A process for producing a d6ac seamless steel tube

Abstract

This invention belongs to the field of metal material processing, specifically disclosing a production process for D6AC seamless steel pipes. Through billet preparation, forging, forging annealing, forging processing, extrusion molding, and a series of heat treatment operations, D6AC seamless steel pipes are obtained. The finished steel pipes have a hardness ≤285HBW, tensile strength ≥1520MPa, yield strength (Rp0.2) ≥1420MPa, elongation ≥9.0%, and grain size ≥5. The production process of this invention has a short process flow, and the produced D6AC seamless steel pipe material has high density, fine grains, uniform and fine microstructure, and few pores and impurities, exhibiting good mechanical properties and high batch-to-batch consistency.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing, specifically a production process for D6AC seamless steel pipes. Background Technology

[0002] The development of D6AC superalloy originated from the US demand for materials for extreme working conditions in the 1960s. At that time, missile engine casings, spacecraft structural components, and other materials needed to withstand high-pressure gas impacts, high-temperature ablation, and complex stress environments. Traditional materials (such as AISI 4340 steel) were insufficient in balancing strength and toughness. By optimizing the carbon content (0.38%-0.43%) and alloy ratio (chromium, molybdenum, nickel, etc.), D6AC superalloy significantly improved its overall performance, becoming a dedicated steel for solid rocket motor casings. Through material composition optimization and process innovation, it has gradually expanded into high-end machinery, energy, and other industrial fields. Its high strength, high toughness, and adaptability to multiple scenarios make it the preferred material for key structural components and continuously drive technological upgrades in related industries.

[0003] In existing technologies, the raw bars for D6AC seamless steel pipes are manufactured using an electric furnace + ladle refining + vacuum degassing process. The raw bars produced by this process have defects such as high inclusion content, high porosity, and high degree of component segregation. After the raw bars are formed into pipes through a hot piercing process, firstly, it is difficult to avoid oblique cracks; secondly, the hot piercing process is lengthy, requiring piercing, rolling, and sizing steps, resulting in significant fluctuations in the final rolling temperature between pipes, high heat loss, and difficulty in ensuring consistency of forming process parameters for the same batch of raw materials, leading to corresponding fluctuations in the performance of the finished product. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a production process for D6AC seamless steel pipes, thereby refining material grains and improving the mechanical properties of the finished product.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a production process for D6AC seamless steel pipe, comprising the following steps:

[0006] S1: Billet preparation: using pure iron and ferroalloys as raw materials, electrode billets are produced by vacuum induction melting, and the electrode billets are smelted into steel ingots by electroslag remelting technology.

[0007] S2: Forged bar, which is formed by heating a steel ingot and forging it into a forged bar; the forging process is upsetting and drawing, with a compression ratio of 4.0 to 7.0;

[0008] S3: Annealing of forged bars, the forged bars obtained in step S2 are annealed;

[0009] S4: Forging bar processing, removing the oxide scale from the outer surface of the forging bar obtained in step S3, and processing the enlarged guide hole;

[0010] S5: Extrusion molding, heating the expanded bar material obtained in step S4 to 1090℃~1130℃ in an electromagnetic induction furnace, and then extruding the medium and thick wall steel pipe using an extrusion unit.

[0011] S6: Anneal the steel pipe obtained in step S5;

[0012] S7: Normalize the steel pipe obtained in step S6;

[0013] S8: Quench the steel pipe obtained in step S7;

[0014] S9: Temper the steel pipe obtained in step S8, and air cool it to obtain the finished pipe;

[0015] The seamless steel pipe comprises, by mass percentage, C: 0.44–0.50, Si: 0.10–0.40, Mn: 0.55–0.95, P: ≤0.015, S: ≤0.015, Cr: 0.80–1.30, Ni: 0.30–0.80, Mo: 0.87–1.13, V: 0.04–0.16, Cu: ≤0.20, with the remainder being Fe and unavoidable impurities.

[0016] As a limitation of the present invention: the outer diameter of the seamless steel pipe is 80-273 mm and the wall thickness is 13 mm-50 mm.

[0017] As a limitation of the present invention: the finished seamless steel pipe has a hardness ≤285HBW, tensile strength ≥1520MPa, yield strength ≥1420MPa (Rp0.2), elongation ≥9.0%, and grain size ≥5.

[0018] As a limitation of the present invention: the heating in step S2 includes: heating the steel ingot to a furnace temperature of 450°C to 500°C and holding it at that temperature for 3 hours; then raising the furnace temperature to 1160°C to 1200°C at a heating rate of 100°C to 120°C / hour and holding it at that temperature for 3 hours to 5 hours.

