A forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots

Abstract

The present application belongs to the technical field of metal plastic forming and forging, and particularly relates to a forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots. The forming process comprises the following steps: taking a multi-rib steel ingot as raw material, cutting off the ingot tail end and the head end of the ingot; after heating the cut steel ingot, sequentially performing blind hole pre-pressing, upsetting, punching and mandrel hole expansion; adopting a staged rolling expansion process, stopping at 45%-50% of the finished product outer diameter in the first fire, and then performing intermediate reheat and second fire rolling expansion. The present application eliminates the inner diameter intensive defects of the raw material ordinary steel ingot from the source through the double compaction of "conical upsetting" and "mandrel compaction", and the physical removal of "large diameter punching". Through actual production verification, the UT flaw detection one-time qualified rate of the 30-ton ASTM A266 ring forgings produced by the process of the present application is increased from less than 25% to more than 95%.

Description

Technical Field

[0001] This invention belongs to the field of metal plastic forming and forging technology, specifically relating to a forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots, and more particularly to a ring forging manufacturing method that eliminates inner diameter flaw detection defects by optimizing the billet preparation and rolling path for large carbon steel ingots with central porosity and segregation defects. Background Technology

[0002] Carbon steel forgings according to ASTM A266 standards are widely used in pressure vessels, metallurgical and mining equipment, and other fields. When producing ultra-large ring forgings with a diameter greater than 8 meters and a weight exceeding 30 tons, large multi-faceted steel ingots (such as octagonal or dodecagonal ingots) are usually selected as raw materials. The riser end face of this type of multi-faceted steel ingot has no obvious concave center and has internal porosity and shrinkage defects (low density steel ingot).

[0003] However, in actual production, it was found that some large steel ingots, due to insufficient riser feeding efficiency (manifested as a flat riser end face without a concave center), resulted in severe shrinkage cavities and extremely deep V-shaped segregation. Furthermore, due to the ingot's geometric characteristics, central impurities exhibited a star-shaped, radiating distribution. When using these large steel ingots as raw materials and employing conventional forging processes (flat anvil upsetting + conventional punching + single-pass rolling expansion), dense forest-like wave defects or full-circle layered tearing easily occur within a depth range of 10-200mm in the inner diameter of the ring forgings, leading to batch defects failing flaw detection.

[0004] Existing solutions typically involve replacing the steel ingots with higher-grade ones (such as multi-faceted round ingots), but this significantly increases costs. How to utilize existing ordinary-grade low-density steel ingots and eliminate their inherent internal defects through process optimization is a pressing technical challenge in this field. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a forming process for manufacturing large ASTM A266 ring forgings based on low-density steel ingots. This process effectively welds together the internal porosity of the raw material and eliminates the impact of severe segregation on flaw detection through specific blanking strategies, enhanced compaction of the billet, and graded recrystallization rolling.

[0006] The technical solution of the present invention is as follows:

[0007] A forming process for manufacturing large ASTM A266 ring forgings based on low-density steel ingots includes the following steps:

[0008] (1) Blanking: Take multi-faceted steel ingots as raw materials, and cut off the tail end and the riser end of the ingot. The cutting rate is set at 22%-25%;

[0009] (2) Billet making: After heating the steel ingot after blanking, blind hole pre-pressing, upsetting, punching and reaming are carried out in sequence;

[0010] (3) Rolling: The graded rolling process is adopted. The first rolling is stopped when the outer diameter of the finished product is 45%-50%. After intermediate reheating, the second rolling is carried out.

[0011] (4) Heat treatment: Cool to room temperature in air.

[0012] Further, the multi-faceted steel ingot mentioned in step (1) is a 3-12 faceted, 30-40 ton steel ingot, and the multi-faceted steel ingot is a low-density steel ingot; the composition of the multi-faceted steel ingot is: C: 0.22%~0.30%; Si: 0.17%~0.35%; Mn: 0.6%~1.2%; Cr: <0.27%; Cu: <0.25%; Ni: <0.25%; P: ≤0.025%; S: ≤0.025%, with the balance being Fe.

[0013] Furthermore, the heating temperature in step (2) is 1220℃-1250℃; the heat preservation time is 8-20h.

