Method of refining grain size of gh4698 alloy bar

Abstract

The application discloses a method for refining grain size of GH4698 alloy bar, and specifically comprises the following steps: obtaining GH4698 alloy ingot through duplex smelting process of vacuum induction melting and vacuum consumable melting; then, carrying out high-temperature homogenizing annealing treatment; finally, carrying out 8-10 fire times upsetting and drawing forging on a quick forging machine, and continuously carrying out re-forging, and then carrying out air cooling after forging to obtain GH4698 alloy bar. Through reasonable collocation of alloy component proportioning, homogenizing annealing and bar forging process, the method can refine the bar organization, and the grain size of the bar is 3-4 grade after heat treatment, and the grain size requirement of 2-6 grade of the large-size GH4698 alloy bar is successfully broken through. Meanwhile, the various performances of the GH4698 alloy bar meet the standard requirements.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, specifically relating to a method for refining the grain size of GH4698 alloy bars. Background Technology

[0002] GH4698 is a Ni-based age-hardening wrought superalloy with a service temperature of 750℃~800℃. GH4698 is a Russian-style alloy. This alloy exhibits high creep strength and tensile strength, good plasticity and comprehensive properties within the 550℃~800℃ range, and maintains stable microstructure over long-term use. Due to its excellent performance, it is widely used in large-scale components of marine gas turbines, as well as high-pressure turbine disks, ring-rolled parts, and fasteners for aero-engines.

[0003] The microstructure of GH4698 alloy consists of a γ matrix, carbides, and γ' phase as a strengthening phase. Based on the actual composition ratio of the alloy, the dissolution temperature of the γ' phase is approximately 1020℃~1040℃. The standard heat treatment regime for the alloy is (1100~1120)℃ / 8h, air cooling; 1000℃ / 4h, air cooling; 775℃ / 16h, air cooling. This alloy has a relatively high solution temperature, indicating it is an over-solution alloy. The grain size of GH4698 alloy bars in the forged state is grade 3~5, which decreases to grade 0~2 after heat treatment. However, current aero-engines require a grain size of grade 2~6 for heat-treated bars. Therefore, refining the grain size of the bars is a significant challenge in alloy development. Summary of the Invention

[0004] The purpose of this invention is to provide a method for refining the grain size of GH4698 alloy bars, resulting in GH4698 alloy bars with uniform microstructure and a grain size of 3 to 4.

[0005] The technical solution adopted in this invention is a method for refining the grain size of GH4698 alloy bars, which is implemented according to the following steps:

[0006] Step 1: Obtain GH4698 alloy ingots through a dual smelting process of vacuum induction melting and vacuum consumable melting;

[0007] Step 2: The GH4698 alloy ingot obtained after Step 1 is subjected to high-temperature homogenization annealing treatment.

[0008] Step 3: The GH4698 alloy ingot obtained in Step 2 is subjected to 8 to 10 upsetting and drawing forging cycles on a high-speed forging machine, and the forging is continuously reflowed in the furnace. After forging, it is air-cooled to obtain GH4698 alloy bar.

[0009] The invention is further characterized in that,

[0010] In step 1, the diameter of the GH4698 alloy ingot is 390mm to 490mm.

[0011] In step 1, the GH4698 alloy ingot has the following chemical composition by mass percentage: C: 0.045%–0.065%, Cr: 14.00%–15.00%, Mo: 2.90%–3.10%, Nb: 1.90%–2.10%, Ti: 2.55%–2.70%, Al: 1.60%–1.75%, B: 0.0030%–0.0045%, Zr: 0.030%–0.045%, Fe: 0.35%–1.00%, with the remainder being Ni. The sum of the mass percentages of the above components is 100%.

[0012] In step 2, specifically: the GH4698 alloy ingot is placed in a natural gas furnace for heating treatment at a temperature of 1170℃~1220℃ and a holding time of 50h~100h. After the holding time is completed, the natural gas furnace is cooled to 600℃~800℃ and then air-cooled.