[0019] As a limitation of the present invention: the forging described in step S2 has an initial forging temperature of 1160-1200°C, a final forging temperature of 850-950°C, a reduction of 30-70 mm per pass, and a feed rate of 70-100 mm.

[0020] As a limitation of the present invention: the annealing in step S3 is carried out in a chamber heating furnace at a temperature of 810°C to 870°C for 6 to 12 hours, and then the furnace is cooled to 300°C to 350°C before being removed from the furnace and air-cooled to room temperature.

[0021] As a limitation of the present invention: in step S4, 5mm to 6mm is removed from one side of the outer circle of the forging bar, and the diameter of the expansion guide hole is 45mm to 80mm.

[0022] As a limitation of the present invention: In step S5, the expanded hole bar is heated twice in the electromagnetic induction furnace; the first heating power is 350KW, and the outer surface temperature of the expanded hole bar reaches 1000℃~1030℃; the second heating power is 800KW, and the outer surface temperature of the expanded hole bar reaches 1090℃~1130℃, thus completing the heating.

[0023] In step S5, after heating and before extrusion, the expanded bar stock is first descaled by high-pressure water at 18MPa to 23MPa, and then lubricated with glass powder.

[0024] The extrusion unit mentioned in step S5 is a horizontal extrusion unit, and the process of extruding medium and thick-walled steel pipes includes:

[0025] ① Hole reaming machine, reaming speed is 150mm~250mm / s, reaming ratio is 1.01~1.40;

[0026] ② Extrusion by an extrusion unit, with an extrusion speed of 100mm~150mm / s and an extrusion ratio of 3~10.

[0027] As a limitation of the present invention: the annealing process described in step S6 includes: heating the steel pipe to 700±10°C in a roller hearth atmosphere protection furnace, holding it at that temperature for 60min~90min, cooling it in the furnace to below 350°C, air cooling it after it is taken out of the furnace, and then pressure straightening it.

[0028] The normalizing treatment described in step S7 includes: heating the steel pipe to 900±10℃, holding it at that temperature for 60 minutes, and then air-cooling it after removing it from the furnace;

[0029] The quenching process described in step S8 includes: heating the steel pipe to 870±10℃, holding it at that temperature for 60 minutes, immersing it in oil for rapid cooling, and air cooling when the steel pipe temperature reaches below 50℃, and cleaning off any residual oil.

[0030] The tempering process described in step S9 includes: heating the steel pipe to 500±10℃, holding it at that temperature for 120 minutes, and then air-cooling it after removing it from the furnace.

[0031] By adopting the above technical solution, the beneficial effects achieved by the present invention compared with the prior art are as follows:

[0032] (1) The original bar stock of the present invention is smelted by vacuum induction + electroslag remelting. Combined with the principle of rapid heating in induction furnace, the internal and external temperature of the billet can be uniformly reached to meet the requirements of extrusion in a short time. Through the above process, the bar stock grains can be refined and the material density can be improved. This avoids the growth of billet grain size caused by long-term heating and heat preservation in ring furnaces, inclined bottom furnaces, etc., and can effectively reduce defects such as porosity and looseness. The control of impurity elements is more precise, and the composition segregation is effectively reduced. Only by making changes to the raw material itself can the various properties of the subsequent pipe be substantially improved.

[0033] (2) This invention uses hot extrusion technology to form pipes, which firstly completely avoids the generation of oblique cracks.

[0034] Secondly, the hot extrusion process has a tight overall process connection, with only two major steps: hole expansion and extrusion. The heat loss during product transfer is much less than that of the hot piercing process, ensuring the consistency of forming process parameters for raw materials in the same batch. The electromagnetic induction heating technology used in hot extrusion, compared with ring furnace heating, can eliminate the problem of severe oxidation and decarburization on the surface of the material, which helps to improve and stabilize the mechanical properties of the product. Furthermore, the extrusion process parameters adopt low-temperature extrusion, controlling the billet exit temperature at 1100-1150℃, which can control the overall grain size of the formed tube and refine the grain size of the tube.

[0035] (3) The original steel ingot of the present invention is produced by the up-drawing process in the forging process, which ensures that the forging ratio is greater than 4.0. By increasing the interlacing of the material structure and the large deformation ratio, the grains of the forging bar are further refined.

