Process for forging large-specification round steel of phi 180 mm-phi 240 mm from 45 carbon structural steel

Abstract

The invention discloses a process for forging large-specification round steel with the diameter of phi 180-phi 240 mm by using 45 carbon structural steel, and aims to solve the problem that the performance of the large-specification 45 carbon structural steel is deteriorated due to mixed crystals and coarse crystals. In order to achieve the purpose, the following technical scheme is adopted: economic refined grain elements aluminum and nitrogen are additionally added to smelting components; heating the steel ingot at low temperature for a short time, and controlling the furnace returning heating temperature and time; during 35MN fast forging, the grain size growth is controlled at the low finish forging temperature, and the finish forging temperature is 800-850 DEG C; during forging, deformation is uniform under large rolling reduction, grains are further crushed, and the refining effect is achieved; and rapid cooling is performed after forging to inhibit grain growth. The method has the advantages that the actual grain size is improved through the process scheme, mixed crystals and coarse crystals are prevented, the actual grain size at the half position of the radius is not smaller than the fifth level, and the requirements of downstream users are met.

Description

Technical Field

[0001] The present invention belongs to the field of metal material manufacturing, and relates to a manufacturing method of large-sized forged round steel of 45 carbon structural steel, specifically to a process for forging large-sized round steel of φ180mm - φ240mm of 45 carbon structural steel. Background Art

[0002] High-quality medium-carbon carbon structural steel 45 steel, with its excellent mechanical properties, good workability and wide practicability, shows significant application prospects in multiple industrial fields. With the rapid development of China's manufacturing industry and the continuous advancement of infrastructure construction, the market demand for large-sized round steel products of 45 steel is also increasing continuously. However, in the production process of steel mills, large-sized round steel products are prone to mixed crystal and coarse crystal situations. Considering from the perspective of grain size inheritance, it is difficult for downstream users of steel mills to eliminate the mixed crystal phenomenon after processing steel with mixed crystal and coarse crystal, resulting in performance degradation. Currently, the φ240mm 45 steel forged material products delivered by suppliers have mixed crystal and coarse crystal, resulting in mixed crystal in the final finished crankshaft. The technical requirements of users for the forged material are to take samples at half of the radius of the round steel and check that the actual grain size of the steel should not be less than grade 5 according to GB / T 6394; at the same time, for the φ190mm 45 steel forged material, the actual grain size measured by sampling at half of the radius is: 6.0 grades (30%), 2 grades (70%), which is also mixed crystal and fails to meet the user requirements. Summary of the Invention

[0003] The present invention discloses a process for forging large-sized round steel of φ180mm - φ240mm of 45 carbon structural steel to solve the problem of deteriorated performance caused by mixed crystal and coarse crystal in large-sized 45 carbon structural steel.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] ⑴ Chemical composition control of steel (mass fraction, %): carbon: 0.46 - 0.50, silicon: 0.25 - 0.35, manganese: 0.75 - 0.80, phosphorus not more than 0.020, sulfur not more than 0.005, chromium: 0.20 - 0.25, nickel not more than 0.30, vanadium: 0.10 - 0.12, copper not more than 0.05, aluminum: 0.020 - 0.040, [H] not more than 1.5×10 -6 , [N]: 0.008 - 0.015.

[0006] ⑵ Smelting process route: converter → LF furnace → RH / VD → ingot casting → steel ingot transfer

[0007] ①Converter process: For batching, blast furnace hot metal is selected, and scrap steel with low residual elements is added. The hot metal weight is 95t - 115t, and the scrap ratio ≤ 15%; tapping temperature is 1610°C - 1650°C, the end-point phosphorus is not more than 0.015%, and carbon is not less than 0.07%; converter tapping deoxidation and alloying: When about 1 / 5 of the tapping amount is reached, alloys and slag materials are added in the order of "silicon manganese, high chromium, aluminum block, lime, refining slag". Alloying composition control: carbon: 0.30% - 0.45%, silicon: 0.15% - 0.30%, manganese: 0.60% - 0.75%, phosphorus is not more than 0.013%, chromium: 0.13% - 0.23%, nickel is not more than 0.25%, copper is not more than 0.05%;