[0014] Further, the blind hole pre-pressing mentioned in step (2) refers to using a conical punch to press a blind hole with a depth of 100-150mm into the center of the upper and lower ends of the steel ingot before upsetting, so as to destroy the deformation dead zone; then pre-pressing, the height of the steel ingot after pre-pressing is less than 50% of the height of the steel ingot after blanking; the cone angle of the conical punch is 120-150°.

[0015] Furthermore, the upsetting ratio in the upsetting step described in step (2) Preferably 2.5-4; the diameter of the punch used for punching is... Set as the average diameter of the steel ingot The ratio is more than 0.5 times, preferably 0.5-0.6; after punching, a hollow ring blank is obtained; the average diameter D of the steel ingot is the average of the large end diameter and the small end diameter of the steel ingot after blanking.

[0016] Furthermore, in step (2), the hollow ring blank is forged by using a lever and a press anvil to press the wall thickness of the hollow ring blank in a full circle. After the lever is used to expand the hole, the inner diameter of the hollow ring blank is 1.06-1.15 times the diameter d of the punch.

[0017] Furthermore, in step (3), the intermediate reheating is carried out at a temperature of 1180℃-1200℃, and the holding time must ensure that the core of the billet is fully heated to induce static recrystallization and micropore diffusion welding. The holding time is calculated based on an effective wall thickness of 0.5-0.8 min / mm. The effective wall thickness is obtained by dividing the blank size after the first rolling and expansion by (outer diameter - inner diameter) / 2.

[0018] Furthermore, the temperature of the first forging in step (3) is 1150-1200℃, and the holding time is 2-4h; the final forging temperature of the second forging is higher than 860℃, preferably 860-950℃.

[0019] Beneficial effects of the present invention

[0020] Compared with the prior art, the present invention has the following significant advantages:

[0021] (1) Turning waste into treasure: This invention can produce first-grade forgings that pass the flaw detection using ordinary steel ingots with certain central quality defects (such as X-series octagonal ingots), which greatly reduces the cost of raw materials.

[0022] (2) Thorough elimination of defects: The present invention eliminates the dense inner diameter defects of the raw material ordinary steel ingot from the source by using the double compaction of "conical upsetting" and "horse bar compaction" combined with the physical removal of "large diameter punching".

[0023] (3) Preventing process cracking: The present invention adopts the strategy of "50% graded rolling expansion + intermediate recrystallization" to eliminate the cumulative damage during the large deformation process and avoid brittle tearing caused by temperature drop and work hardening.

[0024] (4) Verification of reliability: Through actual production verification, the first pass rate of UT inspection for 30-ton ASTM A266 ring forgings produced using the process of this invention has increased from less than 25% to over 95%. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process of this invention. Detailed Implementation

[0026] Example 1

[0027] raw materials

[0028] To manufacture a large ASTM A266 ring forging with an outer diameter × inner diameter × height of Φ10430mm × Φ9710mm × 325mm, the raw material is a 39-ton octagonal steel ingot (flat riser). Figure 1 The raw material steel ingot is shown in the image.

[0029] The upper arc-shaped top is the tail end of the ingot.

[0030] The middle part is an octagonal frustum structure with a large end diameter (the inscribed circle diameter of the octagon) of 1662 mm, a small end diameter of 1420 mm, and a spindle height of 2210 mm.

[0031] The lower riser end is an octagonal frustum structure with a large end diameter of 1662 mm, a small end diameter of 1356 mm, and a spindle height of 200 mm.

[0032] The steel ingot has internal porosity and shrinkage cavities due to insufficient riser feeding.

[0033] The composition of the steel ingot is: C: 0.22%; Si: 0.17%; Mn: 0.6%; Cr: 0.2%; Cu: 0.21%; Ni: 0.22%; P: ≤0.025%; S: ≤0.025%, with the balance being Fe.

[0034] process

[0035] The specific process of this embodiment is referred to Figure 1 Specifically, it includes the following steps:

[0036] Feeding

[0037] The steel ingot is first cut off at the tail end using a sawing device, and then the riser end at the head end is cut off. After the riser is cut off, a large area of ​​looseness and central shrinkage cavity are visible to the naked eye or at low magnification. The weight of the riser end and the tail end cut off accounts for 22% of the total weight of the steel ingot (removal rate) to physically remove the dense area of ​​secondary shrinkage cavity. The steel ingot after cutting is an octagonal frustum structure with a large end diameter of 1662 mm, a small end diameter of 1420 mm, and a body height of 2210 mm.

