa, elongation after fracture A ranges from ≥13%, reduction of area Ψ ranges from ≥40%, Charpy impact test KV2 absorbed energy at 20℃ is ≥60 J, and FATT50 is ≤-70℃.

[0053] By adopting the above technical solution and formulating a reasonable matching of steel ingot base material composition, the martensitic toughening ability and resistance to temper brittleness of the material are improved, resulting in a cold-brittle-resistant 27Cr2Ni3MoV material. Then, the steel ingot corresponding to the cold-brittle-resistant 27Cr2Ni3MoV material is processed through the following steps: ingot heating → billet preparation → annealing → sawing → block heating → forging → normalizing and tempering → rough turning → UT → quenching and tempering → performance testing → machining to obtain a cold-brittle-resistant CrNiMo material turbine impeller forging. This improves the cold-brittle resistance of the forging, achieving a ductile-brittle transition temperature (FATT50) ≤ -70℃. A cold-brittle-resistant CrNiMo material is obtained, and this material is then forged to obtain a turbine impeller forging, achieving the cold-brittle resistance requirement of FATT50 ≤ -70℃, which is used to manufacture turbine impellers with better performance.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0055] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for machining turbine impeller forgings made of CrNiMo material resistant to cold brittleness, characterized in that, It includes: S1; Obtain the steel ingot corresponding to the cold-brittle resistant 27Cr2Ni3MoV material through refining; S2. The steel ingot is used to form a steam turbine impeller forging made of CrNiMo material resistant to cold brittleness; The processing steps in step S2 are as follows: S21. Steel ingot heating; S22, rounded blank; S23. Annealing: During annealing, the holding time at 620-680℃ is (120 min + 40 min / 100 mm thickness) ± 30 min. After furnace cooling to ≤ 400℃, the furnace is removed and air-cooled. The holding time is based on 120 min, and for every 100 mm increase in thickness, the total time increases by 40 min, with a fluctuation of ± 30 min in the holding time. S24. Sawing and cutting the material; S25, block material heating; S26, Forging; S27, normalizing and tempering: normalizing is held at 860-960℃ for (120 min + 40 min / 100 mm thickness) ± 30 min, then removed from the furnace and air-cooled to 350-200℃, then put back into the furnace for tempering: tempering is held at 600-680℃ for (120 min + 100 min / 100 mm thickness) ± 30 min, then removed from the furnace and air-cooled to room temperature; S28, rough turning, used to remove surface defects; S29, UT: Verify internal defects in advance; they must not exceed the standard. S210, tempering, adopts a two-liquid quenching process of water first and then quenching liquid. During quenching, the furnace temperature is ≤600℃, heated to 820-900℃ and held, and then quenched after being taken out of the furnace. The forgings should be quenched in water within 100 seconds after being taken out of the furnace. After water cooling to the surface temperature ≤500℃, the forgings should be immediately transferred to the quenching liquid for cooling until the temperature reaches 250-150℃. Then, they should be taken out of the quenching liquid and put into the tempering furnace, heated to 620-660℃ and held. S211, Performance Testing; S212, Machining; The turbine impeller forgings made of CrNiMo material, which is resistant to cold brittleness, are forged from 27Cr2Ni3MoV material, which is also resistant to cold brittleness. The final mass percentages of each element are as follows: Carbon (C): 0.25%–0.29%, Silicon (Si): ≤0.30%, Manganese (Mn): 0.50%–0.75%, Chromium (Cr): 1.50%–1.80%, Nickel (Ni): 2.50%–3.50%, Molybdenum (Mo): 0.30%–0.60%, Vanadium (V): 0.08%–0.15%, Copper (Cu): ≤0.15%, Phosphorus (P): ≤0.010%, Sulfur (S): ≤0.005%, Arsenic (As): ≤0.012%, Tin (Sn): ≤0.012%, Antimony (Sb): ≤0. 0.003%, Lead (Pb): ≤0.010%, Bismuth (Bi): ≤0.010%, Calcium (Ca): ≤0.010%, H ≤2ppm, O ≤35ppm, N ≤90ppm, the remainder being Iron (Fe).

2. The processing method for the cold-brittle CrNiMo material turbine impeller forging according to claim 1, characterized in that: The mechanical properties of the obtained cold-brittle resistant 27Cr2Ni3MoV material turbine impeller forgings are as follows: tensile strength Rm ranges from 900 to 1050 MPa, yield strength Rel ranges from ≥760 MPa, elongation after fracture A ranges from ≥13%, reduction of area Ψ ranges from ≥40%, absorbed energy in Charpy impact test KV2 at 20℃ is ≥60J, and FATT50 ≤ -70℃.

3. The processing method for the cold-brittle CrNiMo material turbine impeller forging according to claim 1, characterized in that: In step S21, when heating the steel ingot, its furnace loading temperature is ≤600℃, the heating rate is ≤120℃ / hour, and it is heated to 1230℃ and held at that temperature. The holding time is calculated based on the average thickness of the steel ingot, and the holding time is (120 minutes + 30 minutes / 100mm thickness) ± 30 minutes.

4. The processing method for the cold-brittle CrNiMo material turbine impeller forging according to claim 1, characterized in that: When heating the block material in step S25, the furnace temperature should be ≤600℃, the heating rate should be ≤120℃ / hour, and the temperature should be held at 1230℃. The holding time should be calculated based on the average thickness, and the holding time = (120 minutes + 30 minutes / 100mm thickness) ± 30 minutes.

5. The processing method for the cold-brittle CrNiMo material turbine impeller forging according to claim 1, characterized in that: The specific process of forging in step S26 is as follows: upsetting → drawing → upsetting → rotary pressing → rounding → forming. The total upsetting forging ratio is ≥4:1, the total drawing forging ratio is ≥5:1, the forging ratio of the last forging pass is ≥2.5 times the critical deformation degree, the forging ratio is set to 2.5~3.5, the final forging temperature is ≥800℃, and after forging, it is air-cooled to 500-250℃ and then normalized in the furnace.

6. The processing method of the cold-brittle CrNiMo material turbine impeller forging according to claim 1, characterized in that: Step S210: Tempering. During the tempering heat treatment process, the impeller forging is mounted vertically and subjected to double-liquid quenching using water first, followed by quenching liquid. During quenching, the heating rate is ≤80℃ / hour, and the forging is heated to 820-900℃ and held for a holding time calculated based on the average thickness: (120 min + 30 min / 100 mm thickness) ± 30 min. After that, the forging is removed from the furnace and quenched again. After water cooling to a surface temperature ≤500℃, the forging is immediately transferred to the quenching liquid for cooling until it reaches 250-150℃. Then, the forging is removed from the quenching liquid and placed in a tempering furnace. During tempering, the heating rate is ≤80℃ / hour, and the forging is heated to 620-660℃ and held for a holding time calculated based on the average thickness: (120 min + 100 min / 100 mm thickness) ± 30 min. After that, the forging is removed from the furnace and air-cooled to room temperature.

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