[0013] In step 3, during upsetting and drawing forging, the heating temperature is 1050℃~1170℃, the deformation per heat is 25%~40%, the heat preservation coefficient for cold material loading into the furnace is 0.5min / mm~0.8min / mm, and the heat preservation coefficient for hot material returning to the furnace is 0.2min / mm~0.5min / mm.

[0014] In step 3, the diameter of the GH4698 alloy bar is 150mm to 300mm.

[0015] The beneficial effects of this invention are: by preparing GH4698 alloy ingots and performing homogenization annealing, and finally carrying out bar forging process, the bar structure is refined, and the grain size of the heat-treated bar is grade 3 to 4, which successfully breaks through the requirement of 2 to 6 grain size for large-size GH4698 alloy bars. Attached Figure Description

[0016] Figure 1 This is a low-magnification transverse microstructure diagram of a 250mm GH4698 bar.

[0017] Figure 2 This is a longitudinal schematic diagram of the high-magnification microstructure at the edge of a 250mm GH4698 bar.

[0018] Figure 3 A high-magnification longitudinal microstructure diagram of a 250mm GH4698 bar with a diameter of R / 2.

[0019] Figure 4 This is a high-magnification longitudinal schematic diagram of the core microstructure of a 250mm GH4698 bar. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0021] The method for refining the grain size of GH4698 alloy bars according to the present invention is implemented according to the following steps:

[0022] Step 1: Obtain GH4698 alloy ingots through a dual smelting process of vacuum induction melting and vacuum consumable melting;

[0023] The diameter of GH4698 alloy ingots is 390mm to 490mm;

[0024] The chemical composition of the GH4698 alloy ingot, by mass percentage, is as follows: C: 0.045%–0.065%, Cr: 14.00%–15.00%, Mo: 2.90%–3.10%, Nb: 1.90%–2.10%, Ti: 2.55%–2.70%, Al: 1.60%–1.75%, B: 0.0030%–0.0045%, Zr: 0.030%–0.045%, Fe: 0.35%–1.00%, with the remainder being Ni. The sum of the mass percentages of the above components is 100%.

[0025] Step 2: The GH4698 alloy ingot obtained after Step 1 is subjected to high-temperature homogenization annealing treatment.

[0026] Specifically, the GH4698 alloy ingot is placed in a natural gas furnace for heating treatment at a temperature of 1170℃~1220℃ and a holding time of 50h~100h. After the holding time is completed, the natural gas furnace is cooled to 600℃~800℃ and then air-cooled.

[0027] Step 3: The GH4698 alloy ingot obtained after step 2 is subjected to 8 to 10 upsetting and drawing forgings on an 80MN high-speed forging machine, and the forging is continuously recycled. After forging, it is air-cooled to obtain GH4698 alloy bars with a diameter of 150mm to 300mm.

[0028] During upsetting and drawing forging, the heating temperature is 1050℃~1170℃, the deformation per forging is 25%~40%, the heat preservation coefficient for cold material loading into the furnace is 0.5min / mm~0.8min / mm, the heat preservation coefficient for hot material returning to the furnace is 0.2min / mm~0.5min / mm, after being taken out of the furnace, it is wrapped with asbestos for forging, and after forging is completed, it is directly returned to the furnace. The last forging is air-cooled.

[0029] For the solution-treated GH4698 alloy, the strengthening phase γ' phase completely dissolves during solution treatment, leaving only carbides. Therefore, the alloy composition is crucial to ensure a finer microstructure. The specific ingot composition designed in this invention guarantees a sufficient amount of carbides in the alloy. After appropriate high-temperature homogenization, these carbides diffuse and are finally forged into bars, resulting in a relatively dispersed distribution. During solution treatment, the grain boundaries are "pinned," achieving a grain size of 3-4. Simultaneously, all properties of the GH4698 alloy bars meet the standard requirements.

[0030] Example 1

[0031] The method for refining the grain size of GH4698 alloy bars according to the present invention is implemented according to the following steps:

[0032] Step 1: Obtain GH4698 alloy ingots through a dual smelting process of vacuum induction melting and vacuum consumable melting;

[0033] The chemical composition of the GH4698 alloy ingot, by mass percentage, is as follows: C: 0.045%, Cr: 14.00%, Mo: 2.90%, Nb: 1.90%, Ti: 2.55%, Al: 1.60%, B: 0.0030%, Zr: 0.030%, Fe: 0.35%, with the remainder being Ni. The sum of the mass percentages of the above components is 100%.