[0036] In summary, the D6AC seamless steel pipe produced by this invention exhibits high density, fine grains, uniform and delicate microstructure, and few pores and impurities, resulting in excellent mechanical properties and high batch-to-batch consistency. The production process of this invention has a short workflow and is suitable for the processing of seamless pipes in the metal materials processing industry. Attached Figure Description

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0038] Figure 1 This is a flowchart illustrating the production process of an embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram of the structure of the chamber heating furnace in an embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of the structure of the horizontal extrusion unit in an embodiment of the present invention.

[0041] In the diagram: 1-Refractory material layer, 2-Insulation material layer, 3-Furnace body steel frame, 4-Burn, 5-Thermocouple, 6-Exhaust port, 7-Heat exchanger, 8-Lifting device, 9-Furnace door, 10-Furnace body support, 11-Die tail seat, 12-Die middle seat, 13-Die seat, 14-Die support, 15-Extrusion die, 16-Extrusion cylinder middle layer, 17-Extrusion cylinder lining, 18-Extrusion cylinder outer layer, 19-Core rod, 20-Extrusion pad, 21-Extrusion rod. Detailed Implementation

[0042] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the manufacturing process of the D6AC seamless steel pipe described herein is a preferred embodiment and is only used for illustration and explanation of the present invention, and does not constitute a limitation thereof. Example 1

[0043] This embodiment discloses a D6AC seamless steel pipe with specifications of φ125mm (outer diameter) × 27mm (wall thickness), and its chemical composition is shown in Table 1:

[0044] Table 1. Compositional Analysis Data of D6AC Seamless Steel Pipe (Percentage by Mass)

[0045]

[0046] Note: The remainder consists of Fe and unavoidable impurities.

[0047] This embodiment also discloses a production process for D6AC seamless steel pipes, used to produce the aforementioned D6AC seamless steel pipes, such as... Figure 1 As shown, the specific steps include:

[0048] S1: Billet preparation, using pure iron and ferroalloys as raw materials, including ferromolybdenum, ferrosilicon, etc., electrode billets are produced by vacuum induction melting, and the electrode billets are smelted into steel ingots with a diameter of φ600mm by electroslag remelting technology.

[0049] S2: Forging the forged bar. The steel ingot obtained in step S1 is heated and forged into a forged bar. Specifically, the heating includes first heating the steel ingot obtained in step S1 to a furnace temperature of 450℃~500℃ and holding it at that temperature for 3 hours; then raising the furnace temperature to 1160℃~1200℃ at a heating rate of 100℃~120℃ / h and holding it at that temperature for 3 hours~5 hours. The forging adopts an upsetting process with a compression ratio of 6.5, a reduction of 30mm~70mm per pass, and a feed rate of 70mm~100mm; the φ600mm steel ingot billet is heated and forged into a forged bar with a diameter of φ310mm, with an initial forging temperature of 1190℃ and a final forging temperature of 850℃.

[0050] S3: Annealing of the forged bar. The forged bar obtained in step S2 is annealed in a chamber furnace at a temperature of 810℃~870℃ for 6h~12h. Afterwards, the furnace is cooled to 300℃~350℃, and the bar is air-cooled to room temperature to reduce hardness. Figure 2 As shown, the chamber heating furnace includes a refractory material layer 1, an insulation material layer 2, a furnace body steel frame 3, a burner 4, a thermocouple 5, a flue gas outlet 6, a heat exchanger 7, a lifting device 8, a furnace door 9, and a furnace body support 10.

[0051] S4: Forging bar processing: Remove the oxide scale from the outer surface of the forging bar obtained in step S3, and process the expansion guide hole. Specifically, when removing the oxide scale from the outer surface, 5mm to 6mm is removed from each side of the outer diameter of the forging bar. When processing the expansion guide hole, the diameter of the expansion guide hole is 45mm, resulting in an expanded bar with an outer diameter of φ299mm, an inner diameter of φ45mm, and a length of 700mm.

[0052] S5: Extrusion molding involves heating the cold expanded bar stock twice in an electromagnetic induction furnace. The first heating power is 350KW, raising the outer surface temperature of the expanded bar stock to 1000℃~1030℃. The second heating power is 800KW, raising the outer surface temperature of the expanded bar stock to 1090℃~1130℃, completing the heating process. Then, it undergoes descaling with 23MPa high-pressure water, followed by lubrication with glass powder. The internal lubricant uses medium-alkali powder, the external lubricant uses GW7 glass powder from Tianli Chuang Company, and the glass pad powder is also medium-alkali powder. Finally, a 63MN horizontal extrusion press is used to extrude medium-thick wall steel pipes. The extrusion process includes:

[0053] ① Hole reaming machine, reaming speed is 150mm~250mm / s, reaming ratio is 1.01~1.40;

[0054] ② Extrusion by an extrusion unit, with an extrusion speed of 100mm~150mm / s and an extrusion ratio of 3~10.

