N07718 nickel base alloy electroslag ingot forging method

Abstract

The invention relates to the field of high-temperature alloy forging, in particular to a forging process method of an N07718 electroslag ingot, and provides the forging process method of the N07718 electroslag ingot by combining homogenization treatment before electroslag ingot forging, surface turning pretreatment and a heating forging process, so that the surface quality and various properties of a forging stock are greatly improved, and the production requirements are met.

Description

Technical Field

[0001] The present invention relates to the field of superalloy forging, and particularly to a forging method for N07718 nickel-based alloy electroslag ingots. Background Art

[0002] Due to the relatively high contents of niobium, molybdenum, and titanium elements in N07718, its strength and hardness increase accordingly. Moreover, its hot working temperature range is narrow, the hot working deformation rate is small, and the control difficulty during the forging process is great. There are problems such as forging cracking and unqualified properties after forging in the production of N07718 produced by the existing process of vacuum induction + electroslag remelting. Therefore, it is necessary to conduct process research and design on the heating and forging of N07718 electroslag ingots to meet the production requirements.

[0003] By studying the forging process and high-temperature mechanical properties of N07718, the present invention designs a forging process for N07718 with "two upsetting and five drawing" to achieve the purpose of optimizing the grain structure and improving the product performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a forging method for N07718 nickel-based alloy electroslag ingots in view of the above problems.

[0005] The purpose of the present invention is achieved as follows: A forging method for N07718 nickel-based alloy electroslag ingots includes the following steps: Step 1: Pre-treatment before forging of electroslag ingots: Perform homogenization heat treatment on the N07718 electroslag ingots with qualified composition inspection. The homogenization heat treatment: Keep the temperature at 300 - 500°C for 2 - 2.5 h, then increase the temperature to 1120 ± 10°C at a heating rate of 80 ± 5°C / h and keep it for 12 - 12.5 h, then increase the temperature to 1190 ± 10°C at a heating rate of 70 ± 5°C / h and keep it for 48 - 48.5 h, and finally cool the furnace temperature to 850 - 900°C and then take it out of the furnace. After taking it out of the homogenization furnace, perform surface turning processing. After turning, the surface roughness Ra ≤ 3.2 µm, there are no local scratches or protrusions on the surface, and there are no cracks visible to the naked eye. The final size of the N07718 electroslag ingot is φ490 ± 5 mm * L, where L is the length of the steel ingot; Step 2: Forging process of electroslag ingots: The pre-treated N07718 electroslag ingots are loaded into a chamber furnace for heating in a vertical installation furnace. The heating process: The temperature in the furnace is 300 - 500°C, increase the temperature to 900 ± 10°C at a heating rate of 50 ± 3°C / h and keep it for 3.5 - 4 h, then increase the temperature to 1100 ± 10°C at a heating rate of 80 ± 3°C / h and keep it for 11 - 11.5 h, and finally take it out of the furnace for forging; The forging process is processed by the forging process of "two upsetting and five drawing".