[0008] Amount of slag materials added: refining slag 2.7kg / t - 3.0kg / t;

[0009] Amount of deoxidizer added: When 0.07% ≤ [C] ≤ 0.08% at tapping, the aluminum block addition amount is 1.5kg / t of molten steel; when 0.08% < [C] ≤ 0.15% at tapping, the aluminum block addition amount is 1.25kg / t of molten steel; when 0.15% < [C] ≤ 0.30% at tapping, the aluminum block addition amount is 1.0kg / t of molten steel.

[0010] ②LF furnace process: When refining arrives at the station, 4.1kg / t - 4.5kg / t of lime and 200kg - 300kg of refining slag are supplemented;

[0011] Precipitation deoxidation is adopted: According to the first analysis result of the LF furnace, 0.040% - 0.050% of aluminum wire is fed, and the aluminum content is not adjusted during the subsequent refining process;

[0012] Carbon powder and aluminum beans are used for diffusion deoxidation, mixed evenly at 1:1, and added to the slag surface in batches with a shovel until the slag turns white. The total amount of carbon powder and aluminum beans used is controlled at 60kg - 100kg, and the ladle lifting temperature of the LF furnace is 1622°C - 1642°C.

[0013] ③RH / VD furnace process: The RH / VD ultimate vacuum degree is not more than 67Pa, the time to maintain the ultimate vacuum degree is not less than 15min, and the weak argon blowing time is not less than 20min; After the RH tank is opened, a nitrogen-enriched cored wire is used to make the nitrogen content in the steel reach 0.0080% - 0.015%; the ladle lifting temperature is 1537°C - 1547°C.

[0014] ④Mold casting process: Select ingots of 5.5t - 6.7t, and MZ-ZG type protective slag and 850 heating agent are used for pouring.

[0015] ⑶Forging process route: Ingot heating → 35MN quick forging → Return furnace heating → 16MN precision forging → Air cooling → Annealing

[0016] ①Ingot heating: The heating temperature of the trolley furnace and chamber furnace is 1160°C - 1200°C, the holding time is 4h - 6h, and the total time is 8h - 10h.

[0017] ②35MN quick forging: The starting forging temperature of the quick forging is 1000°C - 1050°C, the final forging temperature is 800°C - 850°C, and the trimming temperature is not lower than 700°C; There should be one pass of forging with a large reduction of 100mm - 120mm during the forging elongation process; Control the lower limit of the return furnace holding temperature, heat for 30min - 120min and then take out of the furnace.

[0018] ③When using the 16MN precision forging machine to produce finished products, the starting forging temperature is 850°C - 950°C, the trimming temperature is 700°C, and it is transferred from forging to the heat treatment air-cooling area for air-cooling within 15 minutes.

[0019] ④Air-cooling after forging: The steel materials after air-cooling after forging are placed on the padding iron, and the distance between two materials is not less than 0.5m. Ensure uniform cooling during placement, and put them into the furnace for annealing in time after cooling to 300°C - 400°C.

[0020] ⑤Annealing after forging: The effective cross-section is φ180mm - φ240mm; Execute the following process (see Figure 1 ), slow-cool and wait for materials - heating (the heating rate is not higher than 80°C / h) - holding after uniform temperature (10h - 13h) - cooling (the cooling rate is not higher than 30°C / h) - taking out of the furnace (the furnace outlet temperature is not higher than 400°C).