[0055] like Figure 3 As shown, the 63MN horizontal extrusion press unit includes a die tail seat 11, a die middle seat 12, a die base 13, a die support 14, an extrusion die 15, an extrusion cylinder intermediate layer 16, an extrusion cylinder liner 17, an extrusion cylinder outer layer 18, a mandrel 19, an extrusion pad 20, and an extrusion rod 21.

[0056] S6: Annealing treatment. The steel pipe obtained in step S5 is heated to 700±10℃ in a roller hearth atmosphere protection furnace, held for 60min~90min, cooled to below 350℃ in the furnace, removed from the furnace and air-cooled, and then pressure straightened.

[0057] S7: Normalizing treatment, heat the steel pipe obtained in step S6 to 900±10℃, hold for 60 minutes, and then air cool after removing it from the furnace.

[0058] S8: Quenching treatment. Heat the steel pipe obtained in step S7 to 870±10℃, hold for 60 minutes, immerse in oil for rapid cooling, wait until the temperature of the steel pipe reaches below 50℃, then air cool and clean the residual oil.

[0059] S9: Tempering treatment. The steel pipe obtained in step S8 is heated to 500±10℃, held for 120 minutes, removed from the furnace and air-cooled. After air cooling, the finished pipe is obtained.

[0060] The performance testing items for the steel pipe after annealing in step S6 include: hardness. The performance testing items for the finished pipe include: tensile strength, Rp0.2 yield strength, elongation, and grain size. The test data for samples 1#-1 and 1#-2 are shown in Table 2.

[0061] Table 2 Performance test results of D6AC seamless steel pipes

[0062] Example 2

[0063] This embodiment discloses a D6AC seamless steel pipe with specifications of φ170mm (outer diameter) × 14mm (wall thickness), and its chemical composition is shown in Table 3.

[0064] Table 3. Compositional Analysis Data of D6AC Seamless Steel Pipes (Percentage by Mass)

[0065]

[0066] Note: The remainder consists of Fe and unavoidable impurities.

[0067] This embodiment also discloses a production process for D6AC seamless steel pipes, used to produce the aforementioned D6AC seamless steel pipes. The steps in this embodiment are as follows: Figure 1 As shown, it is largely the same as in Example 1, specifically as follows:

[0068] S1: Billet preparation. In this embodiment, the diameter of the steel ingot prepared is φ550mm; the rest of the process is the same as in Example 1.

[0069] S2: Forging bar. In this embodiment, the compression ratio of forging is 5.5. The φ550mm steel ingot is heated and forged into a φ310mm diameter forging bar; the rest of the process is the same as in Example 1.

[0070] S3: Annealing of the forged bar, this step is the same as in Example 1.

[0071] S4: Forging of the bar, this step is the same as in Example 1.

[0072] S5: Extrusion molding, this step is the same as in Example 1.

[0073] S6: Annealing treatment, this step is the same as in Example 1.

[0074] S7: Normalizing treatment, this step is the same as in Example 1.

[0075] S8: Quenching treatment, this step is the same as in Example 1.

[0076] S9: Tempering treatment, this step is the same as in Example 1.

[0077] The performance testing items for the steel pipe after annealing in step S6 include: hardness. The performance testing items for the finished pipe include: tensile strength, Rp0.2 yield strength, elongation, and grain size. The test data for samples 2#-1 and 2#-2 are shown in Table 4.

[0078] Table 4 Performance test results of D6AC seamless steel pipes

[0079]

[0080] As can be seen from Tables 2 and 4, the finished tubes obtained in Examples 1 and 2 have fine grains and good mechanical properties.

Claims

1. A process for producing a D6AC seamless steel tube, characterized by, Includes the following steps, S1: Billet preparation: using pure iron and ferroalloys as raw materials, electrode billets are produced by vacuum induction melting, and the electrode billets are smelted into steel ingots by electroslag remelting technology. S2: Forged bar, which is formed by heating a steel ingot and forging it into a forged bar. The forging process is upsetting and drawing, with a compression ratio of 4.0 to 7.