[0038] blanking

[0039] 1. Heating and holding: The steel ingot after cutting is sent into the forging heating furnace, heated to the set temperature of 1250°C, and held for a sufficient time to ensure that the core is heated through. In this embodiment, the holding time is 10 hours.

[0040] 2. Conical Punch Pre-pressing: The heated steel ingot is removed and placed upright on the worktable of a 60-100MN hydraulic press. Using a specially designed conical punch (punch cone angle of 140°), blind holes with a depth of 150mm are pressed into the center of both the top and bottom ends of the steel ingot. Pre-pressing is then performed, resulting in a disc-shaped steel ingot with an outer diameter × height of 2120mm × 1049mm. This step establishes a triaxial compressive stress field by breaking down the core deformation dead zone.

[0041] 3. Heavy upsetting: Heavy upsetting is performed on the steel ingot with blind holes using a flat anvil, upsetting to 35% of the initial height of the steel ingot after cutting (2210mm) (i.e., upsetting ratio). (Approximately 2.8), so that the core pores are closed and welded under triaxial compressive stress.

[0042] 4. Punching: Replace with a solid punch with a diameter of Φ800mm to punch holes in the upset billet to form a hollow ring billet.

[0043] 5. Hole enlargement by lever: The hollow ring blank is enlarged by pressing down the entire circumference using a lever and a flat anvil of a press, increasing the inner diameter of the ring blank, further compacting the wall thickness, and adjusting the size of the ring blank to meet the requirements of the ring rolling mill. After enlargement, the inner diameter of the hollow ring blank is 850mm.

[0044] Expansion

[0045] 1. First rolling and expansion: The ring billet after the expansion by the lever is sent into the heating furnace and heated to 1180℃. After holding at this temperature for 2 hours, it is taken out. The first rolling and expansion is carried out on a D53K-12000 radial and axial ring rolling mill. When the outer diameter reaches the blank size of outer diameter × inner diameter × height: Φ5000 × Φ3950 × 502 mm (approximately 48% of the finished product outer diameter), the machine is stopped to obtain the intermediate ring billet.

[0046] 2. Intermediate Reheating: The intermediate ring billet is sent back to the heating furnace, heated to 1180℃ and held for 5 hours to fully induce static recrystallization, refine the grains and promote micropore diffusion welding.

[0047] 3. Second rolling: Take out the ring billet after it has been returned to the furnace and continue rolling it on a ring rolling mill until the finished size is Φ10430mm, and control the final forging temperature to 900℃.

[0048] Heat treatment

[0049] After forging, the ring forging is placed in air to cool to room temperature.

[0050] Results data

[0051] 100% ultrasonic testing (according to JB / T 5000.15-2007 standard) was performed on the rough-machined ring forgings. The results showed that the rough-machined ring forgings had a uniform and dense microstructure, with no dense inner diameter defects (dense forest-like wave defects or full-circumference lamellar tears within the inner diameter area), meeting the Class III standard or higher. Fifty products were produced using this process, of which 48 passed the first-pass test, achieving a first-pass yield of 96%.

[0052] Example 2

[0053] raw materials

[0054] To manufacture a large ASTM A266 ring forging with an outer diameter × inner diameter × height of Φ8632mm × Φ7868mm × 312mm, 32 tons of octagonal steel ingot was selected as the raw material.

[0055] The upper arc-shaped top is the tail end of the ingot.

[0056] The middle part is an octagonal frustum structure with a large end diameter of 1490 mm, a small end diameter of 1266 mm, and a spindle height of 2253 mm.

[0057] The lower riser end is an octagonal frustum structure with a large end diameter of 1490 mm, a small end diameter of 1200 mm, and a spindle height of 600 mm.

[0058] The steel ingot composition is as follows: C: 0.30%; Si: 0.35%; Mn: 1.2%; Cr: 0.2%; Cu: 0.20%; Ni: 0.18%; P: ≤0.025%; S: ≤0.025%, with the balance being Fe.

[0059] process

[0060] Feeding

[0061] The sawing equipment is used to first cut off the tail of the steel ingot, and then the riser end of the steel ingot head is cut off. The weight of the cut-off accounts for 24% of the total weight of the steel ingot. This is to physically remove the dense area of ​​secondary shrinkage cavities. The steel ingot after cutting is an octagonal frustum structure with a large end diameter of 1490 mm, a small end diameter of 1266 mm, and a body height of 2253 mm.