[0021] Description of the invention points of the present invention:

[0022] ①Considering the inhibition of grain size growth through chemical composition, on the basis of the range provided by the user, additional economical grain refinement elements aluminum and nitrogen are added to the melting composition. Aluminum: 0.020% - 0.040%, nitrogen: 0.0080% - 0.0150%;

[0023] ②Low-temperature and short-time heating of the ingot, control the return furnace heating temperature and time to prevent grain growth. The ingot heating temperature is 1160°C - 1200°C, the holding time is 4h - 6h, and the total time is 8h - 10h; Control the middle and lower limits of the return furnace holding temperature, heat for 30min - 120min and then take out of the furnace.

[0024] ③Control the grain size growth by low final forging temperature during 35MN quick forging, and the final forging temperature is 800°C - 850°C.

[0025] ④Uniform deformation with a large reduction during forging, further crush the grains to play a role in refinement, and adopt the forging method of 35MN quick forging + 16MN precision forging to form the material.

[0026] ⑤Rapid cooling after forging to inhibit grain growth: Transfer the steel from forging to the air-cooling area of heat treatment within 15 minutes after forging for air cooling. Place the steel on the padding iron, and the distance between two pieces of material should be no less than 0.5 m, ensuring uniform cooling during placement.

[0027] Benefits of the present invention: Improve the actual grain size through the above process scheme, prevent the occurrence of mixed grains and coarse grains, and make the actual grain size at half of the radius not less than Grade 5, meeting the requirements of downstream users. Description of the Drawings

[0028] Figure 1 It is the annealing process curve. Detailed Implementation Modes

[0029] Implement according to the above technical scheme, and provide the following three preferred embodiments.

[0030] Embodiment 1

[0031] The size and shape of the produced round steel are Φ180 mm.

[0032] ⑴Smelting process flow: Converter → LF → VD → Casting ingot type 5.5 t - 6.7 t octagon → Red conversion;

[0033] ①Converter process: Select 112 t of blast furnace hot metal and 14.67% of scrap steel for batching; tapping temperature is 1625 °C, phosphorus: 0.014%, carbon: 0.09%. After tapping, add 369 kg of silicomanganese, 50 kg of aluminum block, 300 kg of refining slag, and 136 kg of carburant.

[0034] ②LF furnace process: Lime addition amount is 450 kg, refining slag is 300 kg; use a total of 80 kg of carbon powder and aluminum beans for diffusion deoxidation; after the first analysis, feed 140 m of aluminum wire for precipitation deoxidation. The aluminum content in the second analysis is 0.045%, and the tapping temperature of the LF furnace is 1639 °C.

[0035] ③VD process: The ultimate vacuum degree is not greater than 67 Pa, the time to maintain the ultimate vacuum degree is 15 minutes, the weak argon blowing time is 32 minutes, feed 110 m of nitrogen wire, and the tapping temperature is 1542 °C.

[0036] ④Casting: The steel ingot is cast under argon protection, and 8 steel ingots are cast; add MZ-ZG type protective slag and 850 heat generating agent.

[0037] The melting composition results of the steel ingot are shown in Table 1.

[0038] Table 1

[0039]

[0040] ⑵Forging process flow: Ingot heating → 35 MN quick forging → Return furnace heating → 16 MN finish forging → Air cooling → Annealing

[0041] ①Forged with 5.5 - ton octagonal ingots, with a processing ratio of 12.

[0042] ②After the steel ingots are held at 1179℃ - 1200℃ for 8 hours, they are forged on a 35MN quick - forging machine. The starting forging temperature is 1000℃. First, the cap - end is forged, and after cutting off the head, the ingot tail - end is forged in reverse. The final forging temperature is 820℃.

[0043] ③After forging, they are reheated in the furnace for a short time. The starting forging temperature on a 16MN machine is 870℃, and the trimming temperature is 730℃. Then they are transferred to the air - cooling area for cooling.

[0044] ④After air - cooling, the forged materials are annealed. The finished products after annealing are inspected for the actual grain size at half of the radius of the steel according to GB / T6394, and are rated as grade 5.5 - 6.5, with an average of grade 6.

[0045] Example 2

[0046] The size and shape of the produced round steel are Φ210mm.

