High-strength alloy steel rotor shaft forge piece and manufacturing method

Abstract

The invention relates to a high-strength alloy steel rotor shaft forge piece and a manufacturing method. The high-strength alloy steel rotor shaft forge piece comprises, by mass, 0.3% of C, 0.057% of Si, 0.587% of Mn, 1.207% of Cr, 1.06% of Mo, 0.576% of Ni, 0.2610% of V, 0.0029% of P, 0.0011% of S and the balance iron. Or 0.3% of C, 0.059% of Si, 0.591% of Mn, 1.208% of Cr, 1.06% of Mo, 0.574% of Ni, 0.2727% of V, 0.0026% of P, 0.0010% of S and the balance of iron. The steel has the advantages of high temperature resistance, fatigue resistance, good corrosion resistance, high strength, high toughness and excellent hardenability.

Description

Technical Field

[0001] This invention relates to a high-strength alloy steel rotor shaft forging and its manufacturing method, which not only has good high temperature resistance, fatigue resistance, and corrosion resistance, but also high strength, high toughness, and excellent hardenability, belonging to the field of rotor manufacturing. Background Technology

[0002] Rotors are widely used in steam turbines, generators, and other fields. A steam turbine is a rotary power machine that converts the energy of steam into mechanical work. It is mainly used as a prime mover for power generation, and can also directly drive various pumps, fans, compressors, and ship propellers. A generator, on the other hand, is a mechanical device that converts other forms of energy into electrical energy, and the generator rotor is the rotating part of the generator.

[0003] It is evident that the rotor shaft, as one of the key components of the rotating parts of steam turbines and generators, plays a vital role, and therefore the requirements for rotor shafts are becoming increasingly stringent. However, there is no mature technology in this area in China. Summary of the Invention

[0004] Design objective: To design a high-strength alloy steel rotor shaft forging with good high-temperature resistance, fatigue resistance, corrosion resistance, high strength, high toughness, and excellent hardenability, and a manufacturing method thereof.

[0005] Design Scheme: To achieve the above design objectives, 1. The high-strength alloy steel rotor shaft forging material is based on the alloy structural steel material 30CrMoNiV5-11 conforming to SEW555-2001 standard (see table below), and its chemical composition requirements (mass fraction, %) are further optimized: C Si Mn P S 0.28～0.34 ≤0.08 0.50～0.80 ≤0.007 ≤0.007 Cr Ni Mo V 1.20～1.40 0.50～0.75 1.05～1.20 0.25～0.35

[0006] 2. The mechanical properties of high-strength alloy steel turbine rotor shaft forgings shall be further improved on the basis of meeting the requirements of Siemens' "Steam Turbine Shaft Specification 0-2811-6946-21" (see table below): Tensile strength Rm (MPa) Yield strength Rp0.2 (MPa) Elongation A (%) Reduction of area Z (%) Impact toughness value AKv (J) ≤830 550-700 ≥18 ≥45 ≥32 (average)

[0007] 3. The equivalent diameter of internal defects in the final high-strength alloy steel rotor shaft forging shall not exceed 1 mm.

[0008] 4. The high-strength alloy steel rotor shaft forgings are stepped shaft forgings. The main delivery dimensions are stepped shafts, with a maximum diameter of ￠730mm. (Specific dimensions are shown in the figure below.) The forging blank weighs 10.28t, the material ingot weighs 14t, one forging is per ingot, and the forging ratio requirement is ≥4.0. See [details omitted]. Figure 1 . Innovation and innovation: (1) In addition to conventional chemical composition analysis, advanced testing equipment such as direct-reading spectrometers and metallographic microscopes are used to detect inclusions, grain size and other indicators. Strict control is implemented to ensure that the materials meet the specifications at the source.

[0009] (2) To ensure the internal quality of the forgings, the forging ratio should be ≥4. The selected steel ingots should be vacuum degassed and smelted, with an initial forging temperature ≥1250℃ and a final forging temperature ≥800℃. First forging: Press the jaws, upset the steel ingot to φ1420mm, and draw it to 650 octagon. Second forging: Upset the steel ingot to φ1420mm again, draw it to 790 octagon, mark the material, draw the sprue end to 590 octagon, mark the material, change to a narrow anvil and draw it appropriately at V, draw each section to the process dimensions, roll the flange, finish, and straighten the finished product. In order to eliminate the forging internal stress, refine the grains, homogenize the structure, reduce the hardness, facilitate machining, and ensure the mechanical properties of the material, a normalizing + tempering process was formulated. After normalizing and tempering, the riser jaws were sawn off.