0. S3: Annealing of forged bars, the forged bars obtained in step S2 are annealed; S4: Forging bar processing, removing the oxide scale from the outer surface of the forging bar obtained in step S3, and processing the enlarged guide hole; S5: Extrusion molding. The expanded bar obtained in step S4 is heated to 1090℃~1130℃ in an electromagnetic induction furnace. The expanded bar is heated twice in the electromagnetic induction furnace. The first heating power is 350KW, and the outer surface temperature of the expanded bar reaches 1000℃~1030℃. The second heating power is 800KW, and the outer surface temperature of the expanded bar reaches 1090℃~1130℃, completing the heating process. Then, a medium-thick wall steel pipe is extruded using an extrusion unit. S6: Anneal the steel pipe obtained in step S5; S7: Normalize the steel pipe obtained in step S6; S8: Quench the steel pipe obtained in step S7; S9: Temper the steel pipe obtained in step S8, and air cool it to obtain the finished pipe; The seamless steel pipe comprises, by mass percentage, C: 0.44–0.50, Si: 0.10–0.40, Mn: 0.55–0.95, P: ≤0.015, S: ≤0.015, Cr: 0.80–1.30, Ni: 0.30–0.80, Mo: 0.87–1.13, V: 0.04–0.16, Cu: ≤0.20, with the remainder being Fe and unavoidable impurities.

2. The process for producing D6AC seamless steel pipe according to claim 1, characterized in that, The outer diameter of the seamless steel pipe is 80-273 mm, and the wall thickness is 13 mm-50 mm.

3. The process for producing D6AC seamless steel pipes according to claim 1 or 2, characterized in that, The finished seamless steel pipe has a hardness ≤285HBW, tensile strength ≥1520MPa, yield strength ≥1420MPa (Rp0.2), elongation ≥9.0%, and grain size ≥5.

4. The process for producing D6AC seamless steel pipe according to claim 1, characterized by, The heating described in step S2 includes: heating the steel ingot to a furnace temperature of 450℃~500℃ and holding it at that temperature for 3 hours; then raising the furnace temperature to 1160℃~1200℃ at a heating rate of 100℃~120℃ / h and holding it at that temperature for 3 hours~5 hours.

5. The process for producing D6AC seamless steel pipes according to claim 4, characterized in that, The forging process described in step S2 has an initial forging temperature of 1160–1200°C, a final forging temperature of 850–950°C, a reduction of 30–70 mm per pass, and a feed rate of 70–100 mm.

6. The process for producing D6AC seamless steel pipe according to claim 1, characterized by, The annealing in step S3 is carried out in a chamber furnace at a temperature of 810℃~870℃ for 6h~12h, followed by furnace cooling to 300℃~350℃ and air cooling to room temperature.

7. The process for producing D6AC seamless steel pipe according to claim 1, characterized by, In step S4, 5mm to 6mm is removed from one side of the outer diameter of the forging bar, and the diameter of the expansion guide hole is 45mm to 80mm.

8. The production process of D6AC seamless steel pipe according to claim 1, characterized in that, In step S5, after heating and before extrusion, the expanded bar stock is first descaled by high-pressure water at 18MPa to 23MPa, and then lubricated with glass powder. The extrusion unit mentioned in step S5 is a horizontal extrusion unit, and the process of extruding medium and thick-walled steel pipes includes: ① Hole reaming machine, reaming speed is 150mm~250mm / s, reaming ratio is 1.01~1.40; ② Extrusion by an extrusion unit, with an extrusion speed of 100mm~150mm / s and an extrusion ratio of 3~10.

9. The process for producing D6AC seamless steel pipes according to claim 1, characterized in that, The annealing process described in step S6 includes: heating the steel pipe to 700±10℃ in a roller hearth atmosphere protection furnace, holding it at that temperature for 60min~90min, cooling it in the furnace to below 350℃, air cooling it after removing it from the furnace, and then pressure straightening it. The normalizing treatment described in step S7 includes: heating the steel pipe to 900±10℃, holding it at that temperature for 60 minutes, and then air-cooling it after removing it from the furnace; The quenching process described in step S8 includes: heating the steel pipe to 870±10℃, holding it at that temperature for 60 minutes, immersing it in oil for rapid cooling, and air cooling when the steel pipe temperature reaches below 50℃, and cleaning off any residual oil. The tempering process described in step S9 includes: heating the steel pipe to 500±10℃, holding it at that temperature for 120 minutes, and then air-cooling it after removing it from the furnace.

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