[0047] ⑴Smelting process flow: Converter → LF → VD → Pouring ingot type 5.5t - 6.7t octagonal → Red - turning;

[0048] ①Converter process: The charge consists of 115t of blast - furnace hot metal and 14.14% scrap steel; the tapping temperature is 1623℃, phosphorus: 0.012%, carbon: 0.07%. After tapping, 384kg of silico - manganese, 55kg of aluminum blocks, 300kg of refining slag, and 150kg of carburizer are added.

[0049] ②LF furnace process: The lime addition is 450kg, and the refining slag is 300kg; 70kg of carbon powder and aluminum beans are used for diffusion deoxidation; after the first analysis, 160m of aluminum wire is fed for precipitation deoxidation. The aluminum content in the second analysis is 0.055%, and the ladle - hanging temperature of the LF furnace is 1635℃.

[0050] ③VD process: The ultimate vacuum degree is not greater than 67Pa, the time for maintaining the ultimate vacuum degree is 15min, the weak argon - blowing time is 36min, 120m of nitrogen wire is fed, and the ladle - hanging temperature is 1549℃.

[0051] ④Pouring: The steel ingots are cast under argon protection, and 8 steel ingots are poured; MZ - ZG type protective slag and 850 heat - generating agent are added.

[0052] The results of the melting composition of the steel ingots are shown in Table 2.

[0053] Table 2

[0054]

[0055] ⑵Forging process flow: Steel ingot heating → 35MN quick - forging → Re - furnace heating → 16MN precision forging → Air - cooling → Annealing

[0056] ①Forged with 5.5-ton octagonal ingots, with a processing ratio of 9.

[0057] ②After the steel ingots are kept warm at 1179°C - 1200°C for 4 hours, they are forged with a 35MN quick forging machine. The starting forging temperature is 1000°C. First, the cap end is forged, and after cutting the head, the ingot tail end is forged in reverse. The final forging temperature is 820°C.

[0058] ③After forging, they are reheated in the furnace for a short time. The starting forging temperature with a 16MN machine is 880°C, and the finishing temperature is 740°C. Then they are transferred to the air-cooling area for cooling.

[0059] ④After air-cooling, the forged materials are annealed. The finished products after annealing are inspected for the actual grain size at half of the radius of the steel according to GB / T6394, and are rated as grade 5 - 6.5, with an average of grade 5.5.

[0060] Example 3

[0061] The size and shape of the produced round steel are Φ240mm.

[0062] ⑴Smelting process flow: converter → LF → VD → pouring ingot type 5.5t - 6.7t octagonal → red turning;

[0063] ①Converter process: The burden is selected as 110t of blast furnace hot metal and 13.77% of scrap steel; the tapping temperature is 1630°C, phosphorus: 0.015%, carbon: 0.08%. After tapping, 374kg of silicomanganese, 53kg of aluminum blocks, 300kg of refining slag, and 145kg of carburizer are added.

[0064] ②LF furnace process: The lime addition amount is 450kg, and the refining slag is 300kg; 75kg of carbon powder and aluminum beans are used for diffusion deoxidation; after the first analysis, 150m of aluminum wire is fed for precipitation deoxidation. The aluminum content in the second analysis is 0.050%, and the ladle hanging temperature of the LF furnace is 1642°C.

[0065] ③VD process: The ultimate vacuum degree is not greater than 67Pa, the time to maintain the ultimate vacuum degree is 15min, the weak argon blowing time is 36min, 100m of nitrogen wire is fed, and the ladle hanging temperature is 1547°C.

[0066] ④Pouring: The steel ingots are cast under argon protection, and 8 steel ingots are poured; MZ-ZG type protective slag and 850 heat-generating agent are added.

[0067] The results of the melting composition of the steel ingots are shown in Table 3.

[0068] Table 3

[0069]

[0070] ⑵Forging process flow: steel ingot heating → 35MN quick forging → furnace reheating → 16MN precision forging → air cooling → annealing

[0071] ①Forged with 6.1-ton octagonal ingots, with a processing ratio of 7.0.