[0034] The diameter of the GH4698 alloy ingot is 390mm;

[0035] Step 2: Place the GH4698 alloy ingot in a natural gas furnace for heating treatment at a temperature of 1170℃ for 50 hours. After the holding time is completed, cool the natural gas furnace to 600℃ and then air cool it.

[0036] Step 3: The GH4698 alloy ingot obtained in Step 2 is subjected to 8 upsetting and drawing forgings on an 80MN high-speed forging machine, and the forging is continuously recycled. After forging, it is air-cooled to obtain GH4698 alloy bars with a diameter of 150mm.

[0037] During upsetting and drawing forging, the heating temperature is 1050℃, the deformation per forging is 25%, the heat preservation coefficient for cold material loading into the furnace is 0.5min / mm, the heat preservation coefficient for hot material returning to the furnace is 0.2min / mm, after being taken out of the furnace, it is wrapped with asbestos for forging, and after forging is completed, it is directly returned to the furnace, and the last forging is air-cooled.

[0038] Example 2

[0039] The method for refining the grain size of GH4698 alloy bars according to the present invention is implemented according to the following steps:

[0040] Step 1: Obtain GH4698 alloy ingots through a dual smelting process of vacuum induction melting and vacuum consumable melting;

[0041] The diameter of the GH4698 alloy ingot is 440mm;

[0042] The chemical composition of the GH4698 alloy ingot, by mass percentage, is as follows: C: 0.055%, Cr: 14.50%, Mo: 3.00%, Nb: 2.00%, Ti: 2.63%, Al: 1.67%, B: 0.0037%, Zr: 0.038%, Fe: 0.68%, with the remainder being Ni. The sum of the mass percentages of the above components is 100%.

[0043] Step 2: Place the GH4698 alloy ingot in a natural gas furnace for heating treatment at a temperature of 1195℃ for 75 hours. After the holding time is completed, cool the natural gas furnace to 750℃ and then air cool it.

[0044] Step 3: The GH4698 alloy ingot obtained after step 2 is subjected to 9 upsetting and drawing forgings on an 80MN high-speed forging machine, and the forging is continuously recycled. After forging, it is air-cooled to obtain GH4698 alloy bar with a diameter of 220mm.

[0045] During upsetting and drawing forging, the heating temperature is 1110℃, the deformation per forging is 32%, the heat preservation coefficient for cold material loading into the furnace is 0.65min / mm, the heat preservation coefficient for hot material returning to the furnace is 0.35min / mm, after being taken out of the furnace, it is wrapped with asbestos for forging, and after forging is completed, it is directly returned to the furnace, and the last forging is air-cooled.

[0046] Example 3

[0047] The method for refining the grain size of GH4698 alloy bars according to the present invention is implemented according to the following steps:

[0048] Step 1: Obtain GH4698 alloy ingots through a dual smelting process of vacuum induction melting and vacuum consumable melting;

[0049] The diameter of the GH4698 alloy ingot is 490mm;

[0050] The chemical composition of the GH4698 alloy ingot, by mass percentage, is as follows: C: 0.065%, Cr: 15.00%, Mo: 3.10%, Nb: 2.10%, Ti: 2.70%, Al: 1.75%, B: 0.0045%, Zr: 0.045%, Fe: 1.00%, with the remainder being Ni. The sum of the mass percentages of the above components is 100%.

[0051] Step 2: Place the GH4698 alloy ingot in a natural gas furnace for heating treatment at a temperature of 1220℃ for 100 hours. After the holding time is completed, cool the natural gas furnace to 800℃ and then air cool it.

[0052] Step 3: The GH4698 alloy ingot obtained in Step 2 is subjected to 10 upsetting and drawing forgings on an 80MN high-speed forging machine, and the forging is continuously recycled. After forging, it is air-cooled to obtain GH4698 alloy bars with a diameter of 300mm.