[0006] The forging process in Step 2 is carried out as follows: The first heating is upsetting, with a reduction ratio of L / 3, completed in two passes. The first reduction is L / 6, with a reduction speed of 10±2 mm / s, and the second reduction is L / 6, with a reduction speed of 15±2 mm / s. Immediately after upsetting, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100±10 °C, and the heat preservation time is 2 - 2.5 h. The second heating is drawing out. The drawing out starts from the end, and the drawing out specification is 490±5 mm * 490±5 mm * L. The final forging temperature is required to be 900 - 930 °C. After drawing out, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100±10 °C, and the heat preservation time is 2 - 2.5 h. The third heating is upsetting, with a reduction ratio of L / 3, completed in two passes. The first reduction is L / 6, with a reduction speed of 10±2 mm / s, and the second reduction is L / 6, with a reduction speed of 15±2 mm / s. Immediately after upsetting, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100±10 °C, and the heat preservation time is 2 - 2.5 h. The fourth heating is drawing out. The drawing out starts from the end, and the drawing out specification is 490±5 mm * 490±5 mm * L. The final forging temperature is required to be 900 - 930 °C. After drawing out, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100±10 °C, and the heat preservation time is 2 - 2.5 h. The fifth heating is drawing out. The drawing out starts from the end, and the drawing out specification is 420±5 mm * 420±5 mm * L. The final forging temperature is required to be 900 - 930 °C. After drawing out, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100±10 °C, and the heat preservation time is 2 - 2.5 h. The sixth heating is drawing out. The drawing out starts from the end, and the drawing out specification is 350±5 mm * 350±5 mm * L. The final forging temperature is required to be 900 - 930 °C. After drawing out, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100±10 °C, and the heat preservation time is 2 - 2.5 h. The seventh heating is drawing out. The drawing out starts from the end, and the final drawing out specification is φ290 - 295 mm * L. The final forging temperature is required to be 900 - 930 °C. After drawing out, straightening and shaping are carried out.

[0007] The chemical composition and its mass percentage of the N07718 electroslag ingot with qualified component inspection in Step 1 are: C: 0.01% - 0.045%, Cr: 18% - 21%, Ni: 51% - 54%, Mo: 2.8% - 3.2%, Nb: 4.9% - 5.2%, Al: 0.4% - 0.6%, Ti: 0.8% - 1.15%.

[0008] The beneficial effects of the present invention are: By designing the forging process of N07718, the surface quality and various properties of the forging billet are solved, meeting the production requirements. Description of the Drawings

[0009] The present invention will be further described below with reference to the drawings.

[0010] Figure 1 This is the homogenization process diagram of the electroslag ingot of the present invention N07718.

[0011] Figure 2 This is the heating process diagram of the electroslag ingot of the present invention. Detailed implementation manners

[0012] 1. Considering that N07718 contains relatively high molybdenum element (3%), titanium element (1%), and niobium element (5%), since molybdenum element has segregation in the ingot, and niobium and titanium are prone to form precipitates, which reduces the hot plasticity and increases the crack sensitivity, it is easy to cause forging cracking during the processing of the electroslag ingot (φ500*Lmm). Therefore, homogenization heat treatment is required for the material. The change of the heat treatment temperature has a great impact on the material properties. For this reason, the homogenization heat treatment temperature is designed to be insulated in three steps. The first step is to heat the furnace to 500°C and keep it insulated for 2h, the second step is to keep it insulated at 1120°C for 12h, and the third step is to keep it insulated at 1190°C for 48h, which can significantly improve the physical properties of N07718 and provide high-quality raw materials for the later forging processing of the electrode blank.

[0013] 2. Through the analysis and research on the mechanical properties of N07718, it is found that the N07718 material is prone to forging cracking at high temperatures, and the processing performance of the N07718 material is optimal when the forging temperature range is 900 - 1100°C. Therefore, the forging heating process is formulated as follows: Heat the furnace to 500°C and control the temperature rise for 6h. The first step is to keep it insulated at 900°C for 3.5h and control the temperature rise for 2.5h. The second step is to keep it insulated at 1100°C for 11h.

[0014] 3. Considering the requirements of the target specifications, forging ratio, etc. and the specification size of the N07718 electroslag ingot, taking into account the forging temperature range of 900 - 1100°C and the limitations of the material mechanical properties, if a single large reduction upsetting and drawing is used, it will cause forging surface cracking. Therefore, the forging process is set as "two upsetting and five drawing".

[0015] Technical solution: 1. Pretreatment before forging of the electroslag ingot: The N07718 of the Taigang Profile Division is smelted by vacuum induction + electroslag remelting. The specification of the electroslag ingot is φ500*L. After homogenization heat treatment and surface turning, it is heated and forged. The homogenization heat treatment process is shown in Figure 1 , and the specification after turning is φ490*L.