[0072] ②After the steel ingots are heat-insulated at 1179°C - 1200°C for 4 hours, they are forged with a 35MN quick forging machine. The starting forging temperature is 1000°C. First, the cap end is forged, and after cutting the head, the ingot tail end is forged in reverse. The final forging temperature is 820°C.

[0073] ③After forging, short-time re-heating in the furnace is adopted. The starting forging temperature with a 16MN machine is 880°C, and the trimming temperature is 720°C. Then it is transferred to the air-cooling area for cooling.

[0074] ④The forged material is annealed after air-cooling. The finished product after annealing is inspected for the actual grain size at half of the radius of the steel according to GB / T6394, and it is rated as grade 5.5.

Claims

1. A 45 carbon structural steel, characterized in that: Chemical composition control of 45 carbon structural steel: carbon: 0.46% ~ 0.50%, silicon: 0.25% ~ 0.35%, manganese: 0.75% ~ 0.80%, phosphorus not more than 0.020%, sulfur not more than 0.005%, chromium: 0.20% ~ 0.25%, nickel not more than 0.30%, vanadium: 0.10% ~ 0.12%, copper not more than 0.05%, aluminum: 0.020% ~ 0.040%, [H] not more than 1.5 × 10 -6 , [N]: 0.008% ~ 0.015%.

2. According to claim 1, a process for forging large-size round steel of φ180mm~φ240mm of 45 carbon structural steel, characterized in that: ⑴Smelting process route: converter → LF furnace → RH / VD → mold casting → ingot transfer, ① Converter process: the ingredients are blast furnace iron liquid, 95t~115t of scrap iron liquid with low residual elements, and the scrap ratio is not more than 15%; the tapping temperature is 1610℃~1650℃, the final phosphorus is not more than 0.015%, and the carbon is not less than 0.07%; deoxidation and alloying of converter tapping: when the tapping amount is about 1 / 5, alloy and slag are added in the order of "silicon manganese, high chromium, aluminum block, lime, and refined slag", and the alloying composition is controlled as follows: carbon: 0.30%~0.45%, silicon: 0.15%~0.30%, manganese: 0.60%~0.75%, phosphorus not more than 0.013%, chromium: 0.13%~0.23%, nickel not more than 0.25%, copper not more than 0.05%; Slag addition amount: refined slag 2.7kg / t~3.0kg / t; Deoxidizer addition amount: for steel tapping 0.07%≤[C]≤0.08%, the amount of aluminum block added is 1.5kg / t molten steel; for steel tapping 0.08%<[C]≤0.15%, the amount of aluminum block added is 1.25kg / t molten steel; for steel tapping 0.15%<[C]≤0.30%, the amount of aluminum block added is 1.0kg / t molten steel; ②LF furnace process: add 4.1kg / t~4.5kg / t of lime and 200kg~300kg of refining slag at the refining station; Precipitation deoxidation: According to the first analysis result of LF furnace, aluminum wire is fed at 0.040% to 0.050%, and the aluminum content is no longer adjusted during the refining process; Use carbon powder and aluminum beans for diffusion deoxidation, mix them in a ratio of 1:1, add them to the slag surface in batches with a shovel until the slag turns white, the total amount of carbon powder and aluminum beans is controlled at 60kg~100kg, and the LF furnace hanging bag temperature is 1622℃~1642℃; ③RH / VD furnace process: RH / VD ultimate vacuum is not greater than 67Pa, the ultimate vacuum time is maintained for not less than 15min, and the weak argon blowing time is not less than 20min; after the RH tank is opened, nitrogen-enhanced cored wire is used to make the nitrogen content in the steel reach 0.0080%~0.015%; the hanging bag temperature is 1537℃~1547℃. ④Mold casting process: select 5.5t~6.7t ingot, use MZ-ZG type protective slag and 850 heating agent for casting; ⑵Forging process route: ingot heating → 35MN fast forging → return to furnace heating → 16MN fine forging → air cooling → annealing, ① Ingot heating: Trolley furnace, chamber furnace heating temperature 1160 ℃ ~ 1200 ℃, insulation time 4h ~ 6h, total time 8h ~ 10h; ②35MN fast forging: the starting temperature of fast forging is 1000℃~1050℃, the final forging temperature is 800℃~850℃, and the finishing temperature is not less than 700℃; the forging and drawing process requires a large reduction of 100mm~120mm per pass; the return furnace insulation temperature is controlled at the middle and lower limits, and it takes 30min~120min to heat before leaving the furnace; ③ The finished product is turned into 16MN precision forging machine with the starting forging temperature of 850℃~950℃ and the finishing temperature of 700℃. It is transferred from forging to heat treatment air cooling zone for air cooling within 15min; ④ Air cooling after forging: The air-cooled steel after forging is placed on the pad iron, and the distance between the two materials is not less than 0.5m. When placing, ensure uniform cooling. After cooling to 300℃~400℃, put it into the furnace for annealing in time; ⑤ Annealing after forging: effective section φ180mm~φ240mm; perform the following process (see Figure 1), slow cooling - heating (heating rate not higher than 80℃ / h) - temperature equalization and heat preservation (10h~13h) - cooling (cooling rate not higher than 30℃ / h) - furnace discharge (furnace discharge temperature not higher than 400℃).