[0010] (3) A stepped heating method must be adopted during heating, that is, the furnace temperature is gradually increased according to a certain temperature gradient, so that the surface and core of the forging can be heated slowly and synchronously, avoiding excessive thermal stress caused by sudden local temperature rise. During the heating process, it is also necessary to hold the temperature at several key temperature points. The specific heating temperature is as follows: when loading the furnace, heat it up to 600±20℃ for 5 hours, hold it for 4 hours, then heat it up to 1250±20℃ for another 10 hours, and hold it for ≥10 hours.

[0011] Compared with the prior art, this invention has the following advantages: First, it is resistant to high temperatures—its long-term operating temperature can typically reach 500-550℃; second, at around 500℃, its tensile strength and yield strength can still maintain 70%-80% of its room temperature performance; third, it has low fatigue notch sensitivity, is not sensitive to minor defects, machining marks, or stress concentration areas on the surface of the component, and is less likely to cause fatigue cracks from these weak points; fourth, it has good corrosion resistance—it can be used normally in ordinary atmospheres or slightly corrosive environments; fifth, it exhibits outstanding toughness, effectively preventing brittle fracture of components under impact or complex stress, with an impact energy (AKV) at room temperature typically exceeding 32J; sixth, 1) it has a large critical quenching diameter: using oil quenching, the critical quenching diameter can reach 80-120mm, far exceeding most similar high-strength steels; 2) it has uniform properties between the core and surface layers: after quenching, the difference in microstructure and hardness between the core and surface layers is minimal, and subsequent tempering treatment can achieve overall uniform strength and toughness, avoiding the situation of "hard surface and soft core". The problem is that: 3) It has strong adaptability to cooling rate and has a low risk of quenching deformation and cracking. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of a high-strength steel alloy turbine rotor shaft forging.

[0013] Figure 2 This is a schematic diagram of the forging blank for a steam turbine rotor shaft.

[0014] Figure 3 yes Figure 2 Schematic diagram after the first firing.

[0015] Figure 4 This is a schematic diagram of the second upsetting of the steel ingot after the second firing.

[0016] Figure 5 This is a schematic diagram of material distribution after the second firing, where the water outlet is pulled to 590 degrees at an octagonal angle.

[0017] Figure 6 This is a schematic diagram showing the process dimensions of each section after the second firing.

[0018] Figure 7 This is a rough machining dimension drawing of the rotor shaft forging.

[0019] Figure 8 This is a schematic diagram of the heat treatment process for rotor shaft forgings. Detailed Implementation

[0020] See attached document Figure 1 --A high-strength steel alloy turbine rotor shaft forging, (mass fraction %): C 0.3, Si 0.057, Mn 0.587, Cr 1.207, Mo 1.06, Ni 0.576, V 0.2610, P 0.0029, S 0.0011, balance being iron; or C 0.3, Si 0.059, Mn 0.591, Cr 1.208, Mo 1.06, Ni 0.574, V 0.2727, P 0.0026, S 0.0010, balance being iron.

[0021] 1. Forging process: The design process parameters for the high-strength alloy steel rotor shaft forging are as follows: It is forged using 30CrMoNiV5-11 alloy steel, with a forging weight of 10.28t and a material specification of 14t ingot. (See details...) Figure 2 One piece is forged from one ingot, with a forging ratio of 4.3 for upsetting and 5.4 for drawing. Forging temperature: 1250℃~800℃.

[0022] First heating cycle: After the steel ingot is tapped from the furnace, the riser is pressed into the clamps, and then the ingot is upset to a diameter of ￠1420mm. Afterward, the billet is forged into a flat plate with a large reduction and drawn to a length of approximately 950mm (octagonal) and about 2000mm in length. It is then returned to the furnace for reheating. (See...) Figure 3 ; Second upsetting: (1) The steel ingot is upset to a diameter of 1420mm for the second time, then drawn to a 790-degree octagon. The markings are then used for material distribution. See below. Figure 4 ; (2) Pull the water outlet end to 590 octagon, mark the material for distribution; change to a 300 narrow anvil and pull the V-shaped section appropriately longer, see Figure 5 ; (3) Lengthen each section to the process dimensions, roll the flange to round, and finish the work. See below. Figure 6 .

[0023] 2. Rough machining: After forging, rough machining is performed with a 7mm allowance on each side based on the finish-machined dimensions. Following rough machining, ultrasonic testing is conducted to ensure the forging meets the requirements of specification PA 0-1080-1003-31. (See [link]). Figure 7 .