[0016] 2. Heating process of the electroslag ingot: The pretreated N07718 electroslag ingot is loaded into the furnace for heating in a vertical furnace manner. The heating process of the electroslag ingot is shown in Figure 2 .

[0017] This method is implemented for the N07718 electroslag ingot smelted by vacuum induction + electroslag remelting at Taigang. By combining the homogenization treatment before forging, surface turning pretreatment and hot forging process of the electroslag ingot, a forging process method for N07718 electroslag ingot is provided, and the quality of N07718 forged billets is greatly improved, meeting the usage requirements of users.

[0018] Pretreatment before forging of electroslag ingot: Figure 1 For the homogenization treatment process of N07718 electroslag ingot, the N07718 electroslag ingot with qualified composition inspection is subjected to homogenization heat treatment. After the treatment is completed, it is taken out of the furnace for surface turning processing. The final size of the N07718 electroslag ingot is φ490*L.

[0019] Forging process of electroslag ingot: The pretreated N07718 electroslag ingot is charged into the furnace for heating in a vertical furnace. The heating process is shown in Figure 2 , and after the heating process is completed, it is taken out of the furnace for forging.

[0020] The forging process uses the "two upsetting and five drawing" forging process for processing. The forging process is as follows: The first heat is upsetting, with a reduction of L / 3, completed in two passes. The first reduction is L / 6, with a reduction speed of 10 mm / s, and the second reduction is L / 6, with a reduction speed of 15 mm / s. Immediately after upsetting, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100 °C, and the heat preservation time is 2 h; The second heat is drawing. Drawing starts from the end. The drawing specification is 490*490*L, and the final forging temperature requirement is 900 - 930 °C. After drawing is completed, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100 °C, and the heat preservation time is 2 h; The third heat is upsetting, with a reduction of L / 3, completed in two passes. The first reduction is L / 6, with a reduction speed of 10 mm / s, and the second reduction is L / 6, with a reduction speed of 15 mm / s. Immediately after upsetting, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100 °C, and the heat preservation time is 2 h; The fourth heat is drawing. Drawing starts from the end. The drawing specification is 490*490*L, and the final forging temperature requirement is 900 - 930 °C. After drawing is completed, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100 °C, and the heat preservation time is 2 h; The fifth heat is drawing. Drawing starts from the end. The drawing specification is 420*420*L, and the final forging temperature requirement is 900 - 930 °C. After drawing is completed, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100 °C, and the heat preservation time is 2 h; The sixth heat is drawing. Drawing starts from the end. The drawing specification is 350*350*L, and the final forging temperature requirement is 900 - 930 °C. After drawing is completed, it is returned to the furnace for heat preservation. The heat preservation temperature is 1100 °C, and the heat preservation time is 2 h; The seventh heat is drawing. Drawing starts from the end. The final drawing size is φ290*L, and the final forging temperature requirement is 900 - 930 °C. After drawing is completed, straightening and shaping are carried out. Example 1

[0021] The following are the specific embodiments of N07718: furnace number: Z5110153 / Z5120154, steel type N07718.

[0022] Homogenization heat treatment: Insulate at 300°C for 2h, then heat up to 1120°C at a heating rate of 80°C / h and insulate for 12h, then heat up to 1190°C at a heating rate of 70°C / h and insulate for 48h. Finally, cool the furnace temperature to 850°C and then take the product out of the furnace. After taking it out of the homogenization furnace, perform surface turning. After turning, the surface roughness Ra ≤ 3.2 µm, there are no local scratches or protrusions on the surface, and there are no cracks visible to the naked eye.

[0023] The specifications after turning and the forging process after homogenization are as follows in the table.

[0024]

[0025] Finally, a qualified forging product is obtained.