3. According to claim 1, a process for forging large-size round steel of φ180mm~φ240mm of 45 carbon structural steel, characterized in that: ⑴Smelting process: converter → LF → VD → pouring ingot 5.5t~6.7t octagonal → red converter, ① Converter process: The ingredients are 112t of blast furnace iron and 14.67% of scrap steel; the tapping temperature is 1625℃, phosphorus: 0.014%, carbon: 0.09%, and 369kg of silicon manganese, 50kg of aluminum block, 300kg of refined slag, and 136kg of carburizer are added after tapping; ②LF furnace process: lime addition amount 450kg, refined slag 300kg; carbon powder and aluminum beans are used for diffusion deoxidation; 140m aluminum wire is fed after the primary analysis, and the secondary analysis of aluminum: 0.045%, LF furnace hanging bag temperature is 1639℃; ③VD process: the ultimate vacuum degree is not more than 67Pa, the ultimate vacuum degree time is maintained for 15min, the weak argon blowing time is 32min, the nitrogen feeding line is 110m, and the bag temperature is 1542℃; ④ Pouring: The steel ingots are cast with argon protection, and 8 steel ingots are cast; MZ-ZG type protective slag and 850 heating agent are added; The results of ingot smelting composition are shown in Table 1; Table 1 ⑵Forging process flow: steel ingot heating → 35MN fast forging → return to furnace heating → 16MN fine forging → air cooling → annealing, ①Forging with 5.5 ton octagonal ingot, processing ratio 12; ② After the steel ingot is kept at 1179℃~1200℃ for 8h, h35MN is quickly forged with the starting forging temperature of 1000℃. The cap head end is forged first, and then the tail end of the ingot is forged upside down after cutting the head. The final forging temperature is 820℃. ③ After forging, return to the furnace for short-term heating. The starting forging temperature of 16MN is 850℃, the finishing temperature is 730℃, and then transferred to the air cooling area for cooling. ④ After air cooling, the forgings are annealed. The finished round steel after annealing has an outer size of Φ180mm. According to GB / T6394, the actual grain size at half the radius of the steel is tested and rated as 5.5 to 6.5, with an average of 6.