[0062] blanking

[0063] 1. Heating and holding: The steel ingot after cutting is sent into the forging heating furnace, heated to the set temperature of 1230°C, and held for a sufficient time to ensure that the core is heated through. In this embodiment, the holding time is 8 hours.

[0064] 2. Conical punch pre-pressing: Remove the heated steel ingot and place it upright on the worktable of a 60-100MN hydraulic press. Using a specially made conical punch (punch cone angle of 140°), press blind holes with a depth of 120mm into the center of both the top and bottom ends of the steel ingot. After pre-pressing, the steel ingot is disc-shaped with an outer diameter × height of 1760mm × 1120mm.

[0065] 3. High-intensity upsetting: High-intensity upsetting is performed on steel ingots with blind holes using a flat anvil, upsetting to 38% of the initial height of the steel ingot after cutting (i.e., upsetting ratio). Approximately 2.6).

[0066] 4. Punching: Replace with a solid punch with a diameter of Φ750mm to punch holes in the upset billet to form a hollow ring billet.

[0067] 5. Hole enlargement by lever: The ring blank after punching is enlarged by lever, and the inner diameter of the hollow ring blank after enlargement is 800mm.

[0068] Expansion

[0069] 1. First rolling and expansion: The ring billet after the expansion by the lever is sent into the heating furnace and heated to 1190℃. After holding at this temperature for 2 hours, it is taken out. The first rolling and expansion is carried out on a D53K-12000 radial and axial ring rolling mill. When the outer diameter reaches the blank size of outer diameter × inner diameter × height: Φ4300 × Φ3229 × 488 mm (50% of the finished outer diameter), the machine is stopped to obtain the intermediate ring billet.

[0070] 2. Intermediate return: The intermediate ring billet is sent back to the heating furnace, heated to 1190℃ and held for 5 hours.

[0071] 3. Second rolling: Take out the ring billet after it has been returned to the furnace and continue rolling it on a ring rolling mill until it reaches the finished size of Φ8632mm, controlling the final forging temperature at 860℃.

[0072] Heat treatment

[0073] After forging, the ring forging is placed in air to cool to room temperature.

[0074] Results data

[0075] The rough-machined ring forgings underwent 100% ultrasonic testing (according to JB / T 5000.15-2007 standard). The results showed that the rough-machined ring forgings had a uniform and dense microstructure, with no densely packed internal diameter defects, meeting or exceeding Grade III standards. Fifty products were produced using this process, of which 47 passed the first-pass test, achieving a first-pass yield of 94%.

[0076] Comparative Example 1

[0077] raw materials

[0078] Same as Example 1.

[0079] process parameters

[0080] Material cutting: The cutting rate is set at 18% (lower than the 22% of the present invention).

[0081] Blank preparation:

[0082] 1. Same as Example 1;

[0083] 2. Use a flat anvil for conventional upsetting, upsetting to 35% of the initial height of the steel ingot after cutting;

[0084] 3. Punching and reaming of the lever: Same as in Example 1;

[0085] Rolling and expanding: The ring billet after being expanded by the lever is sent into the heating furnace and heated to 1250℃. After holding at this temperature for 2 hours, it is taken out. It is then rolled and expanded directly to the finished size Φ10430mm in one pass on a D53K-12000 radial and axial ring rolling mill (without intermediate re-sizing steps).

[0086] Heat treatment: After forging, the ring forging is placed in air to cool to room temperature.

[0087] Results data

[0088] 100% ultrasonic testing (according to JB / T 5000.15-2007 standard) was performed on the rough-machined ring forgings. The results showed dense forest-like wave defects within a depth range of 10-200 mm in inner diameter, and reduced bottom waves in many places, rendering them unusable. Of the 20 pieces produced using this process, only 5 were barely acceptable, resulting in a first-pass yield of only 25%.

[0089] Comparative Example 2

[0090] raw materials

[0091] Same as Example 1.

[0092] process parameters

[0093] Material removal: The removal rate was 22%.