[0024] 3. Performance heat treatment: To ensure high strength and impact toughness of the turbine rotor shaft forgings, a tempering heat treatment process was specifically developed. This process involves furnace heating to 600±10℃, holding for 4 hours, then furnace heating to 950±10℃, holding for 12 hours, oil cooling for 3 hours, followed by further heating to 300±10℃, holding for 3 hours, then furnace heating at 60℃ / hour to 690±10℃, and finally furnace cooling to ≤250℃ before unloading. Specific process curves are available in [link to process curve]. Figure 8 .

[0025] Test results of this invention: 1. The actual chemical composition of the turbine rotor shaft forging is shown in the table below (mass fraction %). serial number C Si Mn P S Cr Mo Ni V 2025166580 0.3 0.057 0.587 0.0029 0.0011 1.207 1.06 0.576 0.2610 2025166581 0.3 0.059 0.591 0.0026 0.0010 1.208 1.06 0.574 0.2727 2. Mechanical properties of turbine rotor shaft forgings (see table below).

[0026] serial number Tensile strength Rm (MPa) Yield strength ReL (MPa) Elongation A% Reduction of area Z% Impact absorbed energy AKv (J) 2025166580 809 664 20 66 36 / 38 / 44 39.3 (Average) 2025166581 813 669 18.5 63 48 / 48 / 42 46 (Average) 3. The rotor shaft forging was tested by ultrasonic testing and no defects exceeding the standard were found, which meets the requirements of customer specification PA 0-1080-1003-31.

[0027] It should be understood that although the above embodiments provide a relatively detailed textual description of the design concept of the present invention, these textual descriptions are merely simple textual descriptions of the design concept of the present invention, and not limitations on the design concept of the present invention. Any combination, addition, or modification that does not exceed the design concept of the present invention falls within the protection scope of the present invention.

Claims

1. A high strength alloy steel rotor shaft forging characterized by (mass %): C 0.3, Si 0.057, Mn 0.587, Cr 1.207, Mo 1.06, Ni 0.576, V 0.2610, P 0.0029, S 0.0011, and the rest is iron; or C 0.3, Si 0.059, Mn 0.591, Cr 1.208, Mo 1.06, Ni 0.574, V 0.2727, P 0.0026, S 0.0010, and the rest is iron.

2. The high strength alloy steel rotor shaft forging of claim 1, characterized by: The high-strength alloy steel rotor shaft forging has a tensile strength Rm of 809 MPa, a yield strength ReL of 664 MPa, an elongation of 20 A%, a reduction of area of 66 Z%, an impact energy AKv of 36 / 38 / 44 J, and an average value of 39.3 J; or a tensile strength Rm of 813 MPa, a yield strength ReL of 669 MPa, an elongation of 18.5 A%, a reduction of area of 63 Z%, an impact energy AKv of 48 / 48 / 42 J, and an average value of 46 J.

3. A method for manufacturing a high-strength alloy steel rotor shaft forging, characterized by: Forging process: the alloy steel 30CrMoNiV5-11 material is forged into a shape, the forging weight is 10.28 t, the material specification is 14 t ingot, one ingot is forged into one piece, the upsetting ratio is 4.3 and the elongation ratio is 5.

4. The forging temperature is 1250-800°C; First fire: after the steel ingot is discharged, the riser is pressed, then the steel ingot is upset, after upsetting to a diameter of ￠1420 mm, the forging flat plate is elongated to 950 mm eight corners about 2000 mm long, and the furnace is heated again; Second fire: (1) the steel ingot is upset to a diameter of ￠1420 mm for the second time, and is elongated to 790 eight corners, and is marked for material division; (2) the nozzle end is elongated to 590 eight corners, and is marked for material division; the 300 narrow anvil is replaced and the V place is appropriately elongated; (3) each section is elongated to the process size, the flange is rounded, and the finishing work is completed; Rough machining: after forging, the rough machining is performed on the basis of the finishing size with a single side allowance of 7 mm, and after rough machining, the ultrasonic flaw detection is performed to ensure that the internal defect equivalent diameter of the forging is not more than 1 mm; Performance heat treatment: The rotor shaft forging is heated to 600±10°C in the furnace, is kept for 4 hours, is then heated to 950±10°C in the furnace, is kept for 12 hours, is then oil-cooled for 3 hours, is then heated to 300±10°C, is kept for 3 hours, is then heated to 690±10°C at a rate of 60°C / H, is then furnace-cooled to ≤250°C, and is discharged.

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