4. According to claim 1, a process for forging large-size round steel of φ180mm~φ240mm of 45 carbon structural steel, characterized in that: ⑴Smelting process: converter → LF → VD → pouring ingot 5.5t~6.7t octagonal → red converter, ① Converter process: The ingredients are 115t of blast furnace iron and 14.14% of scrap steel; the tapping temperature is 1623℃, phosphorus: 0.012%, carbon: 0.07%, and 384kg of silicon manganese, 55kg of aluminum block, 300kg of refined slag, and 150kg of recarburizer are added after tapping; ②LF furnace process: lime addition amount 450kg, refined slag 300kg; carbon powder and aluminum beans are used for diffusion deoxidation; 160m aluminum wire is fed after the primary analysis, and the secondary analysis of aluminum: 0.055%, and the LF furnace hanging bag temperature is 1635℃; ③VD process: the ultimate vacuum degree is not more than 67Pa, the ultimate vacuum degree time is maintained for 15min, the weak argon blowing time is 36min, the nitrogen feeding line is 120m, and the bag temperature is 1549℃; ④ Pouring: The steel ingots are cast with argon protection, and 8 steel ingots are cast; MZ-ZG type protective slag and 850 heating agent are added; The results of ingot smelting composition are shown in Table 2; Table 2 ⑵Forging process flow: steel ingot heating → 35MN fast forging → return to furnace heating → 16MN fine forging → air cooling → annealing, ①Forging with 5.5 ton octagonal ingot, processing ratio 9; ② After the steel ingot is kept at 1179℃~1200℃ for 4h, h35MN is forged quickly, the starting forging temperature is 1000℃, the cap head end is forged first, the head is cut and the tail end of the ingot is forged upside down, and the final forging temperature is 820℃; ③ After forging, return to the furnace for short-term heating, 16MN forging temperature 850, finishing temperature 730℃, transfer to the air cooling zone for cooling; ④ After air cooling, the forgings are annealed. The finished round steel after annealing has an outer size of Φ210mm. According to GB / T6394, the actual grain size at half the radius of the steel is tested and rated as 5 to 6.5, with an average of 5.

5.

5. According to claim 1, a process for forging large-size round steel of Φ180mm-Φ240mm of 45 carbon structural steel, characterized in that: ⑴Smelting process: converter → LF → VD → pouring ingot 5.5t~6.7t octagonal → red converter, ① Converter process: The ingredients are 110t of blast furnace iron and 13.77% of scrap steel; the tapping temperature is 1630℃, phosphorus: 0.015%, carbon: 0.08%, and 374kg of silicon manganese, 53kg of aluminum block, 300kg of refined slag, and 145kg of recarburizer are added after tapping; ②LF furnace process: lime addition amount 450kg, refined slag 300kg; carbon powder and aluminum beans are used for diffusion deoxidation; 150m aluminum wire is fed after the primary analysis, and the secondary analysis of aluminum: 0.050%, LF furnace hanging bag temperature is 1642℃; ③VD process: the ultimate vacuum degree is not more than 67Pa, the ultimate vacuum degree time is maintained for 15min, the weak argon blowing time is 36min, the nitrogen feeding line is 100m, and the bag temperature is 1547℃; ④ Pouring: The steel ingots are cast with argon protection, and 8 steel ingots are cast; MZ-ZG type protective slag and 850 heating agent are added; The results of ingot smelting composition are shown in Table 3; Table 3 ⑵Forging process flow: steel ingot heating → 35MN fast forging → return to furnace heating → 16MN fine forging → air cooling → annealing, ①Forging with 6.1 ton octagonal ingot, processing ratio 7.0; ② After the steel ingot is kept at 1179℃~1200℃ for 4h, h35MN is forged quickly, the starting forging temperature is 1000℃, the cap head end is forged first, the head is cut and the tail end of the ingot is forged upside down, and the final forging temperature is 820℃; ③ After forging, return to the furnace for short-term heating, 16MN forging temperature 850, finishing temperature 730℃, transfer to the air cooling zone for cooling; ④ After air cooling, the forgings are annealed. The finished round steel after annealing has an outer size of Φ240mm. The actual grain size at half the radius of the steel is tested in accordance with GB / T6394 and is rated as grade 5.5.

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