[0094] Blank preparation:

[0095] 1. Same as Example 1;

[0096] 2. Use a flat anvil for conventional upsetting, upsetting to 35% of the initial height of the steel ingot after cutting;

[0097] 3. Punching and reaming of the lever: Same as in Example 1;

[0098] Expanding:

[0099] 1. First rolling and expansion: The ring billet after the expansion by the lever is sent into the heating furnace and heated to 1180℃. After holding at this temperature for 2 hours, it is taken out. The first rolling and expansion is carried out on a D53K-12000 radial and axial ring rolling mill. When the outer diameter reaches the blank size of outer diameter × inner diameter × height: Φ5000 × Φ3950 × 502 mm (approximately 48% of the finished product outer diameter), the machine is stopped to obtain the intermediate ring billet.

[0100] 2. Intermediate return: The intermediate ring billet is sent back to the heating furnace, heated to 1250℃ and held for 5 hours.

[0101] 3. Second rolling: Take out the ring billet after it has been returned to the furnace and continue rolling it on a ring rolling mill until the finished size is Φ10430mm, and control the final forging temperature to 900℃.

[0102] Heat treatment: After forging, the ring forging is placed in air to cool to room temperature.

[0103] Results data

[0104] The ring forgings after rough turning are subjected to 100% ultrasonic flaw detection (in accordance with the JB / T 5000.15-2007 standard). The results show that although the defects are reduced compared with Comparative Example 1, there are still some areas with excessive defects, mainly concentrated in the core position. Twenty pieces are produced using this process, and twelve are qualified, with a one-time qualification rate of 60%.

Claims

1. A forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots, characterized in that, Includes the following steps: (1) Blanking: Take multi-faceted steel ingots as raw materials, and cut off the tail end and the riser end of the head of the ingot. The cutting rate is set at 22%-25%. The composition of the multi-faceted steel ingot is: C: 0.22%~0.30%; Si: 0.17%~0.35%; Mn: 0.6%~1.2%; Cr: <0.27%; Cu: <0.25%; Ni: <0.25%; P: ≤0.025%. S: ≤0.025%, balance is Fe; (2) Billet making: After heating the steel ingot after blanking, blind hole pre-pressing, upsetting, punching and reaming are carried out in sequence; The upsetting ratio in the upsetting step The diameter of the punch used for punching is... Set as the average diameter of the steel ingot More than 0.5 times the diameter of the steel ingot, and a hollow ring blank is obtained after punching; the average diameter D of the steel ingot is the average of the large end diameter and the small end diameter of the steel ingot after blanking. The aforementioned lever-assisted hole enlargement method utilizes a lever and a press anvil to perform full-circumferential pressing forging of the hollow ring blank wall thickness. After lever-assisted hole enlargement, the inner diameter of the hollow ring blank is 1.06-1.15 times the punch diameter d. (3) Rolling: The graded rolling process is adopted. The first rolling is stopped when the outer diameter of the finished product is 45%-50%. After intermediate reheating, the second rolling is carried out. (4) Heat treatment: Cool to room temperature in air.

2. The forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots according to claim 1, characterized in that: The multi-faceted steel ingot mentioned in step (1) is a 3-12 faceted, 30-40 ton steel ingot, and the multi-faceted steel ingot is a low density steel ingot.

3. The forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots according to claim 1, characterized in that: The heating temperature in step (2) is 1220℃-1250℃; the heat preservation time is 8-20h.

4. The forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots according to claim 1, characterized in that, The blind hole pre-pressing mentioned in step (2) refers to using a conical punch to press a blind hole with a depth of 100-150mm into the center of the upper and lower ends of the steel ingot before upsetting, so as to destroy the deformation dead zone; then pre-pressing, the height of the steel ingot after pre-pressing is less than 50% of the height of the steel ingot after blanking; the cone angle of the conical punch is 120-150°.

5. The forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots according to claim 1, characterized in that, The intermediate reheating in step (3) is heated at a temperature of 1180℃-1200℃, and the holding time must ensure that the core of the billet is fully heated to induce static recrystallization and micropore diffusion welding; the holding time is calculated based on an effective wall thickness of 0.5-0.8 min / mm.

6. The forming process for manufacturing ASTM A266 large ring forgings based on low-density steel ingots according to claim 1, characterized in that, The temperature of the first forging in step (3) is 1150-1200℃, and the holding time is 2-4h; the final forging temperature of the second forging is higher than 860℃.

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