[0053] During upsetting and drawing forging, the heating temperature is 1170℃, the deformation per forging is 40%, the heat preservation coefficient for cold material loading into the furnace is 0.8 min / mm, the heat preservation coefficient for hot material returning to the furnace is 0.5 min / mm, after being taken out of the furnace, it is wrapped with asbestos for forging, and after forging is completed, it is directly returned to the furnace, and the last forging is air-cooled.

[0054] The properties of the GH4698 alloy rods prepared by the method of the present invention were tested, and their mechanical property data are shown in Table 1.

[0055] Table 1 Mechanical properties of GH4698 alloy bars

[0056]

[0057] As shown in Table 1, the properties of GH4698 alloy bars with diameters of Φ150mm and Φ250mm both meet the standard requirements, exhibiting good consistency and a certain margin of safety. The room temperature tensile strength margin of the Φ150mm GH4698 alloy bar is ≥100MPa, and the room temperature impact strength margin is ≥25J / cm². 2 Tensile strength margin at 750℃ ≥ 120MPa, creep rupture margin at 750℃ and 412MPa ≥ 68h; GH4698 alloy bar with Φ250mm specification has a room temperature tensile strength margin ≥ 100MPa and a room temperature impact margin ≥ 13J / cm. 2 The tensile strength surplus at 750℃ is ≥60MPa, and the creep rupture surplus at 750℃ and 412MPa is ≥63h.

[0058] Figure 1 This is a low-magnification transverse microstructure diagram of GH4698 bar. Figure 2 This is a longitudinal schematic diagram of the high-magnification microstructure at the edge of a GH4698 bar. Figure 3 This is a longitudinal schematic diagram of the microstructure of GH4698 bar at R / 2 magnification; Figure 4 The diagram shows a longitudinal high-magnification microstructure of the core of GH4698 bar. As can be seen from the diagram, the bar has a uniform microstructure. The transverse microstructure is uniformly blurred at low magnification and has no metallurgical defects such as shrinkage cavities, cracks, or inclusions. The high-magnification microstructure is relatively uniform and fine, with an average grain size of 3 to 4.

Claims

1. A method of refining the grain size of GH4698 alloy bar characterized by, The method is implemented according to the following steps: Step 1, obtaining a GH4698 alloy ingot through a double smelting process of vacuum induction melting and vacuum consumable melting; The GH4698 alloy ingot has the following chemical components in percentage by mass: C: 0.045%~0.065%, Cr: 14.00%~15.00%, Mo: 2.90%~3.10%, Nb: 1.90%~2.10%, Ti: 2.55%~2.70%, Al: 1.60%~1.75%, B: 0.0030%~0.0045%, Zr: 0.030%~0.045%, Fe: 0.35%~1.00%, and the rest is Ni, and the sum of the above components is 100%; the diameter of the GH4698 alloy ingot is 390mm~490mm; Step 2, performing high-temperature homogenization annealing treatment on the GH4698 alloy ingot obtained after Step 1; specifically, placing the GH4698 alloy ingot in a natural gas furnace for heating treatment, the heating temperature is 1170℃~1220℃, the holding time is 50h~100h, after the holding is completed, cooling the natural gas furnace to 600℃~800℃, and then air cooling; Step 3, performing 8~10 fire times of upsetting and drawing forging on the GH4698 alloy ingot obtained after Step 2 on a quick forging machine, and continuously returning the forged product to the furnace, air cooling after forging, to obtain a GH4698 alloy rod; the diameter of the GH4698 alloy rod is 150mm~300mm; During the upsetting and drawing forging, the heating temperature is 1050℃~1110℃, the deformation amount of each fire time is 25%~40%, the cold charge loading and holding coefficient is 0.5min / mm~0.8min / mm, and the hot charge return and holding coefficient is 0.2min / mm~0.5min / mm; The rod has uniform microstructure, uniform and blurred microstructure in the transverse macrostructure, and no metallurgical defects such as shrinkage cavity, crack and slag inclusion; the high-magnification microstructure is relatively uniform and fine; and the grain size of the rod after heat treatment is 3~4 levels.

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