[0026] The above are only the specific embodiments of the present invention, but the structural features within the scope of protection of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the field of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for forging N07718 nickel-based alloy electroslag ingots, characterized in that: The following steps are involved: Step 1: Pretreatment of electroslag ingot before forging: Perform homogenization heat treatment on the N07718 electroslag ingot that has passed the composition inspection. Homogenization heat treatment: 300-500℃ for 2-2.5h, then heat to 1120±10℃ at a heating rate of 80±5℃ / h for 12-12.5h, then heat to 1190±10℃ at a heating rate of 70±5℃ / h for 48-48.5h, finally cool to 850-900℃ before taking out of the furnace, and perform surface polishing after taking out of the homogenization furnace. After polishing, the surface roughness Ra≤3.2µm, there are no local scratches or protrusions on the surface, and no cracks visible to the naked eye. The final size of the N07718 electroslag ingot is φ490±5mm*L, where L is the length of the ingot; Step 2: Electroslag ingot forging process: The pretreated N07718 electroslag ingot is loaded into a chamber furnace for heating in a vertical furnace. The heating process is as follows: the furnace temperature is 300-500℃, and the temperature is increased to 900±10℃ at a heating rate of 50±3℃ / h and kept for 3.5-4h, and then increased to 1100±10℃ at a heating rate of 80±3℃ / h and kept for 11-11.5h, and finally taken out of the furnace for forging; the forging process adopts the "two upsetting and five drawing" forging process for processing.

2. A method for forging an N07718 nickel-based alloy electroslag ingot according to claim 1, characterized in that: The forging process of step 2 is as follows: The first fire is upsetting, the pressing amount is L / 3, and it is completed in two times. The first pressing amount is L / 6, the pressing speed is 10±2mm / s, and the second pressing amount is L / 6, the pressing speed is 15mm±2 / s. After the upsetting is completed, it is immediately returned to the furnace for insulation. The insulation temperature is 1100±10℃ and the insulation time is 2-2.5h; The second fire is drawing, which starts from the end. The drawing specification is 490±5mm*490±5mm*L. The final forging temperature is required to be 900-930℃. After the drawing is completed, it is returned to the furnace for insulation. The insulation temperature is 1100±10℃ and the insulation time is 2-2.5h. The third fire is upsetting, the pressing amount is L / 3, and it is completed in two times. The first pressing amount is L / 6, the pressing speed is 10±2mm / s, and the second pressing amount is L / 6, the pressing speed is 15mm±2 / s. After the upsetting is completed, it is immediately returned to the furnace for insulation. The insulation temperature is 1100±10℃ and the insulation time is 2-2.5h; The fourth fire is drawing, which starts from the end. The drawing specification is 490±5mm*490±5mm*L. The final forging temperature is required to be 900-930℃. After the drawing is completed, it is returned to the furnace for insulation. The insulation temperature is 1100±10℃ and the insulation time is 2-2.5h. The fifth fire is drawing, which starts from the end. The drawing specification is 420±5mm*420±5mm*L. The final forging temperature is required to be 900-930℃. After the drawing is completed, it is returned to the furnace for insulation. The insulation temperature is 1100±10℃ and the insulation time is 2-2.5h. The sixth fire is drawing, which starts from the end. The drawing specification is 350±5mm*350±5mm*L. The final forging temperature is required to be 900-930℃. After the drawing is completed, it is returned to the furnace for insulation. The insulation temperature is 1100±10℃ and the insulation time is 2-2.5h. The seventh fire is drawing, which starts from the end. The final specification of the drawing is φ290-295mm*L. The final forging temperature is required to be 900-930℃. After the drawing is completed, straightening and shaping are carried out.

3. A method for forging N07718 nickel-based alloy electroslag ingot according to claim 1, characterized in that: The chemical composition and mass percentage of the N07718 electroslag ingot that passed the composition inspection in step 1 are C: 0.01%-0.045%, Cr: 18%-21%, Ni: 51%-54%, Mo: 2.8%-3.2%, Nb: 4.9%-5.2%, Al: 0.4%-0.6%, and Ti: 0.8%-1.15%.

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